Patent Publication Number: US-4925557-A

Title: Multi-purpose rotating membrane filter

Description:
BACKGROUND OF THE INVENTION 
     There continues to be a need for a continuous filter that, with little operator attention, will filter out particles as small as 0.45 microns. Most bacteria will be filtered out with a 0.45 micron pore size filter. The present invention covers use of a rotating, hollow, disc filter in which the disc may be covered with a membrane containing pores or openings of a controlled size that may be smaller than 0.3 microns. 
     We have considered the generalized patent issued to Breton, Ser. No. 3,997,447 which covers use of a rotating disc in a filter unit but differs in several unique aspects. 
     The present invention is intended to provide a unit that may be easily changed to cover many filtration needs. The objectives, then, of this invention include: 
     1. a filter that may with differing controlled pore-size plastic or sintered metal membrane covered rotating elements be used for such diverse purposes as filtering out bacteria, filtering oil out of water to extent of less than 0.1 ppm. oil remaining, filtering tails from beer manufacture to recover more of the desired product, filtering algae and fungi from water etc., etc. 
     2. a filter that will operate with very little back flushing and with very little, if any, manual cleaning for most operations 
     3. a low maintenance filter using well tested mechanical seals and corrosion resistant materials 
     4. a filter system with multiple filters and instrumentation to indicate leakage so that maintenance of one filter unit will reduce but not stop the flow to the system 
     5. a relatively low cost filter system. 
     To achieve these objectives the invention comprises hollow membrane covered discs mounted on a vertical hollow shaft in a cylindrical vessel; with means to rotate the shaft with discs installed and means to draw filtrate out of the center of the vertical hollow mounting shaft; and means to remove solids from the lower portion of the vessel and to draw lighter liquid fluids such as oil or lighter flocculent solids from the top of the vessel. 
     The hollow filter discs may be fabricated with the base of triangular shaped stiffener ribs welded to a central cylindrical hub containing vertical vent pipes and containing openings that will be adjacent to openings in a hollow rotatable mounting shaft when a plurality of discs are stacked vertically on the mounting shaft. One or more, usually four, vent pipes are formed in each hub. The ribs may be covered with a sintered metal layer or membrane which may have more or less controlled pore size of 2 to 50 microns or more. The sintered metal membrane on each side of the hollow disc being formed is also welded to the central cylindrical hub and the peripheral edges of the sintered metal membrane may be welded to each other or may be welded to an open metal &#34;half pipe&#34; or bead to form an expansion joint or may be clamped. Finally the sintered metal may be covered with a controlled porosity membrane that adheres to the sintered metal. 
     Note we have described one way of making the membrane covered disc. The disc may also be made by properly clamping the support metal and sintered metal membrane and controlled pore size plastic membranes together. The method of manufacture must be such as to have a disc that allows liquid to move into the center only thru the controlled pore-size sintered metal or plastic membrane, or thru both membranes and that maintains its structural integrity thru temperature change, rotation, and up to 150 p.s.i. pressure differential. 
     Feed liquid is introduced thru a feed manifold with a maximum of one feed line from the manifold between each adjacent pairs of discs. With the discs rotating the drag from each disc will cause the total mass of liquid to rotate so that as feed is jetted between plates, the heavier materials will be thrown outward by centrifugal force. The rotating disc is normally rotated at a speed to allow only a thin static layer at the surface of the disc The disc surface speed will be greatest at the periphery and least at the hub. The shaft size, disc size, rotational speed and viscosity of the liquid being filtered are all interrelated with the thickness of the static layer on each side of an operating disc. Some experimentation is necessary to optimize these variables for each feedstock. 
     Vent pipes thru the hub of each disc allow lighter oils to travel to the top of the vessel to be drawn off. With 10 psi pressure differential across a disc membrane with 0.5 micron pore size and 4&#34; shaft with a 16&#34; disc and 2000 rpm speed we have demonstrated filtration rates of 4 to 10 gallons per square foot of filter area per minute when filtering less than 2 ppm oil out of water. 
     Periodic cleaning of the filter discs may be accomplished using a centrufugal pump to pump filtrate back thru the hollow rotating shaft and thru the internal hollow disc upwards thru the membrane to dislodge any accumulation on the membrane. A draw off at the bottom of the unit may be valved back into the feed tank. The system may be simply automated to provide for cleaning when flow is restricted to a predetermined percentage of what is normal feed for a clean system or could be automated to backflush at set intervals in some visualized cases where filtration is quite difficult. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention encompasses multiple rotatable hollow membrane covered filter discs mounted on a rotatable shaft in such a manner that the filtrate is drawn off from the center of the shaft and solids or sludge may be drawn off from the bottom of the unit with less dense fluids such as oil being drawn off from the top of the unit. The flow rate thru a unit varies with pore size of the membrane on the filter disc, total membrane filtration area, inlet and exit pressure differential, type of material being filtered, cleanliness of the disc surface and speed of movement of the membrane surface thru the liquid. 
