PRESSURE-SWING DESICCANT COMPRESSED AIR …

1 DH SERIES PRESSURE-SWINGDESICCANTCOMPRESSED AIRDRYERSH ankison DH Series DESICCANT dryers Provide pressure dew points of -40OF, -100OF (-40OC, -73OC)and lower Eliminate water from systems exposed to sub-freezing temperatures Reduce moisture content in critical applications, outlet concentrations of 1 ppb @ 100 psig, (7 kgf/cm2) are possiblePrinciple ofOperationPressure-swing dryersA regenerative DESICCANT dryerconsists of two (dual) towers filledwith DESICCANT . The DESICCANT ( alumina) attracts(adsorbs) water vapor onto its sur-face. Unlike deliquescent chemi-cals, which are used up in theprocess of drying, desiccants canbe regenerated and reused. The two towers are switched onand off-stream, alternatingbetween drying and regenerationso that dry DESICCANT is continu-ously exposed to the air stream. In PRESSURE-SWING (heatless) dryers, DESICCANT is regenerated byexpanding a portion of the driedair (called purge air) to atmospher-ic pressure and passing it over theoff-stream bed.

2 This swing inpressure causes the expanded airto become very dry. The drypurge air pulls (desorbs) moisturefrom the DESICCANT and carries itout of the dryer . Have a lower initial cost than heated type dryers Are simple and reliable - no heaters or blowers to maintain Maintain a constant outlet dew point and temperature - no thermal or dew point spikes after tower switchover Offer long DESICCANT life 3 air enters the dryer , flows through inlet switching valve(A), Tower I where the air isdried, and a system of checkvalves to the dryer outlet. 2. A portion of the dried air is diverted through adjustablepurge rate valve (C), purge ori-fice (D) where it is throttled tonear atmospheric pressure, andTower II. dry, low pressure air, called purge air, regenerates the des-iccant in Tower II by carrying offthe water collected during thedrying stage.

3 The purge air isthen exhausted to atmospherethrough purge/repressurizationvalve (E) and purge muffler (F). regeneration, purge/repressurization valve (E)closes and Tower II fully repres-surizes to line pressure. switching valve (G) then opens, inlet switching valve (A)closes, and purge/repres-surization valve (H) opens. Inletair is now being dried in TowerII while Tower I is being regen-erated. The operation of the inlet switch-ing and purge/repressurizationvalves is sequenced by either afixed time controller (adjustablefor either a 4 or 10 minute cycle)or the optional Sensatherm purge saving system which auto-matically matches purge air use tothe demand on the outletpressure dew points Large DESICCANT beds [ lbs ( kg) of DESICCANT /tower/scfm] Ensures second contact to dry saturatedair at the dryer inlet to thedesired dew point 30% extra DESICCANT provided to compensate for natural top perfor-mance over expected 3 to 5year DESICCANT bed life Large flow diffusers ensure even flow distribution through channelingMinimum purge air.

4 The lowest in the industry Tower design saves 98% of the heat of heatmaintains purge air temperatureduring the purge air s ability to carryoff theamount of purge air required Drying and purging in counterflow notwasted when wet air travelsthrough dry DESICCANT Ability to match purge air use to the demand on the dryer Economizer automatic purge saving systemHankison DH Series dryers produce consistent outlet pressure dew minimum purge air maximum service lifeLong DESICCANT life Towers sized so that air velocity through the bed won t movementand excessive DESICCANT dusting Slow and complete repressuriza-tion of off-stream tower pre-vents bed movement and desic-cant eliminatesdownstream pressure fluctua-tions Upflow water andheavy contaminants to drop outof the air stream as they enter protects bed from contaminantsto be discharged when towerdepressurizesDH Series Features5 Optimally sizedtowers, offering: Performance - large DESICCANT beds ensure sufficient consistent extra desiccantto compensate for initial desic-cant aging Efficiency - sized to retain the heat of air of purge air required Reliability - sized to prevent bed fluidization and DESICCANT desiccantand valve lifeEasy operationStandard instrumentation: Tower pressure gauges Moisture indicator -alerts operator of ele-vated dew point Purge flow indicator Control panel with.

5 On/off switch Tower status lights Cycle/mode indicator lights (shows selection of 4 or 10 minute cycle or test mode) Switching failure alarm - indicates if a tower fails to pressurize or depressurize properly Economizer setting indicator lightsAll instruments and controls arefront mounted for easy visibilityand useEasy to maintain Separate fill and drain ports for ease of DESICCANT replacement Cleanable stainless steel flow diffusers/support screensSafe Pressure relief valves for each tower - mounted after flow dif-fuser to prevent clogging bydesiccant beads Heavy duty mufflers for quiet operation - dryers shipped withextra set of inserts - if backpressure increases after start-up, replace inserts - allowsstart-up of dryers with mufflersin place (Relief valve in mufflersprevents excessive back pres-sure) ASME code constructed (modelsDH-115 and larger are stamped) NEMA 4,4X electrical construc-tion standard 6 Reliable solid state controller Can be field adjusted for.

