All SCR systems in service exhibit good NOx conversion. No tendency toward abnormal deactivation has been observed, irrespectively of the fuel choice (Table 1, Figs 8 and 9).

　

Table 1. SCR systems in operation

Figure 8. "Aurora af Helsingborg" plying between Helsingborg (Sweden) and Helsingoer (Denmark).

　

The exhaust gas temperature of a medium speed engine is high enough for the catalyst to be placed after the T/C turbine. Locating the SCR unit before the T/C turbine as in low-speed crosshead engines, has several drawbacks. If the temperature is too high, the catalyst life may be reduced due to sintering. Having a large volume before the turbine results in reduced load-acceptance behaviour, which is undesirable in marine installations.

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