WO2011019746A1

WO2011019746A1 - Cleanable filtering device

Info

Publication number: WO2011019746A1
Application number: PCT/US2010/045063
Authority: WO
Inventors: R. K. Verma; Sumeet Mehra; Michael H. Francisco
Original assignee: Acuity/Sparkle, Ltd. (Cayman)
Priority date: 2009-08-12
Filing date: 2010-08-10
Publication date: 2011-02-17

Abstract

A filtering device (100) is used for liquid. An inlet (102) is fluidly connected to a lower chamber (112). The lower chamber is in free flow fluid communication with an unfiltered region of the upper chamber (110). A filter (124) separates the upper chamber into the unfiltered region and a filtered region. An outlet (104) from the filtered region provides filtered liquid. A drain (106) releases accumulated waste from the lower chamber and waste dislodged from the filter, during a backflush. To filter, pass liquid from the inlet through the lower chamber, in an upward direction to the unfiltered region of the upper chamber, through the filter, into the filtered region and out through an outlet. To backflush, pass liquid from the outlet through the filtered region, through the filter in a reverse direction, into the unfiltered region of the upper chamber, in a downward direction to the lower chamber and out the drain.

Description

Description CLEANABLE FILTERING DEVICE

TECHNICAL FIELD [0001] The technical field generally relates to the field of liquid

purification and specifically to water or other liquid purification using filters. More specifically, the field is water purification filters that are cleanable.

BACKGROUND [0002] Potable (i.e., drinkable) water is a necessity to which millions of people throughout the world have limited access. Water is often considered to be the most basic and accessible element of life, and seemingly the most plentiful. In every liter of water in rivers or lakes, fifty more lie buried in vast aquifers beneath the surface of the earth. There is no standard for the quantity of water a person needs each day but experts often place the minimum at 100 liters for adults. Most people drink one or two liters, with the rest typically being used for cooking, bathing, and sanitation. Adult Americans consume between 400 and 600 liters of water each day.

[0003] The population of earth continues to expand. If water were spread evenly across the globe, it is likely that there would be a sufficient quantity to satisfy the needs of everyone. However, rain falls inequitably with respect to both time and geographical location. Delhi receives fewer than forty days of rain each year, all in less than four months. In other Indian cities, the situation is worse. Nevertheless, the country must sustain nearly twenty percent of the earth's population with four percent of its water. China has less water than Canada, but contains forty times as many people.

[0004] Producing water that is sufficiently pure for human consumption remains as a major concern. It is not possible to determine from its appearance whether water is safe to drink. Simple procedures, such as boiling or use of a household charcoal filter, are not sufficient for treating water from an unknown source. Even natural spring water should be tested before determining what type of treatment is needed. Brackish water is water that has up to 2,000-5,000 ppm (parts per million) total dissolved solids (TDS). "Mildly" brackish water has a TDS of about 500-1,000 ppm. Drinking water specifications (IS: 10500- 1191) include identifications of both the recommended and "acceptable" levels: a TDS of 500 ppm (up to 2,000 ppm, if no other source is available); 0.3 ppm iron (up to 1.0 ppm); 1.0 ppm fluoride (up to 1.5 ppm); 0.05 ppm arsenic; 0.03 ppm aluminum (up to 0.2 ppm); with a ph of 6.5-8.5.

[0005] There is no source of water which is considered inherently "safe" for drinking. Deep groundwater is generally of high bacteriological quality (i.e., a low concentration of pathogenic bacteria, such as Campylobacter or the pathogenic protozoa Cryptosporidium and Giardia), but may be rich in dissolved solids, especially carbonates and sulfates of calcium and

magnesium. In comparison, the bacteriological quality of shallow

groundwater varies significantly. Arsenic contamination of shallow

groundwater is a serious problem in some areas, notably Bangladesh and West Bengal in the Ganges Delta. Fluoride is also a potentially dangerous contaminant, possibly leading to Flourosis, a serious bone disease.

[0006] Water which is acquired using a pump or other means should then be purified. There are known processes for water purification. The selection among the processes is based upon the particular contaminants present in a water supply. Ultrafiltration membranes use polymer films with chemically formed microscopic pores that can be used in place of granular media to filter water effectively without coagulants. The type of membrane media determines how much pressure is needed to drive the water through the media and determines the size of micro-organisms which are filtered by the media. In ultrafiltration, ultrastatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained up to about 0.01 microns in size. This removes bacteria and many viruses, but not salts (ions), while water and low molecular weight solutes pass through the membrane.

[0007] A system for purifying water may employ multiple filters in differing stages to successively filter from coarser to finer impurities, from debris and dirt on down to bacteria and even viruses and ions, removing these from the raw water entering the system. Systems purifying other liquids may have related stages and filtering requirements.

