Inorganic Chemistry and Scaling in Alkaline Process...

International Colloquium on Black Liquor Combustion and Gasification

Jyvaskyla, Finland July 31 - August 2, 2006

Inorganic Chemistry and Scaling Inorganic Chemistry and Scaling in Alkaline Process Streamsin Alkaline Process Streams

Christopher L. Verrill & Nikolai A. DeMartiniChristopher L. Verrill & Nikolai A. DeMartiniGeorgia Institute of TechnologyGeorgia Institute of Technology

Rainer BackmanRainer BackmanUmea UniversityUmea University

Why Do We Care?Why Do We Care?

This is a black liquor combustion and This is a black liquor combustion and gasification colloquium, but…gasification colloquium, but…

Regardless of future thermo chemical Regardless of future thermo chemical conversion process there will beconversion process there will be–– Spent pulping liquor to concentrateSpent pulping liquor to concentrate–– Strong electrolyte streams to processStrong electrolyte streams to process

Conventional Kraft ProcessConventional Kraft ProcessWoodChips

Brown Stock Washing

White Liquor

Lime Kiln

RecaustCaO

CaCO3

Strong Black Liquor

GreenLiquor

Steam

Digester

Evaporators

Recovery Boiler /

Dissolver

Pulp

PrecipitatorFlue Gas

Dust

Na-CO3-SO4OxalatesCa scales

Ca scales

Integrated Biorefinery ProcessIntegrated Biorefinery ProcessWoodChips Digester

Evaporators

Gasifier w/Quench or Leach


Strong Black Liquor

CO3Liquor Process

Steam

Brown Stock Washing

S RecoveryS Recovery ConversionConversionSyn

Gas

Variable Sulfidity PulpingLiquors

SulfurRaw gas

Pulp

SteamElectricityChemicals

CO2 + H2OVent

Lime Kiln

RecaustCaO

???Ca scales

Na-CO3-SO4OxalatesCa scales

Extraction

Hemis

How Do We Predict Impacts?How Do We Predict Impacts?

Gibbs Free Energy minimizationGibbs Free Energy minimization–– Electrolyte properties databaseElectrolyte properties database–– Pitzer’s method to estimate activity Pitzer’s method to estimate activity

coefficientscoefficients

But, little or no data for key compounds:But, little or no data for key compounds:–– NaNa--COCO33--SOSO44 double saltsdouble salts–– OxalatesOxalates–– CatecholsCatechols

OverviewOverview

BackgroundBackground

NaNa--COCO33--SOSO44 salts in black liquorsalts in black liquor

Sodium oxalate in black liquorSodium oxalate in black liquor

Calcium behavior in black liquorCalcium behavior in black liquor

Calcium deposition in alkaline streamsCalcium deposition in alkaline streams

Green liquor solubility limitsGreen liquor solubility limits

Severe Soluble Scale FoulingSevere Soluble Scale Fouling

11stst effect of fallingeffect of falling--film evaporator ~60% TDSfilm evaporator ~60% TDS

90% of tubes plugged after 6 months operation

Crystallization StudiesCrystallization Studies

NaNa22COCO33 and Naand Na22SOSO44 salts crystallize from BL above salts crystallize from BL above 50% total dry solids content50% total dry solids content

Significant advances by Georgia Tech 1998Significant advances by Georgia Tech 1998--20062006–– Bayuadri, C., Verrill, C. L., Rousseau, R. W., “Stability of sodBayuadri, C., Verrill, C. L., Rousseau, R. W., “Stability of sodium sulfate ium sulfate

dicarbonate (~2Nadicarbonate (~2Na22COCO33·Na·Na22SOSO44) crystals obtained from evaporation of aqueous ) crystals obtained from evaporation of aqueous solutions of Nasolutions of Na22COCO33 and Naand Na22SOSO44,” ,” Ind. Eng. Chem. Res.,Ind. Eng. Chem. Res., aaccepted for ccepted for publicationpublication (2006).(2006).

