Design and verification of a hermetic high-speed turbogenerator concept for biomass and waste heat recovery applications

Many waste heat recovery and biomass applications offer opportunities
for small-scale steam turbines to produce electricity and to improve
systems’ energy efficiency. However, the currently used axial
turbine-based technology is generally characterized by a relatively
large physical size and poor design and off-design performances. To
overcome these challenges, a new compact water-cooled high-speed radial
outflow turbine concept is proposed. While the previous understanding of
the chosen novel rotor water cooling approach indicates general system
feasibility, improved turbine performance, and good potential, the
scientific literature lacks relevant information. Since the design of
high-speed machines is always case-dependent, every concept must be
verified. Hence, to provide verification and new scientific information,
this study combines analytical, numerical, and experimental analyses.
The results predict turbine performance levels comparable with the
previous radial outflow design, and its efficiency was found to exceed
those of conventional turbines. During the experiments, the turbine also
produced electricity from poor-quality steam, and its rotor dynamic
behavior and magnetic bearing performance were close to the predicted
results. These findings are considered a verification of the proposed
concept. Furthermore, the rotor water cooling approach improved the
stability of the system operation and although its physical behavior was
not fully resolved, the study was able to verify its feasibility. In
addition, at below 200 € /kW, the turbogenerator costs are competitive against competing technologies.