Influence of Oxidation–Reduction Layering on Fuel Nitrogen Oxide Emissions during a Char Grate-Fired Process

Abstract

Previous studies have found that the nitric oxide (NO) trend above the fuel seam of a chain boiler is opposite that of a reciprocating grate boiler. We have researched the factors that influence fuel NO emissions during the char grate-fired process by changing the char/oxygen (O2) ratio in a small-scale one-dimensional fixed-bed system. With an increase in the char/O2 ratio compared to the mass loss of char, the advent of excess O2 is delayed and carbon monoxide (CO) is generated. As a result, oxidation–reduction layering of char occurs. Char grate firing leads to an increase in char mass of the complete oxidation layer, and a thicker ash layer covers the char surface. The reduction layer and low-O2 region of the oxidation layer favor NO reduction; therefore, NO emission is delayed or shows a double-peak trend. The ash layer covering and a long residence time at a high temperature increase the NO generation rate of the oxidation layer. However, the overall NO generation rate is controlled by the reduction...