Effect On Combustion Characteristics And NO,SO₂ Formation Of Coal Blends At Constant High Temperature

Coal blending technology, which can improve the safety, economy, coal flexibility and decrease pollutant emissions in the plant, has become a key project. So it has been more practical guiding significance to research on combustion characteristics and pollutant emissions of coal blends at constant high temperature for high efficiency and clean combustion in the future. So far, the gradual heated TGA has widely been adopted to study the combustion characteristics of coal blends which do not coincide with practical industrial application. In this paper, the combustion characteristics, NO and SO₂ generation laws of coal blends at constant high temperature have been studied by means of a improved constant-temperature thermogravimetric test rig. Besides, an improved weighted method was proposed by changing the weight of high volatile coal to predict combustion characteristics of coal blends based on those of single coal. The results show that:The combustion process of volatiles and char overlaps, which is not completely independent. Temperature has little influence on combustion characteristics in initial stage of reaction at high temperature, however, burnout property improves as temperature rises. It also can reduce burnout time with lower quality of coals or with the oxygen concentration increases. It is easier for combustion due to lower activation energy with lignite blending ratio rises or blending lower quality coals. Simultaneously, spherically symmetric shrinking core model was used to describe the combustion process of coal blends at high temperature, which can reflect the nature of reaction. In the initial stage of combustion, the weight loss of coal blends was inhibited by lignite which played a significant role in promoting in later period. In addition, the effect of inhibition became stronger in the initial stage of combustion while burnout time decreased with the increase of lignite ratio in the coal blends. And there are the same results for blending lower quality coals. It was found that with the increase of temperature, the time of inhibition and burnout shortened. It also extends the time of inhibition with the decrease of oxygen concentration. The improved weighted method is better than dynamic model and simple weighted method due to its higher fitness and practical significance.The release of NO promotes with the increase of lignite blending ratio and the NO cumulative emissions obtained by experiment curves and simple weighted curves falls. As the temperature rises, the generation of NO speed up and the NO cumulative emission increases, but not linearly. The more different the quality of blending coals is, the stronger the interaction of NO generation is. With the increase of oxygen concentration, the NO cumulative emission has increased significantly at high temperature.The release of SO₂ promotes with the increase of lignite blending ratio and the SO₂ cumulative emission reduces obviously. Strong interactions have been produced in the process of the formation of SO₂ when blending ratio is 1:1. The peak of SO₂ instantaneous curves generates in advance and rises continuously with the increase temperature. And there are the same results with the increase of oxygen concentration, indicating that the formation rate of SO₂ promotes.