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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
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
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
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
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
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
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
Gasifier w/Quench or Leach
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
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