Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Co-gasification of black liquor and pyrolysis oil at high temperature: Part 1. Fate of alkali elements
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-9074-7439
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-8235-9839
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0003-1806-4187
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-6081-5736
2017 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 202, p. 46-55Article in journal (Refereed) Published
Abstract [en]

The catalytic activity of alkali compounds in black liquor (BL) enables gasification at low temperatures with high carbon conversion and low tar and soot formation. The efficiency and flexibility of the BL gasification process may be improved by mixing BL with fuels with higher energy content such as pyrolysis oil (PO). The fate of alkali elements in blends of BL and PO was investigated, paying special attention to the amount of alkali remaining in the particles after experiments at high temperatures. Experiments were conducted in a drop tube furnace under different environments (5% and 0% vol. CO2 balanced with N2), varying temperature (800–1400 °C), particle size (90–200 µm, 500–630 µm) and blending ratio (0%, 20% and 40% of pyrolysis oil in black liquor). Thermodynamic analysis of the experimental cases was also performed.

The thermodynamic results qualitatively agreed with experimental measurements but in absolute values equilibrium under predicted alkali release. Alkali release to the gas phase was more severe under inert conditions than in the presence of CO2, but also in 5% CO2 most of the alkali was found in the gas phase at T = 1200 °C and above. However, the concentration of alkali in the gasification residue remained above 30% wt. and was insensitive to temperature variations and the amount of PO in the blend. Thermodynamic analysis and experimental mass balances indicated that elemental alkali strongly interacted with the reactor’s walls (Al2O3) by forming alkali aluminates. The experience indicated that adding PO into BL does not lead to alkali depletion during high temperature gasification.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 202, p. 46-55
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-63020DOI: 10.1016/j.fuel.2017.04.013ISI: 000404078500006Scopus ID: 2-s2.0-85017397407OAI: oai:DiVA.org:ltu-63020DiVA, id: diva2:1088484
Note

Validerad; 2017; Nivå 2; 2017-04-12 (andbra)

Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2018-10-18Bibliographically approved
In thesis
1. Alkali-enhanced gasification of biomass: laboratory-scale experimental studies
Open this publication in new window or tab >>Alkali-enhanced gasification of biomass: laboratory-scale experimental studies
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gasification seeks to break carbonaceous materials into synthetic gas (CO+H2) which can be subsequently upgraded into valuable products. Thus gasification can be utilized to convert low grade biomass stocks into carbon-neutral chemicals heat and power. Nonetheless, gasification produces tar and soot as a by-product, impurities which deposit on cold surfaces thereby risking operation downstream of the gasifier. Cleaning the syngas after the gasifier is a conventional way to attenuate the problem, yet a complex and expensive one. Thus, tar and soot should preferably be addressed already in the gasifier. Given that these impurities are non-equilibrium species they could be targeted by using some sort of catalytic material. Alkali elements have precisely shown to possess catalytic activity on char gasification, besides they have also been associated with a decrease in tar and soot. Yet, to design a functional alkali-catalysed gasification process we need to investigate in more detail on what exact products does alkali show an activity on, on what stage, under what circumstances and, on the measure that it is possible, the mechanism. This was investigated on the basis of experimental work that approached the topic from two opposite sides. On the one hand, we studied the effects of diluting the alkali content of a Na-rich black liquor (BL) by blending it with pyrolysis oil (PO), and on the other hand, we investigated adding various amounts of alkali on more conventional types of biomass fuels. Most of the experiments were conducted on a laminar drop tube furnace but the reactivity of BL chars was also studied through thermogravimetric analysis.

Alkali was found to catalyse heterogeneous gasification reactions (e.g. char) and to lead to much lower yields of C2 hydrocarbons, heavy tars and soot, favouring the presence of lighter species over large aromatic clusters. Alkali was hypothesized to reduce the quantity of soot by inhibiting the formation and growth of PAH, key intermediates on the road to soot. Besides, it was found that the initial contact between the alkali and the organic matrix was not critical, neither for gas impurities nor regarding char conversion, suggesting that the activity of alkali was a gas-induced phenomenon. The latter implied the existence of a vaporization-condensation cycle that could supply alkali into the char. Nonetheless, the beneficial effects by alkali were impaired by the affinity of Si to capture K and form potassium silicates which are inert. This interaction effect was particularly noticeable on char conversion as the silicates are not only inert but also liquid and viscous and prompt to encapsulate the char particles, thereby limiting mass transfer.

The experiments with blends of BL and PO showed that the concentration of alkali in BL could be decreased by 30% without any sign of a decrease in the catalytic activity on char gasification, thus indicating the existence a saturation threshold. Furthermore, adding PO into BL lead to a further reduction on the quantities of tar and soot, this finding was attributed to changes in the fuel composition unrelated to alkali. In any case the experiments with BL-based fuels showed lower amounts of tar and soot than those from alkali-impregnated biomass powder. The difference was partially attributed to the content of S in BL. The subsequent investigation targeting the role of S confirmed that S possessed a soot inhibiting role similar to that of alkali, yet unlike K, it did not show a catalytic effect on char gasification.

 

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
alkali, biomass, gasification, tar, soot, potassium, char, syngas, enhanced
National Category
Engineering and Technology Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-71261 (URN)978-91-7790-236-2 (ISBN)978-91-7790-237-9 (ISBN)
Public defence
2018-12-14, E632, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-10-19 Created: 2018-10-18 Last updated: 2018-11-21Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full textScopus

Authority records

Bach Oller, AlbertKirtania, KawnishFurusjö, ErikUmeki, Kentaro

Search in DiVA

By author/editor
Bach Oller, AlbertKirtania, KawnishFurusjö, ErikUmeki, Kentaro
By organisation
Energy Science
In the same journal
Fuel
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 436 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf