Compressed - PDF document

1 Compressed I.Why Do Compressed Air And
Compressed I.Why Do Compressed Air And Gas Need Drying?1II.Applications Requiring Clean, Dry Air1III.How To Measure Moisture Content2IV.Selecting The Right Dryer3V.Types Of Compressed Air Dryers4Refrigerant TypeRegenerative Desiccant TypeHeat of Compression TypeSingle Tower Deliquescent TypeMembrane TypeVI.Specifying ACompressed Air Dryer7VII.What Is ACompressed Air Drying System?9VIII.Additional Literature10Appendices11-13 II RYINGLWAYSwhich will begin to condense into liquid water inthe compressed air or gas system when the air orwhere it can hold no more water vapor.* The temperature at which this happens is known.** This dew point becomes all-important in determining how much drying Condensation in the compressed air system wouldoccur at the inlet air saturation temperature if tem-perature remained constant as air was compressed.However, since there is a rise in temperature duringactual compression, condensation generally isthe compressor. Later, as com-pressed air is discharged and cooled in an aftercool-er, condensation begins to occur. The condensedmoisture must be removed by a separator and trap.The air leaving the aftercooler normally is saturatedat the aftercooler discharge temperature.For many years, problems from moisture in airlines were tolerated. To prevent freezing, alcoholswere injected into the lines and electric heaterswere used during cold periods. Filters were used toseparate moisture and other contaminants but didnot completely solve the problem.The increased use of compressed air and the devel-opment of many new and more sophisticateddevices and controls have accelerated the need forclean dry air. Hence, drying technology advanced,and dryers came into general use.Moisture in compressed air used in a manufacturingplant causes problems in the operation of pneumaticmoisture causes rust and increased wear of movingMoisture adversely affects the color, adherence, andfinish of paint applied by compressed air. Moisture jeopardizes process industries wheremany operations are dependent upon the properfunctioning of pneumatic controls. The malfunc-tio

2 ning of these controls due to rust, scal
ning of these controls due to rust, scale, andclogged orifices can result in damage to product orin costly shutdowns. Additionally, the freezing ofmoisture in control lines in cold weather commonlycauses faulty operation of controls. Corrosion of air or gas operated instruments frommoisture can give false readings, interrupting orshutting down plant processes.PPLICATIONSIn almost every operation, clean, dry compressed airwill result in lower operating costs. Dirt, water andoil entrained in the air will be deposited on the innersurfaces of pipes and fittings, causing an increase inpressure drop in the line. Aloss of pressure is a lossof the energy used to compress the air and a reducedpressure at the point of use results in a loss of performance efficiency. Liquid water accelerates corrosion and shortens theuseful life of equipment and carry over of corrosionparticles can plug valves, fittings and instrumentcontrol lines. When water freezes in these compo-nents, similar plugging will occur.ALVESANDDeposits of sludge formed by dirty, wet and oily airand bearings need frequent maintenance. Operationis slowed down and eventually stopped. Moisturedilutes the oil required for the head and rod of an aircylinder, corrodes the walls and slows response. Thisresults in loss of efficiency and production.Moisture flowing to rubber diaphragms in valvescan cause these parts to stiffen and rupture.Moisture also can cause spools and pistons to pit.In high-speed production, a sluggish or stuckcylinder could create costly downtime. Aclean, dry air supply can prevent many of these potentialproblems.Pneumatic tools are designed to operate withclean, dry air at the required pressure. Dirty andwet air will result in sluggish operation, more frequent repair and replacement of parts due tosticking, jamming and rusting of wearing parts.Water also will wash out the required oils, result-ing in excessive wear. Adecrease in pressure at the tool caused by restrict-ed or plugged lines or parts will cause a reductionin the efficiency of the tool.Clean, dry air at the required pressure will enable

