Air pollution from ships continues at the top of the agenda but the correct solutions to achieve low levels of NOx and SOx gases are far from certain
Air pollution from ships continues at the top of the agenda but the correct solutions to achieve low levels of NOx and SOx gases are far from certain
Difficult decisions will soon need to be made if more reductions in NOx and SOx gases are to be achieved. One current initiative – seen as totally unacceptable by some – centres on directives to compel owners to burn clean distillate rather than economic residual fuels. Alongside this is a move to bunker low-sulphur fuel, especially in the newly created sulphur emission control areas (SECAs) imposed by both IMO and, unilaterally, by the European Union. The first SECA, with a 1.5 per cent sulphur cap, became operational last year in the Baltic Sea, and two more, in the North Sea and English Channel, will be enforced by IMO from November this year.
Ferry operators, in particular, may have to make some tricky decisions, since most are on regular runs, often within a sulphur control area, and some overnight ships often spend long periods in port during the day. It is interesting to note that Rolf Kjaer, newbuilding director for the prominent European operator Color Line, told delegates during April at the 2007 Cruise & Ferry interviews event that his company made a decision some years ago to burn only low sulphur (0.7 per cent) fuel.
Mr Kjaer also said his company had made an early experiment with selective catalytic reduction (SCR) exhaust gas scrubbing equipment to deal with NOx but, speaking to Ferry Technology, he noted that the ‘first-generation’ package was perhaps in advance of its time and had run into a few problems. As a result, for Color Line’s newest ships, including the Superspeed duo, only low-NOx engine designs are being used, which combined with the low-sulphur bunkers, should meet current regulations.
To be fair, all major engine builders have made tremendous strides in reducing polluting gases, especially nitrous oxides (NOx), as well as soot. One possibility is therefore to re-engine with a more modern design. This has been done in one recent operation – replacement of a damaged engine with a brand-new version featuring common-rail fuel injection – by Scandlines for its Birdflight route diesel-electric ferry Prinsesse Benedikte (built in 1997).
A six-cylinder MAN Diesel 32/44CR model – the first example of this new model – has been retrofitted to work alongside four original eight-cylinder engines. The common-rail system plus electronic controls are expected to yield smokeless operation under all conditions, as well as reduced fuel consumption and less NOx.
Debate continues on all sides, however. Greek owners do not see why they should have to buy more expensive distillate or low-sulphur fuel (the latter is said to be not so abundant in the Mediterranean area).
As Ferry Technology reported in its April/May edition, BP Marine/Kittiwake/P&O Ferries, joint promoters of the Krystallon seawater-based exhaust gas scrubbing equipment for SO2, believe their technology is very effective for that duty.
Meanwhile, a company heavily involved in post-combustion solutions or NOx gases, Munters in Sweden, which manufactures marine SCR equipment, has agreed to divest that part of its business to Per Holmström. Mr Holmström has been manager for this section, which had sales totalling SKr20 million in 2005. Munters systems will now be marketed by DEC Marine AB as the DEC SCR converter system (DEC stands for diesel emission control).
In a DEC layout, NOx gases are reduced by the SCR principle, with a small amount of urea/water solution being injected in the exhaust gas, where it is vaporised and contacted with NOx in a heterogeneous catalysis over the SCR catalysts.
The Munters/DEC reference list includes more than 50 ships, including many ferries. Recent new ferry installations of Munters/DEC systems include those on Transpaper and its sisters (Ferry Technology, February/March 2007). Last year, the company retrofitted (at Öresundsvarvet) three ferries operated by Scandlines between Helsingør and Helsingborg: Aurora af Helsingborg and Tycho Brahe (both Wärtsilä diesel-electric engines) and Hamlet, (Wärtsilä main engines and Mitsubishi auxiliaries). The Aurora af Helsingborg plant is an upgrade (to achieve <0.5NOx/kWh) of that originally fitted in 1992.
