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PBE Modeling of Overshoot in Mean Cluster Size Proles in Aggregation-Breakup Processes
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0002-1881-2686
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0001-7995-3151
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In monitoring the mean size of clusters during an aggregation-breakup process, it has been repeatedlyobserved that the mean size increases with time to a maximum and then decreases, resulting in an overshootin the means size prole. The decrease in the mean size prole has often explained as an eect of breakupof aggregates. In this work, we investigate three possible mechanisms that lead to an overshoot by usingnumerical analysis of population balance equations describing aggregation-breakup systems. The consideredmechanisms are deposition of large clusters, restructuring of clusters, and primary particle aggregation, wheretwo clusters aggregate only if one of them is a primary particle. The results show that all the suggestedmechanisms lead to an overshoot. It is only in the case of primary particle aggregation that the decrease inthe mean size is due to the dominance of breakup. Also, restructuring of fractal aggregates to form morecompact clusters explains the overshoot during aggregation-breakup with restructuring of clusters, while inthe case of deposition of large clusters, mass loss due to deposition of large aggregates leads to an overshoot.

Keyword [en]
population balance equations (PBEs), deposition of large clusters, restructuring of aggregates, primary particle aggregation.
National Category
Chemical Process Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-204608OAI: oai:DiVA.org:kth-204608DiVA: diva2:1085604
Note

QC 20170330

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-03-30Bibliographically approved
In thesis
1. Biomass to Biofuel: Syngas Cleaning and Biomass Feedstock
Open this publication in new window or tab >>Biomass to Biofuel: Syngas Cleaning and Biomass Feedstock
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis builds around the idea of a biofuel production process that is comprised of biomass production, biomass gasification, gas cleaning, and fuel production. In this work, we specifically looked into H2S removal as a part of cleaning the producer gas and flocculation of microalgae which is involved in the harvesting of microalgae after biomass production. One of the impurities to remove from the producer gas is hydrogen sulfide which can be removed by using a packed bed of zinc oxide. Despite the regular use, it was only recently shown that during reaction with H2S, nano-size particles of ZnO exhibit void formation and outward growth. In this work, a micro-scale model was introduced to describe the void formation and outward growth. On the macro-scale, the simulations captured pore clogging of pellets due to the outward growth. The pore clogging prevents the full conversion of pellets and consequently leads to shorter breakthrough times of beds. The second problem investigated here deals with the flocculation of microalgae. Microalgae is produced in relatively low concentrations in the incubator liquid medium and during the harvesting, the concentration is increased to an acceptable level. The harvesting process includes a flocculation followed by a filtration or centrifuge unit. During flocculation, microalgae are stimulated to aggregate and form clusters. The experiments showed that the mean size of clusters formed during flocculation increases with time to a maximum and then starts decreasing, resulting in an overshoot in the mean size profile. The size of clusters influence the efficiency of the afterward filtration or centrifuge, thus it is of interest to carefully track the size evolution of clusters, making the studying of overshoot a crucial research topic. In this work, the possible mechanisms behind this overshoot were investigated.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 63 p.
Keyword
Gas-Solid Reaction; ZnO Sul_dation; Outward Growth; Hollow Particles; Algae Flocculation; PBEs; Fractal Clusters; Restructuring of Clusters; Deposition of Clusters; Primary Particle Aggregation.
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-204570 (URN)
Presentation
2017-03-31, LOGOS, Teknikringen 42, plan 6, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170330

Available from: 2017-03-30 Created: 2017-03-28 Last updated: 2017-03-30Bibliographically approved

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