High-speed Steam Turbine Systems for Distributed Generation Applications
2012 (English)In: Proceedings of the ASME 2012 Power Conference. Power 2012, ASME Press, 2012, 7- p.Conference paper (Refereed)
The efficiency of utilization of low-grade solid fuels of either renewable or fossil origin such as biomass, municipal or agricultural wastes, peat, lignite, etc. for distributed generation applications and combined heat and power (CHP) production at small scales can be improved by a simple technology shift. This study evaluates the technical feasibility of a compact power generation package comprising a small steam turbine directly coupled to a high-speed alternator delivering around 2 MW of electricity. Existing high-speed electrical generators at MW-scale are presented and reviewed, and a basic thermodynamic design and flow-path analysis of a steam turbine able to drive such a generator is attempted. Most importantly, the speed-controlled turbogenerator arrangement promises improved electrical efficiency especially at part-load (in off-design mode), compared to the typically low off-design performance of small-scale steam cycles using state-of-art fixed speed turbines. High-speed alternators with related power electronics are nowadays becoming increasingly available for the MW-size market. One such product – a commercial 2 MW permanent-magnet alternator running at 22,500 rpm – has been used as a reference for evaluating the behavior of a speed-controlled steam turbine as a prime mover. The specific turbine losses due to its comparatively small size remain serious. However, a low steam parameter approach suits well for converting, for example, heat-only boilers into CHP units, adding value by local electricity production at affordable costs. Steam superheat temperatures of around or less than 350 C (660 F) would keep the steam volumetric flow sufficiently high in order to restrain the turbine losses and allow for a cost-effective electricity production for enhanced utilization of locally-available solid fuels via steam cycles. Such a steam turbine is possible to manufacture and would deliver a promising performance despite its small size. The possibility for the turbine to be speed-controlled and its characteristics thereof have been evaluated by computer simulations using the in-house code AXIAL by courtesy of the Swedish branch of Siemens Industrial Turbomachinery, steam turbine division. Simulation results show that a reasonable improvement in part-load performance can be achieved for the high-rpm turbine-generator drivetrain: up to 30% better in the load spectrum down to 50% of nominal output, if compared with a fixed-speed arrangement of similar size and parameters.
Place, publisher, year, edition, pages
ASME Press, 2012. 7- p.
high-speed turbine, steam, high-speed generator, small-scale, distributed generation, CHP, biomass
IdentifiersURN: urn:nbn:se:kth:diva-89854OAI: oai:DiVA.org:kth-89854DiVA: diva2:503758
ASME 2012 POWER Conference, Anaheim CA, USA, July 30 - August 3, 2012