Mass flow evaluation of residual droplets of water sprays for cooling suction air using laser transmission method

Abstract

Water spray is used for cooling intake air of gas turbine in thermal power plant. It is necessary to reduce the amount of residual droplets by optimizing the spray amount to keep the plant in good condition. In the actual thermal power plants, a phase Doppler anemometry (PDA), which can provide droplet velocity and diameter of spray, is difficult to apply because it requires precision setting. In this study, a new method for determining the residual droplet flow rate using the laser transmittance for the cooling water spray which can be used at thermal power plants is proposed. A laser transmission method system was applied to a scale-down model of an inlet duct at a laboratory in order to confirm the system reliability. The same types of weather louvers, eliminators, and nozzles installed in the actual thermal power plants were used in the experiment. The effects of optical path length, spatial distribution of spray, flow on conditions, etc. to the measurement accuracy were evaluated at the model case experiment in the laboratory. The residual droplet flow rate calculated by the laser transmission method and that of the PDA measurement are compared. The error of the residual droplet flow rate calculated by the proposed method was about 12.8%. The proposed system was applied to an actual thermal power plant. At the thermal power plant, the residual droplet flow rate was reduced to about 35% by the eliminator compared to the case without the eliminator. Since the residual droplet flow rate can be measured by the laser transmission method, it can be used for optimizing the spray amount in actual thermal power plants. Compared to other methods, the proposed method allows the experimental equipment to be also constructed relatively easily. It is easy to install in an actual thermal power plant. The experimental results demonstrate the effectiveness of the present apparatus as a relative evaluation method.