High-Pressure SCR at Large Diesel Engines for Reliable NOx-Reduction and Compliance with IMO Tier Ⅲ Standards
The ammonia SCR technology is an efficient instrument for denitrification of exhaust gases and therefore an approved technology to comply with the IMO Tier III limits (within Emission Control Areas). It is successfully used in the on-road sector as well as in several maritime and stationary large diesel engine applications. The operation of large diesel engines with highly efficient TC systems (e.g. two-stroke engine with single-stage TC or four-stroke engines with two-stage TC) however shows very low exhaust gas temperatures downstream the TC turbines. At the SCR system, these boundary conditions not only lead to low reaction rates of the nitrous oxides with the reducing agent ammonia but also cause unwanted side reactions of sulfur oxides contained in the exhaust gas with the ammonia. The formation of ammonium sulfate can lead to a blocking of the SCR monolith and therefore to a decrease of reactivity up to a complete deactivation of the system. Those effects not only occur when running on residual oils with increased sulfur contents but already by operation on distillate fuels of higher quality with a sulfur content of 0.1%. SOxscrubbing upstream the SCR-system would result in further decreased temperatures which will further intensify the loss of reactivity. Approaches to solving this problem have to provide higher temperature levels of the exhaust gases at the inlet of the SCR-system. An efficient solution is presented by placing the SCR upstream the turbine of the TC system or between the turbines (in case of two-stage TC). The SCR operation would benefit from the higher exhaust gas temperature levels and an energy consuming reheating of the exhaust gases can be avoided. This would require a rearrangement of the exhaust gas system to accommodate the SCR-catalyst and the dosing unit for the reducing agent upstream of the last turbine stage. In opposition to known and already in-use SCR-systems, which are placed behind the TC turbine, the effects of the increased pressure levels at the pre-turbine position on the SCR system and on the reaction kinetics are still widely unknown. Therefore, the effects on the ammonia storage capacity, the chemical conversion rates as well as on the SCR system itself are investigated experimentally. A synthesis gas test bench and a single cylinder research engine with a CR injection system are used for the analyses. Both test benches offer the opportunity to adjust the operation conditions equal to those upstream the TC turbines of large diesel engines. Here, the exhaust gas temperatures, the composition and especially the pressure level are of main interest. At the synthesis gas test bench the parameters temperature, pressure and space velocity are varied and the effect of those boundary conditions on the SCR system are studied systematically. The results from the synthesis gas test bench are compared with measurements using real exhaust gas at the externally turbocharged single cylinder research engine. Here, the exhaust gas back pressures are also adjusted similar to a pre-turbine application of the SCR. Additionally, the influence of particle loaded exhaust gas is taken into account. The chosen catalyst samples are honeycomb structures with oxides of vanadium, wolfram and titanium which is typically used in maritime applications and conventional arrangements of the SCR system downstream the TC. The research focuses on improving the basic understanding of the SCR system and the effects of the operation conditions upstream the turbine of the TC on its behavior. Within the paper the results of the experimental investigations as well as the analysis of the storage behavior and the reaction kinetics of an ammonia SCR system installed upstream the TC turbine of IMO Tier III compliant large diesel engine will be presented and the potential of this approach will be discussed.
Robert Bank Bert Buchholz Horst Harndorf Rom Rabe Uwe Etzien
FVTR GmbH,Germany Rostock University,Germany
国际会议
上海
英文
1-13
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）