Study On Suspended Pyrolysis Characteristics Of Pulverized Coal

Coal plays an important role in the energy structure of China.It is urgent and significant to research on the clean and high efficient technology of coal utilization.As one of the technologies on clean and high efficient utilization of coal,staged conversion polygeneration technology makes full use of coal values,and it extracts highly active volatile before coal is burned to achieve gas,power and heat.This technology has a promising prospect in China.The existing polygeneration processes are mainly coupled with fluidized bed boiler with designed feed particle size at centimeter level.Most of the power plants in China are pulverized coal boiler,therefore,it is of great significance to explore the polygeneration system coupling with???pulverized coal boiler.Pyrolysis units are the base of the whole system,while,at present,there is a lack of comprehensive understanding of pulverized coal pyrolysis system,and the integrated theoretical system isn't formed yet.Consequently,it is urgent to carry out the research on pyrolysis characteristics of pulverized coal to provide the basic experimental data for the pyrolysis polygeneration system of pulverized coal.In this paper,a kind of typical coal Pingzhuang lignite was choosed.A 4.5m-long subsection heating drop-tube reactor was designed and built,the pyrolysis gas can be detected on-line,and tar and char can be collected,by which the whole product analysis of pyrolysis process could be conducted.Considering two most important parameters in the pyrolysis unit,i.e.,pyrolysis temperature and the length of reactor,the experimental studies of coal pyrolysis were carried out.The pyrolysis gas,tar and char were characterized by gas analyzer,GC-MS,FTIR,BET,and SEM.The combustion characteristics of semi-coke were analyzed by thermogravimetric analysis.Experimental results are shown as follows:Pyrolysis temperature has a significant effect on pyrolysis characteristics of pulverized coal.The content of H₂ and CO increased with the rise of pyrolysis temperature,aliphatic hydrocarbons in tar decreased with temperature,while the number of carbon molecules got larger,and the average molecular weight also increased.The content of aromatic hydrocarbon in tar increased,or say tar fragrance increased,as five ring aromatic hydrocarbons and even six and seven rings emerged.The composition of heterocyclic compounds was changed,and the phenolic content decreased.The volatile fraction of char decreases with the increase of pyrolysis temperature.With the rise of pyrolysis temperature,the specific surface area was increasedfirstly,and then it decreased.The content of surface functional groups and the aromaticity of semi-coke increased with temperature increased.At high temperature,the volatile content from semi-coke and surface functional groups were relatively low,as a result,the reaction activities and combustion characteristics were poor.Different heating length?i.e.,pyrolysis time?had weak effect on pyrolysis characteristics.The increasing of residence time enhanced the methane reforming reaction,no prominent change as a whole,except the slightly increase of H₂ and CO.The content of aliphatic hydrocarbons in tar decreased.The combustion characteristics of semi-coke with different pyrolysis time are similar.Those are because that there is little difference in residence time between different heating lengths.The small coal powder diameter and relatively small feeding quantity decreased the heat and mass transfer resistance.Pyrolysis can be completed in a short time.Heating length and feed amount,particle size of coal,pyrolysis temperature contributed to the final products compositely.