WO2010088720A1

WO2010088720A1 - Method and apparatus for filtering fluids

Info

Publication number: WO2010088720A1
Application number: PCT/AU2010/000100
Authority: WO
Inventors: Robert Joseph Peter Lennon
Original assignee: Robert Joseph Peter Lennon
Priority date: 2009-02-03
Filing date: 2010-02-03
Publication date: 2010-08-12

Abstract

Apparatus for extracting hydrocarbon contaminant from groundwater such as petrol/diesel fuel from subterranean fuel tanks which utilises filter material in a bag confined within a cylinder. A logic circuit imposes a periodic "clean" cycle on the filter and a ram activates a piston to squeeze the filter and extract the hydrocarbon which is collected in a drum. The filter is decompressed, flushed with groundwater and filtering resumes. Screening the groundwater fed to the filter and polishing the filtrate with further filters is optional. A hydrocarbon content monitor or a pressure sensor reports to the logic circuit.

Description

TITLE: METHOD AND APPARATUS FOR FILTERING FLUIDS

FIELD OF THE INVENTION

This invention concerns a method and apparatus for filtering contaminants from fluids.

BACKGROUND OF THE INVENTION

The Environmental Protection Agency monitors operations which contaminate the environment and enforces standards where necessary. Service stations commonly have underground tanks for their storage of hydrocarbon fluids. Sooner or later these tanks whether made of bitumenised steel or more recently fibreglass leak hydrocarbon into the surrounding soil and this mixes with groundwater. A sample of such groundwater may contain as much as 1/6 hydrocarbon by volume. The EPA is aware of the scale of contamination and has regulations for its recovery. The dirty fuel is put to low grade use such as cement kiln firing.

In practice a bore is drilled on the site to reach the groundwater. A perforated pipe is inserted into the bore. A fabric sock covers the immersed end of the pipe and this is the conduit through which contaminated groundwater is raised to ground level for separation into a water component and a hydrocarbon component. The filtration apparatus must be capable of working continuously in order to remove hydrocarbon to regulation levels. Activated carbon and sometimes other filter materials such as zeolites are used to bring down the concentration of hydrocarbons. In Australia for example the filtered groundwater can be returned to a sewer if the concentration of the benzene component falls to lppm and the xylenes, toluene and ethyl benzene components are all 2ppm. In addition the groundwater may contain carbon black from tyre marks washed from the forecourt by rain. This produces a sheen or multi-coloured stain when seen on the surface of the forecourt.

Filtration rates are low being 5-301/mm or 7-43kl/24hr. The filtration rate must be suitably low because of fluctuations in rainfall, ground porosity, etc.

Persons skilled in the art will observe that the method is applicable to liquids generally which are separable through a difference in phase, ie. water/oil, oil/solid, etc.

In Patent No. US 4,032,122, subsurface plumes of contamination in groundwater can be decontaminated by sinking a well on one side of the plume for injecting a gas capable of volatilizing the contaminant and sinking a well on the opposite side of the plume to collect the contaminant. Thereafter the captured contaminant is adsorbed on activated charcoal filters. InPatent No. US 5,076,932, low concentrations of hydrocarbons in water, namely 90ppb, are removed by passing the feed water through the pores of a hydrophobic polypropylene microporous membrane in a closed loop, recycling chamber. The trapped hydrocarbons are released by evaporation. Regulations may not permit this type of separation in urban sites.

Patent No. US 4,595,509 specifically describes the removal of PCBs in low concentrations from water by exposing the feed water to a filter bed of silica particles. A countercurrent of water and ultrasonic vibration regenerates the silica to some extent because hydraulic shearing separates the contaminant from the filter material. The filter material is reused. Such a process removes 85-95% of PCBs from the feed water and these collect as a sludge. This process is effective in reducing contaminant levels compliant with EPA requirements however for small sites, such as urban service stations, it is not adaptable.

SUMMARY OF THE INVENTION

The method aspect of the invention provides a method of separating liquid hydrocarbon contaminants from water comprising the steps of:

a) charging a filter chamber which contains compressible absorbent filter material with water contaminated with liquid hydrocarbon;

b) allowing the hydrocarbon content retained by the material to rise to a predetermined level whereupon;

c) the material in the filter chamber is compressed in order to express hydrocarbon from the chamber;

d) allowing the material to decompress and flushing the decompressed material with water; and repeating the steps.

Preferably the filtration described above is followed by one or more conventional filtration steps. This may be required to extract a specific contaminant, for example a heavy metal ion. The method is useful for C₆-C₃₆ hydrocarbons.

The apparatus aspect of the invention comprises apparatus for remediation of a liquid containing a liquid contaminant comprising a filter chamber with an entry flow path for contaminated liquid and an alternative path for flushing liquid, an exit flow path for filtered liquid and an alternative path for liquid contaminant, a filter space between entry and exit, means to periodically compress and decompress a filter occupying the filter space in order to express contaminant from the filter allowing contaminant to exit the chamber and upon decompression to allow flushing liquid to flush the filter.

