Field of Invention

The present invention relates to a process for processing oil-based functional fluids in order to render them useful. In particular, the processing is intended to yield oil products that are suitable for use in the explosives industry. The invention also relates to oil products produced in accordance with the present invention and their use in the explosives industry. The present invention also provides a plant (system) for implementation of the process of the invention.

Background to Invention

The manufacture of various explosives compositions, such, as emulsion explosives and ANFO explosives, requires the use of a fuel component. Similarly, emulsifiers for use in the formulation of explosive compositions are made using a diluent base oil. Conventionally, the oil used is a virgin oil or it is derived from a used oil that has been re- refined back to virgin quality. To achieve this quality refinement typically involves filtration, dehydration, fractionation, solvent washing and hydrogenation. The use of virgin oils or suitably re-refined used oils has associated cost implications and it would be desirable to employ lower grade oils. Used oil is significantly cheaper than virgin base oil (and heavily re-refined used oil), and does not experience the same kind of price fluctuations associated with crude oil. Moving away from using virgin oil would also be desirable from an environmental perspective since this would reduce consumption of virgin oils and hence reduce the need for crude oil. Substitution of virgin oils with processed used oils has less impact on the environment.

Oil-based functional fluids, such as lubricating and hydraulic oils, generally use the same kind of base oil component that is used in formulating emulsifiers and explosive compositions. However, such oils invariably include a whole host of functional additives and contaminants that prevent the used oil from being employed in the explosives context. The potentially variable composition of such oils can also present problems.

Against this background the present invention seeks to provide a way in which used oils can be processed so that they may be used in the manufacture of emulsifiers for use in explosive compositions, and for the manufacture of explosive compositions. Such a process will have associated environmental benefits as described. To be useful commercially, the process should also be economical when measured against the existing use in the explosives industry of virgin base oils and heavily re-refined used oils.

Summary of the Invention

In accordance with the present invention it has been found that certain additives and contaminants present in used oil-based functional fluids, such as lubricating oils and hydraulic fluids, mean that the (used) functional fluids are not suitable for use in the explosives context. The additives and contaminants are detrimental to the performance of emulsifiers and hence to the formation and stability of explosives emulsions. On the other hand, it has been found that the presence of certain functional additives can be tolerated. Also in accordance with the present invention, it has been found that the problematic additives and contaminants can be removed by a relatively straight forward and cheap treatment regime to yield a treated/processed product that may be used to manufacture explosives compositions, and emulsifiers used in the manufacture of explosives compositions.

Accordingly, in one embodiment the present invention provides a process for treating a used oil-based functional fluid, the process comprising: washing of the functional fluid by contacting the fluid with water followed by settling in order to produce an aqueous phase and an oil phase; separating the oil phase from the aqueous phase; and subjecting the oil phase to dehydration to further remove water from it.

The process of the invention may include additional treatment steps depending upon the characteristics of the feedstock (used) oil being processed. The process may also include quality control measures to ensure that the used oil is suitable for processing in accordance with the present invention. If the used oil does not at the outset exhibit certain characteristics, processing of it in accordance with the invention is unlikely to result in a product suitable for use in the manufacture of explosives compositions or emulsifiers used in making explosive compositions. The process may also include quality control measures to ensure that the product of the process is of a suitable quality for the intended end use.

The present invention also provides a treated oil-based functional fluid produced by the process of the present invention, and to the use of such fluid in the manufacture of explosives compositions and emulsifiers for use in such compositions.

The present invention also provides a method of blasting comprising detonation of an explosive composition prepared using a treated oil-based functional fluid produced in accordance with the present invention. The treated oil-based fluid may be used as a fuel component of the explosive composition or as part of the emulsifier used in the manufacture of an explosive composition.

