Optimization Of Re - Condensation Process And Design Of Control Scheme For A LNG Reception Station

Liquefied natural gas (LNG) is a high-quality and cleaning energy resource with speediest development in the world. Currently, the LNG plants and LNG receiving terminals have been massively constructed in many countries. By the end of2014, more than40LNG plants and24LNG receiving terminals have been under construction, and10LNG receiving terminals have been put in operation. LNG receiving terminal is an important connection component between LNG sources and residential consumers. Significantly, there are several factors, such as compressor or pump operation, heat input from outside, discharge and environmental change, will induce large amounts of gas (BOG) evaporation in the tank, equipment and pipeline. Without a proper disposal, the existence of BOG will affect operation of the device resulting in resources waste and environmental pollution and so on. Therefore, it is important to operate the BOG processing unit steadily, safely and economically.To date, BOG re-condensation process is widely used to recover BOG in LNG receiving terminal.In this paper, process simulation is achieved by the Aspen HYSYS simulator, and device energy of BOG re-condensation process for a LNG receiving terminal is analyzed. The result shows that the most serious energy loss unit is regasification system, and its exergy loss accounted for about80%. The exergy loss of high-pressure pump and compressor accounted for about17%and28%, respectively.Based on process simulation and the analysis of device energy of BOG re-condensation process, the operation parameters are optimized and the process is improved. In this study, LNG flow, CH4content in LNG, LNG pressure and BOG pressure are selected as the important parameters according to the results of sensitivity analysis, and interactive effect of them is analyzed, and response surface method is introduced to get to the equation between these four parameters with the total energy consumption as objective function, then this equation is substituted into Matlab software to obtain the optimum operating parameters. Consequently, the total energy consumption reduced15.06%. The gas load is low due to problems like difficult operation and high energy consumption of compressor and so on, the BOG re-condensation process is further improved. A re-condenser is added in the middle of the two compressors to condense part of the BOG into LNG, which is pressurized by pump. The purpose of this work is to reduce energy of compressor and ensure re-condenser running stably when gas load is low. The energy of compressor of retrofit design of BOG re-condensation process reduced135.76k W, and the percentage is about45.56%. The total energy of process reduced13.98%, and it means that the energy-saving effect is remarkable. Besides, the equipment selection and equipment layout are achieved in this work. The results show that under the current working conditions, the equipment meets all the requirements of production.Meanwhile, control scheme of this retrofitted BOG re-condensation process and particular core equipment, such as compressor and re-condenser, are accomplished, Thus, the operating flexibility and the adaptability of the retrofitted process are improved.