GB2585868A

GB2585868A - Process for preparing a fuel oil

Info

Publication number: GB2585868A
Application number: GB1910297.9A
Authority: GB
Inventors: Murphy Robert
Original assignee: LIVING FUELS Ltd
Current assignee: LIVING FUELS Ltd
Priority date: 2019-07-18
Filing date: 2019-07-18
Publication date: 2021-01-27
Also published as: AU2019208164A1; GB201910297D0

Abstract

A process for producing a fuel for an internal combustion engine from waste cooking oil comprising: subjecting the waste cooking oil to a settling treatment to produce an oil fraction and a sludge fraction; and subjecting the oil fraction to a filtration treatment comprising a plurality of filtration stages: a first stage comprising subjecting the oil fraction to straining to produce a strained oil fraction; a second stage comprising subjecting the strained oil fraction to a coarse filtration to produce a coarse filtered oil fraction; and a third stage comprising subjecting the coarse filtered oil fraction to a fine filtration to produce a fuel oil. Preferably straining is carried out with a strainer mesh with pore size from 240-260 microns; coarse filtration is carried out with one or more filters with pore size from 1-10 microns and fine filtration is carried out with one or more filters with pore size from 0.75-1.5 microns. An apparatus for producing a fuel for an internal combustion engine from waste cooking oil comprising: a settling vessel; and a filtration assembly comprising: a strainer assembly; a coarse filtration assembly; and a fine filtration assembly. A method of starting and operating an internal combustion engine.

Description

PROCESS FOR PREPARING A FUEL OIL

The present invention relates to a process for preparing a fuel oil for use in an internal combustion engine, in particular to a process for preparing a fuel oil from waste cooking oil.

Edible oils and fats are used in a wide range of cooking operations on a commercial scale. Examples of such operations include the frying, in particular the deep fat frying, of foodstuffs, especially to meet the demands for so-called 'fast foods'. As a result of the need for frequent replacement and renewal of such oils, significant amounts of used or waste oils used in such commercial cooking operations are produced and require disposal. The disposal of used or waste cooking oils presents a growing environmental problem. Conventional techniques for disposal, in particular landfill, are no longer favoured. In the past, waste edible oils and fats were used in the preparation of animal feeds. Such use has given rise to concern regarding the possible spread of diseases within the animal population, for example BSE. As a result, the use of waste edible oils and fats in animal feedstuffs has been banned in the United Kingdom since 2004. The options for disposing of waste oils and fats used in cooking are therefore limited.

One method of treating the waste oils and fats that has been proposed is the conversion of the waste materials into so-called 'biodiesel'. The process for converting the waste cooking oil to a useable fuel generally comprises treating the waste oil to an esterification process. Such processes are known in the art.

For example, KR 2002 0034712 discloses a process for making a fuel from rice bran oil and waste cooking oil. The process comprises a first esterification step, in which the purified oil is reacted in a first esterification step with gaseous methyl alcohol in the presence of a PTSA catalyst. A second esterification step comprises treating the oil with methyl alcohol in admixture with sodium hydroxide, after which crude glycerine is allowed to separate from the oil. Methyl ester is recovered by rinsing with hot water, dehydration and distillation.

More recently, GB 2,436,836 discloses a process for the removal of free fatty acids from used cooking oil prior to the production of biodiesel. The process includes mixing the used cooking oil with virgin vegetable oil to provide a mixture having a target free fatty acid content. The resulting mixture is purified by mixing with hot water, prior to centrifuging to remove particulates from the oil. The resulting oil mixture is heated, dried and de-aerated in a vacuum drier. The resulting oil is steam stripped to remove the free fatty acids by distillation, before being processed to a biodiesel by transesterification.

JP 2005 350631 discloses a method for producing a biodiesel fuel from a stock oil containing a free fatty acid. The method comprises removing the free fatty acids and treating the resulting oil with an alkyl catalyst.

FR 2 577 938 discloses a process for neutralising raw vegetable or animal oils composed essentially of glycerides and containing organic acids. The raw oil is contacted with an alcohol, such as methanol or ethanol, in the presence of an ion exchange resin having strongly acidic functional groups. The organic acids present in the raw oil are esterified, without appreciable reaction of the glyceride components.

The preparation of biodiesel by esterification processes is being applied commercially for the processing of waste cooking oils. Simple processing equipment for such treatments are now being made available commercially for small scale production, for example the Twyn Tub 100 biodiesel plant available from Goat Industries, United Kingdom.

Esterification and the preparation of biodiesel is a particularly complex process, relying on the use of a significant number of processing stages and additional components, such as esterification catalysts and the like. It would be most advantageous if an alternative manner of using the waste oil and processing the waste cooking oil into a useable fuel could be provided. In particular, it would be advantageous if the waste cooking oil could be processed using simple processing techniques, requiring little or no additives or chemical treatment.

KR 2001 0045991 discloses an environmentally friendly fuel oil prepared from a mixture of waste cooking oil and agents for accelerating combustion. The fuel oil comprises from 30 to 90 parts by weight of filtered and refined cooking oil, 1 to 60 parts by weight of naphtha, gasoline or thinner, and 0.01 to 10 parts by weight of a low alcohol solution of molybdenum compounds or sodium hydroxide or a mixture thereof. The waste cooking oil may be soya bean oil, castor oil, cottonseed oil, coconut oil, paulownia seed oil, or fish oil. While the fuel oil produced by this process may be environmentally friendly, it relies upon the use of significant quantities of conventional hydrocarbon fuels and additives to render the waste cooking oil useable.

JP 2006 097671 discloses an alternative approach to treating waste cooking oil, in which the waste cooking oil is mixed with waste lubricating oil at a prescribed ratio. The mixture is heat treated to decompose the oils and the resulting gaseous products reformed using a suitable catalyst. The reformed gases are cooled to provide a condensed liquid fuel and purified to produce a reformed fuel oil. The reformed fuel oil may be used as a fuel in a diesel engine or a gas turbine. Again, the process is particularly complex and relies upon the conversion of the waste oil materials into a reformed fuel oil before a useable fuel is obtained.

US 2005/0006290 discloses a mobile biodiesel refinery. The mobile refinery is suitable for processing used cooking oil and the like. The used oil is processed by first heated and then subjected to a straining or filtration process. Thereafter, water is removed by settling from the heated oil. Subsequently, the oil is treated with a catalyst. Again, this process is particularly complex and requires the use of a catalyst to convert the used oil. There is a need for a simpler process for treating used cooking oil and the like.

US 2007/0119095 concerns a hybrid diesel fuel. The fuel is prepared from virgin or waste biosynthetic oil by first heating the oil and passing through a filter. Further filtration is applied should this be required.

A biofuel conversion process is disclosed in US 2006/0236595. The process employs vegetable based oil as a raw material. The oil is blended with catalyst and absorption powders and heated. Thereafter, the resulting mixture is filtered to produce a final refined product.

US 2006/0053684 discloses a process for providing additives to convert contaminants extracted from wastewater into fuels. Contaminants that are processed include grease.

US 6,254,790 discloses a method for filtering suspended materials from cooking substances, in particular cooking oil. The method employs a plurality of filtration steps, after which the filtered oil is held in a heated tank. The treated oil is then returned for use in cooking, such as a deep fryer.

