ASHRAE REFRIGERATION IP CH 26-2010 MARINE REFRIGERATION《船舶制冷》.pdf

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1、26.1CHAPTER 26MARINE REFRIGERATIONRefrigeration Load. 26.1Refrigeration System 26.1Cargo Holds. 26.2SHIPS REFRIGERATEDSTORES 26.4Commodities 26.5Storage Areas. 26.5Ship Refrigerated Room Design. 26.6Specific Vessels 26.6FISHING VESSELS 26.7Refrigeration System Design 26.7Refrigeration with Ice. 26.7

2、Refrigeration with Seawater. 26.8Process Freezing and Cold Storage. 26.8ARINE refrigeration systems are used aboard seagoing ves-Msels and offshore facilities and generally include cargo holdrefrigeration, domestic refrigeration services, and refrigerated con-tainers. These systems differ from stati

3、onary systems not only inphysical aspects but also in the fact that marine systems must bedesigned to handle frequent starting and stopping. Process freezingor chilling plants on vessels might run continuously for weeks, butunder some conditions may be started and stopped daily. Cold stor-ages are u

4、sually shut down after the cargo is discharged, and arerestarted before new cargo is loaded.Personnel changes of engineers and refrigeration crew membersrequire that those unfamiliar with the installation be able, on shortnotice, to trace well-labeled systems and place the plant in opera-tion or mai

5、ntain it without undue hazards to machinery, cargo, orpersonnel.Plant layout aboard ships should be as simple as possible withoutsacrificing reliability. The machinery plant should be close to themain power plant to provide short piping and power connectionsand facilitate close supervision by operat

6、ing personnel. Machineryspaceshouldbeuncrowded,evenattheexpenseofrevenuespace,togive ample room for operation, maintenance, and repair of both theapparatus and the ships structure.All machinery must have sturdy foundations, and all componentsshould be secured against vibration from either themselves

7、 or othermachinery. High-speed machinery should be mounted fore and aft,and all feeds, drains, and vessels must be installed with full consid-eration of the effects of pitch, roll, trim, and list.Refrigeration equipment should not, in general, be kept in thesame enclosed space as internal combustion

8、 engines, becauseengine damage can occur in the event of a refrigerant leak. Locatingrefrigeration equipment close to the main engine space usuallyimproves economy of space and provides easy connection to powerand cooling.REFRIGERATION LOADThis chapter does not discuss load calculations in detail, b

9、ecausethe loads that might be encountered in a marine refrigeration plantvary so widely. However, the methods used to calculate them can befound in Chapter 24, and load calculation considerations are dis-cussed in this chapter in the section on Specific Vessels.REFRIGERATION SYSTEMRefrigerantsRefrig

10、erants for shipboard use must meet the same environmen-tal regulations that apply to land-based systems. The choices aresimilar, but special attention should be given to the availability ofrefrigerants and compressor lubricants at all ports of call.CompressorsGenerally, all of the same types of comp

11、ressors used in stationaryrefrigeration plants can also be applied on ships. Chapter 37 of the2008 ASHRAE HandbookHVAC Systems and Equipment describescompressors in detail and discusses their application and control.Intermittent operation of compressors should be minimized toease the starting load b

12、urden on the vessels electrical generatingplant. Automatic capacity control should be used to react to varyingloads. Oversized compressors should be avoided.The shafts of rotating equipment are usually oriented fore and aftto minimize the gyroscopic bearing loads that occur when a vesselrolls. Compr

13、essor lubrication systems must be able to functionunder all conditions of pitch, roll, trim, and list.Reserve capacity and spare parts must be taken into account inthe design. There must be redundancy built into the system, a com-plement of spare parts to ensure the ability to maintain temperature,o

14、r some combination of the two. ANSI/ASHRAE Standard 26 listsspare parts and tools to be provided on board. Table 1 suggests re-serve capacities for various installations.Condensers and CoolersShipboard condensers are most often of shell-and-tube design,using seawater as the condensing medium. Other

15、types of condens-ers, such as plate-and-frame and double pipe, are sometimes used.Surfaces exposed to seawater must be resistant to corrosion. Cupro-nickel is the most common tube and tube sheet material for refrig-erants other than ammonia. During selection of equipment,installation, and operation,

16、 special consideration must be given topreventing damage from galvanic corrosion, erosion, electrolysis,and anaerobic corrosion. Epoxy coatings and sacrificial anodes areoften used as preventive measures.Considerations for brine (including seawater) coolers and water-cooled oil coolers or subcoolers

