Experimental Study on the Removal of Low-Concentration SO₃ by Trona at Medium Temperatures

Spraying trona in a selective catalytic reduction system is an effective way to control SO3 emission. However, its application in the industry is often hindered by sintering at high temperatures, which reduces the reactivity and limits its wide application. Therefore, in this paper, we study the reaction characteristics of homemade sodium carbonate (Na2CO3) with SO3 in flue gas on a fixed-bed reactor. The mechanism of SO3 removal by trona was studied. It was found that with an increase in internal diffusion resistance, the rate control step of the reaction gradually changed from the joint control of external diffusion and chemical reaction to that of internal diffusion control. The increase in temperature accelerates the decreasing trend of the internal diffusion coefficient. This is mainly due to the sintering of Na2CO3 caused by high temperatures. When the temperature increases from 260 to 380 °C, the conversion rate decreases by 30%. By improving the pore structure, the sintering of Na2CO3 caused by high temperatures has been alleviated. The carbonation degree increases from 0 to 100%, and the conversion rate increases by 20%. Meanwhile, the competitive reaction caused by SO2 is also explored, and it is found that the increase in SO2 concentration only slightly reduces the absorption of SO3.