Raft River 5MW(e) binary geothermal-electric power plant: operation and performance Page: 4 of 8
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B1 iem
through a wet cooling tower in which the energy
was rejected to the atmosphere. Treated geothermal
water was used for cooling water makeup.
COMPONENT DESCRIPTIONS
Pumps
The working fluid pumping was provided by
two parallel vertical turbine pumps at 1515 ft and
1747 gpm each. Each pump had six stages and a 500
hp motor. The pump efficiency at rated conditions
was specified at 78 percent. The pumps were sized
for the minimum condenser pressure of 42 psia.
The geothermal boost pumps provided the head
required to pump the geofluid through the heat
exchangers and through the transmission lines to
the injection pumps. Two parallel, vertical-split
case centrifugal pumps (each with a head of 272 ft
at a flow of 1115 gpm, a design efficiency of
80.5 percent, and driven by a 125 hp electric
motor) provided this capability.
The pumping required to move the cooling
water through the condenser and cooling tower was
provided by two parallel vertical turbine pumps.
At rated conditions each pump provided 7700 gpm of
water at 125 ft head. At these conditions the
efficiency was specified as 83 percent. Each pump
was driven by a 300 hp motor.
Heat Exchangers
The heat exchanger characteristics are
summarized in the following table:
Heat Exchanger
Surface Area
(ft*)
Length
(ft)
Diameter
Weight
(T)
Low temperature
preheater
30,039a
49
50
43
Low pressure
boiler
5,938
42
33/68
20
High temperature
preheater
15,059a
50
35
22
High pressure
boiler
5,938
42
33/68
20
Condenser
59,996
50
88
140
aExtended surface.
The tube material for all geothermal fluid heat
exchangers was admiralty brass. The tube sheets
were aluminum bronze clad carbon steel. The
geothermal side fouling factor was assumed to be
0.0015 hr ft2 F/Btu, and 0.0005 hr ft2 F/Btu was
used on the isobutane side. The condenser was
made of carbon steel throughout, including the
tubes. For design of the condenser, the cooling
water side fouling factor was taken as 0.0010 hr
ft2 F/Btu, and an isobutane side fouling factor
of 0.0005 hr ft2 F/Btu was used.
Cooling Tower
The cooling tower was a crossflow, two-cell,
mechanical draft, wet unit. Each of the 40 by
70-ft cells was equipped with a fan which had an
80 hp motor. The tower was 53 ft high and was
constructed of treated Douglas fir and redwood.
Turbine-Generator
The turbine utilized the barrel design. This
design was easy to seal for high-pressure service,
and facilitates disassembly and reassembly for
maintenance. The rotor had two radial inflow
wheels, and operated at 8000 rpm. Because the
flows from the low and high pressure inlets were
combined to a common outlet, the aerodynamic
thrust load was low.
The generator was rated at 7200kW, 7579 kVA,
1200 rpm synchronous speed, and electrical
conditions of three-phase, 60 Hz and 4160 V. The
generator design power factor was 0.9.
Supply and Injection System
Geofluid was supplied to the operating plant
from three production wells, RRGE-1, 2, and 3.
The spent geofluid was reinjected into wells
RRGI-6 and 7. All of the lines in the supply and
injection system were made of cement-asbestos pipe
with transition to steel pipe at the wells, at
the plant, and at a manifold into which the
individual production-well pipelines joined. The
pipe was buried to a depth of about 2-1/2 ft. The
supply lines were insulated with urethane foam to
limit the temperature drop to less than 1.5°F per
mile. Figure 1 shows the location of the wells
relative to the plant. The pipeline for the
production wells to the plant covered about one
mile in length, and the line from the plant to the
injection wells was about 1.8 miles.
Line-shaft pumps were installed in each
production well. At each injection well, the line
dumped into a pond, and then the geofluid was
pumped from the pond and injected with individual
pumps.
PERFORMANCE ANALYSIS
The plant was tested over a period of three
months. The tests consisted primarily of varying
the geothermal inlet and cooling water conditions
to determine system performance.^ >2) In addi-
tion to the system performance, the behavior of
the individual components was investigated. The
changes in input conditions allowed for a wide
range of operating conditions for the individual
components.
Component Performance
Pumps. The data from the 17 different tests
indicated some deficiencies in the performance of
the pumps. The isobutane feed pumps produced a
head rise approximately five to six percent lower
than the manufacturer's test curve indicated for a
given flow. This was a critical deviation because
a higher than expected pressure drop was found to
exist in the piping between the pump and the high
pressure boiler. The result was the inability to
supply the boiler with the desired amount of
isobutane at the rated geofluid flow; the impact
will be discussed under System Performance.
The geofluid boost pump operated as specified,
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Bliem, C.J. Jr. Raft River 5MW(e) binary geothermal-electric power plant: operation and performance, article, January 1, 1983; Idaho Falls, Idaho. (https://digital.library.unt.edu/ark:/67531/metadc1091912/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.