Marine

Innovative partitioned fuel tank promises emissions-free shipping

Innovative partitioned fuel ta...
Long-haul shipping could be decarbonized relatively quickly and painlessly, says a Northwestern University research team, using solid oxide fuel cells, electric propulsion and onboard carbon capture
Long-haul shipping could be decarbonized relatively quickly and painlessly, says a Northwestern University research team, using solid oxide fuel cells, electric propulsion and onboard carbon capture
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Long-haul shipping could be decarbonized relatively quickly and painlessly, says a Northwestern University research team, using solid oxide fuel cells, electric propulsion and onboard carbon capture
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Long-haul shipping could be decarbonized relatively quickly and painlessly, says a Northwestern University research team, using solid oxide fuel cells, electric propulsion and onboard carbon capture
Long-haul shipping might not need to wait for major energy storage advancements to go completely green, says a Northwestern University research team
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Long-haul shipping might not need to wait for major energy storage advancements to go completely green, says a Northwestern University research team
A movable partition in the fuel tank would allow it to accept CO2 as the fuel is spent, compressed to a point where a given volume of fuel would generate only a slightly larger volume of CO2
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A movable partition in the fuel tank would allow it to accept CO2 as the fuel is spent, compressed to a point where a given volume of fuel would generate only a slightly larger volume of CO2
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Greenhouse gas emissions from the shipping sector are shaping up as one of the toughest slices of the emissions pie to eliminate – and even if they're a relatively small slice (about 1.7 percent of total global emissions), they still need to be dealt with. But giant, heavy ships pushing through water for thousands of miles at a time require extraordinary amounts of energy, and finding viable alternatives to marine diesel is proving extremely difficult.

Onboard nuclear reactors deliver extreme clean range for large boats like nuclear icebreakers and submarines, but they're way too expensive for cargo shipping, which needs to be cheap to sustain the 90 percent share of global commerce it underpins. Batteries are a non-starter due to their crummy energy density. Hydrogen, ammonia and carbon-neutral electrofuels offer some hope, but until they're proven at scale, other alternatives need to be investigated.

Here's a fascinating proposition from a Northwestern University research team: what if big ships just keep on using hydrocarbons, taking advantage of their juicy energy density and well-established delivery infrastructure – but capture all the carbon emissions on board, and offload that carbon to be geosequestered deep underground at each destination port?

Long-haul shipping might not need to wait for major energy storage advancements to go completely green, says a Northwestern University research team
Long-haul shipping might not need to wait for major energy storage advancements to go completely green, says a Northwestern University research team

The ships couldn't use regular combustion engines; these release not only CO2, but large amounts of nitrogen as well, so there would be too much exhaust gas to capture and store on board.

Instead, they would run on electric propulsion, with power generated from hydrocarbons using a solid oxide fuel cell, or SOFC. Typically run in a zero-emissions fashion using hydrogen as fuel, SOFCs are also capable of generating electricity from hydrocarbon fuels, with high efficiency, low cost, and simple machinery. The by-products are water and carbon dioxide, making it simple to capture and store both separately.

“The solid oxide fuel cell is critical," says research team member Travis Schmauss, "because it burns the fuel with pure oxygen, yielding a concentrated CO2 product that is storable. If we just burned the fuel with air, it would be heavily diluted with nitrogen, yielding too much gas to store. When the concentrated CO2 is compressed, it can be stored in a volume not much larger than that needed for the fuel, which saves space.”

The Northwestern plan calls for the ship's fuel tank to be fitted with a movable partition, such that as the fuel is spent, the fuel side of the tank can shrink, and the CO2 can be compressed using standard compressors and used to fill the tank from the other side. Compression, the team reasons, would sap about 2 percent of the energy generated from the SOFC.

A movable partition in the fuel tank would allow it to accept CO2 as the fuel is spent, compressed to a point where a given volume of fuel would generate only a slightly larger volume of CO2
A movable partition in the fuel tank would allow it to accept CO2 as the fuel is spent, compressed to a point where a given volume of fuel would generate only a slightly larger volume of CO2

At the destination port, the reverse could happen; carbon would be pumped out as the fuel is being pumped in, and it could be taken off for long-term sequestration. Using regular hydrocarbon fuel, this would be a zero-emissions process. Using carbon-capture electrofuels, it would even be carbon-negative. Should some form of hydrogen prove a viable alternative, it could run on that.

