Abstract
Large-eddy simulation is applied to a laboratory-scale open-type pulverized coal flame generated by a triple stream burner, and the NO production and reduction in oxy-fuel condition are investigated for the first time. Pulverized Cerrejon coal which is classified as bituminous coal is used as a fuel. The results show that regardless of the equivalence ratio, as the O2 concentration increases from 21% to 40%, O2 consumption becomes marked because gas temperature rises and oxidation reaction is enhanced by the higher concentration of O2. Also, NO is formed rapidly due to the oxidation reaction of nitrogen from volatile matter of coal, and its concentration reaches a few hundred ppm further downstream. After the rapid formation, in the case of equivalence ratio larger than unity, NO decreases, because the reducing atmosphere becomes dominant due to the lack of O2. The trend becomes significant as the O2 concentration in the carrier gas increases from 21% to 40%. In the case of equivalence ratio less than unity, on the other hand, NO does not decrease clearly, because the oxidizing atmosphere contributes to the further formation of NO. Present study shows the usefulness of the large-eddy simulations for predicting the characteristics of pulverized coal flames.
Highlights
Coal is still an important energy resource to satisfy the large demand for low cost electricity in Asian countries, as coal reserves are much more abundant than those of other fossil fuels and widely distributed all over the world
The effects of the O2 concentration and equivalence ratio on the formation process of NO in a laboratory-scale open-type pulverized coal flame generated by a triple stream burner were investigated by means of LES under oxy-firing conditions in which O2/CO2 mixture is used as oxidizer
Regardless of the equivalence ratio, as the O2 concentration increases from 21% to 40%, O2 consumption becomes marked because gas temperature rises and oxidation reaction is enhanced by the higher concentration of O2
Summary
Coal is still an important energy resource to satisfy the large demand for low cost electricity in Asian countries, as coal reserves are much more abundant than those of other fossil fuels and widely distributed all over the world. Regarding the reduction of environmental impact of CO2, carbon capture and sequestration (CCS) is expected as a key technology, and it is believed that oxy-fuel pulverized coal combustion, in which gas mixture of oxygen (O2) and CO2 are used instead of air as oxidizer, has advantages for CCS, with low cost by means of only a retrofit of existing pulverized coal fired power plants [2]. Previous experimental and numerical investigations on oxy-fuel coal combustion technology have been reviewed in several papers [3,4,5,6]. In most of those papers, the flow and gas temperature are measured at selected points in the combustion chamber, the concentration of pollutants is measured only at the outlet of the combustion chamber.
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