Simulation Analysis Of LNG Terminal Operation Process

this paper is concerned with the field operation of the existing receiving station.With the help of Aspen HYSYS Process simulation software,the dynamic model of the LNG handling process,including LNG loading and unloading,is established to study the influence of the parameters on the process operation of the receiving station and the energy consumption of the equipments,and to provide suggestions for improving the economic benefits of the receiving station.On the basis of HYSYS steady-state simulation,the generation of BOG and its impact on the operation of the terminal equipments under different working conditions are calculated.Firstly,it is calculated that the largest generation of BOG is about 37.8t/h under the conditions of unloading at the maximum rate,and of minimum export without loading for rich composition of LNG.Then,it is analyzed that properly increasing the pressure of LNG storage tank can effectively reduce the generation of BOG,and BOG can be effectively reduced When the BOG handling capacity fluctuates.BOG generation has the greatest impact on the condensating LNG rate at the inlet of the Recondenser.Finally,the BOG and condensating LNG entering the Recondenser under the control of the adj controller are simulated.It is analyzed that the LNG mass rate for BOG will be effectively reduced with the increase of the discharge pressure of the BOG compressor and the low-pressure pump in the tank,but the impact degree will continue to decrease with the increase of the pressure.On the basis of PID control scheme,the dynamic model of export process is established to simulate the dynamic change of process operation parameters in case of emergency.Firstly,the simulation results show that the fluctuation of BOG handling capacity has a great response to the power consumption of BOG compressor,the pressure of Recondenser and the mass rate of condensing LNG;secondly,the simulation analysis shows that the pressure and temperature in Recondenser increase continuously when the output volume is reduced and the low-pressure pump is shut down,which has the potential danger of overpressure;finally,the research and analysis is conducted by adding the disturbance of stopping the low-pressure pump,compressor and increasing the speed and load of compressor.When the BOG compressor is shut down,the handling capacity of the BOG will be reduced and the BOG will be vented,which will result in waste.Increasing the load of the BOG compressor has more influence on the pressure of Recondenser than increasing its speed.The dynamic model of two loading modes of tank car in receiving terminal and the loading model of rich and poor liquid are established.Firstly,the loading mode with pressure is simulated and analyzed,which makes the pressure and temperature fluctuate frequently in the tank car.At the end of loading,the pressure of tank car is about 40 higher than one without pressure At the same time,it is found that after the tank car loading,the amount of BOG produced by the lean liquid loading is about 5% higher than that of the rich liquid,and the temperature in the tank car after the lean liquid loading is slightly lower than that of the rich liquid loading.The dynamic model of ship unloading condition in receiving station is established to simulate and analyze the influence of BOG production,rich and poor liquid unloading and coldness keeping circulation flow for ship unloading.The simulation results show that there is a positive correlation between BOG production and ship unloading pressure and ship unloading speed,and the rich composition of LNG transported to the tank changes slightly with the composition of LNG in the tank;and the nitrogen content in the gas phase space of the tank from rich liquid obviously increases a lot,but the methane content in the BOG component in the lean liquid is more than that in the rich liquid.Unloading the ship shall cooperate with loading or export to reduce the generation of BOG in the receiving station and the fluctuation of pressure in the tank,so as to prevent overpressure of the tank as much as possible.It is suggested that when the export pressure is increased,the comprehensive analysis should be carried out in combination with the downstream user demand and the impact on the operation process of the receiving station;before the process operation,it is necessary to regularly check whether the equipments is in normal operation state;when the low-pressure pump in the tank needs to be shut down due to various uncontrollable reasons,the BOG compressor should be shut down first;when the compressor load is increased due to the increase of the BOG handling capacity,the liquid-gas mass ratio should be increased firstly to reduce the hidden danger of overpressure of Recondenser.