Integrated modelling for improving the design and operation of steam power plants

Power producing companies have faced a new situation following the development of unregulated electricity markets. Strong competition forces them to take power production costs into account more carefully in order to maintain or increase profits. Additionally, to promote the efforts to reduce CO2 emissions,legislation and taxation drives operators to increase the use of coal and renewable energy sources more efficiently and over a wider range. This results in an increasing interest in the use of solid-biomass-based fuels in pulverized coal fired power plants. Therefore, fuel flexibility due to the combustion of varying relative shares of coal and biomass poses new challenges for plant operators. The understanding of deposition formation and its behavior and consequences has become a key issue in optimizing plant operation and in securing plant performance and availability. The investigation presented in this dissertation was carried out as part of the EU-ADMONI project. The overall objective of the work presented here is the development of advanced monitoring models for solid fuel fired steam power plants. To obtain such advanced monitoring methods, three kinds of models are to be coupled with each other. They are: Process Monitoring Models, Dynamic Process Models and 3D Boiler Models. This coupling consists of the exchange of different boundary conditions (BCs) with each other. Although the development of an overall monitoring methodology has been outside the scope of this work, this dissertation contains descriptions and examples of the three separate modelling techniques needed to obtain the overall monitoring methodology which can be used for improving the operation of steam power plants. Process monitoring models have been developed to predict or monitor either heat transfer resistances of the heat exchanging equipment of the steam cycle (this is an indicator of the amount of deposit formation) or the overall steam cycle efficiency of the power plant at hand, using the process data provided by the Data Acquisition System (DAS) of the plant. The novelty of the models presented in this work is the investigation of the possible use of exergy analysis within the existing monitoring models to detect a possible decay of plant performance due to arising operational problems. Dynamic process models of the steam cycle have been developed to provide insight in the physics and plant behavior when (co)-firing varying biomass and coal blends. The results of these models can be very important for the design of the control system of plants which are co-firing these kinds of mixtures. Physically based models have been formulated, since no historical data is available in the design phase, and thus black box models were not an option. A methodology for the dynamic modelling of energy conversion systems has been proposed, and the modelling of a simple single pressure, small, steam power cycle, has been done as a "proof-of-concept". An accurate methodology for the simulation of 3D pf combustion has been developed to accurately predict the flow and temperature fields inside the boiler. To be able to accurately predict these phenomena, detailed combustion models are necessary. Various combustion models for solid fuel combustion have been proposed in literature, but an extensive validation of these models is hardly given. Therefore, several combustion models have been validated against experimental data and the most accurate model has been used for full scale 3D boiler