How to Trap Steam Distribution Systems - Armstrong International, Inc.

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How To Trap Process Air HeatersProcess air heaters are used for drying paper, lumber, milk,starch and other products as well as preheating combustionair for boilers.Common examples of this type of equipment are processdryers, tunnel dryers, and combustion air preheaters.Compared with air heaters for space heating, process airheaters operate at very high temperature, 500°F not beinguncommon. These extremely high-temperature applicationsrequire high pressure (and occasionally superheated) steam.Trap Selection and Safety FactorDetermine the condensate load for process air heaters withthe following formula:Q =Where:Q = Condensate load in lbs/hrF = Cubic feet of air per minuteCp =F x Cp x d x 60 min/hr x ∆THSpecific heat of air in Btu/lb—°F(from Table CG-34, page CG-55)d = Density of air—.075 lbs/cu ft∆T = Temperature rise in °FH = Latent heat of steam in Btu/lb(Steam Table, page CG-3)Multiplying by a safety factor of 2—which is recommendedfor all constant pressure process air heaters—indicates thata trap with a capacity of 472 lbs/hr will be required. This isbased on one coil. For higher air temperature rises, additionalcoils in series may be required.Safety FactorsFor constant steam pressure, use a safety factor of 2:1at operating pressure differential. For modulating steampressure, use a safety factor of 3:1 at 1/2 of maximumpressure differential across the trap.InstallationGive piping for an entire piece of process air heatingequipment—including all steam trap connections—adequateallowance for expansion due to the wide temperature variations.Mount traps 10"-12" below the coils with a dirt pocketof at least 6". On both constant and modulated pressureheaters, install a vacuum breaker between the coil and thesteam trap. Install an air vent on each coil to remove air andother non-condensables that can cause rapid corrosion.See Fig. CG-44.Consider a safety drain if condensate is elevated afterthe trap or if back pressure is present. See page CG-47for piping diagram and explanation.EXAMPLE: What would be the condensate load on atunnel dryer coil handling 2,000 CFM of air and requiringa 100°F temperature rise? The steam pressure is 45 psig.Using the formula:Q =2000 x .24 x .075 x 60 x 100915Q = 236 lbs/hrFigure CG-44. Process Air HeaterModulating SteamControl ValveAir VentInverted BucketSteam TrapTrap DrainingStrainer Aheadof ModulatingSteam ControlValveVacuumBreakerAir VentAlternate F&Twith IntegralVacuum BreakerChart CG-13. Recommendation Chart(See Page CG-2 for “Feature Code” References.)EquipmentBeing Trapped1st Choice andFeature CodeConstant Pressure0-30psigAbove30 psig1st Choice andFeature CodeVariable Pressure0-30 psigAbove30 psigProcess AirHeatersAlternate Choice F&T IBLV Alternate Choice IBLV IBLV*Use IBLV above F&T pressure temperature limitations.PLEASE NOTE:1. Provide vacuum breaker wherever subatmospheric pressures occur.2. Do not use F&T traps on superheated steam.A, B, F, I, K, M IB IB B, C, G, H, L F&T *F&TArmstrong Steam and Condensate Group, 816 Maple St., P.O. Box 408, Three Rivers, MI 49093 – USA Phone: (269) 273-1415 Fax: (269) 278-6555www.armstrong-intl.com33CG-28
