Role of iron-based catalysts in reducing NOx emissions from coal combustion

Abstract

Nitrogen oxide (NOx) pollutants emitted from coal combustion are attracting growing public concern. While the traditional technologies of reducing NOx were mainly focused on terminal treatment, and the research on source treatment is limited. This paper proposes a new coal combustion strategy that significantly reduces NOx emissions during coal combustion. This strategy has two important advantages in reducing NOx emissions. First, by introducing iron-based catalyst at the source, which will catalyze the conversion of coke nitrogen to volatile nitrogen during the pyrolysis process, thereby greatly reducing the coke nitrogen content. The second is de-NOx process by a redox reaction between NOx and reducing agents (coke, HCN, NH3, etc.) that occurred during coke combustion. Compared to direct combustion of coal, coke prepared by adding iron-based catalyst has 46.1% reduction in NOx emissions. To determine the effect of iron-based additives on de-NOx performance, demineralized coal (de-coal) was prepared to eliminate the effect of iron-based minerals in coal ash. The effects of iron compounds, additive dosages, and combustion temperatures on de-NOx efficiency are systematically studied. The results revealed that the NOx emission of the coke generated by pyrolysis of de-coal loaded with 3% (mass) Fe2O3 decreases to 27.3% at combustion temperature of 900 °C. Two main reasons for lower NOx emissions were deduced: (1) During the catalytic coal pyrolysis stage, the nitrogen content in the coke decreases with the release of volatile nitrogen. (2) Part of the NOx emitted during the coke combustion was converted into N2 for the catalytic effect of the Fe-based catalysts. It is of great practical value and scientific significance to the comprehensive treatment and the clean utilization process of coal.