Development and validation of a combined heat and power plant model for integration in DYESOPT

Abstract: The liberalization of electricity markets and a growing penetration of renewables has led many countries to feel changes in the operation of their grids. The boundary conditions for the operation of conventional power plants are changing and, as such, an improved understanding of the varying loads and prices on the electricity grid is required to assess the performance of emerging combined cycle gas turbine (CCGT) concepts and to further optimize their design for these new markets in the pursuit of increasing their profitability, especially when considering co-generation of heat and power. A clear consequence of such renewable integration is the need for these plants to be more flexible in terms of tamping-up periods and higher part-load efficiencies. In the pursue of greater power plant dispatch flexibility, new ideas and technologies are being analyzed and tested in new and in already existing installations. Power plant simulations in modeling tools offer the possibility to have first estimates of how profitable it is to implement a new technology, operation scheme or dispatch strategy without having to invest in building the systems or applying any change to the operation of a real power plant. DYESOPT is one of the modeling tools used by researchers and consultants at KTH for simulating and doing techno-economic analyses of thermal energy systems. It has proven to be an accurate and customizable tool for the task. In that sense, the work in this thesis project is to enhance this modeling tool by incorporating a new power plant layout, which will be used in future works for increasing dispatch flexibility of a pilot combined heat and power plant. The power plant modeled consists on a topping Brayton cycle coupled to a bottoming Rankine cycle with three pressure levels, reheat features, and two extractions to feed a district heating system (one extraction from the low-pressure section of the steam turbine, and other from the economizer section of the heat recovery steam generator). The model was built considering the novel ideas to be tested on it and was then validated by comparing its performance against operational data provided by a real power plant during steady state conditions and part load transients. The results show that the validated model is of high relevance for further investigations regarding flexibility increase of CCGT-CHP power plants.