Simulation And Optimization Of Methanol-electric Polygeneration System Based On CFB Unit And Plasma Gasification Coal

As coal-fired power plants using circulating fluidized bed boilers gradually become peak-shaving units,their system efficiency,and energy utilization rate are low.Because it is often used for peak shaving,it runs under low load conditions for a long time.He needs to find new ways to increase his load.Based on the characteristics that the co-production of chemical and power can increase the load and operating efficiency of the power plant,this paper proposes a system strategy for co-production of a system that uses plasma gasification of coal to produce methanol and a coal-fired power plant system that uses a circulating fluidized bed boiler.First of all,this article uses Aspen Plus software to establish some models.These models include plasma gasification coal system model,plug flow reactor methanol synthesis system model,methanol rectification system model using four-tower rectification process,boiler combustion and heat exchange system model,steam turbine and heat recovery system model,etc.These models were compared and verified according to the actual parameters of the industrial site.Based on these models,a polygeneration system was constructed,which includes a system for plasma gasification of coal to synthesize methanol and a circulating fluidized bed boiler system.After the establishment of the co-generation system,the coal supply of thermal power plants has been reduced by 50.50 t/h,and the power generation has increased by 137.53 MW.The cinder emissions of plasma coal gasification equipment have been reduced by 8.40 t/h.The unreacted gas emissions of the methanol synthesis system have been reduced by 57.92 t/h.Both the plasma gasification coal system and the methanol synthesis system have achieved zero emissions of pollutants.After the increased power generation is used in the chemical industry,the energy consumption per unit of methanol production is reduced by 3.51 k W·h/kg.After the establishment of the co-production system,the plasma gasification coal process,methanol synthesis process,and methanol rectification process will be analyzed for exergy balance.The exergy balance analysis results show that the total input exergy of the process is158003.05 MJ/h.The product revenue exergy was 84036.57 MJ/h,and the system exergy efficiency was 53.19%.The total internal exergy loss was 4,1051.02 MJ/h,accounting for25.98% of the total exergy.The total external exergy loss was 32915.45 MJ/h,accounting for20.83% of the total exergy.The total exergy loss of coal slag,purge gas,and steam is 20.81%,which is the main reason for the exergy loss of the methanol synthesis process.Finally,the power system runs under full load and high-efficiency conditions.Aiming at the maximum output of methanol and the optimal utilization of energy,the key parameters of the plasma gasification system and methanol production system are analyzed and optimized.Subsequently,the process,parameters,and energy of the polygeneration system were integrated and optimized.After optimization,the optimal water vapor supply rate is 3000 kg/h,and the optimal air supply rate is 1500 kg/h.The optimal methanol synthesizer pressure is 6MPa,and the optimal reaction temperature is 210°C.The best mass reflux ratio of the pre-rectification tower is 1.5.The best distillation feed ratio of the pressurized column is 0.59,and the best distillation feed ratio of the atmospheric column is 0.25.After optimizing the process,the overall energy consumption of the plasma gasification coal process was reduced by 5.33 MW.The steam extracted from the power generation system has been reduced by48.98 t/h,and the total power generation has increased by 12.50 MW.After the co-production,the power system has achieved long-term high-load and efficient operation.Under different chemical energy consumption conditions,the operating efficiency and energy utilization efficiency of the polygeneration system have been optimized.The results show that the relative power generation of the co-production system,the thermal efficiency of the chemical system,and the exergy efficiency of the co-production system all increase with the increase of the load of the chemical system.