–– Frederick, W. J. Jr.; Shi, B.; Euhus, D. D.; Rousseau, R. W., Frederick, W. J. Jr.; Shi, B.; Euhus, D. D.; Rousseau, R. W., Tappi J.Tappi J. 3(6):73(6):7--13 13 (2004).(2004).

–– Shi, B.; Rousseau, R. W., Shi, B.; Rousseau, R. W., J. Physical Chem. BJ. Physical Chem. B 107: 6932107: 6932--6937 (2003).6937 (2003).–– Shi, B.; Frederick, W. J. Jr.; Rousseau, R. W., Shi, B.; Frederick, W. J. Jr.; Rousseau, R. W., Ind. Eng. Chem. Res. Ind. Eng. Chem. Res. 42(25): 42(25):

63436343--6347 (2003). 6347 (2003). –– Shi, B.; Frederick, W. J. Jr.; Rousseau, R. W., Shi, B.; Frederick, W. J. Jr.; Rousseau, R. W., Ind. Eng. Chem. Res. Ind. Eng. Chem. Res. 42(12): 42(12):

28612861--2869 (2003). 2869 (2003). –– Shi, B.; Rousseau R.W., Shi, B.; Rousseau R.W., Ind. Eng. Chem. Res. Ind. Eng. Chem. Res. 40(6): 154140(6): 1541--1547 (2001).1547 (2001).

Crystals vs. Solution Composition for Na2CO3-Na2SO4-H2O

The species crystallized and it’s composition depends on the ratio of dissolvedCO3 and SO4 in the liquor

Green & Frattali, 100 oC

Schroeder, 150oC

This study, 115oC

0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

0.2 0.4 0.6 0.8 10.2 0.4 0.6 0.8 1

Na2SO4Regions: Na2SO4Regions:

Na 2C

O3/(

Na 2S

O4

+ N

a 2CO

3) m

ole

ratio

s in

sol

id

Na2CO3/(Na2SO4 + Na2CO3) mole ratios in solution

Burkeite Na2CO3bonate

0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

0.2 0.4 0.6 0.8 10.2 0.4 0.6 0.8 1


Na 2C

O3/(

Na 2S

O4

+ N

a 2CO

3) m

ole

ratio

s in

sol

id



Burkeite

Na2SO4

“Dicarbonate”

Na2CO3Green & Frattali, 100 oC

Schroeder, 150oC

This study, 115oC

0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

0.2 0.4 0.6 0.8 10.2 0.4 0.6 0.8 1


Na 2C

O3/(

Na 2S

O4

+ N

a 2CO

3) m

ole

ratio

s in

sol

id



0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

0.2 0.4 0.6 0.8 10.2 0.4 0.6 0.8 1


Na 2C

O3/(

Na 2S

O4

+ N

a 2CO

3) m

ole

ratio

s in

sol

id



Burkeite

Na2SO4

“Dicarbonate”

Na2CO3

Dicarbonate is a Stable Dicarbonate is a Stable Phase in ProcessPhase in Process

12 h

18 h

34 h

XRD of concentrator deposit

Dicarbonate at nucleation

Dicarbonate crystals during aging at 115°C

Solubility MeasurementsSolubility Measurements

Sample filtration apparatusBatch evaporative crystallizer

Schmidl, W., Verrill, C. L., Ball, A. R., and W. J. Frederick, Jr., “Experimental Determination and Modeling of Sodium Salt Solubility in High-Solids Kraft Black Liquor,” Paper 52-1 at the Tappi Fall Tech. Conf., Chicago, IL (October 2003).

Black Liquor Solubility at 120°CBlack Liquor Solubility at 120°CInitial NaInitial Na22COCO33--toto--NaNa22SOSO44 mole ratio = 4.8:1mole ratio = 4.8:1

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

45% 50% 55% 60% 65% 70% 75% 80%Total Solids in Reactor

Perc

ent o

f Dry

Sol

ids

CarbonateSulfate

BL Solubility Predicted by NAELSBL Solubility Predicted by NAELSInitial NaInitial Na22COCO33--toto--NaNa22SOSO44 mole ratio = 4.8:1mole ratio = 4.8:1

