ASHRAE REFRIGERATION SI CH 9-2010 REFRIGERANT CONTAINMENT RECOVERY RECYCLING AND RECLAMATION《制冷容器、回收、再循环及再回收》.pdf

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1、9.1CHAPTER 9REFRIGERANT CONTAINMENT, RECOVERY, RECYCLING, AND RECLAMATIONEmissions Types . 9.1Design 9.1Installation . 9.1Servicing and Decommissioning 9.1Training 9.2Leak Detection . 9.2Recovery, Recycling, and Reclamation 9.2ONTAINMENT of refrigerant is an important considerationCduring service an

2、d maintenance of refrigeration systems. Thepotential environmental effect of chlorofluorocarbon (CFC) and hy-drochlorofluorocarbon (HCFC) refrigerants on ozone depletion,and of these and hydrofluorocarbon (HFC) refrigerants on globalwarming, make it imperative that refrigerants are confined to close

3、dsystems and recovered during service and at the end of life. Con-tainment must be considered in all phases of a systems life, includ-ing (1) design and construction of leaktight and easily servicedsystems, (2) leak detection and repair, (3) recovery during service,and (4) recovery system disposal.

4、Additional reference can befound in ASHRAE Standard 147-2002.EMISSIONS TYPESRefrigerant emissions to the atmosphere are often genericallycalled losses, without distinguishing the causes. However, emissiontypes are very different, and their causes must be identified beforethey can be controlled. Clod

5、ic (1997) identified six types:Sources of fugitive emissions cannot be precisely located.Tightness degradation is caused by temperature variations, pres-sure cycling, and vibrations that can lead to unexpected and sig-nificant increases of refrigerant emission rates.Component failures mostly origina

6、te from poor construction orfaulty assembly.Losses during refrigerant handling occur mainly when charg-ing the system, and opening the system without previously recov-ering the refrigerant.Accidental losses are unpredictable and are caused by fires, ex-plosions, sabotage, theft, etc.Losses at equipm

7、ent disposal are caused by intentionally vent-ing, rather than recovering, refrigerant at the end of system life.DESIGNThe potential for leakage is first affected by system design. Everyattempt must be made to design systems that are leaktight for thelength of their useful service lives, and reliabl

8、e, to minimize theneed for service. Selection of materials, joining techniques, anddesign for easy installation and service access are critical factors indesigning leaktight systems.For example, leaktight service valves should be installed to allowremoval of replaceable components from the cooling s

9、ystem, andlocated for effective liquid refrigerant recovery.Systems should be designed to minimize refrigerant charge to re-duce the amount of released refrigerant in case of catastrophic loss.There are many opportunities for refrigerant charge reduction in ini-tial design. Heat exchangers, piping,

10、and components should be se-lected to reduce the amount of refrigerant in the system (but not atthe expense of energy efficiency).INSTALLATIONProper installation of air-conditioning and refrigeration systemsis critical to proper operation and containment during the useful lifeof the equipment. Tight

11、 joints and proper piping materials are re-quired. Later service requirements are minimized by proper clean-ing of joints before brazing, purging the system with an inert gas(e.g., nitrogen) during brazing, and evacuation to remove noncon-densables. Use an inert gas purge to prevent oxides, which ca

12、n con-taminate the system. Proper charging and careful systemperformance and leak checks should be performed. At installation,systems should be carefully charged per design specifications toprevent overcharging, which can potentially lead to a serious releaseof excess refrigerant, and make it imposs

13、ible to transfer the entirecharge into the receiver for service. The installer also has the oppor-tunity to find manufacturing defects before the system begins oper-ation.SERVICING AND DECOMMISSIONINGProper service is critical in reducing emissions. Refrigeratingsystems must be monitored to ensure t

14、hat they are well sealed,properly charged, and operating properly. The service technicianmust study and maintain service records to determine any history ofleakage or malfunction. The equipment should be checked to detectleaks before significant charge is lost. During system maintenance,refrigerant

15、should not be released; instead, it should be isolated inthe system or recovered by equipment capable of handling the spe-cific refrigerant.An up-to-date maintenance document allows the user to monitoradditions and removals of refrigerant, and whether rechargingoperations are actually associated wit

16、h repairs of leaks. In a retrofit,the new refrigerant must be noted in the service record and clearlymarked on equipment. Technicians must follow manufacturersretrofit procedures, because some system components may beincompatible with different refrigerants. Failure to perform properretrofits may re

