* GB785859 (A)

Description: GB785859 (A) ? 1957-11-06

Improvements in or relating to ribbon type burners

Description of GB785859 (A)

PATENT SPECIFICATION 785,859 Date of A pplication and filing Complete Specification Jan 17, 1956. ),; IV No 1562/56. A pplication made in United States of America on April 19, 1955. Complete Specification Published Nov 6, 1957. Inidex at Acceptance:-Classes 75 ( 1)9 TM)I 2; and 75 ( 3), F 7 (B: E: 5). International Classification:-F 2 ltg lF 23 f. COMPLETE SPECIFICATION Imlpralvtenaeltnts in or D Fdaltin Rg to 9 nfibbcli Type BU Iews 14 i I, JOHN HAROLD FLYNN, a citizen of the United States of America, of 234, Elk Avenue, New Rochelle, New York, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:0 This invention relates to gas burners of the so-called ribbon type, and particularly to burners of this type adapted to provide two or more spaced ribbons or bands of flame from a single burner body. As is well known in the art, ribbon burners comprise in general a hollow casting forming a casing or housing adapted to be supplied with a combustible gaseous fuel mixture which is permitted to issue through ports extending longitudinally of the burner body and is ignited upon emergence from these ports to provide the aforesaid ribbons of flame Burners of this type, but providing only a single ribbon of flame, are known. For increased heating capacity, dual or multiple flame ribbon burners are often desirable and are commonly used, for example, as the heating units in ovens of the traveler or continuous type for baking biscuits crackers, bread and the like from dough material transported through

the oven on conveyor bands Each individual burner is disposed across the width of the oven, that is, transversely of the direction of travel of the conveyor band, to provide an even distribution of heat thereacross, and a series of these burners is arranged in side-by-side relation along the length of the oven to maintain the desired heating effect throughout its extent Since ovens of this type may attain considerable length, as much for example as two hundred and fifty feet or more, a large number of burners may be required. Each of these burners must have means for igniting the gas issuing from its ports, and lPrice 3 s 6 d l where there are two or more spaced ports, as in the case of the burners here under consideration, ignition means for both such ports must be provided High tension sparking electrodes are generally used for this purpose 50 and, in order to reduce the number of such electrodes required in an installation, it has heretofore been proposed to provide but one electrode per burner to ignite the gas at one main burner port and to incorporate in the 55 burner, crossover means for causing propagation of the flame from such first main port across the intervening body of the burner to the other port spaced from the first. While, as just stated, such a crossover 60 arrangement has been proposed heretofore. it is subject to certain serious disadvantages. particularly with respect to lack of sufficient structural rigidity under sustained operation at the high temperature to which such burners 65 are necessarily subjected Since the burners are suspended between longitudinal frame members in the oven, and owing to the construction and arrangement of the crossover pilot arrangement heretofore employed, such 70 prior burners have had a tendency to warp or sag in the middle after relatively short periods of use This results in uneven heat distribution across the oven and leads to the need for frequent replacement of the burners, all at 75 substantial expense Such prior burners have a further disadvantage in that they produce a continuous zone or area of overheating owing to the unvarying position throughout the oven of the crossover pilot flame, resulting 80 in further unevenness in operation of the oven. Accordingly it is a general object of this invention to provide an improved multiple port ribbon burner and integral crossover 85 pilot construction, whereby, upon ignition at a first main port of the ribbon burner, propagation of the flame across the intervening body of the burner to a second main port will be ensured under all conditions Because 90 of the obvious hazard involved should gas issuing from one main burner port fail to be ignited promptly on issuing from the burner port, absolute dependability of cross-piloting is essential This must be true for all possible starting conditions of the burner,

ranging from low turndown or standby to maximum heat output condition Burners according to the present invention are effective in meeting these requirements. In line with the foregoing, it is a further object to provide a burner of this type having improved mechanical strength and design whereby any tendency of the burner body to warp or sag is completely eliminated, even when exposed for long periods to high operating temperatures, thus ensuring both uniformity of heating operation and lower replacement cost The design is such also that local 'hot-spots" or zones of overheating along an oven, due to the crossover pilot flame, can be easily avoided while employing but a single, standard form of burner body construction This of course results in a further economy, as it becomes unnecessary to stock different types of burners, one type being adaptable for use at any point in an oven. Briefly, the foregoing objects and advantages are obtained in accordance with the invention disclosed herein by providing, at one or more points along the body of a multiple-port ribbon burner an improved integral crossover pilot for cross-ikiting the main burner ports Unlike prior constructions, the crossover arrangement herein disclosed permits the burner body to be made substantially without transverse interruption in its wall or web, with the result that the new burner is not subject to the tendency to sag which has characterised burners of this general type heretofore As a further measure, longitudinal or dorsal reinforcing ribs running longitudinally of the burner body are provided to increase its transverse strength. A feature of the invention is the provision of a shield at the crossover point on the burner which permits the employment of a minimum cross-piloting flame but which nevertheless ensures positive travel or propagation of flame from one main port to the other under any operating condition and by providing the crossover at a point asymmetric to the midpoint on the burner length, localized overheating, due to alignment of successive crossover flames in a series of burners along an oven, can be avoided This is made possible, while employing but a single standard design of burner, by installing burners in alternate end-for-end arrangement along the oven so as to effect a staggering of the position of the crossover flame across the width of the oven The staggering effect can of course be further increased by providing more than one available crossover point on the burner body, although only one such point on any particular burner is used. Specific constructions of burner according to the present invention will now be 70 described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a side elevation,

partially broken away and partially in section, of a ribbon 75 burner embodying a preferred form of the crossover pilot; Figure 2 is an end view, looking from the right, of the burner shown in Figure l: Ficure 3 is a fragmentary part-se 2 tional 80 plan view of the burner shown in Figure 1; Fisure 4 is a section taken mainly along the line 4-4 of Figure 1 but also showinou details of the crossover pilot: Figure 5 is a fragmentarv end section on 85 the line 5-5 of Ficure 4: Figures 6 and 7 are, respectivelv side and part-sectional end elevations of the metal shield employed in the crossover pilot: Ficure 8 is a fragamentary underplan view 90 of the shield shown in Figure 6: Figure 9 is a developed view of the shield of FI>-yures 6 and 7; Fi ure 10 is an enlareed sectional view of a jet: 95 Figure 11 is a section similar to Figure 4 of au alternative construction: Fi-ure 12 is a fragmentary section on the line 1 I-12 of Figure 11: Fioures 13 and 14 illustrate the alternative 100 shield of Fi-ures 11 and 12; and Figure 15 is a aerspective view of burners of the present invention installed in a typical band oven. The preferred form of dual flame gas 105 burner 20 illustrated in Figures 1 to 10 includes an elongated tubular body or casing formed from an integral iron casting 21 At its opposite ends the casino 21 has end walls 22 and 24, each of which has a like, centrally 110 located, tapped aperture 26 28 respectively. Either one of these apertures is adapted to receive the externally threaded end of a pipe for supplying under pressure a suitable combustible gaseous mixture into the hollow 115 interior 25 of the casing 21, while a matching threaded plug is adapted to be placed in the opposite end of the casing to close that end against the escape of gaseous fuel The burner 20 is adapted to be supported at its 120 ends in a horizontal position in a conventional band oven 23, as shown in Figure 15. As there illustrated, a series of burners 20 are disposed transversely of the oven, and each burner is supplied with a combustible 125 gas mixture from manifolds 30, 32 extending the length of the oven An endless metal band 33 travels through the oven and carries, in the present instance, goods to be baked on the lower run of the band 130 Referring again more particularly to Figures 1 to 5, the burner body or casing 21 has on diametrically opposite sides external ribs 34, 36, each extending longitudinally of 785,859 location of the crossover pilots in an oven installation to be staggered along the oven. This will be discussed more fully hereinafter 70 Each of the bosses 58, 60 comprises an arcuate rib 62 cast intergrally with the casing and extending laterally across one half thereof This rib serves to increase substantially the wall or web thickness of the 75 burner

casing at this point The rib 62 includes two similar semicircular spaced ridges 64 extending along opposite edges of the rib and merging at their opposite ends into the exposed lateral faces of the ribs 34, 36 of the 80 casing, as shown more particularly in Figures 2 and 3 of the drawings Along the adjacent inner edges of each of the ridges 64 there is a shoulder 66, and between these shoulders, an arcuate web 68 whose external surface is 85 depressed slightly below the horizontal surfaces of the shoulders 66 The outer surface of this arcuate web likewise merges at its ends with the ribs 34, 36 at the upper edges of the slots 38, 40, respectively 90 As shown more particularly in Figure 4, the web 68 is drilled to provide an aligned series of radial pilot gas ports or holes 70 running transversely of the burner Each hole 70 extends through the wall of the cas 95 ing 21 into the interior 25 thereof, and each is counterbored and tapped and has a hollow threaded tip or jet 72 inserted therein As shown more particularly in Figure 10, such tips provide constricted pilot orifices 74 for 100 the controlled escape of gas for cross-piloting purposes This arrangement does not substantiallv interrupt the continuity of the burner casing wall, so that the strength of the burner, particularly with respect to trans 105 verse bending or sagging, is virtually unaffected. In order to get propagation of the pilot flame from the main port 38 along the line of pilot jets 72 to the other main port 40, each 110 crossover formation has a cover means consisting of an arcuate perforated shield 76 of sheet metal, such as stainless steel, which extends across the boss 58 or 60 and is supported on the ridges 64 clear of the pilot jets 115 72 in the web 68 The shield 76 is initially formed from relatively thin flat blank stock. Figure 9 illustrates a strip of such stock which has been perforated to provide two centrally located parallel rows of equally 120 spaced small holes 78, and mounting screw holes 80, 82 This strip is then formed into the arcuate channel shape shown in Figure 6, in which the central panel 84 is dropped slightly with respect to the flanking shoulders 125 86 (Figures 5 and 7) The panel 84 extends in a smooth arc throughout the extent of the strip, whilst the shoulders 86 are flattened, as at 88, at the ends of the strip In this manner, small protruding lips 90, 91 (Figures 130 4 and 8) are formed by the central panel 84 at its opposite ends, the purpose of which will appear more fully presently. The shield 76 is adapted, to be secured to the casing from a point near one of its ends to a point the same distance from the opposite end Each of the side ribs 34, 36, is formed with a longitudinal slot 38, 40, respectively, passing through the casing from the interior to the exterior thereof, and extending substantially throughout the length of the ribs, as seen in Figure 1 These slots 38, 40, constitute

the main ports of the burner and each has disposed within it, in face-toface relationship, a group of transversely corrugated or crimped metal ribbons or bands 42 made of stainless steel or other nonoxidising material These divide the main ports into series of closely spaced high, medium and low velocity gas jets extending longitudinally throughout the extent of the respective slot 38 or 40 Gas escaping through these jets from the interior of the casing 21 produces a continuous ribbon or band of flame when the fuel is ignited at the main burner ports A conventional high tension sparking electrode 43, (Figure 3), mounted by suitable clamp means at one side of the burner, is employed to effect ignition of the fuel at one end of the main port 38. Once ignited the flame then travels the length of this main burner port and across to the other main port 40 as will presently be described. The burner body or casing 21 also includes tipper and lower external or dorsal ribs 44, 46 extending longitudinally from a point adjacent one end of the casing to a point similarly spaced from its other end, and upper and lower internal ribs or fins 48, 50, substantially coextensive with the respective external ribs 44 46 The lower internal fin is continuous throughout its length,, while upper fin 48 has an upward relief or depression 49 at two points along its extent, as best seen in Figures 1 and 5, for fuel distribution purposes, but is otherwise continuous Additional reinforcing of the casing 21 is supplied by vertical posts or tie ribs 52 which extend across the interior of the casing between the fins 48 and 50 on either side of the depressions 49, as shown in Figures 1 to 3 The casing is also provided with internal baffles 54, 56, adjacent the ends and intermediate the extent of the hollow interior 25 of the casing, which assist in getting proper distribution of gas to the several ports. At points approximately one-third and one-half the distance along the body or casing 21 from one end thereof, there is provided a respective external integral, arcuate crossover boss 58, 60, each of which extends between the main port slots 38, 40 Only one of these bosses-in Figures 1-5, the boss 58is used on any given burner to provide crossignition from the main port 38 to the port 40 when fuel issuing at the former is ignited. While only one of these crossover points is used in any given burner, two such points are made available in order to have but a single design of burner, yet permit the transverse 785,859 either boss 58 or 60, whichever is selected, and the boss is drilled and tapped, as at 92 (Figures 3 and 5) in the ridges 64 and on the faces of the ribs 34, 36, to receive screws 94. These latter pass through the holes 80, 82, of the shield and hold it

flush against the boss. The shoulders 86 of the shield engage the ridges 64 and the central panel 84 overlies the pilot jets with clearance, thus providing a semi-annular flame chamber or tunnel 96 beneath the shield into which the jets discharge As will be noted more especially from Figure 5, the holes 78 in the panel 84 are disposed on either side of the centre line of the orifices 74 of the jets 72 These permit combustion air to enter the chamber or tunnel without destroving the baffling effect of the shield in promoting deflection of the gas issuing from the jets 72 Owing to the projection of the lips 90, 91, at the ends of the shield, the chamber 96 is open at opposite ends but it is otherwise closed, except for the holes 78, across the ridges 64 of the crossover boss. When a combustible gas is admitted to the burner and current supplied to the electrode 43, the gas is ignited at the left hand end of the port 38, as viewed in Figures 1 and 3, and the flame travels to the right along this port At the same time gas flows from the several pilot jets 72 under the shield at the crossover point As the flame at the port 38 reaches the crossover gas from the jets is ignited at the end of the shield 76 where the lip 90 projects out over the main port The flame is picked up at the end of the shield and, supported by combustion air picked up at the lips and flowing in through the holes 78 travels from jet to jet beneath the shield until all the jets 72 are lighted At this point, gas issuing from the main port 40 is ignited by flash-back from the lip 91 and thereafter the flame travels along the port 40 until it is also completely lit The flame propagation is sufficiently rapid to insure against any dangerous accumulation of unignited gas, even when the crossover point is remote from the ignition electrode. A cover means, such as the shield 76, is essential to get directed propagation of the pilot flame just described throughout the extent of the crossover Without the shield, a substantially continuous open crossover port from one main port to the other is necessary to get the flame to travel across the intervening body of the burner But such a port greatly weakens the burner and results in its sagging Moreover, such a port causes a lot more gas to escape at the crossover pilot than is desirable and produces a poini in the burner of substantially greater heat output than that at other points along the burner. The mere provision of a series of individual jets, even though quite closely spaced, in order to overcome the foregoing objections, will not produce a dependable crossover pilot With the shield in place, however, cross-i-nition is ensured I under all conditions. This is true not only for all gas locities ironi minimum turn-down to maximum heat out 7 s) put conditions, but for any position of the burner, this is, whether the crossover pilot is on the upper or lowver

side of the burner. During burner operation the pilot flame burns both within the chamber 96 and out 75 side the central panel 84 of the shield, but in any event is of very low height compared to the usual crossover pilot flames obtained heretofore While the flame is continuous in the sense that it ensures cross-ignition from 8 '3 one end of the crossover to the other, it appears to be a flashing rather than a stead\ flame. In a specific design of burner having an overall length of approximately 41 ' and a 85 maximum width of 3-5/8 " from face to face of the ribs 34, 36 the web 68 of the crossover is provided with nineteen 3116 " diameter piloting tips or jets 72 spaced 9 apart over the extent of the semicircular web The 90 orifices in these tips are of the order of 1/16 " diameter The width of the chamber 96 formed by the ridges 64 is about 3/8 ". while the distance between the web 68 and the panel 84 is 3 /16 " The shield 76 is pre 95 ferably of 0 020 " stainless sheet steel and the holes 78 are preferably 0 059 " diameter on one-eighth inch centres, this providing a total of about 94 such holes in the shield The overhang of the lips 90 91 at the ends is 118 '10 ') to 3,'16 " beyond the respective lateral faces of the main burner ports. Figures 11 to 14 illustrate an alternative crossover pilot construction according to the invention which differs from the preferred 105 arrangement shown in Figures 1 to 10 primarily in respect of the form of shield employed Here, the burner 100 has a boss 102 similar to the boss 58 previously described except that there is an internal 11 ( semiannular recess 104 running centrally of the boss betwen the main port slots 106, 108. Internal longitudinal reinforcing fins 110. 112, are provided as before, and fin 110 is chamfered, as at 114 (Figure 12) adjacent 115 each side of the recess 104 to allow proper fuel distribution to the crossover jets 116. The latter are equally spaced around the central web 118 of the boss, each providing metered discharge of gas 12 t In place of the unitary perforated metal shield of the preferred construction, a strip of corrugated metal ribbon 120 (Figures 13 and 14) is employed This has a width just sufficient to pass between the ridges 122 on the 125 boss 102 and to lie against and be supported by shoulders 124 on the adjacent inner edges of the ridges 122 (Figure 12) The shoulders 124 hold the ribbon spaced radially outward from the jets 116 to define a semiannular 13 f) flame space 126 The depth of the shoulders below the outer surfaces of the ridges 1 '2 is substantially that of the thickness of the corrugated ribbon 120, and preferably a 785,859 burner port, and the cover means partly overhangs each main burner port orifice.

