Study On Natural Gas Liquefaction Technology Of Small-Sized Skid-Mounted LNG Device

In China, natural gas resources are scattered. Gas production rate by single-well is of small quantity. Still, there are abundant natural resources dispersed at the borders of oil and natural gas fields. To gather and utilize those resources, small-sized skid-mounted LNG devices are of great help, since they are small in size, flexible to switch and convenient to transfer. In this thesis, the author gives a detailed study on liquefaction technology of small-sized skid-mounted LNG devices:Firstly, this thesis analyzes the prospects of China's liquefied natural gas industry to illustrate the significance of study on liquefaction technology of small-sized skid-mounted LNG devices, introduces the parameters of natural gas and refrigerant and selects PR equation to reveal the gas-liquid balance state, LKP equation to calculate the amount of natural gas and refrigerants like enthalpy and entropy.Secondly, this thesis makes comparative studies on the key parameters of three typical liquefaction processes of N₂-CH₄ expander, propane pre-cooler mixed refrigerant, and novel two-stage mixed refrigerant; adopts the liquefaction process of N₂-CH₄ expander as that of small-sized LNG device; established the mathematics models for equipments like compressor, expander, throttle, mixer, splitter, separator, multi-flow heat exchanger according to AspenPlus software and explores computational methods for them respectively; presents the simulated diagrams of N₂-CH₄ expander's liquefaction process via AspenPlus software.Finally, this thesis systematically analyzes the computational methods, simulated procedures and solving courses of N₂-CH₄ expander's liquefaction process; qualitatively explores the influences on the performance of N₂-CH₄ expander by parameters of refrigerant high pressure, refrigerant low pressure, refrigerant pre-expansion temperature, natural gas outlet temperature of primary heat exchanger, refrigerant components, etc; optimizes the key parameters in N₂-CH₄ expander's liquefaction process to get the temperature, pressure, enthalpy, entropy and mole fractions of each component and then analyzes the influences on the performance of N₂-CH₄ expander by conditions of natural gas sources like natural gas pressure, temperature, methane mole fraction and total flow of natural gas.