Thermal Modeling of a Solar Steam Turbine With a Focus on Start-Up Time Reduction

Abstract

Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in baseload plants. In order to preserve the lifetime of the turbine while still allowing fast starts, it is of great interest to find ways to maintain the turbine temperature during idle periods. A dynamic model of a solar steam turbine has been elaborated, simulating both the heat conduction within the body and the heat exchange with the gland steam, main steam and the environment, allowing prediction of the temperatures within the turbine during off-design operation and standby. The model has been validated against 96 h of measured data from the Andasol 1 power plant, giving an average error of 1.2% for key temperature measurements. The validated model was then used to evaluate a number of modifications that can be made to maintain the turbine temperature during idle periods. Heat blankets were shown to be the most effective measure for keeping the turbine casing warm, whereas increasing the gland steam temperature was most effective in maintaining the temperature of the rotor. By applying a combination of these measures the dispatchability of the turbine can be improved significantly: electrical output can be increased by up to 9.5% after a long cooldown and up to 9.8% after a short cooldown.

Geometric Modularity in the Thermal Modeling of Solar Steam Turbines

“…These are determined through an iterative process which uses the turbine inlet conditions as input, calculates the off-design isentropic efficiency [9,13] and applies Stodola's ellipse law [14] to calculate the mass flows. The heat transfer coefficients within the flow passage are then calculated from these properties and, together with the steam temperatures, form the boundary conditions for the FE model.…”

“…In general, the model is based on previous work by the authors [9]; however, the MATLAB-based model has been supplemented with a COMSOL-based finite-element (FE) heat conduction model. Integration of COMSOL allows more flexibility, including multi-physics applications, while keeping the original advantages of MATLAB related to scripting and algorithm automation.…”

“…The heat transfer coefficients within the flow passage are then calculated from these properties and, together with the steam temperatures, form the boundary conditions for the FE model. Direct calculation of the steam flow with the turbine is not part of this model, the heat transfer coefficients are calculated by the use of a correlation which is dependent only on thermodynamic quantities [9].…”

“…Other works have studied means of changing operating procedures to achieve faster start-up times [7]. Prior simulation work by the authors elaborated a detailed thermal simulation model of a solar steam-turbine [9] and examined turbine modifications allowing faster start-up [11]. However, this model was tied to a specific turbine geometry, and is thus of no use for the evaluation of alternative turbines employed in the next generation of solar tower CSPPs, where both the turbine size and operation temperatures are very different.…”

Flow parameter changes in steam turbine 10 MW during start-up and heating

“…Some publications deal with warming-up of the metal parts of the turbine, relative shifts of stator and rotor parts and their deformations [2] or [3]. Other part of papers deals with similar problems, which means decreasing of starting-up time for steam turbines operating in solar field [4] or the turbines put into combined cycle [5]. Overall view on steam turbine measurement provides [6].…”