CONVERTINGREFORMER FURNACES

TO FUEL OIL FIRINGBy:

Kenneth D. DemarestPoster Wheeler Corporation

Conversion of some of the gas-firing reformer furnaces ofammonia plants to fire fuel oil is now under way; it is alsobeing actively studied for others. The circumstanceswhich are responsible for such conversions have been wellpublicized. All major ammonia producers potentially facethis situation.

The reformer furnaces of the present generation of am-monia plants play a dual role. In addition to their basicfunction of synthesis gas generation they also contributesignificantly, together with extensive waste heat recovery,to supply of power steam. Accordingly, the vital nature ofmaking a major change in the energy supply can not beoverstated. A comprehensive review of what conversioninvolves is certainly warranted.

Primarily, a fundamental aspect of conversion is attribut-able to the functioning of these furnaces as very large re-actors. Process considerations and the componentsutilized require carefully controlled, uniform heat libera-tion. Although total heat release for process purposesranges from 275 MM to 800 MM BTU / HR., a plurality ofrelatively small liberation burners is employed. Thesehave ratings of from 0.8 to 4.0 — 4.5 MM BTU / HR. Cer-tain furnace designs place them in close proximity to thecatalyst tubes in which the gas reforming reaction occurs.This is illustrated by Figure l, an interior view of a gas-firedTerrace Wall furnace. By contrast, conventional largescale utility steam generators are adapted for high releasefiring of lower grade fuels, usually with bushy flamecharacteristics. Figure 2, a view of the interior of this typeof furnace, depicts such firing from the customary largeburners. It is quite apparent from these examples thatsevere constraints apply for converting reformer furnacesfrom gas to oil firing because of their proscribed approachto energy release.

FIGURE 2

any case will provide, at most, no more than 15 to 20per cent of the fuel required, usually less. In manyplants where nitric acid is produced from the basic am-monia product, it is advantageous to use the ammonia unitpurge gas in the nitric acid units rather than as fuel in thereformer furnace. Altogether, such dependence uponnatura! gas as fuel has led to an industry-wide problem ofmajor proportions.

FIGURE 1

For typical reformer furnaces, shown by Figures 3 and4, gas firing simplified matters considerably; availability ofgas offered little incentive for firing oil. It is to be notedthat ammonia plants require outside fuel input other thanfor the purge and vent gas they produce. Burning these in

This'brief summary explains why conversion of the pres-ent generation of large capacity ammonia plant reformerfurnaces from gas to oil firing is not a simple matter. Onlythe major difficulty has been cited. Others of lesser im-portance, but also of substantial magnitude,will be intro-duced later in this discussion. Conversion of reformerfurnaces from gas to oil firing can be characterized aseasier said than done.

Work to date on plant conversions has disclosed generalunfamiliarity with oil burning technique and practicesthroughout the industry. It is thus appropriate to present abrief review of the fundamentals to facilitate understand-ing of what conversion involves.

FIGURE 3

FIGURE 4

BURNER TYPES AND PRACTICE

Prior to discussing the various liquid fuels and limitationswhich prevail in their use, also other related matters, thetypes of oil burners will be described. These fall into twogeneral classifications, fluid assist or atomizing, andmechanically atomizing. Most liquid fuels fired are ofheavier grade than motor gasoline, which for automobileengines is vaporized into the air to provide the combustionmixture. Their volutility characteristics preclude vapori-zation. The function of the oil gun of a burner is to dis-perse the oil into a fine mist of tiny droplets.

24 25

CONVERTINGREFORMER FURNACES

TO FUEL OIL FIRINGBy:

Kenneth D. DemarestPoster Wheeler Corporation

Conversion of some of the gas-firing reformer furnaces ofammonia plants to fire fuel oil is now under way; it is alsobeing actively studied for others. The circumstanceswhich are responsible for such conversions have been wellpublicized. All major ammonia producers potentially facethis situation.

The reformer furnaces of the present generation of am-monia plants play a dual role. In addition to their basicfunction of synthesis gas generation they also contributesignificantly, together with extensive waste heat recovery,to supply of power steam. Accordingly, the vital nature ofmaking a major change in the energy supply can not beoverstated. A comprehensive review of what conversioninvolves is certainly warranted.

Primarily, a fundamental aspect of conversion is attribut-able to the functioning of these furnaces as very large re-actors. Process considerations and the componentsutilized require carefully controlled, uniform heat libera-tion. Although total heat release for process purposesranges from 275 MM to 800 MM BTU / HR., a plurality ofrelatively small liberation burners is employed. Thesehave ratings of from 0.8 to 4.0 — 4.5 MM BTU / HR. Cer-tain furnace designs place them in close proximity to thecatalyst tubes in which the gas reforming reaction occurs.This is illustrated by Figure l, an interior view of a gas-firedTerrace Wall furnace. By contrast, conventional largescale utility steam generators are adapted for high releasefiring of lower grade fuels, usually with bushy flamecharacteristics. Figure 2, a view of the interior of this typeof furnace, depicts such firing from the customary largeburners. It is quite apparent from these examples thatsevere constraints apply for converting reformer furnacesfrom gas to oil firing because of their proscribed approachto energy release.

FIGURE 2

any case will provide, at most, no more than 15 to 20per cent of the fuel required, usually less. In manyplants where nitric acid is produced from the basic am-monia product, it is advantageous to use the ammonia unitpurge gas in the nitric acid units rather than as fuel in thereformer furnace. Altogether, such dependence uponnatura! gas as fuel has led to an industry-wide problem ofmajor proportions.

FIGURE 1

For typical reformer furnaces, shown by Figures 3 and4, gas firing simplified matters considerably; availability ofgas offered little incentive for firing oil. It is to be notedthat ammonia plants require outside fuel input other thanfor the purge and vent gas they produce. Burning these in

This'brief summary explains why conversion of the pres-ent generation of large capacity ammonia plant reformerfurnaces from gas to oil firing is not a simple matter. Onlythe major difficulty has been cited. Others of lesser im-portance, but also of substantial magnitude,will be intro-duced later in this discussion. Conversion of reformerfurnaces from gas to oil firing can be characterized aseasier said than done.

Work to date on plant conversions has disclosed generalunfamiliarity with oil burning technique and practicesthroughout the industry. It is thus appropriate to present abrief review of the fundamentals to facilitate understand-ing of what conversion involves.

FIGURE 3

FIGURE 4

BURNER TYPES AND PRACTICE

Prior to discussing the various liquid fuels and limitationswhich prevail in their use, also other related matters, thetypes of oil burners will be described. These fall into twogeneral classifications, fluid assist or atomizing, andmechanically atomizing. Most liquid fuels fired are ofheavier grade than motor gasoline, which for automobileengines is vaporized into the air to provide the combustionmixture. Their volutility characteristics preclude vapori-zation. The function of the oil gun of a burner is to dis-perse the oil into a fine mist of tiny droplets.

24 25

Atomizing or assist type gum illustrated by Figure 5,usually utili/e steam, but in some cases air, to promoteformation and dispersion of these fine oil particles. Boththe oil and steam, under pressure, are combined in thebody of the gun prior to passage through a small nozzlewhich performs the atomizing function. The spray mixturethen passes through distribution ports of the tip for pur-poses of achieving good flame pattern. A primary airregister surrounds the gun to direct a regulated quantity ofair directly into the spray to facilitate ignition. Thebalance of the combustion air passes through secondaryregisters, and in very large burners even tertiery registers,to envelope the ignited spray and complete combustion.By this means flame is established and propagated. Goodcombustion is essential to minimize soot formation andunburnt oil droplets.which lower efficiency, in that the fullheating value of the oil is not realized. These also foul thetube banks through which the combustion gases pass, im-pairing heat transfer effectiveness.

