Optimization Of External Structure Of Catalytic Reactor For Marine Diesel Engine SCR System

In recent years,exhaust emissions from marine diesel engines have become a major source of atmospheric pollution around the world.In order to control the environmental pollution caused by ship emissions,IMO adopted 'MARPOL73/38 International Convention for the Prevention of Pollution from Ships',and added annex ? 'Rules for the Prevention of Air Pollution by Ships in Conference of the Parties' to put forward more stringent limits on NOx emitted by marine main engines.In China,NOx emission reduction technology has mainly been used in treatment of exhaust from boiler combustion and automobile diesel engines.However,relevant research was found rare in the marine field.Among others,SCR has been regarded a relatively effective and mature after-treatment technology of exhaust from marine diesel engines with the highest NOx conversion efficiency.In the SCR(Selected Catalytic Reduction)system,the external structure design of the catalytic reactor directly affects the stability of gas flow and the uniformity of gas distribution in the SCR equipment.The power of marine diesel engine is large with changeable operating conditions,and thus there are higher requirements for the layout and size design of the catalytic reactor.In this paper,with the marine diesel engine in laboratory taken as the object of study,the 3D design software Solidworks is utilized to conduct three-dimensional modeling for SCR catalytic reactor and change the external shape of the catalytic reactor,including two aspects:taper angle of divergent tube at the air inlet,taper angle of collapsible tube at the air outlet,and position of nozzle at the air inlet in SCR equipment.The computational fluid dynamics software Fluent is used for analog simulation of internal gas velocity,turbulence intensity,pressure loss and gas distribution uniformity coefficient of SCR catalytic reactors with different structures,and finally an optimal external structure of SCR catalytic reactor is optimized.Later,experimental analysis of taper angle of divergent tube at the air inlet,taper angle of collapsible tube at the air outlet,and nozzles at various positions are made on the established experiment table,and the accuracy of analog simulation results is verified.The SCR catalytic reactor designed in this paper can be applied to marine diesel engines in practice.The optimized reactor can greatly improve the stability and uniformity of internal gas flow in the overall equipment,achieve the conversion rate of the ship exhaust NOx up to more than 80%,and meet the requirements of NOx emission reduction by international convention currently.