title: Gas-lift digester configuration effects on mixing effectiveness.
abstract: Computational fluid dynamics simulations were used to study the effect of bottom configuration and a hanging baffle on the mixing inside a gas-lift digester filled with non-Newtonian sludge. The Navier-Stokes and continuity equations were solved numerically using commercially available finite element method-based solver. The results from this simulation were found to be in good agreement with previously reported experimental findings. At a gas recirculation rate of 84.96l/h, the poorly mixed zones inside a flat bottom digester were about 33.6% of the digester volume, while in the case of digesters with 25 degrees and 45 degrees conical bottoms poorly mixed zones were about 31.9% and 29.6%, respectively. The power law viscosity index, n, did not have a significant effect on the mixing pattern under the conditions studied. Introduction of a hanging baffle in combination with a 45 degrees hopper bottom resulted in reduction of the poorly mixed zone by a factor of three compared to a flat bottom without baffle configuration. Although the introduction of a hanging baffle was able to significantly reduce the size of the poorly mixed zones inside a gas-lift digester, further optimization of the digester geometry may lead to additional improvements.
authors.affiliation: Ralph E. Martin Department of Chemical Engineering, University of Arkansas, 3202 Bell Engineering Center, Fayetteville, AR 72701, USA. kkarim@uark.edu
authors.forename: Khursheed
authors.initials: K
authors.lastname: Karim
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Thoma
authors.forename: Muthanna H
authors.initials: MH
authors.lastname: Al-Dahhan
mesh_terms: D003198:Computer Simulation; D005740:Gases / Q000737:chemistry*; D012996:Solutions; D014783:Viscosity
chemical_list: D005740:Gases; D012996:Solutions