Cryogenic Radial Turbine Design for High-Efficiency Hydrogen Liquefaction Plants

Abstract Meeting the rising global demand for liquefied hydrogen will require a scale-up of liquefaction infrastructure. Higher plant capacities increase the viability of novel cycles and components, which can achieve improved performance. It has been shown that switching the final hydrogen expansion from a Joule-Thomson valve to a radial turboexpander (sub-cooled liquid phase) in series with a Joule-Thomson valve (two-phase) increases both yield and efficiency. This paper describes the design of a prototype turboexpander from an aerodynamic, manufacturing and stress perspective. The aerodynamic design is performed using an extended version of the open-source turbomachinery design code turbigen. Using a radial turbine meanline code and geometry parameters, the annulus and blade geometry are sent to a RANS solver with real gas property tables from coolprop. This integrated process enables rapid investigation of the design space. Despite the challenging working fluid conditions, this paper shows that a conventional design methodology (developed for ideal gas radial turbines) can still be used, achieving an isentropic efficiency in excess of 90% for the baseline case. The aerodynamic design is then assessed against mechanical and manufacturability constraints. The design is modified by increasing blade thickness, by aft-loading, by adding fillets and by finding the optimum blade number. The stress analysis shows that this turbine, manufactured with cryogenic stainless steel A286, would be able to withstand the mechanical stresses. The final design is found to suffer from a 0.4% efficiency penalty compared to the baseline aerodynamic design. Incorporating the final turbine performance into a liquefaction cycle model confirms increases in yield of 10.7% and exergetic efficiency of 3.4% compared to the same cycle with a single Joule-Thomson valve expansion.