APV Dryer Handbook
APV Dryer Handbook 12/6/00 10:58 AM Page 81Improving Process Profitability.ContinuouslyA P VD RY E RsmH A N D B O O KsmProcess to Boardroom Automation
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APV Dryer Handbook 12/6/00 10:52 AM Page 3CONTENTSIntroduction .5Dryer Terms .7Section 1. Dryers .8Section 2. Efficient Energy Utilization in Drying.30Section 3. Fluid Bed .37Section 4. Spin Flash Dryers .48Section 5. Spray Dryers.583
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APV Dryer Handbook 12/6/00 10:52 AM Page 5INTRODUCTIONThe drying of materials – whether solids, liquids or slurries – to improve storagelife or reduce transportation costs is one of the oldest and most commonly usedunit operations. Drying of fruit, meat and various building and craft materials dateback before the discovery of fire. The physical laws governing drying remain thesame, even though the machinery to accomplish it has improved considerably!Today, dryers are in operation in most manufacturing industries including chemical,pharmaceutical, process and food. Products that are dried range from organicpigments to proteins, as well as minerals to dairy products. Because of thespectrum of duties required, there is a great variety of dryers available. Thecorrect choice depends on the properties of the feed material and the desiredcharacteristics of the final product. This handbook reviews many types of dryersand provides guidelines for their selection. Certain types of commonly used dryersare reviewed in detail.Since drying is an energy intensive operation, this handbook also providesinformation on techniques to improve efficiency.5
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APV Dryer Handbook 12/6/00 10:52 AM Page 7DRYERTERMSFEED DEFINITIONSSolution: Solids fully dissolvedSlurry: Suspended or dispersedThixotropic: Thins with shearDilatent: Thickens with shearCohesive Paste: Just plain stickyFriable Cake: Dry to touch, breaks upGranules: Very coarse powderDRIED PRODUCT CHARACTERISTICSFine: Typically pigment powders, fillers, talcum powderFree Flowing: Usually over 50 microns, press filling applicationsDustless: Dyes, bulk handling, Kaolin – still free flowingGranular: Coarser and less free flowingWettable: For easy mixing into water – agro chemicals, dyesAgglomertated: Easiest mixing and dissolving – infant formula, creamerCoated: Time release, lecithinated, flavoredLump: Rabbit food, cattle feed, KaolinPOWDER PROPERTIESHygroscopic: Flavors, salts, sugars, HVPHydrophobic: Fats, polymers, coated inorganicsThermoplastic: Lignin, PVA resins, sugars, fatsHeat Sensitive: Protein, pigments, iron oxide, crystalsInert: Mineral, oxides, Kaolin, waste7
APV Dryer Handbook 12/6/00 10:52 AM Page 8DRYERSDryer Selection ChartFEED TYPESolutionThixotropDilatentCohesiveFinePOWDER TYPEDustlessGranulesPowderFlashSpin FlashSprayFreeflowFriableSpray or SBDGranularBandWettableAgglomSpray BedCoatedLumpSpin Flash Fluid Bed Agglom.TrayBandFluid BedGranulationFigure 1. A guide to dryer selectionSELECTION, SIZING, COSTSThroughout the food, dairy, chemical and process industries, there are variousrequirements for thermal drying. Some involve the removal of water or othervolatiles from pasty materials such as pigments, clays, synthetic rubbers andfine chemicals. Others involve the drying of solutions or liquid suspensions suchas whey, milk and coffee. To assist manufacturers in arriving at a reasonablyaccurate first assessment of the type, size and cost of equipment for a particularduty, this article describes the most widely used types of both batch andcontinuous dryers.Three basic methods of heat transfer are used in industrial dryers in variouscombinations. These are convection, conduction and radiation.In the processing industries the majority of dryers employ forced convection andcontinuous operation. With the exception of the indirectly heated rotary dryer and8
