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Title: Waste heat rejection from geothermal power stations

Abstract

This study of waste heat rejection from geothermal power stations is concerned only with the heat rejected from the power cycle. The heat contained in reinjected or otherwise discharged geothermal fluids is not included with the waste heat considered here. The heat contained in the underflow from the flashtanks in such systems is not considered as part of the heat rejected from the power cycle. By following this definition of the waste heat to be rejected, various methods of waste heat dissipation are discussed without regard for the particular arrangement to obtain heat from the geothermal source. Recent conceptual design studies made for 50-MW(e) geothermal power stations at Heber and Niland, California, are of particular interst. The former uses a flashed-steam system and the latter a binary cycle that uses isopentane. In last-quarter 1976 dollars, the total estimated capital costs were about $750/kW and production costs about 50 mills/kWhr. If wet/dry towers were used to conserve 50% of the water evaporation at Heber, production costs would be about 65 mills/kWhr.

Authors:
Publication Date:
Research Org.:
Oak Ridge National Lab., TN (USA)
OSTI Identifier:
6765926
Alternate Identifier(s):
OSTI ID: 6765926
Report Number(s):
ORNL/TM-6533
DOE Contract Number:
W-7405-ENG-26
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; CONDENSERS; OPERATION; COOLING SYSTEMS; GEOTHERMAL POWER PLANTS; WASTE HEAT; BINARY-FLUID SYSTEMS; CONDENSER COOLING SYSTEMS; COOLING PONDS; COOLING TOWERS; COST; EFFICIENCY; FLASHED STEAM SYSTEMS; GEOTHERMAL FLUIDS; HEAT TRANSFER; HEBER GEOTHERMAL FIELD; MATERIALS; RANKINE CYCLE; SALTON SEA GEOTHERMAL FIELD; AUXILIARY SYSTEMS; AUXILIARY WATER SYSTEMS; ENERGY; ENERGY SOURCES; ENERGY TRANSFER; FLUIDS; GEOTHERMAL FIELDS; HEAT; PONDS; POWER PLANTS; SURFACE WATERS; THERMAL POWER PLANTS; THERMODYNAMIC CYCLES; WASTES; WATER RESERVOIRS Geothermal Legacy 150802* -- Geothermal Power Plants-- Power Plant Systems & Components

Citation Formats

Robertson, R.C. Waste heat rejection from geothermal power stations. United States: N. p., 1978. Web. doi:10.2172/6765926.
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Robertson, R.C. Waste heat rejection from geothermal power stations. United States. doi:10.2172/6765926.
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Robertson, R.C. Fri . "Waste heat rejection from geothermal power stations". United States. doi:10.2172/6765926. https://www.osti.gov/servlets/purl/6765926.
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@article{osti_6765926,
title = {Waste heat rejection from geothermal power stations},
author = {Robertson, R.C.},
abstractNote = {This study of waste heat rejection from geothermal power stations is concerned only with the heat rejected from the power cycle. The heat contained in reinjected or otherwise discharged geothermal fluids is not included with the waste heat considered here. The heat contained in the underflow from the flashtanks in such systems is not considered as part of the heat rejected from the power cycle. By following this definition of the waste heat to be rejected, various methods of waste heat dissipation are discussed without regard for the particular arrangement to obtain heat from the geothermal source. Recent conceptual design studies made for 50-MW(e) geothermal power stations at Heber and Niland, California, are of particular interst. The former uses a flashed-steam system and the latter a binary cycle that uses isopentane. In last-quarter 1976 dollars, the total estimated capital costs were about $750/kW and production costs about 50 mills/kWhr. If wet/dry towers were used to conserve 50% of the water evaporation at Heber, production costs would be about 65 mills/kWhr.},
doi = {10.2172/6765926},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Dec 01 00:00:00 EST 1978},
month = {Fri Dec 01 00:00:00 EST 1978}
}
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Technical Report:
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DOI:  10.2172/6765926
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  • Waste heat rejection systems for geothermal power stations have a significantly greater influence on plant operating performances and costs than do corresponding systems in fossil- and nuclear-fueled stations. With thermal efficiencies of only about 10%, geothermal power cycles can reject four times as much heat per kilowatt of output. Geothermal sites in the United States tend to be in water-short areas that could require use of more expensive wet/dry or dry-type cooling towers. With relatively low-temperature heat sources, the cycle economics are more sensitive to diurnal and seasonal variations in sink temperatures. Factors such as the necessity for hydrogen sulfidemore » scrubbers in off-gas systems or the need to treat cooling tower blowdown before reinjection can add to the cost and complexity of goethermal waste heat rejection systems. Working fluids most commonly considered for geothermal cycles are water, ammonia, Freon-22, isobutane, and isopentane. Both low-level and barometric-leg direct-contact condensers are used, and reinforced concrete has been proposed for condenser vessels. Multipass surface condensers also have wide application. Corrosion problems at some locations have led to increased interest in titanium tubing. Studies at ORNL indicate that fluted vertical tubes can enhance condensing film coefficients by factors of 4 to 7.« less

  • Comprehensive computer programs are developed for purposes of determining cooling makeup water requirements and electricity production costs for evaporative (wet) and dry/wet-peaking cooling towers, which are the principal cooling technologies for rejecting the heat from hydrothermal power plants. Parametric economic analyses were performed for both flash steam and binary conversion processes for various combinations of resource temperatures, climatological types, hydrothermal fuel costs, and cooling system makeup water costs. Results of these analyses are presented in a number of curves showing relative busbar cost of electricity as a function of relative amount of cooling makeup water required. These curves show thatmore » use of wet/dry cooling systems can cut makeup water requirements by factors of about 2 to 4 at the cost of an additional 10% to 25% in the busbar price of electricity. Turbine-generator performance curves are constructed for a range of condensing conditions for both the flash steam and hydrocarbon binary-cycle turbines. Estimates of hydrothermal resources in the western United States are also given.« less

  • ;
    The report explains the workings and importance of cooling systems in power plants. Many of the terms used in the energy industry are defined in the chapter reviewing the basic operation of power plants. The rest of the report focuses on the cost and efficiency of various waste heat rejection systems (cooling systems), such as once-through circulating systems, cooling ponds and lakes, spray ponds, and wet and dry cooling towers. The effects of cooling systems on the environment, and on the production and cost of electricity, are also considered.