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Closed-Loop, Evaporative Cooling Systems
Peter G. Demakos, P.E.Niagara Blower Heat Transfer Solutions
Buffalo, NY
EPRI 2008
Agenda
• Closed-loop, evaporative cooling systemsWet Surface Air Coolers (WSAC)
• Technology comparison• Applications• Water and energy savings• Summary/questions
What is a Wet Surface Air Cooler?
• Heat removal device– Cooling liquids– Condensing vapors
Wet Surface Air Cooler
• Where is it applicable?– Aux loop cooling– Direct vacuum steam condensing– Refrigerant condensing– Lowering discharge water temperature
• Where is it being used?
– Numerous simple and combined cycle power plants worldwide
How Does the WSAC Work?
Cooling WaterIn
ProcessIn
Cooling WaterOut
ProcessOut
Water Air & Water
2.) Remove “Shell” Exposing Tubes
3.) Spray Water Directly Over the Exposed Tubes4.) Air is Induced Over Tubes in the Same Direction as the Water
ProcessIn
ProcessOut
ProcessIn
ProcessOut
ProcessIn
ProcessOut
1.) Typical Shell & Tube Heat Exchanger
SENSIBLE
LATENT
2 Water 2 Water flows flows downward downward along with along with the airthe air
3 Heat from the 3 Heat from the process stream is process stream is released to the released to the cascading watercascading water
How Does the WSAC Work? 4 Heat is 4 Heat is transferred transferred
from the from the cascading cascading
water to the water to the air stream via air stream via vaporizationvaporization
1 Air is 1 Air is induced induced downward downward over tube over tube bundlesbundles
6 Fans discharge air 6 Fans discharge air vertically at a high vertically at a high
velocity preventing velocity preventing recirculationrecirculation
5 Air stream 5 Air stream forced to turn forced to turn
180180o o providing providing maximum free maximum free water removalwater removal
Cooling Tower / Heat Exchanger Dry / Air Cooled Wet Surface Air Cooler (WSAC)
Cooling Technology Options
Equipment Configuration
Field ErectedFactory Assembled
Bolted Straight Through Bundlesor
General Specifications
Serpentine Coils
– Low-pressure / High-flow design
– Full flooded spray pattern
– No fill
General Specifications for WSAC
• Spray Water Distribution System
Water Issues
EVAPORATION(GPM) = HEAT LOAD (Btu/hr)/570,000 MAKEUP = EVAPORATION + BLOWDOWN + DRIFT
CYCLES OF CONCENTRATION = (EVAPORATION / BLOWDOWN) +1
Blowdown
Makeup
Spray Pump
DriftEvaporation
OPEN COOLING TOWER
PLANT COOLING
LOAD
EVAPORATION
FRESHMAKEUP
PLANT COOLING
LOAD
Reducing Water Makeup in Existing Open-Loop Systems
EVAPORATION
BLOWDOWN
NEW WET SURFACE AIR COOLER
COOLING TOWER BLOWDOWN FOR MAKEUP
SAVINGS: 525 MW plant →60 million gal/yr
STEAM CONDENSER
AUX LOOP COOLER
Aux Loop Cooler
Schematic of Dry/Wet Cooler
Cooling to 80°F at 95°F DB / 70°F WB
Process stream
inlet
Process stream outlet80
0
50
100
35 45 55 65 75 85 95 105 115
WATER SAVINGS WATER USE
ALL DRY OPERATION
WET/DRY OPERATION
ALL WET OPERATION
Water Savings Using Niagara Dry/WSAC
DRY BULB TEMP (degF)
% W
ATE
R U
SE
WSAC SAVES OVER 50% OF ANNUAL WATER CONSUMPTION
AUX LOOP COOLER
TIAC COND
ACC
Wet / Dry Cooling in a Combined Cycle Power Plant
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16 18 20 22 24
WSAC
Air Cooled
Condenser Cost Comparison
Cooling Tower/ Heat Exchanger
Temp Approach (DegF)
Tota
l Cos
t (M
illion
$)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10 12 14 16 18 20 22 24
WSAC
Comparison of Total Power Required vs. Approach Temp
(100 MM BTU/hr heat load)
Cooling Tower/ Heat Exchanger
Air Cooled
Temp Approach (DegF)
Sys
tem
Pow
er R
equi
rem
ents
(MW
)
WSAC Benefits
Pump less water– Lower horsepower
• Reduced installation costs• More available power for sale• Lower carbon footprint
WSAC Benefits
Can use poor quality water-Reuse plant water-Brackish water, seawater-Agricultural runoff-FGD water
Can run higher cycles of concentration– Less water to purchase– Less water to dispose of
WSAC Benefits
Cocurrent spray system design– Lower discharge height– Lower PM10
WSAC Benefits
Can cool plant discharge water– Reduced thermal effect
WSAC Benefits
Can evaporate blowdown– Smaller evaporation ponds– Less ZLD system capacity– Cost savings
“Expensive to own and operate”
Small Packaged Fluid Cooler
Large Gas Turbine Packaged Fluid Cooler
Combined Cycle Plant –
Aux Loop Cooler
1100 GPM, 160°F Inlet Temp., 120°F Outlet Temp., 80°F Wet Bulb
Steam Condenser
Steam Condenser
670,000 lb/hr Steam Condensers and Auxiliary Fluid Cooler
12,000 Ton Ammonia Condenser Griffith, AZ
Summary
• More efficient cooling/condensing• Improved heat rate• Less HP• Lower carbon footprint• Less maintenance• Water savings
Closed-Loop, Evaporative Cooling Systems
Peter G. Demakos, P.E.Niagara Blower Heat Transfer Solutions
Buffalo, NY
EPRI 2008
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