Gas to liquid mass transfer in rheologically complex fluids

Y Bajón Fernández,E Cartmell,A Soares,E Mcadam,P Vale,C Darche-Dugaret,B Jefferson

doi:10.1016/j.cej.2015.03.051

Abstract

The increase of studies relaying on gas to liquid mass transfer in digested sludge (shear thinning fluid) necessitates a better understanding of the impact of apparent viscosity (μa) and rheology in process performance. Mass transfer retardation due to μa variations was investigated in a pilot scale absorption bubble column for Newtonian and shear thinning fluids with varied superficial gas velocities (UG). A non-linear reduction of mass transfer efficiency with increasing μa was observed, being the impact higher at low μa ranges and high UG. An increase of 114cPo in μ from 1.01 to 115cPo in glycerol solutions saturated with UG=1.73cms−1 led to a reduction of 96% in kLa (α=0.04), while a comparable raise from 115 to 229cPo implied a reduction of 52% (α=0.02).Slug–annular flow regime was identified for shear thinning fluids of high μa (1.0% and 1.5% carboxymethyl cellulose sodium salt solutions), where bubble buoyancy was conditioned by the μ of the fluid at rest and the active volume for mass transfer was reduced because of the presence of stagnant areas. Conditions imitating the rheological variability of anaerobically digested sewage sludge were included within those tested, being a reduction in gas transfer efficiency of 6 percentage points (from 7.6±0.3% to 1.6±0.1%) recorded when increasing μa from 130 to 340cPo. It is thus recommended that rheology and μa variability are accounted for within the design of gas to liquid mass transfer systems involving digested sewage sludge, in order to avoid reductions in process performance and active volume.

Highlights

Unit processes that utilise mass transfer in gas–liquid systems are widely used in both the environmental and industrial sectors in processes such as polyester production [1], fermentation broths cultivation [2], xanthan gum production [3] and wastewater treatment
A recent new area of consideration relates to the anaerobic digestion of organic waste and municipal wastewater in processes such as ammonia stripping from digestate to reduce toxicity [4], and carbon dioxide (CO2) enrichment of sewage sludge or food waste for enhanced biogas production and carbon uptake [5]
ABS ðCmodel À C sensor where Cmodel, concentration estimated with Eq (5); Csensor, concentration measured by the probe;T, volumetric mass transfer coefficient at temperature T;20, volumetric mass transfer coefficient at 20 °C

Summary

Introduction

Unit processes that utilise mass transfer in gas–liquid systems are widely used in both the environmental and industrial sectors in processes such as polyester production [1], fermentation broths cultivation [2], xanthan gum production [3] and wastewater treatment. A recent new area of consideration relates to the anaerobic digestion of organic waste and municipal wastewater in processes such as ammonia stripping from digestate to reduce toxicity [4], and carbon dioxide (CO2) enrichment of sewage sludge or food waste for enhanced biogas production and carbon uptake [5].

Methods

Results

Conclusion