APV Evaporator Handbook

4 K I I I I I ui I I I I i1TiTi I iTiTil5il

third edition

1 1

I

ogy and systems devel acteristics, the per costs.

This Handbook describes the many types of evaporators and operating options which are available through the experience and manufacturing capabilities of companies within the APV Group.

oncentration required, and area ene

CCWI'ENTS EVWORATORS

EWWRATORS

EXXUEERING CONVERSIONS -E TIME IN FILM EVAPORATION BUYI'E TYPE EVAPORATORS

types and design

sdtction

CONTROLS

EVAPORATORS TO 3A SANITARY STANDARDS automation/colorgraphics

ES IN MVR EVAPORATOR TECHNOLOGY " R X S MIR CHEMICAL APPLICATIONS -S OF EVAPORATION RW€&EDEVAPORATORS m I E S OF SATURATED STEAM

&"ture tables

3

10

16 17 20 24

26 28 34 40 42 43

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EVlXPORATORS types and design

In the evaporation process, concentration of a product is accomplished by boiling out a solvent, generally water, so that the end product may be recovered at the optimum solids content consistent with desired product quality and operating economics. It is a unit operation that is used extensively in processing foods, chemicals, pharma- ceuticals, fruit juices, dairy products, paper and pulp, and both malt and grain beverages. It also is a unit operation which, with the possible exception of distillation, is the most energy intensive.

While the design criteria for evaporators are the same regardless of the industry involved, the question always arises as to whether evaporation is being carried out in the equipment best suited to the duty and whether the equipment is arranged for the most efficient and economical use. As a result, many types of evaporators and many variations in processing techniques have been developed to take into account different product characteristics and operating parameters.

TYPES OF EVAPORATORS The more comFon types of evaporators include:

1 batch pan 6 forced circulation 2 natural circulation 7 wiped film 3 rising film tubular 8 plate equivalents of 4 falling film tubular tubular evaporators 5 rising/falling film tubular

batch pan Next to natural solar evaporation, the batch pan as shown in Fig. 1 is one of the oldest methods of concentration. It is somewhat outdated in today’s technology but still is used in a few limited applications such as the concentration of jams and jellies where whole fruit is present and in

FIG 1 JACKETED

processing some pharmaceutical products. Up until the early 1960s, it also enjoyed wide use in the concentration of corn syrups.

With a batch pan evaporator, product residence time normally is many hours. Therefore, it is essential to boil at low temperatures and high vacuum when a heat sensitive or thermodegradable product is involved. The batch pan is either jacketed or has internal coils or heaters. Heat transfer areas normally are quite small due to vessel shapes,

BATCH PAN

3

falling film tubular Following development of the rising film principle, it took almost a further half century for a falling film evaporation technique to be perfected (Fig. 4). The main problem was one of designing an adequate system for the even distribution of liquid to each of the tubes. Distribution in its forerunner, the rising film evaporator, was easy as the bottom bonnet of the calandria always was pumped full of liquid, thus allowing equal flow to each tube.

While each manufacturer has his own tech- FALLING FILM nique, falling film distribution generally is based TUBULAR OUT around use of a perforated plate positioned above

the top tube plate of the calandria. Spreading of liquid to each tube sometimes is fur ther enhanced by generating flash vapor at this point. The falling film evaporator does have the advantage that the film is 'going with gravity' instead of against it. This results in a thinner, faster moving film and gives rise to even shorter product contact time and a further improvement in the value of HTC.

The rising film unit normally needs a driving force or temperature difference across the heating surface of at least 25°F to establish a well developed film whereas the falling film evaporator does not have a driving force limitation. This permits a greater number of evaporator effects to be used within the same overall operating limits, Le., if steam is available at 2.5 psig corresponding to 220°F and the last effect boiling temperature is l2O0F, the total available A T is equal to 100°F. This would limit a rising film evaporator to four effects, each with a A T of 25°F. It would be feasible, meanwhile, to have as many as ten or more effects using the falling film technique.

rising/falling film tubular As illustrated by Fig. 5, the rising/falling film evaporator has the advantages of the ease of liquid distribution of the rising film unit coupled with lower head room requirements. The tube bundle is approximately half the height of either a rising or falling film evaporator and the vapor/ liquid separator is positioned at the bottom of the calandria.

UM

UUM

FIG 5

TUBULAR OUT

_VAPOR

CIRCULAT,ON CIRCUVITION PUMPGIVING HIGH LIOUOR VELOCITIES OVER HEATING SURFACE

5

forced circulation The forced circulation evaporator (Fig. 6) was developed for processing liquors which are susceptible to scaling or crystallizing. Liquid is circulated at a high rate through the heat exchanger, boiling being prevented within the unit by virtue of a hydrostatic head maintained above the top tube plate. As the liquid enters the separator where the absolute pressure is slightly less than in the tube bundle, the liquid flashes to form a vapor.

The main applications for a forced circulation evaporator are in the concentration of inversely soluble materials, crystallizing duties, and in the concentration of ther- mally degradable materials which result in the deposition of solids. In all cases, the temperature rise across the tube bundle is kept as low as possible, generally in the region of 33°F. This results in a recirculation ratio as high as 200 to 330 Ibs. of liquor per pound of water evaporated. These high recirculation rates result in high liquor velocities through the tubes which help to minimize the build up of deposits or crystals along the heating surface. Forced circulation evaporators normally are more expensive than film evaporators because of the need for large bore circulating pipework and large recirculating pumps generally of the axial flow type. Operating costs of such a unit also are considerably higher.

wiped film The wiped or Bgitated thin film evaporator depicted in Fig. 7 has limited applications and is confined mainly to the concentration of very viscous materials and the stripping of solvents down to very low levels. Feed is introduced at the top of the evaporator and is spread by wiper blades on to the vertical cylindrical surface inside the unit. Evaporation of the solvent takes place as the thin film moves down the evaporator wall. The heating medium normally is high pressure steam or oil. A high temperature heating medium generally is necessary in order to obtain a reasonable evaporation rate since the heat transfer surface available is relatively small as a direct result of its cylindrical configuration.

The wiped film evaporator is very satisfactory for its limited applications. However, in addition to its small surface area, it also has the disadvantage of requiring moving parts such as the wiper blades which, together with the bearings of the rotating shaft, need periodic maintenance. Capital costs in terms of dollars per pound of solvent evaporated also are very high.

6

STEAM ER

FIG 8 R IS I NG/FA L L I NG FILM PLAT E EVA PO RAT0 R

JOINT GASKETS

DISCHARGE TO SEPARATOR

PLATE EVAPORATORS The plate equivalent of the tubular evaporator is available in four configurations - rising/falling film, falling film, Paravap and Paraflash plate evaporators. All have been developed by APV to handle the concentration of products which have varying characteristics.

Plate type evaporators now have been sold commercially for nearly 30 years and during that tirpe, over 1600 units manufactured by APV have been installed for concentrating hundreds of different products.

rising/falling film plate The original plate type evaporator, the rising/falling film plate system basically is a flexible, multi-duty unit engineered for medium production runs of heat sensitive products under sanitary conditions and at the lowest possible capital investment.

Operating on a single pass rising and falling film principle, as shown in the Fig. 8 exploded view, the evaporator consists of a series of gasketed plate processing units within a compact frame. As a thin layer of feed liquor passes over the rising and falling film section in each evaporation unit, it is vaporized on contact with adjacent steam heated plates and is discharged with its vapor to a vapor/liquid separator. All evaporation is accomplished in a matter of seconds within the plate pack. The product then is extracted and the vapor passed to a condenser, the next evaporator effect or a mechanical compressor. Product quality is given maximum protection against thermal degradation by means of high heat transfer rates, low liquid holding volume, and minimum exposure to high temperatures.

The plate evaporator has a number of advantages over its tubular counterpart. Since it is designed to be erected on a single level with minimum headroom requirements, in many cases it will fit within an existing building with overhead restrictions as low as E' or 13'. It also can be arranged as single or multiple effects without extensive building modifications or structural steel supports and can handle expanded duties by the addition of more plate units. Systems are available for evaporation rates to 35,000 Ibs/hr with efficient in-place cleaning of all stainless steel product contact surfaces.

7

STEAM . : iT7"""

PRODUCT SECTION

FEE

PROD1 FROM SEPAF

VAPOR AI PRODUCl SEPARATI

FIG. 9 CONDENSATE ' vFd FALLING FILM OUTLET PLATE EVAPORATOR

FINAL PRODUCT TO SEPARATOR

falling film plate The success of the rising/falling film plate evaporator prompted the development of the falling film plate system. This design has several advantages over its predecessor including even lower residence times and higher evaporation capabilities. While the rising/falling film plate unit is restricted to a maximum of 30,000 to 35,000 lbs/hr of water removal, the falling film plate evaporator with its larger vapor ports can accommodate 55,000 to 60,000 lbs per hour of evaporation. One of its unique design features as illustrated in Fig. 9 is that each side of the plate may be used independently of the other, thus permitting two pass operation within the same frame for even shorter residence time and improved product quality.

Paravap Especially designed to concentrate foaming liquids or those with high solids content or non-Newtonian viscosity characteristics, the APV Paravap replaces the wiped film evaporator in many cases. It successfully concentrates corn syrups and soap to better than 97-9896 total

solvents from vegetable oils and similar products. Fig. 10 shows this type of unit in a simple schematic.

Note that a key element in the system is a plate heat exchanger (Fig. 11). While specifically designed for liquidlliquid applications, it has been found that if a fluid is allowed to vaporize within the plate pack, the small plate gap and cor- rugated plate pattern create high vapor velocities (Fig. E). This causes atomization of the liquid

solids or strips hexane and other FIG 10 VACUUM PARAVAP

PRODUCT

within the high velocity vapor stream, resulting in a greater liquid surface area for mass transfer and enabling low residual solvent concentrations to be realized. Although the final product may be extremely viscous after separation from the vapor, the apparent viscosity within the plate pack is very low since only droplets are being transported in the vapor.

