The Modeling And Optimation Of Coal-based Polygeneration System For Acetylene And Power

The thermal plasma process for converting coal to acetylene provide an prospective approach for green, low carbon and effective utilization of coal, and it can solve the pollution problem of the “industrial three-waste” for calcium carbide methods. It is quite significant to promote clean and efficient utilization of coal resources. However, with the rapid expansion of plasma device’s capacity, the potential problems begin gradually reveal, which are high energy consumption, low coal conversion, high excess heat, heavy chemical energy loss, large numbers of purge gas and solid waste are difficult to deal with. The problems have seriously restricted the industrialized production progress for plasma gasification technique.In order to solve the problem of plasma technique, this paper proposes the acetylene and power polygeneration system that are coupled by acetylene chemical system and power system. The model of plasma gasification and acetylene purification are developed by adopting Aspen Plus software, which is used to analyze the exergy equilibrium of these two processes and obtain their exergy flow diagram. According to the simulation results, the total system’s input exergy is 74368.72 MJ·h-1, the earning exergy of product account for 19.03%, the total inner exergy loss account for 9.47%, the external exergy loss account for 71.50%. The steam exergy loss of external exergy loss only account for only 3.48%, but coal cinder and purge gas exergy loss account for 68.02% of the input exergy, which are the main reasons for exergy loss. The results can point optimum design and energy saving reconstruction of polygeneration system in the correct direction. The comparative study on three common power systems show that the power system of coal fired power plant is most suitable to integrate with plasma gasification system to build acetylene and power polygeneration system.Based on the power system of a subcritical coal fired power plant,this paper establish the simulation processes of power system including boiler combustion system, boiler heat transfer surface system, turbine and regenerative system. After enlarge plasma device’s capacity to 78 MW, the acetylene and power polygeneration system is coupled by subsystems according to the polygeneration integration principles including “component counterpart”, “classification conversion”, “energy level counterpart” and “cascade utilization”. The polygeneration system can increase power generation of 112.68 MW, the emission of coal cinder decrease 17.84 t·h-1, the emission of purge gas decrease 8.92 t·h-1, the equivalent unit power consumption of acetylene decrease 22.43 kW·h·kg-1, the thermal efficiency increase 9.87%.The productions of acetylene and electricity for polygeneration system are taken as the optimized object. The key operating parameters of plasma reactor and flowsheet of polygeneration system are optimized to obtain the highest utilization ratio of energy and resource. The simulation results indicate: hydrogen is the optimal work gas, the optimal moisture of coal should be smaller than 5%, the optimal pressure of reactor is 1atm, the optimal temperature of reactor is 2100 K ~3500 K,the optimal numbers of stage for absorber was 24, the effect of methane as carrier gas is not obvious. Then, the process of polygeneration system is optimized after obtain the optimal parameters to simplify the process and improve the energy utilization efficiency. After optimization, energy consumption of the plasma reactor decrease 4.62 MW, regenerative extraction steam decrease 60.728 t·h-1, power generation of the turbine increased 8.16 MW. The performance of polygeneration is evaluated with four evaluation criteria. With the power of plasma reactor increase, the thermal efficiency, exergy efficiency, relative energy saving rate and equivalent generating efficiency of polygeneration system are enhanced, the equivalent energy consumption ratio reduce, and the optimal recycle ratio is 18.