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Aspects of alkali chloride chemistry on deposit formation and high temperature corrosion in biomass and waste fired boilers
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Combustion of biomass and waste has several environmental, economical and political advantages over the use of fossil fuels for the generation of heat and electricity. However, these fuels often have a significantly different composition and the combustion is therefore associated with additional operational problems. A high content of chlorine and alkali metals (potassium and sodium) often causes problems with deposit formation and high temperature corrosion. Some different aspects of these issues are addressed in this thesis.

The overall objective of this thesis was to study and highlight different means by which operational problems related to alkali chlorides can be overcome, reduced or prevented.

The most important results of this thesis are: (1) A full description of the in-situ alkali chloride monitor, its operational principles, the calibration procedure, and an example of a full-scale application was made public in a scientific publication. (2) Efficient sulfation of gaseous alkali chlorides in a full-scale boiler was achieved by injecting ammonium sulfate in a water solution into the hot flue gas. (3) Reduced deposit growth and corrosion rates were achieved by lowering the alkali chloride concentration in the flue gas by sulfation. (4) Evidence of decreased deposit growth and chlorine content in deposits during peat co-combustion. (5) Results are presented from high temperature corrosion tests with different superheater steels in two different combustion environments. (6) Controlled KCl and NaCl condensation under simulated combustion conditions resulted in deposits which consisted of mostly pure phases, in contrast to the solid solution that would be expected under the prevailing conditions at chemical equilibrium.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för tillämpad fysik och elektronik, avdelningen energiteknik och termisk processkemi , 2010. , 45 p.
Series
ETPC Report, ISSN 1653-0551 ; 10-04
National Category
Physical Sciences
Research subject
Physics; Electronics
Identifiers
URN: urn:nbn:se:umu:diva-33667ISBN: 978-91-7459-009-8 (print)OAI: oai:DiVA.org:umu-33667DiVA: diva2:317028
Public defence
2010-06-01, Naturvetarhuset, M450, Umeå University, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2010-05-07 Created: 2010-04-30 Last updated: 2010-05-07Bibliographically approved
List of papers
1. Sulfation of corrosive alkali chlorides by ammonium sulfate in a biomass fired CFB boiler
Open this publication in new window or tab >>Sulfation of corrosive alkali chlorides by ammonium sulfate in a biomass fired CFB boiler
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2007 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 88, no 11-12, 1171-1177 p.Article in journal (Refereed) Published
Abstract [en]

Biomass and waste derived fuels contain relatively high amounts of alkali and chlorine, but contain very little sulfur. Combustion of such fuels can result in increased deposit formation and superheater corrosion. These problems can be reduced by using a sulfur containing additive, such as ammonium sulfate, which reacts with the alkali chlorides and forms less corrosive sulfates. Ammonium sulfate injection together with a so-called in situ alkali chloride monitor (IACM) is patented and known as "ChlorOut". IACM measures the concentrations of alkali chlorides (mainly KCl in biomass combustion) at superheater temperatures. Tests with and without spraying ammonium sulfate into the flue gases have been performed in a 96MW(th)/25MW(e) circulating fluidized bed (CFB) boiler. The boiler was fired mainly with bark and a chlorine containing waste. KCl concentration was reduced from more than 15 ppm to approximately 2 ppm. during injection of ammonium sulfate. Corrosion probe measurements indicated that both deposit formation and material loss due to corrosion were decreased using the additive. Analysis of the deposits showed significantly higher concentration of sulfur and almost no chlorine in the case with ammonium sulfate. Results from impactor measurements supported that KCl was sulfated to potassium sulfate by the additive. (C) 2007 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Amsterdam: Elsevier Bv, 2007
Keyword
biomass combustion, high temperature corrosion, sulfation, kcl, chlorout, iacm, combustion
Identifiers
urn:nbn:se:umu:diva-19737 (URN)10.1016/j.fuproc.2007.06.023 (DOI)0378-3820 (ISBN)
Available from: 2009-03-10 Created: 2009-03-10 Last updated: 2017-12-13Bibliographically approved
2. High temperature corrosion in a 65 MW waste to energy plant
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2007 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 88, no 11-12, 1178-1182 p.Article in journal (Refereed) Published
Abstract [en]

Incineration of municipal solid waste is often associated with high temperature corrosion problems. This paper presents results of full-scale corrosion tests in a 65 MW waste fired combined heat and power plant. A failure case indicated alarmingly high corrosion rate of the superheater tubes. Corrosion tests with five different alloys were carried out within this work in order to determine plant specific corrosion rates on different superheater materials. Additional tests were done to determine the effect on the corrosion rate from adding chlorine containing polyvinyl chloride to the ordinary fuel mix. A corrosion probe with metal temperatures ranging from 320 degrees C to 460 degrees C was used to estimate corrosion loss and to collect deposits. The sampling was performed at a flue gas temperature of 470 degrees C for 10 days. The probe rings were analysed using scanning electron microscope and micrometer measurements to determine the deposit chemistry and corrosion rates. The results showed significant differences in corrosion rates depending on tube material. Chlorine was shown to have a key role in the corrosion process, even at these relatively low temperatures. The results indicated a chlorine induced corrosion mechanism involving volatile iron chloride with a high corrosion rate on the superheater materials typically used. Addition of extra polyvinyl chloride to the fuel mix had an increasing effect on the corrosion. (C) 2007 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier B.V., 2007
Keyword
superheater corrosion, waste incineration, pvc, msw, chlorine
Identifiers
urn:nbn:se:umu:diva-19744 (URN)10.1016/j.fuproc.2007.06.031 (DOI)0378-3820 (ISBN)
Note
This work was supported by Umeå Energi AB. Technical assistance by Vattenfall Research and Development AB is also acknowledged. Available from: 2009-03-10 Created: 2009-03-10 Last updated: 2017-12-13Bibliographically approved
3. Principle, calibration, and application of the in situ alkali chloride monitor
Open this publication in new window or tab >>Principle, calibration, and application of the in situ alkali chloride monitor
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2009 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 80, no 2, 023104-1-023104-4 p.Article in journal (Refereed) Published
Abstract [en]

 The extended use of biomass for heat and power production has caused increased operational problems with fouling and high-temperature corrosion in boilers. These problems are mainly related to the presence of alkali chlorides (KCl and NaCl) at high concentrations in the flue gas. The In-Situ Alkali Chloride Monitor (IACM) was developed by Vattenfall Research and Development AB for measuring the alkali chloride concentration in hot flue gases (>650 oC). The measurement technique is based on molecular differential absorption spectroscopy in the UV range. Simultaneous measurement of SO2 concentration is also possible. The measuring range is 1-50 ppm for the sum of KCl and NaCl concentrations, and 4-750 ppm for SO2. This paper describes the principle of the IACM as well as its calibration. Furthermore, an example of its application in an industrial boiler is given.

Place, publisher, year, edition, pages
American Institute of Physics, 2009
Keyword
bioenergy conversion, boilers, corrosion, flue gases, gas sensors, ultraviolet spectra
Identifiers
urn:nbn:se:umu:diva-19738 (URN)10.1063/1.3081015 (DOI)
Available from: 2009-03-10 Created: 2009-03-10 Last updated: 2017-12-13Bibliographically approved

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