Paraflas h Similar to its tubular counterpart, the APV Paraflash (Fig. 13) is a suppressed boiling forced circulation evaporator mainly used for concentrating products subject to fouling that is too excessive for a film evaporator. While this system uses a plate heat exchanger, vaporization is not allowed to take place within the exchanger itself. Boiling is suppressed either by a liquid static head above the heat exchanger or by the use of an orifice piece in the discharge line. From a heat transfer standpoint, the forced circulation Paraflash is far more efficient than a tubular unit but suffers from a smaller equivalent diameter when large crystal sizes are present.

FIG. 13 VACUUM

I SUPPRESSED BOILING PARAFLASH EVAPORATOR A

FIG. 14 Single effect R56 Paraflash concentrates brewers yeast from 13% to 30% total solids

9

evaporators selection

In choosing the evaporator best suited to the duty on hand, the following factors should be weighed:

1) The evaporator with the highest heat transfer coefficients (HTCs) generally is the falling film type. Higher HTCs lead to smaller surface areas, resulting in minimum capital cost. Wherever possible, therefore, a film evaporator should be considered first.

While the biggest single disadvantage of the film evaporator is its susceptibility to scale build-up on the heat transfer surface, its lower cost offsets this inconvenience on mildly scaling duties, particularly when high evaporative capacities are involved. A typical example of this is spin bath liquors. This solution which results from the production of rayon and cellulose is comprised mainly of sulphuric acid, sodium sulphate and water plus various impurities such as zinc sulphate. Scale builds up over a period of about one week and the evaporator then is boiled out.

In food related industries where the nature of most products is heat sensitive, it generally is desirable or necessary to clean out an evaporator at least once per day for sanitary reasons. In the chemical field, however, a minimum run of a week normally is required and, in many cases, an evaporator will run for months.

2) For evaporation capacities up to about 60,000 lbs/hr of water removal, the possibility of using either a plate or tubular system should be considered. The capital investment is relatively close but the lower cost of installing a plate evaporator together with its compactness, expandability and reduced building requirements generally makes it extremely attractive. Above 60,000 lbs/hr evaporation, the choice lies among various types of tubular evaporators. Available configurations are multi-effect or mechanical vapor recompression.

3) In many cases, the choice of evaporator is determined by the necessary materials of construction (Fig. 15). An example would be a sulfuric acid evaporator where for product concentrations up to 50%, the heating surface normally would be graphite. This immediately indicates use of a tubular evaporator as opposed to a plate unit. With satisfactory temperature and concentration conditions, Incoloy and Hastelloy could be employed using either a tube or plate but would be much more expensive than graphite. Separators and piping would be either a fiber filled phenolic resin or rubber lined carbon steel. Sulfuric acid between 50% and 72% concentration again would normally use graphite as the heating surface providing temperatures are kept below 230/240"F, but piping and vessels would be lead lined steel, tantiron or cast lead. For construction reasons, agraphite tube bundle has to be arranged as a rising film or forced circulation evaporator with the vaporAiquid separator positioned at the top.

10

I I 1 FIG 15

4) More than one evaporator may be used to concentrate a particular product. For example, there may be a main or bulk evaporator followed by a finishing unit. The main evaporator would be used to remove the majority of the water or solvent to a point where the liquid concentration gives rise to restrictions. Among these are boiling point elevation which reduces the overall temperature difference of a multi- effect or MVR evaporator, product viscosity resulting in low HTCs, or saturated liquor resulting in crystallization. A forced circulation crystallizing evaporator very often is the last product stage of a multi-effect evaporator.

Consider the example of concentrating a solution from 4% to 60% total solids, a 15:l concentration ratio. At the 40% total solids level, the viscosity is too high for a film evaporator and the product has to be processed in a Paravap or wiped film unit. However, in concentrating from 4% to 40% or a 10:l ratio, 90% of the feed has been evaporated in the initial evaporator. The finishing unit now has to concentrate only from 40% to 60% or a 1.5:l ratio. This means that 96.43% of the total evaporation has been achieved in a multi-effect or mechanical vapor recompression bulk evaporator at high thermal economy and probably while obtaining good HTCs. Only 3.57% of the duty is confined to a small single effect evaporator which handles the most difficult part of the concentration.

5) When the requirement is for a crystallizing evaporator, there never is any doubt that the stage where crystallization takes place has to be a forced circulation evaporator and, in most cases, a tubular unit. However, when the problem is not one of crystallization but ageneral scalingof the heat transfer surface instead, the Paraflash is much more efficient. As shown in Fig. 16, the circulation rate through the plate is

, I 11

HEAT DUTY BTU/HR 1 5x106 5x106 ELEMENT TOTAL SURFACE FT* FLUID TEMP IN O F

FLUID TEMP OUT "F

1%" OD, 16 SWG. 25' TUBE APV R10 PLATE 2620 2622

160 160 161.08 170

~

~ requirements. considerably less than through a tube and results in much lower horsepower

If crystals are formed and are too large for a plate evaporator to handle, the designer has to determine whether the tubular forced circulation unit should be a single or multiple pass configuration. Normally, forced circulation tubulars are designed with tube velocities of 6 to 8 ft/ second or higher to minimize fouling. In the Fig. 17 comparison between single and three pass configurations, three pass units are shown to have lower circulation rates directly resulting in higher temperature rises, lower log mean temperature differences and, therefore, greater surface area. Even though the circulation rate is less, the pressure drop on the three pass versus one pass is more due to greater overall tube length. This results in larger absorbed horsepower. It generally is concluded, therefore, that a single pass arrangement is less expensive from both the capital and operating cost standpoints.

6) Estimation of HTCs from physical properties is easier and more reliable for forced circulation units than for film evaporators. As a general rule, HTCs used for the latter are determined by experience or test work.

: i

~

1 1 ~

1 j I

j i

SERVICE TEMP " F [ 190

~ FIG 17 COMPARISON SINGLE AND TRIPLE PASS CALANDRIA

190

12

RECIRC RATE GPM TOTAL AP PSI BHP ABSORBED

10,975 1610 16 9 10.8

107 7 10 1

EVAPORATION CONFIGURATION AND ENERGY CONSERVATION With recent downward adjustments in the price of oil there is a tendency to think of the energy crisis as being a thing of the past. However, the upward price revisions of 1974 and 1979 will be repeated in the future. Despite great improvements in oil- finding technology and large increases in spending for exploration, annual oil dis- coveries are only 40'% of what they were 25 years ago. World oil consumption outpaces new findings by 5 billion barrels a year and easily recovered oil no longer exists.

The natural gas situation is a bit more promising, but with theadvent of complete deregulation its price will be subject to market fluctuations. Steam generation from coal represents a minority of installed capacity. Furthermore, as oil supplies diminish, these alternative energies will become more costly. The present cost of raising steam, typically $5.00 to $7.00 per 1000 pounds generated, inevitably will rise. Indeed the time may come when there will be very little steam at all.

To brighten this forecast, engineers can help cut energy consumption even when evaporation requirements seem to become greater every year. This can be done by:

1) installing a greater number of steam effects to an evaporator 2) making use whenever possible of steam thermocompression or mechanical

3) making sure that the feed to an evaporator is preheated to the boiling point in

4) using low grade heat from the evaporator whenever possible 5) insulating equipment to keep losses to a minimum

vapor recompression

the most efficient manner

Some of these points are illustrated by the Fig. 18 schematic of a three effect evaporator with s t e m thermocompression that uses evaporator condensate and inter- effect vapor for feed preheating. Note that even this vapor has been used efficiently in prior effects and that condenser water also may be used if the feed temperature is low. Fig. 19, meanwhile, outlines a four effect evaporator with thermocompression and the use of a slightly different technique with a spray heating loop.

While a greater number of effects increases initial capital investment, savings in operating costs will justify the expenditure if evaporation capacities are large enough and the operating period long enough. A thermocompressor generally adds the equivalent of one or more effects at relatively little capital cost although the surface area in the effects between thermocompressor suction and discharge must be increased. The HTC of these effects generally is very good so the increase in surface area is minimized. Care should be taken, however, to design with a low AT across the thermocompressor to ensure high entrainment ratios of vapor to steam.

It is also important when using a steam thermocompressor not to have a high boiling point elevation in those effects. This will cut down the AT available for heat transfer. Thermocompressors are somewhat inflexible and do not operate well outside of their design conditions. They should not be used when the product may foul the evaporator surface and cause the design pressures and pressure boost across the thermocompressor to rise. Under these conditions, the amount of vapor entrained is reduced and a fall off in evaporator capacity results.

Effective preheating of the feed also can reduce energy consumption considerably. The capital cost of preheaters is fairly small with the plate heat exchangers being particularly effective due to their capability for realizing a very close temperature approach to the heating medium whether it be condenser water, waste evaporator condensate or inter-effect vapor.

13

FIG 18 3-EFFECT STEAM JET RECOMPRESSION

-HIGH PRESSURE STEAM

FIG 19 4-EFFECT THERMOCOMPRESSION

I

14

FIG 70 MECHANICAL RECOMPRESSION EVAPORATOR

5 TO 10% FLOW ENTHALPY '169 BTULB -

While all of these features reduce energy consumption, there still are better methods available. In less than a decade and probably within the next five years, the majority of new large capacity evaporators installed, particularly for bulk duties, will be of the mechanical vapor recompression (MVR) type. The mechanical vapor compressor can be driven by electricity from coal, hydro power or nuclear power even when all the gas and oil has been exhausted or is too expensive to use.

Briefly examining the thermodynamics involved with MVR, the Fig. 20 schematic shows an evaporator with a liquid boiling point of 212°F (atmospheric pressure). All of the water vapor that is boiled off passes to a compressor. In order to keep the energy input to the system as low as possible, the pressure boost across thecompres- sor is limited.,In the majority of cases, this pressure boost will correspond to a saturated temperature rise in the region of 15°F or less.

