| As IMO's requirements for ship emission regulations become more stringent,more and more research is being done on the techniques and methods of ship air pollution control.SOx emissions can be removed by alkali elution such as magnesium-based seawater.The content of nitric oxide in nitrogen oxides accounts for more than 90%,which is difficult to remove by alkali.Regarding the treatment of NOx,more researches are currently conducted on selective catalytic reduction(SCR),exhaust gas recirculation(EGR),alternative fuel technologies and so on.However,EGR will lead to an increase in other pollutants;SCR size is so large that it's real ship applications are limited;LNG alternative fuels will aggravate the greenhouse effect.Hydrodynamic cavitation can produce strong oxidizing hydroxyl radicals;its mechanical agitation can greatly increase the gas-liquid contact area and reduce the gas-liquid mass transfer resistance;its hot spot effect and sonoluminescence phenomenon can create a possible reaction that is not suitable for normal occurrence.Hydrodynamic cavitation combined with NaCIO solution finally oxidizes NO into high-valent nitrogen oxides which are easily soluble in water and finally absorbed by water to achieve the purpose of denitration.Therefore,this paper proposes a denitration scheme for marine diesel engine based on hydrodynamic cavitation enhanced NaClO solution.In order to explore the mechanism and effect of this scheme,and to find the basic laws affecting the denitration of marine diesel engines that affect the hydrodynamic cavitation and enhance the NaCIO solution,this paper has carried out the following work:Theoretical analysis of the theoretical feasibility of hydrodynamic cavitation to enhance the denitration of marine diesel engine with NaCIO solution;construct a practical and effective test-bed,study the conditions required for cavitation under the experimental conditions,study various factors impact on the outlet NO/NO2 concentration and denitration rate,and search for the best reaction conditions.The ship denitration scheme of hydraulic cavitation and enhanced NaClO was designed and detailed energy analysis was carried out.Research indicates:By analyzing the hydraulic characteristics of the jet,it is proved that the experimental device fully satisfies the conditions for cavitation.Under the condition of hydrodynamic cavitation strengthening,the gas-liquid contact area is increased by orders of magnitude.At this time,the denitrification effect is much better than that under non-cavitation conditions;in the cycle time,the optimal denitrification effect can be maintained for more than 6 hours;The NO concentration is continuously increased,and the NOx denitration rate has no obvious regular change,but the highest value can be reached when the inlet NO concentration is 1000 ppm;As the concentration of NaCIO solution increases,the denitration rate increases continuously;With the increasing temperature of NaClO solution,the NOx denitration rate increased first and then decreased.The denitrification rate reached the highest value at 20?.The initial pH value of the solution has a great influence on the denitration effect.The lower the pH value in a certain range,the higher the NOx denitration rate,but the pH value of the solution should not be too low,otherwise the denitration rate will be significantly reduced;The front pressure of the jet has a significant influence on the NOx denitration rate.The higher the front pressure of the jet,the higher the NOx denitration rate.With the increasing back pressure of the jet,the NOx denitration rate tends to increase first and then decrease.The hydrodynamic cavitation-enhanced denitration system of NaClO solution has a simple principle and few key equipments.After energy consumption analysis,it has good economics compared with SCR system.This provides a new idea for the design of the actual system. |
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