“This technology really doesn’t have any major hurdles to making it work,” says Scott Barnett, senior author on the study and an expert on SOFCs. “You just have to replace the fuel tank with the double-chamber tank and add CO2 compressors. And, of course, the infrastructure eventually has to be developed to off-load the CO2, and either sequester or use it.”

Other SOFC researchers would appear not to agree with Barnett's perceived lack of hurdles. In a 2020 study published in the journal Materials for Renewable and Sustainable Energy, researchers Nai Shi at al state that, "when fueled with hydrocarbons, SOFCs encountered great difficulty in both performance and stability, which should be attributed to the sluggish hydrocarbon oxidizing reactions, the severe carbon deposition reactions, and the possible sulfur poisoning reactions in the anode."

Still, Barnett has been working on hydrocarbon-fueled SOFC research for at least 16 years, so there's little reason to doubt his authority on the topic.

It's an interesting proposition, one that doesn't need to wait for future energy fuel developments. If hydrocarbon-fueled SOFCs are genuinely ready for prime time, then perhaps we're looking at a relatively painless solution to green shipping.

The research was published in ACS Energy Letters.

Source: Northwestern University

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10 comments
10 comments
Robert Kowalski
Carbon capture seem to be go to solution for those that want to keep things as they are now. Have carbon capture and storage projects proved successful? Do they leak? Even if they don't leak now - do they require maintenance? Because if they do interest to keep captured CO2 not leaking might disappear after it would be no longer profitable.

Also - what is more profitable - pretending to capture CO2 while capturing only some, and allowing remaining to leak, or to do it right? Because who is going to enforce doing it right in international waters?
Alien
Interesting - based on simple carbon chain chemistry but what about the sulphur that is a constituent of the low cost fuel used in shipping? Isn't that still going to be pumped out as SO2?
FB36
The problem also exists for all current heavy diesel trucks, trains, construction/mining/agriculture/military vehicles & aircraft; NOT just ships!
A general practical solution for making alll of them carbon-neutral would be, all countries need to start producing biodiesel fuel at large scales (from all possible industrial/agricultural/forestry waste/biomass & even trash & sewage)!
CHRSKO
Shipping is already moving to low Sulphur fuel so that really is not a problem. Biofuel has proven to be more energy intensive to produce than the amount of fuel you get out of it, doesn't make sense to burn 5 barrels to make 4. Besides, there wouldn't be enough land left to grow food! This might not be ready for prime time, but it is certainly worth the effort to pursue as a possible solution. I imagine if even a portion of the money and effort that was being put into batteries was shifted to this the problems would be overcome.
John Banister
If you're going to use fuel cells for shipping, consider heptasilane as the fuel. It's quite energy dense, and it doesn't hold on to it's hydrogens so strongly as do alkanes, which means less energy is consumed liberating them. Also, the silicon (or even silicon oxide) can be released without it going into the atmosphere.
MarkGovers
It would be interesting if ships could use tidal movement for energy, there is an awful lot of water sloshing about in the ocean! Or at least supplemental.
Kiffit
Carbon capture has proved to much more difficult, inefficient, expensive, methane leak prone and fruitless considering the billions that have been invested in it to almost no effect so far. It seems to have been more a propaganda tool for the fossil fuel industries than anything else.

https://www.climatecouncil.org.au/resources/what-is-carbon-capture-and-storage/
michael_dowling
Sea trials are currently underway presently for a HFC vessel,so perhaps we should just wait till they start to be incorporated into cargo vessels: https://www.marineinsight.com/shipping-news/worlds-first-commercial-vessel-powered-100-by-hydrogen-fuel-cell-begins-operational-trials/
TpPa
Carbon capture = nuclear waste storage from decades ago. It all comes back to haunt us an will escape one way or another. Then it will be on the news that the worlds largest CO2 storage facility sprung a major leak and over a billion tons of CO2 has leaked into the atmosphere --- SORRY --- Happens every time kind of like Japan's reactor that leaked & still is leaching into the ocean, for God's sake it shows up in fish across the ocean, but yup -- SORRY
TpPa
Towards Mark Govers comment. How about a 3 - 4' pipe under the water level that runs the ships length & within a turbines for generators