CO2 Sequestration Breakthrough Program Phase I:

Geological Sequestration of CO2by Hydrous Carbonate Formation

with Reclaimed Slag(Accelerated Slag Aging Using Steelmaking Off-Gas)

Von L. Richards, Kent Peaslee, and Jeff Smith

Goal: Evaluate the technical and economic feasibility of using steelmaking off-gas to rapidly carbonize (age) steelmaking slag for beneficial re-use.

Slag CO2 Capture PotentialSlag produced per ton steel (NSA)

BOF: 75-150 kg, EAF: 65-80 kg, LMF: 15-20 kg30-50 wt.% CaO / 10-12 wt.% MgO

Kgs of CO2 sequestered per ton slag1000 kgs slag could capture 398.8 kgs CO2398.8 kgs CO2 = 108.9 kgs CO2 (CE)

CO2 per ton liquid steel at furnacesBOF: 187 kg CE EAF: 24 kg CE

Theoretical maximum percentage of offgas CO2 sequestered by slag

BOF: 6-11% EAF: 35-45%

Project Flow

Work Plan

ID Number

Task/Subtask Milestone Description

Planned completion

Actual Completion

Comments

1.0 Kick-off Meeting 3/17/05 3/17/052.0 Survey of Plant Application

2.1 • Written survey form for review by participants and AISI

4/21/05 6/15/05

2.2 • Survey sent out to plants 4/30/05 6/21/05 Rev. based on plant visits2.3 • - Plant visits 6/30/05 6/21/052.4 • - Survey summary 7/15/05 03/17/06

3.0 Literature Survey 7/30/05 8/30/054.0 Bench Evaluation of Kinetics 6/30/06 8/30/07

4.1 • Procedure development 7/30/05 06/30/064.2 • Characterization of slags 12/31/05 06/30/06 Complete to the extent

needed for subsequent work 4.3 • Development of kinetic

models (in existing codes such as Fluent, Metsim)

6/30/06 7/30/07

4.4 • Experimental studies 6/30/06 8/30/075.0 Model Evaluation of Production

System 8/30/06 Projected completion

11/30/07 6.0 Build Bench Pre-pilot Model of

Selected System 10/30/06 06/30/06 built wet system model to do

4.3, 5.0 7.0 Test Runs on Bench Model of

Selected System 1/30/07 9/30/07

8.0 Final Report 2/30/079.0 Oversight and coordination by

industrial sponsors 2/30/07

Carbonate Forming Compounds in Slag (XRF)

Elements(as oxides)

EAFAvg. (8)

BOFAvg. (2)

LMF(Avg. 3)

CaO 32.44 40.71 49.43

MgO 11.20 12.90 6.23

FexOy 26.85 21.68 5.61

SiO2 13.95 11.65 12.96

Al2O3 8.29 5.93 21.26

MnO 5.37 4.59 1.06

TiO2 0.47 0.58 0.34

ZrO2 0.07 0.18 0.20

Cr2O3 1.48 0.36 0.25

K2O 0.05 B.L. 0.01

Na2O B.L. B.L. 0.01

CaO16.76 cm3

CaCO336.89 cm3

Ca(OH)233.08 cm3

ΔH°= -65.2 kJ ΔH°= -112.7 kJ

ΔV=97.4% ΔV=11.5%

ΔH°= -178.1 kJΔV=120.1%

Phase Identification (XRD)(major phases listed)

PDF# Formula MineralA1aEAF

A1bEAF

A1gLMF

B1aBOF

C1aBOF

D1aEAF

E1aEAF

E2aEAF

ΔH°(kJ)

Stability(°C)

Oxide77-2355 FeO Iron Oxide X X X X X74-1225 MgO Periclase X -116.7 40174-1226 CaO Calcium Oxide X -178.1 861Silicate83-0461 Ca2(SiO4) Larnite X X X -105.6 40183-0460 Ca2(SiO4) Larnite X -105.6 40177-0409 Ca2(SiO4) Calcium (di)Silicate X X -105.6 40170-0388 Ca2(SiO4) Calcium (di)Silicate X -105.6 40134-1350 Ca5MgSi3O12 Calcium Magnesium Silicate X - -31-0301 Ca3SiO5 Calcium (tri)Silicate X -141.0 58579-1726 Ca2Al2SiO7 Gehlenite X -113.4 644Aluminate78-0910 Ca12Al14O33 C12A7 X X X X - -82-0579 (Fe0.855Al0.145)(Al0.855Fe0.145)Hercynite (Synthetic) X N/A N.A.Ferrite77-2368 (MgO)0.432(FeO)0.568 Magnesium Iron Oxide X X X -51.0 307

SEM/EDS CharacterizationElement Key: Fe Ca Al Mg

•Fe/Mn metallic particles distributed throughout slag, free of Ca, Si, or Mg.•CaO distributed through matrix, with FeO, SiO2 and Al2O3.