[0008] Filters and filtering devices for purifying liquids come in many sizes, shapes and materials. A filter may be disposable or, in order to lower operating costs, increase operating life span and reduce disposal needs, a filter may be cleanable. [0009] During use, a filter may become clogged by the waste it is removing from the water or other liquid being filtered. The type of waste and the manner in which the filter becomes clogged depend on the type of filtration material in the filter, the position of the filter within a multistage system, the quality of the water or other liquid and other factors. A coarse filter, as found in a preliminary stage of filtering or a prefilter, may become clogged with organic matter. A medium filter may become clogged with sand, dirt and other particles. A fine filter may become clogged with silt, dust slurry and other fine particles. Prefiltering is required to prevent downstream filtration components from becoming clogged too quickly.

[0010] Waste may clog pores of a filter, form one or more films or layers on the surface of a filtration medium, or loosely or densely pack the filter, reducing or even stopping the ability of the filter to pass filtered liquid.

Whether a system uses a single filter or multiple stages of filters, replacing or cleaning a filter is performed as maintenance, periodically or when system performance degrades.

[0011] Replacing a filter is typically done by removing a filtration material, element or device, or removing the entire filter, and disposing of the piece. A new, replacement piece substituting for the one disposed is then reinstalled.

[0012] Cleaning a filter is often done by removing a filtration material, element or device and washing, scrubbing, brushing, spraying or otherwise cleaning then rinsing the piece, and followed by reinstalling the piece as if a new, replacement one was being used.

SUMMARY

[0013] A filtering device for liquid has a lower chamber and an upper chamber. The lower chamber has an inlet and a drain. A filter separates the upper chamber into an unfiltered region and a filtered region. The filtered region of the upper chamber is fluidly connected to an outlet.

[0014] A method for using the filtering device includes filtering a liquid and backflushing the filtering device. In filtering a liquid, liquid passes from the inlet into the lower chamber of the filtering device and then in an upward direction to the unfiltered region of the upper chamber of the filtering device. The liquid passes from the unfiltered region of the upper chamber to the filtered region of the upper chamber by filtering through the filter. The liquid passes from the filtered region of the upper chamber out through the outlet as filtered liquid. [0015] In backflushing the filtering device, liquid passes from the outlet into the filtered region and then in a reverse direction through the filter to the unfiltered region of the upper chamber. The liquid passes from the unfiltered region of the upper chamber in a downward direction to the lower chamber and out through the drain along with waste accumulated in the lower chamber and waste dislodged from the filter.

[0016] A housing, having the inlet, the outlet, the upper chamber, the drain, the lower chamber and containing the filter, may be opened. The filter may be removed from the opened housing and be cleaned or replaced.

Inserting the cleaned filter or a replacement filter into the housing and closing the housing completes servicing or replacing the filter. The housing may include a partially detachable or tapered portion with the drain.

[0017] The upper chamber and the housing may be vented by opening a vent to release air or other gas.

[0018] In a preferred embodiment, the filter includes an outer mesh, an inner bag filter mesh and a stiffener stand. The stiffener stand supports the inner bag filter mesh during backflush.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Fig. 1 shows a front, partial cross-sectional view of an embodiment of a filtering device for liquid, including an inlet, an outlet and a drain. [0020] Fig. 2 shows a front view of a single assembly filtering embodiment.

[0021] Fig. 3 shows a front view of a twin assembly filtering embodiment. [0022] Fig. 4 shows a front view of a quad assembly filtering embodiment.

[0023] Fig. 5 shows a front partial cross-section illustrating a lower chamber, upper chamber and filter of a filtering device embodiment with the housing opened.

[0024] Fig. 6a shows an exploded view of components associated with an up-flow bag filter and spring support.

[0025] Fig. 6b is a front perspective view of the spring support of Fig. 6a. [0026] Fig. 7 shows a vertically sliced cross-section view of an up-flow bag filter.

[0027] Fig. 8 shows a horizontally sliced cross-section (upper region) view of the up-flow bag filter of Fig. 7.

[0028] Fig. 9 shows an additional horizontally sliced cross-section view (lower region) of the up-flow bag filter of Fig. 7.

[0029] Fig. 10 is a liquid flow diagram showing a path a liquid takes during filtration.

[0030] Fig. 11 is a liquid flow diagram showing a path a liquid takes during a backflush cycle. DETAILED DESCRIPTION

[0031] Large size water treatment plants may use microfiltration (MF) and/or ultrafiltration membranes (UF) for the removal of suspended matter, colloids and bacteria from the feed water obtained from lakes, rivers, dams aquifers, and other sources. The feed water from such sources commonly contains a significant amount of large suspended matter like leaves, grass, small floating objects, small fishes, larvae, dead insects and pests in addition to coarse sand or soil particles and salt. Microfiltration and/or ultrafiltration systems are meant for removal of suspended matter that are fine particulate matter. Larger size suspended matter may be trapped in a prefilter. For example, a "bag filter" (e.g., woven or non-woven fabric, wire mesh, or other screen) is used as a prefilter. It may be fitted inside a support or otherwise introduced into a liquid flow. Depending on the size of the particles or suspended matter to be trapped, the mesh size of the bag filter media is selected. Pre-filtration helps in reducing the suspended matter load on the membrane filtration system working upstream of the bag filter.

[0032] Conventional bag filters use a down-flow pattern of the flow of liquids. The bag filter collects most of the coarse suspended matter which is forced downwards by the liquid drag force and the downward force acting on the particles due to gravity. For heavier particles, the buoyancy force acting upward is generally smaller than the forces acting downwards. Due to the resultant downward force, the particles hit the filter media with some momentum and get stuck against the filter material (e.g., in the pores of the filter material or between pores.) Slowly, a layer of particles greater than the mesh size of the filter media starts building up on the filter media. As time passes, the thickness of the layer increases. As most of the particulate matter settles in the lowermost part of the bag, the lower part of the bag gets preferentially blocked up or clogged by the suspended particles. With further passage of time, buildup of this layer of trapped particulates continues from bottom to top of the bag filter. As the area of the clogged part of the bag increases, an increased pressure differential must be applied across the bag in order to maintain the desired flow rate of the filtered liquid. [0033] Generally, in measurements taken to establish a benchmark for conventional filters, a clean bag filter was found to work at a pressure differential of 0.05 to 0.1 bar. With clogged filter media pores, this pressure differential increased to 0.4 to 0.5 bar. With further passage of time, it became difficult to maintain the desired flow rate of the liquid for the available pump discharge head. The excessive pressure differential caused a sharp increase in the consumption of pumping power and consequently in the pumping cost. Also, the excessive pressure differential caused excessive wear and tear of the bag. All of these factors lead to increased maintenance requirements for cleaning the bag, by removing the bag from the filter housing and refitting it after cleaning. The downtime of such a plant is high, leading to loss of production.

[0034] From the analysis of the three forces acting on the suspended particles, it was derived that in the liquid up-flow mode, the buoyancy and drag forces work in the upward direction whereas only the force due to gravity acts downwards. Further, by selecting an appropriate upward flow velocity, it may be possible to achieve a condition in which particles move with very low upward velocity or remain suspended in water. In this case, the suspended particles hit the filter media with much less momentum and the blocking of the pores of the filter media is much less as a result.

[0035] A system with liquid up-flow mode was designed and studied to carry out pre -filtration duty for an ultrafiltration plant of one million liters per day (1 MLD) capacity. To keep the bag filter clean for an extended period, a backwash cycle, using a small volume of filtered liquid, was also included in the new designs. A solenoid valve fitted in the bottom

compartment of the housing was operated during the backwash cycle to dump backwash liquid along with the particulate matter removed from the filter media pores. [0036] Incorporation of the new design of bag filter, operating in up-flow mode, in the above mentioned 1 MLD ultrafiltration plant improved the overall working of the plant to a substantial extent. The down-flow mode prevalent in existing bag filter design needed cleaning of the bag filter once in two days. The cleaning was carried out by removing the bag filter from the disassembled housing, cleaning the bag and refitting. In the new design, the cleaning of the bag filter is greatly reduced. The UF system, using the up- flow bag filter as a prefilter along with a backwash cycle for a few seconds every half hour, has provided a non-stop ultrafiltration system that runs for as long as two months without need of removing the bag filter for cleaning and refitting during this time.

[0037] The design of a filtering device described herein is based on the liquid up-flow mode and is a new development over the available bag filter design commonly used as a prefilter device in large-size microfiltration and ultrafiltration plants for purification of water. Liquid up-flow mode helps to a great extent in reducing the clogging of filter media by suspended matter contained in the liquid being filtered. After a preset filtration cycle time, flushing with clear liquid in the down-flow mode automatically backwashes the filter. Backwash liquid along with suspended matter washed off from the filtration material is dumped through a control valve fitted in the bottom part of filter housing. The frequency and duration of the backwash cycle is preset by an electronic controller. The arrangement of liquid up-flow during a filtration cycle and down-flow during a backwash cycle minimizes clogging of the filtration material and eliminates the need for frequent cleaning. Such a system drastically reduces manual intervention for disassembling a filter or filtration device and refitting after cleaning of the filtration material.

[0038] Although embodiments of the filtering device described herein may be used for water purification, it is understood that the principles, structures and methods apply as well to filters and filtering devices used for other liquids or fluids. It is further understood that other filtration media, filters or filter types may be devised for use within the filtering device. The terms "backflush", "backflush cycle", "back flush" and "back wash" are used interchangeably. "Filter media" and "filtration media" are equivalent terms. Various conventions are used herein to describe interrelations among parts as related to fluids and flows. "Fluid connection", "fluid communication", "fluidly connected", "connected", "passing", "flowing", "through", "into", "from" and other terms or forms of terms may indicate fluid can pass or flow between or among parts. "Free flow" is used to indicate a fluid may flow generally without obstruction. A fluid flow through an orifice, along a pathway, around, past or near an object is nonetheless considered "free flow." A fluid may flow through a filter or filtration media while being filtered by the filter or filtration media. A chamber is herein defined as an enclosed space, compartment or cavity. A chamber is defined by a physical material as well as the space this physical material encloses, and that a chamber may be defined by a housing or a portion of a housing. A "filtering device" is an apparatus used for filtering, and a "filter" is a component having filtration media, a filter being part of a filtration device or filtering device, as used herein. An unfiltered region is a region where unfiltered liquid may be present. A filtered region is a region where filtered liquid may be present.

[0039] Fig. 1 shows an embodiment of the filtering device 100 for liquid. Water enters the filtering device through inlet 102 as raw water to be filtered. Water exits the filtering device through outlet 104 as filtered water. Water as filtered water enters through outlet 104 during a backflush. Water exits the filtering device through drain 106 along with waste (not shown) as waste water.

[0040] A housing 108 encloses upper chamber 110 and lower chamber 112 of the filtering device, as well as a filter 124 contained within the upper chamber 110. Air or other gas may be purged from the upper chamber and - li the housing by a vent 114. Optional pressure gauges 116 and 118 measure pressure at the inlet 102 and the outlet 104 respectively. Drain 106 may have a valve 120, an electrically operated solenoid valve in one embodiment, although another type of valve or means for controlling flow through the drain 106 may be used. Each of inlet 102 and outlet 104 may have a valve (not shown). The respective liquid flows of inlet 102, outlet 104 or drain 106 may be directed or controlled by other means not part of this apparatus. An inlet, an outlet or a drain may be a nozzle or have another shape.

[0041] Drain 106 may be at the bottom or narrowest section of a tapered portion 122 of the housing 108, and the diameter or cross-section area of the drain 106 may be less than the diameter or cross-section area of the outlet 104. In one embodiment, a tapered portion 122 of the lower chamber 112 of the housing 108 is tapered (e.g., a conical shape resembling a funnel). In one example, the ratio of the diameter of the drain 106 to the diameter of the outlet 104 is 1:4. The drain diameter may be sized from 10 to 50 mm, while the inlet and the outlet may be sized from 25 to 200 mm. Other sizes and ratios for further embodiments may be devised by a person skilled in the art. During a backflush cycle, the drain 106 being narrower than the outlet 104 causes a higher velocity of water flow at the drain 106 as compared to the velocity of water flow going in through the outlet 104, which creates a highspeed sweeping action along the tapered portion 122 and out the drain 106. This sweeping action during backflush removes sediment and other accumulated waste more rapidly and thoroughly as compared to a system with a drain of a larger relative diameter or cross-section area. The tapered portion 122 of the housing 108, tapering or becoming narrower towards the drain 106, also gathers accumulated waste closer to the drain 106 as compared to a flat-bottomed region near a drain. A further effect is the tapered portion 122 of the housing 108 makes use of gravity pulling accumulated waste downward along the sloping sides of the tapered portion, again resulting in more thorough removal of sediment and other accumulated waste as compared to a flat-bottomed region near a drain.

[0042] In alternative embodiments, single, twin, quad or multiple assemblies may be connected to run in parallel to achieve high flow rates. Fig. 2 shows a single assembly of the filtering device 200, with a housing 210 having an inlet 202, an outlet 204 and a drain 206. The tower portion 230 has a flanged joint 232 for the bottom tapered portion 222. Fig. 3 shows a twin assembly of the filtering device 300, with a housing 310, an inlet 302, a shared outlet 304 and drains 306 and 356. Fig. 4 shows a quad assembly of the filtering device 400, with a housing 410, and inlet 402, a shared outlet 404 and drains 406, 456, 458 and 460. Figs. 2, 3 and 4 indicate the

arrangements of liquid inlets, outlets and drains with interconnections.

Assemblies having two or more filters may share a common or multiple inlets and a common or multiple outlets, through the use of interconnections or passageways between or among functionally similar chambers. In an embodiment with twin assemblies, nearly half the liquid enters the second housing through the first housing side connection. In an embodiment with quad assemblies, the interconnecting passageways may be sized down or reduced for a housing portion further from an inlet or an outlet. Other arrangements, connections and assemblies may be devised by a person skilled in the art. The apparatus is scalable in dimensions and number of assemblies.

