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