Study on the combustion and NO_x emission characteristics of low rank coal in a circulating fluidized bed with post‐combustion

Abstract

The combustion and NOx emission characteristics of low rank coal have been investigated in a circulating fluidized bed test plat, which was composed of a circulating fluidized bed (CFB) and post‐combustion chamber (PCC). The effects of the air stoichiometric ratio in the circulating fluidized bed furnace and air arrangement in the post‐combustion chamber were studied. In the optimized experimental condition, with the air stoichiometric ratio in the CFB (λCFB) at 0.963, and post‐combustion air (PCA) injected into the PCC using ports PCA1 and PCA3, the NOx emission was reduced to 48.7 mg/m3. The conversion of the fuel‐nitrogen in the coal into NOx did not occur under the reducing atmosphere in the circulating fluidized bed furnace. The final quantity of NOx generated from the combustion in the PCC was formed from gaseous HCN and residual nitrogen in fly ash, which flowed with flue gas from the CFB furnace. Enhancing the burnout fraction of coal in the CFB and using the air arrangement in the PCC could effectively reduce the final emission of NOx.

Experimental methods in chemical engineering: Reactors—fluidized beds

“…Most of the work in fluidized beds is dedicated to pyrolysis, combustion, gasification, and reduction, which require adding solids to the bed as it operates . Transporting solids between the reaction and regeneration zones—circulating fluidized beds—is a common configuration to identify process conditions for scale up for coal combustion and to examine emissions, for example . Rather than circulating solids between two vessels, the two‐zone fluidized bed circulates solids vertically in the same vessel .…”

“…[73,74] Transporting solids between the reaction and regeneration zones-circulating fluidized beds-is a common configuration to identify process conditions for scale up for coal combustion and to examine NO x emissions, for example. [75] Rather than circulating solids between two vessels, the two-zone fluidized bed circulates solids vertically in the same vessel. [41] In vortex fluidized beds, gas injected tangentially to a cylindrical chamber rotates and operates at higher bed densities-higher gas-solid slip velocities.…”

Experimental Research on the Conversion of Fuel Nitrogen in the Postcombustion Chamber of the Circulating Fluidized Bed

“…On this foundation, Zhou et al 25 proposed the postcombustion technology, which could be summarized as lean-oxygen combustion in a CFB furnace followed by postcombustion air (PCA) with excess oxygen in the postcombustion chamber (PCC) after the CFB. Subsequently, the influence of the postcombustion air injection position on the NO x emission was investigated by Gong et al 26,27 In our previous study, the arrangement of multistages of PCA in NO x emissions was investigated, and the ultralow NO x emissions were achieved. 28 Nonetheless, previous studies on postcombustion technology have mainly focused on reaching ultralow emissions by adjusting the operating parameters.…”

Prediction of Chemical Gas Emissions Based on Ecological Environment

“…e model can predict combustion efficiency, particle size distribution of coke and limestone, slag discharge rate of bed material, bed temperature change, and the distribution of SO 2 , NO x , O 2 , CO, CO 2 , and volatile matter along the furnace height. e factors influencing NO x emission from the CFB boiler are combustion temperature and uniformity, excess air coefficient, staged combustion, and so on [8,9]. In addition, the study of deep reduction of NO x in the CFB boiler with the selective noncatalytic reduction (SNCR) technology as the mainstream is also affected by reductant type, reaction temperature, ammonia-nitrogen ratio, and other factors [10][11][12].…”