Primary Study On The Oil-electricity Cogeneration System Of Integrated Pyrolysis And Gasification Of Low-rank Coal

The reserves of low-rank coal account for more than 55%of the total coal reserves in China,which is the main development and utilization of energy in our country in the future.Compared with combustion and gasification,the pyrolysis technology of low-rank coal is a relatively efficient and clean utilization technology due to its moisture and volatile content.The polygeneration technology based on coal pyrolysis and char combustion or gasification is considered to be a promising utilization way of low rank coal.A novel process of the oil-electricity cogeneration system of integrated pyrolysis and gasification of low-rank coal is proposed in this paper.The specific technology is that the coal is rapidly pyrolyzed in the downer bed,and the tar and coal gas are generated greatly due to the high volatile characteristics of low-rank coal.Then the obtained char which carries the reaction heat is delivered to the fluidized bed for gasification.The generated gas is introduced into the pyrolyzer as heat carrier to provide sufficient heat for coal pyrolysis.In addition,the active components in the gas also have a positive effect on the raise of tar yield and content of light components.The mixed gas from pyrolysis and gasification is sent to gas turbine for power generation.The power generation technology selected in this paper is the advanced gas-supercritical carbon dioxide combined cycle power generation system.The selected coal in this paper is Naomaohu long flame coal(NMH).The pyrolysis experiments of Naomaohu coal in nitrogen and simulated coal gasified gas atmosphere were carried out in a small-scale pyrolysis gasification coupling integrated reactor.It is found that the reaction temperature with the highest tar yield was 600^oC.And the tar yield of pyrolysis in coal gas is 2.75%higher than that in nitrogen atmosphere at the reaction temperature of 600^oC,and the content of light components is a much higher 5.03%.The effect of pyrolysis atmosphere on the quality improvement is justified.Based on the experimental data and Aspen Plus software,the oil-electricity cogeneration system of integrated pyrolysis and gasification of low-rank coal with an annual processing capacity of 1 million tons is established.By changing the pressure and temperature of supercritical CO₂working fluid entering the turbine,the model of power generation unit is verified and optimized.Under the condition of pyrolysis temperature at 600 ^oC,oxygen/char ratio and steam/char ratio of 0.6and 0.8 respectively,an oil-electricity cogeneration system with annual tar production of 127400 tons and 232.1 MW electric power is constructed.The energy efficiency of the system is up to 50.68%.If the carbon capture process is added,the energy efficiency will be reduced to 41.93%.Economic analysis and evaluation of the system is also carried out.The total capital investment(TCI)and total production cost(TPC)of the system are calculated.And the economic performance of the system are also analyzed,such as investment payback period(PBP),return on investment(ROI),net present value(NPV)and cost of electricity(COE).The TCI of the system is 2972.59×10⁶CNY,including 2477.16×10⁶ CNY of fixed assets,495.43×10⁶ CNY of working capital,accounting for 83.33%and 16.67%of the TCI respectively,and the production cost is about 512.21×10⁶ CNY.The generation cost of the whole oil power cogeneration system is 0.20 CNY/(k W·h),the NPV is 1129.46×10⁶ CNY,and the ROI is 16.40%,the PBP is only 4.37 years.In addition,the fluctuation of coal price,coal tar price and the influence of the change of production scale on the economic performance are also analyzed.