Detailed Description of the Invention

The process of the present invention remediates a (used) oil-based functional fluid to remove from the fluid certain additives and contaminants that would otherwise interfere with the use of the fluid in the explosives context as described. In the context of the present invention an oil-based functional fluid is "used" if it has already been employed for its intended purpose, for example as a lubricating oil or hydraulic fluid, and that because of its composition (additives and/or contaminants) it is, or is likely to be, unsuitable for the manufacture of an explosive composition or emulsifier for use in making explosive compositions. In this regard the present invention may be applied to render useful a used oil-based fluid that is inherently unsuitable for use in the explosives context as described. Furthermore, the present invention may be applied to render clearly useful a used oil-based fluid that may be borderline suitable for use in the explosives context as described. In this latter case the invention is intended to remove any risk associated with use in the explosives context of such used functional fluids.

The functional fluid may be any oil derived from machinery, for example at a mine site. The functional fluid may be a lubricating oil, such as an engine, transmission or gear oil, a hydraulic oil, or the like. The oil-based functional fluid may be a single fluid or a blend of two or more oil-based functional fluids resulting from collection and mixing of different oil-based functional fluids. Herein the term "functional fluid" is intended to embrace these various possibilities.

Typically, the functional fluid will include a variety of additives that impart desirable properties to the functional fluid based on its intended use. Such additives are described in more detail below.

Dispersants - these are used to moderate lubricant viscosity by keeping soot and other solid contaminants suspended in the oil, avoiding accumulation of solids which may lead to engine damage through loss of lubrication. Dispersants are typically alk(en)ylsuccinimides, for example, reaction products of polyamines and PiBSA. Alkylsuccinimide type dispersants used in engine oils have been tested in the past as surfactants for emulsion explosive compositions, and while they have not performed as well as current PiBSA emulsifiers, the dispersants have not had a destructive affect, and their use can therefore be tolerated.

Detergents - these are used to prevent the formation of deposits on engine components at high temperatures and to neutralise the formation of acidic products of combustion. Typical detergents are oil-soluble organo-metallic compounds, such as calcium sulphonate and calcium alkyl phenate. The surface active nature and the high alkalinity of detergents may cause problems with emulsifiers and emulsion explosives.

Anti-oxidants - these inhibit the oxidation of oil. The most common and effective antioxidant is ZDDP (Zinc Dialkyldithiophosphate). This is a surface active agent and may cause problems with respect to emulsion stability.

Anti-wear agents (or extreme pressure (EP) agents) - these form molecular layers on engine components and protect the engine from wear. The most common and effective anti-wear agent is ZDDP (Zinc Dialkyldithiophosphate).

Viscosity modifiers - these control viscosity at high and low temperatures. Typical viscosity modifiers are styrene-butadiene copolymers, methacrylates and ethylene- propylene copolymers, for example, Paratone™. These types of compounds have been tested in emulsions and are known not to have a destructive affect,

Other species may be present through use or contamination of the fluid, for example due to how it is collected and stored. Such species include coolants, degreaser, brake fluid components and solvents.

Of the various additives/species that may be present, the presence of detergents, inhibitors

r

(such as anti-oxidants and anti-wear agents), coolants, brake fluid, degreaser and solvents have been found to be problematic with respect to incorporation in explosive compositions and/or formulation of emulsifiers for use in formulating such compositions. The presence of other additives/species can be tolerated at the normal concentration levels.

The first step in the process of the invention is a water wash and this is done to remove water-soluble components that would otherwise be detrimental to use of the processed fluid. In particular, the water wash is intended to remove glycols and glycol ethers commonly found in coolants and brake fluids, alkaline species found in detergents, and alcohols, (polar) hydrocarbon solvents and surfactants commonly found in degreasers. The water wash does not remove any oil-soluble species.

In order to be effective the water and fluid to be processed must be mixed thoroughly to ensure intimate contact of the water with water-soluble species present in the fluid and so aid dissolution of these species in the water. The water wash step can be optimised with respect to removal of water-soluble species by varying such things as water temperature, water to oil ratio, residence (mixing) time and/or contact efficiency.

It may be beneficial for the water used in the water wash to be at elevated temperature, as this will result in an oil/water mixture having an elevated temperature. This may enhance uptake of water soluble species. However, it is usually convenient to use water at ambient temperature. The oil temperature will also influence the mixture temperature and the oil is also typically used at ambient temperature. Typically, the intention is to achieve a mixture temperature corresponding to the ambient temperature, and typically this will be from 15- 40°C.

