Liquid purification or separation – Plural distinct separators – Filters
Reexamination Certificate
2002-05-15
2004-12-21
Savage, Matthew O. (Department: 1724)
Liquid purification or separation
Plural distinct separators
Filters
C210S342000, C210S408000, C210S409000
Reexamination Certificate
active
06833071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the filtering of particulate matter from a slurry. More specifically, the present invention relates to the filtering of slurries having a relatively high particulate content utilizing a displacement filtering principle.
2. Description of the Related Art
Separating the liquid and solid components of a liquid-solid mixture, or slurry, is a necessary or desirable process in many industries. In many filtering applications, the slurry is a waste product and it is desirable to separate the solid and liquid matter and dispose of them separately. Often, the solid component may be a hazardous material and the liquid component may be reused or recycled. In other applications, the liquid component may be the final product, such as in the wine industry, for example. In this application, the solid component is desirably separated from the liquid to provide purity and clarity to the wine.
One method for separating liquids and solids is known as surface filtering. In a surface filtering process, the liquid-solid mixture is passed through a filter element under the influence of gravity or a relatively low pressure. The liquid component of the mixture passes through the filter element while the solid component is retained primarily on the surface of the filter element. However, with this type of filtering process, once the surface of the filter element is substantially covered with solid particulate matter, liquid is no longer able to pass through. Thus, surface filter processes are useful only for filtering slurries having a low concentration of solid matter.
A method more suitable for filtering slurries having a relatively high concentration of solids utilizes an apparatus referred to as a tube press. A tube press typically includes a cylindrical tube with a smaller diameter cylindrical filter concentrically positioned therein. A flexible bladder is positioned adjacent the inner surface of the tube. A fixed volume of slurry is introduced into a space between the tube and the inner filter and an inlet to the tube is closed and sealed. Hydraulic fluid is forced under pressure into a gap between the tube and the bladder to expand the bladder. The expansion of the bladder forces the liquid within the tube through the filter, while the solid matter is retained within the tube. However, this method of filtering is inefficient because the tube press only processes a fixed volume of slurry during a filtering cycle. As a result, the solid matter remaining at the end of the filter cycle is typically only a small percentage of the total available volume defined between the tube and the filter. Additionally, solids must be removed and the filter cleaned between each filtering cycle. Consequently, this process is typically used only in applications where the slurry has an extremely high concentration of solids or in applications where an extremely dry particulate “cake” is desired.
Another method of filtering slurries having relatively high concentrations of solid matter uses an apparatus known as a filter press, which operates under a displacement filtering principle. A filter press utilizes a series of filter plates placed adjacent to one another. A space is defined between each pair of the filter plates and each space is lined with filter media. Typically, each of the filter plates include a central aperture. Thus, all of the spaces between each pair of plates communicate with one another. An inlet is provided to introduce slurry into the interconnected spaces on an upstream side of the filter media. One or more outlets communicate with each space on a downstream side of the filter element.
Slurry is introduced through the inlet to fill all of the individual spaces between the filter plates. Once the spaces are filled, the delivery pressure of the incoming slurry is increased such that the liquid component is displaced through the filter media and the solid particulate matter is retained within the spaces upstream from the filter media. The filtered liquid, or filtrate, moves to the outlet(s), where it is discharged. The filter cycle continues until each of the spaces is substantially filled with particulate matter. Thus, the filter press utilizes substantially the entire volume of the spaces rather than relying on the surface area of the filter media, as is the case with surface filtering methods. However, due to the large forces generated by the pressure within the spaces, a large and costly support frame and hydraulic system is necessary to hold the plates together during the filter cycle. In addition, the solid particulate “cake” remaining in each individual space after the filter cycle must be removed in preparation for a subsequent filter cycle. Because as many as a hundred or more individual plates may be used, the cleaning process is very time-consuming and results in excessive down-time in which the filter press is not utilized. Also, due to the provision of multiple plates, which must be separated from one another to allow the particulate matter to be discharged and the filter media to be cleaned, fully automated filtering systems are often prohibitively expensive.
SUMMARY OF THE INVENTION
Advantageously, preferred embodiments and methods utilize a displacement principle for filtering slurries having a relatively high concentration of solids without the above-described disadvantages associated with the filter press. Preferred embodiments utilize a simplified structural arrangement to permit a less costly support structure and closure system to be provided. In addition, preferred embodiments drastically reduce the time necessary for discharging particulate matter and preparing the filter for subsequent use. Furthermore, preferred embodiments are desirably capable of being equipped with simplified and cost-effective automated cleaning systems to preferably completely eliminate the need for an operator and further reduce the down-time of the filter apparatus.
A preferred embodiment is a filter apparatus including a first outlet and a second outlet. The filter additionally includes an annular inner filter defining an external surface, an internal surface and an internal cavity. The first outlet is located downstream from the internal surface of the inner filter. An outer filter surrounds the inner filter and defines an internal surface and an external surface. The inner filter and the outer filter define an annular particulate collection volume. The second outlet is located downstream from the external surface of the outer filter. The filter includes an inlet directing fluid into the particulate collection volume before the fluid passes through either the inner filter or the outer filter. A pressure source is positioned upstream from the inlet and directs pressure through the inlet to force fluid within the particulate collection volume through the inner filter to the first outlet and through the outer filter to the second outlet.
A preferred embodiment is a filter apparatus for dewatering a slurry including a pressure vessel having a first end, a second end, and a one-piece, annular side wall portion. The side wall portion has an internal surface generally defining an internal space and one of the first end and the second end defines an opening to permit access to the internal space. A closure is sized and shaped for selectively closing the opening. The pressure vessel and the closure are configured to withstand a pressure of at least 25 psi in the internal space when the opening is closed. An annular inner filter defines an external surface and an internal cavity, the internal cavity at least partially defining a first outlet space. A substantial portion of the inner filter which forms the external surface includes a first filter media. An outer filter surrounds the inner filter and defines an internal surface facing the external surface. A substantial portion of the outer filter which forms the internal surface includes a second filter media. The first filter media and the second filter media comprise a wo
Duby Sean R.
Knobbe Martens Olson & Bear LLP
Savage Matthew O.
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