Experimental And Simulation Study On Direct Sulfation Of SO₂ With Limestone In O₂/CO₂ Atmosphere

Oxy-fuel combustion technology is considered the world's most feasible of the boiler combustion technology, and compared with the traditional coal combustion technology, which not only can improve the combustion efficiency, recover CO₂ easily, but also significantly reduce SO₂, NOx emissions. So it is a low pollutants discharge and environment-friendly new combustion technology. As a result of the existence of high concentration CO₂, the mechanism of calcium-based desulfurization compared with the conventional combustion atmosphere changes greatly in O₂/CO₂ atmosphere, thus there is greatly important theoretical and application value to do the basic research on desulfurization calcium-based mechanism in oxy-fuel combustion.Compared with the conventional air atmosphere, the high concentration CO₂ atmosphere can inhibit the decomposition of the limestone. So this paper first response to the conditions of desulfurization reaction defined. Through the chemical thermodynamics calculation and the experiment using thermogravimetric analysis, the calcination decomposition characteristics of the limestone are studied to determine the conditions of desulfurization reaction in the O₂/CO₂ atmosphere. The results show that, the beginning decomposition temperature of the limestone in O₂/CO₂ atmosphere is higher than that of in air atmosphere, and the initial decomposition temperature increase as the CO₂ partial pressure increase.The desulfurization experiment at 750℃and 850℃is carried out to study the desulfurization characteristics of the limestone on the thermogravimetric analysis (TGA) and small-scale fixed-bed in O₂/CO₂ atmosphere, as well as at high temperature 950℃, and the micro structure characteristics of the sulfide product from the small-scale fixed-bed is analyzed through pore structure analysis and SEM, XRD analysis. The results showed that: at the same temperature, there is very difference between CaCO3-SO₂ desulfurization reaction and CaO-SO₂ indirect sulfurization reaction. There has higher calcification efficiency in CaCO3-SO₂ desulfurization reaction. At the high temperature, the sulfurization reaction of the limestone is affected by two types of sulfurization reaction in O₂/CO₂ atmosphere.Based on solid-state ion diffusion in the sulfide products layer, a theory model of the CaCO₃-SO₂ desulfurization reaction is stablished, through with the conversion rate of calcium in the process of the CaCO3-SO₂ desulfurization reaction is calculated. And it is compared with the results of the gas molecules model calculations and the result showed that solid-state ion diffusion model fit experimental results better.