The wold’s first low pressure exhaust gas recirculation (EGR) system, developed under ClassNK’s Joint R&D for Industry Program, has been installed on a low-speed two-stroke engine bulk carrier with verification tests to be carried out.
Mitsubishi Heavy Industries Marine Machinery & Engine Co., Ltd. (MHI-MME) and Mitsubishi Kakoki Kaisha Ltd. installed the EGR on a 34,000DWT bulk carrier owned by Shikishima Kisen K.K. The EGR system is designed to meet International Maritime Organization (IMO) requirements regarding nitrogen oxides (NOx) Tier III regulations, which requires ships built on or after 1 January 2016 to significantly reduce their NOx emissions while sailing in NOx Emission Control Areas (ECAs).
The low pressure EGR system works by supressing the formation of NOx by recirculating part of the exhaust gas back to the engine cylinder. The low pressure EGR recirculates exhaust gas between the two low pressure points – the exhaust system tailpipe and the turbocharger inlet. This causes the peak cylinder temperature to be lowered, making it more difficult for NOx to form. This method provides an alternative to urea dosing which reduces the NOx to nitrogen and water vapour.
A low pressure EGR is particularly advantageous as it reduces both initial and running costs compared to a higher pressure EGR that utilises high temperature and high pressure exhaust gas from a turbocharger intake.
During sea trials, the system successfully operated on the low-speed marine diesel two-stroke engine. Following the sea trial and performance testing, the system will now undergo verification tests in commercial voyages. These tests will be long-term and for example establish the availability of caustic soda and the sludge disposal handling process.
In addition to the low pressure EGR for low-speed two-stroke engines, MHI-MME also developed a low pressure selective catalytic reduction (SCR) system.
