采用背压抽汽式汽轮机BEST方案可解决主汽参数提高后回热抽汽过热度和热损失增大的问题。本文以某二次再热超临界机组为原型,搭建了BEST热力系统模型和建立机组热经济性模型,比较了传统机组和BEST机组中各加热器的?效率和热效率随机组负荷的变化,分析了锅炉给水,主汽机和小汽机对BEST机组节能效果的贡献度,并讨论了小汽机抽汽加热给水方式对机组节能潜力的影响。结果表明：BEST设计方案显著降低加热器?损和优化锅炉给水,是提高机组热效率主要因素,但代价是汽轮机一二次再热蒸汽量降低造成主汽轮机做功减少,由此削弱了机组节能效果,通过布置小汽轮机可抵消该削弱作用,且小汽轮机对机组热效率贡献随机组负荷降低而升高的特性,保障了机组低负荷下的节能效果。

The use of a back pressure extraction steam turbine (BEST) scheme can solve the problem of increased superheat degree and heat loss in the regenerative extraction steam after the main steam parameters are increased. Taking a double-reheat supercritical unit as a prototype, this study establishes a thermal system model for a BEST unit and a thermos-economics model, and compares the thermal efficiency and exergy efficiency under different load of each heater for a traditional unit and BEST unit. The contribution of boiler feedwater, main steam turbine, and BEST steam turbine to the energy-saving effect of BEST unit is investigated, and the impact of BEST steam turbine extraction and heating feedwater on the energy-saving potential is examined. The results indicate that the BEST design significantly reduces heater losses and optimizes boiler feedwater, which is the main factor in improving the thermal efficiency. The penalty of BEST unit is a reduction in primary/secondary reheated steam flowrate, which reduces the output of the main turbine and weakens the energy-saving effect of the unit. However, the weakening effect can be offset by the arrangement of auxiliary steam turbine. The contribution of auxiliary stream turbine to the thermal efficiency of BEST unit increases with increasing unit load, thereby ensuring the energy-saving effect of the unit at low loads.