Classifications

• • E—FIXED CONSTRUCTIONS
  • E03—WATER SUPPLY; SEWERAGE
  • E03F—SEWERS; CESSPOOLS
  • E03F5/00—Sewerage structures
  • E03F5/14—Devices for separating liquid or solid substances from sewage, e.g. sand or sludge traps, rakes or grates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
  • B01D29/31—Self-supporting filtering elements
  • B01D29/35—Self-supporting filtering elements arranged for outward flow filtration
  • B01D29/356—Self-supporting filtering elements arranged for outward flow filtration open-ended, the arrival of the mixture to be filtered and the discharge of the concentrated mixture are situated on both opposite sides of the filtering element
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
  • B01D29/44—Edge filtering elements, i.e. using contiguous impervious surfaces

Definitions

• This invention relates to a fluid filter apparatus for use in fluid/ particulate matter separation/ concentration, and in one particular example of the separation of fluid from fluid entrained with waste material, particularly sewage waste.
• the process of filtering fluids and their fluid borne elements can be viewed in two ways. In one way it is the act of removing an unwanted part of what is flowing in the fluid much like the action of sieving. In another way it is the act of separating a portion of the fluid out of the fluid and thus concentrating the remaining fluid.
• a filter element can be used in either operation but what is clear from the known prior art is that regardless of the desired action there will be blocking of the filter to some degree. Once a portion of the filter is blocked its efficiency reduces and over time the filter will completely block. Maintenance of such filters is an unwelcome and typically expensive necessity.
• a filter element used in a suitable filter arrangement will be described in relation to its application to storm water and sewage overflow conditions and in particular to a concentration application in overflow conditions. It should however, be understood that the filter element and the filter arrangement concepts discussed herein, are used as an example only and that the arrangements described can with appropriate adjustment be used for separation and concentration applications.
• Engineers responsible for designing such systems can identify the maximum volume of combined storm water and sewage that can be accommodated into the water treatment plant and hence the capacities of respective pipe systems flowing into that treatment plant.
• alternative flow paths including pipes and open-air conduits communicate the overflow to other parts of the system or directly to an acceptable outflow point.
• the simplest way of providing an overflow mechanism is to include a weir over which flow volumes greater than the maximum calculated, can be directed away from the main flow of storm water and sewage.
• a simple weir has the benefit of being easy to implement and can be installed either at the time of the creation of the pipe system or with difficulty, retrofitted into an existing pipe work system.
• a common alternative to a simple weir is the use of a filter element which is intended to remove solid wastes from the overflow and hence lessen the health related risks.
• This concentrating function is designed to leave the unwanted sewage in the pipe and only overflow relatively clean fluid.
• Such a filter is designed typically to come into operation only when the overflow condition occurs.
• the filters and filter arrangements tried thus far will eventually block and become inoperative.
• Cellulose fibres are long and easily bridge between the elements of the various filters used thus far. As time progresses, the fibres build up until a portion of the available flow path through the filter is blocked. This portion grows, eventually ceasing the flow of fluid through the filter.
• the invention is a filter for concentrating or separating in a fluid stream containing particulate matter
• the filter consists of: a plurality of solid elements in an array having gaps between adjacent solid elements through which spill flow of the fluid passes, and the fluid stream and filter orientated with respect to each other such that the spill flow of fluid through adjacent gaps is bounded by a dividing stream line that terminates on a solid element intermediate adjacent gaps, and further arranged so that the incidence of the dividing stream line to the plane of the array is such that particulate matter larger than said gaps are deflected out of the spill flow between said gaps.
• the filter consists of at least two chambers on the spill flow side of the filter arranged to receive spill flow so as to maintain substantially the same incidence along the fluid flow length of the filter adjacent each said chamber.
• the one or more chambers have spill flow control means sized and positioned to allow spill flow to exit each chamber so as to maintain the incidence.