US 3,984,447 is concerned with a method for reconstituting used cooking oil. The oil is first heated and subjected to a gravity separation to remove components having a high specific gravity. The remaining oil is subject to a plurality of filtration stages, after which a finely divided bleaching clay is added to the oil, prior to a final steam treatment. The clay is removed by filtration. A particular disadvantage of the process of io US 3,984,447 is the reliance on a bleaching clay to refine the oil, which is an additional component that must first be added to the oil and then removed before the final product can be packaged.

A process for the refining of glyceride oils is disclosed in EP 0 348 004. The raw oils processed are from seeds and beans, such as soybean oil, rapeseed oil, sunflower oil, safflower oil, cotton seed oil and the like. The refined oils are used as raw materials in the food industries.

A process for recovering waste cooking oils is disclosed in US 2,558,869. The process is designed for the removal of oil contaminating waste potato chips, in order to allow the waste potato chips to be discarded in a safe manner. The process involves feed the potato chips contaminated with waste oil into an open vat. Hot water at a temperature of from 180 to 200°F is added to the vat through a spray head. A screen is applied to the contents of the vat. The hot water forms a partial emulsion with the waste oil, which is removed from the vat through an overflow line. The water/oil mixture is passed to a separating tank, where gravity is used to separate the oil and water into separate fractions. Oil leaves the separating tank and is fed to a storage reservoir. Oil removed from the storage reservoir is heated and agitated, while a clay, such as fuller's earth, is added. The resulting mixture is passed through a filter screen under the action of compressed air. The refined oil is then reused in frying potato chips or other potato products.

Perhaps most recently, WO 2009/074816 discloses a process for the production of a fuel oil from waste cooking oil. The process of WO 2009/074816 involves two stages.

In a first stage, the waste cooking oil is subjected to a settling treatment, in which the oil is maintained at ambient temperature, while sludge present in the oil is allowed to settle. The first stage produces a sludge fraction and an oil fraction. The oil fraction is subjected in the second stage to filtration. WO 2009/074816 suggests that the second stage may comprise a single filtration operation or a plurality of filtration operations. If a plurality of filter operations are employed, WO 2009/074816 teaches that all the filter stages employ filters having the same pore size, for example 1 micron filters. The waste cooking oil may be screened prior to the first treatment stage, in order to remove large debris.

Despite the considerable efforts already made to efficiently process waste cooking oil, there is a continued need for an improved process for treating waste cooking oil, in particular to produce a refined oil product that is suitable for use as a fuel in an internal combustion engine. It would be advantageous if the process could employ simple treatment of the waste cooking, preferably without the need for any components, such as catalysts, clays or the like, to be added to the waste oil. It would be most beneficial if an oil could be produced that could provide all the fuel requirements for an internal combustion engine, avoiding the need for the use of a second fuel at any time during the operation of the engine.

According to the present invention there is provided a process for producing a fuel for an internal combustion engine from waste cooking oil, the process comprising: i) subjecting the waste cooking oil to a settling treatment to produce an oil fraction and a sludge fraction; and ii) subjecting the oil fraction to a filtration treatment, the filtration treatment comprising a plurality of filtration stages: a) a first stage comprising subjecting the oil fraction to straining to produce a strained oil fraction; b) a second stage comprising subjecting the strained oil fraction to a coarse filtration to produce a coarse filtered oil fraction; and c) a third stage comprising subjecting the coarse filtered oil fraction to a fine filtration to produce a fuel oil.

In a further aspect, the present invention provides an apparatus for producing a fuel for an internal combustion engine from waste cooking oil, the apparatus comprising: i) a settling vessel; a filtration assembly comprising: a) a strainer assembly; b) a coarse filtration assembly; and c) a fine filtration assembly.

It has been found that subjecting the raw waste cooking oil to a first settling stage, in order to remove sludge from the raw waste cooking oil and produce an oil fraction, then subjecting the oil fraction to a filtration treatment comprising a plurality of filter stages, including straining, a coarse filtration and a fine filtration, provides a fuel oil having excellent properties.

One property of the fuel oil is the number and size distribution of the particles in the fuel oil. The number and particle size distribution of particles remaining in the fuel oil produced by the process of the present invention may be defined by ISO cleanliness code set out in International Standard ISO 4406:1999. In particular, the process of the present invention can be used to produce a fuel oil having an ISO cleanliness code of at least or better than 15/13/11 according to ISO 4406:1999. A cleanliness code of 15/13/11 corresponds to a contaminant level of from 160 to 320 particles of 4 micron per millilitre, from 40 to 80 particles of 6 micron per millilitre and from 10 to 20 particles of 14 micron per millilitre.

It has been found that a fuel oil prepared by the process of the present invention may be used as a fuel for an internal combustion engine, in particular a diesel engine, in all phases of the operation of the engine. In particular, it has been found that a fuel oil prepared by the process of the present invention having an ISO cleanliness code of at least 15/13/11 may be used to start the engine, without the need for a second fuel, such as diesel, to be employed.

The present invention may be used to process any waste cooking oil that is produced by a commercial oil-based cooking operation to produce a fuel oil. Examples of waste cooking oils include vegetable oils, for example sunflower oil, rape seed oil, soya bean oil, and olive oil.

In stage i) of the process of the present invention, the raw waste cooking oil is subjected to a settling treatment. The settling treatment is conducted in a suitable settling vessel, into which the raw waste cooking oil is charged. In the settling treatment, components of the raw waste cooking oil are allowed to separate under the action of gravity. In particular, the settling treatment causes the raw waste oil to separate into two major fractions, a sludge fraction having a higher relative density and an oil fraction having a lower relative density. During the settling treatment, the sludge fraction occupies a lower region of the vessel, while the lighter oil fraction occupies a higher region of the vessel above the sludge fraction. If water is present in raw waste cooking oil, this may be present as a third fraction within the vessel.

Some or all of the sludge fraction may be removed from the settling vessel in stages during the settling treatment. Alternatively, the sludge fraction may be removed at the end of the stage i) treatment.

In one preferred embodiment, the oil fraction and the sludge fraction are allowed to remain in the settling vessel for the entire period of the settling treatment.

The sludge fraction and the oil fraction may be removed from the settling vessel in any order. However, it is preferred that the oil fraction is removed from the settling vessel while at least a portion of the sludge fraction is present in the settling vessel. The oil fraction to be processed in stage ii) of the process is preferably withdrawn from the upper region of the settling vessel above the sludge fraction in the lower region of the settling vessel. In particular, the oil fraction is removed from the settling vessel at a position in the vessel spaced apart from and above the interface between the oil fraction and the sludge fraction. In this way, entraining sludge in the oil fraction being removed is avoided.

In one preferred embodiment, the oil fraction is removed from the settling vessel at the surface of the oil fraction, for example using a floating draw off head. Suitable apparatus for removing the oil fraction from the settling vessel in this way is known in the art.

In an alternative embodiment, the sludge fraction and, if present, the water fraction may be removed from the settling vessel, leaving the oil fraction in the settling vessel, which may be discharged separately to provide feed for stage ii) of the process.

