Thermo-economic evaluation, optimization and synthesis of large-scale coal-fired power plants
Thermo-economic evaluation, optimization and synthesis of large-scale coal-fired power plants
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DOI：
10.14279/depositonce-5451
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发表时间：
2016
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影响因子：
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通讯作者：
Ligang Wang
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文献类型：
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作者：
Ligang Wang
要解决与今天广泛使用化石燃料有关的众所周知的问题，例如全球变暖，一个关键的杠杆是设计高能效和高成本效益的煤粉发电厂。未来的燃煤电厂将具有高温高压、多热源、多产品和多种可用技术的综合，以有效利用不同等级的热量。这就明确了系统改进和优化的意义。本文逐步研究了改进和优化煤粉电厂系统结构的方法，即所使用的部件及其相互关系。将基于火用的分析与工程师的判断相结合，可以有效地提出结构改进建议。结构优化（最优综合）不是一项微不足道的任务，可以通过数学规划（即基于上部结构和自由优化方法）最好地解决，因为通常涉及结构替代方案的自动生成和识别。本文将进一步发展基于火用分析、基于上部结构和自由合成方法及其在煤粉电厂中的应用。传统的基于火用的分析只能确定低效率的位置和程度，而高级分析通过将每个低效率分解为内生/外生和可避免/不可避免的部分及其组合，进一步揭示其来源和可避免性。本文介绍了一种计算内源火用破坏的新方法，并对现代超超临界燃煤电厂进行了详细、全面的评价。结果表明，在大多数组件中，超过一半的可避免的低效率是内生的，并且不同组件的比例差异显著。目前，现代工业设计只能避免整个系统近10%的成本。此外，还建议将对流引导加热面移进炉内，提高空气预热温度以提高性能。基于上部结构的综合方法要求用户通过上部结构建模来手动定义先验的潜在解空间。本文采用基于上部结构的综合方法研究了未来电厂设计的经典考虑因素，如再加热和给水预热的次数、再加热压力和温度、给水预热器中给水的焓升分布。这些有希望的结构选择不太可能被排除在由模拟器构建的定义良好的图形上层结构之外。通过特殊设计的突变和交叉操作，对结构备选方案和其他连续决策变量进行持续操纵和优化，同时通过系统仿真对每个备选方案进行评估。讨论了最佳再热比下蒸汽工况的匹配问题。研究发现，只有当各温度等级对应的节流压力达到一定值时，才能充分发挥提高蒸汽温度等级的效益。此外，增加蒸汽条件
A key lever to cope with the well-known issues related to today’s extensive use of fossil fuels, e. g., global warming, is to design highly energy-efficient and cost-effective pulverized coal-fired power plants. Future coal-fired power plants will be with high temperature and pressure levels, multiple heat sources, multiple products, and many available technologies integrated to efficiently utilize different-grade heat. This pinpoints the significance of the system improvement and optimization. This thesis investigates progressively the methodologies for the improvement and optimization of system configurations of pulverized-coal power plants, i. e., the employed components and their interconnections. Structural improvement can be effectively proposed by combining exergy-based analysis with engineers’ judgments. The structural optimization (optimal synthesis) is not a trivial task and can be best addressed by mathematical programming (i. e., superstructure-based and -free optimization methods), since automatic generation and identification of structural alternatives is usually involved. This thesis involves further development of the exergy-based analysis, superstructure-based and -free synthesis approaches and their applications to pulverized-coal power plants. Conventional exergy-based analysis can only identify the location and magnitude of inefficiencies, while an advanced analysis further reveals their source and avoidability by splitting each inefficiency into endogenous/exogenous and avoidable/unavoidable parts and their combinations. In the thesis, a new approach of calculating endogenous exergy destructions is introduced and a modern ultra-supercritical coal-fired power plant is evaluated in detail and comprehensively. The results show that over half of the avoidable inefficiencies within most components are endogenous, and the portion differs significantly for different components. Only nearly 10% of the costs of the whole system could be avoided for modern industrial designs at present. In addition, moving convection-leading heating surfaces into the furnace and increasing air preheating temperature are suggested for performance enhancement. The superstructure-based synthesis approach requires the user to manually define a priori the potential solution space through the modeling of a superstructure. In this thesis, superstructure-based synthesis is applied to investigate classical considerations for future plant design, e. g., numbers of reheating and feedwater preheating, reheating pressure and temperature, enthalpy-rise distribution of feedwater in feedwater preheaters. These promising structural alternatives are less likely excluded from the well-defined graphical superstructure built by a simulator. Structural alternatives and other continuous decision variables are continuously manipulated and optimized by specially-designed mutation and crossover operations, while each alternative is evaluated by system simulations. The matches of steam conditions are discussed with optimal reheating ratios. It is found that only when the throttle pressure reaches a specific value corresponding to each temperature level could the benefits from increasing steam temperature levels be fully obtained. Moreover, increasing steam conditions