| With the increasing awareness of energy saving,the proportion of million units in China’s thermal power generating units is increasing,more and more small generating units are being replaced by million units,and more millions of units are also undergoing economic transformation.The addition of a make-up valve between the 5th and 6th stages of the turbine’s high-pressure cylinder allows the turbine to continue to increase its output by making up steam when it reaches rated operating conditions during peak power consumption.Although the addition of a charge valve can increase output,there are other problems,such as reduced flow efficiency,reduced efficiency of certain stages and increased rotor vibration.It is therefore necessary to consider the impact of various factors on the efficiency of the turbine’s high-pressure cylinders after the addition of a charge valve.In this paper,we use numerical simulation to build a model of the charge valve and the dynamic and static lobes of stages 5 and 6,and use the fluid simulation software CFX to numerically simulate the increase of the charge valve in stages 5 and 6 and between stages of the high pressure cylinder of a 1000MW turbine,analyse the flow of the charge steam in the charge chamber,and then analyse the effect of the charge steam on the efficiency of stage 6.The main elements are as follows:Firstly,under the condition that the steam replenishment volume is 14%of the rated main steam volume,the steam replenishment valve in the middle into the steam,side into the steam straight small tube and the middle into the steam,side into the steam curved small tube four models of steam replenishment chamber flow simulation calculations,we obtained the following conclusions:the middle into the steam,side into the steam curved small tube,the middle into the steam,side into the steam straight small tube these four replenishment methods,there is a return vortex in the chamber,side into the steam straight,curved small tube The vortices are greater in the straight and curved side inlets.The pressure distribution is more even on the five sides of the middle inlet pipe.The temperature distribution is more reasonable on the five sides of the side inlet bends.The velocities and pressures at the exit of the small tubes are lower for the two types of steam make-up:intermediate inlet and lateral inlet and bend.The total pressure loss coefficient is 3.05 for the straight side inlet pipe,2.88 for the curved side inlet pipe,3.02 for the straight middle inlet pipe and 2.51 for the curved middle inlet pipe,and 3522 W/m~3?K for the curved middle inlet pipe,the smallest of the four.Then,for the four steam replenishment models of straight and curved small tubes with side inlet and straight and curved small tubes with intermediate inlets,the impact of steam replenishment of 6%,10%,14%,18%and 22%of the rated steam flow on the 5th and 6th stage blades of the through-flow section was simulated and analysed,and the following conclusions were obtained:the impact of steam from the straight small tube outlet on the steam of the through-flow section increased continuously with the increase of steam replenishment,while the impact of steam from the curved small tube outlet on the steam of the through-flow section changed relatively little with the increase of steam replenishment.The impact of steam on the through-flow portion of the steam at the exit of the bent pipe increases with the amount of steam replenishment.The steam from the straight small tube is gradually shifted downwards in the direction of the 6-stage blade as the steam flow increases along the blade height,while the steam from the curved small tube is mainly concentrated at and above the top 50%of the blade.In the six-stage static leaf inlet position,the straight small tube steam replenishment leads to uneven mass flow distribution,while the curved small tube steam replenishment is more uniform.The mixing of the steam from the straight pipe and the through-flow section causes a significant local increase in the turbulent energy and velocity distribution at the sixth stage static lobe inlet,whereas the effect of the bent pipe on turbulent energy and velocity is only at the 50%of the lobe height and is less significant.The straight small tube makes up for the large changes in the angle distribution of the six-stage static lobe inlet,resulting in a reduction in flow capacity,while the bent small tube makes up for the significant change in angle only at 22%of the steam volume.The entropy increase at the six-stage inlet is also greater for straight small tubes,with14%of the inlet already occupied by half of the area,while the entropy increase at 22%of the inlet is only about half for bent small tubes.The viscous losses are greater at the inlet and outlet of the straight small tube,while the bent small tube only has losses at the inlet position of 30%of the tube wall area,and by numerical comparison the viscous losses of the straight small tube flow in the tube are greater.The efficiency of the sixth stage is only 6%higher than the efficiency of the bent tube,and the efficiency of the other steam replenishment is lower than that of the bent tube,and the efficiency of the sixth stage is lower than 50%after the 10%steam replenishment.The final determination of the best steam replenishment for 10%of the rated steam volume,intermediate steam intake,export bend small tube model is more reasonable. |
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