During the optimization studies of a 10-MWe (net) OTEC power system the ammonia turbine design study led to selection of a four-stage, double-flow axial turbine yielding 89.6 percent efficiency at 1800 rpm. To maximize power at off-nominal conditions, variable nozzles are used for the first stage. The turbine is directly connected to a four-pole, 60-Hz synchronous generator having 97.2 percent efficiency. This study was limited to state-of-the-art hardware designs for axial- and radial-flow turbines, single- and double-flow designs, and variations in the base diameter and number of turbine stages. The gasdynamic calculation procedure and the effects of the turbine generator control scheme, turbine blade design, materials (annealed AISI Type 403 steel is chosen for the blading), and seals and bearings are addressed in this paper. The estimated mass-production cost of the turbine-generator set is approximately $150/kWe at 10-MWe (net) size in 1979 dollars. Single-flow-axial and radial-inflow turbines would have lower performance without sufficiently lower cost to be cost-effective, since each percentage point of turbine efficiency is estimated to be worth 17 to $28/kWe.

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