Numerical Simulation And Experimental Investigation For Natural Gas Cooling Process Based On Bphe

With the continuous optimization of China’s energy structure,coal,oil and other traditional fossil energy have been gradually replaced.Before the large-scale application of new energy such as solar energy and hydrogen energy,natural gas,as a relatively clean energy source,has occupied an increasingly prominent position in China’s energy structure.In view of the existing natural gas liquefaction processes and devices,the widely used plate-fin heat exchanger has inevitable disadvantages of low tolerance to carbon dioxide-based impurities and easy clogging.Based on a novel LNG cold box project,this thesis adopts a combination of theoretical design,numerical simulation and experimental investigation,to carry out numerical simulation and experimental research of natural gas liquefaction cold boxes based on the brazed plate heat exchangers.The main contents are given as follows.Based on the conservation of energy and materials,the general theories and method of natural gas process design calculation were introduced,and thermodynamic models of the key equipments in the liquefaction process were established.A mixed refrigerant cycle(MRC)for natural gas liquefaction by using the brazed plate heat exchanger was designed and developed for a small-scale natural gas liquefaction device.The thermodynamic state parameters of each node in the liquefaction process were presented.The theoretical calculation of the unit energy consumption for the liquefaction process was 0.467 KW·h/Nm~3.The numerical simulation was conducted to study the cooling and heat transfer process of natural gas in brazed plate heat exchangers under large temperature spans.Based on several reasonable assumptions,and variable property interpolation fitting for cryogenic fluids,the temperature and pressure characteristics of the pre-cooling,liquefaction,and subcooled heat exchangers were simulated and analyzed.The detailed experimental investigations for the novel cold box was carried out to test the liquefaction performance and the carbon dioxide tolerance,and to reveal the dynamic equilibrium process of the carbon dioxide blocking in the brazed plate heat exchanger.The results showed that the cold box had a continuous and stable liquefaction capacity of 35000Nm~3/d,and the carbon dioxide tolerance for the cold box adopted brazed plate heat exchanger(specific surface area～500m~2/m~3)was 2000ppm-5000ppm when worked at feed gas pressure was 3.3MPa,liquefaction temperature was-138℃and subcooled temperature was-150℃,which improved by two orders of magnitude compared with the traditional plate-fin heat exchanger.In comparison of theoretical design,numerical simulation and experimental results,it showed that the averaged discrepancy between the experimental data and simulation results was 7.78%,which verified the reliability of the assumptions,numerical model and method.The averaged discrepancy between the experimental data and theoretical design was4.08%,which confirmed the design parameters and theoretical method.The research methods and results provided a certain reference for the numerical simulation of brazed plate heat exchangers which involving large temperature spans heat transfer of cryogenic fluids,and also provided guidance for the engineering design and development of natural gas liquefaction cold boxes.