The predictions for exhaust quality were within 0.4% of the measured values. Efficiency predictions were in error by as much as 5% of the measured values. Predictions of efficiency reflected the combined errors in prediction of power and mass flow rate. For most conditions, predictions of power were within 3.3% of the measured values. Mass flow rates werre predicted to within 2.7% of the measured values. The predictive ability observed during validation of the model is adequate for use in modeling of hybrid geothermal energy conversion systems. These explicit equations were combined with a steam table subroutine to produce a computer model for prediction of mass more » flow rate, power, efficiency and exhaust quality at a given set of operating conditions. Statistical curve fitting methods were adapted to produce equations for mass flow rate and power output in terms of the three variables associated with the data matrix. The inlet quality, engine speed and pressure ratio were independently varied to produce a three-dimensional data matrix of 104 data points. Testing of a Lysholm helical screw expander having a rotor diameter of 5.12 inches and an expansion ratio of 5.3 was performed with simulated geothermal fluid at an inlet pressure of 120 psia. The HSE was found to be a rugged energy conversion machine for geothermal applications, but some subsystems were found to require further development. A comparison with a 1-MW back-pressure turbine showed that the HSE can compete more » favorably under certain conditions. Improvements in machine efficiency of 3.5 to 4 percentage points were observed over some test periods with some scale deposition. The HSE was designed with oversized internal clearances in the expectation that adherent scale would form during operation.
For most operations efficiency increased approximately logarithmically with shaft power, while inlet quality and rotor speed had only small effects.
Typical machine efficiencies of 40 to 50% were calculated. The range of conditions under which the HSE was tested included loads up to 933 kW, mass flowrates of 14,600 to 395, 000 lbs/hr, inlet pressures of 64 to 220 psia, inlet qualities of 0 to 100%, exhaust pressures of 3.1 to 40 psia, total dissolved solids up to 310,000 ppM, and noncondensible gases up to 38% of the vapor mass flow. The objectives were to provide data on the reliability and performance of the HSE and to assess the costs and benefits of its use. A 1-MW geothermal wellhead power plant incorporating a Lysholm or helical screw expander (HSE) was field tested between 19 by Mexico, Italy, and New Zealand with technical assistance from the United States.
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