3 the production worker to start operating
the production worker to start operating immedi-ately at an efficient level, with no time lost to purgelines or drain filters and will help to maintain pro-ductivity and prolong tool life.Control air supplied to transmitters, relays, inte-grators, converters, recorders, indicators or gaugesis required to be clean and dry. Asmall amount ofmoisture passing through an orifice can cause *The maximum water vaporupon the temperature andpressure. The amount ofcontain - relative to themost it can contain is rela-present to the quantitypresent at saturation at thesame temperature).**Dew Point. The tempera-ture at which water vapordense or change fromexpressed at an operatingpressure or at atmosphericpressure. Operating pres-sure should be specifiedwhen using pressure dewpoint. The relationshipbetween pressure andatmosphere dew point is IRANDRYING malfunction of the instrument and the process itcontrols. Moisture and resultant corrosion particlesalso can cause damage to instruments and plugPneumatic thermostats, which control the heatingand air conditioning cycles in large and smallbuildings, also require clean, dry air.Instruments and pneumatic controllers in powerplants, sewage treatment plants, chemical andpetrochemical plants, textile mills and general efficient operation.The Instrument Society of America (ISA) has pub-lished ISA-S7.3 Quality Standard for Instrument Air.RESERVATIONOFWhen used to mix, stir, move or clean a product, airmust be clean and dry. Oil and water in compressedair used to operate knitting machinery will cause theused to blow lint and thread off finished fabrics, con-taminants in the air may cause product spoilage.If air is used to blow a container clean before pack-aging, entrained moisture and oil may contaminatethe product. Moisture in control line air can causethe wrong mixture of ingredients in a bakery, theincorrect blend in liquor, water-logged paint, orruined food products.In some printing operations, air is used to lift orposition paper, which will be affected by dirty, wetair and any water on the paper will prevent properadhesion of the i

4 nks.In pneumatic conveying of a product
nks.In pneumatic conveying of a product such as papercups or cement, dry air is essential.Supersonic wind tunnels are designed to simulateatmospheric conditions at high altitudes wheremoisture content is low. These chambers use largevolumes of air, which must be dried to a very lowdew point to prevent condensation in the tunnelair stream.REATHINGThe air coming from an air compressor, whetherlubricated or oil free type, is not suitable for breath-ing. Treatment of the air is required before the aircan be considered suitable for breathing and certainhealth and safety standards must be met.In industrial plants, air may be supplied to respira-Administration (OSHA) standard OSHA:1910:13dapplies and requires drying, filtration and treat-ment to meet specific levels, including carbonmonoxide, with an alarm system.The Compressed Gas Association (CGA) Standardly is specified for plant breathing air systems.Medical air for hospitals must meet National FireProtection Association (NFPA) Standard NFPA-99.encompassing pollutants havebeen established in an International Standard ISO8573-1. For moisture content, these are as follows: ¡CDEWPOINT 1-70-100 2-40-40 3-20-4 4+3+38 5+7+45 6+10+50 7not specifiedObviously there are times when it is desirable toknow with varying degrees of accuracy the moisturecontent of the compressed air. Methods are availablewhich will give you readings, which vary fromapproximations to precise measurements.Atypical exampleis silica gel, which when treated with a solution ofcobaltous chloride*, is dark blue in color when dry.As moisture is adsorbed, the color changes to pinkat approximately a 0¼F dew point.Dew Point Cup. polished stainless steel cup placed in a containertemperature of the polished surface is lowered byimmersing dry ice (solid carbon dioxide) in an ace-tone solution contained in the cup. The temperatureThis device permits direct gauge reading of the dewpoint temperature of the sample, as determined bypolished vessel in which a refrigerant is being evap-orated. Dew point temperatures can be determinedat either system or atmospheric pressur

