Abstract
Experimental investigations into the combustion behaviors of single pulverized coal particles are carried out based on high-speed imaging and image processing techniques. A high-speed video camera is employed to acquire the images of coal particles during their residence time in a visual drop tube furnace. Computer algorithms are developed to determine the characteristic parameters of the particles from the images extracted from the videos obtained. The parameters are used to quantify the combustion behaviors of the burning particle in terms of its size, shape, surface roughness, rotation frequency and luminosity. Two sets of samples of the same coal with different particle sizes are studied using the techniques developed. Experimental results show that the coal with different particle sizes exhibits distinctly different combustion behaviors. In particular, for the large coal particle (150–212μm), the combustion of volatiles and char takes place sequentially with clear fragmentation at the early stage of the char combustion. For the small coal particle (106–150μm), however, the combustion of volatiles and char occurs simultaneously with no clear fragmentation. The size of the two burning particles shows a decreasing trend with periodic variation attributed to the rapid rotations of the particles. The small particle rotates at a frequency of around 30Hz, in comparison to 20Hz for the large particle due to a greater combustion rate. The luminous intensity of the large particle shows two peaks, which is attributed to the sequential combustion of volatiles and char. The luminous intensity of the small particle illustrates a monotonously decreasing trend, suggesting again a simultaneous devolatilization/volatile and char combustion.
Highlights
Renewable energy has been attracting much attention in recent years due to environmental concerns, conventional fuels such as pulverized coal will remain a major worldwide energy resource for years to come due to their wide availability and competitively low cost, with the development of new combustion technologies such as co-firing coal and biomass and oxycoal combustion [1]
The V-drop tube furnaces (DTFs) used in this study is an electrically heated drop tube furnace equipped with a 1400 mm long quartz tube with an inner diameter of 50 mm, capable of maintaining gas temperatures up to 1050 °C within the 1000 mm-long heated zone [24,25]
It has been found that the coal with different particle sizes and shapes exhibits distinctly different combustion behaviors
Summary
Renewable energy has been attracting much attention in recent years due to environmental concerns, conventional fuels such as pulverized coal will remain a major worldwide energy resource for years to come due to their wide availability and competitively low cost, with the development of new combustion technologies such as co-firing coal and biomass and oxycoal combustion [1]. While the effects of chemical composition and other fuel properties of coal on combustion have been widely studied, the physical characteristics of a pulverized solid fuel, such as particle size, and shape have been found to have a significant impact on the ignition and combustion behaviors of fuel particles, and the flame stability, combustion efficiency. Depending upon the fuel properties, and the heating rate, particle size, combustion environments (temperature and stoichiometry, etc.) and the volatile matter evolution, the homogeneous ignition and heterogeneous ignition of fuel particles may occur sequentially or simultaneously [4]. This makes it more difficult to characterize the combustion behaviors of fuel particles. The measurement and characterization of individual fuel particles are required to explore the insight into the combustion mechanism of fuel particles, and advance the knowledge to optimize combustion processes and validate computational modeling results
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