Experimental research on the NOx evolvement of pulverized coal combusted in CO2, Ar and N2 atmospheres

Abstract

A fixed-bed reaction platform was employed to study the influences of combustion atmospheres (O2/N2, O2/Ar and O2/CO2), oxygen concentrations, combustion temperatures, and particle diameters on the combustion behavior of Shen Hua (SH) bituminous. It was found that in O2/CO2, the fuel-NO yield per O2 consumption (YNO) is the lowest among the three atmospheres. All the tests in O2/CO2 show that YNO decreases with increasing combustion temperature. On the basis of the tests in N2 and Ar atmospheres at high temperature (1873K), the inhibition of fuel-NO by thermal-NO was revealed quantitatively. As the combustion temperature increases, the pulverized coal ignites earlier and the combustion durations get shorter. When at a low temperature (1273K), the combustion duration in the CO2 atmosphere is twice or three times longer than that in N2 and Ar atmospheres. When the temperature is above 1573K, the combustion durations in CO2 atmosphere are nearly the same as that of the other two atmospheres, indicating the high temperature would guarantee similar combustion characteristics between O2/CO2 and O2/N2. Furthermore, according to all the fuel-NO cumulative curves of the reaction processes, a cumulative percentage mathematical model (CPM) describing the fuel-NO release process in context of oxygen concentration, temperature, burnout rate, and atmosphere was proposed for comprehensive understanding of experimental results. As the combustion temperature and oxygen concentration increases, larger portion of fuel-NO is formed prior to coal burnout due to the enhanced char gasification and pyrolysis at high temperature. This phenomenon is enhanced in CO2 atmosphere, which further facilitates the reduction of fuel-NO.