Abstract:
A system for use in filtering a slurry using air pressure to squeeze the slurry material and dewatering it. The system including a source of slurry, a chamber, a filter belt that passes through the chamber, a manifold inlet supplying the slurry to a first side of the filter belt to form a uniform moist cake of the filter material, an inlet seal and an outlet seal to seal a belt inlet nd a belt outlet formed on the chamber, and a source of the pressurized air selectively applicable to the chamber to dry the moist cake of filtered material.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
         [0001]    U.S. Provisional Application for Patent No. 60/436,233, filed Dec. 26, 2002, with title, “System for Solid-Liquid Separation” which is hereby incorporated by reference. Applicant claims priority pursuant to 35 U.S.C. Par. 119(e)(1).  
           [0002]    Statement as to rights to inventions made under federally sponsored research and development: Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention relates generally to dewatering equipment and more particularly, to a system that semi-continuously filters both fibrous materials and particulate materials from slurries, producing a substantially dry filter cake. The system further deposits the cake in containers, and when required, returns the relatively clean filtrate to be reused.  
           [0005]    2. Brief Description of Prior Art  
           [0006]    Solid-liquid separation is a major unit operation that exists in almost every flow scheme related to the chemical process industries, ore beneficiation, pharmaceutics, food, or water and waste treatment. The lack of cost effective equipment to handle these major unit operations and the enormous pollution problems caused by fluid production systems has resulted in industries abandoning many thousands of refuse ponds. The coal industry has created several hundred coal refuse slurry ponds holding an estimated 2 to 3 billion tons of discarded fine coal particles. Each year an estimated 30 million more tons are discarded into these waste ponds. Most of these slurry ponds are abandoned, un-monitored, and pose an enormous environmental hazard.  
           [0007]    Existing methods of slurry management by industry using slurry ponds, concrete pools or plastic lined pools for slurry storing or processing are not environmentally sound. Tighter governmental monitoring of slurry ponds has brought about the need for active solid-liquid separation devices that are both economical and environmental effective. Prior art systems have not been effective. Many such prior art systems are not automated or continuous, or semi-continuous. Such prior art systems typically use disposable filter or cloth. Other systems may also use elastomeric diaphragms which limit the chamber size. Others apply heat or chemicals or both which reduce the reliability and raise the cost of operation. Centrifuges and belt presses have not been the answer in most cases. Some inventions use compression chambers that separate with an upper part and lower part that require hundreds of thousands pounds of force to hold the two parts together. Although these work for low throughputs, the design limits their applications and the cost per gallon slurry processed is high. Some use stacked multiple chambers increasing the complexity and manufacturing costs while reducing the reliability. Vacuum disc filters have proved unreliable, have low throughput, and fail to produce “dry” solids that meet industry standards. Others have tried the vacuum-atmosphere technique, with and without membranes, which has not been effective in creating “dry” solids.  
           [0008]    Dewatering equipment can be used to clean up these environmental liabilities. The dewatering equipment needed must be of reasonable cost, non-labor intensive, reliable, adaptable to different slurries, and able to handle high throughput. It must make the disposal of or reuse of the treated materials both economical and environmental effective.  
           [0009]    As will be seen from the subsequent description, the preferred embodiments of the present invention overcome short comings of the prior art.  
         SUMMARY OF THE INVENTION  
         [0010]    More throughput for less cost while meeting industry “dry” solids standards is the principal objective of the present invention. Poiseuille&#39;s Law as applied to filter cakes confirms that the higher the pressure the faster the liquid flows through the filter cake. The present invention uses air pressure to squeeze the filter cake and dewater it. Air pressure is the optimum method for dewatering a uniformly distributed cake. It is more troublefree than methods using membranes or diaphragms and air moving through the cake helps to produce a substantially dry cake.  
           [0011]    The design of the present invention allows the operator to adjust both the time intervals and amount of pressure for the cake buildup and for the cake dewatering. These variables are adjusted to optimize the dewatering cycle for maximum throughput per hour.  
           [0012]    From the equation, pressure=force/area (P=F/A), to have enough pressure to perform the squeeze and have enough area for high throughput requires a very high force. The higher the force the costlier the equipment plus reliability and leaks become a problem. Unlike U.S. Pat. No. 5,573,667 that uses separable plate members that require up to one million pounds of force to hold the plates together during this squeeze, the present invention uses a fixed filter chamber with openings and sealing means at each end of the chamber for entrance and exit of a filter belt. The openings require very little force to actuate or keep closed during the squeeze cycle. Both structural find economical requirements limit the maximum width of each opening to between 4 and feet. As long as the width of the belt and the chamber width is of this optimum width (4 to 6 feet), the length of the chamber can vary for the job at hand and the cost of manufacturing the apparatus remains reasonable. For a four foot wide belt, the filter area can vary from 32 to 96 square feet. For extremely high throughputs, two or more chambers can be connected in parallel and operated by the same computer.  
