Thermodynamic Characteristic Research On Solar Aided Coal-fired Power Generation System

Integrating solar thermal energy into conventional power plant-solar aided coal-fired hybrid power system could not only reduce coal consumption and emission, but also it is the most efficient way to utilize solar energy (for power generation). Due to the system steability, more easily controlled mass and temperature of the parabolic trough collector, so the parabolic trough collector is selected as the main energy resource of medium and high temperature in the paper. The integration of solar and coal-fired power system saves the heat store and steam turbine system, and reduces the electricity cost. In additional, the solar thermal energy as the energy carrier is easy to integrate with thermal system. The research on solar aided coal-fired hybrid system can settle the integrating project problem, the heat transfer and conversion mechanism between different mass and heat flow.The thesis focus on the research of the thermal characters of solar collector system and integration power system, based on the detailed investigations of correlative research and industry development. The developed models are applied to analyze the system quantitatively. The main reseach work and the results are listed below.Firstly, the dynamic model of solar parabolic trough collectors (including water/steam and thermal oil as the heat transfor fluid) has been developed in this paper. Different working conditions of the collector structure and thermal parameters have been considered in the models. The simulated results are validated using the selected real test data on typical summer and winter days, and the steam generating process from unsaturated water to superheated steam has been studied in the startup simulation for the water/steam type. The disturbance analysis validates the model's dynamic responses and confirms the relations between output fluid characters and solar radiation, inlet fluid temperature, flow rate and collector area. Therefore, the models can be used to analyze and predict the performancse of the solar collector systems.Secondly, a simplied coal-fired thermal power system model is developed. The model consistes of steam turbine stages model, condenser model, feedwater heater model, water mixer model, boiler model and so on. The model is validated by the comparision between simulated values and designed values in same working conditions. The thermal system model can be used to analyze the dynamic and working characters in different working conditions.Thirdly, the medium-or-low temperature solar heat is integrated into conventional coal fired power plant in different coupling modes, including both water/steam and thermal oil types. The steam from solar steam direct generating system is entered the new or original steam turbine, or heat from thermal oil to replace parts of the extraction steam to preheat feedwater. A coal-fired power plant is chosen as the case study to analyze all the possible coupling modes respectively, based on the developed power plant models. The main characters, including coal and steam consumption rate, solar thermal electricity efficiency, parameters distribution are analyzed. The results indicate that the solar thermal oil integrating mode create higher efficiency and simpler system structures, great stability than other modes.In the end, the developed integrating model has been used to study the energy and economic benefits of the hybrid thermal power system with typical 200MW, 300MW and,600MW subcritical,600MW super-critical, and 600MW,1000MW ultra supercritical fuel power units separately. The solar heat in the temperature range from 260℃to 90℃are integrated with above mentioned power units to replace the extraction steam (to preheat the feedwater) in power boosting and fuel saving operating modes. The results indicate that the solar integrating technique can achieve higher solar (to power) efficiency comparing to the solar alone power plant and is more suitable to be adopted in subcritical and supercritical plants than in ultra supercritical plants. The solar energy can play a significant and ecumenically competitive role in providing base load power generation in the hybrid power sytem.