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Ash Formation in Pilot-Scale Pressurized Entrained-Flow Gasification of Bark and a Bark/Peat Mixture
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umeå University.
SP Energy Technology Center AB.
SP Energy Technology Center AB.
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Number of Authors: 8
2016 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, 10543-10554 p.Article in journal (Refereed) Published
Abstract [en]

Pressurized entrained-flow gasification (PEFG) of bark and a bark/peat mixture (BPM) was carried out in a pilot-scale reactor (600 kWth, 7 bar(a)) with the objective of studying ash transformations and behaviors. The bark fuel produced a sintered but nonflowing reactor slag, while the BPM fuel produced a flowing reactor slag. Si was enriched within these slags compared to their original fuel ash compositions, especially in the bark campaign, which indicated extensive ash matter fractionation. Thermodynamically, the Si contents largely accounted for the differences in the predicted solidus/liquidus temperatures and melt formations of the reactor slags. Suspension flow viscosity estimations were in qualitative agreement with observations and highlighted potential difficulties in controlling slag flow. Quench solids from the bark campaign were mainly composed of heterogeneous particles resembling reactor fly ash particles, while those from the BPM campaign were flowing slags with likely chemical interactions with the wall refractory. Quench effluents and raw syngas particles were dominated by elevated levels of K that, along with other chemical aspects, indicated KOH(g) and/or K(g) were likely formed during PEFG. Overall, the results provide information toward development of woody biomass PEFG and indicate that detailed understanding of the ash matter fractionation behavior is essential.

Place, publisher, year, edition, pages
2016. Vol. 30, no 12, 10543-10554 p.
National Category
Energy Systems Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-61329DOI: 10.1021/acs.energyfuels.6b02222ISI: 000390072900057OAI: oai:DiVA.org:ltu-61329DiVA: diva2:1062968
Funder
Swedish Energy AgencyBio4Energy
Note

Validerad; 2017; Nivå 2; 2017-01-12 (andbra)

Available from: 2017-01-09 Created: 2017-01-09 Last updated: 2017-10-19Bibliographically approved
In thesis
1. Aspects of Ash Transformations in Pressurised Entrained-Flow Gasification of Woody Biomass: Pilot-scale studies
Open this publication in new window or tab >>Aspects of Ash Transformations in Pressurised Entrained-Flow Gasification of Woody Biomass: Pilot-scale studies
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Pressurised entrained-flow gasification (PEFG) of woody biomass has the potential to produce high purity syngas for the production of vital chemicals, e.g., biofuels. However, ash-related issues such as reactor blockages and refractory corrosion need to be addressed before this potential can be realised from a technical perspective. These undesirable consequences can be brought about by slag formation involving inorganic ash-forming elements and the chemical transformations that they undergo during fuel conversion. The objective of this study was to elucidate the ash transformations of the major ash-forming elements and the slag formation process. A pilot-scale PEFG reactor was used as the basis of the study, gasifying different woody biomass-based fuels including wood, bark, and a bark/peat mixture. Different ash fractions were collected and chemically analysed. Reactor slags had elemental distributions differing from that of the fuel ash, indicating the occurrence of fractionation of ash material during fuel conversion. Fly ash particles from a bark campaign were also heterogeneous with particles exhibiting differing compositions and physical properties; e.g., molten and crystalline formations. Si was consistently enriched in the reactor slags compared to other major ash-forming elements, while analyses of other ash fractions indicated that K was likely volatilised to a significant extent. In terms of slag behaviour, near-wall temperatures of approximately 1050-1200 °C inside the reactor were insufficient to form flowing ash slag for continuous extraction of ash material during firing the woody biomass fuels alone. However, fuel blending of a bark fuel with a silica-rich peat changed the chemical composition of the reactor slags and bulk slag flow behaviour was evident. Thermochemical equilibrium calculations supported the importance of Si in melt formation and in lowering solidus and liquidus temperatures of Ca-rich slag compositions that are typical from clean wood and bark. Viscosity estimations also showed the impact that solids have upon slag flow behaviour and corresponded qualitatively to the experimental observations. Corrosion of reactor refractory was observed. The mullite-based refractory of the reactor formed a slag with the fuel ash slag, which caused the former to flux away. Reactor blockages were also resultant because of the high viscosity of this slag near the outlet.  A preliminary study into the corrosion of different refractories was also carried out, based on firing a bark/peat mixture.  Alumina-rich refractories consisting of corundum, hibonite, mullite, and andalusite tended to form anorthite and exhibited varying degrees of degradation. Infiltration of slag was evident for all the samples and was a severe mode of degradation for some refractories. For fused-cast periclase and spinel-based refractories, slag infiltration was limited to voids and no extensive signs of refractory dissolution were found. This is also supported by a thermochemical equilibrium calculations mimicking slag infiltration that incorporated viscosity estimations. The findings from this thesis contribute towards the development of woody biomass PEFG by highlighting issues concerning ash fractionation, slag behaviours and ash\slash refractory interaction that should be investigated further.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword
woody biomass, gasification, ash transformation, slag behaviour, refractory corrosion
National Category
Bioenergy
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-62914 (URN)978-91-7583-874-8 (ISBN)978-91-7583-875-5 (ISBN)
Public defence
2017-06-22, E231, Universitetsområdet, Porsön, 97187, Luleå, 10:00 (English)
Supervisors
Funder
Bio4EnergySwedish Energy Agency
Available from: 2017-04-13 Created: 2017-04-06 Last updated: 2017-05-30Bibliographically approved

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