To produce the oil fraction that is subjected to further treatment in stage h) of the process, the raw waste cooking oil is allowed to settle under the action of gravity at the ambient temperature. In this respect, 'ambient temperature' is a reference to the temperature of the surroundings of the settling vessel holding the waste cooking oil during the stage i) treatment. The ambient temperature is from 20 to 30°C.

If the temperature of the raw waste cooking oil is at or above 20°C, the settling treatment is conducted without heating the waste cooking oil. If the raw waste cooking oil is provided at a temperature below 20°C, it is preferably heated to a temperature of at least 20°C.

In one preferred embodiment, the raw waste cooking oil is delivered to the processing facility and is charged to the settling vessel in which the settling treatment of stage i) of the process is effected and the waste oil held at a temperature of from 20 to 30°C during the settling treatment to produce the oil fraction, which is then removed from the settling vessel for treatment in stage ii) of the process.

In this embodiment, the waste cooking oil is allowed to remain in the settling vessel and the components settle for a period sufficient to produce an oil fraction. The length of time required to produce the oil fraction will depend upon the nature and properties of the raw waste cooking oil, in particular the amount and type of contaminants in the oil.

A typical period of time for the settling treatment of stage i) is from 1 to 30 days, more preferably from 2 to 25 days. It is preferred that the raw waste cooking oil is subjected to the settling treatment for at least 1 day, more preferably at least 2 days. The settling treatment may be applied for up to 21 days, for example up to 7 or 14 days, again depending upon the nature and composition of the raw waste cooking oil.

The sludge fraction removed from the settling vessel may be disposed of in any suitable manner.

The settling treatment of this embodiment may be conducted in a single stage. Alternatively, the settling treatment may comprise a plurality of settling stages, for example two, three or more settling stages.

In one preferred embodiment, the sludge fraction removed from the settling vessel is fed to a second settling vessel and allowed to undergo a second settling treatment. Again, this settling treatment is preferably at ambient temperature. The second settling treatment is preferably at least 1 day, more preferably at least 2 days. The second settling treatment may last for up to 30 days, more preferably up to 25 days.

In this second settling treatment, remaining oil is allowed to separate from the sludge fraction under the action of gravity, to produce further oil fraction. This oil fraction is removed from the vessel, as described above, and is combined with the oil fraction produced in the first settling treatment for further processing in stage ii) of the process.

In an alternative preferred embodiment of the settling treatment, the raw waste cooking oil is heated and then allowed to settle into the sludge fraction and the oil fraction, as the oil cools to ambient temperature. In this embodiment, the raw waste cooking oil is heated to a temperature of from 30 to 150°C, more preferably from 40 to 120°C, still more preferably from 50 to 100°C.

The waste oil is allowed to settle in the settling vessel for from 1 to 10 days, more preferably from 2 to 8 days.

A portion of the sludge fraction may be removed from the settling vessel at one or more intervals during the settling treatment. For example, the heated raw waste cooking oil may be allowed to settle for a first period, preferably from 2 to 6 days, after which a portion of the sludge fraction is removed from the settling vessel. Thereafter, the waste oil remaining in the settling vessel is allowed to settle for a second period, preferably from 2 to 6 days, after which the sludge fraction formed is removed from the settling vessel. The oil fraction remaining in the settling vessel may then be removed for further processing.

In embodiments in which the raw waste cooking oil is heated at the start or during the settling treatment, it is particularly preferred that the oil fraction, less any sludge fraction that has been removed, is subjected to a final settling treatment and allowed to settle at ambient temperature, that is a temperature of from 20 to 30°C, for a period of at least 1 day, more preferably at least 2 days, before the oil fraction for feeding to stage ii) of the process is finally recovered. This settling treatment may be carried out with the oil fraction remaining in the settling vessel. Alternatively, the oil fraction may be removed from the settling vessel and fed to a second settling vessel for the final settling treatment.

The settling treatment may be conducted batchwise, semi-batchwise or continuously. In batchwise operation, the raw waste cooking oil is allowed to remain in the settling vessel until the sludge fraction and the oil fraction have fully formed, after which the oil fraction and the sludge fraction are removed, as described above. In semibatchwise operation, the raw waste cooking oil is allowed to settle in the settling vessel, with fresh raw waste cooking oil being fed to the vessel and/or sludge fraction and/or oil fraction removed from the settling vessel during the settling treatment. In continuous operation, raw waste cooking oil is fed continuously to the settling vessel, while both sludge fraction and oil fraction are continuously removed from the settling vessel.

In stage h) of the process of the present invention, the oil fraction produced in stage i) of the process is subjected to filtration. The filtration treatment comprises a plurality of filtration stages a) to c).

Pore or opening sizes of the strainer and filters referred to herein are nominal ratings, unless otherwise indicated.

In filtration stage a), the oil fraction produced in stage i) of the process is strained in a strainer assembly. Suitable straining apparatus is known in the art. In one preferred embodiment, the strainer assembly comprises a basket strainer.

The strainer assembly comprises a strainer having a mesh, through which the oil fraction is passed. In the strainer, larger particles remaining in the oil fraction are removed from the oil and held in the strainer mesh. The size of the pores or openings in the strainer mesh will be determined by the solid particles remaining in the oil fraction, in particular their size.

The pores or openings of the strainer mesh are preferably at least 100 micron in size, more preferably at least 150 microns, still more preferably at least 200 microns. The pores of the strainer mesh may be up to 500 micron, more preferably up to 400 microns, still more preferably up to 350 microns, more preferably still up to 300 microns. A strainer mesh having pores or openings of from 150 to 350 microns is preferred, more preferably from 200 to 300 microns, more preferably still from 220 to 280 microns, still more preferably from 230 to 270 microns, especially from 240 to 260 microns. A strainer mesh of 250 microns, (60 Mesh) is particularly preferred for many embodiments.

The strainer treatment may be a single stage treatment, in which oil is strained through a single strainer. Alternatively, the strainer treatment may comprise a plurality of stages, in which oil is strained through a plurality of strainers in turn.

For the single stage strainer operation, the strainer assembly may comprise a single strainer. Alternatively, the strainer assembly may comprise a plurality of strainers, with the plurality of strainers arranged to operate in parallel For the strainer operation comprising a plurality of stages, each stage may employ a single strainer. Alternatively, some or all of the strainer stages may employ a plurality of strainers arranged in series. The number of strainers in the stages may be the same or different. The pore size of the strainer mesh in the stages may be the same or different. If different, it is preferred that the pore size of the strainers decreases as the oil passes through the strainer stages.

For many embodiments, filtration stage a) comprises a single strainer stage employing a single strainer.

The oil fraction may be passed through the strainer at any suitable temperature. A temperature of from 10 to 90°C is preferred, more preferably from 20 to 85°C, still more preferably from 25 to 80°C. The oil fraction may be heated before being fed through the strainer assembly. In one preferred embodiment, the oil fraction is fed to the strainer from the settling vessel without heating and the straining treatment applied at ambient temperature, that is a temperature up to 30°C, preferably from 20 to 30°C.