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* GB785860 (A)

Description: GB785860 (A) ? 1957-11-06

Improvements in or relating to rotary piston blowers

Description of GB785860 (A)

PATENT SPECIFICATION 785,860 o Date of Application and filing Complete Specification Jan 17, 1956. ' No 1576/56. Application made in Germany on Jan 17, 1955. Complete Specification Published Nov 6, 1957. Index at Acceptance:-Class 110 ( 2), A( 1 85 A: 21): X: 3 B). International Classification:-Fo 4 d. COMPLETE SPECIFICATION "Improvements in or relating to Rotary Piston Blowers" I, MANFRED DUNKEL, a German citizen, personally responsible partner of E Leybold's Nachfolger, of 504, Bonner Strasse, K 6 In-Bayental, Germany, a German Kommanditgesellschaft, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:The present invention relates to rotary piston blowers of the Roots type with auxiliary pumps for operation in vacuum where shafts and rotary pistons are cooled, and has for object improvements in such arrangements. Roots blowers are known to be used for one or more high vacuum stages in a multistage pump arrangement for very low suction pressures Much higher compression ratios can be obtained in a chamber under vacuum

than one at higher or positive pressures because flow resistance in the gaps or slots of the blower is much higher and the resulting return flow is reduced This is in itself an advantage, but there is also the concommitant disadvantage of reduced heat conductivity of the gas at low pressure This will lead to unduly high temperature of the rotors as well as of the vacuum seals of the shaft The rotors will expand considerably at high temperature, and this may cause mutual fouling of the rotors or of rotor and casing, leading to seizure of the pump. It is known to prevent the temperature rise of rotors or rotary piston blowers by interior cooling Air, water or oil for instance, may be used as a cooling agent The cooling agent enters through a longitudinal bore of the rotor shaft into the hollow rotor, and flows through it to run out again through the shaft. On applying such methods of cooling to rotary piston blowers which operate at negative pressures in excess of 40 Torr, particular difficulties will, however, be enlPdeie 3 s 6 d l countered These difficulties, the nature of which will be briefly described, can be obviated according to the invention When using air or water cooling, both shafts of the rotors must extend outside the apparatus in 50 order to provide inlet and outlet for the cooling air or water, as the bearing chambers will, when working under vacuum, normally be evacuated by connecting them to the auxiliary pump This, however, demands 55 additional work in design and construction. Difficulty of control is a further disadvantage of air or water-cooling, making it frequently impossible to prevent overcooling. In accordance with the invention these 60 difficulties can be obviated by cooling the shafts by a fluid, preferably oil, which circulates in a vacuum In this way it is not necessary to extend the rotor shafts to the exterior of the apparatus for the purpose of 65 providing inlet and outlet for the cooling fluid The circulating cooling fluid will in turn pass through a heat exchanger, where it is cooled down to the required temperature The simplest method is air cooling, but 70 cooling with a liquid, as a rule with water, also has its particular advantages as in this case the amount of liquid admitted to the heat exchanger can be controlled by a thermostat immersed in the liquid circulating 75 in the pump In this way, the temperature in the rotor can also be set to the required value In this connection one or two fluid pumps can be driven by the shafts of the rotary piston, or may be directly coupled with 80 them. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which Figs 1 and 2 show two embodiments 85 thereof by way of examples. In Fig 1, the ends of the shafts 1 and 2 are provided with

longitudinal bores 3, 4, 5 and 6 which are connected to the rotors 11, 12 by bores 7, 8, 9 and 10 Cooling oil is 90 injected by the pipes 13 and 14 which pass through stuffing boxes 15, 16 to the left of the Figure and carried by centrifugal force into the rotors It enters through the bores 3 and 4 through the bores 7 and 8 at right angles thereto into the chamber of rotors 11, 12. An exchange of heat takes place between the heated inner wall of each rotor and the cooling oil The oil leaves the inner chamber through the bores 9 and 10, emerges through the holes and bores 5, 6 at the right side of the bearings and collects in the emptied bearing housing 17 acting as an oil sump The pipes 13 and 14 can be sealed by packing towards the inner chamber of the shaft This packing preferably comprises lip packings (of the cup ring type) There it is cooled down to a constant temperature level by the cooling coil 18 and the thermostat 19 and is delivered again by the circulation pump 20, arranged below-the oil level, to the injection pipes 13 and 14 A cover 21 for the evacuated bearing is arranged at the left of the Figure, and is connected to the housing 17 by an oil pipe 22 The circulation pump has to be arranged below the oil level because as a result of the low pressure above the oil the pump cannot be used for sucking but only for delivery The oil under pressure, which is provided by the circulation pump, can also be used for cooling and lubrication of the bearings, gear wheels and shaft packings. Where the centrifugal force is not sufficient for the delivery of the cooling agent to the rotor, the injection tubes 13 and 14 can be tightened by lip packings replacing the stuffing boxes 15 and 16, and the cooling agent be forced under pressure through the rotors. Fig 2 shows a further embodiment The shafts 1 and 2 are provided with continuous longitudinal bores and -are not in connection with the inner chambers of the rotors The transmission of heat is effected through the metal connection between shafts and rotors. As in Fig 1, pipes 13, 14 extend into the borings of the rotor shafts The fall in pressure necessary for the fluid flowing through the shafts is obtained by the diaphragms 23 and 24 (originally designated 15 and 16 in Fig 2) This operation requires that the cross-section of the shaft borings be greater than the annular cross-section formed from diaphragm 23 and pipe 13 or diaphragm 24 and pipe 14 The cooling means only flows through the shafts in which the circumiference is similar to Fig 1 The cooling oil is injected through the shafts, the oil, as described in connection with the first embodi 60 ment, entering the rotor shafts through bores on the left side of the Figure but leaving the rotor shafts on the right side With sufficiently high centrifugal force the pressure for the passage through the rotor shafts is pro 65 vided by the diaphragms 23 and 24, otherwise the

diaphragms have to be replaced by lip packings Apart from this, the recirculation of the cooling agent is similar to that in the embodiment of Fig 1 70

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* GB785861 (A)

Description: GB785861 (A) ? 1957-11-06

Louvre

Description of GB785861 (A)

PATENT SPECIFICATION 785,861 o, Date of Application and filing Complete Specification Jan 19, 1956. No 1842 /56. Application made in South Africa on Jan 19,1955. Complete Specification Published Nov 6, 1957. Index at Acceptance:-Class 137, A 2 C 1. International Classification:-F 24 f. COMPLETE SPECIFICATION " Louvre " We, Ai R Li TE Louv R Es, SOUTH AFRICA, LIMITED, of 49, Coventry Street, Ophirton, Johannesburg, Union of South Africa, a company registered in the Union of South Africa, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to louvres comprising several louvre boards each edge-mounted in a pair of slotted holders which are carried on side frames The louvre boards are usually glass blades and adjustable by pivotal movement of the holders about the pivot pins. In current practice penetration of the blades into their slots is

limited by stop surfaces with which they make contact, and when thus located they are commonly constrained against removal by closing the open end of the slots, for instance by bending over one of the walls defining the slot This procedure presupposes a bendable material and virtually excludes cast or extruded metals. In any case nefarious prising open of the bent-over zones of the holders is not unduly difficult, and once this has been achieved the blades may be removed to allow ingress to the room. The object of the present invention is to provide a simple locking device for the blades which adds little if anything to the cost of the louvre. According to the invention the louvre includes, in at least one holder of each pair and preferably both, an insert which is located between the board and the slot, is shaped to prevent withdrawal of the board from the slot, and is itself constrained against withdrawal from the slot. Stated more specifically, each insert comprises a first formation that engages the holder and constrains the insert against withdrawal, and a second formation that engages the board to prevent it from being drawn out of the slot The first formation may be a tongue that engages a recess in the holder, while the second formation may be an end flange that overlies the edge of the board. The invention is illustrated in the accom 50 panying drawings in which Fig 1 is a face view of the louvre, Fig 2 is an "exploded" view of one holder, a board and an insert; Fig 3 is a section on the line 3-3 of Fig 55 1 drawn to a larger scale and Fig 4 is a section on the line 4-4 of Fig 3. In the drawings the frame in which the glass blades are mounted is numbered 10 60 The blades, numbered 11 are each edgemounted in slots 12 provided in a pair of holders 13 The holders are pivotally mounted about pivot pins 14 located about midway of each holder and journalled in the 65 side members of the frame 10. The holders are ganged together at one or both sides of the frame by a bar 15 that is moved, to open and close the blades in concert, by mechanism, which, not being pertin 70 ent to this invention, is not illustrated The mechanism is actuated by a handle 16. Examination of Fig 2 will show that each holder 13 has a shoulder 17 near to its outer end, that is to say the end that is at the out 75 side of the frame 10 The shoulder extends across the slot 12 to limit the penetration of the blade into the slot Towards its inner end one wall 12 a of the slot has a shallow rebate 18 with a sloping floor 19 that results 80 in a definite step 20 in the wall 12 a. The wall 12 a in the zone 30 between the step 20 and the outer extremity of the holder is set back somewhat so that the width of the

slot 12 is slightly greater in that zone than it 85 is in the zone 30 a beyond the step 20. The slot is dimensioned in the zone 30 a to receive the blade 11 snugly and with no significant play When the blade has been inserted into its pair of holders, a sheet metal 90 insert 21, preferably of spring steel, occupies the space in the zone 30 between the blade and the wall 12 a. The insert is shaped to provide a flat body 22, a side flange 23 and an end flange 24. The two flanges are connected at their meeting edges the insert being drawn rather than bent, so that the body and the flanges form a single rigid entity. When the insert is in its place in the assembly the side flange 23 is sandwiched between the blade edge 1 a and the floor 12 b of the slot, so that it is constrained against movement in the plane of the blade, while the end flange 24 overlies the edge lib of the blade Thus, if the insert is itself constrained against withdrawal from the slot 12, the blade 11 will be likewise constrained. To achieve constraint of the insert against withdrawal it and the holder are formed with interengaging formations that are designed to allow free entry of the insert into the assembly before interengagement occurs A convenient device for this purpose is a tongue 25 that is pressed out of the body 22 and deformed to be oblique to its plane, the free end 25 a of the tongue being directed towards the flanged end 24 of the insert When the insert is propelled into the slot 12 between the blade 11 and the wall 12 a, the natural resiliency of the metal of the insert allows the tongue to bend into the plane of the body 22, until the free end 25 a of the tongue passes the step 20, which occurs as the end flange 24 encounters the edge 1 lb of the blade The tongue then springs back for its free end 25 a to interengage with the step 20 and effectively constrain the insert against withdrawal. The inserts may be located either after insertion of the blade into its holders, or simultaneously with such insertion. When assembly has been completed the blade is securely held in the holders, being constrained against movement in two dimensions by the holders and in the third by the inserts The inserts are themselves constrained against movement, in two dimensions by the blade and holder and in the third by the steps 20. While the tongues 25 have been shown 50 pressed out of the bodies 22 of the inserts, they could equally well occur in the side flanges 23, in which case the steps 20 would be cut within the floors 12 b of the slots 12.

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* GB785862 (A)

Description: GB785862 (A) ? 1957-11-06

Improvements in and relating to heat exchange systems

Description of GB785862 (A)

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The EPO does not accept any responsibility for the accuracy of data and information originating from other authorities than the EPO; in particular, the EPO does not guarantee that they are complete, up-to-date or fit for specific purposes.

COMPLETE SPECIFICATION. Improvements in and relating to Heat Exchange Systems. We, FOSTER WHEELER LIMITED, a British Company, of Foster Wheeler House, 3 Ixworth Place, London, S.W.3, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to heat exchangers of the type in which heat is

exchanged between a liquid such as molten sodium or radio-active water and a second fluid such as steam or non-active water where it is extremely important that the two fluids should not come into contact. In a "shell and tube" heat exchanger, in which the tubes are fed with one fluid inlet and outlet headers separated from the shell space through which the other fluid is circulated, by plates in which the tubes are mounted, the most likely point for leaks to occur is at the joints between the tubes and the tube plates. It is therefore desirable to use double tube plates so that, in the event of a leakage of either fluid at a tube joint the fluid will only penetrate in to the space between the tube plates and the two fluids will not come into contact. It is an object of this invention to improve the security of such a heat exchanger. In accordance with the invention a gas or vapour inert to either of the fluids, is supplied to this space between the tube plates under a pressure substantially equal to that of the liquid or one of the liquids. The liquid or one ob the liquids in such systems is usually maintained under pressure by an inert gas such as nitrogen supplied to an expansion tank and the gas is conveniently supplied to the space between the tube plates from the same source at its point of application to the liquid system either directly or by means of a diaphragm transmitter. This arrangement relieves the liquid tube joint of any substantial pressure difference in operation and thus minimises the risk of liquid leakage. This may make permissible the use of an otherwise unsuitable nonwelded or non-brazed joint. Preferably the expansion tank in such a system is arranged in accordance with our Application No. 37800/54 (Serial No. 772,765) and the gas supply for the tube plate space drawn from the gas space of the tank. The space between the tube plates may conveniently communicate with units for detecting the leakage of either fluid. A typical heat exchanger in accordance with the invention is shown in the accompanying drawing by way of example. The drawing shows a shell and tube heat exchanger having double tube plates 10 12 and 101, 121 so as to minimise the risk of the gaseous fluid such as steam on the tube side coming into contact with a liquid such as molten sodium on the shell side in the event of a leak developing at any of the joints between the tubes 14 and the plates 10 and 101. The tube joints may be made by expanding welding or brazing or any combination of those methods. The spaces 16 and 16l between the double tube plates are each provided

with two pipe connections 18, 20 and 181 and 201. The connections 18, 181 are provided for the supply of a gas under a pressure substantially equal to that of the liquid and inert to either of the heat exchanging fluids. In the type of system referred to above in which steam is superheated by heat exchange with molten sodium maintained under pressure by nitrogen gas supplied to a header tank, the connections 18, 181 would be connected to the gas space of the tank. The connection 20 and 201 communicate with units for detecting the leakage of either fluid. What we claim is : - 1. A "shell and tube" heat exchanger for exchanging heat between a liquid and a second fluid having double tube plates in which a gas or vapour inert to either of the heat exchanging fluids is supplied to the space between the tube plates under a pressure substantially equal to that of the liquid or one of the liauids. 2. A heat exchanger according to Claim 1 in which the space between the tube plates is provided with a connection to a unit for detecting leakage of either fluid. 3. A shell and tube heat exchanger substantially as described with reference to the accompanying drawing. 4. A heat exchange system including a heat exchanger according to any preceding claim in which a liquid such as molten sodium is maintained under pressure by an inert gas such as nitrogen supplied to an expansion tank and in which the gas is supplied to the space between the tube plates of the heat exchanger from the expansion tank. PROVISIONAL SPECIFICATION. Improvements in and relating to Heat Exchange Systems. We, FOSTER WHEELER LIMITED, a British Company, of Foster Wheeler House, 3 Ixworth Place, London, S.W.3, do hereby declare this invention to be described in the following statement: This invention relates to heat exchangers of the type in which heat is exchanged between a gaseous fluid such as steam and a liquid such as molten sodium where it is extremely important that the two fluids should not come into contact. In a "shell and tube" heat exchanger, in which the tubes are fed with one fluid from inlet and outlet headers separated from the shell space through which the other fluid is circulated by plates in which the tubes are mounted, the most likely point for leaks to occur is at the joints between the tubes and the tube plates. It is therefore desirable to use double tube plates so that, in the event of

a leakage of either fluid at a tube joint the fluid will only penetrate in to the space between the tube plates and the two fluids will not come into contact. It is an object of this invention to improve the security of such a heat exchanger. In accordance with the invention a gas inert to either of the fluids, is supplied to the space between the tube plates under a pressure sulbstantially equal to that of the liquid. The liquid in such systems is usually maintained under pressure by an inert gas such as nitrogen supplied to a header tanK and the gas is conveniently supplied to the space between the tube plates from the same source at its point of application to the liquid system. This arrangement relieves the liquid tube joint of any substantial pressure difference in operation and thus minimises the risk of liquid leakage. Preferably the header tank in such a system is arranged in accordance with our Application No. 37800/54 (Serial No. 772,765) and the gas supply for the tube plate space drawn from the gas of the tank. The space between the tube plates may conveniently communicate with units for detecting the leakage of either fluid. The tube joints may be made by expanding, welding or brazing or any combination of these methods.

