Über die Trennung und Vereinigung von Dampf in Großkraftwerken

Dissertation von Alan Matschke
Universität Stuttgart, 2012

The main objectives for the improvement of utility boilers are to increase their overall efficiency. Therefore, steam parameters need to be increased leading to temperatures which may exceed the limiting temperatures of the tube materials. Considering these aspects, the single tube temperatures of a powerplant have to be determined to prevent material failure. In order to account for the mutual impact of combustion and water-steam-cycle, a coupled simulation is performed to calculate the single tube temperatures.

Apart from the interaction of combustion and water-steam-cycle, the design of the heat exchanger headers is relevant. On the basis of a detailed investigation of the pressure distribution in steam distributors and headers, a new quality regarding the prediction and calculation of single tube temperatures will be obtained.

By means of a similarity analysis, the governing geometry relations associated with the pressure change in steam distributors and headers are identified. The parametrisation of this approach is done by comparing the measured pressure values of an air-flow divider-collector-combination. The portability of the air-flow results to water, respectively steam is approved.
Based on the experimental data, computational fluid dynamic simulations of all governing geometrical relations are performed. The validity of the similarity based approach is shown for nearly all geometrical relations corresponding to real utility boiler application. Deviations between experiment and calculations based on the similarity approach are only evident for very short distances of separating tubes originating from secondary vortices. However, the impact of these vortices to the global mass distribution is minimal.

The comparison between measured and calculated single tube temperatures from a lignite-fired utility boiler shows the good match between the simulated and measured temperatures. The single tube temperatures of a heat exchanger across the boiler width are calculated correctly. The predicted temperatures of vertically arranged tubes show certain discrepancies due to the fact that the soot-blowing equipment leads to different deposit thicknesses within the heat exchanger. This effect is currently neglected in the coupled simulation.

By enabling the use of high performance computing, a significant reduction of computing time for the coupled simulation is achieved. This is a necessary condition to optimize utility boilers already in operation and those yet to be built.

To the top of the page