NUMERICAL SIMULATION FOR FGD WASTEWATER EVAPORATION IN THE FLUE DUCT OF A 2×350 MW COAL-FIRED UNIT

A series of numerical simulations were conducted for FGD wastewater evaporation occurred in a flue duct of a 2×350 MW coal-fired unit. The evolution and distribution of gas-liquid was revealed and the dependence of residence time and required distance for evaporation on spray parameters and unit load was discussed. The results showed that the liquid droplet could evaporate completely as the droplet diameter was less than 80 μm; while the diameter of liquid droplet increased from 40 μm to 80 μm, the residence time for evaporation increased from 0.26 s to 0.62 s and the required distance for droplet evaporating completely increased from 6.15 m to 13.41 m; the residence time and required distance for evaporation had a linear relation with the droplet diameter. It also presented that enhancing the injection-angle decreased the residence time of evaporation; as the injection-angle was 90°, the required distance of evaporation was the largest; in contrast, when the injection-angle was 120°, the required distance of evaporation was the smallest; while the injection-direction was opposite to the flow direction of flue gas, the residence time of evaporation was the longest and required distance of evaporation was the shortest in the three cases; the residence time of evaporation was larger with a lower load; an obvious increase in the required distance of evaporation was observed with the load dropping from 75% to 50%.