The characteristics of coal-char oxidation under high partial pressure of oxygen

The process of coal combustion with oxygen, which separates nitrogen from air in advance, has attracted much attention because of its prospects for increasing combustion efficiency and reducing emissions from power plants. In order to model this combustion process and design a suitable type and dimension of combustor, it is necessary to know the combustion characteristics, especially of char, which is considerably slower than the decomposition and combustion of volatile matter. This paper proposes a pulse technique to simulate the characteristics of coal-char combustion with high partial pressure of oxygen in the temperature range 1273-1573 K. For the study, 3 different types of coal were selected: Berau coal from Indonesia, Newlands coal from Australia and Hebi (semi-anthracite) coal from China. Oxygen or the mixture of nitrogen and oxygen was taken as the pulse gas. An on-line gas chromatograph with TCD was used to detect the concentration of CO and CO(sub2) in the reacted pulse gas. Helium was used both as the carrier gas and reference gas in TCD. Results show that the apparent reaction rate increased strongly as a function of oxygen concentration up to 100% under 0.18 MPa operating pressure. The reaction orders for the 3 chars were close to unity and activation energies were about 20 kcal/mol throughout the temperature range. (Original abstract - amended)