This breakthrough engine technology assures compliance with EPA tier 4 and IMO tier III emission limits, without the need for an SCR after-treatment system. This in-cylinder emissions reduction technology takes up significantly less system weight and space compared to SCR technology, is less complex to install and is easy to operate
Air pollutants in the exhaust gasses of sea-going ships are governed by increasingly stringent standards defined in the International Maritime Organization’s (IMO) Maritime Pollution Convention (MARPOL). US-flagged vessels operating in US waters or in the designated North American and US Caribbean Sea Emission Control Areas (ECA) must comply with emissions limitations defined in the US Code of Federal Regulations (CFR), governed by the US Environmental Protection Agency (EPA).
From 1 January 2021, the list of ECAs for which the IMO tier III NOX emission limits are in effect is expanding to include the Baltic Sea and the North Sea; these limits now also apply to recreational ships with a length above 24 m and below 500 GT, which had been exempted until 31 December 2020.
A common technology to meet IMO tier III and the more stringent EPA tier 4 NOX limits involves reducing NOX in the exhaust gas through a Selective Catalytic Reduction (SCR) after-treatment system. A reductant – usually a urea solution – is injected in the engine exhaust gas and funneled through a mixing chamber to a reactor containing a catalyst; this enables a series of chemical reactions, converting nitrogen oxides to yield nitrogen and water. An SCR after-treatment system typically includes the SCR reactor, dosing pumps, stainless-steel piping, a mixing chamber, and a stainless-steel urea storage tank. A complete SCR system takes up quite some space and adds significant weight to a ship: eg for a ship with 2 x 2,500 bkW engine power, the additional weight of the SCR equipment can easily total 10 MT, plus another 10 – 50 MT for the urea storage tank, depending on the required range. The space taken up by the SCR system can easily total 15 – 20 m3 plus 10 – 50 m3 for the urea tank.
For all ship types, any additional space and weight taken up by machinery results in less space and weight available for payload, passenger accommodation, or tanks, thus compromising profitability, comfort, or range. Other challenges with urea-based after-treatment systems include the burden of handling urea on board the ship and controlling ammonia slip, with its sharp suffocating odor. Moreover, urea may not be readily available in more remote locations.
Fortunately, there is a solution that overcomes these challenges: advanced exhaust gas recirculation (EGR) technology. Wabtec’s advanced EGR solution minimises the formation of NOX during combustion, as opposed to reducing NOX in the exhaust through a series of chemical reactions in an after-treatment system. This breakthrough engine technology assures compliance with EPA tier 4 and IMO tier III emission limits, without the need for an SCR after-treatment system. This in-cylinder emissions reduction technology takes up significantly less system weight and space compared to SCR technology, is less complex to install and is easy to operate. Additional benefits include no visible smoke, even during speed or load changes, and no need for a diesel particulate filter to meet the 0.04 g/kWh particulate matter emissions limit specified by the US EPA.
Since its introduction in 2016, this technology has been successfully deployed on many ship types globally, including ferries, expedition cruise ships, offshore support vessels, workboats, dredgers and naval ships.
A white paper describing this technology and its key benefits is available here
and a video can be viewed here: