A backflush filter system

Abstract

A backflush filter device (1) comprising a pressurised storage tank (2) having a top end (12) and a bottom end (14), a hollow screen (3) having a plurality of apertures (5) on its surface and configured to envelope the storage tank (2), and a backflush reservoir (4) configured to accommodate a liquid and which is in fluid communication with the bottom end (14) of the storage tank (2) via a backflush valve (6), wherein the liquid in the backflush reservoir (4) is forced upwards under pressure from air released from the pressurised storage tank (2) and exiting through the apertures (5) of the screen (3).

Description

[0001] Title

[0002] A backflush filter system

[0003] Field of the Invention

[0004] The invention relates to a backflush filter system. Specifically, the invention relates to a backflush filter system for use in vacuum tankers that are deployed to clear blocked pipes, sewage systems, recover the water fraction of liquid waste, and the like.

[0005] Background to the Invention

[0006] In various stationary liquid filtering or screening processes, regular screen cleaning is performed. An intermittent liquid backflush is used, especially for sand filters. To improve the effect of such a backflush system, it is also well-known to install a blower (or a compressor), enabling the regular backflush to be performed with some continuous mixture of liquid and air.

[0007] Backflushing of such a screen is never seen and / or used on vacuum tankers, likely because a water pump sufficiently powerful to perform a decent backflush flow would be very heavy, bulky, and expensive. Such screens are traditionally cleaned continuously by mechanical scrapers, wipers, or brushes. Usually, the screen is a rotating screen with a stationary wiper or scraper. One disadvantage using a rotating screen is the tendency to churn large fat balls from smaller fat particles, which stay trapped inside the screen. Another disadvantage is the clogging effect caused by the scraper ’’smearing” the fat into the screen mesh. A further disadvantage is that when the debris clogging the screen is scraped off the screen, it first piles up on the scraper, then detaches from the scraper, and, because it is not being transferred away from the screen, the debris is sucked back onto the screen in the form of a filter cake to clog the screen again. For any fully submerged screen, the pressure drop across the screen might be reaching 0.5 bar, which creates a suction at the surface of the screen, sucking softer particles through the screen, and creates a very compact, closed structure of the filter cake. This means that either the vacuum tank or filter needs to be shut down and manually cleaned, causing loss of revenue.

[0008] KR100977059 describes a wastewater purification apparatus which may be transportable by a vehicle and may comprise a filter, whereby the filter may be cleaned by a filter cleaning device which may intermittently expelled outward by a high pressure air supply in an oscillation type reverse-flow filtration tank. Chinese Patent No. CN 104623952 discloses a sewage treatment vehicle filtration method and describes the use of water under pressure to clean out the vehicle filtration system.

[0009] It is an object of the present invention to overcome at least one of the above-mentioned problems.

[0010] Summary of the Invention

[0011] The main aspect of the invention is backflush filter device and system that cleans a screen or filter of debris from wastewater, polluted water, seawater, and the like. The claimed device uses an intermittent explosive blast of grey water through the screen. The blast of grey water under pressure lasts for 3 seconds or less, and it is repeated every 3 to 50 minutes. The stages of the cleaning use water, water and air, and air. A single stroke water pump with pressurised air is used to generate the blast. The method is used in wastewater, sewage cleaning trucks, seawater filtering systems, and the like. There is also a piston within the tank of the cleaning truck that allows the grey water to be recycled within the truck. The piston comprises a moveable partition wall having a seal or stop that separates clean water in a front compartment from the extracted waste in a rear compartment, while the grey water is recycled, thereby allowing the screen or filter to be cleaned repeatedly while the truck removes tons of waste. It means that the truck does not have to go back to base to offload its cargo of waste until such time that the grey water is no longer recyclable. The piston also houses the screen or filter. The piston is one continuous piece.

[0012] There is provided, as set out in the appended claims, a backflush filter device (1) comprising a pressurised storage tank (2) having a top end (12) and a bottom end (14), a hollow screen (3) having a plurality of apertures (5) on its surface and enveloping the storage tank (2), and a backflush reservoir (4) configured to accommodate a liquid and which is in fluid communication with the bottom end (14) of the storage tank (2) via a backflush valve (6), wherein the liquid in the backflush reservoir (4) is forced upwards under pressure from air released from the pressurised storage tank (2) and exiting through the apertures (5) of the screen (3). In one aspect, the backflush filter device (1) further comprises a pump (8) configured to take liquid from the backflush reservoir (4) and transfer the liquid to a holding tank for further processing.

[0013] In one aspect, the storage tank (2) and the screen (3) are cylindrical.

[0014] In one aspect, the screen (3) comprises an outward facing surface (13) and an inward facing surface (15), and wherein the inward facing surface (15) faces the storage tank (2).

[0015] In one aspect, the screen (3) further comprises at least one spacer attached to the inward facing surface (15) at one end and to the storage tank (2) at the other end.

[0016] In one aspect, the pressurised storage tank (2) contains air under pressure at between 1 .5-20 bar.

[0017] In one aspect, the air is expelled from the storage tank (2) for between 10 to 3000 ms and repeated every 2 to 120 minutes.

[0018] In one aspect, the storage tank (2) is partly filled with a water-based liquid or an oil-based liquid, and stored under pressure. This utilises the dissolved air flotation system which clarifies wastewater or oil-based liquids by removal of suspended solids, oils, greases, and the like. This is achieved by dissolving air in the wastewater or oil-based liquids under pressure and then releasing the air at atmospheric pressure in a flotation tank.

[0019] In one aspect, the water-based liquid is selected from greywater, wastewater, seawater, polluted water, contaminated water, or any water-based liquid that is contaminated and requires purification. In one aspect, the liquid selected is greywater.

[0020] In one aspect, the oil-based liquid is selected from crude oil, refined oil, heavy fuel oil, waste cooking oil, cooking oil, mineral oil, motor oil, oil paints, or any commercial or otherwise liquid with an oil base that is contaminated and requires purification.

[0021] In one aspect, there is provided a method of cleaning a screen (3) using the backflush filter device (1) described above, the method comprising the steps of: (a) releasing pressurised air from the storage tank (2) via the backflush valve (6) to create a backflush event to clean the screen (3); and (b) recharging the storage tank (2) with air to create another backflush event. The backflush event in (a) lasts for a few seconds while the even in (b) is likely to last for a minute or more.

[0022] In one aspect, the pressurised air is released from the storage tank (2) for between about 10 ms to about 3000 ms at between 1-10 psi, and repeated every 2 to 120 minutes.

[0023] In one aspect, the backflush reservoir (4) is recharged with water entering through the screen (3).

[0024] In one aspect, a pump (8) transfers an oil-based liquid or a water-based liquid from the backflush reservoir (4) through a liquid transfer valve (9). In one aspect, the pump (8) is submersible or non-submersible.

[0025] In one aspect, the storage tank (2) is partially filled with the oil-based liquid or the waterbased liquid and stored under pressure. Storing under pressure exploits the dissolved air flotation system.

[0026] In one aspect, the storage tank (2) is depressurised during backflush event.

[0027] In one aspect, the backflush event comprises expulsion of water from the backflush reservoir (4).

[0028] In one aspect, when most of the water in the backflush reservoir (4) is exhausted, the backflush event comprises expulsion of water and air to transfer debris away from the screen (3).

[0029] In one aspect, when the water in the backflush reservoir (4) is exhausted, the backflush event comprises expulsion of air only from the storage tank (2).

[0030] In one aspect, the water-based liquid is selected from greywater, wastewater, seawater, polluted water, contaminated water, or any water-based liquid that is contaminated and requires purification. In one aspect, the liquid selected is greywater.

[0031] In one aspect, the oil-based liquid is selected from crude oil, refined oil, heavy fuel oil, waste cooking oil, cooking oil, mineral oil, motor oil, oil paints, or any commercial or otherwise liquid with an oil base that is contaminated and requires purification.

[0032] As the water in the backflush reservoir is displaced by air, the backflush media is gradually changing from mainly being backflush water into mainly being compressed air. Due to the density of air being way less than the density of water, the backflush effect will gradually be reduced. The density of the debris being backflushed off the screen will be close to the density of water.

