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the useable engine room volume ex- cluding the urea tanks. THE SCR MIXING TUBE AND CATA-LYST MODULEThe SCR mixing tube and catalyst module comprise about 70% of the total system weight excluding the urea solution. The mixing tube needs to be positioned close enough to the engine exhaust to allow for high enough tem- peratures to facilitate the decomposi- tion of the urea solution into ammo- nia. Minimum exhaust temperature varies based on installation, but 400 degrees Fahrenheit is a good ballpark number, according to Tenneco. An inherent level of acoustic noise reduc- tion is provided by the SCR on the or- der of 20-25 dBA. Depending on the vessel noise frequency requirements, a smaller silencer and spark arrestor is necessary upstream of the SCR. UREA STORAGE AND TRANSFER As a rule of thumb, a designer should allocate 5% of the total fuel volume for the urea solution. For larger vessels, a day tank is positioned in proximity to the urea dosing sys- tems. The urea solution is corrosive to bare steels and aluminums. As such, epoxy phenolic paint systems are re- quired for coating carbon steel stor- age tanks; which are widely available from marine coating companies. Wet components of pumps need to be poly/plastic or stainless steel. The urea solution is not ß ammable or toxic in ambient temperatures but decompos- es to ammonia when exposed to high temperatures, such as those caused by engine room Þ res. Since gaseous am- monia is a toxic inhalant, safety pre- cautions are necessary Ð such as stain- less steel piping in the engine room. OPERATING LOGISTICSA 32.5% urea solution has been broadly available for years on our highways as Diesel Exhaust Fluid (DEF). This percentage provides for the lowest freezing point of 11 de- grees Fahrenheit. For marine use, a 40% urea solution is favored as it comprises less volume and weight with a manageable freezing point of 32 degrees Fahrenheit; the same as water. Ship service companies, such as Wilhelmsen Ship Services (WSS), currently deliver a 40% Urea Solution to U.S. ports. Today, the deliveries are made by tank truck directly to the ves- sel in port, or by 260-330 gallon totes which can be loaded on board. As de- mand increases, urea solution will be- come readily available at fueling piers. CAPEX AND OPEX The International Association for Catalytic Control of Ship Emissions to Air (IACCSEA) indicates CAPEX are $25-$63 per hp and OPEX from $3.0 to $7.1 per 1000 hp-hr for an SCR System [6]. Based on this data, an SCR system for 150 foot Ocean Tug could translate to an initial cost of $200-to-500,000 USD and a re- curring $125-300,000 per year, based on 5,000 operating hours per year. CERTIFICATION REQUIREMENTS Unlike IMO, the EPA allows only the engine manufacturer package to ob- tain emissions certiÞ cation for new en- gines. This means that shipyards, own- ers, or 3rd parties cannot perform their own packaging of lower tiered engines with an SCR after-treatment system to achieve Tier 4 certiÞ cation. This will limit engine selection for a few years to come. To date, only a small percentage of EPA Tier 4 compliant engines have been publicly released, increasing risk on new U.S. vessel build projects. THE WAY FORWARD ÉThe Tier 4 compliance strategies identiÞ ed herein are more complex than the previous generations of en- gines; translating to cost, technical, and performance implications for the designer, shipbuilder, and operator. The optimum solution for a speciÞ c application depends on the operatorÕs requirements. These include, but are not limited to: areas of operation, load proÞ le, endurance, and ultimately to- tal ownership costs. What we can expect to see in the com- ing months and years, are announce- ments from engine makers indicating EPA Tier 4 certiÞ ed engine packages. Some international engine manufactur- ers may opt not to invest in certifying an EPA Tier 4 engine, if the demand is not large enough. Rather, they will wait to the international implementation of IMO Tier III before introducing NOx abatement systems. This could limit engine options to U.S. customers for up to the next seven years. EMISSIONS REGULATIONS www.marinelink.com MN 45MN November2013 Layout 32-49.indd 45MN November2013 Layout 32-49.indd 4510/28/2013 3:21:14 PM10/28/2013 3:21:14 PM
