Experimental study on pyrolysis of Xinjiang Naomaohu coal in a moving bed with baffled internals

In order to extract the oil and gas resources naturally present in low-rank coal to obtain high-quality tar and gas products, and to solve the technical bottlenecks that the existing pyrolysis technology cannot handle small-sized coal, low tar yield, and poor tar quality, etc,a new externally-heated pyrolysis technology for the moving bed with baffled internals was proposed. Taking the Naomaohu coal in Xinjiang as the research object, the effects of pyrolysis temperature, temperature control by stages, and multi-stage gas gathering on the distribution and quality of coal pyrolysis products were investigated. The feasibility and advancement of the new reactor (baffled internals and multi-stage gas gathering system) to strengthen the pyrolysis reaction of small-size low-rank coals were verified. The results show that the moving bed pyrolysis process with baffled internal components can handle low-rank coal with small particle size. The baffled internals can strengthen the movement of the particles and can significantly increase the heat transfer rate of the particles. When the particles enter the second bed (about 40 min), they can reach the target temperature, and the temperature distribution throughout the experiment is relatively stable. The tar obtained by pyrolysis of Naomaohu coal at low temperature has low quality, and the content of fatty hydrocarbons in tar is high. Properly increasing the temperature will promote the secondary reaction of tar and help to improve the quality of tar. The tar quality can be improved by establishing a gradually increasing temperature gradient. The multi-stage gas collection system ensures that the volatile matter is discharged in time and inhibits the secondary cracking reaction of the volatile matter at high temperature. For Xinjiang Naomaohu coal with a particle size of 0.4 mm to 6.0 mm, when the coal feed rate is 5.0 kg/h, the residence time is 2.0 h, and the pyrolysis temperature is 550 ℃, the highest tar yield is 10.81%, which is 82.5% of Gray-King tar yield. The content of heavy components with a boiling point greater than 360 ℃ is 15.0%, and the tar yield and quality under this condition are high. While the baffled internals strengthen the pyrolysis reaction, the tar yield and quality can be effectively improved by synergistically regulating the reactor temperature and the staged gas collection.