Filter Cloth Materialslower operating costsPEEK™ replacement screens excel inhigh temperature and aggressivechemical environments. They aredesigned to provide improved per-formance and lower operating costsfor screeners, filters, dryers andother equipment. Material offersexcellent chemical resistance inenvironments up to 500°F. Pore sizesdown to 12 microns are available.Sefar America Inc.

Use InfoLINK 4H1103 or Call 800-287-0093

Case Scalefor in-motion weighingAC4000 Case Scale’s design insuresreliability and maintenance-freeoperation. Weightable is virtuallydamage proof, with overload pro-tection up to 1000 pounds.Controlled by AC4000 electronics,scale is capable of weighing up to140 packages per minute, depend-ing on package length. Case scalehas four 250-lb. steel load cells inthe conveyor section that elimi-nates any off-center loading errors. Thermo Electron Corp.

Use InfoLINK 4H1102 or Call 800-287-0093Valve ActuatorFM-approved

Watchdog® Fusible link Shutoff ValveActuator is a self-contained, spring

loaded device that automaticallyshuts off or opens 1/4” through

4” fire safe ball valves to con-tain spreading of flammableor toxic material in danger-ous situations. Availablewith heat activated ThermalLinks or ETL Link elements,actuators can also be man-ually operated as standardfire safe valves. EssexFluid Controls

Use InfoLINK 4H1101 or Call 800-287-0093

PRODUCTS, SYSTEMS & SERVICES FOR THE GLOBAL CHEMICAL PROCESSING INDUSTRY

AUGUST 2004Use

To obtain immediate product information online log ontowww.chemicalequipment.com• Identify the InfoLINK code

(example 4X1254)• Enter the code in the InfoLINK search

window• Click "Go" for product info• Or, simply call 1-800-287-0093

� � ���

��

���

Slurry & Metering PumpsGLV Series valveless meter-ing pump from NeptuneChemical Pump is designedto eliminate gas lockingduring sodium hypochloriteinjection. Pump is designedspecifically for 12-15%sodium hypochlorite orother chemicals withsevere off gassing prob-

lems. More details are available in the Slurry &Metering Pumps Spotlight on Page 14.

THERMAL PROCESSING &

HEAT TRANSFERISSUE

THERMAL PROCESSING &

HEAT TRANSFERISSUE

Care And Feeding Of BrazedAluminum Heat Exchangers

Brazed aluminum plate-finheat exchangers are highlyefficient heat transferdevices that represent aquantum leap in technology and design. See page 20 for further details.

Scales & Weighing SystemsHardy Instruments’CompactLogix® WeighScale Module is a singlechannel PLC-style mod-ule optimized for usewith Allen-BradleyMicroLogix™ 1500 and CompactLogix™

controllers. Further information on this andother weighing equipment is on page 10.

FEATURE ARTICLE

LATEST INNOVATIONS

by Dan Markussen, Principal SalesEngineer and Account Manager forChart Industries’ Heat ExchangerGroup

Brazed aluminum plate-fin heatexchangers are highly efficientheat transfer devices that repre-

sent a quantum leap in technology anddesign. Produced in a vacuum furnacethat joins the fins and parting sheet at aspecific temperature, they are used for

a wide range of cryogenic andnon-cryogenic applications,including industrial gas produc-tion, natural gas processing,refinery and petrochemical pro-cessing, and hydrogen and heli-um liquefaction.

Brazed aluminum plate-finheat exchangers offer the ben-efits of compact design (typi-cally 20% the size of compara-ble performance carbon orstainless steel shell and tubeexchangers), close tempera-ture approaches, flow optionsand a unique ability toexchange heat with multiplestreams. Collectively, thesehelp to lower installation andoperating costs and minimizeengineering, insulation, sup-port systems, testing, docu-mentation, transportation, andsite arrangements.

That said, the performance,safety and quality characteristics ofheat exchangers can only be ensuredthrough proper installation and care.Given the impact of heat exchangers onoverall plant operational performance,a piecemeal strategy of installation andmaintenance is simply not sufficient.Rather, the potential of brazed alu-minum plate-fin heat exchangers canbest be realized by strictly adhering toestablished standards and procedures,from the time of initial purchase andinstallation onward.

Purchasing Considerations:Codes: The design, construction and

testing of brazed aluminum plate-finheat exchangers are governed by rec-ognized international codes that applyto pressure vessels. Brazed aluminumplate-fin heat exchangers from ChartIndustries are designed and manufac-tured in accordance with Section VIII,Division I of the ASME Pressure VesselCode, carry the “U” stamp, and are reg-istered with the National Board ofBoiler and Pressure Vessel Inspectors.Associated piping is normally designedand manufactured in accordance withthe ASME B31.3 Piping Code.

Considerations: Consideration shouldbe given only to exchangers that meetone of the recognized internationaldesign codes, and adhere to strict quali-ty control procedures, including:

• Hydrostatic and pneumatic prooftesting

• Performance flow testing• External and vacuum helium leak

detection• Dye penetrant and radiographic

testingIdeally, a total commitment to quality

and reliability should be manifestedthrough full accreditation to EN ISO9001.

