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Advanced Gasification of Biomass/Waste for Substitution of Fossil Fuels in Steel Industry Heat Treatment Furnaces
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Energy and Furnace Technology)ORCID iD: 0000-0002-4689-2927
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.
Keyword [en]
Biomass, Pretreatment, Gasification, Pressure drop, Steel industry, Fuel switch, Energy efficiency
National Category
Chemical Process Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-190938ISBN: 978-91-7729-053-7OAI: oai:DiVA.org:kth-190938DiVA: diva2:953814
Public defence
2016-09-27, F3, Lindstedtvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160825

Available from: 2016-08-29 Created: 2016-08-18 Last updated: 2016-08-29Bibliographically approved
List of papers
1. Gasification characteristics of steam exploded biomass in an updraft pilot scale gasifier
Open this publication in new window or tab >>Gasification characteristics of steam exploded biomass in an updraft pilot scale gasifier
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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.

Keyword
Gasification, Steam explosion pretreatment, TGA (thermo gravimetric analysis)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-148349 (URN)10.1016/j.energy.2014.04.100 (DOI)000338388000044 ()2-s2.0-84902553880 (ScopusID)
Funder
EU, European Research Council
Note

QC 20140805

Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2016-08-25Bibliographically approved
2. Gasification Characteristics of Hydrothermal Carbonized Biomass in an Updraft Pilot-Scale Gasifier
Open this publication in new window or tab >>Gasification Characteristics of Hydrothermal Carbonized Biomass in an Updraft Pilot-Scale Gasifier
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2014 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 3, 1992-2002 p.Article in journal (Refereed) Published
Abstract [en]

Biocoal pellets were gasified in an updraft high-temperature agent gasification (HTAG) unit with preheated air at 900 degrees C to study the performance of the air gasification of hydrothermal carbonized biomass. In comparison to raw biomass, hydrothermal carbonization increased the carbon content from 46 to 66% and decreased the oxygen content from 38 to 16%. As a result, the heating value of biomass on a dry basis was increased from 19 to 29 MJ/kg after hydrothermal carbonization. Thermogravimetric analysis (TGA) of biocoal featured early decomposition of hemicellulose and a shoulder attached to the cellulose peak corresponding to lignin decomposition. Char gasification demonstrated a peak near conversion of 0.2. Syngas with 7.9 MJ Nm(-3) lower heating value (LHV) was obtained from gasification experiments performed in the pilot-scale gasifier. The maximum cold gas efficiency was 80% at the lowest equivalence ratio (ER) and also resulted in high-purity syngas. The LHV and cold gas efficiency were higher than that of the previously studied unpretreated biomass pellets. The fuel conversion positively correlated with the fuel residence time in the bed, and almost 99% conversion could be achieved for a residence time of 2 h. The superficial velocity (or hearth load) and specific gasification rate were higher than the reported values of updraft gasifiers because of the high-temperature operation and specific fuel used.

Keyword
Sewage-Sludge, Enzymatic-Hydrolysis, Waste Biomass, Pretreatment, Fuel, Cellulose, Products, Water, Coal, Tar
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-144550 (URN)10.1021/ef402342e (DOI)000333381200045 ()2-s2.0-84897824136 (ScopusID)
Note

QC 20140428

Available from: 2014-04-28 Created: 2014-04-24 Last updated: 2016-08-25Bibliographically approved
3. Performance of High Temperature Air/Steam Gasification of Hydrothermal Carbonized Biomass
Open this publication in new window or tab >>Performance of High Temperature Air/Steam Gasification of Hydrothermal Carbonized Biomass
2014 (English)In: 22nd European Biomass Conference and Exhibition, 2014, 626-631 p.Conference paper (Refereed)
Abstract [en]

In order to effectively use the biomass resources for thermal applications, use of biomass pretreatment technologies like hydrothermal carbonization are emerging. With the aim of studying the gasification performance of hydrothermal carbonized biomass (biocoal) in high temperature air/steam medium, gasification of two types of biocoal pellets produced from spent grain and horse manure, was carried out in a fixed bed updraft gasifier. Steam gasification gave syngas having 10-11 MJ/Nm3 of LHV with both types of biocoal. The syngas yield and thus cold gas efficiency was higher with gasification of spent grain biocoal, but syngas purity in terms of tar and particulates was better with gasification of horse manure biocoal.