With respect to the water to oil ratio used it is preferred to undertake the water wash with the minimum effective amount of water as water must be removed in subsequent steps. In practice the water to oil weight ratio will generally be 5:1 to 1 : 10, preferably 4: 1 to 1 :9, such as 1 :1 to 1 :9. In some embodiments a water to oil weight ratio of 3:7 has been found to be useful.

The residency (mixing) time will preferably be as short as possible to enhance throughput. Desirably, the residence time will be no more than 2 hours, preferably no more than 1 hour, more preferably no more than 30 minutes and most preferably no more than 15 minutes.

The contact efficiency relates to the manner in which the water and fluid are mixed together. As explained it is preferred that the water and fluid come into intimate contact with each other so that water-soluble species are effectively transferred to the wash water. Vigorous mixing would achieve this but this can result in a significant amount of emulsion being formed and this can make subsequent separation of the aqueous phase and oil phase difficult. Emulsion formation also impacts on the efficiency of the process of the invention since water and oil are consumed when an emulsion is formed. It is preferred therefore that the water and fluid are mixed in a way that avoids an emulsion being formed. Some emulsion formation may be tolerated when implementing the process of the invention provided this does not impact unduly on the intended process outcomes. Formation of an emulsion impacts on the amount of water that is available for washing of functional fluid and the amount of aqueous phase that can be recovered when the oil phase and aqueous phase are separated. As a guide, in the separation step it is preferred to recover at least 85%, more preferably, at least 90%, of the total volume of water that has been used in the washing step. In other words, preferably no more than 15%, more preferably no more than 10%, by volume of the total amount of water used is consumed in emulsion formation.

The ratio of water to fluid may also influence the tendency to form an emulsion. Vigorous mixing may also entrain water in the oil phase. With these issues in mind, it has been found useful to add the water to the fluid and to stir the two together using a low shear impeller.

The manner in which water is added to the used fluid should be carefully controlled to avoid mixing of the two before use of the impeller. The reason for this is that the fluid is likely to contain emulsifier and formation of an emulsion is undesirable. In practice water may be introduced slowly at the bottom of a vessel containing the used fluid, thereby displacing the used fluid upwards. The water should be introduced in a manner that will cause little or no turbulence. In this regard the water may be delivered at a low velocity through a relatively large diameter pipe. A diffuser may also be used to help reduce interaction between the fluid and water as water is introduced into the vessel.

The impeller that is used in practice of the invention imparts low shear. Impellers may be rated by reference to a power number based on the amount of shear produced. Preferably, the impeller used has a power number of less than 3.0, more preferably less than 1.5 and more preferably still less than 0.25.

Generally, the vessel in which the used fluid and water are charged is cylindrical. Preferably, the vessel will be squat (relatively large diameter and relatively low height) in appearance as this will provide increased surface area of fluid/water when compared with a taller design and reduce dead mixing spots. Typically, the aspect ratio of height of liquid in the vessel to diameter of the vessel will be 1 :1 to 1 :3. If the aspect ratio is 1 :<1 a plurality of impellers may be required to avoid dead mixing spots.

The size of the impeller may also be important. Generally, the diameter of the impeller will' be 1/3 to 1/2 of the vessel diameter. The impeller should be positioned at the fluid water interface to maximize fluid/water contacting and thus cleaning of the fluid. Generally, the impeller will be positioned about 1/2 to 1 impeller length (diameter) from the bottom of the vessel. This together with the requirement to have the impeller positioned at the fluid/water interface places a limit on the form of vessel that may be used effectively.

In practice these various parameters will need to be balanced against the amount of water entrained in the fluid and the uptake of water soluble species in the water. For example, increasing the water temperature, the stirring speed, the applied shear and the mixing time will each enhance the uptake of water soluble species, but also the amount of water entrained in the fluid. Increasing the water to fluid ratio generally decreases the uptake of water soluble species whilst increasing the amount of water entrained in the fluid.

