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Vol. 21, No. 5
Present Trends in Dust Recovery Everett P. Partridge1 1440 EASTPARKPLACE,ANN ARBOR,MICH.
UST resulting from industrial operations has been regarded from three successive viewpoints. It was first
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dried milk and fruit juices, gas black and bone black, pulverized coal, and dyes. As a result of this development new stimulus has been given to the design and application of ingenious systems to still other fields,
considered somewhat in the light of an unavoidable nuisance. Dust-producing plants, such as cement mills, 10cated themselves as far as possible where there were no neighTypes of Equipment for Dust Collection bors to complain of the object,ionable conditions which they produced. They then went into operation with calm resignaThe various types of apparatus for the removal of dust from tion to the inevitable high rate of labor turnover, the gradual gas streams may be conveniently classified for discussion on destruction of equipment, and the loss of mRterial resulting the basis of what can be done with the dust after it is collected. from this policy. When the plant happened to be a flour Certain systems, intended chiefly for the removal of ordinary mill and a stray spark started things going, the company incidental dust from the atmosphere, do not allow of ready either went out of business or built a second plant as dusty recovery of the separated material. It is obvious that these as the first. systems might be applicable to some cases where a dust reThis attitude, reminiscent of the way our ancestors of the sulting from a manufacturing process had negligible value Middle Sges regarded disease, gave way gradually as it came but must be removed in order to prevent a nuisance. Some to be realized that it represented neither good engineering of them are also used for the recovery of precious metal dust, nor good bminess. It was natural that the viewpoint toward but for general use economic considerations necessitate the industrial dust should then grow to be that of prevention types of apparatus allowing simple recovery. Care must be exercised in analyzing any particular probonly. Equipment was developed t o reduce or t o eliminate lem of dust the produccollection tion of free from the dust, and to viewpoint of c o l l e c t the the value of dust from operations the material in which its collected, production since it is enseemed inevtirdy possiitable. This ble that an apparently attitude rew o r t h 1e s s garded dust dust may a s a nuih a v e some s a n c e , in profitable some c a s e s m e a n s of as a positive u tilization. danger , but as essentialOne firm en. gaged i n ly n o t h i n g producmore than a ing crushed waste material. l i m e s tone f o r road Recently, gravel inhowever, engineers with oz&yM ds tua sl lte dr e ainvestiga i m o v a l and * * tive m i n d s collection and i m a g i . - _ - -~ apparatus in nation have Courlesy oj ine UUSIKero%rrrng and Conweyrng Company order to obbeen discovFigure 1-Elevation of Crusher Plant Making Road Gravel tain a bonus ering t h a t Air filters recover dust from gyratory crushers scalping screens and chutes to storage bins. This dust is sold as agricultural limestone. Enough W A S recovered during the first &ar of operation to pay for the filter installation, for dust-free there is no while the dust-free gravel produced commanded a special bonus. g r a v e l . It such t h i n g as a waste material. I n the field of dust elimination subsequently developed that the fine dust collected had SUEthey have found frequently that the finely divided material cient value as agricultural limestone to pay for the equiptaken out of circulation was either a valuable fraction of the ment within a year. SysTsllrs FOR DUSTCOLLECTION WITHOUT RECOVERYmain plant output or a by-product worth more per unit of weight than the main product. They have also been dis- Only brief mention will be made of those types of equipment covering that dust-collecting apparatus may form a very effi- which are intended chiefly for the removal of incidental dust cient unit process in the preparation of such materials as from air, and which leave the separated material in a condition from which it cannot readily be recovered. Two general 1 Assoaate editor, INDUSTRIAL A N D ENGINEERING CHEMISTRY. '
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Electrical precipitation describes the principle upon which types exist. The first type depends upon a water spray, arranged in any one of a number of ingenious ways, through the Cottrell system operates. It removcs suspended particles, which dust-laden air is passed, with removal of those particles either solid or liquid, from a gas stream by producing an electhat are wetted by the spray. The second type, loosely styled trical charge upon the particles and then utilizing the pull of a “filter,” depends upon passing the air to be cleaned through a powerful electrical field to cause them to travel to an o p small, tortuous channels, the surfaces of which are covered positely charged surface to which they adhere. By the use with some sticky medium which holds all particles impinging of a special transformer and mechanical rectifier, a unidirecupon it. Use is found for equipment of these two types tional corona discharge is obtained a t a potential of from chiefly in cleaning the cooling air supplied to motors and 50,000 to 75,000 volts. This