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Biomass gasification in ABFB: Tar mitigation
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
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 [en]
Ash, biomass, char, gasification, iron-based, petcoke, tar
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-154530ISBN: 978-91-7595-257-4 (print)OAI: oai:DiVA.org:kth-154530DiVA: diva2:757339
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
List of papers
1. Tar Variability in the Producer Gas in a Bubbling Fluidized Bed Gasification System
Open this publication in new window or tab >>Tar Variability in the Producer Gas in a Bubbling Fluidized Bed Gasification System
2014 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 12, 7494-7500 p.Article in journal (Refereed) Published
Abstract [en]

Previous studies in an atmospheric bubbling fluidised bed (BFB) gasification system indicated significant tar variability along the system. In this paper the experimental procedure has been improved for reliable results and understanding of tar variability in the producer gas. By introducing a new sample point for tar analysis to the system, experiments 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 because of thermo- and catalytic effects. Thermogravimetric analysis of the filter sample indicated 14 % of volatile inorganic compounds, and additional analysis of inorganic parts showed alkali and alkaline earth metal content, well known as tar breakdown catalysts.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-154532 (URN)10.1021/ef5015617 (DOI)000346759800022 ()2-s2.0-84949119025 (Scopus ID)
Note

QC 20150122

Available from: 2014-10-22 Created: 2014-10-22 Last updated: 2017-12-05Bibliographically approved
2. Biomass gasification in an atmospheric fluidised bed: Tar reduction with experimental iron-based granules from Höganäs AB, Sweden
Open this publication in new window or tab >>Biomass gasification in an atmospheric fluidised bed: Tar reduction with experimental iron-based granules from Höganäs AB, Sweden
2011 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 176, no 1, 253-257 p.Article in journal (Refereed) Published
Abstract [en]

The present study investigates the effect of several experimental iron-based granules on biomass tar decomposition. The iron-based materials were provided by Höganäs AB and were all in their metallic state when they were applied in a secondary catalytic reactor. Bark-free birch was employed as fuel in an atmospheric fluidised bed reactor, and the tar concentration and gas composition in the producer gas were measured before and after the catalytic bed. The results demonstrate a clear tar reduction capacity for all the tested iron-based materials.

Keyword
Biomass gasification, Tar cracking, Iron-based materials, Catalyst characterisation Article Outline
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-33050 (URN)10.1016/j.cattod.2010.12.019 (DOI)000296527900049 ()2-s2.0-80054049467 (Scopus ID)
Note
2nd International Symposium on Air Pollution Abatement Catalysis (APAC). Cracow, POLAND. SEP 08-11, 2010. QC 20120313Available from: 2011-04-28 Created: 2011-04-27 Last updated: 2017-12-11Bibliographically approved
3. Iron-based materials as tar depletion catalysts in biomass gasification: Dependency on oxygen potential
Open this publication in new window or tab >>Iron-based materials as tar depletion catalysts in biomass gasification: Dependency on oxygen potential
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.

Keyword
Biomass gasification, Oxygen potential catalytic tar reduction, Metallic iron
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-33072 (URN)10.1016/j.fuel.2011.06.002 (DOI)000300615900008 ()2-s2.0-84857040381 (Scopus ID)
Note
QC 20120326Available from: 2011-04-28 Created: 2011-04-28 Last updated: 2017-12-11Bibliographically approved
4. Co-gasification of petroleum coke and biomass
Open this publication in new window or tab >>Co-gasification of petroleum coke and biomass
2014 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 117, no Part A, 870-875 p.Article in journal (Refereed) Published
Abstract [en]

Gasification may be an attractive alternative for converting heavy oil residue - petroleum coke into valuable synthetic gas. Due to the low reactivity of petroleum coke, it is maybe preferable to convert it in combination with other fuels such as biomass. Co-gasification of petroleum coke and biomass was studied in an atmospheric bubbling fluidised bed reactor and a thermogravimetric analyser (TGA) at KTH Royal University of Technology. 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. The activation energy Ea determined from the Arrhenius law for pure petcoke steam gasification in the TGA was 121.5 kJ/mol, whereas for the 50/50 mixture it was 96.3, and for the 20/80 blend - 83.5 kJ/mol.

Keyword
Activation energy, Biomass, Co-gasification, Fluidised bed, Petroleum coke
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-139257 (URN)10.1016/j.fuel.2013.09.050 (DOI)000327766900097 ()2-s2.0-84887119133 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20140108

Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2017-12-06Bibliographically approved

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