Hybrid Wet/Dry Co

for Power Plant

Hybrid Wet/Dry Coo

for Power Plants

Chuck Kutscher

Aaron Buys

Chris Gladden

NREL

NREL/PR-550-40026Presented at the 2006 Parabolic Trou

Parabolic Trough Technology W

February 14, 2006

gh Technology Worksho

p held on Februar

y 14-16, 200

NREL/PR-550-40026Presented at the 2006 Parabolic Trough Technology Workshop held on February 14-16, 2006
Disclaimer and Government License

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specific commercial product, process, or service by trade name, trademark, manufacturer, or othimply its endorsement, recommendation, or favoring by the Government or any agency thereof. authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the agency thereof. 
Outline Outline

• Overview of cooling options• Analysis of evaporative enha

air-cooled geothermal power 

• Field measurements at geoth• Preliminary analysis of troug• Improvements to air-cooled c
Water-Saving Opti

Water-Saving Opti

Approach Pros 

ACC + WCC in Series - ACC can handle 

desuperheating load

- C- C

ACC + WCC in Parallel - Simple design

- Improves approach to 

dry bulb

- C

ACC w/ Evap Media - Can achieve good 

approach to wet bulb 

on inlet air

- C- P

ACC w/ Spray Nozzles - Simple, low cost of 

nozzles

- Low pressure drop

- O

- C- N- P

Deluge of ACC - Highest enhancement - W
Relevance Relevance

• Air-cooled geothermal plants especially susc

high ambient temperature

• Plant power decreases ~1% of rated power f

1oF rise in condenser temperature

• Output of air-cooled plant 

can drop > 50% in summer, when electricity is highly valued

Unit 200 Pe

-

500

1,0001,5002,0002,5003,000

40 45 50 55 

Ambient Temp

Net Output - kW
Spreadsheet Model 

Evaporative Enhancem

to Existing Air-Cooled 

Spreadsheet Model 

Evaporative Enhancem

to Existing Air-Cooled 
System 1 - Spray C

System 1 - Spray C

• Low cost, low air pressure drop• High water pressure• Over-spray and carryover or cost o

eliminator

• Nozzle clogging
System 2 - Munters 

System 2 - Munters 

• High efficiency, minimum carryover• High air pressure drop (reduces air 

rate and decreases LMTD)

• High cost
System 3 – Hybrid C

System 3 – Hybrid 

• Inexpensive and simple, used in poult

industry

• Over-spray, carryover, and nozzle cle
System 4 – Deluge 

System 4 – Deluge 

• Excellent performance• Danger of scaling and deposition wit

pure water 

Example Analys

Net Power Produ

Example Analys

Net Power Produ

Total Kilowatt-hours Produced

500,000600,000700,000800,000900,000

Kilowatt-hours N

SMDH

Jan Feb Mar Apr May Jun Jul Aug Sep Oct 
Example Cost Res

Example Cost Res

5.2

6.4

7.6

7.2

8.5

9.9

5.7

7.2

8.7

3.5

0.01.02.03.04.05.06.07.08.09.0

10.0

Cents/kWh

System 1 - Spray

Cooling

System 2 -

Munters Cooling

System 3 -

Hybrid Cooling

Syste

Deluge 

Incremental Cost of Added Electricity

Discount Rate = 10%, Plant Life = 25 years

Note: Value of electricity will be affected by timand capacity payments.

Note: Value of electricity will be affected by timand capacity payments.
Geothermal Anal

Conclusions

Geothermal Analy

Conclusions

• Deluge most attractive if scalin

issues can be addressed

• Systems 1 to 3 obtain ~40 kW

water; deluge can produce an ~60 kWh/kgal

• Results very sensitive to water 

electric rate structure, installati
Coated Fin Test Re

Coated Fin Test Re

OMP-coated fin unaffected by salt spray

Pla
Measurements at Mam

Measurements at Mam
Measurements at Mamm

Binary-Cycle Geothermal Po

Measurements at Mamm

Binary-Cycle Geothermal Po

Munters system

Hybrid spray
Mammoth Measure

Results: 2001

Mammoth Measure

Results: 2001

• Field instrumentation: Type T thermoco

dew point (chilled mirror) hygrometer, hanemometer

• Munters had 79% saturation efficiency

hybrid was 50%

• Flow rate with Munters dropped 22-28%• Munters increased net power 62% 

(800 kW to 1,300 kW) at 78oF ambient
Munters Performan

Mammoth

Munters Performan

Mammoth

Unit 200 Performance Data

-

500

1,0001,5002,0002,5003,000

40 45 50 55 60 65 70 

Ambient Temperature °F (@weathe

Net Output - kW 

before Munters
Mammoth Measure

Results: 2002

Mammoth Measure

Results: 2002

• Munters system modified, brin

cooling water. Munters efficiefrom 79% to 66%
Geothermal Conclu

Geothermal Conclu

• All operators of air-cooled plants interested in e

enhancement

• Costs at existing plants are site-specific and ne

$2.00 per thousand gallons

• Reclaimed water becoming more widely availa• Two-Phase Engineering showed successful us