OIL TIPSLEEVEATOMIZER BODYSTEAM TUBEOIL TUBEGUIDE TUBEOIL BODY RECEIVEROIL BODY

CLEVISCLEVISHANDLEGUIDE SLEEVESGASKETSGUIDE PINSBOLTSATOMIZER ADAPTERATOMIZER TIP ISPC)

FIGURE 5

Mechanically atomizing oil guns rely on the effect of highpressure alone to achieve droplet formation. They arebetter suited to lighter grades of oil and are quite sensitiveto fouling. A number of tiny holes are utilized in theburner tip for breakup of the oil into the desired mist.Primary and secondary registers again provide air forignition and proper combustion. Any foreign material inthe oil, or oil of poor quality which may congeal in theholes, causing plugging, will affect flame pattern andproper combustion. Obviously, mechanically atomizingoil guns lack the effect of the atomizing steam or air as ameans of maintaining clean ports besides aiding formationand dispersion of the droplets. Mechanical atomizing dis-penses with the additional piping system and source ofsupply for the atomizing agent, but requires a high pres-sure fuel supply. Because of the limitations cited, it is inlimited usage.

Only nominal pressure is required for firing gas, higher forair inspirating types of burners than for raw gas burners.Steam or air atomizing oil burners require pressures of up

to 150-160 psig; mechanically atomizing burners requireseveral hundred pounds pressure. Good mixing is requiredfor gas, as well as oil, but is much easier to achieve.Heavies in gas will plug burners more likely with raw gastype than air-inspirating, but the incidence of burnerfouling is considerably less. Fires are much easier to adjust,and excess air can be safely carried at lower levels, 10 percent to 15 per cent, compared with 20 per cent to 30 percent, unless gas heating value is variable. In both casesfiring rate is controlled by pressure but there is muchgreater latitude with gas, affording a higher rate of turn-down. For oil burners this is limited to about four to five.However, the unvarying heating value of oil is a distinct ad-vantage, contributing to stability of operation, as comparedwith gas fuel when it varies. Also, heavier grades of oil willrequire heating to maintain viscosity on the order of 3-5centipoises, for fluidity characteristics ensuring goodatomization.

An item to discuss is use of pilots. These are seldom usedin gas fired process furnaces although quite common inindustrial gas fired boilers. Also, because of safety regula-tions, such boilers will be fitted with flame detection andproof devices to prevent full operation until satisfactorycombustion has been established. Oil firing usually in-volves gas pilots with spark ignitors. In process furnacesfiring oil with a relatively small number of large capacityburners, pilots with or without ignitors are employed forconvenience in lighting-off, which is more difficult with oilthan gas. Reformer furnaces, as noted previously, usuallyhave a large number of rather small capacity burners, anddispense with pilots because gas has commonly been fired.The only safety device employed has been a FactoryMutual proof system to insure that all burner cocks areclosed prior to admitting gas to the burner manifolds, andproceeding with light-off. Practically all installations todate capable of firing oil have been fitted with com-bination oil-gas burners which can be lit-off on gas, andthe oil in turn lit-off from the gas. A continuous gas pilotsystem for the large number of burners if solely for oilfiring would, in itself, consume a substantial quantity ofgas, and is otherwise undesirable. Because of the high fire-box temperatures which prevail in reformer furnaces,flameouts are a rare occurance. Fuel cut offs from actionof interlock systems in response to detection of otheroperational deficiencies are more common. If the inter-ruption is of short duration, provided all burner cockshave been closed, light-off of individual gas burners inturn can be done from the hot walls. For re-establishing oilfiring, in the interest of safety and expeditiously resumingoperation, a light-off device such as an LPG torch, orbetter still, a hose fitted torch piped for gas and air.commonly known as a "rosebud", should be on hand. Toavoid oil spills, verify all burner cocks as closed beforefuel oil is re-admitted to the system.

FUEL OIL CHARACTERISTICS

Fuel oils, in common usage fall into two general classifi-cations, deriving from how they are produced in refining.The first classification, distillate oils, reflects that theyhave been fully in vapor form in the distillation sectionfrom which they are recovered by fractionation. Whenwithdrawn in liquid form, they may even be steam strip-ped to drive off entrained lighter material, thus controllinginitial boiling point. Distillates are the lighter grades of oil.

The other classification, residual oils, implies that theseare bottom products, of heavier character. As a generalrule, the volatility of petroleum oils decreases as the liquidspecific gravity and average molecular weight increases.Residuals have generally been termed "Bunker" oils fromtheir shipboard usage. Obviously, their residual nature in-dicates that they will probably be of poorer character thanthe distillates, and will contain whatever remains, so tospeak, in the bottom of the pot.

TABLE 1

DETAILED REQUIREMENTS FOR FUEL OILS8

Grade of Fuel Oil

Carbon

Water Resi-and due

Pour Sedi- on 10 AshFlash Point, ment, per- weight,Point, deg. F vol- cent per-deg. F (deg. urne Bot- cent(deg. C) C) per

DistillationTemperatures,deg. F (deg. C)

Trade descriptions of these oils are covered in ASTMSpecification D396-69 of which Table l reproduced hereinsets forth their characteristics.

The table omits heating values for which there is a generalrelationship with the oil specific gravity. The lower heat-ing value of No. 2 oil is 18,000 — 18,500 BTU / Lb.; No. 6oil, 17,000 — 17,500 BTU / Lb.

Commenting on these, No. l oil is almost non-availableand is most likely being used as jet fuel. No. 2 is generallyavailable and is the usual domestic fuel oil. Both grades ofNo. 5 are not in general usage, but possibly in limitedavailability. No. 4 is used to some extent, is obtainable to acertain degree, and is the heaviest oil that normally can befired without heating for handling and to insure properviscosity at the burners. All of these are distillates. No. 6

Saybolt Viscosity, s

No. 1A distillate oil intended forvaporizing pot type burnersand other burners requiringthis grade of fuel.

No.2

A distillate oit for generalpurpose domestic heating foruse in burners not requiringNo. 1 fuel oil.

No. 4Preheating not usually re-quired for handling or burning.

100 orlegal(38)

100 or 20"legal (-7)(38)

130or 20legal (-7)(55)

No.5(Light) 130orPreheating may be required legaldepending on climate and (55)equipment.

No. 5 (Heavy)Preheating may be requiredfor burning and, in cold cli-mates, may be required forhandling

No. 6Preheating required for burn-ing and handling.

130 orlegal(55)

150(65)

0.05 0.35

0.50

1.00

1.00

540(282)

640 (32.6)'(37.93) .(338)

2.0" 3.6

0.10

0.10

0.10

45 125

150 300

(5.8) (26.4)

(32) (65)

350 750 (23) (40) (75) (1621 (42) (81)

(900) (9000) 45 300 (92) (638)

j It is the intent of these classifications that failure to meet any requirement of a given grade does not automatically place an oil in the next lower grade unless in fact it meets allrequirements of the lower grade.

t, In countries outside the United States other sulfur limits may apply.c Legal requirements to be met.

a Lower or higher pour points may be specified whenever required by conditions of storage or use. When pour point less than O F is specified, the minimum viscosity shall be 1.8 cSt(32.0 s. Saybolt Universal) and the minimum 90 percent point shall be waived.

, The 10 percent distillation temperature point may be specified at 440 F (226 C) maximum for use in other than atomizing burners.' Viscosity values in parentheses are for information only and not necessarily limiting.

g The amount of water by distillation plus the sediment by extraction shall not exceed 2.00 percent. The amount of sediment by extraction shall not exceed 0.50 percent. A deduction in quantity shall be made for all water and sediment in excess of 1.0 percent.

2627

FUEL OIL CHARACTERISTICS

Fuel oils, in common usage fall into two genera! dassifi-cations, deriving from how they are produced in refining.The first classificaüon, distillate oils, reflects that theyhave been fully in vapor form in the distillation sectionfrom which they are recovered by fractionation. Whenwithdrawn in liquid form, they may even be steam strip-ped to drive off entrained lighter material, thus controllinginitial boiling point. Distillates are the lighter grades of oil.

The other classificaüon, residual oils, implies that theseare bottom products, of heavier character. As a generalrule, the volatility of petroleum oils decreases as the liquidspecific gravity and average molecular weight increases.Residuals have generally been termed "Bunker" oils fromtheir shipboard usage. Obviously, their residual nature in-dicates that they will probably be of poorer character thanthe distillates, and will contain whatever remains, so tospeak, in the bottom of the pot.

TABLE 1

Trade descriptions of these oils are covered in ASTMSpecification D396-69 of which Table l reproduced hereinsets forth their characteristics.

The table omits heating values for which there is a generalrelationship with the oil specific gravity. The lower heat-ing value of No. 2 oil is 18,000 — 18,500 BTU / Lb.; No. 6oil, 17,000 — 17,500 BTU / Lb.

Commenting on these, No. l oil is almost non-availableand is most likely being used as jet fuel. No. 2 is generallyavailable and is the usual domestic fuel oil. Both grades ofNo. 5 are not in general usage, but possibly in Hmitedavailability. No. 4 is used to some extent, is obtainable to acertain degree, and is the heaviest oil that normally can befired without heating for handling and to insure properviscosity at the burners. All of these are distülates. No. 6

DETAILED REQUIREMENTS FOR FUEL OILSa

Grade of Fuel Oil

FlashPomt,deg. F<deg.Cl

PourPoint,deg. F(deg.

C!

WaterandSedi-ment,vol-umepercent

Car-bon

Resf-due

on 10per-centBot-

torm,P»cent

Distrilation Sa y bol t Viscosity, sTemperaturfes,deg. F (deg. Ci

Ash

per- 10cent per- 90 percent Universalat

cent Pomt 100 F (38 C)Point

Furol at122F

(50 C}

Kinematic Viscosity, cSt

Cop-Grav- per Sul

. itv Strip fur.deg Cor- per-

At 700 F At 122 F AP' r°s<on «nt(38 C) (50 C}

Min Max Max Max Max Max Min Max Min Max Min Max Min Max Min Max Min Max Max

No. 1A distillate oil tntended forvaporizing pot-type burnersand other burners requiringthis grade of fuel.

No.2A distillate oil for generalpu r pose dom«stic heating foruse in burners not requiringNo. 1 fuel oil.

No. 4Pre heat ing not usually re-quired for handfmg or burning.

No.S(Light)Preheating may be requireddepending on cl i mat e andequipment.

No. 5 (Heavy)Preheating may be requiredfor burning and, in cold clj-mates, may be required forhandfmg

No. 6Preheating required for burn-ing and handling.

100 of Od tracé 0.15legai •(38}

420(215)

100 orlegal(38)

130 orlegal(55}

130 orlegal(55)

130 orlegal(551

150165)

20"[-7Ï

20(-7)

0.05 0.35

0.50

1.00

0,10

0.10

550(2B&)

540° 640 <32.6l' (37.93)(282) (338)

45 125

150 300

1.4 2.2 35

2.0' 3.6 30

No. 3 0.5or

legaf

0.5'or

legal

(5.8) (26.4)

(32) (65)

1.00 0.10 350 750 (23) (40) (75) (162) (42) (81)

2.00! (900) (9000) 45 300 (92) (638)

j 1t is the intent of these classifications that faïture to meet any requirement of a given grade does not automatically place an oil in the next lower grade unless in fact it meets allrequtrements of the lower grade.iy In countries otrtside the United States other sul f u r limits may apply.c Legal requirements to be met.d Lower or higher pour points may be specified whenever required by conditions of storage or use. When pour pomt Jess than O F is specified, the minimum viscosity shall be 1.8 cSt(32.0 s. Saybott Umversal) and the minimum 90 percent point shall be waived.e The 10 percent distillation te m pe rat u re point may be specif red at 440 F (226 C) maximum for use in other than atomizing burners.f Viscosity values in parentheses are for information only and not necessarjly limiting.g The amount of water by distillation plus the sediment by extraction shall not exceed 2,00 percent, The amount of sediment by extraction shall not exceed 0.50 percent. A deduction m quantity shall be made for all water and sediment in excess of 1.0 percent.

27

oil of residual character is the general industrial work-horse, but is presently under a cloud because of environ-mental pollution restrictions in effect. Sulfur content ofNo. 6 oil is frequently on the order of 3-5 per cent. EPAstandards preclude sulfur content in excess of 0.7 per cent.For use in reformer furnaces, a limitation of 0.5 per cent isdesirable, for other reasons.

Certain other aspects of oils are to be noted. There is acertain fixed nitrogen content, mainly in No. 6 oil, some ofwhich will form nitrogen oxides when fired. Such oxidesare also formed from the combustion air. Various limita-tions are now in effect for the quantity so discharged tothe atmosphere, quite restrictive in some localities. Thelatter limit the quantity from a single source to as low as150 Ibs. / hr. total. Fortunately, the combustion character-istics of most reformer furnaces are such that this will notbe a problem for the usual installation, as it is for largeutility boilers.

A much more unfavorable situation is presented by metaloxides contained in oils, again most prevalent in No. 6 oil.The worst offender is vanadium pentoxide. While this canbe handled in industrial furnaces where the tubes are notof high alloy materials and are relatively cool, it is apositive menace in reformer furnaces. This was reportedby Williams and Sawyer1 at the last meeting of this group.At temperature levels of 1500° F or higher, vanadium is afluxing agent for nickel. Reformer furnaces almost univer-sally have catalyst tubes of centrifugally cast HK-40 witha nickel content of 20 per cent, or even higher nickel con-tent alloys, and have metal temperatures of 1500° F andhigher. When vanadium is present in other than tracéquantities, 5-10 ppm, tube deterioration of a very high andrapid order can be anticipated, precluding the use of thatparticular oil. This problem has been countered in largeindustrial and power boilers with uncooled tube supportsby use of 50-50 and 60-40 (chromium and nickel) alloys,but these cannot be considered for reformer tube usage.Besides being extremely costly, they are almost unwork-able, and do not have physical properties suitable for suchan application.

Other metal oxides, of sodium and magnesium, againmainly in No. 6 oil, also are a problem. Corrosive attack isnot so drastic or severe, but laydown at temperature levelsof 1100 ° F and higher is a nuisance, and not easy tö re-move. In large industrial or power units, this laydown isminimized by operating with extremely low excess com-bustion air, 5 per cent or less. This cannot be considered aviable practice for reformer furnaces which do not, ingeneral, have the highly sophisticated combustion systemswhich the other units feature. It is thus unlikely for re-formers which will be converted to fire oil, hence contentof these metals should be limited to about 20 ppm,maximum.

Other hinderances from the bottom sediment and water,and ash content of oils, will be dealt with elsewhere in thisdiscussion.

Summing up, use of oils up to No. 4 has promising pos-sibilities for reformer furnace conversions. Considerableeffort is now being devoted to producing low-sulf ur heavyfuel oil, and new refining installations have been and arebeing made. Despite this, there has been no indiciation ofsignificant improvement from the standpoint of metalscontent. For this reason, No. 6 oil cannot be consideredfor reformer furnace usage, unless a day-in day-out re-liable supply of satisfactory quality can be arranged.

The information so far presented about oil has dealt withthose considered standard. Various other grades are alsoavailable, particularly in the vicinity of oil refineries.Diesel oil, which approaches No. 2 fuel oil in character-istics, may be obtainable, and is very satisfactory. Also,other distillates with characteristics in between the stand-ard grades and quite suitable for fuel usage are a pos-sibility. None of these should be overlooked when con-version from gas to oil firing is being considered.

CONVERSION APPROACH

In considering the actual mechanics of undertaking con-version, how this is done will depend upon the type of re-former furnace involved. In the case of the FosterWheeler Terrace Wall type previously illustrated, actualconversion is very much simplified. The original concep-tion of this design visualized combination firing of eitheroil or gas. Such burners were developed, and installattonshave been in service for over ten years. Figure 6 illustratesa typical combination gas and oil burner. To convert asolely gas fired furnace requires removal of the presentburners and burner blocks and replacing them with eithercombination or only oil firing models. Minor modifica-tions of the terraces are necessary, and the proper pipingneeds to be installed. Also the available draft must bechecked, because for the same furnace duty, somewhatmore flue gas characterizes oil firing. This applies for alltypes of furnaces which may be converted. The burners,themselves, are available in corresponding liberations, withoil guns of flat flame type, compatible with the firebox. Inshort, from a mechanical standpoint, this can be judgedrelatively simple. Figure 7 is an interior view of an oilfired terrace wall furnace.

These are some furnace varieties, both Foster Wheelerand of competing manufacturers, which employ a flat wallwith the burners similarly disposed in horizontal layers.The burner blocks penetrate the walls and the gas headsfire up along the walls. These models also can be con-verted with almost equal ease. An oil gun of side penetra-

tion type, firing at right angles to its direction of instal-lation has been developed. This is available for makingsuch conversions, and, again, compatibility is afforded.

FIGURE 6

SECTIONAL SIDE VIEW

BURNER TILEOILCONE TILEGAS HEAO ASffY.AIR REGISTER ASS'Y.PI LOT BOSSPRIMARY AIR ROTORPRIMARY AIRSTATOROIL BODY RECEIVER ASS'Y.OIL GUN ASS'YGUIDE TUBECHOKE PLATEREGISTER COVER PLATE

PART SECTIONAL ELEVATIOU "X-X"

o

'M̂2

b:: -y \ ^VGASCONN.

. „ f (MAtE N.P.M

BOTTOM VIEW

OIL BURNERASS'Y. \

FLOOR/

MOUNTING DETAIL

FIGURE 7

Another model of furnace in large usage, the top firedtype, featuring burners firing downwards between rows oftubes, of which thé M. W. Kellogg Co. furnace is charac-teristic, also has been adapted for oil firing. The referencerelative to vanadium attack of high alloy tubes previouslycited also reports operation of one of these furnaces firingeither No. 2 oil or gas. It mentioned that only a portion ofthe burners were combination type but that the intention ofthe operators was to so convert additional burners to in-crease oil firing capability. Also, this reference mentionedburner plugging, which will be dealt with further along inthis presentation. The ability of this furnace to fire oil isthus established.

The particular installation reported upon was builtoriginally for combination firing. The bulk of these in-stallations are for firing gas solely. It will be difficult butby no means impossible to convert them for oil firing be-cause of the roof construction which features a suspendedarch. Removal and replacement of the arch will be en-tailed in order to effect the burner change. Regardless,this large group of ammonia furnaces also can satis-factorily be converted to fire oil.

The remaining group of furnaces in large usage, of whichSelas furnaces are representative, is of the type which em-ploys a large number of very small burners, disposed uni-formly over the side walls. These burners are of a specialshort, or no-flame type, which fire directly at the tubes.The large number of burners, by itself, poses a problem.However, the greatest difficulty is the configuration andorientation of the burners, which is not very well suited foroil firing. At the time of writing it does not appear that aproven burner has yet been developed for the full range ofoil fuels which could be installed accompanying, or inplace of, the gas burners. Such development work hasbeen under way. A burner which is limited to firing No. 2oil at the heaviest, or lighter material, is available, andcould be fitted in place of the gas burners with somechanges in mounting. These require a pressurized airsystem which is a considerable drawback. In various in-stances the wall burners have been supplemented by flooror roof oil burners firing along the walls. This measureprovides a portion of the liberation, and would alleviate,but not fully solve, the situation.

What seems to offer the best possibilities would be to usethe floor burners mentioned, and in place of the wallburners, use the wall penetration type previously cited.One or more layers of these could be installed, and theregular burner openings closed off with refractories. This,although quite laborious, would also solve the problem.

Another important aspect of these conversions requiresconsideration. Many ammonia primary reformers utilizeauxiliary firing. The purpose is to increase steam output,

28 29

tion type, firing at right angles to its direction of instai-lation has been developed. This is available for makingsuch conversions, and, again, compatibility is afforded.

FIGURE6

SECTIONALSIDE VIEW

flURKERTILEOILCONE TILEG AS HEAO AS? VAIR ftEGISTËR ASS'Y.PI LOT BOSSPRIMABV AIRRQTORPRIMARV AIRSTATORQIL BODY RtCElVER ASS'Y.O IL CUN ASS'YG UI DE TUBECMOKE PLATEREGISTER COVER PLATE

O1L CONN

PART SECT1QNAL ELEVATIOW "X-X"

BOTTOM VtEW

OILBURNERASS'Y.

FLOO

CourtMy ofJOHN ZINK COMPftNY

VA*/ •

NG

1

-*

'

•

>

^ 4~ ^ f- 'iilT11

1 _ . __

MOUNTtNG DETAIL

Fl GURE 7

Another model of f urnace in large usage, the top firedtype, featuring burners firing downwards between rows oftubes, of which the M. W. Kellogg Co. furnace is charaoteristic, also has been adapted for oil firing. The referencerelative to vanadium attack of high alloy tubes previouslycited also reports operation of one of these f urnaces firingeither No. 2 oil or gas. It mentioned that only a portion ofthe burners were combination type but that the intention ofthe operators was to so convert additional burners to in-crease oil firing capability. Also, this reference mentionedburner plugging, which will be dealt with further along inthis presentation. The ability of this furnace to fire oil isthus established.