Desirably, the process of the invention employs a combination of low water to fluid ratio (e.g. 3:7), ambient temperature (15-25°C), low shear (30-60rpm) and low residence time (15 minutes). The rate of addition of the water may also have an impact on the efficacy of the process. A relatively low rate of addition e.g. 8-10 kg/min may be beneficial. The efficacy of the water wash step can be assessed by sampling and analyzing of the aqueous and fluid phases.

In an embodiment of the invention it is desirable to neutralize acidic or alkaline species that may be present in the functional fluid being treated and that will not be removed from the functional fluid by treatment in accordance with the invention. Such species may interfere with the intended end use of the treated functional fluid. Acidic or alkaline species may be neutralised by including suitably alkaline or acidic species in the water used for washing of the functional fluid. By way of example, certain types- of functional fluids may contain acidic combustion products such as nitric acid and hydrochloric acid. These may be neutralised using a suitable base such as sodium hydroxide or sodium carbonate. Alkaline species such as calcium carbonate may be neutralised with suitably weak or strong acids such as phosphoric acid, acetic acid and hydrochloric acid. Of course, any species added to the wash water to neutralize acidic or alkaline species should not impact on the intended end use of the treated functional fluid.

c

After the water washing step the aqueous phase and oil phase are allowed to settle. Settling allows partitioning of the .phases so that they may then be separated by simple draining. Typically, a longer settling time is preferred as this has been found to lead to increased water removal as a result of increased partitioning. Generally, the settling time is no more than 48 hours, for example, no more than 24 hours, such as from 2 to 24 hours. This step typically reduces the amount of water in the oil phase to below 10% by volume.

After the aqueous phase and oil phase have been separated from one another the oil phase is dehydrated to further remove water from it. Dehydration removes any free water, emulsified water and entrained water from the oil phase. Dehydration is generally carried out at elevated temperatures and under reduced pressure to achieve a reduced water content. The temperature and pressure that can be achieved wiU depend upon the nature and scale of apparatus used. Desirably, dehydration also leads to stripping of light (volatile) organic species that may be present. Such light organics might otherwise cause instability problems to downstream explosive compositions. Light organic components tend to have the effect of lowering the flash point of the finished oil product. Desirably, from a safety perspective, the product should have a suitable flash point based on its intended use. For example, when the product is to be used in formulating an explosive composition, the flash point will vary depending upon the context in which the explosives composition is to be used. For standard usage the flash point may need to be at least 61°C, for hot ground usage the flash point may need to be at least 100°C and for underground usage the flash point may need to be at least 130°C. It may be necessary to ensure that light organic components are stripped (distilled) from the oil in the dehydration step in order to satisfy this characteristic.

The required water content following dehydration will vary depending upon the intended use for the processed oil. If the processed oil is to be used for manufacture of an emulsifier, the water content should be no more than 0.05% by weight. However, when the processed oil is intended to be used for manufacture (blending) of an explosive composition, higher residual water content may be tolerated. In this intended use the water content should be no more than 2% by weight, for example no more than 1 % by weight.

In an embodiment of the invention it may be advantageous to add a demulsifier to the fluid being processed in order to reduce the amount of water that is entrained or consumed in emulsion formation during the water washing step. This enables more thorough mixing to be undertaken which in turn leads to more thorough cleaning of the oil and faster separation of phases. Conventional demulsifiers may be used (for example sulfonic acids such as dodecylbenzene sulfonic acid (DDBSA) at the usual treat rates. DDBSA is typically used at a treat rate of 0.01 to 5% by weight. . Useful demulsifiers are commercially available, such as Nalco EC2045A. In practice the Total Base Number (TBN) of the oil may be measured and the amount of demulsifier to be used calculated on the basis of the acid equivalent needed for neutralisation. The demulsifier is added to the oil before any water is introduced. The demulsifier should end up in the aqueous phase and be separated from the oil phase when the two phases are partitioned. However, to the extent that any demulsifier remains in the oil phase, it is important that the demulsifier that is used does not interfere with the intended end use of the oil.

