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)

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

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

16

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

17

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.

20

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

21

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

27

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