The Research Of Natural Gas Deep Purification Technology In Lng Plant

Liquefied natural gas plant generally includes purification unit, liquifaction unit and storage unit. Before the natural gas feed into purification installation, the impurities of carbon dioxide, moisture, hydrogen sulphide, heavy hydrocarbons and mercury etc. must be removed deeply to keep them from corroding the pipes and valves, or jaming the pipes and valves under the cryogenic conditions, and ensure the stable operation of crogenic liquefied plant. This paper bases on Inner Mongolia 10×104m3 liquefied natural gas project, carry out a series of basic research on deep acid gas removing technology and deep dehydration drying technology, provide the theoretical foundation and technical support for deep purification unit's design in LNG plant.This paper analyzes the research status of the acid gas removing and dehydration technology in domestic and foreign. Expound the advantages and disadvantages of various pre-treatment technology. Determine the deep purification process in the LNG plant and analyze the process of the acid gas removing and dehydration in detals.This paper analyzes the theory of the gas-liquid equilibrium which are involved in the separation of natural gas deep purification, and introduce the physical and chemical properties of several common amines in alcohol amine absorption method. Analyze the variables and establish the the mathematical model of gas-liquid contact in the absorption process, lay the basis for the numerical simulation and optimization of deep acid gas removing process. Optimize and analysize the acid gas removing performance of MEA, DEA and MDEA alcohol amine solution, determine that the regeneration power of MDEA solution is 1/3 time less than MEA, so use the MDEA aqueous solution to remove the acid gas deeply in LNG plant. For MDEA solution, make deeper numerical simulation on the process to research the operational performance of the absorber and regeneration tower. In case of meeting the absorption and regeneration targets , determine the circulation rate of alcohol amine solution in LNG plant is 7000kg/h, the heat load of regeneration tower is 422.2kW and operational temperature of regeneration tower is 380K. This paper analyzes the theory of the molecular sieve dehydration process, determine the diffusion mechanism of water molecules , mass transfer rate and mass transfer coefficients in the adsorption process. For fixed-bed adsorption process, establish the mathematical model, programming with matlab to research the main parameters'influence on the adsorption properties, recommend the optimal gap rate is 0.3, gas flow rate of hole tower is 0.12m/s. Then study the adsorption load curve and breakthrough curve of the fixed-bed adsorption dehydration, determine the adsorption cycle of molecular sieve deep dehydration drying are 7.3 hours in LNG plant.