Patent Application
20160176141
The present invention relates to processing of bulk materials. More particularly, the present invention relates to separation of liquids from bulk materials and to a screw press arrangement for separating liquids from bulk materials such as livestock manure.
Numerous industries utilize compression devices such as screw press liquid separators to remove liquid from bulk materials such as wood chips, livestock manure, byproducts of food processing operations, or other fibrous materials. The screw press liquid separators are based on the principle of a screw rotating inside a cylindrical or conical cage that forces the bulk material from the inlet of the screw to an output in a manner that compresses the bulk material. The cage can be equipped with holes, usually conically drilled, or slots or bars arranged in such a fashion as to provide for drainage of the liquid that is squeezed from the bulk material.
The various uses of screw press liquid separators involve a number of mechanisms for creating pressure between the chamber and the shaft bearing flights. The inner diameter of the chamber may be cylindrical, conical, or may contain restricted areas. All of these features together with variations in the diameter of the shaft or diameters of the flutes on the shaft can produce changes in the pressure exerted on the wood chips or other material being treated in the screw press liquid separator. The chamber of the plug screw feeder may be comprised of bars, screens or be solid depending upon whether the screw press liquid separator is being used to drive off excess water from materials such as livestock manure or being used to refine materials such as wood chips or both remove excess fluid and refine. In various applications the pressure and throughput is controlled by the voids if any in the chamber, the restrictions in the chamber, the shaping of the shaft or flutes and the torque applied to the screw feeder. Numerous examples of screw press liquid separators are known in the art.
U.S. Pat. No. 5,515,776 discloses a worm screw press having drainage perforations in the press jacket. The size of the shaft for the worm screw increases in cross-sectional area in the flow direction of the drained liquid.
U.S. Pat. No. 7,357,074 is directed to a screw press with a conical dewatering housing with a plurality of perforations for the drainage of water from bulk solids compressed in the press. A perforated casing or jacket is used.
U.S. Pat. No. 3,394,649 discloses a worm press used for the dewatering of sludges or cellulose pulp suspensions and comprises a hollow worm shaft having apertures at the end of the pressure zone. Through these bores still further liquid can be drained into the hollow shaft, this liquid draining inside the shaft in a direction opposite to the conveyance direction.
These prior-art worm screw configurations appear to operate for their intended purposes, but require the use of tapering screws, screw jackets or both, or require hollow shafts with provision for drainage. All of these features complicate their construction.
Therefore, there is a need for a new screw press arrangement for separating liquids from bulk materials which is not associated with these disadvantages.
The present invention relates to a screw press liquid separator. The screw press liquid separator includes an elongated housing having an inlet end and a discharge end. A perforated screw cradle is disposed within the housing and has an inlet portion having a material inlet disposed at the inlet end of the housing and a compression portion. A screw formed on a shaft is disposed within the screw cradle. A first portion of the screw extends from an input end and a second portion of the screw extends to a discharge end and is completely surrounded by the compression portion. A first portion of the shaft has a first diameter extending from the input end to the discharge end of the screw, and a second portion of the shaft disposed within the compression portion of the screw cradle-extending past the output end of the screw has a second diameter larger than the first diameter. A transition portion of the shaft disposed between the first and second portions has a diameter that tapers from the second diameter to the first diameter. A first discharge guide extends from a top portion of the discharge end of the housing and a second discharge guide extends from a bottom portion of the discharge end of the housing. Two opposing discharge doors are pivotally mounted to the discharge end of the housing and are movable within a volume defined by the first and second discharge guides. The discharge doors are biased to close together against the discharge end of the housing. A plurality of paddles are affixed to and radially extend from the shaft at a position beyond an arc defined by pivotal motion of the discharge doors. A motor is rotatably coupled to the shaft.
These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. In some instances, well-known features have not been described in detail so as not to obscure the invention.
Referring first to
In
Screw 26 is disposed in a screw cradle 28. Screw cradle 28 is formed from perforated sheet metal to allow extracted liquid to exit the screw cradle 28. The clearance between the screw and the cradle should be enough to allow free motion of the screw within the cradle but tight enough to prevent solids in the bulk materials from becoming trapped between the outer edges of the screw and the inner walls of the screw cradle. In a non-limiting exemplary embodiment of the invention used to press the liquid from cow manure, a 12-inch diameter screw is disposed within a screw cradle having a 12.125-inch diameter. Persons of ordinary skill in the art will appreciate that the clearance will be affected at least in part by the nature of the bulk material being processed, the average size of solids in the material, as well as the size of debris that may be expected to be encountered in the bulk material.
A first portion 30 of the screw cradle 28 below inlet hopper 18 is u-shaped with an open top to permit the bulk material to be introduced into screw press 10. A second portion 32 of screw cradle 28, shown in isometric form in
As the bulk material is driven through the screw cradle in the area of the transition region 40 of the screw shaft, the pressure exerted on the bulk material increases as the volume defined by the cylindrical portion 32 of the screw cradle decreases, thus forcing more of the liquid out of the bulk material. According to the present invention, the decrease in volume defined by the cylindrical portion 32 of the screw cradle should be enough to exert significant extra pressure on the bulk material but not so much that it restricts the flow of bulk material to the point where it binds the screw or deforms the screw cradle. In an exemplary non-limiting embodiment of the invention extracting liquid from cow manure having a 12-inch diameter screw disposed in a 12.125-inch interior-diameter cradle, the first diameter of the screw shaft is about 3.50 inches, and the second diameter of the screw shaft in region 38 is about 6 inches, and the transition region 40 has a length of about 6-8 inches over which the diameter of the shaft increases linearly, although persons of ordinary skill in the art will appreciate that the diameter of the screw shaft could increase other than linearly over the length of the transition region 40. In any actual embodiment of the present invention, the minimum increase in shaft diameter can be selected to be large enough to compress the bulk material sufficiently to extract liquid, and the maximum increase in shaft diameter can be selected to avoid binding and jamming the screw press. As will be readily appreciated by persons of ordinary skill in the art, selection of the minimum and maximum shaft diameter values for any particular application will depend on factors including the diameter of the screw, the desired speed at which the screw will be rotated, and the nature of the bulk material being processed, including the compressibility and average size of the solid material components of the bulk material. As a starting point, the maximum shaft diameter can be approximately half of the diameter of the screw. This value can be adjusted empirically.
Referring again to
Referring again to
Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained in this disclosure.
