Materials and Chemistry 1

Post Combustion Capture

Dr. Thor Mejdell, SINTEFResearch manager CO2 Capture Processes

IEA GHG International CCS Summer School 2010Spitsbergen, 22-28 August

Materials and Chemistry 2

Main routes for CCS

Power plant Conventional

CO2capture

CoalOilNatural gas

CO2 storage

1

Gasification Reforming

Water-shift

CO2capture

Power plant Hydrogen-rich fuel2

Air separation Power plant Oxy-fuel combustion

Waterremoval

3

Exhaust, 0.3-0.5% CO2

Exhaust, 0.1-0.5% CO2

OHOH 222 22 ⇔+

COH +2 22 COH +

OHCOOCH 2224 2+⇔+

2O

Post combustion processes will probably be the main route for some time Are used today, existing power plants may easily be retrofitted. It will probably be too late to wait for new power stations. Normal lifetime 30 -50 years! May also be used on other large stationary emission points (industry)

Materials and Chemistry

Post combustion technologies Because the partial pressure of CO2 in the exhaust gases

from power plants is very low (4 -12 kPa), a very limited number of technologies are feasible.

Absorption of CO2 with chemical reaction is practically the only feasible alternative today.

Possible alternatives on a longer term Membranes Adsorption onto porous particles with amine functionality

Note: If the exhaust gas is pressurized more technologies are feasible

3

Materials and Chemistry 4

A typical absorption capture process

Materials and Chemistry

The CO2 is transferred from gas to liquid

H2O CO2(liquid) Ionicspecies

H2O CO2(gas)Gas

Liquid

Interface

Absorption of CO2 with chemical reaction

The amine reacts selectively with CO2

Materials and Chemistry

The solvent(liquid) is an aqueous solution with amines:

MEAMonoethanolamine

Piperazine PZ MDEAMethyldiethanolamine

AMPAminomethylpropanol

Materials and Chemistry

Reversible reactions:

−+ +↔+ RNHCOORNHlCORNH 322 )(2

)()( 22 lCOgCO ↔Dissolution of CO2 in solvent

Reversible reaction with amine to form carbamate

Key properties:Equilibrium constantsRate of reactionHeat of reaction

Materials and Chemistry 8

Equilibrium isotherms for MEA

The partial pressure of CO2 may be 1000 times higher at 120 C compared to 40 C!

Materials and Chemistry 9

Temperature swing process

2 2 2 2 22CO HNR NR COO H NR− +→+ +←

Materials and Chemistry 10

Main challenges: Reduction of costs, especially energy costs Better absorbents (amines)

Less energy demanding Faster (lower absorber height – smaller investment costs) Less environmental impact (lower gas slip, less degradation etc)

Better and cheaper units Columns, heat exchangers, etc Packing materials

Better integration, both with the power station and between the different unit operations in the capture process May give substantial energy reductions Important with reliable simulation software.

Materials and Chemistry 11

The search for economically favorable absorbents Screening apparatus – experimental

testing of a large number of chemicals Molecular simulation

Experimental characterization of absorbents and packing materials Gas-liquid equilibria, kinetics, viscosity

and diffusivity Degradability Corrosion

Establishment of basic models Thermodynamic models Kinetic models Effective gas/liquid contact area

Modelling and optimization of full scale plants Early stage Matlab calculations: steam

consumption, absorber height CO2SIM – rigorous models of absorber,

desorber, membrane-contactor and whole plants

Research activities:

Validation of models for absorption and desorption Pilot plants Testing rig for packing materials, liquid

distribution, effective contact area etc.

Technical and economical calculation of industrial plants Dimensioning, CAPEX and OPEX

calculations Related to simulations in ProTreat, Hysys

and CO2SIM

Studies of environmental impacts of the technology Degradation chemistry General ecotoxicology and

biodegradation

Materials and Chemistry

Modelling

Computational chemistry (Molecular modelling ): Reaction mechanism Predicting solubility and equilibrium constants

Thermodynamic modelling, i.e. gas/liquid equilibrium Activity coefficients Speciation, NMR measurements Models fitted to experimental data

Kinetic modelling Models fitted to experimental data

Simulation models of absorber/desorber units (rate based calculations) Packed towers Membrane contactors

Materials and Chemistry

Total steam requirement (MJ/mol CO2 captured)

( )( )

2 2

2

2

, ,

*,

satH O Top Des H O freebasis vap

strip H OCO Top Des Rich

P T xQ H

P T α= ∆

2 2Tot CO H O AmP P P P= + +

( )sensrich lean Am

Cp TQC

ρα α

∆=

−

Conc. CO2

Reboiler

Overhead condenser

Lean/Rich heat exch.

