Study On Pyrolysis Characteristics Of Hanjiawan Lump Coal

In this paper,Hanjiawan coal was used as raw material,and the experiment was carried out by using a self-designed coal pyrolysis device.Unlike traditional fixed bed pyrolysis,the main body of the device is horizontal,which can not only satisfy the pyrolysis of pulverized coal samples,but also satisfy the pyrolysis of large diameter lump coal,and can monitor the temperature and weight changes of samples in real time.The experimental part of this paper is mainly divided into four groups: pyrolysis of regular cylindrical lump coal,pyrolysis of circular cakes lump coal,pyrolysis of regular cylindrical briquette coal and pyrolysis of regular cylindrical crushed coal pile.The pyrolysis experiments of briquette and crushed coal can be used as supplement and contrast for lump coal pyrolysis experiments.The influence of the diameter of lump coal on heat transfer process,temperature gradient distribution and the analysis of volatilization in lump coal is investigated.The results show that the larger diameter is,the greater internal heat transfer resistance is,the bigger the maximum temperature difference between coal surface and center is,the smaller the yield of semi-coke is,the yield of tar and water first increase and then decrease,the higher the pyrolysis gas yield is,and the higher the pyrolysis degree of semi-coke is.It is explained that the diameter affects the heat transfer,and the heat transfer determines the mass transfer.The effects of temperature on lump coal pyrolysis are also investigated.Taking H2,CH4 and CO as examples,their yields in different temperature ranges are calculated.The results show that their values increase with the increase of temperature.The comparative experimental results show that the internal heat transfer process in pyrolysis of regular cylindrical lump coal can be simplified to two-dimensional heat transfer model(axial and radial),and that in pyrolysis of circular cake lump coal,the internal heat transfer process can be simplified to one-dimensional heat transfer model(axial).In the pyrolysis process of lump coal,the shorter path(the direction of lower thermal resistance)will be preferred in the heat transfer process from coal surface to coal center.The pyrolysis process of briquette is similar to the isomorphic lump coal,and the pyrolysis law is similar to that of lump coal.Both of them are equivalent to a whole coal as a heat transfer unit.The thermal resistance mainly comes from the inside of the system,and the main influencing factors are diameters.But the pyrolysis of crushed coal pile is different from the former two because each coal particle is an independent pyrolysis unit.Because the particle diameter is small and the internal heat transfer resistance can be neglected,the pyrolysis degree of crushed coal pile is mainly related to temperature.Through the kinetic analysis of pyrolysis gas products of lump coal,the kinetic parameters at different diameters and temperatures are calculated.The results show that the change of lump coal diameter has little effect on the activation energy of gas products,while the activation energy of gas products mainly varies with temperature.