Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
1999-10-08
2002-07-30
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Including geographic feature
C210S783000, C210S791000, C210S158000, C210S160000, C210S391000
Reexamination Certificate
active
06426009
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to removing debris from waste flowing in a channel to a waste treatment facility, and more particularly to methods and apparatus for causing a large area travelling screen to pause and provide improved cleaning of the screen.
2. Description of the Related Art
Basins are used to remove certain undesired solid materials from liquid, for example, to clarify the liquid. For example, basins are used in water and waste water treatment plants, and in industrial waste water plants. Undesirable solid materials include non-settleable colloidal solid material that is mixed with chemicals to agglomerate and form solid materials that will settle from the liquid. In water and waste water treatment plants, undesirable solid materials include organic solids. In industrial processes, undesirable materials may include a variety of materials, such as fibers, which are not amenable to agglomeration and settling, for example.
Water, waste water, and liquid industrial wastes are treated in basins to remove such undesirable solid materials. The word “liquid” as used herein to describe the present invention refers to water, waste water, and liquid industrial wastes. These undesirable solid materials include particles that are suspended in the liquid. Some particles are removed from liquid by settling in low flow rate settlers, for example. Many undesirable solid materials are not removable by settling. For example, these include: (1) man-made materials such as plastics; (2) construction debris, containers and other large items that may be carried by the liquid but are not suspended in the liquid; and (3) many other materials (e.g., paper towels) that are carried by the liquid but do not degrade in the manner in which biodegradable materials (e.g., food) degrade.
For purposes of differentiating the undesirable, suspended solid materials from such other undesirable, non-settleable larger materials, these undesirable, suspended, settleable materials are referred to herein as “solids” or “settleable solids”, whereas these undesirable, non-settleable larger materials are referred to herein as “screenable solid materials”, or “debris”, because the debris are preferrably removed in “screening” equipment which permits the liquid and the settleable solids to flow past such equipment into the basin for settling of the settleable solids. Examples of such debris may include plastic products, paper, and dental floss.
If such debris are not removed before flowing into the basin, the debris may interfere with settling, debris in sludge from the settler may interfere with the removal of the sludge from the basin, and the sludge recovered from the basin may include some of the debris. The debris in the sludge is not desirable as it reduces the value of the sludge, and lessens the rate of settleable solids removed by settling per gallon of liquid.
Efforts have been made to improve ways of removing debris from liquids by screening. The removed debris may be referred to as “screenings”, for example. Fixed bar screens have worked effectively to remove debris in applications in which a channel for guiding a flow of the liquid and debris is not buried tens of feet under ground. For example, a prior art fixed bar screen offered for sale by Meurer Industries, Inc. has a front rake capable of cleaning the bar screen in a superior manner.
When the channel is buried tens of feet under ground, for example, too much time may be taken in moving the removed screenings up from the channel to the level of the floor of the treatment plant. Also, in many cases the stroke of a rake along the bars of the bar screen is too slow, and the extension of the rake arm down to the channel results in the rake arm extending many feet above the plant floor when the rake carries the removed debris up to the level of the floor. Therefore, although the efficiency of the basic screening operation of a bar screen may be acceptable, in certain applications the overall efficiency of bar screening is lacking as too slow or requiring too much height above the plant floor.
Others have attempted to improve screening by the use of so-called travelling screens. In these screens, an endless mesh screen is continuously moved into the liquid and the debris to gather the debris from the channel. As such screen continuously moves, the screen advances out of the liquid. In one type of travelling screen an endless screen continues to move out of the liquid and continue to move past a debris removal station at which the collected debris is brushed off such screen. See U.S. Pat. No. 5,387,336, for example. Alternatively, the collected debris may be removed from the screen by air or liquid, for example.
In one type of typical tooth-type travelling screen, the teeth are pivotally mounted and engage cams as the teeth continuously move. The cams cause one tooth to pivot and scrape against adjacent teeth in an attempt to remove the debris from the teeth. See U.S. Pat. No. 4,188,294, for example.
However, such blowing, brushing, teeth scraping, and other current attempts to remove the debris from the continuously moving travelling screens are not efficient enough. Thus, significant amounts of the debris stay on the travelling screen and move back into the channel. Unfortunately, the return path of such travelling screens is downstream of an upstream path that the liquid and the debris engage for removal of the debris. The debris is washed off this downstream path back into the liquid, which greatly lessens the efficiency of the travelling screen.
Further, even when the channel is near the ground, the area of a fixed bar screen through which the liquid flows is generally limited to the cross-sectional area of the channel, e.g., the channel width by the depth of the liquid and debris in the channel. Attempts to provide more screen area include providing a semicircular shape for each of a series of screen elements of a travelling screen. However, it is difficult to properly physically remove the debris from such semicircular screens, and the same problem of reintroducing the debris to the liquid downstream of the screen exists.
In view of the forgoing, what is needed is a way to efficiently remove the debris from a travelling screen so as to minimize the problem of reintroducing the debris to the liquid downstream of the screen. Further, the relatively high efficiency of fixed bar screens should be achieved while minimizing that problem.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by more efficiently removing debris from a travelling screen so as to minimize the problem of reintroducing the debris to the liquid downstream of the screen. Further, while minimizing the problem the relatively high efficiency of fixed bar screens is achieved.
The present invention fills these needs by providing improved travelling screen elements for separating debris from liquid. Each of the screen elements has a filter surface through which the liquid but not the debris may flow. The filter surface is defined by a pair of planar plates, each of the plates having openings through which the liquid but not the debris may flow. A connector between the plates positions the plates relative to each other at a selected fixed angle. In one embodiment of the present invention, the selected fixed angle may be about ninety degrees. In this embodiment, the connector may be formed integrally with each of the plates. The integral version may be defined when the planar plates and the connector are formed from one sheet, and the connector is in the form of a bend to define the fixed angle and the two plates.
Provisions may also be made to mount one travelling screen element adjacent to another such element, and to move the adjacent elements into and out of the liquid and the debris in the channel. Each of the screen elements may have an angular cross section. One positioning of the series of elements is with some of the elements in the channel and relative to each other so that the a
Brauch Joseph Karl
Meurer Charles Lonnie
Martine, Jr. C. E.
Meurer Industries, Inc.
Upton Christopher
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