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Computational Fluid Dynamics Modeling of Biomass Gasification in Fixed-bed Reactors Using Highly Preheated Agent
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.ORCID iD: 0000-0002-1861-6490
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass gasification is considered to be one of the most promising energy recovery technologies for the widespread utilization of biomass. Mathematical models have been developed to understand the gasification process inside gasifiers. As the oldest type of gasifier, fixed-bed gasifiers have been widely studied by using zero-dimensional and one-dimensional models; however, only a limited number of two-dimensional models for this type of reactor can be found in existing literature.

The primary goal of this thesis is to develop a two-dimensional computational fluid dynamics (2-D CFD) model for fixed-bed gasifiers that considers the complex kinetic mechanisms, the flow field, and a series of chemical reactions inside gasifiers. The model was evaluated for both downdraft and updraft fixed-bed gasifiers through comparison with existing data from a demonstration-scale high temperature agent gasification (HTAG) system. The results demonstrated that this model can reasonably predict the performance of fixed-bed gasifiers when high-temperature air/steam is used as the gasifying agent. The performances of fixed-bed gasifiers were also discussed under the framework of HTAG technology. This CFD model is a potentially powerful tool for analyzing the performance sensitivity of a fixed-bed gasifier, which will further aid in the design and operation of this type of system.

Biomass should be produced in an ecologically and economically sustainable manner. Therefore, the optimization of the gasification process was further studied to improve gasification performance and efficiency. A zero-dimensional kinetic-free model was introduced based on an updraft fixed-bed gasifier. A thermodynamic analysis was conducted based on the first and second laws of thermodynamics for various S/B ratios and preheating temperatures of the gasifying agent. A practical operating region for the HTAG process was proposed for industrial applications.

According to the results, the HTAG technology relies on an external heat source and uses super-heated air combined with steam; this results in a limited need for feedstock combustion and produces syngas with a high H2 fraction and a low tar content. Based on energy and exergy efficiency analyses from a HTAG application, plasma melting of municipal solid waste (MSW), HTAG technology is demonstrated to be preferable from environmental and energy (exergy) efficiency perspectives.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , x, 63 p.
Keyword [en]
biomass, high temperature agent gasification, CFD modeling, exergy efficiency
National Category
Engineering and Technology Energy Systems
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-147988ISBN: 978-91-7595-207-9 OAI: oai:DiVA.org:kth-147988DiVA: diva2:733778
Public defence
2014-08-29, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140711

Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2017-03-02Bibliographically approved
List of papers
1. Investigation on pyrolysis behavior of three biomass materials
Open this publication in new window or tab >>Investigation on pyrolysis behavior of three biomass materials
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-147993 (URN)
Note

QS 2014

Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2014-07-11Bibliographically approved
2. Two-Dimensional Computational Fluid Dynamics Simulation of Biomass Gasification in a Downdraft Fixed-Bed Gasifier with Highly Preheated Air and Steam
Open this publication in new window or tab >>Two-Dimensional Computational Fluid Dynamics Simulation of Biomass Gasification in a Downdraft Fixed-Bed Gasifier with Highly Preheated Air and Steam
2013 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 6, 3274-3282 p.Article in journal (Refereed) Published
Abstract [en]

Biomass gasification is regarded as one of the most promising energy recovery technologies for the widespread use of biomass. Mathematical models have been developed to understand this process in downdraft fixed beds using zero- and one-dimensional models, but only a limited number of two-dimensional (2D) models for downdraft fixed-bed reactors can be found in the literature. In this study, a 2D computational fluid dynamics (CFD) model was developed to study the gasification process in a downdraft configuration, considering drying, pyrolysis, combustion, and gasification reactions. The gas and solid phases were resolved using an Euler-Euler multiphase approach, with exchange terms for the momentum, mass, and energy. The standard k-epsilon turbulence model was used in the gas phase. The model results were compared to existing data from a demonstration-scale fixed-bed downdraft gasifier. The simulation results exhibit a reasonable agreement with the experimental data. Parameter studies were performed on the basis of the developed model, which indicated that an external heat source for the high-temperature agent gasification (HTAG) technology using superheated air combined with steam resulted in a limited combustion need in the gasifier and produced syngas with a high H-2 fraction and low tar content, which is environmentally preferable.