The filter chamber may be a piston and cylinder.

A second filter chamber may be connected to the outlet of the first filter chamber.

A polishing filter may be connected to the outlet of the second filter chamber.

The "clear" cycle may be initiated in at least two ways. As the filter approaches saturate the resistance to flow increases. A pressure sensor upstream of the compressible filter informs a logic circuit which initiates the "clear" sequence. Alternatively a hydrocarbon monitor measures the ppm hydrocarbon content in the filtrate and once the predetermined level is detected the logic circuit signals the interruption of feed and the limitations of the "clear" sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention is now described with reference to the accompanying drawings, in which: Figure 1 is a diagram of the filter system for a fuel service station.

Figure 2 is a diagrammatic view of the filter cylinder when the filter is compressed by the ram.

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS

The service station site has a subterranean fuel tank 2 and a sewer 4. Tank 4 leaks hydrocarbon fuel into groundwater 6. Bore 8 has liner 10 which is perforated at the lower section to allow ingress of groundwater contaminated with petrol or diesel oil.

A 2" dip tube 12 draws contaminated groundwater from the liner. Submersible pump 14 draws the stream through a slotted wall screen 16 which in turn is covered by a fabric filter sock 18. Screen 16 is closed by end cap 20. Above ground riser 22 directs feed water to a filter chamber 24 containing a l-5μ fabric filter bag 26. Chamber 24 discharges into sump 28 which exceeds the volume of the main filter chamber 30. In line pump 32 supplies a constant head of 60-80 inches of water (71/rnin) to main filter chamber 30 and this is monitored by pressure sensor 32 upstream of the sump 28.

Main filter chamber 30 is a 200mm dia and 951 capacity. The chamber is closed by a cylinder head (see Figure 2) with a continuous gallery 34 which opens into multiple, circumferential ports 36 in the chamber wall. Piston 38 of double acting ram 40 sits above the ports 36 as shown during the filtering process. The piston has a tether 42 on its lower face for the attachment of knitted filter bag 44. The bag is of the knitted polyester type used in road construction for soil retention and is 200mm in diameter. The lower end of the bag is fastened to tether 46 which is surrounded by squeeze cup 48 at the lower end of the chamber. The filter bag is filled with 1.5kg of a particulate EVA polymer obtainable under the trade mark RECOVERIT. This is obtainable from Robinson Foam Products Pty. Ltd., Albury, New South Wales, Australia. The bag assumes the shape of the chamber and acts as a plug thereby filtering the feed water which exits the chamber through outlet 50 to reach two way valve 52. Valve 52 discharges either to sump 54 or collection drum 56. Pump 32 empties sump 54 through first, second and third polishing filters 58, 60, 62 and finally into a Mycelx Technologies cartridge filter 64 which provides visual inspection of the departing filtrate before it is released into sewer 4.

On/off valves 66, 68, 70 and 72 are of the type which allow flow sampling. Analysis of the filtrate allows the operator to identify any filter which is not polishing to the intended extent.

A hydrocarbon content monitor 76 is connected to the exit line of sump 54. This is of the type used to measure low levels of hydrocarbons in feedstock and this reports the ppm of filtrate hydrocarbons leaving chamber 30. Such monitors are available from specialist suppliers. Logic controller circuit 78 takes input from monitor 76. The equipment is calibrated for the level of contamination which is shown to be present in a sample of contaminated groundwater and which will initiate a cleaning frequency of 1-2 hours which in turn will give a 1 -2 month filter life. All the polishing filters and the main filter chamber contain the same filter material.

The double action of the ram requires that the chamber drains prior to the CLEAN cycle and when the piston is raised in the dry chamber, displaced air is free to leave the chamber. For this purpose an air bleed valve 80 directs air through conduit 82 from the main chamber 30 to the space above the liquid in sump 28. This space in turn is vented by conduit 84 to drum 56. The drum 56, sumps 28, 54 and all the filtering components are grouped together above bund 86. Both sumps and the collection drum are vented to atmosphere through a granulated activated charcoal filter (not shown).

When the monitor reports a hydrocarbon ppm value which indicates that the main chamber filter material in bag 44 is approaching saturation, the logic circuit 78 initiates the CLEAN cycle which is as follows:

In line pump 32 and submersible pump 14 both switch off. Air bleed valve 80 allows air into the chamber and the feed water drains into sump 54 for about 30 seconds. Valve 54 directs the contaminant in the filter bag 44 to collection drum 56. Ram 40 descends, squeezing filter bag 44 against cup 48. Contaminant is released by the particulate filter material. After a short dwell period valve 52 reconnects the chamber to sump 54. Piston 38 rises pushing air out of the chamber into sump 28 and drawing filtrate from sump 54 into the chamber assisting the decompression of the filter material. When the piston stops above ports 36 the bag is pulled to its full length. The air bleed closes and the pumps 16, 32 resume sending contaminated water into the chamber which exits into the sump 54 and passes through the polishing filters 58, 60, 62. In operation sump 54 is substantially full so there is always sufficient volume to flush the chamber. Each of the three sumps has a float switch which signals to the control circuit if the liquid level in the sump exceeds 85% of the available volume in order to maintain a vapour space above the liquid.

