Abstract:
The device of the present invention removes liquid from sludges, such as water from an industrial pretreatment sludge. The device includes a chamber with an inlet for introducing the sludge to be dewatered into the chamber. The device includes a hydraulically driven reciprocating piston which functions as a containment wall at one end of the chamber and as a means to subject the sludge to mechanical pressure for dewatering, with seals sufficient to contain the sludge within the chamber during operation. The device includes a reciprocating end cap which functions as a containment wall at the end of the chamber opposite the reciprocating piston. The end cap includes a micro porous membrane filter assembly for retention of solids, support structure for the filter, a void area for vacuum pump evacuation to assist in dewatering, and an outlet for the liquid displaced from the sludge. At the conclusion of the dewatering process the end cap is retracted and the dewatered sludge is discharged from the chamber by the extension of the reciprocating piston.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention comprises an apparatus and a method for the removal of liquid from sludges, slurries, or suspensions, hereinafter collectively referred to by the generic term “sludge”. 
         [0002]    It is well known that in numerous industries sludge is produced as a byproduct of industrial processes. It is often desirable to separate the liquid and solid constituents of the sludge in order to reuse or dispose of the recovered material, be it liquid or solid. 
         [0003]    More particular mention may be made in the treatment of sludges produced from the chemical pretreatment of industrial waste streams, as in the printing industry. The waste streams that result from cleaning the ink from printing presses is treated to precipitate and flocculate solid contaminants, the end result being water which can be reused or released to sewer or septic systems and a sludge of, typically, 5% solids and 95% water. The sludge must be dehydrated before it can be disposed of, pursuant to landfill regulations. 
         [0004]    In the interest of clarity and convenience I will assume sludge comprised of water and particulate contaminants for the remainder of this application, while acknowledging the sludge may be composed of any number of liquid/solid compositions. The removal of water from sludge is universally referred to, and will be hereinafter, as “dewatering”. 
         [0005]    A variety of apparatuses are known whose object it is to effect the dewatering of the aforementioned sludges. These include recessed plate filter presses, both horizontally and vertically oriented, continuous belt presses, screw presses, rotary drum vacuum systems, and thermal dewatering systems, to name a few. Each of these technologies has considerable drawbacks. For example, the horizontally oriented, recessed plate filter press, which is the most popular method in the sludge dewatering industry, is limited by long cycle times (an average of four to eight hours per batch of sludge), limited efficacy (25 to 60% solids percentage depending on the nature of the sludge), contaminated effluent from inefficient sludge capture, and labor intensive cleaning and replacement of filter cloths. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention overcomes many of the limitations of the prior art by utilizing compaction pressures in excess of 50 bar in conjunction with a maximum vacuum pressure of less than 0.007 millibar and a novel filter assembly unique in the industry. The invention is comprised of a chamber, with an inlet for admitting the sludge to be dewatered, which functions as a dewatering chamber, a hydraulically driven piston mounted within the chamber, acting as a wall of the chamber and compressing the sludge as it traverses axially along the length of the chamber, and a hydraulically driven end cap abutting the face of the chamber. The end cap functions as a wall of the chamber opposite the piston and contains the filter assembly for retention of the particulate matter. The end cap also contains, behind said filter assembly, a support plate for the filter assembly and a void area evacuated by a vacuum pump for vacuum assist in the dewatering process, an outlet for connection to said vacuum pump, and an outlet for the effluent produced in the dewatering process. 
         [0007]    The chamber mentioned above is horizontally oriented and has flanges at each end. The flanges serve to secure the chamber in its mounts and, in the case of the flange at the discharge end of the chamber, as a mating surface for the end cap. 
         [0008]    The piston has, preferentially, a groove machined into its circumference for sealing elements. The diameter of the piston, the dimensions of the groove, and the compression chamber walls are machined to close tolerances to provide sealing against leakage to pressures several times those generated internally during a sludge compression cycle. The piston is actuated by the ram of a double acting hydraulic cylinder. Extension of the piston compresses the sludge, driving the water through the filter assembly. At the end of the dewatering cycle the end cap is retracted from the face of the dewatering chamber and the piston is extended to the end of the dewatering chamber, ejecting the dewatered solids into a drum or hopper. To begin the next cycle the end cap is extended to the face of the dewatering chamber and the piston is retracted to the opposite end of the chamber. 
         [0009]    The filter assembly mentioned above consists of a circular microfiltration membrane and a circular support screen of equal diameters, the periphery of which are bound and sealed by a rubber gasket. The inside diameter of the filter assembly gasket is equal to the inside diameter of the compression chamber. This gasketed assembly is affixed by an epoxy to a perforated support plate that is part of the end cap. The opposite face of said gasket abuts the face of the compression chamber flange and functions as the primary seal between the compression chamber and the end cap. The filter assembly offers two distinct advantages over the filter cloth used in filter presses. First, the surface of the membrane is flat, as opposed to the textured surface of a filter cloth. This flat surface can not entrap the retained particulate matter like a filter cloth does. For this reason the cake releases cleanly at the end of the dewatering cycle as the end cap is retracted from the compression chamber. In a filter press the cake often needs to be pried off manually or blown off of the surface of the cloth media by compressed air. Second, the pore size of the membrane is equal to or less than the diameter of any particulates that need to be retained. For this reason the membrane will not allow particulates to flow through and contaminate the effluent and, more importantly, the membrane can not become clogged, as the filter cloths in filter presses frequently are. 
         [0010]    The end cap serves four primary functions: 1) As the chamber wall opposite the compression piston; 2) As housing and support for the filter assembly; 3) As an evacuation chamber for vacuum dewatering, and; 4) As an outlet for the effluent. The mating surfaces of the compression chamber and end cap are machined to close tolerances and sealed against leakage by the above mentioned gasket and by a sealing element, preferentially an o-ring, which rests in a groove machined into the face of the end cap. The sealing element is of larger diameter than the outside diameter of the gasketed filter assembly. This seal provides protection against leakage at pressures several times those generated internally in the system. The end cap is actuated by the ram of a double acting hydraulic cylinder of equal bore to the hydraulic cylinder which actuates the compression piston. When the ram of the hydraulic cylinder is extended the end cap is pressed against the flange of the compression chamber, sealing the dewatering chamber. At the end of the dewatering cycle the ram of the hydraulic cylinder is retracted, withdrawing the end cap from the compression chamber flange to allow the piston to eject the dewatered solids. The end cap is then extended to the compression chamber prior to the commencement of the next dewatering cycle. 
         [0011]    Introduction of the sludge into the compression chamber is controlled by a valve connected to the chamber inlet. At the commencement of each dewatering cycle the valve is opened and the sludge is pumped into the chamber, preferentially by a progressing cavity pump. This valve is then closed and the pump is shut down when the compression chamber is full. 
         [0012]    Preferentially, all aspects of system operation are fully automated and controlled by a Programmable Logic Controller, hereinafter referred to as the PLC. 
         [0013]    The present invention combines compaction pressures in excess of 50 bar, the microfiltration filter assembly, and near absolute vacuum to dewater the sludge more thoroughly and rapidly than current systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a front elevation view of the preferred embodiment of the invention; 
           [0015]      FIG. 2  is a cross-sectional view of the enclosure; 
           [0016]      FIG. 3  is a cross-sectional view of the piston and the piston seals; 
           [0017]      FIG. 4  is a transverse view of the end cap and filter assembly; 
           [0018]      FIG. 5  is a cross-sectional view of the end cap; 
           [0019]      FIG. 6  is an enlargement of the upper left hand corner of  FIG. 5 ; 
           [0020]      FIGS. 7-10  are cross-sectional views of the enclosure at progressive stages of the dewatering process. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The present invention is designed to remove the liquid from any number of solid/liquid matrices commonly referred to by the generic term “sludge”. In the interest of clarity I will, for the purposes of this discussion, consider an application where water is removed from sludge, and the invention will hereinafter be referred to as a sludge dewatering system, while acknowledging that the liquid may be of any composition chemically compatible with the wetted parts of the system. 
         [0022]    Referring now to  FIG. 1 , there is shown a sludge dewatering system  100  constructed in accordance with the invention. The invention is comprised of a preferentially horizontally oriented chamber  1 , hereinafter referred to as the dewatering chamber, a piston  10  mounted on the end of the ram  15  of a double acting hydraulic cylinder  16 , said piston  15  mounted within said chamber  1  and traversing axially along the length of the chamber  1  and acting as a wall of the chamber  1 , an end cap  30  mounted on the ram  55  of a second double acting hydraulic cylinder  56  situated opposite the first hydraulic cylinder  16 , said end cap  30  also traversing axially in regards to the chamber  1  and abutting the face of the chamber  1  and functioning as a wall of the chamber  1  during the dewatering process, a filter assembly  40  affixed to a support plate  33  within the end cap  30  and serving as the face of the end cap  30  toward the piston  10 , a hydraulic power unit  20  and control valves  20 ,  21  for the operation of hydraulic cylinders  16  and  56 , respectively, a vacuum pump  51 , an actuated valve  5  for the admittance of the sludge into the chamber  1  through sludge inlet  4 , and a Programmable Logic Controller  66  (hereinafter referred to as the PLC  66 ) for automation and control of system operation. 
