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Publications (10 of 39) Show all publications
Sadegh-Vaziri, R. & Bäbler, M. (2019). Providing sulfur free syngas to a fuel cell system. In: Energy Procedia: . Paper presented at 2018 Renewable Energy Integration with Mini/Microgrid, REM 2018, 28 September 2018 through 30 September 2018 (pp. 448-453). Elsevier Ltd
Open this publication in new window or tab >>Providing sulfur free syngas to a fuel cell system
2019 (English)In: Energy Procedia, Elsevier Ltd , 2019, p. 448-453Conference paper, Published paper (Refereed)
Abstract [en]

Fuel cells are viable alternatives as power backup systems for mini-grids. In this work a case is considered, where the hydrogen fuel to the fuel cells is supplied from biomass gasification. However, the producer gas obtained from biomass gasification needs to be cleaned of impurities and contaminants. In this work we examined the superiority of the hot producer gas cleaning, which results in a better thermal efficiency since the heat loss from the system is reduced. In order to have a viable hot cleaning process, sulfur should be removed at 800°C and this was shown possible by promising primary data from the experiments where H 2 S was removed down to an acceptable level. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Biomass, Gasification, Sulfur, Biomass Gasification, Cleaning process, Fuel cell system, Mini grids, Power Backup, Primary data, Producer gas, Thermal efficiency, Fuel cells
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-252109 (URN)10.1016/j.egypro.2018.12.041 (DOI)000471291100073 ()2-s2.0-85063768741 (Scopus ID)
Conference
2018 Renewable Energy Integration with Mini/Microgrid, REM 2018, 28 September 2018 through 30 September 2018
Note

QC 20190524

Available from: 2019-05-24 Created: 2019-05-24 Last updated: 2019-07-29Bibliographically approved
Jayawickrama, T. R., Haugen, N. E., Bäbler, M., Chishty, M. A. & Umeki, K. (2019). The effect of Stefan flow on the drag coefficient of spherical particles in a gas flow. International Journal of Multiphase Flow, 117, 130-137
Open this publication in new window or tab >>The effect of Stefan flow on the drag coefficient of spherical particles in a gas flow
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2019 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 117, p. 130-137Article in journal (Refereed) Published
Abstract [en]

Particle laden flows with reactive particles are common in industrial applications. Chemical reactions inside the particle can generate a Stefan flow that affects heat, mass and momentum transfer between the particle and the bulk flow. This study aims at investigating the effect of Stefan flow on the drag coefficient of a spherical particle immersed in a uniform flow under isothermal conditions. Fully resolved simulations were carried out for particle Reynolds numbers ranging from 0.2 to 14 and Stefan flow Reynolds numbers from (-1) to 3, using the immersed boundary method for treating fluid-solid interactions. Results showed that the drag coefficient decreased with an increase of the outward Stefan flow. The main reason was the change in viscous force by the expansion of the boundary layer surrounding the particle. A simple model was developed based on this physical interpretation. With only one fitting parameter, the performance of the model to describe the simulation data were comparable to previous empirical models. The Authors.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Drag coefficient, Stefan flow, Boundary layer, Multiphase reactive flow
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-255367 (URN)10.1016/j.ijmultiphaseflow.2019.04.022 (DOI)000474496000010 ()2-s2.0-85065836366 (Scopus ID)
Note

QC 20190730

Available from: 2019-07-30 Created: 2019-07-30 Last updated: 2019-07-30Bibliographically approved
Bäbler, M., Liberzon, A., Saha, D., Holzner, M., Soos, M., Lüthi, B. & Kinzelbach, W. (2018). Breakup of individual colloidal aggregates in turbulent flow investigated by 3D particle tracking velocimetry. In: Multiphase Flow Phenomena and Applications: Memorial Volume in Honor of Gad Hetsroni: (pp. 83-96). World Scientific Publishing Co. Pte. Ltd.
Open this publication in new window or tab >>Breakup of individual colloidal aggregates in turbulent flow investigated by 3D particle tracking velocimetry
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2018 (English)In: Multiphase Flow Phenomena and Applications: Memorial Volume in Honor of Gad Hetsroni, World Scientific Publishing Co. Pte. Ltd. , 2018, p. 83-96Chapter in book (Other academic)
Abstract [en]

Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence where their breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with fractal dimension around 2.2, and their size varies from 0.9 to 3.1 mm which is large compared to the Kolmogorov length scale η = 0.15 mm. 3D-PTV allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines which enables us to access the Lagrangian stress history of individual breakup events. The analysis suggests that aggregates are mostly broken due to accumulation of drag stress over a time interval of order Kolmogorov time scale, O(τη). This finding is explained by the fact that the aggregates are large, which gives their motion inertia and which increases the time for stress propagation inside the aggregate.

