Mohawk Innovative Technologies and VELO3D have collaborated to develop a solid oxide fuel cell (SOFC) technology, a promising new technology for energy preparation that has moved from the research stage to commercialization by reducing the price of anode exhaust gas recovery blowers by 60% with Velo3D.
Recently, according to Mohou.com, Mohawk Innovative Technologies and VELO3D have collaborated to develop a solid oxide fuel cell (SOFC) technology, a promising new technology for energy preparation, which has moved from the research stage to commercialization by reducing the price of anode exhaust gas recovery blowers by 60% with the help of Velo3D.
△Anode Exhaust Gas Recovery Blower
The U.S. Department of Energy (DOE) has been investing in SOFC for many years ($750 million since 1995 according to their website) as part of an ongoing effort to decarbonize energy production. The DOE describes SOFC as an electrochemical device that generates electricity directly from the oxidation of hydrocarbon fuels (usually natural gas) while eliminating the actual combustion step. Basically, a SOFC is like an indefinite battery that is constantly being recharged - without the need to burn the gas that charges it.
Small package, big energy output
Solid oxide fuel cells are very attractive because they produce a lot of energy in a very small package," said Dr. Jose Luis Cordova, vice president of engineering at Mohawk Innovative Technologies (MITI). Mohawk, a 28-year-old company based in Albany, New York, specializes in "clean technology" - the design of efficient, economical, oil-free turbomachinery products with low environmental impact, including renewable energy turbogenerators, oil-free turbocompressors/blowers and electric motors. said Jose Luis Cordova, "SOFCs are compact and can be built in a factory and then transported to the specific locations where they are needed to support distributed energy production. SOFCs are also very efficient. Unlike ordinary batteries, they don't lose power over time because you can continue the electrochemical reaction almost indefinitely as long as you provide the reagents."
ΔMohawk Innovative Technologies has partnered with Velo3D to 3D print fuel cell components to reduce costs (dramatically).
While more than 40,000 100 kW fuel cells (each capable of powering 50 homes) were shipped around the world in 2019, widespread adoption of the technology is limited by the high cost of manufacturing many SOFC parts and the rapid wear and tear of these parts due to exposure to the gases that make them operate so efficiently.
Facing cost and durability issues
To help overcome these challenges, Mohawk has designed some of these key components to last longer and work more efficiently. One prime example is the anode exhaust recovery blower (AORB) - a key component of the "balance of plant" (the machinery that supports the SOFC fuel stack).
Jose says, "During operation, each fuel cell uses only about 70 percent of its input gas. The remaining approximately 30% is discharged directly into the system along with water (the product of the electrochemical reaction). And you don't want to waste that remaining gas or water; you want to send it back to the beginning of the process. That's where the AORB comes in: it's basically a low-pressure compressor or fan that recovers the exhaust gas and sends it back to the front end of the fuel cell."
A typical 250 kW SOFC plant would use two of these, says Jose. the SOFC balance-of-plant designers thought this blower would be an off-the-shelf unit. However, conventional blowers are prone to corrosion and degradation because of the process gases in the system. The hydrogen in the mixture can attack the blower's alloys and can also damage the magnets and electrical components of the motor that powers the blower. Most blowers also contain lubricants, such as oil, that can also degrade. As a result, you end up with blowers that have very low reliability - a large portion of the balance-of-plant cost - and your SOFC plant requires an overhaul every two to four thousand hours. "
This statistic falls far short of the U.S. Department of Energy's goal of 40,000 hours of operating life for a typical SOFC and a reduction in installed costs from an average of $12,000/kW (kilowatt of electrical energy) to $900/kW.
Jose Luis Cordova said, "So we realized that Mohawk's proprietary oil-free compliant foil bearing (CFB) technology, specialized coatings and decades of turbomachinery expertise were a good fit for this challenge."
Additive manufacturing provides the answer
The U.S. Department of Energy grant provided Mohawk with the means to design and test an AORB prototype in a SOFC demonstration power plant operated by FuelCell Energy. Rigorous testing under realistic operating conditions measured durability and performance. The latest version showed no significant degradation in components or output, and completely eliminated any performance or reliability issues.
However, the cost of AORB remains prohibitively high. This is due in large part to its high-speed centrifugal impeller, which operates continuously under extreme mechanical and thermal stress. For maximum service life, the part must be made of expensive, high-strength, nickel-based, corrosion-resistant superalloy materials such as Inconel 718 or Haynes 282, which are difficult to machine or cast. Achieving optimal aerodynamic efficiency in the impeller requires complex three-dimensional geometry, which is a challenge for manufacturing. On top of that, due to the current nascent state of the SOFC market, the relatively small production quantities of impellers make economies of scale difficult to achieve.
