Greening the low speed fleet

01 Jun 2012
'Alexander Maersk', used for first-stage sea trials of exhaust gas recirculation

'Alexander Maersk', used for first-stage sea trials of exhaust gas recirculation

The Motorship recently visited MAN Diesel’s two-stroke headquarters in Copenhagen, where we learned about the company’s latest moves to keep ahead of the game in respect of emissions reduction, particularly with respect to the EEDI.

Senior vice-president promotion and sales Ole Grøne says that worldwide shipping is being increasingly regulated, with new ships subject to the energy efficiency design index (EEDI), and needing to consider IMO Tier III NOx limits, while all ships will be affected by the lower fuel sulphur levels being introduced first in emissions control areas (ECA) and then globally. This will affect over 45,000 ships larger than 2,000dwt, of which some 23,500 are powered by low speed engines.

“As far as ECAs are concerned, there is only potential for more, not fewer, ECAs,” says Mr Grøne. The Baltic and North Seas and North America are in existence, the Norwegian and Barents Seas are likely by 2015, while Japan, Australia, the Arctic , Antarctic and the Caribbean including Panama could become ECAs in the comparatively near future, followed by the Mediterranean and Malacca Straits. The company’s own study of its customers, i.e. ships powered by MAN B&W brand engines, shows that 27% of all ships visited the European ECA areas in 2011, and 25% of the ships visited the North American ECA area. Of these, 26% visited ECA ports on more than 10 occasions. So the lower sulphur limits in 2015 will have a big impact on shipping as a whole.

As far as greenhouse gases (GHG) are concerned, Mr Grøne reminded us that the EEDI rules come into force on 1 January 2013. The basic EEDI figure can be reduced by a number of measures: speed reduction; hull optimisation; propeller optimisation; engine efficiency measures such as derating; and technical measures such as waste heat recovery. Efficiency measures for modern MAN B&W engines can result in reductions of between 7% and 11% from the EEDI reference figure for specific fuel oil consumption (SFOC) of 190g/kWh.

The engine type can also have a bearing on EEDI – increasing the stroke-to-bore ratio, allowing a larger propeller to be used at lower rpm, shows potential fuel savings of 4% to 7% when comparing the new G-ME engines with the previous super-long-stroke S-ME design. One of the greatest potential reductions in EEDI can result from using LNG as a fuel: the ME-GI dual-fuel engine shows a 23% reduction in CO2 when using LNG, including the oil used as pilot fuel. This is due to the lower carbon content of natural gas and the lower SFOC in gas mode. The ME-GI engine avoids methane slip, caused by unburned CH4, which has an adverse effect on GHG emissions.

Mr Grøne states that “The efficiency of vessels will have to be improved from 2013 and onwards in order to reduce the EEDI as planned.” He believes that it will be possible for MAN Diesel & Turbo to achieve some 55% to 60% of the required efficiency gain through engine and propeller optimisation, and the use of waste heat recovery systems, leaving 40% to 45% of the gains to be found through improved ship design and changes in operating procedures.

IMO has started to implement measures to reduce CO2 from shipping, with the mandatory technical measures for new ships (the EEDI) and operational measures (SEEMP) for all ships; these will be followed by economical measures, which will probably also be mandatory. The economical measures are yet to be determined, but proposals include a carbon contribution (i.e. a fuel levy contributing to an international GHG fund), a carbon capping and trading scheme, or an incentive scheme, involving rebates or similar.

To meet Tier III NOx limits, operators of MAN B&W engines will have a choice between NOx reduction with selective catalytic reduction (SCR) or NOx prevention with exhaust gas recirculation (EGR). Both technologies are expected to be available well before implementation of Tier III, and a complete Tier III engine programme is promised by 2015. Whether SCR or EGR is the better solution will depend on operating patterns.

For SOx reduction, Mr Grøne says that all current MAN two-stroke engines can run on ultra low sulphur fuels and be set up to switch reliably between heavy fuel oil (HFO) and distillates. Currently, the greatest consumption of HFO (about 65%) is consumed by about 10% of ships, these being the largest vessels operating over the longest distances. So installation of scrubbers on a few thousand of the largest ships would allow a significant proportion of bunkers to remain as high sulphur HFO, which is expected to have a price advantage post-2015 of at least $300/ton. MAN, through partner companies, can offer either wet or dry scrubber systems.

Søren Jensen, vice-president for emission reduction technologies, explained in more detail how gas engines, EGR, SCR and scrubbers can achieve the required emission reductions. “MAN Diesel & Turbo has opted for high pressure gas injection for its dual-fuel two-stroke engine,” he said. “This offers the benefits of no power reduction, no methane slip, and no knocking. We have already had 10 years experience of this technology operating a 12K90MC-GI-S engine at the Chiba power plant between 1994 and 2003.”

