Experimental Investigation On Char Burnout And Char Nitrogen Conversion In Fixed Bed Reactor

Due to the current energy situation, coal's major role in our country's energy consumption will not change recently. However, combustion of large quantity of coal will lead to serious environmental problems. To utilize coal resource in a more efficient and more environmentally friendly way, the research of coal combustion and the pollutant release has a far-reaching significance.This paper studies the regular patterns of combustion and the NOx release using different coal char samples under different oxygen concentration and varied temperatures. To rule out the influence of thermal NOx and Prompt NOx to the results of the experiments, the experiments are conducted by burning the coal char in the mixture of oxygen and nitrogen.The one-dimension thermostatic tube furnace is used to produce the coal char particles of a typical bituminous coal and a typical lean coal under two temperatures (900℃,1100℃) . The pyrolysis temperature increase renders a more complete liberation of coal volatiles. The bubbles generated by the pyrolysis of coal particles breach the surfaces of coal particles, enlarge the surface area of produced coal char and make the char surface structure more complex. In the process of pyrolysis, carbon and nitrogen consumption rates are pretty much the same and hydrogen consumption rate is greater than carbon and nitrogen consumption rates. The results of XPS indicate that in the pyrolysis process of coal particles activity of the N atoms in the surface is stronger than the N particles inside atoms, N elements of the particle surface during the pyrolysis is easier to enter the product with the volatile gas. When the pyrolysis temperature is 1100℃, XPS has been unable to detect the presence of the N elements of the coal char surface.A one-dimension fixed bed reactor is used to conduct the combustion experiments of four coal char samples (YA900, YA1100, PA900, and PA1100) . The increase of oxygen concentration and reaction temperature helps improve the combustion rate in the fixed bed and reduce the CO concentration in the flue gas. Under the condition of this experiment, the coal char is in the chemical reaction control area at the beginning, and then turn to the diffusion control area. In the process of coal char's anaerobic heat in the fixed bed, the nitrogen oxides release mainly in the form of N2O, while in the process of coal char's combustion, they release in the form of NO. With the oxygen concentration in the reaction gas increased, the conversion rates of YA900 and YA1100 from coke nitrogen to NO decrease; But for PA900 and PA1100, When the oxygen concentration of 5%, the conversion rate from coke nitrogen to NO is higher than concentration of 2% and 10%. With the reaction temperature increased, conversion rates from coke nitrogen to NO of PA900 and PA1100 decrease, while YA900 and YA1100 are showing the opposite pattern.