Depending upon the water content of the oil phase after partitioning and separation of the phases, it may be necessary to treat the oil phase to further remove water before the dehydration step. Thus, if the water content of the oil phase exceeds about 10% by weight, it is preferred to further remove water from the oil phase before dehydration. This can be done by centrifuging the oil phase or by using a coalescer. The intention is that the oil phase has a water content of at most 10% by weight prior to being dehydrated. Dehydration is intended to further reduce the water content to the level required based on the intended end use for the oil. The water content of the oil can be determined by Karl Fischer titration.

The functional fluid which is processed in accordance with the present invention should have certain characteristics that render it suitable for processing. Desirably, before washing with water is undertaken the functional fluid should have a particulates size of no more than 100 μπι, preferably no more than 50 μηι, most preferably no more than 25 μπι. If the fluid contains solids having a greater particle size then the fluid should be filtered _^ during the process of the invention. Sump oil from an engine for example is likely to have ,a significant content of large sized (400 μπι) particles, and filtration would then be required. Conventional filtration methodology may be employed. In actual fact, when recovering and collecting used oils, filtration is commonly applied anyway. Equipment using functional fluid may also include filters to remove particulate matter that may be present in the fluid. This is certainly the case in some hydraulic systems.

Additionally, or alternatively, filtration to remove particulates may be undertaken at the end of the process during the dehydration phase. Here the oil will be at elevated temperature (usually at least about 70°C) and it will have a reduced viscosity that makes filtration easier. A candidate oil for use in the present invention may be subjected to acceptance testing in order to determine its suitability for use in the process of the present invention. This is likely to be necessary where the oil to be processed varies in quality and composition. Such acceptance testing is likely to involve routine measurements as to density, water content, flash point and viscosity. Detailed testing using Fourier transform IR spectroscopy (FTIR), gas chromatography and a metal screen (ICPMS) may also be used to determine the content of the oil. The presence of other species, such as polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH), may also be assessed. If the quality and composition of the oil to be processed will be essentially uniform, repeated detailed testing should not be necessary.

By way of example a used functional fluid suitable for processing in accordance with the present invention may have the following array of properties.

TABLE 1

Physical / Chemical Property Test Method Specification Limits

Appearance Visual ■ Liquid

Colour Visual Black/Brown

Odour Olfactory None - Mild, Not Irritating

Particulate size μηι) Filtration <250μιη

Flash Point - PMCC (°C) ASTM D93 > 61

Water Content (%w/w) ASTM E203 < 10%

Density ® 15°C (g/mL) ASTM D5002 0.87 - 0.90 Viscosity @ 40 ^° C (cP) ASTM D445 25 - 90

Arsenic (ppm) USEPA 200.7 <5

Cadmium (ppm) USEPA 200.7 <2

Chromium (ppm) USEPA 200.7 <10

Lead (ppm) USEPA 200.7 <100

Halogens (ppm) USEPA 200.7 <1000

Polychlorinated Biphenyls (ppm) EPA VIC 6013 <2

Polycyclic Aromatic Hydrocarbons (ppm) USEPA 8100 <1000

If the starting functional fluid already contains water as a separate but present phase, it may be advantageous to remove this water by settling and phase partitioning before implementing the process of the invention. The product of the process of the present invention is a treated functional fluid comprising a base oil that enables its use in the manufacture of explosive compositions and/or in the manufacture of emulsifiers for use in such compositions. The treated fluid will include components that will not adversely influence the intended use.

