The Need for Speed: Technical Options for Hydrogen Compressors

Abstract The use of Hydrogen as energy carrier is a key concept for carbon reduction. For most applications, hydrogen will have to be compressed, and the amount of hydrogen volume will require centrifugal compressors as the compressors of choice. Centrifugal compressors have been used in refineries for hydrogen compression for decades. However, unlike hydrogen in refinery applications, the hydrogen used as energy carrier will be relatively pure, and thus has a very low mole weight and a high heat capacity. Hydrogen as a light gas with a high heat capacity requires significantly more work (or enthalpy rise) to achieve a certain pressure ratio than other gases like natural gas or CO2. To achieve a sufficiently high pressure ratio with Hydrogen, one has the choice to either have a larger number of compressor stages, or to increase the tip speed of the impellers. A large number of stages may be commercially unattractive, although methods are suggested to reduce the impact. The increase in tip velocity increases the stress levels in the impeller. The paper discusses a number of methods to increase the work input per impeller while managing stress levels, including open face and closed face impellers, as well as material options. The study indicates the need for high tip speed as key to competitive hydrogen compressors. The resulting issues regarding materials, efficiency, and compressor architecture are addressed.