Tug newbuildings can be fitted with medium-speed diesel engines to comply with US EPA Tier 4 emissions requirements without having SCR technology installed
Tug owners can meet stringent environmental air quality regulations for their newbuilds without emissions abatement technology by installing new compliant engines to comply with IMO Tier III and US Environmental Protection Agency (EPA) Tier 4 emissions requirements.
By using marine gasoil instead of heavy fuel oil, vessel owners will avoid sulphur oxide (SOx) emissions. This is not usually an issue for tugs as the majority use marine diesel fuel. But these engines emit nitrogen oxides (NOx) and particulate matter (PM) which needs to be removed to comply with US EPA Tier 4 requirements.
Some owners have installed selective catalytic reduction (SCR) systems to remove NOx and PM. This can be expensive to install and costly to operate as it needs urea replenishment and catalyst replacement. Plus, an SCR needs space in the engineroom and tank capacity for the urea.
Wabtec subsidiary GE Transportation has developed an alternative approach to reduce NOx emissions for compliance with EPA Tier 4. It uses exhaust gas recirculation (EGR) and two-stage turbochargers on its medium-speed engines to reduce NOx without compromising on fuel efficiency. These engines have been installed on tugs operated by Foss Maritime, Shaver Towing, Reinauer Transportation and Ingram Marine.
GE Transportation director global sales Sander Jacobs says this technology is a major differentiator for its engines. “We have introduced different ways to meet IMO Tier III and US EPA Tier 4 emissions requirements,” he said during Riviera Maritime Media’s Maritime Air Pollution Conference, Americas, in March 2020.
“Our technology offers cost benefits to operators, savings in operating costs and savings in space and weight provisions they can then put into the vessel to carry more passengers, cargo and fuel for longer journeys,” said Mr Jacobs.
Combining EGR with medium-speed diesel main engines removes the need for SCRs and all the extra equipment, such as urea tanks, pumps and injectors, mixing tubes, catalytic converter housing and the control systems. There are no additional costs for urea transportation or extra maintenance and training.
“Our engine has unique in-cylinder emissions reduction technology”
“As a company, we have invested significant amounts to reduce emissions,” said Mr Jacobs. “Our engine has unique in-cylinder emissions reduction technology.” GE has supplied, or has on order, around 100 EPA Tier 4 and IMO III-compliant marine engines. It has more than 400,000 hours of operation on marine engines with GE’s in-engine emissions solution.
With cooled EGR, NOx formation is minimised by controlling the combustion temperature below the threshold at which NOx is formed. “We collect the exhaust and feed this into a cooler to reduce the temperature,” Mr Jacobs explained.
“This reduces NOx, but we need to do more as it reduces efficiency. So, we increase peak cylinder pressure and high-pressure common-rail fuel injection. We partly redesigned the engine to withstand the higher pressure,” Mr Jacobs continued.
GE also included a two-stage turbocharging arrangement with these engines. These are two radial low-pressure and one high-pressure turbocharger, with EGR mixing chamber, exhaust bypassing, intercooling and aftercooling.
The high-pressure common-rail fuel system operates at 2,200 bar and has double-walled piping and a leak alarm. GE introduced advanced combustion controls to its engines to optimise efficiency.
“Our technology comprises multiple building blocks, which enable us to meet minimum NOx levels in the exhaust without compromising on fuel efficiency,” said Mr Jacobs.
GE’s EGR solution costs up to 50% less to install than an equivalent SCR after-treatment solution, said GE Transportation sales leader for marine and stationary power in Americas Patrick Webb.
“In case studies on tugs, when comparing our medium-speed engines with an SCR on medium-speed and high-speed engines, there are 50% savings in space and weight,” he said.
GE estimated installation costs for its medium-speed (GE 8L250MDC) engines with EGR that develop 2500 brake kW at 1,000 rpm would be US$279,000 in Europe. In comparison, it would be US$528,000 for a medium-speed engine with SCR (producing 2,600 kW at 900 rpm) and US$508,000 for a high-speed engine with SCR (2,460 kW at 1800 rpm).
“When related to costs of operations, there is US$125,000 per 2 MW annual savings in fuel as our engines are optimal in their power band, and because there is no need for replenishing urea.” GE calculated annual operating costs for its 8L250MDC engines with EGR to be US$2.86M. This is compared with US$2.93M for an equivalent medium-speed engine with SCR and US$3.12M for a high-speed engine.
Mr Webb reminded delegates of the additional costs for transporting urea to remote ports for SCRs and the reliability of GE engines. “During the roll-out, out of 10M hours we had 99% uptime in engine operations in the field,” he said. “And, we have seen 60,000 hours between engine overhaul.”
There are no catalyst cleaning, replacement or disposal efforts with GE’s EGR technology for medium-speed engines. There are also no stainless steel urea transfer pipes or compressed air valves and piping.
Most of the tugs operating with GE’s medium-speed engines with EGR technology are in the US. These include Shaver Towing’s Samantha S harbour and coastal tug and Reinauer’s inland pusher Bert Reinauer which are both powered by a pair of 12-cylinder 12V250MDC engines. Other examples are Foss Maritime subsidiary Young Brothers’ Kapena-class tugs operating in Hawaii, and Ingram’s inland waterways tug Mark Duley. These are all powered by two 8L250MDC engines with EGR.
The key benefits for owners are the space and weight savings, simpler and cheaper installation and easier and more cost-effective operation, said Mr Jacobs.
“There are no urea logistics hassles or onboard handling and no additional operating settings to worry about,” he said. “As a company we have invested significant amounts to reduce emissions.”
He says the maritime industry should pull together to improve air quality standards. “Our industry needs to do its part to reduce emissions, increase awareness and share technologies that enable, ultimately, reductions in air pollution,” says Mr Jacobs.
GE is doing its part through developing EGR that reduces NOx and PM, while not requiring catalytic metals or urea as in SCR systems.
NOx emissions compliance class notations unveiled
Classification society ABS has introduced new class notations to demonstrate vessels are built with engines complying with IMO Tier III requirements for NOx emissions.
NOx notation recognises vessels’ propulsion complies with appropriate Marpol requirements.
ABS’s LEV notation denotes low-emissions vessels are equipped with engines complying with EU regulations on SOx and NOx.
To support these notations, ABS published an advisory in May for building and retrofitting vessels for NOx compliance to IMO Tier III requirements. This is an overview of available technologies and evaluation of considerations for selecting compliance options.
This guide outlines the process for statutory and class approval and details best practices for installation and integration of exhaust emissions control systems and their operation.
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