The particular instaliation reported upon was builtoriginally for combination firing. The bulk of these in-stallations are for firing gas solely. It will be difficult butby no means impossible to convert them for oil firing be-cause of the roof construction which features a suspendedarch. Removal and replacement of the arch will be en-tailed in order to effect the burner change. Regardless,this large group of ammonia furnaces also can satis-factorily be converted to fire oil.

The remaining group of furnaces in large usage, of whichSelas furnaces are representative, is of the type which em-ploys a large number of very small burners, disposed uni-formly over the side walls. These burners are of a specialshort, or no-flame type, which fire directly at the tubes.The large number of burners, by itself, poses a problem.However, the greatest difficulty is the configuration andorientation of the burners, which is not very well suited foroil firing. At the time of writing it does not appear that aproven burner has yet been developed for the full range ofoil fuels which could be installed accompanying, or inplace of, the gas burners. Such development work hasbeen under way. A burner which is limited to firing No. 2oil at the heaviest, or lighter material, is available, andcould be fitted in place of the gas burners with somechanges in mounting. These require a pressurized airsystem which is a considerable drawback. In various in-stances the wall burners have been supplemented by flooror roof oil burners firing along the walls. This measureprovides a portion of the liberation, and would alleviate,but not fully solve, the situation.

What seems to offer the best possibilities would be to usethe floor burners mentioned, and in place of the wal]burners, use the wall penetration type previously cited,One or more layers of these could be instailed, and theregular burner openings closed off with refractories, This,although quite laborious, would also solve the problem.

Another important aspect of these conversions requiresconsideration. Many ammonia primary reformers utilizeauxiliary firing. The purpose is to increase steam output,

29

or superheat of steam otherwise produced. It is notneeded for process requirements. Furnaces which havetheir convection banks mounted above the fireboxes arefitted with a firing zone beneath the bank proper. Moreconventional burners usually are employed for this usage,simplifying the change. What is more apt to be a concernis the auxiliary firebox proportions. Because firing isdirected into the large volume of very high temperaturecombustion gases emanating from the catalyst tube fire-boxes, good combustion is not normally a worry. Thusthese zones are rather limited in size. In changing over tooil-firing, which of necessity has a very definite flamepattern, improper combustion and impingement on thetubes could result, and must be taken into account. Theshortest possible flame is mandatory.

Those furnaces which are top-fired differ in that the heatrecovery convection bank is grade mounted, adjoining thereformer proper. What are known as tunnel burners areused. These fire into the interconnecting flue, or im-mediately before the tube bank. In some cases quite highintensity burners are used. Replacing these with oilburners again introduces the problem of flame character-istics. Whereas many gas applications are relatively flame-less, a definite flame pattern always characterizes oilfiring. This is only to caution those considering conversionof thé need for achieving proper combustion and avoidingflame impingement. Some remodeling of the installationto assure this may be required.

Probably what is the chief drawback to reformer con-version has yet to be mentioned. Beyond doubt, it is thetime required, and consequent loss of production. Allow-ing for the major size of most of the plants, today's am-monia market assures that this will be quite costly. Ab-solutely minimum time out is essential; whatevermeasures can shorten this must be adopted. It will be mostadvantageous-if conversion can be planned for a sched-uled shutdown or regular turnaround. Very drasticmeasures may be justified to assure the availability ofcomponents and preparedness for quick installation atsuch times. Those who have already taken steps towardsconversion will testify to the validity of this message.

OPERATING PROBLEMS

Heretofore, only the mechanical problems of conversionhave been considered. Other aspects need citing. Varyingdegrees of extra effort characterize firing oil, as comparedwith gas firing. Firing oil is a way of life, and it is no acci-dent that gas firing has been so widely used. In addition towhat was gas availability until recently, and no economiedisadvantage of significant proportions, gas firing makeslife much simpler for the operators. Gas needs no special

handling and treatment other than a knockout drum in thesupply line to drop out moisture and heavy constituents.Burners will plug but only over a long period of time.Cleanoff of the convection bank heat transfer surfaces israrely needed unless some other improper conditionarises, such as spalling of refractories, etc. These pointsare being noted only to focus attention on the same itemswhere oil is involved.

Proceeding in reverse order variable convection bankcleaning may be expected, depending both upon the oilitself, and how it is handled and fired. It was mentionedearlier that proper combustion was essential to insurelittle or no unburnt oil droplets, or soot formation. Thesedefinitely will deposit on the transfer surface in the con-vection bank. Such incidence is much more likely withthe heavier oils, which will probably contain some ash, aswell.

Oil-fired equipment for other services, with expectationsof this laydown occurring, is designed to do somethingabout it. Finned transfer surface is avoided, at most studsare used. Soot blower lanes are provided, and the sootblowers installed. Even water wash systems are used. Inshort, arrangements are made to live with the situation.Few, if any, ammonia furnaces have such facilities. Solidwall convection banks have been used; tubes haveclosely spaced fins. The necessity of firing the best oil underthe most favorable circumstances is clearly indicated.

A convection section rebuild job would be the best way torectify this, however traumatic the plant shutdown, orcostly as well. It is not visualized that this will be done toany great extent. Steam lancing ports may be cut into thewalls to permit a manual cleaning job. Although exceed-ingly laborious, it would help. Water wash systems may alsobe put in, but will be effective only when the furnace isdown. Some oil additives have been developed tominimize these deposits but they are intended for theheavier, lower quality oils. It is evident that everythingpossible must be done to minimize unnecessary con-vection bank fouling.

This leads to the burners and their care. It was mentionedpreviously that the burner tips and ports play a most im-portant role. The reference cited previously for oil firingreported burner plugging. The effect of such plugging isimproper combustion, and the result, fouling, alsolowered efficiency. It is obligatory that this be handled thebest way possible. A substantial number of spare burnerguns can be kept on hand in clean condition, racked upby the furnace. As soon as a dirty burner tip is noticed, thegun should be removed, and a clean one installed. Thedirty guns accumulate and are cleaned at regular intervals,

then put in the rack, ready for use when needed. Thecleanups must be programmed and a cleaning stationhandy to the furnace provided. Further, it is helpful togive burners a steam purge both prior to lighting-off and be-fore removal from service, by means of cross connectingthe steam and oil unes through a block valve.

Still proceeding in reverse direction, oil storage andhandling practices have a marked effect on burner clean-liness. Whoever supplies the oil stores it in tanks anddelivers it either by tank-wagon or pipeline. Accumula-tions in tankage are almost unavoidable hence somebottom sediment and water may be anticipated. Thisshould be as little as possible. Deliveries as a matter ofroutine profitably can be sampled and analyzed at regularintervals because suppliers may become careless. Oilsupply contracts should provide for a maximum of suchcontamination. Enforcing this is obviously beneficial.

The storage system itself requires watching, also as asource of accumulations. Tankage blowdown at regularintervals will be helpful, and facilities for so doing pro-vided. Next, the transfer system must have dual filters ofno coarser than 50 mesh. These should also be attended to

at regular intervals, as need warrants. Naturally, adequacyand reliability of the oil pumps is highly desirable. Forproper operation, looping of the oil line is desirable, withprovision for draining and flushing out, particularly whennot in service. Sizing should be ample. Further, dependingupon the grade of oil and climatic conditions of the in-stallation, heating, insulation, and even line tracing maybe indicated. All of these measures are advocated to con-tribute to continuity and reliability of operation as well asto minimize burner and furnace maintenance. A finalcautionary matter is to provide sloped steam lines withdrip pockets and blow points thus preventing water slugsto the burners.