As you can imagine, additive manufacturing offers a compelling answer to reducing production costs," said Jose Luis Cordova. While the initial project with FuelCell Energy continues to evolve, Mohawk is getting calls from R&D groups looking for help with their own fuel cell component designs. With many of these manufacturers and integrators still in the research phase, each had different operating conditions in mind. Using traditional manufacturing methods to make just the small amount of custom impellers or volutes they wanted would be very expensive. Therefore, we started looking at additive manufacturing. We researched additive manufacturing system manufacturers ourselves and contacted LPBF supplier Velo3D.
Collaboration in terms of capabilities
With its goal of reducing costs and improving SOFC performance, DOE is enthusiastic about innovative manufacturing methods such as additive manufacturing," says Jose Luis Cordova. Their funding (through the Small Business Industrial Research Program) supports our current collaboration with Velo3D, as well as our previous collaboration with FuelCell Energy. Another benefit is that this work is helping to advance 3D printing technology as a whole as we learn more and more about its capabilities and potential."
Matt Karesh, Mohawk Project Leader at Velo3D, said, "Working hand-in-hand with a company like Mohawk, who is willing to work with us and give us feedback, has driven our internal process parameters and capabilities forward and helped guide us on how to make our printing methods better. "
Cost-effectiveness of additive manufacturing
Our traditional, subtractively manufactured impellers were up to $15,000 to $19,000 per piece," says Jose Luis Cordova. When we use 3D printing, in small batches of about eight, rather than one at a time, that comes down to $500 to $600, which is a very significant cost reduction. In addition to cutting manufacturing costs, LPBF was a technology that was able to give us the design flexibility that we were looking for. Additive manufacturing is not limited by the number, angle or pitch of the impeller blades, all of which have a direct impact on aerodynamic efficiency. We now have the geometric precision we need to both achieve higher performance rotating turbine mechanical designs and reduce the associated manufacturing costs."
Selecting the perfect alloy
When 3D printing the impeller on the Velo3D Sapphire system (at Duncan Machine, a contract manufacturer in the Velo3D global network), the choice was made to use Inconel 718 - one of the nickel-based alloys that has high temperature tolerance and can best withstand the stress of rotation.
Inconel appealed to us because it is chemically inert enough and retains its mechanical properties at quite high temperatures, definitely more than aluminum or titanium," said Hannah Lea, mechanical engineer at Mohawk.
Although Velo3D had already certified Inconel 718 for their machine, Mohawk did additional material research to increase knowledge about the 3D printed version of the superalloy. Hannah Lea said, "Our testing showed that the mechanical properties of LPBF 3D printed Inconel 718, such as yield stress and creep tolerance, were higher than those of the cast material. This is more than adequate for high pressure centrifugal blower and compressor applications in the operating temperature range."
Iteration made easy
As the impeller work progressed, Mohawk engineers worked with Velo3D experts on design iterations, modifications and printing strategies. says Jose Luis Cordova, "It was really interesting because we didn't need to make any major design modifications to the original impeller we were using. With Velo3D's sapphire system, we can just print what we want. We did make some process adjustments and tweaks in terms of support structure considerations and surface finish modifications."
As the impeller project progressed, additive manufacturing provided a faster turnaround time than casting or milling because parts could be printed, evaluated, iterated, and printed again quickly. In subsequent 3D printing runs, multiple examples of the old and new impeller designs can be made simultaneously on the same build plate to compare results.
Due to the relatively small size of the impeller (60 mm in diameter), it was necessary for the team to develop a "sacrificial shroud" - a temporary printed housing that maintains the authenticity of the blade during fabrication.
Sacrificial shrouds and smoother surfaces
Velo3D's Matt Karesh says, "What's really interesting about this approach is that shrouded impellers are essentially unreachable for most current additive manufacturing technologies because they require all the traditional support structures." Instead of going unsupported, we're using a reduced support approach. mohawk says they don't end up needing the shroud, but the shroud would make their parts better, so they usually cut it off after attaching this thing that's usually extremely difficult to print. Using Velo3d's technology, they were able to build a one-off shroud on the impeller, get the wing and runner shape they wanted, and then it was a very simple machining operation to remove the shroud."
According to Mohawk engineer RochelleWooding, surface finish was another focus: "In our early iterations, the surface was a little rough. The interesting thing about the sacrificial shroud is that it provides us with a flow path through the blade, and we can use extrusion honing to correct the roughness. We needed to iterate further to determine how much material to add to the blade to achieve the blade thickness we wanted. The final surface finish we achieved was comparable to the cast part in terms of aerodynamically matching what we were aiming for."
Future testing, a look ahead
The next steps are to retrofit the AORB with the new impeller and test it under field conditions, says Jose Luis Cordova: "We expect that the successful execution of these two tasks will fully demonstrate that 3D printed Inconel parts supplied by LPBF technology are a viable and reliable alternative for manufacturing turbomachinery components. Work is already underway to manufacture other blower components, such as housings and volutes, using additive manufacturing technology.
Jose Luis Cordova concludes: "With these DOE-funded projects, we have been able to develop a library of common parts. Based on the initial idea, we now have at least three completely different platforms that can serve different power capabilities to support future advances in clean energy."