* GB785863 (A)

Description: GB785863 (A) ? 1957-11-06

Improvements in or relating to carbonization of carbonaceous materials

Description of GB785863 (A)

PATENT SPECIFICATION Date of Application and filing Complete Specification: Feb 7, 1956. I S i l D No 3780/56. Application made in United States of America on Feb 14, 1955. Application made in United States of America on June 23, 1955.

Complete Specification Published: Nov6, 1957. Index at acceptance:-Class 55 ( 1), AK( 1: 4: 5 B: 6 A). International Classification:-Cl Ob. COMPLETE SPECIFICATION Improvements; in or relating to Carbonization of Carbonaceous Materials We, THE M W KELLOGG COMPANY, a corporation organised under the laws of the State of Delaware, United States of America, of Foot of Danforth Avenue, Jersey City 3, State of New Jersey, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to method and means for treating solid materials and more particularly to method and apparatus for the fluidized treatment of carbonaceous materials such as coal, shale, lignite, oil sands, etc, at low temperatures Still more particularly, it relates to unitary method and means for drying, preheating, pretreating and carbonizing fluidized carbonaceous materials at low temperatures. The treatment of carbonaceous solids to form valuable liquid, gaseous and solid products is well known in the art An example of one process frequently employed entails the treatment of solids, such as coal at elevated temperatures whereby volatile materials are released from the solids and a valuable solid residue is formed It has been the practice in the past to carry out carbonization in both non-fluid and fluid systems; however, the present invention is concerned with a carbonization process of the fluid type wherein the various steps are performed with a finely divided feed material which is maintained in a highly turbulent state of agitation by the passage therethrough of a fluidizing medium. In carrying out fluidized carbonization of carbonaceous materials, it has been found that several process steps are necessary in order to provide a workable operation and assure a maximum yield of desirable vapor, liquid and solid products More usually, the first step in the carbonization process concerns the proper preparation of the raw feed material This involves not only proper selection and sizing of the carbonaceous solids to provide a readily fluidizible feed, but also includes drying the k Price 3 solids to a minimum moisture content prior to further processing It has been found that certain finely divided carbonaceous materials, though easily fluidized at low temperatures, when subjected to more elevated temperatures suffer a change in physical characteristics and become soft and gummy and the particles tend to agglomerate For example, many coals pass through a so-called " plastic " state, usually at a temperature between about

7000 F and about 8000 F wherein the coal particles tend to stick together and form large particles which resist fluidization Several methods of combating this agglomerating tendency of coals and other carbonaceous materials have been suggested, one of the more successful of which comprises subjecting the finely divided solid particles to a mild oxidation treatment prior to further high temperature processing It has been found that this method of treatment alters the physical characteristics of the carbonaceous material so as to minimize agglomeration of the solid particles The changes which take place in the solids in a treatment of this type are not clearly understood; however, according to one theory the mild oxidation " case hardens " the particles thereby substantially nullifying their sticking tendencies when they pass through the plastic state. When processing carbonaceous materials, therefore, the step after the drying operation preferably involves pretreating the dry solid particles at an elevated temperature in the presence of a limited amount of oxygen During this process a portion of the vaporizable compounds present in the carbonaceous solids are released The third and last step in the conventional solids carbonization process concerns the treatment of carbonaceous material at a still higher temperature whereby the remaining vaporizable compounds are released therefrom and a carbonaceous product residue is produced The vaporizable portion of the coal which is commonly known as " tar " comprises numerous organic compounds having a wide range of boiling points As used herein, the term " tar " includes any volatile organic 785863 compounds released from the coal, either liquid or vapor and either cracked or uncracked The composition of the carbonaceous residue remaining after vaporization of the tar depends on the type of carbonaceous feed material used For example, when carbonizing coal the residue material is commonly called "char " Although the description and discussion of the invention will be directed primarily to coal carbonization, the term " char " will be used hereinafter in a broader sense to designate any residue solids remaining after carbonization. In addition to the three processing steps just described, a fourth operation is usually necessary In carrying out the drying step it is usually preferred to heat the carbonaceous feed only to the minimum temperature necessary to remove the surface water, which is, of course, the boiling point of water at the pressure conditions maintained during this operation The pretreating operation, however, is carried out at an elevated temperature, substantially above the temperature at which the solids leave the drying zone Only a portion of the heat required in this operation is supplied by the oxygen consumed therein The remaining heat required is furnished by what may be called a preheating step It is possible to provide the required

preheat in conjunction with the drying operation or the pretreating operation, or it may be made an entirely separate and independent part of the carbonization process. Each of the aforementioned processing steps, i.e, drying, preheating, pretreating and carbonization is customarily carried out in a separate vessel, which necessitates the use of numerous transfer lines and standpipes, and extensive supporting steel work Such installations besides being mechanically complex have poor thermal efficiency and result in a process with high utility costs. It is an object of this invention to provide an improved method and means for carrying out a solids carbonization process. Another object of this invention is to provide unitary method and apparatus for carrying out the successive steps of drying, preheating, pretreating and carbonizing of carbonaceous materials. It is still another object of this invention to provide improved method and means for increasing product yield in the carbonization of carbonaceous materials. These and other objects of the invention will become more apparent from the following detailed description and discussion. In the method of this invention, the aforementioned objects are achieved by providing a unitary carbonization system comprising drying and preheating zones superimposed upon a carbonizing zone and a pretreating zone disposed within the carbonizing zone, said pretreating zone being in open communication with the carbonizing zone and below the level of the solids present therein. In carrying out the process of this invention, a finely subdivided solid carbonaceous feed is introduced into a drying zone where 70 the solids are elevated in temperature and retained in a fluidized state for a period of time sufficient for the removal of surface water. The solids are thereafter passed downwardly as a confined stream into a fluidized solids bed 75 in a pretreating zone of higher temperature wherein they are subjected to a mild oxidation and then passed upwardly and directly into an adjacent and superposed fluidized solids bed in a carbonizing zone of still higher term 80 perature where volatile constituents of the carbonaceous solids are removed, without the use of external transfer lines or standpipes. It is within the scope of this invention to treat various carbonaceous materials in the 85 manner described, including coals, shales, lignites, asphalts, oil sands, etc The invention is particularly exemplified, however, by its application to the treatment of coal, and further discussion of the invention is directed to 90 the use of this material It is not intended, however, that this particular application should limit the scope of the invention in any way. The first step to be considered in a process 95 for the carbonization

of coal as previously mentioned is concerned with surface water present in the coal feed which may, unless removed, prevent fluidization of the coal One of the problems encountered when handling 100 carbonaceous materials such as coal in a fluidized system results from the tendency of the finely divided solids to agglomerate because of water condensed thereon Most coals coming from a treating plant, for example, have a 105 relatively high surface or "free" water content, usually between about 2 and about 15 per cent by weight, or higher Unless removed, this moisture causes the finely divided coal particles to stick together and resist 110 fluidization Even after fluidization is achieved, moisture may cause packing or bridging in process equipment of restricted cross section, such as, for example in feed hoppers, standpipes, etc It is not always economically fea 115 sible to remove all the moisture from the coal; however, it has been found that agglomeration and packing of coal particles due to the presence of water is minimized if between about per cent and about 90 per cent of the 120 water initially present is removed. It has been suggested in the past to dry carbonaceous solids with air and other gases at high temperatures This method, although workable, suffers from several deficiencies Be 125 cause of the low heat capacity of most gases, sufficient heat for drying is not provided by this method unless the drying gas is present in large quantities and at elevated temperature The use of a large amount of gas is 130 785,863 of coal from the low temperature zone through the heater to the high temperature zone and back to the low temperature zone to provide both the sensible heat acquired by the dry solids and the heat of vaporization of the 70 water released therefrom When operating in accordance with the zonal temperature ranges given, the amount of coal circulated relative to the raw coal feed rate is between about 2 and about 5 pounds per pound 75 The heat transfer surface required for drying and preheating the coal is preferably provided by a conventional shell and tube heat exchanger with the solids being passed through the tubes in indirect heat exchange 80 with a hot fluid passed through the exchanger shell The heat required to dry the coal is provided by a fluid heating medium which may be a petroleum oil or vapor, or mixtures thereof, or other liquid or vapor material 85 which is easily transported and can withstand relatively high temperatures In general, liquid heating fluids are more satisfactory than gases because of their high specific heats and low volume relative to gases 90 Examples of suitable heating fluids are residual petroleum oils, synthetic heat transfer liquids, inorganic salt mixtures, lead, mercury, etc The temperature at which the heating medium is employed varies with the tem 95 perature maintained in the drying zone and with the heat transfer characteristics of the heating medium Usually, it is

preferred to introduce the heating medium at a temperature between about 3500 F and about 10000 100 F Temperatures greater than this are not desirable because of the danger of over heating coal particles in contact with the heat transfer surface. The amount of heat exchange surface re 105 quired to carry out the drying and preheating operations varies depending on several factors including the quantity of coal to be heated, the amount of moisture in the coal, heat transfer coefficients, etc More usually a surface 110 area between about 0 02 and about 0 30 square feet per pound of fresh coal feed per hour is sufficient to provide the desired drying and preheat. Operation of the drying portion of the car 115 bonization process in the manner previously described provides a dry, easily fluidizable solid material which may be subjected to further processing without danger of agglomeration or equipment plugging due to water This 120 method of operation is carried out without the disadvantages of previous drying methods and results in only slightly more than the minimum dust recovery problem Operation in the manner described also has positive advantages 125 in that the drying step is carried out with a high degree of thermal efficiency and a minimum amount of heat exchange equipment It has been found in the operation of conventional indirect heat exchangers wherein heat 130 expensive because of compression requirements, and it complicates the recovery of solids from the drying medium The use of elevated temperatures is also undesirable since high temperature may cause a substantial part of the volatile material in the coal to vaporize and mix with the drying medium and thus further complicate the recovery problem Furthermore, high gas temperatures may elevate the temperature of the coal to the plastic state and cause agglomeration of the coal particles thereby resulting in an inoperable condition. Other methods of drying coal have also been suggested; however, all of the processes presently in use suffer from serious deficiencies of one type or another In the drying process disclosed herein, drying problems are reduced to a minimum by using a two zone drying and preheating system and supplying the heat required for this operation through indirect heat exchange In carrying out the drying operation, raw coal suitably subdivided for fluidization, that is, of a size between about and about 400 mesh is introduced into a first zone wherein it is commingled with dry heated coal in sufficient quantity to elevate the entire mass of coal to a temperature suitable to effect the removal of water The dry coal is then passed through a heater where it is further elevated in temperature by indirect heat exchange with a hot fluid and then into a second zone The higher temperature coal in the second zone serves as the source of the coal commingled

with the wet coal feed, and in addition, provides preheated coal for the next phase of the carbonization process The entire drying and preheating step is conveniently conducted in a fluid system with both the low and high temperature zones containing a dense phase bed of fluidized coal Adequate turbulence to maintain each dense phase bed is provided by maintaining a linear gas velocity therein between about 0 5 and about 5 feet per second, or more usually between about 0 75 and about 3 _ feet per second Under normal operating conditions the density of the beds thus provided varies between about 10 and about 40 pounds per cubic foot The temperatures in the two zones may vary, depending on the residence time of the coal in each zone and the moisture content of the raw coal feed However, usually the first zone is operated at a temperature between about 2200 F and about 3250 F, and the second zone is preferably maintained at a temperature of between about 3500 F and about 6000 F. Fluidization of the solids in the low temperature zone is partially provided by moisture released from the coal and may be augmented by the introduction into this zone of air or an inert gas such as, for example flue gas, steam, etc The coal in the high temperature or preheating zone is maintained in a fluid state by the introduction of a similar gasifying medium. It is necessary to circulate a sufficient amount 785,863 is transferred to a mixture of entrained solids and gases that the rate of heat transfer is sensitive to the concentration of solids in the fluid stream, with streams of high solids concentrations giving substantially higher heat transfer coefficients than gaseous mixtures containing only a few solids It is important, therefore, when transferring heat in this manner to prevent dilution of the gas solids stream with additional gases, for example water vapor By operating the drying step in the aforedescribed manner, substantially all of the moisture removed from the coal is separated therefrom in the first low temperature zone This assures a minimum amount of vaporization of water from the coal in its passage through the exchanger and therefore a minimum dilution of this stream The net result is a process having a constant high heat transfer rate. Another reason and advantage in carrying out the drying process as described relates to the velocity of the solid-gas stream flowing through the heat exchanger When using a tubular solids heater it is necessary to pass the fluidized solids therethrough at a rather high velocity, usually between about 10 and about feet per second in order to overcome the pressure drop in the exchanger tubes and maintain the solids in a fluidized state This i particularly true in an up-flow type of heater wherein the solids tend to settle in a direction opposite to the flow of the fluidizing medium If solids containing

water are passed through the exchanger, being heated in the course thereof, the water is converted to steam which increases the velocity of the gassolids stream and may create a serious erosion problem. The proposed method of operation provides still a further advantage by virtue of the removal of water from the coal prior to the heating step Passage of coal through the heater requires the use of standpipes and transfer lines which of necessity employ sharp bends and turns In addition, conventional exchangers, more usually of the tube and shell type, also present flow paths of restricted cross section An attempt to pass a wet coal through such a system might very well lead to agglomeration of the coal particles and plugging, the very results which are sought to be prevented by the drying step This operating hazard, as well as those previously mentioned, of course, is avoided by the drying method described herein. After leaving the drying zone, the coal passes downwardly as a confined stream through a carbonization zone and into a pretreating zone enclosed within the carbonization zone In the pretreating zone the coal is contacted with air or other oxygen containing gas and partially burned to provide the pretreating and case hardening effect previously discussed The temperature at which this important process step is carried out may vary over a range between about 600 ' F and about 8250 F; however, more usually it is preferred to pretreat the coal in a more narrow range of temperature, that is between about 70 6500 F and about 800 F As in the previous operations, the coal pretreatment is carried out in a conventional dense phase fluidized bed, wherein the coal is maintained in a turbulent fluid state by-passage therethrough of a gasi 75 form medium Adequate turbulence to maintain the dense phase bed is provided by maintaining a linear gas velocity therein between about O 5 and about 5 feet per second Under normal operating conditions, the density of the 80 dense phase bed thus provided varies between about 10 and about 40 pounds per cubic foot. Generally, a portion or all of the fluidizing medium is supplied in conjunction with the oxygen required for pretreating This may be 85 accomplished by diluting the oxygen with air, by using air alone or by diluting air or oxygen with steam or other inert gas Thus, it is within the scope of the invention to supply the pretreatment oxygen to the pretreating 90 zone in a gaseous stream of varying oxygen content The amount of oxygen required for pretreating is usually between about 0 02 and about 0 08 pounds per pound of dry coal feed. To provide sufficient time for the pretreating 95 combustion reactions to take place, the rate of introduction of coal to the pretreating zone is adjusted to allow an average particle residence time therein of between about 10 and about minutes Upon entering the pretreating

