Thermochemical Studies of Relevance for Black Liquor Combustion and Gasification - The System Na 2 CO 3 -Na 2 S

Transcription

1 Thermochemical Studies of Relevance for Black Liquor Combustion and Gasification - The System CO 3 - S Mathias Råberg Anders Larsson, Gustav Lindberg, Anders Nordin, Dan Boström, Björn Warnqvist, Erik Rosén, Rainer Backman * Energy and Process Technology, University of Umeå, SE Umeå * Åbo Akademi, Process Chemistry Group

2 Contents I. Research program (Black Liquor Gasification) II. Uncertainties in thermochemical data III. Phase diagram studies - CO 3 - S IV. Conclusions V. Future work On-going projects VI. Uncertainties in thermochemical data VII. Thermochemical equilibrium studies

3 I. Research program Construction materials (Åbo) Corrosion Smelt layer thickness Design verification program (Chemrec) Technical design Inorganic reactions (UmU, Åbo) Gas phase reactions Smelt formation Green liquor quality Center of of Black Liquor Gasification CFD modeling (LTU, ETC) Gasification reactor Quench Counter current condensor Gasification reactions (CTH, Åbo) Kinetic models Evaporation, pyrolysis, char conversion

4 II. Uncertainties in thermochemical data Earlier published data of the binary phase diagram CO 3 - S The phase diagram CO 3 S according to Ovechkin (Zh. Neorg. Khim. 16, 1971) The phase diagram CO 3 S according to Tegman and Warnqvist (Acta Chem. Scand 26, 1972)

5 III. Phase diagram studies on the system CO 3 - S Objectives: - Re-determination of liquidus lines, in the CO 3 rich area, and melting points of the pure components - Determination of the extension of the CO 3 (ss) solid solution in the CO 3 - S system Methods: - High Temperature Microscopy, HTM - High Temperature X-Ray Powder Diffraction, HT-XRD Chemicals - CO 3 and S prepared according to Tegman and Warnqvist (Acta Chem. Scand. 26, 1972)

6 Experimental set-up, HTM

7 TS 1500 Hot Stage and the heater assembly

8 Experimental equipment, HT-XRD BRUKER AXS (Analytical X-ray System), D8 Advance

9 HTK 16 High Temperature Camera Pt sample stage

10 HTM results Sample with X Na2S = 0.15 a. Sample at 25 ºC b. Partly melted, 815 ºC c. Close to melting point, 822 ºC d. Crystallized during cooling, 700 ºC

11 Results from the melting point study X Na2S First melt appears, mean (ºC) Melting point, mean (ºC)

12 HT-XRD results T (ºC) CO 3 ( C) θ-Scale A series of HT-XRD diffraction patterns of pure CO 3 in the temperature interval ºC

13 Lin (Cps) S (25 C) θ-Scale Diffraction pattern of pure S at 25 ºC

14 X Na2S = Pure Pure Na2CO3 Na2CO3 Pure Na2CO3 Na2CO3 Na2CO3 in in mixture mixture Na2S Na2S in in mixture mixture T (C) θ-Scale 2θ-Scale

15 Phase Diagram CO 3 - S T ( o C) CO 3 X Na2S S

16 Phase Diagram CO 3 - S 1200 HTM data Previous estimated data T ( o C) CO 3 X Na2S S

17 Phase Diagram CO 3 - S 1200 HTM data HT-XRD data Previous estimated data T ( o C) CO 3 X Na2S S

18 Phase Diagram CO 3 - S Liquid 900 CO 3 (s) + L S(s) + L T ( o C) CO 3 (ss) 600 CO 3 (s) + S(s) CO 3 X Na2S S

19 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 CO 3 (ss) solid solution in the CO 3 - S system was determined

20 V. Future work Other systems: -K 2 CO 3 -K 2 S - S-K 2 S - S-NaCl, K 2 S-KCl

21 VI. Uncertainties in thermochemical data Objective: Method: Sensitivity analysis - 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 - Systematically performing chemical equilibrium calculations (with H 2 S, 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.

22 Stability of S relative to CO 3 S(s)+CO 2 +H 2 O= CO 3 (s,l)+h 2 S with different data, pco 2 = 0.15 bar, ph 2 O = 0.20 bar log[h 2 S/bar] CO 3 S SGPS-s,l SGTE96-s,l Fact51-s,l HSC5-s,l Rosén-s Backman-s Temperature [ C]

23 VII. Thermochemical equilibrium studies Objective: Method: - Investigation of the equilibrium between S and CO 3 to get more reliable data - 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 S - Reducing atmosphere to prevent formation of S 2 - Aqueous titration method for the determination of H 2 S formed

24 Preliminary results Temperature dependence for the equilibrium constant of the reaction S(s) + H 2 O(g) + CO 2 (g) CO 3 (s) + H 2 S(g) (Previous data: Köszegi, Rosén. Trans Roy Inst. Technol. 1964)

25 Acknowledgements Swedish Energy Agency, STEM