brine

• Can reduce average cost of electricity by abou

depending on cost of water

• Capacity payments can be as high as 30 ¢/kW

cost of electricity by 2–3 ¢/kWh


Parabolic Trough P

Preliminary Analy

Parabolic Trough P

Preliminary Analy

UW EES Model

Power Out and Ht. Rejection

vs. Condenser

Pressure and Field Flowrate

UW EES Model

Power Out and Ht. Rejection

vs. Condenser

Pressure and Field Flowrate

NREL Hour-by-hour

EES Model

Of Condenser Types and

Evap Cooling

NREL Hour-by-hour

EES Model

Of Condenser Types and

Evap Cooling

NREL Excel Model

Of Costs

NREL Excel Model

Of Costs

Excelergy

Field Flowrate vs. 

TMY2 Radiation

Excelergy

Field Flowrate vs. 

TMY2 Radiation
Cases Examined Cases Examine

• Air-Cooled• Water-Cooled• Air-Cooled with Spray Enhan
General Assumptio

General Assumpti

• 30 MW

e SEGS plant, Dagge

• $0.18/kWh electricity (€0.15• Water at $1.95/kgal ($515/m

• 15% interest rate• 30-year life
Water-Cooled Pla

Water-Cooled Pla

• Shell-and-tube condenser + •

Twb = 68°F (20°C)

• Approach = 10°F (5.6°C)• Range = 20°F (11.1°C)• Pinch = 5°F (2.8°C)• U = 400 Btu/h-ft

2-°F (2270 W
Air-Cooled Plan

Air-Cooled Plan

• Finned tube condenser• Tdb = 104°F (40°C)• ITD = 40°F (22°C)• Pinch = 5°F (2.8°C)• U = 150 Btu/h-ft

2-°F (850 W/
Evaporative Pre-Co

Evaporative Pre-Co

• 300 psig spray nozzles• 70% evaporation efficiency• 80% saturation efficiency• Munters DRIFdek mist elimin
Net Electricity Produced Per Year for Different 

0

100002000030000400005000060000700008000090000

100000

Water Cooled Air Cooled 

Yearly Electricity Produced [MWe-hr] 
0

2000400060008000

1000012000

0 1 2 3 4 5 6 7 8 9 

Month Number

Electricity Produced [MWe-hr] Water Cooled

Evaporatively Pre-cooledAir Cooled
Effect of Purchase Price of Electricity on Yea

(Water Cost = $2/kgal)

-4.0%-2.0%

0.0%2.0%4.0%6.0%

0.00 0.04 0.08 0.12 0.16 

Price of Electricity [$/kWh]

Percent Increase in Yearly Revenue 

(Compared to Air-Cooled) 

Water CooledEvaporatively Pre-cooled
Effect of Water Price on Yearly Reven

(Electricity Price = $0.18/kWh)

0.0%1.0%2.0%3.0%4.0%5.0%6.0%

0.00 1.00 2.00 3.00 4.00 5

Price of Water [$/1000 gallons]

Percent Increase in Yearly Revenue 
Water Use for Different Condenser Ty

0

102030405060708090

Water Cooled Evaporative

Millions of Gallons of Water Per Year 
Next Steps Next Steps

• Evaluate potential for water r• Develop full plant EES mode• Improve cost estimation• Analyze parallel wet-dry syste
Brief Review of NREL 

on Advanced Fins 

Air-Cooled Condens

Brief Review of NREL 

on Advanced Fins f

Air-Cooled Condens
McElroy Enhanced 

McElroy Enhanced 
Test Section Test Section
Heat Transfer vs. 

Hydraulic Power 

Different Fin Types (Staggered 

14.0016.0018.0020.0022.0024.0026.0028.0030.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 

Hydraulic Power / Bare Tube Area (kW S

Heat Transfer / Tube Area (kW/m^2) Plain Fin Staggered Perforated Fin Staggered Pe
Tabbed Fin Conc

Tabbed Fin Conc

Tabbed Plate Fin Tabbed Plate Fin Tabbed Plate 

Tabbed Plate 
Individual Fins Individual Fins

GEA fins w/spacers GEA fins w/spacers NREL tabbe

NREL tabbe
Detailed CFD Model Isome

Heat Flux and Total Pr

Detailed CFD Model Isome

Heat Flux and Total Pre

Surface Heat Flux Surface Heat Flux Total P

Total P

Recent Tabbed F

CFD Results

Recent Tabbed F

CFD Results

Heat Transfer Vs. Hydraulic Power (Sea Leve

05

1015202530

0 25 50 75 

Hydraulic Power (Watts)

Heat Transfer (kW) v2.2 v2

v2.4 v2v2.6 v2Plain PX-fin (Approximated)