ASTM E974-00(2006)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E974 − 00(Reapproved 2006)
Standard Guide for
Specifying Thermal Performance of Geothermal Power
Systems
This standard is issued under the fixed designation E974; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The following sections describe a guide for determining the thermodynamic excellence of
geothermal power systems. This guide may be used to establish and compare performance levels of
alternative geothermal plant designs using equal or different resource conditions and is intended as a
means for supplying information in support of geothermal plant optimization.
It is also the purpose of this guide to promote the common use of pertinent comparison criteria for
geothermal power systems, and to discourage the use of some criteria which may range from less
useful to misleading.
1. Scope output to the ideal work available from the geofluid, provides
a more equitable basis for evaluation of the thermodynamic
1.1 This guide covers power plant performance terms and
excellence of geothermal systems.
criteria for use in evaluation and comparison of geothermal
energy conversion and power generation systems. The special
3. Calculations
nature of these geothermal systems makes performance criteria
commonly used to evaluate conventional fossil fuel-fired
3.1 Fossil Fuel-fired Power Plants—Thermal efficiency and
systems of limited value. This guide identifies the limitations
heat rate are useful and valid criteria for evaluation and
of the less useful criteria and defines an equitable basis for
comparison of fossil fuel-fired power plants. Thermal effi-
measuring the quality of differing thermal cycles and plant
ciency is the ratio of net work generated to the heat that is
equipment for geothermal resources.
theoretically available from the fuel. Conventional usage
1.2 This standard does not purport to address all of the
within the electric generating industry defines thermal effi-
safety concerns, if any, associated with its use. It is the
ciency (in dimensionless form) as:
responsibility of the user of this standard to establish appro-
η 5 3600/HR (1)
t
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. where:
3600 = kJ equivalent of 1 kWh, and
2. Significance and Use
HR = heat rate, the ratio of energy supplied to the net
output, kJ/kWh.
2.1 Thermal efficiency and heat rate are frequently utilized
to evaluate the thermodynamic quality of fossil fuel-fired
3.1.1 Forfossilfuel-firedpowerplantsheatrateisexpressed
power plants. Evaluation of geothermal systems using similar
as:
definitions of thermal efficiency and heat rate is inappropriate,
HR 5 M 3FC/W (2)
except for plants which operate on a cycle, such as binary ~ F !
plants. A utilization factor, defined as the ratio of net work
where:
M = fuel flow rate, kg/h,
F
FC = fuel higher heating value, kJ/kg, and
This guide is under the jurisdiction of ASTM Committee E44 on Solar,
W = net output, kW.
Geothermal and OtherAlternative Energy Sources and is the direct responsibility of
SubcommitteeE44.15onGeothermalFieldDevelopment,UtilizationandMaterials.
3.1.2 Thermal efficiency and heat rate are applicable to
Current edition approved March 1, 2006. Published March 2006. Originally
approved in 1983. Last previous edition approved in 2000 as E974 - 00. DOI:
plants which operate on a cycle, and include the effectiveness
10.1520/E0974-00R06.
of energy conversion associated with the fuel combustion, the
Kestin, J., DiPippo, R., Khalifa, H.E., and Ryley, D. J., “Source Book on the
effect of heat rejected in exhaust gases and condensate, and
Production of Electricity From Geothermal Energy,” DoE/RA/28320-2, U.S. De-
partment of Energy, 1980, pp. 243–257. DOI: 10.1520/E0974-00R06. allowance for equipment and balance of plant auxiliary power
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E974 − 00 (2006)
losses. Thus, thermal efficiency and heat rate provide an 3.3.2 Utilization factor is presented as a guide for design
equitable basis for ranking and comparing fossil fuel-fired evaluations and the selection of suitable design conditions for
plants of alternative design.
equipment specifications. Utilization factor for a typical single
flash steam cycle is presented as a function of rejection
3.2 Geothermal Power Plants—Geothermal plants using
temperature in Fig. 2, the rejection temperature that results in
flashed steam (see Fig. 1a and Fig. 11b) do not operate on a
the highest utilization is referred to as the optimum tempera-
cycle but involve a series of energy conversion processes.
ture. For multiflash cycles (including flash-binary) optimum
Thereforeevaluationofsuchplantsusingasimilardefinitionof
values can be identified for each flash level. For binary cycles,
thermalefficiencyandheatrateisinappropriateandwillleadto
erroneous conclusions regarding the effectiveness of the plants. optimum temperatures tend to vary with the secondary fluid
The exception to this is the case of binary plants (see Fig. 11c) selected. Optimum rejection temperature can also be identified
which operate on a cycle and which receive a heat supply. (See
for hybrid cycles such as those employing total flow machine
...