           [0013]    Keeping the filter belt narrow has several advantages. A long, narrow chamber is much easier to design and build to handle high pressures. An interior four foot filter belt grid requires a lot less structural strength than one eight foot wide. Four foot wide doors are also a lot less likely to warp under pressure than 8 foot doors. Further, uniform distribution of the solids on the filter belt is easier to achieve in a relatively narrow, rectangular chamber.  
           [0014]    For different applications, only the length of the chamber changes; the doors, the belt washer, the rollers, the catch tray, are preferably for an approximate four foot wide filter belt. This all adds up to cost savings plus keeping the system narrow as discussed above also makes it easy to transport. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective partial sectional view of the present invention, a system for solid-liquid separation.  
         [0016]    [0016]FIG. 2 is an enlarged side partial sectional view of the exit sealing means to the system&#39;s chamber.  
         [0017]    [0017]FIG. 2A is an enlarged side partial sectional view of the exit sealing means of FIG. 2 in a closed position.  
         [0018]    [0018]FIG. 2B is an enlarged cross-sectional view illustrating the filter belt, filter belt grid, and sealing shelf within the system&#39;s chamber.  
         [0019]    [0019]FIG. 3 is an enlarged side view of the entrance sealing means to the system&#39;s chamber.  
         [0020]    [0020]FIG. 4 is a schematic view of the present invention including optional equipment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    In accordance with the present invention, a system for solid-liquid separation  10  is disclosed. The system  10  provides semi-continuous filtering of both fibrous materials and particulate materials from slurries, producing the required dry filter cake. The system  10  generally uses a fixed filter chamber member with openings at each end of the chamber for entrance and exit of a filter belt. The openings each include sealing means that require very little force to actuate, or keep closed during the squeeze cycle. In general, the present invention uses an air operated seal to seal the entrance opening for the filter belt, and a special gasket arrangement that seals the exit opening. Linear actuators known in the art are used to close the exit of the chamber for the cake buildup and squeeze cycles, and to open the exit for the discharge of the dry cake. These preferred embodiments save not only in the cost of operating the equipment, but in manufacturing the system  10 .  
         [0022]    FIGS.  1 - 4  illustrate a preferred embodiment of the system for solid-liquid separation  10  made in accordance with the present invention. FIG. 1 is a perspective view of the system  10 . The system  10  includes a chamber member  12  having at least one entrance opening  20  and at least one exit opening  22 , for entrance and exit of a filter belt  30 . As shown in FIG. 1, the chamber  12  further having a top wall  12 A, and end walls  12 B that define an inner chamber  15 .  
         [0023]    As shown in FIG. 2B, the chamber member  12  further includes an internal filter grid  31  positioned on a sealing shelf  32  that extends the perimeter of the filter belt grid  31 . In application, the filter belt  30  moves along the filter belt grid  31  within the chamber member  12 . In particular, the filter belt  30  is disposed on a first shelf  32 A of the sealing shelf  30 , and the filter belt grid  31  is disposed on a second shelf  32 B of the sealing shelf  32 .  
         [0024]    The basic operating principle of the system  10  consists of three phases: In the first phase, slurry  100  (see FIG. 4) is pumped with a slurry pump  102  at a high rate into the chamber member  12  at the location designated “A” in FIG. 4. The slurry  100  collects (not shown) on the filter belt  30  within the chamber  15 . As the solids begin to build up on the belt  30 , the solids  110  become the main filter element, and a seal is formed between the filter belt  30  and the first shelf  32 A by the solids within the slurry  100 . Filtrate  115  is cleaned and recycled back for reuse. As the solids  110  become thicker and more dense, the speed of the filtrate  115  through the solids  110  slow to a point where it is more efficient to stop the slurry pump and do the squeeze. The second phase has air pressure  104  between two and six atmospheres supplied to ine chamber  15 . The squeeze from the pressure removes the remaining filtrate  115  from the solids  110  until the moisture reaches a specified level. Phase three consists of releasing the sealing means as will be discussed thereby opening the entrance and exit openings  20 ,  22 , and turning the filter belt  30 . As the belt  30  turns over rollers  32 , the cake of solids  110  break up and is preferably deposited down a chute  35  (shown in FIG. 1) into all awaiting container (not shown). The filter belt  30  can move in and out of the chamber  15  of the chamber member  12  by manual cranking or, an electric motor(s) (not shown) can be used to turn the filter belt  30 . In the alternative, a continuous belt can be used.  