5 e.This device relies on the relationship
e.This device relies on the relationship between pressure and temperatureduring adiabatic expansion. Asample of gas enters asmall chamber where it is compressed, then rapidlyvented to atmospheric pressure. The point at whichfog appears establishes a relationship with theamount of compression, and from this the dew IRANDRYING two strips of metal, which form the electrodes of acapacitor. Water vapor passing across the electrodescauses a change in electric impedance and this isused as a measurement of dew point temperature.element which contains a moisture adsorbing mate-rial. Achange in the moisture content of the ele-ment is detected by an electronic network and isused as a measurement of dew point temperature.Infrared Analyzer.This instrument uses two beamsof infrared radiation. One beam travels through acomparison cell and the other through the samplecell. The difference in absorption in the radiation isused as a means of measurement of the dew pointFrequency Oscillator Analyzer.This moisture analyzer uses the change in frequency of a hygro-point measurement. RYERBefore looking at the several types of dryers avail-ing which dryer is best for the specific requirements.NOWTHESESOFTHEprofessional who knows or learns the particularend uses, the amount of moisture which each usecan tolerate and the amount of moisture whichneeds to be removed to achieve this level.Air which may be considered dry for one applica-tion, may not be dry enough for another. Dryness is relative. Even the desert has moisture. There isalways some moisture present in a compressed airsystem regardless of the degree of drying. Differenttypes of dryers, therefore, are available with vary-ing degrees of pressure dew point ability.To specify a dew point lower than required for anapplication is not good engineering practice.(Naming a pressure dew point is how to state thedegree of dryness wanted.) It may result in morecostly equipment and greater operating expense.NOWTHEEMPERATURESTo determine whether or not the compressed air willremain sufficiently dry, we must know the end use ofthe air and the tem

6 perature at which it must work. In an in
perature at which it must work. In an industrial plant where the ambient tempera-ture is in the range of 70¡F or higher, a dryer capa-ble of delivering a pressure dew point 20¡F lowerthan ambient, or 50¡F, may be quite satisfactory.Summer temperatures do not require a very lowdew point whereas winter temperatures may dic-tate a much lower dew point. In winter, the temper-ature of the cooling medium, air or water, usually islower than in summer, resulting in a variation ofthe air temperature to the dryer. This will affect thesize of the dryer needed, since the same dryer mustwork in both summer and winter temperatures andrelative humidities.Many chemical processing plants, refineries, andpower plants distribute instrument and plant airthroughout the facility with lines and equipmentdifferent temperature conditions exist at the sametime in the same system. Also, a dryer, which maybe satisfactory for high daytime temperatures maytures. In areas where freezing temperatures areencountered, a lower pressure dew point may berequired. In general, the dew point should be speci-fied 20¡F lower than the lowest ambient tempera-ture encountered in order to avoid potential con-densation and freezing. To specify a winter dewpoint when only summer temperatures will beencountered, can result in over-sizing the equip-ment and increased initial and operating costs. For plant air and instrument air, primary considera-tions in specifying a dryer are condensation andfreezing. In a system where a lot of internal pipecorrosion could occur, high humidity in the airstream should be avoided.NOWTHEWhile many dryers have a standard rating of 100¡F saturated inlet air temperature and 100 PSIGoperating pressure, it is important to check on theperformance of the units obtained in In addition to plant and instrument air applications,there are many other uses requiring moistureremoval to a low dew point. For example, railroadtank cars which carry liquid chlorine are padded(charged) with compressed air to enable pneumaticto form hydrochloric acid; therefore, the compressedair must have a minimum moi

7 sture content to prevent severe corrosio
sture content to prevent severe corrosion. Droplets of moisture in wind tunnel air at high-testing velocities may have the effect of machinegun bullets, tearing up the test models.Air used for low temperature processing (for exam-ple, liquefaction of nitrogen or oxygen) can form iceon cooling coils, thus requiring defrosting. Thelower the moisture content of the air, the longer theperiods between defrosting shutdowns. * The EEC has re-classifiedManufacturers and usersbefore using or specifyingthis product.Hygroscopic:which picks up moisture. IRANDRYING For these and similar temperature applications, compressed air must not only be free of liquid phasewater but must also have a minimum content ofvapor phase water. Usually specified for theserequirements are dew points in the range of -40¡F to-100¡F at pressure.With these characteristics in mind, what types ofdryers are available?RYERSDifferent methods can be used to remove the mois-ture content of compressed air. Current dryer types-Heatless (no internal or external heaters)-Heated (internal or external heaters)-Heat of Compression-Non-regenerative single towerEach of these dryer types will be discussed in someRYERSAlthough it does not offer as low a dew point as canbe obtained with other types, the refrigerant typedryer has been the most popular, as the dew pointgeneral industrial plantrefrigerator or home airconditioning system. Thecompressed air is cooledin an air to refrigerant35¡F, at which point thecondensed moisture isdrained off. The air isthen reheated in an air tomeans of the incomingair which also is pre-cooled before enteringthe air to refrigerant heatexchanger. This meansthat the compressed air leaving the dryer has a pres-sure dew point of 35 to 40¡F. Alower dew point isnot feasible in this type of dryer as the condensatewould freeze at 32¡F or lower.In a non-cycling refrigerant dryer, the refrigerantcirculates continuously through the system. Sincethe flow of compressed air will vary and ambienttemperatures also vary, a hot gas bypass valve orunloader often is used to regulate the flow of therefrigera

