Gas and liquid contact apparatus – Contact devices – Rotating
Patent
1988-04-01
1990-02-27
Miles, Tim
Gas and liquid contact apparatus
Contact devices
Rotating
B01F 304
Patent
active
049044206
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and a device for introducing gas into a liquid by using a vessel for taking in the liquid, provided with a revolving paddle assembly with a mainly horizontally rotatable shaft, which paddles are adapted to introduce the gas into the liquid from the gas space above the liquid.
From EP-B 0 005 553 a device is known which is suitable for this purpose, in which scoops which are connected by means of spokes to the rotatable shaft are movable along the inner wall of the partly cylindrical vessel with an open top and through the liquid present therein, a small part of the trajectory thereof leading through the gas space above the liquid. In the upper part of the trajectory the liquid flows from the scoops and through the gas and will, then, absorb gas, and, furthermore, gas is scooped by the scoops into the liquid and will escape in the lower part of the trajectory as gas bubbles. Since said bubbles then arrive in the rearward part of the preceding scoop, a direct escape of the gas towards the liquid surface is prevented. The gas transfer towards the liquid is, however, rather low, since the collected bubbles will easily coalesce again to form a larger gas cushion so that the contact area with the liquid is reduced accordingly. Such a device provides, therefore, a relatively low gas introduction.
The invention aims at providing a method and a device enabling a considerably higher gas introduction into the liquid. To that end the method according to the invention is characterised in that the vessel is partly filled with the liquid, and the paddles are driven at such a speed that the liquid is pushed upwards in the sense of rotation, after which the liquid shooting downwards brings about the formation of a hydraulic jump, and the overturning portion of the liquid splashes down into this jump, thus introducing gas into the liquid.
The paddles moving through this hydraulic jump bring the gas bubbles into the liquid. At a given gas bubble co-centration as many bubbles will leave the liquid as there are introduced. The gas bubbles leave the liquid at the hydraulic jump, which results, there in a violent agitation of the liquid. Thereby a large boundary surface between liquid and gas is obtained.
From aeration experiments with tap water it has appeared that it is possible to introduce more than 5000 mg/1.h oxygen, which is considerably more than is possible with the current devices. An aeration efficiency of about 2.5 kg/kWh oxygen can be obtained thereby.
In addition to dissolving a gas into a liquid, this method can also be used for removing volatile components from a liquid, and then care should be taken that the gas escaping from the liquid with the removed components will be exhausted separately from the gas supply.
If required the introduction of gas into the liquid can be improved by supplying the gas under pressure.
The invention provides a device for the execution of this method, comprising a vessel with a supply and a discharge for the liquid, and a paddle wheel directed along the horizontal axis of this vessel and adapted to introduce gas into the liquid from a gas space situated in said vessel above the liquid, said device being characterised in that the width of the paddles of the paddle wheel, when driving said paddle wheel at the operational velocity, is sufficient for pushing the liquid up to a highest point in a first quadrant where the paddles are moving upwards, but, on the other hand, the outer layer of the liquid splashing downwards in the next quadrant will not enter the paddle ring moving downwards in said quadrant.
In particular the wall of this device is, at least in said first quadrant, sustantially coaxial with the axis of the paddle wheel, and is situtated at a small distance from the outer edges of the paddles. In this manner the liquid can be driven by the paddles towards the highest point, and thus an optimal effect is obtained.
For an optimal operation a gas space should still be present within the paddle ring afer pushing up the water, which restricts th
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patent: 3348829 (1967-10-01), Grimes
patent: 3358422 (1967-12-01), Van Der Schee
patent: 3658305 (1972-04-01), Newtson
patent: 4101384 (1978-07-01), Faust et al.
patent: 4468326 (1984-08-01), Kawert
Miles Tim
Pielkenrood Vinitex B.V.
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