Keyword
Gasification, Fixed bed, Hydrothermal Carbonization, Biocoal
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-160950 (URN)10.5071/22ndEUBCE2014-2AV.2.14 (DOI)000351053500115 ()978-88-89407-52-3 (ISBN)
Conference
22nd European Biomass Conference and Exhibition, 2014
Note

QC 20150410

Available from: 2015-03-05 Created: 2015-03-05 Last updated: 2016-08-25Bibliographically approved
4. Pressure drop prediction of a gasifier bed with cylindrical biomass pellets
Open this publication in new window or tab >>Pressure drop prediction of a gasifier bed with cylindrical biomass pellets
2014 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 113, 258-266 p.Article in journal (Refereed) Published
Abstract [en]

Bed pressure drop is an import parameter related to operation and performance of fixed bed gasifiers. Up to date, limited literature is found on pressure drop prediction of beds with cylindrical pellets and none was found for gasifying beds with cylindrical pellets. In this paper, an available pressure drop prediction correlation for turbulent flows in a bed with cylindrical pellets which has used equivalent tortuous passage method was extended for a gasifier bed with shrinking cylindrical pellets and for any flow condition. Further, simplified graphical representations introduced based on the developed correlation can be effectively used as a guide for selecting a suitable pellet size and designing a grate so that it can be met the system requirements. Results show that the method formulated in the present study gives pressure drop approximation within 7% deviation compared to measured values with respect to performed runs. Available empirical correlation with modified Ergun constants for cylindrical pellets gave pressure drop within 20% deviation after the effect of shrinkage was taken into account.

Keyword
Biomass, Gasification, Fixed bed, Pressure drop
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-141300 (URN)10.1016/j.apenergy.2013.07.032 (DOI)000329952500027 ()2-s2.0-84882587413 (ScopusID)
Note

QC 20140213

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2016-08-25Bibliographically approved
5. Performance of an effectively integrated biomass multi-stage gasification system and a steel industry heat treatment furnace
Open this publication in new window or tab >>Performance of an effectively integrated biomass multi-stage gasification system and a steel industry heat treatment furnace
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2016 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 170, 353-361 p.Article in journal (Refereed) Published
Abstract [en]

The challenges of replacing fossil fuel with renewable energy in steel industry furnaces include not only reducing CO2 emissions but also increasing the system energy efficiency. In this work, a multi-stage gasification system is chosen for the integration with a heat treatment furnace in the steel powder industry to recover different rank/temperature waste heat back to the biomass gasification system, resulting higher system energy efficiency.A system model based on Aspen Plus was developed for the proposed integrated system considering all steps, including biomass drying, pyrolysis, gasification and the combustion of syngas in the furnace. Both low temperature (up to 400 °C) and high temperature (up to 700 °C) heat recovery possibilities were analysed in terms of energy efficiency by optimizing the biomass pretreatment temperature.The required process conditions of the furnace can be achieved by using syngas. No major changes to the furnace, combustion technology or flue gas handling system are necessary for this fuel switching. Only a slight revamp of the burner system and a new waste heat recovery system from the flue gases are required.Both the furnace efficiency and gasifier system efficiency are improved by integration with the waste heat recovery. The heat recovery from the hot furnace flue gas for biomass drying and steam superheating is the most promising option from an energy efficiency point of view. This option recovers two thirds of the available waste heat, according to the pinch analysis performed. Generally, depending on the extent of flue gas heat recovery, the system can sustain up to 65% feedstock moisture content at the highest pyrolysis temperature studied.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Biomass gasification, Energy efficiency, Fuel substitution, Integration, Pyrolysis, Steel industry, Biomass, Carbon dioxide, Combustion, Flue gases, Flues, Fossil fuels, Fuels, Furnaces, Gasification, Heat treatment, Iron and steel industry, Steelmaking, Synthesis gas, Temperature, Waste heat, Waste heat utilization, Waste incineration, Waste treatment, Biomass gasification system, Biomass pre treatments, Combustion technology, Heat treatment furnaces, Pyrolysis temperature, Waste heat recovery systems, Heat treating furnaces
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-186964 (URN)10.1016/j.apenergy.2016.03.003 (DOI)000374601400032 ()2-s2.0-84960153754 (ScopusID)
External cooperation:
Note

QC 20160518

Available from: 2016-05-18 Created: 2016-05-16 Last updated: 2016-08-29Bibliographically approved

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