The present invention relates to fuel processing technologies, and more particularly to an enhanced apparatus and method for fuel filtration.

Liquid fuels for internal combustion engines and the like are distributed to petrol filings stations, gas stations etc. by tanker trucks, which regularly replenish the fuel stored in large tanks at those stations. In between replenishments, the fuel in the storage tanks is gradually depleted by supplying to customers at the stations. An issue with fuel stored at stations is that certain components of the liquid fuel remain for long periods within the storage tanks, and the fuel generally is susceptible to taking on contaminants. As used herein, "fuel" means any hydrocarbon based fuel, excluding aircraft fuels.

Fuel contamination is a well-known subject with a wide variety of solutions offered to purify or clean the fuel. Fuel contamination however is not due to a single contaminant but to several processes and elements that work together to cause instability and increased waste - held in suspension and located at the bottom of the storage tanks. In certain countries, for example, regulations require that hydrocarbon based fuels supplied for road, sea and general offroad use contain a minimum percentage (e.g. 7%) of biofuels, and the latter tends to suffer from stratification and, due to its hygroscopic nature, collect more water and accumulate at the bottom of storage tanks.

The known fuel contaminants - generally particulates - can be dividing into four distinct groups, as follows.

1. Oxidization Waste - exposure to the atmosphere triggers fuel degradation resulting in the formation of asphaltines.

2. Water Ingress - fuel is hydroscopic and will absorb moisture.

3. Organic waste - The presence of water supports microbial activity resulting in the development of biofilm, colonies and suspended organic waste.

4. Inorganic waste - rust particles, dust and paraffin crystals typically smaller than 5 micron.

Known filter systems can remove these particulates, but not without compromising flow rates, using increased pressure differentials and/or involving frequent filter plugging. It is known to use fuel polishing systems that make use of conventional filters and combination centrifuge and element filters for this purpose.

US7883627B1 discloses an automated system for fuel polishing stored fuel in multiple storage tanks, and methods for making and using such systems. The methods include the use of an apparatus comprising a pump having a flow velocity sufficient to suspend settled impurities in a fuel storage tank, at least a first and second fuel storage tank each having an inlet and an outlet; said at least one filter; a fluid pathway connecting said pump, said fuel storage tanks, and at least one filter; a first three-way valve positioned at a junction between the inlet of at least said first and second fuel storage tanks; a second three-way valve positioned at a junction between the outlet of at least said first and second fuel storage tanks; and a system controller component operably connected to said first and second three-way valve to automatically control the position of each valve without manual intervention.

The principals used in such fuel polishing systems to achieve the desired result are based on atomization of fuel droplets, and the use of paper or fibre glass filter media having maximum possible surface areas to prevent rapid plugging. Filter plugging also gives rise to the need for frequent filter changes to keep the flow sustainable.

Fuel recirculation or fuel polishing systems have been in the market for several years but have always faced several drawbacks, making it an impractical solution for managing large volumes of fuel. In particular, higher flow rates are only achieved by placing a larger number of filters (filter elements) in parallel or by increasing the pore size on the filter media (elements).

With such known systems, slow flow rates (of typically 120 litres per minute) make this an impractical solution to deal with more than 5 000 litres of fuel in a normai workday. In addition, the rate of filter plugging reduces the pump lift, thus requiring the pump to be installed before the filters, thereby pressurizing the whole system, with the potential of explosions due to fuel being under increased pressure and arising from static buildup. The pressure buildup further increases the risk of dramatic failures and fuel spills.

The present invention seeks to address the aforementioned and other issues. According to one aspect of the present invention there is provided a fuel filtration apparatus, for filtering fuel stored in a storage tank, comprising, coupled in succession: a fuel inlet port; one or more filter stages; and a fuel outlet port.

Preferably, there are a plurality of filter stages.

Preferably, at least one of the one or more of the filter stages comprises a mesh- based filter and none of the filter stages utilise disposable filter elements/media. Preferably, said mesh based filter employs a stainless steel a wire mesh woven with round stainless steel wire. Preferably, said wire mesh is woven to 25 micron pore size. Preferably, the stainless steel wire comprises round 316 stainless steel threads.