Desirably, after processing in accordance with the present invention the product fluid has the following array of properties: '

TABLE 2

In the manufacture of explosive compositions the product of the invention may be used to replace all or some (usually only some e.g. up to 50% by volume) of the fuel oil used to make emulsion explosives or the fuel oil used to make ANFO explosives. In the manufacture of emulsifiers the product of the process is itself used as diluent oil in which components, e.g. PIBSA and amine, are reacted. In this case the treated fluid produced in accordance with the invention must be especially dry (no more than 0.05% by volume water). Typically, in the context the treated fluid will replace up to 100% of the virgin base oil or re-refined base oil that is otherwise used in emulsifier manufacture. Replacement of such virgin oil or re-refined oil will lead to financial savings and provide environmental benefits. The present invention also provides a plant (system) for treating functional fluid in accordance with the process of the invention. The plant comprises a washing tank, a settlement tank and a polisher. In the washing tank functional fluid is washed with water noting the underlying principles of the invention. The washing tank may be of the design shown in Figure 1. The settlement tank is adapted to receive liquid from the washing tank and allow further separation of water from oil phase. The settlement tank will also include one or more conduits for tapping off liquid from the settlement tank. The polisher is intended to achieve dehydration of oil phase transferred to it from the settlement tank. The polisher is adapted to heat the oil phase under vacuum to achieve dehydration. After washing oil phase may be recirculated between the settlement tank and polisher. The plant may also comprise a storage tank for treated functional fluid. The contents of that tank should be ready for use. The plant may also be configured to recycle wash water removed form the washing tank and/or settlement tank for use in washing a subsequent batch of functional fluid.

In a preferred embodiment the plant is mobile. For example, the individual plant components may be supplied in a ready to use configuration in a shipping container, or as mobile platform on a vehicle.

Brief Discussion of Drawings

Embodiments of the present invention are illustrated in the accompanying non-limiting drawings in which:

Figure 1 is a schematic illustrating a washing tank for implementing part of the process of the present invention;

Figure 2 is a flow chart illustrating a process in accordance with the present invention; and

Figure 3 is a schematic showing a modular unit for implementing a process of the present invention. Figure 1 illustrates a washing tank (1) that may be used for implementing the process of the present invention. The tank (1) is typically cylindrical and in use will include a layer of functional fluid (2) over a layer of water (3). Initially, the functional fluid (2) is provided into the tank (1) and water introduced slowly at the bottom of the tank (1) through a conduit (8). A diffuser (7) is used to minimize turbulent mixing of the functional fluid (2) and water (3) as water is delivered into the tank. The volumes of functional fluid (2) and water (3) used are pre-determined. After the functional fluid (2) and water (3) have been delivered into the tank (1) a low shear impeller (5) positioned at the interface of the functional fluid (2) and water (3) is rotated on a shaft (4). Headspace (6) is provided above the functional fluid (2).

Rotation of the impeller (5) is intended to cause low shear contacting of the functional fluid (2) and water (3) with minimal or no emulsion formation. In this way the functional fluid (2) is contacted with and washed by the water (3) with certain species present in the functional fluid (2) being taken up by the water (3). After this washing step has been carried out water (containing species from the functional fluid (2)) can be removed from the tank (1) through the conduit (8). The residual oil phase (i.e. washed functional fluid) may then be transferred to a settling tank to allow further water to separate from the oil phase. This also allows the tank (1) to be used to process another batch of functional fluid.

According to Figure 2 used oil is initially subjected to acceptance testing in order to confirm that it has basic characteristics for use in the present invention. The kinds of tests that may be employed are noted above. The oil is also filtered using a ΙΟΟμπι filter to remove particulates above this size.

Processing involves an initial water wash and this takes place in a dedicated washing tank equipped with an agitator. Usually oil is delivered into the tank first followed by water. A portion of the water (e.g. 70%) may be delivered into the oil rapidly with the remainder being added more slowly. The various washing parameters and their influence on contaminant uptake and water retention have been discussed above. After washing the resultant oil/aqueous phase mixture may be allowed to remain in the washing tank for a period (say about 30 minutes) after which some phase partitioning should have already taken place. At this point a portion of the aqueous phase can be tapped off with the oil phase then being transferred to a settling tank. As an alternative the mixture may be transferred to the settling tank immediately after washing has taken place. In the settling tank (further) phase partitioning is allowed to take place and the aqueous phase removed. The aqueous phase may be recycled to the water washing step depending upon its characteristics in terms of re-usability.

