Numerical Simulation And Engineering Design Of SCR System For Ship Exhaust

As the most important means of ocean transportation,the ship has undertaken 80%of international trade transportation,and has caused 15%of global nitrogen oxide emissions.More stringent emission control regulations have been implemented at home and abroad,which requires denitrification of ship exhaust.However,due to the limited space of the ship and the safety of the navigation of the ship,the research on the process selection and system miniaturization design of the denitration system is particularly urgent.At the same time,due to the special low temperature tail gas conditions of the marine diesel engine,the denitration system is required to have a high denitration efficiency.In this paper,the flow field and reaction field performance of ship SCR?selective catalytic reduction?denitration system are studied by the combination of computational fluid dynamics and response surface method,which provides theoretical guidance and key design parameters for the industrial application of ship denitration system.Firstly,a three-dimensional numerical model of ship SCR denitrification system is established,in which the original size of SCR reactor is 2.50 mx1.2 mx1.2 m.The effects of diesel engine load change?100%,75%,50%,25%?and urea decomposition mixing chamber on the performance of ship SCR system?UI,P,NO_x removal rate,ammonia escape rate?were studied.Experimental verification was carried out from the aspects of NOx removal rate and ammonia slippage.With the reduction of diesel engine load,the denitration efficiency is obviously reduced.When the load is 25%and 50%,the system out-selling efficiency is 64.3%and 72.9%,respectively,which cannot meet the emission standards required by regulations.Furthermore,a mixing chamber is added to the inlet pipeline to increase the mixing degree of tail gas and reductant,and the effects of mixing chamber,different mixing chamber and nozzle distance x_m?1m,2m,3m?on SCR system are compared.The setting of mixing chamber significantly increases UI value of the cross section of the catalyst,enhances the mixing effect of the exhaust gas and the reducing agent in the system,and the mixing chamber is arranged to increase the inlet pipe pressure drop?35?P_m.When the distance between mixing chamber and nozzle is close or far,i.e.x_m=1m and3m,the effect of mixing chamber and nozzle on the denitrification efficiency of the system is small.When x_m=2m,the effect of mixing chamber on the denitrification efficiency of the system is certain.At the same time,when the diesel engine load decreases,the UI of catalyst inlet section decreases and the?35?P_m decreases.Starting from solving the problem of miniaturization of ship SCR system and improving denitration efficiency,based on the original size of the SCR reactor provided by the shipyard,numerical simulation study was carried out on the reduction of catalyst size,and the catalyst length l_c and catalyst radius r_c were reduced.The influence of ship SCR system performance,and the regression equations of main performance parameters and l_c?2.5m¹.7m?,r_c?1.2m⁰.9m?,x_m?1m,2m,3m?were established by response surface method.High line and response surface analysis,get the interaction relationship between various factors:the degree of influence on Y₁,l_c>r_c=x_m;the degree of influence on Y₂,l_c>x_m.>r_c.And the optimal value range of lc,rc and xm is obtained by solving the return equation:l_c?2.07².3m?,r_c?0.93¹.08m?,x_m=2m,and the volume is reduced by 15.9%⁴5.2%after optimization.The feasibility of the regression model for predicting NOx removal rate and ammonia slip is verified by experiments.Under the conditions of working conditions 1,2,and 3?l_c=0.19 m,0.217m,0.23m,r_c=0.098m,0.093m,0.106m,x_m=2m?,the average errors of Y₁ and Y₂ are 4.3%and 11.7%,all within acceptable limits.On this basis,according to the Tier3 emission regulations of the International Maritime Organization and the actual engineering requirements of the?Guangzhou International MAN B&W 6G50ME-C9.5 diesel exhaust denitration project?.A ship SCR tail gas denitration system with a treatment capacity of 49,500 m3/h and an exhaust gas temperature of 563 to 674 K was designed.