Effects of the T-abrupt exit configuration of riser on fuel properties, combustion characteristics and NOx emissions with coal self-preheating technology

NOx generated from coal combustion brings about severe environmental problems. Among many combustion technologies, coal self-preheating combustion technology is valued for its great potential of low NOx combustion, while in-depth studies on the structure of the self-preheating device (SPD) have not been carried out, which makes it difficult to further reduce NOx. In addition, disposal of coal gasification fly ash (CGFA), a kind of solid waste, is still mainly dissipated in landfills, resulting in the pollution of soil, water and wastes energy. In order to optimize the SPD structure for further reducing NOx and provide technical support for the engineering utilization of CGFA, the properties of preheated fuel (coal gas and coal char), the behavior characteristics of combustion and NOx emission under different He/Hr (the ratio of projected height to the riser height) were investigated on a 30 kW bench-scale test rig. Stable and high efficient MILD combustion was achieved without manifest flame front. The results revealed that appropriate increase of He/Hr ratio was conducive to the release of fuel-N during preheating, facilitating the conversion of fuel-N to N2. For BC and CGFA, the pre-removal effect of fuel-N in the SPD reached the best when He/Hr ratio was 3/8 and 1/4, respectively. The increase of He/Hr ratio was not salutary to improving the combustion reactivity of BC, while for CGFA, the modification effect on the combustion reactivity of coal char could reach the best when He/Hr ratio = 1/4. Both NOx emission and the conversion ratio of fuel-N to NOx of BC and CGFA could reach the optimal value when He/Hr ratio was 1/4.