METHOD AND APPARATUS FOR RECYCLING AN AGGREGATE CONTAMINATED WITH A HYDROCARBON

Abstract: The present invention relates to a method and apparatus for recycling an aggregate contaminated with a hydrocarbon. More particularly it relates to a method and apparatus for cleaning ballast, for example, the stone chippings used on railway tracks. It could however be used to clean, for example, pebbles from an oil contaminated beach. The method comprises the steps of: i) subjecting the aggregate to a prewash, ii) solvent washing the aggregate to remove the hydrocarbon contaminant, iii) rinsing the aggregate with water to remove residual solvent containing the hydrocarbon contaminant, iv) separating off the solvent containing the hydrocarbon contaminant and water from the aggregate, and v) recycling the cleaned aggregate. The apparatus comprises: i) means for extracting and/or transferring the aggregate to the apparatus; ii) means for prewashing the aggregate; iii) means for transferring the aggregate to a solvent treatment circuit; iv) means for transferring the aggregate to a water treatment circuit; v) means for transferring the cleaned and decontaminated aggregate for recycling, and vi) means for collecting waste streams from the solvent and water treatment circuits.

Description: DESCRIPTION METHOD AND APPARATUS FOR RECYCLING AN AGGREGATE CONTAMINATED WITH A HYDROCARBON The present invention relates to a method and apparatus for recycling an aggregate contaminated with a hydrocarbon. More particularly it relates to a method and apparatus for cleaning ballast, for example, the stone chippings used on railway tracks. It could however be used to clean, for example, pebbles from an oil contaminated beach. For the most part, aggregates contaminated with hydrocarbons are not cleaned and recycled but collected and disposed of on, for example, landfill sites. This is expensive since the aggregates usually need to be replaced and dumping costs can be high. It is also environmentally unfriendly. US 4203493 discloses a method and apparatus for cleaning railway ballast. The method comprises tumbling ballast in a drum with water. However cleaning is inefficient. It is an aim of the present invention to devise an improved method of cleaning an aggregate contaminated with a hydrocarbon so the aggregate can be recycled and the hydrocarbon disposed of safely and in a controlled manner. It is another aim of the invention to devise an apparatus for cleaning an aggregate contaminated with a hydrocarbon so the aggregate can be recycled and the hydrocarbon disposed of safely and in a controlled manner. Ideally the apparatus should be mobile so that the method of the invention can be conducted in situ. According to a first aspect of the present invention there is provided a method of cleaning and recycling an aggregate contaminated with a hydrocarbon comprising: i) subjecting the aggregate to a prewash, ii) solvent washing the aggregate to remove the hydrocarbon contaminant, iii) rinsing the aggregate with water to remove residual solvent containing the hydrocarbon contaminant, iv) separating off the solvent containing the hydrocarbon contaminant and water from the aggregate, and v) recycling the cleaned aggregate. According to another aspect of the present invention there is provided an apparatus, for conducting the method of the invention, comprising; i) means for extracting and/or transferring the aggregate to the apparatus ii) means for prewashing the aggregate; iii) means for transferring the aggregate to a solvent treatment circuit; iv) means for transferring the aggregate to a water treatment circuit; v) means for transferring the cleaned and decontaminated aggregate for recycling, and vi) means for collecting waste streams from the solvent and water treatment circuits. Preferably the apparatus is a mobile apparatus which is provided with its own means of power and propulsion. Alternatively the apparatus could be provided with wheels, runners or the like and is connected to, for example, a locomotive or tractor. In yet a further embodiment the apparatus could be a stationed apparatus. In a preferred embodiment the method comprises: i) transferring the aggregate contaminated with a hydrocarbon to a cleaning apparams. This is most preferably achieved using a hose and applying suction via, for example, a vacuum extractor. Other methods such as, for example, using a digger arm will of course be apparent to the skilled man. The actual means will depend on whether the apparatus is fixed or mobile; ii) optionally screening the aggregate to remove, for example, undersized particles, and litter. This can be achieved by methods familiar to the skilled man such as, for example, sieving, and/or passing the aggregate across an air stream. iii) the aggregate is then subjected to a pre-wash in water to remove, for example, fines for example, clay, which can cause "sticking" problems; iv) the aggregate is then subjected to a solvent wash. The solvent could be any solvent capable of removing a hydrocarbon contaminant from the aggregate. However, particularly favoured is a citrus extract because it is not subject to COSHH regulations. The citrus extract is preferably a citrus peel oil such as for example a folded oil and/or a terpene. More preferably still the citrus extract is an orange extract. The citrus extract may be used neat or diluted with a bulking agent such as a de-aromatized iso paraffin. By using a citrus extract, as opposed to a more traditional organic solvent it is possible to recycle the hydrocarbon waste, separating it from the solvent by strongly agitating it. Alternatively the cleaning solvent with oil contamination can be used as a low grade fuel and burnt. The wash is preferably conducted in a tank, such as, for example, a drum or trommel, which is subjected to agitation. The solvent with hydrocarbons dissolved therein is separated off, the waste stream being collected; v) the aggregate is then