Ammonia as refrigerant

Khattak, M. A., Engineering Horizons (Pakistan), 1991, (Aug.), 33 Chlorine reacts with ammonia and compounds to form the treacherously explosive nitrogen trichloride. A change was made to ammonia as refrigerant in the production of liquid chlorine some months later minor explosions when transferring the chlorine... 

The most commonly used absorption-refrigeration system operates with water as the refrigerant and a lithium bromide solution as the absorbent. This system is obviously limited to refrigeration temperatures above the freezing point of water. It is treated in detail by Perry and Green.t For lower temperatures the usual system operates with ammonia as refrigerant and water as the solvent. 

Increased drying temperature a new heat pump with ammonia as refrigerant and with a new compressor designed for pressures of 6 to 7 MPa allows condensing temperatures above 100°C. 

Many condensable vapours have been used as refrigerants, but the main ones are the chlorofluorocarbons (Freons ), ammonia and carbon dioxide. 

Several types of fluids are used as refrigerants in mechanical compression systems ammonia, halocarbon compounds, hydrocarbons, carbon dioxide, sulfur dioxide, and cryogenic fluids. A wide temperature range therefore is afforded. These fluids boil and condense isotherm ally. The optimum temperature or pressure at which each can be used can be deterrnined from the economics of the system. The optimum refrigerant can be deterrnined only... 

Attenuation Another alternative to intensification is attenuation, using a hazardous material under the least hazardous conditions. Thus large quantities of liquefied chlorine, ammonia, and petroleum gas can be stored as refrigerated liquids at atmospheric pressure instead of storing them under pressure at ambient temperature. (Leaks from the refrigeration eqmpment should also be considered, so there is probably no net gain in refrigerating quantities less than a few hundred tons.) Dyestuffs which form explosive dusts can be handled as slurries. 

Transport refrigeration - HCFC-22 and CFC-502 have been the refrigerants of choice for transport refrigeration units, although some applications are using ammonia as the refrigerant. The alternatives include various HFC blends. 

Organic fluorine as a separate industry that began in the late 1920s with the discovery by Midgle of fluorocarbons for use as refrigerants. Ammonia was unsuitable because of the hazard and unpleasant smell from minute leaks. Sulfur dioxide had similar problems. The best refrigerant was... 

As far as refrigeration is concerned, this system produces ammonia liquid as the refrigerant that is evaporated in the process unit requiring the refrigeration. In principle this is the same operation at the evaporator as if the system were one of compression. The method of removal of the heat of the ammonia vapor and then the reliquelaction are the points of difference between the systems. 

The safety aspects of ammonia plants are well documented and there is reason to expect an increase in the use of ammonia as a refrigerant. 

Misguided substitutions such as the introduction of CFCs as a safe substitute for ammonia as a refrigerant were already mentioned in the introduction. The example... 

An ideal heat pump uses ammonia as the working fluid. The saturation temperature of the refrigerant in the evaporator is 22°F and in the condenser it is 98°F. The refrigerant is circulated at the rate of 0.051 Ibm/sec. Determine the compressor power required, heating load, and COP of the heat pump. 

Nonfluorine CFC substitutes have been considered, but few are fully satisfactory. For example, we could go back 50 years to the use of anhydrous ammonia as a refrigerant, but NH3 is as toxic now as it ever was. Cyclopentane could be used as a foam-blowing agent, but it is less effective than HCFC-141b and besides would contribute to the volatile organic compound load in the troposphere, which is the root cause of ozone pollution (Section 8.3.2). On the other hand, supercritical CO2 is emerging as an alternative to CFCs in various steps in the preparation of fluorocarbon polymers (Section 8.1.3). 

A refrigeration cycle to make ice from water with ammonia as the working fluid or energy carrier. Nearly 45% of the compression power is lost due to heat exchange in the evaporator and the condenser. 

For this example the anhydrous ammonia is stored as refrigerated liquid at a temperature of -33°C and one atmosphere of pressure. The tank is vented to a system which recovers any vapors that boil off. The configuration of the tank is identical to that shown in Figure 7.12, and the accident causing the release is the same as in the pressurized storage example described above. 

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