Gas Liquefaction

Gas liquefaction is the process of refrigerating a gas to a temperature below its critical temperature therefore liquid can be formed at a suitable pressure. And gas liquefaction refers to an unusual case of gas refrigeration. The gas is primarily compressed to high pressure in an ambient temperature compressor. This elevated pressure gas is passed through a countercurrent heat exchanger to a throttling valve or extension engine. Upon extending to the lower pressure, cooling may occur and some liquid may be formed. The cool, low pressure gas comes back to the compressor inlet to recur the cycle.

The basic principle

The intention of the countercurrent heat exchanger is to warm the low-pressure gas prior to recompression and concurrently to cool the high-pressure gas to the lowest temperature possible prior to expansion. Both refrigerators and liquefiers function on this same fundamental conception. A notable distinction between refrigerators and liquefiers is that in a constant refrigeration process, there is no gathering of refrigerant in any part of the system. This contrasts with a gas-liquefaction, where liquid accumulates and is pulled back.

Analysis and design of the system

 Thus, in a liquefying system, the whole mass of gas that is warmed in the countercurrent heat exchanger is less than the gas to be cooled by the amount that is liquefied, creating an unbalanced flow in the heat exchanger. In a refrigerator, the warm and cool gas flows are the same in the heat exchanger. This results in impartial flow condition. The thermodynamic principles of refrigeration and liquefaction are identical. Nevertheless, the analysis and design of the two systems are quite different because of the condition of balanced flow in the refrigerator and unbalanced flow in liquefier systems.

Thermodynamic process

The requirement of refrigeration for gas liquefaction is achieved in a thermodynamic course when the process gas absorbs heat at temperatures below that of the environment. A process for producing refrigeration at liquefied gas temperatures commonly comprises equipment at ambient temperature in which the gas is compressed and heat is rejected to a coolant. During the ambient-temperature compression process, the enthalpy and entropy, but usually not the temperatures of the gas are decreased.

The reduction in temperature of the gas is usually accomplished by heat exchange between the cooling and warming gas streams followed by an expansion of the high-pressure stream. This expansion that happens either through a throttling device where there is a reduction in temperature only or work-producing service where both temperature and enthalpy are reduced.

Questions:

• What is gas liquefaction?
• What is the role of gas liquefaction?