System Design And Experimental Study Of Marine Diesel Engine Exhaust Gas Desulfurization Technology Based On Sodium-alkali Seawater

With the increase of the number of oceangoing ships,the pollution of the SOx in marine diesel engine exhaust gas has become more and more serious,which has attracted the attention of the world.According to the provisions of the MARPOL Convention Annex VI,since January 1,2015,oceangoing ships in the ECA shall take use of the fuel oil contented sulfur less than 0.1%while burning.In order to meet the increasingly stringent requirements of the conventions,more and more countries have increased the researches and developments of desulfurization technology of exhaust gas in the marine diesel engine.At present,the research and development of the wet exhaust gas washing technology is more mature,and its application prospects are also the most broad.In this paper,by summarizing and analyzing the existing wet exhaust gas washing technology,I propose an improved desulphurization system of ship diesel engine waste gas,based on the method of sodium-alkali seawater.This desulphurization system is comprised with open and closed working modes.In open mode,the sodium alkali seawater is used as the washing liquid in the desulphurization system,which not only enhances the ability of desulphurization system,but also makes the washing liquid after being desulphurizated satisfy the requirements that pH value of the washing liquid is higher than 6.5 stipulated in the IMO;in closed mode,the system is set up two lye recycling tank,in which high concentrations of alkali interchange in the operation process,greatly increasing the running time of the system in closed mode;desulfurization system is taken use of the hydrocyclone group as the centrifugal treatment device applied for the washing waste liquid.The system can adjust the flow rate of the washing water according to the running time,which improves the flexibility of the separation system.In order to verify the feasibility of the method of sodium-alkali seawater desulfurization in open mode,the experiment of flue gas desulfurization was carried out on the experimental platform of the simulated ship exhaust gas desulfurization.The experiment is focused on the concentration of NaOH and Na₂CO₃ in seawater,the effects of SO₂ gas concentration in flue gas on the desulfurization rate and the pH value of washing liquid,and the joint experiment of NaOH and Na₂CO₃ seawater desulfurization was carried out.The result shows:where the concentration of NaOH in seawater increases from 0 to 4mmol/L,the desulfurization rate of the washing liquid would increase by about 4.5%;where the concentration of NaOH increases to-5 mmol/L,the desulfurization rate remains unchanged.Where the concentration of SO₂ in flue gas is 1143 mg/m3,the pH value of the washing liquid after desulfurization would increase from 6.25 to 9.90 with the increase of NaOH concentration from 0 to 5mmol/L.Where the SO₂ concentration in flue gas increases from 1143 mg/m3 to 2857 mg/m3,the desulfurization rate of the sodium alkali seawater and seawater would decrease by 15%and 20%respectively,and the pH value of the washing liquid after desulfurization would decrease by about 3.5.Under the same conditions,the desulfurization rate of NaOH seawater is higher than that of NaaCO3 seawater 1%-2%,but the ability of Na₂CO₃ to maintain pH value is much better than that of NaOH.