Experiment Research On Co-combustion Of Gangue And Coal-bed Gas In CFB

Gangue, which is a waste from the processing of coal-mining production, has despoiled plenty of land and become one of the largest solid wastes in China. So, it is enormously important to handle gangue so as to change it into a resource. However, the effect of disposing gangue with common equipments is not effective since gangue has some characteristics such as high ash content, low volatile, high ignition point etc. Circulating fluidized bed (CFB) has some advantages such as high combustion efficiency, excellent pollution control, widely weight adjustment range and so on in the field of disposing inferior fuels. The combustion stability of CFB is remained fluctuant when the heat value and characteristics of fuel undulate largely. In order to solve the problems of disposing gangue in CFB, it is effective to inject gas fuel into CFB to realize the aim of strengthening gas-solid mixture, improving flow field and stabilizing combustion. Nevertheless, the research on co-combustion characteristic of gas-solid fuels in CFB is not detailed, which impedes heavily the development of CFB co-combustion technique.First, cold jet characteristic experiment is conducted, the influence of jet flow and jet heights position on gas velocity and section average solid concentration are analyzed. Second, the co-combustion experiment of gangue and coal-bed gas is carried on in CFB. Temperature field, combustion efficiency and NOX emission are tested with different combustion parameters such as: co-combustion ratio(R), excess air ratio, second air ratio etc. The results indicate that: gas velocity of dense phase decreases and the average velocity of gas increases with jet ratioλ.Influence of jet on gas velocity and solid concentration occurs mainly in the region below jet position since the dynamic block region is created because of the effect of jet. The solid concentration in dense phase raises with the increase of jet ratio, meanwhile the increase of height of jet position widens the dense areas.With the increase of co-combustion ratio(R), temperature in dense phase decreases and that in dilute phase goes up. In the meantime, the temperature difference reduces so as the temperature distribution becomes evener. Combustion efficiency rises with the increase of R, but its procession develops gently. The temperature in dense phase and dilute phase decline and combustion efficiency improves with the increase of excess air ratio. However, when excess air ratio reaches about 1.35 between 1.40, the increase gradation of combustion efficiency approaches 0 and combustion efficiency is maximal. As second air ratio increases, temperature in dense phase enhances and combustion efficiency increases at first, and then decreases.Because of reduction of coal-bed gas on NOX, the NO emission decreases with combustion ratio's increase and that rises with increases of excess air ratio, and then decreases with second air ratio's raise. During the experiment range, NO emission scope varies between 25~40 mg·Nm-3 on the basement of minimum value in each condition. According to the operating experience of practical CFB, the level of NO emission is between 70~200 mg approximately. In that way, NO emission level in this experiment is eligible, which suggests the pollution control is successful.The paper lays a foundation for further research of co-combustion of gangue and coal-bed gas in CFB. It offers essential reference for development of the disposing technique and has notable reference value for extensive industrial application.