Simulation Of Calcium-looping Process In CO₂ Capture From Coal-fired Power Plants

The flue gas of coal-fired power plants is the main source of CO₂ because of its large flue gas flow and concentrated emission.At present,the high-temperature calcium-based CO2 capture technology has become one of the most potential CO2capture technologies due to its low energy loss and easy access to adsorbent materials.Based on the analysis of the characteristics of coal-fired flue gas and the reaction principle,a high-temperature calcium-looping CO₂ capture process was designed for the 350MWe coal-fired power plant as a reference.The operating parameters of the reference power plant were simulated and optimized by Aspen Plus software,and the fluidization characteristics in the carbonate reactor were analyzed.This paper analyzed the carbon dioxide-calcination reaction principle of CO₂capture process and the cyclic absorption characteristics of adsorbent?CaO?from a theoretical perspective.The pore structure of CaO determines that the conversion rate of the absorption reaction under high temperature conditions cannot reach 100%.The porosity and specific surface area are greatly affected by the reaction temperature,which in turn affects the maximum conversion rate,resulting in a single conversion rate of about 0.7 and a cyclic conversion rate of about 0.17.Taking the 350 MWe coal-fired power plant as a reference,the calcium-looping process takes place in circulating fluidized bed.When the CO₂ capture rate is required to be at least 90%,the solid inventory in the carbonator needs to be at least 607.7 tons.In order to ensure the decomposition heat of CaCO3,the theoretical amounts of coal should be 99.37 tons/hr at least,which is supplied by oxygen-combustion.The theoretical combustion temperature of heating coal is 2250?.Aspen Plus software?V8.6?was used to simulate the high-temperature calcium-looping process.By analyzing the carbonator temperature,calciner temperature,make-up flow,purge rate,gas-solid separation efficiency and CO2recovery rate on the system optimization index,optimization parameters of the 350MWe coal-fired flue gas system were determined.The conclusions are:the carbonator temperature is 630?,the calciner temperature is 950?,make-up flow is 0.04F_CO2,purge rate is 0.04,gas-solid separation efficiency is 1 and CO₂ recovery rate is 0.6.The system optimization indicators are:carbonized CO2 capture rate is 88.31%,net flue gas CO₂ concentration is 2.62%,system CO₂ capture rate is 91.97%,solid circulation is 673.53 tons/hr,and CO2 production is 753.51 tons/hr.The carbonation fluidized bed of the CO₂ capture system was simulated with the1-D Fluidized bed model.The fluidization characteristics of the fluidized bed dense phase zone and the whole bed were obtained,which were the velocity and volume fraction of the bubble in the dense phase zone and the gas-solid phase in the full bed height,respectively.Under the treatment scale of the reference power plant,the bed height of the carbonized fluidized bed is 40m,of which the dense phase zone height is3.22m and the dilute phase zone height is 36.78m.The total mass of circulating particles in the fluidized bed reactor is optimized to 710096 kg.When the flue gas enters the fluidized bed at superficial velocity of 1.86 m/s,the CO2 capture rate can reach 96.86%,and the minimum fluidized flow rate of flue gas is 400 kg/s.