More recent test results, from the company’s research engine in Copenhagen inaugurated in 2011, suggest that engine performance is identical running on gas or oil fuel, and the expected efficiency improvement on gas has been confirmed. Operating on gas, NOx has been reduced by 30%, well below Tier II requirements, with the highest reduction at high engine loads. By tuning the engine for optimum SFOC, it has been possible to achieve reductions in SFOC of 3.1, 5.7 and 1.9g/kWh at 75%, 50% and 25% engine load respectively, with a slight NOx penalty below about 70% load but a significant improvement in NOx at full load. Methane slip is restricted to 0.2g/kWh at 25% to 100% load, resulting in a reduction in global warming potential of about 20% for the ME-GI.

As a result, the ME-GI add-on platform will be made available for all ME engine types from the S35ME to the K98ME.

Both EGR and SCR solutions for Tier III NOx limits have been the subject of service test programmes. Results of the tests have shown that after 500h of running with EGR on 3% sulphur content HFO, the cylinder condition was not affected, and deposits on the EGR blower and the cooler were minimal. Work is now proceeding on the second-generation EGR, with an integrated design, to be incorporated on the main engine of a Maersk newbuilding at HHI in Korea, The SCR has been shop tested on a 6S46MC-C engine. In order to achieve the high temperatures – 300°C to 350°C minimum - necessary for the SCR to function correctly, it needs to be installed before the turbine. Although the technology has been proven in power plants, there are challenges at low load in marine installations. For Tier III operation the exhaust gas passes through the SCR, and for non-Tier III operation the exhaust gas goes direct to the turbine. The SCR is due to be tested in service by MAN and Hitachi Zosen, onboard a 38,000dwt general cargo ship, the Santa Vista.

MAN has also been involved in a scrubber field trial, using an Aalborg/Alfa Laval wet scrubber operating on either fresh water or seawater, retrofitted to a DFDS ro-ro ship Tor Ficaria, with a MAN B&W 9L60MC-C main engine. The installation was carried out at FSG in Germany as part of a lengthening conversion.

The latest news on slow steaming with MAN B&W engines was outlined by Per Rud, vice-president of MAN PrimeServ. He explained that up to Summer 2008, normal practice with container ships was to travel at full service speed. After that, in response to volatile fuel pricing, it became common for operators to slow down to 40% engine load or less. As overcapacity with shipping became a further problem, it was not uncommon for container ships to run at 10-15% load, which became known as super-slow steaming. The latest trend is ultra-slow steaming, at which ships operate at less than 10% of engine load, which has been implemented by some operators this year. Naturally, ultra-slow steaming poses new challenges to suppliers of engines and related items.

MAN Diesel & Turbo has been carrying out a survey of its customers to gain feedback about their slow steaming habits and expectations, which will enable the company to issue recommendations as to how to best deal with slow steaming operations. From initial responses, as expected, saving fuel cost (95%) is the most important reason for adopting slow steaming, with better utisation of existing fleet capacity (34%) second. Respondents who had retrofitted engine modifications have far fewer reservations about slow steaming than customers who have not; and some 75% of respondents had achieved better than expected fuel savings as a result of engine retrofit measures.

The retrofit measures offered by MAN include turbocharger cut-out, slide fuel valves, Alpha Lube upgrade (to reduce cylinder oil consumption) and engine de-rating (adjustment of engine settings, re-matching turbochargers and similar modifications).

Mr Rud believes that ultra-slow steaming will involve major engine modifications, including de-rating, and may need new propellers to achieve maximum benefit.

Finally, Jörg Albrecht, head of turbocharger marketing, outlined the influence of turbochargers on the EEDI. The EEDI measuring point is normally at 75% MCR, so solutions that improve fuel consumption at lower loads only have little or no effect on EEDI.

Turbocharger cut-out, i.e. cutting out one turbocharger of four on a large engine, a measure that provides good savings at part load (e.g. when slow steaming) has no edfect on the EEDI. Another measure to save fuel at part load, the exhaust gas bypass, offers good fuel savings but only has a small effect on the EEDI. Similarly, MAN’s VTA (variable turbine area), which has proved very effective at saving fuel at part load, has only a small effect on the EEDI.

A turbo compound system, where the power turbine drives a generator which feeds power into the vessel’s electrical system, offers a significant improvement in EEDI, no change in fuel consumption below 50% but good fuel savings above this point.

Two-stage turbocharging, which is applicable to four-stroke engines only, enables the charge air pressure to be increased while simultaneously reducing exhaust emissions. Throughout the range 25% to 100%, fuel consumption is significantly improved; most markedly at the EEDI measuring point of 75% load, so two-stage turbocharging can have a highly positive effect on the EEDI.

Links to related companies and recent articles ...

MAN Diesel & Turbo

view more