Lean solvent

Desorber

Reflux

Qsens+Qdes+Qstrip

T≈120C

∆T≈10C

2des absCOQ H= ∆

Materials and Chemistry

• Regeneration energy requirement• Rate of absorption• Cyclic capacity• Water solubility• Vapor pressure• Corrosiveness• Chemical stability (Stable in process, degradable in nature)• Molecular weight• Viscosity• Foaming properties• Toxicity• Cost and availability

Solvent selection criteria

Materials and Chemistry 15

Ecotoxicity and biodegradability

Skeletonema - EC50

100

101

102

103

104

105

EDA1.3-propane-diamine

MEAMPA

4-amino-1-butanolAMP

MMEAEAE

AEEADETAAMPD

DEABHEDGA

DMMEADEEAAEPDMDEAMIPADIPA

PyrrolidinePiperidinePiperazine

MorpholineHydroxyethylpiperazine

TMPDAGlycine

SarcosineAlanineDMAPA

Dimethylam.DMPAPETAACHP

TertBut EtanolamineSpermidine

SpermineSulfolan

TriethylamineDMPDA

MAPA

EC-50 (mg/L)

BOD

0 20 40 60 80 100EDA

1.3-propane-diamineMEAMPA

4-amino-1-butanolAMP

MMEAEAE

AEEADETAAMPD

DEABHEDGA

DMMEADEEAAEPDMDEAMIPADIPA

PyrrolidinePiperidinePiperazine

MorpholineHydroxyethylpiperazine

TMPDAGlycine

SarcosineAlanineDMAPA

Dimethylam.DMPAPETAACHP

TertBut EtanolamineSpermidine

SpermineSulfolan

TriethylamineDMPDA

MAPA

BOD (% of ThOD)

Materials and Chemistry

Experimental screening

N2

CO2

Water Bath

Absorber Saturator

Purge

IR CO2 AnalyzerCondenser

Data AcquisitionSystem

MFC

TIC TI

FI

Heater

MFC

P = 1 bar, T = 40C CO2-N2 gas mixture : 10 vol% CO2

Materials and Chemistry

Typical screening results

Materials and Chemistry 18

Examples laboratoryequipment

Equilibrium high temperature

Equilibrium low temperature

Measurement of absorption enthalpyKinetics/mass transfer

Materials and Chemistry

Experimental gas liquid data used to fit parameters in an equilibrium model

0.001

0.01

0.1

1

10

100

1000

0.00 0.20 0.40 0.60 0.80 1.00

CO2 loading / (mol CO2/mol AEEA)

pC

O2 /

kPa

40 C

55 C

70 C

95 C

120 C

Materials and Chemistry 20

15 cm ID absorber, 4.5m10 cm ID desorber

Water wash / inlet gas conditioner section

Fully instrumented and automated to run on a 24 hour basis

Lab Pilot at SINTEF/NTNU

Materials and Chemistry 21

Materials and Chemistry 22

30m (11 floors) high SINTEF-building.

New Pilot plant at Tiller, Trondheim

Materials and Chemistry

Casebuilder view

Simulation of the whole plant

Materials and Chemistry

Comparing pilot runs with simulations

Model validation Compare runs Check of the experimental data Adjust if necessary some of the parameters in the simulators

The validated simulations models may then be used to find optimal values for post combustion. Optimal designs (height and diameters) Optimal run parameters (circulation rates, temperatures etc)

0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.360

0.04

0.08

0.12

0.16

0.2

0.24

0.28

0.32

0.36P3 loading CO2

1

2

34

5

67

Exp

erim

enta

l loa

ding

Simulation loading

Materials and Chemistry

Optimization important for cost reductions

Optimizing criteria Minimum energy consumption (MJ/kg CO2 captured) Minimum total costs €/kg CO2 avoided (need then cost calulation

software.