     Prototype testing has shown that with the rotation speed to move the surface of the disc thru the liquid at a speed of over 20 ft./sec. that the disc filtration capacity will remain approximately constant over six hours. 
     The invention may be described as follows: 
     a. a compartmented cylindrical body containing a hollow rotatable shaft with openings in the shaft to communicate with the central chamber of hollow membrane covered filter discs mounted on said shaft with sealing rings to allow only liquid (filtrate) that comes thru the filters to enter the shaft; the membrane covering may be a sintered metal membrane alone or a sintered metal membrane covered with an adhering controlled pore size plastic membrane, 
     b. a draw-off chamber with proper seals to allow draw off of material from the rotating hollow shaft, 
     c. a draw-off from the top of the cylindrical body to draw-off lighter liquid such as oil that tends to travel toward the rotating shaft and travel upward thru vent pipes in the disc or thru the hub of each hollow membrane covered filter disc to the top of the vessel, 
     d. a sludge or solids draw-off from the bottom section of the compartmented cylindrical body, 
     e. a feed inlet manifold with a multiplicity of take off&#39;s thru the wall of the top compartment of the compartmented cylindrical vessel to jet feed into the liquid at intervals as close as between each pair of the hollow membrane-covered filter discs, 
     f. means to measure the total feed to the unit and means such as a centrifugal pump to maintain feed pressure from 40 psi to above 100 psi, 
     g. automatic valving and pressure means to allow flushing the filtrate from the unit backwards thru the hollow shaft and thru the controlled pore size membrane of the filter discs. During this operation feed flow would be stopped and either the sludge draw would be opened or alternatively means to direct the liquid from the filter unit to the feed tank could be used. 
     The details of a preferred embodiment of the total unit including the hollow membrane-covered filter disc and necessary seals around the rotating hollow shaft will become clear from the attached drawings and explanation thereof. 
     Minor changes may easily be made by one of normal skill in the mechanical arts and we mean only to be limited to the general design and spirit and purpose as outlined in these claims and specifications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the assembled unit with feed inlet manifold and with hub size of the disc and total disc size in relatively correct proportions. 
     FIG. 2 shows a top view of the disc indicating vent pipes thru the hub and relative size of hub and disc 
     FIG. 3 shows a section A--A of the disc in FIG. 1 indicating the openings thru the hub leading to openings in the hollow mounting shaft thereby allow the open interior of the disc to communicate with the hollow mounting shaft interior. 
     FIG. 4 shows section B--B of disc in FIG. 1 indicating the vertical vent pipes thru the hub to allow a lighter fluid such as oil to flow to an upper liquid draw off point. 
     FIG. 5 shows an edge view of the disc wherein the sintered metal membrane is welded to an open bead ring that may act as an expansion joint. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In FIG. 1 we show the assembled unit comprising: 
     a. an upper body segment 1 containing the hollow rotary shaft 4 with inlet feed manifold 5 with a multiplicity of feed openings 6, that with the usual 50-100 psi feed pressure, jet feed between each pair of hollow membrane covered filter discs 7. The hollow rotary shaft 4 has a spline type disconnect 8 to allow easy removal and installation of the hollow rotary shaft 4 with the multiplicity of hollow membrane covered filter discs 7 mounted thereon. In this top segment we also have a double fluid seal 9 and an adjustable thrust bearing 10. Sludge drawn-off is thru opening 22 while oil or fluids lighter than water may be drawn off thru outlet 23. A clean out draw-off 26 may be used to return feed or back flushed liquid to the feed tank. We show O ring seals 25 to protect the upper shaft bearing 24, 
     b. an intermediate body segment 2 contains double fluid seals 14 and the lower end of hollow rotary shaft 4 with openings 12 to allow filtrate to exit the unit thru filtrate discharge 13. A driver spline connection 16 drives the hollow rotary shaft 4 thru a drive shaft connected with drive gear 19. The drive shaft goes thru lower body segment 3 which also holds dual bearings 17 for the drive shaft which is connected to drive gear 19. Drive gear 19 is, in one embodiment, driven by motor drive gear 20 mounted on a drive shaft of motor 21. Belt drive, chain drive, or direct gear drives could all be used, 
     c. the total unit is mounted on baseplate 18, the rotary drive shaft 4 may be belt or gear driven by a power source which could be a motor or a motive source driven by steam, electricity or fossil fuel. 
     FIG. 2, 3, 4, and 5, show details of the hollow membrane-covered filter disc. 
