Simulation Research On Carbon Capture Process Of Flue Gas Of Coal And Biomass Oxygen-enhanced Combustion By ASPEN PLUS

The global climate issues caused by the emission of greenhouse gas are threatening the safety of mankind.Power industry accounts for about one-third of the anthropogenic carbon emissions.As a result,the carbon reduction of power plants has become a research hotspot due to the urgency of controlling global warming.Climate crisis and shortage of fossil fuels impel the application of renewable energy.As a carbon-based renewable energy with“zero”CO₂ emission,biomass has been applied in direct-fired power generation.However,controlling the current carbon concentration in the atmosphere makes it necessary to implement carbon capture in power plants.The combination of biomass power generation with carbon capture can realize power production with negative emission of CO₂,which is helpful to alleviate the climate crisis.In the world,traditional coal-fired power plants without carbon capture account for a large proportion,which makes the research on decarbonization process and biomass blending retrofit of engineering significance.The present thesis aims to provide some references for coal and biomass combustion carbon capture retrofit of large power plants in aspects of tower size and operating parameters in a simulated way.First,Aspen Plus software for process simulation was adopted to simulate the oxygen-enhanced combustion of coal and biomass in 300 MW power plant.The flue gases of various fuels（Shenhua coal,peanut hull,rice straw and rice hull）,biomass heat input ratios（0,0.25,0.5,0.75 and 1）,oxygen concentrations（21%,26%and 31%）and cooling temperatures（40℃,50 ℃ and 60 ℃）were obtained.The results indicated that the mass of flue gas and CO₂ mole fraction varied with fuel composition and calorific value.The descending order of flue gas amount was rice straw,Shenhua coal,peanut hull and rice hull,while the CO₂ concentration of flue gas increased in this order.Compared with Shenhua coal,the flue gas from peanut hull,rice stalk and rice hull decreased by about 1%,increased by about 21%and decreased by about 10%respectively when the combustion flue gas at 21%oxygen concentration is cooled to 40 ℃.Reducing the cooling temperature of flue gas and increasing oxygen concentration are conducive to obtain less and higher CO₂ concentration flue gas.The amounts of flue gas at 40 ℃ from Shenhua coal,peanut hull,rice stalk and rice hull decreased by about 1%,5%,5%and 4%,respectively,when comparing to 60 ℃.Oxygen concentration had the most significant influence on the flue gas volume.When the oxygen concentration increased from 21%to 31%,the flue gas amount of the four fuels decreased to about 70%of the original level.Secondly,the absorption and stripper devices were designed considering coal-fired flue gases at three different oxygen concentrations,respectively,thus three couples of sizes were obtained.The oxygen concentration indicated geometry and size of tower facilities.With increasing oxygen concentration,the size of absorber decreased significantly,which showed19%and 34%cut-down in volume at 26%O₂ and 31%O₂,respectively,compared to that of21%O₂.While stripper had less change in size,the volume reduced by 8%and 16%,respectively.Subsequently,the decarbonization process with monoethanolamine（MEA）was simulated.The effects of lean solvent loading,MEA concentration,stripper operating pressure,temperature difference of process heat exchanger and removal percentage on regeneration energy requirement were investigated.In the range of variations,the results showed the thermal energy requirement first reduced and then rose with the increase of lean solvent loading or MEA content.The smaller temperature difference of exchanger contributed to recovering more heat.The rising stripper pressure can decline the energy consumption for regeneration and condenser.The thermal energy requirement increased with increasing carbon removal rate,especially when carbon removal rate exceeded 90%.The results showed that regeneration energy was a coupling result of multiple factors.The minimum regeneration energy consumption was 3.44 MJ/kg CO₂ at 0.22 lean liquid load,30%MEA,heat transfer temperature difference of 5℃ and stripper pressure of 1.9bar.At last,the simulation was presented with the combined process of combustion and carbon capture.By varying lean solvent loading,the optimum lean loading and minimum thermal energy requirement of each kind of flue gases was obtained.The results showed that the capture thermal energy requirement for coal mixed with biomass could be increased or decreased compare to that of single coal fuel.The less oxygen required and higher carbon content per quantity of heat of fuel resulted in less flue gas and higher CO₂concentration,and further lower thermal energy consumption for CO₂ regeneration could be reached.However,overall,the impact of fuel change on regeneration energy consumption was not of great significance.At 21%O₂,the regeneration energy consumptions of peanut hull and rice hull were declined by 0.2%and 1.4%,respectively,and rice stalk was increased by1.5%compared to that of coal.In addition,the effect of oxygen concentration on the regeneration energy consumption was not significant due to the application of towers with different structures and sizes.The minimum regeneration energy consumption for coal-fired flue gas at 26%O₂ and 31%O₂ was 0.7%and 1.4%lower than that of 21%O₂,respectively.The minimum thermal energy requirement for regeneration of rice hull flue gas was 3.37MJ/kg CO₂ at 31%O₂,while the maximum was 3.49 MJ/kg CO₂for rice stalk at 21%O₂.