Experimental research on effects of multi-layer injection of the high-temperature preheated pulverized coal on combustion characteristics and NOX emission

Under the background of carbon peak and carbon neutrality, clean and efficient utilization of coal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broad prospects for application, nevertheless, previous studies have mainly focused on limiting NOX generation by simply applying air staging method in the combustor, which made further NOX reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOX emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the selfpreheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%-15.48% and 600 mm - 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 - 0.99 s and 0.87 1.11 s, respectively. What's more, under the same reburning parameters, Alxa lignite coal had the largest NOX reduction rate (32.15%), with NOX emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOX reduction rate (5.34%) and the highest NOX emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOX emission (45.75 mg/m3, @6%O2) with the NOX reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.