• Fig 1 depicts a top perspective view of a filter arrangement according to the invention
• Fig 2 depicts a cutaway version of the filter arrangement of Fig 1;
• Fig 3 depicts a top view of the filter arrangement of Fig 1;
• Fig 4 depicts a side view of the filter arrangement of Fig 1;
• Fig 5 depicts a further embodiment of the filter arrangement of Fig 1;
• Fig 6 depicts a close up perspective view of the filter element
• Fig 7 depicts a side view of the principle of dividing streamline separation
• Fig 7a depicts a variant of the filter element depicted in Fig 7;
• Fig 8 depicts a top view of a further embodiment of a filter assembly showing individual partitions located above a filter element
• Fig 9 depicts a side view of the filter assembly of Fig. 8.
• Fig 10 depicts a perspective cut away view of the filter element used in the embodiments for Figs. 8 and 9;
• Fig 11 depicts a top persecutive view of the filter element used in the embodiments for Figs. 8 and 9.
• inline filter arrangements A number of embodiments of inline filter arrangements will be described.
• the embodiments described first can be considered larger scale variants of a specific portion of the later embodiments.
• the described embodiments described may have advantages in applications not explicitly referred to herein but the later embodiments have been found to be particularly useful in the storm water/ sewage overflow situation, but of course may have use in other applications.
• an inline filter arrangement 10 is installed along an existing storm water/ sewage pipe 12 in which storm water and sewage flow from pipe 12 to pipe 12' through the filter arrangement 10.
• An overflow pipe 14 runs parallel to pipe 12' for a distance after the filter arrangement 10.
• the inline filter arrangement depicted in this embodiment is preferably arranged so that it has the same fall as the pipe 12 between the filter arrangement inlet 16 to the filter arrangement outlet 18.
• the inline filter arrangement can be used at any location along or at the termination point of a storm water pipe system.
• the filter arrangement may also be used other than in-ground situations and may also be used in storm water only systems as well as industrial fluid filtering applications.
• Fluid and entrained pollution/ sewage enters the filter arrangement 10 via pipe 12 and inlet 16 so as to pass below a filter element 20 which in this embodiment comprises a "cheese grate" screen as will be described in detail later in the specification.
• the filter element 20 in this embodiment is shown running parallel to the lower surface 22 of the filter arrangement 10.
• Arrows marked 'M' show the continuation flow of incoming storm water and sewage while arrows marked 'F' indicate the flow of filtered water (spill flow).
• the filter element 20 may be sloped so that it is closer to the lower surface 22 at the outlet end than the inlet end of the filter arrangement 10.
• the filter may be angled so that the side of the filter is higher on the side of the filter arrangement at which wall 24 is located and lower on the opposite side which is nearer the middle of the filter arrangement 10.
• the height of the filter element 20 above the lower surface 22 is generally determined with knowledge about the range of the rate of incoming storm water and sewage entering the filter arrangement and the particular rate is known, about 50% of the pipe work inner diameter, that should be reached before the incoming fluid needs to be concentrated so as to produce a spill flow.
• the height of the filter element is set above the lower surface 22 at approximately 50% of the diameter of the incoming and pipe 12. This setting is such that at that a predetermined incoming flow rate, storm water and sewage will rise to that level and the filter/ concentration action will commence.
• the final height of the filter is also dependent upon other factors, such as filter element 20 efficiency, the dimensions of the incoming pipe 12, the filter assembly dimensions in length and breadth and the outgoing pipe 12' dimensions (which are typically the same as the incoming pipe 12).
• filter element 20 efficiency the dimensions of the incoming pipe 12
• the filter assembly dimensions in length and breadth the dimensions of the outgoing pipe 12' dimensions (which are typically the same as the incoming pipe 12).
• the length of the filter arrangement 10 seems long compared with the diameters of the pipe work (12, 12' and 14) that length may be shorter or longer depending on the volumes of incoming and spill flow desired and the type of fluid or entrained particulate matter.
• filtered fluid flowing through the filter element 20 falls off the side of the filter element nearest the middle of the filter assembly 10 into a overflow chamber 25 which is preferably of equal volumetric dimensions to that of the chamber on the filter side of the filter arrangement 10.
• the overflow chamber 25 communicates filtered fluid to the filtered fluid outlet 26 of the filter arrangement, which is in fluid communication with overflow pipe 14. The reason the overflow chamber 25 is the same dimensions as the filter size dimensions is so that if necessary incoming fluid can be diverted without restriction.