The strainer assembly may be operated at any suitable pressure to achieve the required flow of oil fraction through the strainer. The oil fraction is preferably pumped under pressure to the inlet of the strainer. The pressure of the oil fraction at the inlet of the strainer is greater than 1 bar up to a maximum pressure of 12 bar.

In filtration stage b), the strained oil fraction produced in filtration stage a) of the process is subjected to a coarse filtration treatment in a coarse filtration assembly.

Suitable coarse filter apparatus is known in the art. In one preferred embodiment, the coarse filter assembly employs one or more coarse filter bags.

The coarse filtration assembly comprises a coarse filter having a mesh, through which the strained oil fraction is passed. In the coarse filter, particles remaining in the strained oil fraction are removed from the oil and held in the filter. The size of the pores or openings in the coarse filter will be determined by the solid particles remaining in the strained oil fraction, in particular their size.

The pores or openings of the coarse filter are preferably at least 0.5 micron in size, more preferably at least 1 micron. The pores of the coarse filter may be up to 20 micron, more preferably up to 15 microns, still more preferably up to 10 microns, more preferably still up to 7.5 microns. A coarse filter having pores or openings of from 0.5 to 20 microns is preferred, more preferably from 1 to 15 microns, more preferably still from 1 to 10 microns, still more preferably from 1 to 5 microns.

The coarse filter treatment may be a single stage treatment, in which the strained oil is passed through a single coarse filter. More preferably, the coarse filter treatment comprises a plurality of stages, in which oil is passed through a plurality of coarse filters in turn.

For the single stage coarse filter operation, the coarse filter assembly may comprise a single coarse filter. Alternatively, the coarse filter assembly may comprise a plurality of filters, with the plurality of filters arranged to operate in parallel For the preferred coarse filtration operation comprising a plurality of coarse filtration stages, each stage may employ a single coarse filter. Alternatively, some or all of the coarse filtration stages may employ a plurality of coarse filters arranged in parallel. The number of coarse filters employed in the coarse filtration stages may be the same or different.

In the preferred multi-stage coarse filtration treatment, it is preferred that the first coarse filtration stage employs a coarse filter having a pore or opening size that is larger than the pore or opening size of the filters in the subsequent filtration stage or stages. In one preferred embodiment, the first coarse filtration stage employs a coarse filter having a pore or opening size of from 2 to 10 microns, preferably from 3 to 8 microns, more preferably from 4 to 6 microns, especially 5 microns. The further coarse filtration stage or stages employ filters having a pore or opening size lower than that of the first coarse filtration stage, preferably from 0.5 to 5 microns, more preferably from 0.75 to 4 microns, still more preferably from 1 to 3 microns.

The coarse filtration treatment may employ two, three, four or more coarse filtration stages. In one preferred embodiment, the coarse filtration treatment employs four coarse filtration stages. Preferably, each of the four coarse filtration stages each employ a plurality of coarse filters arranged in parallel.

In a particularly preferred embodiment, the coarse filtration treatment employs four coarse filtration stages, as follows: In a first coarse filtration stage, the strained oil fraction is passed through coarse filters having a pore size of from 4 to 6 microns, preferably 5 microns.

In a second coarse filtration stage, the filtered oil fraction leaving the first stage is passed through coarse filters having a pore size of 0.5 to 2 microns, preferably 1 micron.

In a third coarse filtration stage, the filtered oil fraction leaving the second stage is passed through coarse filters having a pore size of 0.5 to 2 microns, preferably 1 micron.

In a fourth coarse filtration stage, the filtered oil fraction leaving the third stage is passed through coarse filters having a pore size of 0.5 to 2 microns, preferably 1 micron.

The oil fraction may be passed through the coarse filtration assembly at any suitable temperature. A temperature of from 10 to 90°C is preferred, more preferably from to 85°C, still more preferably from 25 to 80°C. The strained oil fraction may be heated before being fed the coarse filtration assembly or during the coarse filtration, for example between consecutive stages of the coarse filtration. In one preferred embodiment, the oil fraction is fed to the coarse filtration assembly from the strainer assembly without heating and the coarse filtration treatment applied at ambient temperature, that is a temperature up to 30°C, preferably from 20 to 30°C.

The coarse filtration assembly may be operated at any suitable pressure to achieve the required flow of the strained oil fraction through the coarse filters. The strained oil fraction may be pumped under pressure to the inlet of the coarse filtration assembly. Alternatively, the strained oil fraction is fed to the inlet of the coarse filtration assembly at the pressure of the oil fraction leaving the strainer assembly. The pressure of the oil fraction at the inlet of the coarse filtration assembly is greater than 1 bar up to a maximum pressure of 12 bar.

In filtration stage c), the coarse filtered oil fraction produced in filtration stage b) of the process is subjected to a fine filtration treatment in a fine filtration assembly. Suitable fine filter apparatus is known in the art. In one preferred embodiment, the fine filtration assembly employs one or more cartridge filters, preferably absolute cartridge filters. The fine filtration treatment may also be referred to as a 'polishing' treatment.

The fine filtration assembly comprises a fine filter having a mesh, through which the coarse filtered oil fraction is passed. In the fine filter, fine particles remaining in the coarse filtered oil fraction are removed from the oil and held in the filter. The size of the pores or openings in the fine filter will be determined by the solid particles remaining in the coarse filtered oil fraction, in particular their size.

The pores or openings of the fine filter are preferably at least 0.25 micron in size, more preferably at least 0.5 micron, still more preferably at least 0.75 micron. The pores of the fine filter may be up to 2 microns, more preferably up to 1.5 micron, still more preferably up to 1.4 microns, more preferably still up to 1.25 microns. A fine filter having pores or openings of from 0.5 to 1.5 microns is preferred, more preferably from 0.75 to 1.25 microns, more preferably still from 0.8 to 1.2 microns, still more preferably from 0.9 to 1.1 microns. A fine filter pore size of 1 micron is particularly preferred.

It is particularly preferred that the fine filter has an absolute rating of from 0.5 to 1.5 microns, more preferably 1 micron.

The fine filter treatment may be a single stage treatment, in which the coarse filtered oil is passed through a single fine filter. Alternatively, the fine filter treatment may comprise a plurality of stages, in which oil is filtered through a plurality of fine filters in turn.

For the single stage fine filter operation, the fine filtration assembly may comprise a single fine filter. Alternatively, the fine filtration assembly may comprise a plurality of fine filters, with the plurality of filters arranged to operate in parallel.

For a fine filtration treatment comprising a plurality of fine filtration stages, each stage may employ a single fine filter. Alternatively, some or all of the fine filtration stages may employ a plurality of fine filters arranged in parallel. The number of fine filters employed in the fine filtration stages may be the same or different.

For many embodiments, a single fine filtration stage is sufficient to produce a fuel oil of the required specification for use in an internal combustion engine.

The oil fraction may be passed through the fine filtration assembly at any suitable temperature. A temperature of from 10 to 90°C is preferred, more preferably from 20 to 85°C, still more preferably from 25 to 80°C. The coarse filtered oil fraction may be heated before being fed the fine filtration assembly or during the fine filtration, for example between consecutive stages of the fine filtration. In one preferred embodiment, coarse filtered the oil fraction is fed to the fine filtration assembly from the coarse filtration assembly without heating and the fine filtration treatment applied at ambient temperature, that is a temperature up to 30°C, preferably from 20 to 30°C.

