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going green alleviate this problem and are already offering retrofit packages for operation on standard HFO grades. The reducing agent required is ammonia, and this is transported and stored in the form of urea, which breaks down into ammonia when injected into a diesel engine’s exhaust gas stream. Obviously, this is an extra consumable that has to be bought, transported and stored, with associated tanks taking up additional space aboard ship, as do SCR’s other components. Anyone following the onhighway emissions debate in Europe will know that SCR has long been the NOx emissions technology of choice for most of Europe`s truck builders. In terms of costs, a rule of thumb for SCR is between €4,000 and €5,000 per MW of engine output for the installed hardware, while the consumable urea is estimated at €25 per hour for every MW of engine power.
Fallback Solutions
At a minimum, SCR represents a secure position from which engine builders can pursue other NOx-reduction technologies. Among these are solutions involving advanced primary measures to achieve a so-called strong Miller Cycle, humidification of intake air and exhaust gas recirculation (EGR), the latter especially on low-speed, two-stroke en-
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“ECAs.” Logically, ECAs are waters close to areas of population or other environmentally sensitive locations, including straits, port approaches and landlocked seas like the Baltic. Not everyone is waiting until 2016 to designate ECAs. For example, the North Sea, the Baltic and the English Channel are already designated, and individual countries are already imposing penalties (Norway) or offering tax breaks (Sweden) to ships based on their Tier III compliance. Currently, the only reliable way to meet NOx emissions limits more stringent than Tier II is with selective catalytic reduction (SCR). In fact, with NOx conversion rates of up to 85 percent, SCR represents a quick fix for NOx problems, and demand is already growing for retrofits on vessels wishing to ply the first ECAs or take advantage of incentives and tax breaks. The technique involves the injection of a reducing agent into the exhaust stream of a diesel engine in the presence of a catalyst, which converts oxides of nitrogen back into harmless nitrogen and water. The only drawback is that it works better with low-sulphur fuels since fuel sulphur content can form sulphates, which mask the catalyst and reduce its performance at the lower exhaust gas temperatures associated with low-load engine operation. However, engine builders are working with turbocharger bypasses to
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