Pulverized coal-fired power plants are increasingly used in electric grid load compensation. The intermittent electricity production of wind and solar power plants causes sudden load changes in the electric grid which must be balanced by operating steam power plants cyclically. Rapid load changes cause new challenges to plant operators. Dynamic simulation is a powerful tool for investigating the transient behavior of a power plant that is operated cyclically. Process changes and new control strategies are often needed when base load power plants are used in cyclic operation mode. New solutions can be tested with a computer-aided dynamic simulation software. A dynamic model of pulverized coal-fired power plant requires a realistic coal mill model. Also it is important to define thermo-mechanical stresses in stress-prone boiler components during the cyclic operation. These features improve the transient simulation of pulverized coal-fired power plants.This thesis focuses on examining and improving the transient simulation of pulverized coal-fired power plants in dynamic simulation software Apros. The main objectives of this thesis are implementation and validation of a generic coal mill model as well as the verification and validation of Apros thermo-mechanical stress calculation. The coal mill model was implemented by using the user component feature of Apros, whereas the thermo-mechanical stress calculation was implemented with a stress solver component which has been earlier added to Apros component library. Two pulverized coal-fired power plant simulation models were utilized in the validation experiments. Model of reference plant A was received from the plant operator whereas modelling of reference plant B was part of this work. The dynamic validation of the coal mill model was done by simulating the same load change transients that have been measured during cyclic operation of the reference plants. The stress calculation was verified against literary reference and validated against calculation based on standard EN-12952-3 (Water-tube boilers and auxiliary installations. Part 3: Design and calculation for pressure parts of the boiler). In addition stresses were defined during load change transients in critical once-through boiler components.The validation of the coal mill model did not completely give desired results during the load changes. The model was unable to simulate the dynamics of the coal storage inside the mill realistically, when the plant load was changed. Apros stress calculation corresponded to the literary verification reference. It was noted in the validation that stress concentration factors should be used in Apros calculation when the stresses are defined in pipe connections. The stresses during the load change transients seemed realistic and they remained under the defined stress limits.
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