Finally, customers and/or users ofbrazed aluminum exchangers shouldonly consider suppliers that conform tothe standards of ALPEMA (BrazedAluminum Plate-Fin Heat ExchangerManufacturers’ Association). ALPEMAstandards provide consistent qualityand conformance guidelines for thedesign and manufacture of brazed alu-minum exchangers. More informationregarding ALPEMA may be obtainedfrom www.alpema.org.

Installation ConsiderationsInitial Inspection: Upon arrival, a

heat exchanger should be inspected forshipping damage and/or contamination.For units shipped unpressurized, checkunder the shipping covers for contami-

The Care And Feeding Of BrazedAluminum Heat Exchangers

Brazed aluminum plate-fin heatexchangers offer the benefits ofcompact design (typically 20%

the size of comparable per-formance carbon or stainless

steel shell and tube exchangers), close temperatureapproaches, flow options and aunique ability to exchange heat

with multiple streams.

AArrttiicclleeFFeeaattuurree

nation of the port openings. For unitsshipped pressurized (normally to 15psig) with dry air or nitrogen, eachstream should include a valve and cou-pling to which a pressure gauge can bemounted. A positive pressure should beindicated on the gauge when the valvesare opened. If a stream does not indicatea positive pressure it should be repres-surized with dry air or nitrogen to 15psig. If, after repressurizing, the positivepressure is not maintained, the valveand couplings should be checked forleakage and replaced if they are deter-mined to be the source of leakage. If theleakage continues, the manufacturershould be contacted for resolution.

Storage: Store heat exchangers in anindoor location away from any primarywork. Exchangers that are shipped inprotective crates or on wood or steelchannel skids should be stored in theoriginal shipping package. Exchangersshould not be stacked unless the pack-aging has been designed specifically forstacking. For properly designed packag-ing, stacking should be limited to twohigh and to exchangers of the same size.

The storage area should providelevel, uniform support with gooddrainage. It should be located in an areacharacterized by minimal temperaturefluctuations and low vibration and bekept away from fluids that are corrosiveto aluminum. Additionally, exchangersshould be properly covered and sealedto prevent dirt, sand, water or other for-eign materials from entering nozzles,ports or other openings.

Lifting and Handling:Before moving an exchanger, con-

firm its weight, dimensions and lift con-nection locations. Select the appropri-ate hoisting machines, spreader bars,slings, shackles and other material han-dling tools to match the height andweight of the exchanger, as well as theangle and direction of the hoisting. Alifting diagram is often provided by theexchanger vendor that describes spe-cific lifting instructions.

Pipe Loads:Manufacturers provide the maxi-

mum allowable bending moment andthe axial loads that can be safelyapplied at each nozzle location of theexchanger. Sufficient piping stress

analysis should be conducted to assureapplied loads are within manufacturers’specified limits.

Dryout:Purge and dryout the exchanger

prior to start up in order to removemoisture and heavy hydrocarbons thatmay freeze out at low operating tem-peratures. A thorough dryout must beperformed at the commissioning andafter subsequent shutdown wheremoisture may have reached theexchanger. A warm dry gas should beused to achieve adequate dryness. Alldead legs in the piping should also bedrained and purged.

Maintenance And Care ConsiderationsThermal Stresses: While manufactur-

ers of leading brazed aluminum plate-finheat exchangers designtheir products for thespecified pressure loads,potentially significant ther-mal stresses can arisefrom unsteady operatingconditions such as largeflow fluctuations, unstableflow in boiling channels, orinadequate plant controlsystems, as well as tran-sient operating conditionsthat include start-up, shut-down, plant upsets, derim-ing, and cool-down/warm-up cycles. To reduce thepossibility of damage or failure of theheat exchanger, consider the followingguidelines:

• Regulate the pressure and externalloads and limit temperature differ-ences between adjacent streams atany point in the heat exchanger tothose specified by the manufacturer

• When deriming, bring the exchang-er back to operating conditionsslowly to avoid excessive thermalstress. Follow a manufacturers’ rec-ommended practice when movingsignificantly out of the specifiedoperating range of the equipment.

• Exercise care in applications wherea liquid is totally vaporized withinthe exchanger. Boiling to total dry-ness can produce large tempera-ture differences and induce flowinstabilities

• Design and operate plant equip-

Heat exchangers from Chart Industriesare designed and manufactured inaccordance with Section VIII, Division Iof the ASME Pressure Vessel Code,carry the “U” stamp, and are registeredwith the National Board of Boiler andPressure Vessel Inspectors.

ment and piping connected to theexchanger to prevent flow excur-sion and instabilities

• Limit frequently repeated temperaturefluctuations of any stream to + 1°C

Where any of the above conditionsare a concern, a user should consultwith the manufacturer to determine ifthe exchanger is within its acceptableoperating range.

Fouling & Plugging: Fouling andplugging in brazed aluminum exchang-ers is rare due to the fact that theprocesses in which the equipment istypically used are clean. However,before purchasing brazed aluminumplate-fin heat exchangers, fluid condi-tions must be examined for the pres-ence of solids and foreign particleswhich could form deposits duringoperation - especially in low tempera-ture regions.