Place, publisher, year, edition, pages
World Scientific Publishing Co. Pte. Ltd., 2018
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-247224 (URN)10.1142/9789813227392_0005 (DOI)2-s2.0-85058892728 (Scopus ID)9789813227392 (ISBN)9789813227385 (ISBN)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-02Bibliographically approved
Sadegh-Vaziri, R., Ludwig, K., Sundmacher, K. & Bäbler, M. (2018). Mechanisms behind overshoots in mean cluster size profiles in aggregation-breakup processes. Journal of Colloid and Interface Science, 528, 336-348
Open this publication in new window or tab >>Mechanisms behind overshoots in mean cluster size profiles in aggregation-breakup processes
2018 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 528, p. 336-348Article in journal (Refereed) Published
Abstract [en]

Aggregation and breakup of small particles in stirred suspensions often shows an overshoot in the time evolution of the mean cluster size: Starting from a suspension of primary particles the mean cluster size first increases before going through a maximum beyond which a slow relaxation sets in. Such behavior was observed in various systems, including polymeric latices, inorganic colloids, asphaltenes, proteins, and, as shown by independent experiments in this work, in the flocculation of microalgae. This work aims at investigating possible mechanism to explain this phenomenon using detailed population balance modeling that incorporates refined rate models for aggregation and breakup of small particles in turbulence. Four mechanisms are considered: (1) restructuring, (2) decay of aggregate strength, (3) deposition of large clusters, and (4) primary particle aggregation where only aggregation events between clusters and primary particles are permitted. We show that all four mechanisms can lead to an overshoot in the mean size profile, while in contrast, aggregation and breakup alone lead to a monotonic, "S" shaped size evolution profile. In order to distinguish between the different mechanisms simple protocols based on variations of the shear rate during the aggregation-breakup process are proposed.

Place, publisher, year, edition, pages
Academic Press, 2018
Keywords
Population balance modeling, Colloidal aggregation, Shear aggregation, Aggregate breakup, Restructuring, Flocculation, Fractal aggregates, Turbulence
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-233260 (URN)10.1016/j.jcis.2018.05.064 (DOI)000440127000036 ()29885609 (PubMedID)2-s2.0-85048509507 (Scopus ID)
Funder
Swedish Research Council, 2012-6216
Note

QC 20180817

Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2019-10-29Bibliographically approved
Sadegh-Vaziri, R. & Bäbler, M. (2018). Modeling of slow pyrolysis of various biomass feedstock in a rotary drum using TGA data. Chemical Engineering and Processing, 129, 95-102
Open this publication in new window or tab >>Modeling of slow pyrolysis of various biomass feedstock in a rotary drum using TGA data
2018 (English)In: Chemical Engineering and Processing, ISSN 0255-2701, E-ISSN 1873-3204, Vol. 129, p. 95-102Article in journal (Refereed) Published
Abstract [en]

Design and optimization of biomass gasification faces the challenge of feedstock variation. Specifically, design calculations require kinetic rate expressions for the given feedstock, whose rigorous determination is demanding and often exceeds available recourses in an early development stage. In this work, we model the slow pyrolysis of biomass for the production of biochar. The aim is to predict the conversion of raw biomass to biochar as a function of the process conditions. Here, we will show that TGA data processed with an isoconversional method is enough to obtain an effective rate expression which allows for predicting the behavior of the biomass at an arbitrary temperature evolution. Such rate expressions can then be used in the process model to simulate conversion of raw biomass to biochar. To illustrate the feasibility of this approach we consider four vastly different biomass, namely spruce wood, pulp, lignin and xylan–lignin, undergoing slow pyrolysis in an indirectly heated rotary kiln reactor. The results of our modeling are compared to experimental data obtained from a 500 kW pilot plant pyrolyzer and to a more detailed process model.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Biomass pyrolysis, Isoconversional, Process model, Rotary drum
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-228722 (URN)10.1016/j.cep.2018.05.002 (DOI)000435059000012 ()2-s2.0-85047165839 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180530

