Development of a Centrifugal Hydrogen Pipeline Gas Compressor

Written by Francis A. Di Bella, PE and Dr. Colin Osborne of Concepts NREC - Tuesday, January 12 2010

The compressor selection uses six stages, each operating at 60,000 rpm with a tip speed of less than 2,100 ft/s. Each compressor, shown in Figure 4, is 8 inches in dia. and has an overall stage efficiency of between 79.5 and 81%, for an overall compressor efficiency of 80.6%.

Materials Selection Validation

The material chosen for the compressor is an aluminum alloy. The choice is based on its mechanical strength-to-density ratio or (S_yield/ρ), which can be shown to be a characteristic of the material’s ability to withstand centrifugal forces. Several grades of aluminum have a strength-to-density ratio that is similar to titanium and high strength steels at the 140°F (max) operating temperatures that will be experienced by the hydrogen compressor by providing intercoolers between each of the six stages. However, unlike titanium and most steels, aluminum is recognized by the industry as being very compatible with hydrogen, not showing any susceptibility for hydrogen embrittlement. Aluminum also helps to reduce the weight of the rotor, which leads to an improved rotor dynamic stability at the 60,000 operating speed. A rotor stability and critical speed analysis has confirmed that the overhung design is viable.

The project team includes researchers at Texas A&M (Dr. Hong Liang and Graduate Assistant Matt Sanders) who are collaborating with CN to confirm the viability of aluminum alloys for this compressor application. A Test Protocol has been established based on a series of discussions with notable researchers in several national laboratories including:

• Sandia National Labs (Fracture Mechanics Testing; Dr. Chris San Marchi)
• Savannah River National Labs (Specimen “Charging” with Hydrogen Plus Tensile Testing with H₂; Dr. Andrew Duncan)
• Argonne National Labs (Dr. George Fenske)