Technical and economical analysis of a novel rotary air preheater system

The injection of ammonia as a reducing agent into the selective catalytic reduction (SCR) system is usually excessive in order to achieve the strict NOx removal efficiency, which results in the formation of ammonium bisulfate on account of the reaction between the escaped ammonia and sulfur oxides in the flue gas. Ammonium bisulfate is viscous and corrosive and can seriously affect the rotary air preheater (RAPH) as well as other exhaust systems. The mitigation strategies require additional operating expenses of cleaning, ash-blowing. To address the problem, a split design of the rotary air preheater is provided in this paper. A traditional RAPH is split into two sub-preheaters, between which the recirculating flue gas extracted from the cold end of the second preheater is mixed with the main flue gas. After the mixing point, a reaction chamber is installed to induce the reaction between ammonia and sulfur trioxide to form as much (NH4)(2)SO4 as possible. Thus, the blockage and corrosion can be avoided both in the two preheaters by a proper split design and continuous adjustment of the recirculation flow rate. To realize the calculation of temperature distribution, a numerical finite difference method is adopted to model the preheaters. The economical analysis of the proposed system including break-even curves is also conducted, which is given as references for the measures to relieve the blockage problem in the RAPH.