• undershot overflow filter best describes the use of the filter element in this embodiment as the bulk of fluid containing particulate matter (contaminates) flows under the filter element (continuing flow) and the filtering (concentration) function of the filter arrangement is used to cope with an overflow (spill flow) condition.
• the flow of incoming fluid is arranged to submerge the filter element 20 to a depth where the vertical components of velocity of the fluid are small relative to the flow passing below the filter so that fluid passes up through the filter element but not the particles contained in the fluid passing below except those smaller than the gap.
• This characteristic of the filter arrangement is described in greater detail later in the specification and is referred to as dividing stream separation.
• the conditions to achieve dividing stream separation can be achieved in a number of ways. When using the embodiment disclosed in Fig 1, an arrangement of weirs and/ or header tanks can be positioned downstream of the filter assembly to create some of the conditions required.
• the filter arrangement 10 into which the filter element 20 is positioned is used in conjunction with weirs and/ or header tanks to control the relative velocities of the water flowing parallel and normal to the filter mesh so that the storm water sewage approaches the plane of the filter element 20, in this example a mesh, at an angle of less than approximately 3% which is an expression representative of the velocity components normal and parallel to the plane of the filter mesh.
• This is referred to as "the incidence” in this specification.
• face velocity normal component
• There is a continuation flow velocity (parallel component) defined as the mean velocity component parallel to the filter element of that continuation flow at a point outside the boundary layer.
• the incidence can also be varied by adjusting the depth of the spill flow fluid above the filter element relative to the depth of the continuation flow that eventually flows downstream of the filter.
• Methods and apparatus for adjusting both of these depths include the placement of valves, restrictions and weirs external and internal of the filter arrangement. As the incoming flow rate changes, the depths can be optimised and controlled by, for example, using notched weirs where the depth of water upstream of the weir has a desired relationship to the flow over the weir or by using apertures in multiple isolating chambers above portions of the filter element as will be described in more detail later in this specification.
• the filter element may be curved or comprise planar sections set at different angles relative to adjacent sections so as to provide a curved (non-planar) shape but will have an average plane for any particular region of the filter element for the purposes of referring to the incidence.
• FIG 5 A further embodiment of the filter arrangement is depicted in Fig 5 that shows a wall 28 positioned at one side and rising above the filter element 20 along the longitudinal center line of the filter arrangement 10.
• the wall 28 causes fluid and small amounts of entrained pollution, that has flowed up through the filter element 20, to flow in the direction of the continuation flow 'M' until it reaches aperture 30 in wall 28.
• the filtered fluid flow 'F' (spill flow) passes through the aperture and falls into the overflow chamber 25 and then flows into the overflow pipe 14.
• the length of the filter arrangement 10 is shown to be long with respect to the diameter of the pipe work but this is merely an example and it could be longer or shorter dependant on the sewage pipe work.
• the filter arrangement is likely to be different but the spatial arrangement of the filter element to the flows will be the same.
• the inlet 16 opens to a continuation flow chamber 32.
• This chamber has a lower surface common to the lower surface 22 of the filter arrangement such that incoming fluid flows towards the outlet 18 of the filter arrangement along the same gradient.
• the incoming fluid will continue to flow as continuation flow 'M', through the filter arrangement 10 until the incoming flow of water is such that the level of fluid in the filter arrangement rises above the filter element 20.
• the fluid will continue to flow through the inlet 16 and outlet 18 of the filter arrangement 10, it will also pass a portion of the fluid (spill flow) flowing into the arrangement through the filter element 20 thus allowing more fluid to pass into the filter arrangement 10.
• a rounded half circle shape 35 is located across the bottom of wall 36 so as to streamline the flow of water entering the filter arrangement 10 from the incoming pipe 12. Reduction of turbulence at the location above the bottom level of the wall 36 eliminates an undesirable re-circulation region below wall 36.
• a sloped ramp 37 at the bottom of the wall 36 above the filter element that is closest to the outlet 18.
• the sloped ramp is shown in Fig. 4 extending into the outlet pipe 12' but the ramp could be located completely within the filter arrangement 10. The reduction of turbulence at the outlet reduces turbulence at the end of the filter element that would otherwise adversely affect the effectiveness of the filter arrangement.
