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Thermochemical equilibrium study of slag formation during pressurized entrained-flow gasification of woody biomass
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-0555-5924
Umeå university, Åbo Akademi, Energy Technology and Thermal Process Chemistry, Umeå University.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
2015 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 7, p. 4399-4406Article in journal (Refereed) Published
Abstract [en]

The potential slag formation behavior during pressurized entrained-flow gasification (PEFG) of woody biomass has been studied from a thermodynamic perspective with respect to compositional, temperature, and pressure variations. An ash transformation scheme was proposed on the basis of the melt formation potential that arises when gaseous K species are present with Si and Ca. Databases and models in FactSage 6.4 were used to carry out thermochemical equilibrium calculations within ChemSheet. It was found that increasing pressure and increasing Si content expanded the range of operating conditions that are conducive of melt formation, while increasing temperature and increasing Ca content diminished the range. The results from the calculations compared qualitatively well to experimental results and provide further information needed in the development of PEFG reactors for woody biomass

Place, publisher, year, edition, pages
2015. Vol. 29, no 7, p. 4399-4406
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-9129DOI: 10.1021/acs.energyfuels.5b00889ISI: 000360026900044Scopus ID: 2-s2.0-84937119010Local ID: 7b0a4616-f50d-4b0f-8950-ea8a563e4c2aOAI: oai:DiVA.org:ltu-9129DiVA, id: diva2:982067
Note
Validerad; 2015; Nivå 2; 20150608 (ohmmar)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically 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
Keywords
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: 2017-11-24Bibliographically approved

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