Keyword
Biomass, Chemical reactors, Combustion, Computational fluid dynamics, Synthesis gas, Turbulence models, Two dimensional
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-125756 (URN)10.1021/ef4003704 (DOI)000320911200043 ()2-s2.0-84879342955 (Scopus ID)
Note

QC 20130814

Available from: 2013-08-14 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
3. Effect of bed height on the performance oa a biomass fixed-bed gasifier
Open this publication in new window or tab >>Effect of bed height on the performance oa a biomass fixed-bed gasifier
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-147994 (URN)
Note

QS 2014

Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2014-07-11Bibliographically approved
4. Energy and Exergy Analysis of High Temperature Agent Gasification of Biomass
Open this publication in new window or tab >>Energy and Exergy Analysis of High Temperature Agent Gasification of Biomass
2014 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 7, no 4, 2107-2122 p.Article in journal (Refereed) Published
Abstract [en]

A chemical equilibrium model was developed to predict the product composition of a biomass gasification system using highly preheated air and steam. The advantages and limitations of this system were discussed from a thermodynamic viewpoint. The first and second law analyses have been conducted for various preheating temperatures and steam/biomass mass (S/B) ratios. The results demonstrated that the chemical energy output of the produced syngas is highest when the S/B ratio is 1.83 under the conditions used in this study. However, higher S/B ratios have a negative effect on the energy and exergy efficiencies. Higher preheating temperatures increase the chemical energy of the produced syngas and the two efficiencies. The peak values for the energy and exergy efficiencies are 81.5% and 76.2%, respectively. Based on the calculated limitation values, where the highest chemical energy (exergy) of the produced syngas and maximum achievable efficiencies are determined, a thermodynamically possible operating region is suggested.

Keyword
biomass gasification, high temperature agent, Aspen model, exergy
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-147061 (URN)10.3390/en7042107 (DOI)000336217000013 ()2-s2.0-84899138296 (Scopus ID)
Note

QC 20140625

Available from: 2014-06-25 Created: 2014-06-23 Last updated: 2017-12-05Bibliographically approved
5. A thermodynamic analysis of solid waste gasification in the Plasma Gasification Melting process
Open this publication in new window or tab >>A thermodynamic analysis of solid waste gasification in the Plasma Gasification Melting process
Show others...
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, 405-413 p.Article in journal (Refereed) Published
Abstract [en]

Plasma Gasification Melting is a promising technology for solid waste treatment. In this work, a thermodynamic analysis has been conducted to evaluate the advantages and limitations of the PGM technology. According to the characteristics of the PGM, the whole process was divided into four sections such as drying, pyrolysis, char gasification and inorganics melting. The energy and exergy in each section has been calculated. According to different usage of syngas, two kinds of energy and exergy efficiencies are defined. The results show that the PGM process produces a tar-rich syngas. When considering the raw syngas (syngas with tar), the energy and exergy efficiency of PGM process is very high. The effects of operating conditions on the thermodynamic performance of the PGM process have been analyzed. Considering the energy and exergy of clean syngas, it is beneficial to increase sensible heat input to the PGM system. However, high sensible heat input or high steam injection is not suggested when considering the energy and exergy efficiency of raw syngas.

Keyword
Energy, Exergy, Gasification, MSW, Plasma
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-136088 (URN)10.1016/j.apenergy.2013.03.054 (DOI)000329377800040 ()2-s2.0-84884284117 (Scopus ID)
Conference
4th International Conference on Applied Energy (ICAE), July 01-04, 2012, China
Note

QC 20131205

Available from: 2013-12-05 Created: 2013-12-03 Last updated: 2017-12-06Bibliographically approved

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