6 10minute cycle [produces -40OF (-40OC) dew point @ 100OF (38OC)inlet] or 4 minute cycle [pro-duces -100O(-73OC) dew point @ 100OF (38OC) inlet] Includes Purge Economizer Switch - allows purge air reduc-tion when dryer operating atreduced loads Test Mode - Allows manual sequencing to verify valve operationOptional - Sensatherm auto-matic purge saving systemAccurate purgeflow control Adjustable, highly accuratecontrol valve Flow always travels through valve in same direction toensure consistent flow pattern Separate control valve and orifice allow indication of purgeflow rateDurable air control valves formaximum reliabilityInlet and purge/repressuriza-tion valvesModels DH-25 thru DH-260 Top-of-the line ASCO pilot operated solenoid valvesModels DH-370 and larger Air operated butterfly valves offer high cycle life Resilient elastomeric seats for leak free service Low profile.

7 Nickel plated disksoffer low pressure drop Stem bushings ensure smooth opeeration No field lubrication required Repair kits available - can be serviced in fieldDH Series Features7 Options Models for higher working pressures Models for severe environments, process industries, drilling rigs, : Prefilters - eliminate solid and liquid contaminants - prolongthe life of the DESICCANT bed Afterfilters - remove DESICCANT dust (filters for 1 and available) Factory mounting of filter packagesElectrics: Choice of 120V/1ph/60Hz,110V/1ph/50Hz, 240V/1ph/60Hz,220V/1ph/50Hz, 12 VDC, 24 VDC NEMA 7 optional (NEMA 4/4X standard)Instrumentation: High dew point alarm Dew point monitorActuators Pneumatic actuators combine power and durability Double acting rack and pinion uses air power to both openand close valve Dual pistons offer large control area, high torque, rapidresponse Position indicator shows if valve is open or closed Valves may be operatedmanually Actuators isolated from air stream, can t be contaminatedby incoming moisture Purge/repressurization valves include a spring assist to holdthem closed prior to start-upand upon loss of pressure -protects DESICCANT bed fromoutside contamination andallows easy start-up Pilot air filtered through onemicron in-depthfilter and depend-ably controlled forsure actuation NAMUR mount pilot valves with bidirectional seal, balanced spool.

8 And hermetically sealed coilCheck valves Soft seated for sure closuresand minimal wearActivated aluminadesiccant Won t disintegrate in water (like silica gel) High crush strength Resistant to abrasionHankison DH Series DESICCANT dryersare completelyassembled, piped,and wired at thefactory, shippedready for operationafter utility hook-up Structural steel frame complete with floor stand Shipped with full charge of DESICCANT Lifting lugs for ease of transporting Optional factory mounting of pre and afterfiltersNRTL/CStandard models are CSA (CanadianStandards Association) certified, attestingconformity to both CSA standard No. 236 and UL (UnderwritersLaboratories) Standard UL automaticpurge saving system Minimizes purge air usage when operating at reduced loads Automatically matches purge air use to the demand on the systemAt full load, a tower contains fiveminutes of drying capacity.

9 At lessthan full load, the amount ofpurge air used may be minimizedby keeping a tower on line until itsfull drying capacity is utilized. For example, at 50% of load atower is able to stay on line for 10minutes (instead of the usual 5), at33% of load, it is able to stay online for 15 minutes. By doing this,purge air use is matched to thedemand on the system - at 50% ofload, 50% of the normal purge airis used; at 33% of load, 33% of thenormal purge air is used. Hankison s patented Sensathermpurge saving system matchespurge air use to the demand onthe dryer by monitoring thechanges in temperature within thedesiccant beds. These changes arethe result of heat that is releasedduring the drying stage (heat ofadsorption) and readsorbed duringthe regeneration stage. Thedegree of temperature change isan indirect measure of the watervapor content in the compressedair system and is used to deter-mine the time a tower stays online during the drying transducers (thermistors) are used as sensingdevices - they are simpler, morereliable, and more rugged thanthe humidity, pressure, and flowtransducers used by used on the Sensatherm system require system is based on saving the heat of adsorption - towersswitch before heat is purge air efficiency andminimizing the amount of purgeair :1.

10 As Tower II goes off line and begins the regeneration stage,sensor B1 takes a temperaturereading. the end of the regeneration stage, sensor B1 takes anotherreading. Sensatherm s microprocessoruses this temperature differenceto calculate the temperature risethat will occur during the dryingstage as the bed becomes fullyloaded. Tower II returns to the drying stage, sensor B2 takes areading and begins monitoringthe temperature rise. 5. When the calculated tempera-ture rise occurs, indicating thatthe bed is fully loaded, theprocessor signals the Tower togo off-line for regeneration. Features: Choice of operating modes Two fixed cycle times - 10 minute cycle for -40OF (-40OC)outlet dew point or 4 minutecycle for -100O(-73OC) outletdew point Choice of -40OF, 0OF, or +40OF (-40OC, or + ) out-let dew point in the demandmode Tower Status Lights Demand meter - indicates average demand on the dryer Alarms for switching or temperature probe failure Diagnostic mode - A complete maintenance tool - permits man-ual sequencing through dryeroperation to verify condition ofvalves and temperature probes A2A1B2B1100 F102 F110 F115 F108 F100 F98 F98 F98 F97 F90 F85 F9 Prefilter/Afterfilter packagesHankison integrally mounted pre-filter/afterfilter packages include ahigh efficiency oil removal filterpiped to the inlet of the dryer anda one micron particulate filterpiped to the outlet of the Hankison coalescing type oilremoval filter prefilters the inletair and protects the DESICCANT bedfrom oil contamination.