The fine filtration assembly may be operated at any suitable pressure to achieve the required flow of the coarse filtered oil fraction through the coarse filters. The coarse filtered oil fraction may be pumped under pressure to the inlet of the fine filtration assembly. Alternatively, the coarse filtered oil fraction is fed to the inlet of the fine filtration assembly at the pressure of the oil fraction leaving the coarse filtration assembly. The pressure of the oil fraction at the inlet of the fine filtration assembly is greater than 1 bar up to a maximum pressure of 12 bar.

In a further aspect, the present invention provides a fuel oil obtainable by the process hereinbefore described.

As noted above, the fuel oil produced by the process of the present invention is particularly suitable for use as a fuel for an internal combustion engine. As also noted above, the fuel oil is of sufficiently high quality to be able to operate the internal combustion engine using the fuel oil during all phases of its operation, including start-up, without the need for the use of an alternative fuel, such as diesel.

In a still further aspect, the present invention provides a method of operating an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process as hereinbefore described.

In a still further aspect, the present invention provides a method of starting an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process as hereinbefore described; and starting the engine using the fuel oil as the only fuel.

Embodiments of the present invention will now be described, by way of example only, having regard to the accompanying drawings, in which: Figure 1 is a schematic representation of one embodiment of the process and apparatus of the present invention; Figure 2 is a schematic representation of a second embodiment of the process and apparatus of the present invention; Figure 3 is a diagram of one embodiment of an apparatus to perform the settling treatment of stage i) of the process of the present invention; and Figure 4 is a diagram of one embodiment of an apparatus to perform the filtration treatment of stage ii) of the process of the present invention.

With reference to Figure 1, there is shown a schematic representation of one embodiment of the process and apparatus of the present invention, generally indicated as 2. As shown in Figure 1, raw waste cooking oil is delivered to the processing plant, for example by a road-going tanker 4. The raw waste cooking oil is pumped into a settling vessel 6, in which the setting treatment of stage i) of the process is carried out. The settling treatment produces an oil fraction and a sludge fraction. The oil fraction is fed from the settling vessel 6 to a filtration assembly 8 for the stage h) processing, either directly or via an intermediate storage facility (not shown for clarity). The sludge fraction produced in the settling treatment is removed from the settling vessel 6 and disposed of according to established practices. The filtration treatment of stage ii) produces a fuel oil product. The fuel oil product may be led to a storage facility 10 comprising one or more product storage vessels, where the fuel oil is stored until required to be shipped or used as a fuel. An internal combustion engine 12 is shown in Figure 1, which may receive fuel directly from the filtration assembly 8 or from the storage facility 10, as required.

Turning to Figure 2, there is shown a schematic representation of a second embodiment of the process and apparatus of the present invention, generally indicated as 102. As shown in Figure 2, raw waste cooking oil is delivered to the processing plant, for example by a road-going tanker 104. The raw waste cooking oil is pumped into a first settling vessel 106, in which the setting treatment of stage i) of the process is carried out. The settling treatment produces an oil fraction and a sludge fraction. The oil fraction is fed from the first settling vessel 106 to a filtration assembly 108 for the stage ii) processing, either directly or via an intermediate storage facility (not shown for clarity). The sludge fraction produced in the settling treatment in the first vessel is removed from the first vessel 106 and fed to a second settling vessel 110. The sludge fraction is allowed to undergo a second settling treatment in the second settling vessel 110, to produce an oil fraction and a sludge fraction. The oil fraction is removed from the second settling vessel and is combined with the oil fraction recovered from the first settling vessel 106 to form the feed to the filtration assembly 108. The sludge fraction remaining is removed from the second settling vessel 110 for disposal.

The filtration treatment of stage ii) produces a fuel oil product. The fuel oil product may be led to a storage facility 112 comprising one or more product storage vessels, where the fuel oil is stored until required to be shipped or used as a fuel. An internal combustion engine 114 is shown in Figure 2, which may receive fuel directly from the filtration assembly 108 or from the storage facility 112, as required.

Turning to Figure 3, there is shown a diagram of one embodiment of an apparatus for performing the settling treatment of stage i) of the process. The apparatus, generally indicated as 202, comprises an oil feed line 204 for introducing raw waste cooking oil into a first settling vessel 206 and a second settling vessel 208. The two settling vessels 206, 208 are operated in parallel to produce an oil fraction and a sludge fraction from the waste oil feed.

The raw waste cooking oil undergoes a settlement treatment in the two settling vessels 206, 208 to produce an oil fraction and a sludge fraction. The dotted lines in the settling vessels in the figures represent the interface between the sludge fraction in the lower portion of the vessel and the oil fraction in the upper portion of the vessel.

The oil fraction is removed from the settling vessels 206, 208 by a floating draw off head 210, which draws oil from the surface region of the oil fraction and delivers the oil fraction to an oil fraction product line 212. The sludge fraction is removed from the lower region of each of the settling vessels 206, 208 and is produced through a sludge product line 214.

In the embodiment shown in Figure 3, two settling vessels 206, 208 are employed and operated in parallel. It will be understood that the number of settling vessels may be varied, depending upon the volume of raw waste cooking to be processed.

Details of a preferred embodiment of the settling treatment carried out in stage i) of the process will now be described.

In stage i) of the process, raw waste cooking oil in the settling vessel undergoes a settling treatment, in which the heavier components settle to form a sludge fraction, leaving an oil fraction comprising lighter components. If the raw waste cooking oil contains a significant amount of water, this can separate as a third fraction. The settling and separation of the fractions occurs under the action of gravity.

In one preferred embodiment, the settling treatment in the settling vessels 6, 106, 206, 208 is conducted as follows: The raw waste cooking oil is allowed to remain in the vessel without agitation and without heating. The settling treatment is conducted at ambient temperature, that is the temperature of the surroundings of the settling vessels 6, 106, 206, 208 at a temperature of from 20 to 30°C. The waste cooking oil is allowed to remain in the settling vessel 6, 106, 206, 208 for at least 2 days to allow the settling under gravity to occur.

The oil fraction to be subjected to filtration in stage ii) of the process is removed from a region of the settling vessel 6, 106, 206, 208 above the interface between the oil fraction and the sludge fraction. For example, the oil fraction may be withdrawn from the settling vessel 6, 106, 206, 208 using a floating draw-off head. The sludge fraction is removed from the settling vessel and is disposed of following appropriate procedures.

In the process scheme shown in Figure 2, the sludge fraction removed from the settling vessel 106 is fed to a second settling vessel 110, as described above. In the second settling vessel 110, the sludge fraction undergoes a second settling treatment. Again, the settling treatment in the settling vessel 110 is conducted at ambient temperature, that is the temperature of the surroundings of the settling vessel 110 at a temperature of from 20 to 30°C. The sludge fraction is allowed to settle for a period of at least 2 days, to allow further oil fraction to form. The oil fraction is removed from a region of the settling vessel 110 above the interface between the oil fraction and the sludge fraction. For example, the oil fraction may be withdrawn from the settling vessel 110 using a floating draw-off head. The sludge fraction is removed from the settling vessel and is disposed of following appropriate procedures.