8 nt and maintain stable operating conditi
nt and maintain stable operating conditionswithin the refrigerant system. In most designs, therefrigerant evaporates within the air to refrigerantcompression by an air or water to refrigerant heatexchanger (condenser). Atypical schematic diagramis shown in Figure 1.This design provides rapid response to changes inoperating loads. While older refrigerant type airdryers have used CFC refrigerants such as R12 andR22, newer designs are in compliance with theMontreal Protocol and use chlorine free refrigerantssuch as R134Aand R407C. The properties of thesenewer refrigerants require careful attention to therefrigeration system design, due to differences inoperating pressures and temperatures.Cycling type refrigerant dryers chill a mass sur-rounding the air passage in the evaporator. This massminum block, beads or related substance, which actsas a heat sink. The compressed air is cooled by theheat sink which has its temperature controlled by athermostat and shuts off the refrigerant compressorduring reduced loads, providing savings in operatingof Refrigerant Type Air Dryers include:¥Low initial capital cost.¥Relatively low operating cost.¥Low maintenance costs.¥Not damaged by oil in the air stream (Filtration normally is recommended).of Refrigerant Type Air Dryers¥Limited dew point capability.of Direct Expansion Control include:¥Low and precise dew point.¥Refrigerant compressor operates continuously.of Direct Expansion Control¥No energy savings at partial and zero air flow.of Cycling Control include:¥Energy savings at partial and zero air flow.of Cycling Control include:¥Dew point swings.¥Reduced life of refrigerant compressor from¥Increased size and weight to accommodate the¥Increased capital cost. IRANDRYING EGENERATIVERYERSwater vapor in the air stream. Adistinction needs tobe made between adsorb and absorb. Adsorb meansthat the moisture adheres to the desiccant, collectingin the thousands of small pores within each desic-changed and the moisture can be driven off in aregeneration process by applying dry purge air, bymoisture is dissolved in and used up by the mois-tur

9 e as in the deliquescent desiccant type
e as in the deliquescent desiccant type dryer.are of twin tower con-struction. One towerdries the air from thecompressor while thedesiccant in the othertower is being regen-erated after the pres-sure in the tower hasbeen reduced toatmospheric pressure.ture or humidity inthe on-line tower.In the heatless regener-heaters are used. Purge air requirement can rangeup to 18% of the total air flow. The typical regenera-tive desiccant dryer at 100 psig has a pressure dewcan be obtained. Atypical schematic diagram isshown in Figure 1.Heat reactivated regenerative desiccant dryers maythe internal type, steam or electricity may be usedin heaters embedded in the desiccant bed. Thisreduces the amount of purge air required for regen-eration to about 5%. The purge air plus normalregeneration to prevent elevated air temperaturesgoing downstream.In externally heated regenerative desiccant dryers,the purge air is heated to a suitable temperatureand then passes through the desiccant bed. Theamount of purge air is approximately 5-10% of theair flow through the dryer. The purge air can beeliminated if a blower is used for circulation ofatmospheric air through the desiccant bed.To protect the desiccant bed from contaminationfrom oil carry-over from the air compressor, a coa-lescing filter is required upstream of the dryer. Toprotect downstream equipment from desiccant dustor ÒfinesÓ, a particulate filter downstream of thedryer also is recommended.of Regenerative Desiccant Type Dryers¥Very low dew points can be achieved withoutpotential freeze-up.¥Moderate cost of operation for the dew points¥Heatless type can be designed to operate pneumat-ically for remote, mobile or hazardous locations.of Regenerative Desiccant Type¥Relatively high initial capital cost.¥Periodic replacement of the desiccant bed ¥Oil aerosols can coat the desiccant material, rendering it useless if adequate pre-filtering is¥Purge air usually is required.EATOFRYERSHeat of Compression Type Dryers are RegenerativeDesiccant Dryers which use the heat generated dur-ing compression to accomplish desiccant regenera-tion, so th