The water content of the oil phase before (and after) de-watering may be determined to ensure that the oil phase is suitable for further processing. ater removed in this step may be recycled back to the water wash step if still suitable for that purpose.

The next step of the process involves dehydration of the oil phase to further reduce its water content as required depending upon the intended end use. Dehydration involves heating the oil phase under vacuum.

After dehydration the oil is in principle ready to be used. However, the process will also typically involve a quality control and validation testing step to ensure product quality and suitability for end use. This usually involves subjecting the oil to a battery of tests such as gas chromatography, flash point analysis, kinematic viscosity, digital density and Columetric Karl Fischer and FTIR. The intention is to establish that the processed oil has the necessary physical properties and chemical composition to be useful in formulating an explosive composition or emulsion. Prior to use the oil may be stored as necessary.

The process of the invention may be implemented using a modular arrangement of equipment, for instance as illustrated in Figure 3. Preferably, the arrangement is mobile so that processing may be implemented at a mine site or the like. This is more likely to be the case for explosives manufacture rather than emulsifier manufacture. In this regard it may be possible to implement the process of the present invention using used functional fluid from machinery in the vicinity of the mobile unit/mine site. Alternatively, used functional fluid may be collected from various sources and processed at a dedicated processing plant.

One embodiment of this invention comprises miniaturisation of the process to fit into a standard 20 foot shipping container, and a typical arrangement of components that would facilitate this is shown in Figure 3. Variations on this design involve the use of multiple shipping containers. The process comprises washing, separation and dehydration which are fundamental to the current invention, with coarse and fine filtration also included in the design shown in Figure 3. Firstly, used lube oil and then water is charged into the washing tank via a strainer using the pump. The oil/water mixture is agitated using low shear to facilitate dissolution of water soluble contaminants into the aqueous phase without forming an emulsion. The mixture is then allowed to stand so that the phases separate, at which point the aqueous phase is drained from the washing tank. The remaining oil, which will contain about 10 % water, is transferred to the settlement tank. Further water is drained from the settlement tank as it separates from the oil and the washed oil is then recirculated between the settlement tank and the polisher. The polisher heats the oil to an elevated temperature under a vacuum and dehydrates the oil until the water content is around 1 %. The final product is discharged to a storage tank ready for use as a fuel for mining explosives. Much of the wash water may be recycled for use in the next batch.

The following non-limiting examples illustrate embodiments of the invention.

Example 1: Effect of Surface Active Contaminants on ANE Stability

To accurately determine the impact of surface active contaminants on ANE stability a number of model emulsions were prepared. A control ANE was prepared by adding an 80 % AN solution to a 25 % emulsifier in diesel fuel blend at 75°C in a ratio of 93:7. The following five additives and contaminants were added at a level of 1 % to five separate fuel blends and the corresponding ANEs prepared in the same manner as the control.

1. OLOA 219C detergent from Chevron Oronite 2. OLOA 269R inhibitor from Chevron Oronite

3. Shell Dobatex Degreaser

4. Castrol antifreeze/antiboil

5. Castrol brake fluid

The presence of these additives and contaminants in the model emulsions produced measurable differences in the ANE properties. The detergent and inhibitor samples produced faster refinement and a larger mean droplet size; the degreaser caused faster refinement and high levels of crystallisation; the coolant produces faster refinement; and the brake fluid reduced the efficiency of the chemical gassing reaction.

Example 2: Evaluation of Alternative Oil Treatment Methods

Four alternative methods of washing the oil were investigated and included acid washing, solvent washing, water washing and amine washing. Typical raw used oil supplied by Country Wide Fuels was used for the testing. Each of the methods is described below:

Acid Wash

A 2.4%w/w Sulphuric Acid solution was added to the used lube oil to give a final Sulphuric Acid concentration of 0.3%w/w. The mixture was stirred and heated to 70°C for 2 hours, before being allowed to cool. The mixture was centrifuged at 4000g for 20min and then the oil decanted from the sludge. The oil was then dehydrated at 100°C for 30 mins to remove the residual water.