In this example, there is a pressure boost of 4.5 psi across the compressor. Assuming that there is a pressure loss of 0.5 psi in the system, the effective pressure on the steam side of the evaporator is 18.7 psia. This compressed water vapor condenses and gives up its latent heat, thus vaporizing more water from the liquid that is being concentrated. The latent heat of vaporization of water at atmospheric pressure is 970 Btu/hr. Note that it only requires a theoretical energy input of 18 BtuAb to raise the water vapor from 14.7 to 19.2 psia. The theoretical steam economy, therefore, is 970/18=54. When compressor efficiency is taken into account, this figure is brought down to between 32 and 35 which is another way of saying that the MVR system is equivalent to a 32-35 effect steam evaporator. Related to energy costs of 4 cents per KW hr for electricity for the compressor drive and $6.00 per 1000 lbs of steam for a conventional steam evaporator, the MVR system then becomes the economic equivalent of just under a 19 effect evaporator.

The MVR has another definite advantage over steam. The condensate is available at high temperature and is ideal for evaporator feed preheating, particularly if the condensate rate is as high as 90% of the feed rate, i.e., a 10:l concentration ratio within the evaporator. There are many such evaporators in operation where the sole energy input to the system is through the compressor with steam requirements limited to approximately 15 minutes during start up.

While Fig. 20 illustrates an evaporator system that uses a compressor, it will be shown that the use of a turbo fan in place of the centrifugal compressor not only yields lower boost but also provides more surface area and better operating economics.

15

engineering conversions

to convert from HEAT CAPACITY Calories/(Gram) ("C)

DENSITY Gram/Mil li I iter

THERMAL CONDUCTIVITY Kilocalorie/

Watt/( m) ("C) VISCOSITY

Cent i sto kes Dynamic Viscosity

Pound-Mass/( Ft) (Sec) Kinematic Viscosity

CmYSec PRESSURE Kilo Pascal Bar Inches Hg Absolute Atmosphere Torr mm Hg ENTHALPY Calorie/Gram WORWENERGY (Kilowatt) ( H r) (Horsepower)(Hr) Calorie HEAT TRANSFER COEFFICIENT Kilocalorie/

Watt/(cm2)(°C)

(Hr)(m)("C)

(Hr)(m2)(OC)

to

Calories/(Gram) (Mole) ("C) Btu/( Pound) (OF)

Pounds/Gallon Pounds/Cubic Ft.

Btu/( Hr) (Ft) (OF)

Centipoise

Centipoise

Centistokes

psi

psia

Btu/Pound-Mass

Btu

Btu/( Hr)( Ft2)("F)

multiply by

Molecular Weight 1 .o 8.33

62.42

0.671 9 0.5778

Specific Gravity

1488.2

100

0.14504

0.491 2

0.01 908 0.01 908

14.504

14.696

1.8

3412.1 2544.4

0.003968

0.2048 1761.1

16

residence time in film evapora~on Since many pharmaceutical, food and dairy products are extremely heat sensitive, optimum quality is obtained when processing times and temperatures are kept as low as possible during concentration of the products. The most critical portion of the process occurs during the brief time that the product is in contact with a heat transfer surface which is hotter than the product itself. To protect against possible thermal degradation, the timekemperature relationship therefore must be considered in selecting the type and operating principle of the evaporator to be used.

For this heat sensitive type of application, film evaporators have been found to be ideal for two reasons. First of all, the product forms a thin film only on the heat transfer surface rather than occu- pying the entire volume. Residence time within the heat exchanger thus is greatly reduced. Secondly, a film evaporator can operate with as low as a six degree F steay-to-product temperature difference. With both the product and heating surfaces close to the same temperature, localized hot spots are minimized.

As previously described, there are rising film and falling film evaporators as well as combination rising/falling film designs. Both tubular and plate con tions are available.

RISING FILM EVAPORATORS In a rising film design, liquid feed enters the bottom of the heat exchanger and when evaporation begins, vapor bubbles are formed. As the product continues up either the tubular or plate channels and the evaporation process continues, vapor occupies an increasing amount of the channel. Eventually, the entire center of the channel is filled with vapor while the liquid forms a film on the heat transfer surface.

The effect of gravity on a rising film evaporator is twofold. It acts to keep the liquid from rising in the channel. Further, the weight of the liquid and vapor in the channel pressurizes the fluid at the bottom and with the increased pressure comes an increase in the boiling point. A rising film evaporator therefore requires a larger minimum AT than does a falling film unit.

The majority of the liquid residence time occurs in the lower portion of the channel before there is sufficient vapor to form a film. If the liquid is not preheated above the boiling point, there will be no vapor and since a liquid pool will fill the entire area, the residence time will increase.

17

FALLING FILM EVAPORATORS As liquid enters the top of a falling film evaporator, a liquid film formed by gravity flows down the heat transfer surface. During evaporation, vapor fills the center of the channel and as the momentum of the vapor accelerates the downward movement, the film becomes thinner. Since the vapor is working with gravity, a falling film evaporator produces thinner films and shorter residence times than a rising film evaporator for any given set of conditions.

TUBULAR AND PLATE FILM EVAPORATORS When compared to tubular designs, plate evaporators offer improved residence time since they carry less volume within the heat exchanger. In addition, the height of a plate evaporator is less than that of a tubular system.

ESTIMATING RESIDENCE TIME It is difficult to estimate the residence time in film evaporators, especially rising film units. Correlations, however, are available to estimate the volume of the channel occupiet by liquid. Formula 1 is recommended for vacuum systems.

For falling film evaporators, the film thickness without vapor shearingcan be calculated by formula 2.

Since the film is thin, this can be con- verted to liquid volume fraction in a tubular evaporator by formula 3.

For a falling film plate evaporator, formula 4 is used. As liquid travels down the plate and evaporation starts, vapors will accelerate the liquid. To account for this action, the rising film correlation is used when the film thickness falls below that of a falling film evaporator. In practice, the film thickness may be less than estimated by either method becausegrav- ity and vapor momentum will act on the fluid at the same time.

Once the volume fraction is known, the liquid residence time is calculated by formula 5. In order to account for chang- ing liquid and vapor rates, the volume fraction is calculated at several intervals along the channel length. Evaporation is

i

1

(3) 4m d

R L = -

(4) 2m R L = 7

R,AL t=- q,

(a) two stages (b) three stages (c) plate gap .3" assumed

assumed to be constant along with channel length except for flash due to high feed temperature.

The table shows a comparison of contact times for typical four effect evaporators handling 80 GPM of feed. The tubular designs are based on 2"diameter by 30 feet. Designs using different tube lengths, incidentally, do not change the values for a rising film tubular system.

The given values represent total contact time on the evaporator surface which is the most crucial part of the processing time. Total residence time would include contact in the preheater and separator as well as additional residence within inter- connecting pipi?g.

While there is noexperimental data available to verify these numbers, experience with falling film plate and tubular evaporators shows that the values are reasonable. It has been noted that formula 2 predicts film thicknesses that are too high as the product viscosity rises so, in actuality, 4th effect falling film residence times probably are somewhat shorter than charted.

SUMMARY Film evaporators offer the dual advantages of low residence time and low temperature difference which help assure a high product quality when concentrating heat sensitive products. In comparing the different types of film evaporators that are available, falling film designs provide the lowest possible A T and the falling film plate evaporator provides the shortest residence time.

19

plate type evaporators

Toeffectively concentrate an increasing variety of products which differ by industry in such characteristics as physical properties, stability, or precipitation of solid matter, equipment manufacturers have engineered a full range of evaporation systems. Included among these are a number of plate type evaporators.

Plate evaporators initially were developed and introduced by APV in 1957 to provide an alternative to the tubular systems that had been in use for half a century. The differences and advantages were many. The plate evaporator, for example, offers full accessibility to the heat transfer surfaces. It also provides flexible capacity merely by adding more plate units, shorter product residence time resulting in a superior quality concentrate, a more compact design with low headroom requirements, and low installation cost.

These APV plate evaporation systems are made in four arrangements-rising/ falling film, falling film, Paravap, and Paraflash-and may be sized for use in new product development or for production at pilot plant or full scale operating levels.

rising/falling film plate The principle of operation for the risinglfalling film plate evaporator (RFFPE) involves the use of a nurqber of plate packs or units, each consisting of two steam plates and two product plates. As shown in Fig. 1, these are hung in a frame which resembles that of a plate heat exchanger. The first product passage is a rising pass and the second, a falling pass. The steam plates, meanwhile, are arranged alternately between each product passage.

The product to be evaporated is fed through two parallel feed ports and is equally distributed to each of the rising film annuli. Normally, the feed liquor is introduced at a temperature slightly higher than the evaporation temperature in the plate annuli, and the ensuing flash distributes the feed liquor across the width of the plate. Rising film boiling occurs as heat is transferred from the adjacent steam passage with the vapors that are produced helping togenerate a thin, rapidly moving turbulent liquid film.

During operation, the vapor and partially concentrated liquid mixture rises to the top of the first product pass and transfers through a ‘slot’ above one of the adjacent steam passages. The mixture enters the falling film annulus where gravity further assists the film movement and completes the evaporation process. The rapid movement of the thin film is the key to producinglow residence time within the evaporator as well as superior heat transfer coefficients. At the base of the falling film annulus, a rectangular duct connects all of the plate units and transfers the evaporated liquor and generated vapor into a separating device. Steam and condensate ports connect to all the steam annuli (Fig. 2).

The plate evaporator is designed to operate at pressures extending from 10 psig to full vacuum when using any number of effects. However, the maximum pressure differential normally experienced between adjacent annuli during single effect operation is 15 psig. This, and the fact that the pressure differential always is from the

1

I 2o

steam side to the product side, considerably reduces design requirements for sup- porting the plates. The operating pressures are equivalent to a water vapor saturation temperature range of 245°F downwards and thus are compatible with the use of nitrile or butyl rubber gaskets for sealing the plate pack.

Most rising/falling f i h plate evaporators are used for duties in the food, juice and dairy industries where the low residence time and 100 to 200°F operating range temperatures are essential for the production of quality concentrate. An increasing number of plate evaporators, however, are being operated successfully in both pharmaceutical and chemical plants on such products as antibiotics and inor- ganic acids. These evaporators are available a s multi-effect and/or FIG. 1 Risindfallina film plate evaporator in final - . multistage systems to allow relatively high concentration ratios to be carried out in a single pass, non-recirculatory flow.

