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EVALUATION OF DIFFERENT BIOMASS GASIFICATION MODELING APPROACHES FOR FLUIDIZED BED GASIFIERS
Mälardalen University, School of Business, Society and Engineering, Future Energy Center. Mälardalen Högskola.ORCID iD: 0000-0002-0895-8286
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-6279-4446
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-3485-5440
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-7233-6916
2016 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 91, 69-82 p.Article in journal (Refereed) Published
Abstract [en]

To develop a model for biomass gasification in fluidized bed gasifiers with high accuracy and generality that could be used under various operating conditions, the equilibrium model (EM) is chosen as a general and case-independent modeling method. However, EM lacks sufficient accuracy in predicting the content (volume fraction) of four major components (H2, CO, CO2 and CH4) in product gas. In this paper, three approaches—MODEL I, which restricts equilibrium to a specific temperature (QET method); MODEL II, which uses empirical correlations for carbon, CH4, C2H2, C2H4, C2H6 and NH3 conversion; and MODEL III, which includes kinetic and hydrodynamic equations—have been studied and compared to map the barriers and complexities involved in developing an accurate and generic model for the gasification of biomass.

This study indicates that existing empirical correlations can be further improved by considering more experimental data. The updated model features better accuracy in the prediction of product gas composition in a larger range of operating conditions. Additionally, combining the QET method with a kinetic and hydrodynamic approach results in a model that features less overall error than the original model based on a kinetic and hydrodynamic approach.

Place, publisher, year, edition, pages
Västerås, 2016. Vol. 91, 69-82 p.
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-31591DOI: 10.1016/j.biombioe.2016.05.002ISI: 000382524100008Scopus ID: 2-s2.0-84967194662OAI: oai:DiVA.org:mdh-31591DiVA: diva2:928454
Available from: 2016-05-15 Created: 2016-05-15 Last updated: 2016-12-27Bibliographically approved
In thesis
1. Biomass gasification in fluidized bed gasifiers: Modeling and simulation
Open this publication in new window or tab >>Biomass gasification in fluidized bed gasifiers: Modeling and simulation
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Using woody biomass as a resource for production of biofuel, heat and power through gasification has been studied for years. In order to reduce the cost of operating and to design the full-scale gasification plant developing a general model to be applicable for different ranges of input data with acceptable level of accuracy, is needed. In order to develop such model for the gasifier, as the main component in the process, three major models have been studied in this thesis; theoretical model (Equilibrium model), semi-empirical model (modified equilibrium model, kinetic combined with hydrodynamic model) and empirical model (statistical model).

Equilibrium model (EM), shows low accuracy in predicting the content ofmajor components in product gas especially CH4 and CO. Therefore to improve the accuracy of prediction modification of EM is needed. Analyzing the semi-empirical approaches show that although the accuracy of EM can be improved, the generality of the modified models are still low. Therefore two new modified models have been developed. The first model is based on including data from wider range of operating condition to develop the empirical equation. The second model is based on combining QET and reaction kinetics for char gasification approaches. The first model decreases the overall error from 44% to 31% while the overall error of second model is decreased from 36% to 8%. Other semi-empirical model for fluidized bed gasifiers which is not equilibrium-based is developed by combining reaction kinetics with hydrodynamic equations. Investigating different hydrodynamic models show that combining two-phase-structure model with reaction kinetics for bubbling fluidized bed gasifiers improves the accuracy of the kinetic-only model.

The third type of approaches, investigated in this thesis, towards developing a general model is the empirical model. This model has been developed based on Partial least square (PLS) approach. The PLS-R model show high level of accuracy within the specific range of empirical data used for developing the model. Further analysis on the experimental dataset by PLS-R model show that equivalence ratio (ER) is the operating parameter with the most significant impact on the performance of fluidized bed gasifiers. Optimizing the operation of fluidized bed gasifiers based on this model shows that high gas quality (high volume fraction of H2, CO and CH4 and low volume fraction of CO2), high carbon conversion and low tar yield is achieved when ER≈0.3, Steam to Biomass ratio≈0.7, moisture content≈9% and particle size≈3mm and olivine is the bed material. 

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2016
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 216
National Category
Chemical Process Engineering Energy Systems
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-33426 (URN)978-91-7485-296-7 (ISBN)
Public defence
2016-12-02, Pi, Mälardalens högskola, Västerås, 09:15 (English)
Opponent
Supervisors
Available from: 2016-10-18 Created: 2016-10-18 Last updated: 2016-11-11Bibliographically approved

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