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

Abstract

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.