No abstract

The increasing share of fluctuating renewable energy sources leads to changing requirements for conventional power plants. The changing characteristics of the residual load requires the conventional fleet to operate with higher load gradients, lower minimum load at improved efficiency levels as well as faster start-ups and provision of ancillary services. Despite the requirements from the electricity market, the value of improving those flexibility parameters is hard to evaluate for power plant operators. In order to quantify the additional benefit that can be achieved by improving flexibility parameters on a certain power plant in a changing market environment, an adjustable load dispatch model has developed for that purpose. Using past electricity market data, the model is validated for typical coal and a typical gas fired power plants by reproducing their operational schedule. In the next step, the model is used to apply parameter changes to the power plants specifications and economic effects are demonstrated. General statements are derived on which flexibility parameter needs to be improved on each power plant type. Furthermore, specific economic evaluations are shown for the reference power plants in order to present the ability of the developed tool to support investment decisions for modernization projects of existing power plants.

No abstract

The increasing share of fluctuating electricity feed-in from wind energy and photovoltaic systems has a significant impact on the operating regime of conventional power plants. Since frequent load changes were not the focus of optimization in the past, there is still potential for improving the transient operating behavior. Exergy analyses are increasingly used to determine optimization potentials in energy conversion processes, but are mostly limited to stationary conditions. In order to perform an exergy analysis of the transient operation of a combined cycle power plant on component level, detailed information on the state and process variables of the individual components is required. These are not completely accessible via measurement data alone. For this reason, a comprehensive dynamic simulation model was developed, which includes the process components and the power plant control system. With the help of the implemented exergetic balance and state equations, the desired exergy quantities can be determined. The simulation results are used to evaluate the transient operating behaviour at different load change gradients and control actions on the basis of exergetic parameters. The exergy analysis results in an improved understanding of the causes of exergy destruction in the system, which can be used for optimization approaches. As expected, the main causes of exergy destruction are combustion processes and increased temperature gradients during transient operation. Overall, however, only moderately increased exergy destruction can be determined for the transient operation of the investigated plant compared to the steady state.