Design And Optimization Of Chemical Looping Gasification Process Based On Molecular Simulation

China’s energy distribution is extremely unbalanced with a"coal-rich,oil-poor,gas-poor"energy structure.Coal is a reliable energy source in China and also an important raw material for metallurgical and chemical industries,mainly used in combustion,coking,gasification,low-temperature dry distillation,hydrogenation and liquefaction etc.However,the massive consumption of coal resources will inevitably lead to a sharp increase in carbon emissions and even cause irreversible environmental pollution.On September 22,2020,General Secretary Xi Jinping proposed at the 75th session of the United Nations General Assembly that“China will increase its independent national contribution,adopt stronger policies and measures,and strive to peak CO₂ emissions by2030 and achieve carbon neutrality by 2060”.In this context,the comprehensive,rational and effective development and utilization of coal resources by transforming coal into clean fuel for clean and efficient conversion of coal has become an important issue that needs to be urgently solved in the field of coal chemical industry as it can guarantee energy security and promote ecological civilization.Based on the current research status,this paper makes a comprehensive study of Coal Chemical Looping Gasification（CCLG）process by means of Molecular Dynamics（MD）simulation combined with experimental,steady-state simulation and dynamic simulation.The downstream product design was carried out based on the CCLG process,and the process optimization method was used to ensure the quality of the product while taking carbon emission reduction as the primary target.At first,a series of simulations with copper oxide as the oxygen carrier were carried out to investigate the purity of the syngas produced by the CCLG process at different temperatures and oxygen carrier masses by a MD simulation approach in ReaxFF force field.The results show that the optimum reaction temperature is 850°C and the optimum C/O mass ratio is 1:1.5.In order to cross-refer with the simulation results,a series of CCLG experiments were also designed for the oxidation process using the same reaction temperatures and oxygen carrier masses as the simulations.The results of MD simulations were compared with experimental data,and the mechanism of the reaction was analyzed at the molecular level.Also,the trend of the syngas content with temperature and C/O ratio in the MD simulation and experimental results were observed to be quite consistent,which also proved the development potential of MD simulations in chemical looping gasification field.Afterwards,the optimized CCLG process was performed by steady-state simulation.Methyl methacrylate（MMA）and ethylene glycol（EG）were finally selected as the downstream products of high quality syngas produced by CCLG process,from various aspects such as foreign dependence and domestic production capacity under the current national conditions.After that,steady-state simulations of the designed processes were performed separately to verify the feasibility of the process.The results showed that the amount of directly emitted CO₂ was 0.0001 kg-CO₂/kg-MMA for the CCLG-MMA process and 0.0003 kg-CO₂/kg-EG for the CCLG-EG process.It can be seen from the results that the CCLG-MMA process and the CCLG-EG process own the advantages of low CO₂ emissions,high atomic utilization.Then a control scheme was developed for the final production process,and the stability of the control scheme was verified by adding disturbances using dynamic simulation to achieve safe and stable operation of the devices.Finally,the operating conditions of the CCLG-MMA process and the CCLG-EG process were optimized by sensitivity analysis and the pinch point analysis.Heat exchanger network optimisation techniques can reduce the process energy consumption by 38.5%for the thermal utilities and 37.2%for the cold utilities,with a total cost saving of 35.2%.