Open loop scrubbers release sulphur exhaust that they clean in ships back into the sea and are thus more harmful than closed loop scrubbers
There has been a huge increase in the use of open-loop scrubbers in ships in just last one year, even as a debate about their viability in mitigating sulphur emissions from ships has also escalated.
According to GlobalData, a data and analytics company, there are currently 3,756 vessels with scrubbers installed, compared to just 767 in 2018. Out of these, only 65 have closed-loop, rest are all open-loop.
The International Maritime Organisation’s (IMO) adopted the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI in 2008 that regulates the prevention of air pollution from ships and prohibits deliberate emissions of ozone-depleting substances such as sulphur oxides and nitrous oxides.
Following the adoption, exhaust scrubbers have become one of the most preferred ways of reducing sulphur exhaust as they ‘scrub’ pollutants out of emissions.
However, out of the two types those are being used widely, while closed-loop scrubbers retain the sulphur emissions for safer disposal at port, open-loop scrubbers release pollutants back in the sea after turning the sulphur dioxide into sulphuric acid.
“The IMO outlined that it approves the use of open-loop scrubbers, deeming them as an ‘equivalent’ – which is defined as ‘any fitting, appliance or apparatus to be fitted in a ship or other procedures, alternative fuel oils, or compliance methods used as an alternative’. However, it has strict guidelines for discharge of wash water from exhaust gas cleaning systems,” GlobalData’s ship technology writer Varsha Saraogi, said in a statement.
Ahead of the implementation of the IMO’s sulphur cap in 2020, uncertainty around the sustainability of open-loop scrubbers continues to escalate in the shipping industry, Saraogi said.
“Under the regulation, the amount of sulphur in fuel oil used on board ships – which was 3.5 per cent m/m (mass/mass) – will be limited to 0.50 per cent m/m from January 1, 2020. So far, open-loop systems have witnessed more uptake in the industry compared to closed units,” she “noted.
She added that there are also hybrid scrubbers, which switch between open and closed-loop depending on situations such as local rules which may or may not prohibit the discharge of water.
A spokesperson from the IMO told GlobalData: “The wash water must meet strict criteria, so that discharge wash water should have a pH of no less than 6.5. A Group of Experts on the Scientific Aspects of Marine Environmental Protection task team has been established to assess the available evidence relating to the environmental impact of discharges of exhaust gas cleaning system effluent. The next session of the sub-committee will be held in February 2020.”
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