Characteristic Analysis And Dehumidification Method Of Wet Steam Condensing Flow In Steam Turbine

The later several stages of the low pressure cylinder of the condensing steam turbine and the full stages of the nuclear steam turbine all work in the wet steam zone.With the increase of the wetness,the wet steam brings two problems to the steam turbine.The first is that the steam condensing process deviates from the equilibrium state which produces wetness losses.The second is that the secondary droplets carried by the wet steam will produce erosion and impact on the turbine blade,which threaten the safe operation of the steam turbine.Therefore,the study of heat and mass transfer mechanism in the process of wet steam two-phase condensing flow is of great theoretical significance to improve the efficiency of steam turbine.Based on the two fluid numerical model of Eulerian / Eulerian fluid flow description,analyzes various complex flow phenomena in condensation flow were analyzed and a control method for condensation flow of wet steam was proposed.On the premise of ensuring the accuracy of numerical calculation,three condensation control methods were put forward for the White stator cascade,i.e.end wall fences coupling heating,blade surface heating and parallel channel.For the last stage stator cascade of a real steam turbine low pressure cylinder,the influence of different steam parameters at the beginning and end of the cascade on the two-phase flow of wet steam was evaluated from the mechanism,and the optimization method of non-axisymmetric end wall was provided.The results show that:(1)For the White static cascade,the position on the suction surface(point D)has a significant impact on the distribution of steam parameters in the cascade channel,while the position of the pressure surface(point C)has little influence on the distribution of steam parameters and the cascade performance.In view of the strength and economy of the condensation shock wave,the appropriate width of the parallel channel should be selected,and the recommended width range is 3～5 mm.As for the method of end wall fences coupling heating,the comprehensive performance of the cascade can be optimized by selecting the position and heating intensity of endwall blade reasonably.With the increase of heating intensity,the aerodynamic performance of cascade can be improved first and then worsened gradually,and the enthalpy drop of steam increases first and then decreases rapidly,while the entropy increase of steam decreases first and then increases;the wetness and droplet diameter at the outlet of cascade can be reduced by installing the end wall fence;the dehumidification effect of cascade is more significant after heating measures are taken,but the dehumidification benefit of unit heating intensity decreases;the best optimization method is obtained under the premise of maintaining or even slightly optimizing the aerodynamic performance of the cascade,the overall steam wetness is significantly reduced,and the flow loss and other irreversible losses are slightly reduced,while the enthalpy drop is increased.Similar to the end wall fences coupling heating,the blade surface heating can also optimize the comprehensive performance of the cascade,but it is necessary to pay attention to the selection of heating intensity.(2)For the last stage stator cascade of a real steam turbine low pressure cylinder,raising the steam temperature can delay the generation of condensation,alleviate the deterioration of the aerodynamic performance of the cascade,at the same time,it can better control the steam wetness,but increase the water drop radius;increasing the initial and terminal pressure drop can increase the steam Mach number,while the total pressure loss is also increased;raising the back pressure can control the wetness,and enlarge the water drop radius.The non-axisymmetric end wall can significantly affect the distribution of steam parameters below its height.The placement of the non-axisymmetric end wall reduces the local steam entropy increase and increases the local steam enthalpy drop.In the control of the steam enthalpy entropy value,the F series is the best,the M series is the second,the B series is the worst;in different height series,the 0.05 series is the best,the 0.10 series is the second,the 0.03 series is the worst.In terms of wetness control,M0.05 has the best optimization effect,8.07 % less than ORI;in the aspect of total pressure loss control,F0.10 has the best performance,6.91 % less than ORI.The design conditions of B0.10 are not recommended.