Thermochemical Studies of Relevance for Black Liquor
Combustion and Gasification - The System Na2CO3-Na2S
Anders Larsson, Gustav Lindberg, Anders Nordin, Dan Boström,
Björn Warnqvist, Erik Rosén, Rainer Backman*
Energy and Process Technology, University of Umeå,SE-901 87 Umeå
*Åbo Akademi, Process Chemistry Group
Mathias Råberg
Contents
I. Research program (Black Liquor Gasification)
II. Uncertainties in thermochemical data
III. Phase diagram studies
- Na2CO3-Na2S
IV. Conclusions
V. Future work
-----------On-going projects------------
VI. Uncertainties in thermochemical data
VII. Thermochemical equilibrium studies
Center ofBlack LiquorGasification
Center ofBlack LiquorGasification
Inorganic reactions(UmU, Åbo)
Inorganic reactions(UmU, Åbo)
•Gas phase reactions•Smelt formation•Green liquor quality
CFD modeling(LTU, ETC)
CFD modeling(LTU, ETC)
Gasificationreactions
(CTH, Åbo)
Gasificationreactions
(CTH, Åbo)Design
verification program(Chemrec)
Designverification program
(Chemrec)
Constructionmaterials
(Åbo)
Constructionmaterials
(Åbo)
•Corrosion•Smelt layer thickness
•Technical design•Kinetic models•Evaporation, pyrolysis, char conversion
•Gasification reactor•Quench•Counter current condensor
I. Research program
The phase diagram Na2CO3 – Na2S according to Ovechkin (Zh. Neorg. Khim. 16, 1971)
The phase diagram Na2CO3 – Na2S according to Tegman and Warnqvist (Acta Chem. Scand 26, 1972)
II. Uncertainties in thermochemical data
Earlier published data of the binary phase diagram Na2CO3-Na2S
• Objectives:
- Re-determination of liquidus lines, in the Na2CO3 rich area, and melting points of the pure components
- Determination of the extension of the Na2CO3(ss) solid solution in theNa2CO3-Na2S system
•Methods: - High Temperature Microscopy, HTM
- High Temperature X-Ray Powder Diffraction, HT-XRD
• Chemicals- Na2CO3 and Na2S prepared according to Tegman and Warnqvist
(Acta Chem. Scand. 26, 1972)
III. Phase diagram studies on the system Na2CO3-Na2S
Experimental set-up, HTM
TS 1500 Hot Stage and the heater assembly
Experimental equipment, HT-XRD
• BRUKER AXS (Analytical X-ray System), D8 Advance
• HTK 16 High Temperature Camera
• Pt sample stage
HTM results
a. Sample at 25 ºC b. Partly melted, 815 ºC
c. Close to melting point,822 ºC
d. Crystallized during cooling,700 ºC
Sample with XNa2S = 0.15
1190-1
858-0
8177570.2
8307800.15
8427950.1
Melting point,mean (ºC)
First melt appears, mean (ºC)
XNa2S
Results from the melting point study
Na2CO3 (25-800 °C)
2θ-Scale
800
600
550
520
510
500
490
480
470
460
450
440
430
420 400
375
365
355
345
335
200 25
T (ºC)
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
A series of HT-XRD diffraction patterns of pure Na2CO3 in the temperature interval 25-800 ºC
HT-XRD results
Na2S (25 °C) Lin (Cps)
0
10
20
30
40
50 60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
2θ-Scale 23 30 40 50 60 70 80 90
Diffraction pattern of pure Na2S at 25 ºC
0
100
200
300
400
500
600
700
800
23 28 33 38 43 482θ-Scale
T (C
)Pure Na2CO3
XNa2S = 0.1
0
100
200
300
400
500
600
700
800
23 28 33 38 43 482θ-Scale
T (C
)Pure Na2CO3 Na2CO3 in mixture Na2S in mixture
XNa2S = 0.1
0
100
200
300
400
500
600
700
800
23 28 33 38 43 482θ-Scale
T (C
)Pure Na2CO3 Na2CO3 in mixture Na2S in mixture
XNa2S = 0.15
0
100
200
300
400
500
600
700
800
23 28 33 38 43 48
2θ-Scale
T (C
)Pure Na2CO3 Na2CO3 in mixture Na2S in mixture
XNa2S = 0.2
Phase Diagram Na2CO3-Na2S
400
500
600
700
800
900
1000
1100
1200
0 0.2 0.4 0.6 0.8 1
XNa2S
T (o C
)
Na2CO3 Na2S
Phase Diagram Na2CO3-Na2S
400
500
600
700
800
900
1000
1100
1200
0 0.2 0.4 0.6 0.8 1
XNa2S
T (o C
)
HTM data Previous estimated data
Na2CO3 Na2S
Phase Diagram Na2CO3-Na2S
400
500
600
700
800
900
1000
1100
1200
0 0.2 0.4 0.6 0.8 1
XNa2S
T (o C
)
HTM data HT-XRD dataPrevious estimated data
Na2CO3 Na2S
Phase Diagram Na2CO3-Na2S
400
500
600
700
800
900
1000
1100
1200
0 0.2 0.4 0.6 0.8 1
XNa2S
T (o C
)
Na2CO3 Na2S
Na2CO3(s) + Na2S(s)
Liquid
Na2S(s) + LNa2CO3(s) + L
Na2CO3(ss)
IV. Conclusions
• Phase diagram studies:- HTM: Re-determination of liquidus lines and melting
points of the components were made
- HT-XRD: The extension of the Na2CO3(ss) solid solution in the Na2CO3-Na2S system was determined
V. Future work
• Other systems:- K2CO3-K2S
- Na2S-K2S
- Na2S-NaCl, K2S-KCl
• Objective:
- Perform sensitivity analysis for the black liquor combustion/gasification chemistry in order to identify species with the most uncertain data and to compare the effect of these uncertainties with the variation in fuel and process variables
• Method:- Systematically performing chemical equilibrium
calculations (with H2S, COS, Na-gases, melting temperatures etc. as target/indicator variables) with uncertainties in thermochemical data included according to an extensive factorial design.
- A program that handles input/output files and changes in thermochemical data has been developed. The program uses ChemApp for equilibrium calculations.
Sensitivity analysisVI. Uncertainties in thermochemical data
Na2S(s)+CO2+H2O=Na2CO3(s,l)+H2Swith different data, pCO2 = 0.15 bar, pH2O = 0.20 bar
-3
-2
-1
0
400 500 600 700 800 900 1000
Temperature [°C]
log[
H2S
/bar
]SGPS-s,lSGTE96-s,lFact51-s,lHSC5-s,lRosén-sBackman-s
Na2CO3
Na2S
Stability of Na2S relative to Na2CO3
• Objective:
- Investigation of the equilibrium between Na2S and Na2CO3 to get more reliable data
• Method:
- Equilibrium studies in a vertical tube-furnace
• Improvements from previous studies (Köszegi, Rosén. Trans Roy Inst. Technol. 1964):
- Lower and better controlled gas flow
- In-situ production of Na2S
- Reducing atmosphere to prevent formation of Na2S2
- Aqueous titration method for the determination of H2S formed
VII. Thermochemical equilibrium studies
Temperature dependence for the equilibrium constant of the reaction Na2S(s) + H2O(g) + CO2(g) Na2CO3(s) + H2S(g)
(Previous data: Köszegi, Rosén. Trans Roy Inst. Technol. 1964)
Preliminary results
Acknowledgements
• Swedish Energy Agency, STEM