FeFe/Mn

E1γ (EAF) E1β (LMF Si-Killed)

Fe/Mn

•Fe/Mn metallic particles distributed throughout slag, free of Ca, Si, or Mg.•CaO distributed through matrix, with FeO and Al2O3.

•Fe/Mn metallic particles distributed throughout slag (10-50 μm), free of Ca, Si, or Mg.•CaO distributed through matrix, with a ~10mm particle of Al2O3.

E2γ (EAF) E2β (LMF Al-Killed)

Large blocks (100-500μm) of MgO spread throughout slag as discrete particles. •Small particles (5-25μm) of Al2O3 present.

Fe/Mn

Al2O3

MgO

SEM/EDS CharacterizationElement Key: Fe Ca Al Mg

Carbonate Phase Stability

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

1.00 1.50 2.00 2.50 3.00 3.501/T (°K-1) x 1000

log

P CO

2

1.00 1.50 2.00 2.50 3.00 3.50

Temperature (°C)

727 394 227 127 60 13

(Carbonate Stable)

(Oxide Stable)

Operating RegionpCO2=350 PPM-11%

MgO·SiO2

2CaO·SiO2

3CaO·SiO2

CaO

2CaO.Fe2O3 (Ca,Mg)O

MgO

CaO.Fe2O3

MgO.Fe2O3

Reactor Design Conditions

Furnace

Ladle

CanopyHoods

4th Hole

Fans

Baghouse

Cle

an O

ffga

s

GranulatedSlag

ReducedCO2

Offgas

CarbonatedSlag

RawOffgas

Combust& Quench

ProposedReactor

(EAF Application Shown)Pressure:

Direct after baghouse, ~ 1 atm.Temperature:

Maximum allowable to increase reaction rate150°C (typical baghouse limit)>300°C (allowed by thermodynamics)

Gas Composition:<15 vol. % CO2 (remainder N2 and O2)CO, SOx, and NOx not significant (PPM amounts)

Research Approach

Gas phase contact with slagTGA ApparatusHumidificationTemperature

Aqueous system contact with slagBatch and Two-Stage ReactorsLeaching/PrecipitationDirect Carbonization

TGA ApparatusGas Metering

(Ar, CO2, N2, Air)0-10.00 l/min

GasHumidification

Tube FurnaceReactor

25-1100°C

Balance0.001g accuracy

Sample SuspendedIn Reactor

0-400g range

DAQ

TGA Reaction

CaO

Reacting Gas (CO2/H2O)

CO2H2O

CaO+CO2→CaCO3

Gel = CO32-/HCO3

-/Ca2+/H+/OH-

Furn

ace

Wal

l

Furn

ace

Wal

l

TGA Results

0

2

4

6

8

10

12

14

16

18

0 5000 10000 15000 20000

% Carbonated

Time (sec)

300°C Dry500°C Dry300°C Humid500°C Humid

CaO, anaerobic grade CO2, P=1atm

TGA Results

0.001

0.010

0.100

10 100 1000 10000 100000

Frac

tion C

arbo

nate

d

Time (sec)

200°C Dry

300°C Dry

400°C Dry

500°C Dry

CaO, anaerobic grade CO2, P=1atm

TGA ResultsSlag E1β, anaerobic grade CO2, P=1atm

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0

% Carbonated

Time (hrs)

300°C Dry500°C Dry300°C Humid500°C Humid

Aqueous Sequestration

Description Reaction Ca leaching )(22

)()(2)(−+ +→+ OHCaOHCaO aqls

CO2 dissolution −+ +→+ 2)(3)(2)(2 2 aqlg COHOHCO

Carbonate precipitation )(3

2)(3

2)( saqaq CaCOCOCa →+ −+

Ca direct carbonization −− +=++ OHCaCOOHCOCaO slaqs 2)(3)(22

)(3)(

Water dissociation )(222)(2 lOHHOH →+ +−

Scenario 1: Fresh or recirculated water is supplied into Reactor 1, the leachate containing calcium ions is pumped to Reactor 2 in whichcalcium carbonate precipitates. The spent leachate (containing residual dissolved CO2) is discharged or recirculated into Reactor 1 after de-gasing.

Scenario 2: Recirculated solution is supplied to Reactor 2 for saturation with CO2, the CO2 saturated water is pumped to Reactor 1 for direct reaction with slag.

Pump

CleanedOffgas

Reactor 2

Reactor 1

StabilizedSlag

FreshSlag

Lower CO2

Offgas

WaterRecirculation

Loop

Ca Leaching Kinetics

Selective structure morphologyof Ca leaching in aqueous solution and macro reaction kinetics were described

Carbonization Kinetics

Modified shrinking core model was used for description of slag carbonization kinetics when product layer had different density and diffusivity

Carbonization vs. Leaching

Reactor Design

The different process scenarios were modeled and experimentally studied. The METSIM model developed can be used for the design of an optimized CO2 sequestration reactor system based on different slag fractions and compositions

Two interconnected reactors design gives the possibility for carbonization of existing industrial slag stream

Water out

CleanedOff-gas

Reactor 2Reactor 1

FreshSlag

StabilizedSlag

Lower CO2Off-gas

Pump

Water in

METSIM Model of Aqueous Process

F

H

G

L

M24

2526

27

19 FROM 15

TO 12 1816

17 21

20

22

A

B

C

D

E F1

8

432

75

3

10

6

FROM 20

TO 17119

12

13

14

15

Reactor 1 Reactor 2

Experimental 20 L reactor

Leaching and Precipitation(scenario one)

METSIM model shows that both increasing the slag/solution ratio and the solution residence time in Reactor 1 produces a higher concentration of

calcium ions in solution.

Direct Slag Carbonization (Scenario two)

Aqueous Process Modeling Conclusions

Continuous Ca leaching by fresh water:

Preventing formation of CaCO3 product layerAllows for precipitated CaCO3Water requirement higher

Direct carbonization in two-stage process:

Minimize the fresh water make-upProduct layer blinding partially overcome by increasing the slag surface area (i.e. decreasing the particle size), and increasing the residence time in the first reactor.

Grinding: Metal Recovery & Sequestration Value

Slag Type

PowerCost ($/t)

CO2Cost($)

MetalValue($/t)

Sequest.Potent.

(kg CO2)

CO2 Tax Credit

($)

Net

EAF ($2.19) ($1.21) $18.85 13.7 $0.75 $16.21 BOF ($2.41) ($1.33) $21.64 25.9 $1.43 $19.32 LMF ($1.82) ($1.01) $9.44 4.0 $0.22 $6.83 Overall ($2.16) ($1.20) $17.55 23.7 $1.31 $15.50

Feed Rate=1000 kg/hr, F80=2.54cm, P80=100µmElectric=$0.07/kWh, Power Correction=1.50Metal Scrap Value=$300/tCO2 Tax=$0.025/lb @ 1.55 pounds CO2 per kWhSequestration Efficiency=50%

Publications1. Rawlins, C.H., Richards, V.L., Peaslee, K.D., and Lekakh, S.N., “Sequestration

of CO2 from Steelmaking Offgas by Carbonate Formation with Slag,” AISTech 2006 Proceedings, Vol. II, 2006, pp. 1133-1144.

2. Rawlins, C.H., Richards, V.L., Peaslee, K.D., and Lekakh, S.N., “Steelmaking Slag as a Permanent Sequestration Sink for Carbon Dioxide,” Steel Times International, Vol. 30, No. 7, October 2006, pp. 25-28.

3. Rawlins, C.H, Richards, V.L., Peaslee, K.D., and Lekakh, S.N., “Experimental Study of CO2 Sequestration by Steelmaking Slag,” TMS2007 Materials Process Fundamentals, Edited by P. Anyalebechi, TMS, 2007, pp. 193-202.

4. Rawlins, C.H., Lekakh, S.N., Richards, V.L., and Peaslee, K.D., “The Use of Steelmaking Slag for Mineralogical Sequestration of Carbon Dioxide-Aqueous Processing,” AISTech 2007, Vol. II, 2007.

5. Rawlins, C.H., Lekakh, S.N., Richards, V.L., and Peaslee, K.D., “Mineralogical Sequestration of Carbon Dioxide through Aqueous Processing of Steelmaking Slag,” MS&T’07, 2007.

6. Lekakh, S.N., Rawlins, C.H., Robertson, D.R., Richards, V.L., and Peaslee, K.D., “Aqueous Leaching and Carbonization of Steelmaking Slag for Geological Sequestration of Carbon Dioxide,” Metallurgical and Materials Transactions B, manuscript accepted with required revisions Sept. 2007.

Projected deployment

Assuming second phase for development 2008-2010Deployment in production could occur between 2012 and 2017 because it uses a current co-product and has some economic benefit

Future Work

Catalytic AccelerationMicroscale modeling of heterogenous multiphase reaction with synthetic slagEvaluation of cooling rate and glassy phase effectsMicroscale optimization

GrindingIron recoveryCO2 SequestrationSlag processing

Acknowledgement

DOFASCOGallatin SteelHylsaUS SteelArcelorMittal Steel

PraxairNucor Timken Co.IPSCO

•U.S. Dept. of Energy and AISI for their financial sponsorship

•Corporate Partners: