Efficient heat current modelling and off-design simulation of a gas-steam combined cycle cogeneration system

Abstract Gas-steam combined cycle cogeneration systems have been widely implemented for their high energy utilization efficiency. Although thermo-economic analysis and design optimization of this kind of system have been widely researched, they encounter increasing regulation demands considering the higher penetration of volatile renewable energy and terminal users’ heat loads. Therefore, it is important to do efficient off-design simulations under variable operating conditions. This work presents an efficient and precise modelling and off-design simulation method of the triple-pressure steam part of a combined cycle. Based on the heat current method to model the heat transfer and heat-work conversion process, the governing equations are separated into linear topology constraints and non-linear elementary constraints. This enables the primal-decomposition-based method to solve different equations using linear system solvers, cutting plane methods, and fixed-point iteration correspondingly. Simulation based on a real system shows nearly global convergence across all permitted operating conditions of heat and cold sources, while conventional fixed-point iteration using the complete and accurate model does not converge. Comparisons with real operating results show a relative error of less than 0.71%.