Research On Formation Of Tar During Coal Pyrolysiss And Deep Processing Of Tar

Based on National863Program "circulating fluidized bed combustion clean utilization of coal pyrolysis technology development", this paper carried out the research on characteristics of coal pyrolysis and deep processing of coal tar., which can help to understand the effect of pyrolysis behavior on tar yield and composition of tar and have a direct role in guiding the industrial application of multi generation technology for coal. The research on characteristics and deep processing of low temperature tar can provide the basic data for the comprehensive utilization, process design and the development of downstream products of low temperature tar.To study the effect of different types of coal, different size, and heating rate on coal pyrolysis characteristics, the pyrolysis process was investigated by TG-FTIR in inert atmosphere. The results showed that the increase of coal particle size can reduce the weightlessness ratio, and weightlessness peak temperature increases with the increasing of heating rate. Huainan Pansan bituminous coal can react intensely at400-550℃and release a large amount of CH4, CO, CO2and gaseous aliphatic hydrocarbons and aromatic hydrocarbons.To further investigate the effect of temperature on yields and compounds of tar and char, the rapid pyrolysis process of Huainan coal using a tube furnace at450℃,550℃,650℃,750℃and850℃. The tar was isolated to aliphatic hydrocarbon, aromatic hydrocarbon, non-hydrocarbon and asphaltene, and characterized by chromatography mass spectrometry (GC-MS). The results gained from chromatography and GC-MS showed effect of pyrolysis temperature on the tar group and component. Tar yield increased with increasing temperature and then declined. The char yields decreased and the gas yields increased with pyrolysis temperature,. With the increase of temperature, the fraction of aromatics increased while aliphatic hydrocarbon and non-hydrocarbon decreased. The major contents of saturated hydrocarbon were C16-C30hydrocarbon. The major contents of aromatics were naphthalene, phenanthrene, anthracene, fluorene and their derivatives. Content of anthracene, fluorene and their derivative increased with temperature. The major contents of non-hydrocarbon were phenol, ester, quinoline based substance, which were not influenced by temperature obviously. With the increase of temperature, the weight loss of char decreased.Influence of pyrolysis temperature and coal type on the yield, basic characteristics and composition of coal tar was investigated on a circulating fluidized bed heat-power-gas-tar multi-generation system. Proximate analysis, elemental analysis, density, toluene insoluble, softening point and viscosity of tar obtained from different pyrolysis temperatures were measured. Group composition of tars obtained from different pyrolysis temperatures were identified using neutral aluminum oxide and silica gel. The results shows changes of physical properties, chemical properties and group composition of tars with pyrolysis temperature. The coal tar of Huainan Pansan was dehydrated and distilled into7fractions. The fractions analysis by gas chromatography-mass spectrometry (GC-MS). Comparing of huainan pansan coal in fluidized bed and fixed bed pyrolysis experiment results, tar yield change of fluidized bed and fixed bed with the pyrclysis temperature was the same. Tar yield is first increases with the increase of pyrolysis temperature and then decreases. The tar yield of fluidized bed is more than50%higher than fixed bed. Compared with the fixed bed, aromatic hydrocarbon and asphalt content of fluidized bed is higher, and aromatic hydrocarbon and non-hydrocarbon content is lower.Distillations of mixed tars using different distillation apparatus were tested. Considering the tar has high content of water, ash and high viscosity, study on dehydration, ash removal and viscosity reduction was carried out to improve the liquidity of tar. The results show that demulsifier have good dehydration effect, and water content can be reduced to1.94%under optimum operating conditions. Tar was dissolved in toluene and filtered with filter paper, and ash transferred to toluene insoluble completely. The main reason for the effects of coal tar liquidity is toluene insoluble and other heavy components, rather than the ash. Comparison of several additives, ethanol has better result to improve fluidity of coal tar. The viscosity of tar can be reduced94%by adding5%ethanol.Recovery of phenol from the wastewater produced in the multi-cogeneration system has been studied. Based on the theoretical analysis, experimental results and costs, butyl acetate was selected as the extractant and99.6%of the volatile phenols in the wastewater were recovered in two stages of extraction using a feed:solvent ratio of4:1(v/v) at25℃.Isolation of phenols from the middle oil fraction (170-230℃) of tar produced in the multi-cogeneration system has been investigated for the purpose of recovering valuable pure phenols, such as phenol, cresols, xylenol and ethyl-phenol. Phenolic compounds were separated from the middle oil by liquid-liquid extraction using alkali and sulfuric acid. The yield of tar acids from the middle oil fraction is up to37%, which is much higher compared with those of metallurgical coke plants. Phenols content of the fraction(170-230℃) is37%, and the main compounds are lower phenol. The phenol content of the fraction (230-280℃) is23%, which main contain higer phenols。Hydrofining of low temperature coal tar distillate (IBP-460℃), obtained from muti-generation, was performed to investigate the effects of reaction temperature, hydrogen pressure, volume ratio of hydrogen to oil and liquid hourly space velocity (LHSV) on the characteristics of product. Experiments were carried out over alumina-supported WO3, M0O3and NiO catalysts in a fixed-bed hydrogenation reactor of100ml in volume. The hydrogenation product was cut into gasoline fraction (IBP-180℃) and diesel fraction (180-360℃). Mass fraction of gasoline is18%and mass fraction of diesel oil is67%. The octane number of gasoline fraction is68.2. The cetane number of diesel fraction is31. The gasoline fraction; diesel fraction can be used as high quality blending component.