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Optimization Analysis of Combined Heat and Power Plant of Multistage Gas Turbine for Marine Applications

Nowadays, the rising demand for energy and serious environmental pollution become the motive to improve the energy structure, saving energy and optimize energy utilization. Based on a gas turbine, a marine multistage gas turbine combined heat and power (CHP) structure is proposed. The CHP system includes the top gas turbine Brayton cycle, the intermediate water Rankine cycle (WRC) and the bottom organic Rankine cycle (ORC). According to the method of screening organic Rankine cycle refrigerant to select the appropriate organic working fluids, and their physical characteristics are described. Based on the modular modelling method, the 3-stage CHP system is established. In order to more effectively absorb low temperature waste heat, three different kinds of 3-stage CHP structures were designed to recover the heat in the exhaust gas from the heat recover steam generator (HRSG). The thermodynamic model of the combined heat and power system of marine multistage gas turbine was used to simulate the performance of three different types of 3-stage CHP structures, the optimal 3-stage CHP structure was selected by comparing and analyzing the simulation results. Based on the simulation results of the design point, it is found that the introduction of the optimal 3-stage CHP structure can increase the power output by about 8.5% and improve the cycle thermal efficiency by about 4.32% compared with a conventional 2-stage CHP cycle where only gas turbine topping cycle and water Rankine bottoming cycle are included.