| Diesel engine usually is used for the main power device.Due to the diversity of impurities in the fuel,Combustion is usually inadequate.The exhaust gas contains SOX,NOX and PM pollutants.These pollutants cause great harm to the atmosphere,buildings and human.Besides,the treatment of sulfur oxides has received extensive attention.The International Maritime Organization formulates more stringent restrictions on sulfur oxides.The related research also has received extensive attention.Among the existing desulfurization methods of ship exhaust gas,the more mature one is wet desulfurization,which uses seawater as absorbent.In this thesis,the seawater desulfurization system was the research object.Based on the diesel engine flue gas characteristics carried out the preliminary design of the system,the material balance model of the system was established in MATLAB software.Then,steady state analysis was carried out in Aspen Plus to study the influence of operating parameters to achieve the best desulfurization effect based on the material balance model.Furthermore,the dynamic analysis of the seawater desulfurization system was carried out in Aspen Plus Dynamics,and the response of the system under external disturbance was studied.Finally,life cycle assessment models of seawater desulfurization system,sodium-alkaline desulfurization system and magnesium-based desulfurization system were established in Ga Bi software.The influences of the three systems during the construction and operation stages were evaluated.The main research contents of this thesis were as follows:First of all,according to the actual exhaust characteristics of Marine diesel engine,the preliminary design of the system was carried out,the system divided into flue gas transport subsystem,seawater supply subsystem,absorption tower subsystem,oxidation aeration subsystem and seawater proton control system.The functions of each subsystem were designed.The material balance model of the system was established in Matlab to calculate the fuel consumption,fuel consumption rate and electricity consumption of the system.Next,the flue gas state parameters of cooling device,connecting flue duct and pressurized fan inlet and outlet were calculated.Finally,according to the desulfurization efficiency and gas velocity,the flue gas removal quantity and the tower diameter of desulfurization tower were computed.Secondly,the steady state analysis of seawater desulfurization process was carried out in Aspen Plus software.When the flue gas volume was 73483.8 kg/h,the optimal desulfurization efficiency reached 97.85%,which was consistent with the target desulfurization efficiency of the actual system.Then sensitivity analysis was used to study the influence of operating parameters such as flue gas temperature,flue gas volume,SO2content,seawater spray volume and p H.The results showed that when the reaction temperature was 40～50℃,the content of SO2 in flue gas was 1200 ppm,the oxygen content was controlled in the range of 3～13.5%,the amount of seawater spraying was 170 m3/h,and the amount of oxidized air was not less than 2800 m3/h,the system achieved the target desulfurization efficiency,and the discharge water quality met the relevant requirements.Then,based on the steady-state model of the seawater desulfurization system,the control analysis of the dynamic model was carried out in Aspen Plus Dynamics.When the smoke volume and SO2 content were disturbed by±5%,the PI controller adjusted the disturbance and made the system return to a stable state.Then,the PID parameters were compared and analyzed.The results showed that adding differential coefficient brought fluctuation to the stable process of the system,while increasing integral coefficient eliminated the steady-state error.Finally,the seawater desulfurization system,the sodium-alkaline desulfurization system and the magnesium-based desulfurization system were evaluated by LCA method.From the environmental point of view,the sodium alkaline desulfurization system produced the most carbon dioxide and chloride,1.30×106 kg and 4.07×104 kg,respectively.The seawater desulfurization system emitted 1.24×103 kg CO2 and 14.8 kg chloride.From the economic point of view,the cost of using seawater as desulfurizer was negligible,and the cost of using Na OH was the highest,which was$30,000.From the perspective of energy,the sodium alkaline desulfurization system consumed more than 10 times as much primary energy as the other two systems during the construction stage.In summary,among the three desulfurization systems studied,the seawater desulfurization system had the best performance. |