Preferably, one filter stage comprises a centrifugal filter for filtering out particulates less than or equal to a predetermined size. Preferably, said predetermined size is in the range 1-5 micron, and more preferably is 1 micron. Preferably, said centrifugal filter is provided with activated aluminium spheres within the chamber thereof. Preferably, said activated aluminium spheres have an average diameter lying in the range 1 to 5 mm, and more preferably 3 to 4mm. Preferably, said centrifugal filter comprises a final filter stage of said one or more filter stages.

According to another aspect of the present invention there is provided a fuel filtering system, comprising: the fuel filtering apparatus as described herein, and

a suction pump, disposed downstream of the fuel filtering apparatus.

According to another aspect of the present invention there is provided a method method of filtering fuel, comprising: providing a fuel filtration apparatus, the fuel filtration apparatus being as described herein; connecting the fuel inlet to a storage tank; passing the fuel from the storage tank through said one or more filter stages; and outputting filtered fuel at said fuel outlet port.

An advantage of the invention is the lack of filter elements that can be clogged up: this means there is only a nominal pressure differential and no decrease in the pump lift ability. Removing the fi er elements also means there is no restrictions in the system that limit flow rate, with maximum flow rates limited only by the internal diameter of the suction hose. The lack of serviceable filter elements also means there is no human contact with the fuel, removing the risk of exposure to hazardous chemicals and additive. Where filter media are used heretofore, filter efficiency and application were determined by the type of fuel and the size of the pores in the filter media. By removing the filter elements, there are no restrictions - other the limits in viscosity the pump can lift - in the type of fuel filtered through the system. Removing the filter elements and increasing the lag time in the gravity based centrifuge means there is no loss in efficiency in removing particulates down to 5 micron particle size.

A further advantage of the invention is that it operates on negative pressure, thereby preventing the occurrence or risk of any leak, and reducing the risk of system failure.

A further advantage of the invention is that it allows for a measured dosage of fuel detergent to be added and blended into the fuel during the process, in particular though delivering the dosed fuel to the bottom of the storage tank, thus ensuring contaminants and emulsions are effectively treated and lifted off the tank bottom.

Embodiments of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a fuel filtering installation using a fuel filtration apparatus according to an embodiment of the invention;

Figure 2 is a detailed side view of the fuel filtration apparatus of Fig. 1 ;

Figure 3 is a plot of the relation between inlet port internal diameter (y-axis) and main body (centrifuge chamber 217) diameter in relation to the volumetric flow rate it is required to handle, at the third and fourth filter stages in the fuel filtration apparatus of Fig. 2;

Figure 4 is a plot of residence time vs flow rate at the third and fourth filter stages in the fuel filtration apparatus of Fig. 2; and

Figure 5 is a plot of residence time vs length of centrifuge chamber 217 at the fourth filter stage in the fuel filtration apparatus of Fig. 2.

In the following, like references will be used to describe like elements. Unless indicated otherwise, and design feature disclosed or illustrated herein may be used in conjunction with any other design feature disclosed or illustrated herein.

Figure 1 is a schematic view of a fuel filtering installation 100 using a fuel filtration apparatus 102 according to an embodiment of the invention. At the installation 100, a fuel storage tank 104 contains fuel 106 to be processed, and this is accessed via multichannel fuel tank port 108. The fuel storage tank 104 may be a large, underground storage tank located at a petrol or gas filling station.

The operation is as follows.

Using suction head 110 (preferably located at or near the base 111 of storage tank 104 and at the far side thereof), contaminated fuel is extracted via extraction line 1 12. The fuel passes through fuel tank port 108 to fuel filtration apparatus 102, entering at inlet port 11 . The operation of fuel filtration apparatus 102 will be described later.

