Opportunities for Flexible Operation of a Combined Heat and Power Plant in Power Systems with Volatile Electricity Prices

Examensarbete för masterexamen
Master Thesis
Hansson, Julia Björck
Östlund, Linnéa
To combat climate change,renewable energysources are preferred in energy systems. Among these are wind and solar, which are characterised by low operational costs and that their energy output depends on weather conditions. The implementation of large amounts of non-dispatchable power generation, that are placed early in the meritorder,results in larger and more frequent variations in netpower supply in the energy system. This, consequently, leads to volatile electricity prices. For existing power plants to operate profitably in such systems, they need to have flexible operating strategies to profit from high electricity prices. Furthermore, it is preferable to avoid power production during hours with low electricity prices without having to shut down the plant. In this study, a combined cycle gas turbine combined heat and power(CCGT-CHP) plant located in Gothenburg, Sweden has been analysed in order to find profitable operational strategies for scenarios of possible future energy markets. This study is performed in two steps. In the first, a detailed steady-state process model is derived based on an analysis of historical process data and operating patterns at the reference plant. In the second step, the process model was linearised and implemented into an optimisation model to analyse the CCGT-CHP plant’s profitability and operational strat egies in possible future energy systems. Linear equations were derived for power and heat output, as well as fuel consumption, using factorial design and linear regression methods. The equations were validated against process model outputs. The study concludes that the profitability of flexibilisation measures is highly dependent on the energy system in place. In general, an increased share of non dispatchable power sources increases the profitability of operating the plant with full steam turbine bypass. This strategy further implies alternative strategies for both gas turbine and supplementary firing operations. However, the optimisation model without the possibility of steam turbine bypass, given historical power market data, proposed a similar operation as the one used at the reference CCGT-CHP plant during the reference year. Nonetheless, fuel taxation and future energy systems could give rise to the need for new operating strategies. If the fuel price is increased, full steam turbine bypass is vital to operate in a profitable manner. That is, operate the plant for heat production. However, for a changed electricity mix in the system, the CCGT-CHP plant could have an important part in the electricity system as well.
Energi, Hållbar utveckling, Energiteknik, Energy, Sustainable Development, Energy Engineering
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