Thermodynamic analysis of geothermal power systems employing separating expanders

A thermodynamic analysis was performed in order to study the possibility of upgrading the thermodynamic performance of a direct-steam geothermal power plant through the use of a separating expander which produces work while achieving effective separation of the two phases. One such device is the Biphase rotary separator. Preliminary testing of this device demonstrated that the isentropic efficiency is about 34% and that the separation efficiency is greater than 99.5%. The analysis indicates that separating expanders can provide a marked thermodynamic improvement over the flash tank arrangement. The analysis shows that even with relatively inefficient separators similar to the prototype tested an improvement of 18 to 21% is possible depending on the initial temperature of the liquid (the improvement is greater for low initial temperature). If the efficiency of the separating expanders can be upgraded from 30% to 50%, single stage systems can produce from 35% (T/sub i/ = 250/sup 0/C) to 52% (T/sub l/ = 150/sup 0/C) more work than the equivalent single-flash systems. On the other hand, with the same level of expander efficiency, the two-stage system reflects a 26% advantage over the equivalent dual-flash system. It should be noted, however, that the optimum intermediate temperatures exhibit amore » pronounced dependence on the efficiency of the expanders. It is also noted that the Biphase device is not the only one that can achieve separation of the phases while producing work. The same functions may be performed by a combination of a total flow expander and a conventional separator. (JGB)« less