Development of a 1MWe RCG-unit

Abstract

The Rankine Compression Gas turbine (RCG) is a new type of combined steam and gas turbine (STaG). The novelty of the RCG is that all shaft power is delivered by a free power turbine that is driven by the expansion of the combustion gases. The compressed air used for combustion is fully produced by the steam turbine driven compressor. Therefore, the RCG offers flexible load characteristics that make it applicable in decentralized power generation, me- chanical drives and ship propulsion which are typically in the 1-10MW range. This thesis presents the three step plan that is executed to develop the RCG. First, a feasibility study is done, then, an experimental set-up is tested and, finally, a real-scale pilot installation of 1MWe is designed for a combined heat and power application. The feasibility is studied with a thermodynamical model. The results show that the RCG is technologically and economically feasible with robust radial turbomachinery components, such as a centrifugal turbo compressor, radial expansion turbine and an impulse steam turbine (zero-reaction turbine). To ensure a short start-up time, the RCG is designed with a subcritical once-through steam generator, which is not commercially available in the MW-range. Therefore, a subcritical once-through steam generator was especially designed. An experimental set-up at the Technische Universiteit Eindhoven(TU/e) shows that the chosen key components of the RCG-layout result in stable operation and a start-up time of about 15 minutes. In its intended fields of application, the RCG must have the ability to go from part-load to full-load within minutes. With a one-dimensional transient model, the transient behaviour of the system and the effect of possible actuators is simulated. The transient model may be used to develop an operating strategy of a real-scale RCG, since the behavior of the set-up and the model proved to be similar. An improved operating strategy is developed where the auxiliary burner is fired during transients (auxiliary burner overdrive) and an aircooler controls the steam temperature. This operating strategy reduces the response time to approximately 250 seconds. Next, a more advanced set-up was realized. The first aim was to gain experience with operating the RCG with industrial soft- and hardware. The second aim was to develop a start-up procedure, since the transient model can not simulate a start-up. The experiments show that the start-up procedure of the once-through steam generator needs special attention; without precautions, the steam temperature rises to a dangerous peak level before settling at a safe working point. This is solved with the aircooler, and experiments show that this ensures safe steam temperatures during a cold start. Finally, a 1MWe pilot installation was designed for a pilot project, a combined heat and power (CHP) application. The pilot was designed with the ability to run on crude (bio) fuels, more specifically glycerol, the waste product of biodiesel production. The pilot installation has an electrical efficiency of ??= 0.20 and will be available for investment costs of about 1 mln euro. This combination of performance and investment costs results in an estimated payback time of 2.6 years. It is therefore expected that it has the potential to become commercially successful.