| Abstract |
It is shown that the Trilateral Flash Cycle (TFC) system approximates fairly closely to the ideal requirements for power recovery from liquid resources. A limitation, to this, which has hitherto prevented such a cycle being used in practice, is the lack of availability of suitable two-phase expanders for power outputs in excess of approximately 1 MWe. At resource temperatures in the range of 170 - 200oC, working fluids suitable for this cycle can perform the expansion process across the entire saturation envelope so that they start as high pressure saturated liquid and end at low pressure, as dry or even superheated vapour. Existing types of turboexpanders can then be used to produce high power outputs with good efficiencies by carrying out the expansion in two stages. In the first stage, the working fluid enters a radial inflow turbine, from which approximately one third of the output is recovered by two-phase expansion, and the working fluid leaves it 80% dry. The liquid can then be removed by a simple gravity separator and used to preheat the condensate. The separated dry vapour then enters a conventional turbine, of the axial or radial inflow type for the second stage of expansion, in which approximately two thirds of the power is recovered. Detailed numerical studies have shown that, this simple system, which requires only two heat exchangers and known components of proven efficiency, can recover approximately 60% of the ideal maximum power. |