Hentschel, J; Kahlert, S.; Kohlhepp, A.; Schatte, G.
Energy Valley Bavaria “Flexible Power Plants” – Dynamics in Steam Generation
The integration of a rising share of renewable energy poses a challenge for the conventional generators and the transmission network in the power system. The fluctuating power production of the renewables leads to a lower capacity utilization and a more dynamic operation of the conventional power plants. To ensure a cost-efficient and stable supply system, changes in the conventional power plant technology and network infrastructure are essential. The “Munich School of Engineering” launched the interdisciplinary project „Flexible Power Plants“ which aims to bridge the gap between the power generation and the electrical network to provide innovative solutions for future’s power system.
The common ground of most conventional power plants is the fact that they generate steam at high temperature and pressure by combusting a carbon-based fuel. The live steam is then expanded in a turbine to generate electrical power. The steam generation plays a key role in raising the efficiency and in power plant dynamics. High efficiencies demand high temperatures and pressures of the live steam. At the Institute for Energy Systems, the transient behavior of steam generators is to be investigated. First, dynamic process models of a combined cycle power plant and a coal fired steam power plant are developed to analyze the overall power plant behavior. Furthermore, experiments to obtain a more detailed insight into the heat transfer and the fluid properties in evaporators are going to be performed. The dynamic process simulation consists of the process model, as well as the control system, and allows the prediction of the power plant performance during a more flexible operation. The steam generator contains thick-walled components, such as the steam header and the steam drum, which are highly sensitive to thermal stresses due to temperature changes. The goals are to increase the flexibility of the power plant and to minimize the negative effect of the load cycling on the critical components. Different measures are analyzed using dynamic simulation. The start-up of power plants has to be accelerated to reduce fuel costs and CO2 and NOx emissions. To better address the need of controllability in power generation, optimized control strategies for steam generators are developed in order to increase the load flexibility. Providing more balancing power can add to the stability of the overall power system. The mentioned dynamic operation strongly interferes with the thermo-physical behavior of the evaporation process. Especially in the near critical region (temperatures of about ± 50 K around the pseudocritical temperature) large changes in the thermo-physical properties lead to significant deviations between the calculated and the real behavior of the heat transfer. This can lead to unsafe conditions that may result in damage of the power plant’s evaporator. Thus, the suitability of the evaporators of existing power plants for dynamic loads as well as the potentials of optimization for future power plants have to be studied. To be able to archive both goals the experimental test facility HIPER (HIgh Pressure Evaporation Rig) is currently under construction at the Institute for Energy Systems. The basic layout of HIPER is a closed water loop that can feed an evaporation test section with variable conditions regarding mass flux density, pressure and enthalpy at the inlet of the evaporation tube. The evaporation tube itself can be subjected to variable heat flux densities and heat flux density distributions, the inclination of the tube can be adjusted. The boundary conditions can be changed dynamically. The main components of the test rig are a high pressure piston pump, a preheater, a backpressure throttle, the evaporation tube as well as a feed water tank and a cooling system. The Evaporation tube itself can be exchanged in a modular fashion to study different geometries (diameter, internal ribs or one-sided heating). «
The integration of a rising share of renewable energy poses a challenge for the conventional generators and the transmission network in the power system. The fluctuating power production of the renewables leads to a lower capacity utilization and a more dynamic operation of the conventional power plants. To ensure a cost-efficient and stable supply system, changes in the conventional power plant technology and network infrastructure are essential. The “Munich School of Engineering” launched the... »