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Black liquor gasification: experimental stability studies of smelt components and refractory lining
Umeå University, Faculty of Science and Technology, Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Black liquors are presently combusted in recovery boilers where the inorganic cooking chemicals are recovered and the energy in the organic material is converted to steam and electricity. A new technology, developed by Chemrec AB, is black liquor gasification (BLG). BLG has more to offer compared to the recovery boiler process, in terms of on-site generation of electric power, liquid fuel and process chemicals. A prerequisite for both optimization of existing processes and the commercialization of BLG is better understanding of the physical and chemical processes involved including interactions with the refractory lining. The chemistry in the BLG process is very complex and to minimize extensive and expensive time-consuming studies otherwise required accurate and reliable model descriptions are needed for a full understanding of most chemical and physical processes as well as for up-scaling of the new BLG processes. However, by using these calculated model results in practice, the errors in the state of the art thermochemical data have to be considered. An extensive literature review was therefore performed to update the data needed for unary, binary and higher order systems. The results from the review reviled that there is a significant range of uncertainty for several condensed phases and a few gas species. This resulted in experimental re-determinations of the binary phase diagrams sodium carbonate-sodium sulfide (Na2CO3-Na2S) and sodium sulfate-sodium sulfide (Na2SO4-Na2S) using High Temperature Microscopy (HTM), High Temperature X-ray Diffraction (HT-XRD) and Differential Thermal Analysis (DTA). For the Na2CO3-Na2S system, measurements were carried out in dry inert atmosphere at temperatures from 25 to 1200 °C. To examine the influence of pure CO2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. The results include re-determination of liquidus curves, in the Na2CO3 rich area, melting points of the pure components as well as determination of the extent of the solid solution, Na2CO3(ss), area. The thermal stability of Na2SO3 was studied and the binary phase diagram Na2SO4-Na2S was re-determined. The results indicate that Na2SO3 can exist for a short time up to 750 °C, before it melts. It was also proved that a solid/solid transformation, not reported earlier, occurs at 675 ± 10 °C. At around 700 °C, Na2SO3 gradually breaks down within a few hours, to finally form the solid phases Na2SO4 and Na2S. From HTM measurements a metastable phase diagram including Na2SO3, as well as an equilibrium phase diagram have been constructed for the binary system Na2SO4-Na2S. Improved data on Na2S was experimentally obtained by using solid-state EMF measurements. The equilibrium constant for Na2S(s) was determined to be log Kf(Na2S(s)) (± 0.05) = 216.28 – 4750(T/K)–1 – 28.28878 ln (T/K). Gibbs energy of formation for Na2S(s) was obtained as ΔfG°(Na2S(s))/(kJ mol–1) (± 1.0) = 90.9 – 4.1407(T/K) + 0.5415849(T/K) ln (T/K). The standard enthalpy of formation of Na2S(s) was evaluated to be ΔfH°(Na2S(s), 298.15 K)/(kJ mol–1) (± 1.0) = – 369.0. The standard entropy was evaluated to be S°(Na2S(s), 298.15 K)/(J mol–1 K–1) (± 2.0) = 97.0. Analyses of used refractory material from the Chemrec gasifier were also performed in order to elucidate the stability of the refractory lining. Scanning electron microscopy (SEM) analysis revealed that the chemical attack was limited to 250-300 μm, of the surface directly exposed to the gasification atmosphere and the smelt. From XRD analysis it was found that the phases in this surface layer of the refractory were dominated by sodiumaluminosilicates, mainly Na1.55Al1.55Si0.45O4.

Place, publisher, year, edition, pages
Umeå: Energiteknik och termisk processkemi , 2007. , 37 p.
Series
ETPC Report, ISSN 1653-0551 ; 07-06
Keyword [en]
black liquor gasification, DTA, stability, thermal analysis, thermochemical data, HTM, HT-XRD, metastable, phase diagram, refractory lining, SEM
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:umu:diva-1151ISBN: 978-91-7264-339-0 (print)OAI: oai:DiVA.org:umu-1151DiVA: diva2:140392
Public defence
2007-09-07, KB3A9, KBC-huset, Umeå Universitet 901 87, Umeå, 10:00
Opponent
Supervisors
Available from: 2007-05-16 Created: 2007-05-16Bibliographically approved
List of papers
1. Sodium and sulfur process chemistry in black liquor gasification and combustion: review of basic thermochemical data
Open this publication in new window or tab >>Sodium and sulfur process chemistry in black liquor gasification and combustion: review of basic thermochemical data
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2407 (URN)
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-01-13Bibliographically approved
2. Improvement of the binary phase diagram Na2CO3 -Na2S
Open this publication in new window or tab >>Improvement of the binary phase diagram Na2CO3 -Na2S
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2003 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 17, no 6, 1591-1594 p.Article in journal (Refereed) Published
Abstract [en]