17、 are similar to those for condensers.Materials of construction must be compatible with the mediumbeing cooled or being used for cooling.Shell-and-tube condensers are normally fitted with dual drains inorder to drain freely under all conditions of pitch, roll, trim, or list.As an alternative, they ma

18、y be installed on an angle great enough tocompensate for the maximum angle of vessel trim or list that may beencountered.ThepreparationofthischapterisassignedtoTC10.6,TransportRefrigeration.Table1 OperatingandReserveCapacitiesofCondensingUnitsNo. of Units,100% LoadAdditional or ReserveUnit, %Total N

19、o.of Units1 100 225033331/3 442555 or more 20 6 or more26.2 2010 ASHRAE HandbookRefrigerationReceivers and Refrigerant DistributionReceivers, either vertical or horizontal, must be installed so as toretain a liquid seal at their outlet under all conditions of pitch, roll,trim, or list. They should b

20、e fitted with an impact-resistant levelglass,andmaybeadditionallyfittedwithelectroniclevelindication.All of the same methods of refrigerant distribution that are usedin stationary refrigeration plants are also used in shipboard refriger-ation, including the use of secondary refrigerants. Generally,

21、thesame requirements must be met, in addition to those imposed byoperating at sea.Take care to ensure proper operation at any vessel angle that maybe encountered. For direct-expansion systems, piping must ensureadequate oil return. Liquid-level controls used for flooded and recir-culating systems sh

22、ould be located in the middle of vessels ratherthan at either end. Provisions must be taken in vessel design to min-imize liquid sloshing caused by sea conditions.System piping must be able to withstand the stresses of operationatsea,includingvibration,impact,andflexingoftheshipsstructure.ControlsRe

23、cent technological developments have significantly changedhow marine refrigeration plants are controlled. Electromechanicalcontrols, which in earlier decades supplanted manual controls, arenow increasingly being supplanted with solid-state controls in newand existing installations. The proliferation

24、 of electronics has influ-enced temperature and pressure controls, motor controls, level con-trols, data and trend logging, compressor sequencing, and leakdetection. Microprocessors are becoming the common method ofcompressor control. As solid-state technology advances, its advan-tages become increa

25、singly pronounced. Automatic sequencing ofmultiple compressors has become as simple as entering parameterson a keypad. Electronic temperature controls are very precise, caneasily be provided with multiple set points for varying duties, andcan be located several hundred feet away from the space they

26、con-trol.Pressures, temperatures, amperages, flow rates, liquid levels,events, and virtually any other information required can be deliv-ered electronically to one or more central locations for monitoringand control. Computer technology allows logging these data forlong- and short-term storage. The

27、data can even be transmitted bysatellite from a vessel at sea to a shore-based facility.Electronic leak detection equipment can reduce the potential foraccidental exposure to dangerous levels of refrigerant vapor in con-fined spaces.Applications of solid-state technology are too numerous, andevolvin

28、g too quickly, to list completely in this chapter. Changes incontrols technology are probably the most significant in marinerefrigeration over the last few years. Note, though, that sophisti-cated controls are not a substitute for sound design and construction.Whatever control system is used, proper

29、 documentation must beprovided; operating instructions must provide enough detail forusers to operate the system with a minimum amount of training.Thermometers and ThermostatsThe thermometer (or thermostat display) is the principal indicatorofhowarefrigeration plantisfunctioning. Accurate controlofs

30、pace/room temperature depends on proper placement of the sensor(s) inthat space. In spaces where the product is held just above freezing,placement is critical to avoid freezing the product. Sensors used withforced-air evaporators in this type of application should be placed inthe delivery airstream,

31、 which is the point of critical temperature.Thus, if 32 to 33F air is delivered, the product will be cooled aseffectively as possible without risk of freezing. In spaces where awider variance in temperature is tolerable, sensor placement is lesscritical. However,alwaysattempt toplacethem inthemostre

32、presen-tative location.Temperature recorders are essential to proper operation and con-trol of cargo refrigeration systems. These can be paper charts, elec-tronic media storage, or some combination of the two. The shipperor buyer of the product or cargo often specifies the type of recordingdevice.El

33、ectronic thermometers and thermostats have come into wideuse. They allow for long distances between the sensor and the con-troller or display, are very precise, can often be tied in with micro-processor system controls and data logging systems, and many canbe calibrated in the field. In a large refr

34、igerated space, multiple sen-sors can be combined to give an average reading to the display orcontroller.CARGO HOLDSArrangementArrangement and dimensions are determined by the ships struc-ture, compliance with compartmentalization of the hull as related towatertight integrity, vessel stability, and

35、fire resistance. Cargo holdsshould not be designed exclusively for high-temperature service un-lessitiscertainthatthevesselwillalwaysremaininthatlimitedtrade.Refrigeration controls must be located where they can be readilyaccessed by operating personnel regardless of whether holds are fullof cargo.