10 ey can be considered as Heat Reactivated
ey can be considered as Heat Reactivated.There are two types, theSingle Vessel Type andthe Twin Tower Type.The Single Vessel Heat ofCompression Type Dryerprovides continuous dry-is accomplished with arotating desiccant drumin a single pressure vesselair streams. One airstream is a portion of the hot air taken directly fromthe air compressor at its discharge, prior to theaftercooler, and is the source of heated purge air forregeneration of the desiccant bed. The second airstream is the remainder of the air discharged fromthe air compressor after it passes through the airaftercooler. This air passes through the drying sec-tion of the dryer rotating desiccant bed where it isdried. The hot air, after being used for regeneration, IRANDRYING Hot unsaturated air used for regeneration Cold saturated Dry air Hot passes through a regeneration cooler before beingcombined with the main air stream by means of anejector nozzle before entering the dryer.The Twin Tower Heat of Compression Type Dryeroperation is similar to other Twin Tower HeatActivated Regenerative Desiccant Dryers. The dif-ference is that the desiccant in the saturated toweris regenerated by means of the heat of compressionfrom the hot air leaving the discharge of the aircompressor. The total air flow then passes throughthe air aftercooler before entering the drying tower.Towers are cycled as for other RegenerativeDesiccant Type Dryers.of Heat of Compression Type Dryers¥Low electrical installation cost.¥Low power costs.¥Minimum floor space.¥No loss of purge air.of Heat of Compression Type¥Applicable only to oil free compressors.¥Applicable only to compressors having a continuously high discharge temperature.¥Inconsistent dew point.¥Susceptible to changing ambient and inlet airtemperatures.¥High pressure drop and inefficient ejector nozzle¥Booster heater required for low load (heat) RYERShygroscopic desiccantaffinity for water. Thedissolved in the liquidformed. These hygro-scopic materials areblended with ingredientsto control the pH of theeffluent and to preventcorrosion, caking andchanneling. The desic-through t

11 he dryer. Onbe added two or three times
he dryer. Onbe added two or three times per year to maintain aproper desiccant bed level. Deliquescent dryers normally are designed to give adew point depression from 20¼F to 50¼F at an inlettemperature or 100¼F. This means that with air enter-ing at 100¼F and 100 PSIG, a leaving pressure dewpoint of 80¼F to 50¼F may be obtained (a reduction of20¼F to 50¼F from the inlet temperature). Dew pointsuppression of 15 to 50¡F is advertised. This type ofdryer actually dries the air to a specific relativehumidity rather than to a specific dew point.of Single Tower DeliquescentDesiccant Type Dryers include:¥Low initial capital and installation cost.¥Low pressure drop.¥No moving parts¥Requires no electrical power.¥Can be installed outdoors.¥Can be used in hazardous, dirty or corrosiveenvironments.of Single Tower Deliquescent Type¥Limited suppression of dew point.¥Desiccant bed must be refilled periodically.¥Regular periodic maintenance.¥Desiccant material can carry over into down-stream piping if there is no after-filter and if thedryer is not drained regularly. Certain desiccantmaterials may have a damaging effect on down-stream piping and equipment.¥Some desiccant materials may melt or fusetogether at temperatures above 80¡F.RYERSrecent years. Membranes commonly are used for gasseparation such as in nitrogen production for foodstorage and other applications. The structure of themembrane is such that molecules of certain gases(such as oxygen) are able to pass through (permeate)a semi-permeable membrane faster than others (suchas nitrogen) leaving a concentration of the desiredgas (nitrogen) at the outlet of the generator.When used as a dryer in a compressed air system,specially designed membranes allow water vapor(a gas) to pass through the membrane pores fasterthan the other gases (air) reducing the amount ofwater vapor in the air stream at the outlet of themembrane dryer, suppressing the dew point. Thedew point achieved normally is 40¡F but lower of additional purge air loss. IRANDRYING of Membrane Type Dryers include:¥Low installation cost.¥Low operating cost.¥Can be inst