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

45% 50% 55% 60% 65% 70% 75% 80%Total Solids in Reactor

Perc

ent o

f Dry

Sol

ids

CarbonateSulfatePred CO3Pred SO4

Pre

dict

ed c

ritic

al s

olub

ility

Pre

dict

ed

trans

ition

to

Na2

CO

3

NaNa--COCO33--SOSO44 in BL: Statusin BL: Status

Sodium sulfate dicarbonateSodium sulfate dicarbonate phase phase ~2Na~2Na22COCO33⋅⋅NaNa22SOSO44 has higher tendency to foul has higher tendency to foul heated surfaces than burkeiteheated surfaces than burkeite

Dicarbonate is stable at industrial conditions!Dicarbonate is stable at industrial conditions!

Models can’t predict dicarbonateModels can’t predict dicarbonate

Solubility data obtained from 115Solubility data obtained from 115--145°C145°C–– Fitting Pitzer parameters is underwayFitting Pitzer parameters is underway

Impetus for Continued WorkImpetus for Continued Work

Severe scaling events triggered by subtle Severe scaling events triggered by subtle changes in liquor chemistrychanges in liquor chemistry–– Need for rapid liquor analysis methodsNeed for rapid liquor analysis methods

New makeNew make--up strategies for BLG systems up strategies for BLG systems with limited ability to reduce SOwith limited ability to reduce SO44, even , even higher COhigher CO33/SO/SO44 ratios expected!ratios expected!

Sodium Oxalate DepositionSodium Oxalate DepositionNa2C2O4 deposits

starting in 2nd effect

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

3 4 5 6 7 8 9

[Na+] (mol/L)

[C2O

42-] (

mol

/L) 70 % d.s.

60 %

50 %

150ºC

130ºC 113ºC

40 %

High oxalate

Avg. oxalate

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

3 4 5 6 7 8 9

[Na+] (mol/L)

[C2O

42-] (

mol

/L) 70 % d.s.

60 %

50 %

150ºC

130ºC 113ºC

40 %

High oxalate

Avg. oxalate

LS = [Na+]2[C2O42-]

DeMartini, N. A.; Verrill, C. L. “Evaporator Fouling Mitigation – Case Studies,” Paper 34-2 at TAPPI EPE Conf., Philadelphia, PA (Aug 2005).

Ulmgren & Rådeström, “Deposition of sodium oxalate in the black liquor evaporation,” 2001 ICRC Proc, Whistler, BC

Sodium Oxalate in BLSodium Oxalate in BL

StatusStatus–– Simplified solubility model is useful, butSimplified solubility model is useful, but–– Inconsistent data between 90 and 110°CInconsistent data between 90 and 110°C

Impetus for Continued WorkImpetus for Continued Work–– Interactions with NaInteractions with Na--COCO33--SOSO44 salts neededsalts needed–– Recycle of ECF & TCF effluents is increasing Recycle of ECF & TCF effluents is increasing

oxalate ion concentration!oxalate ion concentration!

Calcium Behavior in BLCalcium Behavior in BL1975 survey (Grace) 43% of responding mills 1975 survey (Grace) 43% of responding mills had CaCOhad CaCO33 scale problemsscale problemsLimiting max steam pressure solved manyLimiting max steam pressure solved many1997 survey (Schmidl & Frederick) 44% of 1997 survey (Schmidl & Frederick) 44% of responding mills had CaCOresponding mills had CaCO33 scale problemsscale problemsModified cooking: BL has different time/ Modified cooking: BL has different time/ temperature profile than historicaltemperature profile than historical–– lower cooking temperatureslower cooking temperatures–– early extractionearly extraction–– contact between cool liquor and chipscontact between cool liquor and chips

Calcium Scaling Mechanism

+− +⎯⎯→⎯ 22 CaOrgheat

)(323

2 cCaCOCOCa →+ −+ HTX surface

Suspendedparticles

Stea

m

Frederick et al. 1977-1982

Frederick et al. 2000

Significant Liquor-Liquor Differences

Frederick & Grace, 1977

Calcium Forms in Black LiquorInorganic calciumInorganic calcium

with with

Soluble calciumSoluble calcium, free Ca, free Ca2+ 2+ + Lignin+ Lignin--CaCa2+2+: :

withwith

Total calcium = Inorganic calcium + Soluble calciumTotal calcium = Inorganic calcium + Soluble calcium

−+ +⇔ 23

23 )( COCasCaCO

923

2 109.2]][[ −−+ ×== COCaKsp

nCaLnLCa ⇔++2

269]][[

][2 == + n

nCaL LCa

CaLKn

How To Measure Soluble Ca?How To Measure Soluble Ca?

Dilute to 5% TDS, Dilute to 5% TDS, centrifuge and filtercentrifuge and filter

The ratio of soluble to The ratio of soluble to total calcium changes total calcium changes with dilutionwith dilution

Need new methods Need new methods for sampling or for sampling or in situ in situ measurement

10 20 30 40 50 60 70

0.01

0.1

1

Rat

io, s

olub

le/to

tal C

aTotal solids content, %

][][

23−=

COCLR

T

nα

measurement

Xin-Sheng Chai 2006

Calcium Behavior in BLCalcium Behavior in BL

StatusStatus–– Reasonable mechanism for formation CaReasonable mechanism for formation Ca--

organic bondsorganic bonds–– Good data at 25°C to explain Ca distribution Good data at 25°C to explain Ca distribution

during pulp washingduring pulp washing

Impetus for Continued WorkImpetus for Continued Work–– Dilution affects measurement of soluble CaDilution affects measurement of soluble Ca–– Pulp mill impacts on scaling and deactivation Pulp mill impacts on scaling and deactivation

treatments cannot be predicted by modelstreatments cannot be predicted by models

Ca Salts in Alkaline StreamsCa Salts in Alkaline Streams

0

20

40

60

80

100

120

0 50 100 150 200

Total Na (g/l as Na2O)

Na 2

CO

3 (g/

l as

Na 2

O)

55°C

75°C95°C

TTAsat

Frederick, W.J. Jr., R. Krishnan, Ayers, R.J., “Pirssonite Deposits in Green Liquor Processing,” TAPPI J. 73(2):135-140 (1990).

Pirssonite deposit in raw green liquor line

Feed Water

Reactor

Quench

SecondaryAir

Black Liquor

Steam

ECO

AtomizingSteam

QuenchCirculation

Punp

Green Liquor

BottomSection

Gas Flow

Venturi CirculationPump

Venturi

CondsensatePump

Bleed to Quench

Cooling

Section

Gas

Absorption

Section

Wash

Section

DemisterFresh Mill Water

Product Gas to No. 2 Power Boiler

Cooler

Cooler

WeakWash

Scrubber

No. 2 Power Boiler

BurnerNo. 1

66 GPM270°F 70% DS

13,400 CFM900°F

1,750°F

160 GPM 202 °F

No. 6 oil18 GPM

HVLCLVHC

20,300 CFM105°F

200,000850 PSIG

825 °F

CoolingWater

BurnerNo. 2

Black Liquor

Atomizing Steam

Secondary Air

Bleed to Quench

Green Liquor

Product Gas to No 2 Power Boiler

Fresh Mill Water

Fresh Weak Wash

Fresh Weak Wash

Fresh MillWater

2.54

0.07

2.45 (of which 2.14 is in dregs)

0.10

0.31

0.51

0.46

Trial Date: 13-Jun-05Units: lb/s

0.0

Gasifier Scrubber Into Out ofIn Out Out/In In Out Out/In system system Out/In

3.02 2.45 81.0% 0.97 0.41 42.5% 3.58 2.45 68.4%

200-210°F

160-170°F

220-225°F

Film Generator

Quench Spray Pump

92-94% Ca+CO3

26

Equilibrium Solubility Diagram (NAELS)

0.0E+001.0E-052.0E-053.0E-054.0E-055.0E-05

75 100 125 150 175 200

Temperature (oF)

[Ca2+

] (m

ol/k

g H

2O)