100 zone, dry preheated coal at a relatively low temperature becomes intimately mixed with higher temperature pretreated coal and is swiftly elevated to the temperature level prevailing in this zone As the temperature of the 105 dry coal is increased, a portion of the lower boiling tar components present in the coal are vaporized and passed into the fluidization and combustion gases Since oxygen is relatively non-selective in its action, this phase of the 110 carbonization process may involve the consumption of a portion of the tar For this reason, it is desirable to limit the introduction of oxygen to the pretreating zone to the minimum amount necessary to prevent agglomera 115 tion of the solids and maintain an operable system Equally important to the operability of the pretreating system is the temperature of the solids bed maintained therein Consideration of this important point is taken up 120 in detail at a later point in the discussion. As previously mentioned, the pretreating zone is disposed within the carbonizing zone. For reasons to be more fully considered later, the coal pretreatment step is carried out in a 125 dense phase fluidized bed of solids adjacent to and in upwardly open communication with a second dense solids bed which is contained within the carbonization zone The preheated solids introduced into the pretreating zone 130 785,863 the other hand, the grid need not be limited to this location and other physical arrangements may be used when desired. In addition to the desirable process features which result therefrom, the pretreating and 70 carbonization vessel arrangement presents a number of advantages of a mechanical nature. For example, the arrangement of the two zones in effect eliminates one vessel, simplifies the transfer of solids from the preheater 75 to the pretreater and from there to the carbonizer, decreases solids recovery costs by eliminating one set of cyclones, eliminates the transfer line which would be required if the pretreating and carbonization steps were car 80 ried out in separate vessels, etc, thereby providing a highly efficient process both thermally and mechanically. Pretreated coal, fluidizing and combustion gases, and volatile tar compounds released 85 from the coal in the pretreating zone pass into the carbonization zone wherein the major portion of the volatile components in the coal are removed and a valuable residue char is formed. This, the major step of the process, as far as 90 product formation is concerned, is also conveniently carried out in a dense phase fluidized bed similar to the drying, preheating and pretreating beds previously described In order to effect removal of the volatile coal components, 95 a large amount of heat must be introduced to the combustion zone

Conventionally, this heat may be supplied from one or more of several sources, for example it may be provided in an inert gas such as a fuel gas heated to a high 100 temperature, or it may be supplied from a combustible gas such as fuel gas mixed with oxygen or it may be furnished from the combustion of oxygen or an oxygen containing gas with a portion of the carbonaceous feed This 105 invention is concerned primarily with the method of supplying heat wherein a portion of the carbonaceous feed, viz pretreated coal, is burned with oxygen or an oxygen containing gas However, it is within the scope of the 110 invention to supply a portion of the heat by either of the other two methods mentioned. When using the aforementioned method of providing heat, the gasiform fluidizing medium required to maintain the dense phase in the 115 carbonization zone is generally furnished by the combustion gases If necessary, however, deficiencies in the quantity of fluidizing medium may be made up by the introduction into the carbonization zone of a flue gas, steam 120 or other extraneous inert gas. The carbonization of coal to remove distillable tars therefrom and produce a char residue product is conducted over a wide range of temperatures usually between about 7000 125 F and about 24000 F The preferred thermal range of operation is determined to a great extent by the type of liquid product desired; for example, when it is preferred to distill the coal tars with a minimum of cracking of vola 130 completely fill this zone and pass upwardly therefrom into the carbonization solids bed. The carbonized solids or char on the other hand occupy only a portion of the carbonization zone, the remainder comprising a conventional dilute phase of relatively very low solids concentration superposed above the dense phase char bed By this arrangement of one zone within another, a common vapor space is provided which serves to accommodate the fluidizing and combustion gases from both zones. It is necessary to the efficient operation of the carbonization process that the pretreating and carbonization steps be kept separate and carried out at substantially different temperatures Thus, it is essential that solids from the higher temperature char bed be prevented from passing into the pretreating zone In the method of this invention, pretreating and carbonization are maintained as separate operations by placing a grid or perforated plate between the two zones The number and size of the openings in the grid or plate are fixed to provide sufficient pressure drop to prevent back mixing, that is passage of solids from the carbonization zone to the pretreating Zone, but insufficient to prevent the flow of solids from the pretreating zone The grid preferably encloses the entire top of the pretreating zone in order that the solids entering the carbonization zone may be

uniformly distributed over a maximum area Under normal operating conditions the cross-sectional area of flow through the grid is between about 1 per cent and about 10 per cent of the cross-sectional area of the pretreating zones The openings of the grid are usually circular in nature and are of a sufficient size to allow passage of the largest coal particles More usually holes between about -4 and about 1 inch in diameter are adequate The major factor in preventing back mixing through the grid is the high velocity of vapors and solids therethrough It is contemplated sizing the area of flow through the grid to provide a pressure drop between about -t and about 3 psi With this drop in pressure, velocities through the grid are in the order of between about 50 and about 200 feet per second By the aforedescribed means of dividing the two zones, it is possible to maintain them in open communication, yet at substantially different temperatures, and at the same time introduce pretreated solids and vapors into the carbonization zone in an evenly distributed manner. As will become apparent from the subsequent discussion, the physical location of the separating grid is important in determining carbonization product yields More usually the pretreating zone openly communicates with the dense char bed in an upward direction. This is necessary if the gases and pretreated solids are to be introduced into the carbonization zone in an evenly distributed manner On 785,863 tile constituents, namely low temperature carbonization, the temperature is held to a minimum of about 7000 F and not more than about 10000 F The type of coal is also of importance in establishing the operating temperature since some coals are more difficult to distill than others Contra to the pretreatment step, which is carried out entirely in the dense phase, the carbonization zone contains a dense phase bed superposed by a disperse or dilute phase which may have a solids concentration as low as 0 001 pounds per cubic foot Gases from both zones pass into this phase which provides a preliminary rough separation of vapors and solids Further solids separation is provided by conventional means, such as, for example cyclones, filters, etc. Substantially all of the desirable constituents of coal are removed at the aforementioned carbonization temperatures within avery short period of time, that is between about 0 25 and about 10 minutes As a further precaution to prevent agglomeration of the coal particles in the carbonizing zone, it is preferred to maintain a substantial ratio of char to fresh feed therein This serves to dilute the fresh pretreated coal, which provides the desired beneficial effect; however, it also makes it necessary to substantially increase the coal residence time At the usual char to fresh feed ratios maintained in the carbonization zone, that is between about 5 pounds per pound and

about 50 pounds per pound, the particle residence time therein is between about 2 minutes and about 200 minutes, more usually between about 20 minutes and about minutes. Carbonization may be carried out over a wide range of pressures; however, the pressure is usually maintained between atmospheric and 500 psig, preferably between about atmospheric and about 100 psig Since a driving force is necessary for the passage of coal from the pretreating zone into the carbonization zone the pretreating zone must operate at a pressure above the pressure in the carbonization zone; more usually the differential pressure between the two zones is between about and about 2 psi By virtue of its physical location above the pretreating zone, the drying zone may operate at a pressure either higher or lower than the pressure in the former zone More usually, it is convenient to maintain the pressure in the drying zone lower than the pressure in the pretreating zone and as a result the drying zone is ordinarily operated at zetween about 1 and about 20 psi less than the pretreating zone. As previously mentioned, this invention is not limited in its scope to the treatment of coal, but encompasses the use of other carbonaceous feed materials, for example shales, asphalt, oil sands, etc Similar processing considerations are important and similar operations are required when carbonizing these feed materials other than coal The conditions appropriate for each specific feed material are well known to those skilled in the art and for this reason do not need repeating here. The use of a unitary system for carrying 70 out the carbonization of coal provides unexpected advantages and allows the use of several novel processing schemes For example, in the conventional coal carbonization unit wherein the coal pretreating step is car 75 ried out in a separate vessel it is necessary to withdraw pretreated coal from this vessel and pass it through a transfer line to a carbonization zone Since oxygen is used in the carbonization zone as well as in the pretreating 80 zone, it has also been the practice to introduce pretreated solids and oxygen together into the carbonization zone More usually the oxygen in the form of air has been used for fluidizing and transporting the 85 pretreated solids between the two zones. This method of moving the pretreated solids is effective; however, it has been found that it results in an excessive consumption of tar compounds by burning, thereby reducing 90 the amount of tar produced in the process. The reason or reasons for this are not clearly understood but are believed to be related to the time during which tar vapors and oxygen are in contact In order to obtain an effective 95 coal pretreatment,

it is necessary to provide an average coal particle residence time in the pretreating zone of several minutes Since oxygen is introduced into the pretreating zone continuously, the solids in this zone, are, of neces 100 sity, in contact with oxygen for substantially this period of time On the other hand, gases entering and released in the pretreating zone reside therein for only a few seconds, more usually between about 5 and about 20 seconds 105 and subsequently pass from this zone Thus, tar vapors released from the coal in the pretreating zone are in contact with oxygen for a very short period of time compared to the time of oxygen-solids contact When the pre 110 treated coal and effluent gases from the pretreating zone, containing oxygen are passed to a carbonization zone through a transfer line, the total time of contact between the tar vapors and oxygen is substantially increased, 115 by as much as 100 per cent or more depending on the length of the transfer line and the velocity of the gases therein The additional few seconds of contact time between the coal particles and oxygen provided by use of the 120 transfer line is, however, insignificant If it is assumed that oxygen shows equal preference for tar and coal it is obvious that the combustion of tar is increased by use of a processing method which includes the use of a 125 transfer line with oxygen in the transferring medium. When utilizing the conventional method of transferring solids from a pretreating vessel to a separate carbonization vessel, it has fur 130 785,863 In the method of this invention, this is accomplished by introducing combustion oxygen into a dense phase bed of char in the carbonization zone in the lower portion thereof whereby the oxygen is substantially con 70 sumed before the fluidizing and combustion gases pass into the upper portion of the bed. The pretreated coal is introduced into the top portion of the same dense phase bed below the surface thereof and is heated by contact with 75 the hot char in a relatively oxygen-free atmosphere Both during and after the solids heating process, the char is in contact with ascending fluidization and combustion gases These vapors exert a stripping effect on the char and 80 assist in the removal of volatile tar components Thus the favorable results of this operation may be attributed to a combination of heating and stripping although it is probable that the primary separating effect is provided 85 by the heat transferred to the pretreated coal. The total gases from both zones after leaving the solids bed enter the dilute phase thereabove and are passed from the system. In addition to the advantages already men 90 tioned, the proposed method of operation eliminates another defect of previous carbonization processes Because of the relatively low temperatures used in the pretreating operation, it is difficult to provide for com

95 plete consumption of the oxygen introduced into the pretreating zone As a result, the effluent gases from this zone usually contain some free oxygen In normal operations, for example the amount of oxygen "break 100 through" may be as high as 10 to 15 per cent of the total introduced When pretreating is carried out in a conventional manner in a separate vessel in a conventional dense phase bed, unconsumed oxygen passes into the dilute 105 phase of the pretreating zone and reacts therein with tar vapors released from the coal In the method of this invention, there is no dilute solids phase in the pretreating zone and oxygen which is not consumed in this zone passes 110 into a dense phase bed of char in the carbonization zone along with the combustion gases and pretreated coal Here the oxygen has at least an equal change to react with solids rather than tar, thus effectively increasing the 115 tar yield. The depth of solids bed required in the carbonization zone to successfully carry out the invention depends on several factors, including the velocity of the lluidizing medium 120 therein, the degree of turbulence in the fluidized bed, the temperature at which carbonization is carried out and the diameter of the bed In general, it has been found that a bed of depth normally maintained in commercial 125 catalyst regeneration processes is adequate although deeper beds may be used to assure the complete absence of tar-oxygen contact The depth of coal maintained in the pretreating zone is less critical; however, here too the de 130 ther been found that substantial amounts of coke are deposited on the transfer line The result is a restriction in the flow between the two vessels which may eventually cause a shutdown This phenomenon also apparently is related to the residence time of the tar vapors in the transfer line At the temperatures maintained in the pretreating zone it is not difficult to visualize some thermal cracking of the tar compounds Any appreciable deposition of coke due to cracking would of course immediately become apparent in such a zone of relatively small cross-section. It is also possible that the coking is due either partially or entirely to the combustion of tar in the transfer line rather than by cracking. Whichever the cause, however, the occurrence of coke as described presents a problem which can seriously affect the operability of the carbonization process. In the method of this invention these problems are avoided by passing pretreated solids directly from the pretreating zone into the carbonizing zone without the use of a transfer line, thus minimizing contact between the tar vapors and oxygen and reducing the time during which these vapors are maintained at the pretreating temperature Oxygen required in the carbonization zone is introduced into this zone

separately from the pretreated solids. The direct passage of solids between the two zones is provided by using contiguous openly communicating zones disposed within a single vessel in the manner previously described. Solid particles leaving the pretreating zone pass through the grid or perforated plate into the carbonization zone where they are immediately commingled with high temperature char solids The heat transfer characteristics of the dense highly turbulent char bed are such that the pretreated coal is rapidly heated to carbonization temperature During this process, the remaining and major portion of the volatile constituents of the coal are vaporized and pass upwardly through the char bed. Thus the solids region adjacent to the grid separating the two zones is particularly rich in volatile materials The separate introduction of pretreated coal and oxygen into the carbonization zone is effective in reducing the consumption of tar already vaporized; however, unless the pretreated coal is maintained free from contact with oxygen in this zone for a period of time sufficient for the remaining tars to be distilled, a substantial portion of these volatile components may also be consumed Thus, in addition to passing the pretreated solids directly from the pretreating zone to the carbonization zone, it is further desirable to introduce these solids into a region of the latter zone which is free or relatively free of oxygen, whereby remaining tar materials are distilled therefrom and removed from the carbonization zone before the pretreated coal enters the region of combustion. 785,863 gree of oxygen consumption is an important factor in determining bed depth Usually in either zone a bed of between about 10 feet and about 40 feet in depth is maintained, although, if desired, more shallow beds and beds up to feet in depth may be used It is not necessary that the beds be of equal depth and either may be greater or lesser in depth than the other. Both the pretreating and carbonization steps are carried out in conventional fluid beds which are maintained by passing a fluidizing medium through finely subdivided particles of solids The amount of vapor and solids introduced into these beds per unit of time is important in determining both the volume of the beds and the degree of solids turbulence therein It is desirable in carrying out these processing steps, to maintain solids beds of relatively constant size having a sufficient flow of fluidizing medium therethrough to provide adequate turbulence of the fluidized solids. Therefore, control of vapor and solid flow rates to the fluid beds is of utmost importance. In carrying out the pretreating of finely subdivided coal particles,

it has been found that the rate of combination of oxygen with coal at a given temperature is dependent on the size distribution of the coal particles, that is on the amount of coal surface presented to the oxygen If the coal particles increase in size the coal surface is decreased and the amount of oxygen consumed in unit time is also decreased On the other hand, when the coal particles decrease in size the reverse occurs. Conventionally, coal particle size distribution on a commercial scale is provided by mechanical crushing and grinding Any variation in the operation of the equipment employed for this purpose, which is not uncommon, usually means a change in the size distribution of the coal produced As previously mentioned, if the coal particle size suddenly increases the amount of oxygen consumed in the pretreater decreases and the temperature therein also dedecreases If this occurs, the obvious solution which springs to mind is to introduce more oxygen into the pretreating zone This has the effect of increasing the concentration of oxygen in the pretreating zone whereby the combustion reaction rate is accelerated and the temperature may be brought back to its former level Unfortunately, however, introduction of more oxygen into this zone requires decreasing the quantity of air introduced into the carbonization zone unless the temperature in the latter zone is also increased Obviously, an increase in carbonization temperature is undesirable from the viewpoint of uniformity of operation and product yields Furthermore, withdrawal of oxygen from the carbonization zone decreases the vapor velocity in this zone and affects the degree of turbulence and size of the dense phase bed maintained therein, both of which are equally undesirable Still another disadvantage of increasing the amount of oxygen entering the pretreating zone lies in the fact that only a portion of the additional oxygen is consumed in the pretreatment and the remainder along with the unreacted por 70 tion of the original oxygen passes from the pretreating zone into the carbonization zone. Here it is consumed at least in part by reactions which involve tar rather than the nonvolatile portion of the coal 75 In the method of this invention it has been found that the problem of temperature decrease due to changes in the size distribution of the fresh coal feed is substantially eliminated and effective temperature control ob 80 tained in the pretreating zone by recycling a small, variable quantity of hot char from the carbonization zone to the pretreating zone. Not only is this method of temperature control simple in operation, but it is without the 85 defects attendant with attempts to control the temperature by varying the oxygen to carbon ratio The amount of char required for effective temperature control may vary at any