[0033] Due to the density of air being way less than the density of water, the buoyancy of the air bubbles subsequently backflushed through the screen will transfer a lot of the debris (which has just been backflushed off the screen surface) upwards towards the surface, far away from the screen, forcing each individual debris into possible new journeys downwards.

[0034] In one aspect, there is provided a piston for use in a wastewater truck, wherein the piston comprises a moveable partition wall having a stop or seal that separates a holding tank into (a) a front compartment adapted to store clean water; and (b) a rear compartment adapted to store extracted waste material and the backflush filter device (1) described above.

[0035] Some of the advantages of the claimed invention include:

[0036] • The absence of any mechanical scraper or wiper, as used in the filters of the prior art devices, will improve the quality of the screened water recycled back into the wastewater or sewage truck.

[0037] • The screen is vented between the inside and the outside. This means that air is allowed in. As the water flow capacity of the pump exceeds the water flow passing through the screen, the water level inside the screen drops, increasing the pressure drop across the screen wall, and thus increasing the water flow through the screen. Over time, the screen gets so clogged (and so the flow of water passing through the screen is so low), that the water level inside the screen drops to a suction port of the pump, and the pump will “catch air” (detectable through hydraulic pressure monitoring), thus triggering a backflush event. Keeping the pressure drop across the screen low, being gravitational head only, the filter cake (debris / clogging) formed outside of the filter will be less compact (that is, more porous or penetrable for a longer time). This also improves the flow of water through the screen and also improves the quality of the screened water.

[0038] • There is no cavitation in the submersible pump when the filter is blocked due to the venting of the screen. • The venting of the inside of the filter provides an option to detect when to perform a backflush, as the monitored hydraulic pressure powering the submersible pump will be dropping significantly as the pump is catching air.

[0039] • The device of the claimed invention can be retrofitted inside any vacuum tank and no additional external piping is needed.

[0040] This invention is significantly limiting the number of moving parts in the screening system, thus reducing maintenance and replacement of parts due to less wear and tear.

[0041] Definitions

[0042] In the specification, the term “backflush” or “backwash” should be understood to mean a process that refers to pumping water backwards through a filters media, sometimes including intermittent use of compressed air during the process. Backflushing is a form of preventive maintenance so that the filter media can be reused.

[0043] In the specification, the term “greywater” or “grey water” should be understood to mean filtered liquid that previously contained debris, domestic wastewater generated in households, office buildings, factories, and the like from streams without faecal contamination.

[0044] In the specification, the term "screen” or “filter” should be understood to mean a series of holes, slits, or perforations in a flat metal or plastic sheeting that can remove particulate matter from a liquid.

[0045] In the specification, the term “liquid” should be understood to mean any liquid, for example, water-based or oil-based liquids.

[0046] In the specification, the term “water-based liquids” should be understood to mean greywater, wastewater, seawater, polluted water, contaminated water, or any liquid that is contaminated and requires purification.

[0047] In the specification, the term “oil-based liquid” should be understood to mean any liquid that has, as its base, a nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic and lipophilic (mixes with other oils). Oils may be animal, vegetable, or petrochemical in origin, and may be volatile or non-volatile. Examples of an oil-based liquid include, but are not limited to, crude oil, refined oil, heavy fuel oil, waste cooking oil, cooking oil, mineral oil, motor oil, oil paints, or any commercial or otherwise liquid with an oil base. Preferably, the oil-based liquid is liquid derived from petrochemicals such as , crude oil, refined oil, and heavy fuel oil.

[0048] In the specification, the term “water-based liquid” should be understood to greywater, wastewater, seawater, polluted water, contaminated water, or any water-based liquid that is contaminated and requires purification.

[0049] Brief Description of the Drawinas

[0050] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-

[0051] Figure 1 illustrates a side view of a backflush filter device of the claimed invention.

[0052] Detailed Description of the Drawinas

[0053] The present invention provides backflush filter device and a method of using the same. Utilising compressed air, not directly as a backflush media, but a rapid displacement (single stroke) pump that immediately activates and maintains the pressure for short periods of time to displace an accumulated charge of screened backflush water. This backflush water will instantly accelerate out through any screen or filter aperture. The instantaneous impact or shock of the backflush water through the filter is crucial to clear all areas of the filter. The water within a small collection tank for screened water is used as the primary backflush media.

