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Mechanisms behind overshoots in mean cluster size profiles in aggregation-breakup processes
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.ORCID iD: 0000-0002-1881-2686
Max Planck Inst Dynam Complex Tech Syst, Proc Syst Engn, Sandtorstr 1, D-39106 Magdeburg, Germany..
Max Planck Inst Dynam Complex Tech Syst, Proc Syst Engn, Sandtorstr 1, D-39106 Magdeburg, Germany.;Otto von Guericke Univ, Proc Syst Engn, Univ Pl 2, D-39106 Magdeburg, Germany..
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.ORCID iD: 0000-0001-7995-3151
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. Vol. 528, p. 336-348
Keywords [en]
Population balance modeling, Colloidal aggregation, Shear aggregation, Aggregate breakup, Restructuring, Flocculation, Fractal aggregates, Turbulence
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-233260DOI: 10.1016/j.jcis.2018.05.064ISI: 000440127000036PubMedID: 29885609Scopus ID: 2-s2.0-85048509507OAI: oai:DiVA.org:kth-233260DiVA, id: diva2:1239614
Funder
Swedish Research Council, 2012-6216
Note

QC 20180817

Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2019-10-29Bibliographically approved
In thesis
1. Modeling in Biomass Harvesting, Biomass Pyrolysis and Producer Gas Cleaning
Open this publication in new window or tab >>Modeling in Biomass Harvesting, Biomass Pyrolysis and Producer Gas Cleaning
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass is a viable alternative in order to mitigate the environmental effectscaused by the aggressive use of fossil feedstock during the last century.This thesis builds around the idea of a biofuel production process that iscomprised of biomass production, biomass gasication, gas cleaning andfuel production. Biomass production includes microalgae synthesis followedby harvesting to supply microalgae to the gasication process. In the gasi-cation process, the prepared microalgae is dried, pyrolyzed and gasiedto obtain a producer gas containing syngas and impurities. The producergas is cleaned from the impurities and fed to a fuel production unit, e.g. amethanation process.This thesis investigates three distinct aspects related to this processscheme, namely the occulation of microalgae as part of harvesting, biomasspyrolysis as a part of gasication, and sulfur removal from the producer gasas a part of gas cleaning.The investigation of occulation focuses on secondary phenomena thataccompany the aggregation and breakup of the suspended particles, namelyrestructuring, decay of oc strength and settling. For the study of theconsidered phenomena, a population balance model is developed.Slow pyrolysis of biomass is studied on both the reactor scale and thepellet scale. A model for a rotary drum reactor, using principles of isoconversionalanalysis, is developed for the study of dierent biomass feedstock.The proposed model allows for deriving a preliminary reactor design withminimal experimental input data. A one-dimensional nite volume schemeis developed for the investigation of pyrolysis on the pellet scale. The proposedscheme accounts for convective and diusive heat and mass transfer,and is tested against analytical solutions and commercial software packages.Sulfur removal by metal oxides in a packed bed is studied on both thesystem level and the process level. Criteria for the selection of metal oxidesand the design of packed bed units are derived. A detailed analysis isundertaken to study the reaction of H2S with ZnO in a packed bed, wherethe nano-particles of ZnO experience void formation and outward growth.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 80
Series
TRITA-CBH-FOU ; 2019:65
Keywords
PBE modeling of flocculation; Pyrolysis in Rotary Kilns; Pellet Pyrolysis; Gas Cleaning; Desulfurization.
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-263085 (URN)978-91-7873-367-5 (ISBN)
Public defence
2019-11-28, Kollegiesalen, Brinellv. 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 2019-10-29

Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-11-06Bibliographically approved
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