Experimental study on zero liquid discharge (ZLD) of FGD wastewater from a coal-fired power plant by flue gas exhausted heat

Abstract

Recent research determined that the conventional flue gas desulfurization (FGD) wastewater zero liquid discharge(ZLD)processes have many limitations, such as long process, high investment, high operating cost, and maintenance. In this experimental study, a FGD wastewater was evaporated using the exhausted heat from the flue gas in a 330 MW coal-fired power plant. The numerical simulation and engineering practice results were compared, and the key operating parameters were obtained, such as boiler load conditions, the ratio number of droplets captured by the flue wall to the total number of droplets, optimization of atomizing nozzle layout, the atomization droplet diameter, flue gas enthalpy value, accurate calculation on the change of flue gas, and fly ash characteristics after the injection of FGD wastewater. We found that under different boiler load conditions, the higher temperature and the faster the speed of the flue gas, the less time it takes for the complete evaporation of the wastewater droplets. Different amounts of FGD wastewater can be completely dried, the properties of fly ash do not change much, and no negative impacts were found on the downstream process. Moreover, it was found that when the optimum atomization cone angle of a single flue structure was 65°, the size of vortex inversely proportional related to the distance between sprayer and the wall of flue duct, that was conducive to the continuous diffusion of the local droplets in the nozzle region to other regions. This wastewater evaporation treatment method is a feasible technology for ZLD of FGD wastewater with characteristics of short process, lower investment, low operating cost, and less maintenance than conventional membrane method for wastewater reduction and evaporative crystallization system.