[0054] Referring now to the figures, where Figure 1 illustrates a general embodiment of a backflush filter device of the present invention. Specifically, Figure 1 illustrates a side view of a backflush filter device of the present invention, and is generally referred to by reference numeral 1. The backflush filter device 1 is designed as a stationary vertical cylindrical screen, filtering water inwards from the outside. The backflush filter device 1 comprises a storage tank 2 substantially enveloped by a screen 3. The screen 3 has an upper zone 16, a lower zone 18, an outward facing surface 13, and an inward facing surface 15 (facing the storage tank 2). The screen 3 typically has a mesh configuration comprising a plurality of apertures 5 arranged in a pattern and which envelopes the storage tank 2. The outward facing surface 13 of the screen 3 is typically smooth. The storage tank 2 comprises a housing 11 having a top end 12 and a bottom end 14, wherein the top end 12 sits proud of a top surface 10 of the liquid being filtered in, for example, a holding tank. The storage tank 2 is configured to hold pressurised air. The bottom end 14 is connected to a backflush kick-off or rapidly opening valve 6 that is adapted to release the pressurised air from the storage tank 2 into the backflush reservoir 4. The rapidly opening valve 6 ensures the explosive nature of the release of the pressurised air from the storage tank 2. The backflush reservoir 4 is in fluid communication with a pump 8 and is continuously being refilled by screened water. The pump 8 is typically a hydraulically powered pump, which intakes liquid from the backflush reservoir 4, and the pump 8 transfers the filtered or screened liquid through a liquid transfer valve 9 for further processing / cleaning. The pump 8 can be a submersible pump or a non-submersible pump.

[0055] The backflush valve 6 releases pressurised air from the storage tank 2, which is expelled with force into the backflush reservoir 4, charging the liquid therein and forcing the liquid up and out through the apertures 5 of the screen 3.

[0056] Only the water in the backflush reservoir 4, which lies upstream of the liquid transfer valve 9, that is used for the backflush event. Having passed through the liquid transfer valve 9, the water cannot be used for a further backflush event, but is reused by a jetting pump on the vacuum truck for jetting / cleaning, for example, sewer pipes.

[0057] For the backflush filter device 1 described herein to remove any debris or deposits clinging to the outward facing surface 13 of the screen 3, a fast flow rate of expelled air from the storage tank 2 and liquid from the backflush reservoir 4 must be provided to achieve the desired cleaning effect. However, as it is only the outward surface 13 of the screen 3 that requires cleaning, the fast flow of liquid and liquid mixed with air is not needed for a long period of time. Ideally, the debris or deposits (also called filter cake) are transferred away by the explosive nature of the expelled air and liquid from the backflush reservoir 4, and do not return back onto the outward facing surface 13 from which they have just been removed. In use on any truck-mounted vacuum tanker, the chassis is equipped with a pneumatic system for servicing brakes, air suspension, and various other pneumatic consumers. This system is equipped with an option for servicing the bodyworks, such as a vacuum tanker body (the holding tank), with pneumatic power. The pressurised air in the storage tank 2 is accumulated over time (a gradual build up via, for example, the pneumatic systems of a truck on which the holding tank is secured) and so it is possible to intermittently expel the air via the fast-acting backflush valve 6, to release all this accumulated pneumatic or pressurised energy within a very short time frame, releasing an immediate powerful impact. As the fast flow rate is applied for only a short period of time, it does not necessarily imply that high power must be supplied continuously to achieve this.

[0058] The air in the storage tank 2 is typically stored at 2- 10 bar (29- 145 psi) . The air is expelled from the storage tank 2 at 1-10 bar (14.5-145 psi). The time that the air is expelled from the storage tank 2 for between 10 ms to 3000 ms and the expelling of air is repeated every 2 minutes to 120 minutes.