Summarizing what has been discussed, it will suffice tostate that merely converting from firing gas to oil is onlypart of the picture. Considerably more will have to betaken into account in order that such operation will bemost effective and efficiënt, and least troublesome. Hencethe aim herein has been to present the picture not only ofhow conversion can be undertaken, but also what elsemust be done to insure satisfaction.

DEMAREST, KENNETH D.

1Sawyer, J. G. & Williams, G. P., "Turndown Efficiency of a SingleTrain Centrifugal Ammonia Plant", AlChE Ammonia Safety Sympo-sium, Vancouver, B. C., 1973.

30 31

or superheat of steam otherwise produced. It is notneeded for process requirements. Furnaces which havetheir convection banks mounted above the fireboxes arefitted with a firing zone beneath the bank proper. Moreconventional burners usually are employed for this usage,simplifying the change. What is more apt to be a concernis the auxiliary firebox proportions. Because firing isdirected into the large volume of very high temperaturecombustion gases emanating from the catalyst tube fire-boxes, good combustion is not normally a worry. Thusthese zones are rather limited in size. In changing over tooil-firing, which of necessity has a very definite flamepattern, improper combustion and impingement on thetubes could result, and must be taken into account. Theshortest possible flame is mandatory.

Those furnaces which are top-fired differ in that the heatrecovery convection bank is grade mounted, adjoining thereformer proper. What are known as tunnel burners areused. These fire into the interconnecting flue, or im-mediately before the tube bank. In some cases quite highintensity burners are used. Replacing these with oilburners again introduces the problem of flame character-istics. Whereas many gas applications are relatively flame-less, a definite flame pattern always characterizes oilfiring. This is only to caution those considering conversionof thé need for achieving proper combustion and avoidingflame impingement. Some remodeling of the installationto assure this may be required.

Probably what is the chief drawback to reformer con-version has yet to be mentioned. Beyond doubt, it is thetime required, and consequent loss of production. Allow-ing for the major size of most of the plants, today's am-monia market assures that this will be quite costly. Ab-solutely minimum time out is essential; whatevermeasures can shorten this must be adopted. It will be mostadvantageous-if conversion can be planned for a sched-uled shutdown or regular turnaround. Very drasticmeasures may be justified to assure the availability ofcomponents and preparedness for quick installation atsuch times. Those who have already taken steps towardsconversion will testify to the validity of this message.

OPERATING PROBLEMS

Heretofore, only the mechanical problems of conversionhave been considered. Other aspects need citing. Varyingdegrees of extra effort characterize firing oil, as comparedwith gas firing. Firing oil is a way of life, and it is no acci-dent that gas firing has been so widely used. In addition towhat was gas availability until recently, and no economiedisadvantage of significant proportions, gas firing makeslife much simpler for the operators. Gas needs no special

handling and treatment other than a knockout drum in thesupply line to drop out moisture and heavy constituents.Burners will plug but only over a long period of time.Cleanoff of the convection bank heat transfer surfaces israrely needed unless some other improper conditionarises, such as spalling of refractories, etc. These pointsare being noted only to focus attention on the same itemswhere oil is involved.

Proceeding in reverse order variable convection bankcleaning may be expected, depending both upon the oilitself, and how it is handled and fired. It was mentionedearlier that proper combustion was essential to insurelittle or no unburnt oil droplets, or soot formation. Thesedefinitely will deposit on the transfer surface in the con-vection bank. Such incidence is much more likely withthe heavier oils, which will probably contain some ash, aswell.

Oil-fired equipment for other services, with expectationsof this laydown occurring, is designed to do somethingabout it. Finned transfer surface is avoided, at most studsare used. Soot blower lanes are provided, and the sootblowers installed. Even water wash systems are used. Inshort, arrangements are made to live with the situation.Few, if any, ammonia furnaces have such facilities. Solidwall convection banks have been used; tubes haveclosely spaced fins. The necessity of firing the best oil underthe most favorable circumstances is clearly indicated.

A convection section rebuild job would be the best way torectify this, however traumatic the plant shutdown, orcostly as well. It is not visualized that this will be done toany great extent. Steam lancing ports may be cut into thewalls to permit a manual cleaning job. Although exceed-ingly laborious, it would help. Water wash systems may alsobe put in, but will be effective only when the furnace isdown. Some oil additives have been developed tominimize these deposits but they are intended for theheavier, lower quality oils. It is evident that everythingpossible must be done to minimize unnecessary con-vection bank fouling.

This leads to the burners and their care. It was mentionedpreviously that the burner tips and ports play a most im-portant role. The reference cited previously for oil firingreported burner plugging. The effect of such plugging isimproper combustion, and the result, fouling, alsolowered efficiency. It is obligatory that this be handled thebest way possible. A substantial number of spare burnerguns can be kept on hand in clean condition, racked upby the furnace. As soon as a dirty burner tip is noticed, thegun should be removed, and a clean one installed. Thedirty guns accumulate and are cleaned at regular intervals,

then put in the rack, ready for use when needed. Thecleanups must be programmed and a cleaning stationhandy to the furnace provided. Further, it is helpful togive burners a steam purge both prior to lighting-off and be-fore removal from service, by means of cross connectingthe steam and oil unes through a block valve.

Still proceeding in reverse direction, oil storage andhandling practices have a marked effect on burner clean-liness. Whoever supplies the oil stores it in tanks anddelivers it either by tank-wagon or pipeline. Accumula-tions in tankage are almost unavoidable hence somebottom sediment and water may be anticipated. Thisshould be as little as possible. Deliveries as a matter ofroutine profitably can be sampled and analyzed at regularintervals because suppliers may become careless. Oilsupply contracts should provide for a maximum of suchcontamination. Enforcing this is obviously beneficial.

The storage system itself requires watching, also as asource of accumulations. Tankage blowdown at regularintervals will be helpful, and facilities for so doing pro-vided. Next, the transfer system must have dual filters ofno coarser than 50 mesh. These should also be attended to

at regular intervals, as need warrants. Naturally, adequacyand reliability of the oil pumps is highly desirable. Forproper operation, looping of the oil line is desirable, withprovision for draining and flushing out, particularly whennot in service. Sizing should be ample. Further, dependingupon the grade of oil and climatic conditions of the in-stallation, heating, insulation, and even line tracing maybe indicated. All of these measures are advocated to con-tribute to continuity and reliability of operation as well asto minimize burner and furnace maintenance. A finalcautionary matter is to provide sloped steam lines withdrip pockets and blow points thus preventing water slugsto the burners.

Summarizing what has been discussed, it will suffice tostate that merely converting from firing gas to oil is onlypart of the picture. Considerably more will have to betaken into account in order that such operation will bemost effective and efficiënt, and least troublesome. Hencethe aim herein has been to present the picture not only ofhow conversion can be undertaken, but also what elsemust be done to insure satisfaction.

DEMAREST, KENNETH D.

1Sawyer, J. G. & Williams, G. P., "Turndown Efficiency of a SingleTrain Centrifugal Ammonia Plant", AlChE Ammonia Safety Sympo-sium, Vancouver, B. C., 1973.