discharge takes place from wire generators, and in purifying the air circulated in public electrodes placed in the gas stream. These electrodes are buildings or used in such special processes as the drying of placed axially in a pipe or are suspended between plate surgelatin, in which contamination by atmospheric dust and airborne bacteria must be minimized. SYSTEMSFOR DIJST COLLECTION WITH RECOVERY-A~~ types of equipment for dust collection other than the two mentioned above allow the ready recovery of the fine material separated out. Such recovery is, of course, not always practiced, not even when it might be profitable. I t is possible, however, and where recovery becomes an important factor in the choice of equipment the following types find application. Equipment for the recovery of dust from gas streams may be classified on the basis of the principle utilized. The four following types result: (1) sedimentation by gravity; (2) separation by centrifugal force; (3) electrical precipitation: (4) filtration. Sedimentation by gravity is the oldest and simplest principle used for the removal of dust from gas streams. The settling chamber has been a familiar nuisance in the smelting industry for years. It is now practically obsolete as an agency for dust removal, though it still serves as a cooling flue for hot gases. Fair separation of large particles can be obtained in the settling chamber under carefully controlled conditions of rate of flow, turbulence, and temperature of the gas stream. The inadequacy of the method is evident, however, when it is realized that a spherical particle of unit density and a diameter of 1 X lo-* cm. settles a t a rate of only 30 cm. per second in absolutely still air. Such a particle represents merely the ELEVATION - D 0’ largest range of industrial dusts. Although a settling chamber Courtesy of the Dusl Recovering and Conveying Company will serve for the practical removal of such particles, the Figure 2-Elevation of S m a l l Dried-Milk P l a n t space requirement for the sedimentation of fine dusts is proAir filters recover comp‘etely the valuable materidl carried out of the spray drier by the effluent air stream. hibitive and the separation is unsatisfactory. Centrifugalforce is utilized for dust collection in the cyclone separator, which exists in many varieties, all of which have faces, the pipe or plates being connected t o the opposite side the common characteristic of passing a dust-laden stream of of the high-potential line. The suspended particles in the gas in a spiral path a t a velocity sufficient to cause the sus- gas stream passing through the corona discharge are charged pended particles to be thrown out against the containing by adsorption of ions from the ionized gas and then move wall, down which they drop by gravity into a container at the toward the oppositely charged surfaces upon which they debottom. Cyclones are generally const,ructed as a cylindrical posit, being removed either by gravity or by mechanical housing ending in a conical bottom, with a tangential inlet to cleaners. The efficiency of removal of suspended particles is a functhe upper part of the cylindrical section and an outlet for cleaned gas through an internal axial duct leading out through tion of the length of exposure of the gas stream to the electhe top. The various dimensions of cyclones are adapted to trical field within the precipitator, but is practically indegive gas velocities suitable for the separation of various pendent, within ordinary liniits, of the concentrvtion of the materials, or of various sizes of these materials. Velocities suspended material. The efficiency guaranteed for ordinary as high as 1500 feet per second are claimed for some special installations is 90 per cent, although units may be built to cyclones of small diameter. give practically complete recovery if it is desired. The power Although cyclone separators operate most efficiently upon consumption varies from 5 to 10 kilowatt-hours per million gases containing particles of uniform large size, it is possible cubic feet of gas treated. The Cottrell apparatus has two fields of operation in to use two of them in series for the simultaneous removal and partial sizing of dust having a considerable range of particle which it is unrivaled. The process of electrical precipitadiameter. As in the case of the settling chamber, however, fine tion is not affected by temperature; hence it may be designed dusts cannot be efficiently recovered in a cyclone separator. for operations up to 650’ C. or 1200’ F., and its construction One advantage of the cyclone is its simple and rugged con- is so simple that it may be readily made from corrosionstruction without moving parts. It can be fabricated from resistant materials and employed for the treatment of acid special alloys to handle streams of corrosive gases, and it can gases, particularly acid mists Electrical precipitation is handle hot gases. It is, in fact, frequently found good prac- therefore the general solution for the removal of suspended tice to use a cyclone for cooling a hot gas stream and simul- particles from a gas stream which is corrosive or must be taneously removing the coarser particles from it, as a pre- treated while hot. Since cyclone separators also can operate liminary to complete dust removal in a filter, which can only under these conditions, they are sometimes used as prelimibe used a t low temperatures. nary separators in series with Cottrell units.
