by: BO SVENSSON

Tier III, which will enter into force January 2016, will require a reduction of the existing Tier I NOx level by 80% across the entire speed limit for new marine engines, even if only in defined local areas near shore. These new requirements impose a sense of urgency in developing future emission control technologies to apply to new as well as existing engines. Manufacturers and suppliers to this market are well aware of this situation and their focus is clear.

The skid-mounted exhaust gas recirculation (EGR) scrubber (top) with the cooler and water mist catcher (below) as installed at Alexander Maersk. The scrubber is completely new and was specially designed by MAN Diesel for the EGR upstream system.
The skid-mounted exhaust gas recirculation (EGR) scrubber (top) with the cooler and water mist catcher (below) as installed at Alexander Maersk. The scrubber is completely new and was specially designed by MAN Diesel for the EGR upstream system.

“Since our first testing of EGR [exhaust gas recirculation] back in 2004, MAN Diesel has been convinced that EGR technology is the route to decrease emission of NOx from their two-stroke engines,” said Søren H. Jensen, vice president, research and development, MAN
Diesel. “EGR is one of many methods to reduce NOx emissions from marine diesel engines and the method has been used in some four-stroke engines, but has not yet been commercially available on two-stroke engines onboard ships.”

In 2007, MAN Diesel tested an EGR system at its low-speed test engine in Copenhagen, Denmark, and achieved a considerable NOx reduction, with a marginal negative effect on the specific fuel oil consumption (SFOC). Also, other emission parameters and engine components were only slightly affected by the EGR process (see D>W, March 2008).

In 2007 MAN Diesel tested its second EGR system at its low-speed test engine in Copenhagen, Denmark, and achieved a considerable NOx reduction. Only a marginal negative effect on the specific fuel oil consumption (SFOC) was recorded
In 2007 MAN Diesel tested its second EGR system at its low-speed test engine in Copenhagen, Denmark, and achieved a considerable NOx reduction. Only a marginal negative effect on the specific fuel oil consumption (SFOC) was recorded

MAN Diesel is involved in two large projects concerning environmental issues. One is the HERCULES-B, which is a European Commission (EC)-funded project with focus on engine efficiency and emissions. One of the specific tasks has been emission reduction methods, and the task leader comes from MAN Diesel. A major focus has been EGR in order to reduce NOx. The objective is to reduce NOx by 80% (Tier III) on a two-stroke test engine with minimum deteriorations regarding specific fuel oil consumption (SFOC) penalty and other emissions. Other objectives are reducing NOx by 50% on a seagoing vessel, by test of a full-size prototype EGR system, and an investigation of long-term effects on engine components.

Earlier this year MAN Diesel performed what they call an “extreme EGR test” carried out on their 4T50ME-X test engine. One of the results was an 87% NOx reduction obtained at 75% load with an SFOC penalty of 5 g/kWh. An SFOC penalty of only 2 g/kWh was obtained at 80% NOx reduction at 75% load.

“We are now working on the next step of developing our EGR system being the installation of a complete system at Alexander Maersk, a containership of 1092 TEU capacity,” said Jensen. “The EGR system will be installed and tested on the 10 MW MAN 7S50MC engine during early 2010 according to plans.” This is also part of another important project for MAN Diesel, the “Green Ship of the Future,” in which a number of companies besides MAN Diesel are involved, among them Maersk, Odense Lindö, Aalborg Industries and APV to mention a few. Also here, the specification and design of an EGR system is in focus, including system integration with engine room and other auxiliary systems. Alexander Maersk has been identified as the ship for the first EGR installation.

The integration with the engine of Alexander Maersk means removal of the existing two MET 42SE turbochargers and the installation of a new ABB A175-L turbocharger with variable turbine area. A new charge-air pipe will be required and an EGR gas outlet pipe will be fitted. The system will be optimized to achieve for best gas mixing and low pressure drops.

A principal sketch of the EGR system as fitted at Alexander Maersk. The main components are the exhaust-gas wet scrubber, cooler, high-pressure blower and water treatment system.
A principal sketch of the EGR system as fitted at Alexander Maersk. The main components are the exhaust-gas wet scrubber, cooler, high-pressure blower and water treatment system.

Early on, MAN Diesel saw the need for an efficient scrubber to clean the exhaust gas and, if possible, also reduce some of the emission components. Accordingly, MAN Diesel started designing its own, completely new scrubber specially made for the EGR upstream system. Over the last few years, the scrubber has been extensively tested as to its influence on engine performance, combustion temperatures and emission data. Measurements confirmed an up to 90% particle trapping efficiency in combination with up to 70% SOx removal, without any water carryover.

Source: WWW.DIESELGASTURBINE.COM

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