Effect of Char Particle Size on NO Release during Coal Char Combustion

Abstract

In this study, the effect of particle size on the release of NO during the char combustion under particle packed-layer conditions was investigated at combustion temperatures of 900–1400 °C. The results show that, after pyrolysis, the small size char favored more pores and specific surface area. No significant variations of the intrinsic reactivity of O2 and NO with char particle size were measured. By increasing char particle size, more NO conversion from nitrogen in char (char-N) was found regardless of the combustion temperature and bulk oxygen concentration. This can be explained as follows. By increasing char particle size, less O2 penetrated into the pores and then more NO formed which was attributed to a less accessible pore surface area and a decreased NO reduction time. The effects of reaction temperature and bulk oxygen concentration were also discussed. A quantified description using a first-order reaction model shows that the char particle size will finally influence the accessible pore surface area and depth of O2 diffusion, which will directly determine the char-N/NO conversion. The evolution of nitrogen functionality with particle size and burnoff were also presented to demonstrate migration tendency of the char-N. The larger ratio of O/C in smaller size particle as determined using XPS (X-ray photoelectron spectroscopy) further confirmed higher pore diffusion. In addition, nitrogen was found to be preferentially retained in the char when carbon is oxidized.

Formation of NO and N2O during Raw and Demineralized Biomass Char Combustion

“…All chars contained large amounts of pyridinic (N6), pyrrolic (N5), and quartenary (NQ) nitrogen with differences in the relative distributions of these. In general, the relative abundance of N6 and NQ in chars increases with the severity of heat treatment, i.e., temperature and holding time, due to the thermal stabilities of these compounds. ,, The results here show a small discrepancy between the demineralized samples, with the only exception being DM pine wood. Notably, the nitrogen content in this char was low, thereby raising question as to the usability of a deconvolution method for extracting functionality data, seen in Supporting Information (Figure S5).…”

Effect of temperature and reaction atmosphere on nitric oxide emission during a char grate‐fired process in local flue gas recirculation

“…However, previous studies on nitrogen (N) migration and NO emissions from coal combustion have mainly focused on coal-fired power-plant boilers, such as pulverized coal and circulating fluidized bed boilers. While these studies have examined the effects of different factors, including coal rank, [3][4][5] pore structure, [5][6][7] particle size, [8][9][10] graphitization degree, [11,12] temperature, [13,14] and O 2 concentration, [15][16][17][18] few have examined coal-fired industrial boilers and the grate-fired process. This study attempts to fill that research gap.…”