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Comparison of Geothermal Power Conversion Cycles

Description: Geothermal power conversion cycles are compared with respect to recovery of the available wellhead power. The cycles compared are flash steam, in which steam turbines are driven by steam separated from one or more flash states; binary, in which heat is transferred from flashed steam to an organic turbine cycle; and dual steam, in which two-phase expanders are driven by the flashing steam-brine mixture and steam turbines by the separated steam. Expander efficiencies assumed are 0.7 for steam turbines, 0.8 for organic turbines, and 0.6 for two-phase expanders. The fraction of available wellhead power delivered by each cycle is found to be about the same at all brine temperatures: 0.65 with one stage and 0.7 with four stages for dual stream; 0.4 with one stage and 0.6 with four stages for flash steam; 0.5 for binary; and 0.3 with one stage and 0.5 with four stages for flash binary.
Date: December 1, 1976
Creator: Elliott, David G.
Partner: UNT Libraries Government Documents Department

Preliminary assessment of the velocity pump reaction turbine as a geothermal total-flow expander

Description: A preliminary evaluation was made of the Velocity Pump Reaction Turbine (VPRT) as a total flow expander in a geothermal-electric conversion cycle. Values of geofluid effectiveness of VPRT systems were estimated for conditions consisting of: a 360/sup 0/ geothermal resource, 60/sup 0/F wet-bulb ambient temperature, zero and 0.003 mass concentrations of dissolved noncondensible gas in the geofluid, 100 and 120/sup 0/F condensing temperatures, and engine efficiencies ranging from 0.4 to 1.0. Achievable engine efficiencies were estimated to range from 0.47 to 0.77, with plant geofluid effectiveness values ranging as high as 9.5 Watt hr/lbm geofluid for the 360/sup 0/F resource temperature. This value is competitive with magnitudes of geofluid effectiveness projected for advanced binary plants, and is on the order of 40% higher than estimates for dual-flash steam and other total flow systems reviewed. Because of its potentially high performance and relative simplicity, the VPRT system appears to warrant further investigation toward its use in a well-head geothermal plant.
Date: June 1, 1984
Creator: Demuth, O.J.
Partner: UNT Libraries Government Documents Department

Analysis of a radial-outflow reaction turbine concept for geothermal application

Description: The radial-outflow reaction turbine, a pure-reaction turbine designed to improve the conversion efficiency of geothermal energy into electrical power is described. It also has potential as a total-flow turbine for low-temperature water. The principle of incomplete expansion can be used to obtain a reduction in turbine size when the turbine exhausts into a low-pressure condenser. And, by adding this turbine to single- and two-stage flashed-steam systems, the conversion efficiency of systems utilizing low- and high-energy wellhead sources, respectively can be improved. The Appendix outlines the analysis of the radial-outflow reaction turbine and leads to an expression for engine efficiency.
Date: May 25, 1978
Creator: House, P.A.
Partner: UNT Libraries Government Documents Department

Empirical modeling of a Lysholm helical screw expander

Description: 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 inlet quality, engine speed and pressure ratio were independently varied to produce a three-dimensional data matrix of 104 data points. 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. These explicit equations were combined with a steam table subroutine to produce a computer model for prediction of mass flow rate, power, efficiency and exhaust quality at a given set of operating conditions. The predictive ability observed during validation of the model is adequate for use in modeling of hybrid geothermal energy conversion systems. Mass flow rates werre predicted to within 2.7% of the measured values. For most conditions, predictions of power were within 3.3% of the measured values. Predictions of efficiency reflected the combined errors in prediction of power and mass flow rate. Efficiency predictions were in error by as much as 5% of the measured values. The predictions for exhaust quality were within 0.4% of the measured values. Isentropic engine efficiencies of over 43% were measured during the tests. An observed peak in efficiency represented an optimum pressure ratio and a trade-off between lower leakage fractions at high speeds and low inlet qualities, increasing frictional losses at high speeds, and increasing fluid and power densities at low qualities.
Date: January 1, 1984
Creator: Brown, K.A.
Partner: UNT Libraries Government Documents Department

Thermodynamic analysis of geothermal power systems employing separating expanders

Description: 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 a 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)
Date: January 1, 1978
Creator: Khalifa, H.E. & Michaelides, E.
Partner: UNT Libraries Government Documents Department

Hybrid staging of a Lysholm positive displacement engine with two Westinghouse two stage impulse Curtis turbines

