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Georgia Tech team furthers four-stroke-cycle active-membrane piston reactor for enhanced SMR for H2 production

17 February 2017

Steam methane reforming is currently the primary pathway for hydrogen production worldwide. However, due to its high operating temperature and use of sequential units for the reaction stages, industrial SMR does not scale down well for distributed, point-of-use applications such as fuel cell vehicle refueling stations.

Seeking to develop an SMR system suited for such distributed applications, a team from Georgia Tech in 2014 proposed the sorption-enhanced CO2/H2 Active Membrane Piston reactor (CHAMP-SORB)—a variable-volume batch reactor for the production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. Now, in a paper published in the ACS journal Industrial & Engineering Chemistry Research, the team has developed a comprehensive analysis of the system, focused on understanding the heat/mass transfer and reaction/separation interactions to develop guidelines for scale-up.

Prior work has established the thermodynamic viability of the CHAMP-SORB concept to achieve 90% fuel conversion at 400 °C and 2:1 steam to carbon ratio, as well as demonstrated the performance enhancements enabled by incorporation of CO2 and H2 removal in the absence of transport-limitations using the bench-scale reactor prototype. However, as the reactor is scaled up to a realistic production size, consideration of heat and mass transfer effects become necessary to develop the strategy for a practical design of the CHAMP-SORB reactor.

In this paper we present a comprehensive transport-reaction model, which carefully considers all relevant heat and mass transfer processes and their interplay with reactions and separation in application to the CHAMP-SORB for low-temperature steam reforming of methane. The model, which includes thermal effects of reaction and sorption and incorporates the Maxwell-Stefan description of diffusion for multispecies mass transfer, is applied to the most important, H2 producing, compression step of the CHAMP-SORB cycle.

—Anderson et al. (2017)

The CHAMP-SORB device operates at temperatures much lower than conventional steam reforming processes, consumes substantially less water and could also operate on other fuels such as methanol or bio-derived feedstock. It also captures and concentrates carbon dioxide emissions, a by-product that now lacks a secondary use—although that could change in the future.

The reactor operates at only a few cycles per minute—or more slowly—depending on the reactor scale and required rate of hydrogen production.

Key to the reaction process is the variable volume provided by the piston rising and falling in a cylinder. As with a conventional engine, a valve controls the flow of gases into and out of the reactor as the piston moves up and down. The four-stroke system works like this:

  • Natural gas (methane) and steam are drawn into the reaction cylinder through a valve as the piston inside is lowered. The valve closes once the piston reaches the bottom of the cylinder.

  • The piston rises into the cylinder, compressing the steam and methane as the reactor is heated. Once it reaches approximately 400 ˚C, catalytic reactions take place inside the reactor, forming hydrogen and carbon dioxide. The hydrogen exits through a selective membrane, and the pressurized carbon dioxide is adsorbed by the sorbent material, which is mixed with the catalyst.

  • Once the hydrogen has exited the reactor and carbon dioxide is tied up in the sorbent, the piston is lowered, reducing the volume (and pressure) in the cylinder. The carbon dioxide is released from the sorbent into the cylinder.

  • The piston is again moved up into the chamber and the valve opens, expelling the concentrated carbon dioxide and clearing the reactor for the start of a new cycle.

Master.img-001
Schematic of CHAMP-SORB reactor cycle. The reactor utilizes four strokes per cycle: (a) retracting piston to fill the reactor, (b) extending piston to produce H2 via SMR at constant pressure and then opening valve to exhaust products, (c) retracting piston to desorb CO2, and (d) extending piston to desorb and produce a purified CO2 as the final product. Credit: ACS, Anderson et al. (2017). Click to enlarge.

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 G. Fedorov, a professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering

Fedorov’s lab first carried out thermodynamic calculations suggesting that the four-stroke process could be modified to produce hydrogen in relatively small amounts where it would be used. The goals of the research were to create a modular reforming process that could operate at between 400 and 500 degrees Celsius, use just two molecules of water for every molecule of methane to produce four hydrogen molecules, be able to scale down to meet the specific needs, and capture the resulting carbon dioxide for potential utilization or sequestration.

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 G. Fedorov

The CHAMP system could be scaled up or down to produce the hundreds of kilograms of hydrogen per day required for a typical automotive refueling station, or a few kilograms for an individual vehicle or residential fuel cell, Fedorov said. The volume and piston speed in the CHAMP reactor can be adjusted to meet hydrogen demands while matching the requirements for the carbon dioxide sorbent regeneration and separation efficiency of the hydrogen membrane. In practical use, multiple reactors would likely be operated together to produce a continuous stream of hydrogen at a desired production level.

We took the conventional chemical processing plant and created an analog using the magnificent machinery of the internal combustion engine. 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.

