Design And Analysis Of Organic Rankine Combined System Of Marine Diesel Engine With SCR System

IMO emission control areas have been asked for combination control of NOx and SOx emission,and EEDI also asks for the energy efficiency of the ship.Therefore,put forward feasible combined denitration and desulfurization,at the same time to achieve effective energy saving,realize effective integration solution of such new technology or method is one of the important research contents of the ship energy saving and emission reduction technology.SCR and EGR can effectively remove NO_X in the exhaust gas,compared with EGR.Denitrification efficiency of SCR is higher,and the waste heat in the exhaust gas can be better recovered and utilized.Organic Rankine cycle(ORC)can recover the heat in the low temperature heat source,therefor,this dissertation presents a SCR-Organic Rankine combined system,and the whole system and the key components of the system were developed and analyzed in detail.The main contents and conclusions of this paper are as follows:Organic Rankine cycle design and analysis system is established to study the influence of the thermodynamic cycle parameters on the performance of the organic Rankine cycle system.Taking Weichai WD615.C-27 marine diesel engine as the study,an organic Rankine waste heat recovery system is designed.The exhaust heat source is divided into 2 sections as the preheating source and the evaporating heat source respectively,and the outlet temperature of the exhaust gas is set as 85°C.Select 1-Butene as working fluid according to the principle of working substance screening.According to the system requirements and the exhaust gas parameters,the double H-fin and tube heat exchanger is selected as the evaporator.According to the principle of the fin and tube heat exchanger and the design calculation method,the detailed dimension parameters and calculation table in the evaporator are given.The evaporator was simplified and the simplified geometric model was meshed by using Gambit to set the fins as a solid grid and the exhaust gas basin as a fluid grid.Using FLUENT for numerical simulation,the data of theoretical calculation are used as the boundary condition,secreting the appropriate turbulence model,and using the governing equation to solve the velocity-pressure coupling field.By comparing the flow field distribution characteristics of exhaust gas inlet velocity v=1.68m/s,3.68m/s,5.68m/s,7.68m/s,an important conclusion was drawn,the bigger gas inlet velocity is,the smaller tailed flow area is.But the increasing of speed can't eliminate the wake region.It will also increase the outlet temperature and pressure loss,fan load.In this dissertation,a mathematical model for describing the concentration of acid solution on the fin surface is established by utilizing the theory of phase equilibrium and fugacity equation theory.Armed with this model,a MATLAB program was written to predict the concentration of acid concentration in the surface,which was the boundary condition of the FLUENT numerical model.The user defined function(UDF)was written,and the condensation rate of sulfuric acid vapor under different flue gas conditions was investigated.The results show that the three-dimensioal distribution of the acid solution mass fraction is consistent with that of the fin temperature.The increase in water vapor could result in a sharp reduction of the acid solution mass fraction and an increase in deposition,leading to a serious risk of low temperature corrosion.In contrast,increase the exhaust gas temperature will reduce the corrosion risk by reducing the condensation rate and increase the acid mass fraction.