Stainless Steel World Magazine March 2023 | Page 31

traditional blowers tend to corrode and degrade ; the hydrogen in the mixture attacks the alloys the blowers are made of and also damages the magnets and electrical components of the motors that power the blowers . Most blowers also contain lubricants , like oil , that degrade as well . So you end up with very low-reliability blowers – representing a significant portion of the balance-of-plant cost – and your SOFC plant needs an overhaul every two to four thousand hours .” This statistic falls far short of the DOE ’ s goal of an operating lifetime of 40,000 hours for a typical SOFC – as well as an installation-cost reduction from an average of USD 12,000 / kWe ( kilowatt of electrical energy ) to USD 900 / kWe . Time to rethink those blowers ! “ 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 ,” says Cordova . materials like Inconel 718 or Haynes 282 that are difficult to machine or cast . In addition , achieving optimal aerodynamic efficiency in an impeller requires complex three-dimensional geometries that are a challenge to manufacture . And because of the incipient nature of the current SOFC market , impellers are produced in relatively small batches , and economies of scale are difficult to realize . How to bring that cost down ? Additive manufacturing ( AM , aka 3D printing ) provided a compelling answer . While the original project with FuelCell Energy was evolving , Mohawk was also getting calls from R & D groups looking for help with their own fuelcell component designs . “ Because many of these manufacturers and integrators were still at the research stage , each one had a different operating condition in mind ,” says Cordova . “ Using traditional manufacturing , to make just the handful of the custom impeller wheels or volutes they wanted , would have been extremely expensive . So that ’ s where we started looking at AM ; we did our own research into AM system makers and connected with laserpowder-bed fusion ( LPBF ) provider Velo3D .”

Collaborating on capabilities With its goal of reducing costs and improving performance of SOFCs , the DOE is enthusiastic about innovative manufacturing methods such as AM , says Cordova . “ Their

Additive manufacturing offers answers DOE funding provided the means for Mohawk to design and test AORB prototypes in a demonstrator SOFC power plant run by FuelCell Energy . Rigorous testing under realistic operating conditions measured durability and performance , with the latest versions demonstrating no significant degradation in parts or output and complete elimination of any performance or reliability issues . Yet the cost of an AORB remained prohibitively high – in large part due to its high-speed centrifugal impeller , which operates continuously under extreme mechanical and thermal stress . For longest life , this part must be made from expensive , high-strength , nickelbased , corrosion-resistant superalloy

A 3D-printing trial build with multiple impeller designs for an AORB

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