Research On Optimization Of Coal-based Polygeneration Based On Energy And Material Utilization Analysis

Coal-based polygeneration system is one significant strategic choice to solve the energy sustainable development and evironmantal pollution problem, characterized by higher efficiency, lower pollution and better peak shaving capacity. The system design and optimization of polygeneration plants is one of key issues on the development and generalization of this technology. This thesis has performed study on the process optimization of polygeneration cases, including the basic configuration selection and the local processes optimization. This research provides guide and insight into system design.The configuration design and technical choice of polygeneration system exhibits high flexibility, then how to evaluate system performance comprehensively is of great importance. The thesis proposes a new evaluation method: firstly design a physical exergy efficiency to measure the energy utilization performance of physical processes in polygeneration systems; secondly, use the carbon and hydrogen elements utiliztion ratios to measure the material conversion performance. Using these two indicators, we compare the system cases of different configurations and the optimal case with better energy and material utilization performance can be selected; the energy utilization performance is further improved with the advanced technologies.Coal-based gasification is one of key technologies in the polygeneration system, and the cold gas efficiency of gasifiers and the utilization of syngas sensible heat both can impact the overall energy efficiency. This study focuses on the coal-water slurry preheating technology, designs three integration cases and systematically analyses the influence of integration of this technology on the energy efficiency performance of wet feed IGCC systems, with or without carbon capture. Result indicates that this technology not only can improve the gasification process, but also can increase the overall energy efficiency.A large number of heat streams at various temperature and pressure levels exist in a polygeneration plant, and integration of these heat streams in a heat recovery steam generator(HRSG) has great potential to further enhance energy efficiency of such a plant. In this thesis, a mixed-integer nonlinear programming model is developed for the design optimization of a HRSG with consideration of all alternative matches between heat streams and demands. Based on the optimization result, we analyze the design rules of single HRSG and the HRSG considering external heat streams, and the influence of key model parameters on the optimized layout.Economic performance is one key factor influencing the commercialization of polygeneration technology. This research investigates the accumulated capacity and developing trends of main facilities in polygeneration systems, establishes a learning curve model of equipment investment, and analyzes how the equipment investment of different polygeneration cases varies over time.