APV Dryer Handbook 12/6/00 10:52 AM Page 9the film drum dryer, units in which heat is transferred by conduction are suitableonly for batch use. This limitation effectively restricts them to applications involvingsomewhat modest production runs.Radiant or so called “infra-red” heating is rarely used in drying materials suchas fine chemicals, pigments, clays or synthetic rubbers. Its main application is inoperations such as the drying of surface coatings on large plane surfaces, sinceefficient utilization generally requires a line of sight between the material beingirradiated and the heat source or emitter. In all the dryers considered here,however, there is a radiant component in the heat transfer mechanism.Eav Evaporation (average)Evaporation rate Evaporation rate Fluids,Pastes,Granules,(kg/m2h)liquid dewatered Powders pellets,Operation(lb/ft2hr)Mean rate Eav Mean rate Eav suspension cakeextrudatesFORCED0.15 - 0.25.7 – 1.2CONVECTION(cross-airflow)Eav 0.2Eav 1poorfairfairgoodbatchFORCED1.0 – 2.05 – 10CONVECTION(throughflow)Eav 1.5Eav 7.5goodbatchAGITATED PAN1.0 – 5.05 – 25(sub-atmospheric) Eav 3.0Eav 15fairfairfairpoorbatchAGITATED PAN1.0 – 5.05 – 25(atmospheric)Eav 3.0Eav 15fairfairfairpoorbatchDOUBLECONE TUMBLER1.0 - 3.05 – 15(sub-atmospheric) Eav 2.0Eav 10poorfairpoorbatchFLUIDIZED BED2 – 5010 – 250(throughflow)Eav 26Eav 130goodgoodcontinuousCONVEYOR BAND 2.0 – 10.010 – 50(throughflow)Eav 6.0Eav 30fairgoodcontinuousFILM DRUM3.0 – 6.015 – 30(atmospheric)Eav 4.5Eav 22goodfaircontinuousPNEUMATIC50 – 250250 – 1250or FLASHEav 150Eav 750fairgoodfaircontinuousROTARY1.0 – 3.0*15 – 50(indirect)Eav 2.0Eav 33poorgoodfaircontinuousROTARY2.0 – 6.0*30 – 100(direct)Eav 4.0Eav 65fairfairgoodcontinuousSPIN FLASH4.0 – 18*70 – 300Eav 11Eav 185goodgoodfaircontinuousSPRAY0.3 – 1.6*5 – 25Eav 1.0Eav 15goodcontinuous*Note: Evaporation rates for rotary, Spin Flash, and spray dryers are expressed in lb/ft3hr.Table 1. Product classification and dryer types as an aid to selection9
APV Dryer Handbook 12/6/00 10:52 AM Page 10Direct heating is used extensively in industrial drying equipment where muchhigher thermal efficiencies are exhibited than with indirectly heated dryers. Thisis due to the fact that there are no heat exchanger losses and the maximum heatrelease from the fuel is available for the process. However, this method is notalways acceptable, especially where product contamination cannot be tolerated.In such cases, indirect heating must be used.With forced convection equipment, indirect heating frequently employs acondensing vapor such as steam in an extended surface tubular heat exchangeror in a steam jacket where conduction is the method of heat transfer. Alternatively,systems which employ proprietary heat transfer fluids can also be used. Theseenjoy the advantage of obtaining elevated temperatures without the need forhigh pressure operation, as may be required with conventional steam heating.This may be reflected in the design and manufacturing costs of the dryer.Furthermore, in addition to the methods listed above, oil- or gas-fired indirectheat exchangers can also be used.In general, dryers are either suitable for batch or continuous operation.A number of the more common types are listed in Table 1, where an applicationrating based on practical considerations is given. In the following review, someof the factors likely to influence selection of the various types are discussed forparticular applications.BATCH DRYERSIt will be apparent that batch operated equipment is usually related to smallproduction runs or to operations requiring great flexibility. As a result, the batchtype forced-convection unit certainly finds the widest possible application of anydryer used today.The majority of designs employ recirculatory air systems incorporating largevolume, low pressure fans which with the use of properly insulated enclosures,usually provide thermal efficiencies in the region of 50 to 60%. However,in special applications of this type of dryer that call for total air rejection, thisfigure is somewhat lower and is largely related to the volume and temperatureof the exhaust air. Capital investment and installation cost are relatively low.The use of fan systems minimizes both power requirements and operating costs.In contrast, labor costs can be high.10
APV Dryer Handbook 12/6/00 10:52 AM Page 1180004 THRUFLOUNITSTYPE ‘C2’ 2-TRUCKEXTRUDED MATERIALOUTPUT (LBS/24HRS)3 THRUFLOUNITSTYPE No. 22-TRUCKFILTER CAKETYPE ‘C2’ 2-TRUCKFILTER CAKE200040002 THRUFLOUNITSOUTPUT (KGs/24HRS)30006000100020001 THRUFLOUNIT005101520NUMBER OF TWO-TRUCK UNITS2530Figure 2. Comparative performance curves for Thruflo and conventional unitsIn such a plant, the drying cycles are extended, with 24 to 45 hours being quitecommon in certain cases. This is a direct result of the low evaporative rate, whichnormally is in the region of 0.15 to 0.25 lb/ft2hr. (0.7 to 1.2 kg/m2h).Following the recent trend and interest shown in preforming feedstock with regardto the design of extruding and tray-filling equipment for de-watered cakes – it isnow possible to obtain the maximum benefit of enhanced evaporative rates byusing through-air circulation dryers when handling preformed materials.Figure 2, shows how ahigh-performance dryercan produce 1950 lbs (890kg) of dried material in a 24hour period, at a terminalfigure of 0.5% moisture (whenhandling a preformed filtercake having an initial moisturecontent of 58%). Thesignificant improvement inperformance can be seenFigure 3. Thruflo dryerfrom the curve, where the11
