The Experimental And Model Study Of The Sequential SO₂/CO₂ Capture Behavior By Modified Ca-based Sorbent

Calcium-Looping?Ca-L?method using the modified calcium-based sorbent with high efficiency is a mature technology which can be applied to capture CO₂ from the flue gas after combustion.However,the presence of SO₂ in the flue gas will aggravate the attenuation of CO₂ capture performance during the capture process.Moreover,the directly abandonment of the inactivated modified calcium based sorbent will cause secondary pollution to the environemnt.The above problems restrict the further industrial application of Ca-L method.Sequential SO₂/CO₂ technology directly using spent modified calcium-based sorbent or hydration activated spent sorbent is considered to be one of the effective solutions to the above problems.In this study,the modified calcium-based sorbent which was added with inert metal oxide MgO and Al₂O₃ respectively were used to analyze the reaction characteristics in the sequential SO₂/CO₂ capture process.The effects of cycle number on the sulfation conversion,the specific surface area and the total pore volume of the sorbent were investigated.The kinetic model was established to analyze the sulfation reaction.To find the optimum hydration condition,the experimental scheme was designed for hydration activation reaction based on the response surface methodology.The internal relationship between the pore structure of the modified calcium-based sorbents and the fractal dimension was analyzed by fractal theory.The results show that the modified calcium based sorbent added with inert metal oxide MgO or Al₂O₃ all have the higher cyclic stability than the natural calcium-based sorbent.The carbonation conversions of MCMA and CaO/Ca₁₂Al₁₄O₃₃3 were 42.47%and 49.99%after 50 cycles,respectively.The spent calcium-based sorbent was used to capture SO₂ directly,and the sulfation conversions of MCMA and CaO/Ca₁₂Al₁₄O₃₃were 35.48%and 28.44%after 35 cycles,respectively.The sulfation reaction has two distinct stages:the first stage with chemical reaction-controlled and the second stage with product layer diffusion-controlled.The most sulfation conversion was obtained in the first stage.The shrinking unreacted core model was selected to analyze the kinetic characteristics of the modified calciun-based sorbents in the process of sulfation reactions.The values of k_d were much less than those of k at the same Ca-L cycle numbers.For the hydration activated spent modified calcium-based sorbent,the optimal hydration condition including the hydration temperature,the hydration time and the liquid-solid ratio are 80 ^oC,15 min and 1:1 respectively.Under the optimal hydration condition,the sulfation conversion was 67.17%,which was more than the conversion rate of the fresh calcium-based sorbent?69.32%?.The modified calcium-based sorbent had obvious fractal characteristics.With increasing the cycle numbers,the surface fractal dimensions has been on the decline,and the structure fractal dimensions remanined about the same,which indicates that the modified calcium-based sorbent has good skeleton structure.The sulfation conversion and the carbonation conversion were all linearly dependent on the surface fractal dimension.