In an alternative embodiment, the settling treatment is conducted in the settling vessel 6, 106, 206, 208 as follows: The raw waste cooking oil is fed to the vessel 6 and is heated to a temperature of from 50 to 100°C and the components of the oil allowed to settle for a period of 2 days. Thereafter, at least a portion of the sludge fraction formed in the vessel is removed from the base of the vessel. The components of the oil remaining in the vessel 6 are allowed to settle for a further 2 days, after which the sludge fraction formed is removed from the base of the vessel. The oil remaining in the vessel is allowed to settle further for a period of 2 days at ambient temperature, to produce the oil fraction, which is removed from the vessel 6 and subjected to the filtration treatment of stage ii) of the process in the filtration assembly 8. The oil fraction to be subjected to filtration in stage ii) of the process is removed from a region of the vessel 6 above the interface between the oil fraction and the sludge fraction. For example, the oil fraction may be withdrawn from the vessel 6 using a floating draw-off head. Any sludge remaining in the vessel is removed and disposed of in accordance with normal procedures.

Turning to Figure 4, there is shown a filtration assembly for use in stage ii) of the process of the present invention. The filtration assembly, generally indicated as 302, comprises a plurality of filter assemblies, as described in more detail below, mounted on a platform 304.

As noted above, the filtration treatment applied to the oil fraction produced in stage i) of the process comprises three stages. The first stage a) of the filtration treatment is a straining treatment. The filtration assembly 302 comprises a strainer assembly 310. The first stage of the filtration treatment comprises subjecting the oil fraction received from the settling treatment to straining in the strainer assembly 310. The strainer assembly 310 comprises a strainer 312 comprising a strainer basket retained in a strainer housing. The oil fraction is fed to an inlet 314 of the strainer 312. The strainer basket has openings of 60 mesh. The strainer basket is cleanable.

In the embodiment shown in Figure 4, the strainer assembly 310 comprises a single strainer 312. Two or more strainers may be employed, if required. If a plurality of strainers are employed, they may be employed in series, in parallel or a combination of both series and parallel, depending upon the requirements to be met, for example the flow rate of oil fraction to be accommodated and the straining duty to be performed, in turn determined by the amount and nature of the material present in the oil fraction that is to be removed.

The strained oil fraction leaves the strainer 312 through a strainer outlet line 316, which passes the strained oil fraction to be processed in the second stage of the filtration 25 treatment.

As described above, the second stage b) of the filtration treatment is a coarse filtration treatment applied to the strained oil fraction. The filtration assembly 302 comprises a coarse filtration assembly, generally indicated as 320. The second stage of the filtration treatment comprises subjecting the strained oil fraction received from the strainer assembly 310 to a coarse filtration in the coarse filtration assembly 320. The coarse filtration assembly 320 of the embodiment shown in Figure 4 comprises four coarse filtration units 324, 326, 328 and 330 arranged in series. In this way, the strained oil received from the strainer assembly 310 is subjected to coarse filtration in four stages.

The first coarse filtration unit 324 comprises three coarse filter assemblies 324a, 3124b, 324c arranged in parallel. The first coarse filtration unit 324 comprises an inlet header 324d for receiving strained oil from the strainer outlet line 316 and distributing the strained oil to each of the coarse filter assemblies 324a, 324b, 324c. An outlet header 324e receives filtered oil from each of the coarse filter assemblies 324a, 324b, 324c, which is fed to the second coarse filtration unit 326 by a feed line 332.

Each of the coarse filter assemblies 324a, 324b, and 324c of the first coarse filtration unit 324 comprises three filter bags retained within a ported filter housing. The filter bags have a pore size of 5 microns.

The second coarse filtration unit 326 is of a similar configuration to the first coarse filtration unit 324 and comprises three coarse filter assemblies 326a, 326b, 326c arranged in parallel. The second coarse filtration unit 326 comprises an inlet header 326d for receiving coarse filtered oil from the feed line 332 and distributing the filtered oil to each of the coarse filter assemblies 326a, 326b, 326c. An outlet header 326e receives filtered oil from each of the coarse filter assemblies 326a, 326b, 326c, which is fed to the third coarse filtration unit 328 by a feed line 334.

Each of the filter assemblies 326a, 326b, and 326c of the second coarse filtration unit 326 comprises three filter bags retained within a ported filter housing. The filter bags have a pore size of 1 micron.

The third coarse filtration unit 328 is of a similar configuration to the first and second coarse filtration units 324, 326 and comprises three coarse filter assemblies 328a, 328b, 328c arranged in parallel. The third coarse filtration unit 328 comprises an inlet header 328d for receiving coarse filtered oil from the feed line 334 and distributing the filtered oil to each of the coarse filter assemblies 328a, 328b, 328c. An outlet header 328e receives filtered oil from each of the coarse filter assemblies 328a, 328b, 328c, which is fed to the fourth coarse filtration unit 330 by a feed line 336.

Each of the coarse filter assemblies 328a, 328b, and 328c of the third coarse filtration unit 328 comprises three filter bags retained within a ported filter housing. The filter bags have a pore size of 1 micron.

The fourth coarse filtration unit 330 is of a similar configuration to the first, second and third coarse filtration units 324, 326, 328 and comprises three coarse filter assemblies 330a, 330b, 330c arranged in parallel. The fourth coarse filtration unit 330 comprises an inlet header 330d for receiving coarse filtered oil from the feed line 336 and distributing the filtered oil to each of the coarse filter assemblies 330a, 330b, 330c. An outlet header 330e receives filtered oil from each of the coarse filter assemblies 330a, 330b, 330c and discharges the coarse filtered oil into a feed line 338.

Each of the filter assemblies 330a, 330b, and 328c of the third coarse filtration unit 330 comprises three filter bags retained within a ported filter housing. The filter bags are high-efficiency filter bags have a pore size of 1 micron.

The number of filtration assemblies in each of the coarse filtration units 324, 326, 328 and 330 may be varied, as required by the coarse filtration duty to be performed.

Similarly, the number of coarse filtration units and, hence, the number of coarse filtration stages may also be varied, again depending upon the coarse filtration duty to be performed.

The filtration assembly 302 further comprises a fine filtration assembly, generally indicated as 340. The third stage of the filtration treatment comprises subjecting the coarse filtered oil fraction received from the coarse filtration assembly 320 to a fine filtration in the fine filtration assembly 340. The fine filter assembly 340 of the embodiment shown in Figure 4 comprises six fine filter assemblies 342a, 342b, 342c, 342d, 342e, 342f arranged in parallel. In this way, the coarse filtered oil received from the coarse filtration assembly 320 is subjected to a fine filtration in a single stage.

The fine filtration assembly 340 comprises an inlet header 344 for receiving coarse filtered oil from the feed line 338 and distributing the oil to the inlet of each of the six fine filter assemblies 342a, 342b, 342c, 342d, 342e, 342f. Similarly, the fine filtration assembly 340 comprises an outlet header 346 for receiving fine filtered oil from the six fine filter assemblies 342a, 342b, 342c, 342d, 342e, 342f and discharging the fine filtered oil from the filtration assembly 302.

