Numerical Simulation Of Flue Gas Desulfurization Spray Tower Of Marine Vessel

With the rapid development of the world shipping industry, SOx emissions problems from ships have become increasingly prominent. International Maritime Organization (IMO)has carried out strict rules. Using flue gas desulfurization (FGD) method is the most attractive solution to deal with the relevant provisions. There is no mature ship FGD technology at present, so it requires combining the reality of ships and designing the rational desulfurization process.Combined ship’s particularities with several mainstream FGD process, we used seawater as absorbent and spray tower which is simple-structured and easy to maintain as absorber.Flow and temperature field in spray tower and absorption process of SO2 was studied.Unstructured tetrahedral and hexahedral hybrid grid of simplified model of spray tower was established by using ICEM-CFD. Euler-Lagrange multiphase flow model and κ-εturbulence model was adopted. Boundary conditions were set through CFX. High precision second-order backward Euler algorithm was used to calculate the flow and temperature field.CEL language was used to compile the source term which described the absorption process.Effects of gas inlet angle, flue gas velocity, droplet diameter on the flow and temperature field was considered, then proper flue gas inlet angle and droplet diameters for absorption simulation was selected. The effects of droplet diameter, liquid-gas ratio, gas velocity on SO2 absorption was also considered.Results show that the influence of different gas inlet angle on tower pressure drop can be neglected, but the influence of different gas inlet angle on the velocity distribution uniformity inside tower at different heights and droplet evaporation was noteworthy. Combining with structural strength of spray tower, the flue gas inlet angle of 15° was ultimately selected.When droplet diameter is less than 0.7 mm, the flue gas flow can significantly affect droplet falling motion, and some droplets are taken out of the tower by flue gas, causing anti-mixing,doing adversely on the mass transfer. The final choice of droplet is diameter ≥ 0.7 mm to do absorption simulation. Heat exchange between droplets and flue gas was fast and soon reached equilibrium state. Depending on the selected droplets, during the evaporation droplet temperature drops about 1.1 K, mass reduction is approximately 0.3%, and influence of droplet evaporation on the droplet motion can be neglected.SO2 concentration below the nozzle is lower than the tower wall region. Along the column height direction, SO2 concentrations decreased. Larger the droplet diameter is,the lower the desulfurization rate. When flow-rate of flue gas is 3000 m3/h and liquid to gas ratio is 6 L/m3, the desulfurization rate difference between diameter of 0.7 mm and 1.5mm droplets is 51.3%. Reasonable flue gas flow-rate can increase the desulfurization rate. Desulfurization rate increases with the liquid to gas ratio, but the growth rate gradually declined. When liquid to gas ratio is 9 L/m3, the desulfurization rate is 97.3%.