Turboexpanders advance green-hydrogen liquefaction

Radial inflow turbines, or turboexpanders, have been used in hydrogen-rich applications in the petrochemical industry since the early 1960s. Turboexpander design for hydrogen is challenging due to high isentropic enthalpy drop across the stage, low discharge volume, and required high operating speeds. Hydrogen turboexpanders have unique aerodynamic and mechanical designs, including low-flow coefficient turboexpander wheels, high peripheral speeds, heat soak and thermal management, special materials, and non-contaminating sealing systems.

Expansion through a turboexpander is a near-isentropic process in which energy extracted from a working fluid is converted to mechanical work. This mechanical work is absorbed by a variety of devices, which are classified into two major categories: energy dissipating and energy recovery. Energy dissipating turboexpanders reject the produced work, typically in the form of heat. Energy recovery expanders in contrast convert the work to useful and free energy, often via a directly coupled booster compressor or generator. While turboexpander utility typically focuses on the energy extraction from the fluid (refrigeration), the free energy recovered by a loading mechanism can directly improve the specific power of a given process.

Decades of advancements in turboexpander technology means that green-hydrogen production via electrolysis is increasingly viable. As a result, the demand for turbomachines to carry out cryogenic hydrogen services is growing. Numerous hydrogen-rich turboexpanders designed and operating in the field have validated the evolution of the design process. With careful evaluation, these machines can be adapted and qualified for hydrogen liquefaction at all scales, and as a result contribute to the worldwide reduction of greenhouse gases.