Conversion of Black Liquor in a Fluidized Bed Steam Reformer

Kevin WhittyInstitute for Combustion & Energy Studies (ICES)

The University of Utah

7th International Colloquium on Black Liquor Combustion and GasificationJuly 31 – August 2, 2006

Jyväskylä, Finland

2

Outline

Intro – BL steam reforming• Fluidized bed steam reforming• Commercial installations• Steam reforming research

This study – Experimental systemLiquor conversion in a steam reformer• Fate of organic carbon• Factors impacting carbon conversion• Development-scale versus full-scale

Conclusions

3

Outline

Intro – BL steam reforming• Fluidized bed steam reforming• Commercial installations• Steam reforming research

This study – Experimental systemLiquor conversion in a steam reformer• Fate of organic carbon• Factors impacting carbon conversion• Development-scale versus full-scale

Conclusions

4

Black Liquor Steam ReformingAlternative to combustion in recovery boiler• Improved energy efficiency• Better environmental performance• Can improve pulp yield and quality• Safer technology

Fluidized bed reforming• Steam for fluidizing and reactant• Operating temp. ~1120°F (605°C)• Endothermic process – indirect

heating• Bed solids made of "ash" product

from reformingDevelopers• MTCI – Process development• TRI – Commercial installations

Black liquor

Productgas+air

Fluegas

Bed solids Steam

Product gas

PulsedheatersBlack liquor

Productgas+air

Fluegas

Bed solids Steam

Product gas

Pulsedheaters

5

Norampac Steam Reformer

Photos courtesy of Norampac

Trenton, ON, CanadaStartup June 20031x100 tds/day reformerCarbonate liquorNo product gas conditioning –Sent directly to boilerBed heaters fired on natural gas

6

Big Island, VirginiaStartup Spring 20042x100 tds/day reformerCarbonate liquorProduct gas handling• Superheater• Venturi scrubber• Gas cooler• H2S scrubber

Bed heaters fired with clean product gas

G-P Big Island Steam Reformer

Photos courtesy of Georgia-Pacific Corp.

7

Steam Gasification Research

Atmospheric studies• 1980s – 1990s• Van Heiningen

Pressurized studies• 1990s• Whitty, Frederick, Hupa (Åbo Akademi)• VTT Finland

In-house development at MTCI• 1980s – 1990s• Proprietary

8

Outline

Intro – BL steam reforming• Fluidized bed steam reforming• Commercial installations• Steam reforming research

This study – Experimental systemLiquor conversion in a steam reformer• Fate of organic carbon• Factors impacting carbon conversion• Development-scale versus full-scale

Conclusions

9

U.Utah Steam Reforming System

Water

Bed solids

Internalcyclone

After-burner

Dry gas to analyzers

Freeboard

Bed heaters

CW in CW out

Boiler

R.O.

AirNaturalGas

Condensate

Cooler/condenser

Black Liquor Tank (heated)

Circ.pump

Feedpump

Lockhopper

Distributor

Superheater

Soften Steam

Air

N2

Steam

Exhaust

Air Nitrogen

Pressure control valve

Pressurerelease

Gas to slipstream reactors

H2O in

H2O out

H2O

Natural gas

10

Gasification Research Facility

Fluidized bedsteam reformer

Boiler

Fuel tank Product gas cooler

Afterburner

Superheater(under grating)

Slipstreamreactors

Entrained-flowgasifier

11

Steam Reformer Bed Section

LiquorInjector

PowerLeads

ThermocoupleLeads

SamplePort

SamplePort

HeaterBundles

Thermocouple

12

Steam Reformer Bed Section

13

Outline

Intro – BL steam reforming• Fluidized bed steam reforming• Commercial installations• Steam reforming research

This study – Experimental systemLiquor conversion in a steam reformer• Fate of organic carbon• Factors impacting carbon conversion• Development-scale versus full-scale

Conclusions

14

Black Liquor Conversion

Char

Pyrolysis

Volatiles,tars

Droplet Solids

Drying

Moisture

Smelt

Char gasification

H2O H2, CO, CO2

H2O(g) + C(s) H2(g) + CO(g)

H2O(g) + CO(g) H2(g) + CO2(g)

15

Fate of Organic Carbon

Gas(CO, CH4, CO2)

Tars

Bed Solids

Organiccarbon

16

Carbon ConversionApproximate fate of organic carbon

Gases: 95-99%Tars: 0%Bed Solids: 0.5-2%

PDU

UtahGases: 65-85%Tars: 10-30%Bed Solids: 2-8%

Big IslandGases: 58-80%Tars: 4-20%Bed Solids: 10-25%

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Tars – Variation in Results

Residence time• Utah: 2 + 8 seconds in bed + freeboard• Big Island: 10 + 7 seconds in bed + freeboard

Temperature• Utah freeboard exit temperature: 420°C (790°F)• Big Island freeboard exit temp: 590°C (1095°F)

Measurement technique• Utah: Cold trap to –20°C with dichloromethane• Big Island: Difference from system balance plus

cold trap measurements• MTCI PDU: No specific effort to trap tars

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Char Conversion Studies

Determine factors that impact char carbon conversion (residual bed carbon)• Temperature• Presence of product species (H2 and CO)

Consider difference between small scale PDU studies and full-scale systems• Small-scale systems achieve >95% conversion

to gases (+ tars)• Full scale system achieving only 70-85% carbon

conversion

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Bed Carbon versus TimePure steam. No liquor feed.

