Operating characteristics and optimization mechanism of the final stage of steam turbine under ultra-low load conditions
Constructing a power system predominantly based on renewable energy sources imposes increasingly stringent demands on deep peak shaving capability and ultra-low-load operation of coal-fired power generating units,thereby presents more severe challenges to the safe operation of steam turbine units under low-load conditions.This paper employs numerical simulation methods,focusing on an in-depth analysis of the operational performance of the last stage of a steam turbine under low-load conditions,and explores various solutions for their working mechanisms and optimization effects under ultra-low-load conditions.It is found that,when the unit transitions from medium-low load to ultra-low load,vortex clusters such as gap vortices,backflow vortices,and separation vortices emerge near the last stage blades,with their extent gradually expanding as the load decreases.Reducing the back pressure of the unit and operating the low-pressure cylinder with cylinder-cutting are effective strategies to attenuate steam turbine vortex flow and enhance the last stage's performance,with a combined application of these strategies yielding better results.For instance,under 20%turbine heat acceptance(THA)conditions,reducing the back pressure from 4.9 kPa to 2.5 kPa significantly diminishes the influence range of the last stage vortex cluster,increasing the rotor blade torque from-38 N·m to 73 N·m,thereby markedly improves the last stage performance.Under 10%THA conditions,employing a combination of reduced back pressure and low-pressure cylinder-cutting can completely eliminate the tip clearance vortex,with the radial lengths of the backflow vortices and separation vortices reducing by more than 50%.The optimized rotor blade torque increases by approximately 130 N·m,significantly enhancing the last stage performance.
万方数据
维普