[0043] Fig. 5 shows an embodiment of the lower chamber 512, the upper chamber 510 and a filter 600 for the filtering device, although other types of filtration materials, construction methods and structures may be used.

Housing 508 is shown opened. Other means or locations for opening the housing, such as by partially or completely removable or detachable pieces, or an access port or door may be devised. [0044] Filter 600, contained within the upper chamber 510, divides the upper chamber 510 into an unfiltered region 528 and a filtered region 526. Filter 600, in this embodiment, has an outer mesh 602, and an inner bag filter 604 supported on a stiffener stand 606. The outer mesh 602 is of a coarser filtration or pore size than the inner bag filter 604. For example, the inner bag filter 604 may be a mesh of a 25 to 800 μm size, while the outer mesh 602 may have 10 to 30 mesh wires per centimeter or perforations of a 2 to 10 mm size. Mesh spacing, density or size and perforation or pore size of a filter or filter media are commonly known as the characteristic pore size of the filter or filter media, in contrast with a filter bed made of sand or other granular material, which does not have a characteristic pore size.

[0045] Fig. 6a depicts the assembly components relating to the filter 600. Stiffener stand 606 fits inside inner bag filter 604. Inner bag filter 604 fits inside the outer mesh 602. Compression spring 608 fits below the assembled outer mesh 602, inner bag filter 604 and stiffener stand 606.

[0046] In one embodiment, the parts making up the filtering device are: filter housing 108, 210, 310 or 410, as in Fig. 1, 2, 3 or 4, outer mesh 602, inner bag filter 604, stiffener stand 606, a sealing gasket (not shown), compression spring 608, a clamp (not shown, an alternative replacement for the bottom flanged joint) and solenoid valve 120 as in Fig. 1. Other housings or means of fastening housing sections together may be devised.

[0047] The assembly procedure for the up-flow bag filter is as follows:

[0048] The stiffener stand 606 is inserted in the inner bag filter 604, to keep the bag fabric or wire mesh "open". The inner bag filter 604 along with the stiffener stand 606 is inserted into the outer mesh 602. The outer mesh 602 containing the inner bag filter 604 and the stiffener stand 606 is inserted into the tower portion of the housing and seated against a ring inside the tower portion 210 of the housing. The compression spring 608 is placed in position to bias a seal between the inner surface of the bag and the spaces between the housing and the outer mesh 602. The tapered portion 222 of the housing 210 is then joined to the tower portion 230 of the housing 210 either by a flanged joint 232 or by a clamping assembly (not shown).

[0049] The stiffener stand 606 has two upright loops 612 and 614 and a flat ring 616 or washer as a base. The stiffener stand 606 supports the inner bag filter 604 by keeping the inner bag filter 604 partly extended, and during backflush the stiffener stand 606 prevents the inner bag filter 604 from collapsing or turning inside out. Other stiffener stands may be devised by a person skilled in the art, in keeping with the function of providing support for the inner bag filter 604.

[0050] During filtering, the inner bag filter 604 may stretch or inflate slightly. The outer mesh 602 limits the inflation or stretching of the inner bag filter 604. Thus, with the inner bag filter 604 deployed between the stiffener stand 606 and the outer mesh 602, the inner bag filter 604 has support during fluid flow in either a filtration direction or a reverse direction.

[0051] A sealing gasket (not shown) may be placed over the stiffener stand 606 and seated at the flat ring 616 of the stiffener stand 606 prior to inserting the stiffener stand 606 into the inner bag filter 604. Alternatively, a sealing gasket may be placed over the inner bag filter 604 after the inner bag filter 604 is placed onto the stiffener stand 606, prior to inserting the inner bag filter 604 and stiffener stand 606 into the outer mesh 602. Other means of providing a seal may be employed. [0052] In Fig. 6b, an embodiment of the compression spring 608, inverted with respect to the depiction in Fig. 6a, is shown in perspective view as compression spring 610. Compression spring 608 has a flat ring or washer 618 or 620 at the top, to press the filter into the tower portion 230 of the housing 210. At the bottom of the compression spring 608 or upside down compression spring 610, a spring 622 or 624 seats against the tapered portion of the housing. Rods 626 or 628 between the spring 622 or 624 and the washer 618 or 620 transfer force from the compression of the spring 622 or 624 to the washer 618 or 620. Closing the housing 210 by assembling the tapered portion 222 to the tower portion 230 compresses the spring 622 or 624, which then biases the base of the filter 600 so that the filter 600 seals in the housing 210 and remains in place. Fasteners (not shown) may secure the filter components or the housing. Although bolts, screws or a clamp may be used, a person skilled in the art may devise other means of securing. Fluid flows freely around or past the spring 622 or 624 and the rods 626 or 628 of the compression spring 608 or 610, so that the compression spring 608 or 610 does not obstruct fluid flow. [0053] Referring to Figs. 7, 8 and 9 a vertically sliced cross-section view and two horizontally sliced cross-section views click save of a preferred embodiment of a filter 600 are shown. An inner bag filter 604, supported on a stiffener stand 606, provides filtration. An outer mesh 602, of a coarser mesh size than the inner bag filter 604, prevents the inner bag filter 604 from inflating due to water flow from the inside of the inner bag filter 604 during filtration. In a complementary manner, the stiffener stand 606 prevents the inner bag filter 604 from collapsing due to water flow from the outside of the inner bag filter 604 during backflush. Water being filtered moves from an unfiltered region 708 through the filtration materials in a forward or filtration direction 712 into a filtered region 710. Whereas in the filter 600 liquid flows in a filtration direction 712 past the stiffener stand 606, through the fabric or mesh of the inner bag filter 604 and through the perforations in the outer mesh 602, in other filters the water may pass through additional layers, or only one layer, or other materials. In other filter designs, the water may flow in another direction. Fluid flows freely around or past the stiffener stand 606, so that the stiffener stand 606, when used, does not obstruct fluid flow.

