Study On Dynamic Behavior Of Distributed Energy System Based On Coal-bed Methane

Coal-bed methane in Shanxi province is largely reserved and concentrative distributed, with outstanding development and utilization value, especially low concentration coal-bed methane. Because low concentration coal bed methane is difficult to long-distance transport, local utilization is the best solution. So the distributed energy system based on coal-bed methane will have broad prospects. As a kind of cascade energy utilization system, distributed energy has the advantages of energy saving and environmental protection, high efficiency and reliable, flexible and convenient. In this thesis, a distributed energy system based on coal-bed methane is established, and the dynamic characteristics of the system are studied, providing the technical basis for the design of the integrated control system of the distributed energy system.The system takes the gas engine as the power core, including heat recovery steam generator, steam turbine, single effect lithium bromide absorption heat pump and other equipment. The rated electric load of the system is 800 kW, heating load is 300 kW, and cooling load is 129 k W.Each part of the distributed energy system is divided reasonably and modeled respectively based on the modular modeling theory. A mean value model concluding combustion and emission models for an engine has been developed. The influence of the change of the concentration of component in coal-bed methane on the system performance is considered. The heat recovery steam generator is divided into the single-phase medium heat transfer model and the evaporation system model. Convective heat transfer coefficient of gas side and working medium side is confirmed according to the structure of the heat exchanger. A model of static characteristics adding dynamic first order link is built for the turbine. At last the single-effect lithium bromide absorption heat pump model is established using the lumped parameter method.Dynamic simulation model of the distributed energy system is established using software of Matlab/Simulink. Correctness and rationality of the model is validated by comparing the steady state performance data with the design values. In this case, unit electricity, heat and cold load and performance response to step changes in coal-bed methane flow, to step changes in concentration of component in coal-bed methane, to step changes in extraction steam flow, to step changes in cooling water flow, to step changes in chilled water flow and to step changes in chilled water inlet temperature is researched. Results show that the dynamic change of the engine and turbine is fast and the average response time is about 5 to 10 seconds. The inertia of the heat recovery steam generator and absorption heat pump is big and the average response time is about 1000 to 1500 seconds. In this thesis, the dynamic response curve and the corresponding transfer function are obtained, and the factors that affect the dynamic characteristics of the distributed energy system are analyzed, which lays the foundation for the design of the control system.