Each of the six fine filter assemblies 342a, 342b, 342c, 342d, 342e, 342f comprises a plurality of absolute filter cartridges having a pore size of 1 micron.

The number of filtration units in the fine filtration assembly 340 may be varied, as required by the fine filtration duty to be performed. Similarly, the number of fine filtration stages may also be varied by arranging two or more fine filter assemblies in series, again depending upon the fine filtration duty to be performed.

Referring again to Figure 1, as shown, the fuel oil produced in the filtration assembly 8 by stage ii) of the process is used as a fuel to operate the internal combustion engine 12. The engine 12 may be operated on the fuel oil from the filtration assembly 8 with little or no modification. In particular, the fuel oil may be used to operate the engine 12 during all phases of its operation, including start-up, without the need for an additional fuel, such as diesel.

The internal combustion engine 12 may be used to drive any suitable apparatus or machinery. For example, the internal combustion engine 12 may be used to drive a generator to produce electricity.

The fuel oil may be led directly from the filtration assembly 8 to the inlet of the engine 12. Alternatively, or in addition, at least some of the fuel oil may be routed to the fuel storage facility 10, from where it may be fed to the engine 12, as required. Fuel oil may also be shipped, for example by tanker, from the fuel storage facility 10 for use at other locations.

Embodiments and aspects of the present invention are summarised in the following numbered clauses: 1. A process for producing a fuel for an internal combustion engine from waste cooking oil, the process comprising: i) subjecting the waste cooking oil to a settling treatment to produce an oil fraction and a sludge fraction; and iii) subjecting the oil fraction to a filtration treatment, the filtration treatment comprising a plurality of filtration stages: a) a first stage comprising subjecting the oil fraction to straining to produce a strained oil fraction; b) a second stage comprising subjecting the strained oil fraction to a coarse filtration to produce a coarse filtered oil fraction; and c) a third stage comprising subjecting the coarse filtered oil fraction to a fine filtration to produce a fuel oil.

2. The process according to clause 1, wherein the fuel oil has an ISO 4406:1999 cleanliness code of at least 15/13/11.

3. The process according to either of clause 1 or 2, wherein a portion of the sludge fraction and/or the oil fraction is removed during the settling treatment.

4. The process according to either of clauses 1 or 2, wherein both the oil fraction and the sludge fraction are held in a settling vessel for the duration of the settling treatment.

5. The process according to any preceding clause, wherein the settling treatment is conducted in a vessel, the oil fraction being removed from the vessel at a position spaced apart from and above the interface between the oil fraction and the sludge fraction.

6. The process according to clause 5, wherein the oil fraction is removed from the vessel at the surface of the oil fraction.

7. The process according to any preceding clause, wherein the settling treatment is conducted with the waste cooking oil at an ambient temperature from 20 to 30°C.

8. The process according to clause 7, wherein, if the waste cooking oil is below 20°C, the waste cooking oil is heated to at least 20°C, otherwise the settling treatment is conducted without heating the waste cooking oil.

9. The process according to any preceding clause, wherein the settling treatment is at least 2 days.

10. The process according to clause 9, wherein the settling treatment is from 2 to 25 days.

11. The process according to any preceding clause, wherein the process further comprises: i) a) subjecting the sludge fraction produced in the settling treatment of step i) to a second settling treatment, to produce a further oil fraction and a sludge fraction.

12. The process according to any preceding clause, wherein in step fi) a) the oil fraction is strained through a strainer mesh having a pore size of from 100 to 500 microns.

13. The process according to clause 12, wherein the strainer mesh has a pore size of from 150 to 300 microns.

14. The process according to clause 13, wherein the strainer mesh has a pore size of from 240 to 260 microns.

15. The process according to any preceding clause, wherein in step ii) a) the oil fraction is subjected to straining in a single stage.

16. The process according to any preceding clause, wherein the straining in step ii) a) is conducted at a temperature of from 20 to 30°C.

17. The process according to any preceding clause, wherein in step ii) b) the oil fraction is coarse filtered through one or more coarse filters having a pore size of from 0.5 to 20 microns.

18. The process according to clause 17, wherein the coarse filter has a pore size of from 1 to 10 microns.

19. The process according to any preceding clause, wherein in step ii) b) the strained oil fraction is subjected to coarse filtration in a plurality of stages.

20. The process according to clause 19, wherein in a first stage the strained oil fraction is subjected to a coarse filtration through a coarse filter having a pore size of from 3 to 8 microns.

21. The process according to clause 20, wherein in a second stage, the strained oil fraction is subjected to a coarse filtration through a coarse filter having a pore size of from 1 to 3 microns.

22. The process according to clause 21, wherein the coarse filtration in step i) b) comprises: subjecting the strained oil fraction to a first coarse filtration stage through a coarse filter having a pore size of 4 to 6 microns; subjecting the coarse filtered oil from the first coarse filtration stage to a second coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns; subjecting the coarse filtered oil from the second coarse filtration stage to a third coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns; and subjecting the coarse filtered oil from the third coarse filtration stage to a fourth coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns.

23. The process according to any preceding clause, wherein the coarse filtration in step ii) b) is conducted at a temperature of from 20 to 30°C.

24. The process according to any preceding clause, wherein in step ii) c) the coarse filtered oil fraction is filtered through a fine filter having a pore size of from 0.25 to 2 microns.

25. The process according to clause 24, wherein the fine filter has a pore size of from 0.75 to 1.5 microns.

26. The process according to clause 25, wherein the fine filter has an absolute rating of 1 micron.

27. The process according to any preceding clause, wherein in step ii) b) the coarse filtered oil fraction is subjected to fine filtration in a single stage.

28. The process according to any preceding clause, wherein the fine filtration in step ii) c) is conducted at a temperature of from 20 to 30°C.

29. The process according to any preceding clause, further comprising feeding the fuel oil to the fuel inlet of an internal combustion engine.

30. An apparatus for producing a fuel for an internal combustion engine from waste cooking oil, the apparatus comprising: i) a settling vessel; ii) a filtration assembly comprising: a) a strainer assembly; b) a coarse filtration assembly; and c) a fine filtration assembly.

31. The apparatus according to clause 30, wherein the settling vessel comprises a draw off head for removing an oil fraction.

32. The apparatus according to either of clauses 31 or 32, wherein the strainer assembly is a single stage strainer assembly.

33. The apparatus according to any of clauses 30 to 32, wherein the strainer assembly comprises a strainer having a pore size of from 100 to 500 microns.

34. The apparatus according to clause 33, wherein the strainer has a pore size of from 150 to 300 microns.

35. The apparatus according to clause 34, wherein the strainer has a pore size of from 240 to 260 microns.

36. The apparatus according to any of clauses 30 to 35, wherein the coarse filtration assembly comprises one or more coarse filters having a pore size of from 0.5 to 20 microns.

37. The apparatus according to clause 36, wherein the one or more coarse filters have a pore size of from 1 to 10 microns.

38. The apparatus according to any of clauses 30 to 37, wherein the coarse filtration assembly comprises a plurality of coarse filtration stages arranged in series.