How to Trap Shell & Tube Heat Exchangers & Submerged CoilsSubmerged coils are heat transfer elements that areimmersed in the liquid to be heated, evaporated orconcentrated. This type of coil is found in virtually everyplant or institution that uses steam. Common examples arewater heaters, reboilers, suction heaters, evaporators andvaporizers. These are used in heating water for process ordomestic use, vaporizing industrial gases such as propaneand oxygen, concentrating in-process fluids such as sugar,black liquor and petroleum, and heating fuel oil for easytransfer and atomization.Different application requirements involving constant or variablesteam pressure determine which type of trap should beused. Trap selection factors include the ability to handle airat low differential pressures, energy conservation and theremoval of dirt and slugs of condensate. Three standardmethods of sizing help determine the proper type and sizetraps for coils.Safety Factor1. Constant Steam Pressure. INVERTED BUCKETTRAPS OR F&T TRAPS—use a 2:1 safety factorat operating pressure differentials.2. Modulating Steam Pressure. F&T TRAPS ORINVERTED BUCKET TRAPS.1. 0-15 psig steam—2:1 at 1/2 psi pressure differential.2. 16-30 psig steam—2:1 at 2 psi pressure differential.3. Above 30 psig steam—3:1 at 1/2 of maximumpressure differential across the trap.3. Constant or Modulating Steam Pressure withSyphon Drainage. An automatic differential condensatecontroller with a safety factor of 3:1 should be used.An alternate is an IBLV with a 5:1 safety factor.Apply the safety factor at full differential on constant steampressure. Apply the safety factor at 1/2 maximum differentialfor modulating steam pressure.Shell and Tube Heat ExchangersOne type of submerged coil is the shell and tube heatexchanger (Fig. CG-45). In these exchangers, numeroustubes are installed in a housing or shell with confined freearea. This ensures positive contact with the tubes by anyfluid flowing in the shell. Although the term submerged coilimplies that steam is in the tubes and the tubes are submergedin the liquid being heated, the reverse can also betrue, where steam is in the shell and a liquid is in the tubes.Trap Selection for Shell and Tube Heat ExchangersTo determine the condensate load on shell and tubeheaters, use the following formula when actual ratingis known.* (If heating coil dimensions alone are known,use formula shown for embossed coils. Be sure to selectapplicable “U” factor):Q =L x ∆T x C x 500 x sgHWhere:Q = Condensate load in lbs/hrL = Liquid flow in GPM∆T = Temperature rise in °FC = Specific heat of liquid in Btu/lb-°F (Table CG-33,page CG-55)500 = 60 min/hr x 8.33 lbs/galsg = Specific gravity of liquid (Table CG-33)H = Latent heat of steam in Btu/lb (Steam Table, page CG-3)EXAMPLE: Assume a water flow rate of 50 GPM withan entering temperature of 40°F and a leaving temperatureof 140°F. Steam pressure is 15 psig. Determine the condensateload.Using the formula:50 GPM x 100°F x 1 Btu/lb-°F x 500 x 1.0 sgQ == 2,645 lbs/hr945 Btu/lb* Size steam traps for reboilers, vaporizers and evaporators(processes that create vapor) using the formula forEMBOSSED COILS on page CG-30.Figure CG-45. Shell And Tube Heat Exchangers(Typical Piping Diagram)Steam MainBy-PassStrainerHot Water OutModulatingSteamControl ValveAir VentDrainHeat Exchanger(Steam in Shell)34CG-29Cold Water InUse safety drain F&T trapwhen going to overheadreturn. See page CG-47for explanation.To DrainPrimary TrapTo LowPressure ReturnArmstrong Steam and Condensate Group, 816 Maple St., P.O. Box 408, Three Rivers, MI 49093 – USA Phone: (269) 273-1415 Fax: (269) 278-6555www.armstrong-intl.comAlternate ToOverhead Return
Page 1 and 2: How to Trap Steam Distribution Syst
Page 3 and 4: How to Trap Steam Distribution Syst
Page 5 and 6: How to Trap Steam Tracer LinesSteam
Page 7 and 8: How to Trap Superheated Steam Lines
Page 9: How to Trap Space Heating Equipment
Page 14 and 15: How to Trap Shell & Tube Heat Excha
Page 16 and 17: How to Trap EvaporatorsEvaporators
Page 18 and 19: How to Trap EvaporatorsTable CG-22.
Page 20 and 21: How to Trap Jacketed KettlesFigure
Page 22 and 23: How to Trap Closed, Stationary Stea
Page 24 and 25: How to Trap Rotating Dryers Requiri
Page 26 and 27: How to Trap Flash TanksInstallation

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