Study On The DeNO_x、Carbon Deposition And Regeneration Of Marine Diesel Engine SCR

Selective Catalytic Reduction (SCR) technology is the only denitration technology whichmeets the marine diesel engine emission regulations of Tire-III. In response to increasinglystringent ship NOXemission regulations, researchers and ship manufacturers begin to keep aneye on the SCR technology. At present, there are several main problems about the application ofSCR systems: First, the size of SCR system is too big, and it is relatively difficult to arrange it inthe limited space of ship. Second, there is a large number of thin, sticky particles covered on thesurface of the catalyst when heavy oil is burned, which can lead to the decrease of catalyst’sactivity in a short time. The cost will be greatly increased if frequently replace with the freshcatalysts on account of the high price of V2O5-WO3/TiO2series of SCR catalysts. The deNOXactivity of the honeycomb SCR catalyst with the size of L×W×H=150mm×150mm×480mmand the hole density of cpsi86is studied in a high space velocity. The reasons of carbondeposition of the honeycomb SCR catalyst are analyzed in this paper. At last, several measureswhich used to prevent carbon deposition and two regeneration technical solutions of deactivatedhoneycomb SCR catalyst are proposed. The main research contents and the results as follows:(1)A SCR deNOXsystem is built on the exhaust piping of diesel engine with type ofYC6A220C, which is produced by Guangxi Yuchai Machinery Co., Ltd. The denitrationefficiency of honeycomb SCR catalyst is mainly discussed with a space velocity of20000~45000h-1, temperature of250~360℃，NH3/NO molar ratio of0.8~1.1. Results showthat the denitration efficiency of the SCR catalyst reach above87.1%in space velocity range of35000~45000h-1when the temperature is300~360℃and the NH3/NO molar ratio is1~1.1;(2) In order to test the catalyst in the velocity range of35000~40000h-1denitrationefficiency can meet the Tire-III on medium speed machine and emissions low speed machinerequirements, test NO concentration of1300ppm and1900ppm catalyst for denitrationefficiency at360℃, results show that the NH3/NO molar ratio is1~1.1, catalyst for denitration (3) Tests of particle show that the diameter of article produced by diesel engine mainly between0.178～0.237μm, which belong to the sub-micron particles. These particles deposited in the channel surface of catalyst mainly suffering the Brownian motion force, thermophoretic force and turbulent fluctuating force. Denitration experiments also test the effect of deposited carbon on denitration activity of catalyst. The results show that the carbon deposition on the surface of the catalyst is loose in the early time, the soot on the surface of the catalyst can be brought out of the catalytic converters by a strong flow pulses. Because the time of experiment is short, as well as the impact of strong airflow pulse, the effect of carbon deposition on denitration effect of catalyst is not obvious. But in practical application, catalyst is easily blocked by carbon. This paper starts from the selection of catalyst, design of test conditions and SCR system, puts forward five measures to prevent carbon deactivation of catalyst.(4) Against the coking deactivation of SCR catalyst, two technical schemes of cold regeneration is proposed. One is ozone oxidation regeneration technology for carbon deposition of ship diesel engine SCR catalyst. It utilizes the strong oxidizing of ozone, quickly oxide the diesel engine particles deposited on the surface of the catalyst efficiently under low temperature(180～250℃). The other is NO2oxidation regeneration technology for carbon deposition of ship diesel engine SCR catalyst. It makes use of the strong oxidizing of NO2at a high temperature oxide the diesel engine particles to achieve the purpose of regeneration.(5) The system structure of the catalyst with high hole density and high space velocity can be more compact,and the size can be smaller which can reduce the investment at the same time. Take12V46C type marine diesel engine as an example, the initial investment cost decreased by30～70%. The cost of the device of ship diesel engine SCR carbon regeneration by ozone is similar with the initial investment of catalyst, both of which are about250thousand yuan.