Experimental Investigation on NO_x Generation Characteristic and Burnout Performance of Co-Combustion of Carbon-Based Solid Fuels under Deep-Staged Combustion

Abstract

With the development of low-rank coal chemical industry, the production of low-volatile carbon-based solid fuels, such as pyrolyzed and gasified semi-cokes, is ever-increasing. However, it is difficult to use such fuels efficiently because of their poor burnout performance and high NO x generation during the combustion process. Co-combustion of semi-cokes with bituminous coal is a promising approach for large-scale utilization of semi-cokes with ultra-low volatile content. Nevertheless, the NO x generation and burnout characteristics of co-combustion of multiple carbon-based solid fuels are yet to be fully understood. In this paper, the cocombustion characteristics of semicokes and bituminous coal were investigated using a deep-staged co-combustion system. The experimental results indicate that NO x generation displays an increasing trend with the mass fraction of gasified semi-coke. The unburned carbon (UBC) generation in fly ash increases with the proportions of gasified and/or pyrolyzed semi-cokes. The NO x generated from char-N of semi-cokes is reduced by CO and CH i generated from volatile-N of bituminous coal. Compared to air combustion, the increase of oxygen concentration of the O 2 /CO 2 atmosphere is useful for the blended fuels to reduce NO x generation and improve burnout performance because of the prolonged residence time under oxygen enrichment conditions. The conversion of fuel nitrogen to NO x (N-NO x ) and the nitrogen left in ash (N-ash) in O 2 /CO 2 and O 2 /Ar atmospheres decrease with increasing oxygen concentration, with more fuel nitrogen converted into N 2 . When the oxygen concentration of over-fire air varies from 21 to 100%, the NO x generation is increased by 23% and the UBC is decreased by 45%. The present study can offer better understanding on large-scale clean utilization of pyrolyzed and gasified semi-cokes in the utility coal-fired power plants.

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

“…Wang et al evaluated the effects of the excess air coefficient in the primary combustion zone and the burnout air port position on the NO x emission and burnout ratio. Through years of research, simple depth air-staged combustion technology has been successfully applied in industrial pulverized coal boilers. , Recently, Wang et al tried to further reduce the NO x emission of depth air-staged combustion by cocombustion of carbon-based solid fuels. − The experimental results indicated that blending bituminous coal could improve the combustion characteristics and reduce the NO x generation of semicoke. In addition, some scholars have investigated depth air-staged combustion under an oxygen-enriched atmosphere …”

“…Currently, many scholars have paid attention to fuel-N conversion. Wang et al , investigated the fuel-N conversion path in deep air-staged combustion and proved that volatile-N could promote fuel-N conversion to N 2 . Bi et al proved that NH 3 could reduce NO x to N 2 and then increase the ratio of fuel-N converted to N 2 in the absence of O 2 .…”

Combustibility and Cofiring of Coal Gasification Fine Ash with High Carbon Content in a Full-scale Pulverized Coal Furnace

“…The topic on cofiring of coal with highly volatile carbonaceous wastes is of interest to researchers due to the positive effect on the coal combustion and burnout performance. − The cofiring of waste coal gangue, which contains 60–70% ash and 10–15% carbon in dry basis, with the coal has been conducted on the laboratory scale, and it was concluded that cocombustion is a good energy recovery pattern for the waste carbonaceous material utilization. The cofiring of gasified semicoke and bituminous coal was experimentally studied in a drop-tube furnace, and the effect of oxygen and combustion temperature on the unburned carbon of the semicoke was investigated. The blending ratio of semicoke when cofiring with the bituminous coal was recommended to be lower than 40% based on the burnout data in a DTF .…”