The validated simulations models is used to find optimal values for the specific solvent. Optimal designs (height and diameters) Optimal run parameters (circulation rates, temperatures etc)

If possible, optimize the combined power & capture plant Heat integration may give lower energy consumption More complex process, the operability of the plant may be worse

Materials and Chemistry

Integration absorption/power plant (Gibbins and Crame 2004)

Materials and Chemistry

Bolland: Reduction of efficiency

EQWP αη −−

=Efficiency

Power output withoutCO2 capture

Mechanical work for separation

Heat for separation

Fuel energy QP∆

=α

60 80 100 120 140 160 180 200 220 240 260Saturated steam , temperature [0C]

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Rat

io o

f in

crem

enta

l pow

er re

duct

ion

to in

crem

enta

l hea

t out

put, α

0.3 0.5 0.8 1.3 2 3 5 7 10 20 40Steam pressure [bar]

Materials and Chemistry

Absorber diameter of 50 or 75 cm Testing various absorber packings

Liquid distribution and pressure drop Efficient gas-liquid area Gas and liquid distribution Back mixing and entrainment

Better models for simulations

Gas-Liquid contactorsTest of different packings

Materials and Chemistry

CO2

Gas with CO2

CO2

n Membrane is not selective, it only separates the gas and liquid phases

n Diffusion through pores followed by reaction in liquid; CO2-absorption with alkanolamine solutions

Micro-porous Membrane

Absorption Liquid

Alternative to packed tower: Membrane gas-liquid contactor

Materials and Chemistry

Advantagesl No foaming, channeling,

entrainment or floodingl Contact area independent of

flowl Higher contact area, 500 - 1500

(m2/m3) l 70% reduction of size and

weight

Compared to a packed tower

Disadvantages:l Possible mass transfer resistance in

the membraneè Requires hydrophobic

membrane material, eg. PTFEl Phases are bound to laminar flow

(significant improvements with mixing points)

l Probably more expensive

Materials and Chemistry

Other post combustion techniques

Membrane gas separation Adsorption

Advantage No transport of liquid phase

Disadvantage More complex process At the moment more costly

Materials and Chemistry

Membrane gas separator

Want membranes with High Permeability [ mol/(m2 bar h) ] for CO2

High selectivity for CO2

Feed gas Retentatemembrane

Permeate

Permeate

membrane

Materials and Chemistry

Fixed site carrier (FSC) membraneFacilitated transport

– Membrane must be humidified – Temperature variations are less important (Tmax ~ 80°C)

60 65 70 75 80 85 90 95 1000

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Humidity index

CO

2 per

mea

nce

[m3 (S

TP)/(

h m

2 bar

)]

Single gas experiments with FSCM at 25°C and dp 0.5 bar

82 84 86 88 90 92 94 96 98 1000

100

200

300

400

500

600

Humidity index

Sel

ectiv

ity

Single gas experiments with FSCM at 25°C

CO2/CO at dp 1 bar

CO2/N2 at dp 0.5 bar

Per

mea

nce

Sel

ectiv

ity

Materials and Chemistry

Temperature swing adsorption

Pressure ~1barTemperature ~50ºCf.ex. 10-14 %vol CO2

Materials and Chemistry

Aspects with adsorption for post comb

VPSA (Vacuum pressure swing adsorpion is probably not feasible, TSA is the only current option (or TSA+VPSA)

Cyclic capacity and adsorbent lifetime Pressure drop Moisture Heat transfer Valves

Materials and Chemistry

Summary

Post combustion is relatively easy to implement Absorption with chemical reaction is the preferred method Commercial bidders is available High consumption of thermal energy Research and development to reduce the energy penalty Better solvents

More energy efficient Less environmental impact

Process modeling and optimization is important for energy reduction

Materials and Chemistry

Chemical Absorption(MEA)

Adsorption(PSA)

Membrane Separation(Polymer)

Capital 36% Electricity 59%

Others 12%

Capital 17% Electricity 80%

Others 2%

Capital 24%Electricity 27% Steam 36%

Others 4%

Cost for CO2 separation technologies(CO2 capture from coal fired power plant:CO2 13.2%)

Steam 2%

Materials and Chemistry

Size of absorption tower

Example:

400 MW NG fired power station

Exhaust gas rate:2000000 m3/h flue gas

Typical gas velocity: 2m/s

Tower cross sectional area:280 m2

Diameter: 19 m

Height: 35 m