Preliminary Study On The Comprehensive Utilization Of Pyrolysis-gasification Of Maitreya Lignite

In recent years,under the background of low carbon development and green economy,the demand for coal exploitation and utilization has been increasing.Because lignite has the characteristics of high moisture content,high ash content,high volatile content,low calorific value,easy to break and easy to be transported over long distances,so it has not been used on a large scale.In this paper,based on the coal utilization in China and the rich lignite resources in Yunnan Province,the pyrolysis and gasification of Yunnan Mile lignite are carried out.Firstly,the non-isothermal thermogravimetry was used to study the pyrolysis characteristics of Yunnan Mile lignite,and the effect of heating rate and particle size on the pyrolysis process was explored,and the kinetics of the pyrolysis data was analyzed;Then,the distribution of pyrolysis gas products?H₂,CO,CH₄,CO₂?was analyzed using a horizontal tube furnace and a gas chromatograph;Finally,the physical properties of pyrolytic solid product semi-coke and the reactivity of CO₂-gasification were studied.The following results and conclusions were obtained.1.The pyrolysis process of Mile lignite is divided into three stages.In the first stage,dehydration degassing peaks were formed at about 90°C with a weight loss rate of 13.51%;The second stage produced a pyrolysis peak around 400°C with a weight loss rate of 27.71%;The third stage produced many insignificant small peaks with a weight loss rate of 13.73%.Heating rate is the most important influencing factor of pyrolysis process.With the heating rate increasing,the characteristic parameters of all stages of coal pyrolysis increase.According to reaction kinetics,lignite pyrolysis is most intense and the reaction rate is the largest in the temperature range of 270-569 degrees.The particle size also has a certain effect on the pyrolysis process.With the increase of the coal particle size,the activation energy in each stage decreases gradually,that is,the required energy is reduced.2.The final temperature of pyrolysis is the most important factor affecting the distribution of gas products.With the increase of final pyrolysis temperature,the volume fraction of CO₂ and CH₄ decreases,and the volume fraction of H₂ and CO increases.The distribution of major gases:H₂ was produced at 400?and then increased continuously;The volume fraction of CO rises first,then decreases at600?,and then increases gradually;The volume fraction of CH₄ has been increasing,reaching the maximum at 600?,and then decreasing;The volume fraction of CO₂ is decreasing.3.The CO₂-gasification reaction of coal char under different pyrolysis conditions can be seen:The higher the final pyrolysis temperature,the greater the activation energy of gasification reaction of coal char;The slower the heating rate of pyrolysis,the greater the activation energy of gasification reaction of coal char;The heat preservation time is restricted by the end temperature of pyrolysis.Only when the final temperature of pyrolysis is higher,the activation energy of gasification reaction of coal char increases with the prolongation of pyrolysis and heat preservation time;Therefore,the higher the temperature of the pyrolysis,the slower the heating rate and the longer the holding time,the worse the gasification reactivity of the coal char.