Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Biomass to Biofuel: Syngas Cleaning and Biomass Feedstock
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.ORCID iD: 0000-0002-1881-2686
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 [en]
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: urn:nbn:se:kth:diva-204570OAI: oai:DiVA.org:kth-204570DiVA: diva2:1085282
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
List of papers
1. A Medium-Scale 50 MWfuel Biomass Gasification Based Bio-SNG Plant: A Developed Gas Cleaning Process
Open this publication in new window or tab >>A Medium-Scale 50 MWfuel Biomass Gasification Based Bio-SNG Plant: A Developed Gas Cleaning Process
2015 (English)In: Energies, ISSN 1996-1073, Vol. 8, no 6, 5287-5302 p.Article in journal (Refereed) Published
Abstract [en]

Natural gas is becoming increasingly important as a primary energy source. A suitable replacement for fossil natural gas is bio-SNG, produced by biomass gasification, followed by methanation. A major challenge is efficient gas cleaning processes for removal of sulfur compounds and other impurities. The present study focuses on development of a gas cleaning step for a product gas produced in a 50 MWfuel gasification system. The developed gas cleaning washing process is basically a modification of the Rectisol process. Several different process configurations were evaluated using Aspen plus, including PC-SAFT for the thermodynamic modeling. The developed configuration takes advantage of only one methanol wash column, compared to two columns in a conventional Rectisol process. Results from modeling show the ability of the proposed configuration to remove impurities to a sufficiently low concentrations - almost zero concentration for H2S, CS2, HCl, NH3 and HCN, and approximately 0.01 mg/Nm(3) for COS. These levels are acceptable for further upgrading of the gas in a methanation process. Simultaneously, up to 92% of the original CO2 is preserved in the final cleaned syngas stream. No process integration or economic consideration was performed within the scope of the present study, but will be investigated in future projects to improve the overall process.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-172500 (URN)10.3390/en8065287 (DOI)000357489700033 ()2-s2.0-84933558353 (ScopusID)
Note

QC 20150825

Available from: 2015-08-25 Created: 2015-08-25 Last updated: 2017-03-28Bibliographically approved
2. Numerical investigation of the outward growth of ZnS in the removal of H2S in a packed bed of ZnO
Open this publication in new window or tab >>Numerical investigation of the outward growth of ZnS in the removal of H2S in a packed bed of ZnO
2017 (English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 158, 328-339 p.Article in journal (Refereed) Published
Abstract [en]

Sulfidation of zinc oxide is a viable option for the removal of hydrogen sulfide from raw syngas and biogas. Recent experiments showed that sulfidation of nanoscopic zinc oxide particles leads to an outward growth and the formation of voids inside the particles. In this work, we derive a micro-scale model to describe this phenomenon. The model accounts for nucleation and growth of voids inside the particles, diffusion of Zn and O through the product layer, and deposition of the solid product at the particle surface as a result of the reaction between ZnO and H2S. The model is thus opposite to the well known shrinking core model where an inward growth of the product layer is assumed. To explore the effect of the outward growth on the dynamics of a packed bed adsorber the micro-scale model is combined with a macro-scale model that accounts for intra-pellet diffusion and convection along the packed bed. In the limit of fast nucleation and growth of voids inside the zinc oxide particles, the micro-scale model shows a qualitatively similar conversion profile to the shrinking core model, while when nucleation controls an inflection point in conversion profile is found. On the macro-scale, the outward growth can cause the clogging of pores inside the pellets which prevents the pellets from reaching full conversion. This leads to shorter breakthrough times of the packed bed due to the sealing of unreacted zinc oxide. Our results thus provide a possible explanation of the incomplete conversion of zinc oxide in packed beds.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Gas-solid reaction, Syngas cleaning, H2S removal, ZnO sulfidation, Outward growth, Hollow particles
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-199459 (URN)10.1016/j.ces.2016.10.038 (DOI)000389068900033 ()2-s2.0-84993996109 (ScopusID)
Note

QC 20170123

Available from: 2017-01-23 Created: 2017-01-09 Last updated: 2017-03-28Bibliographically approved
3. PBE Modeling of Overshoot in Mean Cluster Size Proles in Aggregation-Breakup Processes
Open this publication in new window or tab >>PBE Modeling of Overshoot in Mean Cluster Size Proles in Aggregation-Breakup Processes
(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
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:nbn:se:kth:diva-204608 (URN)
Note

QC 20170330

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-03-30Bibliographically approved

Open Access in DiVA

The full text will be freely available from 2017-09-30 15:18
Available from 2017-09-30 15:18

Search in DiVA

By author/editor
Sadegh-Vaziri, Ramiar
By organisation
Energy Processes
Chemical Process Engineering

Search outside of DiVA

GoogleGoogle Scholar

Total: 30 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf