Hybrid Wet/Dry Cooling for Power Plants

Hybrid Wet/Dry Cooling for Power Plants

Chuck KutscherAaron Buys

Chris GladdenNREL

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

Parabolic Trough Technology WorkshopFebruary 14, 2006

gh Technology Workshop held on February 14-16, 2006, in Incline Village, Nevada.

NREL/PR-550-40026Presented at the 2006 Parabolic Trough Technology Workshop held on February 14-16, 2006, in Incline Village, Nevada.

Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-99GO10337 with the U.S. Department of Energy (the “DOE”). The United States Government (the “Government”) retains and the publisher, by accepting the work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes.

Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe any privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the Government or any agency thereof. The views and opinions of the authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the DOE, the Government, or any agency thereof.

OutlineOutline• Overview of cooling options• Analysis of evaporative enhancement of

air-cooled geothermal power plants• Field measurements at geothermal plant• Preliminary analysis of trough plant• Improvements to air-cooled condensers

Water-Saving OptionsWater-Saving OptionsApproach Pros Cons

ACC + WCC in Series - ACC can handle desuperheating load

- Cost of dual equipment- Condensate temp. very

limited ACC + WCC in Parallel - Simple design

- Improves approach to dry bulb

- Condensate temp. limited by dry bulb

ACC w/ Evap Media - Can achieve good approach to wet bulb on inlet air

- Cost of media- Pressure drop lowers

flow rate and LMTDACC w/ Spray Nozzles - Simple, low cost of

nozzles- Low pressure drop

- Overspray and water waste

- Cost of water treatment or mist eliminator

- Nozzle maintenance- Potential damage to

finned tubesDeluge of ACC - Highest enhancement - Water treatment or

protective coating needed

RelevanceRelevance• Air-cooled geothermal plants especially susceptible to

high ambient temperature

• Plant power decreases ~1% of rated power for every1ºF rise in condenser temperature

• Output of air-cooled plant can drop > 50% in summer, when electricity is highly valued

Unit 200 Performance Data

-

500

1,000

1,500

2,000

2,500

3,000

40 45 50 55 60 65 70 75 80 85Ambient Temperature °F (@weather station)

Net

Out

put -

kW

Spreadsheet Model of Evaporative Enhancements

to Existing Air-Cooled Plants

Spreadsheet Model of Evaporative Enhancements

to Existing Air-Cooled Plants

System 1 - Spray CoolingSystem 1 - Spray Cooling

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

eliminator• Nozzle clogging

System 2 - Munters CoolingSystem 2 - Munters Cooling

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

rate and decreases LMTD)• High cost

System 3 – Hybrid CoolingSystem 3 – Hybrid Cooling

• Inexpensive and simple, used in poultry industry

• Over-spray, carryover, and nozzle cleaning

System 4 – Deluge CoolingSystem 4 – Deluge Cooling

• Excellent performance• Danger of scaling and deposition without

pure water

Example Analysis:Net Power ProducedExample Analysis:

Net Power Produced

Total Kilowatt-hours Produced

500,000

600,000

700,000

800,000

900,000

Kilo

wat

t-hou

rs

No EnhancementSpray CoolingMunters CoolingDeluge CoolingHybrid Cooling

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Example Cost ResultsExample Cost Results

5.2

6.4

7.67.2

8.5

9.9

5.7

7.2

8.7

3.54.2

4.9

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0C

ents

/kW

h

System 1 - SprayCooling

System 2 -Munters Cooling

System 3 -Hybrid Cooling

System 4 -Deluge Cooling

Incremental Cost of Added ElectricityDiscount Rate = 10%, Plant Life = 25 years

$0/kgal$0.5/kgal$1/kgal

Note: Value of electricity will be affected by time-of-day ratesand capacity payments.

Note: Value of electricity will be affected by time-of-day ratesand capacity payments.

Geothermal Analysis Conclusions

Geothermal Analysis Conclusions

• Deluge most attractive if scaling/corrosion issues can be addressed

• Systems 1 to 3 obtain ~40 kWh/kgal of water; deluge can produce an average of ~60 kWh/kgal

• Results very sensitive to water costs, electric rate structure, installation costs

Coated Fin Test ResultsCoated Fin Test Results

OMP-coated fin unaffected by salt spray

Plain fin pitted

Measurements at MammothMeasurements at Mammoth

Measurements at MammothBinary-Cycle Geothermal Power Plant

Measurements at MammothBinary-Cycle Geothermal Power Plant

Munters system

Hybrid spray/Munters system

Mammoth Measurement Results: 2001

Mammoth Measurement Results: 2001

• Field instrumentation: Type T thermocouples, optical dew point (chilled mirror) hygrometer, handheld anemometer

• 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 Performance at Mammoth

Munters Performance at Mammoth

Unit 200 Performance Data

-

500

1,000

1,500

2,000

2,500

3,000

40 45 50 55 60 65 70 75 80 85Ambient Temperature °F (@weather station)

Net

Out

put -

kW

after Munters

before Munters

Mammoth MeasurementResults: 2002

Mammoth MeasurementResults: 2002

• Munters system modified, brine used for cooling water. Munters efficiency dropped from 79% to 66%

