Trilateral Flash Cycle System - A High Efficiency Power Plant for Liquid Resources

Abstract

The Trilateral Flash Cycle (TFC) system is basically a binary power plant in which expansion starts from the saturated liquid rather than the saturated, superheated or supercritical vapour phase. By this means the transfer of heat from a liquid heat source to the working fluid is achieved with almost perfect temperature matching. are thereby minimised and hence, provided that the two-phase expansion process is efficient, its potential power recovery is 14 - 85% more than from ORC or flash steam systems. The preferred working fluids for it are light hydrocarbons. Extensive analytical and investigations shown that, contrary to the total flow experience, by correct design and working iluid choice, twin screw machines are most suitable for two-phase expansion. Thus adiabatic efficiencies of over 70% were obtained from a 25 experimental machine and values in excess of 80% are predicted for multi megawatt units if built with two stages. At higher temperatures, expansion to dry vapour is possible. The expander may then contain a final turbine stage. A detailed engineering design study of a TFC plant for power recovery from a Hot Dry Rock source has been carried out for the Department of Energy. This showed the fully installed cost for TFC plant to be $1700 per KW and $1300 per gross.