Process Simulation And Energy Optimization Of Synthesis Gas To Methanol In TBCFB System Based On Self-heat Recuperation Theory

In China,the energy consumption structure dominated by coal resources will be not easily changed for a short time.The modern coal chemical industry,as an important method of coal utilization,can effectively improve the comprehensive utilization of coal.Among them,coal to methanol which is a significant aspect of the modern coal chemical industry still exists some problems such as high energy consumption and high carbon dioxide emissions with a large amount of low-grade heat waste.According to such energy structure and related utilization techniques,energy-saving carbon reduction become a vital approach to achieve large-scale carbon reduction.The triple bed combined circulating fluidized bed（TBCFB）technology proposed by the University of Tokyo can effectively improve the efficiency and the level of comprehensive coal utilization.Then,the coal-based polygeneration system with such technology as the core can also give full play to the advantages of its hierarchical conversion.In addition,a new energy cycle theory---self-heat recuperation（SHR）could increase the energy quality coefficient of process logistics which makes full use of low-grade heat and leads to the system energy loss reduction.Therefore,this work mainly studies the methanol synthesis process in a coal-based polygeneration system with the TBCFB,constructs a new methanol production process using TBCFB synthesis gas as raw material,and uses chemical process simulation software to simulate and model verify this process,also the energy optimization is further carried out based on the self-heat recuperation theory.The main researches are as follows:Through the sensitivity analysis of bubbling fluidized bed gasification in the TBCFB,the optimal water-to-carbon ratio for methanol synthesis without synthesis conversion is determined.The results show that when the water-to-carbon ratio reaches 2.7,the produced synthesis gas CO and H₂ from coke gasification could meet the requirements of methanol synthesis feed gases,which followed a new methanol synthesis process.During this newly designed process,the raw material gas produced by TBCFB is directly used to remove excess CO₂ and H2S gases by low-temperature rectisol technology,and then undergoes the low-pressure methanol synthesis and three-column rectification refining without water gas shift.Then,using the chemical process simulation software to establish this process,this work first compared the simulation results with industrial data to verify the accuracy of the model and analyzed the waste heat of each unit to determine the energy target.It is demonstrated that the methanol synthesis unit is a threshold problem,which could meet the energy demand through its own heat exchange network design,and recover up to 1604 k W of heat without additional heat sources;the low-temperature rectisol and the methanol distillation unit are pinch points,among which rectisol recover a maximum of 9113 k W of heat,but still requires 2105 k W of cold utilities and 1445 k W of thermal utilities.The waste heat analysis provides a theoretical basis for further energy-saving optimization;methanol distillation can recover a maximum of13,985 k W of heat,and 14375 k W of heat utilities,and 14229 k W of cold utilities are required.On the basis of the above waste heat analysis,the optimization plan and operating conditions of the self-heat recuperation of the low-temperature methanol washing and methanol rectification unit are determined through the analysis,and the heat exchange network design is redesigned for the optimized process,and the energy consumption of the process before the optimization is performed by comparison.The results show that the energy consumption of the TBCFB methanol synthesis process after the optimization of self-heat recuperation is significantly reduced.Here,the cold utility project of the low-temperature rectisol unit saves29.4%,while the thermal utility project saves 49.8%,and the total energy consumption saves25.8%;The cold utility project of the methanol distillation unit saved 69.5%and the total energy consumption saved 26.1%.Thus,the TBCFB methanol synthesis process based on the self-heat recuperation theory shows great energy-saving potential and provides a theoretical guide for optimizing the TBCFB low-rank coal clean conversion polygeneration system.