• the critical overflow rate will likely be defined by the water authority engineers based on calculated needs and the capacity of the existing pipe work system to provide an alternative route for the overflow fluid that unfortunately will be unfiltered.
• the wall 38 will be extended to the roof of the filter arrangement or be otherwise configured so as to ensure that no overflow of unfiltered fluid enters the overflow chamber 25 or overflow pipe 14. Unfiltered overflow will then need to be directed by an upstream weir to another filter-like arrangement or to an acceptable outfall or even a different treatment plant to that which it would otherwise have been expected to be directed to.
• the filter element 20 comprises in this embodiment, a "cheese grate” mesh, a detailed illustration of which is provided in Fig 6.
• arrows indicate how fluid containing sewage flows under the filter element (mesh) 20. While doing so, a certain portion of the fluid flows backward through the mesh (relative to the continuation flow) and then flows above the mesh 20. It has been found that the flow pattern above the mesh 20 is a good indicator of how evenly the mesh is operating.
• One filtered fluid flow arrangement is to have the filtered flow (spill flow) move sideways off the mesh 20 and into the overflow chamber 25.
• the mesh 20 is working evenly, the water has little or no flow in the same direction as the main flow, i.e. no stream-wise flow and it only moves sideways.
• a stream-wise component above the mesh 20 seems to indicate that there is some re-circulation. The sideways movement appears to result from the momentum of spill flow falling into the overflow chamber 25 and water surface tension forces.
• Fig. 6 depicts a bottom view of a portion of one mesh type (referred to herein as a cheese grate mesh) with the arrow 'M' showing the direction of the continuation flow of the storm/ sewer fluid.
• Fig 7 pictorially depicts the mechanism that produces the results described above and that is evident in other embodiments that are yet to be described in this specification.
• the mechanism is referred to herein as "dividing streamline separation”.
• Solid lines show the mesh/ grate elements and the dotted lines in the water are virtual in the sense that they do not exist but will in this particular example, assist the depiction of the method of operation of the filter.
• Line 70 represents the top of the continuation flow chamber 32 in particular, the lowest portion of partition wall 36. Unfiltered fluid is shown flowing into the region below the filter element 20 and dotted line 72 defines a height XI of fluid which will flow upwards into the gap between grate element (a) and grate element (b). Upwards flow of water (spill flow) and not entrained particulate matter, occurs as a result of a number of influences. Control of the previously mentioned incidence angle of the continuation flow onto the mesh along its length is an important influence on the successful use of the filter arrangement.
• Dividing streamline separation contributes to non-blocking of the mesh because the fluid borne particles passing through the mesh are much smaller than the separation between the mesh apertures, viz. the dimensions of XI and larger particles are drawn further along the filter arrangement.
• This arrangement appears counter-intuitive and indirect contrast to the way in which existing screens and filters work that eventually trap particles between their elements because the particles are being drawn towards and into the gaps between solid elements of the mesh/ grate and are larger than the provided gap.
• Particles are larger than the gap bridge across the gap between mesh elements whatever their spacing or orientation.
• any entrained particle or cellulose fibre flowing in the stream having less than height XI will pass through the filter element while particles and other fibres, the bulk of which primarily fit below dotted line 72, will flow past that particular portion of the filter element.
• a filter configuration of this type has been found to be non-blocking in most conditions including low and high flow rates and regardless of the nature of the entrained contaminates, for example and in particular, long cellulose fibres such as those described previously.
• the dotted lines depicted are merely schematic and will vary in shape and spacing dependent on flow rates (continuation and spill) so as to reflect the principle as understood and described herein.
• the "cheese grate" mesh has been found useful in certain circumstances in that there is little or no collection of debris, however other mesh or grating types could be used and have a similar or better results.
• the mesh or grate may be formed of a parallel array of rectangular, square or round bars which are located laterally with respect to the flow path.
• FIGs 8 and 9 show ten (10) independent compartments above an elongate filter element.
