Industry Insight: Wärtsilä Explains the Impact of Bunker Sulfer Content on Scrubber Performance

Sigurd Jenssen says that scrubber operators can save energy by enforcing their own personal sulfur limit.

Update: Corrected Robin Meech prediction to 6,000 scrubbers by 2025.

In the coming months and years the maximum permissible level of sulfur in marine fuel is set to drop not only within Emissions Control Areas (ECAs), but as whole, globally.

Using scrubbers to clean vessels' exhaust gases is one of the options available to operators who must, in one way or another, achieve compliance with the new rules.

While scrubbing technology itself isn't particularly new, its use on-board vessels is, so ship owners naturally have a lot of questions about how the technology can help with tightening environmental regulations.

One question we've been asked that seems of particular interest is whether operators using scrubbers still need to limit the sulfur content of the bunkers they use in order to achieve compliance, or can scrubbers achieve the appropriate level of compliance using any ISO 8217 specification fuel?

Ship & Bunker talked to Sigurd Jenssen, Director, Exhaust Gas Cleaning at Wärtsilä Ship Power, to get a better understanding on the matter.

Sulfur Content

"In terms of technology and performance the fuel Sulfur content is not a critical factor, for our designs," said Jenssen.

"Our standard offering is a scrubbing performance that guarantees compliance with the new Emissions Control Area (ECA) rules from 2015 (0.10 percent sulfur), based on a fuel of maximum 3.5 percent sulfur. But we have installations in service that scrub from 4.5 percent down to 0.10 percent equivalency, and have tested even higher concentrations in our test facility.

"The key is to use the right amount of wash water, and distribute it correctly.

"It is possible to offer a lower scrubbing efficiency, but we are of the opinion that it is better to be on the safe side, given that there is some uncertainty on what the bunker suppliers will be offering."

Energy Savings

Scrubbing from 4.5 percent to 0.10 percent equivalency requires more energy than scrubbing bunkers with a lower sulfur content, and Jenssen explained that scrubber operators can save energy by enforcing their own personal sulfur limit.

"There are some savings to be had if designing for a lower sulfur content, primarily on OPEX, and we can of course design for that. It is really up to the customer and their expectations of the future fuel market," he said.

"On some installations we have indeed designed for a lower maximum sulfur content of 2.5 percent. But it is important to make this decision upfront, as it would be costly to upgrade to accommodate a higher sulfur content at a later stage."

By designing for a 2.5 percent sulfur, Jenssen said an operator could expect savings from the scrubber system of around 15 to 20 percent compared to a design for 3.5 percent sulfur fuel.

"The energy required to run an open-loop scrubber is typically 2-3 percent of the engine power, so you save maybe 0.4 percent to 0.5 percent of the total energy consumption," he added.

Robin Meech recently predicted that by 2025 there will be about 6,000 scrubbers will be in operation.