Simulation And Optimization Of Small-Sized Skid-Mounted Natural Gas Liquefaction Process

The natural gas, with its high calorific value and cleaning characteristic, has become one of the main energy in the 21st century and its consumption is increasing. Small liquefied natural gas (LNG) device has some advantages of small volume, skid-mounted, motor transport, convenient parking, and can be developed and utilized in small scattered gas fields or remote areas to improve energy utilization. In this paper, simulation analysis and research of R22 precooled mixed refrigerant liquefaction recycle process in a natural gas liquefaction plant in Yinchuan are crried out, and some problems during the operation are analysed and supply improvement measures.In this paper, R22 pre-cooled mixture refrigeration cycle liquefaction process is established using the Aspen Plus simulation software. According to the design parameters, the process is simulated and the result data is closed to the actual operation conditions, which proves the selected model is reasonable. Due to the calculation,66.553 kmol/h(1042.7kg/h) LNG can be acquired when the feed material flow rate of nature gas is 70kmol/h. The liquefaction ratio is 89.36%, and the work consumption between mixed cooling agent compressor and R22 compressor is 360 kW and 134 kW respectively, at the same time, the work consumption per kilogram is 0.474 kW·h/kg. When compared with multi-staged LNG process, whose work consumption per kilogram is 1.44 kW-h/kg, the R22 process has the following characteristics:small energy consumption, there are not so many equipment and operated conveniently. Thus R22 process is economical and saving. What is more, with the available energy calculation and analysis of the equipment in R22 process, the result is listed here: compressor is 178.9 kW, plate-swing heater is 157.8 kw, throttle valve is 59.1 kw and water condenser is 28.3 kw. So the main available energy loss are compressor and the plate-swing heater. To decrease the loss, it is suggested to increase the adiabatic efficiency of compressor and enlarge the heat transfer squares of the plate-swing heater.The compressor minimum work consumption and the minimum energy total consumption between compressor and R22 pre-cooling operation are selected as objective functions. The optimum variables are the temperature of feed natural gas into pre-cooling heat exchanger, pressure and temperature of high and low cooling agent and mole fraction of CH4 in natural gas. After simulation, the energy consumption is 463 kW which decreased by 31 kw compared to the non-optimized case.At last, the hydrops problems and mixed cooling agent filling problems in the process are also analysed and some improved advices are given.