Dynamic Performance Simulation Of Plate-Fin Heat Exchangers In Small Scale MRC-LNG Plant

During the designing process of the natural gas liquefaction plant, parametersdescribed the static performance of the device always be used to select the heat ex-changing equipment, but the dynamic performance and the applicability to the varia-tional working conditions were not quantitatively analyzed. In view of the operationcondition can not always follow the design one, in order to control the operation bet-ter, a reliable mathematical model was needed to predict the dynamic performance ofthe device. A model was established in this paper, and it described the dynamic char-acteristics of the plate-fin heat exchanger which was used in the Mixed-RefrigerantCycle (MRC) Liquefied Natural Gas (LNG) plant, and the study was instructive toimprove the controlling performance of the device.First of all, a model was established to predict thermal properties of the natu-ral gas and mixed refrigerant, it can determine phase and percentages of the multi-component mixtures by calculating the phase equilibrium, then the thermodynamicand transport properties were acquired, and they provided support for the calculationof thermal properties in dynamic model. In other words, the property model mainlyfocused on the drastic changes of the mixture's thermal properties in low temperature,which might reduce the accuracy of the dynamic model.Secondly, a mathematical model was established for a multi-?ow, phase-changeplate-fin heat exchanger, which was based on the theory of gas-liquid two-phase ?owand phase equilibrium. Heat transfer and ?ow characteristics in the heat exchangerwere described according to the mass equation, momentum equation, energy equa-tion and phase equilibrium equation. The governing equations were dispersed by im-plicit scheme in time dimension and second-order upwind scheme in space dimension.Based on the modularized modeling method, the model was established in Simulinkenvironment using C MEX S-function. Subsequently, using the Graphical user inter-face (GUI) which was provided by MATLAB, software was developed to simulate thedynamic performance of the plate-fin heat exchanger.Finally, static and dynamic performance of the plate-fin heat exchanger werestudied using the developed software. The cooling process of a plate-fin heat ex- changer was simulated in the case of the inlet and initial parameters were known. Atthe same time, the pressure profile and temperature profile of the ?uid, the tempera-ture profile of the parting sheet were acquired in steady state. Later, a step disturbanceof the refrigerant's ?ow rate was given, the responses of outlet temperature was re-ceived. Results in steady state fitted the professional software well and it made themodel credible. At last, the cooling process of two plate-fin exchangers was simu-lated, and the system testing of multi-plate-fin heat exchangers in the dynamic modelwas successful completed.