| The demand for energy of the rapid domestic economy development increased sharply in recent years. Coal production and utilization made a great contribution to the sustainable development of social economy, lead to some serious environmental problems and also a series of socio-economic issues. Therefor, it is important to explore some kinds of high efficient and clean coal conversion technology. Meanwhile, the exploitation and utilization of low quality coals with a large amount of reserves are taken into account gradually due to the continuously comsuption of high quality coal.Coal fractional conversion polygeneration technology is one of the represent of coal resource utilization. In this technology, electric power, chemical industry and construction materials are gathered together as an integrated system and to realize the optimization of overall efficiency. However, an integrated theoretical system isn’t formed and the corresponding theoretical research is lagged behind the development of the engineering application due to the laking of comprehensive and profound research of the polygeneration system. In addition to electricity, the char, low caloric value coal gas and synthesis gas are also the primary production of polygeneration system. Therefore, the system integrated benefit improvement, the deep-understanding of the coal pyrolysis mechanism, the expansion of pyrolysis products comprehensive utilization and the rational distribution and optimization of the system become key issues of the polygenration tehchnology.In this article, diffirent rank of coals such as Shenhua coal (SH), Zhundong coal (ZD), Baorixile coal (BRXL) and Zhaotong coal (ZT) were conducted as the research objects. The influences of particle size and pyrolysis temperature on the characterization of devolatilization and the varying pattern of tar components were studied through fixed pyrolyzer. Results show that, the devolatilization rate and volume increased greatly along with the rising pyrolysis temperature, the volume of decomposed volatile increased from 93ml/g to 395ml/g when the pyrolysis temperature increased from 500℃ to 1000℃. While the effect of particle size on the volume and rate of devolatilization is not as obvious as that of pyrolysis temperature. When the pyrolysis temperature is higher than 800℃, the concentration of CH4 and H2 in coal gas increased rapidely for the polycondensition and dehydrogenation reaction of aromatic structure in high rank coals. Furthermore, the calorific value of coal gas increased incessantly with the pyrolysis temperature also. For example, calorific value of coal gas of SH and ZT increased from 15.33MJ/Nm3 to 16.33MJ/Nm3, and 7.16MJ/Nm3 to 16.71MJ/Nm3 respectively.In this study, the existence of CO2 and vapour which act as heat carrier may promote the gasification reaction between semicoke and CO2 and vapour at high temperature circumstance. The influence of temperature and atmosphere on semicoke gasification properties were tested by thermal analysis. The carbon conversion efficiency, reaction rate and activation energy were applied to evaluate the difficulty of semicoke gasification properties. Study results confirms that the higher the gasification temeperature, the higher the carbon conversion of semicoke, and also the easier the gasification reaction well be. The conversion of BRXL semicoke reach 80.63%at 1000℃ and atmospheric pressure.Semicoke which is one of the main produts of the polygeneration system, can be used for combustion derectly or as activated carbon and absorbent. And also can be used in coal gasification and chemical industry as coke-water-slurry. Semicokes obtained in different pyrolysis temperature were made into slurry. The solid concentration of semicoke water slurry elevated to more than 60% from 40% of raw coal water slurry and possessed a favourable rheological behavior and stability because of the reduction of hydrophilic oxygen-containing functional group.Lignite is very active and is a suitable pyrolysis material. But the transformation and utilization is very high due to the high moisture concentration. Hence, a kind of nonevaporation upgrading method, hydrothermal dewatering, was applied to upgrade lignite in this study. The pyrolysis and combustion properties of upgraded coals were evaluated by characteristic parameters, such as initial mass loss temperature, terminate mass loss temperature and maximum mass loss rate, et al. Meanwhile, the coal properties, micro pore structure and the content of alkali element were also detected to investigate the deep reason of hydrothermal dewatering influence on lignite macroscopic properties. The results reveal that, the pyrolysis and combustion characteristic curves of upgraded coals are postponed towards to high temeperature and stability of lignites are improved. The maxmum mass loss rates are also promoted which is benefit for the pyrolysis and combustion of lignite. For example the maxmum mass loss rates of ZT pyrolysis and combustion improved 32.46% and 66.67% respectively. Whatmore, the reaction activation energy of upgraded coal are improved indicating that lignite pyrolysis and combustion properties get closer to high rank coals. The pyrolysis activation energy of ZT and ZD increased 16.43KJ/mol and 5.03KJ/mol respectively.A lot of infratest are required to choose a suitable pyrolysis coal with the characteristics of large reservation, versatile quality and complex structures. To cut down large amount of experiments, an advanced coal pyrolysis model, CPD model, was employed to predict the devolatilization characteristics and coal pyrolysis products distribution. Compared with the experimental results, simulative results of coal pyrolysis products distribution and devolatilization characteristics by the CPD model present to be accurate to some extent. The deviations of CO2 and CO simulative results, which produced only in the first pyrolysis round, are within 2%. While the deviations veracity of CH4 and H2 are a little lower due to the secondary craking of tar and the interaction between semicoke and gas. |
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