Development of a High-Temperature, Long-Shafted, Molten ... - NREL

Development of a High-Temperature, Long-
Shafted, Molten-Salt Pump for Power Tower
Applications
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Daniel L. Barth
Nagle Pumps, Inc.
James E. Pacheco
William J. Kolb
Earl E. Rush
Sandia National Laboratories
Forum 2001, Solar Energy: The Power to Choose
April 24, 2001, Washington, DC

Molten Salt Power Tower Technology
Hot Salt
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Conventional
EPGS
Steam Generator
Cold Salt

Limitations of Pumps Used at Solar Two
Hot side used cantilever pumps
because no suitable bearing materials
had been proven for use in “hot” salt
service (e.g., 570 deg C)
Because the hot pumps were a
cantilever design, their length was
limited to 3 m.
The short length precluded mounting
the pump directly in the storage tank,
thus requiring separate pump sumps.
Cold pumps used salt lubricated
bearings
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
CONTAINMENT
EARTH BERM.
EL. 100'-0"
EL. 79'-5"
LOW POINT
DRAIN PIT
RS & SGS SUMPS
Do not appear in this
Section
ACCESS LADDER
COLD NITRATE
SALT TANK
FOUNDATION
COOLING PIPES
PUMP
MAINTENANCE
PLATFORM
(STEAM DRUM /EVAPORATOR)
STEAM GENERATOR
(SUPERHEATER)
INSULATED TANK
FOUNDATION
RS
PUMP
SUMP
SGS
PUMP
SUMP
SII RECEIVER
TOWER STRUCTURE
ACCESS LADDER
HOT NITRATE
SALT TANK
RS & SGS Pumps
(Typical)
FOUNDATION
COOLING PIPES
EL. 100'-0"
ACCESS LADDER
EL. 81'-8"
EL. 100'

Pumps Mounted in the Tanks Would
Greatly Simplify the Molten-Salt System
Eliminate the pump sumps,
control and shut off valves, level
instrumentation and associated
heaters
Reduce heat loss
Allow the steam generator
system to drain directly into the
tanks
Sandia National Laboratories
teamed with Nagle Pumps to
develop a long-shafted salt pump
as part of the DOE Concentrating
Solar Power Program
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
ELEV. 14630 mm
ELEV. 12954 mm
SGS STEAM DRUM
SGS PREHEATER
SGS EVAPORATOR
SGS SUPERHEATER
TSS HOT SALT
STORAGE TANK
SGS STARTUP
FEEDWATER HEATER
STATIONARY STIFF
LEG DERICK
SGS REHEATER
TSS COLD SALT
STORAGE TANK
GRADE (0 mm)
Desirable characteristics
of bearing materials:
Non-galling
Low corrosion
Easily machined
Low cost

7.6 m long
Salt lubricated bearings
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Description of Test Pump
Modified Nagle YWS design
5 yoke assembly
Several bearing/sleeve
materials tested at once
Yoke
Assembly
Bearings
Sleeve

Yoke
Number
Bearing / Sleeve Materials Tested
Journal Sleeve
Material
(Mounted to Shaft)
Selected for their non-galling characteristics
and compatibility with nitrate salts
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Bearing Material (Mounted to Yoke Assembly)
1 (Top) NPI 420 Stainless 60-45-10 Ductile Iron (Full Length)
2 Stellite 6B Ni-Resist Type 1 (Upper)
60-45-10 Ductile Iron (Lower)
3 NPI 420 Stainless Gray Cast Iron Grade 40 (Upper)
Gray Cast Iron Grade 40 (Lower)
4 Tribaloy T-900 Ni-Resist Type 1 (Upper)
Ni-Resist Type 1 (Lower)
5 (Bottom) Stellite 6B Gray Cast Iron Grade 40 (Full Length)

Characterize the pump, simulate
operating modes and operate
pump for extended time periods
Pump head versus motor current
as a function of flow rate (at 345,
400, 455, 510 and 565 deg C)
Endurance test: 7 hours on, 1
hour off continuously around the
clock at full flow at 565 deg C.
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Tests Conducted

Pump curves matched design
specifications
Pump operated for over 5000
hours
Measurements before and after
showed there were no vibration
problems
After all testing was completed,
the pump was disassembled,
bearing and sleeve were
inspected and dimensions were
measured
All bearings and sleeves were
reusable, only requiring polishing
of the surfaces
S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Test Results
Pump Head, m
45
40
35
30
25
20
27
15
21
0 50 100 150 200 250 300 350
Flow Rate, liters/ min
26
25
24
23
22
Current, Amps

S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Test Results (continued)
Best combination was Stellite 6B sleeve with a
gray cast-iron bearing.
In place of Stellite 6B, lower cost NPI 420
stainless steel could be used.
Tribaloy T-900 showed heavy pitting on the
bearing surface and is unsuitable
Ductile iron had heavy scale buildup and flaking
and is not recommended as a bearing material.
Ni-Resist faired will as a bearing material but is
more expensive than gray cast iron

S O L A R � T H E R M A L � E N E R G Y
Sun����Lab
Sandia National Laboratories, Albuquerque, NM
National Renewable Energy Laboratory, Golden CO
Implications of the Results
Pump lengths of 15 m can be commercially built
for mounting in the storage tanks in a molten salt
power tower.
Heat loss will be reduced by 10 to 20% over the
previous design because the pump sumps,
valves, and interconnecting piping will be
eliminated. The capital cost of the storage system
will be reduced as well.
This pump design can also be used in parabolic
trough plants that use molten salt thermal storage.