Characterization And Modeling Of SO₂ On The Cyclic Calcination And Carbonation Of Calcium-based Sorbent For CO₂ Capture

The global warming, caused mainly by higher level of CO₂ in the atomophere, has gotten more and more attention in recent years. Becaused of the high economic efficiency,the CO₂ capture and storage technology based on calcium-based sorbent calcination/carbonation cycles has been the most promising technology. In the past years, a lot of research has been done to investigate the cycle characteristics, but the influence of SO₂ on the cycle performance has been hardly reported. So in this work, using customized constant temperature CO₂ absorbing device, the influence of SO₂ on the calcium cycle was investigated in detail, which is more similar to the real gas condition in the circulating fluidized bed boiler.The influence of SO₂ on the calcium cycles was studied, and at the same time, the influence of calcination temperature, reaction time, SO₂ concentration and limestone character were also investigated. The results of the experiments show that the CO₂ capture performance of the sorbents is reduced by the SO₂ in the carbonation atmosphere,but the decrease of the carbonation capability is not proportional to the increase of the SO₂ concentration in the flue gas. In the tested carbonation temperature range（620-680℃）, both the carbonation ratio and the sulfation ratio of the sorbent raised with the increase of the carbonation temperature, so the carbonation ratio improvement caused by the rising carbonation temperature is greater than the reduction effect caused by the sulfation reaction. The carbonation time can influence the carbonation conversion of the cycle, but obviously it is not the major factor. The SO₂ influence is different on the carbonation of different kind of limestones, but the total effect is similar.A grain model taking into account the influence of two processes of the carbonation sulfation of CaO, which can describe the simultaneous carbonation and sulfation reaction of limestone. Based on the product layer solid state ion diffusion, the influence carbonation temperature and SO₂ concentration on the simultaneous carbonation and sulfation reaction of CaO was calculated, and the calculated results fit the experiment results well. The carbonation conversion vs cycle times in the CCS process by calcium cycle were tested with customized device, and the results were predicted by least squares support vector machine（LS-SVM） mode. The results show that there is a clear decrease of the calcium activity in the calcium cycly. The calcium activity is influenced not only by the cycle times, but also by the sorbent character, calcination condition, and carbonation condition. And the sorbent size, carbonation temperature, calcination temperature, calcination time duration, and the SO₂ concentration in the carbonation atmosphere are the main factors that influence the carbonation characteristic significantly.LS-SVM can be used to to describe the calcium cycle characteristic visually and accurately, which can be the new way to predict the calcium cycle characteristic.The prediction with different particle size, SO₂ concentration and carbonation temperature show that sorbents with size 38-75μm have the lowset carbonation conversion and sorbents with size 250-355μm have the highest carbonation conversion. Higher SO₂ concentration will decrease the carbonation conversion, and the optimum temperature is in the range of 680-710℃.