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Alkali transformation during single pellet combustion of soft wood and wheat straw
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0003-4428-3201
2016 (Engelska)Ingår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 143, s. 204-212Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Controlling slag and deposit formation during thermochemical fuel conversion requires a fundamental understanding about ash transformation. In this work, a macro-TGA reactor was used to determine the release of ash forming elements during devolatilization and char combustion of single pellets. Soft wood and wheat straw were combusted at two temperatures (700 °C and 1000 °C) and the residual ashes were collected and analyzed for morphology, elemental and phase composition. The results showed that the single pellet combustion exhibit similar release character as in grate boilers. The temporal release was found to be both temperature and fuel dependent. For wood, the release of potassium occurred mostly during char combustion regardless of furnace temperature. Similar results were found for straw at 700 °C, but the temperature increase to 1000 °C implied that the release occurred already during devolatilization. The differences are presumably explained by different fuel phase compositions. The residual ash were composed of three different categories of phases; crystalline compounds, molten ash (glass) and char, and the work concludes that K was captured by crystalline K/Ca-carbonates as well as in amorphous glassy silicates for wood, and by almost fully molten ash of glassy silicates for straw. The fuel conversion processes occurring on a grate influence the fuel combustibility in terms of e.g. burnout, slag formation and release of fine particle and deposit forming matter, and the present work has given novel insights into the specific alkali behavior during biomass fuel conversion.

Ort, förlag, år, upplaga, sidor
2016. Vol. 143, s. 204-212
Nyckelord [en]
Biomass, Combustion, Ash, Alkali, Release, Single pellet
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:umu:diva-102732DOI: 10.1016/j.fuproc.2015.11.016ISI: 000369455300023Scopus ID: 2-s2.0-84949570884OAI: oai:DiVA.org:umu-102732DiVA, id: diva2:809418
Projekt
Bio4Energy
Forskningsfinansiär
Bio4EnergyTillgänglig från: 2015-05-04 Skapad: 2015-05-04 Senast uppdaterad: 2024-07-02Bibliografiskt granskad
Ingår i avhandling
1. Fine particle emissions and slag formation in fixed-bed biomass combustion: aspects of fuel engineering
Öppna denna publikation i ny flik eller fönster >>Fine particle emissions and slag formation in fixed-bed biomass combustion: aspects of fuel engineering
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

There is a consensus worldwide that the share of renewable energy sources should be increased to mitigate climate change. The strive to increase the renewable energy fraction can partly be met by an increased utilization of different biomass feedstocks. Many of the "new" feedstocks puts stress on certain challenges such as air pollution emissions and operation stability of the combustion process. The overall objective was to investigate, evaluate, and explain the effects of fuel design and combustion control - fuel engineering - as primary measures for control of slag formation, deposit formation, and fine particle emissions during biomass combustion in small and medium scale fixed-bed appliances. The work in this thesis can be outlined as having two main focus areas, one more applied regarding fuel engineering measures and one more fundamental regarding the time-resolved release of ash forming elements, with particular focus on potassium.

The overall conclusion related to the abatement of particle emissions and slag formation, is that the release of fine particle and deposit forming matter can be controlled simultaneously as the slag formation during fixed-bed biomass combustion. The methodology is in this perspective denoted “fuel engineering” and is based on a combined approach including both fuel design and process control measures. The studies on time-resolved potassium release showed that a Macro-TG reactor with single pellet experiments was a valuable tool for studying ash transformation along the fuel conversion. The combination of dedicated release determinations based on accurate mass balance considerations and ICP analysis, with phase composition characterization by XRD, is important for the understanding of potassium release in general and time-resolved data in particular. For wood, the results presented in this work supports the potassium release mechanism from "char-K" but questions the previously suggested release mechanism from decomposition of K-carbonates. For straw, the present data support the idea that the major part of the potassium release is attributed to volatilization of KCl. To further explore the detailed mechanisms, the novel approach developed and applied in this work should be complemented with other experimental and analytical techniques.

The research in this thesis has explored some of the challenges related to the combined phenomena of fuel conversion and ash transformation during thermochemical conversion of biomass, and has contributed with novel methods and approaches that have gained new knowledge to be used for the development of more effective bioenergy systems.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå Universitet, 2015. s. 73
Nyckelord
Renewable energy, biomass, thermochemical fuel conversion, combustion, fine particle emissions, slag formation, fixed-bed, ash chemistry, fuel engineering, release
Nationell ämneskategori
Kemiska processer Energiteknik Naturresursteknik
Identifikatorer
urn:nbn:se:umu:diva-102687 (URN)978-91-7601-274-1 (ISBN)
Disputation
2015-05-25, KBC-huset, sal KB3A9, Umeå Universitet, Umeå, 13:00 (Svenska)
Opponent
Handledare
Tillgänglig från: 2015-05-04 Skapad: 2015-04-30 Senast uppdaterad: 2024-07-02Bibliografiskt granskad

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Fagerström, JonathanSteinvall, ErikBoström, DanBoman, Christoffer

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