[0054] In a backflush cycle, filtered water moves from the filtered region 710 in a reverse direction 714 through the filtration materials to the unfiltered region 708. Backflushing dislodges waste from the filtration materials. Dislodged waste may then be removed from the filtration materials and the filter by the flow of the water in a backflush cycle.

[0055] A person skilled in the art may devise a filter having a forward or filtration direction or a reverse direction differing from the embodiment shown in Figs. 6-9, such as by filtering from outside to inside or from top to bottom. Another filter may be used in the filtering device by suitably arranging the chambers, fluid communications, pathways and other construction details without departing from the scope of the claims. [0056] There are two main modes of operation for the filtering device, along with additional modes in preferred embodiments. The two main modes of operation are filtration or filtering, and a backflush cycle or backflushing. Filtering provides filtered water, while backflushing is a way of cleaning the filtering device, restoring operation efficiency for filtering and extending the operating lifespan of the filtering device.

[0057] During filtration, water or other liquid flows along the path through the filtering device 1000 shown in Fig. 10 as a liquid flow diagram for filtering. In a preferred embodiment of the filtering device 1000 during filtration, water or other liquid to be filtered flows along the filtration path 1002. Water enters through the inlet 1004 as raw water and flows into the lower chamber 1006. Water flows along the filtration path 1002 from the lower chamber 1006 in an upward direction 1022 to the unfiltered region 1008 of the upper chamber 1010. Large particulate matter, debris or other waste may settle out of the water in the unfiltered region 1008 of the upper chamber 1010 or the water in the lower chamber 1006. This waste and other settled matter may accumulate in the lower chamber 1006, to be removed during a backflush cycle. Continuing along filtration path 1002, water flows from the unfiltered region 1008 through the filter 1012 in a filtration direction 1014 into the filtered region 1016 and becomes filtered water, leaving waste behind in the unfiltered region 1008. Water flows along filtration path 1012 from the filtered region 1016 to the outlet 1020 where it is available as filtered water.

[0058] In a preferred embodiment, as shown in Fig. 1, pressure gauges 116 and 118 measure the water pressure at the inlet 102 and the outlet 104 respectively. The difference in the pressure gauge readings indicates the pressure differential across the filter 124 such as a bag filter assembly or other filter as used in the filtering device 100. Differential pressure for filtration has been observed in a range of 0.01 to 0.07 Mpa, depending on the load of suspended matter and volumetric flow rate of the liquid. Other ranges for other conditions or other filters may apply.

[0059] With reference to Fig. 5 or Fig. 10, waste left behind in the unfiltered region 528 or 1008 may accumulate on the surface of filter 600 or 1012 as a film or layer, occupy pores in the filter 600 or 1012, remain in suspension in the water occupying the unfiltered region 528 or 1008 or settle and accumulate in the lower chamber 512 or 1006. Other mechanisms whereby a filter filters a liquid may apply. [0060] During a backflush cycle, water or other liquid flows along the path through the filtering device 1100 shown in Fig. 11 as a liquid flow diagram for backflushing. In a preferred embodiment of the filtering device 1100 during a backflush cycle, water or other liquid flows along the backflush path 1102. Filtered water may be used for backflushing, for example of a 5 to 10 second duration once every half an hour. Water enters through the outlet 1020 and flows into the filtered region 1016. Continuing along backflush path 1102, water flows from the filtered region 1016 through the filter 1012 in a reverse direction 1114 into the unfiltered region 1008 of the upper chamber 1110. Waste may be dislodged from a filtration material of the filter 1012 or from elsewhere along the backflush path 1102 and become entrained in the water flow. Water flows along the backflush path 1102 from the unfiltered region 1008 of the upper chamber 1010 in a downward direction 1122 to the lower chamber 1006. From the lower chamber 1006, water flows out through the drain 1124. Waste (not shown) accumulated in the lower chamber 1006 or entrained in the water flow is backflushed out by and with the water flowing out through the drain 1124.

