| Chemical-looping combustion(CLC) is one of the most advanced CO2capture technology. In this paper, the reactive adsorption kinetics of nano CaO with CO2of the multiple-cycled pretreatment adsorbents, the reactive adsorption characteristics of multiple-cycled adsorbents in fixed bed, and CO2capture properties in a circulating fluidized bed, were studied, which were important for preparation of adsorbent, determination of parameters and design of reactor in CO2capturing process.Firstly, a nano CaO based micro-sphere sorbent with high sorption capacity was prepared, this sorbent had a average particle size of50μm, and its attrition property and fluidity made sure that this micro-sphere sorbent could be used in circulating fluidized bed.Secondly, this paper studied on the reactive kinetics of nano CaO with CO2in a multiple-cycled sorbent. After experienced42cycles in a fixed bed, the reactive sorption rate of the sorbent with CO2was tested in thermogravimetric analysis(TGA) at550℃-630℃under a N2atmosphere with0.010-0.020MPa CO2. According to the gas-solid reactive adsorption model, we fitted the experimental data, got the kinetics equation of reactive sorption, and the activation energy for carbonation is77.7kJ/mol, the average relative deviation of the sorption ratio is less than6.38%. The reactive sorption rate of multiple-cycled sorbent in the fast surface reaction regime was similar to the fresh sorbent, but the activation energy of former was higher.The paper concerned the reaction characteristics of sorbent after multiple cycles in the fixed bed reactor. The research shows that when the residence time was more than4s, CO2in the fluid was adsorbed completely by nano CaO in the sorbent. The effects of temperature, partial pressure of CO2and W/F ratio on the reaction sorption were researched under the following reaction conditions:a temperature of550-600℃, a CO2partial pressure of0.01-0.02MPa, W/FCo2=1176-2352g·mol·min-1. The results showed that as the reaction temperature increasing, the reaction sorption speeds up; increasing the CO2partial pressure increased the reaction rate of the sorbent. The sorption conversion curve was not a typical sigmoid-type conversion curve in the fixed bed reactor, for there were two peaks on the reaction rate curve(dX/dt) and the character of two-peak were more and more obvious as the CO2partial pressure increasing or the reaction temperature decreasing. The reaction rate of the sorbent in the fixed bed reactor was quite high, and the reaction conversion of the sorbent in the fixed bed reactor was half of the conversion in TGA after the fast chemical reaction.This paper also studied CO2capture properties of nano CaO based sorbents in circulating fluidized bed. In cold model experiment, the linear relationships between sorbent circulating amount and pressure in top of cabonator (P3)、sorbent quality in regenerator and pressure in bottom of regenerator (P1) were firstly studied, and then cold model looping was also conducted continuously and stably.In hot model experiment, absorption experiment in single fluidized bed was conducted firstly to investigate effects of temperament, CO2partial pressure and gas-sorbent ratio on absorption. Results showed that absorption was poorer in fluidized bed than in fixed bed due to its short contact time of gas and solid; increased temperature can improve absorption effect and reduce CO2concentration; though increased CO2partial pressure can speed up reactive absorption rate of sorbent, but it also bring high CO2concentration in exit; increased sorbent quality and reduced gas-solid ratio in cabonator can prolong contact time of gas and solid, improve absorption effect and reduce CO2concentration in exit. In circulating absorption study, effects of operation conditions on absorption effect were the same as those in fluidized bed absorption experiment. In this hot model experiment, the wear rate of sorbent was5.27%.In brief, nano CaO based carbondioxide sorbents can capture CO2at a high rate, after multiple cycled, the CO2capturing rate of sorbents has litter change and the sorption capacity keep stable, so this sorbent can be used in circulating fluidized bed to capture CO2. The results of above studies will be a reference to the preparation of adsorbent and the design of circulating fluidized bed in CO2capture process. |
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