CaCO3Ca2+

Note: Rotojet casing temp is 195-200F, internal surfaces 200-210F

Calcium in Alkaline StreamsCalcium in Alkaline Streams

StatusStatus–– Extremely low solubility of Ca salts at high pH Extremely low solubility of Ca salts at high pH

allows good prediction by simple modelsallows good prediction by simple models

Impetus for Continued WorkImpetus for Continued Work–– More data at high temperature and high ionic More data at high temperature and high ionic

strength needed for global modelsstrength needed for global models–– Role of soluble hydrated forms of CaCORole of soluble hydrated forms of CaCO33 at at

these conditions an unknownthese conditions an unknown

Sulfur Species in GL: StatusSulfur Species in GL: Status

Can predict sulfur Can predict sulfur species with solution species with solution models up to 100°Cmodels up to 100°C

Cannot predict Cannot predict species distribution if species distribution if any Oany O22--containing gas containing gas contacts liquid phasecontacts liquid phase

Rainer Backman 2006

Momentary digression…

Gasification of Spent Liquorsfrom High Yield Pulping Processes

Christopher Verrill

Chuck Courchene & Scott Sinquefield

***Ingrid Nohlgren***AIChE Annual Meeting April 2005

Impetus for Exploratory Project

• Gasification studies use conventional kraft black liquor as raw material

• BLG enables kraft process modification:• How will these spent liquors differ from kraft?• How will these liquors behave in gasifier?• What processing steps will be required to

reform pulping liquors?• How will chemical make-up be impacted?

Sulfur Reduction Efficiency~2 sec residence time in 10% CO2, 10% H2O in N2

0

10

20

30

40

50

60

70

80

90

100

kraft ASAQ SS

Sulfu

r R

educ

tion,

mol

% S

in L

iquo

r So

lids

Char red 900°CChar red 1000°CTot red 900°CTot red 1000°C

Conclusions from Study

• Significant rate and yield differences• ASAQ and SS gasify slower than kraft• SO4 deadload buildup may be issue for kraft

and SS

• Fate of sulfur from ASAQ liquor• Less sulfur to gas phase• Good reduction of SO4 but little SO3 in residue• MS/SAQ pulping liquors may be more easily

reformed by gasification than ASAQ

Conventional Kraft ProcessConventional Kraft ProcessWoodChips

Brown Stock Washing

White Liquor

Lime Kiln

RecaustCaO

CaCO3

Strong Black Liquor

GreenLiquor

Steam

Digester

Evaporators

Recovery Boiler /

Dissolver

Pulp

PrecipitatorFlue Gas

Dust

Na + S make-uptypically Na2SO4rich streams

Integrated Biorefinery ProcessIntegrated Biorefinery ProcessWoodChips Digester

Evaporators



Strong Black Liquor

CO3Liquor Process

Steam

Brown Stock Washing

S RecoveryS Recovery ConversionConversionSyn

Gas

Variable Sulfidity PulpingLiquors

SulfurRaw gas

Pulp

SteamElectricityChemicals

CO2 + H2OVent

Lime Kiln

RecaustCaO

Unexpected deposits, e.g., Na2SO3? Higher water quality sensitivities?

Extraction

HemisMake up strategy =avoid sulfate?

Worse scaling from 1) lower SO4 levels?2) Ca-org changes?

ConclusionsConclusions

Fundamental measurements of key Fundamental measurements of key species needed at high ionic strength and species needed at high ionic strength and high temperaturehigh temperature

Methodology for implementing data into Methodology for implementing data into models is importantmodels is important

Verification of model predictions with Verification of model predictions with industrial observation and controlled industrial observation and controlled experiments are ultimately neededexperiments are ultimately needed

AcknowledgementsAcknowledgements

XinXin--Sheng Chai, IPST @ Georgia TechSheng Chai, IPST @ Georgia Tech

Steven Lien, IPST @ Georgia TechSteven Lien, IPST @ Georgia Tech

Pete Thorn, WeyerhaeuserPete Thorn, Weyerhaeuser

Craig Brown, WeyerhaeuserCraig Brown, Weyerhaeuser

Several mills remaining anonymousSeveral mills remaining anonymous

Inorganic Chemistry and Scaling in Alkaline Process...

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