Calcium magnesium acetate and urea advanced reburning for NO control with simultaneous SO 2 reduction

Abstract

Calcium magnesium acetate (CMA) shows potential as a reductant for simultaneous NO x and SO x removal from coal-fired combustion plant. The performance of urea co-injection with CMA on NO reduction in an ‘advanced reburn’ (AR) configuration has been investigated with a view to optimization of the process in a pulverized coal-fired furnace operating at 80 kW. The impact on SO 2 reduction has also been investigated. Urea/CMA solution was sprayed into the reburn zone of the furnace using twin-fluid atomizers over a range of reductant/NO stoichiometric ratios (NSR). The influence on NO reductions of primary zone stoichiometry ( λ 1) was investigated for a range of CMA reburn feed rates (Rff) and reburn zone stoichiometry ( λ 2). In addition, the effect of temperature on the SNCR performance of urea was investigated. Optimum process conditions were categorized either by maximizing NO and SO 2 reductions (Modes A and B, respectively) or maximizing reductant utilization efficiencies (Modes C and D). NO control was best performed at λ 1=1.05, but SO 2 reductions were greatest at more fuel-lean primary zone conditions ( λ 1=1.15). Highest NO reductions of 85% under AR-rich conditions were achieved under Mode A, but were only slightly higher compared with reductions of 79% under Mode B, where SO 2 reductions were optimized at 85%. N-utilization was also at an acceptable level of 25% compared to the maximum utilization efficiency which was obtained at NSR=1.5 of 30% for the same conditions of stoichiometry operating in Mode C. Operation at this lower level of reburn (9.6%) could significantly reduce the consumption of CMA with some impact on NO reduction (73%). SO 2 removal performance would be compromised severely with reductions lowered from 75% at Mode A to 35% at Mode C. Optimizing Ca utilization (Mode D) resulted in poor NO and SO 2 reductions, at 61 and 22%, respectively, and can be discounted as a viable option. The technique offers flexibility of operation depending on the emission control requirements.