Study On Highly Performance Calcium-based Sulfur Retention Additives

Coal is the main energy in china's energy structure. SO2 from coal combustion is one of the major air pollutants, leading to serious environmental pollution. Thus, it is urgent to control the emission of SO2. Among all kinds of desulphurization technologies, dry calcium-based retention technique is the most suitable one for civil coal combustion, small-scale industrial furnace as well as old boiler due to its simple process and low cost. However, low desulfurization efficiency and low utilization ratio of calcium have limited the development of this technology when using calcium-based absorbent alone. A new economic method, doping some additives into the Ca-based absorbent, has been developed to resolve this problem.It was found that alkali metal salts and rice straw ash(RSA) are both appropriate calcium-based absorbent additives, by investigating the desulphurization promoting of three different pure chemical additives and two different solid wastes. Compared with pure chemical additives, RSA is more suitable for civilian coal. The effect of rice straw ash ratio, Ca/S, combustion conditions were investigated, and civil briquette experiments were carried out at the scene. The phases of the sulfur retention ash were also analyzed by XRD. The calcium-based sulfur retention absorbent was treated by Acetic acid and activated fly ash (FA), and the sulfur retention efficiency was greatly improved when the temperature is above 1100℃.The results of the experiment show that the optimize process conditions of RSA/ CaCO3 sulfur retention absorbent are as fellow: mass ratio of CaCO3 and straw ash is 10:1, the Ca/S ratio is between 1.5-2.5, the temperature is between 800℃-900℃,the amount of additional water is 4%, and the air flow is 150 ml/min. The sulfur retention rate of RSA/CaCO3 is above 70%, When Ca/S = 2.0, the air flow is 150 ml/min and the temperature is 800℃.The Civil briquette experiments results show that, the sulfur retention absorbent has the higher sulfur retention efficiency to both anthracite and bituminous coal, which reached to 90%. The sulfur retention rate increased from 16% to 40% at 1100℃by acetate-quality processing and activated FA; when the temperature is 1250℃, the sulfur rate reached to 20%.The XRD patterns indicated that, the main form of sulfur in the sulfur retention ash are CaSO4 when temperature is below 1000℃; 2Ca2SiO4·CaSO4 is found when the sulfur retention temperature is 1100℃; the absorption peaks of 3CaO·Al2O3·CaSO4 are also found When the temperature rises to 1250℃.