39. The apparatus according to clause 38, wherein the coarse filtration assembly comprises a first stage coarse filter having a pore size of from 3 to 8 microns.

40. The apparatus according to clause 39, wherein the coarse filtration assembly comprises a second stage coarse filter having a pore size of from 1 to 3 microns.

41. The apparatus according to clause 40, wherein the coarse filtration assembly 10 comprises: a first coarse filter stage having a pore size of 4 to 6 microns; a second coarse filter stage having a pore size of 0.5 to 2 microns; a third coarse filter stage a pore size of 0.5 to 2 microns; and a fourth coarse filter stage having a pore size of 0.5 to 2 microns.

42. The apparatus according to any of clauses 38 to 41, wherein each coarse filter stage comprises a plurality of coarse filter assemblies arranged in parallel.

43. The apparatus according to any of clauses 30 to 42, wherein the fine filtration assembly comprises one or more fine filters having a pore size of from 0.25 to 2 microns.

44. The apparatus according to clause 43, wherein the fine filtration assembly comprises one or more fine filters having a pore size of from 0.75 to 1.5 microns.

45. The apparatus according to clause 44, wherein the one or fine filter has an absolute rating of 1 micron.

46. The apparatus according to any of clauses 30 to 45, wherein the fine filtration assembly consists of a single stage fine filter.

47. The apparatus according to clause 46, wherein the fine filtration assembly comprises a plurality of fine filter assemblies arranged in parallel.

48. The apparatus according to any of clauses 30 to 47, further comprising an internal combustion engine for receiving at a fuel inlet fuel oil from the fine filtration assembly.

49. A method of operating an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process of any of clauses 1 to 29.

50. A method of starting an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process of any of clauses 1 to 29; and starting the engine using the fuel oil as the only fuel.

Claims

CLAIMS1. A process for producing a fuel for an internal combustion engine from waste cooking oil, the process comprising: i) subjecting the waste cooking oil to a settling treatment to produce an oil fraction and a sludge fraction; and iv) subjecting the oil fraction to a filtration treatment, the filtration treatment comprising a plurality of filtration stages: a) a first stage comprising subjecting the oil fraction to straining to produce a strained oil fraction; b) a second stage comprising subjecting the strained oil fraction to a coarse filtration to produce a coarse filtered oil fraction; and c) a third stage comprising subjecting the coarse filtered oil fraction to a fine filtration to produce a fuel oil.
2. The process according to claim 1, wherein the fuel oil has an ISO 4406:1999 cleanliness code of at least 15/13/11.
3. The process according to either of claims 1 or 2, wherein both the oil fraction and the sludge fraction are held in a settling vessel for the period of the settling treatment.
4. The process according to any preceding claim, wherein the settling treatment is conducted in a vessel, the oil fraction being removed from the vessel at a position spaced apart from and above the interface between the oil fraction and the sludge fraction.
5. The process according to claim 4, wherein the oil fraction is removed from the vessel at the surface of the oil fraction.
6. The process according to any preceding claim, wherein the settling treatment is conducted with the waste cooking oil at an ambient temperature from 20 to 30°C.
7. The process according to any preceding claim, wherein the settling treatment is from 2 to 25 days.
8. The process according to any preceding claim, wherein the process further comprises: i) a) subjecting the sludge fraction produced in the settling treatment of step i) to a second settling treatment, to produce a further oil fraction and a sludge fraction.
9. The process according to any preceding claim, wherein in step ii) a) the oil fraction is strained through a strainer mesh having a pore size of from 240 to 260 microns.
10. The process according to any preceding claim, wherein the straining in step ii) a) is conducted at a temperature of from 20 to 30°C.
11. The process according to any preceding claim, wherein in step fi) b) the oil fraction is coarse filtered through one or more coarse filters having a pore size of from 1 to 10 microns.
12. The process according to any preceding claim, wherein in step ii) b) the strained oil fraction is subjected to coarse filtration in a plurality of stages.
13. The process according to claim 12, wherein in a first stage the strained oil fraction is subjected to a coarse filtration through a coarse filter having a pore size of from 3 to 8 microns.
14. The process according to claim 13, wherein in a second stage, the strained oil fraction is subjected to a coarse filtration through a coarse filter having a pore size of from 1 to 3 microns.
15. The process according to claim 14, wherein the coarse filtration in step i) b) comprises: subjecting the strained oil fraction to a first coarse filtration stage through a coarse filter having a pore size of 4 to 6 microns; subjecting the coarse filtered oil from the first coarse filtration stage to a second coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns; subjecting the coarse filtered oil from the second coarse filtration stage to a third coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns; and subjecting the coarse filtered oil from the third coarse filtration stage to a fourth coarse filtration stage through a coarse filter having a pore size of 0.5 to 2 microns.
16. The process according to any preceding claim, wherein the coarse filtration in step ii) b) is conducted at a temperature of from 20 to 30°C.
17. The process according to any preceding claim, wherein in step ii) c) the coarse filtered oil fraction is filtered through a fine filter having a pore size of from 0.75 to 1.5 microns.
18. The process according to claim 25, wherein the fine filter has an absolute rating of 1 micron.
19. The process according to any preceding claim, wherein the fine filtration in step ii) c) is conducted at a temperature of from 20 to 30°C.
20. The process according to any preceding claim, further comprising feeding the fuel oil to the fuel inlet of an internal combustion engine.
21. An apparatus for producing a fuel for an internal combustion engine from waste cooking oil, the apparatus comprising: i) a settling vessel; a filtration assembly comprising: a) a strainer assembly; b) a coarse filtration assembly; and c) a fine filtration assembly.
22. The apparatus according to claim 21, wherein the settling vessel comprises a draw off head for removing an oil fraction.
23. The apparatus according to either of claims 21 or 22, wherein the strainer assembly comprises a strainer having a pore size of from 240 to 260 microns.
24. The apparatus according to any of claims 21 to 23, wherein the coarse filtration assembly comprises one or more coarse filters having a pore size of from 1 to 10 microns.
25. The apparatus according to any of claims 21 to 24, wherein the coarse filtration assembly comprises a plurality of coarse filtration stages arranged in series.
26. The apparatus according to claim 25, wherein the coarse filtration assembly comprises: a first coarse filter stage having a pore size of 4 to 6 microns; a second coarse filter stage having a pore size of 0.5 to 2 microns; a third coarse filter stage a pore size of 0.5 to 2 microns; and a fourth coarse filter stage having a pore size of 0.5 to 2 microns.
27. The apparatus according to any of claims 21 to 26, wherein the fine filtration assembly comprises one or more fine filters having a pore size of from 0.75 to 1.5 microns.
28. The apparatus according to claim 27, wherein the one or fine filter has an absolute rating of 1 micron.
29. The apparatus according to any of claims 21 to 28, further comprising an internal combustion engine for receiving at a fuel inlet fuel oil from the fine filtration assembly.
30. A method of operating an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process of any of clauses 1 to 20.
31. A method of starting an internal combustion engine comprising feeding to the fuel inlet of the internal combustion engine fuel oil produced by the process of any of clauses 1 to 20; and starting the engine using the fuel oil as the only fuel.