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INDUSTRIAL A N D ENGINEERING CHEiMISTRY
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Of the processes gas stream. The in which electrical W0D maximum allowBEL1 r-ONVEI. R able value for precipitation finds a p p l i c a t i o n , the c o t t o n filters i s recovery of oxides 95" C. or 200" F. and of acid mists This limit can be from smelting raised slightly if o p e r a t i o n s , of wool cloth is subpotash dust from stituted for cotton, cement kiln gases, INDIChTE FL< W but even then the B,h temperature must and the removal of WORYERS not exceed 115' C. tar from manufactured gas may be or 240' F. Ancited as typical. other factor that A recent adaptamust be carefully tion of the Cottrell controlled is hu5-1" R f C 5 R O l N G THERMOMETER midity, since conprocess has been for the removal of densation of water fly ash from the AP'?Or-i C ? l l l E I D R LTER SUPPORTS. from the gas Courtesy of the Dust Recoeering and Conveying Company s t a c k gases of stream upon the Figure 3-Elevation of Grinding U n i t w i t h D u s t Recovery S y s t e m plants fired may 'OmCyclone separator and air filter in series eliminate dust and provide 99.5 per cent recovery of fines w i t h p o w d e r e d from ball mill. Cyclone separator handles larger particles and partially cools gas stream. Air filter pletely upset their removes fine dust not trapped by cyclone separator. Thermostatic control of emergency atmospheric coal. air inlet prevents overheating of cloth filters. operation by clogFiltration of gas ging. The linear streams for the removal of dust was first practiced on a air velocity across the filter cloth area is variable, depending large scale in the smelting industry, which developed the upon the characteristics and amount of material to berebaghouse, the now obsolete progenitor of the modern air moved, but generally varies between 2.5 and 10 feet per second. filter. Some modern filters still use the baghouse system I t is obvious that none of the air filters described can be of positive pressure-that is, the forcing of dust-carrying operated continuously. The optimum cycle of operation degas through a filter medium against the pressure of the pends largely upon the concentration of suspended material atmosphere. The air filter on the housewife's vacuum in the gas stream, upon the particle size, and upon the tendcleaner is a homely example of this type of filter. Industrial ency of the particles to cohere and thus build up a resistance filters of this type, however, are open to the serious objection to gas flow. A filter might, for instance, operate satisfacthat the fan pushing the gas stream through the filter must torily for eight hours upon fine silica dust in the effluent air handle dusty air. Where the dust is abrasive, the life of the from a cyclone separator, but develop high resistance in thirty fan is liable to be uneconomically brief. I n other cases, minutes upon gas black. I n order to obtain the equivalent where dust of a combustible nature is to be handled, the use of continuous operation, i t is necessary to use two or more of a fan on the dust-carrying air stream introduces a serious filter units in parallel, so that while one unit of a group is cut out for cleaning filtration may still be carried on. Since, explosion hazard. The objections to the pressure type of air filter have been for any given set of conditions, efficient filtration depends met by placing the fan on the clean-air side of the filter and largely upon the velocity a t which the gas stream passes using it as an exhauster rather than as a pusher. Practically through the filter, it is important that this velocity be held as all industrial air filters are of this vacuum type. They nearly constant as possible. This result can be approximated are built in two chief styles. The first is adapted from the with increasing accuracy as the number of filter units in paralplate-and-frame filter press used for the filtration of liquids, lel is increased. One very excellent installation handling the and uses a Iarge number of cloth-covered wooden frames set dust from tumbling barrels in a large foundry uses groups of UD within a metal shell and dividing this shell into two ten filter units each. * tiahtlv " compartmentfl, one for the admission of &sty air and the Utilization of Dust Recovery Equipment as a Unit Process periodic removal of the dust collected by the filter frames, the The possibilities latent in the field of dust collection are other for the removal of filtered air. The frame style of vacuum air filter is not used so exten- only beginning to be realized. Industry in general still holds sively as is the stocking type, in which the filter medium con- the second attitude mentioned a t the beginning of this article, sists of a number of cylinders of filter cloth mounted vertically that of controlling dust because it is a nuisance or a hazard or within a cylindrical metal shell ending in a cone bottom. an economic loss. Thus we have equipment applied to the These filter cloth cylinders are open only a t the bottoms, coIIection of dust from the operations of mixing, crushing, which are attached to holes in the lower sheet of the cylindri- grinding, drying, and packing, generally only with the thought cal shell. Dusty air is introduced within the cone bottom