TY - THES

T1 - Investigation on flow pattern in a cylindrical centrifugal force separator used in plastic recycling

AU - Barros Bahia, Renata Cibele

N1 - embargoed until 29-11-2022

PY - 2017

Y1 - 2017

N2 - Recycling of post consumer plastics is a key issue to promote sustainable and efficient utilization of resources especially regarding short running hydrocarbons. Not only recycled plastic material and whose quality faces challenges of acceptance on the market, but also established recycling processes and process chains need to be optimized continuously. This master thesis studies a cylindrical centrifugal force separator used for plastics processing in a new wet density separation concept to prepare post-consumer plastics for chemical (feedstock) recycling. Former separator is able to treat various post consumer plastic containing waste fractions. Its main purpose is to separate polyolefins in the conducted sink-float process under the strong influence of the centrifugal field when water is applied as separation medium. Theoretical approaches to calculate relevant flow parameters of centrifugal force separators have been mainly determined empirically, because its exact physical description is not yet consolidated. The first step of this work is to test, if already existing calculation rules for conical centrifugal force separators e.g. common gas cyclones or hydrocyclones can also be used for the relatively unknown cylindrical centrifugal force separator. Results of these calculations were unsatisfactory. Consequently, to better understand the emerging flow patterns and to estimate relevant flow variables’ magnitude a study of the velocity field inside the cylindrical centrifugal force separator is performed using Computational Fluid Dynamics (CFD) powered by COMSOL Multiphysics. The simulation starts with a simple geometry and laminar flow conditions and is further extended to a more complex geometry comprising all openings of the separator and turbulent flow conditions. All cases concentrate on single phase flow (water). Particularly the axial and tangential velocity components are studied. It is observed that the axial velocity profiles are similar to those ones of common hydrocyclones. The tangential velocity in dependence on the radius approaches the trend known from rotational vortices and thus differs significantly from that one related to common hydrocyclones. This is further confirmed by comparable studies.

AB - Recycling of post consumer plastics is a key issue to promote sustainable and efficient utilization of resources especially regarding short running hydrocarbons. Not only recycled plastic material and whose quality faces challenges of acceptance on the market, but also established recycling processes and process chains need to be optimized continuously. This master thesis studies a cylindrical centrifugal force separator used for plastics processing in a new wet density separation concept to prepare post-consumer plastics for chemical (feedstock) recycling. Former separator is able to treat various post consumer plastic containing waste fractions. Its main purpose is to separate polyolefins in the conducted sink-float process under the strong influence of the centrifugal field when water is applied as separation medium. Theoretical approaches to calculate relevant flow parameters of centrifugal force separators have been mainly determined empirically, because its exact physical description is not yet consolidated. The first step of this work is to test, if already existing calculation rules for conical centrifugal force separators e.g. common gas cyclones or hydrocyclones can also be used for the relatively unknown cylindrical centrifugal force separator. Results of these calculations were unsatisfactory. Consequently, to better understand the emerging flow patterns and to estimate relevant flow variables’ magnitude a study of the velocity field inside the cylindrical centrifugal force separator is performed using Computational Fluid Dynamics (CFD) powered by COMSOL Multiphysics. The simulation starts with a simple geometry and laminar flow conditions and is further extended to a more complex geometry comprising all openings of the separator and turbulent flow conditions. All cases concentrate on single phase flow (water). Particularly the axial and tangential velocity components are studied. It is observed that the axial velocity profiles are similar to those ones of common hydrocyclones. The tangential velocity in dependence on the radius approaches the trend known from rotational vortices and thus differs significantly from that one related to common hydrocyclones. This is further confirmed by comparable studies.

KW - Kunststoffrecycling

KW - Altkunststoffe

KW - Dichtetrennverfahren

KW - zylindrische Zentrifugalkraftscheider

KW - Hydrozyklon

KW - Computational Fluid Dynamics (CFD)

KW - plastic recycling

KW - post-consumer plastics

KW - density separation

KW - cylindrical centrifugal force separator

KW - hydrocyclone

KW - computational fluid dynamics

M3 - Master's Thesis

ER -