         [0023]    In the preferred embodiment, the dewatering chamber  1 , hydraulic cylinders  16  and  56 , piston  10  and end cap  30  are mounted axially on a steel support platform  80 . The hydraulic cylinders  16  and  56  are fixedly mounted to support blocks  85  and the dewatering chamber  1  is positioned and restrained from movement along the horizontal axis by support blocks  86 . The support platform  80  rests on steel support structures  75  and  76  that elevate the platform above the surface of steel skids  70 , which serve as the base of the system  100  and upon which are arranged the hydraulic power unit  20 , the vacuum pump  51 , a drum  90  for collection of the dewatered solids discharged from the system  100 , a progressing cavity pump  6  for transfer of the sludge from, preferentially, an intermediate holding tank into the dewatering chamber  1 , and an electrical control and distribution panel  65  which houses the PLC  66  and required system electrical components. The steel support platform  80  has cutouts for the dewatering chamber inlet  4 , to which is attached, between the support platform  80  and the progressing cavity pump  6 , an electrically actuated high pressure stainless steel ball valve  5 , and for the discharge of the dewatered solids from the end of the dewatering chamber  1  into the drum  90 . 
         [0024]    Referring now to  FIG. 2 , the dewatering chamber  1  is preferentially of stainless steel. The interior of the chamber  1  is machined to meet the mating tolerance requirements of the piston  10 /chamber  1  assembly. The dewatering chamber  1  has two flanges  2 ,  3 , one at the end of the chamber  1  nearest the hydraulic cylinder  16  connected to the piston  10  and the other at the opposite end of the dewatering chamber  1 , respectively, said flanges  2 ,  3  restricting lateral movement of the chamber  1  during system operation by contact with the dewatering chamber support blocks  86  mounted on the chamber platform  80 . The flange  3  at the discharge end of the dewatering chamber  1  is machined to meet the mating tolerance requirements of the end cap  30 . The dewatering chamber  1  has, in proximity to its discharge end, an inlet  4  for the sludge. 
         [0025]    The piston  10  is preferentially of stainless steel. The diameter of the piston  10  is determined by the inside diameter of the dewatering chamber  1 . The piston  10  is machined to meet the mating tolerance requirements of the piston  10 /chamber  1  assembly. 
         [0026]    Referring now to  FIG. 3 , a groove  12  is machined into the circumference of the piston  10  for, preferentially, o-ring  13  and two backup rings  14 , one on either side of the o-ring  13 . A coupling  111  is integrated into the face of the piston  10  toward the hydraulic cylinder  16  for mounting the piston  10  onto the ram  15  of the hydraulic cylinder  16 . 
         [0027]    Referring now to  FIGS. 4-6 , the end cap  30  is preferentially of stainless steel. The face of the end cap  30  toward the dewatering chamber  1  is flanged, the diameter of which is equal to the diameter of the dewatering chamber flange  3 . The face of the end cap  30  is machined to meet the tolerance mating requirements of the dewatering chamber flange  3 . A dovetail groove  31  is machined into the face of the end cap  30  for, preferentially, an o-ring  32 . Inset within the circumference of the end cap  30  is a filter assembly  40 . The filter assembly  40  is comprised of a micro porous filtration membrane  41 , preferentially a polycarbonate film with pore size of one micron or less, the diameter of membrane  41  equal to the outside diameter of the dewatering chamber  1 , a filter support screen  42  of equal diameter, preferentially a woven stainless steel mesh with a five micron particle retention rating, and a rubber gasket  43  of ring construction peripherally binding the membrane  41  to the support screen  42 , sealing their edges, and serving as a seal between the end cap  30  and the dewatering chamber  1  during the dewatering cycle. The inside diameter of the gasket  43  is equal to the inside diameter of the dewatering chamber  1 . The filter assembly  40  is preferentially affixed to a perforated stainless steel support plate  33  by an epoxy on the surface of the gasket  43  on the support screen  42  side of the filter assembly  40 . The support plate  33  has a groove machined along its periphery, the width of the groove equal to the width of the gasket  43  and the depth of the groove equal to the distance between the surface of the support screen  42  and the face of the gasket  43 , allowing the support screen  42  to lie flat against the support plate  33 . Behind the support plate  33  is a void area bounded by the cylindrical walls of the end cap  30  and the plate which is the face of the end cap nearest the hydraulic cylinder  56  which actuates the end cap  30 . A stainless steel cylinder  34  1/20 th  the diameter of the support plate  33  is centrally affixed to the back of the support plate  33  and extends to the end plate of the end cap, providing additional support against deflection of the support plate  33  during system operation. The cylindrical wall of the void area of the end cap  30  has a vacuum outlet  35  and a drain outlet  36 . The vacuum outlet  35 , situated 90 degrees from horizontal, is connected to a vacuum hose which is connected to a vacuum pump  51 . Preferentially, a vacuum trap is situated in the vacuum line. The drain outlet  36 , situated 270 degrees from the horizontal, is connected to a drain valve  45  which permits outflow of the effluent from the dewatering process while maintaining a positive seal against vacuum loss. A coupling  37  is integrated into the face of the end cap  30  end plate for mounting the end cap  30  onto the ram  55  of the hydraulic cylinder  56 . 