of preventing the waste or contamination of material. In below this lower sheet, passes up within the cylindrical filter certain cases, however, imaginative engineers have expanded stockings, which retain the dust and allow clean air t o pass the function of apparatus for dust collection until it takes new into the body of the shell, from which it is exhausted by a rank as a unit process. One of the first developments of dust collection as a necesfan. The dust collected within the filter stockings is removed periodically by automatic shaking, accompanied by sary integral part of a manufacturing process was in the procut-off of the incoming dusty air, and in many cases by the duction of gas black. The old, cumbersome, inefficient blowing of air through the filter stockings in a direction re- method of obtaining this material by deposition on metal versed from that of filtration. The dust shaken from the plates hung over open gas burners, with subsequent scraping filters settles into the cone bottom, from which it may be to remove the product, could be replaced by a compact, conremoved as desired through discharge gates or by a continu- tinuous burner of high efficiency only if some way could be devised for separating the elusive product from the stream of ous conveyor. The use of cloth filters imposes a temperature limit on the burned gas. Owing to the extreme fineness of the particles, 1
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filtration seemed the only possible solution. The first in- of the air filter. The first of these is concerned with the restallation in this country was built to filter the gas while duction of the explosion hazard in connection with the grinding hot, and consisted of an ordinary unit of the vacuum type of combustible materials. It is proposed that the stack gases of in which the cloth filter stockings were replaced by cylinders the plant in question should be cooled by the use of economizers of monel-metal filter screen. This filter screen was not in- or air preheaters t o a temperature sufficiently low for filtration tended as the actual filtering medium, however, but merely in cloth filters. After cleaning in the filters, this gas would as the foundation for it. Owing to the coherence of the then be circulated a t a slow rate through the grinding rtp particles, the gas black itself built up an efficient filter layer paratus to maintain an inert atmosphere in contact with the on the screens. Cleaning was accomplished by pistons, which material being ground. The effluent gas from the grinders moved vertically within the cylinders a t intervals and scraped would then be passed through another set. of filters to prevent off all of the deposited material in excess of a certain thick- loss of product and then exhausted clean to the atmosphere. A second ingenious application of the air filter is suggested ness which was left permanently on the filter. This installation has been in operation six years. Since it was designed it has for the use of central-station power plants. One of the obbeen found practicable to cool the gases leaving the burner to a jections to the use of powdered coal a t present is the difficulty point a t which cloth filters may be used, and a gas black plant of reducing the ash nuisance in the stack gases to a point that has recently been put in operation with this type of equipment. is satisfactory for modern urban standards. Another one, Another field in which dust collection has become a stand- more serious from the standpoint of operation, is the difficulty ard unit process is the manufacture of dried milk. Here the encountered in pulverizing coal that is wet, owing to its tendfunction of the air filter is to remove all of the powdered ency to ball up in the grinders. It is proposed to overcome product from the air stream leaving the drier. Since this air both of these objectionable features by the use of air filters. stream contains a considerable amount of moisture, it cannot Stack gases, carrying a large percentage of the total ash probe returned through the system, and a relatively large amount duced in the combustion of the powdered fuel, must first be of air must be filtered. The dried milk removed by the filter is cooled by the use of economizers and air preheaters to a temreturned to the shell of the drier on a continuous conveyor, the perature that will allow the use of cloth filters. The ash final product being removed from the bottom of the drier. would then be completely removed in these filters, and the In grinding operations giving a very fine product, the air cleaned stack gas would be passed through the coal pulverizfilter again serves as a valuable unit, since it retains all of ers, where it would serve the double purpose of preventing exthe fines, while preliminary removal of coarser particles . -._ , *, may be effected by a cyclone separator operated in closed F U R W E BUILDING , circuit with the grinding or pulverizing equipment. By tapping off a portion of the effluent air from a cyclone separator to an air filter in this may, it has been possible to produce bone black consistently finer than 350 mesh without loss of material. The air filter again serves as an indispensable adjunct in cases where pneumatic 'U-NE COOLER \ conveying is applied to materials that dust readily. In some installations-for instance, in