This week a new paper has been published in the IFRF Combustion Journal (http://www.journal.ifrf.net), entitled:
“Bed Material Consumption in Biomass Fired Fluidised Bed Boilers Due to Risk of Bed Agglomeration – Coating Formation and Possibilities for Regeneration”
Elisabet Brus / Anders Nordin
S-901 87 Umeå, Sweden
Previous studies have shown that many biomass fuels result in critical agglomeration temperatures in the same range as typical operating process temperatures for fluidised beds. As soon as a sufficiently thick coating on the bed particles has been formed, the risk for severe agglomeration and defluidisation is often significant. Frequent bed change is therefore the normally method applied to ensure problem-free operation, but this is associated with additional costs and not sustainable on a long-term basis.
The objectives of the present work were therefore to; i) collect full-scale bed material samples to determine coating characteristics and growth as functions of time; ii) estimate the critical coating thickness/age of the bed particles by SEM/EDS analysis and experimental determinate the agglomeration temperatures for the collected bed material; iii) experimentally evaluate if size fractionation and mechanical treatment could be used to reduce the bed material consumption.
Bed material samples from two bubbling and two circulating full-scale fluidised bed boilers, with previous documented bed agglomeration problems, were collected. All plants used typical wood-based fuel mixtures. The coating formation rates on the bed particles were found to be significant, with an initial rate of some mm per day, but decreasing with time. The coating material was generally found to consist of Ca- and Mg-silicates as well as P, although the form in which it was present was not determined. The experimentally determined fuel specific agglomeration temperatures were found to agree well with the corresponding critical temperatures for the full-scale bed materials, as well as with the experiences reported by the different plant operators. The critical coating thickness was found to be relatively thin (<10 mm), and was reached within a few days. Unfortunately, regeneration by sieving and bed removal at different heights seemed relatively ineffective. Mechanical treatment (soft grinding) resulted in a breakdown of the original quartz bed material particles and the desired selective scavenging of the coating could not be obtained.
The full paper may be downloaded from the server, in the “New Papers” section (http://www.journal.ifrf.net/articles.html), by clicking on the Acrobat PDF icon alongside the title.
Readers should note that today we publish an IFRF Handbook Combustion File entitled: CF50: “What is fluid bed agglomeration?” (See related article in today’s MNM). Dr. Neil Fricker, Editor-in-Chief – IFRF Combustion Handbook, plans to publish further combustion files on related topics in the coming weeks.
Publication in the Journal
The Editor-in-Chief (See associated article in this edition of the MNM) would like to remind all potential authors that publication in the Journal is open to all. If you have interesting results to publish in the field of, or related to, industrial combustion, we invite you to prepare a paper according to the guidelines given in the Author’s Guide on the website (http://www.journal.ifrf.net/).
Papers may be regular “articles” (typically up to 20 pages) or Communications (typically up to 4/5 pages). Review papers can of course be longer. Remember that figures and graphics in general can be in full color. This advantage should be encouraged.
All manuscripts and associated files, proposed for publication should be sent by the Corresponding Author in a compressed/zip file, as an email attachment to email@example.com. This file should include a statement that the proposal’s content is unpublished material that has not being submitted for publication elsewhere. When an article by the author(s) is cited in the proposed article as “in press”, a copy of this article should accompany the proposed article and should be included in the compressed file.
The Editor-in-Chief looks forward to receiving your proposals.