         [0025]    [0025]FIG. 2 is an enlarged side view of the exit opening  22  and exit sealing means  22 A of the present invention. In particular, the exit sealing means  22 A includes a hinged door  40  hinged to an upper surface  23  adjacent the exit opening  22  using connections  41  known in the art. Linear actuators  45  are used to open and close the door  40  in relation to the exit opening  22 .  
         [0026]    As shown in FIG. 2, the exit opening  22  in relation to the chamber member  12  is constructed having an angled opening designated as letter “B”, preferably a 60 degree angle opening. The door  40  includes an end  40 A. A first gasket  46  is affixed to the end  40 A of the door  40  and extends along a surface  46 A, and past horizontal gasket  48 . When the door  40  is in the closed position as shown in FIG. 2A, the surface  46 A is in sealing contact with the edges of the filter belt  30 .  
         [0027]    The gasket  48  is affixed to the inside of the first gasket  46 . The gasket  48  is preferably disposed at a 35 degree angle. When the door  40  is in the closed position, the gasket  48  is in sealing contact with the top surface of the filter belt  30 . In the preferred embodiment, both the angle B of 60 degrees and the angle of 35 degrees of gasket  48  as described above are such as to minimize the wear of the gaskets and filter belt.  
         [0028]    [0028]FIG. 3 is an enlarged view of the entrance opening  20  and entrance sealing means  20 A. FIG. 3 illustrates the sealing means  20 A in an open position. In particular, the chamber member  12  includes an angled projection member  50  that outwardly extends from the upper surface of the chamber member  12 . The projection member  50  having a top surface  50 A and a lower surface  50 B. A seal  52  is appropriately attached to the lower surface  50 B of the projection member  50  so that the seal  52  is disposed directly above the filter belt  130  at entrance slot  56 . The seal  52  extends the necessary distance past the edges of the filter belt  30  to secure a sealing at the belt edges. In the preferred embodiment, the seal  52  is an air operated seal known in the art.  
         [0029]    As shown in FIG. 3, the entrance opening  20  in relation to the chamber member  12  is constructed having an angle opening designated as letter “C”, preferably a 45 degree angle. Further, for proper sealing, the seal  52  is attached to the projection member  50  so that a midpoint  54  is positioned directly above the entrance slot  56 .  
         [0030]    In application, the seal  52  shown deflated in FIG. 3, can be expanded so that a compression seal exists between the seal  52  and the filter belt  30  and in particular, where the midpoint  54  of the projection member  50  contacts the entrance slot  56 .  
         [0031]    [0031]FIG. 1 shows the generally rectangular shaped chamber member  12  that the inventor has found optimum. It is imperative to have as wide a filter belt  30  as possible and still keep the cost of the apparatus reasonable. At four feet, the wall thickness and costs are reasonable. Any wider than four feet, the cost starts increasing quickly. If more throughput is required, the chamber member  12  can easily be made longer up to approximately twenty-four feet. Ninety-six square feet of filter area can process thousands of gallons of normal slurry per hour. It is obvious that the cost of the apparatus per foot filter area goes down as the chamber member  12  gets larger.  
         [0032]    From the equation, pressure=force/area (P=F/A) one can see that to have enough pressure to do the squeeze in a reasonable time and enough area for the required throughput, one must use an enormous amount of force. Force is directly related to expense, therefore it appears to be a very expensive concept. For example, the force required to hold two chambers together while applying 100 pounds per square inch of pressure on 100 square feet of filter area is almost 1.5 million pounds of force. U.S. Pat. No. 5,573,667 uses massive hydraulic presses and a super structure made of massive amounts of material to perform the job. Knowing force (F) is the variable in the equation that is more directly a function of the cost of the equipment, the present inventor designed a system that uses said fixed chamber member  12  with the openings  20 ,  22  for the entrance of the filter belt  30  into the chamber  15 , and to remove the dry solids  110  from the chamber  15 .  
