Simulation And Optimization Of Medium And Small Scale Lng Processes And Study On Its Dynamic Response To Perturbation

In30years, world`s energy demand will surge by75%and natural gassupply will increase65%. Through2025, natural gas will surpass coal as thesecond largest energy supply in the world. In China, coal accounts for68.2%in the energy structure and natural gas3.9%. With the gradual exhaustion ofcoal reserve and the environmental issues, especially the recent occurrence ofheavy fog and haze all over China, China`s energy structure will witnessenormous change in the future and because of good attributes of natural gas,China`s natural gas industry will enjoy a big boom. Except the ordinarynatural gas reserve, how to explore and liquefy the unconventional naturalgas is the research hotspots.In this article, we come up with four LNG processes according thespecific characters of medium and small scale LNG facilities. Combining themethods of steady simulation, whole process optimization and dynamicsimulation, we study the detailed processes and process parameters, theprinciple of system performance under change of inlet parameters of naturalgas. The conclusion and summarized principle support the theoretical foundation in the design of LNG processes for medium and small scalefacilities.In the steady simulation of four processes, confirm the detail ofprocess arrangement and parameters of key notes through whole processreferring to specific patents. Then make the assumptions of the inletparameters of natural gas and mixed refrigerant to build simulation model inHYSYS. Through the API in MATLAB and HYSYS, study the principle ofpower consumption and refrigerant flow rate change. Based on thecalculation of steady model, use exergy thermal model to assess the process.In the optimization, choose the most complex process CII to performthe optimization calculation. Firstly, use the cost analysis method to select theobject function. Then analyzes the NOF (Number of Freedom) to find out thedetermining constraints (also called manipulated variables), and then usingHYSYS model as Sever via API and GA programs to optimize the CIIprocess. The optimization method of combining two external software andthe GA program and adjusting programs for HYSYS model can be adapted tooptimization calculation of similar process.In dynamic simulation, firstly, build dynamic models for maincomponents in the LNG process and transfer the steady model into dynamicenvironment. With the running of dynamic model, change the heater and PIDcontroller to exert perturbation on the process and observe the principle ofreaction of power consumption and refrigerant flow rate.The conclusion and observed principle about the detailed processparameters, processes`reaction to changes of inlet parameters of natural gas,will help to design medium and small scale LNG facilities.Limited to the lack of time and personal knowledge, especially aboutthe design and sizing of multi stream heat exchanger and compressors, thedynamic study of the processes only is constrained to the basic model.