The conventional feedwater pump turbine is selected based on the unit maximum continuous output condition, so the efficiency of feedwater pump turbine will be much lower when the unit runs under and below THA condition. In order to improve the efficiency of the feedwater pump turbine, the optimization on selection of the feedwater pump turbine was carried out. According to the principle that the supplementary steam can increase the turbine output, taking the turbine output under THA condition as the type selection criteria for the feedwater pump turbine, higher output can be realized by opening the supplementary steam, thus it is possible to improve the operating efficiency of the feedwater pump turbine under and below THA condition. Combining with the actual case of type selection of feedwater pump turbine for a double-reheat unit, the parameters of the feedwater pump turbine before and after optimization were calculated to investigate the steam consumption of the feedwater pump turbine under different conditions and its influence on the unit heat consumptions. The results show that, after type optimization, under THA, 75％THA and 50％THA conditions, the inlet mass flow of the feedwater pump turbine decreased by 1.9, 1.2, 0.8 t/h, separately, and the unit heat rate decreased by 3.08, 3.42 and 3.62 kJ/(kW·h) respectively. This optimization method for feedwater pump turbine's type selection can be applied in ultra-supercritical double-reheat units.%传统给水泵小汽轮机以机组最大出力为选型基准,在机组THA及以下工况运行时小汽轮机运行效率相对下降较多.为提高小汽轮机运行效率,有必要开展给水泵小汽轮机优化选型研究.利用汽轮机补汽增大出力的原理,以机组THA工况对应出力为小汽轮机设计选型基准,需要更大出力时通过开启补汽来实现,可相对提高THA及以下工况小汽轮机运行效率.结合某二次再热机组给水泵小汽轮机选型分析实例,对优化前后小汽轮机工作参数进行计算,对比分析不同工况下小汽轮机耗汽量及对机组能耗指标的影响.结果表明,优化选型后,THA、75％THA和50％THA工况下对应小汽轮机进汽流量分别降低1.9、1.2、0.8 t/h,汽轮机热耗分别降低3.08、3.42、3.62 kJ/(kW·h).该小汽轮机优化选型方法可在超超临界二次再热机组上推广应用.
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