Fast selective catalytic reduction (SCR) process in fixed and fluidized bed reactors

Abstract

Fast Selective Catalytic Reduction (SCR) characteristics of $NO_x$ by $NH_3$ over different catalysts (supported/unsupported) has been determined in a fixed bed and a dual bubbling fluidized bed reactor. The experiments were carried out with the simulated feed gas having the same composition as of the power plant in “Korea” and it contains about 8% water, 10% oxygen concentration and nearly 150 ppm NO but some experiments were also performed by varying concentrations of oxygen, nitric oxide and nitrogen dioxide in the feed gas. Among all the catalysts tested, $Co_3O_4$ based catalysts are seemed to be the most active ones for both NO oxidation and $NO_x$ reductions even at high space velocity (SV) and at low temperature in the fast SCR process. Over $Co_3O_4$ catalyst for NO oxidation, the effects of calcination temperatures, $SO_2$ concentration, optimum SV for 50% conversion of NO to $NO_2$ were determined. In the presence of $SO_2$ , the Pt based promoted catalysts found to be less affected but $Co_3O_4$ exhibited adversely. These Pt based catalysts were also tested for different concentrations of oxygen, nitric oxide and nitrogen dioxide. On treating these catalysts with different $O_2$ concentration it is seen that the conversion of NO to $NO_2$ increases with increasing $O_2$ concentration from 3 to 12%, but it levels off at higher concentrations due to the saturation effect of $O_2$ concentration on the active site. The conversion to $NO_2$ decreases with increasing feed concentration of NO and also decreases by the addition of $NO_2$ to the feed. These both observations suggest that oxidation of NO on Pt based catalysts is auto-inhibited by the reaction product $NO_2$. Among the different calcination temperatures, $Co_3O_4$ exhibits the maximum NO conversion at 300℃. The NO conversion decreases with increasing calcination temperature due to sintering. NO conversion decreases with increasing SV and the optimum SV for 50% NO conversion is found to be ...