Fig.6: The engine room of the world's first marine vessel with a Selective Catalytic Converter (SCR) fitted to the main engine (a 6S50MC two-stroke engine of 7,860 kW)
Fig.6 shows the engine room of the first of four such vessels, all with 6S50MC main engines fitted with an SCR plant. The method, the system design and the main results (more than 93% reduction) are described in detail in [3] and [4].
It should be mentioned, however, that an engine with high-pressure direct gas injection (12K80MC-GI-S) and a very large SCR has been in operation since 1994 in a power plant in Japan. Besides being the largest gas engine in the world, this is probably also the large bore engine with the lowest NOx emissions worldwide. The very strict local regulations in the Tokyo area require very low NOx emissions so it was necessary to ensure more than 99% NOx reduction. This requires a very large SCR that must be placed between the engine and the turbocharger turbines in order to have the right temperature level for the catalyst (300-400℃). Thus, the thermal inertia of the catalyst has a strong influence on the engine performance during the warming up of the plant.
This was known from the above mentioned marine plants (see [4]) to be a source of turbocharger instability which could be controlled by suitable operation of the auxiliary blowers on the engine. For the (much larger) catalyst on the 12K80MC-GI-S engine, dynamic simulations of the engine operation at the design stage had indicated that more was needed to obtain a satisfactory load-up capability after a cold start. As a consequence of the calculation results, the engine was equipped with a 6 MW gas burner, situated between the engine and the SCR, and operated to heat up the catalyst, resulting in a very satisfactory load-up capability [5].
The application of the IE concept (which, however, was not available when these plants were established) might have facilitated the dynamic operation and contributed to turbocharger stability by supplying more energy to the turbine when needed, This could have been done by opening the exhaust valves earlier and by retarding fuel injection. However, the large burner used in the Chiba plant could hardly have been omitted by the application of the IE concept.
CONCLUSION
Environmental friendliness will be one of the dominant development goals in the years to come, and there are well proven methods available for ensuring compliance with international and national regulations for marine diesel engines. These methods can be applied with no negative effects on the general engine behaviour and reliability.
REFERENCES
[1] Pedersen, P.S., 'New R&D Centre in Copenhagen for Two-Stroke Low-Speed Engines'. MAN Publication research engineering manufacturing 1994/95' MAN AG, Munich 1995. pp.28-35
[2] Pedersen, P.S., 'The Intelligent Engine: Prospects and Experience from Service'. ISME Tokyo 2000, paper T033
[3] Sφndergaard, K., et al, "NOx Control for Large Manne Engines". Paper D.15, 19th CIMAC Congress, Florence 1991.
[4] Egeberg, C.-E., et al, "Applicairon Technology for Low Speed Diesels". Paper D.60, 20th CIMAC Congress, London 1993.
[5] Fukuda, T., et al, "Development of the World's First Large-Bore Gas-Injection Engine". Paper D.51, 21st CIMAC Congress, Interlaken 1995
