Numerical Simulation Of Nuclear Power Plant Steam/Water Preseparator

The main steam of nuclear power plants is close to saturated steam. After doing work in the high pressure cylinder, the moisture of steam could get to 12-13% and if the exhaust steam of high pressure cylinder continues working in the low pressure cylinder, the moisture of steam could reach as high as 20～24%, which would bring vast moisture loss and endanger the safety of low pressure cylinder blades. Therefore, external moisture separators should be set to separate the moisture of the steam and reheat it before the steam entering the low pressure cylinder so as to guarantee the security and economic operation of nuclear power plants. Traditional moisture separators work by forcing the steam go through the corrugated plates, which would result in quite a few problems such as accelerated corrosion, reentrainment, excessive superheat degree of reheat steam, large pressure loss and so on. In order to improve separating efficiency and decrease pressure loss, this article proposed a swirl vane moisture preseparator by improving the traditional structure based on the design parameters and numerical simulation results.This paper takes a 1250MW nuclear power unit as object and establishes the controlling equations of steam/water two phase flow and the coupled equations of droplet flowing in gaseous phase. On this basis factors such as the tangential speed, radius of hub, rotational flow and diameter of droplet were simulated by CFX, afterwards qualitative and quantitative analysis was made.Primary and secondary factors affecting moisture separating efficiency and pressure loss were obtained by numerical calculation, on the base of which this article puts forward the method of separating small droplets. By this means, the difficulty of capturing small size droplets which easily escape from the separator with the flow could be resolved.Synthesize all the factors influencing the moisture separating efficiency and pressure drop, methods to improve separator performance were proposed. Increasing radius of hub could improve tangential speed of the flow. Setting interlayer separator cartridge could increase the probability of small droplets colliding wall surface. Setting a drip ring at the end could gather the droplets near the wall surface, in this way the droplets could be separated efficiently and the pressure loss could be reduced within limits. After the stem passes separating zone, tangential speed turns into axial speed, which means angular kinetic energy turns into pressure energy, by this means the pressure drop in the moisture pre-separator could be decreased.The numerical calculation results of this article provide suggestions and have some reference for the design and modification of moisture preseperators.