Gasification of black liquor is an attractive alternative to the traditional recovery boiler. However, in process modeling of gasification, thermodynamic data for the key components are quite uncertain, which will reduce the reliability of the modeling of the chemical processes in a gasifier. The objective of this work was to experimentally re-determine and improve data on the binary phase diagram Na2CO3−Na2S, especially on the Na2CO3 side of the system, which is the region of interest concerning black liquor combustion and gasification, and also the region with the most significant uncertainties. Measurements were carried out in a dry inert atmosphere at temperatures from 25 to 1200 °C, using high-temperature microscopy (HTM) and high-temperature X-ray powder diffraction (HT-XRD). To examine the influence of pure CO2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. This paper presents new data complementary to earlier published data on the binary phase diagram Na2CO3−Na2S. These include re-determination of liquidus curves, in the Na2CO3-rich area, melting points of the pure components, as well as determination of the extent of the solid solution, Na2CO3(ss), area.

Place, publisher, year, edition, pages
American Chemistry Society, 2003
Identifiers
urn:nbn:se:umu:diva-2408 (URN)10.1021/ef0340256 (DOI)
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2017-12-14Bibliographically approved
3. Thermal stability of Na2SO3 and re-determination of the binary phase diagram Na2SO4-Na2S
Open this publication in new window or tab >>Thermal stability of Na2SO3 and re-determination of the binary phase diagram Na2SO4-Na2S
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2409 (URN)
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-01-13Bibliographically approved
4. Determination of thermodynamic properties of Na2S using solid-state EMF measurements
Open this publication in new window or tab >>Determination of thermodynamic properties of Na2S using solid-state EMF measurements
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2007 (English)In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 39, no 1, 44-48 p.Article in journal (Refereed) Published
Abstract [en]

To obtain reliable thermodynamic data for Na2S(s), solid-state EMF measurements of the cell Pd(s)|O2(g)|Na2S(s), Na2SO4(s)|YSZ| Fe(s), FeO(s)|O2(g)ref| Pd(s) were carried out in the temperature range 870 < T/K < 1000 with yttria stabilized zirconia as the solid electrolyte. The measured EMF values were fitted according to the equation Efit/V (±0.00047) = 0.63650 − 0.00584732(T/K) + 0.00073190(T/K) ln (T/K). From the experimental results and the available literature data on Na2SO4(s), the equilibrium constant of formation for Na2S(s) was determined to be lg Kf(Na2S(s)) (±0.05) = 216.28 − 4750(T/K)−1 − 28.28878 ln (T/K). Gibbs energy of formation for Na2S(s) was obtained as ΔfG(Na2S(s))/(kJ · mol−1) (±1.0) = 90.9 − 4.1407(T/K) + 0.5415849(T/K) ln (T/K). By applying third law analysis of the experimental data, the standard enthalpy of formation of Na2S(s) was evaluated to be ΔfH(Na2S(s), 298.15 K)/(kJ · mol−1) (±1.0) = −369.0. Using the literature data for Cp and the calculated ΔfH, the standard entropy was evaluated to S(Na2S(s), 298.15 K)/(J · mol−1 · K−1) (±2.0) = 97.0.

Place, publisher, year, edition, pages
Elsevier, 2007
Keyword
sodium sulfide; EMF, hermochemical data
Identifiers
urn:nbn:se:umu:diva-2410 (URN)10.1016/j.jct.2006.06.003 (DOI)
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2017-12-14Bibliographically approved
5. Stability of the Monofrax® L refractory container material used in high-temperature black liquor gasification
Open this publication in new window or tab >>Stability of the Monofrax® L refractory container material used in high-temperature black liquor gasification
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2411 (URN)
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-01-13Bibliographically approved

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