Patent Application
20130233778
The present invention relates to the field of solids/liquid separation. More particularly, the invention relates to apparatus improvements related to the method for improving belt press dewatering described in U.S. Pat. No. 7,964,105 (Moss) and U.S. Pat. No. 7,381,329 (Moss).
Numerous examples of belt presses are provided in the prior art—for example, U.S. Pat. No. 7,381,329 (Moss), U.S. Pat. No. 6,454,102 (Thompson), U.S. Pat. No. 5,592,874 (Blauhut), U.S. Pat. No. 5,545,333 (Louden et al.) and U.S. Pat. No. 4,681,033 (Crandall et al.). In general, a belt press has a frame with an upper belt and a lower belt. Both upper and lower belts are typically liquid permeable [see U.S. Pat. No. 6,454,102 (Thompson), U.S. Pat. No. 5,592,874 (Blauhut), U.S. Pat. No. 5,545,333 (Louden et al.), U.S. Pat. No. 5,109,764 (Kappel et al.), U.S. Pat. No. 4,986,910 (Uyama et al.), U.S. Pat. No. 4,961,862 (Janecek), U.S. Pat. No. 4,879,034 (Bastgen), U.S. Pat. No. 4,836,100 (Johnson et al.), U.S. Pat. No. 4,681,033 (Crandall et al.), U.S. Pat. No. 4,181,616 (Bahr), U.S. Pat. No. 4,147,101 (Heissenberger et al.), and U.S. Pat. No. 3,942,433 (Wohlfarter)], although U.S. Pat. No. 5,022,989 (Put) suggests a non-permeable upper belt combined with a permeable lower belt is more advantageous. U.S. Pat. No. 4,986,910 (Uyama et al.) discusses the limitation of twin permeable filter fabrics for dewatering sludges.
Belt presses can employ several stages at which different techniques are used to remove the liquid from a mixture of solids and liquid. The use of these different stages improves filtering efficiency throughout the belt filter press.
In a typical belt press with multiple stages, the mixture initially enters a gravity screening zone of the belt press where free water drains through the lower permeable belt by gravity. The gravity screening zone is used primarily to remove free water. At the end of the gravity screening zone, the mixture could be near 10% solids. U.S. Pat. No. 6,454,102 (Thompson), U.S. Pat. No. 5,545,333 (Louden et. al.), U.S. Pat. No. 5,240,609 (Langley), U.S. Pat. No. 5,066,399 (Sugihara et al.), U.S. Pat. No. 5,022,989 (Put), U.S. Pat. No. 4,986,910 (Uyama et al.), U.S. Pat. No. 4,961,862 (Janecek), U.S. Pat. No. 4,836,100 (Johnson et al.) and U.S. Pat. No. 4,181,616 (Bahr) describe belt presses with gravity screening zones.
After the gravity screening zone, the mixture of solids and liquids enters the wedge zone where the upper belt and the lower belt carrying the mixture of solids and liquid converge with one another, applying progressively increasing pressure as the mixture is compressed between the belts. The degree to which the mixture is compressed corresponds to the angle of convergence of the belts, also called the wedge angle. The wedge angle may be fixed at all times or mechanically adjusted prior to running the filter press to accommodate a particular mixture. Wedge zones are shown in U.S. Pat. No. 7,381,329 (Moss), U.S. Pat. No. 6,454,102 (Thompson), U.S. Pat. No. 5,545,333 (Louden et al.), U.S. Pat. No. 5,240,609 (Langley), U.S. Pat. No. 5,109,764 (Kappel et. al), U.S. Pat. No. 5,066,399 (Sugihara et al.), U.S. Pat. No. 5,022,989 (Put), U.S. Pat. No. 4,986,910 (Uyama et al.), U.S. Pat. No. 4,961,862 (Janecek), U.S. Pat. No. 4,879,034 (Bastgen), U.S. Pat. No. 4,836,100 (Johnson et al.), 4,681,033 (Crandall et al.), U.S. Pat. No. 4,181,616 (Bahr), U.S. Pat. No. 4,053,419 (Pay), U.S. Pat. No. 3,942,433 (Wohlfarter), U.S. Pat. No. 3,894,486 (Sparowitz et al.) and U.S. Pat. No. 3,796,149 (Heissenberger).
Some belt presses have a higher pressure zone wherein the upper and lower belt follow a path between progressively smaller press rolls which may be either perforated or solid drums. The pressure imparted to the material between the upper and lower belts in the high pressure stage increases greatly from the largest perforated drum or solid roller to the smallest perforated drum or roller. High pressure zones are shown in U.S. Pat. No. 5,545,333 (Louden), U.S. Pat. No. 5,240,609 (Langley), U.S. Pat. No. 5,066,399 (Sugihara et. al), U.S. Pat. No. 4,986,910 (Uyama et al.), U.S. Pat. No. 4,879,034 (Bastgen), U.S. Pat. No. 4,836,100 (Johnson et al.), 4,681,033 (Crandall et al.), U.S. Pat. No. 4,181,616 (Bahr), U.S. Pat. No. 3,942,433 (Wohlfarter), and U.S. Pat. No. 3,796,149 (Heissenberger). Except for Uyama et al., each of these inventors teach us that gradually increasing compression pressure through the use of press rollers arranged in decreasing diameters in the direction of movement of the solids/liquid mixture corresponds to a progressive degree of liquid removal. Likewise, increasing shearing force through multiple changes in the direction of movement of the solids/liquid mixture by Z-shaped or S-shaped pathways also corresponds to a progressive degree of liquid removal.