17、sult in system failure and subsequent loss of refrig-erant.When a system is decommissioned, recover the refrigerant forrecycling, reuse, or disposal. Special care is required to properlyclean or reclaim used refrigerants to industry-recognized standards(see AHRI Standard 700).The preparation of this

18、 chapter is assigned to TC 3.8, Refrigerant Contain-ment.9.2 2010 ASHRAE HandbookRefrigeration (SI)TRAININGTechnician training is essential for proper handling and contain-ment of refrigerants. Training must provide a basic understanding ofthe environmental effects of refrigerants; recovery, recycli

19、ng, andreclamation of refrigerants; leak checks and repairs; and introduc-tion to new refrigerants. The service operator requires continuoustraining to understand new designs, new refrigerants and their com-patibility with lubricants, new low-emission purge units, retrofittingrequirements, and servi

20、ce practices.LEAK DETECTIONLeak detection is a basic element for manufacturing, installing,and servicing systems, because it makes it possible to measure andimprove containment of refrigerant. Leak detection must be per-formed as the final step after the system is completed in the factoryor in the f

21、ield. It is good practice to regularly leak test the equip-ment.There are three general types of leak detection: global, local, andautomated performance monitoring.Global DetectionThese methods indicate whether a leak exists, but do not identifyits location. They are useful at the end of constructio

22、n, and when thesystem is opened for repair or retrofit.System Checking. These approaches are applicable to a systemthat has been emptied of its charge.Pressurize the system with a tracer gas and isolate it. A pressuredrop within a specified time indicates leakage.Evacuate the system and measure the

23、vacuum level over a speci-fied time. A pressure rise indicates leakage.Place the system in a chamber and charge with a tracer gas. Thenevacuate the chamber and monitor it for leaks with a mass spec-trometer or residual gas analyzer.Evacuate the system and place it in an atmosphere with a tracergas.

24、Monitor for leaks with a mass spectrometer or residual gasanalyzer.Many of these tests use a tracer gas, often nitrogen or helium. Itis not good practice to use a refrigerant as the tracer gas.Continuous Monitoring During Operation. Electronic leakdetectors in machinery rooms may be effective if (1)

25、 they are sensi-tive enough to refrigerant dilution in the air, and (2) air is circulatedproperly in the room. Note, however, that these detectors only mon-itor equipment in the room.Receiver Monitoring. On large systems that have a receiver andreceiver-level monitoring device, the following procedu

26、re can mon-itor refrigerant levels over time:1. Set evaporator pressure regulator and solenoid valves fully open.2. Close heat reclaim valve (if equipped).3. Open split condenser valve (if equipped).4. Ensure that no system or circuit is in defrost.5. Pump refrigerant into receiver and condenser unt

27、il pressurereaches 35 kPa minimum.6. Allow system to equalize and pump down again to 35 kPa min-imum.7. Check and record receiver level.This level should remain fairly constant if all of the system set-tings are consistent. From this record, large leaks over time can bedetected.Local DetectionThese

28、methods pinpoint locations of leaks, and are usually usedduring servicing. Sensitivity varies widely; it is usually stated asppm/volume but, for clarity, mass flow rates (g/year) are often used.Table 1 compares sensitivities of various testing methods.Visual checks locate large leaks (85 g/year) by

29、seeking telltaletraces of oil at joints.Soapy water detection (bubble testing) is simple and inexpen-sive; a trained operator can pinpoint leaks of 50 g/year maximum.Tracer color added to the oil/refrigerant mixture shows the leakslocation. The tracer must be compatible with the various materialsuse

30、d in the refrigeration circuit.Electronic detectors of different types can detect leaks as low as3 to 50 g/year, according to their sensitivity. They must be usedwith proper care and training.Ultrasonic detectors register noise generated by the flow of gasexiting through the leak, and are less sensi

31、tive than electronic de-tectors; they are easily disturbed by air circulation.Helium and HFC mass spectrometers with probes or hoods candetect leaks at very low levels (less than 1.5 g/year).Automated Performance Monitoring SystemsMonitoring parameters such as temperatures and pressures helpsidentif

32、y any change in the equipment. It also provides data useful forperforming diagnostics on the condition of heat exchanger surfaces,proper refrigerant pumping, and shortage of refrigerant charge.Automated diagnostic programs are nw being developed to producepre-alarm messages as soon as a drift in ref

33、rigerant charge isobserved. These developments are in their early stages, but their gen-eral adoption would give better control over discovering refrigerantleaks. Equipment room monitors are currently used. On low-pres-sure systems, it is also possible to monitor equipment tightness bymonitoring pur