handling grain-it is desirable to separate the dust developed during handling, while in others-for e x a m p l e , t h e t r a n s f e r of h i s h e d cement-it is imperative that all the fines be DAMPER retained in the product. The first situation may be met by using a cyclone and an air filter in series with separate .END ELtVATION-.A-A* SIDE ELEVATION discharge, w h i l e f o r t h e Courtesy of the Dial Recovertng and Conveyrng Company second situation the same Figure &Layout of Metal Oxide Recovery S y s t e m equipment would be used Furnace gases carrying oxide fumes pass through coolers t o air filters where oxide is completely removed, elimi nating nuisance and recovering valuable material Thermostatic control oi emergency atmospheric air inlet pre with a common discharge. In vents overheating of cloth filters. Vertical U tube coolers require little space either case the cyclone is necessaryto handle the bulkof the load and separate the larger par- plosion and drying the coal during grinding. The gas from ticles, while the filter is necessary to capture the fines, whether the pulverizers would be filtered again to retain powdered nuisance or values, which are carried through coal. and would finallv be exhausted t o the atmosuhere in a - the cvclone. thoroughly clean coidition. One of the problems in the Proposed Applications of Air Filters develoDment of such a scheme would be the maintenance of Two new developments, not yet applied commercially but the ga$ stream above the condensation point, since all the deserving consideration, have been suggested in the application combined water of the coal, plus the water produced by oomI
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Coiirfcsy of The Research Corporalion Figure 5-Plan of Plate-Type Electrlcal Precipitation Unit Used for Removal of Ash Dust from Stack Gases Units of this type give 90 per cent recovery of the fly ash from the stack gases of P large centra Istation using boilers of 2000 to 3000 rated horsepower driven a t 200 to 300 per cent of rating and fired with powdered fuel.
bustion of its net hydrogen, plus the moisture removed in drying, must pass the second filter and must do so a t a temperature above the dew point to prevent clogging of the filter. The air filter in entering this field nil1 have to compete with the electrical precipitation process, which has already been adapted to the removal of fly ash from powdered-fuel boiler installations. Analysis of Problems in Dust Collection
The choice of equipment for dust recovery is a matter likely to be complicated by secondary considerations. The actual design of equipment is, of course, the job of the man who knows something about i t ; in the present state of the art it is largely a matter of experience and experiment. I n considering a dust problem the factor of completeness of recovery desired is the fundamental point of attack. This frequently is affected by other than strictly economic considerations; for example, lead oxide is a health hazard and cement dust is a nuisance, in addition to any loss of valuable material. Whatever the basic reason for recovery, the degree of efficiency required may determine the type of equipment without recourse to other considerations, since the cyclone separator, the electrical precipitator, and the air filter represent increasingly complete recovery, in the order in which they are named. I n cases on a strictly economic basis it may be necesssry to draw a close balance between the value of the recoverable material and the difference in cost between the inexpensive cyclone separator and the more costly electrical precipitator or air filter. Modern manufacturing methods, however, will increasingly tend to use the cyclone only as a preliminary ~eparator,with final recovery in one of the other two types of equipment, the choice depending upon the characteristics of the product and of the process by which it is made. Table I-Total
Annual Cost for Some Installations of Electrical Precipitation Units
RATEDCAPACITY
KINDOB
D U S T COLLECTED
ANNUALC O S T PER c u . FT./MIN.
Cu.f t . / m i n . 1,500 20,000
70,000 500,000
Non-corrosive dust Valuable dust trom polishing operations Precious-metal dust from refining operations Ash dust
60.33 0.20
0.076 0.06
Although it is impossible to lay down general cost figures for dust recovery equipment, owing to the wide diversity in the requirements of individual installations, some data of specific units of various capacities have been made available to the writer. Table I shows the data for four installations of Cottrell electrical precipitators. The figures for annual cost per
cubic foot per minute capacity include interest and depreciation on the installation cost, power for operation, repairs and renewals, and a small allowance for labor, which with the Cottrell precipitator has been found to be nominal. As has been stated before, the power requirement for electrical precipitators varies between 5 and 10 kilowatt-hours and the repair costs are low. Information concerning three filter installations is shown in Table 11. In this table, however, only the actual instnllation cost per cubic foot per minute capacity is given, instead of the annual cost as in Table I. Table 11-Initial
Equipment Cost for Some Filter Installatiom KINDOF DUST INITIAL COST RATEDCAPACITY COLLECTED PER c u . PT./MIN.