The problem with all prior art is if the porous belt filter fabric becomes clogged or blinded, then liquid can not be separated from the solids/liquid mixture. In U.S. Pat. No. 4,986,910 (Uyama et al.), the inventors teach us that liquid in the solids/liquid mixture is removed only in the vertical direction through the filter fabric(s). To overcome the problem with blinding or clogging, the inventors formed pellets from pre-dehydrated sludge as an intermediate step prior to high compression pressing. The gaps between pellets that were then passed through the high compression zone provided a pathway for liquid to escape to the filter cloth and exit the solid/liquid mixture. The inventors claimed a higher removal rate of liquid in the high compression zone when forming pellets prior to high compression pressing
Another problem with the prior art practitioners whom rely on multiple press rollers of decreasing diameter and multiple changes of direction is described in U.S. Pat. No. 4,879,034 (Bastgen) who argues that pressure plates are superior to multiple press rollers because multiple press rollers have sections of reduced pressure between pinch points of multiple press rolls. Liquid that is pressed out in high compression zones at the pinch points will be sucked back into the solid/liquid mixture in low compression zones between the pinch points.
Another disadvantage of belt presses is that their mechanical design is complex, and maintenance and repair is time-consuming and costly. U.S. Pat. No. 4,584,396 (Crandall et al.) describes a frame design to minimize time and effort to replace belts, particularly endless belts which require a special frame that can be separated or disassembled. U.S. Pat. No. 4,971,691 (Meylor and Finn) describes a belt press design that is easy to assemble and re-assemble for cleaning and replacement of worn parts.
The object of U.S. Pat. No. 7,964,105 (Moss) was to provide a method for improving all belt press designs by either adding or enhancing the high compression zone using a superior method, the net result being to produce press cakes with higher solids content and less liquid. The object of this invention is to provide apparatus improvements to designs that implement enhanced high compression zones using multiple pinch points wherein material being deliquified is:
In this invention, each combination of pinch point roller and return roller(s) may have a separate, lower permeable belt that is different in material, fabric weave pattern, warp and weft thread diameters, opening size, and/or percent of open area than the lower permeable belt in any other combination of pinch point roller and return roller(s). The purpose of having different, individual lower permeable belts for each pinch point is to optimize deliquifying for each pinch point and to lower the replacement cost of belts when the rate of wear and frequency of replacement is different for different sections of the high compression zone.
In a further preferred embodiment, hydraulic cylinders at each corner of the rectangular frame provide a mechanical means to lift the upper frame to provide space for ease of replacement of individual lower permeable belts. The hydraulic cylinders can also provide means for automatic recovery from jamming of the belt press by a foreign object that becomes permanently lodged in the wedge zone or between one of the pinch points. Foreign objects can become lodged in the wedge zone or between the small gap between pinch point rollers so as to obstruct and halt the operation of the moving belts. A magnetic detector, shaft rotational motion detector, or other shaft rotational counter can detect whether the rate of rotation of individual rollers has slowed or stopped, allowing an electronic or digital controller to automatically power the hydraulic cylinders to raise the upper frame so that the foreign object can pass between the pinch points without need for human intervention to raise the upper frame, remove or dislodge the foreign object, lower the upper frame, and return the belt press to normal operation.
In the '329 patent, four screw-and-bolt assemblies and springs were used to adjust the spacing and compression pressure between the upper non-permeable belt and the lower permeable belt at each corner of the rectangular upper assembly and lower assembly. In the '105 patent, separate screw-and-bolt assemblies and springs at the axial bearing rod of each upper roller and lower-belt roller pair were used to adjust the spacing and compression at each pinch point independently in the higher compression zone. Independent adjustment of the gap width and compression force between the upper and lower rollers is essential in deliquifying polymer-conditioned organic sludges. Very wet sludges need larger gap widths and lower compression forces to prevent gelatinous sludges from being forced into the openings of the permeable lower belt and preventing the permeable belt from separating liquid from solids. As the sludges become more deliquified, the gap widths need to be reduced and the compression pressures need to be increased to accomplish greater levels of deliquifying.
In a further preferred embodiment, an apparatus implementation of the independent gap width and compression adjustment is provided. The purpose of this design is to increase stability for long shafts used in wider belt presses so that high torques produced by higher mass flowrates will not deform the structural bearing rods of each roller.
The subject of the invention are apparatus improvements to the method for removal of liquid from the press cake in the high compression zone of a belt press which was previously described in U.S. Pat. No. 7,964,105 (Moss) and depicted in
The subject of this invention is depicted in
In a further preferred embodiment which is depicted in
In a further preferred embodiment which is depicted in
In a further preferred embodiment, each pinch point gap width separator vertical threaded rod (30) may incorporate a spring compression assembly (36) so that an increase in the flow of press cake through the gap will increase the compression pressure in the pinch point. The compression force of the springs (30) at each pinch point can be adjusted independently by raising or lowering the position of the spring compression adjustment bolts (34) at each pinch point compression upper roller.
Independent adjustment of the gap width and spring compression force is essential in deliquifying polymer-conditioned organic sludges. Very wet sludges need larger gap widths and lower compression forces to prevent gelatinous sludges from being forced into the openings of the permeable lower belt and preventing the permeable belt from separating liquid from solids. As the sludges become more deliquified, the gap widths need to be reduced and the compression pressures need to be increased to accomplish greater levels of deliquifying.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.
