Combined Effect Of H₂O And SO₂ During Carbonation On CO₂ Capture In Calcium Looping

Calcium looping is one of the most promising carbon capture technology for coal-fired power plants,due to its advantages of high capture efficiency,wide source of raw materials and low economic cost.However,the combined effect of H₂O and SO₂ in coal flue gas on CO₂ capture by calcium looping is not clear,which limits the application of calcium looping in actual coal flue gas conditions.Therefore,the thermostatic thermogravimetric system was used to systematically study the combined effect of H₂O and SO₂ on CO₂ capture in calcium looping,and characterization of nitrogen adsorption and morphology were employed to further explore the mechanism of H₂O and SO₂.Finally,considering the combined effects of H₂O and SO₂,the random pore reaction model of calcium cycle was established.It is expected to provide theoretical support for the development of calcium looping technology.The research results are as follows:（1）The independent influence mechanism of H₂O and SO₂ on calcium looping in carbonation atmosphere was proved.In the carbonation stage,H₂O improves the adsorbent pore structure and reduces the diffusion resistance of CO₂ in the CaO particle pore,accelerating the carbonation rate in the rapid reaction stage.Thus,H₂O improves the carbonation conversion rate.For example,when the carbonation stage contains 20%H₂O,the carbonation conversion rate in the 10th cycle increases by 4.41%compared with the condition without H₂O.When SO₂ acts alone,SO₂ and CO₂ compete for CaO reaction sites.And Ca SO₄ blocks particle pores and hinders the diffusion of CO₂,therefore reducing the carbonation conversion rate.In addition,the hindering effect becomes more obvious with the increase of cycle number.（2）The combined effect and mechanism of H₂O and SO₂ on calcium looping in carbonation atmosphere were proved.When the carbonation atmosphere contains10%H₂O,the pore clogging of absorbent becomes more serious with the increase of SO₂ concentration from 0%to 0.1%,resulting in a decrease in the ability of circulating CO₂ capture.When the carbonation atmosphere contains 0.05%-0.1%SO₂,the absorbent pore volume increases gradually with the increase of H₂O concentration from 0%to 20%,the large pores increase significantly,and the carbon capture capacity is improved.The combined effect of H₂O and SO₂ is reflected in the fact that H₂O weakens the blocking effect of SO₂ on CO₂ capture and improves the carbonation conversion rate of absorbent.（3）Considering the sintering of CaO particles,the effect of H₂O and the simultaneous carbonation/sulfuration reaction,the random pore model of calcination,carbonation and sulfuration reaction of calcium based adsorbent was established.The reaction model can accurately describe the chemical reaction processes such as calcination,carbonation and sulfuration.The calculation results show that the outer layer of the adsorbent particles has a higher conversion rate,while the closer it is to the inside of the particles,the lower the conversion rate.In addtion,the conversion difference between the inner and outer layer of the adsorbent particles increases with the reaction time.H₂O improves the local carbonation conversion rate of the inner and outer layers of particles,while SO₂reduces the local carbonation conversion rate of particles.At the same time,CaO still maintains a high local carbonation conversion rate under the synergism of H₂O and SO₂.