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Two-Dimensional Computational Fluid Dynamics Simulation of Biomass Gasification in a Downdraft Fixed-Bed Gasifier with Highly Preheated Air and Steam
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.ORCID iD: 0000-0002-1837-5439
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
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.

Place, publisher, year, edition, pages
2013. Vol. 27, no 6, 3274-3282 p.
Keyword [en]
Biomass, Chemical reactors, Combustion, Computational fluid dynamics, Synthesis gas, Turbulence models, Two dimensional
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-125756DOI: 10.1021/ef4003704ISI: 000320911200043Scopus ID: 2-s2.0-84879342955OAI: oai:DiVA.org:kth-125756DiVA: diva2:640580
Note

QC 20130814

Available from: 2013-08-14 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Computational Fluid Dynamics Modeling of Biomass Gasification in Fixed-bed Reactors Using Highly Preheated Agent
Open this publication in new window or tab >>Computational Fluid Dynamics Modeling of Biomass Gasification in Fixed-bed Reactors Using Highly Preheated Agent
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
biomass, high temperature agent gasification, CFD modeling, exergy efficiency
National Category
Engineering and Technology Energy Systems
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-147988 (URN)978-91-7595-207-9 (ISBN)
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

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Yang, Weihong

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