The improvement of gas turbines flexibility has been driven by more use of renewable sources of power due to environmental concerns. There are different approaches to improving gas turbine flexibility, and they have performance implications for the bottoming cycle in the combined cycle gas turbine (CCGT) operation. The CCGT configuration is favourable in generating more power output, due to the higher thermal efficiency that is key to the economic viability of electric utility companies. However, the flexibility benefits obtained in the gas turbine is often not translated to the overall CCGT operation. In this study, the flexibility improvements are the minimum environmental load (MEL) and ramp-up rates, that are facilitated by gas turbine compressor air extraction and injection, respectively. The bottoming cycle has been modelled in this study, based on the detailed cascade approach, also using the exhaust gas conditions of the topping cycle model from recent studies of gas turbine flexibility by the authors. At the design full load, the CCGT performance is verified and subsequent off-design cases from the gas turbine air extraction and injection simulations are replicated for the bottoming cycle. The MEL extension on the gas turbine that brings about a reduction in the engine power output results in a higher steam turbine power output due to higher exhaust gas temperature of the former. This curtails the extended MEL of the CCGT to 19% improvement, as opposed to 34% for the stand-alone gas turbine. For the CCGT ramp-up rate improvement with air injection, a 51% increase was attained. This is 3% point lower than the stand-alone gas turbine, arising from the lower steam turbine ramp-up rate. The study has shown that the flexibility improvements in the topping cycle also apply to the overall CCGT, despite constraints from the bottoming cycle.

由于对环境的关注，更多地使用可再生能源驱动了燃气轮机灵活性的提高。有多种提高燃气轮机灵活性的方法，并且它们对联合循环燃气轮机（CCGT）运行中的触底循环具有性能影响。CCGT配置有利于产生更多的功率输出，因为较高的热效率是电力公司经济可行性的关键。但是，在燃气轮机中获得的灵活性优势通常不会转化为整个CCGT的运行。在这项研究中，灵活性的改进是最小环境负荷（MEL）和加速率，分别通过燃气轮机压缩机的空气抽取和喷射来促进。这项研究已模拟了触底周期，基于详细的级联方法，还使用了作者最近对燃气轮机灵活性的研究得出的顶部循环模型的排气条件。在设计满负荷条件下，将验证CCGT性能，并复制燃气轮机抽气和喷射模拟过程中随后的非设计案例，以进行底部循环。燃气轮机上的MEL扩展会导致发动机功率输出降低，这是由于前者的排气温度较高而导致蒸汽轮机功率输出更高。这使CCGT的MEL降低了19％，而独立燃气轮机的改善为34％。对于通过空气喷射提高CCGT的升温速率，可提高51％。这比独立燃气轮机低3％，由较低的汽轮机加速率引起。研究表明，尽管自下而上的周期有所限制，但自上而下的灵活性改善也适用于整个CCGT。