Pyrolysis Using Solid Heat Carrier Of Yunnan Lignite And Study On Combustion Characteristics Of Char From Pyrolysis

The resources of lignite are rich in our country, so it is signality to implement high efficiency and clean utilization of lignite. Low-temperature pyrolysis of lignite which is also called low-temperature retorting, has more simple technological conditions compared with coal gasification and liquefaction, advantage of mild conditions, less investment, lower cost, and further utilization of products.In the paper, we choose two different kinds of brown coal, Zhaotong lignite (high ash,high fixed carbon) and Qujing lignite(moderate ash,moderate fixed carbon), as the material for pyrolysis experiment using solid heat carrier, and make a comparative analysis of Zhaotong lignite and Qujing lignite.Experimental investigation has proved:(1) The optimum reaction temperature is 510℃for Zhaotong lignite. Its tar yield reaches to 8.88%(d), and its oil recovery rate is 83.0%. The optimum reaction temperature is 510℃for Qujing lignite. Its tar yield reaches to 7.17%(d), and its oil recovery rate is 84.35%. (2) The char from Zhaotong lignite have the high calorific value, about twice than the raw coal, and the ash of char is high (54%-57%), so it usually used as fuel. The ash of Zhaotong char is moderate (20%-26%), and the fixed carbon is a little higher (63%-68%). The char, which calorific value is about 70-90% higer than the raw coal, can be used as fuel, or as the gas-making material to get synthetic oil, methanol, dimethyl ether and so on. (3) The coal gas from the pyrolysis in the optimum temperature has high heat value (higher than 14.7MJ/m3), so it can be used for hydrogen production and syngas.The two different kinds of char, which are received from the pyrolysis using solid heat carrier, are chosen to make the study of combustion characteristics for different heating rates (5℃/min,10℃/min,20℃/min,30℃/min,40℃/min), different oxygen concentration (4%, 8%,12%,16%,20%), and different particle diameter sizes (0.2-0.5mm,0.5-1.0mm, 1.0-2.0mm,2.0-3.0mm).Experimental investigation has proved:(1) The heating rate has big effects on TG and DTG curves. With the heating rates increase, TG and DTG curves of two different chars move to the higher temperature zone, so are the ignition temperature, temperatures in maximum combustion rate, and burnout temperature. We find that the activation energy and pre-exponential factor correspondingly decrease as the heating rate increases. The rising velocity of burnout temperature is faster than ignition temperature's. The burning time is prolonged as the heating rates increases. (2) The oxygen concentration also has large influence on TG and DTG curves. With the oxygen concentration increases, TG and DTG curves of two different chars move to the lower temperature zone, so are the ignition temperature, temperatures in maximum combustion rate, and burnout temperature. However, the activation energy increases with oxygen concentration increases, and thus the reactivity of char increases. (3) When the diameter of particles changes, no obvious regulation is found in TG/DTG curves and the final weight loss rate has no specific change either.