Kawasaki Heavy Industries has reported a successful sea trial of an arrangement employing a combination of Exhaust Gas Recirculation (EGR) and emulsion fuel to reach Tier III NOx emission levels with no fuel penalty.
Trial
The Kawasaki Ecology & Economy System (K-ECOS) with EGR, emulsion fuel, water treatment, a turbocharger cut-out system and integrated controls was installed on a Kawasaki-MAN B&W 7S60ME-C8.2 main engine driving Kawasaki Kisen Kaisha’s pure car/truck carrier Drive Green Highway. After a successful sea trial before the vessel’s entry into service early this year, the system will now be tested in service over a two-year period.
Results after fitting the equipment
Performance in shop tests showed:
- The system in ‘NOx Tier III mode’, employing the EGR and running on emulsion fuel, achieved NOx emissions of 3.3 g/kWh, under the Tier III limit of 3.4g for low-speed engines.
- The scrubber successfully removed 97% of the fuel sulphur content from the exhaust.
- Fuel consumption in NOx Tier III mode, with the full K-EOCS system active and running on emulsion fuel, was greater than in basic mode with regular diesel fuel by 0.4-0.8g/kWh, but was still similar to the performance of the current engine.
- In ‘auto turbocharger cut-out mode’, which uses emulsion fuel and sequential turbocharger control but does not activate EGR, the fuel saving compared to basic mode reached a maximum of 4.8% at around 60% engine load.
System description
The EGR system used was of a high-pressure type, with a portion of the exhaust taken from upstream of the turbocharger. It is equipped with a wet scrubber for cooling, dust removal and the de-sulphurisation of exhaust gas, as well as an electric blower to compensate for up the pressure difference between the exhaust gas and scavenging air.
The water treatment plant is used to clean water that has been used by the wet scrubber to clean exhaust gas. It is compliant with IMO guidelines and features a centrifugal separator and a tube settling tank. The system is equipped with sensors to monitor when the water is compliant for discharge and features a data recorder that can log the water quality at discharge.
The emulsion fuel system, which uses a mechanical mixer within the fuel system to prevent the fuel from standing (and potentially separating) in a tank, was developed previously by Kawasaki. It has been subjected to a separate four-year service test, with a three-year inspection revealing no abnormal wear to engine or emulsion system.
System Operation
The operation of EGR reduces the amount of exhaust gas to the turbocharger, resulting in a reduction of scavenging air, compression and maximum combustion pressure and diminishing fuel efficiency. For this reason, the turbocharger cut-out system is used to bypass one of the two turbochargers while the EGR is in operation, to maintain pressures and fuel efficiency equivalent to normal operation.
Report conclusion
The paper described K-ECOS as the ‘ultimate environmentally friendly system’ and concluded: “K-ECOS is a scalable system capable of selecting configuring technologies depending on vessel type, service pattern and budgets, and the authors would like to propose the most cost-effective system configurations for individual systems to ship owners and shipyards.”
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Source: Motorship