instant from as low as zero to about 5 pounds 90 per hour per pound of coal present in the pretreating zone; however, more usually the quantity of char required to compensate for temperature upsets is relatively low, that is between 0 01 and about 2 pounds per hour 95 per pound of coal present in the pretreating zone The recycle char flow rate may be controlled manually or more usually by the installation of a temperature controller in the recycle line It is contemplated that a small 100 amount of char will be recycled continuously when using this method of temperature control in order to prevent plugging of the recycle line The amount of heat introduced into the pretreating zone in this continuous char 105 stream, however, is very small compared to the total heat required in the pretreating zone, usually not more than about 5 per cent thereof. During normal operation a major portion, 110 more usually at least 90 per cent of the oxygen introduced into the pretreating zone is consumed therein Because of this, the problem of increasing pretreating temperature due to a decrease in the average particle size of the 115 coal is not nearly as critical as temperature movement in the opposite direction The unconsumed oxygen even if totally reacted can raise the pretreating temperature only a few degrees The major reason for temperature 120 control is to prevent excessive drops in temperature which may affect the operability of the process On the other hand, increases in pretreating temperature will rarely, if ever, have any deterimental effect on operability, al 125 though increased temperature may lower the yield of tar products Other operating changes besides particle size may affect the temperature in the pretreating zone; for example, there may be a temporary variation in the 130 785,863 the heat transfer coefficients of the flowing streams and other operating variables; however, more usually a surface area between about 0 01 and about 0 10 square feet per pound of char product per hour is adequate to 70 provide the desired cooling. Normally, only a portion of the heat contained in the product char can be removed economically by indirect cooling, particularly when using a common circulating heat ex 75 change fluid To further cool the char and provide a more easily handled product, water is injected into the partially cooled fluidized char which is then passed into a receiver or char hopper The quantity of water used for 80 this purpose may vary; however, usually it is preferred to limit it to not more than the amount necessary to cool the char to the dew point of water at the pressure existing in the receiver, thus converting the entire quantity of 85 cooling water to steam By operating in this manner, advantage is taken of the high vaporization heat of water to provide maximum cooling with a minimum of water consumption and at the same time provide additional 90 vapors to maintain the char in the hopper in a

fluidized state The cooled product is then conveniently removed from the hopper, defluidized by contact with additional water which condenses the fluidizing steam and is 95 passed from the system by means of a conveyor or other suitable means. The water used to cool the hot char may be introduced thereto prior to entry of this material into the char hopper, or after the 100 char enters the hopper, or a portion may be admitted at both localities It is preferred that the char be cooled to as low a temperature as possible; however, if a suitable use for higher temperature steam exists, the amount of cool 105 ing water may be controlled to provide a char temperature in the receiver substantially above the dew point of water Also, although it is preferred to maintain the char in the hopper in a fluidized states the defluidization of this 110 material may be accomplished therein by inereasing the amount of cooling water introduced into the char to the point where liquid water is present in the hopper The char is then removed from this vessel as a slurry 115 rather than as a fluidized mass. The amount of water required to accomplish the second stage of the char cooling process varies with the initial temperatures of both the char product and the water and the 120 final temperature of the char More usually the water is introduced at a low temperature, i e. between about 600 F and about 100 F The pressure in the char hopper or receiver is also desirably maintained at a low level, usually 125 less than the pressure in the carbonizer, viz. between about 0 and about 5 psig Setting the pressure establishes the dew point temperature and accordingly the amount of water required as quench, which is usually between about 130 rate of introduction of fresh coal into this zone It is within the scope of this invention to provide a degree of temperature control by the aforedescribed method immaterial of the causes of temperature variation, however, the proposed mode of operation is directed primarily to eliminating the problem resulting from recurrent variations in feed coal particle size. Hot char product from which the major portion of the volatile constituents of the coal have been removed is withdrawn from the lower portion of the carbonizer and is passed through a cooler wherein the temperature of the char is lowered by indirect heat exchange with a fluid cooling medium When operating in accordance with the ranges of process variables previously enumerated the amount of this material varies between about 0 6 and about 09 pounds per pound of wet feed coal. The remainder of the raw material delivered to the process is now in a vapor state, comprising a mixture of steam, combustion gases and tar vapors The apparatus used in conjunction with the char cooling

preferably comprises one or more conventional tubular heat exchangers similar to those previously described in conjunction with drying and preheating the coal feed The type and quantity of cooling fluid passed through the exchanger may be varied to meet the particular needs of the process In general, fluids similar to those previously disclosed for use in drying and preheating the coal are used This operation is simplified and the cost is substantially reduced, if a common fluid medium is used for both coal drying and preheating, and for cooling the product char When operating with this type of system, a continuous circulating fluid stream is provided, which extracts heat from the hot char product and transfers it to the fresh coal feed Inasmuch as the heat removed from the char in the cooling operation may not be sufficient to provide the heat required for drying and preheating the coal feed, or vice versa, it is desirable when using a common heat exchange fluid to provide an additional heat source, such as for example a conventional tubular heater, or an additional source of cooling, such as for example a water cooler, which ever is required. In this preliminary cooling step, the char temperature is usually reduced to between about 7000 F and about 4000 F, although it may be brought to a still lower temperature if desired The cooling fluid may be introduced to the cooler at any low temperature; however, when a common circulating stream is used the inlet temperature, of necessity, conforms to the temperature of the fluid leaving the heaters which serve the drying and preheating stages of the carbonization process, i.e between about 6500 F and about 3500 F. The size of the cooler required varies with the amount and temperature of the char product, 785,863 0.05 and about 0 15 pounds per pound of char product. The cool char which accumulates in the char hopper forms a dense fluidized solids bed above which there exists a conventional dilute phase zone of low solids concentration The solids density in the dense phase bed is usually between about 15 and about 25 pounds per cubic feet; whereas, the concentration of solids in the dilute phase is very small, often less than 0 1 pounds per cubic feet Vapors and solids leaving the hopper dilute phase pass through conventional separation means, for example cyclones, for the removal of a major portion of the solids and thence to a secondary solids recovery system In order to minimize the facilities required for separating entrained solids, the overhead gases from the feed coal drier and preheater, which contain entrained coal particles, are also introduced into the secondary solids recovery system. In one embodiment, this system comprises a vertical elongated scrubbing tower, with baffles suitably dispersed therein to provide good liquid-vapor contact Within this tower, the combined vapors from

the drier and preheater and char hopper are scrubbed with water to remove entrained coal and char particles As in the preceding cooling step, the quantity and temperature of the scrubbing water is controlled to maintain a suitable temperature within the scrubber so that a minimum amount of the steam introduced in the two vapor streams is condensed Preferably the scrubbing liquid is supplied by recycling a warm solids-water slurry from the bottom of the scrubber and combining with this stream necessary makeup water from an outside source Since the solids-water slurry is at the dew-point temperature of the steam in the scrubber, usually between about 212 F and about 2400 F, this method of operation provides a relatively high temperature scrubbing stream and a minimum of steam is condensed in the process In addition, by recycling, it is possible to closely control the scrubbing operation for maximum solids removal. The recovered solids are removed from the scrubbing system as a slurry in the scrubbing water This slurry is conveniently mixed with char removed from the char hopper in order to lower its temperature and to reduce the dust problem associated with the finely divided solids product As a result of this, the product char solids contain a mixture of coal and char; however, the amount of coal recovered in this operation is insignificant when compared to the char, being only between about 0 1 and about 0 8 per cent thereof by weight, and when combined with the char is insufficient in quantity to alter its properties or characteristics. It is apparent that the aforedescribed method of solids recovery offers several important advantages The combination treatment of gases from the char hopper and the drying and preheating zones substantially reduces the number of cyclones or other solids recovery equipment required In addition, controlling the scrubbing operation to prevent 7 C condensation of the fluidizing steam provides an important heat economy and reduces the amount of scrubbing water required for the operation Furthermore, introducing recovered coal into the char product not only provides a 75 convenient method of disposing of this material, but also increases the char yield without affecting the properties of the char. As previously mentioned, the effluent vapors from the carbonizer comprise gaseous products 80 of combustion and various tar compounds plus a small amount of entrained char The major portion of the tar materials in the gases condense to liquids at ordinary temperatures and form a valuable product of the carbonization 85 process To effect the separation of the normally liquid tar, the carbonizer gas stream is passed to a quench tower where the vapors are contacted with a low temperature liquid tar. This material not only provides the cooling 90 effect necessary to

condense liquid tars but also effects the removal of entrained solids from the gases The scrubbing and condensing liquid is preferably obtained by circulating tar condensed in the quench tower through a 95 cooler and recycling it to the upper portion of the tower Within the tower are provided suitable baffles or plates whereby intimate contact between ascending gases and downflowing liquid is effected The pressure at which this 100 operation is carried out is controlled by the pressure in the carbonization zone, being somewhat lower, usually between about 10 and about 2 psig It has been found that the major portion of the desirable liquid tar compounds 105 are condensed by cooling the carbonizer gases to between about 150 F and about 800 F. The remaining vaporous tar compounds and combustion products form a gas, which although low in heat content, may be used as a 110 fuel If desired, of course, a further separation between the uncondensed tar compounds and combustion and fluidization gases may be effected. In the past, difficulty has been encountered 115 in physically separating all of the condensed tar constituents from the uncondensed tar vapors and combustion gases Experience has shown that when tar vapors are quenched in the manner described, a portion of the tar 120 condenses as very small droplets which form a dispersion or "fog" in the uncondensed gases The dispersed tar is unaffected by subsequent after-cooling of the gases and is separated therefrom only with difficulty, 125 usually by passing the gases through a special separating means, such as, for example, a Cottrell precipitator It has been found that a major portion of this entrained liquid tar may be successfully removed in the quench tower 130 785,863 tion of the drier vessel 10; however, in the lower portion thereof, the dry coal is confined within an annular space lying between the walls of the drier and a cylindrical elongated conduit extending upwardly through the 70 bottom of the drier Within this conduit lies a preheating zone 14 in which there is maintained a higher temperature dense bed of coal particles which overflow continuously into the lower temperature dry solids bed 12 Above 75 the dense beds of dry and preheated coal is a dilute phase 16 of low solids concentration. Water vapors released from the coal pass up-wardly through this space into a cyclone 18 from which separated solids are returned to 80 the dense phase of dry coal, and from which the vapors leave the drier through conduit 20. To provide the sensible heat required to heat the wet coal and the latent heat of vaporization of the water present therein, a 85 stream of dry coal is removed from the annular drying zone 12 through conduit 22, entrained in fluidizing steam and passed upwardly through conduit 26 and coal heater 28 wherein the temperature of the coal is in 90 creased to about 4800 F From the heater the hot coal is passed into

conduit 14 from which it eventually overflows to the drying zone. In order to maintain the desired temperature in the drying zone, it is necessary to overflow 95 about 2 pounds of solids from conduit 14 per pound of wet coal introduced into the unit. Thus the solids circulation rate through the coal heater 28 is about 3 pounds of coal per pound of wet feed The heat required in the 100 combined drying and preheating operation is supplied by passing the circulating solids stream in indirect heat exchange with a cat cracker decanted oil having an A Pl gravity of about 15 This material is introduced to 105 heater 28 through conduit 30 at a temperature of about 680 F and exits therefrom through conduit 32 at a temperature of about 4000 F. The foregoing method of drying the coal is simple in application and in addition to effect 110 ing removal of moisture from the coal, it provides a ready means of adding to the coal the amount of preheat required before pretreating the coal, the next step in the process. Although the hot coal leaving heater 28 115 enters zone 14 in a fluidized condition, it may be desirable to introduce additional gases, such as for example steam through conduit 13. Generally, the water vaporized in the drying zone is adequate to provide the desired turbu 120 lence in the dry solids bed; however, if necessary, an additional quantity of fluidizing gases may also be introduced to zone 12 The amount of fluidizing gases passed through each zone is controlled to provide a velocity there 125 in of about 2 feet per second, thereby maintaining a solids density in each bed of about pounds per cubic foot As previously mentioned, the effluent gases from both zones pass through a conventional cyclone 18 for the 130 by passing the gas stream through a mixt extractor, thereby effecting substantially complete separation of liquid tar from vapors. As previously mentioned, the material used to condense tar from the carbonizer vapors also serves as a scrubbing medium to effect removal of entrained char from these gases. The amount of solids concerned usually is quite small, being between about 1 and about 10 per cent of the char product If it is contemplated using the tar product as a fuel the presence of this minor quantity of solids usually is not detrimental; however, for other uses of the tar, it may require further treatment to remove the char solids. In order to more clearly describe the invention and provide a better understanding thereof, reference is had to the following drawings of which: Figure 1 is a diagrammatic illustration in cross section of process equipment used in carrying out a preferred embodiment of the invention comprising a unitary coal carbonization system which includes a dryer,

preheater, pretreater, carbonizer, char hopper, solids recovery system, tar quench tower and associated lines and heat exchange equipment. Figure 2 is a diagrammatic illustration in cross section of another embodiment of a coal drier, preheater, and associated heat exchange equipment. Figure 3 is a diagrammatic illustration in cross section of still another embodiment of a drier, preheater and associated heat exchange equipment and includes in addition, feed hopper means for reducing the average moisture content of the coal Feed hopper permits wet coal to be fed prior to drying. Figure 4 is a diagrammatic illustration in cross section of a process arrangement for cooling product char produced in the carbonization process. Figure 5 is a diagrammatic illustration in cross section of a method of introducing wet solids into the drier from a feed hopper, somewhat similar to that disclosed in Figure 3. Referring now to Figure 1, a finely subdivided coal at a temperature of about 600 F. having a particle size distribution between about 10 mesh and about 10 microns is delivered through conduit 2 into feed standpipe 4 wherein it is maintained in a dense turbulent state by passage therethrough of a fluidizing medium Entering the system the coal contains about 8 % of surface water by weight. From standpipe 4 the fluidized coal passes downwardly through conduit 6 where it is entrained in additional gases, in this instance steam, and passed upwardly through conduit 8 to a drier and preheater vessel 10 which is at a substantially higher elevation Within the drier vessel there is maintained a dense highly turbulent bed 12 of dry coal particles at a temperature of about 2700 F The upper portion of this bed occupies the entire cross sec785,863 separation of entrained solids which are returned to zone 12 In spite of this, some solids, in quantity equal to about 0 2 per cent by weight of the wet feed are retained in the gases and leave the system through conduit 20. The combined drying and preheating vessel forms a part of a single unitary vessel structure being superposed above a carbonization vessel 36 which contains within its lower portion a pretreating zone 42 Passage of solids from the preheating zone 14 to the pretreating zone 42 is effected by flowing them downwardly through a standpipe 44 enclosed within the carbonizer vessel Inasmuch as the standpipe passes through the carbonizer before it reaches the pretreating zone, it is exposed to the high temperatures in the former zone and it may be desirable to provide some form of insulation to protect this conduit The rate of flow of solids from the preheating zone 14 to the