     In FIG. 2 we show a top view of the hollow membrane covered filter disc 30. The hub 32 is large enough to have a shear velocity at the outer portions of the hub 32 of a minimum of 10 ft./sec. when the hollow rotatable mounting shaft 4 is rotated at 1350 rpm - in one embodiment. With 10 ft./sec. speed at one point on the hub 4 there is a very thin static layer on the disc 30 as it rotates. Rotation speed and size are interrelated to allow the surface of the membrane to move a minimum of 10 ft./sec. with a velocity of above 30 ft./sec being a normal or expected speed. 
     A multiplicity of vertical vent pipes or openings 33 in the peripheral part of hub 32 allow less dense fluids such as oil to travel upward toward the upper discharge nozzle 23, FIG. 1 with these vent pipes 33 also allowing lighter flocculent solids to move upward to prevent covering of a portion of the disc 30 with solids. 
     A multiplicity of horizontal openings 35 allow movement of filtrate from the interior of discs 30 to an open collector ring 34 that allows filtrate to move thru holes or openings at this point in shaft 4, FIG. 1 to the center portion of shaft 4 and down thru outlet holes 12, FIG. 1 to the filtrate exit. 
     FIG. 3 shows a section A--A to further elucidate the structure of disc 30, FIG. 2. 
     A section view AA shows two of a multiplicity of openings 35 that lead from the internal portions of disc 30, FIG. 2 to the interior of collector ring 34 which in turn allows filtrate flow into the hollow shaft 4, FIG. 1. 
     Also indicated are the inner support struts 31 with sintered metal membrane 37 with 2-50 micron openings, welded to struts 31. 
     The sintered metal membrane 37 is welded to the hub inner support struts 31 and, at the peripheral edge, to itself. A controlled pore size plastic membrane 38 may be fused to the surface and outer edge of the sintered metal membrane 37. 
     An O-ring seal 39 between each disc 30, FIG. 2 as it is positioned on shaft 4, FIG. 1 prevents leakage of unfiltered material into the hollow shaft 4. 
     FIG. 4, section B--B of FIG. 2, is showing two of a multiplicity of vertical vent openings or pipes 33 thru each hub 32 and also showing inner support struts 31 containing openings 40 so that filtrate in the disc 30 interior moves freely. 
     FIG. 5 shows an end section of another embodiment of the outer peripheral edge of disc 30, wherein the sintered metal membrane 37 is welded to an open bead expansion joint 41. The porous controlled pore size plastic membrane 38 is fused to the sintered metal membrane 37. The drawing shows the layers 37 and 38 separated for clarity. 
     
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Legend - Drawings                                                         
No&#39;s  Description                                                         
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FIG. 1                                                                    
1     Filter body - feed segment                                          
2     Filter body - draw off segment                                      
3     Filter body - lower bearing &amp; support segments                      
4     Hollow rotatable mounting shaft                                     
5     Inlet manifold                                                      
6     One of multiple feed lines to feed between discs                    
7     One of multiple rotating membrane-covered hollow                    
      filter discs                                                        
8     Spline to allow removal of upper section of the                     
      rotatable hollow mounting shaft 4                                   
9     Double fluid seal                                                   
10    Adjustable thrust bearing                                           
12    Discharge openings from center of shaft 4                           
13    Filtrate effluent                                                   
14    Double seals                                                        
16    Spline drive joint                                                  
17    Bottom shaft bearing                                                
18    Base plate                                                          
19    Shaft drive wheel                                                   
20    Drive gear                                                          
21    Drive motor                                                         
22    Sludge draw off                                                     
23    Oil draw off                                                        
24    Top bearing                                                         
25    O-ring seals                                                        
FIG. 2                                                                    
30    Hollow membrane-covered filter disc                                 
31    Inner support struts                                                
32    Hub                                                                 
33    One of multiple vent pipes                                          
34    Collector ring or open interior hub 32                              
35    One of multiple openings connecting interior of                     
      filter disc 30 with open interior 34 of hub 32                      
FIG. 3                                                                    
31    Inner support strut                                                 
32    Hub                                                                 
35    Connecting openings between disc 30 interior and hub                
      interior 34                                                         
37    Sintered metal membrane - may be 2 to 50 micron                     
      pore size                                                           
38    Controlled pore size plastic membrane adhering to                   
      sintered metal membrane 37                                          
39    O ring seal between hubs 32                                         
FIG. 4 Shows section B-B of FIG. 2                                        
40    Openings in inner support struts 31                                 
33    Vent pipes thru hub 32                                              
39    O ring seal between hubs 32                                         
FIG. 5                                                                    
41    An open bead expansion joint edge used in one                       
      embodiment of disc 3                                                
31    Inner support strut                                                 
37    Sintered metal membrane                                             
38    Controlled pore size plastic membrane covering fused                
      to sintered metal membrane 37                                       
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