[0061] In a preferred embodiment, as shown in Fig. 11, a valve 1126 opens and closes the drain 1124 at the bottom of a tapered portion 1128 of the lower chamber 1006 and housing 1130. The valve 1126 may be electrically operated by a solenoid. The solenoid may be triggered, and the valve at the drain opened, by a difference between an inlet pressure and an outlet pressure. This pressure difference, as determined by inlet and outlet pressure gauges, indicates the pressure differential across the filter and can be compared to a specified or calculated value to indicate when the filter has become clogged and a backflush is needed. Pressure values may be read manually, or the pressure values may be read as data into an electronic controller. In this manner, a backflush may be initiated manually or automatically, through the use of a controller or a timer. Backflush may be initiated manually, for example if there is an interruption in flow or if the manually read pressure values differ by more than a specified amount.

Backflush may be initiated automatically by a timer. Backflush may be initiated automatically by a controller if the pressure difference, indicating pressure differential across the filter, exceeds a preset pressure. During a backwash cycle, the filtered liquid enters the housing 1130 through the outlet 1020 and passes to the filtered region 1016 of the upper chamber 1010 from the outlet 1020, then flows in a reverse direction 1014 through the filter media. Particles and other waste are disengaged from the filter media, flow to the lower chamber 1006, and are dumped down out of the tapered portion 1128 of the housing 1130 along with the backwash liquid.

[0062] Additional modes or steps of operation in a preferred embodiment include purging, servicing the filter and replacing the filter. Any or all of these modes or steps may improve or restore operating efficiency or prolong the operating lifespan of the filtering device.

[0063] During operation of the filtering device, air or other gas may accumulate in the upper chamber. Purging, by opening the vent 114, shown in Fig. 1, releases air or other gas from the upper chamber 110 or the housing 108. A gas purge vent may be manually or automatically operated. A person skilled in the art may substitute another vent.

[0064] When servicing the filter, the housing 508 is opened, as shown in Fig. 5. The housing 508 contains the filter 600. After the filter 600 is removed from the housing 508, the filter 600 is cleaned by washing, application of chemicals, blowing with air or other gas, tapping, shaking, rinsing or other suitable means. After cleaning, the filter is inserted into the housing 508 and the housing 508 is closed.

[0065] When replacing the filter, the housing 508 is opened, as shown in Fig.5. After the filter 600 is removed from the housing 508, a replacement filter is inserted into the housing 508 and the housing 508 is closed.

[0066] Thus, as described and shown herein, the filtering device 100 provides an apparatus and a method for purification of water or other liquid. The filtering device 100 has modes of operation for filtration, backflushing, purging, servicing the filter or replacing the filter.

[0067] The newly developed filtration design, with up-flow filtration, can handle liquids having a high content of suspended solids, including small fishes, fish eggs, grass, leaves, coarse sand or soil particles, larvae and pests as often encountered in a filtration system applied to lake, river and other water sources. Loading on the filter media from suspended matter is much reduced due to the use of an up-flow mode in the new design, and clogging of the filter media is significantly less. The filtering device 100 needs

considerably less pressure differential across the filter media for achieving the desired flow rate over a long period of time and consequently gives appreciable savings in pumping costs. Filter media may extend to double the normal lifespan as the filter media is subjected to less pressure differential for a given flow rate. Operation for long periods of time without manual intervention is possible since the interval until the filtering device is opened for removal, cleaning and replacement of the filtration media is greatly lengthened. This decreases costs for manual labor as well as downtime.

[0068] When using the filtering device 100 as a prefilter for a large-size water filtration plant using microfiltration and ultrafiltration membranes, the loading of suspended material on the microfiltration and ultrafiltration membrane surfaces can be significantly reduced. Further reduction in the suspended matter loading on the membranes can be achieved by using a finer pore size for the filter media in the filtering device when used as a prefilter. Therefore, frequency and duration of chemical cleaning cycles for the microfiltration and ultrafiltration membranes will be reduced. Savings in chemical cleaning costs are achieved, and the life of microfiltration and ultrafiltration membranes can be significantly increased, thereby providing significant savings in membrane replacement costs. Overall advantages of the filtering device 100 are: significant reduction in the downtime of a filtration system; lower filtration loads on microfiltration and ultrafiltration systems downstream of the filtering device; decreased chemical cleaning requirements for microfiltration and ultrafiltration membrane systems and significant increase in the useful life of the membranes in these systems.

