Research On The System Integration Of DeNO_x And Noise Reduction For A Shenzhen Towboat

In response to the call of the Chinese government,Shenzhen Human Settlements Committee drew up a project named as the Shenzhen Blue Sustainable Action Plan in2018.The project has stated it clearly that the exhaust of diesel-powered towboats need to be disposed to reduce the nitric oxides emission up to the limit of IMO Tier III,in order to achieve the“Green Port”.However,the space was so limited for those in-use ships that there was little chance to install the SCR system.Given that catalyst is porous and has some effect on noise reduction,it can be proposed to design an integrated system for denitrification as well as noise reduction with the space of original muffler.During the process of designing the integrated system,denitrification performance,noise reduction performance and pressure loss were three critical issues.Regarding the Shenzhen in-use towboat as research object and on the premise of not influencing the diesel engine’s initial performance,this paper designed an integrated system for both emission and noise reduction,which provides guidance for the optimization of an integrated aftertreatment system and the emission upgrade of in-use ships.The main research contents are as follows:(1)Design and research of initial design.According to the existing catalyst type and SCR system structure research,the initial design scheme which fit the space was proposed.Through the three-dimensional simulation,performance on denitrification,noise reduction and pressure loss were analyzed.The result shows as follows:as for the initial design,pressure loss can meet the need,denitrification and noise reduction performance cannot satisfy the requirement.Based on the above,optimization directions were proposed.(2)Research on the improvement of denitrification efficiency.Establishing models in AVL BOOST and AVL FIRE,the effects of pore density and expansion angle on denitrification can be researched.The results show that when the volume of catalyst is constant,the conversion efficiency of NO_x increases with the increase of pore density.Compared with 40 degree and 75 degree,the system has a higher conversion efficiency of NO_x when the expansion angle is set as 60 degree.(3)Research on the improvement of noise reduction.Establishing different structural models and simulating them with the help of Virtual.Lab Acoustics,the influence of expansion angle,contraction angle and the layout of noise elimination elements on the noise reduction can be researched.The results are as follows:for the frequency band from 0 to 750 Hz,the transmission loss increases with the increase of the expansion angle;for the frequency band from 750 Hz to 1000 Hz,a smaller expansion angle has better muffling performance.Increasing the contraction angle causes slight effect on the transmission loss.However,when the contraction angle is up to 180 degree,namely remove the contraction section,transmission loss value has evident increasement and the value is about 4 dB(A).Compared with 114 mm inserted pipe and 57 mm perforated pipe,inserting a 57 mm inserted tube at the end of the system has a significant improvement on noise reduction performance.(4)Research on the optimization proposal.On the basis of the initial design and taking NOx conversion efficiency and noise reduction requirement into consideration,the optimum system structure is proposed.Aiming at the four operating conditions of E3 test,the evaluation is conducted from three aspects which are denitrification performance,noise reduction performance and pressure loss.The result shows that the optimum design can meet the design goal,namely NOx conversion efficiency is not less than 80%,the transmission loss value is not less than 42.12 dB(A),and the pressure loss is not more than 3.5 kPa.