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Q&A: Carbon voyage

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Researchers in the Penn State Department of Mechanical Engineering received a $2 million grant from the Navy Decarbonization Research Consortium to study shipboard carbon capture and alternative fuel utilization. The project is summarized in a Q&A with Associate Professor Brian Fronk. Credit: Kate Myers/Penn State. All Rights Reserved.

August 9, 2023

By Sarah Small

UNIVERSITY PARK, Pa. — The Navy Decarbonization Research Consortium is a public-private collaboration that aims to advance interdisciplinary research to help the U.S. Navy meet the complex challenges of platform decarbonization, with a focus on ships and aircraft, according to the consortium website. As part of this initiative, Penn State Associate Professor of Mechanical Engineering Brian Fronk and Professor of Mechanical Engineering Jacqueline O’Connor, have received a three-year, $2 million grant from the Office of Naval Research to develop a shipboard carbon-capture system for use with naval gas turbines. Penn State Distinguished Professor of Mechanical Engineering Adri van Duin will also assist with the research.

Below is a Q&A with Fronk detailing the planned research.

Q: What is carbon capture, and what are “e-fuels”?

Fronk: Carbon capture is the process of removing carbon dioxide, either directly from the atmosphere or from the exhaust of equipment, like gas turbines, that burn fuels containing carbon. The captured carbon can then be sequestered to prevent it from entering the atmosphere or recycled to produce new carbon-containing fuels that can be used in existing ships and engines.

Hydrocarbon fuels produced using electricity from renewable or nuclear sources are considered “e-fuels.” They are essentially synthetic versions of the liquid fossil fuels we are familiar with. These alternative fuels are energy-dense — the higher the density, the more energy can be stored and transported for the same volume — and yet have low net carbon emissions and can theoretically be produced anywhere.

Q: How does this apply to the U.S. Navy?

Fronk: In ship applications, the hydrogen feedstock for this fuel can be obtained from seawater through electrolysis, while the carbon dioxide feedstock could be captured via a shipboard system from the atmosphere, exhaust or also from seawater. Thus, it supports the Navy decarbonization mission while also offering a pathway to distributed production and utilization of alternative fuels, providing a logistical advantage.

A key thing to note, there is an energy penalty for capturing carbon, meaning it uses energy to power the equipment to do so, potentially contributing emissions depending on the energy source. However, there is less of a penalty if there’s more carbon to capture. Ships typically use gas turbine engines for power and propulsion, and it is less energy-intense to capture carbon from gas turbine exhaust, where carbon dioxide makes up approximately 5% to 15% of the exhaust, than directly from the atmosphere, where carbon dioxide typically makes up around 0.05%.

Q: How do you plan to capture the carbon from turbine exhaust?

Fronk: The most mature carbon-capture systems for land-based applications use chemical solutions to absorb carbon dioxide from the atmosphere or exhaust gas, but the use of chemical-based carbon capture on ships is not ideal due to health and safety concerns. In this project, we will separate the carbon dioxide by compressing, cooling and expanding the exhaust gas to directly produce frozen carbon dioxide — dry ice — from the exhaust stream. This system can be made compact, relatively simple to operate and integrated into existing and future naval ships.

To promote more efficient capture, we will also explore the use of exhaust gas recirculation (EGR), where a percentage of the exhaust gas is circulated back to the inlet to increase the concentration of carbon dioxide. This technology has been used in commercial truck and car engines for some time but has not been widely applied to gas turbines, although there is a lot of interest.

Q: What are goals of the project? Any broader applications?

Fronk: We are excited about our integrated approach to consider the complex problems of alternative fuel utilization, exhaust gas recirculation and carbon capture together. This has not been widely considered in open literature. Insights from this work can also be applied to the commercial maritime and land-based power system industry as they work towards decarbonization.

In addition to developing an exhaust gas carbon-capture system designed for shipboard operation, the team will conduct lab-scale combustion experiments with current and potential future fuels — with and without EGR — to understand how gas turbine performance may change. Simulations will also be conducted to understand the thermodynamic behavior of exhaust gas at the very low temperatures where carbon dioxide turns solid.

Our project also will have a workforce development component. Each summer, we may host several cadets from the U.S. Naval Academy to conduct research at Penn State, helping to train them on technology they may see in the future fleet.

College of Engineering Media Relations

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