Marine Diesel Engine ‘Mighty Midget’ Exhaust Gas Scrubber

By George Backwell at January 19, 2013 05:00
Filed Under: Company News, Scrubbers

Small-size, big performance, exhaust gas emission scrubbers by Green Tech Marine were recently installed by Norwegian Cruise Lines (NCL) in their Pride of America, following on the heels of an earlier pilot installation aboard Royal Caribbeans’ Liberty of the Seas. The scrubbers will be installed in March during the ship’s dry- docking in Pearl Harbor Naval shipyard to replace the ships silencers and clean the exhaust of four 8 MW engines,  in what the manufacturers claim to be the biggest marine scrubber installation in the world at this time.

'Pride of America': Photo credit Wikimedia CCL 2

Paraphrasing Shakespeare’s Hamlet: ‘To scrub, or not to scrub, that is the question’ … For to be legal and comply with reduced SOX emission limits, in Emission Control Areas (ECA’s) ships can either operate on low-sulphur residual and distillate fuels or fit exhaust gas treatment systems (EGTS) otherwise known as SOX scrubbers. These systems clean the exhaust gas to reduce SOX emissions to a level that is equivalent to the required fuel sulphur content, while still offering flexibility to burn marine diesel oil as occasion demands.

Scrubber Units: Image courtesy of Green Tech

Successful operation of the hybrid (closed and open loop modes, or as silencer only in ‘dry mode’ outside of ECA limits) sea-water scrubber system installed in the Liberty of the Seas pilot test a year earlier warranted a statement of compliance from classification society DNV, which doubtless carried weight with NCL when they opted to install the system in their Pride of America. The small footprint and low weight of the Green Tech system commends itself, as no space is lost to passenger or crew space, and the installation needs no steel work modification; the scrubber takes up about the same amount of space as the silencer it replaces.

Features of the GTM R15 Scrubber

Energy Efficiency

The major energy consumers are the pumps but the pre-treatment and mixing unit also take up a significant amount. All pumps are equipped with frequency converters to keep the energy consumption and wear at the lowest possible level; by this means energy efficiency is claimed to be less than 1.5% of ship’s main engine power.
Intake sea-water, exhaust gas discharge and overboard wash-water discharge are constantly monitored for SOx, NOx, CO2, pH, PAH and turbidity and there is a graphical touch-screen display. The control system constantly monitors the process  to obtain best energy efficiency and emission reduction.

Control Room 'Liberty of the Seas': Image courtesy of Green Tech

Corrosion-free, weight saving and certified glass-fiber Reinforced Epoxy (GRE) or plastic piping systems are used for the entire installation.
Open Loop Mode
During most of the time GTM R15 is operated using Open Loop. The same amount of fresh sea water that is fed into the process is, after wash-water cleansing, discharged overboard.
Closed Loop Mode
While in port or other restricted areas the discharge of wash-water may be prohibited. The GTM R15 scrubber can then be operated (for up to three days) in Closed Loop mode, with wash-water discharge to a holding tank.




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