Gasification Characteristics Of Lignite In A Fluidized Bed Gasifier

Lignite is one of important coal resources in China. As lignite has high moisture and volatile matter contents, how to use it has become a highlight in clean coal technology. Production of feed gas in chemical industry and poly-generation based on fluidized-bed gasification technology are clean utility ways of lignite. Carbon conversion, gas yield, gasification efficiency and syngas characteristics determines the economy and stability of the whole gasification system. In this dissertation, the steam gasification characteristics of Xiaolongtan lignite is investigated in a self-developed fluidized-bed gasifier. The main conclusions are as follows.(1) A fluidized-bed gasification setup is developed, and two units of the setup are improved and optimized during commissioning process. The heating furnace uses silicon-molybdenum rods as heating element, whose power is 30 kw, and the highest temperature reaches up to 1600 ℃. A screw feeder is manufactured for the fluidized-bed gasifier. By adjusting the auger rotation rate driven by the motor, the feed rate of lignite could be accurately controlled. There is a well linear relationship between the feeding amount and the motor speed, which can meet the demand of feeding amount.(2) Steam gasification experiment of lignite are carried out in the above fluidized-bed gasifier. Effects of bed temperature, steam flow rate and particle size on the gasification behavior are explored. When the bed temperature is increased, the carbon conversion and gasification efficiency are increased. H2 and CO concentration are increased, CO2 concentration is decreased, and CH4 concentration keeps essentially unchanged. When steam flow is increased, the carbon conversion, gas yield and gasification efficiency are increased, the concentration of H2, CO and CO2 in the syngas is increased while the CH4 concentration is decreased. In this experiment, compared to the bed temperature and the steam flow, particle size shows only slightly influence on the gasification process.(3) The weight loss properties of lignite with/without minerals during pyrolysis is analyzed by the TG-DTG apparatus. The results indicate that after removing the minerals, weight loss of lignite sample is almost same as the raw lignite, but the pyrolysis rate of the lignite with no minerals accelerates. And then investigate the influence of minerals in coal on gasification characteristics. In the experiment, although the carbon conversion keeps no change, the concentration of H2 and CO2 are decreased respectively about 55% and 25%, CO concentration is increased about 50%, and CH4 concentration is fallen slightly. From the above, the inherent minerals in the lignite show a positive influence on the gasification process, which improves the composition of the syngas.