Start-up Optimization of Uniper RoCa3 Power Station

Abstract

The rapid growth of renewable generation has modified the role of combined cycle power stations in the energy industry. Due to the strong increase of intermittent renewable sources, (solar, wind) the key feature for the operational excellence of combined cycle power stations is flexibility. In particular, the capability to start an installation quickly and efficiently after a shutdown period leads to lower operational cost and a higher capacity factor. However, most of existing thermal power stations worldwide are designed for continuous operation, with no special focus on an efficient start-up process.

In most current start-up procedures the GT controls ensure maximum heat flow to the HRSG, without feedback from the steam cycle. The steam cycle start-up controls work independently, with as main control parameter: the limitation of the thermal stresses in the steam turbine rotor. In this paper, a novel philosophy for the start-up optimization of an existing 200 MW CCGT power station is presented. In this new start-up procedure, a feedback loop is established between the steam turbine, the boiler and the gas turbine start-up controls. This feedback loop ensures that the steam turbine can be started up more quickly together with a significant reduction in stresses.

The methodology implied the creation of a flexible and accurate dynamic model in the Simulink$^{TM}$ environment. The full detailed model consists of more than 100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls etc). The mathematical submodels in the component blocks are mainly based on physical models and for a lesser part on experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against real process data related to the three start-up types (cold start, warm start, hot start). The start up model was extended in order to establish feedback loops between the steam cycle, boiler and gas turbine start-up controls. These feedback loops control for example the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine.

The extended model was used to define the optimal trends for the most important operating variables for cold and warm start-up types. These optimization actions were tested real power station start-ups, leading to a start-up time reduction of more than 30%, and a reduction in thermal stresses above 10% for cold starts.