Experimental Investigation into Combustion Characteristics of Two Sub-bituminous Coals in O₂/N₂and O₂/CO₂Environments

Abstract

There are still arguments on the coal combustion reactivity under conventional and oxy-coal combustion atmospheres. The selection of the experimental device in such a study is crucial. A laminar entrained flow reactor system that is capable of producing a similar combustion environment of a utility furnace in terms of the high heating rate and temperature was adopted in this study. This study investigated the characteristics of sub-bituminous coal combustion in its processes of devolatilization and char oxidation by examining the structure and length of the flame. The effects of the particle size and oxygen molar fraction in N2 and CO2 diluent gases were studied. The O2 mole fraction was varied from 0 to 50%. The flame became shorter as the O2 concentration increased. It means that reactivity in both the devolatilization and char oxidation processes increased in a higher O2 concentration environment. It was barely seen that the volatile burning realm shrunk, O2 diffusion accelerated, and luminosity concentrated near the burning particle as the O2 concentration increased. The larger size coals showed thicker and longer flames, and there is a small difference in the burning time between two different sub-bituminous coals. When the O2/CO2 and O2/N2 environment effects are compared, the flame was shorter in the oxy-fuel condition than in the O2/N2 condition.