APV Dryer Handbook 12/6/00 10:52 AM Page 12corresponding number of conventional two-truck recirculatory units would bebetween seven and eight for the same duty. The advantage is more apparentwhen it is seen that respective floor areas occupied are 55 ft2 (5 m2) for the Thruflodryer pictured in Figure 3, and 245 ft2 (22 m2) in the case of conventional unitsusing transverse air flow.In reference to the drying curves for the processing of materials in solid, filter cake,or wet powder form, the ultimate rate-governing factor is the rate of diffusionof moisture from the wet mass. This becomes increasingly so during the fallingrate period of drying. This situation, however, can be improved by preforming theproduct to increase the effective surface area presented to heat and mass transfer.The logical extension of this technique is total dispersion drying, i.e., flash orpneumatic dryers, fluid beds, etc. where discrete particles can be brought intocontact with the hot gas. This produces rapid heat transfer with correspondinglyshort drying times.Batch type fluidized bed dryers have, therefore, superseded forced convectionunits in many cases – notably in the drying of pharmaceuticals and for theprocessing of certain thermoplastics. These machines generally are availablein a range of standard sizes with batch capacities from 50 to 200 lbs/h(23 to 90 kg/h), although much larger units are made for special applications.When considering a fluid bed dryer, it is important to ensure that the feedmaterial can be fluidized, both in its initial and final condition. It also should beremembered that standard fan arrangements are not equally suitable for a varietyof materials of different densities. Therefore, it is necessary to accurately determinethe minimum fluidizing velocity for each product.If the feedstock is at an acceptable level of moisture content for fluidization, thefluid bed type of dryer provides many advantages over a batch type tray dryer.Simplified loading and unloading results in lower labor costs – high thermalefficiencies are common and the drying time is reduced to minutes, as opposedto hours in conventional units. Current developments of this type of equipmentinclude techniques for the simultaneous evaporation of water and the granulationof solids. This makes these units ideal for use in the pharmaceutical field.The various batch dryers operate by means of forced convection. The transfer12
APV Dryer Handbook 12/6/00 10:52 AM Page 13of thermal energy increases thevapor pressure of the absorbedmoisture, while the circulated airscavenges the overlying vapor.Good conditions are maintainedfor continued effective drying.Alternatively, and where thematerial is thermosensitive,implying low temperatures withconsequently low evaporativerates, some improvement canbe effected by the use ofsub-atmospheric dryers, i.e.,Figure 4. Double cone vacuum dryerPhoto courtesy of Mitchell Dryers Limited,Carlisle, Englandby reducing the vapor pressure.Several different configurationsare in use and all fall into thecategory of conduction-typedryers. The most usual type of heating is by steam, although hot water or oneof the proprietary heat transfer fluids can be used.Figure 5. Conical section of a large spray dryer with secondary fluid bed dryer13
APV Dryer Handbook 12/6/00 10:52 AM Page 14Two particular types are the double-cone dryer shown in Figure 4 with capacitiesup to 400 ft3 (11 m3) and the agitated-pan dryer not normally larger than 8 ft(2.4 m) in diameter, where average evaporative rates per unit wetted area usuallyare in the region of 4 lb/ft2hr (25 kg/m2h). These units are comparatively simpleto operate and when adequately insulated are thermally efficient, although dryingtimes can be extended. They are especially suitable for applications involvingsolvent recovery and will handle powders and granules moderately well.However, with some materials, the tumbling action in double-cone dryers and theaction of the agitator in agitated-pan machines can produce a degree of attritionin the dried product which may prove unacceptable.Similarly, large rotary vacuum dryers are used for pigment pastes and othersuch materials, especially where organic solvents present in the feedstock needto be recovered. These units are normally jacketed and equipped with an internalagitator, which