30 31

DISCUSSION

ED JOHNSON, Allied Chemical: When we were burningBunker C some years ago in our South Point ammonia re-formers we found that when we had vanadium we were<jetting attack, and it seemed to be aggravated by the pres-ence of sodium. Have you found any correlation betweenthe existence of sodium in the attack of vanadium on H K40alloy?DEMAREST: l can't truthfully say that l have but it'squite possible. Th is is not a simple situation.JOHNSON: It's very complexDEMAREST: Büt the vanadium has definltely been identi-fied as the fluxing agent for nickel.JOHNSON: We found when we had a vanadium contentbelow one part per million, even with sodium, we wereaway scot free except that the ash contained in Bunker Coil fouled our convection section. This leads to my secondquestion which is: we found that with any Bunker C wecould obtain—and this goes back 10 years ago when youcould get some really good Bunker C—that this type of oilhad too much ash for what we called our waste heat boilers,l guess you'd cal) it the convection section now. We'd con-tinually plug up our primary reformer flueside waste heatboilers, because apparently as the gas went through theboiler it also went through the fusion temperature of theash and we had quite a mess there. How wou ld you copewith this?DEMAREST: Wefl, going back to the experience in indus-trial boilers—and l can assure you we would not build afinned convection bank for this service, at most we'd usestudded tubes with plenty of soot blower lanes and ade-quate soot blowing capacity.JOHNSON: That might do the job. Our boilers that weregiving us trouble were unusual in that they were fire-tubedso that here it was almost impossible to clean them in run.We had a circulating ball system to circulate steel bal l s andfinally we solved it. We went off on to number two oilwhen the vanadium got too high and solved our ash prob-lem simultaneously.O. On your furnace—and this is probably typical of manyfurnaces—but on your furnace could you actually fire distil-late oil or even heavy oil without removing the fin section?There's no way in the world to keep the soot out of thatsection, is there?DEMAREST: No. See, we were asked to excerpt ourpapers. So there's a bit of discussion in the actual paperitself—with the fin tube section only the lightest oil will besuitable, and fired under the best circumstances, which lwas trying to emphasize; anything beyond that is going tobe quïte difficult. It's going to be hard to put in steamlancing doors and to go in there and do something about it.

A water wash is only effective when the furnace is down,and to the best of my knowledge the additives which theyhave—and they remind me óf old-fashioned boiler watercompound—seem to be most effective if they are with theheavier fuels. In other words, something built strictly forthis type of service would be built accordingly.

But in the meantime l think if people are careful andthey follow the—as l say, the prescription of medicine l laidoutr they'll be able to get along one way or another,MARTY FANKHANEL, Heat Research Corp.: I have acomment first with regard to your statement about theSawyer and Williams paper, l believe the design in this caseactually was for 100 percent oil firing and the referencemade to an expansion of oil firïng in that paper was mostlikely due to the situation of interruptible gas supply forfuel. It was not a case of a limitation on the capability offire oil.

In addition, the comment relating to plugging of thosebumers had to do with the fact that there was an intermit-tent firing situation. Consequently on some annual or semi-annual basis there was a need to start up a system whichhad been dormant for a long period of time. This of coursecreated problems with mill-scale, being in piping, and sud-denly plugging burners, and of course the usual situatïon ofmaïntenance. This is a comment, generally.

In addition, l have a few questions for you. Ken. One,you refer to a preferred half percent sulfur limit, l'd likeyou to comment on the need for that or the desirability ofthat. And you also mention a vanadium content limit, butyou didn't specify exactly what that meant in terms ofPPM.

And finally, since this is a safety symposium, l wonder ifyou'd comment on the subject of flame monitoring of oilfiring and the use of—or preference for mechanical safetyinterlocks in oil firing.DEMAREST: Well, l'd say that it's almost constituting anew paper. But answering the first part, and they were notquestions, they were observations—the tone of my com-ment was the fact that the ability of that furnace to fire theoil was very well established, and as l read that paper it wasindicated that not all the burners were equipped as combi -nation burners, and so l think—well, that will take care ofthat situation.

And whether it was an interruptible situation or not, thekind of housekeeping l have described is absolutely neces-sary. Now tet'sget back to your specific questions. Numberone, l think was a matter of sulfur content. Now there, thelimitation at 0.5 percent is not for environmental reasons,but what is the peculiar activities of sulfur at a high temper-ature level in these furnaces, because so operating you getsome polymerization and other effects which—this is morefrom experience than actual data, it is desirable to avoid.And in these particular reformer fuVnaces—this is a wellestablished history—firing oil up to 0.5 percent sulfur con-tent has been satisfactory.

Now would you repeat your other question?FANKHANEL: Yes, l referred to the comment about asmall amount of "vanadium—you didn't indicate exactlywhat content you suggest as a limitatïon, say, in terms ofPPM.DEMAREST: Well, in this particular case l would say thatmost desirably it should be held to not over 5 PPM butdefinitely not over ten PPM. Now coming back to vanadi-um, l mentioned in th& paper, but did not mention inspeaking, that there is quite a movement on foot to pro-duce low sulfur heavy fue! oils now. Major refining installa-tions are being made for this end.

However, l have no information that they are similarlylimiting metats content. So in my view l see no future forthese oils in reformer furnaces.FANKHANEL: l had a last question. l know it's a largesubject, but as l mentioned it's a safety topic and l won-dered if you had a comment on flame monitoring or safetyinterlocks?DEMAREST: Well, there is a bit of a discussion aboutthat in the paper. The reformer furnaces present a verydifficult problem for flame monitoring because the usualdevices are not fully effective due to the hot walls. Nowwhat we call the ultraviolet detector, the purple peeper,can't distinguish between the flame and the waH. Nowcoming back to safety, flame out in these reformer furnacesis a very infrequent occurrence.

What is much more likely to occur is a cutoff or mal-function in other areas that trips off the SIS system, Now

32

DISCUSSION

ED JOHNSON, Allied Chemical: When we were burningBunker C some years ago in our South Point ammonia re-formers we found that when we had vanadium we weregetting attack, and it seemed to be aggravated by the pres-ence of sodium. Have you found any correlation betweenthe existence of sodium in the attack of vanadium on H K40 alloy?DEMAREST: l can't truthfully say that l have but it'squite possible. This is not a simple situation.JOHNSON: It's very complexDEMAREST: Büt the vanadium has definitely been identi-fied as the fluxing agent for nickel.JOHNSON: We found when we had a vanadium contentbelow one part per million, even with sodium, we wereaway scot free except that the ash contained in Bunker Coil fouled our convection section. This leads to my secondquestion which is: we found that with any Bunker C wecould obtain—and this goes back 10 years ago when youcould get some really good Bunker C—that this type of oilhad too much ash for what we cal led our waste heat boilers,l guess you'd cal l it the convection section now. We'd con-tinually plug up our primary reformer flueside waste heatboilers, because apparently as the gas went through theboiler it also went through the fusion temperature of theash and we had quite a mess there. How would you copewith this?DEMAREST: Wel l, going back to the experience in indus-trial boilers—and l can assure you we would not build afinned convection bank for this service, at most we'd usestudded tubes with plenty of soot blower lanes and ade-quate soot blowing capacity.JOHNSON: That might do the job. Our boilers that weregiving us trouble were unusual in that they were fire-tubedso that here it was almost impossible to clean them in run.We had a circulating ball system to circulate steel ballsandfinally we solved it. We went off on to number two oilwhen the vanadium got too high and solved our ash prob-lem simultaneously.Q. On your furnace—and this is probably typical of manyfurnaces—but on your furnace could you actually fire distil-late oil or even heavy oil without removing the fin section?There's no way in the world to keep the soot out of thatsection, is there?DEMAREST: No. See, we were asked to excerpt ourpapers. So there's a bit of discussion in the actual paperitself—with the fin tube section only the lightest oil will besuitable, and fired under the best circumstances, which lwas trying to emphasize; anything beyond that is going tobe quite difficult. It's going to be hard to put in steamlancing doors and to go in there and do something about it.

