Optimization Of BOG Recondensing System For LNG Receiving Station

As China's demand for natural gas and other clean energy gradually increased,liquefied natural gas(LNG)industry has entered a period of vigorous development,LNG in the proportion of energy consumption continues to increase,imports increased year by year.In the LNG storage and transportation process,LNG receiving station in an important part of the import and export,China LNG receiving station construction development into the golden period.However,with the acceleration of the construction of the receiving station and the expansion of the scale of operation,the processing and control of the Boiling Off Gas(BOG)are becoming more and more difficult,and the energy consumption such as BOG processing is large,and the control system can not role and other issues.China's LNG receiving station BOG treatment mostly use re-condensation process.It is necessary to optimize the BOG re-condensation process and control system of the receiving station..Based on the field parameters of a LNG receiving station,this paper focuses on the BOG re-condensation process and control scheme of the receiving station,and puts forward a feasible optimization scheme on the basis of reasonable analysis.The main contents are as follows:(1)Establish the unit model of the receiving station and calculate the amount of BOG generated.The static simulation flow of the receiving station is established,and the key parameters in the re-condensation process are studied by single factor variable method.The main influencing factors of BOG re-condensation system are analyzed,and the general rule of re-condensation system operation is obtained.(2)According to the present situation of the BOG treatment process of the receiving station,it is proposed to use the preheating re-condensation process of the low temperature LNG of the high-pressure pump outlet to cool the BOG before entering the re-condenser.Calculate the minimum throughput required for both safe and stable operation.Based on the minimum flow rate of the process,the different re-condensation process is compared and optimized.Using pre-cooling re-condensation process,the BOG temperature from-42.2?pre-cooled to-100? after the re-condenser,When the BOG throughput is the same,the minimum external throughput can be reduced by 15.02%and the total energy consumption of the system is reduced by 8.7%.Through the process optimization,the key points of the pre-cooling re-condensation process operation parameters are obtained.(3)According to the receiving station control program to establish the system dynamic process,In the dynamic process to add the actual production may occur in different disturbances,observe the dynamic response of the system.It is found that there is a problem that the condensing system pressure and condensed LNG flow,especially the re-condenser level control,is unstable when the current re-condensation control system has a large amount of BOG treatment.(4)Analysis of the current control system problems mainly by the re-condenser pressure using cascade ratio control caused.It is proposed to add a control circuit for the re-condenser to directly adjust the re-condenser pressure with condensed LNG flow.When the BOG treatment capacity is more stable,the reseller pressure using the original cascade ratio control mode,When the BOG handling volume fluctuates,the re-condenser pressure control switches to the additional direct feedback control mode.In order to solve the current re-condenser control instability.In this paper,the BOG re-condensation system of the receiving station is optimized from the perspectives of process and control system.The research results can provide some reference and support for the optimization and improvement of the re-condensation system of the receiving station.