constantly lifts and turns the material. Here, heat transfer is entirelyby conduction from the wall of the dryer and from the agitator. Due to the natureof their construction, initial cost is high relative to capacity. Installation costs alsoare considerable. In general, there are limited applications for these dryers.CONTINUOUS DRYERSFor the drying of liquids or liquid suspensions, the evaporator of choice is usuallyeither a drum dryer or a spray dryer.A typical film drum dryer with a 4 ft (1.2 m) by 10 ft (3 m) long drum willevaporate about 600 lb/h (270 kg/h) of water. A typical spray dryer as shownin Figure 5 will evaporate 22,000 lb/h (10,000 kg/h).Where tonnage production is required, the drum dryer is at a disadvantage.However, the thermal efficiency of the drum dryer is high in the region of 1.3 to1.5 mass units of steam per mass unit of water evaporated (65 to 75% efficiency)and for small to medium production runs, it does have many applications.Drum dryers are usually steam heated, although work has been done to developeunits for direct gas or oil heating. Completely packaged and capable ofindependent operation, these dryers can be divided into two broad classifications:single drum and double drum.14
APV Dryer Handbook 12/6/00 10:52 AM Page 15As seen in Figure 6, there are a number of different feeding arrangements fordrum dryers, all of which have a particular use. In practice, these variants arenecessary because of the differing characteristics of the materials to be driedand due to the fact that no universally satisfactory feeding device has yet beendeveloped. This again illustrates the needfor testing, not only in supportof theoretical calculations for theDISCHARGEDISCHARGEdetermination of the best dryerDRYER WITH SPRAY FEEDsize, but also to establish whethera satisfactory film can be formed.DISCHARGEDouble drum machines normallyFEED ANDSPREADINGROLLERSemploy a “nip” feed device, withthe space between the drumsDRYER WITH BOTTOMROLLER FEEDcapable of being adjusted toSPREADINGROLLERFEEDTROUGHFEEDROLLERSprovide a means of controllingthe film thickness. Alternately,DISCHARGEand in the case of the singleDISCHARGEDRYER WITH TOPFEED ROLLERSdrum types, a variety of feedingmethods can be used to applyDRYER WITH TOPROLLER FEEDmaterial to the drum. The mostDISCHARGEcommon is the simple “dip”feed. With this arrangement,good liquor circulation in theFLAKING AND CHILLINGMACHINE WITH DIP FEEDFEEDtrough is desirable in orderDISCHARGESIDE TROUGH FEEDto avoid increasing theconcentration of the feedDISCHARGEby evaporation. Again,FEEDsingle drum dryersuse top rollerDISCHARGEDISCHARGEDISCHARGEfeed. While thenumber of rollsFEEDDRYER WITH PLAINDIP FEEDfor special applications,DOUBLE DRUM DRYERWITH CENTER FEEDDOUBLE DRUM DRYER WITHCENTER FEED AND BOTTOMDISCHARGEis related to theFigure 6. Feeding arrangements for drum dryers15
APV Dryer Handbook 12/6/00 10:52 AM Page 16particular application and the material being handled, generally this methodof feeding is used for pasty materials such as starches. Where the feed is verymobile, rotating devices such as spray feeds are used.It must be emphasized that the method of feeding the product to the dryer isof paramount importance to selection or design. There are, of course, certainmaterials which are temperature-sensitive to such a degree that their handlingwould preclude the use of an atmospheric drum dryer. In such cases, specialsub-atmospheric equipment may provide the answer, although the capital costin relation to output generally would restrict its use to premium grade products.As an alternate, the spray dryer offers an excellent solution to a host of dryingproblems. Many materials, such as dairy and other food products, which wouldsuffer from thermal degradation if dried by other methods, can often be handledby spray drying (due to the rapid flash evaporation and its accompanying coolingeffect). The continuous method of operation also lends itself to large outputs andwith the correct application of control equipment, to low labor costs.SPRAY DRYERSFundamentally, the spray drying process is a simple one. However, the designof an efficient spray drying plant requires considerable expertise along withaccess to large scale test facilities, particularly where particle size and bulk densityrequirements in the dried product are critical. The sizing of spray dryers on apurely thermal basis is a comparatively simple matter since the evaporation isentirely a function of the t across the dryer. Tests on small pilot scale equipmentare not sufficient in the face of such imponderables as: possible wall build-up,bulk density and particle size predictions. Atomization of the feed is of primeimportance to efficient drying and three basic feed devices are used extensively:(1) single fluid nozzle or pressure type, (2) two-fluid nozzle or pneumatic type, and(3) centrifugal (spinning disc).The single fluid nozzle produces a narrow spray of fine particles. While amultiplicity of nozzles of this type are used in tonnage plants to obtain the desiredfeed rate, due to the high pressure employed [up to 7000 PSIG (475 BARG)]excessive wear can result, particularly with abrasive products.16