Processed, decontaminated fuel resulting from the filtration by fuel filtration apparatus 102 exits outlet port 1 16 of the fuel filtration apparatus 02 under action of suction pump 1 18 (preferably a double diaphragm air pump), which creates a negative pressure on line 120. The clean fuel exits suction pump 118 at pump exit 122 and is fed via dispensing hose 123 with an in-stream flow meter 124 coupled to data collector 126 to fuel tank port 108 via line 127.

From the fuel tank port 108, the clean fuel passes via delivery return line 128 into the storage tank 104, with the delivery return exit 130 preferably being disposed, at or near the base 11 1 of storage tank 104, and at a (near) end opposite to suction head 1 10.

The effect of this arrangement, in use, is to create a steady circulation of fuel (see arrow A), rather than turbulent flow.

Figure 2 is a detailed side view of the fuel filtration apparatus 102 of Fig. 1 . As mentioned above, contaminated fuel enters (arrow B) inlet port 114. The fuel filtration apparatus 102 is a multistage filtration system, and in this embodiment it comprises a four-stage system. According to the disclosed embodiment, the staged filtration is capable of removing specific fuel contaminants down to a particular size (e.g. 1 micron), including ferrite particles smaller than 5 micron, without loss of flow velocity and nominal increase in pressure differential. The successive filter stages will be described hereinafter.

Stage 1. The first filter stage 202 comprises a magnetic filtration stage, in which a strong permanent magnet 204 is employed, with its axis of elongation (pole-to-pole direction) disposed transverse to the flow (indicated by arrows C) of fuel. Magnetic filtration arrangements are know to persons skilled in the art, and magnet 204 suitably comprises a 10,000 Gauss Neodymium bar magnet typically used in the oil industry and described in studies by the Society of Petroleum Engineers (SPE 38990 Study of Paraffin Crystallization Process Under The Influence of Magnetic Fields and Chemicals) available from specialist manufacturers.

As will be appreciated by persons skilled in the art, the magnetic strength needed is calculated based on the actual work performed by the magnetic field, i.e. the level of energy transferred and absorbed by specific elements within the range of effective field calculated as

iiW in relation to the temperature and the specific permeability of the material.

Inorganic debris, mostly ferrite based, act as a nucleus for an asphaltine pearl that collects more and more debris as it moves through a volume of fuel. These pearls are hardened paraffin crystallization. In the first filter stage 202, magnet 204, arranged in the stream, perpendicular to the flow, softens the paraffin crystals and collects the ferrite particles, removing the nucleus of the pearl, and breaking the waste up into smaller particulates. The fact that the magnetic field also act as a softener for the paraffin crystals allows any plates to shatter in the turbulence entering the main filter vessel (described below).

The first filter stage 202 provides efficient removal of oxidization waste, such as asphaltines.

Stage 2.

The second filter stage 204 comprises mesh-based filtering. Here, a high carbon stainless steel a wire mesh 206, woven with round stainless steel wire to 25 micron pore size, is employed in main vessel 208. The stainless steel wire preferably comprises round 316 stainless steel threads. As will be understood by persons skilled in the art, 316-grade steel is stainless steel with the, or one of the, highest available carbon contents currently available. The second filter stage 204 is based on the following: the strength of molecular bonds of water in water droplets limits their ability to rapidly pass through any porous media smaller than 25 micron without increased hydrostatic or suction pressure. Using its repellent properties, the high carbon stainless steel woven wire mesh 206 collects water droplets suspended in the fuel, acting as a coaleser. Any water droplets that get pushed through the mesh 206 will be smaller than 25 micron with a specific gravity small enough to allow it to homogenously distribute through the fuel.

Optionally, between first filter stage 202 and second filter stage 204, an additive may be injected, or introduced by suction tube of a few mm diameter connected to the supply, into the fuel to enhance the process. The additive suitably comprises a dispersant, examples of which will be well known to persons skilled in the art.

The second filter stage 204 provides efficient removal of water droplets.

According to this embodiment of the invention, the mesh 206 is in the form of a (filter) bag through which the fuel passes. Use of the high magnetic resistance of the stainless steel mesh 206 woven of round 316 stainless steel threads means that heavy organic and inorganic debris are retained, without allowing the pores to clog; debris 212 collects on bottom of the filter bag (mesh 206) rather than in the flow path (arrows D) of the fuel.

