Marine Diesel Engines – Exhaust Gas Emissions – Paying a Price

By George Backwell at November 16, 2010 12:50
Filed Under: General

Marine Diesel engines have a remarkable ability to work with a variety of fuels, ranging from Heavy Fuel Oil (HFO) to Liquid Natural Gas (LNG) as well as a range of distillates of refined crude oil in between. Not surprisingly the ship-owner's fuel of choice for large two-stroke Diesel engines over the years has been HFO, the low-price by-product of oil refinery output. Onboard fuel oil treatment being taken care of by purifiers/calorifiers prior to fuel injection, and more recently by advanced computer driven fuel cleaning systems.

Unfortunately HFO is high in nitrogen, sulfur and ash, greatly increasing the NOx and SOx content in marine Diesel engine exhaust gas emissions, a fact which has led pollution control agencies worldwide – IMO, EU and other, localised, Emission Control Areas (ECA) –  to set progressively exacting limits in revised MARPOL VI.

A bleak future for ship-owners who were not already planning for year 2015 (when sulfur limits in the ECA's will be restricted to 0.1% m/m) was forecast by Per Brinchmann at the annual Bunker Oil and Energy seminar hosted by Wilhelmsen Ship Services in late October 2010,  explaining that it is technically almost impossible to supply HFO within that limit. He went on to suggest Diesel engines be powered by alternative fuels, including perhaps LNG and Gas Oil, and by fitting exhaust gas scrubbers.

Brinchmann was echoing a view expressed by Paulo Tremuli, Wartsila's Director of R & D Ship Power, Italy, in January, 2008 in a paper on the company's future intentions for exhaust gas emissions abatement: "Not much can be done at engine level to reduce sulfur emissions: what's in the fuel will be found in the exhaust." Tremuli forecasted at the same time a focus on the development of cleaning exhaust gas by means of sea-water scrubbers, or by fresh-water scrubbers with an added alkaline solution – systems that are indeed now on the market.

In the meantime, ship-owners find themselves caught between 'a rock and a hard place' since whatever their choice, capital and running costs will be increased in their highly competitive market.  Ironically, environmentalists themselves will be among those to pick up the tab when the extra costs of meeting Tier lll emission targets inevitably begin to trickle down to customers.

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