Simultaneous Synthesis Of Heat-Coupled Coal To Synthetic Natural Gas-Methanol Polygeneration Process

Recently,the profitability of coal to synthetic natural gas project has been greatly weakened due to the problems of high process energy consumption,serious decline of natural gas price and large fluctuation of supply and demand.The single product structure has become a bottleneck restricting the healthy development of coal chemical industry.Therefore,it is an important direction for future development to optimize the process,upgrade the production structure,improve the comprehensive energy efficiency and build a sustainable coal chemical industry chain.The coal based polygeneration process can realize diversified,high value and energy-saving production of end products through coupling downstream process paths of coal chemical industry,which is an important way to solve the above problems.A new polygeneration process is proposed based on the design of Coal to Synthetic Natural Gas Process and Coal to Methanol Process.Importantly,Simultaneous design of Coal to Synthetic Natural Gas-Methanol Polygeneration Process（CTSM）coupled with heat integration is studied,mainly focusing on the poor universality of thermodynamic model,insufficient waste heat recovery and weak correlation between process synthesis and heat integration.The main research conclusions are as follows:（1）An optimization design method of Coal to Synthetic Natural Gas-Methanol Polygeneration Process in series（S-CTSM）and parallel scheme（P-CTSM）is proposed.In this process,a waste heat recovery steam cycle（WHRSC）is introduced to fully recover the waste heat from the shift unit,methanation unit and methanol synthesis unit.The energy consumption of the Rectisol unit is greatly decreased by increasing the CO₂ concentration of the syngas to be deacidified,the effect of key parameters on process performance is discussed.Ultimately,a comprehensive techno-economic analysis is performed.The results indicate that the product cost of P-CTSM is reduced by 9.06%and its exergy efficiency is increased by 2.36%compared with the single production process.Therefore,P-CTSM is a preferable scheme to improve economic performance and overall energy efficiency.（2）A novel hybrid simulation-optimization method is proposed for simultaneous design of the heat-integrated polygeneration process based on P-CTSM.An extended Duran-Grossmann（D-G）model is established which can address isothermal phase change and non-isothermal phase change.The genetic algorithm is adopted to optimize the key parameters of key reaction units and WHRSC in the P-CTSM,aiming to maximize the exergy efficiency.Compared with the base case obtained by a sequential method,the presented method yields a2.22%increase of the overall exergy efficiency and a 44.05%improvement of power generation.Furthermore,the interaction among different subsystems reveals that process synthesis has a stronger effect on heat integration.（3）In order to solve the problem that the above method still does not realize the simultaneous synthesis of chemical process and heat exchanger network and has low solution efficiency,a simultaneous synthesis method for chemical process and heat exchanger network based on surrogate models is presented.The neural network-based surrogate model is established to replace the complex mechanism model,which can simplify the difficulty while ensuring the accuracy of mechanism model.With surrogate model formulation incorporated into heat integration,an enhanced transshipment-based model is introduced to optimize the variable heat exchanger network,aiming at the maximized annual profit.Finally,the gasification unit and methanol synthesis unit are taken as examples to demonstrate the effectiveness of the proposed method.