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Marine Propulsion & Auxiliary Machinery

Marine Propulsion & Auxiliary Machinery

Expert: scrubbers with filters better than distillates for human health

Fri 24 Nov 2017 by Jamey Bergman

Expert: scrubbers with filters better than distillates for human health
‘Ship tracks’ are bright streaks of cloud forming around the particles emitted in ship exhaust that can be seen from space

There is a significant threat to public health from the particulate matter emitted by marine engines as long as fuel oils are the predominant energy source used to power them, according to Dr Ralf Zimmermann of the University of Rostock in Germany, but that threat can be mitigated if fine particle filters are installed on vessels’ exhaust gas cleaning systems. 

Presenting research at the Asian Emissions Technology Conference in Singapore, Dr Zimmermann showed that, while neither scrubber technologies nor low-sulphur fuels are enough to reduce the risk that ships pose to human populations on their own, the addition of fine particle filters to an exhaust gas cleaning system (EGCS) could help to prevent both death and disease directly associated with maritime vessel emissions.

Showing a satellite image of ‘ship tracks’ or bright streaks of cloud forming around the particles emitted in ship exhaust, Dr Zimmermann explained that, while overall shipping emissions are lower than those coming from road traffic, they are more concentrated and have a greater impact on populations in port cities and those living near heavily-trafficked shipping routes.

He cited a landmark study by Corbett in 2007 which found that each year, some 60,000 deaths worldwide are directly attributable to ship pollution.

Dr Zimmermann questioned the approach taken by IMO in regulating ship emissions, noting the lack of regulations on particulate matter and, more importantly, fine particulate matter.

“Are we doing the right thing [by focusing] on fuel, sulphur content and NOx, to really tackle health effects?” he asked.

He said one-third of particulate matter in ship emissions was independent of fuel type and that, under some lower load conditions (70% and 50%), there were higher concentrations of particulate matter in emissions from engines running on both heavy fuel oils and lower-sulphur refined fuels.

Depending on conditions, reducing levels of fine particulates, he said, could be “low or not measurable”.

Extrapolating from the lack of reduction in fine particulates in emissions and the shipping industry releasing its own studies showing total emissions holding steady at 2008 levels, it would seem unlikely that particulate-related deaths linked to shipping emissions would have reduced.

Dr Zimmermann’s research showed that even small dosages of particulate matter from HFOs and MGOs equating to several weeks’ exposure in a human lung were linked to cell death and saw detrimental – albeit differentiated – biological effects between the different fuel types.

“There are fewer pollutants in the lighter fuels, but there are more soot structures,” he said. “The pure soot of [these distillate] fuels actually caused higher cell death than our heavy fuel exposure, which was for us a big surprise,” he said.

“We could not see that the particles from lighter fuels – MGO [and others] – were less harmful than those from heavy fuel oils.”

There is a greater long-term cancer risk from HFOs, according to Dr Zimmermann’s work, but still a pronounced risk from the acute effects of lighter fuels.

“We should not think that we can solve the problem [of public health impacts] by a fuel change. And the question we have to discuss is if [adding scrubbers or changing to low-sulphur fuels] really helps ... It’s a big question mark.”

Dr Zimmermann said scrubbers remove 30-70% of particulate matter but did not remove most of the fine particulates that have the worst effects on human health.

“The particles which are relevant for health are not covered well by scrubbers,” he said. “And we have the MGO emissions that have a high set of toxicities, so they have acute effects on the cells.

“It’s not harmless just to move away from heavy fuel oil. Also with lighter fuels, we have a class one human carcinogen that we are emitting in quite high amounts.

“In conclusion, low sulphur fuel or scrubbers are not sufficient to mitigate severe health effects and the public health impact in port cities and coastal regions,” Dr Zimmermann said. “It makes no sense to [legislate against particulate matter] indirectly via sulphur. Particle numbers or particle mass of fine particles are what we need to fight, nothing else.”

“I believe that exhaust gas treatment systems including filtering is the only option close to the coasts to mitigate these problems. And, I think, in that way, scrubbing is very important because only after scrubbing will you be able to do filtration, otherwise your filters will block far too early.”

With his research firmly focused on the health effects of particulate matter in the two most-discussed compliance options for IMO’s 2020 sulphur cap, Dr Zimmermann did not go into the climatic impacts linked with the continued use of petroleum in shipping. Nor did he discuss alternative fuels, such as LNG as fuel, which studies have shown emits virtually no particulate matter or sulphur and reduces emissions of nitrogen oxides by up to 90%. LNG also offers a less dramatic reduction in carbon dioxide emissions. 


Dr Zimmermann is full Professor of Analytical Chemistry, Institute of Chemistry, University of Rostock. His research was funded by the German Science Foundation and other organisations. 

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