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Co-gasification of black liquor and pyrolysis oil at high temperature: Part 2. Fuel conversion
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
Number of Authors: 42017 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 197, p. 240-247Article in journal (Refereed) Published
Abstract [en]

The efficiency and flexibility of the BL gasification process may improve by mixing BL with more energy-rich fuels such as pyrolysis oil (PO). To improve understanding of the fuel conversion process, blends of BL and PO were studied in an atmospheric drop tube furnace. Experiments were performed in varying atmosphere (5% and 0% CO2, balanced by N2), temperature (800–1400 °C), particle size (90–200 μm and 500–630 μm) and blending ratio (0%, 20% and 40% of PO in BL on weight basis). Additionally, pine wood was used as a reference fuel containing little alkali. The addition of PO to BL significantly increased the combined yield of CO and H2 and that of CH4. BL/based fuels showed much lower concentration of tar in syngas than pine wood. Remarkably, the addition of PO in BL further promoted tar reforming in presence of CO2. Unconverted carbon in the gasification residue decreased with increasing fractions of PO. Small fuel particles showed complete conversion at 1000 °C but larger particles did not reach complete conversion even at T = 1400 °C.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 197, p. 240-247
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-62177DOI: 10.1016/j.fuel.2017.01.108ISI: 000398669900026Scopus ID: 2-s2.0-85013444316OAI: oai:DiVA.org:ltu-62177DiVA, id: diva2:1077214
Note

Validerad; 2017; Nivå 2; 2017-02-27 (andbra)

Available from: 2017-02-27 Created: 2017-02-27 Last updated: 2018-10-18Bibliographically approved
In thesis
1. Alkali-enhanced [ABO1] gasification of biomass  [ABO1]I belive the effect of alkali on tar and soot is not properly a catalytic one. I suggest enhanced as a more correct (yet vague) term
Open this publication in new window or tab >>Alkali-enhanced [ABO1] gasification of biomass  [ABO1]I belive the effect of alkali on tar and soot is not properly a catalytic one. I suggest enhanced as a more correct (yet vague) term
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, 13:42 (English)
Opponent
Supervisors
Available from: 2018-10-19 Created: 2018-10-18 Last updated: 2018-10-19Bibliographically approved

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Bach Oller, AlbertKirtania, KawnishFurusjö, ErikUmeki, Kentaro

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