Parameter analysis of atomized droplets sprayed evaporation in flue gas flow

Abstract

Spraying flue gas desulfurization (FGD) wastewater into the flue duct is a promising technology to achieve zero emission of wastewater by evaporation in thermal power plants. To deal with the scale and corrosion on flue duct walls resulted from the incomplete droplets evaporation, a combined Eulerian-Lagrangian model was developed to reveal the thermo-fluid behavior of the FGD wastewater spray evaporation in the flue gas. The effects of several control factors under various operating conditions were conducted numerically and validated against experimental data. Because of the complex influences of numerous parameters, the Least-Square support vector machine (LSSVM) model based on numerical results is employed to predict the evaporation rate of droplets. The dominant factors, including that of droplets size distribution, flue gas velocity and flow rate, full cone angle and spray direction of nozzle, were analyzed to reveal their impacts on the droplets sprayed evaporation rate and distance, respectively. It is concluded that spaying droplets in the co-flow direction of flue gas can contribute the dispersion of droplets and enhance the relative movement of two-phase flow, achieving the maximum evaporation rate of droplets. An optimized arrangement of multiple nozzles having a small flow rate is proposed to improve the evaporation rate of droplets. The proposed LSSVM model can expeditiously predict the evaporation rate of droplets along the flue duct with high accuracy. The findings can be used to guide the design of spraying FGD wastewater treatment under practical operating conditions in power plants.