pretreating zone 42 is controlled to maintain a more or less constant level in vessel by a conventional plug valve 58 in contact with the bottom terminus of the standpipe 44 The pretreating zone 42 is separated in part from the carbonization zone 40 by a vertical baffle 66 attached at the bottom and sides to the inner wall of the carbonizer vessel 36 The bottom portion of the treating zone contains a distribution grid 60 for distributing fluidizing gases throughout the pretreated coal. The pretreating zone opens upwardly into the carbonizing zone 40 and is separated therefrom by a grid 54 through which pretreated solids and vapors pass from the former to the latter zone. The pretreating operation involves contacting the coal particles with a controlled amount of oxygen, viz, about 0 04 pounds per pound of preheated coal, whereby the coal particles are partially oxidized In this manner, the physical characteristics of the particles are altered so as to nullify their tendency to adhere to each other as they are elevated in temperature and pass through the so-called " plastic " stage The effectiveness of the pretreating step is dependent not only on the extent to which the coal particles are oxidized, but is also a function of the pretreatment temperature, which is substantially increased over the preheating temperature, that is to about 7250 F The heat required to elevate the coal to this temperature is in normal operation supplied entirely from the heat of combustion of the coal In carrying out the pretreating step, oxygen is introduced through conduit 64 and is distributed in the lower portion of the pretreating zone through grid 60 The oxygen may be supplied in a relatively pure state; however, more usually, it is preferred to use air, not only from the viewpoint of cost, but also to supply the additional gases necessary to maintain the solids in the pretreating zone in a fluidized state Although the air admitted to the system normally suffices for this purpose, additional gases such as, for example, steam, flue gas, etc, may be introduced through conduit 64 for fluidization purposes 70 Coal entering the pretreating zone commingles with the solids contained therein and is partially oxidized and rapidly increased in temperature to that of the dense phase bed In this process about 4 per cent by weight of the 75 preheated coal is reacted with the oxygen and converted to combustion products The resulting mixture of pretreated coal and combustion gases, along with any portion of unconsumed oxygen, passes upwardly through the pre 80 treating zone and through gird 54 into the carbonization zone 43 Within this zone there is maintained a dense phase turbulent bed of solid char particles at a substantially higher temperature, that is about 950 'F Inasmuch as 85 the pretreating zone is entirely beneath the top level of the solids in the carbonization zone, the grid 54

serves the dual purpose of distributing the solids and gases leaving the pretreating zone and at the same time prevents 90 passage of solids from the carbonization zone to the pretreating zone By use of this separating means, it is possible to maintain two contiguous, yet distinct and separate dense phase beds of solids at quite different temperatures 95 The preheated coal from zone 14 contains a large number of organic tar compounds varying widely in molecular structure and boiling point The increase in temperature in this zone releases a portion of the lower boiling of these 100 volatile compounds which pass upwardly into the carbonization zone 43 along with the pretreated solids and other gases Upon entering the latter zone, the pretreated solids are quickly elevated to the temperature prevailing 105 therein and large additional amounts of volatile components are released from the coal. The total time required in the two zones to carry out the process of tar removal is of short duration; however, in order to prevent 110 solids from agglomerating and thereby assure an operable fluid process, it is desirable to maintain a large excess of pretreated solids in the pretreating zone and a similar excess of carbonized solids or char in the carbonization 115 zone This is effectively provided by sizing the pretreating and carbonization zones to allow an average particle residence therein of about minutes and about 60 minutes, respectively. The pretreated solids bed is maintained in a 120 highly turbulent state by controlling the flow of vapors therethrough to provide a gas velocity of about 1 2 feet per second and a solids density of about 25 pounds per cubic foot. Usually, this is effected by varying the oxygen 125 rate through conduit 64; however, if necessary, an extraneous gas (not shown) is admitted to zone 42 The degree of turbulence and density of the solids in zone 43 is regulated in a similar manner 130 785,863 in detail In order to compensate for variations in temperature in this zone, provision is made to pass hot char from the carbonization zone to the pretreating zone through conduit 48 and standpipe 50 The quantity of this 70 stream at any given instant may vary over a wide range, depending on the rapidity with which the size distribution of the coal particles changes It is desirable to pass a small amount of char, namely about 0 01 pounds per pound 75 of coal feed, continuously into the pretreating zone through the char recycle system The continuous char recycle allows more complete temperature control since slight increases in the pretreating temperature can be compensated 80 for by decreasing or entirely halting the flow of char The motive force required to transfer the char between the two zones is supplied by superheated steam admitted to recycle conduit 48 through conduit 68 85

The final products of the carbonization process comprise a mixture of tar vapors, steam and combustion gases, and carbonaceous char solids Distribution of these products, based on the wet coal feed, is approximately 8 per cent 90 steam, 14 per cent tar compounds and 76 per cent char The remainder of the coal is converted to combustion products to supply the process heat requirements The gaseous products pass from the dense phase bed of char 95 43 upwardly into a dilute phase 47 and from there through a cyclone separator 46 and conduit 52 Solids recovered in the cyclone are returned to the dense char bed below the surface thereof Char solids product are re 100 moved from the bottom of the carbonizer 36 through conduit 62, are picked up by a stream of fluidizing steam and are passed through conduit 72 upwardly through a char cooler 74 for preliminary cooling The fluidized char 105 solids enter the cooler at a temperature substantially the same as that maintained in the carbonization zone, i e, about 9250 F, and exit from the cooler at a temperature of about 500 TF To extract the heat from the char, a 110 cat cracker decanted oil of about 15 A Pl gravity is introduced into the cooler through conduit 32 at a temperature of about 400 F This material flows through the cooler countercurrent to the char and exits therefrom through 115 conduit 30, being heated in its passage through the cooler to about 600 'F To provide a process of maximum thermal efficiency, a continuous circulating fluid system (not shown) is used in which a common hydrocarbon fluid 120 accomplishes both char cooling and the drying and preheating of the coal feed Substantially more heat is required in the drying and preheating operation than is obtained by cooling the char Therefore, in order to thermally 125 balance the system, it is necessary to supply an additional amount of heat to the oil prior to its introduction into the coal heater 28 This may be done in any conventional manner, such as, for example, by passing the decanted oil 130 The heat required for carbonizing the coal feed is also supplied by burning a portion of this material For this purpose, about 0 03 pounds of oxygen per pound of pretreated coal feed is introduced into the carbonization zone 43 In this operation also the oxygen is introduced in the form of air rather than in a pure state, for the reasons previously given Since one of the important features in optimizing liquid product yield is minimum contact between oxygen and volatile tar constituents, the oxygen required for carbonization is introduced into the bottom of the carbonization zone through conduit 70 which is at a point remote from the area of introduction of pretreated coal into the same zone Oxidation and combustion of the carbonized coal particles proceeds rapidly and is substantially completed before the carbonizer fluidizing and combustion gases reach the elevation at which the pretreated coal is present in quantity The heat released by the

combustion reactions is quickly transmitted throughout the dense char bed providing a hot turbulent mass into which lower temperature pretreated solids are introduced. The transfer of heat from the char particles to the pretreated solids in turn is equally swift and these solids reach the general char bed temperature level within a very short period of time The process of devolatilization also proceeds at a fast rate and, by the time the pretreated solids reach the zone of combustion, they are substantially free of volatile tars. By reason of the location of withdrawal conduit 62, char product from the main upper portion of the carbonization solids bed is forced to flow downwardly through the space provided between baffle 66 and the wall of the carbonizer vessel 36 Hot combustion and fluidizing gases flow upwardly through the same space countercurrent to the descending char and provide a stripping action which assists in the removal of tar compounds from the char The removal of volatile components from the coal in the carbonization zone, therefore, is effected in two ways, i e, by elevating the pretreated coal particles to the carbonization temperature and by passing these particles downwardly countercurrent to ascending combustion and fluidizing gases before withdrawing them from the carbonization zone Without a doubt, increased temperature is the major factor in effecting tar removal; however, the stripping action of the combustion gases contributes to the total tar yield by removing some residual volatile materials. As mentioned in the previous discussion, the size distribution of the coal particles introduced to the carbonization unit is subject to variation, particularly in commercial operations where the crushing and grinding equipment used must handle large quantities of coal. The effects of size distribution on oxygen consumption and the temperature in the pretreating zone have also previously been discussed 785,863 14 785,863 through a conventional fired heater (not shown) or other conventional heating means. The lower temperature char leaving cooler 74 is passed into a char pot 98 from which it flows downwardly through conduit 80 into a char hopper 84 where it accumulates in a conventional dense phase fluidized bed 88, superposed by a dilute phase 86 Although a substantial amount of heat is removed from the char in the cooler, this material is still much too hot to be yielded as product It is preferable, for convenience in handling the char, that it be cooled to a much lower temperature and, if possible, by a more efficient method than indirect heat exchange The large amount of additional cooling required is conveniently and economically furnished by introducing water into the char through conduit 82 prior to passage of the char into the char hopper 84.

The water is immediately converted to steam, thus providing, in addition to the cooling effect, additional fluidizing medium suitable for maintaining the solids in conduit 80 in a turbulent state The amount of water combined with the char is controlled to provide a temperature in the char hopper at or slightly above the dew point of water at the pressure existing therein In this specific illustration, the hopper pressure is about 3 5 psig and the temperature of the dense char bed 88 is about 230 CF These conditions are maintained by cooling the char with about 0 07 pounds of 800 F water per pound of char Operating in this manner prevents liquid water from passing into the hopper, and the solids contained therein are readily maintained in a fluid state. Steam which results from the char cooling disengages from the solids in bed 88, passes upwardly through dilute phase 86 and a conventional cyclone separator 90 for the removal of entrained solids, and thence through conduit 108 into a secondary solids recovery tower 98. Before entering this tower, the char hopper gases are joined through conduit 20 by the gaseous effluent from the drier and preheater Within the solids recovery tower 98 which contains a number of baffles 106, the combined gases containing both char and coal solids are scrubbed with water introduced through conduit 100, and spray ring 104 The resulting solids-water slurry is withdrawn from the bottom of the recovery tower through conduit 110, is diluted with additional water from conduit 94 and then combined with char removed from the bottom of the char hopper through conduit 92 The slurry water serves to condense any steam remaining in the char released from the hopper, thereby defluidizing this material The total solids product comprising char admixed with a small amount of coal is then removed from the unit by a conveyor or by other suitable means (not shown). The temperature in the solids recovery tower is about 2160 F, which, at the pressure existing therein, that is about 2 psig, is equal to the dew point of water It is preferred in carrying out the solids recovery process that a minimum amount of the steam introduced to tower 98 be condensed In order to assure this result, the temperature of the scrubbing water is 70 maintained at substantially the same level as the temperature within the tower This is conveniently accomplished by heating the water prior to its introduction to the recovery tower, or more preferably by recycling hot slurry 75 from conduit 110 to the top of the recovery tower (not shown) Even when using recycle slurry for scrubbing, however, it is necessary to introduce extraneous warm make-up water through conduit 100 to compensate for water 80 in the slurry combined with the char product. The scrubbed gases, consisting of essentially solids-free steam, accumulate in the upper portion of tower 98 and are removed therefrom

through conduit 102 This gas, although low 85 in pressure and temperature, contains a large amount of latent heat and may be used in any conventional service where low pressure steam is of value. Tar vapors formed in the pretreating and 90 carbonization zones, together with the gaseous products of combustion, pass from the carbonizer 36 through conduit 52 and are introduced into a tar quench tower 112 A substantial portion of the tar in these gases consists of 95 compounds which are liquid under normal atmospheric conditions These compounds are readily condensed in the quench tower by contacting the hot gases with a quantity of cool liquid tar The liquid tar also serves as a 100 scrubbing medium and operates to remove char solids entrained in the hot gases In carrying out this step, the vapors are introduced into the bottom of the tar quench tower and pass upwardly around baffles 114 counter 105 current to liquid tar introduced into the tower through conduit 142 The cooler vapors subsequently pass through a number of perforated trays 116, through a mist extractor 118 to remove entrained liquid droplets and exit from 110 the quench tower through conduit 120 The liquids and solids removed from the vapors by the scrubbing tar are transferred from the bottom of the quench tower through pump 136 and are passed through conduit 138 and cooler 115 A portion of the cooled material is returned to the quench tower through conduit 142 and the remainder is yielded as product through conduit 138 The temperature of the gases leaving the top 120 of the quench tower is about 1600 F This is still substantially above atmospheric temperature and in order to lower the temperature of the gases still further they are passed through a water cooler 122, where additional 125 tars are condensed, and then into an accumulator 124 where a further separation of gas and liquid takes place This final cooling step reduces the temperature of the gases to about F The gases are released from the accu 130 785,863 ties may be provided An alternate arrangement of the pretreating and carbonization zones is also contemplated, in which pretreating is carried out in a cylindrical zone centrally disposed within the carbonization zone, sealed therefrom and separated at the top in a manner similar to the pretreater of Figure 1. In this apparatus arrangement, combustion in the carbonization zone would be carried out in an annular space surrounding the pretreating zone Although internal circulation of char from the carbonization zone to the pretreating zone for temperature control is preferred for a number of reasons, it is also within the scope of the invention to carry out this step through external means These and other modes of operation are explained in more detail in the subsequent discussion of certain other embodiments of the invention. The following data are presented to illustrate a typical commercial

carbonization operation based on the processing arrangement of Figure 1. mulator through conduit 126 and pass into a Cottrell precipitator 128 Liquid is removed from the precipitator through conduit 132, is combined with accumulator liquid from pump 130 and conduit 134, and this combined stream is in turn added to the tar product passing through conduit 138 The final vapor product comprising primarily combustion gases and steam leaves the precipitator and the unit through conduit 130. The preceding discussion has been directed to a preferred embodiment of the invention as specifically illustrated in Figure 1 It is not intended that the material presented be construed in any limiting sense, but that other equipment, process conditions, flows, etc are also used within the scope of the invention. For example, to limit the possibility of equipment plugging prior to the drying operation it may be desirable to introduce wet coal directly from a mechanical conveyor, such as a bucket elevator, into the dryer vessel 10 Again, to provide a more flexible process, less dependent, or even separate, drying and preheating faciliEXAMPLE Flows Wet Coal-10 to 400 mesh Water Content Dry Coal Char Product Volatile Product Solids Content Pretreater Air Carbonizer Air Char Recycle (For Pretreater Temperature Control) Feed Coal Heater Coal Circulation Rate Heating Fluid-15 i A Pl hydrocarbon oil Product Char Cooler Cooling Fluid-15 i A Pl hydrocarbon oil Cooling Water Injected into Char Product Water to Solids Recovery Tower Tar Quench Tower Reflux Lb/Hr 450,000 35,000 415,000 345,000 60,000 1,000 80,000 50,000 25,000 1,250,000 1,550,000 1,550,000 28,000 96,000 580,000 -785,863 16 785,863 Temperatures Wet Coal Drying Zone Preheating Zone Pretreating Zone Carbonization Zone Char Hopper Solids Recovery Tower Tar Quench Overhead Feed Coal Heater Coal In Coal Out Heating Fluid In Heating Fluid Out Product Char Cooler Char In Char Out Cooling Fluid In Cooling Fluid Out Cottrell Precipitator Product Char Tar Product Pressures Drying Zone Preheating Zone Pretreating Zone (Top) Carbonization Zone (Disperse Phase) Char Hopper Solids Recovery Tower Tar Quench Tower Average Residence Time of Coal In Pretreating Zone Carbonization Zone Gas Velocity in Drying Zone Preheating Zone Pretreating Zone Carbonization Zone Density of Solids in Drying Zone Preheating Zone Pretreating Zone Carbonization Zone As previously noted, the amount of oxygen consumed in the carbonization process and the conditions under which it is consumed are very important in determining the type and quantity of the gaseous, liquid and solid products derived from the carbonization process In order to obtain maximum product yields, it is desirable that the proportion of the total oxygen consumed in the pretreating step be limited to the