APV Dryer Handbook 12/6/00 10:52 AM Page 17FEEDAIR INLETCENTRIFUGALATOMIZERAIR INLETNOZZLEATOMIZERAIR OUTLETFEEDAIR OUTLETAPRODUCTBPRODUCTFigure 7. Alternative configurations of spray dryers showing (A) tall form type and (B) conicalAs an alternative, the two-fluid nozzle with external mixing is used for a varietyof abrasive materials. This system generally is limited to small capacity installations.Normally, the feed is pumped at about 25 PSIG (1.7 BARG) merely to inducemobility, while the secondary fluid is introduced at 50 to100 PSIG (3.5 to 6.8BARG), producing the required atomization.Centrifugal atomization achieves dispersion by centrifugal force, with the feedliquor being pumped to a spinning disc. This system is suitable for, and generallyused on, larger productions. When stacked or multiple discs are employed, feedrates of 60,000 lb/hr (27,000 kg/h) are not uncommon.Many different spray dryer configurations, along with a variety of air flowpatterns, are in current use. The nature of the chamber geometry selected isstrictly related to the system of atomization used. An example of this is the towerconfiguration designed to accommodate the inverted jet of the two-fluid nozzle,whereas the cylinder and cone of the more usual configuration is designed for thespray pattern produced by a disc type atomizer, shown in Figure 7. The productcollection systems incorporated in spray drying installations are many and varied,and can constitute a substantial proportion of the total capital investment. In somecases, this can be as high as 20 to 25% of the installed plant cost. It also mustbe remembered that to be suitable for spray drying, the feed must be in pumpablecondition. Therefore, consideration must be given to the up-stream process, i.e.,17
APV Dryer Handbook 12/6/00 10:52 AM Page 18whether there is any need to re-slurry or dilute, in order to make the feed suitablefor spray drying. As a rule of thumb, the limiting viscosity for good atomizationis 250 – 300 Centipoise.The economic viability of a drying process ultimately depends on the cost perpound of the dried product. The spray dryer usually has a greater amount ofwater to remove by thermal methods than other types. For example, to dry20,000 lbs/hr (9,000 kg/h) of a 30% solids/water slurry to 0.5% moisture,the spray dryer would have an approximate diameter of 30 ft for the evaporationof 14,000 lbs/hr (6,360 Kg/h). If, however, the feed solids were increased to50% by evaporation, the hourly evaporation rate would decrease to 6,000 lbs/h(2,700 Kg/h) and the chamber diameter would be about 20 ft (6 m), witha corresponding decrease in thermal input and air volume. The former systemwould, as a result, also require larger fans and product collection systems.The overall thermal efficiency would remain substantially constant at 76% withincreasing feed solids. However, the cost per pound of dry product is significantlylower when drying from the higher feed solids.Spray drying does have many advantages, particularly with regard to the finalproduct form. This is especially so where pressing grade materials are required,i.e., in the production of ceramics and dust-free products such as dyestuffs.With the introduction of new geometries and techniques, there has been furtherdevelopment into areas such as foods, and in the production of powders whichmay be easily reconstituted. These spray dryers usually incorporate one or twofluid beds – static and vibrating – for the final drying and cooling of theagglomerated powder.ROTARY DRYERSAnother type of dryer, popular in the chemical and process industries, is thecontinuous rotary dryer. This machine is generally associated with tonnageproduct, and as a result of its ability to handle products having a considerablesize variation, can be used to dry a wide range of materials. The principlesources of thermal energy are oil, gas and coal. While typical inlet temperaturesfor direct-fired dryers using these fuels is in the order of 1200 F (650 C), they18
