Research About Equipment And Technology Of Ship Exhaust Desulfurization

With the increasing demands of the international community on environmental protection,the emission standards of marine exhaust gas are becoming more and more stringent.By comparing and summarizing the existing technologies,it is concluded that combination of seawater desulfurization has advantages in the control of marine exhaust gas desulphurization,which includes the use of seawater to make desulfurizer as open loop system and caustic alkali added to fresh water as desulfurizer for closed loop system.In order to purify tail gas,the 6DL-26 offshore diesel(heavy oil)unit was used as the test equipment of the pilot plant,and the sulfur oxides were absorbed in the scrubber by using seawater or fresh water plus caustic soda as desulfurizer.The waste liquid was oxidized by aeration and adjusted by pH,and then discharged into the sea after reaching the discharge standard for washing water stipulated by CCS.Scrubber is the core equipment to achieve the process and venturi tube pretreatment device let exhaust gas cooling and humidification,A bar grid structure is used to optimize the flow field of the exhaust gas entering the scrubber.Through simulation,it was found that the bar grid structure changed the direction of the velocity of the exhaust gas.Because the movement direction of the exhaust gas caused the movement time of the exhaust gas in the scrubber tower to increase,the mass transfer reaction time increased and the desulfurization efficiency was improved.Meanwhile,the exhaust gas moves upwards along the bar grid wall with less resistance,and the pressure drop in the equipment is smaller.The orifice plate is installed in the middle of the scrubber.The lower exhaust gas flow rate is evenly distributed through the orifice plate and the exhaust gas is in direct contact with the scrubbing water to fully absorb the sulfur oxides in the flue gas.Through the CFD simulation of the gas-phase flow in the scrubber,it was found that the two-layer arrangement of the bar grid and the orifice plate had an optimized effect on the exhaust gas flow field,and at the same time,the flow velocity of the exhaust gas in the scrubber was reduced.The scrubber tower is equipped with a staggered arrangement of spiral conical nozzles.The nozzles are divided into three layers,five on each floor.The staggered rows of nozzles atomize the scrubbing water and distribute it evenly throughout the tower,reducing wastage caused by wash water flowing away directly along the tower wall.At the same time,the atomized washing water uniformly covers the scrubbing tower and contacts with the exhaust gas counter currently to delay the residence time of the exhaust gas in the tower.The structure of the venturi section was optimized and a dust removal tank was installed below the venturi.The CFD simulation of the gas-liquid-solid three-phase flow of the structure is performed.As a result,it was found that when the rightmost axis of the dust removal tank coincides with the central axis of venturi,the flow field can be effectively optimized,and the turbulence between gas and liquid phases can be promoted,and some of the waste slag in the exhaust gas can be discharged from the dust removal tank.The high-speed movement of the exhaust gas at the location of the dust removal tank has a small pressure drop,which helps to reduce the power consumption of the marine diesel engine.Through the analysis of the water consumption of the open-loop system for ship exhaust gas purification devices,it was found that when the venturi tube pretreatment device consumes 30%of the total water consumption,a better cooling and dust removal effect can be achieved,which is beneficial to washing.Further exhaust gas desulfurization inside the tower.Three layers of spray are used in the scrubber tower,and better desulfurization effects can be achieved when the second layer and the third layer are sprayed simultaneously.Alkalinity,salinity,pH-and temperature of the flue gas all have an effect on the desulfurization effect.Among them,the alkalinity of seawater and pH have a great influence on the desulfurization effect.Flue gas temperature is negatively correlated with the desulfurization effect,and the higher the temperature,the worse the desulfurization effect.