Abstract: With the increasingly stringent national environmental protection policies, the ultra-low emission transformation of industrial coal-fired grate boilers and the highly efficient utilization of biomass resources or wastes are becoming increasingly urgent in China. This study first proposes a novel and simple configuration for industrial grate boilers to integrate the decoupling combustion and flue gas recirculation or co-firing technologies, so as to reduce pollutant emission but improve thermal efficiency. Burning coal briquettes in the novel grate boiler, the original NO_x emissions can be remarkably decreased to as low as 56 mg· m^-3, corresponding to the reduction efficiency of 82.8% in comparison with the average value in traditional coal-fired grate boilers. Co-firing coal briquettes with straw pellets in the novel grate boiler, the strongest synergistic effect of NO_x reduction is observed at the blending mass fraction of 50%, in which the NO_x emissions can be further mitigated by at most 16.0% on top of the already reduced amount by decoupling combustion to reach less than about 165 mg· m^-3. The novel grate boiler allows co-firing Chinese medicine residue with high water content at the blending mass fraction of up to 30% on the premise of low NO_x and CO emissions. All experimental results in this study demonstrated the obvious superiorities of the novel grate boiler in reducing NO_x and CO emissions and mitigating both slagging tendency and slag carbon content, which can be attributed to either the cumulative effects of decoupling combustion with flue gas recirculation or the synergistic effects of co-firing coal-biomass blends. The newly-developed travelling-grate decoupling combustion technology can be expected to provide an economical and convenient measure for the ultra-low NO_x emission transformation of industrial coal-fired grate boilers as well as the clean and highly efficient consumption of biomass wastes with high water content or difficulty to burn in China.

Key words: Decoupling combustion, NO_x emission, Coal briquette, Straw pellet, Medicine residue, Grate boiler

摘要： With the increasingly stringent national environmental protection policies, the ultra-low emission transformation of industrial coal-fired grate boilers and the highly efficient utilization of biomass resources or wastes are becoming increasingly urgent in China. This study first proposes a novel and simple configuration for industrial grate boilers to integrate the decoupling combustion and flue gas recirculation or co-firing technologies, so as to reduce pollutant emission but improve thermal efficiency. Burning coal briquettes in the novel grate boiler, the original NO_x emissions can be remarkably decreased to as low as 56 mg· m^-3, corresponding to the reduction efficiency of 82.8% in comparison with the average value in traditional coal-fired grate boilers. Co-firing coal briquettes with straw pellets in the novel grate boiler, the strongest synergistic effect of NO_x reduction is observed at the blending mass fraction of 50%, in which the NO_x emissions can be further mitigated by at most 16.0% on top of the already reduced amount by decoupling combustion to reach less than about 165 mg· m^-3. The novel grate boiler allows co-firing Chinese medicine residue with high water content at the blending mass fraction of up to 30% on the premise of low NO_x and CO emissions. All experimental results in this study demonstrated the obvious superiorities of the novel grate boiler in reducing NO_x and CO emissions and mitigating both slagging tendency and slag carbon content, which can be attributed to either the cumulative effects of decoupling combustion with flue gas recirculation or the synergistic effects of co-firing coal-biomass blends. The newly-developed travelling-grate decoupling combustion technology can be expected to provide an economical and convenient measure for the ultra-low NO_x emission transformation of industrial coal-fired grate boilers as well as the clean and highly efficient consumption of biomass wastes with high water content or difficulty to burn in China.

关键词: Decoupling combustion, NO_x emission, Coal briquette, Straw pellet, Medicine residue, Grate boiler