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Biomass gasification in fluidized bed gasifiers: Modeling and simulation
Mälardalen University, School of Business, Society and Engineering, Future Energy Center. (Future energy)ORCID iD: 0000-0002-0895-8286
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: urn:nbn:se:mdh:diva-33426ISBN: 978-91-7485-296-7OAI: oai:DiVA.org:mdh-33426DiVA: diva2:1038409
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
List of papers
1. Modelling and Simulation of Biomass Conversion Processes
Open this publication in new window or tab >>Modelling and Simulation of Biomass Conversion Processes
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2013 (English)In: Proceedings - 8th EUROSIM Congress on Modelling and Simulation, EUROSIM 2013, 2013Conference paper (Refereed)
Abstract [en]

By utilizing biomass gasification, the energy contentof the biomass can be utilized to produce gas to be used forcogeneration of heat and power as well as other energy carrierssuch as fuels for vehicles. The concept is suitable forapplication to existing CHP plants as well as for utilizing spentliqour in small scale pulp and paper mills. The introductionwould enable flexible energy utilization, use of problematicfuels as well as protects the environment by e.g. avoiding therelease of toxic substances. In this paper, the possibilities todevelop this concept is discussed. In this paper we comparedifferent gasification processes with respect to what gas qualitywe get, and how the gasification can be modelled usingdifferent modelling approaches, and how these can becombined. Results from simulations are compared toexperimental results from pilot plant operations in differentscales and with different processes like CFB and BFBTechnologies, athmospheric and pressurized, and using steam,air and oxygen as oxidizing media.

Keyword
Biomass, gasification, modelling, simulation, CHP, agricultural residue
National Category
Energy Systems
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-21749 (URN)10.1109/EUROSIM.2013.91 (DOI)000361021500088 ()2-s2.0-84929593503 (ScopusID)978-076955073-2 (ISBN)
Conference
8th EUROSIM Congress on Modelling and Simulation, Cardiff 9-13 September 2013
Available from: 2013-10-01 Created: 2013-10-01 Last updated: 2016-10-18Bibliographically approved
2. EVALUATION OF DIFFERENT BIOMASS GASIFICATION MODELING APPROACHES FOR FLUIDIZED BED GASIFIERS
Open this publication in new window or tab >>EVALUATION OF DIFFERENT BIOMASS GASIFICATION MODELING APPROACHES FOR FLUIDIZED BED GASIFIERS
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
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:mdh:diva-31591 (URN)10.1016/j.biombioe.2016.05.002 (DOI)000382524100008 ()2-s2.0-84967194662 (ScopusID)
Available from: 2016-05-15 Created: 2016-05-15 Last updated: 2016-10-18Bibliographically approved
3. Assessment on the impact of including hydrodynamics on the performance of kinetic based models for bubbling fluidized bed gasifiers
Open this publication in new window or tab >>Assessment on the impact of including hydrodynamics on the performance of kinetic based models for bubbling fluidized bed gasifiers
(English)Manuscript (preprint) (Other academic)
Keyword
Kinetic, hydrodynamics, biomass gasification, fluidized bed gasifiers, modeling
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:mdh:diva-33425 (URN)
Available from: 2016-10-17 Created: 2016-10-17 Last updated: 2016-10-18
4. The influence of different parameters on biomass gasification in circulating fluidized bed gasifiers
Open this publication in new window or tab >>The influence of different parameters on biomass gasification in circulating fluidized bed gasifiers
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2016 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 126, 110-123 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of biomass gasification has been studied for decades. However, for circulating fluidized bed (CFB) gasifiers, the impacts of different parameters on the gas quality and gasifiers performance have still not been fully investigated. In this paper, different CFB gasifiers have been analyzed by multivariate analysis statistical tools to identify the hidden interrelation between operating parameters and product gas quality, the most influencing input parameters and the optimum points for operation. The results show that equivalence ratio (ER), bed material, temperature, particle size and carbon content of the biomass are the input parameters influencing the output of the gasifier the most. Investigating among the input parameters with opposite impact on product gas quality, cases with optimal gas quality can result in high tar yield and low carbon conversion while low tar yield and high carbon conversion can result in product gas with low quality. However using Olivine as the bed material and setting ER value around 0.3, steam to biomass ratio to 0.7 and using biomass with 3 mm particle size and 9 wt% moisture content can result in optimal product gas with low tar yield.

National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:mdh:diva-32432 (URN)10.1016/j.enconman.2016.07.031 (DOI)000385326400011 ()2-s2.0-84980563382 (ScopusID)
Available from: 2016-08-04 Created: 2016-08-04 Last updated: 2016-11-10Bibliographically approved
5. BIO-METHANE PRODUCTION THROUGH DIFFERENT BIOMASS GASIFIERS
Open this publication in new window or tab >>BIO-METHANE PRODUCTION THROUGH DIFFERENT BIOMASS GASIFIERS
2013 (English)Conference paper (Refereed)
Abstract [en]

Considering sustainability of energy resources and environmental concerns have led to activities all over the world seeking alternatives for current methods of fuel production. Gasification of biomass to supply bio-methane is one of those options. Bio-methane is carbon neutral and meets the needs of combustion engines in vehicles.Focusing on vehicle fuel production reveals the need for wide research to understand different types of gasifiers in order to find the possibilities for more methane production.In this paper data collected from different experimental setups are summarized and analyzed.Fluidized bed gasifiers show higher methane concentrations in the produced gas while entrained flow and downdraft gasifiers may be the least suitable types for high methane yields.Heating value of the product gas and cold gas efficiency are also studied as the important parameters for evaluating the characteristics of the product gas. This analysis shows that by increasing the equivalence ratio, the heating value of the product gas decreases while the efficiency may not follow the same trend.

National Category
Engineering and Technology Energy Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-21655 (URN)
Conference
International Conference on Applied Energy, ICAE 2013, Jul 1-4, 2013, Pretoria, South Africa
Available from: 2013-09-25 Created: 2013-09-25 Last updated: 2016-10-18Bibliographically approved

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