The rising/falling film plate evaporator should be given consideration for various applications that

require operating temperatures between 80-210°F w have a capacity range of 1000-35,000 lbs/hr water removal w have a need for future capacity increase since evaporator capabilities can be

w require the evaporator to be installed in an area that has limited headroom w where product quality demands a low timekemperature relationship

where suspended solid level is low and feed can be passed through 50 mesh

stages of f a b r ~ t i o n .

extended by adding plate units or by the addition of extra effects

screen

21

A ‘Junior’ version of the evaporator is available for pilot plant and test work and for low capacity production. If necessary, this can be in multi-effect/multistage arrangements such as the system illustrated by Fig. 3.

falling film plate Incorporating all the advantages of the original rff plate evaporator system with the added benefits of shorter residence time and larger evaporation capabilities, the falling film plate evaporator has gained wide acceptance for the concentration of heat sensitive products. With its larger vapor ports, evaporation capacities are typically up to 50-60,000 lbskr.

The falling film plate evaporator consists of gasketed plate units (each with a product and a steam plate) compressed within a frame that is ducted to a separator. The number of plate units used is determined by the duty to be handled.

As shown in Fig. 4, one of the important innovations in this type of evaporator is the patented feed distribution system. Feed liquor first is introduced through an orifice (1) into a chamber (2) above the product plate where mild flash-

FIG. 3 Three-effect, four-stage ‘Junior’

FIG. 4 Typical product and steam plate unit for falling film plate evaporator.

ing occurs. This vaporfliquid mixture then passes through a single product transfer hole (3) into a flash chamber (4) which extends across the top of the adjacent steam plate. More flash vapor results as pressure is further reduced and the mixture passes in both directions into the falling film plate annulus through a row of small distribution holes (5). These assure an even film flow down the product plate surface where evaporation occurs. A unique feature is the ability to operate the system either in parallel or in series, giving a two-stage capability to each frame. This is particularly advantageous if product recirculation is not desirable.

In the two-stage method of operation, feed enters the left side of the evaporator and passes down the left half of the product plate where it is heated by steam coming from the steam sections. After the partially concentrated product is discharged to the separator, it is pumped to the right side of the product plate where concentration is completed. The final concentrate is extracted while vapor is discharged to a subsequent evaporator effect or to a condenser.

Paravap The operating principle of the Paravap represents an application of the thin film, turbulent path evaporation process and in many cases, replaces the wiped or agitated film evaporator. Since it has no mechanical moving parts within the heat transfer

22

FIG. 5 Single effect R86 Paravap

FIG. 7 Single effect, forced circulation Paraflash

area, costly maintenance repairs common to wiped film systems are eliminated. It is especially designed to concentrate liquids with high solids contents or non-New- tonian viscosity characteristics.

or hot oil directed into alternate passages within a plate heat exchanger, boiling begins as the liquid contacts the heated plates. The small plate gap and high velocity flow pattern (Fig. 6) atomizes the feed and provides a greater liquid surface area for mass transfer. Since the vapor carries the feed in the form of minute particles, the apparent viscosity within the heat exchanger plate pack is very low. The final product, however, may be extremely viscous after separation from the vapor.

Advantages include low residence time to minimize thermal degradation, low rates of fouling, and economical operation.

Typical applications: concentrating soap to final product consistency; concentrating apple puree from 25 to 40"brix, grape puree to 50"brix, cherry puree to 60"brix, fruit juices to 95% solids, and sugar or corn syrup solutions to over 97%; solvent stripping duties such as hexane from oil.

Paraflash Operating under a suppressed boiling, forced circulation principle, the APV Paraflash is used to concentrate products subject to fouling too excessive for film evaporators. Unlike the Paravap, vaporization does not occur within the heat exchanger plate pack. Instead, liquor flashes as it enters a separator, crystallization takes place, and a suspended slurry results. Suppressed boiling combined with high liquid velocities deters scaling on the heat transfer surface, minimizes cleaning downtime, and promotes longer production runs.

The Paraflash can be used in single or multiple effects for such products as grape juice (tartrate crystals), coffee, wheat starch, distillery effluent, and brewer's yeast (suspended solids).

With feed liquor and the heating medium of steam, hot water

FIG, 6

PRODilCT OR COOLlNG

LIOUIO

,

23

process controls microprocessor automation /colorgraphics

As food and chemical processing methods have become more complex, techniques for controlling process equipment and systems have kept pace. The popular trend is toward full automation through the use of microprocessor based electronic monitor/ control systems. However, the ready availability of sophisticated controls does not necessarily mean that all process control must go that route. Since process and control should be mated for optimum productivity and cost effectiveness, only the amount of control necessary for a given application should be used. This may involve any of three approaches-manual, analog, or microprocessor automation.

manual control The simplest method of control is that which involves a dedicated operator who monitors system variables and makes the adjustments required to return the process to standard or specification.

When the volume of material being processed is small or when the cost of labor is not a significant factor in the cost of production, manual control of evaporation has proved to be satisfactory. Various components such as pumps and valves are activated in proper sequence by the operator via pushbutton or selector switch. Control of system variables, i.e., steam flow, steam pressure, feed flow, temperature, and product concentration, can be maintained to specification either by the operator or by self- acting controllers.

analog control Providing semi-automation, analog loops assume control of evaporation once the operator has sequentially selected on/off or openklose modes and has determined the desired set point for any number of variables. Thereafter, evaporator functions automatically are monitored and adjusted as necessary to maintain equilibrium.

While alarms may be incorporated for variables not within standard, the operator then is relied upon to re-establish equilibrium.

microprocessor control For optimum processing with increased productivity and the elimination of product variances due to human error, evaporator systems may be operated under completely automated microprocessor control. Available monitorkontrol micro systems start with the compact, yet powerful, ACCOS 3 MLC which can control up to 108 items and extend through the larger ACCOS 2S+. The latter can individually handle up to 756 functions or, when interconnected with additional units and a supervisory controller, form a network encompassing more than 3000 items. These include start up procedures, calculation and adjustment of product values and equipment settings, routine or emergency shutdown procedures, automatic CIP, and other monitoring or actions. Systems are programmed in plain English so that plant engineers and operating personnel may write or make modifications without involving automation specialists.

Colorgraphic displays also are available to provide a color visualization of the current state of process equipment for the operator in an unmistakable fashion.

24

Typical colorgraphics present high resolu- tion displays in vividcolors to helpoperators constantly monitor the statusof equipment operation.

an ACCOS 2S+ process control system

25

tubular evaporators to&sanitarystamdards As many small processors band together to form centrally located cooperatives, a corresponding change is occurring in the equipment that is required to handle large scale concentration of liquid food and dairy products in an efficient, economical manner. Plate type evaporators with their water removal limitations of typically 60,000 lbs/hr are being replaced by tubular systems of double or triple that capacity.

To meet the processing needs of these large food and dairy cooperatives, the design and fabrication of tubular evaporators have been brought into compliance with the legal standards established by various official regulatory groups for sanitary operations.

The tubular evaporator system consists primarily of three components: a vertical heating tube bundle which is housed within an insulated steam

a distribution device which allows even liquid flow over the tube circumfer-

a separator to efficiently extract liquid droplets from the vapor steam and

To these are added basic feed tanks, preheaters, ductwork, product and CIP piping,

jacket or calandria

ence and, therefore, prevents ‘dry spots’ on the heat transfer surface

thereby minimize carry-over of product

and necessary pumps.

manufacturing to 3A While tubular evaporators designed for chemical processing duties generally are manufactured of carbon or pickled stainless steel, the very nature of the products handled in the dairy and food fields neces- sitates the use of highly polished stainless steel for all product contact surfaces.

The basic evaporator effect, for example, consists of a shell, a top and bottom tube sheet, and a bundle of 2” diameter seamless seal welded heat transfer tubes numbering anywhere from 100 to 1000 or more depending upon the requirements of the evaporation duty. This is topped by a feed distribution system and a cover or bonnet that clamps to the calandria. Beneath this unit is the product sump or discharge area and adjacent, the vapor/ liquid separator.

As shown in the Fig. 1 cutaway draw- ing, feed is charged to the system

FIG. 1 Cutaway of tubular evaporator calandria and vauor/liauid - r . . -

INLET- separator.

GASKET - ~%VTION PLATE

GASKET

26

through an inlet at the top of the bonnet and floods the surface of the distribution system. As the liquid flows through many small holes, it spreads evenly across the entire face of the top tube sheet which is mounted about one inch below and eventually moves into each of the heat transfer tubes that extend the full height of the calandria.

Since there are many product contact surfaces in this portion of the evaporator (the inside of the feed inlet piping, both top and bottom of the distribution plate, the top of the tube sheet, and the interiors of all tubes), the 304 stainless steel used is polished to a #4/150-180-or-340 grit. APV finishes thus match and very often exceed 3A standards which call for a surface finish equivalent to 150grit. Furthermore, the one inch riser which is added perpendicularly to the tube sheet to form a product reservoir is fabricated with a minimum l/'' radius polished fillet weld. This eliminates any possibility of pockets in which product may collect. Gaskets sealing the perimeter of both the distribution and tube sheet plates are made of dairy grade neoprene.

While the evaporator shell normally is fabricated of 304 stainless, polishing is not required since there are no product contact areas.

At the bottom of the evaporator effect, all areas come in contact with product and, consequently, are of polished stainless. This includes the underside of the bottom tube sheet, the product sump, ductwork leading to the adjacent separator and the interior of the separator itself. When sight glasses, manways, nozzles and light glasses are added, interior welds are ground and polished smooth and flush while the components themselves are mounted at a minimum 3" angle to allow for proper drainage. Finally, downstream ductwork between vessels is sloped from 3" to 5" away from the product contact surfaces. In effect, nothing is installed at less than a 90" angle so that possible product traps are eliminated and the entire system is both cleanable and drainable.

27

advances in RlvIt evaporator technology

In recent years, mechanical vapor recompression (MVR) technology has been introduced and widely accepted as an effective approach to powering medium to large capacity evaporators for both chemical and sanitary applications. While experience has shown that the higher capital cost of this equipment relative to that of steam driven evaporation systems has been offset by significant energy savings, advances in MVR technology now have reduced energy requirements even further.

