Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
1998-03-16
2001-05-29
Redding, David A. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S286600, C435S293200, C422S176000, C261S079200
Reexamination Certificate
active
06238912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for contacting gas and liquid. More particularly, but not exclusively, it relates to a method of and apparatus for initiating and at least partially effecting a fermentation or bioreaction process in which a gas such as oxygen or an oxygen containing gas, is introduced into a liquid, which may contain a solid phase therein. The reactor into which the gas and liquid are fed may contain a micro-organism. aerobic in the case of the gas being oxygen, which causes a reaction of the solid or liquid phase.
As stated above, the gas used is preferably oxygen or an oxygen containing gas, such as air. However, the invention is not limited to use of air or oxygen, and other gases may be used within the scope of the present invention. Similarly, the liquids involved are usually aqueous, but other liquids, which term includes mixtures of liquids or emulsions or dispersions, also fall within the scope of the present invention. In this connection, the term liquid will be used herein for convenience to refer to such liquids and to liquids containing solids in the form of suspensions or solutions.
2. Discussion of the Background
It is known to carry out such bioreactions in a stirred vessel, wherein air is introduced by means of sparge pipes into a tank containing liquid (as defined above as including possibly solid phases). After a period of time, the chosen micro-organism will have effected sufficient reaction for clear or treated liquid to be run off, possibly after a settling stage. One disadvantage with this process is the length of time taken to effect the reaction, which may be as long as 24 hours, and of course the amount of space needed to accommodate the volume of liquid/solids to be treated. It would be advantageous if a similar reaction could be accomplished within a shorter time and also using an apparatus which occupies a smaller volume. Indeed, it would also be advantageous to effect an improved gas/liquid contact in a short time, possibly as little as 20 seconds, and then allow a bioreaction to take place at a slower rate in a second or subsequent reactor. The improved gas/liquid contact and possible recirculation may enable overall treatment times to be reduced considerably, say from 24 hours to 2 hours.
So-called waterfall columns are known in which a jet of liquid is introduced into a gas filled space, entraining some of the gas to form a shallow froth above the liquid in the reactor.
It is known from British Patent No 1596738 to mix gas and liquids more effectively by introducing them co-currently in a downward flowing reactor. Such mixing however, can still create a gas space above the froth, although it can produce gas bubbles of such a size that the interfacial area between gas and liquid is increased, and therefore the contacting process is improved. Use of such apparatus, however, produces a zone of froth at an uppermost part of the reactor column wherein gas/liquid contact and mass transfer is not at its most effective.
It is also known from U.S. Pat. No. 4,834,343 to increase further the contact between gas and liquid by introducing at least part of the flow in a direction tangential to the longitudinal axis of the reactor. However this process has been carried out only in reactor columns having a “swirl” zone of substantially constant diameter and volume. This “swirl” zone is formed by the mixture in that zone of a vertically downward fluid stream at the top of the column, with a tangential inlet below it. This has been found to be unsatisfactory.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus which can further improve the contact between gas and liquid (as defined above optionally to include a solid phase) and enable a bioreaction to be carried out in and subsequent to the reactor.
According to a first aspect of the invention, there is provided a method of contacting a gas and a liquid which comprises providing an elongate substantially cylindrical reactor having adjacent a first end thereof an inlet region of reduced cross sectional area, introducing at least some of the gas and/or the liquid into said inlet region in a direction tangential to the longitudinal axis of the reactor to cause rotational flow of the gas/liquid mixture within said inlet region and therefrom into the remainder of the reactor and at such a velocity as to cause more intimate mixing of the liquid and gas within the confines of said inlet region.
The velocity should be such that the flow re-disperses any large bubbles of gas that might accumulate at the top of the column. Also the exit downflow velocity from around the diameter of the insert, which being greater than the downflow velocity below the insert, reduces the tendency for larger bubbles to rise to the top of the column.
The high inlet velocity introduction of the gas/liquid mixture into a relatively confined area promotes mixing of the gas and liquid and minimises gas separation from the mixture.
The gas and liquid may be combined initially at or upstream of a Venturi constriction or orifice plate which is itself at or upstream of the reactor inlet region.
The constriction or orifice may preferably be located at the point of tangential entry, and thereby serve to disperse the gas and produce only small bubbles.
In this case the velocity of flow of the gas/liquid at the constriction may optionally be greater than 150 cms/sec.
The method may further include introducing a liquid and/or gas stream through a second inlet disposed at an intermediate region of said reactor which may be so arranged that said gas and/or liquid introduced therethrough flows in a direction either generally longitudinally of the reactor, or in a rotational direction.
In this case, the second inlet may be disposed at a point where the rotational flow in the reactor causes a central vortex region to form.
In one embodiment of the method, the first inlet may be provided for liquid, as defined herein, which is recirculated from a second reactor fed from the outlet of this first reactor, and the second inlet may be provided for fresh liquid, optionally including gas, to be treated.
Alternatively, or additionally, the fresh material may be introduced through said second inlet at a comparatively slow rate.
The second inlet for liquid and/or gas to the reactor may comprise a pipe extending into the intermediate region of the reactor and adapted to cause rotational movement of material inlet thereby in either a co-current or countercurrent sense with respect to the direction of rotational movement of the gas/liquid/solid content thereof induced as a result of the initial tangential inflow.
The pipe comprising the second inlet may extend longitudinally into the reactor.
Alternatively the pipe comprising the second inlet may extend transversely into the reactor.
The method may include heating the gas and/or liquid introduced through the first or second inlet so as to raise the overall temperature of the liquid within the reactor.
Additionally or alternatively, the method may comprise introducing additional liquids and/or gas by means of a third inlet for liquid which may be provided at an intermediate region of said reactor.
Said third inlet may be so disposed that the liquid introduced therethrough is directed tangentially to the longitudinal axis of the reactor.
In this case the liquid so introduced may be so directed as to be co-current with the previously generated rotational flow.
Alternatively, the liquid so introduced may be so directed as to be counter-current to the previously generated rotational flow.
According to a second aspect of the present invention, there is provided an apparatus for contacting gas and/or liquid, comprising an elongate reactor, inlet means adjacent a first end thereof and outlet means therefrom adjacent a second end thereof, the inlet means comprising an inlet for gas and/or liquid disposed to direct the incoming gas and liquid tangentially to the longitudinal axis of the reacto
Ellis Stephen Robert Mercer
Moore Philip Coley
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Redding David A.
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