Geothermal ConclusionsGeothermal Conclusions

• All operators of air-cooled plants interested in evaporativeenhancement

• Costs at existing plants are site-specific and negotiable; $0.50 to $2.00 per thousand gallons

• Reclaimed water becoming more widely available

• Two-Phase Engineering showed successful use of nozzles with brine

• Can reduce average cost of electricity by about 0.3 ¢/kWh, depending on cost of water

• Capacity payments can be as high as 30 ¢/kWh and lower average cost of electricity by 2–3 ¢/kWh

Parabolic Trough PlantPreliminary Analysis

Parabolic Trough PlantPreliminary Analysis

UW EES ModelPower Out and Ht. Rejection

vs. CondenserPressure and Field Flowrate

UW EES ModelPower Out and Ht. Rejection

vs. CondenserPressure and Field Flowrate

NREL Hour-by-hourEES Model

Of Condenser Types andEvap Cooling

NREL Hour-by-hourEES Model

Of Condenser Types andEvap Cooling

NREL Excel ModelOf Costs

NREL Excel ModelOf Costs

ExcelergyField Flowrate vs.

TMY2 Radiation

ExcelergyField Flowrate vs.

TMY2 Radiation

Cases ExaminedCases Examined• Air-Cooled• Water-Cooled• Air-Cooled with Spray Enhancement

General AssumptionsGeneral Assumptions• 30 MWe SEGS plant, Daggett weather• $0.18/kWh electricity (€0.15/kWh)• Water at $1.95/kgal ($515/m3, €430/m3)• 15% interest rate• 30-year life

Water-Cooled PlantWater-Cooled Plant• Shell-and-tube condenser + cooling tower• 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-ft2-°F (2270 W/m2-°C)

Air-Cooled PlantAir-Cooled Plant• Finned tube condenser• Tdb = 104°F (40°C)• ITD = 40°F (22°C)• Pinch = 5°F (2.8°C)• U = 150 Btu/h-ft2-°F (850 W/m2-°C)

Evaporative Pre-CoolingEvaporative Pre-Cooling• 300 psig spray nozzles• 70% evaporation efficiency• 80% saturation efficiency• Munters DRIFdek mist eliminator

Net Electricity Produced Per Year for Different Condenser Types

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

Water Cooled Air Cooled Evaporatively Pre-Cooled

Year

ly E

lect

ricity

Pro

duce

d [M

We-

hr]

0

2000

4000

6000

8000

10000

12000

0 1 2 3 4 5 6 7 8 9 10 11 12 13Month Number

Ele

ctric

ity P

rodu

ced

[MW

e-hr

]

Water CooledEvaporatively Pre-cooledAir Cooled

Effect of Purchase Price of Electricity on Yearly Revenue(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 0.20 0.24

Price of Electricity [$/kWh]

Perc

ent I

ncre

ase

in Y

early

Rev

enue

(C

ompa

red

to A

ir-C

oole

d)

Water CooledEvaporatively Pre-cooled

Effect of Water Price on Yearly Revenue(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 5.00 6.00 7.00

Price of Water [$/1000 gallons]

Perc

ent I

ncre

ase

in Y

early

Rev

enue

Water CooledEvaporatively Pre-cooled

Water Use for Different Condenser Types

0

10

20

30

40

50

60

70

80

90

Water Cooled Evaporatively Pre-cooled

Mill

ions

of G

allo

ns o

f Wat

er P

er Y

ear

Next StepsNext Steps

• Evaluate potential for water restrictions• Develop full plant EES model• Improve cost estimation• Analyze parallel wet-dry system

Brief Review of NREL R&Don Advanced Fins for

Air-Cooled Condensers

Brief Review of NREL R&Don Advanced Fins for

Air-Cooled Condensers

McElroy Enhanced FinsMcElroy Enhanced Fins

Test SectionTest Section

Heat Transfer vs. Hydraulic Power

Different Fin Types (Staggered Array)

14.00

16.00

18.00

20.00

22.00

24.00

26.00

28.00

30.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00

Hydraulic Power / Bare Tube Area (kW SL / m^2)

Hea

t Tra

nsfe

r / T

ube

Are

a (k

W/m

^2)

Plain Fin Staggered Perforated Fin Staggered Perforated Fin 2 Staggered

Tabbed Fin ConceptTabbed Fin Concept

Tabbed Plate FinTabbed Plate Fin Tabbed Plate Fin Heat ExchangerTabbed Plate Fin Heat Exchanger

Individual FinsIndividual Fins

GEA fins w/spacersGEA fins w/spacers NREL tabbed circular finNREL tabbed circular fin

Detailed CFD Model Isometric Views:Heat Flux and Total Pressure

Detailed CFD Model Isometric Views:Heat Flux and Total Pressure

Surface Heat FluxSurface Heat Flux Total PressureTotal Pressure

Recent Tabbed Fin CFD Results

Recent Tabbed Fin CFD Results

Heat Transfer Vs. Hydraulic Power (Sea Level)

0

5

10

15

20

25

30

0 25 50 75 100 125Hydraulic Power (Watts)

Hea

t Tra

nsfe

r (kW

)

v2.2 v2.3v2.4 v2.5v2.6 v2.7Plain Plain/RibbedX-fin (Approximated)