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AssigneeThe Penn State Research Foundation
InventorsPaul M. Kubera, John R. McWhirter, Bradley S. Dominik, Prakash G. Balan
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A system for providing improved bulk liquid mixing and effective gas-liquid contacting for mass transfer of the gas to the liquid, especially a non-Newtonian liquid, the viscosity of which decreases when under shearing conditions (shear thinning), in an upright tank. A process, such as fermentation which produces commercial quantities of polysaccharides such as xanthan gum. may be carried out in the tank. An upright draft tube is mounted within the tank and has a lower end spaced from the tank bottom and an upper end spaced below the surface of the liquid in the tank. A plurality of mixing impellers in the draft tube are sufficiently close to each other to establish a field or pattern of agitation to cause shear thinning and upflow throughout the draft tube and which may produce turbulence at the liquid surface. A plurality of radially inwardly projecting. circumferentially spaced baffles extend from the draft tube and are proximate the mixing impellers to prevent swirling of the liquid within the draft tube. Gas may be sparged into the vessel in or adjacent to the lower end of the draft tube. A circulating co-current flow of gas and liquid, with intimate gas-liquid contact, is induced up through the draft tube and out the upper end of the draft tube so as to provide a high rate of mass transfer from the gas to the liquid. The flow including entrained gas turns down through the annular region between the tank wall and the draft tube for recirculation of the liquid and gas above the surface of the liquid, resulting in high gas holdup and gas-liquid contact in the downflow annular region and in the upflow draft tube region, without gas flooding of the impellers. The concentration of dissolved gas and the effectiveness of the system for gas-phase mass transfer is determined by reaeration of a test sample of the liquid. Additional surface aeration can be provided with a surface impeller having a plurality of blades with vertical portions and outwardly inclined portions, the vertical portions being inclined with respect to radial lines from the axis of rotation of the impeller.
A system for circulating a liquid medium in a tank which facilitates transfer of a gaseous element to said liquid medium, said system comprising a plurality of impellers which establish flow of said medium in opposite directions in said tank between regions where reversal of said flow occurs, a tube in said tank, a tube having an axis and opposite ends, each of said opposite ends being in proximity with a different one of said regions, said impellers being disposed in said tube and being rotatable about said axis, said impellers each producing a field or pattern of agitation which shears said liquid medium, said impellers being in sufficiently closely spaced relationship along said axis and extending radially of said axis across said tube such that said agitation is established substantially throughout the entire volume of said tube, means for inhibiting flow due to said agitation which swirls around said axis, and flow of said liquid medium in one of said opposite directions being inside said tube and flow in the other of said opposite directions being outside said tube.
A system for mixing and aerating a high viscosity, shear thinning liquid comprising an upright vessel having a longitudinally extending upright axis and including a bottom wall and a side wall upstanding from said bottom wall and extending to an upper rim, said vessel being adapted to be filled with the liquid up to a level defining a static liquid surface;
The method of providing bio-reaction in a tank which comprises the steps of introducing a slurry of a bacteria containing liquid and a growth medium into the tank, which slurry increases in viscosity as the bio-reaction proceeds, circulating said slurry upwardly and downwardly in inner and outer coaxial regions of said tank, said inner region occupying at least about twenty-five percent of the volume of said tank which contains said slurry, with the aide of a draft tube which separates said regions, said circulating step including the step of shearing said liquid throughout said inner region, and said shearing step comprising producing axial flow in said inner region while inhibiting swirl therein.
The method of circulating a non-Newtonian liquid in a tank which comprises the steps of circulating said liquid upwardly and downwardly in inner and outer coaxial regions of said tank below the surface thereof, said inner region occupying at least twenty-five percent of the volume of said tank which contains said non-Newtonian liquid, said circulating step including the steps of shearing said liquid throughout said inner region, and said shearing step further comprises producing axial flow in said inner region while inhibiting swirl therein.
The method of determining the overall liquid phase mass transfer coefficient, kLa, in a high viscosity, opaque liquid medium which comprises the steps of first calibrating the D.O. probes in a fully aerated equilibrium solution of the liquid medium by employing a specific modification of the Winkler D.O. titration procedure for accurately measuring the D.O. level in a high viscosity, opaque solution, (2) then stripping the solution of dissolved oxygen by aerating with a non-oxygen containing gas such as nitrogen, (3) then reaerating the solution with air or other oxygen containing gas back to saturation while measuring the dissolved oxygen content of the liquid medium over time with the calibrated D.O. probes, and (4) then calculating the value of kLa by statistically fitting the measured D.O. concentrations versus time data to the equation C═C*-(C*-C) exp (-(kLa)t) where C is the dissolved oxygen concentration at any time t, C* is the equilibrium dissolved oxygen concentration in the liquid medium at the test conditions, and CO is the initial D.O. concentration of the test liquid at time to during the unsteady state reaeration test.
A surface aeration impeller rotatable about an axis comprising blades extending above and below a surface of a body of liquid medium to be aerated, said blades being inclined at acute angles with respect to radial lines spaced from each other at successive angular increments about said axis so as to scoop liquid at said surface and spray said liquid outwardly away from said axis.
The impeller according to claim 55 wherein said blades have vertical portions and portions extending from said vertical portions which are bent upwardly to define angles between the surfaces thereof facing outwardly from said axis and the outwardly facing surfaces of said vertical portions of said blades which are greater than 90° thereby to further enhance the scooping and spraying action of said surface aeration impeller.
The impeller according to claim 55 wherein said a plurality of blades are spaced at successive angles about said axis, each of said blades having a vertical portion disposed with respect to a different one of said radial lines to define an acute angle there between, and said blades each having a portion which is tilted upwardly away from said axis and defines an angle of greater than 90° with respect to said vertical portion.
Dependencies are inferred from the claim text.