Performance Study And Optimized Design Of Marine Sieve Tray Tower

According to the international maritime organization?IMO?and domestic vessel emission control regulations,reducing SO₂emissions has become a top priority.Seawater desulfurization system has the advantages of high desulfurization efficiency and low operating cost,it has become one of the mainstream technologies of marine SO₂control.Based on MAN 5S50 Marine diesel engine,a I type sieve tray tower was designed,and then it was optimized by the combination of experiment and numerical methods.The main conclusions are as follows:1.The test bench of desulfurization system was built,and the main influencing factors of SO₂absorption were explored through the control variable method,including liquid-gas ratio,absorption liquid concentration and SO₂concentration.The experimental results show that the liquid-gas ratio is an important factor affecting the desulfurization efficiency,all other factors play less important roles.With the increase of liquid-gas ratio from 3.1L/m³to 7.0L/m³,the desulfurization efficiency increased from 67.3%to 99.3%.As the SO₂concentration in the exhaust gas increases,the desulfurization efficiency will gradually decrease.In the process of SO₂concentration varying from 686ppm to 1371ppm,the desulfurization efficiency decreased from70.68%to 48.69%.Na HCO₃was used to simulate the alkalinity of seawater.When the p H value was constant at 8.21,the concentration of Na HCO₃increased from0.0232mol/L to 0.1022mol/L,desulfurization efficiency increased from 97.25%to99.22%.2.Based on the relative parameters of exhaust gas of MAN5S50 Marine diesel engine,a type I desulfurization tower was designed.It includes sieve plate,spray layer,mist eliminator,conical gas-liquid deflector.Among them,two spray layers were set,and 30 nozzles were set in each layer.The flow rate of each nozzle is 15m³/h.Two layers of sieve plate were set,and the aperture of the sieve plate is 15mm,reaching 36%of the hole opening rate.The thickness of the sieve plate is 5mm.The material and energy balance of the gas-liquid mass transfer process in the tower was calculated.When the flow rate was 7000nm³/h and the liquid-gas ratio was 10,the spray volume was about 749m³/h and the seawater evaporation volume was about34m³/h.3.According to the physical model of sieve plate tower in the literature,the numerical model was established by using ANSYS software,and the results of calculation and experiment were compared.It was found that using 0.6 million unstructured grids,1.5 million unstructured grids and 0.6 million structured grids,the calculated pressure drop are consistent with the experimental ones.The mesh independence of the model was verified.Furthermore,different numerical models of sieve plate were studied.It was found that results calculated by solid model of sieve plate is consistent with that using the porous media model.The reliability of porous media model replacing solid model was verified.4.Based on the reliable numerical model,the type I sieve plate tower was optimized,The optimization results show that the pressure drop of 400Pa can be reduced when the conical gas-liquid deflector was changed to hollow.The turbulence ring between the first layer sieve plate and the conical gas-liquid deflector can improve the gas distribution and effectively solve the gas adherent flow.The fixed arrangement of the sieve plate was changed into gravity adaptive arrangement,which effectively solved the problem of uneven distribution of gas caused by ship shaking.The pressure drop of desulfurization tower will not be affected when the spray angle changes from 100 to 60 degrees.Therefore,in order to reduce the impact of seawater on the wall of desulfurization tower,the spray angle was changed from 100 to 60degrees.