Effects of volatile matter and oxygen concentration on combustion characteristics of coal in an oxygen-enriched fluidized bed

Abstract

Oxygen-enriched combustion in fluidized bed is a promising clean coal combustion technology which can efficiently control the emission of coal-fired pollutants, especially CO2. In this paper, by using several judging methods, the combustion characteristics of five kinds of coal under four different oxygen concentrations (20.9%, 27.8%, 40.7% and 52.7%, CO2 as equilibrium gas) were measured in the small-scale fluidized bed reactor with electric heating in detail. The oxygen consumption and volatile release characteristics were explored online. The influence of coal types, volatile matter and oxygen concentration on coal combustion characteristics was analysed. It’s found that the higher the bed temperature was, the faster the reaction rate was and the more oxygen consumption was. At a certain oxygen concentration and proper bed temperature, the separated combustion of volatile and char were observed. When the oxygen concentration was high, the separation phenomenon was more obvious. High-volatile, a certain bed temperature and oxygen concentration were the basic factors for the formation of separated combustion. The total volatile matter is not comprehensive as the index of reaction combustion characteristics and the effect of combustible components should be specifically considered. It’s found that for the coal with high combustible components, the separated combustion is more obvious. Volatile matter plays a dual role in the ignition and combustion of coal. The volatile matter (lower volatile matter) of some coals has a great promoting effect on coal combustion at higher temperature, while that (higher volatile matter) of other coals is not, which is closely related to the properties of char and the diffusion of volatile matter in pores.