Modeling of plant simulation of MRC plant under variable working conditions and operation optimization

A LNG plant with MRC cycle would not work under the designed condition all the time. It is significant to know the performance of a fixed MRC plant working at changed working condition. The problem involves the problem of plant simulation, which is somewhat similar to but actually different with the process simulation which is used in the design of a LNG plant. A model of MRC plant simulation was established and brief comparison between the two kinds of simulations was made. Here, the performance of main devices at different working conditions is simulated using fitting method and the rest is regarded as constant. The calculation of devices in the MRC process is connected using the HYSYS soft so as the entire plant simulation at different conditions could be carried out. Two kinds of MRC plant of LNG are studied. One kind is the LNG plant with SMR cycle which generally used in small-scale plant. The other is the plant with C3-MR process which often used in large base-load plant is studied. The follow cases, including ambient temperature variations, feed gas pressure variations and load variations, are simulated and evaluated. The adaptabilities of the two LNG processes are analysis and compared. The results show the SMR cycle has good adaptability under changed working condition. Since C3-MR process is more sophisticated and has more devices, the effect of changed working conditions on the performance of the LNG plant is larger. The results could be referred in the selection of liquefaction process in medium-scale LNG plant. To reduce the energy consumption, it is necessary for LNG plant operation to adapt the mixture refrigerant composition and other process parameters to the changed working conditions for LNG plant. The operation optimization is a reasonable way to obtain the object. The operation optimization is also rather different with the design optimization. The operation optimization should be conducted on the basis of plant simulations. Here, the object function is to minimize the operation power consumption and corresponding constraint condition of operation should be made. The BOX method is used to solve the optimization problem. The operation optimizations of SMR plant and C3-MR plant are done under the same condition of changed ambient temperature. The results show that the obvious energy saving could be achieved for the both kinds of plants, although the total energy consumptions is still higher than that of design optimizations. The SMR plant also shows better performance at changed working conditions than that of C3-MR plant. The work could be referred for actual operation of a MRC plant for variable working conditions.