Portland State University. Department of Applied Science
Nan Teh Hsu
Date of Award
Master of Science (M.S.) in Applied Science
1 online resource (95 p.)
Two different problems of optimization in the utilization of geothermal energy are presented: First, the thermodynamic optimization for a geothermal power plant using a single- or double-flash process is considered; in this analysis, the optimum flash temperature giving the maximum power output is determined. Second, an economic optimization for space heating systems using geothermal energy is developed to obtain operating conditions for which the total (capital and operating) cost is a minimum.
Both graphical and analytical methods are used in the thermodynamic optimization to determine the optimum flash temperature. The graphical method is based on thermodynamic data provided by an i-s (enthalpy-entropy) diagram for water and steam, in the analytical method, first and second order approximations (first and second degree polynomial approximations), are used for the functions which express enthalpy differences in terms of flash temperature.
Numerical results are provided by computer programs developed for the analytical method. These results cover the temperature range normally encountered in practice. In the case of the single-flash cycle, results from both the graphical and analytical method using the first order approximation indicate the same optimum flash temperature; however, the correction factor resulting from the second order approximation improves the value of the temperature by a correction of about -2 ° C. Optimum flash temperatures for the double-flash cycle are similarly determined using the analytical method with a first order approximation.
In the economic optimization of space heating systems, the analysis is made on the basis of the annual total cost per unit area of wall surface. It takes into account the cost of the geothermal fluid, cost of wall insulation, and heat exchanger cost. For a specific case where the inlet temperature to the heat exchanger is at 100° C and the outlet temperature at 28° C, the minimum annual cost to maintain a space at 20°C with an outside temperature of -l0°C is given at $0.0257 per square meter of wall area while the optimum thickness for the wall insulation is 0. 126 meter.
Additional improvement in the optimization of flash temperature can be made by using a second order approximation method for the double-flash power cycle.
Hassoun, Talal Hussein, "Optimization of single- and double-flash cycles and space heating systems in geothermal engineering" (1974). Dissertations and Theses. Paper 1976.