Cu.jl./min. 1?.000 15,000 400.000
Powdered milk Ash dust Zinc oxide
$0.80 0.50 0.50
Under proper operating conditions the annual replacement cost for air filters should not exceed $10 to 820 per 1000 cubic feet per minute capacity. The power cost is small, since properly designed filters cause a pressure drop of only 2 to 3 inches of water. I n connection with the economic aspect of the problem of choosing dust recovery equipment, the matter of local conditions may frequently play an important part. A plant located in a desert does not have to worry about, the pending lawsuits of a community outraged by its dust nuisance.. On the other hand, it may have to provide extraordinarily excellent working conditions in order to obtain labor. Similarly, it may be profitable for a public utilities corporation to install the most elaborate equipment for dust recovery on plants burning powdered coal, simply because of the intangible return in good will from such a public policy, even though the ash collected is a t present a waste material with no great promise of utilization. It should be emphasized, in conclusion, that the application of dust-collecting equipment to any specific process is more than a problem in sheet-metal construction and more than a problem that can be solved painlessly by the installation of two or ten or a hundred units of a perfectly standardized apparatus built to satisfactorily fit all conditions. In the present state of the art the engineer in the field of dust recovery is a specialist selling consulting service rather than selling cyclones, or air filters, or electrical precipitators. The firm which insists on buying equipment rather than such consulting service is liable to discover the old truth that the best apparatus in the world will not perform efficiently under conditions for which it was not intended.
May, 1929
IND UXTRIAL AND ENGINEERING CHEMIXTRY
Acknowledgment The miter wishes to indicate his indebtedness to F. L. Jorgensen, of the Dust Recovering and Conveying Company,
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Cleveland, Ohio, for information concerning air filters and their application,and to The Research Corporation,New York, N. y., for data on electrical Precipitation.
Evaporation’ Philip De Wolf JOUBBRI& GOSLIN MACHINE & FOUNDRY C O . , N E W YORK.N. Y
VAPORATIOX,” used in the sense that the chemical industry applies it, means the boiling off of water, and mater alone, from a solution containingwater. If m y thing but wvater. is boiled off, the operation is called “distillation”-the dividing line being so drawn for no better reason than that it has ah-ays been so drawn. This evaporation may be done by heating a liquid in a kettle over a fire, by passing hot gases over the liquid in a flat pan, by passing hot gases up a tower whi!e the liquid runs down, by spraying from the periphery of a rapidly revolving disk through hot gases, or by exposing to the sun. All these methods find legitimate application in tlie chemical industry. However, most of the evaporation in industry is done in closed vessels, which hold the liquid, the heat being applied through a steam coil or some modification of it, immersed in the liquid, and the vapors resulting from the evaporation being taken away t o some form of condenser. To such a machine the term “evapnrator” is applied. I n multiple effect the condenser is the heating coil of the next vessel, until the last one, which is an ractual condenser. Such a series takes advantage of the facts that the lower the pressure the lower is the boiling point and that heat flows from
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boils the liquor in the last effect. It is necessary, of course, to have the heating vapor enough hotter than the liquor to be boiled to do the job economically, and that is one of the most important features of design. Inasmuch as the limitation of space precludes doing justice to the subject of heat transfer in this connection, this paper will be confined to descriptions of operating conditions, and their effect upon de sign, for the local conditions do not in any way affect the fundamental conditions. Principle of Operation
Boiling points of solutions vary a t different concentrations. This and other factors must be worked out and, in addition to the heat necessary to take care of them, the heating vapors must be 15” F. higher than the liquor, to insure a good boil. So, assuming in the case under discussion that an average of 12’ F. is necessary to take care of the factors mentioned, the vapor coming to each steam chest (or callandria) must be a t least 27” F. higher than the vapor from the liquor it is to boil. If you have 10 pounds of steam a t 240” F., and your condenser runs a t 27 inches, for which the temperature is 116” F., you have an over-all heat drop of 124” F. Divide this by 27, and
Figure 1-Evaporator Flow Sheet Liquor is viscous at high concentration so i t is passed through Nos. 2. 3, 4, and finished in No. 1 a t higher temperature. removal not shown.
the warmer to the colder object. The condenser creates a high vacuum (or low pressure) in the last “effect,” as each vessel is called, and the liquor therein boils a t a correspondingly low temperature. Vapor a t a higher temperature and pressure comes into the steam chest qf the last effect from the boiling liquor in the next to the last effect; it is condensed and its latent heat passes through the steam-chest walls and 1
Received February 9, 1929.
Condensate
you get 416/2,.You would use the even number and install a four-effect machine-a quad. Figure 1 shows a typical layout, with the temperatures and pressures of the vapors and liquids. The whole point is that the heating steam is condensed on the wall of the callandria, which is kept cool enough to do this by the liquor to be evaporated, and in condensing gives up its latent heat. This latent heat and the sensible heat due to