34、ge unit run time, which can indicate leaks.RECOVERY, RECYCLING, AND RECLAMATIONThe procedures involved in removing contaminants when recy-cling refrigerants are similar to those discussed in Chapter 7. Ser-vice techniques, proper handling and storage, and possible mixingor cross contamination of ref

35、rigerants are of concern. Building own-ers, equipment manufacturers, and contractors are concerned aboutTable 1 Leak Test Sensitivity ComparisonTesting MethodLeakage Rate at 101.325 kPa, cm3/s1101102103104105106107109Bubble testing (air under water) X X XPressure decay X X XVacuum decay (outside-in)

36、 X X X XAcoustical (ultrasonic) X X X XAtmospheric accumulation X X X X XHalogen sniffer (heated diode) X X X X X XHalogen sniffer (infrared) X X X X X X XHydrogen sniffing X X X X X X XHelium sniffing X X X X X X XMass spectrometer (hard vacuum) X X X X X X X X XRefrigerant Containment, Recovery, R

37、ecycling, and Reclamation 9.3reintroducing refrigerants with unacceptable levels of contaminantsinto refrigeration equipment. Contaminated refrigerant can nega-tively affect system performance, and may lead to equipment failureand release of refrigerant into the atmosphere.Installation and Service P

38、racticesProper installation and service procedures, including proper evac-uation and leak checking, are essential to minimize major repairs.Service lines should be made of low-permeability hose material andshould include shutoff valves. Larger systems should include isola-tion valves and pumpdown re

39、ceivers. ASHRAE Standard 147describes equipment, installation, and service requirements.Recovering refrigerant to an external storage container and thenreturning the refrigerant for cleanup inside the refrigeration systemis similar to the procedure described in Chapter 7. Some additionalair and mois

40、ture contamination may be introduced in the serviceprocedure. In general, because contaminants are distributedthroughout the system, the refrigeration system must be cleanedregardless of whether the refrigerant is isolated in the receiver,recovered into a storage container, recycled, reclaimed, or r

41、eplacedwith new refrigerant. The advantage of new, reclaimed, or recycledrefrigerant is that a properly cleaned system is not recontaminatedby impure refrigerant.ContaminantsContaminants found in recovered refrigerants are discussed indetail in Chapter 7. The main contaminants are moisture, acid,non

42、condensables, particulates, high-boiling residue (lubricant andsludge), and other condensable gases (Manz 1995).Moisture is normally dissolved in the refrigerant or lubricant,but sometimes free water is present. Moisture is removed by passingthe refrigerant through a filter-drier. Some moisture is a

43、lso removedby lubricant separation.Acid consists of organic and inorganic types. Organic acids arenormally contained in the lubricant and are removed in the oil sep-arator and in the filter-drier. Inorganic acids, such as hydrochloricacid, are removed by noncondensable purging, reaction with metalsu

44、rfaces, and the filter-drier.Noncondensable gases consist primarily of air. These gases cancome from refrigeration equipment or can be introduced during ser-vicing. Control consists of minimizing infiltration through properequipment construction and installation (ASHRAE Standard 147).Proper service

45、equipment construction, connection techniques, andmaintenance procedures (e.g., during filter-drier change) also reduceair contamination. Typically, a vapor purge is used to remove air.Particulates can be removed by suction filters, oil separators, oilfilters, and filter-driers.High-boiling residues

46、 consist primarily of refrigerant lubricantand sludge. Because different refrigeration systems use differentlubricants and because it is a collection point for other contami-nants, the lubricant is considered a contaminant. High-boiling resi-dues are removed by separators designed to extract lubrica

47、nt fromvapor-phase refrigerant, or by distillation.Other condensable gases consist mainly of other refrigerants.They can be generated in small quantities by high-temperature oper-ation or during a compressor motor burnout. To maintain purity ofthe used refrigerant supply as well as the performance a

48、nd durabilityof the particular system, refrigerants should not be mixed. In gen-eral, separation of other condensable gases, if possible, can only bedone at a fully equipped reclamation center. Mixed refrigerants are a special case of other condensable gasesin that the refrigerant would not meet pro

49、duct specifications even ifall moisture, acids, particulates, lubricant, and noncondensableswere removed. Inadvertent mixing may occur because of a failure toDedicate and clearly mark containers for specific refrigerantsClear hoses or recovery equipment before switching to a differentrefrigerantTest suspect refrigerant before consolidating it into large batchesUse proper retrofit proceduresRecoveryTo recover means to remove refrigerant in any condition from asystem and to store it in an external container. Recovery reducesrefrigerant emissions to the atmosphere and is a necessa