The purpose of the thesis is to develop a methodology for overall evaluation of the material stress of boiler components based on simulations. This methodology can be used by power plant manufacturers and operators to design and optimize boilers. On the one hand the methodology should help to demonstrate potential for increased efficiencies by steady-state simulations and on the other hand it should assist to identify potential for increased load change rates by transient modeling.
The material fatigue of a boiler component is calculated by superimposing creep stress (steady state simulation) and cyclic stress (transient modeling), therefore both types of stress are considered in this thesis.
Creep stress especially affects boiler components of base load power plants with high operating hours at full-load. Steady state simulations were used to identify the critical boiler components by using simulation programs to investigate the combustion and flue-gas-side, water-steam-cycle and material fatigue.
In this thesis a Computational Fluid Dynamics (CFD) simulation program AIOLOS is used to calculate temperature imbalances on the flue gas side of the boiler. The coupling of this CFD simulation program with the water-steam-cycle simulation program DYNAMIK allows for the detailed calculation of heat transfer from the flue-gas-side to the water-steam-side. Thereby, each heating tube and distributor-collector of the heat exchanger are considered to calculate the imbalances on the water-steam-side in the parallel tubes. Based on the calculated wall temperatures, the coupled lifetime calculation program ALIAS allows for conclusions regarding creep stress and lifetime consumption. The results help to identify potential in terms of uniformity of the material fatigue and thus reduced lifetime consumption within a heat-exchanger.
The thick-walled components of power plants operated in mid and peak load are stressed especially by cyclic stress due to frequent load changes. The goal of the transient modeling is to demonstrate the cyclic stress in thick-walled components which are located in the high-temperature range. In this thesis the calculation program was developed by using an existing method to calculate cyclic stress, which is based on the measured water/steam temperature, pressure and mass flow profile. The program calculates the temporal profiles of the radial wall temperature differences within thick-walled components. The program coupled with a lifetime calculation program allows for the computation of the lifetime consumption. The results of the transient modeling allow for the analysis of the cyclic stress of a load change and could be used to optimize the load change of power plants.
The thesis is published by Cuvillier.