The ram is mounted so as to be retractable sufficiently to give access to chamber 30 in order to exchange filter bags during service visits. The chamber volume gives a filter life of 1-2 months for average levels of contamination. The hydrocarbon monitor can be calibrated for either petrol and diesel oil contamination. If the hydrocarbon monitor reports a high level of contamination the control circuit software slows the pump rate and conversely speeds it suitably if the level is low.

The apparatus can process fluids entirely in the vapour phase. Contaminants coalesce to liquid in the filter material.

We have found the advantages of the above embodiment to be:

1. No activated charcoal is required as in the prior art system for treatment of the feed liquid.

2. Bags containing fresh filter granules are easily swapped during service visits.

3. Extra filters can be added if an objectionable contaminant, eg. a metal ion is detected in concentrations which exceed regulations for sewer disposal, eg. zeolites.

It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of separating liquid hydrocarbon contaminants from water comprising the steps of:

d) allowing the material to decompress and flushing the decompressed material with water;

and repeating the steps.

2. A method as claimed in Claim 1, wherein water contaminated with liquid hydrocarbon is fed to the filter chamber, the filtered water is returned to a sewer and the separated liquid hydrocarbon is collected for disposal.

3. A method as claimed in Claim 1 or 2, wherein the degree of saturation of the filter material is measured and when a predetermined saturation level is reached, the entry flow is interrupted and compression of the absorbent filter material ensues.

4. A method as claimed in any one of Claims 1-3, wherein the filter material. is confined in a bag, one end of which is connected to a static end of the chamber while the other end is connected to a ram.

5. Apparatus for remediation of a liquid containing a liquid contaminant comprising a filter chamber with an entry flow path for contaminated feed liquid and an alternative path for flushing liquid, an exit flow path for filtered liquid and an alternative path for liquid contaminant, a filter space between entry and exit, means to periodically compress and decompress a filter occupyingthe filter space in order to express contaminant from the filter allowing contaminant to exit the chamber and upon decompression to allow flushing liquid to flush the filter.

6. Apparatus as claimed in Claim 5 , wherein the chamber is a cylinder with a sliding piston which is advanced and retracted by a ram in order to compress and decompress the filter material.

7. Apparatus as claimed in Claim 5 or 6, wherein one or more polishing filters downstream of the chamber exert an extra filtration stage on the filtrate from the chamber.

8. Apparatus as claimed in any one of Claims 5-7, wherein the chamber and associated filters are grouped together above a bund of appropriate volume.

9. Apparatus as claimed in any one of Claims 5-8, wherein a sensor monitors the pressure of the feed liquid upstream of the filter space in order to measure the saturation level of the filter.

10. Apparatus as claimed in any one of Claims 5-9, wherein the chamber discharges to a filtrate sump and in decompression the filtrate flows in the reverse direction into the chamber and flushes the filter material.

11. Apparatus as claimed in any one of Claims 5-10, wherein the filter material is contained in a permeable bag, one end of which is connected to the piston and the opposite end is connected to the adjacent end of the chamber.

12. Apparatus as claimed in any one of Claims 5-11, wherein a filter upstream of the chamber subjects feed liquid to a preliminary screening.

13. Apparatus as claimed in any one of Claims 5-12, wherein a sensor monitors the filtrate hydrocarbon content downstream of the filter material and a control device activates the ram which a predetermined hydrocarbon content indicates filter saturation.

14. Apparatus as claimed in Claim 13, wherein the control device opens and closes an air inlet to the chamber in order to allow gravity drainage of feed liquid from the chamber prior to filter compression.

15. Apparatus as claimed in any one of Claims 5-14, wherein the filter material is a granulated ethylene vinyl acetate copolymer.

16. A method of separating a liquid contaminant from a carrier liquid comprising passing contaminated carrier liquid through a chamber containing compressible filter material until a predetermined level of saturation is reached, connected the chamber to a collection vessel, compressing the filter material to express contaminant so that contaminant leaves the chamber, connecting the chamber to a source of flushing liquid, decompressing the filter and flushing the filter material, and reconnecting the chamber to the source of contaminated carrier liquid.

17. A method of separating a vapour contaminant from a carrier vapour comprising passing contaminated carrier vapour through a chamber containing a compressible filter material until a predetermined level of saturation is reached, connecting the chamber to a collection vessel, compressing the filter to express the contaminant so that contaminant leaves the chamber, connecting the chamber to a source of flushing gas, decompressing the filter material and flushing the same with flushing gas, and reconnecting the chamber to the source of contaminated vapour.