Georgia Tech researchers have demonstrated a CHAMP reactor, which uses the four-stroke engine cycle to create hydrogen while simultaneously capturing carbon dioxide emission. (Credit: Candler Hobbs, Georgia Tech)
An internal combustion engine is not treated as one when it is transformed into a modular reforming reactor capable of making hydrogen available to power fuel cells wherever there is a supply of natural gas.
A laboratory-scale hydrogen reforming system has been demonstrated by researchers through the addition of a hydrogen separating membrane, carbon dioxide sorbent and a catalyst to the century-old four-stroke engine cycle. The green fuel is produced by this system at relatively low temperature in a process that can be scaled up or down in order to meet particular requirements.
The process will possibly provide hydrogen at the point of use for neighborhood power plants or residential fuel cells, fueling municipal buses or other hydrogen-based vehicles, supplementing intermittent renewable energy sources such as photovoltaics, and electricity and power production in natural-gas powered vehicles.
The device, known as the CO
2/H 2 Active Membrane Piston (CHAMP) reactor, works at temperatures much lower than standard steam reforming processes, uses substantially less water and is also capable of working in other fuels such as bio-derived feedstock or methanol. Additionally, the device also captures and concentrates carbon dioxide emissions considered to be a by-product that currently lacks a secondary use even though that could change in the years to come.
Compared to standard engines that operate at thousands of revolutions per minute, the reactor works at only a few cycles per minute, and at times even more slowly, depending on the required rate of hydrogen production and reactor scale. Spark plugs are absent as no fuel is combusted.
We already have a nationwide natural gas distribution infrastructure, so it’s much better to produce hydrogen at the point of use rather than trying to distribute it. Our technology could produce this fuel of choice wherever natural gas is available, which could resolve one of the major challenges with the hydrogen economy.
Andrei Fedorov, Professor,
Georgia Institute of Technology
The February 9
th issue of the journal Industrial & Engineering Chemistry Research has published a paper explaining the operating model of the CHAMP process, including a significant step of internally adsorbing carbon dioxide, which is a byproduct of the methane reforming process, such that it can be concentrated and expelled from the reactor for utilization, storage or capture.
Three Georgia Tech Ph.D. graduates have reported other implementations of the system as thesis work since the commencement of the project in 2008. The research was supported by the U.S. Civilian Research & Development Foundation (CRDF Global), Department of Defense through NDSEG fellowships, and the National Science Foundation.
The variable volume provided by a piston rising and falling in a cylinder is considered to play a vital role in the reaction process. In standard engines, the flow of gases into and out of the reactor is controlled by a valve as the piston moves up and down. The four-stroke system works like this:
Steam and natural gas are brought into the reaction cylinder through a valve as the piston inside is lowered. After the piston reaches the bottom of the cylinder the valve closes.
The piston rises into the cylinder, compressing methane and steam as the reactor is heated. Catalytic reactions occur inside the reactor, generating carbon dioxide and hydrogen, once it reaches approximately 400 °C. The hydrogen leaves through a specific membrane, and this is followed by the sorbent material absorbing the pressurized carbon dioxide. This sorbent material is mixed with the catalyst.
The piston is lowered, decreasing the volume (and pressure) in the cylinder, after the hydrogen escapes from the reactor and carbon dioxide is tied up in the sorbent. The carbon dioxide is now made to enter the cylinder after being released from the sorbent.
The piston is now moved up for one more time into the chamber and the valve opens, driving out the carbon dioxide and clearing the reactor for the commencement of a new cycle.
All of the pieces of the puzzle have come together. The challenges ahead are primarily economic in nature. Our next step would be to build a pilot-scale CHAMP reactor.
Andrei Fedorov , Professor, Georgia Institute of Technology
The aim of this project is to address a few of the challenges involved in the use of hydrogen in fuel cells. Most of the hydrogen presently used is developed in a high-temperature reforming process in which methane is merged with steam at about 900 °C. As many as three water molecules will be needed by the industrial-scale process for every molecule of hydrogen, and the low density gas that is obtained must be transported to where it could be used.
Thermodynamic calculations were initially carried out by Fedorov’s lab and these calculations suggested that the four-stroke process could be altered to generate hydrogen in comparatively small amounts where it would be used.
The research aimed at developing a modular reforming process capable of operating at 400 °C and 500 °C, using only two molecules of water for each molecule of methane to develop four hydrogen molecules, scaling down to meet the particular requirements, and capturing the resulting carbon dioxide for potential sequestration or utilization.
We wanted to completely rethink how we designed reactor systems. To gain the kind of efficiency we needed, we realized we’d need to dynamically change the volume of the reactor vessel. We looked at existing mechanical systems that could do this, and realized that this capability could be found in a system that has had more than a century of improvements: the internal combustion engine.
Andrei Fedorov , Professor, Georgia Institute of Technology
Fedorov stated that it is possible to scale the CHAMP system up or down in order to develop the hundreds of kilograms of hydrogen per day essential for a typical automotive refueling station – or a few kilograms for a residential fuel cell or an individual vehicle.
It is also possible to adjust the piston speed and volume in the CHAMP reactor to meet hydrogen demands while simultaneously matching the requirements for the regeneration of carbon dioxide sorbent and separation efficiency of the hydrogen membrane. Practically, multiple reactors would probably be operated together to develop a constant stream of hydrogen at a specific production level.
“We took the conventional chemical processing plant and created an analog using the magnificent machinery of the internal combustion engine,” Fedorov said. “The reactor is scalable and modular, so you could have one module or a hundred of modules depending on how much hydrogen you needed. The processes for reforming fuel, purifying hydrogen and capturing carbon dioxide emission are all combined into one compact system.”
This publication is based on work supported by the National Science Foundation (NSF) CBET award 0928716, which was funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5), and by the National Science Foundation under Cooperative Agreement OISE- 9531011 and by award 61220 of the U.S. Civilian Research & Development Foundation (CRDF Global).