minimum required to provide an operable process, that is a process wherein particle agglomeration is allowed to reach the maximum possible without resulting in an inoperable condition This point is important, for if an excessive amount of oxygen is used in the pretreating zone, valuable tar components are consumed therein and the tar yield is correspondingly reduced Also, the introducOF. 270 480 725 950 230 216 270 480 500 400 950 500 400 470 350 Psig. 3.8 6.0 11.0 8.0 3.5 2.0 6.0 Minutes Ft./Sec. 2.0 2.5 1.0 1.5 Lb./Cu Ft. 22 785,863 In carrying out the drying operation, wet coal is introduced into the drying zone solids bed wherein it is quickly elevated in temperature with a concurrent release of surface water as steam A stream of dry coal is passed from 70 this bed through a first indirect tubular heater and is then returned to the drying zone to supply the heat required therein The range of temperature through which drying may be effected is substantially the same as for the 75 drying process previously discussed It is necessary to provide sufficient residence time in the drier for the coal to become heated to the drying temperature and for the water vapors released therein to escape from the solids bed; 80 more usually a residence time of between about 1 and about 15 minutes is sufficient The amount of solids circulated through the heater varies with the moisture content of the coal and the temperature maintained in the drying 85 zone; more usually, the solids circulation rate is maintained between about 2 and about 15 pounds of solid per pound of wet coal feed. With circulation rates of this order of magnitude, it is necessary in order to provide the 90 heat required for drying to increase the temperature of the coal during passage through the heater to between about 250 and about 500 '1 F Heat is transmitted to the dry coal solids from a hot fluid stream, preferably 95 selected from the group of fluids previously listed This material is admitted to the heater in sufficient quantity and at an adequate temperature to provide the necessary transfer of heat As stated before, it is usually preferred 100to introduce this fluid into the heater at a temperature between about 350 '1 F and 10000 F. In addition to the solids circulated through the drying zone a further amount of solids is 105 passed from this zone through the first heater, then through a second heater and into the preheating zone In the latter heater, additional thermal energy is transferred to the coal to provide the necessary degree of preheat needed 110 for the pretreating operation Since the preheated coal is the only source of feed to the pretreating zone, the second solids stream must contain at least an amount of coal equivalent to the wet coal feed on a dry basis This 115 quantity of solids, however, is not sufficient to provide the

solids density in the second heater necessary for good heat transfer To remedy this, an additional stream of solids is recycled from the preheater to the inlet of the second 120 heater More usually it is preferred to circulate coal solids through the preheating zone at a rate between about 2 and about 10 pounds per pound of wet coal feed The variables and operating conditions contemplated for use in 125 this portion of the process, in general, conform in magnitude to those previously given in the general discussion of coal preheating. For example, the temperature in the preheating zone is usually maintained between about 130 tion of an excessive amount of oxygen produces more than the required amount of "case hardening" which retards devolatilization of the coal and encourages cracking, particularly in the carbonization zone On the other hand, if insufficient pretreatment oxygen is used, there is a danger that the carbonaceous particles may adhere together and that the process may become inoperable In addition to the quantity of oxygen used, the pretreatment temperature is also important in determining the operability of the fluidized carbonaceous solids system and it is preferred to carry out the pretreating step at an elevated temperature At temperatures normally used in this operation, it is impossible to supply all of the heat required in the pretreating zone by burning carbonaceous material therein and at the same time provide a degree of pretreating consistent with optimum product yields For this reason, it is necessary to provide an additional large quantity of heat from another source, usually by preheating the carbonaceous solids in a conventional manner, such as, for example by indirect heat exchange with a hot fluid The further amount of heat required to raise the carbonaceous material from pretreating temperature to the carbonizing temperature and to carry out the carbonization process is then supplied by oxygen introduced in the carbonization process. A process for supplying the necessary preheat, in conjunction with drying of the wet coal feed, as illustrated in Figure 1, has been described in detail This method of preparing the coal for pretreatment, although it possesses many advantages, is relatively inflexible in operation For reasons of heat transfer efficiency, the temperature in the drying zone is preferably maintained at the minimum necessary to drive off surface water introduced with the wet coal Similarly the preheater temperature, once established, is more or less fixed and cannot be varied without seriously affecting the subsequent pretreating and carbonization steps. In an operating unit the range of variation of these temperatures serves to limit the amount of coal solids circulated through the coal heater This is important since the heat transfer coefficient of the gas-solids stream passing through the heater is directly proportional

to the quantity of solids in said stream, and, therefore, it may be desirable to vary the composition of this stream. A more flexible drying and preheating process arrangement wherein the advantages of a variable composition gas-solids stream are realized is possible if the two steps are made somewhat less interdependent In one embodiment of such an arrangement, the dry and preheated solids are again maintained in dense phase fluidized beds similar to those illustrated in Figure 1; however, in this instance the beds are entirely separated and solids do not flow from the preheating zone into the drying zone. 785,863 350 and about 650 'F A similar heating fluid is used to supply heat to the solids in the second heater and the quantity and temperature of this material is suitably adjusted to give the desired results. The aforedescribed method of drying and preheating provides a number of advantages over the method illustrated in Figure 1 For example, it provides a more flexible process in which coal circulation rates through the heaters and the temperatures in the drying and preheating zones can be varied more or less independently of each other This increased flexibility of operation is particularly important from the viewpoint of obtaining maximum heat transfer rates in the heaters and reducing the heating surfaces to a minimum As previously mentioned, the heat transfer coefficient is directly proportional to the density of solids in the gases passing through the tubular heater. That is, when the concentration of solids in the gas is increased the heat transfer coefficient increases, and when the solids density decreases the heat transfer coefficient is lowered The density of the gas-solids mixture in turn is determined by two factors, the velocity of the fluidizing gases and the solids circulation rate. When the solids circulation rate is relatively fixed, as in the drying and preheating method of Figure 1, the only= way in which solids density can be changed is by varying the velocity of the fluidizing gas Thus, if it is desired to increase solids density, the velocity of the fluidizing gas must be decreased, and conversely a decrease in solids density is brought about by increasing the velocity of the fluidizing medium Unfortunately, this variable can only be manipulated within certain limits For example, at a velocity below about 0 25 feet per second solids do not remain in suspension and at high velocities erosion of the heat exchange equipment may become a problem. With the system of preheating and drying just described, it is possible to vary both the solids circulation rate and the fluidizing gas velocity thereby providing a more flexible operation. Another important advantage of this method of operating lies in the fact that the drying and preheating steps are carried out in entirely

separate heaters rather than in one heater The efficiency of heat transfer in an exchanger is a function not only of heat transfer coefficients but also of temperature difference between the heat source and the heat absorbing stream The greater the average difference between these temperatures, the more efficiently is the heat exchanged The use of a separate heater for drying the coal provides a substantially higher temperature differential in this heater than exists in the heater of Figure 1 Since the major portion of the heat required in the two heating steps, usually between about 55 and about 75 per cent, is transferred in the first heater, a more thermally efficient process results from this method of operation This is true even though the temperature difference in the preheat exchanger is less favourable than the temperature difference in the heater of Figure 1 The thermal advantage of the twoheater system is further enhanced by passing a substantial part of the solids to be preheated through the first exchanger, wherein a portion of the required preheat is provided The net result is a more efficient drying and preheating process which substantially decreases heaat exchange equipment requirements Still another important advantage results from the use of the two-exchanger system It often happens in commercial installations that heat exchange equipment must be limited in physical dimensions, particularly in height With the use of vertical type heaters as contemplated herein the restriction of exchanger length becomes an important problem In a system where the rate of solids circulation, and thus the solids concentration or density, can be varied it is possible to obtain similar results to those which are produced in the apparatus of Figure 1 with an exchanger of lower surface area This, of course, means a shorter exchanger which simplifies the supporting structure and allows a greater variety of equipment location. Although in the aforedescribed operation there is no passage of solids from the preheating zone to the drying zone, as in the process illustrated by Figure 1, this method of treating the coal may be carried out in similar apparatus with only a slight modification, that is by extending the vessel which encloses the preheating zone above the level of the dense phase bed of solids in the drying zone Thus this system also provides the advantages of carrying out both drying and preheating in a single vessel. In order to more clearly illustrate this aspect of the invention, reference is had to Figure 2. Referring to Figure 2, drying and preheating of the coal are carried out in a vertical cylindrical vessel 10 somewhat similar to that illustrated in Figure 1 Internally vessel 10 is divided into concentric zones 12 and 14 by a cylindrical member which terminates

below the inside top of vessel 10 and extends downwardly outside and below vessel 10, being supported on the carbonizer vessel 36 The drying portion of the process is carried out in the annular space which forms zone 12 in a dense phase turbulent bed of dry coal particles, the upper level of which lies below the top terminus of the cylindrical member Preheated coal is accumulated in zone 14 and is maintained therein in a similar dense phase bed, also having an upper level below the top of the cylindrical member whereby the two beds are kept entirely separate. Vapors released within the two zones enter a common dilute phase 16 above the solids bed, pass through a conventional cyclone 18 for the removal of entrained solids, and exit from the system through conduit 20 Wet coal 7 c 8 l C 785,863 and return to the preheating zone through conduit 34 To maintain the preheater temperature at about 480 "F, it is necessary to provide a rate of solids withdrawal from bed 14 for circulation through heater 152 of about 5 pounds per pound of wet coal feed This quantity of solids combined with the solids from the feed coal heater 144 produces a temperature of about 450 'F entering heater 152. In its passage through the latter heater the coal is further elevated in temperature to about 480 'F. The heat required to carry out the drying and preheating step is supplied by using a hot hydrocarbon oil similar to that mentioned in the discussion of Figure 1 A separate stream of oil may be used in each of the two heaters; however, it is preferred to use a common heating fluid for both services with the oil being passed through the heater countercurrent to the fluidized coal, the sequence of passage through the heater being opposite to the coal stream circulated from the drying zone The flow of oil through the heaters is maintained at a sufficient rate to provide an inlet temperature to the dry coal heater 152 of about 675 "F. At the coal circulation rates illustrated, the oil leaves the dry coal heater at about 580 'F and the feed coal heater 144 at about 400 "F. As previously described in the discussion of Figure 1, preheated coal passes from zone 14 downwardly through standpipe 44 into a pretreating zone 42 contained within the carbonization zone 36 Fluidization of the solids within zone 14 is maintained by introducing a small amount of steam through conduit 13. The remainder of the coal carbonization process and product recovery system conforms to the illustration of Figure 1 as described in the preceding discussion. A typical application of this embodiment of the invention on a commercial scale is illustrated by the following data. solids are introduced to the drier through conduit 8 and enter the

dense turbulent bed 12 where they are quickly heated to the drying temperature, that is to about 270 "F At the pressure maintained on the system, namely about 4 psig, this is considerably above the boiling point of water As a result, the water introduced with the coal is quickly converted to steam which escapes to the dilute phase 16 and from the drying and preheating system as previously described To provide the large amount of heat required for this operation, a stream of solids is removed from the dense phase bed 12, passed downwardly through conduit 22, entrained in steam and passed upwardly through conduit 26 and feed coal heater 144 An amount of heated solids equal in quantity to the wet coal feed rate, that is about per cent of the total solids passed through the heater, is further passed through the dry coal heater 152 and returned to the preheating zone 14 The remainder of the dry heated coal is passed through conduit 150 to the drying zone 12 The total quantity of coal circulated through the feed coal heater 144 is about 10 pounds per pound of wet coal feed and in its passage through this heater the coal is elevated in temperature from about 270 TF to about 3250 F Passage of the aforementioned solids stream through heater 152 does not provide a sufficient concentration of solids in the heat to assure good heat transfer To increase the solids density in this stream to a more desirable level, a second stream of solids is circulated from the preheating zone 14 also through heater 152, and is returned to zone 14 The circulated solids are removed from the aforesaid zone through conduit 157, entrained in fluidizing steam introduced through conduit 155 and the mixture is combined with solids leaving the feed coal heater 144 through conduit 158 The total solids then pass through the heater 152 EXAMPLE Flows Wet Coal-10 to 400 mesh Water Content Dry Coal Feed Coal Heater Coal Circulation Rate Heating Fluid-15 i A Pl hydrocarbon oil Dry Coal Heater Coal Circulation Rate Heating Fluid-15 i A Pl hydrocarbon oil Lb/Hr. 450,000 35,000 415,000 4,500,000 1,550,000 2,250,000 1,550,000 s O 785,863 785,863 Temperatures Wet Coal Drying Zone Preheating Zone Feed Coal Heater Coal In Coal Out Heating Fluid In Heating Fluid Out Dry Coal Heater Coal In Coal Out Heating Fluid In Heating Fluid Out Gas Velocity in Drying Zone Preheating Zone Density of Solids in Drying Zone Preheating Zone The problem of water in the coal feed has been previously discussed in detail in conjunction with the drying phase of the carbonization process The problem of operability in the pre-drying portion of the unit, however, has not been considered As shown in Figure 1, before entering the unit, wet coal is introduced into a feed standpipe 4 from which it is further passed into a transfer line 8 for introduction into a drier and preheater There is always a possibility that this portion of the system may become inoperable when handling

coals of high water content This is particularly true if the flow in any part of the system is momentarily interrupted, such as by an equipment failure or a temporary loss of fluidizing medium As an answer to this problem, another method of operation has been conceived in which the dangers of solids plugging or packing due to water in the coal is eliminated In carrying out this embodiment of the invention, wet coal ground to a suitable size is introduced into an elevated feed hopper in a non-fluidized condition Elevation of the non-fluid solids to the hopper level is accomplished through the use of a conventional solids conveying apparatus, such as for example a bucket elevator Within the hopper there is maintained a dense phase fluidized bed of coal having a lower average moisture content and a higher temperature than the wet feed coal Wet coal entering the hopper commingles with the solids in this bed and because of the excellent mixing characteristics thereof, is quickly elevated in temperature and distributed throughout the dry solids The result is a mixture of wet and dry coal which is readily maintained in a fluidized state In a separate drier and preheater vessel there is provided a second dense phase bed of dry coal at a temperature substantially higher than the solids in the hopper The average moisture content of the coal in the feed hopper is maintained below the level of the wet coal feed by circulating dry solids from the second dense phase bed to the hopper and by returning an equal amount of solids plus the fresh feed from the hopper to the dry coal bed The amount of solids circulated varies depending primarily on the water content and fluidization properties of the wet coal More usually, however, an operable process is provided by employing a dry coal circulation rate between about 1 and about 3 pounds per pound of wet feed coal. It is preferred to carry out the mixing of wet and dry solids in as small a vessel as possible, both for reasons of economy and to limit supporting superstructure, since the feed hopper is normally located near the drier and preheater vessel It is also preferred to perform this operation without the installation of cyclones or other expensive solids recovery apparatus In the method of this invention, a system is provided in which the wet and dry solids are mixed in a turbulent solids bed characterized by its high density and low fluidizing gas velocity The result is a minimum of solids entrainment in the effluent gases To maintain the solids in the feed hopper in a fluidized state, a small amount of inert gas, such as, for example, air or flue gas is introduced into this vessel Ordinarily, the amount of such gas is regulated to provide a velocity in the solids bed of between about O 25 OF. 270 480 270 325 465 400 450 480 500 465 Ft/Sec. 2.0 2.5 Lb/Cu Ft.

785,863 21 and about 0 5 feet per second, which provides a solids density therein between about 40 and about 30 pounds per cubic feet It is important that the temperature in the feed hopper be prevented from exceeding the boiling point of water since any substantial amount of vaporization in the feed hopper would result in increased gas velocities and excessive entrainment of solids from the bed Due to the method of introducing the wet solids into the system, it is preferred to operate the hopper at essentially atmospheric pressure Accordingly, the temperature therein is suitably maintained between about 100 and about 200 1 F. The turbulent nature of the fluid bed in the feed hopper serves to quickly distribute the wet feed coal throughout the solids contained therein As a result, only a very short solids residence time is provided in this vessel, and even though a high circulation rate of dry coal is employed this stage of the coal carbonization process is easily carried out in a vessel small in size relative to the drier and preheater. The feed hopper may be physically located adjacent to the drier and preheater vessel in any conventional manner For example, the hopper may be placed along side the drier but below the level of the dense phase bed contained within the latter vessel With such an installation, dry coal is conveniently passed downwardly into the solids bed, the hopper and a stream of solids of low water content consisting of the recycled dry coal plus the fresh feed is removed from the hopper and passed upwardly into the drying zone in a fluidizing medium such as steam Although an installation of this type is perhaps preferable from an operating standpoint, it is much more desirable structurally to place the feed hopper above and support it on the drier and preheater This presents an additional problem, however To provide the required dry coal recycle, it now becomes necessary to entrain coal from the drying zone in a fluidizing medium and pass the mixture upwardly from the drying zone into the feed hopper The amount of fluidizing medium required to accomplish this, more usually between about 0 001 and about C 0 05 pounds per pound of dry coal circulated is much greater than the quantity of vapor which can be handled in the feed hopper without excessive solids entrainment One method of overcoming this difficulty is to use a mixed fluidizing gas containing primarily steam and only sufficient air to maintain the partially dried solids in the feed hopper in a fluidized condition The major portion of the steam in the fluidizing gas immediately condenses upon entering the feed hopper solids bed and is distributed throughout the coal particles The small amount of fluidizing air used and the uncondensed steam pass through the dense phase bed into a dilute phase and from there through a conventional solids separation means.

