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Multiobjective Dynamic Optimization for Optimal Load-Following of Natural Gas Combined Cycle Power Plants under Stress Constraints
Industrial & Engineering Chemistry Research ( IF 3.8 ) Pub Date : 2021-09-24 , DOI: 10.1021/acs.iecr.1c01461 Yifan Wang 1 , Debangsu Bhattacharyya 1 , Richard Turton 1
Industrial & Engineering Chemistry Research ( IF 3.8 ) Pub Date : 2021-09-24 , DOI: 10.1021/acs.iecr.1c01461 Yifan Wang 1 , Debangsu Bhattacharyya 1 , Richard Turton 1
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With the increasing penetration of intermittent renewable energy sources into the electric grid, there is an associated need for conventional thermal power plants that are designed to operate at base-load conditions to cycle their load rapidly and frequently and operate under low-load conditions. Fast load-following operations lead to plant efficiency loss and the reduction of equipment life. A high-fidelity dynamic model of a natural gas combined cycle power plant, with rigorous equipment level submodels, is developed to capture the plant transient performance and the thermomechanical stress evolution at the high-pressure drum is computed to assess the drum life consumption. Stress evolution is modeled for the location of the edge at the drum/downcomer junction that experiences high circumferential stress amplitude during the fast load-following operation, leading to higher fatigue damage than locations considered under existing design standards. A dynamic optimization problem is solved for optimal load-following operation. Depending on the value of the stress constraint and the desired ramp rate, satisfying the desired stress constraint may be infeasible without relaxing the ramp rate. A multiobjective dynamic optimization problem is solved using a lexicographic approach that minimizes ramp rate relaxation and maximizes efficiency while satisfying stress constraints, avoiding spraying to saturation, and maintaining main steam and reheat steam temperature within bounds. It was observed that the optimal ramp rate can be highly nonlinear as opposed to the industry-standard linear ramp rate. Nonlinear optimal ramp-rate profiles not only help to avoid stress constraints that may be unavoidable by using the linear profile but also result in higher efficiency than the linear profile. The study shows that there is a strong tradeoff between the relaxation in the plant ramp rate and the time-average thermal efficiency.
中文翻译：
应力约束下天然气联合循环电厂最优负荷跟随的多目标动态优化
随着间歇性可再生能源越来越多地渗透到电网中，相关的传统火力发电厂需要设计为在基本负载条件下运行，以快速频繁地循环负载并在低负载条件下运行。快速负载跟踪操作会导致工厂效率损失和设备寿命缩短。开发了具有严格设备级子模型的天然气联合循环发电厂的高保真动态模型，以捕获电厂瞬态性能，并计算高压汽包处的热机械应力演变以评估汽包寿命消耗。应力演化是针对在快速负载跟随操作期间经历高周向应力幅的鼓/降液管接头处的边缘位置建模的，导致比现有设计标准考虑的位置更高的疲劳损坏。解决了动态优化问题以获得最佳负载跟随操作。根据应力约束的值和所需的斜率，在不放松斜率的情况下满足所需的应力约束可能是不可行的。多目标动态优化问题使用字典式方法解决，该方法在满足应力约束、避免喷射至饱和以及将主蒸汽和再热蒸汽温度保持在界限内的同时，最小化斜率松弛并最大化效率。据观察，与行业标准的线性斜率相比，最佳斜率可能是高度非线性的。非线性最佳斜率曲线不仅有助于避免使用线性曲线可能不可避免的应力约束，而且还导致比线性曲线更高的效率。研究表明，在工厂缓变率的松弛和时间平均热效率之间存在很强的权衡。
更新日期：2021-10-06
中文翻译：
应力约束下天然气联合循环电厂最优负荷跟随的多目标动态优化
随着间歇性可再生能源越来越多地渗透到电网中，相关的传统火力发电厂需要设计为在基本负载条件下运行，以快速频繁地循环负载并在低负载条件下运行。快速负载跟踪操作会导致工厂效率损失和设备寿命缩短。开发了具有严格设备级子模型的天然气联合循环发电厂的高保真动态模型，以捕获电厂瞬态性能，并计算高压汽包处的热机械应力演变以评估汽包寿命消耗。应力演化是针对在快速负载跟随操作期间经历高周向应力幅的鼓/降液管接头处的边缘位置建模的，导致比现有设计标准考虑的位置更高的疲劳损坏。解决了动态优化问题以获得最佳负载跟随操作。根据应力约束的值和所需的斜率，在不放松斜率的情况下满足所需的应力约束可能是不可行的。多目标动态优化问题使用字典式方法解决，该方法在满足应力约束、避免喷射至饱和以及将主蒸汽和再热蒸汽温度保持在界限内的同时，最小化斜率松弛并最大化效率。据观察，与行业标准的线性斜率相比，最佳斜率可能是高度非线性的。非线性最佳斜率曲线不仅有助于避免使用线性曲线可能不可避免的应力约束，而且还导致比线性曲线更高的效率。研究表明，在工厂缓变率的松弛和时间平均热效率之间存在很强的权衡。
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