Postcombustion Capture Amine Scrubbing By Gary T. Rochelle Department of Chemical Engineering The University of Texas at Austin July 7, 2014
Postcombustion Capture
Amine Scrubbing
By
Gary T. Rochelle
Department of Chemical Engineering
The University of Texas at Austin
July 7, 2014
Some Message
• The Problem : CO2 from Existing Coal Power
• The Solution: Amine Scrubbing deployed by 2020
• Advances in Solvents and Processes
– Reduce Energy from 400% to 200% of Minimum W
– Provide Stable, Benign Amine Systems
• As Limestone Slurry Rules FGD after 30 yrs;
Amine Scrubbing will dominate CO2 capture
2. Absorption/stripping = The technology
• Near Commercial
• Tail End Technology for Existing Plants
– Oxycombustion and gasification are not.
• Expensive in $$ and energy
CO2 Capture & Storage
Boiler ESP
Flyash
FGD
CaSO4
CaCO3
Abs/Str
Disposal
Well
Turbines
150 atm CO2
Coal
Net
Power
3-6 atm stm
-NOx
NH3
12% CO2
5% O2
10 ppm SO2
40oC
Packed
Absorber
1 bar
Stripper
2 bar
Packing
or Trays
30 wt% MEA CO2
Reboiler
45 psig stm
Amine Scrubbing (Bottoms, 1930)
DT=5C
115C
Other process components
• Additional gas pre-cleaning to remove
– SO2 -- neutralizes amine
– SO3 – causes amine aerosols
– NO2 – results in carcinogenic nitrosamine
– Chloride -- causes corrosion
– Particulate-- fouls equipment, causes amine aerosols
– Gypsum -- fouls solvent
• Gas precooling to 40oC to min energy use
• H2O wash to remove volatile & aerosol amine
• CO2 compression to 150 bar for storage
Gas Turbine/ Combined Cycle
• Modern CH4 power, sometimes base-loaded
– Compress 300% excess air
– Inject and burn CH4 to get 2000+F
– Expand to atm pressure (1000F)
– Extract heat in steam boiler to 300F
• 3-5% CO2 without recycle, 15% O2
– Does not require direct contact cooler
• 6-7% CO2 with recycle, 5-10% O2
• Get energy from low P steam
Tail End Technology Development
Characteristic of Absorption/Stripping
• Low risk, low cost, less calendar time
• Resolve problems in small pilot plants
– Using real flue gas
• Demo Full-scale absorbers with 100
MW gas
Other Solutions for Existing Coal Plants
• Combustion with O2 producing mostly CO2
– O2 plant gives equivalent energy consumption
– Gas recycle, boiler modification for high CO2
– Gas cleanup, compression including air leaks
• Coal Gasification
– Remove CO2 and burn H2 in new combined cycle
– O2 plant, complex gasifier, cleanup, CO2 removal
• Neither is Tail end
– Both require high development cost & time
Issues of absorption/stripping
Practical Problems = 40-70 $/MWh
• Energy = 20-25% of power plant output
– 10-15%, Low P steam (25-35% of steam flow)
– 5-10%, CO2 Compression
– 3%, Fans and pumps
– $15/ton CO2 (0.25 MWh/ton CO2 x $60/MWhr)
• Capital Cost $1000-1500/kw (e.g., $800 million-$1.2
billion for a 800MW plant)
– Absorbers same diameter as FGD, 50 ft packing
– Strippers somewhat smaller + heat exchangers
– Compressors
– $20-50/ton CO2 for capital charges & maintenance
• Amine degradation/environ. impact ($1-5/ton CO2)
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T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
Why amine scrubbing is here to stay
1. It was first: history repeats
2. It is remarkably energy efficient
3. Capital cost will come down
4. “Problems” are manageable
11
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
1. History Repeats in the Power Industry
CaCO3 Slurry:::Amine Scrubbing
CaCO3 Event Amine
1948 1st commercial plant 1980
1970 Too commercial for Gov. support
But too costly, too dirty to use
1990
1970-82 Government funds advanced alts
In hope of game changer
1995-
1975-85 Govern. & EPRI fund test facilities 2010-
1977 Power Industry deploys 250+ MW 2017?
2014 First choice dominates 2030 ?
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
1. It was first: The “MEA” 1G Standard
Amine scrubbing with absorption/stripping
Post-combustion technology
80 years experience in acid gas treating
Amine capture processes (Econamine & KS-1)
30 wt % (7 m) MEA benchmark (1st generation)
Reasonably fast, high DHabs, low m, low cost
Not thermally or oxidatively stable
13
Background
Aqueous Abs/Str: Near commercial– 100’s of plants for treating H2 & natural gas
• MEA and other amine solvents
• No oxygen
– 10’s of plants with gas combustion
• Variable oxygen, little SO2
• Fluor, 30% MEA, 1000 tpd (80 MW gas), 15% O2
• MHI, KS-1, 283 tpd (30 MW), <2% O2
– A few plants with coal combustion
• Abb-Lummus, 20% MEA, 6,8,33 MW
• Fluor, 30% MEA, 0.1,0.2,0.2,(6) MW pilots
• CASTOR, 30% MEA, 1 MW
• MHI, KS-1, 1, 25 (7) MW
• Cansolv, 125 MW
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
2. 2G is Remarkably Energy Efficient.
e.g. Piperazine [PZ] (5-8 m, 30-40 wt%)
2G/3G amine technology
Fastest rate of CO2 absorption
Resistant to oxidation & thermal degradation
High-T/P advanced flash process
Twice the capacity of 7 m MEA
Sufficiently high DHabs = 65-70 kJ/mol
Higher chemical cost, greater viscosity, constrained by solid precipitation
15
Background
2. Advanced Flash Stripper is remarkably efficient
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5K Avg. LMTD
Lean Solvent0.30 Ldg.
