Chapter 16 - Solid fuels flameless combustion

Abstract

Flameless, also called moderate or intense low-oxygen dilution (MILD) combustion, is an advanced technology to increase combustion stability, enhance thermal efficiency, and reduce pollutant emissions. Flameless combustion of solid fuels has received much less attention than gaseous fuels, and its burning characteristics are not well understood. As solid fuels, particularly pulverized coal, form the majority of available fuel sources, there is a need to extend understanding of flameless combustion to pulverized coals. Furthermore, flameless combustion characteristics of biomass have not been investigated comprehensively. The goal of employing flameless combustion technology to biomass fuels is to eliminate noxious pollutants emissions from renewable and sustainable solid fuels. This chapter presents a technical review of flameless combustion characteristics of solid fuels covering the most recent experimental and computational studies. A complementary experimental case study on the impact of the co-flow oxygen concentration on the flameless combustion characteristics of grape marc as a biomass fuel has been concisely reported. A vitiated co-flow vertical flameless combustion furnace of maximum 60kW heat capacity is utilized in this experimental campaign. Three different cases with a co-flow oxygen concentration of 6%, 9%, and 12% (v/v) were considered for the investigation. Stable flameless combustion of pulverized grape marc was achieved for all cases. No detectable flame front was observed for any of the experimental cases. A semiuniform thermal field inside the combustion chamber was measured for all cases. The increase of the co-flow oxygen has a positive effect in reducing the NO emission. A fivefold reduction of exhaust NO was measured for the largest co-flow O2 case compared with the lowest O2 case. Future potential research directions on the flameless combustion of solid fuels are described at the end of this chapter.