Premium
Bubble shape, gas flow and gas–liquid mass transfer in pulp fibre suspensions
Author(s) -
Ishkintana L. K.,
Bennington C. P. J.
Publication year - 2010
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.20282
Subject(s) - bubble , mass transfer , hardwood , volumetric flow rate , suspension (topology) , softwood , kraft paper , pulp (tooth) , mass transfer coefficient , superficial velocity , chemistry , analytical chemistry (journal) , chromatography , kraft process , materials science , mechanics , composite material , flow (mathematics) , medicine , physics , pathology , homotopy , pure mathematics , mathematics , biology , ecology
Abstract Gas–liquid mass transfer in pulp fibre suspensions in a batch‐operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical‐capped/dimpled‐elliptical bubbles. At relatively low mass concentrations ( C m = 2–3% for the softwood and C m ≅ 7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas–liquid mass transfer rate, k L a , decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in k L a occurred between C m = 2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed.