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Gasification characteristics of steam exploded biomass in an updraft pilot scale gasifier
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
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2014 (English)In: Energy, ISSN 0360-5442, Vol. 71, 496-506 p.Article in journal (Refereed) Published
Abstract [en]

Pretreatment of biomass becomes more and more important due to the large scale application of biomass having low energy density. In this paper, steam exploded biomass pellets (Black pellets) and unpretreated biomass pellets (Gray pellets) were gasified with air and steam at an updraft HTAG (High Temperature Agent Gasification) unit. Decomposition characteristics of pellets were first analyzed with TGA (thermo gravimetric analysis). Early decomposition of hemicellulose and cellulose were seen with Black pellets around 241 degrees C and 367 degrees C respectively. Introducing CO2 led comparatively high mass loss rate with Black pellets. Gasification of Black pellets resulted in syngas with high CO and hydrocarbon contents while Gasification of Gray pellets resulted in high H-2 content of syngas. LHV (lower heating value) of syngas was high around 7.3 MJ/Nm(3) and 10.6 MJ/Nm(3) with air gasification and steam gasification respectively. Even with significantly low syngas temperature with gasification of Black pellets, only slightly high total tar content was seen compared to that of Gray pellets gasification. Phenolic compounds dominated the tar composition. In general, steam gasification of Black pellets seems to be more feasible if syngas with high energy value is desired. If higher H-2 yield is preferred, gasification of unpretreated pellets likely to be more attractive.

Place, publisher, year, edition, pages
2014. Vol. 71, 496-506 p.
Keyword [en]
Gasification, Steam explosion pretreatment, TGA (thermo gravimetric analysis)
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-148349DOI: 10.1016/ 000338388000044ScopusID: 2-s2.0-84902553880OAI: diva2:736212
EU, European Research Council

QC 20140805

Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2016-08-25Bibliographically approved
In thesis
1. Advanced Gasification of Biomass/Waste for Substitution of Fossil Fuels in Steel Industry Heat Treatment Furnaces
Open this publication in new window or tab >>Advanced Gasification of Biomass/Waste for Substitution of Fossil Fuels in Steel Industry Heat Treatment Furnaces
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the current trend of CO2 mitigation in process industries, the primary goal of this thesis is to promote biomass as an energy and reduction agent source to substitute fossil sources in the steel industry. The criteria for this substitution are that the steel process retains the same function and the integrated energy efficiency is as high as possible.

This work focuses on advanced gasification of biomass and waste for substitution of fossil fuels in steel industry heat treatment furnaces. To achieve this, two approaches are included in this work. The first investigates the gasification performance of pretreated biomass and waste experimentally using thermogravimetric analysis (TGA) and a pilot plant gasifier. The second assesses the integration of the advanced gasification system with a steel heat treatment furnace.

First, the pyrolysis and char gasification characteristics of several pretreated biomass and waste types (unpretreated biomass, steam-exploded biomass, and hydrothermal carbonized biomass) were analyzed with TGA. The important aspects of pyrolysis and char gasification of pretreated biomass were identified.

Then, with the objective of studying the gasification performance of pretreated biomass, unpretreated biomass pellets (gray pellets), steam-exploded biomass pellets (black pellets), and two types of hydrothermal carbonized biomass pellets (spent grain biocoal and horse manure biocoal) were gasified in a fixed bed updraft gasifier with high-temperature air/steam as the gasifying agent. The gasification performance was analyzed in terms of syngas composition, lower heating value (LHV), gas yield, cold gas efficiency (CGE), tar content and composition, and particle content and size distribution. Moreover, the effects on the reactions occurring in the gasifier were identified with the aid of temperature profiles and gas ratios.

Further, the interaction between fuel residence time in the bed (bed height), conversion, conversion rate/specific gasification rate, and superficial velocity (hearth load) was revealed. Due to the effect of bed height on the gasification performance, the bed pressure drop is an important parameter related to the operation of a fixed bed gasifier. Considering the limited studies on this relationship, an available pressure drop prediction correlation for turbulent flow in a bed with cylindrical pellets was extended to a gasifier bed with shrinking cylindrical pellets under any flow condition. Moreover, simplified graphical representations based on the developed correlation, which could be used as an effective guide for selecting a suitable pellet size and designing a grate, were introduced.

Then, with the identified positive effects of pretreated biomass on the gasification performance, the possibility of fuel switching in a steel industry heat treatment furnace was evaluated by effective integration with a multi-stage gasification system. The performance was evaluated in terms of gasifier system efficiency, furnace efficiency, and overall system efficiency with various heat integration options. The heat integration performance was identified based on pinch analysis. Finally, the efficiency of the co-production of bio-coke and bio-H2 was analyzed to increase the added value of the whole process.

It was found that 1) the steam gasification of pretreated biomass is more beneficial in terms of the energy value of the syngas, 2) diluting the gasifying agent and/or lowering the agent temperature compensates for the ash slagging problem in biocoal gasification, 3) the furnace efficiency can be improved by switching the fuel from natural gas (NG) to syngas, 4) the gasifier system efficiency can be improved by recovering the furnace flue gas heat for the pretreatment, and 5) the co-production of bio-coke and bio-H2 significantly improves the system efficiency.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 82 p.
Biomass, Pretreatment, Gasification, Pressure drop, Steel industry, Fuel switch, Energy efficiency
National Category
Chemical Process Engineering
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-190938 (URN)978-91-7729-053-7 (ISBN)
External cooperation:
Public defence
2016-09-27, F3, Lindstedtvägen 26, Stockholm, 10:00 (English)

QC 20160825

Available from: 2016-08-29 Created: 2016-08-18 Last updated: 2016-08-29Bibliographically approved

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Gunarathne, Duleeka SandamaliChmielewski, Jan KarolYang, WeihongBlasiak, Wlodzimierz
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