A water wash is only effective when the furnace is down,and to the best of my knowledge the additives which theyhave—and they remind me óf old-fashioned boiler watercompound—seem to be most effective if they are with theheavier fuels. In other words, something built strictly forthis type of service would be built accordingly.

But in the meantime l think if people are careful andthey follow the—as l say, the prescription of medicine l laidout, they'll be able to get along one way or another.MARTY FANKHANEL, Heat Research Corp.: l have acomment first with regard to your statement about theSawyer and Williams paper, l believe the design in this caseactually was for 100 percent oil firing and the referencemade to an expansion of oil firing in that paper was mostlikely due to the situation of interruptible gas supply forfuel. It was not a case of a limitation on the capability offire oil.

In addition, the comment relating to plugging of thoseburnefs had to do with the fact that there was an intermit-tent firing situation. Consequently on some annual or semi-annual basis there was a need to start up a system whichhad been dormant for a long period of time. This of coursecreated problems with mill-scale, being in piping, and sud-denly plugging burners, and of course the usual situation ofmaintenance. This is a comment, generally.

In addition, l have a few questions for you. Ken. One,you refer to a preferred half percent sulfur limit, l'd likeyou to comment on the need for that or the desirability ofthat. And you also mention a vanadium content limit, butyou didn't specify exactly what that meant in terms ofPPM.

And finally, since this is a safety symposium, l wonder ifyou'd comment on the subject of flame monitoring of oilfiring and the use of—or preference for mechanical safetyinterlocks in oil firing.DEMAREST: Well, l'd say that it's almost constituting anew paper. But answering the first part, and they were notquestions, they were observations—the tone of my com-ment was the fact that the ability of that furnace to fire theoil was very well established, and as l read that paper it wasindicated that not all the burners were equipped as combi-nation burners, and so l think-well, that will take care ofthat situation.

And whether it was an interruptible situation or not, thekind of housekeeping l have described is absolutely neces-sary. Now let's get back to your specifie questions. Numberone, l think was a matter of sulfur content. Now there, thelimitation at 0.5 percent is not for environmental reasons,but what is the peculiar activities of sulfur at a high temper-ature level in these furnaces, because so operating you getsome polymerization and other effects which—this is morefrom experience than actual data, it is desirable to avoid.And in these particular reformer furnaces—this is a wellestablished history—firing oil up to 0.5 percent sulfur con-tent has been satisfactory.

Now would you repeat your other question?FANKHANEL: Yes, l referred to the comment about asmall amount of 'vanadium—you didn't indicate exactlywhat content you suggest as a limitation, say, in terms ofPPM.DEMAREST: Well, in this particular case l would say thatmost desirably it should be held to not over 5 PPM butdefinitely not over ten PPM. Now coming back to vanadi-um, l mentioned in th& paper, but did not mention inspeaking, that there is quite a movement on foot to pro-duce low sulfur heavy fuel oils now. Major refining installa-tions are being made for this end.

However, l have no information that they are similarlylimiting metals content. So in my view l see no future forthese oils in reformer furnaces.FANKHANEL: l had a last question. l know it's a largesubject, but as l mentioned it's a safety topic and l won-dered if you had a comment on flame monitoring or safetyinterlocks?DEMAREST: Well, there is a bit of a discussion aboutthat in the paper. The reformer furnaces present a verydifficult problem for flame monitoring because the usualdevices are not fully effective due to the hot walls. Nowwhat we call the ultraviolet detector, the purple peeper,can't distinguish between the flame and the waH. Nowcoming back to safety, flame out in these reformer furnacesis a very infrequent occurrence.

What is much more likely to occur is a cutoff or mal-function in other areas that trips off the SIS system. Now

in this case comparing this with a gas installation-and wehave quite a few of them—where the Factory Mutual Burn-er System is used—you can't come back there until you'veproved that the burners are shut off, and if this is of veryshort duration you can light off from the walls.

Now in the case of oil l can see no use for having themultiplicity of pilots around for all the burners that youhave. So someone is going to have to be sure that the burn-ers are all cut off and then you cpme back with a torch.Q. What about safety interlocks. Ken?DEMAREST: Well, l certainly recommend these in anycase, but l would say to light off again on oil you've got todo it differently than you do with gas. And you don't wantto spill oil all over the furnace either.Q. In your experience with firing the fuel oil number six,do you have any experience with such fuel with ash corro-sion of the lining of the furnace?DEMAREST: In this case, no. Now l think what you'rereferring to is that in the mainly refinery practice wheremany regular heaters have been fired on heavy oil for years,and there's provision for doing this, they have had situ-ations where you have spalling of refractories and that soitof thing, and your sulfurous material getsdown behind therefractory and corrodes the casing out.

Now we do not recommend firing that kind of stuff inreformer furnaces to begin with. Or under the same circum-stances. Now to my knowledge we have not at any time hada case of casing corrosion in these furnates, but it is quitecommon in the normal crude heaters, vacuüm heaters andso forth.Q. l was thinking that the ash might dissolve the actualbrick lining. You're probably using a fairly high level refrac-tory in the furnace proper, with the vanadium and othermetallic oxides fluxing the refractory.DEMAREST: Well, l've tried to rule out handling some of

those materials because the furnace just can't cope withthem. Now answering your question otherwise, the bestreference l can give you is an installation which has beenoperating now in Germany for six years. It's been firing oilin high temperature service through to as heavy as distillateslop, and to my knowledge they have had no corrosion oranything like that.

They've had laydown in the convection bank that theyhad to clean out but they haven't had actual deterioration.JOHNSON: In regard to the ash corrosion, we fired oilevery winter for about eight years, from 1952 to 1960, andwe never had any sign of ash corrosion on the refractoryeither on gas or oil, and further to what Marty mentionedabout the trouble we had with our burners in our Hopewellplant, he's absolutely correct. We did have some troubleswitching from gas to oil—due to our seasonal type offiring—switching back and forth—but in addition we foundthat in trying to get a gas-type flame on Number 2 oil wewere exceeding the atomizing steam pressure and in doingthe high Delta P cut the burner nozzles from a circle to anellipse, and when this would happen the oil would dribbleout on the wide end of the ellipse and then coke up, butsolving this was merely a matter of shifting back to theoriginal design conditions.DEMAREST: Yes. Well, l think that's a matter of design.Now our burners were designed particularly for this, for theflame pattern. l can teil you—and it's a funny story in ourcompany—New Year's Eve about twelve years ago a bunchof us went down to our pilot plant to see a testing out of aburner because it was going out on a job that was specified;it had to burn 100 percent gas, 100 percent oil or anycombination of both.

And to get the proper flame pattern so that the tipsdidn't interfere, you know, this is a bit of a situation. Itisn't something you just go out and get a burner and do.

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