APV Dryer Handbook 12/6/00 10:52 AM Page 19may be as high as 1600 F(850 C), depending largelyon the nature of the productDIRECT FIRINGhandled. Where feedmaterials are thermo-sensitive,steam heating from an indirectheat exchanger is also usedPARALLEL FLOWextensively. These dryers areavailable in a variety ofdesigns, but in general, canbe divided into two mainCOUNTER-CURRENT FLOWtypes: those arranged fordirect heating and thosedesigned for indirect heating.As seen in Figure 8, certainINDIRECT/DIRECT FIRINGvariants do exist. For example,the direct/indirect dryersimultaneously uses both systems.Where direct heating is used,the products of combustion arein intimate contact with theINDIRECT FIRING CONDUCTION TYPEmaterial to be dried.MATERIALSIn the case of indirect systems,HEAT FLOWFigure 8. Typical rotary dryer arrangementsthe hot gases are arrangedto circulate around the dryer shell. Heat transfer is then conducted and radiatedthrough the shell.With the indirect-direct system, hot gases first pass down a central tube, coaxialwith the dryer shell, and return through the annular space between the tube andshell. The material being cascaded in the annulus picks up heat from the gases,as well as by conduction from direct contact with the central tube. This designis thermally, highly efficient. While there are a number of proprietary designsemploying different systems of air flow, the two main types most commonly usedare parallel and counter-current flow. With parallel flow, only high moisture content19
APV Dryer Handbook 12/6/00 10:52 AM Page 20material comes intocontact with the hotgases and, as a result,higher evaporative ratescan be achieved thanwhen using countercurrent flow.In addition, manythermo-sensitive materialscan be driedsuccessfully by thismethod. Such anarrangement lends itselfFigure 9. Fixed tube rotary dryerPhoto courtesy of Mitchell Dryers Limited, Carlisle, Englandto the handling of pastymaterials, since the rapid flashing off of moisture and consequent surface dryinglimits the possibility of wall build-up or agglomeration within the dryer. On the otherhand, counter-current operation normally is used where a low terminal moisturecontent is required. In this arrangement, the high temperature gases are brought intocontact with the product immediately prior to discharge, where the final traces ofmoisture in the product must be driven off.In both these processes, however, gas velocities can be sufficiently high to produceproduct entrainment. Therefore, they would be unsuitable for low density or fineparticle materials such as carbon black. In such cases, the indirect-fired conductiontype dryer is more suitable, since the dryer shell is usually enclosed in a brickhousing or outer steel jacket into which the hot gases are introduced. Since heattransfer is entirely by conduction, conventional flighting and cascading of thematerial is not used. Rather, the inside of the shell is fitted with small liftersdesigned to gently turn the product, while maintaining maximum contact withthe heated shell.The steam tube unit is another type of indirectly heated dryer, which is particularlyuseful for fine-particle or heat-sensitive materials. This dryer can be of either the fixedtube variety – equipped with conventional lifting flights designed to cascade theproduct through a nest of square section tubes; or alternately, a central rotating tube20
APV Dryer Handbook 12/6/00 10:52 AM Page 21nest. Figure 9 shows a fixed-tube rotary dryer which normally has an electricalvibrator fitted to the tube nest to eliminate the possibility of bridging of theproduct, with consequent loss of heat transfer surface. Since the heat exchangeris positioned within the insulated shell in this type of dryer, the air rejection rate isextremely low and thermal efficiencies are high. In general, this design is suitableonly for free flowing materials.A considerable amount of work has been done on the development of varioustypes of lifting flights, all designed to produce a continuous curtain of material overthe cross section of the dryer shell. Other special configurations involve cruciformarrangements to produce a labyrinth path. The object is to give longer residencetimes where this is necessary. When the diffusion characteristics of the materialor other process considerations call for extended residence times, these machines,no doubt, will continue to find application.PNEUMATIC DRYERSWhere total dispersion of the product in a heated gas stream can be achievedwith a significant increase in evaporative rates, pneumatic or continuous fluid beddryers are preferred. The capital cost of these alternatives is generally lower andmaintenance is limited to such components as circulating fans and rotary valves.When considering these two types of dryers, it is convenient to examine EDPRODUCTRE-CYCLECLEANOUTDUCTHEATERMAINFANAMAIN FANBVENTURIFigure 10. (A) Multipass and (B) air recycle arrangements in flash dryers21
