Liquid purification or separation – With means to add treating material – Directly applied to separator
Patent
1993-11-02
1995-10-17
Lithgow, Thomas M.
Liquid purification or separation
With means to add treating material
Directly applied to separator
2611222, 119263, B01F 304, C02F 320
Patent
active
054587719
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to apparatus for the treatment of liquid media by gasification. One application of such apparatus is to the gasification of liquid media which contains organic matter degradable by the action of gases thereon, for example, the aeration or oxygenation of sewage or other waste water. Another application is in the aeration or oxygenation of the water in fish or eel farms.
BACKGROUND ART
A wide range of aeration devices have been used and described in the prior art. Oxygen does not dissolve easily or quickly in water and it is therefore in principle desirable to utilize fine bubble aerators wherein the bubbles are about 2 mm in diameter. Smaller bubbles have a larger specific surface area for oxygen transfer into the liquid, and also rise more slowly through the liquid to give a longer time for the oxygen to transfer before the bubble reaches the liquid's surface. Coarse bubble aerators are less efficient in the mass of oxygen transferred per unit of energy utilized in generating the bubbles at a chosen depth in the liquid.
One known and widely used prior art fine bubble aerator is the porous ceramic diffuser device. These devices are usually secured in fixed positions to fixed air supply pipework at the base of a treatment vessel. They are efficient in terms of oxygen transfer per unit of consumed energy, but suffer from a substantial problem of fouling and clogging. If the air supply is turned off the foul water can enter the pores and the pipework and clog them with particles of organic matter, providing a habitat for growth of organisms in the pores. Dirt particles in the air supply also tend to lodge in the fine pores. One solution is never to turn off the air supply, but this can be inflexible in terms of plant operation, undesirable in terms of controlling dissolved oxygen levels and inefficient in overall energy use. It is possible to filter the air supply but this is expensive and again leads to energy inefficiency. Another solution is regular closure and draining of the plant for cleaning and unblocking or replacement of the diffusers, again leading to significant inefficiency and expense in operation.
Another known and used prior art device is an apertured pipe or other apertured air supply structure closely covered by a porous rubber sleeve, e.g. clamped in position by adjustable bands or clips. The air supply through the pipe flows out through the apertures and tends to pressurise and inflate the porous sleeve away from the pipes so that fine bubbles issue through the pores into the liquid. When the air supply is turned off the porous sleeve can collapse back onto the pipe. The pores remain in communication with the pipe apertures and thus fouling and clogging can arise as with the porous ceramic diffusers. If the pores are made finer to reduce clogging, then correspondingly the energy loss and inefficiency in forcing the air through the pores increases, i.e. it is necessary to create a high pressure drop across the porous sleeve.
DISCLOSURE OF INVENTION
An object of the present invention is to make it possible to provide an improved fine bubble aerator retaining the advantages of fine bubble size but mitigating the above described problems of clogging, high pressure drop and inefficiency.
The document DE-A-3316140 describes apparatus for the gasification of liquids comprising a support, an apertured flexible membrane extending over said support, and gas supply means to introduce gas to flow between the membrane and the support to inflate the membrane away from the support such that gas from the inflated space discharges through the apertures as fine bubbles and such that when the gas supply ceases the membrane collapses into area contact with the support to substantially seal the apertures.
The present invention is characterized in that: plurality of gas outlets oriented to direct the gas to flow into the space between said membrane and said support in directions substantially parallel to said support and the membrane when substantially unflexed.
When
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