0%

2%

4%

6%

8%

10%

12%

14%

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (hours)

Org

anic

Car

bon

Con

tent

(wt%

)

Reaction order = 0.0

0.5

1.0

20

Lab-Scale Char Conversion StudiesInfluence of hydrogen on gasification rate

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

H2 partial pressure, bar

0

4

8

12

16

20M

ax. r

ate

(x10

4 ), s

–12% H2

4% H2

21

Lab-Scale Char Conversion Studies

2% CO

4% CO

0.70.10.0 0.30.2 0.50.4 0.60

2

4

6

8

10

12

14

CO partial pressure, bar

Max

. rat

e (x

104 )

, s–1

Influence of carbon monoxide on gasification rate

22

Bed Carbon versus TimePure steam. No liquor feed.

0%

2%

4%

6%

8%

10%

12%

14%

0 2 4 6 8 10 12 14 16 18 20 22 24

Hours

Carb

on C

onte

nt [w

t%]

23

Bed Carbon versus TimeAddition of 25% H2

Ave. 0.75%C/hr

0%

2%

4%

6%

8%

10%

12%

14%

0 2 4 6 8 10 12 14 16

Time (hours)

Car

bon

Con

tent

(wt%

)

Pure Steam

Steam with 25% H2

Pure Steam

Steam with 25% H2

25% H2 Present

Ave. 0.16%C/hr

24

Bed Carbon versus TimeAddition of CO

Ave. 0.56 %C/hr

Ave. 0.75 %C/hr

Ave. 0.52 %C/hr

Ave. 0.48 %C/hr

0%

2%

4%

6%

8%

10%

12%

14%

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (hours)

Car

bon

Con

tent

(wt%

)Pure Steam

With CO addition

Pure Steam

With CO addition6.4% CO 2.6% CO

25

Reactor Comparison

17 psia 44 psia

Parameter PDU Utah Full-scale

Bed height, ft 4 5 33Bed area, ft2 2.3 0.54 104Bed mass, lb 725 200 233,000Steam feed, lb/hr 223 42 12,250BLS feed, lb/hr 14 12 6,400Steam/fuel ratio 16 3 2Feed/bed area 6 22 61

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

0% 20% 40% 60% 80% 100%

Percent through Bed (bottom to top)

Par

tial P

ress

ure,

atm

H2O - Full Scale

H2O - PDU H2 - Full Scale

H2 - PDU

Full versus PDU ScaleGas partial pressures through reactor

Steam only with no liquor injectionAssumes 0.5 wt% of bed (as C) converted per hourUses bed mass, steam flows from real systemsAssumes water-gas shift always at equilibriumAssumes bed solids are well-mixed

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0% 20% 40% 60% 80% 100%

Percent through Bed (bottom to top)

Parti

al P

ress

ure,

atm

H2 - Full Scale

H2 - PDU

CO - Full Scale CO - PDU

H2 and COSteam and H2

27

Full versus PDU ScaleRates and associated conversions

Full/PDU ratios at top of bed:

PH2: 7.8

PCO: 53.0

Rate (van Heiningen): 0.706

Rate (Whitty 1): 0.600

Rate (Whitty 2): 0.021

Decrease from 97% to 75% carbon conversion requires that the rate becomes 20% as fast (for reaction order = 0.5)

[ ][ ][ ] [ ]22

/200,252

9

42.1103

HOHeOHCRate

T

+×

=−

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

++=

⎟⎠

⎞⎜⎝

⎛ −−

COOH

H

T

pp

peRate

09.7449.0

1

01.910

2

2

1923

1000,284

( )

COCOH

COOH

ppp

ppRate6595.0869.3943.2

07119.0157.1312.310

2

222

4

+−−

++=×

Whitty 2

Whitty 1

Van Heiningen

28

BL Char vs. Bed Solids

Black liquor charBET Surface area:

5-100 m2/g

Reformer bed solidsBET Surface area:

< 0.5 m2/g

50 µm 50 µm

29

Outline

Intro – BL steam reforming• Fluidized bed steam reforming• Commercial installations• Steam reforming research

This study – Experimental systemLiquor conversion in a steam reformer• Fate of organic carbon• Factors impacting carbon conversion• Development-scale versus full-scale

Conclusions

30

ConclusionsHigher concentrations of product gases in large fluidized bed reformer contributes to decreased conversion relative to small system• Higher concentrations of H2 and CO• Higher pressure of large system

Surface area of particles in large reformer may also contribute to lower conversion• Pressure at black liquor injection point roughly 3

times higher• May impact coating of black liquor

Fundamental rate information for bed solids would be useful

31

Acknowledgements

U.S. Department of EnergyGeorgia-Pacific CorporationThermochem Recovery InternationalNorampac CorporationÅbo Akademi UniversityMauricio NaranjoCarolina RubianoMike SiddowayAdriaan van Heiningen

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