Liquefaction principle
The liquefaction of natural gas follows the thermodynamic phase transition law. When the temperature is below the critical point (methane-82.6 ℃), the transition from gas to liquid phase can be achieved by pressurization or cooling. Under normal pressure, it needs to be cooled to -162 ℃ to complete liquefaction, while under 4.5MPa pressure, it only needs to be cooled to -84 ℃. This process requires overcoming the kinetic energy of gas molecules and achieving internal energy reduction through compressor work and heat transfer through a heat exchanger.
Technological process
Preprocessing stage
The raw gas needs to go through three purification stages:
-Deacidification treatment: removes acidic gases such as hydrogen sulfide and carbon dioxide to prevent solid blockages in pipelines at low temperatures
-Dehydration and mercury removal: Use molecular sieves to adsorb water to below 1ppm, reducing mercury content to 0.01 μ g/m ³
-Heavy hydrocarbon separation: Separation of C5+components by condensation to avoid low-temperature wax deposition
Core liquefaction process
The mainstream liquefaction technologies include three categories:
-Mixed refrigerant process: using a mixture of nitrogen, methane, ethane and other working fluids, achieving a low temperature of -160 ℃ through single-stage compression, reducing equipment investment by 30% but increasing energy consumption by 20%
-Stepwise refrigeration process: using propane (-40 ℃), ethylene (-100 ℃), and methane (160 ℃) in three stages to gradually cool down, with the lowest energy consumption but high equipment complexity
-Expansion mechanism refrigeration process: suitable for small devices, natural gas is expanded by a turbine to an absolute pressure of 0.1-1MPa, and the cooling capacity is generated by its own pressure drop. The energy consumption is 35% higher than that of mixed refrigerants
The liquefaction of natural gas follows the thermodynamic phase transition law. When the temperature is below the critical point (methane-82.6 ℃), the transition from gas to liquid phase can be achieved by pressurization or cooling. Under normal pressure, it needs to be cooled to -162 ℃ to complete liquefaction, while under 4.5MPa pressure, it only needs to be cooled to -84 ℃. This process requires overcoming the kinetic energy of gas molecules and achieving internal energy reduction through compressor work and heat transfer through a heat exchanger.
Technological process
Preprocessing stage
The raw gas needs to go through three purification stages:
-Deacidification treatment: removes acidic gases such as hydrogen sulfide and carbon dioxide to prevent solid blockages in pipelines at low temperatures
-Dehydration and mercury removal: Use molecular sieves to adsorb water to below 1ppm, reducing mercury content to 0.01 μ g/m ³
-Heavy hydrocarbon separation: Separation of C5+components by condensation to avoid low-temperature wax deposition
Core liquefaction process
The mainstream liquefaction technologies include three categories:
-Mixed refrigerant process: using a mixture of nitrogen, methane, ethane and other working fluids, achieving a low temperature of -160 ℃ through single-stage compression, reducing equipment investment by 30% but increasing energy consumption by 20%
-Stepwise refrigeration process: using propane (-40 ℃), ethylene (-100 ℃), and methane (160 ℃) in three stages to gradually cool down, with the lowest energy consumption but high equipment complexity
-Expansion mechanism refrigeration process: suitable for small devices, natural gas is expanded by a turbine to an absolute pressure of 0.1-1MPa, and the cooling capacity is generated by its own pressure drop. The energy consumption is 35% higher than that of mixed refrigerants
