Experimental Study On NO_x Removal By Wet Oxidation Method In A Marine RPB Reactor

Large low-speed tow-stroke diesel engines are widely used as main propulsion power plants in ocean going vessels,and the exhaust gas emitted contains a large amount of nitrogen oxides(NOx),causing serious damage to the environment.In order to meet the increasingly stringent requirements on marine NOx emission abatement,some De-NOx technologies are being developed for marine vessels.Among them,wet De-NOx method has some advantages,such as high NOx removal efficiency,good economy and easy to remove multiple pollutants simultaneously,becoming a reaserch focus in the marine exhaust gas De-NOx area.The types of taditional wet scrubbing reactors mainly include spray column and bubble column,which will occupy a large space onboard and are difficult to meet the pratical needs of ships.Rotating packed bed(RPB)reactor based on Higee technology,has some obvious advantages for marine applicaiton due to its small size and much high mass transfer efficient.In this paper,RPB used as reactor and NaClO2 as oxidant additive were combined toremove NOx from simulated diesel engine exhaust gas,and NO removal performance and related reaction mechanism were investigated.According to our experimental scheme,a RPB reactor was designed and fabricated,and it was used to build a wet scrubbing De-NOx system.Then a series of experiments were conducted to study NOx removal from simulated marine exhaust gas by cyclic wet scrubbing using NaClO2 solution in the RPB reactor.And the effects of various operating parameters on NOx removal performance were investigated.The relevant reaction mechanism had also been discussed.The details are as follows:Firstly,according to experimental conditions based on simulated marine exhaust gas,an RPB reactor was designed and fabricated.The types of device structure,packing and rotor of RPB reactor were chosen for marine application.The sizes of key parts were calculated,and the mechanical strength of RPB reactor was analyzed based on the mechanical properties of reactor parts.According to analysis results,the engineering drawings were drawn and reviewed,and the manufacture of main parts and assembly of RPB reactor was carried out.At last,the RPB reactor was tested to confirm that its performance could meet our experimental requirements.Secondly,a wet scrubbing system for NOx removal from simulated marine exhaust gas was built based on the RPB reactor.A series of experiments were conducted to study the effects of various operating parameters such as rotational speed of RPB rotor,pH value of absorbent solution,NaClO2 concentration,NO and SO2 concentrations,liquid-gas ratio on NOx removal performance by cyclic wet scrubbing using NaClO2 solution.And the relevant reaction mechanism had also been discussed.The results showed that,NOx removal performance could be improved by increasing the rotational speed of RPB rotor or NaClO2 concentration within a certain range.The pH value of scrubbing solution imposed significant effect on NOx removal efficiency.With the decrease of pH value,the ratio of ClO2-to HClO2 and ClO2 in scrubbing solution increased,thereby enhancing NOx removal efficiency.When scrubbing solution pH value was 4,NO oxidation and NOx removal efficiency were 100%and 72.3%,respectively.The coexisting SO2 in exhaust gas could enhance NOx removal performance greatly,indicating that this wet scrubbing process had great potentials for simultaneously removing NOx and SOx.With the increase of NO inlet concentration,NO oxidation efficiency decreased gradually.When NO initial concentration was high in marine exhaust gas,it could be effectively removed by increasing the concentration of oxidant.It suggested that this novel wet scrubbing process possessed an excellent denitration performance for a wide range of NO concentration.Finally,the rate equations of De-NOx reaction occurred in RPB reactor was derived based on the classical reaction kinetics theory and relevant experience model.The reaction orders were solved by fitting experimental data.According to their effects on reaction rate,the order of operationg prarmeters was:initial NaClO2 concentration>rotational speed of RPB rotor>inlet NO concentration>concentration of OH-in scrubbing solution.