[0059] During the fast discharge of air and water through the screen 3, the charge of backflush liquid in the backflush reservoir 4 is gradually displaced by compressed air, and the air pressure in this (now increasing) air volume will be dropping accordingly. Once most of the liquid has been expelled from the backflush reservoir 4, the backflush process will still go on, first as a powerful liquid / air mix, but gradually turning into a fast air flow at a rapidly dropping pressure. This gradual reduction in pressure in the storage tank 2 causes a gradually reduced cleaning effect. Lower density backflush media (for example, air) will escape through the screen 3 faster than backflush media with higher density (for example, water). The main effect of the flow of air is no longer to clean the screen 3, but to transfer or keep debris away from the outward surface 13 of the screen 3. Large air bubbles escaping off the screen 3 following a backflush event will transfer most debris or deposits (such as fatty deposits, dirt, etc.) off the screen 3 and up towards the surface 10 of the liquid in the holding tank. Small and micro air bubbles embedded in the debris will provide buoyancy, making the debris remain at the surface 10 of the liquid in the holding tank for a longer time.

[0060] When the liquid being recovered enters into the holding tank (usually under a vacuum), an immediate gravitational separation of the debris within the liquid will take place. With the floating debris or sludge fraction rising towards the surface 10 of the cleaning water in the holding tank, the upper zone 16 of the screen 3 will soon get blocked by debris. In a zone known as a settling solid sediments fraction zone of the holding tank, which is where the lower zone 18 of the screen 3 is located, the screen 3 will soon get blocked by debris as well. The screening process will occur in the zone between upper zone 16 and the lower zone 18, which will remain clear of debris. The device 1 of the claimed invention is typically housed in a vacuum (holding) tank used to take in and clean liquids such as wastewater, sewage, seawater, and the like. The vacuum tank typically comprises a piston that traverses the length of the tank. The piston within the vacuum tank allows the filtered liquid (also known as grey water) to be recycled within the vacuum tank. Within the piston is a moveable partition wall that has a seal or stop that creates two compartments, a rear compartment that allows the retrieved waste to be compartmentalised or isolated, and a front compartment that stores clean water used to flush the screen 3 and keeps the clean water separated from the waste in the rear compartment. This arrangement improves the flexibility / versatility of the vacuum tank.

[0061] The absence of any mechanical scraper / wiper will improve the quality of the screened water. Especially regarding the fat fraction, which tends to be smeared into the screen if cleaned by mechanical scrapers.

[0062] To withstand the repeating backpressure impact from the power of the backflush process, the screen 3 is structurally sturdy, strong, and rigid. The typical shape of the screen 3 is a vertical cylinder. The typical shape for the storage tank 2 for pneumatic storage is a cylinder. Because of the rather limited space available inside a vacuum tank of a vacuum tanker, it will be an advantage to install the storage tank 2 inside the hollow cylindrical screen 3. To protect the screen 3 from mechanically being squeezed out of shape, a plurality of spacers are positioned on the inner surface 15 of the screen 3, which support the screen 3 against the storage tank 2.

[0063] The main backflush valve 6 must open very rapidly to achieve the powerful backflush blast required to clear the screen 3 of debris.

[0064] In some instances, backflushed water can enterthe storage tank 2 before repressurising, and if the pressurised air is fed into the storage tank 2, the saturated pressurised air and water can, when expelled into the backflush reservoir 4, cause a dissolved air flotation effect on the smaller clogging particles on the screen 3. This improves the gravitational separation process upstream of the screen 3.

[0065] One of the advantages of the backflush filter device 1 of the claimed invention is that it can be retrofitted to existing contaminated liquid extraction systems, and one can take a whole piston comprising the screen 3, the backflush system described herein and further cleaning (processing) stages, and retrofit this inside the tank of a non-recycling-vacuum- tanker, thus turning a non-recycling-vacuum-tanker into a recycling-vacuum-tanker.

[0066] In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms “include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

[0067] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims1. A backflush filter device (1) comprising a pressurised storage tank (2) having a top end (12) and a bottom end (14), a hollow screen (3) having a plurality of apertures (5) on its surface and enveloping the storage tank (2), and a backflush reservoir (4) configured to accommodate a liquid and which is in fluid communication with the bottom end (14) of the storage tank (2) via a backflush valve (6), wherein the liquid in the backflush reservoir (4) is forced upwards under pressure from air released from the pressurised storage tank (2) and exiting through the apertures (5) of the screen (3).

