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Iron-based materials as tar depletion catalysts in biomass gasification: Dependency on oxygen potential
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.ORCID iD: 0000-0002-6326-4084
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
2012 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 95, no 1, 71-78 p.Article in journal (Refereed) Published
Abstract [en]

A study has been performed using experimental iron based granules as a tar breakdown catalyst in a biomass gasification gas. Previous examinations established that metallic iron located in a separate catalytic bed reactor has a stronger influence on the tar content and composition in the product gas than their corresponding iron oxides. The results from the present study show that tar diminution in the product gas is dependent on temperature, catalyst material and oxygen potential. Typically, values of 50-75% tar reduction were achieved when varying the catalytic bed temperature between 750 and 850 degrees C. Also, the oxidation state of the catalyst material has an influence on the tar content and gas composition in the gas. When changing the gasification temperature from 800 degrees C to 850 degrees C the oxygen potential in the producer gas also changes, resulting in a transition from oxidative to reductive conditions in the gas. This implies that when the gasification temperature is 800 degrees C, the catalyst is transformed from its metallic state to the iron oxide, wustite. Consequently, the tar reduction capacity of the catalyst is reduced by approximately 20%. In view of the overall results it can be concluded that the catalysts in their metallic states in general exhibits a better tar cracking capacity than their corresponding oxides. The iron material used is sintered iron powders manufactured at Hoganas AB, Sweden. The iron materials were dispensed in the metallic state.

Place, publisher, year, edition, pages
2012. Vol. 95, no 1, 71-78 p.
Keyword [en]
Biomass gasification, Oxygen potential catalytic tar reduction, Metallic iron
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-33072DOI: 10.1016/j.fuel.2011.06.002ISI: 000300615900008Scopus ID: 2-s2.0-84857040381OAI: oai:DiVA.org:kth-33072DiVA: diva2:413305
Note
QC 20120326Available from: 2011-04-28 Created: 2011-04-28 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Iron-based materials as tar cracking catalyst in waste gasification
Open this publication in new window or tab >>Iron-based materials as tar cracking catalyst in waste gasification
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The treatment of municipal solid waste (MSW) in Sweden has changed during the past decades due to national legislation and European Union directives. The former landfills have more or less been abandoned in favour of material recycling and waste incineration. On a yearly basis approximately 2.2 million tonnes waste are incinerated in Sweden with heat recovery and to some extent also with electricity generation, though at a low efficiency. It is desirable to alter this utilisation and instead employ MSW as fuel in a fluid bed gasification process. Then electrical energy may be produced at a much higher efficiency. However, MSW contain about 1 % chlorine in the form of ordinary table salt (NaCl) from food scraps. This implies that the tar cracking catalyst, dolomite, which is normally employed in gasification, will suffer from poisoning if applied under such conditions. Then the tar cracking capacity will be reduced or vanish completely with time. Consequently, an alternative catalyst, more resistant to chlorine, is needed.

Preliminary research at KTH has indicated that iron in its metallic state may possess tar cracking ability. With this information at hand and participating in the project “Energy from Waste” an experimental campaign was launched. Numerous experiments were conducted using iron as tar cracking catalyst. First iron sinter pellets from LKAB were employed. They were reduced in situ with a stream of hydrogen before they were applied. Later iron-based granules from Höganäs AB were tested. These materials were delivered in the metallic state. In all tests the KTH atmospheric fluidised bed gasifier with a secondary catalytic reactor housing the catalytic material was deployed. Mostly, the applied fuel was birch. The results show that metallic iron possesses an intrinsic ability, almost in the range of dolomite, to crack tars. Calculations indicate that iron may be more resistant to chlorine than dolomite. The exploration of metallic iron’s excellent tar cracking capacity led to the innovative manufacture of an iron catalytic tar cracking filter as well as a general knowledge of its tar cracking capacity. This filter with dual functionality would be a general improvement of the gasification process since it among other things would make the process denser.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 73 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:27
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-33043 (URN)978-91-7415-941-7 (ISBN)
Public defence
2011-05-19, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110428Available from: 2011-04-28 Created: 2011-04-27 Last updated: 2011-04-28Bibliographically approved
2. Biomass gasification in ABFB: Tar mitigation
Open this publication in new window or tab >>Biomass gasification in ABFB: Tar mitigation
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass gasification may be an attractive alternative for meeting future energy demand. Although gasification is a mature technology, it has yet to be fully commercialised due to tar formation. This study focuses on the tar mitigation in gas produced in an atmospheric bubbling fluidised bed (ABFB) gasification system.

Previous studies indicated significant tar variability along the system. In this work the experimental procedure has been improved for reliable results and better understanding of tar variability in the producer gas. After having introduced a new sample point for tar analysis to the system, experimental results indicated tar reduction in the gasifier, probably due to continuous accumulation of char and ash in the bed, as well as in the ceramic filter owing to thermal and catalytic effects.

Iron-based materials, provided by Höganäs AB, were applied in a secondary catalytic bed reactor for tar decomposition in the producer gas. It was found that tar concentration depends on catalytic and gasification temperatures and catalyst material. When changing the gasification temperature from 850 °C to 800 °C the conditions in the producer gas also changed from reductive to oxidative, transforming the initial metallic state of catalyst into its oxidised form. It may be concluded that the catalysts in their metallic states in general exhibit a better tar cracking capacity than their corresponding oxides.

Due to the low reactivity of petroleum coke, an alternative may be to convert it in combination with other fuels such as biomass. Co-gasification of petroleum coke and biomass was studied in this work. Biomass ash in the blends was found to have a catalytic effect on the reactivity of petroleum coke during co-gasification. Furthermore, this synergetic effect between biomass and petcoke was observed in the kinetics data. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xviii, 71 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:35
Keyword
Ash, biomass, char, gasification, iron-based, petcoke, tar
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-154530 (URN)978-91-7595-257-4 (ISBN)
Public defence
2014-11-03, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141022

Available from: 2014-10-22 Created: 2014-10-21 Last updated: 2014-11-04Bibliographically approved

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