         [0033]    The described sealing means  20 A,  22 A, require basically no energy to sealingly hold closed during the slurry pumping phase or the squeeze phase, and little energy to move to the open or closed position. Preferably, opening the entrance sealing means  20 A is preferably just enough for the filter belt  30  to enter the chamber  15  through the entrance opening  20 . Likewise, the door  40  at the exit opening  22  is minimally opened and closed as required. In particular, opening the exit sealing means  22 A so that the filter belt  30  and dry solids  110  can exit the chamber  15  through the exit opening  22 . By using an air operated seal  52  to seal the entrance opening  20  as discussed above, and using the linear actuators  45  with the first and second gasket  46 ,  48  arrangement for sealing the exit opening  22 , one experienced in the art can see that the system  10  is easily automated.  
         [0034]    The present invention is designed to be as reliable and trouble free as possible with few moving parts. The application of the air operated seal  52  to form an airtight seal on the filter belt  30  at the entrance opening  20  of the chamber  12  as discussed, is the preferred method. The unique method of having the air seal  52  attached to the angled projection member  50  so that the seal  52  activates at an angle as shown in FIG. 3, reduces the internal torque on the seal, increases the sealing area, and minimizes wear therefore increasing reliability.  
         [0035]    An important way this invention minimizes wear and improves reliability is by having the exit sealing means  22 A close and seal to the filter belt  30  at an angle as discussed. Another aspect of this invention is the unique application for sealing the edges  31  of the filter belt  30 . When the exit sealing means  22 A is in the closed position, the gasket  48  affixed to the first gasket  46  of the door  40  so that surface  46 A extends below the edge of the filter belt  30  so when the door  40  is closed, the peal squeezes towards the filter belt  30  sealing the edges  31 .  
         [0036]    Another important aspect of the present invention is the method used to evenly distribute the solids as a buildup on the filter belt  30 . The preferred embodiment uses a distribution manifold  13  with an internal disperser  14  disposed within the chamber member  12  to supply the slurry to the contents within the chamber  15 . Without an evenly distributed solid cake, the air pressure will not effectively squeeze the filtrate from the cake.  
         [0037]    After the slurry  100  is pumped into the chamber  15  and the solid cake  110  is built up to the required thickness, the present invention has a method for drawing the remaining slurry left on top of the cake  110  back to the slurry mixing tank using a pump  126 , as shown in FIG. 4. This conserves energy, reduces the squeeze time, third increases the throughput per hour.  
         [0038]    Further detailing the operation of the system  10  with references to FIG. 4, slurry  100  is brought into mixer tank  200 . The slurry can be combined with filtrate introduced by valve  202  and recycled belt cleaning water from pump  128 . When the valve  204  opens, the slurry mix can flow through pump  102  to the valve  206 . Prior to opening valve  206 , a precoat feed  208  can supply belt precoat material through valve  210 . The precoat material can be mixed with water from a supply  212  through valve  216 . The belt precoat mixes with the water in mixer  220  and can flow through valves  224  and  206  to precoat the belt  30  within chamber  12 . The precoat material makes the belt  30  easier to clean for example depending upon the slurry the system  10  is used on. Slurry material can then flow through the input A and manifold  13  onto the belt  30  until the thickness of the solids cake  110  reaches the point where slurry flow falls below a desired level. Air pressure from compressed air tank  104  is applied to chamber  12  through the valve  230 . The pressure will squeeze the filtering material into a relative dry cake  110 . The valve  230  is closed and chamber  12  is opened so that belt  30  can be moved by rollers  32 . Cake  110  will break off the belt  30  when it passes over a roller  32 . Any material stuck to the belt  30  can be washed off in belt washer  125  using water from supply  212  through the valve  232  and/or compressed air from tank  104  through valve  234 . The water and air in belt washer  125  can be applied to the opposite side of the belt from where material was caked to aid in the removal. The valves, belt and seals shown can be controlled manually or can be operated and controlled automatically by an automatic controller such as a programmable controller not shown.  
         [0039]    [0039]FIG. 4 further illustrates the system  10  with optional equipment. Some slurries are more gelatinous and require belt precoating to help the solids separate from the belt  30 . Other slurries require body-aid and some require precoating and body-aid. Some industries have value in the solids and require one or more cake wash cycles. A belt washer  125  is necessary to clean the filter belt  30  in certain applications. Other slurries require only the combined belt cleaning properties of an air pressure cleaning rod (not shown) and the top edge of the chute  35  as a scraper. After testing the slurry, a custom dewatering apparatus is built with the options necessitated by that specific slurry.  
         [0040]    From the foregoing, it is seen that the present invention provides an effective and efficient means for solid-liquid separation that is cost effective and easily transportable.  
         [0041]    Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but is merely providing illustrations of the presently preferred embodiments of the present invention.  
         [0042]    Thus the scope of the invention should be determined by the appended claims in the formal application and their legal equivalents, rather than by the examples given.