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Performance of an effectively integrated biomass multi-stage gasification system and a steel industry heat treatment furnace
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-8045-6344
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Swerea KIMAB AB, Sweden. (ENHETEN PROCESSER)ORCID iD: 0000-0002-1837-5439
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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) PublishedText
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. Vol. 170, 353-361 p.
Keyword [en]
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: urn:nbn:se:kth:diva-186964DOI: 10.1016/j.apenergy.2016.03.003ISI: 000374601400032ScopusID: 2-s2.0-84960153754OAI: oai:DiVA.org:kth-186964DiVA: diva2:929359
Note

QC 20160518

Available from: 2016-05-18 Created: 2016-05-16 Last updated: 2016-08-29Bibliographically 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.
Keyword
Biomass, Pretreatment, Gasification, Pressure drop, Steel industry, Fuel switch, Energy efficiency
National Category
Chemical Process Engineering
Research subject
Materials Science and Engineering
Identifiers
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)
Opponent
Supervisors
Note

QC 20160825

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

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