Simulation Of Ship Exhausts Purification Technology Based On HSC Chemistry

As a means of transportation,ships account for 80%of the total volume of goods transported in the world.However,due to the widespread use of low-quality diesel oil,the tail gas of ships contains more air pollutants such as SOx（sulfur oxide）,NOx（nitrogen oxide）and PM（particulate matter）.The purification of Marine exhaust is mainly to control the content of SO₂ and NO.There are dry and wet desulfurization technologies developed.The denitrification technology developed for NO pollutant can be divided into reduction method and oxidation method.The method of simultaneous removal of SO₂ and NO at one time is an integrated technology of desulfurization and denitrification.In this thesis,the core chemical reactions of the existing mature or new desulfurization and denitrification technologies were extracted and simulated by using the thermodynamic calculation software HSC Chemistry.Firstly,we studied three desulphurization technologies commonly used in Marine exhaust:ammonia desulphurization,magnesium desulphurization and calcium desulphurization,and simulated the chemical reactions respectively.The effects of desulfurizer dosage,gas-liquid ratio,reaction temperature and reaction pressure on sulfur migration and desulfurization rate were investigated successively.In ammonia desulphuization,sulfur element can migrate to ammonium sulfite and ammonia bisulfite.When NH₃/SO₂≤1,sulfur elements migrate to ammonium sulfite;When NH₃/SO₂≥2,sulfur elements migrate to ammonium bisulfite.When 1<NH₃/SO₂<2,it’s a mixture of the two.The reaction temperature will affect the desulfurization rate of ammonia desulfurization.Under 70-120℃,the desulfurization rate will decrease from 99%to below 80%,so ammonia desulfurization needs to be carried out below 70℃.In magnesium desulphurization,the sulfur element migrates to magnesium sulfite,and the two reactants react in a molar ratio of 1:1.In calcium desulphurization,sulfur element migrates to calcium sulfite substance,and the two reactants also react according to the molar ratio of 1:1.The desulfurization reaction rules of magnesium method and calcium method are quite similar,and the equilibrium constants of the reaction are very large.The desulfurization rate of these two methods can reach more than 99%.And the reaction temperature and reaction pressure do not affect the sulfur migration and desulfurization rate of the two reactions,so the desulfurization reaction can be carried out at higher temperature and atmospheric pressure.Secondly,the denitrification reaction of NO in the ship tail gas was simulated,and the reduction denitrification reaction with ammonia gas and the oxidation denitrification reaction with hypochlorous acid were simulated respectively.Although the reaction principles of the two are different,the denitrification efficiency can reach more than 99%.When ammonia is used for reduction,NO is reduced to nitrogen.When hypochlorous acid is used for oxidation,NO is oxidized to the form of nitric acid.Finally,through the comparison of desulfurization and denitration technologies,it is found that the method of oxidation and absorption can remove NO and SO₂ at the same time,and achieve the purpose of desulfurization and denitration integration.Therefore,we further simulated the desulfurization and denitration integration reaction with ozone,chlorine dioxide and hydrogen peroxide as oxidants.The effects of oxidizer dosage and gas-liquid ratio on the equilibrium composition of the reaction were discussed.The simulation results show that the three oxidants can convert SO₂ to sulfuric acid and oxidize NO to nitric acid,and the desulfurization and denitrification rates can reach more than 99%.The NO₂ intermediate is produced in the reaction process,but when hydrogen peroxide is used,the content of NO₂ intermediate is the lowest,so it is a better oxidant.The results can be used to guide the development and design of Marine exhaust treatment technology,and have certain theoretical guiding significance and practical reference value.