Description: The University of California at Berkeley has tested and modeled satisfactorly a hybrid staged Lysholm engine (positive displacement) with a two stage Curtis wheel turbine. The system operates in a stable manner over its operating range (0/1-3/1 water ratio, 120 psia input). Proposals are made for controlling interstage pressure with a partial admission turbine and volume expansion to control mass flow and pressure ratio for the Lysholm engine.
Date: June 1, 1982
Creator: Parker, D.A.
Partner: UNT Libraries Government Documents Department

Conceptual design of a 10MW regenerative isobutane geothermal power plant. Technical report No. 18

Description: At present, there are basically three different systems for converting energy in geothermal fluid into power: vapor-flashing system, total flow system, and binary system. A comparison of the power production processes was made on the basis of work output in Kwh per 1000 pounds of geothermal fluid for self flowing wells with wellhead pressure of 100 psia and for wells with downhole pumps. For simplicity, the assumptions were made that the enthalpy of the geothermal fluid in the reservoir is approximately equal to that at the wellhead, that the thermodynamic properties of geothermal fluid may be approximated by those of water, and that the pressure effects on the properties of fluid are negligible. The results showed that the performance of the two-stage vapor-flashing system is not appreciably improved by using a downhole pump. The total flow system is simple, but its success depends mainly on the development of a reliable machine with sufficiently high thermal efficiency. The regenerative isobutane system is impractical, if the geothermal fluid temperature is below 380/sup 0/F. But, when the brine temperatures range from 485 to 600/sup 0/F, the regenerative isobutane system with downhole pump exhibits superior performance as compared to two-stage vapor-flashing system, basic isobutane system, or total flow system.
Date: October 15, 1976
Creator: Gupta, A.K. & Chou, J.C.S.
Partner: UNT Libraries Government Documents Department

Performance characteristics of the Lysholm engine

Description: The performance of a 5 in. diameter rotor Lysholm engine prototype running on simulated geothermal flows from 16 to 100% quality is described. Staging was performed with conventional Westinghouse 25 kW steam turbines demonstrating that such a process is feasible. Maximum efficiency and power noted were 37.2% and 26.3 kW respectively, but inhibiting factors were discovered which, upon correction, should allow efficiencies around 50% and powers up to 35 kW. Larger engines with minor modifications should get better efficiencies. Data was taken for inlet pressures of 75 to 120 psia and speeds of 3000 to 9000 rpm's. Further testing under similar conditions is planned.
Date: January 1, 1980
Creator: Berger, R.E.
Partner: UNT Libraries Government Documents Department

Definition of requirements for geothermal power conversion system studies

Description: Candidate power conversion systems and criteria for comparing these systems are listed. The elements of each conceptual design and standard approaches to equipment design are described. The methods used to calculate heat and mass balances and the data used in the calculations are described. The method used in developing the economics of each system is described and factors such as construction wage rates common to all systems are included. Standard methods for developing the conceptual designs and corresponding economics are defined so that the results of each system study can be readily compared to those of the others. The candidate conversion systems are: multistage flash/binary; two stage flash with scrubbing; total flow; multistage flash/direct contact (Bechtel patented process); four stage flash/binary; binary with direct contact heat exchangers; hybrid-flash/binary; hybrid-flash/total flow; and flash/dual cycle binary. (MHR)
Date: June 30, 1977
Partner: UNT Libraries Government Documents Department

Numerical study of boundary layer injection as a scale control method

Description: A boundary layer injection method of controlling scale-buildup in geothermal two-phase flow nozzles is studied. The object of this study is to set an upper limit on the ratio of the injected mass flow rate to the free stream mass flow rate that is necessary to isolate the scale carrying free stream flow from the nozzle wall. In order to develop a numerical model of the boundary layer flow, assumptions are made which reduce the results to order of magnitude approximations. Two configurations of nozzles with various injection flow rates are tried. It is found by numerical experiment that a nozzle with injection through a 1 mm thick ring near the inlet, is more efficient at isolating the free stream than a porous nozzle. A mass flow rate ratio of 0.173% was necessary to achieve this effect. It may be concluded that an upper limit on the mass flow rate ratio is about 2.0% with injection through a ring near the inlet, and that boundary layer injection is a reasonable method of controlling scale-buildup. A glossary of variables, program documentation and listings are presented for programs GMD15SR8, TRACK11, and TRACK12.
Date: September 26, 1975
Creator: Feiereisen, W.
Partner: UNT Libraries Government Documents Department

Unalaska geothermal exploration project. Electrical power generation analysis. Final report