Solvent Wash

Used lube oil, Acetone and Diisopropyl Ketone (DIPK) were combined in the ratio 1 :2:2. The mixture was then stirred manually for 1 minute before being centrifuged at 4000g for 20min. The liquid oil was then decanted from the solid residue, and the excess solvent was removed by heating to 140°C for approximately 3 hours. Water Wash

Used lube oil and water were stirred with a low shear impeller in a ratio of 1 : 1 at 50°C for 30 minutes. The water and oil mixture was then allowed to settle and the majority of the water was drained off. The remaining oil was then centrifuged at 4000g for 20min to remove water. After centrifuge the oil was dehydrated at 105°C for 30 mins to remove the residual water.

Amine Wash

Used lube oil and Heptane (Shell) were combined in a ratio of 1 :1. Ethylene Diamine (EDA) was then added to give a final concentration of 5w/w% in the mixture. The mixture was stirred for 30 mins at room temperature and then centrifuged at 4000g for 20min. The liquid oil was decanted from the solid residue and then heated at 110°C for 2 hours to remove the excess Heptane.

The table below compares analysis results of the raw unwashed used oil to oil washed by the various methods.

yco cs encompasses coo ant, ra e u an egreaset components.

The data in the table demonstrates that each of the types of washes is effective at removing different types of species from the oil. For example a solvent wash is very effective at reducing the ash content; an acid wash is particularly effective at reducing the calcium content associated with detergents; and, the amine wash is effective at reducing the zinc content associated with ZDDP. The water wash is the most effective at reducing the glycolics, which are of greatest concern with respect to the stability of ammonium nitrate emulsions used in explosives.

Example 3: Evaluation of the Water Wash Method to Remove ANE Poisons

Dehydrated Fuel Oil from Country Wide Fuel Oil was used as the base stock. The used lube oil was spiked with contaminants and then a water wash was carried out in an attempt to remove the contaminants. NMR was used to analyse the oil before and after the treatment process to determine the effectiveness of the process. The contaminants used were:

^■ Castrol Anti-Freeze/ Anti-Boil - 95% MEG

^■ Castrol Brake Fluid Response DOT4 - polyglycol based . ^{■ ■} Shell Dobatex Degreaser - contains ethoxylated alcohols, butoxy ethanol, d- limonene and a sulphonate surfactant

Each contaminant was added to the oil at a level of 5%, the oil was then stirred in order to disperse the contaminant.

Water Wash

Used lube Oil (with contamination) and water were stirred with a low shear impeller in a ratio of 1 : 1 at 50°C for 30 minutes. The water and oil mixture was then allowed to settle and the majority of the water was drained off. The remaining oil was then centrifuged at 1800g for 5min in order to further reduce the water content. After centrifuge the oil was dehydrated at 105°C until the water content was below 0.5%.

The data in the table demonstrates that a water wash is effective at removing emulsion poisons from used lube oil. Although the process did not completely remove the contaminants, it can be optimised to be more effective.

Example 4: Testing of Water Washed Used Oil in ANE

Used lube Oil and water were stirred in a ratio of 2.5: 1 at 40°C for 15 minutes. The water and oil mixture was then allowed to settle and the majority of the water was drained off. The remaining oil was then centrifuged at 1800g for 5min to remove water. After centrifuge the oil was dehydrated at 145°C until the water content was below 0.05%.

A control ANE was prepared by adding a 75 % AN solution to a 15 % emulsifier in diesel fuel blend at 75°C in a ratio of 92:8. Two variants were prepared: Firstly, half of the diesel in the fuel blend was replaced with unwashed used lube oil; and secondly, half of the diesel in the fuel blend was replaced with water washed used lube oil.

Evaluation of ANE properties indicated that the washed oil containing emulsion performed more like the control in the areas of refinement, gassing, droplet size and stability compared with the unwashed oil containing emulsion. The PPAN doped emulsion with the unwashed used oil showed significantly inferior stability to the washed oil emulsion which was similar to the control.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.