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2019-10-29Bibliographically approved
Sadegh-Vaziri, R. & Bäbler, M. (2017). PBE Modeling of Flocculation of Microalgae: Investigating the Overshoot in Mean Size Profiles. In: Proceedings of the 9th International Conference on Applied Energy: . Paper presented at 9th International Conference on Applied Energy, ICAE 2017, Cardiff, United Kingdom, 21 August 2017 through 24 August 2017 (pp. 507-512). Elsevier, 142
Open this publication in new window or tab >>PBE Modeling of Flocculation of Microalgae: Investigating the Overshoot in Mean Size Profiles
2017 (English)In: Proceedings of the 9th International Conference on Applied Energy, Elsevier, 2017, Vol. 142, p. 507-512Conference paper, Published paper (Refereed)
Abstract [en]

Microalgae is considered as a viable feedstock to biomass gasification. After synthesis in water medium, microalgae are separated and dried to a suitable degree to be fed to the gasification process. In order to achieve an efficient separation, a flocculation process is employed, in which microalgae primary particles aggregate and form larger clusters. Although flocculation is a well-established process, there are still some unknown issues related to it, that are worth further research. Experiments show that the mean size of clusters during flocculation goes through a maximum and then decreases with time. We refer to this pattern in the mean size profile as the overshoot. Studying this phenomenon is crucial since the size of clusters has a significant effect on the overall efficiency of the separation of microalgae from water. In this work, we aim at investigating the mechanisms behind the overshoot. The flocculation process is modeled as an aggregation-breakup system by using population balance equations (PBEs). The primary results show that the aggregation and breakup alone cannot lead to the overshoot in the mean size profile. Thus, we suggested three mechanisms that can lead to the overshoot: deposition of large clusters (DLC), restructuring of clusters (RC), and primary particle aggregation (PPA). These mechanisms were examined with numerical simulations and it was revealed that all three lead to the overshoot.

Place, publisher, year, edition, pages
Elsevier, 2017
Series
Energy Procedia, ISSN 1876-6102 ; 142
Keywords
aggregation, breakup, depostion of clusters, Microlagae flocculation, PBE, primary particle aggreagtion, resutructuring of clusters
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-224400 (URN)10.1016/j.egypro.2017.12.079 (DOI)000452901600078 ()2-s2.0-85041538183 (Scopus ID)
Conference
9th International Conference on Applied Energy, ICAE 2017, Cardiff, United Kingdom, 21 August 2017 through 24 August 2017
Funder
Swedish Research CouncilSwedish Energy Agency
Note

QC 20180319

Available from: 2018-03-19 Created: 2018-03-19 Last updated: 2019-01-07Bibliographically approved
Sadegh-Vaziri, R. & Bäbler, M. (2016). A hollow core shell model for describing chemisorption of H2S from raw syngas in a packed bed reactor of ZnO. In: 22nd International Congress of Chemical and Process Engineering, CHISA 2016 and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, PRES 2016: . Paper presented at 22nd International Congress of Chemical and Process Engineering, CHISA 2016 and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, PRES 2016, 27 August 2016 through 31 August 2016 (pp. 66-67). Czech Society of Chemical Engineering
Open this publication in new window or tab >>A hollow core shell model for describing chemisorption of H2S from raw syngas in a packed bed reactor of ZnO
2016 (English)In: 22nd International Congress of Chemical and Process Engineering, CHISA 2016 and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, PRES 2016, Czech Society of Chemical Engineering , 2016, p. 66-67Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Czech Society of Chemical Engineering, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-236890 (URN)2-s2.0-85050755943 (Scopus ID)9781510859623 (ISBN)
Conference
22nd International Congress of Chemical and Process Engineering, CHISA 2016 and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, PRES 2016, 27 August 2016 through 31 August 2016
Note

