CO₂ Capture Characteristics And The Influence Of Sulfation Of NaBr Modified Calcium-based Sorbent

CO₂ capture technology based on carbonation-calcination cyclic reactions of calcium oxide,referred to as the calcium looping technology,is one of the most widely studied and promising CO₂ capture technologies.However,the technology encounters two difficulties:firstly,in the long-term cycle,calcium-based sorbents are prone to sintering and lead to a decrease in adsorption capacity;secondly,the presence of a small amount of SO₂ in flue gas will seriously affect the CO₂ capture performance of calcium-based sorbents.Aiming at the above two problems,this paper improves the cycling performance of different types of calcium-based sorbents by alkali metal modification,and studies the effect of sulfation on the CO₂ capture capacity of alkali metal modified sorbents.Firstly,the method of modifying calcium-based sorbents by adding trace amounts of Na Br was proposed in this thesis.Three different types of calcium-based precursors,including pure CaCO₃,dolomite,and sol-gel calcium-based sorbents,were screened as raw materials,and during the preparation of CaO-based sorbents using the above three raw materials,they were respectively doped with Na Br Modified to obtain the required three modified calcium-based sorbents:CaO/Na Br,dolomite/Na Br,SG-CaO/Na Br.And the carbonation and sulfation effects of three calcium-based sorbents after doping and modification were compared and studied.Cyclic carbonation/calcination experiments were carried out on a thermogravimetric analyzer,the effects of Na Br modification on the crystal structure,pore size distribution,specific surface area surface morphology of calcium-based sorbents were analyzed by X ray diffraction analyzer,specific surface area and pore size analyzer,scanning electron microscope and other research instruments.The experimental results showed that for pure CaCO₃ and dolomite sorbents,Na Br doping had a positive effect on the CO₂ capture performance of calcium-based sorbents,the CO₂ capture capacity of the CaO/Na Br after 50 cycles was 0.22 g CO₂/g sorbent,which was 3.67 times that of pure CaO.In contrast,dolomite/Na Br had the highest stability,and the CO₂ capture capacity after 50 cycles was only reduced by about 10%.However,for SG-CaO,Na Br doping had a negative impact:Na Br doping greatly reduced the CO₂ capture capacity of the sorbent,and most of the pores of the sorbent disappeared and the crystalline experienced severe sintering.Then,the relationship between pore structure and fractal dimension of different calcium-based sorbents was studied by fractal theory.The analysis results showed that the fractal dimensions of pure CaCO₃ and its Na Br-modified calcium-based sorbent and dolomite and its Na Br-modified calcium-based sorbent gradually decreased with the increase of cycles during 50 cycles of carbonation/calcination reactions.For the sorbent prepared by the sol-gel method,the fractal dimension was more complicated due to its nanostructure characteristics.The fractal dimension of SG-CaO was higher than that of SG-CaO/Na Br after 20 cycles.Therefore,more abundant pore structure was observed in the apparent morphology diagram.Finally,the cyclic carbonation/sulfation-calcination experiments of different calcium-based sorbents were carried out with 0.1%,0.2%and 0.3%different concentrations of SO₂in a self-made thermogravimetric reactor.The cyclic CO₂ capture performance and cumulative SO₂ capture performance of calcium-based sorbents were studied.The experimental results showed that although there was a competitive reaction between SO₂and CO₂,Na Br had different modification effects on different types of sorbents.In the presence of SO₂,after 10 cycles of reactions,the CO₂ capture capacity of CaO/Na Br sorbent was more than 1.68 times that of pure CaO;the CO₂ capture capacity of dolomite/Na Br sorbent was more than 1.53 times that of dolomite.For the sorbent prepared by sol-gel method,Na Br showed a negative effect,and the CO₂ capture capacity of the SG-CaO/Na Br sorbent after 10 cycles was slightly lower than SG-CaO.The results showed that Na Br could effectively enhance the CO₂ capture capacity of CaO-based sorbents prepared from pure CaCO₃ and dolomite precursors.