| In-situ CO2separation can be achieved by the integration of coal gasification and CO2absorption by CaO. In this dissertation, the CaCO3regeneration process with CaSO4as oxygen carrier was studied, to reveal chemical equilibrium, reaction rate, emission of sulfur-containing gases, and eutectic possibility of calcium-based materials in the process. The main work and results are shown as follows:1. Thermodynamic analysis of CaO regeneration system with CaSO4oxygen carrierBased on the chemical equilibrium of the process, the reaction condition of CaO regeneration system with CaSO4oxygen carrier was studied and several findings were obtained. In order to ensure the calcium carbonate decomposes completely, there existed minimum flow rates of H2O and carbon in the CaO regeneration reactor at every given pressure. Compared with the CaO regeneration process using oxy combustion of carbon, the minimum flow rates of H2O and carbon were higher in the CaO regeneration process using CaSO4oxygen carrier. The yields of H2S and SO2in product gas declined with the increasing temperature and decreasing pressure. With the decreasing temperature difference between CaO regeneration reactor and CaS oxidation reactor and the decreasing pressure, the exchange of heat and solid mass between the reactors declined, while Gs increased.2. Pressurized TGA expriments of CaSO4oxygen carrier and cokePressurized TGA experiments were performed with coke and CaSO4mixed samples in H2O and N2atmospheres. The weight loss rate of coke with CaSO4in pure N2atmosphere declined rapidly, and the final carbon conversion was lower than that of coke in steam atmosphere. Compared with the reaction between coke and CaSO4in pure N2atmosphere, the introduction of H2O into the atmosphere can improve the reaction rate in the early period, but the rate declined as the reaction proceeded, and the final conversion of CaSO4and carbon decreased with the increase of partial pressure of steam in the atmosphere.3. Pressurized fixed-bed expriments of CaO regeneration system with CaSO4 oxygen carrierCaO regeneration experiments with CaSO4oxygen carrier were performed in a pressurized fixed-bed reactor, and the effects of reaction conditions on the yields of sulfur-containing gases were studied. It was found that the H2S yield declined with the increasing temperature and decreasing pressure of H2O. With the temperature increasing from900to950℃, the volume fraction of H2S declined from2635to2174ppmv, while the total amount of H2S yield declined from936mg to918mg. With the pressure of H2O decreasing from2.4to1.67MPa, the volume fraction of H2S in product gas decreased from2635to165ppmv.4. DTA&TG measurement and analysis of CaO-CaS-CaSO4systemTG and DTA measurements of CaO-CaS-CaSO4mixtures with different molar fractions were performed using an atmospheric thermal analyzer under a nitrogen atmosphere. It was found that eutectic phenomenon of CaS and CaSO4mixture samples did not exist within700-1300℃. The conclusion was also correct for the samples of CaO, CaS and CaSO4mixture within700-1500℃.5. Thermodynamic analysis of direct hydrogen production from coal with CaSO4oxygen carrierThermodynamic analysis of direct hydrogen production from coal with CaO regeneration by CaSO4oxygen carrier was performed and several findings at the pressure of3.0MPa were obtained. The H2yield in gasification reactor increased with the increasing temperature of CaO regeneration reactor, while the yields of sulfur-containing gases in CaO regeneration reactor declined. The yields of sulfur-containing gases produced from regeneration reactor decreased with the increase of Ca/C ratio in the gasification reactor, while the yield of H2from gasification reactor had a similar trend. Compared with the simulation results by assuming that the solid products out of regeneration reactor could be separated perfectly, less H2was produced when the solid products would not be separated, while the yields of sulfur-containing gases increased. |
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