12 alled outdoors.¥Can be used in hazardous
alled outdoors.¥Can be used in hazardous atmospheres.¥No moving parts.of the Membrane Type Dryers¥Limited to low capacity systems.¥High purge air loss (15 to 20%) to achieverequired pressure dew points.¥Membrane may be fouled by oil or other ¥High initial capital cost.RYERATINGSThe standard conditions for the capacity rating inscfm of compressed air dryers, are contained inCAGI ADF 100, Refrigerated Compressed Air Dryers ÐMethods for Testing and Rating*.These commonly arecalled the three 100s. That is, a dryer inlet pressure of100 psig, an inlet temperature of 100¡F and an ambi-ent temperature of 100¡F. If the plant compressed airsystem has different operating conditions, this willaffect the dryer rating and must be discussed withthe supplier to ensure compatibility.RYERThe air dryer with certain auxiliary equipmentof the whole plant compressed air system. Variouscomponents comprising the dryer subsystem shouldbe selected on the basis of the overall requirementsand the relationship of the components to each other.There are just three main factors to analyze inselecting the appropriate dryer (including size) toprovide your required performance Ð dew point,operating pressure and inlet temperature.Refrigerant dryers provide a pressure dew point of35¡F or 50¡F at operating pressure based on saturatedinlet air temperature of 100¡F.Regenerative desiccant dryers generally provide a pressure dew point of minus 40¡F or lower, atoperating pressure and 100¡F saturated inlet airtemperature.Deliquescent dryers are more sensitive to the satu-rated inlet temperature and, based upon a saturatedinlet air temperature of 100¡F, provide a dew pointfrom 64¡F to 80¡F at operating pressure.Membrane dryers deliver pressure dew points rang-ing from -40¡F to 50¡F or higher, if required. The dry air flow from a membrane dryer is dependenton the inlet dew point and pressure of the supplyair and outlet pressure dew point required by theapplication. Supply air temperature has no appre-ciable impact on capacity. PERATINGAt higher pressures, saturated air contains lessmoisture per standard cubic

13 foot than lower pres-sure saturated air.
foot than lower pres-sure saturated air. Drying air at the highest pressureconsistent with the plant design will result in therelationship between operating pressure and watercontent. Taking air at 100 PSIG as the normal pres-sure, a subsequent decrease in pressure results in asubstantial increase in the water to be removed. Athigher pressures the water content curve tends toincrease at a slower rate.EMPERATUREThe temperature of air entering the dryer usually isclose to the temperature at which it leaves the after-cooler. Saturated air at 100¡F saturated containsalmost twice the amount of moisture of saturated airat 80¡F. For every 20¡F increase in the temperature ofsaturated air, there is an approximate doubling ofthe moisture content. Thus it is desirable to operateThe moisture content of saturated air at a given temperature, in grains per cubic foot, is given inWith that in mind, a dryer specification is needed. * CAGI ADF 100 can beordered through the CAGI IRANDRYING Water vapor Water vapor Compressed airIn Compressed airOut Sweep air To provide a good basis for the purchase of eachtype of compressed air dryer the following samplespecifications are given:Refrigerant Type1.Inlet Conditions Flow scfm Operating Pressure Inlet Temperature2.Performance Outlet Dew Point Pressure Drop- 3.Design Pressure TemperatureAmbient Temperature- Minimum Maximum 4.Utilities______ Volts______ Phase______ Hz. Cooling Water Temperature Electric Enclosure NEMA-1 General Purpose NEMA-4 Weatherproof NEMA-7 Explosion Proof NEMA-12 Dust TightRegenerative Desiccant Type1.Inlet Conditions Flow scfm Operating Pressure Inlet Air Temperature2.Performance Outlet Dew Point Pressure Drop3.Design Pressure Temperature 4.Utilities______ Volts______ Phase______ Hz. ______ PSIG______ TemperatureWater______ F______ PSIGElectric Enclosure NEMA-1 General Purpose NEMA-4 Weatherproof NEMA-7 Explosion Proof NEMA-12 Dust TightSingle Tower Deliquescent Type1.Inlet Conditions Flow scfm Operating Pressure Inlet Air Temperature Ambient Temperature2.Performance Outlet Dew Point Pressure Drop- Maximum Allowa

