Techno-economic Evaluation Of Low Grade Coal Staged Conversion Polygeneration Systems Combined Pyrolvsis And Combustion

Low grade coal accounts for 46%of China's total coal resources.Confined to its lower energy and economic value,it is difficult to be utilized.Compared with direct combustion,liquefaction and gasification,pyrolysis-based polygeneration technology could co-produce oil,gas and electricity in the same system through coal staged conversion.It is a good way to utilize low grade coal and is expected to ease China's oil and gas shortages.According to the literature review,there are no reliable theoretical researches on the building,optimization,and feasibility analysis of low grade coal pyrolysis-based staged conversion polygeneration system.Therefore,process simulation and techno-economic evaluation have been conducted in this thesis,aimed to provide reliable information and data for the industrial application of low grade coal pyrolysis-based polygeneration technology.Based on the polygeneration facility coupling an atmospheric pressure fluidized bed pyrolyzer with a CFB boiler for the simultaneous production of gas,tar,electricity and steam proposed by Zhejiang University,this paper established two 2×350MWe supercritical low grade coal pyrolysis-based staged conversion polygeneration systems.The target products of the first system are methanol,oil,and electricity,while which of the second system are SNG,oil,and electricity.The two systems employ the following products technical scheme:1)part of H2 is extracted from coal gas and used for hydrofining tar into oil in both systems;2)char is combusted in conventional supercritical circulating fluidized bed boiler and producing high pressure steam for electricity generation in both systems;3)coal gas is firstly synthesized into methanol,and the tail gas is further utilized in a gas turbine to generate electricity in the first system;while in the second system,the coal gas is used for SNG synthesis.The technical process,the reaction and the technical parameters of units in both systems are determined.Besides,the utilization of waste heat and the thermal integration degree of the system are improved.Detailed models of both systems were built and simulated with Aspen Plus.The accuracy of the methanation model is verified and the optimum operation parameters of both system were sought by sensitivity analysis.With reliable technical and economic data such as system parameters,equipment investment,market price and so on,the system efficiencies,as well as economic indicators such as fixed capital investment,internal rate of return(IRR)and payback period are calculated and compared.Furthermore,the uncertainty of the market fluctuation on the polygeneration systems was also studied to give a more comprehensive assessment of the two systems.The results revealed that the net energy conversion efficiency,IRR and the dynamic investment payback period of system 1 are 49.07%,25.7%and 6.99 years,respectively.In system 2,the net energy conversion efficiency is 50.02%,the IRR is 21.63%,and the dynamic investment return period is 8.3 years.Uncertainty analysis showed that both systems are good at withstanding wild market fluctuation.So from the point of view of economics,system 1 has a better performance than system 2 under the market price of 2016.The results provide a reliable reference for the promotion of low grade coal pyrolysis-based staged conversion polygeneration system in China.