         [0028]    In operation, the sludge dewatering system  100  is automated and controlled by the PLC  66 . For preference, the sludge to be dewatered is transferred from the point of generation to an intermediate holding tank. The holding tank is equipped with a float switch that sends a signal to the PLC  66  when there is sufficient sludge to fill the dewatering chamber  1  and commence a dewatering cycle. At the beginning of each dewatering cycle the piston  10  is situated immediately to the rear of the sludge inlet  4  in the chamber  1 . If a dewatering cycle is not currently underway, the PLC  66  turns on the hydraulic power unit  20  and energizes the solenoid coil of a hydraulic valve  21  which will commence retraction of the piston  10  away from the discharge end of the chamber  1 . At the same time the PLC  66  actuates the ball valve  5  that controls sludge flow into the dewatering chamber  1 , opening the valve  5 , and the PLC  66  starts the progressing cavity pump  6 , filling the dewatering chamber  1  with the sludge. When the piston  10  has fully retracted the face of the piston  10  opposite the sludge contacts a limit switch  60  affixed to the flange  2  of the dewatering chamber  1 . The limit switch  60  sends a signal to the PLC  66  indicating the dewatering chamber  1  is full of sludge. The PLC  66  simultaneously de-energizes the previously energized solenoid coil  21 , reverses the actuation of the ball valve  5 , closing it, and shuts down the progressing cavity pump  6 . The PLC  66  then actuates the solenoid coil of the hydraulic valve  21  that controls the extension of the piston  10 . The piston  10  begins to traverse axially along the length of the dewatering chamber  1  toward the end cap  30 , decreasing the volume of the dewatering chamber  1  and exerting pressure on the sludge, compacting the particulate matter against the filter assembly  40  of the end cap  30  and forcing the effluent into the void area behind the support plate  33 , where it drains out of the outlet  36 . When the compaction pressure has reached a predetermined point, the first set point of an electrohydraulic pressure switch  23  signals the PLC  66  and the PLC  66  in turn activates the vacuum pump  51 . The vacuum pump  51  produces a vacuum in the void area in the end cap  30  to a maximum vacuum of less than 0.007 millibar. 
         [0029]    A second set point of the electrohydraulic pressure switch  23  signals the PLC  66  when the maximum operating pressure has been reached. After maximum pressure and vacuum have been maintained for a predetermined length of time, as determined in each individual application by the nature of the sludge being dewatered, but generally less than two minutes, the PLC  66  deactivates the vacuum pump  51  and de-energizes the solenoid coil  21  that controls extension of the piston  10 , relieving pressure within the dewatering chamber  1 . The PLC  66  then energizes the solenoid coil  22  that controls retraction of the end cap  30 , the end cap  30  is fully retracted, and the solenoid coil  22  is de-energized. Next the PLC  66  energizes the solenoid coil  21  to extend the piston  10 . The piston  10  extends until the face of the piston  10  is flush with the face of the dewatering chamber flange  3 , ejecting the dewatered solids from the chamber  1 , and the solenoid coil  21  is de-energized. The solids fall through the cutout in the support plate  80  and into a receptacle, preferentially a drum  90 . The PLC  66  energizes the solenoid coil  21  to retract the piston  10 , drawing the piston  10  to a position immediately to the rear of the sludge inlet  4 , and then de-energizes the coil  21 . Then the PLC  66  energizes the coil  22  to extend the end cap  30 , driving the end cap  30  flush against the flange  3  of the dewatering chamber  1 , and then de-energizes the coil  22 . During the dewatering cycle the end cap  30  is restricted from movement by a pilot operated hydraulic check valve  24 . The hydraulic cylinders  16 ,  56  responsible for the motion of the piston  10  and the end cap  30  are equal in chamber bore and operating pressure specifications, so the internal pressure developed by the hydraulic cylinder  56  holding the end cap  30  in place during the dewatering cycle will not exceed manufacturer recommendations. At this point the system is ready to begin the next dewatering cycle.