APV Dryer Handbook 12/6/00 10:52 AM Page 22together since both share similar characteristics. Both employ forced convectionwith dispersion of the feedstock, and as a result of the intimate contact betweenthe drying medium and the wet solids, both exhibit much higher drying rates thanany of the other dryers previously mentioned.In a fluidized bed dryer, the degree of dispersion and agitation of the wet solidsis limited, whereas in a pneumatic dryer, the degree of dispersion is total and thematerial is completely entrained in the gas stream. This is often an advantagebecause the drying medium is used as a vehicle for the partially dried product.Other operations such as product classification can also be carried out whererequired. Another feature of fluid bed and flash dryers is that the method ofoperation allows many temperature-sensitive materials to be dried without thermaldegradation, due to the rapid absorption of the latent heat of vaporization. Thisgenerally permits high-rate drying, whereas in other types of dryers, lowertemperatures would be necessary and correspondingly larger and more costlyequipment would be required.A good degree of temperature control can be achieved in fluid bed dryers andthe residence time of the material can be varied either by the adjustment of thedischarge weir or by the use of mul
AGITATED PAN 1.0 – 5.0 5 – 25 (sub-atmospheric) Eav 3.0 Eav 15 fair fair fair poor batch AGITATED PAN 1.0 – 5.0 5 – 25 (atmospheric) Eav 3.0 Eav 15 fair fair fair poor batch DOUBLE CONE TUMBLER 1.0 - 3.0 5 – 15 (sub-atmospheric) Eav 2.0 Eav
ELECTRIC DRYER OWNER’S MANUAL GUIDE D’UTILISATION DE LA SÉCHEUSE ÉLECTRIQUE Table of Contents Dryer Safety.2 Dryer Safety.2 Dryer Maintenance and Care.5 Cleaning the Dryer Location.5 Cleaning the Dryer Interior.5 Removing Accumulated Lint.5 Cleaning the Lint Screen.5 Changing the Drum Light (on some models).6 Check Your Vent System for Good Airflow.6 .
Installation Instructions supplied with your dryer for final product check. DRYER USE Starting Your Dryer Before using your dryer, wipe the dryer drum with a damp cloth to remove dust from storing and shipping. 1. Load clothes loosely into the dryer and close the door. Do not pack the dryer
1. This measure is for the replacement of an existing non-cycling refrigerated compressed air dryer with a higher efficiency refrigerated dryer. 2. Heat of compression desiccant compressed air dryer must replace a non-heated desiccant dryer and a heated/ blower purge desiccant compressor air dryer must replace an existing membrane type dryer. 3.
air load, the dryer’s refrigeration system only operates to maintain the mass at design temperature. The result is near-zero power consumption with immediate restart capability. dryer power consumption load on dryer standard dryer MTA savings DE Hybrid MTA savings MTA savings compressed air flow dryer powe
Twin air dryer, use MM35, WABCO System Saver Twin Air Dryer. To download these publications, go to wabco-na.com. 3.2 Air Dryer Identification The System Saver HP air dryer has the governor integrated into the body of the air dryer and also has an integrated purge tank. Figure 1. Fig. 1 4013285a PURGE T
d) Slowly open the air inlet valve to pressurise the dryer. e) Slowly open the air outlet valve. The dryer is now operating (drying). f) Always leave the dryer running while the air compressor is operating. g) After stopping the dryer wait at least 3 minutes before starting it again. 3.3 Stopping the dryer a) Use the switch to stop the dryer.
SAHARA's T Heatless regenerative air dryer is the most reliable dryer ever built. Since this unit requires neither heaters nor blowers, it is inherently more trouble-free than any heat-reactivated dryer. Gravity is a powerful force and the T Heatless dryer has been specifically designed to fully utilize the force of gravity to optimize dryer
dryer; therefore, the dryer becomes its own compressed air consumer. It is important to realize that for a basic heatless air dryer, the purge flow is related to the rating of the air dryer, and is not the percentage of the air flowing through it. For a 1000 cfm heatless air dryer, the 15 to 20 percent purge air loss would be between 150 and .