36、When controls, piping, or other equipment, such as evap-orators, are located near hatches, adequate measures must be takento prevent damage from impact by cargo, hatch covers, etc.The greater the number of subdivisions in the refrigerated com-partments, the greater the loss to the ships revenue-gene

37、ratingspaces, because of the volumes occupied by insulated partitions,cooling apparatus, piping, and accesses. Thus, the all-refrigeratedship, with only the main structural boundaries insulated, makes themostefficientuseofashipsrefrigeratedenclosures.Thisefficiencycomes with disadvantages, such as t

38、he difficulty in providing uni-form temperatures throughout, and the inability to maintain differ-ent cargoes at different temperatures.Space CoolingCargo is tightly packed in refrigerated holds of all types ofvessels, with no aisles or clearances, presenting challenges to thedesigner. Cooling can b

39、e by extended-surface overhead-mountedcoils, prime surface coils, or forced air.For operation below freezing, the designer must considerwhether defrosting will occur during operation, as with forced-airhandlers, or after cargo is unloaded, as with prime surface coils. Thehold design must allow for d

40、raining defrost water from the space,because it cannot usually be discharged to the outside of the space,as in stationary plants.Insulation and ConstructionInsulation. Moisture-, vapor-, and water-resistant insulation isof particular importance aboard ship because of frequent andextreme temperature

41、cycles caused by intermittent refrigeration. Ontermination of refrigeration at discharging ports, insulation is atlower temperatures than the open room; often, the room surfaces aredripping wet with atmospheric moisture, which enters through theopen door or hatch. Both warm and cold sides should be

42、moisture-sealed equally; cold-side breather ports are not recommended.Other common sources of water in ships cold storages are meltingice and defrosting cool surfaces.Severe service conditions, which subject the insulation to injuryor change by mechanical damage or vibration, and intermittentrefrige

43、ration place exacting requirements on insulation for shipscoldstorages.Theidealshipboardcompositeinsulation shouldhavethe following characteristics:High insulating valueImperviousness to moisture from any sourceMarine Refrigeration 26.3Light in weightFlexibility and resilience to accommodate ships s

44、tresses andloadingGood structural strengthResistance to infiltrating airResistance to disintegration or deteriorationFire resistance or fireproof self-extinguishing qualitiesOdorlessnessNot conducive to harboring rodents or verminReasonable installation costWorkability in constructionIn the United S

45、tates, the properties of the insulation and thedetails of construction should meet approval by the U.S. CoastGuard and U.S. Public Health Service. For information on insula-tion materials and moisture barriers, see Chapters 23 and 25 to 27 ofthe 2009 ASHRAE HandbookFundamentals.Construction. The thr

46、ee principal parts to the cold storageboundaryaretheenvelopeorbasicstructure,theinsulatingmaterial,and the room lining.The envelope is usually partly composed of the ships hull,watertight decks, or watertight main bulkheads with members thatresist vapor entry from the warm side. Inboard boundaries o

47、utlin-ing cold storages should have an equal ability to resist moisture. Acontinuous steel internal bulkhead with lap seams and weldedstiffeners provides a boundary of adequate strength and tightness.Details of design may accommodate dimensioned insulators orfacilitate means of fastening these mater

48、ials. Doorway main bucksof steel channel provide good structure, but are usually a source ofsweating on low-temperature rooms because of heat gain throughthe metal. Wooden door bucks minimize sweating but counteractefforts to eliminate concealed wooden structure.Partitioning bulkheads may be of simi

49、lar detail, but airtightsealing is less important. Some installations are framed with angle-bar grids, between which the insulator is installed. In passengervessels (over 12 passengers), Coast Guard regulations on fire-resistant construction restrict wood assembly. Under no circum-stances should wood be a part of the deck assembly, because itdeteriorates rapidly under the prevailing conditions.The assembled boundary of a ships cold storage must withstandheavy deck loads and several bulkhead thrusts of cargo when thevessel rolls or pitches in a heavy sea; it must also be able to