MVR defined Simply stated, with mechanical recompression the water vapor boiled off in the evaporator is passed to an electrically powered compressor and is compressed through 1-3 psi. This raises the temperature of the vapor which then is used as the heating medium. The difference in enthalpy between the vapors on the heating and process sides is comparatively small with a resultant reduction in energy consumption and, depending upon regional steam and power costs, an operating cost equivalent to at least an 8-30 effect evaporator. Theoretical thermal efficiency may exceed that of a 60-effect steam evaporator.

Typically, Figure l a shows a single effect steam evaporator operating at atmospheric pressure (14.7 psia) with vapor being produced at 212°F and sent to a condenser. The heat source for this system is steam at 17.2 psia, condensing at 220°F.

In Figure lb , the same evaporator is shown operating with mechanical vapor recompression. In this case, the vapor at 2l2"F, 14.7 psia, is sent to a compressor where its pressure is raised to 17.2 psia. It then is charged to the steam side of the evaporator as the heating medium, condensing at 220°F. Savings are realized in two areas: no steam is required for evaporation although nominal amounts are required for startup and compressor seals, and since the vapor from the evaporator is not sent to a condenser, cooling water requirements are dramatically reduced.

It will be shown later that excess vapor is produced due to the inefficiencies in the compression cycle. This excess vapor is used to compensate for vent and radiation losses and at times, as an assist to preheating. TABLE 1 SATURATED A T AT

development of MVR evaporators To a large extent, the design of MVR evaporators has been dictated by the capabilities of the compressors available at the time. The primary limitation has been the compression ratio (discharge pressure divided by suction pressure) that can be achieved since this determines the temperature difference available for the evaporator. For example, if an evaporator is run at 212°F and atmosDheric Dressure and a comwes-

VARIOUS COMPRESSION RATIOS, "F

sion ratio of 1.4 isA used, the steam prlssurs at the discharge of the compressor is 1.4 x 14.7 psia or 20.58 psia. Since water vapor at 20.58 psia condenses at 229.5'F,

28

FIG. 1A SINGLE EFFECT EVAPORATOR

CONDENSER

I FEED

STEAM PRODUCT CONDENSATE

the allowable temperature difference AT for the evaporator is 17.5"F before losses are considered. Table 1 shows the total temperature differences for a number of conditions.

CENTRIFUGAL COMPRESSORS The relatively high volume of vapor encountered in evaporators requires the use of centrifugal compressors in most cases. Initially, centrifugal compressors on steam were limited to a compression ratio of 1.4 which in turn limited the available temperature difference to between 13 and 17.5"F depending on boiling temperature. Only film evaporators could use MVR since there was not sufficient temperature difference to consider forced circulation designs. Furthermore, products having significant boiling 800 HP centrifugal compre5sor

is carefully moved into position point elevation were excluded from this technique. Two trends developed in recent years, however, have increased MVR capabilities

and applications. First of all, improved design allows centrifugal compressors to run at higher

speeds, increasing compression ratios approximately to 2.0 to 1. Consequently, a AT of 27 to 36°F now can be obtained and thus, MVR can be used with forced circulation systems and for the evaporation of products with boiling point elevations.

Secondly, advances in evaporator design allow the operation of film evaporators with a lower AT, thereby minimizing energy requirements. For some products, film evaporators can be calculated with a AT (excluding losses) in the range of 6°F.

29

FIG 2 MULTIPLE EFFECT MVR, CENTRIFUGAL COMPRESSOR WITH FINISHER

SLPERHEATER - - COMPRESSOR

t *-- CENTRIFUGAL COMPRESSOR

FINISHER

FIG. 3 SINGLE EFFECT MVR EVAPORATOR WITH CENTRIFUGAL COMPRESSOR AND ROTARY BLOWER DRIVEN FINISHER

By increasing the AT available and decreasing the AT required, it also became possible to design multiple effect MVR evaporators. Figure 2 illustrates a double effect MVR system with a forced circulation finisher operating across all effects. With this arrangement, the flow to the compressor is reduced and the finisher, operating at the higher concentration, takes advantage of the full AT available.

30

FANS The next development in MVR design was an apparent reversal of prior advances.

As the required AT across a film evaporator decreased, it became possible to provide that A T by using a fan. This produces a compression ratio on the order of 1.2 to 1, providing approximately 7 or 8°F AT (before losses) for evaporation. The MVR system previously discussed and shown in Figure 2 is typical of fan use. It should be noted that the fan MVR technique can be used only on single effect film evaporators handling product without significant boiling point. Where the heat transfer coefficient of the product is low, it sometimes is better to make use of the higher AT available from a centrifugal compressor.

Where fans can be used, however; the horsepower requirement usually is less than in centrifugal compressor designs. Furthermore, fans do not require that the inlet vapor be superheated. Instead, this is done either by a separate heat exchanger using steam or by recycling some of the compressor discharge vapor to the compressor suction.

It is, incidentally, a common practice to use a fan evaporator to concentrate a product up to a point where a larger A T is required and then to switch to a small steam or MVR finishing evaporator for final concentration.

I I

BOILING BOILING TEMP. 130°F TEMP. 170°F

CR AT HP CR AT HP

OTHER DESIGNS Rotary blowers are low capacity positive compressors which occasionally are used with small MVR evaporators of up to approximately 15,000 lbs/hr capacity. This generally is a finishing type evaporator.

In some cases, two compressors will be arranged in series as is shown in Figure 3. Here, the bulk of the evaporation is done in a single effect MVR system having a centrifugal compressor. Some of the compressor discharge vapor then is further compressed in a blower in order to operate a finishing evaporator.

estimating compressor power requirements To calculate estimated power requirements for an MVR compressor, power and A T values for both centrifugal compressors and fans have been plotted in Figures 4 and 5 respectively. These values compare reasonably well with installed MVR systems.

BOILING TEMP. 212'F

CR AT HP

HORSEPOWER PER 10WIHR COMPRESSOR INLET FLOW

1.3 11.65 10.01

1.4 15.03 12.99

1.6 21.23 18.54

1.8 26.81 23.63

2.0 31.89 28.34

2.2 36.57 32.74

14

13

12

LL 11

f 10

3 9

3 5

8 8 + 7

5 4

3

2

1

1 2 3 4 5 6 7 8 9 1 0 1 1

HORSEPOWER PER 1WMtiHR FLOW

NOTE: Vapor assumed to be superheated 10°F by external steam.

1.3 13.53 10.67

1.4 17.47 13.85

1.6 24.69 19.76

1.8 31.20 25.18

2.0 37.16 30.20

2.2 41.31 34.88

. 1.3 10.00 9.3s

1.4 12.91 12.1E

1.6 18.21 17.3@

1.8 22.98 22.15

2.0 27.31 26.57

2.2 31.30 30.69

FIG. 5 HORSEPOWER VS A T FOR FANS

BOILING TEMP. 130°F

CR AT HP

1.1 3.59 2.99

1.2 6.91 5.79

1.3 10.00 8.43

FANS

BOILING TEMP. 1 7OoF

CR AT HP

1.1 4 .173 .19

1.2 8.04 6.18

1.3 11.65 9.00

BOILING TEMP. 212°F

CR AT HP

1.1 4.85 3.41

1.2 9.34 6.60

1.3 13.53 9.60

31

TABLE 2 COMPARISON OF TYPICAL MVR DESIGNS (APPROXIMATE) boiling temperature - 130" F evaporation rate - 60,00O#/hr

HP/1000 #/HR VAPOR FLOW

TOTAL HORSEPOWER

EQUIVALENT BTU

EQUIVALENT STEAM #/HR

EQUIVALENT STEAM ECONOMY

AVERAGE AT PER EFFECT BEFORE LOSSES, OF

5.79 17.38 26.57

374.4 521.4 531.4

884,133 1,326,963 1,352.413

870 1315 1347

69 45.6 44.5

6.9 9.1 9.1

NOTE In this example, the fan horsepower is lower than either of the centr i fugal designs, bu t the lower AT required thegreater the surfacearea

Table 2, meanwhile, compares the power requirements for different MVR designs. Note that it is possible to calculate an equivalent steam economy by converting horsepower to Btu/ h r and multiplying by 2545. This value then is divided by the latent heat to arrive at the equivalent steam used.

thermodynamics of MVR To fully comprehend the potential of MVR evaporation, it is important that the thermodynamics of this technique be

TABLE 3 PROPERTIES OF WATER VAPOR

1.7568 I 1.7442 I 1.7596 I examined. This analysisinvolves Table 3 as well as the steam and MVR evaporator schematics shown in Figures l a and lb.

The first two columns of Table 3 give the properties of saturated water vapor at 14.7 psia, 212°F and at 17.2 psia, 220°F. These values can be used to estimate the energy requirements for an evaporator operating at these conditions.

Looking first at the steam evaporator shown in Figure la , water at 17.2 psia, 220°F has an enthalpy (heat content) of 188.2 BtuAb while steam at the same conditions has an enthalpy of 1153.4 Btu/lb. The difference between the vapor and liquid is the latent heat or 965.2 Btu/lb. In other words, in order to produce one pound of steam at 220°F, 17.2 psia, from water at 220°F, 17.2 psia, the addition of 965.2 Btu/lb of energy is required.

32

In the case of the MVR evaporator, however, the vapor at 17.2 psia, 220°F (enthalpy 1153.4 Btu/lb) is produced from vapor at 2l2"F, 14.7 psia (enthalpy 1150.5 Btdlb). Theo- retically, only 2.9 Btu/lb of energy must be added.

The compressor, a fan in this case, operates under the requirement that the entropy of the discharge vapor be at least as high as the entropy of the inlet vapor. Since inefficiencies in the compression cvcle will result in an exit entropy

llM6

& 4 >

$ 11534 c

: 11505

S-ENTROPY BTUiLB F

FIG. 6 ENTHALPY/ENTROPY DIAGRAM

above that of the inlet entropy,the temperature of the existing vapor and energy input to the compressor must be increased.