• the filter element comprises an array of parallel louvres located laterally with respect to the continuation flow and with each generally planar filter element angled with respect to the flow so that the gaps between louvres are directed in an opposite direction to the continuation flow M as is depicted in Fig 10.
• the arrangement of the louvres in cross-section is not unlike that depicted in Fig 7 so that a condition for dividing streamline separation can occur.
• the length L of the louvre, the thickness T, the gap G and the pitch P of the individual louvres of the grill are all variables relevant to some of the characteristics of such an a filter arrangement. It is preferable to flatten the lower edge of the louvres, which lie at the interface of the filter element to pass forward flow as is depicted in Fig 7a. This modification is intended to lessen the possibility of turbulence at this region.
• the face velocity is the mean spill flow velocity component that is normal to the plane of the filter element 20. It is numerically equal to the spill flow volume rate divided by the face area of the panel of the filter element as described previously.
• Spill flow is that flow of filtered water filtered fluid leaving the filter apparatus and the spill ratio is a ratio of the volume of filtered outflow (spill flow) over the total fluid flowing into the filter assembly.
• a filter assembly accepting 21 litres per second having a spill flow of 10 litres per second has a spill ratio of approximately 48 per cent.
• the continuation flow would be 11 litres per second.
• Modifying the tilt of the filter element can initially and at certain continuation flow rates be beneficial, but beyond a certain angle (which is different for different flow rates) the positive effect can transform into a negative effect such that face velocity not only reduces but reverses, ie, the filtered fluid above the filter element is sucked back into the continuation flow.
• a certain angle which is different for different flow rates
• Compartmentalising the filter that is, shortening the filter length and keeping the parameter of spill ratio, uniform face velocity and incidence constant within the region below the filter and respective partition helps to achieve a desirable outcome.
• the face velocity can be difficult to control.
• an active system It is possible, to at least in an active system, control the spill flow from each compartment.
• an active system is not an ideal arrangement as it adds complexity and cost to a filter arrangement that in the stormwater pipe system is mostly remote of maintenance personnel.
• Such a system using moveable weirs or valve actuations is possible in appropriate application such as industrial filtering where specific spill ratios may be required and maintenance of the mechanical/ hydraulic elements is less of an issue.
• the challenge therefore is to passively account for different spill flows where there exists a wide range of input flow rates.
• Some of the devices that may be used as an outlet control for the spill flow control feature include a broad crested weir, an orifice, a combination of the two, a v-notch control and a slit.
• a simple circularly shaped orifice is preferred.
• the outlet control device is preferably located above the filter element on a sidewall of a respective chamber.
• the circular orifice should be positioned so as to provide a head of water (acting like a weir) above the level of the filter element at a height such that not only is the spill flow from each chamber known (because of the known aperture area), but which also maintains a head in the chamber that is beneficial to the maintenance of the incidence and the inter-related face velocity.
• Additional orifices above an " existing one can be used to regulate spill flow when higher flow rates into the filter arrangement are encountered. Those orifices may be the same or different to those previously mentioned.
• Fig 11 depicts a filter arrangement of the above configuration in operation and the spill flow can be seen emitting from three circularly shaped orifices located one above the other in each of the chambers used in that embodiment.
• the spill flow aperture is shown as circular holes arranged substantially one above the other however a slot of appropriate dimension could also be used for the purposes described.
• any configuration of filter element 20 which exhibits the non-blocking characteristics desired, using a dividing streamline separation principle is likely to be useful in certain circumstances including as mentioned previously in industrial applications requiring non-blocking filters to separate fluid from fluids entrained with particulate matter (particulate that may include long thin strands of material).

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• 2001
  • 2001-07-12 CA CA002415216A patent/CA2415216A1/en not_active Abandoned
  • 2001-07-12 KR KR10-2003-7000007A patent/KR20030040343A/ko not_active Application Discontinuation
  • 2001-07-12 EP EP01949111A patent/EP1299600A4/en not_active Withdrawn
  • 2001-07-12 JP JP2002509601A patent/JP2004502063A/ja active Pending
  • 2001-07-12 NZ NZ523794A patent/NZ523794A/en unknown
  • 2001-07-12 WO PCT/AU2001/000833 patent/WO2002004755A1/en not_active Application Discontinuation

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