Energy Consumption of Water Capture

8/11/2019 Energy Consumption of Water Capture

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Documentnumber

A new source of waterEnergy consumption of water capture

for gas-/coal-fired power plants

By: Ludwin Daal


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Contents

Water capture by membranes

Purpose

Case definition

- Process considerations

- Model and settings

- Assumptions

Results Coal and Gas cases

- Consumption improvements on vacuum andpressure drop on ID fan

- Savings

Conclusions


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Working principle water vapour capture

Flue gas

P = 1atm

H2O

Hollow membrane fibre

Special Coating

Vacuum

NOx

H2OSO2

CO2

H2O

NOx

SO2

CO2

H2O

Micro scale Macro scale

Vacuum &

Condenser

O2

N2

N2

O2

Flue gas

P = 1atm

H2O

Hollow membrane fibre

Special Coating

Vacuum

NOx

H2OSO2

CO2

H2O

NOx

SO2

CO2

H2O

Micro scale Macro scale

Vacuum &

Condenser

O2

N2

N2

O2

3


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Principle water capture

400 MW coal fired powerplant:

Emits 150 m3 water perhour to the atmosphere

Needs 30 m3/h water

20% capture

Furnace F

luegasDesulphurization

ESP Membranes

Furnace F


ESP Membranes

Furnace F


ESP Membranes

Equiv. Gas Fired plant: Emits 100 - 150 m3 water per hour

Needs about 1 m3/h water

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Field test Waste to Energy plant

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12 years preliminary research

Background:

- Power companies expected doubling of water tariff in the 90s

- Surface water needed extensive water treatment steps

- Research by KEMA, University of Twente & Dutch Power industry

Overview of general technology development:

Field tests flue gas Relative humidity Duration Results (1) Year

Coal fired power plantafter reheat max. 60 C

95-99% 32 weeks 0.2 L/m2/h

500 1000 S/cm

2003

Coal fired power plantafter FGD 46 -48 C

100% >5000 hours 1.4 L/m2/h

20 S/cm

2006

Waste to Energymax. 65 C

100% 1 year 3-4 L/m2/h

40 S/cm;

2007

Gas burner at 40-50 C 70% 20 hours ~1 L/m2/h 2009

Gas burner at 80-90 C 10% 100 hours ~0.03 L/m2/h 2010

>40% water capture, results warrent a follow up!

(1) water flux in litre liquid water per m2 membrane area per hour; water purity in specificconductivity


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Goal / ambition of EU project: Capture of

evaporated water - CapWa

produce a commercially available membrane modularsystem suitable for industrial applications within 3-4

years. The produced demin water from this systemshould be competitive with existing demin watertechnologies. The starting point will be the water

vapour selective composite membranes that aredeveloped in the proof of principle project.

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www.watercapture.eu


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Purpose energy modelling: why, what for?

Confirm feasibility / perspective

What to focus on with respect to OPEX

- Most energy intensive aspects

ID fan (pressure drop)

Vacuum pump

Air cooled condensing

Not The Final Word

- Revision should & will follow

- Field testing to validate results


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Driving force concept selection


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Case definition: (1) application factors, ...


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Coal Gas

Selected plant IEC Ruthenberg Gas Natural AcecaPlant info 550 MW unit CC 380 MW, GE9FA turb.

CO2(v/v) 13.0% 4.0%

N2(v/v) 70.0% 74.0%

O2(v/v) 3.8% 14.0%

H2O (v/v) 13.2% 8.0%

Flue gas temperature 55 C 110 C

Flue gas flow 1900000 m2/h 24413 kg/h

Case definition: (1) application factors, ...


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... (2) location factors, and...

CapWa technology for hot / arid areas, therefore:

- No water cooling

- Only Air Cooled Condensors (ACC)

- Two temperatures: 20 C & 50 C (exit flow)


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... (3) membrane process factors

Recovery: plant self-sufficiency

Pressure drop: 10 mbar

Permeate compos.: 99% H2O, 1% CO2 v/v

Driving force generation

- Liquid ring pump: t 50%, cooled 80 C

- Steam jet pump: th14.8%, 3 bar steam, ...

Membrane area & separation implicit

-Hidden in pressure drop, composition

Assumption: fixing these variables is OK,

they should have no big influence on each other / results*


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Case summary, model

Number of cases:

- 2 applications coal, gas

- 2 cooling temperatures 20 C and 50 C- 2 vacuum methods steam jet, liquid ring

- 2 recoveries low and high

2 x 2 x 2 x 2 = 16 cases

Note: worst case scenarios

- Reference case: water cooling to 12 C

Model: KEMAs proprietary SPENCE

process modelling software package


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Example SPENCE CapWa model scheme

Slide is not for reading every

number, but for the big picture

2. FG cooler (gas PP)

13. Membrane unit

4. ID fan

6. Condensor (+ACC)

9. Suction (+ACC)

10. Condensor

(for steam jet)8. Liq. water pump


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First results Coal cases Trend is important..

Reference


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Results Gas cases similar trends as Coal


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Further improvements in modeling work

Coal cases: reference & ACC (50oC); Gas case: ACC (50oC )

3-step recompression of vacuum system

determined p for fibres placed in row with 20% water recovery


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Performance calculations by SPENCEProporionate energy consumption


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Proportionate of energy consumption on OPEX

Membranes26%

Piping18%

Condensor4%

Vacuum pump2%

energy50%

Membranes44%

Piping30%

Condensor7%

Vacuum pump3%

energy16%

ACC Cooling water system

Pie diagrams for a 600 MWe coal plant with 20% capture rate 37 m3/hr


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Proportionate CapEx and OPEX of a Gas unit (Dry region)

Difference between Coal fired units is amount of watercaptured

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membranes17%

piping28%

ID fan32%

Condensor19%

Vacuum pump4%

Membranes36%

Depreciationothers32%

Maintenanceothers5%

Energy27%

Pie diagrams for a 380 MWe gas plant 40% capture rate 1 m3/hr at ACC 35oC


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Energy savings achievable for Coal units

DescriptionSaved

[kWe]

Capture

rate Remarks Likelihood

No reheating of flue

gas by low pressure

steam

3300 >70%

Additional water loss

at FGD due to high

inlet temperatures

NO, hardly any cases

like this, increase use

of wet stack

Energy recoverybefore FGD - 3rd

condensate preheater

6960 70%?

High CapEx and

OPEX for plastic /

ceramic heat

exchanger

NO, new power plants

are not built this way

due to poor payback

time

Condensate preheating 924 >12%

In wet cold areas

access to coolingwater, if accessible

by piping

YES, if piping can be

reached. Also savingscombined with the

savings described here

For a 600 MWe coal plant with x amount of capture


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Analysis: trends and conclusions

Liquid ring pump better than steam jet

Relative order of cases same for gas & coal

After improvements: vacuum generation consumes most

energy (pump & ACC)

Water price in interesting range:


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Analysis: recommendations

...some assumptions not valid!

- Fixed recovery (pressure range too wide)

- Fixed membrane area

So: further modelling and field validation necessary:

- Recovery dependent on vacuum pressure

- Membrane area (hence pressure drop) variable effectsOPEX and CapEX

Separately: strive to reduce non-condensables in permeate

- Optimise selectivity

- CO2 removal before recompression?


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Energy Consumption of Water Capture