Change search
ReferencesLink to record
Permanent link

Direct link
Slagging in fixed-bed combustion of phosphorus-poor biomass: critical ash-forming processes and compositions
Luleå, Sweden.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. (Thermochemical Energy Conversion Laboratory)
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. (Thermochemical Energy Conversion Laboratory)
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. (Thermochemical Energy Conversion Laboratory)
Show others and affiliations
2015 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 2, 894-908 p.Article in journal (Refereed) Published
Abstract [en]

Slagging in combustion facilities is not welcomed, because it may cause technical and operational problems, as well as extra costs. Increased understanding of the critical slagging subprocesses makes it easier to suggest semiempirical models and fuel indexes for predicting the slagging tendencies of different fuels. That could open the biomass market for potentially more troublesome raw materials. The objective of this work was to determine critical ash-forming processes and compositions in the fixed-bed combustion of phosphorus-poor biomass fuels. This was achieved by performing a systematic review of data and experience gathered from combustion experiments in a small grate burner of 36 different biomasses, as well as chemical analysis of their bottom ashes and slags. The paper presents a discussion of the slagging tendency in phosphorus-poor biomass by combining three different slagging classifications, culminating in a proposed starting point for a new slagging index. The slag (ash particles >3.15 mm in size) formed during the combustion experiments has been described according to the fraction of fuel ash that forms slag (expressed in terms of weight percent), the visual sintering category (1-4), and the viscosity predictions. The results explain that both the fraction of melt and its viscosity are critical for the slag formation process in phosphorus-poor biomasses. In addition, fuels with low Si/K ratio along with a higher Ca concentration may form a low viscous carbonate melt that is not prone to form slag. Increased Si and lowered Ca concentration will increase the amount of formed silicate melt formed, as well as its viscosity, thus resulting in a more sticky melt.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015. Vol. 29, no 2, 894-908 p.
National Category
Energy Engineering Chemical Engineering
URN: urn:nbn:se:umu:diva-101613DOI: 10.1021/ef502531mISI: 000349943300050OAI: diva2:801749
Available from: 2015-04-10 Created: 2015-04-07 Last updated: 2015-04-30Bibliographically approved
In thesis
1. Fine particle emissions and slag formation in fixed-bed biomass combustion: aspects of fuel engineering
Open this publication in new window or tab >>Fine particle emissions and slag formation in fixed-bed biomass combustion: aspects of fuel engineering
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2015. 73 p.
Renewable energy, biomass, thermochemical fuel conversion, combustion, fine particle emissions, slag formation, fixed-bed, ash chemistry, fuel engineering, release
National Category
Chemical Process Engineering Energy Engineering Environmental Engineering
urn:nbn:se:umu:diva-102687 (URN)978-91-7601-274-1 (ISBN)
Public defence
2015-05-25, KBC-huset, sal KB3A9, Umeå Universitet, Umeå, 13:00 (Swedish)
Available from: 2015-05-04 Created: 2015-04-30 Last updated: 2015-05-08Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Fagerström, JonathanBoman, ChristofferBoström, Dan
By organisation
Department of Applied Physics and Electronics
In the same journal
Energy & Fuels
Energy EngineeringChemical Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 119 hits
ReferencesLink to record
Permanent link

Direct link