Mechanism Of Coal-based Distributed Energy Supply System Integration And Cascade Utilization Of Energy

With the continuous development of structural reforms on the energy supply side in China,the clean and efficient conversion of fossil fuels and utilization of low-temperature waste heat by improving quality has become an important direction for energy conservation and emission reduction in industries.The distributed energy supply technology based on the supercritical water gasification of coal is one of the technologies with great potential to realize the high-efficiency,clean and low-carbon utilization of coal.This dissertation is to study several key problems of the coal-based distributed energy system.Three parts are included:the mechanism of comprehensive cascade utilization of the chemical energy and physical energy of coal,the integration of distributed cogeneration system based on the supercritical water gasification of coal,and thermodynamic analysis and experimental verification of a new hybrid heat pump for the utilization of low-temperature waste heat.Based on the research and analysis of different coal gasification methods,a new method for the comprehensive cascade utilization of the chemical energy and physical energy of coal is proposed,which combined the supercritical water coal gasification process with the syngas utilization process,and the high-temperature flue gas of a gas turbine is used to provide heat for the gasification process.The proposed method makes full use of the advantages of the supercritical water coal gasification process,such as the low gasification temperature and clean production.At the same time,it realizes the comprehensive cascade utilization of the chemical energy and physical energy of coal by integrating the coal gasification process and power generation subsystem.Based on the concept of energy level,the change rule of fuel energy conversion and utilization in the process of supercritical water gasification of coal is deeply studied.The energy level equations describing chemical exergy of coal,the exergy of gasification reaction heat,the chemical exergy of supercritical water and the chemical exergy of syngas in the process of supercritical water coal gasification has been established,and the chemistry conversion mechanism of coal in the process of supercritical water gasification of coal has been revealed.The syngas utilization process was analyzed,and the performance improvement mechanism of a power generation system based on supercritical water gasification of coal was explored.Based on the comprehensive utilization method of chemical energy and physical energy,a distributed cogeneration system based on supercritical water coal gasification was proposed.The syngas produced by the supercritical water coal gasification process is used as the fuel of a gas turbine,the high-temperature heat of the exhaust gas from the gas turbine provides heat for the gasification reaction process,and the mid and low-temperature heat is used to produce supercritical water and process steam,realizing the comprehensive cascade utilization of the chemical energy and physical energy of coal.The net power generation efficiency of the system reaches 49.95%,and the comprehensive energy utilization rate is 89.61%.To separate the carbon dioxide in the flue gas with low-energy consumption,and an improved coal-based distributed cogeneration system is proposed,which uses pure oxygen as the oxidant and carbon dioxide as the cooling medium for gas turbine.The simulation analysis results show that under the condition of nearly complete separation of carbon dioxide,the net power generation efficiency of the proposed system reaches 44.65%,and the comprehensive energy utilization rate of the system is as high as 83.13%.The research results in this paper provide a new way for the efficient,clean and low-carbon utilization of coal.To solve the problem of a large amount of low-temperature heat discharge,a hybrid absorption-compression heat pump is proposed to recover the low-temperature heat in the coal-based distributed energy system to produce more process steam.Two new coal-based distributed cogeneration systems are integrated for the scenarios of the centralized and decentralized layout of gasifiers,and the thermal performance of these proposed systems are analyzed in detail.To provide theoretical support for the application of coal-based distributed energy system,an economic performance analysis of the coal-based distributed energy system combined with a hybrid absorption-compression heat pump under the scenario of centralized gasification coal and syngas decentralized utilization is comprehensively analyzed.An absorption-compression heat pump experimental platform is built to recover low-temperature sensible heat to produce process steam.The heat pump recovers low-temperature(80-150?)flue gas waste heat to produce saturated process steam(0.3-0.5 MPa).Through experimental tests,the low-temperature waste heat is recovered to produce process steam at a temperature of 154?,the heat output reaches 70.15 kW,the heating coefficient performance reaches 0.31,and the electric coefficient performance is 5.29.The technical feasibility of process steam generation by recovering low-temperature sensible waste heat is verified by experiments more than 400 hours,which provides a new technical solution for the utilization of low-temperature sensible waste heat in the process industry.