MILD Combustion of Solid Fuels: Its Definition, Establishment, Characteristics, and Emissions

Moderateor intense low-oxygen dilution (MILD) combustion has theadvantages of high thermal efficiency and ultralow NO x emissions. This technology has attracted extensiveattention from the combustion community since 1990 or so. The earlydevelopment of MILD combustion technologies required highly preheatingthe combustion air externally, thus limiting the range of its industrialapplications, especially for burning solid fuels. Later, this technicallimitation was gradually overcome, particularly becoming possibleto burn solid fuels without preheating under MILD conditions. Significantprogress has since been made in solid-fuel MILD combustion. Some examplesinclude the development of solid-fuel MILD burners utilizing low-volatileresidual char and high-volatile biomass, low emissions of pollutantssuch as NO x and fine particles, MILD oxy-fuelcombustion, and pilot-scale demonstrations and industrial applications.Solid fuels adopted for MILD combustion comprise coal, residual char,biomass, and sludge. This paper reviews the research progress achievedso far for solid-fuel MILD combustion. The definition of solid-fuelMILD combustion is first introduced. Then, the establishment approachis discussed. The combustion features and NO x emission mechanisms are investigated in detail. The advantagesof MILD oxy-fuel combustion are also presented. The future developmentof solid-fuel MILD combustion is proposed finally. This review coversthe fundamentals and applications of MILD combustion of solid fuels.

Automated summary

Moderateor intense low-oxygen dilution (MILD) combustion has the advantages of high thermal efficiency and ultralow NOx emissions. This technology has attracted extensive attention since 1990. Initially, the development of MILD combustion technologies required preheating the combustion air externally, limiting its industrial applications for burning solid fuels. However, this limitation has been overcome, and significant progress has been made in solid-fuel MILD combustion, including the development of burners utilizing different types of solid fuels and the reduction of pollutant emissions.