2. The backflush filter device (1) of Claim 1 , further comprising a pump (8) configured to take liquid from the backflush reservoir (4) and transfer the liquid to a holding tank for further processing.

3. The backflush filter device (1) of any one of the preceding claims, wherein the screen (3) comprises an outward facing surface (13) and an inward facing surface (15), and wherein the inward facing surface (15) faces the storage tank (2).

4. The backflush filter device (1) of any one of the preceding claims, wherein the screen (3) further comprises at least one spacer attached to the inward facing surface (15) at one end and to the storage tank (2) at the other end.

5. The backflush filter device (1) of any one of the preceding claims, wherein the pressurised storage tank (2) contains air under pressure at between 1 .5-20 bar.

6. The backflush filter device (1) of any one of the preceding claims, wherein the air is expelled from the storage tank (2) for between 10 to 3000 ms and repeated every 2 to 120 minutes.

7. The backflush filter device (1) of any one of the preceding claims, wherein the storage tank (2) is partly filled with a water-based liquid or an oil-based liquid, and stored under pressure.

8. The backflush filter device (1) according to Claim 7, wherein the oil-based liquid is selected from crude oil, refined oil, heavy fuel oil, waste cooking oil, cooking oil, mineral oil, motor oil, oil paints, or any commercial or otherwise liquid with an oil base that is contaminated and requires purification.

9. The backflush filter device (1) according to Claim 7 or Claim 8, wherein the waterbased liquid is selected from greywater, wastewater, seawater, polluted water, contaminated water, or any water-based liquid that is contaminated and requires purification.

10. The backflush filter device (1) of any one of the preceding claims, wherein the liquid selected is greywater.

11. The backflush filter device (1) of any one of the preceding claims, wherein the storage tank (2) and the hollow screen (3) are cylindrical.

12. A method of cleaning a screen (3) using the backflush filter device (1) of Claim 1 , the method comprising the steps of: (a) releasing pressurised air from the storage tank (2) via the backflush valve (6) to create a backflush event to clean the screen (3); and (b) recharging the storage tank (2) with air to create another backflush event.

13. The method of Claim 12, wherein the pressurised air is released from the storage tank (2) for between about 10 ms to about 3000 ms at between 1-10 psi, and repeated every 2 to 120 minutes.

14. The method of Claim 12 or Claim 13, wherein the backflush reservoir (4) is recharged with water entering through the screen (3).

15. The method of any one of Claims 12 to 14, wherein a pump (8) transfers an oilbased liquid or a water-based liquid from the backflush reservoir (4) through a liquid transfer valve (9).

16. The method of any one of Claims 12 to 15, wherein the pump (8) is submersible or non-submersible.

17. The method of any one of Claims 12 to 16, wherein the storage tank (2) is partially filled with the oil-based liquid or the water-based liquid and stored under pressure.

18. The method of any one of the Claims 12 to 16, wherein the storage tank (2) is depressurised during backflush event.

19. The method according to Claim 18, wherein the backflush event comprises expulsion of water from the backflush reservoir (4).

20. The method according to Claim 18 or Claim 19, wherein when most of the water in the backflush reservoir (4) is exhausted, the backflush event comprises expulsion of water and air to transfer debris away from the screen (3).

21. The method according to any one of Claims 12 to 20, wherein the water-based liquid is selected from greywater, wastewater, seawater, polluted water, contaminated water, or any liquid that is contaminated and requires purification.

22. The method according to any one of Claims 12 to 20, wherein the oil-based liquid is selected from crude oil, refined oil, heavy fuel oil, waste cooking oil, cooking oil, mineral oil, motor oil, oil paints, or any commercial or otherwise liquid with an oil base.

23. A piston for use in a wastewater truck, wherein the piston comprises a moveable partition wall having a stop or seal that separates a holding tank into (a) a front compartment adapted to store clean water; and (b) a rear compartment adapted to store extracted waste material and the backflush filter device (1) of Claim 1 .

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