Experimental Studies On Tar Formation During Coal Pyrolysis On The Muti-product System And Deep Processing Of Tar

As one of important research directions on clean coal technology, coal gasification technology is significant in highly utilization of coal in China. The circulating fluidized bed multi-product cogeneration system developed by Zhejiang University achieves coal tar,gas,steam and power cogeneration and has a very broad application prospects. On this basis, an integrated experimental research on tar formation during coal pyrolysis on the muti-productsystem and deep processing application of tar was presented in this thesis.The influence of pyrolysis temperature and coal type on the yield,basic characteristics and composition of coal tar was inverstigated on a 1MW multi-product cogeneration system. According to the results, the coal with higher volatile has a higher tar yield and the tar yield increase to a maximum and then decrease with the continuing increase of pyrolysis temperature. GC-MS analysis showed that benzene,phenols and alkanes forme more easily at a low temperature not like naphthalenes at a high temperature. Results that the light components has a lager proportion in the tar at lower and higher pyrolysis temperature indicated that tar components tend to be distributed in both low boiling point region and high boiling point region at high pyrolysis temperature. Moreover, the oxygen content in coal has a significantly impact on the phenols content.Experimental research on the 12MW multi-product cogeneration system, was also investigated. Analysis of physical and chemical characteristics showed that ash content, high hydrocarbon ratio, softening point, viscosity and asphaltene content of heavy tar were high and increased with the pyrolysis temperature. In this paper, mechanical dewatering, filtration and additives were selected to solve application problem caused by high moisture content, high ash content and high viscosity.In order to deepen the tar processing and utilization, two atmospheric vacuum distillations apparatuses were used to cut the tar distillate, other methods and apparatuses,such as GC-MS\FT-IR and chromatography were also used to analysis the tar distillate composition at different temperature ranges. It was indicated that there was a certain proportion of sulfide\nitride and olefin and the phenols content of tar distillate at 170℃-230℃was very high. Thus, further processing of tar distillate about extraction of phenols and hydrotreating was carried out.In order to improve the environment friendliness of this system, the extraction and recovery of phenols in wastewater from the coal-pyrolysis multi-production co-generation system has been investigated. According to the experimental results, the volatile phenols contained in the wastewater can be reduced to following the national emission standards after multi-stages extraction using butyl-acetate as extractant.