14 ble 3.Design Pressure TemperatureAmbient
ble 3.Design Pressure TemperatureAmbient Temperature- Minimum Membrane Type1.Inlet Conditions Flow scfm Operating Pressure Inlet Air Temperature Ambient Temperature2.Performance Outlet Dew Point Pressure Drop- Maximum Allowable3.Design Pressure TemperatureAmbient Temperature- Minimum Maximum IRANDRYING These specifications are of a general nature for most plant and instrument and air applications. Add special requirements along with any additional data regarding the application.Certainly good suppliers are available who can assess your system and specify the drying equipment, buteven the finest supplier does a better job when the operator or owner or buyer of the apparatus is himself HATRYINGWhile the dryer is the heart of the matter, good dry-ing performance usually requires it to be supportedLEFTTORIGHTYPICALFLOWDIAGRAMSOFDRYINGSYSTEMSSingle Tower Deliquescent.Filters are shown in the flow diagrams as single com-ponents. Local operating conditions and selection ofequipment will dictate which filters may be requiredAlso dual filters and block valves may be considered.To ensure the expected performance and reliability ofthe compressed air system, good attention must beexercised in the selection of all components. Atypicalsystem may include several of the following items:to increase the pressure of the air tothat desired in the system. Numerous types andpressure ratings are available. Compressor dis-charge pressure must allow for pressure dropsthrough downstream treatment equipment, pipingto remove the heat of compression andcool the air to within 10¡F to 15¡F of the coolinging the compressor is condensed in the aftercooler.to remove liquids condensed by theaftercooler. An automatic trap discharges the liquidsto smooth compressor pulsations, andfunction as a reservoir of compressed air. It alsopermits liquid water, oil, and solid particulate matternot removed by the aftercooler-separator to settleout of the air stream. Adequate drain provision, withappropriate treatment, is essential.Areceiver before a dryer is filled with saturated air.Asudden demand for air exce

15 eding the dryer rat-ing, may result in o
eding the dryer rat-ing, may result in overloading the dryer and ahigher downstream dew point. Areceiver placedafter the dryer will be filled with air already drieding the dryer performance and presure dew point. IRANDRYING ISO CLASS ISO CLASS to remove solid and liquidentrainments which remain in the air or whichhave condensed in the piping. All dryers aredesigned for an inlet condition of only saturated airthe dryer.remove contaminants,such as the aerosols ofwater and oil, from anair stream by causingthe particles to unite, ordroplets formed may beremoved.Oil Vapor Filter Ðcompressors. Oil in thecompressed air system isbe hazardous. It can also contaminate desiccants,thereby reducing their ability to adsorb water. to remove water vapor. See Section Vfor a description of the compressed air dryer types.to remove dust, pipe scale, and desic-cant particles from the dry compressed air stream.All condensate discharges to sewer orITERATURENational Fluid Power Association ¥ Glossary of Terms for Fluid Power American National Standards Institute¥ ANSI Standard B93.2 Ð 1971Compressed Air & Gas Institute ¥ Compressed Air & Gas Handbook¥ ADF 100 Ð Refrigerated Compressed AirDryers Ð Methods for Testing and Rating¥ ADF 200 Ð Dual Tower Regenerative DesiccantCompressed Air Dryers Ð Methods for Testing¥ ADF 300 Ð Single Tower (Non-Regenerative)Desiccant Compressed Air Dryers Ð Methodsfor Testing and Rating¥ ADF 700 Ð Membrane Compressed Air DryersÐ Methods for Testing and Rating¥ Adsorption Ð C. L. Mantell IRANDRYING IRANDRYING A P ATEREMPERATURESHART OISTUREPERATURATEDIRORASAT IRANDRYING 7,000 grains = 1 pound1 pound = 0.833 gallons at 60¡F3-100¡F = .00007 gr/ft3 A ATURATEDEMPERATURESHART IRANDRYINGTo obtain the dew point temperature expected if the gas were1. Using Òdew point at pressure,Ó locate this temperature on A HART 2. Read horizontally to intersection of curve corresponding to3. From that point read vertically downward to curve corre-4. From that point read horizontally to scale on right hand side5. If dew point temperatures of atmospheric pressure are EWPOINTAT, ¡F.