Gas and liquid contact apparatus – Contact devices – Rotating
Reexamination Certificate
1999-10-14
2001-02-27
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Rotating
C261S093000, C261S122100, C261SDIG007
Reexamination Certificate
active
06193221
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to gas-liquid, gas-slurry, and gas-sludge reactions, and more particularly to a method of and apparatus for creating sub-micron bubbles in liquids, slurries, and sludges.
BACKGROUND OF THE INVENTION
Gas-liquid, gas-slurry, and gas-sludge reactions (hereinafter referred to collectively as gas-liquid reactions) present unique problems not found in single phase reactions. The rate and efficiency of gas-liquid reactions is dependent on the amount of contact between the gas and the liquid. The contact occurs at the interface of the liquid and the gas and is, therefore, dependent upon the surface area of the gas bubbles in the liquid. For a given amount of gas, the smaller the bubbles, the greater the surface area. It is therefore advantageous to produce smaller bubbles in order to achieve the best reaction efficiency.
The efficiency of gas-liquid reactions is particularly important in wastewater treatment systems. For example, one of the primary processes in treating municipal and some industrial wastewater streams is known as an activated sludge system. In an activated sludge system, incoming wastewater, typically under gravity flow conditions, enters a large, typically rectangular aeration basin. Within the basin a manifold system of aerators served by one or more large air compressors puts air into the wastewater. The oxygen in the air allows naturally occurring bacteria (the activated sludge) to oxidize contaminants in the wastewater.
The aerators used in conventional wastewater treatment plants are typically disks with small pores which are referred to as diffusers. Conventional diffusers are able to produce bubbles in the 100-500 micron range. These relatively large bubbles tend to rise quickly in the aeration basin, limiting the amount of oxygen that can transfer from the gas bubble to the water. As a result, extremely large quantities of air must be passed through the diffuser in order to ensure that an appropriate amount of oxygen enter the water.
Conventional diffusers tend to plug over time. When a diffuser is plugged, the air pressure behind the diffuser can blow the diffuser head completely off of the riser pipe to which it was attached. If a diffuser head blows off of the riser pipe, the pressure drop across the diffuser is eliminated. As the diffusers and riser pipes are manifolded together, any reduction in pressure drop reduces efficiency across the entire system.
Replacing a conventional diffuser requires that the activated sludge system or a portion of the system be taken off line and drained so that the diffuser may be replaced. Thus, a need exists for improvements in the art of diffuser design which facilitate the generation of sub-micron sized bubbles in the wastewater treatment systems.
Diffuser manufacturers have heretofore attempted to generate sub-micron sized bubbles in activated sludge systems by fabricating diffusers with very small outlet holes. All such attempts have been unsuccessful because the problem of diffuser plugging is exacerbated when diffuser outlet hole size is reduced.
SUMMARY OF THE INVENTION
The present invention comprises a method and apparatus which overcomes the foregoing and other difficulties that have long since characterized the prior art. In accordance with the broader aspects of the invention there is generated a stream of sub-micron sized gas bubbles. Due to their extremely small size, the gas bubbles have an extremely large surface area which increases reaction efficiency. Smaller pores in a gas permeable partition facilitate the formation of smaller bubbles. Additionally, high velocity relative movement between a liquid and the partition surface aids in shearing the bubbles off the surface while they are still small.
In accordance with first, second, and third embodiments of the invention, a gas permeable tube is positioned within an outer tube and water or other liquid is caused to continuously flow through the annular space between the two tubes. Gas is directed into the interior of the gas permeable tube and is maintained at a pressure high enough to cause gas to pass into the water or other liquid and prevent the flow of water or other liquid into the interior of the gas permeable tube. As the water or other liquid passes over the gas permeable tube, gas bubbles are continually sheared off of its surface. The gas bubbles thus generated are sub-micron in size and therefore present an extremely large surface area. The gas permeable tube may also be rotated relative to the liquid.
In accordance with a fourth embodiment of the invention, there is provided a hollow disk which supports a gas permeable partition. The disk is positioned within a water or other liquid filled container. Gas is directed into the interior of the disk and is maintained at a pressure high enough to cause gas to pass outwardly through the partition and into the water or other liquid and to prevent the flow of water or other liquid into the interior of the disk. The disk and the partition are moved at a high speed relative to the liquid. As the gas permeable partition moves relative to the water or other liquid, gas bubbles are continually sheared off of its surface. The gas bubbles thus generated are sub-micron in size and therefore present an extremely large surface area.
A fifth embodiment of the invention is particularly adapted to wastewater treatment. In accordance therewith, an activated sludge system employs a rotating diffuser, rather than the conventional static diffuser. Rotational power is supplied by air pressure flowing through jets located along the circumference of the diffuser. The rotational motion of the diffuser, coupled with the water head pressure on top of the diffuser, produces a frictional force on the small air bubbles emanating from the pores of the diffuser. This frictional force shears the air bubbles off the diffuser head before the air bubbles are completely formed, thus producing sub-micron sized bubbles and higher oxygen transfer efficiency due to the larger overall surface area. Further, the rotational motion tends to keep the pores in the diffuser cleaner than in a conventional diffuser, resulting in less plugging and thus less maintenance.
REFERENCES:
patent: 2075384 (1937-03-01), Vretman
patent: 3118958 (1964-01-01), White
patent: 4029724 (1977-06-01), Muller et al.
patent: 4228112 (1980-10-01), Hise
patent: 4521349 (1985-06-01), Weber et al.
patent: 5954925 (1999-09-01), Sherman
Bushey C. Scott
GRT, Inc.
O'Neil Michael A.
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