Experimental Study On CO₂ Capture Of Flue Gas From Cement Industrial Using Ca-based Sorbents Modified With Vermiculite

Cement industry is pillar industry of our country’s economic development and the progress of the society, which has an indelible contribution to the development of economy. But as a resource and energy consumption industry, to a large extent, it discharged large amounts of carbon dioxide which influenced our country and even the world environmental protection. In cement industry, limestone is not only can be used as a raw material to product cement, but also can be used as the Ca-based sorbents to capture carbon dioxide from industrial flue gas. CCCR technology（a Ca-based sorbents Cycling Calcination/Carbonation Reaction technology） is a kind of new and effective method to capture CO₂ in flue gas from industry. However, Ca-based sorbents in the capture CO₂ existed a problem: its capture efficiency decreases heavily because of the sintering of particle surface under the high temperature with the increase of cyclic reaction times. So the research emphasis of this paper is to improve the resistance to sintering and the cycling carbonation rate of Ca-based sorbents.Based on the cement industry as the background, this paper use modified Ca-based adsorbents to capture CO₂ from the cement flue gas. Two differential producing area vermiculites, Xinjiang and Hebei, were studied as modifying agents to change the surface of limestone, improve the CO₂ capture capability of limestone. Vermiculite as unique two-dimensional layered silicate minerals structure, it has thermal expansion and temperature resistance. We can add it as a skeleton to the Ca-based sorbents, to change the particle surface morphology. The small parcel of vermiculite in the particle surface of Ca-based sorbents, can rapidly expanding in the process of heating up for the first time. It can be obstacles the contact of limestone particles in the process if cycling calcination/carbonation reaction, to delay the onset of sintering phenomenon and to improve the cycling carbonation rate of Ca-based sorbents. The effect of type, process mode and amount of vermiculite material on the cycling carbonation rate of modified Ca-based adsorbents were analyzed. The capability of CO₂ capture between accumulation and half suspension state were also compared, and the main research conclusions are as follows:（1）The main research of vermiculites comes from Xinjiang and Hebei as additive. Through different ways of processing modified Ca-based sorbents, according to the capability of CO₂ capture of Ca-based adsorbents analysis the best vermiculite origin and the optimal processing method: the purification of Xinjiang vermiculite modified effect is best. In addition, it found that vermiculite in circulation process has a small amount of N2 adsorption in the heating stage and set free it in cooling stage. But to release a quantity is very small, which can be neglected.（2）Adding vermiculite materials to Ca-based sorbent, it is not a linear relationship between additive amount and improvement effect. It shows that the maximum cycling carbonation rate can be by 6.66% when adding 1% vermiculite materials to Ca-based sorbent. The average of carbonation rate in 14 cycles can be by 9.91%.（3）For different particle size of Ca-based sorbents, it is by comparing before and after the modification of cyclic calcination/carbonation ability to capture CO₂,think of modified particle size in the range of 80¹25um works best.（4）After dozens of circulation, modified sorbents has excellent particle morphology and the pore distribution compared with unmodified Ca-based sorbent. From the microstructure of modified sorbents, limestone particles can be kept a good morphology and sintering phenomenon was also delayed. The microporous was more than the unmodified Ca-based sorbents. And the distribution of pore was more optimization. The pores of unmodified Ca-based sorbents are mainly distributed in 70¹20nm after 40 cycles, compared with it, the modified Ca-based sorbents’ pores are mainly distributed in 50¹00nm.