Global demands for petrochemicals and green-hydrogen usage are rising and expected to continue for at least the next decade. Green-hydrogen liquefiers are needed for the worldwide reduction of greenhouse gases and global commitments to net zero by 2050. Hydrogen is a long-term energy carrier and storage solution, and with renewable-energy costs shrinking overall, green-hydrogen production via electrolysis is increasingly becoming a viable solution. As a result, the demand for turbomachines to carry out cryogenic hydrogen services is growing.
Hydrogen is typically produced by SMR (steam methane reforming), with syngas (hydrogen and carbon monoxide) generated by the reaction of hydrocarbons with water. Hydrogen produced by SMR is considered “grey” when carbon dioxide is released to the atmosphere in the process. “Blue” hydrogen is similarly produced, only much of the waste carbon dioxide is captured to reduce its environmental impact. The future of hydrogen however is “green”, where hydrogen produced by electrolysis uses zero-carbon electricity sourced from renewables.
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.
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