Refrigerating Systems. Three-stage (ternary) cascade refrigeration system
Cascade cooling cycles are commonly used in the liquefaction of natural gas, consisting mainly of hydrocarbons paraffin series, of which methane has a lower boiling point at atmospheric pressure. Cooling down the temperature can be provided at the triple cascade cooling cycle, using propane, ethane and methane, whose boiling point at atmospheric pressure 231.1 K, 184.5 K and 111.7 K (Haywood, 1980). Simplified schematic diagram of the cascade loop is shown in Fig. 3.40. In operation, compressed methane, steam and cooled by heat exchange with propane propane in the evaporator before being reduced by heat exchange with ethane ethane in the evaporator, which reduces the degree of irreversibility of participating in cooling and condensation of methane. In addition, due to the high temperature after compression gas at the compressor outlet passes first through a water-cooled chiller. In large-scale plant of this type compressors become rotary turbo machines instead of piston-type ones.
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