Figure 6 is an enthalpy/entropy diagram for water vapor. The vapor at 14.7 psia, 2l2"F, is shown at point A. During compressions the entropy remains constant (ideally) or increases (actually). With typical efficiencies for this duty, the discharge temperature may be expected to rise to 243°F where the enthalpy is 1164.6 Btu/lb. The energy input from the compressor is 14.1 Btu/lb.

In order to cool the vapor to its condensing temperature of 220"F, 11.2 BtuAb of heat is removed. This can be done by introducing condensate at 220°F from the steam side of the evaporator. The 11.2 Btu/lb of heat removed from the vapor is absorbed into the condensate, some of which will vaporize and give off what is known as 'excess vapor: For every pound of vapor cooled, 11.2 Btu of heat is absorbed in the condensate which requires 965.2 Btu/lb to boil. Therefore, for each pound of vapor leaving the compressor, 11.21965.2 or 0.0116 pounds of excess vapor are available.

This excess vapor is used in several ways. Since there is a slight difference in latent heat between the steam and vapor, slightly more steam is required than the vapor generated. Other excess vapor is used to cover losses due to radiation and venting, is made available in some instances for preheating, or is sent to a condenser. It is significant to note that the condenser on an MVR evaporator is responsible only for vent and excess vapors. This results in a much lower cooling requirement than is necessary for steam evaporators.

It is possible to calculate an equivalent steam economy for an MVR system. In this example, for every pound of water evaporated, 970.3 Btu is absorbed. The compressor supplies 14.1 Btu but with motor and gear losses, probably requires 14.5 Btu of energy. The equivalent economy (970.3114.5) is 67 to 1. Since one horsepower is equivalent to 2545 Btu/hr, the compressor in the example requires 14.512545 or 0.0057 HP per l b k r of evaporation.

It should be noted that pressure losses through the evaporator which must be absorbed by the compressor have not been considered in this example. These losses would be taken into account either by higher compressor horsepower or by lower AT over the heat transfer surface.

33

evaporators for chenzical applications

The APV range of evaporators covers many duties in the concentration of chemicals with both film and forced circulation systems being available as required.

Film evaporators are used when there is little or no risk of fouling of the heating surfaces. Where such a risk is present, forced circulation units are recommended. All designs are suitable for multi-effect evaporation. At low concentrations, mechanical vapor recompression should be employed.

After selecting the type of evaporator required for a particular duty, the most important factor deciding its suitability is the materials of construction. In general non-metallic surfaces are employed but in certain special cases, at low concentrations and temperatures and in the presence of inhibiting ions, conventional materials such as standard grades of stainless steel or copper can be used. Higher grades of stainless steel are suitable under some conditions and titanium has been successfully employed with anodic protection.

APV evaporators are constructed from various standard corrosion-resistant materials according to the characteristics of the feed solution and the temperature of operation. As an example, concentration of a sulfuric acid solution of up to 50% at 302°F (150°C) would call for main plant items of filament wound fiberglass reinforced epoxy resin and heating and cooling surfaces of impervious graphite. If the sulfuric acid solution is between 50 and 80% with temperatures up to 230°F (llO"C), main plant items should be lead-lined mild steel protected with refractories or carbon tiles. Heat transfer surfaces again would be of impervious graphite.

TYPICAL APPLICATIONS sulfuric acid nickel sulfate During the electrolytic refining of copper, impurities build up in the electrolyte causing an increase in electrical resistance and ultimately giving contamination of the refined copper. One of the major elements involved is nickel, frequently introduced with the copper scrap used in the manufacture of the anodes.

Nickel may be removed by evaporating the electrolyte after separation of copper from solution by electro-winning until the sulfuric acid in the liquor reaches 70 percent w/w. At this concentration, virtually all the nickel is precipitated as nickel sulfate crystals which may be separated and sold. The recovered acid is returned to the electrolyte.

Due to the high b.p.e. (boiling point elevations) of the liquor and the high cost of materials to withstand the 70 percent acid, evaporation is usually done in two stages. The first stage concentrates the acid up to 45-50 percent total solids, at which point filament wound fiberglass reinforced epoxy resin and graphite materials may be used, while the second stage requires materials such as homogeneously lead- lined mild steel and silicon iron. Graphite heating surfaces are used in both cases.

34

Single effect forced circulation sulfuric acid

evaporator is constructed from lead, graphite, silicon

iron and Keebush plastic.

The bulk of the evaporation is carried out in the first stage and the evaporator at this point may be in a single or multiple effect configuration depending upon the capacity involved.

Although nickel sulfate is precipitated only in the final stages of concentration, it usually is necessary to employ forced circulation throughout because the accumulation of calcium in the electrolyte leads to calcium sulfate scaling on the heating surfaces of the system. Even with forced circulation, there is an accumulation of scale but it may be removed by washing at regular intervals. Mechanical descaling is rarely, if ever, required even though severe scaling may occur on tubular heaters used for heating the same electrolyte.

The methods just described are proven evaporation applications in a hydrometal- lurgical duty and although the information refers to the extraction of nickel from electrolyte, a similar process may be used for other serious contaminants. Other processes under consideration involve the leaching of ores with acid that must be recycled for water removal at some stage to maintain the material balance in the circuit.

titanium sulfate The production of titanium dioxide pigments involves reaction between sulfuric acid and the ore which contains iron, titanium sulfate and other compounds.

After pretreatment which includes the crystallization of iron as ferrous sulfate, the liquor is heated and hydrolyzed to precipitate titanium dioxide. Prior to this operation, the concentration of liquor has to be adjusted by the evaporation of water. It is essential that this process takes place in an evaporator with short heat contact times in order to avoid the premature hydrolysis that occurs with prolonged heating

35

and subsequently causes fouling of the heat surface and blockage of the tubes. Although the liquor contains a high proportion of sulfuric acid, the presence of

other ions in solution may inhibit corrosion so that copper often can be used for heat transfer surfaces. In some applications where minimal pickup is required for special products, graphite is employed. The remainder of the equipment is manufactured from filament-wound fiberglass reinforced epoxy resin which is completely resistant to the liquors involved.

Generally, single or multiple effect rising film evaporators are used for this duty, the number of effects being determined by throughput and by assessing the cost of operation against the increase in capital required for additional equipment.

In some cases, it is economically attractive to operate the evaporator as a single effect unit at atmospheric pressure using the vapor given off for preheating. The liquor is discharged at a temperature in excess of 212°F ( l O O O C ) , reducing the subsequent thermal load at the hydrolysis stage.

spin bath and coagulating bath liquors Some synthetic fibers or films such as rayon and cellophane are produced from cellulose. In the process, the cellulose is extracted in alkaline solutions containing sulfur compounds. This liquor is neutralized by injection into sulfuric acid under controlled conditions and the cellulose is deposited as a fiber or film of the required form and thickness.

Water accumulates in the liquor from various sources, particularly from the chemical reaction between the acid and alkali, and must be removed to maintain the volume and concentration in the bath. While it is most convenient to use an evaporator for this purpose, careful design is necessary to prevent fouling on the vapor side. The liquors are corrosive because of the sulfuric acid present and exhibit a tendency to scale due to the sulfur based materials. In addition, various volatile compounds are present. In general, rising film evaporators are recommended for this duty in either single or multiple effect depending upon the capacity required. Materials of construction are filament-wound fiberglass reinforced epoxy resin for all contact parts with impervious graphite for heat transfer surfaces.

In addition to water, sodium sulfate accumulates in the liquor due to reaction between the acid and alkali. It may be removed as Glauber’s salt by flash evaporation at a high vacuum in a specially designed crystallization system. Again, corrosion resistant materials are used because of the sulfuric acid content.

strong acids During many organic reactions, sulfuric acid is present in large quantities to act as a dehydrating agent, absorbing water and thereby maintaining the reaction rate. To permit continuous operation and prevent the rejection of diluted acid, it is necessary to remove the water from the acid.

This evaporation process is complicated by the presence of many intermediate and residual organic products which have a high tar content and can cause serious scaling on the heating surfaces. Therefore, forced circulation systems operating under vacuum generally are applied. After discharge from the vapor/liquor separator into a settling vessel, liquor is circulated through the appropriate calandria by means of glandless recirculation pumps.

36

APV rising/falling film tubular evaporator concentrated 1500 Ibs/hr of phosphoric acid from 5% to 50'71. Fabricated of corrosion resistant plastics and Karbate

The capacities required sometimes can justify multiple effect evaporation although this is not always favored due to difficulties in design with the high boiling point elevation involved, the low steam cost prevailing in some refineries, and a desire to employ the simplest possible system.

caustic soda Mercerizing is a process during which the surface of cotton is polished by the removal of loose fibers. As the cloth is immersed in a 50 percent sodium hydroxide solution, loose fibers are washed away and the solution is diluted to 15-20 percent. Following evaporation of the weak liquor to 30 percent, flake caustic is added to re- establish a 50 percent concentration.

Since steam is needed in the dyeing and calendaring phases of cotton processing, it is best that evaporation be done with the first effect at atmospheric pressure. The process thus lends itself to the use of rising film and/or falling film plate evaporators which also make possible the use of low level structures.

electrolytic cell liquors In the diaphragm cell process, liquors produced at 10 percent sodium hydroxide and 15 percent sodium chloride require crystallization of the salt and concentration to 50

37

percent sodium hydroxide. Required liquid flow and evaporation rates necessitate the use of multi-effect evaporation. Care must be taken to minimize sodium chloride solubility and therefore, maximize crystal yield. Special attention must be paid to solubility/temperature/concentrations.

phosphoric acid ,Phosphoric acid can be produced by the digestion of phosphate rock (calcium phosphate and fluoride among others) in sulfuric acid, better known as the “wet process” acid. Since calcium sulfate normally is a constituent, scaling must be considered. Phosphate rock varies in composition and in general, periodic cleaning is required even in forced circulation evaporators.

