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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
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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
luegasDesulphurization
ESP Membranes
Furnace F
luegasDesulphurization
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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Thank you for your attention