Although fouling may not be causedby the process streams themselves, it ispossible that fouling may arise fromcontaminants in the process fluids. Atypical example is the use of seal oilwith refrigerant streams, which coulddeposit as a solid film on the fin sur-faces and reduce the thermal perform-ance of the exchanger.

If the liquid/solid transformation ofthe fouling agent is reversible with tem-perature, changing the operating condi-tions of the heat exchanger and thuswarming up the fouled zone may elimi-nate the deposits. In cases where this isnot effective, solvent cleaning may beused. Brazed aluminum plate-fin heatexchangers can be modified ordesigned to incorporate solvent injec-tion systems.

Plugging occurs when fin channelsinside an exchanger are blocked bysolid particles that entered the unit.Plugging can be detected by higherpressure drop in affected streams anddiminished heat transfer performance.Typically, thermal performance isaffected by the plugging medium beingdistributed to various passages andthroughout the width of the exchanger.To prevent plugging, check the cleanli-ness of the connecting pipes to ensurethat rust, debris and dust does notenter the exchanger. Filters on the feedstreams should be installed upstreamof the exchanger where there is a possi-bility of contaminating the processfluid. A recommended mesh size of 177

microns (80 Tyler) is capable of cover-ing most applications.

Remedy for Fouling & Plugging: Ifthe heat exchanger is fouled orplugged, several options exist for clean-ing it. When the fouling is solid andcoats the fins in the heat exchanger, theexchanger will typically need to becleaned by chemical removal through aseries of deriming, back flushing, anddrying procedures.

Deriming and back flushing involvesthe use of heat and solvents to removehydrates, heavy hydrocarbons, waxymaterials, compressor oils or other sol-uble matter that freeze or collect in theheat exchanger.

When systems for injecting methanolduring operation have not been provid-ed, shut down and purge the heatexchanger and allow it to warm anddefrost itself by natural heat leak or byan approved derime procedure.Typically, the combination of warmingand back flushing a solvent such astrichloroethane, toluene, propylene, ormethanol prove successful for this pur-pose. However, cleaning solvents shouldalways be selected with regard to thesuspected fouling agent. If the foulingagent is unknown, a sample should bechemically analyzed to determine itscomposition.

If a water based solvent is used toderime or back flush, or if water acci-dentally gets introduced into the heatexchanger, the exchanger must be com-pletely dried before returning to servicein order to prevent plugging or rupturecaused by freezing. Use dry air, nitrogenor other dry gas.

If the heat exchanger is fouled orplugged by particulate matter, backpuffing procedures are typically suc-cessful in cleaning the exchanger.

Since particulates normally causeblockages in the heat exchanger at theinlet ports and distributors, puffing inthe reverse direction of normal operat-ing flow is required to prevent pushingthe particulates farther into the heatexchanger. The back puffing procedureinvolves attaching a rupture disk to theinlet nozzle or flange of the heatexchanger stream to be backpuffed andpressurizing the stream with a dry gasup to the manufacturer’s approved pres-sure. However, extreme caution shouldbe exercised as the rupture of the diskand the release of gas can result in a

rapid discharge of gas and flying debriswhich could cause serious- and poten-tially fatal - personal injury. It is prudentto discuss the procedure and verify therecommended pressure with the heatexchanger manufacturer prior toattempting the procedure.

When back puffing, the pluggedstream is slowly filled with dry air ornitrogen until the rupture disk bursts. Ifthe intended rupture pressure isreached and the rupture disk has notburst, the stream should be depressur-ized and a new rupture disk installed.

The sudden release of gas out of theexchanger will help dislodge the partic-ulate matter. This back puffing proce-dure should be repeated five to tentimes, or until the amount of particulateremoved becomes minimal and the dis-charge cloud is clear.

Process Environments ContainingMercury: Longtime fears about mer-cury’s corrosive effects on aluminumhave fueled some reluctance toembrace brazed aluminum technology.In reality, mercury will only react withcertain alloys of aluminum and thenonly when liquid mercury is allowed toexist in contact with the heat exchang-er and there is water present.

Mercury removal systems upstreamof the exchanger are commonlyinstalled so that brazed aluminumplate-fin heat exchangers may be usedwith streams containing mercury.Operators may also use special shut-down procedures to restrict moistureand maintain temperatures below 100°C. In addition to mercury removal sys-tems, equipment from Chart Industriescan be designed to be mercury tolerant.Chart’s proprietary mercury-tolerantdesigns allow corrosive mercury to bepresent in the aluminum exchangerwithout causing the exchanger to fail.

Leaks: A leaking heat exchangershould be repaired as soon as possible.Prolonged operation may lead to fur-ther damage, especially when the causeis due to cyclical thermal or mechanicalfatigue. Continued operation of anexternally leaking exchanger installedin a perlite insulated cold box may leadto further damage and increased leak-age from perlite erosion.

Chart Industries Energy & Chemicals Group

Reprinted with permission from Chemical Equipment