Sulfuric acid plants often are located along coastal areas and a further problem in concentration stems from the use of sea water in the direct contact condensers. With silica present in the phosphate rock, fluorine reacts to form hydrofluorosilicic acid (HzSiFs) which in turn, forms a sodium salt from the NaC1. Sodium fluorosilicic can block the condensers.

ammonium nitrates This material has several significant properties:

a) low viscosity which allows it to be concentrated to 99+ percent w/w when it is prilled.

b) above 95 percent, ammonium nitrate has an enormous boiling point elevation which requires exceedingly high steam pressures for heating. This presents considerable mechanical problems.

c) any organic impurity has the potential for explosion-such that extra low carbon stainless steels must be used for heat transfer surfaces and the use of mineral oils for heating is excluded.

The type of evaporator best suited for ammonium nitrate depends upon the initial and final concentrations. For the range below 70 percent and up to 80-85 percent, rising film multi-effect evaporator units have been used successfully. For 80-96 percent concentrations, conventional falling film systems have been employed. Above 96 percent, however, falling film with a heated air sweep would be used due to partial pressure conditions. In areas of relatively low humidity, 99+ percent water to water can be achieved.

ammonium sulfate Ammonium sulfate is used in battery spacer plate production and also has been crystallized. In this process, small but regular sized crystals are mixed with a PVC type plastic and dissolved out of the final sheet which then is used as spacer plate. Stainless steel has been successfully employed as the material of construction.

barium salts The production of barium salt involves the use of sodium sulfide, a material which closely resembles caustic soda in both physical and corrosive properties. It generally is concentrated in a high vacuum crystallizer for the production of barium hydroxide with rubber lined mild steel being used as the material of construction due to corrosion considerations. With liquid temperatures below 72”F, two hydrates- mono and penta-can be produced on separate flakers.

38

a

It

Ready for dissembly and shipping, this APV Paraflash

evaporator will concentrate potassium hydroxide solution

from 15-40'X total solids a t an evaporation rate of 3200

d h r . The system incorporates an R405 Paraflow equipped

with Incoloy plates and is expandable to double its

original capacity.

hydrochloric acid/chloride salts APV evaporators have been applied to steel pickling liquors. In the past, sulfuric acid was used incorporating crude ferrous sulphate cooler crystallizers and neutralizers. Now, hydrochloric acid is used, giving faster pickling times and a better steel finish.

glycerine Sweet water glycerine containing no NaCl has been handled in simple stainless steel film evaporators by salt and oleo chemical producers. For sodium chloride bearing liquors as in spent lye for industrial detergent and soap manufacture, cupronickel alloys must be used.

When the glycerine is contaminated with salt, the special application of forced circulation crystallizers has been employed for the recovery of the glycerine liquor and separation of the NaCl salts.

methylene chloride Methylene chloride is used as a cleaner during the manufacture of printed circuit boards. Since any residual moisture or other contaminants can have an adverse effect on the life of the circuit boards, the APV Paraflash evaporator has been used to concentrate the methylene chloride for return to the wash process.

39

economies of evaporation

Although concentration of liquids by evaporation is an energy intensive process, operating costs often are reduced by using a multiple effect evaporator. Total energy savings, however, must be weighed against the increased capital cost for each evaporator effect that is added.

multiple effect evaporation When evaporating water, the general rule of thumb is to use 1000 Btu/hr per pound of water removed. In a multiple effect system, however, water vapor from the first effect becomes the heating medium for evaporation at reduced pressure in a subsequent effect. Since one pound of steam generally will evaporate one pound of water vapor for every effect installed, approximately four pounds of water will be boiled off for each pound of steam used in a typical four effect system as shown in Fig. 19 on page 14. Such an evaporator thus requires only 250 Btu/hr for each pound of water evaporated. The number of effects used depends upon the available overall temperature difference within the system. Increasing the effects from four to eight would further reduce energy use by half. For multiple effect evaporators, therefore, steam usage in Btu/hr can be approximated by multiplying by 1000 the amount of water removed in lbs/hr and dividing by the number of effects in use.

Other economic factors involve cooling water and electricity. Since three to six gallons of condenser cooling water are needed for every pound of steam applied to the first effect, the cost of the cooling water used and of treated make-up water must be considered. Added energy also is required for pumping, particularly when water is supplied from a cooling tower. The remaining factor, energy for circulating and transfer pumps, is fairly constant regardless of the type of evaporator used.

multiple effect evaporation with TVR Thermo vapor recompression (TVR) generally is used to increase steam efficiency in a multi-effect evaporator. As shown in Fig. 1, 3rd effect vapor is split with one stream being recompressed to the steam side pressure with high pressure steam as the motivating force. This compressed steam combines with vapor from the boiling side and mixes in the venturi to form a medium pressure steam. Basically, one half of the 3rd effect vapor is reused to raise six effect steam efficiency to that of a nine effect system. While this requires added surface in the first three effects, the ther-

I OVER FLOW STEAM

FIG. 1 MULTIPLE EFFECT TVR EVAPORATOR WITH THERMAL COMPRESSION ACROSS THREE EFFECTS FEED t

40

mocompressor and ducting modifications, these added costs normally are much less than that of an additional three effects.

evaporation by mechanical vapor recompression Mechanical vapor recompression (MVR) is used for medium and large duties where maximum energy efficiency is required. As previously mentioned, this form of evaporation uses as the heating medium water vapor compressed to a higher pressure and temperature. This pre- cludes the need for most external sources of energy. Depending upon the temperature difference required across the evaporator, a typical system (Fig. 2) consumes as little as 10 to 30 Btu of energy per pound of water evaporated and is far more cost efficient than multiple effect evaporators even when factoring electrical energy to power the compressor. Cooling water needs are insignificant and electrical power for pumps sel- dom exceeds normal standards.

On the other hand, MVR evaporators require low temperature differences and, therefore, large heat transfer surface areas. This, combined with compressor costs, results in a high capital investment. Even so, recent cost reductions for compressors and heat transfer surface now make MVR systems very cost competitive.

cost comparison Table A presents a comparison of energy and capital equipment costs for multi- effect evaporators, those with TVR units, and MVR systems. Note that cooling water has been excluded as too small a cost in the overall project while steam consumption includes preheating feed from ambient to boiling temperature based on 75% water removal.

FIG. 2 Tubular MVR stillage evaporator

Electric

Energy cost per hour

Energy cost per year

Cost per hour

I 12,200 Ibs/hr I 5,800 Ibs/hr I 1,50OIbs/hr I I st?2t per hour $91 5 0 $43.50 $11.25

70 KW 70 KW 250 KW $ 4.20 $ 4.20 $15.00

$95.70 $47.70 $26.25

$574,200 $286,200 $157.500

Capital equipment cost

Annualized cost of capital employed

Total annual cost

$500,000 $750,000 $775,000

$125,940 $188,910 $195,207

$700,140 $475,110 $352.707

41

I I

paekaged evaporators

For evaporation systems of small to moderate size, it often can be economical to fabricate and supply separators, heat exchangers, tanks, pumps and other components as fully preassembled packages or as major modules which are quickly reas- sembled at the job site.

Figure 1 pictures two single effect Paraflash systems for the recovery of 1, 1, 1 trichloroethylene. These are fully preassembled on a carbon steel skid and include all piping and controls. All that is required for operation is hook up to utilities, Le., steam, cooling water, instrument air, and electricity. The system dimensions are 10'9" by 11'10" by 14'3" high.

The Figure 2 photo illustrates a typical rising/falling film plate evaporator designed for the concentration of a heat sensitive food product. This prepackaged evaporator is arranged as a single effect with thermal vapor recompression and has a vacuum system tha t enables the feed liquor to boil at 75°F. Capacity is 1500 Ibs/hr of water removal and system dimensions are 6 '6 by 17'6" by 15'9" high. Again, all necessary pumps, piping, wiring and controls were provided.

A slightly different concept was used in fab- ricating a two stage Paravap system for the stripping of isopropyl alcohol and water from a fabric softener. While this system was preassembled at the factory as is shown by Figure 3, dimensions of 12'0" by 22'6" by 14'6" high pre- cluded shipment as a single unit. Rather, the evaporator was broken down into major components to facilitate transport and match- marked to simplify installation.

Both of these approaches to packaged evaporation systems have proved to be beneficial in a number of ways. Factory fabrication and pre-installation of wiring and piping tends to be more efficient and economical than field work while erection time is reduced considerably. This results in significant savings in local labor costs.

42

properties of saturaked &eam

temperature tables

Absolute Specific Latent Temp. Pressure Vacuum Volumes Heat “ F PSlA In Ha FVIlb Btullb

32 0.08859 29.741 3304.7 1075.5 32.018 0.08865 29.741 3302.4 1075.5 33 0.09223 29.734 3180.7 1074.9 34 0.09600 29.726 3061.9 1074.4

35 36 37

39 38

0,09991 29.718 2948.1 1073.8 0.1 0395 29.71 0 2839.0 1073.2 0.10815 29.701 2734.4 1072.7 0.1 1249 29.692 2634.2 1072.1 0.11698 29.683 2538.0 1071.5

45 46 47

49 48

0.14744 29.621 2037.8 1068.1 0.15314 29.61 0 1965.7 1067.6 0.15904 29.597 1896.5 1067.0 0.16514 29.585 1830.0 1066.4 0.1 7144 29.572 1766.2 1065.9

50 0.17796 29.559. 1704.8 1065.3 51 0. i 8469 29.545 1645.9 1064.7 52 0.1 91 65 29.531 1589.2 1064.2 53 0.19883 29.516 1534.8 1063.6 54 0.20625 29.501 1482.4 1063.1

55 56 57

59 58

0.21392 29.486 1432.0 1062.5 0.22183 29.470 1383.6 1061.9 0.23000 29.453 1337.0 1061.4 0.23843 29.436 1292.2 1060.8 0.24713 29.418 1249.1 1060.2

60 0.2561 1 29.400 1207.6 1059.7 61 0.26538 29.381 1167.6 1059.1

63 0.28480 29.341 1092.1 1058.0 64 0.29497 29.321 1056.5 1057.4

62 0.27494 29.362 1 129.2 1058.5

43

Temp. “ F

65 66 67 68 69

Absolute Pressure PSlA

0.30545 0.31626 0.32740

0.35073 0.33889

Specific Vacuum Volumes In Hg Ft3Ilb

29.299 1022.1

29.255 957.2 29.231 926.5

29.277 989.0

29.207 896.9

I Latent Heat Btullb

1056.9 1056.3 1055.7 1055.2 1054.6

70 0.36292 29.182 868.4 1054.0 71 0.37549 29.157 840.9 1053.5 72 0.38844 29.130 814.3 1052.9 73 0.401 77 29.103 788.8 1052.4 74 0.41550 29.075 764.1 1051.8