Description: The objective of this study was to determine the most cost-effective power cycle for utilizing the Makushin Volcano geothermal resource to generate electricity for the towns of Unalaska and Dutch Harbor. It is anticipated that the geothermal power plant would be intertied with a planned conventional power plant consisting of four 2.5 MW diesel-generators whose commercial operation is due to begin in 1987. Upon its completion in late 1988, the geothermal power plant would primarily fulfill base-load electrical power demand while the diesel-generators would provide peak-load electrical power and emergency power at times when the geothermal power plant would be partially or completely unavailable. This study compares the technical, environmental, and economic adequacy of five state-of-the-art geothermal power conversion processes. Options considered are single- and double-flash steam cycles, binary cycle, hybrid cycle, and total flow cycle.
Date: April 1, 1984
Partner: UNT Libraries Government Documents Department

The effect of expansion-ratio limitations on positive-displacement, total-flow geothermal power systems

Description: Combined steam-turbine/positive-displacement engine (PDE) geothermal power systems are analyzed thermodynamically and compared with optimized reference flash-steam plants. Three different configurations of combined systems are considered. Treated separately are the cases of self-flowing and pumped wells. Two strategies are investigated that help overcome the inherent expansion-ratio limitation of PDE's: pre-flashing and pre-mixing. Parametrically-obtained results show the required minimum PDE efficiency for the combined system to match the reference plant for various sets of design conditions.
Date: February 1, 1982
Creator: DiPippo, R.
Partner: UNT Libraries Government Documents Department

Investigation of clean water test sites for prototype turbomachinery. [Two-phase impulse expander]

Description: Expanded development of total-flow expander technology in order to obtain efficient energy extraction from the liquid flow component of the geothermal well flow, in addition to steam enthalpy conversion, has been undertaken by the University of California, Lawrence Livermore Laboratory (LLL). The flow conditions necessary for this type of complete system performance characterization are beyond the capabilities of the test facility utilized in the preliminary tests at the LLL hot-water test facility. As an alternative to increasing the existing facility to meet the expanded test requirements, test facilities in the industrial California community are being surveyed to assess their capability in supporting future tests of the LLL expander. Biphase Engines, Inc. of Santa Monica, California was contracted by LLL to perform this survey. The goal of the Biphase Engines survey is to identify organizations with, first, an interest in supporting the LLL turbine test program and, second, to review their test capabilities with respect to the turbine test requirements. The results of the survey are described in the following sections which includes a listing of all organizations contacted. The responses to all inquiries are given. The affirmative responses to the test-support requirement are detailed with a description of the test facility, range of operating conditions, facility modifications and auxiliary equipment required and costs thereof, and testing schedule costs. (JGB)
Date: January 5, 1978
Creator: Cerini, D.J.
Partner: UNT Libraries Government Documents Department

Design considerations for a two-phase turbine

Description: A two-phase turbine, using a low-quality steam-water mixture as a working fluid, was designed, built, and tested in the laboratory. Two-phase fluids are found naturally in most geothermal fields throughout the world and can also be used in the conversion of waste heat from industrial sources. The thermodynamic and fluid-dynamic properties of such fluid mixtures are reviewed, with specific reference to the selection and design of an appropriate expander. Various types of practically realizable expanders are considered, and the choice of a single-stage, axial-flow, impulse turbine is explained. Also the basic design parameters, including sizing and blade and nozzle geometry, are described.
Date: May 25, 1978
Creator: Comfort, W.J. III & Beadle, C.W.
Partner: UNT Libraries Government Documents Department

Light scattering technique for determining droplet size distributions in two-phase liquid-dominated nozzle jets

Description: A method for determining the droplet size distribution from measurements of the scattered light intensity in the forward scattering lobe was developed for two-phase, single-component, liquid-dominated nozzle jet flows containing small droplets (dia < 10 ..mu..m for visible light wavelengths). The technique is based upon matching the measured scattered light intensity profile with a summation of the intensity contributions of a series of appropriately spaced narrow band size distributions. A numerical optimization technique is used to determine the strengths of the individual bands which yields the best agreement with the measured scattered light intensity profile. The narrow band intensity contributions are calculated using Mie scattering theory which is accurate for small multiparticle light scattering. Application of the technique to the determination of the droplet size distribution (Sauter mean dia near 1.8 ..mu..m) in a low quality steam-water nozzle jet is described. The purpose of the research is to be able to evaluate particular nozzle designs.
Date: January 1, 1978
Creator: Alger, T.W. & Giedt, W.H.
Partner: UNT Libraries Government Documents Department