Cold Rich BPS 5%
Warm Rich BPS 14% 121 oC
25% H2O 20K LMTD
5% H2O
Flash
Rich Solvent0.40 Ldg Steam heater
150 oC
Alternative stripper configurations8 m PZ, 150oC
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32
33
34
35
36
37
0.26 0.28 0.30 0.32 0.34
WE
Q(k
J /
mo
lC
O2)
Lean loading (mol CO2 / mol alkalinity)
Advanced flash stripper
Flash stripper+Cold rich BPS
Simple stripper
Interheated stripper
10%
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
Estimated Total Equivalent Work 12% CO2, 90% Removal, 150 bar, 40 °C
0
100
200
300
400
500
2000 2004 2008
W (
kW
h/
ton
ne C
O2)
Year
PZ
MEA
0.72 GJ/t
1.08 GJ/t
18
Minimum Work = 109 kWh/tonne = 0.39 GJ/t
Energy Analysis
CO2 Separation = 46 kWh/tonne = 0.17 GJ/t
Compression = 63 kWh/tonne = 0.23 GJ/t
pumpcomp
stm
sinkstm
equivWW
T
TTQ75.0W
Thermodynamic Efficiency of Common Separation Processes
Process Efficiency (%)Wminimum / Wactual
CO2 Capture by Amine Scrubbing 54
Cryogenic Air Separation 25
Common Distillation 15-35
Water Desalination by Reverse Osmosis 21
Therefore it is improbable that we will be better than 200 kwh/ton CO2,with any technology.
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MEA-SS PZ-SS PZ-AFS
CAPEX 22.2 22.1 19.4
Absorber 5.2 4.7 4.7
Amine/Amine Exchangers 1.8 4.8 5.2
Reboiler/Steam Heater 4.3 5.7 2.3
Compressor 5.6 3.6 3.5
All Other Units 5.3 3.3 3.7
3. Capital Costs will Decrease.Annualized Equipment Cost for Amine Scrubbing, $/tonne CO2
3. Opportunities to decrease CAPEX
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Absorber
Merge SO2 polish, DCC, CO2 absorption, water wash
Single vessel, concrete, intercooling
Cross Exchanger, Steam heater
Greated DP, Less expensive plate and frame
Larger single unit
Compressor
Greater stripper P
Larger single unit
Intercooled, supersonic
4. Amine “Problems” will be solvedAs with CaCO3 scrubbing
Problem Resolution
Corrosion Use StainlessInhibitors
Control Chemistry
Oxidation Stable Amine (PZ)Inhibitors
Thermal Degradation Stable Amine (PZ)Lower Stripper T
Nitrosamine Thermal decompositionReduce NOx
Amine Aerosol Advanced water wash?Nonvolatile amine
Aqueous Solvent Alternatives
MEA is hard to beat
• Stripper Energy Requirement
• Mass Transfer Rates
• Makeup and Corrosion
Carbonate & Tertiary/Hindered Amines
HO-CH2-CH2-N-CH2-CH2-OH ↔ MDEAH+ + HCO-3
׀CH3 60 kJ/gmol, slow
Methyldiethanolamine (MDEA)
CH3׀ ׀HO-CH2-CH2-NH2 + CO2 ↔ AMPH+ + HCO-
׀3CH3 60 kJ/gmol, slow
2-Aminomethylpropanolamine (AMP, KS-1(?))
CO3= + CO2 + H2O ↔ 2 HCO-
3 20 kJ/gmol
Carbonate Bicarbonate very slow
+ CO2 ↔ +HPZ-COO-
Piperazine (PZ)
Primary and Secondary Amines
60-85 kJ/gmol, fast
CH2-CH2
HN NH
CH2-CH2
2 HO-CH2-CH2-NH2 + CO2 ↔
HO-CH2-CH2-NH-COO- + MEAH+
Monoethanolamine (MEA)
MEA Carbamate (MEACOO-)
2 NH3 + CO2 ↔ NH2-COO- + NH4+
Ammonia
Fast Solvents
Amine (m)Capacity
-∆Habs
@PCO2 =1.5kPa
kg,’avg x1e-7
@40 °C
Deg rate
@135oC
mol/kg solv kJ/mol mol/s·Pa·m2 1e-9 s-1
PZ 8 0.79 70 8.5 1.2
1-MPZ 8 0.83 67 8.4 7
MDEA/PZ 5/5 0.99 70 8.3 45
2-MPZ/PZ 4/4 0.84 70 7.1 3
MDEA/PZ 7/2 0.80 68 6.9 45
2-MPZ 8 0.93 72 5.9 5
HEP 7.7 0.68 69 5.3 35
MEA 7 0.47 82 4.3 134
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
Why Advanced Capture Processes
flounder1. Separation driven by mechanical compression is
not energetically competitive with thermal swing.
2. Anhydrous solvents, slurries, and solids are not
more reversible than amine solutions.
3. Solids and slurries have poor equipment
alternatives for heat exchange & contacting
4. More expensive solvents & polymers will not
compete in the dirty coal environment
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T H E U N I V E R S I T Y O F T E X A S A T A U S T I N
Texas Carbon Management Program
Why amine scrubbing is here to stay
1. It was first: history repeats
2. It is remarkably energy efficient
3. Capital cost will come down
4. “Problems” are manageable
28