Urea-SCR system for pollution control in marine diesel engines
Tier III emission control of the International Maritime Organization (IMO) requires the substantial reduction of nitrogen oxides (NOx) emission from marine diesel engine. Tier III is expected to require a dedicated NOx emission control technology such as the selective catalytic reduction. In our experience of on-board catalyst test in an exhaust gas of heavy fuel oil (HFO) and the subsequent development and evaluation of the urea-SCR system are described in this paper. The preliminary catalyst test was conducted by the slipstream type reactor mounted onto a marine diesel engine which was fueled by high sulfur HFO. On-board durability test showed that the honeycomb structured SCR catalyst suffered from the deposition of the mixture of soot and oil mist contained in the exhaust gas and deactivated readily. The deactivation was more severe at lower operational temperatures. This experimental test suggests the importance of the reduction of the soot and oil mist in the exhaust gas to prevent the possible deactivation of the SCR catalyst. Subsequent development and evaluation of the urea-SCR system was performed by the exhaust gas of the low sulfur marine diesel fuel at the test bench of the works. The system consisted of the afterburner to maintain the specific temperatures of exhaust gas, the aqueous urea injection system, and the honeycomb structured SCR catalysts. The dimensions of the piping and the reactor were designed to achieve a uniform distribution of urea with assistance of a computational fluid dynamics (CFD). The diesel particulate filer (DPF) was installed as a potential option to reduce the particulates upstream of the SCR catalyst. The urea-SCR system was operated at temperatures between 270C and 350C and at the ratio of equivalent NH3 and NOx between 0.4 and 0.95. The performance test has successfully proven that the system can reduce NOx efficiently according to the stoichiometric ratio of NOx and urea injected. The experimental results were confirmed to be essentially consistent with the CFD calculations. On-line gas analysis revealed that urea decomposition proceeded by sequential steps. Urea injected into the exhaust piping thermally decomposed into isocyanic acid and ammonia. Isocyanic acid was further decomposed by hydration and formed ammonia over the catalyst. Unreacted ammonia was detected downstream of the SCR catalyst however it was nominal concentration. Both the afterburner and DPF was confirmed to reduce the soot as well as oil mist in the exhaust gas. Particularly DPF can eliminate more than 80% of the total amount of the soot/oil mist mixture. The emphasis can be placed on the importance of the appropriate setting of the operational parameters such as residence time of the exhaust gas in the catalyst ant its temperature.
Yoshinori Izumi Hiroaki Ohara Hiroyuki Kamata Hayato Nakajima Takeshi Yamada Mamoru Irie Kouji Moriyama Kenji Goto
IHI Corporation,Japan Diesel United,Ltd.,Japan Japan Marine United Corp.,Japan
国际会议
上海
英文
1-5
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）