Dersch Dry Cooling

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solar thermal power plants

Water saving heat rejection for

Jürgen Dersch, Christoph Richter

Institute of Technical Thermodynamics



Overview

Overview

Project goals

Simulation tool

First results

Outlook

Slide 2 > NREL Trough Meeting 2007 > Dersch

Heat rejection technologies




Research Project „EFCOOL“

Research Project „EFCOOL“

Title: “Water efficient cooling of solar thermal power plants”

Solar Paces Task III Activity „Efficient Cooling Strategiesfor Solar Thermal Power Plants“

Motivation: Solar thermal power plants with Rankine cyclesneed heat rejection for condensation of the turbine exhauststeam in order to reach low exhaust pressures and torecycle the working fluid

Typically ambient temperatures are high and water is rareat sites showing attractive annual DNI values



EFCOOL TasksEFCOOL Tasks

Investigation of different heat rejection technologies for

STPP

Developing of a simulation tool for annual calculations atdifferent sites

Identification of potential enhancements for existing coolingtechnologies

Investigation of new operation strategies for STPP with

l


respect to cooling (e.g. the usage of thermal storage to shiftthe cooling oad to night hours)



Cooling technologies

(Heller System)

Air cooled condenser (ACC)

Hybrid cooling

temperatures.


Cooling technologies

Once through cooling

Most efficient and cheapest technolgy but rarely applicable for STPP

Wet cooling tower

Efficient at moderate investment costs but high water consumption

Indirect dry cooling

Less efficient and more expensive than wet cooling but almost no water

consumption for cooling.

Less efficient and more expensive than wet cooling but almost no waterconsumption for cooling.

Combination of wet and dry cooling technologies.

Dry cooling with water usage during time periods with peak ambient



Wet Cooling Tower

Ambient wet bulb temperature defines

the condenser pressure

temperature)

Surface condenser (TTD~3K)

Cooling water and boiler feed waterare separated

Natural draft or cooling towers with

fans are possible

Source: SPX


Wet Cooling Tower

(less fluctuations than dry bulb



Heller SystemHeller System

j(TTD~0.5K)

mixed

Source: EGI


Dry bulb temperature defines thecondenser pressure

Direct contact et condenser

Cooling water and boiler feed water are

Large underground storage tanks areused to drain the system

Ratio cooling water flow / boiler feedwater appr. 50

Natural draft or cooling towers with fans

are possible



Air Cooled Condenser

necessary

l

configurations


Air Cooled Condenser

Dry bulb temperature controls thecondenser pressure

Steam is condensed without theusage of an intermediate medium

Large cooling surfaces are

The ACC should be ocated closeto the turbine

Typically forced draft A-frame



The Annual Simulation ToolThe Annual Simulation Tool

Steady state models in MS Excel

Based on empirical equations or performance mapsgenerated by other more sophisticated tools or delivered bysuppliers

Part load characteristics are considered

simplified IEA method


Levelized electricity cost (LEC) calculation using the

Hour by hour calculation with meteo data for different sites



0.20

0.25

0.30

0.35

0.40

5 10 15 20 25 30 35 40 45

t dry bulb in °C

g r o s s

e f f i c i e n c y

Wet Cooling 60% Load

Wet Cooling 100% Load

Heller Cooling 60% Load

Heller Cooling 100% Load rel. humidity: 40%

0.6

0.7

0.8

0.9

1.0

1.1

1.2

5 10 15 20 25 30 35 40 45

t dry bulb in °C

r e a v e

c e n c y

0.2

0.4

0.6

0.8

1.0

cooling load

Examples of the Performance Maps

l t i e

f f i i

y

i

Turbine


Examples of the Performance Maps

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00 0.20 0.40 0.60 0.80 1.00 1.20

load

r e l a t i v e e f f i c i e n c

operat ng range

Heller Cooling SystemWhole Plant



Condenser Temperatures and Ambient Conditions

0

10

20

30

40

50

60

70

80

90

Wet cooling, phi 40%

Wet cooling, phi 100%

Wet cooling, phi 0%

Condenser Temperatures and Ambient Conditions

c o n d e n s e r t e m p e r a t u r e i n ° C

Heller System

10 15 20 25 30 35 40 45 50

ambient dry bulb temperature in °C


5




Meteo Data of Different Sites (DNI > 250W/m²)Meteo Data of Different Sites (DNI > 250W/m²)

0

200

400

600

800

1000

-10 0 10 20 30 40 50

Temperature in °C

D N I i n W / m 2

0

0.2

0.4

0.6

0.8

1

-10 0 10 20 30 40 50

Temperature in °C

r e

l . H u m i d i t y

0

200

400

600

800

1000

-10 0 10 20 30 40 50

Temperature in °C

D N I i n W

/ m 2

0.00

0.20

0.40

0.60

0.80

1.00

-10 0 10 20 30 40 50

Temperature in °C

r e l . H u m i d i t y

Spain

California



Results of Annual Calculation (Heller Systemcompared to Wet Cooling)


Results of Annual Calculation (Heller Systemcompared to Wet Cooling)

1 . 0

5

0 . 9

5 0 . 9

9 1 . 0

4

0 . 0

4

1 . 0

6

0 . 9

5 1 . 0

5

0 . 9

4 0 . 9

9 1 . 0

1

0 . 0

3

1 . 0

6

0 . 9

1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

s o l a r f

i e l d

s i z e

a n n u

a l n e t e

f f i c i e

n c y

a n n u

a l n e t e

l e c t r i

c o u t p

u t L E

C

a n n u

a l w a t e

r c o n

s u m p t i o n

t o t a l i n

v e s t c

o s t s

a n n u

a l O & M

c o s t s

Spain California

Reference is the sameplant at the same sitewith wet cooling tower

Gross output 55 MW

Water costs 1.0 €/m3



of LEC on Water CostsSensitivitySensitivity of LEC on Water Costs

L E C i n € / k W h

0.24

0.22

0.20

0.18

0.16

0.14

0.12

wet cooling Spain

Heller cooling Spainwet cooling Cal.

Heller cooling Cal.

0 2 4 6 8 10 12 14 16

water costs in €/m³




Conclusions and Next Steps

Change-over to dry cooling for STPP would reduce the water demand

significantly (>95% reduction) The electricity generation costs will increase by up to 5% (depending on

water cost) compared to evaporative cooling

Hybrid cooling technologies to enhance the cooling at high dry bulbtemperatures

Usage of storage technologies to shift the cooling loads partly to times with

lower ambient temperatures


Conclusions and Next Steps

Financing of the EFCOOL project by the German Federal Ministry for the Environment, NatureConservation and Nuclear Safety is gratefully acknowledged

Documents

Dersch Dry Cooling