Since additional water is introduced into the feed hopper in this method of operation, it is necessary to circulate more dry coal to this vessel when it is located above rather than below the drier and preheater vessel However, 70 the amount of water introduced as fluidizing steam is very small, usually less than about 10 per cent of the water present in the wet feed coal. A somewhat different drying and preheating 75 arrangement is provided in this embodiment of the invention Among other things, the heat required for drying and pretreating is furnished by the use of entirely separate heaters That is, all of the solids circulated to supply heat to 80 the drying zone are passed through one heater and the total solids circulated through the preheating zone are passed through a second heater This method of operating provides a process arrangement which is more flexible 85 than either of the systems previously discussed. For reasons of economy, the drying and preheating steps are carried out in a single vessel. To simplify construction of this vessel and provide easier access to the preheating zone, 90 the two zones are separated by a transverse baffle through which solids are allowed to flow from the drying to preheating zone The drying zone is again maintained within a temperature range between about 215 and about 95 300 'F and above the dew point of water at the pressure existing therein The pressure maintained in the drying step is also the same, being between about 1 and about 30 psig. The dryer solids circulation rate is somewhat 100 lower in the system illustrated by Figure 2, since none of the preheat is supplied from these solids In normal operation, coal is circulated through the dryer at between about 2 and about 15 pounds per pound of wet feed 105 coal Conditions for preheating the dry coal also are similar to those discussed during consideration of the several other embodiments of the invention These include a preheating temperature between about 350 'F and about 110 650 'F, a pressure in the preheating zone between about 1 and about 30 psig and a solids circulation rate through the dry coal heater between about 2 and about 10 pounds per pound of wet coal feed In carrying out 115 this embodiment of the invention, it is again preferred to use the same heating fluid in both heaters selected from among the group previously considered The temperature of the heating fluid and the quantity of this material 120 required is of the same order of magnitude as described for the systems of Figures 1 and 2. The conditions of solids density and velocity under which heat is transferred to the dry and preheated solids are maintained at an optimum 125 through the flexibility of the process. In order to more clearly describe this aspect of the invention and

provide a better understanding thereof, reference is had to Figure 3. Referring to this figure, wet finely subdivided 130 785,863 coal containing about 8 per cent water is introduced from a feed means through conduit 162 into feed hopper 166 in a non-fluidized condition Within this vessel which is at atmospheric pressure there is maintained a conventional dense phase fluid bed of coal particles 172 having a temperature of about 1950 F and containing on the average about 3 3 per cent water Above the dense phase is a dilute phase 170 of low solids concentration Gases leaving the dense bed pass through this zone and are released from the hopper through conduit 164. The wet solids entering the dense phase bed 172 are quickly increased in temperature to the i S level of the solids contained therein and due to the turbulent nature of the bed are mixed and dispersed throughout the hopper As a result, a highly operable process is provided and the possibility of solids agglomeration and equipment plugging is eliminated. Support for the feed hopper is provided by a subjacent drier and preheater vessel 10 containing two dense phase turbulent beds of coal 12 and 14 separated by a baffle 181 Above the beds is a common dilute phase 16 containing a conventional cyclone 18 through which vapors pass for the removal of entrained solids. The solids in bed 12, which comprises the drying zone, are supplied from the dense bed 172 through standpipe 174 The flow of solids between the two beds is controlled by a slide valve 175 or other conventional means In order to provide the lower solids water content required in bed 172, dry coal from bed 12 is passed upwardly through conduit 176 into the feed hopper 166 The motive force necessary to transfer this solids stream is supplied by steam introduced into the bottom of riser 176 through conduit 178 Upon entering the feed hopper, most of the fluidizing steam is almost immediately condensed and distributed throughout the solids bed 172 To provide solids turbulence in bed 172 and maintain the coal therein in a fluid state, a small amount of non-condensable gas, in this specific illustration air, is introduced either through conduit 171 or through conduit 178 or both Taking into account the amount of water introduced to the feed hopper as fluidizing steam, a solids circulation rate of about 2 pounds per pound of wet coal feed is required to provide the desired temperature and solids water content. The temperature in the drying zone is maintained at about 270 'F by circulating a quantity of the solids from this zone through a feed coal heater 144 Sufficient heat is provided by this operation, not only to heat the solids in the drying zone but also to vaporize the water introduced with the coal from the feed hopper In carrying out this operation, a 6 circulating solids stream at a rate of about 8

pounds of coal per pound of wet feed coal is removed from bed 12, passed downwardly through conduit 22, entrained in fluidizing steam from conduit 126 and is passed up 6 ' wardly through heater 144 and conduit 150, through which it is returned to the dry solids bed A hot hydrocarbon fluid at a temperature of about 465 F is supplied to heater 144 through conduit 146 and is removed therefrom 7 C through conduit 148 at about 400 OF. In this specific illustration, dry coal in an amount equal to the coal in the wet feed is introduced to the preheater solids bed 14 through an opening 180 in baffle 181 These 75 solids are quickly preheated from the temperature maintained in bed 12 to the preheating temperature, that is about 480 'F The heat required in this stage of the carbonization process is supplied by passing a solids stream from 80 the preheating zone through a dry coal heater in a manner similar to that just described. Preheated solids in an amount equal to about 6 pounds per pound of dry coal is passed downwardly through conduit 160, is entrained 85 in steam from conduit 158 and is passed upwardly through heater 152 and returned to the preheating zone through conduit 34 The heat transferred to the coal in heater 152 is supplied from the same heating fluid used in 90 heater 144 but prior to the passage of this fluid through the latter heater Thus, the temperature of the heating fluid leaving the dry coal heater through conduit 156 is equal to the temperature of this material entering heater 95 144 Since the amount of heat required in the preheating step is substantially less than that required to dry the coal, the temperature drop of the heating fluid through heater 152 is much lower, namely about 35 F thus requiring an 100 inlet heating fluid temperature of about 500. Transfer of solids from the preheating zone to the pretreating zone (not shown) is effected in a similar manner to that previously discussed in the consideration of Figures 1 and 2, 105that is, by passing the solids downwardly through standpipe 44 which extends within the carbonization vessel 36. A typical application of this embodiment of the invention on a commercial scale is illus 110 trated by the following data. 785,863 785,863 EXAMPLE Flows Wet Coal-10 to 400 mesh Water Content Dry Coal Coal Circulation Through Feed Hopper Feed Coal Heater Coal Circulation Rate Heating Fluid-15 MA Pl hydrocarbon oil Dry Coal Heater Coal Circulation Rate Heating Fluid-15 i A Pl hydrocarbon oil Temperatures Wet Coal Feed Hopper Drying Zone Preheating Zone Feed Coal Heater Coal In Coal Out Heating Fluid In Heating Fluid Out Dry Coal Heater Coal In Coal Out Heating Fluid In Heating Fluid Out Pressures Feed Hopper Drying and Preheating Zones Gas Velocity in Feed Hopper Drying Zone Preheating

Zone Density of Solids in Feed Hopper Drying Zone Preheating Zone Another method of introducing wet coal into the coal carbonization system whereby plugging of equipment and lines is avoided is illustrated in Figure 5 In carrying out this embodiment of the invention, wet finely subdivided coal at a temperature of about 601 F. * and again having a moisture content of about 8 per cent by weight is introduced into a feed hopper 166 in a non-fluidized state This material may form a level in the feed hopper, however, more generally, the feed rate to this vessel is sufficient to maintain it completely full of solids From the hopper the wet solids pass downwardly through a conduit 176 into a fluidized stream of hot dry solids passing substantially in a parallel direction The two streams are commingled and the wet coal is raised in temperature and distributed throughout the dry solids The entire mass is readily maintained in a fluidized condition within the descending portion of conduit 193 by the introduction of a small amount of air or other inert gas through conduit 194 Below the feed hopper is a drier and preheater vessel 10 Lb./Hr. 450,000 35,000 415,000 1,250,000 3,600,000 1,550,000 2,900,000 1,550,000 OF. 270 480 270 325 465 400 480 510 500 465 Psig. 0 Ft/Sec. 0.3 1.8 1.8 Lb/Cu Ft. 36.0 27.0 27.0 similar to that shown in Figure 1 The mixture of solids of lower moisture content passes downward through conduit 193 and enters a dense phase bed 12 of dry solids where the moisture contained in this material is converted to steam Above the dense bed 12 is a dilute phase 16 into which the vaporized water passes From the dilute phase, the water vapor is introduced into a conventional cyclone 18 and after the removal of solids is released from the drier and preheater 10 through conduit The dry solids circulating stream into which wet coal is introduced from the feed hopper 162 is supplied from the dense phase bed 12, being entrained in fluidizing steam through conduit 190 and passed upwardly through the initial part of conduit 192 This stream reverses its direction by passing in a curved path and contacts the wet solids while flowing in a downwardly direction As in the previously described operation, illustrated by Figure 3, the major portion of the fluidizing steam condenses during the mixing of the two solids streams Similarly in this embodiment of the invention, it is desirable to maintain the pressure at the point where the wet solids are introduced into conduit 192 at substantially atmospheric pressure. The temperatures, pressures, solid circulation rates, gas flow rates, etc, employed in this embodiment of the invention are similar to those previously described in the discussion of Figure 3 The method and

means for supplying the heat required for drying and preheating are also similar to those previously discussed and may conform to the systems of Figures 1, 2, or 3 or combinations thereof. One important difference between this method of wet feed introduction and that previously described lies in the reduction of fluid beds from 3 to 2, since in this embodiment, the material in the feed hopper is maintained in a non-fluid condition Actually, the feed hopper amounts only to a wide extension of conduit 176, and may be substituted for by a similar conduit of appropriate dimensions. The illustration shows commingling of wet and dry solids in conduit 193 in substantially parallel flow This is not intended, however, in a limiting sense and combination of the two streams at an angle up to and including the perpendicular is contemplated although flows approaching parallel are preferred and provide greater operability. The remainder of the coal carbonization process, although not shown, conforms generally to the process illustrated in Figure 1. Another important aspect of the coal carbonization process relates to the method of removing heat from the product char to provide a more easily handled material The method of char cooling illustrated in Figure 1 wherein the char is passed through a tubular cooler effectively reduces the temperature of this material; however, because of its relative inflexibility, it is necessarily restricted to operation within rather narrow limits for maximum thermal efficiency To provide a 70 more thermally efficient system an expedient similar to that used in the drying and preheating steps, namely circulation of solids through the heat transfer apparatus, is also resorted to for cooling the char The amount 75 of solids circulated through the char cooler in this operation varies depending on the inlet temperature of the char and the amount of cooling desired More usually a solids circulation rate of between about 1 and about 10 80 pounds per pound of product char is provided The proportion of the total char cooling obtained in this operation may, of course, be varied by changing the cooler surface area and the temperature of the cooling 85 fluid For reasons of economy, it is usually preferred to use as a cooling medium the fluid stream provided to dry and preheat the coal However, when a common stream is used it is necessary to weigh the desirability 90 of maximum char cooling as against the necessity of a high temperature heating medium for drying and preheating Actually, when carbonizing coal under the conditions previously described a balanced system is not 95 possible and heat is added to the fluid leaving the char cooling step from an outside source. More usually the cooling fluid leaves the char cooler at a temperature between about 4000 F and about 9000 F 100 With the above operating conditions, the char which passes from the carbonizer at a temperature

between about 7009 and about 10000 F is reduced in temperature in the cooler to between about 400 F and about 105 7000 F This material is again accumulated in a char pot; however, the use of recirculation requires the maintenance of a conventional fluid bed in this vessel, which was not necessary in the system of Figure 1 110 The accompanying drawing, Figure 4, is referred to in order to provide a clearer understanding of this embodiment of the invention Referring to the drawing, hot char at a temperature of about 950 F is removed 115 from the carbonization vessel through conduit 62, entrained in a fluidizing steam and passed upwardly through conduit 72 and into char cooler 74 Prior to entering cooler this stream is joined by a circulating stream of cooler 120 char from conduit 182, the latter material having a temperature of about 600 F The combined stream is cooled in the char cooler by indirect heat exchange with a petroleum oil introduced through conduit 32 from about 125 720 F to about 6000 F This oil, in turn, is heated in the cooler from about 4000 F. to about 4706 F and exits therefrom through conduit 30 The total cooled solids pass upwardly from the exit of the char cooler 130 785,863 2 A process according to claim 1, in which temperature variations in the pretreating zone are compensated for by recycling a small, variable quantity of hot devolatilized residue from the carbonizing zone to the pre 70 treating zone, the amount of heat continuously supplied thereby being small in comparison with the total heat required for pretreating. 3 A process according to claim 1 or 2, in which the fluidized material is preheated and 75 dried by heating and drying in a drying zone in a dense phase fluidized bed followed by heating the dried material in a preheating zone in a second dense phase bed, said pretreating zone being enclosed within the car 80 bonizing zone and openly communicating therewith through a grid, combustion gases being passed through the grid directly into the enclosing carbonizing zone beneath the level of said dense phase bed of devolatilized 85 residue, and additional oxygen being introduced into the dense phase bed of residue to burn a portion of the devolatilized residue and provide the heat required to elevate the pretreated solids to the carbonizing tempera 90 ture and thereby vaporizing the volatile components therefrom. 4 A process according to claim 3, in which the drying and preheating steps are carried out in contiguous openly communicating zones 95 with the heat required for drying supplied by flowing solids from the preheating zone to the drying zone and in which the heat required for preheating is supplied by removing drying solids from the drying zone, pass 100 ing said solids upwardly through a plurality of confined zones in indirect heat exchange with a heated fluid and introducing the thereby heated solids into the preheating zone.

A process according to claim 3 or 4, in 105 which carbonaceous solids entrained in the gases leaving the drying zone are recovered in admixture with the devolatilized residue in a series of steps which comprise cooling the devolatilized residue removed from the 110 dense phase bed, introducing said residue into a confined zone containing a dense phase fluidized bed of said residue superposed by a dilute phase, removing cooled residue from said dense phase bed, passing gases from the 115 dilute phase through a preliminary solids recovery step wherein a major portion of solids entrained in the gases are removed therefrom and returned to the dense phase bed, passing the gases from the drying zone through a 120 similar solids recovery step, thereafter combining the two gases, passing the combined gases through a second solids recovery step wherein the remainder of the entrained solids are removed and combining the latter solids 125 with the cool product residue. 6 A process according to claim 5, in which the cooled residue removed from the confined zone as product is slurried in water and the solids in the combined gases are re 130 through conduit 76 into a dense phase bed 188 of char maintained within a char pot 98. Fluidizing gases containing entrained solids escape from this bed, pass through a conventional cyclone 186, and the solids free gases are removed through conduit 184 The major portion of the solids introduced into bed 188 are returned to the inlet of the char cooler 74 through conduit 182 The remainder, equal in quantity to the net char yield is withdrawn through conduit 80 and passed to a char hopper (not shown) The amount of solids circulated from the char zone through the char cooler is determined according to the operating conditions required in the process In this specific illustration, the char recycle rate is about 4 pounds per pound of hot char The advantages of the increased flexibility provided by solids recirculation plus the effect of this expedient on heat transfer surface required and the thermal efficiency of this type of heat exchange system have been discussed previously and need not be repeated here It may be noted, however, that the use of solids circulation is particularly advantageous when it is desirable to restrict the length of the cooler. The drying and preheating phases of the carbonization process may be carried out in separate vessels rather than in contiguous zones in a single vessel as shown Also downflow tubular exchangers may be used rather than the upflow type; however, the former, being much more efficient, are preferred.

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