QC 20181212

Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2018-12-12Bibliographically approved
Saha, D., Babler, M. U., Holzner, M., Soos, M., Luethi, B., Liberzon, A. & Kinzelbach, W. (2016). Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry. Langmuir, 32(1), 55-65
Open this publication in new window or tab >>Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry
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2016 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 1, p. 55-65Article in journal (Refereed) Published
Abstract [en]

Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of similar to 2.2, and their size is 1.4 +/- 0.4 mm, which is large, compared to the Kolmogorov length scale (eta = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., d(frag) sigma(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-182159 (URN)10.1021/acs.langmuir.5b03804 (DOI)000368321700008 ()26646289 (PubMedID)2-s2.0-84954286349 (Scopus ID)
Funder
Swedish Research Council, 2012-6216
Note

QC 20160218

Available from: 2016-02-18 Created: 2016-02-16 Last updated: 2017-11-30Bibliographically approved
Samuelsson, L. N., Bäbler, M. U. & Moriana, R. (2015). A single model-free rate expression describing both non-isothermal and isothermal pyrolysis of Norway Spruce. Fuel, 161, 59-67
Open this publication in new window or tab >>A single model-free rate expression describing both non-isothermal and isothermal pyrolysis of Norway Spruce
2015 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 161, p. 59-67Article in journal (Refereed) Published
Abstract [en]

A strictly isoconversional rate expression has been derived for pyrolysis of biomass. This rate expression, derived from non-isothermal thermogravimetric experiments using heating rates 2-10 K/min, can successfully predict the conversion rates of experimental data at heating rates 1-100 K/min and quasiisothermal experiments at 539-650 K. The methodology used is based on an extension of the incremental integral method by Vyazovkin (2001). Being able to derive an intrinsic reaction rate expression from non-isothermal data, without any assumption regarding the chemical processes present, opens up for the possibility to model industrial pyrolysis reactors, with a variety of temperature profiles.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Model-free, Isoconversional, Pyrolysis, Biomass, Thermogravimetry, Kinetics
National Category
Energy Engineering Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-176322 (URN)10.1016/j.fuel.2015.08.019 (DOI)000362304600008 ()2-s2.0-84940476206 (Scopus ID)
Note

QC 20151117

Available from: 2015-11-17 Created: 2015-11-03 Last updated: 2017-12-01Bibliographically approved
Norberg Samuelsson, L., Moriana, T. R., Bäbler, M. U., Ek, M. & Engvall, K. (2015). Model-free rate expression for thermal decomposition processes: The case of microcrystalline cellulose pyrolysis. Fuel, 143, 438-447
Open this publication in new window or tab >>Model-free rate expression for thermal decomposition processes: The case of microcrystalline cellulose pyrolysis
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2015 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 143, p. 438-447Article in journal (Refereed) Published
Abstract [en]

We explore the possibility to derive a completely model-free rate expression using isoconversional methods. The Friedman differential method (Friedman, 1964) and the incremental integral method by Vyazovkin (2001) were both extended to allow for an estimation of not only the apparent activation energy but also the effective kinetic prefactor, defined as the product of the pre-exponential factor and the conversion function. Analyzing experimental thermogravimetric data for the pyrolytic decomposition of microcrystalline cellulose, measured at six different heating rates and three different initial sample masses (1.5-10 mg), revealed the presence of secondary char forming reactions and thermal lag, both increasing with increased sample mass. Conditioning of the temperature function enables extraction of more reliable prefactors and we found that the derived kinetic parameters show weak dependence on initial sample mass. Finally, by successful modeling of quasi-isothermal experimental curves, we show that the discrete rate expression estimated from linear heating rate experiments enables modeling of the thermal decomposition rate without any assumptions regarding the chemical process present. These findings can facilitate the design and optimization of industrial isothermal biomass fed reactors.

Keywords
Model-free, Isoconversional, Kinetics, Thermogravimetric analysis, Pyrolysis, Cellulose
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-160361 (URN)10.1016/j.fuel.2014.11.079 (DOI)000347688700052 ()2-s2.0-84918767293 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20150227

Available from: 2015-02-27 Created: 2015-02-19 Last updated: 2017-12-04Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7995-3151

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