DEC claims approximate capital retrofit investment costs of 45,000/MW for a passenger ferry and 77,000/MW for a freight roro design.
An interesting new upstream solution launched last year by Wärtsilä is Wetpac humidification. This technology involves the introduction of pressurised water into the scavenge air after the turbocharger, and its aim is to reduce NOx formation by lowering combustion temperature.
The water evaporates immediately due to the compressed air’s high temperature and enters the cylinders as steam, thus lowering temperatures. Wärtsilä claims NOx reductions of up to 50 per cent but a large volume of water is needed – around twice that of the fuel oil consumption.
Another leading manufacturer of exhaust gas scrubbing equipment is Argillon, producer of Sinox SCR technology (originally devised by Siemens). The honeycomb catalyst employed in a Sinox arrangement for diesel engines is a fully ceramic body with square flow channels.
Argillon can plan, construct and commission a complete plant geared to the required limits for removal of nitrous oxides (NOx), hydrocarbons, carbon monoxide and particulates. An electronic control system with sensors ensures that the correct quantity of additive solution is injected into the exhaust gas so as to convert as much of the nitrogen oxides as possible and in line with engine load.
Today, Sinox systems are working in a number of ferries, achieving annual NOx reduction figures of up to 1,561 tonnes (for the 30MW machinery on the 1980-built Gotland, now Scandinavia).
IMO has, of course, been at the forefront of the debate. At its April meeting, the Sub-Committee on Bulk Liquids and Gases (which was examining revisions to Annex VI) studied recent discussions of a working group on air pollution relating to: current Annex VI limits on exhaust emissions (known as Tier I); current best available engine technology with potential reductions of NOx emissions by 15-25 percent (Tier II); and more stringent limits needing further advances or downstream treatment (Tier III).
It was agreed that Tier II – a possible reduction of 2-3g/kWh across the current NOx curve attainable through engine advance – would be implemented on 1 January 2011. For Tier III, the years 2015/2016 are considered appropriate for implementation; such regulations would apply to new engines.
Three possible detail options were considered:
• 80 per cent reduction from Tier I levels, using SCR or so-called humid air motor technology, to be applied to all marine engines within 50 nautical miles from shore
• 83-85 per cent reduction from Tier I levels, using SCR or humid air motors, for large ships only, in specific near-shore areas
• 40-50 per cent reduction from Tier I levels, using advanced in-engine modifications or exhaust gas recirculation, for all engines worldwide.
On sulphur content of fuel, the working group had prepared a table outlining various options and noted that a final solution might be hybrid:
• regulation 14 (current situation)
• regulation 14, plus global sulphur cap (unchanged or lower) and a SECA sulphur cap lowered first to 1.00 per cent, possibly by 2010, then to 0.50 percent, possibly by 2015
• within a defined limit from shore, a lower SOx standard or burn low-sulphur distillate fuel; alternatively, owners could fit gas scrubbers
• lowering of sulphur cap (max 3.0 per cent in 2012, max 1.5 per cent in 2016) or use of alternative mechanisms (such as scrubbing). Also, distillate fuel to be used in SECAs, port area and estuaries, with gradual lowering of sulphur content (max 1.0% in 2011, max 0.5% in 2015), or use of alternative mechanisms
• distillate fuel for all ships, with sulphur cap of 1.00 per cent by 2012, then reduced further to 0.5 per cent, possibly by 2015
• global caps as in previous item but allow for use of residual fuel in combination with alternative mechanisms.
Several options therefore remain open for the industry – including as yet relatively untapped techniques such as engine exhaust gas recirculation or more use of LNG as fuel – and it remains to be seen which will become dominant. As Mr Tim Wilson, from Lloyd’s Register’ FOBAS division, notes in an article in the new edition of our associate journal Marine Propulsion, it is essential that the debate remains focused and that every avenue is explored and scientifically supported – while still retaining the greatest flexibility for operators. FT
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