Predicting Behavior of Coal Ignition in Oxy-fuel Combustion

Abstract

In oxy-fuel combustion technology, the coal is burned in a mixture of pure oxygen and recycled flue gas with high content of CO2 gas. Burning the coal in oxy-fuel combustion with O2 and CO2 environment will affect the combustion performance compare with air (O2/N2) environment. Based on previous researches indicated that oxygen concentration is required to be increased, so that the combustion behaviour similar as in air environment.This paper describes the characteristics of coal ignition and combustion in oxy-fuel combustion applying the non- isothermal thermogravimetric analysis. Experimental results find out the activation energy of three different coal ranks in O2/N2 and O2/CO2 environment. Temperature of coal sample and inert reference material can simultaneously measured in TG-DTA. Based on activation energy and TG-DTA data, predicted coal particle ignition temperature can be calculated and then validated. The result is successfully applied both in air and O2/CO2 environment. In comparison to the conventional combustion, thermogravimetric curves of coal combustion in O2/CO2 tend towards higher temperature zone. The species in flue gas during burning test in TGA were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O2/N2 environment, much more CO is produced in O2/CO2 coal combustion process. Refer to two film model, the delay in oxy-fuel combustion may be caused by the incoming O2 unbalance with much CO gas, and this can be solved with increasing O2 concentration in O2/CO2 environment.