—Andrei G. Fedorov

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 award 61220 of the U.S. Civilian Research & Development Foundation (CRDF Global) and by the National Science Foundation under Cooperative Agreement OISE- 9531011. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of NSF or CRDF Global. Graduate work of David M. Anderson, the first author on the paper, was conducted with government support under an award by the DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a.

Resources

  • David M. Anderson, Thomas M. Yun, Peter A. Kottke and Andrei G. Fedorov (2017) “Comprehensive Analysis of Sorption Enhanced Steam Methane Reforming in a Variable Volume Membrane Reactor,” Industrial & Engineering Chemistry Research doi: 10.1021/acs.iecr.6b04392

  • Anderson, D. M.; Kottke, P. A.; Fedorov, A. G. (2014) “Thermodynamic Analysis of Hydrogen Production Via Sorption-Enhanced Steam Methane Reforming in a New Class of Variable Volume Batch-Membrane Reactor” Int. J. Hydrogen Energy 39, 17985 doi: 10.1016/j.ijhydene.2014.03.127

February 17, 2017 in Hydrogen, Hydrogen Production, Natural Gas | Permalink | Comments (9)

Comments

What will they do with the captured CO2?

I'm not sure what the point is.

NG is already reformed in current fuel cells:

'To generate electricity, an ene-farm pumps natural gas from a local utility into its fuel cell, which uses a processor to extract the hydrogen and mix it with oxygen from the surrounding air. The reactions produce enough power to cover about half the demand of an average family, Tokyo Gas says, and the byproduct is excess heat that can supply a home with hot water. Toshiba estimates that its ene-farms can cut a home’s carbon dioxide footprint in half. Tokyo Gas estimates that ene-farms save a household about $400 to $500 a year on their power and heat bills.'


https://www.bloomberg.com/news/articles/2015-01-15/fuel-cells-for-homes-japanese-companies-pitch-clean-energy

SOEC stacks take water/electricity in then can produce hydrogen/oxygen at fuel stations, get the heat from an SOFC and electricity from wind contracts, sell the oxygen to reduce costs.

SOFCs take in natural gas then produce electricity/water/CO, hydrogen and CO can make any liquid fuel you want. That way the CO is used twice and you can get biomethane from landfill and water treatment.

Still produces the hydrogen by burning carbon...not a good process. Electrolysis from solar and wind and water is the winner, if you must have hydrogen.

Today 95% of H2 production is by Fossil Fuel Steam Reformation, predominately Steam Methane Reformation (SMR). However this is a high temperature (up to 900 degrees C) large scale process.
The Tokyo Gas System does use an SMR with Selective Oxidation Catalyst @ 650 degrees Centigrade (Ga Tech is at 400 degrees). See http://www.tokyo-gas.co.jp/techno/english/menu3/3_index_detail.html. Also, it does not have Carbon Capture, though it is a Combined Heat and Power System.
The Ga Tech SMR Process appears to use a K2CO3-promoted hydrotalcite material as the CO2 sorbent. The adsorbent can be regenerated or reused (reference: http://pubs.acs.org/doi/suppl/10.1021/acs.iecr.6b04392).
Linde Engineering has solutions for handling CO2 Removal and could partner for sequestering or reusing the CO2.

The Ga Tech SMR Process looks like a possible solution to a distributed H2 system that could either efficiently supply FCEV at a cost half that of Electrolysis systems or produce distributed FC electricity to backup Renewable Electric Generation. It would also be virtually CO2 free and could provide Carbon Capture (CCS) at a cost significantly less than Coal CCS or other large scale CCS systems.

Lad,
It is bio carbon from renewable methane, you use it once to get electricity and heat, then use it twice to make renewable fuel.
Don't be so absolute, think outside the box.

More here:
http://newenergyandfuel.com/http:/newenergyandfuel/com/2017/02/21/the-engine-that-makes-hydrogen-fuel-from-natural-gas/

I've re-thought this.

It should be way better than high temperature steam reforming as it is presumably more efficient being lower temperature, able to be sited right on the forecourt and with a highly recoverable and reusable waste stream.

Sell lots of carbonated soda in the filling station shop, and its job done! ;-0

The conversion requires heat and pressure, if you are getting the pressure from a piston that takes energy. Steam provides its own pressure and heat, thus Steam Reforming is the most prevalent method.

Where will the energy come from to run this? It occurred to me that an obscure nuclear reactor concept called CAESAR would do. This uses compressed and decompressed steam to moderate neutrons. Apparently it could exploit enough delayed neutrons to a)allow spent nuclear fuel to provide meaningful quantities of neutrons within a small space in a given time, and b)cause meaningful increased fission of this fuel before a critical mass explosion occurs.

But I have found no proposals on how to harness the energy of this intermittently expanded steam. There, now you have one.

Note, the stoichiometric increase of the reactants sustains the piston mechanically. But I think some variation of a Wankel type rotary engine would be mechanically more efficient and expose less lubricant to the reaction chemistry.

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