Claims

What is claimed is: 1. A filtering device for filtering liquid comprising:

an inlet;

a lower chamber fhiidly connected to the inlet wherein liquid is able to flow from the inlet into the lower chamber;

a drain at the bottom of the lower chamber, the drain positioned to release accumulated waste from the lower chamber during backflush;

an upper chamber above the lower chamber;

a filter having a characteristic pore size positioned in the upper chamber and separating the upper chamber into an unfiltered region which is in free flow communication with the lower chamber and a filtered region separated from the unfiltered region by the filter; and

an outlet from the filtered region.

2. The filtering device of claim 1 further including:

a valve regulating discharge from the drain.

3. The filtering device of claim 2 further including:

a solenoid configured to open and close said valve.

4. The filtering device of claim 1 further including:

a gas purge vent on the upper chamber.

5. The filtering device of claim 1 wherein the filter includes:

an outer mesh;

an inner bag filter inside the outer mesh; and

a stiffener stand inside the inner bag filter; wherein

the stiffener stand supports the inner bag filter during backflush.

6. The filtering device of claim 1 wherein:

the lower chamber tapers towards the drain.

7. The filtering device of claim 1 wherein:

the filtering device has a detachment mechanism providing access to the filter.

8. The filtering device of claim 1 wherein:

a drain diameter is less than an outlet diameter.

9. A filtering device for liquid comprising:

a housing;

an inlet to the housing;

an outlet from the housing;

a drain from the housing; and

a filter within the housing dividing the interior of the housing into an unfiltered region and a filtered region, the filter having a characteristic pore size; wherein

the filter is positioned within the housing such that a liquid entering the inlet flows into the unfiltered region, flows in an upward direction through the filter into the filtered region and flows out through the outlet as a filtered liquid; and wherein

filtered liquid entering the outlet during a backflush flows into the filtered region, flows through the filter in a reverse direction into the unfiltered region, then backflush liquid flows in a downward direction out through the drain along with particles dislodged from the filter.

10. The filtering device of claim 9 wherein:

the unfiltered region includes an unfiltered region of an upper chamber, the filter being within the upper chamber; and

the unfiltered region further includes a lower chamber, the lower chamber being fluidly connected to the inlet and having the drain.

11. The filtering device of claim 9 wherein:

the housing has a vent, the vent being openable to purge a gas from the upper chamber.

12. The filtering device of claim 9 wherein the filter includes: an inner bag filter; and

a stiffener stand within the inner bag filter, the stiffener stand keeping the inner bag filter at least partially extended during a backflush.

13. The filtering device of claim 12 wherein the filter further includes:

an outer mesh in which the inner bag filter and the stiffener stand are disposed.

14. The filtering device of claim 9 wherein:

the drain has a valve controlled by a solenoid.

15. The filtering device of claim 9 wherein:

the housing includes a tower portion enclosing the filter; and the housing further includes a tapered portion having the drain, the tapered portion being at least partially removable from the tower portion.

16. The filtering device of claim 15 wherein:

the filter is removable from the housing when the housing is opened by at least partially removing the tapered portion from the tower portion.

17. The filtering device of claim 15 wherein:

the drain is at a bottom of the tapered portion, the bottom of the tapered portion being a narrowest section of the tapered portion; and

the narrowest section of the tapered portion has a smaller cross-section area than a cross-section area of the outlet.

18. A method for using a filtering device comprising:

(a) filtering a liquid by passing the liquid through a filter having characteristically sized pores in a filter flow direction from an unfiltered region into a filtered region in the filtering device, wherein said filter flow direction is at least in part against a force of gravity;

(b) passing filtered liquid through an outlet from the filtered region; (c) backflushing the filter at a selected time by passing filtered liquid at least in part in a direction of gravitational force back through the filter; and

(d) passing backflush liquid at least in part in a direction of

gravitational force from the filter out through a drain.

19. The method for using the filtering device of claim 18 further comprising: settling particles from the liquid by passing the liquid through a lower chamber; and

the lower chamber having an interior included in the unfiltered region.

20. The method for using the filtering device of claim 19 further comprising: backflushing the particles settled from the liquid by passing backflush liquid through the lower chamber and out the drain; and

the lower chamber having the drain.

21. The method for using the filtering device of claim 18 further comprising: purging a gas by opening a gas purge vent.

22. The method for using a filtering device of claim 18 further comprising: opening the filtering device;

removing the filter from the filtering device;

inserting a replacement filter into the filtering device; and

closing the filtering device.

23. The method for using a filtering device of claim 18 wherein:

in step (c), backflushing the filter includes directing liquid from the outlet through the filter.

24. The method of claim 23 wherein:

a first velocity of the liquid passing out through the drain is greater than a second velocity of the liquid passing through the outlet during backflushing.

25. The method for using a filtering device of claim 18 wherein:

the liquid passing through the drain is controlled by a solenoid valve.