75 76 77

79 78

0.42964 29.047 740.3 1051.2 0.44420 29.01 7 717.4 1050.7 0.4591 9 28.986 695.2 1050.1 0.47461 28.955 673.9 1049.5 0.49049 28.923 653.2 1049.0

80 0.50683 28.889 633.3 1048.4 81 0.52364 28.855 614.1 1047.8 82 0.54093 28.820 595.6 1047.3 83 0.55872 28.784 577.6 1046.7 84 0.57702 28.746 560.3 1046.1

0.59583 28.708 543.6 1045.6 0.61 51 a 28.669 527.5 1045.0 0.63507 28.628 51 1.9 1044.4 0.65551 28.587 496.8 1043.9 0.67653 28.544 432.2 1043.3

90 0.69813 28.500 468.1 1042.7 91 0.72032 28.455 454.5 1042.2 92 0.74313 28.408 441.3 1041.6 93 0.76655 28.361 428.6 1041.0 94 0.79062 28.312 416.3 1040.5

95 96 97

99 98

0.81534 28.261 404.4 1039.9 0.84072 28.210 392.9 1039.3 0.86679 28.1 57 381.7 1038.8 0.89356 28.1 02 370.9 1038.2 0.92103 28.046 360.5 1037.6

100 0.94924 27.989 350.4 1037.1 101 . 0.97818 27.930 . 340.6 1036.5 102 1.00789 27.869 331.1 1035.9 103 1.03838 27.807 322.0 1035.4 104 1.06965 27.743 313.1 1034.8

105 106 107

109 i oa

1.10174 27.678 304.5 1034.2 1.1347 27.61 1 296.1 a 1033.6 1.1684 27.542 288.1 1 1033.1 1.2030 27.417 280.30 1032.5 1 .ma5 27.400 272.72 1031.9

110 1.2750 27.325 265.39 1031.4 11 1 1.3123 27.249 258.28 1030.8 112 1.3505 27.172 251.38 1030.2 113 1.3898 27.092 244.70 1029.6 114 1.4299 27.001 238.22 1029.1

Absolute Specific Latent Temp. Pressure Vacuum Volumes Heat "F PSlA In Ha Ft3Ilb Btullb

115 116 117 118 119

1.471 1 26.926 231.94 1028.5 1.51 33 26.840 225.85 1027.9 1.5566 26.752 219.94 1027.3 1.6009 26.662 214.21 1026.8 1.6463 26.569 208.66 1026.2

120 1.6927 26.475 203.26 1025.6 121 1.7403 26.378 198.03 1025.0 122 1.7891 26.279 192.95 1024.5 123 1.8390 26.177 188.03 1023.9 124 1.8901 26.073 183.24 1023.3

125 126 127 128 129

1.9428 25.966 178.60 1022.7 1.9959 25.858 174.09 1022.2 2.0507 25.746 169.72 1021.6 2.1068 25.632 165.47 1021.0 2.1 642 25.515 161.34 1020.4

130 2.2230 25.395 157.33 1019.8 131 2.2830 25.273 153.44 1019.3 132 2.3445 25.148 149.66 101 8.7 133 2.4074 25.020 145.98 1018.1 134 2.4717 24.889 142.41 1017.5

135 136 137 138 139

2.5375 24.755 138.94 101 6.9 2.6047 24.618 135.57 1016.4 2.6735 24.478 132.29 1015.8 2.7438 24.335 129.11 101 5.2 2.8157 24.188 126.01 1014.6

140 2.8892 24.039 123.00 101 4.0 141 2.9643 23.886 120.07 1013.4 142 3.041 1 23.730 117.22 1012.9 143 3.1195 23.570 1 14.45 1012.3 144 3.1997 23.407 111.76 1011.7

145 146 147 148 149

3.2816 23.240 109.14 1011.1 3.3653 23.069 106.59 1010.5 3.4508 22.895 104.11 1009.9 3.5381 22.71 8 101.70 1009.3 3.6273 22.536 99.35 1008.7

150 . 3.7184 22.351 . 97.07 1008.2 151 3.81 14 22.161 94.84 1007.6 152 3.9065 21.968 92.68 1007.0 153 4.0035 21.770 90.57 1006.4 154 4.1025 21.569 . 88.52 1005.8

155 156 157 158 159

4.2036 4.3068 4.4122 4.5197 4.6294

21.363 86.52 1005.2 21.153 84.57 1004.6 20.938 82.68 1004.0 20.719 80.83 1003.4 20.496 79.04 1002.8

160 4.7414 20.678 77.29 1002.2 161 4.8556 20.035 75.58 1001.6 162 4.9722 19.798 73.92 1001.0 163 5.091 1 19.556 72.30 1000.4 164 5.2124 19.309 70.72 999.8

45

Temp. " F

165 166 167 168 169

Absolute Pressure PSlA

5.3361 5.4623 5.591 1 5.7223 5.8562

Vacuum In Hg

19.057 18.800 18.538 18.271 17.998

Specific Volumes Ft31lb

69.18 67.68 66.22 64.80 63.41

Latent I Heat Btullb

999.2 998.6 998.0 997.4 996.8

170 5.9926 17.720 62.06 996.2 171 6 1318 17.437 60.74 995.6 172 6.2736 17.148 59.45 995.0 173 6.4182 16.854 58.19 994.4 174 6.5656 16.554 56.97 993.8

175 176 177 178 179

6.7159 16.248 55.77 993.2 6.8690 15.936 54.61 992.6 7.0250 15.61 8 53.47 992.0 7.1840 15.295 52.36 991.4 7.3460 14.965 51.28 990.8

185 186 187 188 189

8.384 12.851 45.313 987.1 8.568 12.477 44.400 986.5 8.756 12.094 43.508 985.9 8.947 11.705 42.638 985.3 9.141 11.310 41.787 984.7

190 9.340 10.905 40.957 984.1 191 9.541 10.496 40.146 983.5 192 9.747 10.076 39.354 982.8 193 9.956 9.651 38.580 982.2 194 10.168 9.219 37.824 981.6

195 196 197 198 199

10.385 10.605 10.830 11.058 11.290

8.777 37.086 981 .O 8.329 36.364 980.4 7.871 35.659 979.7 7.407 34.970 979.1 6.935 34.297 978.5

200 11.526 6.454 33.639 977.9 201 11.766 5.966 32.996 977.2 202 12.01 1 5.467 32.367 976.6 203 12.259 4.962 31.752 976.0 204 12.512 4.447 31.151 975.4

205 206 207 208 209

12.770 13.031 13.297 13.568 13.843

3.921 30.564 974.7 3.390 29.989 974.1 2.848 29.428 973.5 2.297 28.878 972.8 1.737 28.341 972.2

210 14.123 1.167 27.816 971.6 21 1 14.407 0.588 27.302 970.9 21 2 14.696 0.000 26.799 970.3

46

Absolute Specific Latent Temp. Pressure Volume Heat " F PSlA Ft31lb Btullb

212 21 3 21 4 21 5 21 6

228 232 236

240 244 248 252 256

260 264 268 272 276

280 284 288 292 296

308 312 31 6

320 324 328 332 336

360 364 368 372 376

14.696 14.990 15.289 15.592 15.901

26.799 26.307 25.826 25.355 24.894

970.3 969.7 969.0 968.4 967.8

954.8

24.968 26.826 28.796 30.883 33.091

35.427 37.894 40.500 43.249 46.147

49.200 52.414 55.795 59.350 63.084

16.321 15.260 14.281 13.375 12.538

11.762 1 1.042 10.375 9.755 9.180

8.6439 8.1 453 7 6807 7.2475 6 8433

952.1 949.5 946.8 944.1 941.4

938.6 935.9 933.1 930.3 927.5

924.6 921.7 91 8.8 91 5.9 91 3.0

910.0 907.0 904.0

0 9

89.643 94.826

100.245 105.907 11 1.820

4.9138 4.6595 4.4208 4.1966 3.9859

894.8 891.6 888.5 885.3 882.1

1 17.992 3.7878 878.8 124.430 3.6013 875.5 131.142 3.4258 872.2 138.138 3.2603 868.9 145.424 3.1044 865.5

153.010 160.903 169.113 177.648 186.517

2.9573 2.8184 2.6873 2.5633 2.4462

862.1 858.6 855.1 851.6 848.1

195.729 2.3353 844.5 205.294 2.2304 840.8 215.220 2.1311 837.2 225.516 2.0369 833.4 236.193 1.9477 829.7

4 /

APV Crepaco Inc. Executive and International Headquarters 9525 West Bryn Mawr Ave., Rosemont (Chicago), IL 60018 (708) 678-4300 Fax: (708) 678-4407

Engineering and Manufacturing 395 Fillmore Ave., Tonawanda, NY 14150/(716) 692-3000 100 South CP Ave., Lake Mills, WI 53551 /(414) 648-8311 1303 Samuelson Rd., Rockford, IL 61109/(815) 397-5000 165 John L. Dietsch Sq., Attleboro Falls, MA 02763/(508) 695-7014

Regional Sales Offices: Los Angeles (Cerritos), CA/(213) 926-9700 Rosemont (Chicago), IL/(708) 678-4300 Montvale, NJ/(201) 930-0001 Nashville, TN/(615) 255-0342 Dallas (Irving), TX/(214) 257-3455

Sales Offices: Minneapolis, MN Charlotte, NC Mt. Laurel, NJ Columbus OH Salt Lake City, UT Seattle, WA

In Canada: APV Canada, Inc. - Toronto (416) 850-1852 Montreal (514) 737-0006 Vancouver (604) 420-4344

International Offices: Tokyo, Japan Torreon, Mexico Taipei, Taiwan

1190

Documents

APV Evaporator Handbook