The Investigation of Comparative Kinetics of Fuel Combustion in the Air Atmoshere and in the Oxygen and Carbone Dioxide Atmoshere

Abstract

The issues of solid fuels combustion in oxygen atmosphere with CO₂ recirculation are discussed. It was shown that circulating fluidized bed is the most promising technology for oxyfuel combustion and greenhouse gases sequestration. The major differences between conventional air and oxyfuel combustion are given. The description of methods of experimental research aimed at investigation of comparative kinetic characteristics of fuel combustion is presented. Using TGA method the comparative study of the main stages of coal combustion process was conducted under traditional air and oxygen environment conditions. The results of experimental study and subsequent analysis of obtained data are given. It was shown that char combustion in both atmospheres within intra-kinetic mode has similar behavior and is described by very close values of activation energy (154 kJ / mol O₂ / N₂ and 157 kJ / mol O₂ / CO₂). The lower intensity of sample conversion in O₂ / CO₂ environment within the second stage is attributed to an earlier process transition to intra-diffusion mode, which results from reduced oxygen diffusion activity in CO₂ environment. Tests performed in the Ukraine Coal Power Institute reveal that lower diffusivity of O₂ in CO₂ medium leads to lower specific combustion rate and particles overheating at the same temperature level. The effect is enhanced with decrease of coal metamorphism degree and increase of particle size and correlates with fundamental conclusion implying the necessity to increase O₂ concentration during oxyfuel combustion within in CFB up to 24-32% vol.