The case for onboard carbon dioxide capture on long-range vehicles
Proposed method can be implemented based on existing technologies

Date:
August 18, 2021
Source:
Northwestern University
Summary:
A research team offers a practical way to make ships CO2 neutral
-- or even CO2 negative -- with CO2-capturing solid oxide fuel
cells. After 'burning' traditional carbon-based fuels, the fuel
cell generates concentrated CO2 that can be stored on-board the
ship. From there, the CO2 can either be sequestered or recycled
into a renewable hydrocarbon fuel.



FULL STORY ==========================================================================
When people talk about how to eliminate vehicles' carbon dioxide (CO2) emission, often the conversation often focuses on electrifying cars,
trucks and buses. Yet cargo and tanker ships, which are responsible for 3%
of all CO2emissions, are rarely a part of the discussion.


==========================================================================
Now a Northwestern University research team offers a practical way
to make ships CO2neutral -- or even CO2negative -- with CO2-capturing
solid oxide fuel cells. After "burning" traditional carbon-based fuels,
the fuel cell generates concentrated CO2that can be stored on-board the
ship. From there, the CO2can either be sequestered or recycled into a
renewable hydrocarbon fuel.

The team presents its analysis in "Viability of vehicles utilizing
on-board CO2capture," published today (Aug. 18) in the journal ACS Energy Letters. In the paper, the team looks at various factors, including fuel storage volumes and mass requirements for a wide range of vehicle classes
-- from light-duty passenger vehicles to tanker ships -- and compares
onboard CO2capture to battery electric and hydrogen fuel cell options.

"It might be harder for people to see onboard CO2capture as climate
friendly because it uses conventional, carbon-based fuels," said
Northwestern's Scott A.

Barnett, senior author of the study. "People tend to assume hydrogen
fuel cells and electric vehicles are more climate friendly. In reality,
they often are not. Electricity might come from burning coal, and
hydrogen is often produced by natural gas, which generates a lot of
CO2in the process." An expert on solid oxide fuel cells, Barnett is
a professor of materials science and engineering at Northwestern's
McCormick School of Engineering. He coauthored the paper with Travis
Schmauss, a Ph.D. candidate in his research group.

Why batteries aren't a viable solution Responsible for producing about
a gigaton of CO2each year, ships can consume up to 250 tons of fuel per
day. While it might seem tempting to replace this massive amount of fuel
with batteries, that's simply not an option.



========================================================================== "Some tanker ships require enough fuel to circumnavigate the globe as a
part of their regular multivoyage operation," Barnett said. "We calculated
that the battery pack for a long-range tanker would take up more room
than the storage capacity of the ship. A hydrogen fuel tank also would
be too large. When it comes to long-range vehicles, carbon-based fuel
combined with on-board CO2capture is arguably the best way to make these vehicles CO2neutral." The proposed method also has potential advantages
for shorter-range vehicles.

Battery electric and hydrogen fuel cells, however, are already being implemented for those vehicle types, so the researchers instead suggest implementing a CO2-neutral range extender.

Storage solution To store the CO2on board, Barnett's team has proposed
a patent-pending dual- chamber storage tank. One chamber stores a
carbon-based fuel. After the fuel cycles through the fuel cell to create energy, the CO2byproduct is pressurized and introduced into the second
chamber. The partition between the chambers can move -- shrinking the fuel chamber as the fuel is used, making space for CO2in the other chamber.

"The solid oxide fuel cell is critical because it burns the fuel with
pure oxygen, yielding a concentrated CO2product that is storable,"
Schmauss said.

"If we just burned the fuel with air, it would be heavily diluted
with nitrogen, yielding too much gas to store. When the concentrated
CO2is compressed, it can be stored in a volume not much larger than
that needed for the fuel, which saves space." "This technology really
doesn't have any major hurdles to making it work," Barnett added. "You
just have to replace the fuel tank with the double-chamber tank and
add CO2compressors. And, of course, the infrastructure eventually has
to be developed to off-load the CO2and either sequester or use it."
Moving toward net-zero With this scenario, the researchers say it is
possible to make long-range vehicles CO2negative. This is possible
with bio-fuels, such as ethanol, because the plants used to produce the
fuel have consumed CO2from the atmosphere. Then, after the vehicle has
used the fuel, the captured CO2is removed from the ship and sequestered underground or used in producing a renewable fuel. If a vehicle uses a
fossil fuel instead of a bio-fuel, then the resulting overall cycle is
closer to net-zero.

========================================================================== Story Source: Materials provided by Northwestern_University. Original
written by Amanda Morris. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Travis A. Schmauss, Scott A. Barnett. Viability of Vehicles
Utilizing On-
Board CO2 Capture. ACS Energy Letters, 2021; 3180 DOI: 10.1021/
acsenergylett.1c01426 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818153720.htm

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