In this way, the second filter stage 204 also provides efficient removal of organic waste.

Stage 3.

A third filter stage 214 is implemented in a centrifugal filter 215. At this point, due to the action of previous filter stages, any particulate matter within the fuel is at a size of <= 25um.

The fue( enters at centrifuge inlet 216 under pressure, and flows downwards in a direction (arrows E) internally of centrifuge chamber 217 by nozzle 218 so as to be incident upon vortex plates 220.

The centra! part of centrifuge chamber 217 is filled with a quantity of activated aluminium spheres (not shown). These 3 to 4 mm dia. spheres are placed in the centrifuge chamber 217 with the volume calculated based on the total surface area required within the specific volume of the centrifuge chamber 217 under a specific pressure in accordance to required absorbed volume.

In third filter stage 214, passing fuel over an activated aluminium surface allows the particles within the fuel to be charged and thus form larger molecules.

Particulate smaller than 25 micron, biofuel fuel stratification products and phase separated ethanol bonded with water all require a physical reaction and applied energy to re-blend the fuel homogenously and in order to bond the small particulates together to achieve a larger mass; and when the latter is achieved, it allows gravity to separate the elements.

Stage 4.

A fourth filter stage 219 is also implemented inside the centrifuge chamber 217 of centrifugal filter 215. A centrifugal action is provided by vortex plates 220. The fuel from nozzle 2 8 is incident at an angle upon vortex plates 220. This angle may be of the order 10-20 degrees, and is preferably c. 15 degrees. This flow causes a forced circulation of the fuel - at a rotational speed dependent on the inflow rate - within the centrifuge chamber 217.

In this fourth filter stage 219, passing the blend (fuel plus aluminium spheres) through centrifuge 215 with a sufficient settling time allows gravity to push the debris (not shown) together, resulting in heavier particles that remain at the bottom of the centrifuge chamber 217, while the lighter fuel is siphoned off at the top, i.e. via centrifuge outlet 116, which outputs the cleaner, filtered fuel. This debris, typically of the order of a cupful, can be removed via drain 221.

The fourth filter stage 219 provides efficient removal of inorganic waste, such as rust particles, dust and paraffin crystals.

Figure 3 is a plot of the relation between inlet port internal diameter (y-axis) in inches and main body (centrifuge chamber 217) diameter (in inches) in relation to the volumetric flow rate it is required to handle, at the third and fourth filter stages (centrifugal filter 215) in the fuel filtration apparatus of Fig. 2; Figure 4 is a plot of residence time vs flow rate in gallons per hour (gph) at the third and fourth filter stages in the fuel filtration apparatus of Fig. 2. The plot shows the time in seconds for the contaminants to settle out of the fuel, based on specific gravity of the typical contaminants. In this embodiment, the settling time needs to be >= about 1.200 s, and the operational range is therefore illustrated by the substantially flat portion on the plot to the right of point P _{1 t} i.e. above a flow rate of about 2400 gph.

Figure 5 is a plot of residence time vs length (vertical depth in Fig. 2) of centrifuge chamber 217 at the fourth filter stage in the fuel filtration apparatus of Fig. 2, for a given fuel viscosity and flow rate. In this embodiment, given the settling time, the operational range of centrifuge chamber 217 depth is illustrated by the substantially flat portion on the plot to the right of point P ₂ .

The end result is a fuel filtering system 102 with flow rates only limited by the diameter of inlet port 1 14, with no reduction in flow rate or increase in pressure differential and the ability to remove all contaminants down to a size of the order of a micron.

In certain embodiments, fuel filtering at a rate of tens of thousand of litres per hour is afforded, meaning that an enter storage tank at a filling station can be processed within matter of hours, and within a working day. The fuel filtration apparatus according to the invention may be constructed so as to be mountable on a truck, for deployment at remote filling stations as and when needed.