subjected to a rinse or wash in water. The rinse or wash is preferably conducted in a tank such as, for example, a drum or trommel, which is subjected to agitation; vi) the water and residual solvent/hydrocarbon mixture is then separated off leaving a clean aggregate which can be recycled. The waste stream is again collected; and vii) the waste streams are then treated so that the hydrocarbons can be disposed of safely in a controlled manner as outlined in iv) above. The apparatus for use with the method can be fixed, in which case the aggregate is brought to and from the apparatus. More preferably it is a mobile apparatus. In a preferred embodiment, a mobile apparatus is provided with a power source and propulsion means. A method and apparatus according to the invention are described below, by way of example only, with reference to the following figs, in which: - Fig. 1 is a schematic plan view of a mobile ballast washer; Fig. 2 is a schematic side elevation of the mobile ballast washer of Fig. 1; Fig. 3 is a process flow chart illustrating the stages of a method according to one aspect of the invention; Fig. 4 is a process flow chart illustrating the solvent circuit for the method according to Fig. 3; Fig. 5 is a process flow chart illustrating the water circuit for the method according to Fig. 3; Fig. 6 is a side elevation of a mobile apparatus according to a preferred embodiment of the invention; and Fig. 7 is a rear view of the mobile apparatus of Fig. 6. Referring to Figs. 1 and 2 an apparatus 10 comprises a platform 12 which supports the components of the apparatus. A suction hose 14 is mounted to the platform 12 in a manner enabling it to be directed such that it can draw aggregate into the apparams. A vacuum extractor 16 provides the force necessary to lift the surface ballast from the track to the apparams. The aggregate is then optionally screened before being directed into a hopper 18 where it is stored. A conveyor 20 provides the means for transferring the ballast from the hopper to a solvent drum 22. On the way it undergoes a pre- wash. A conveyor means for example an Archimedean screw then transfers the aggregate to a water drum 24. The respective waste streams from the solvent drum and water drum are directed to a respective solvent sump 26 and water sump 28. The cleaned aggregate then passes for recycling via a conveyor 30 and movable chute 32. The mobile apparatus is powered by way of a power and propulsion unit 34 which may be separate to or integral with platfoπn 12. Referring to Figs. 3, 4 and 5 an apparams 10 of the type referred to with reference to Figs. 1 and 2 can be used to recycle oily railway ballast in situ. The top layer of oily ballast is vacuumed up and conveyed to hopper 18 where it is screened - undersized solids and fines being drawn off in a waste stream. The ballast is pre-washed, for example by spraying with water, and then conveyed to drum 22 where it under goes a solvent wash in a solvent circuit (Fig. 4) For example, the contaminated aggregate from the hopper is subjected to a solvent wash with a citrus extract in a drum or trommel. The hydrocarbon contaminant is removed from the aggregate and d e solvent waste containing dissolved hydrocarbon is drawn off into a solvent sump where it is filtered to remove solids and fines. The solvent with dissolved hydrocarbons may be stored for disposal or returned to the feed tank to be recycled. The solvent washed aggregate is then conveyed to drum 24 where it undergoes a water wash (Fig. 5). For example, the solvent washed aggregate is conveyed from the solvent wash drum to a water wash drum where any remaining solvent with dissolved hydrocarbon is picked up and this waste stream is then passed to a water sump. It is men passed over a weir or skimmer to separate the solvent waste containing dissolved hydrocarbon contaminant from the water. The water is then filtered to remove solids and fines and returned to the water feed tank and the solvent waste is returned to the solvent tank. The cleaned ballast is then conveyed by .Archimedean screw or a chute for storage or is returned directly to the track. In the embodiment illustrated with reference to Figs. 6 and 7, like numbers are used to illustrate like parts. A hose 14 sucks up the top 150mm of ballast which experiments have shown contains 90% of the contamination. The hose is provided on a swing arm 15. The aggregate is sucked up and optionally undergoes a dry screen before passing into a hopper 18. From there it passes into a drum 21 where it undergoes a prewash or wet screen to remove, for example, fines. The drum 21 is vertically disposed above solvent drum 22 which in turn is disposed above the rinse drum 24. Each drum is open and rotates about a central axle 23. Associated or integral with each axle is a spray arm 25 such that fluid can enter the drum under operation from a fluid pump and be sprayed onto the ballast within the drum. Each drum is open and perforated below so that the fluid passes through into respective solvent and water sumps 26 and 28. Since the solvent is less dense and immiscible with the water, the waste streams can be recycled and returned to respective holding tanks 31 and 33. Each drum has a plurality of shaped blades 27 which serve to retain the ballast in the drum whilst it is rotated in a given direction but, enable the ballast to be "thrown" into the neighbouring drum by altering me direction of rotation of the drum. The last drum in the series is positioned such that the clean ballast can be thrown back onto the track. It should be noted that in contrast to prior art water washing methods in which the ballast is "immersed" in water the aggregate in the drums is "wetted" by the production of the sprays.

Claims: CLAIMS 1. A method of cleaning and recycling an aggregate contaminated with a hydrocarbon comprising: i) subjecting the aggregate to a prewash, ii) solvent washing the aggregate to remove the hydrocarbon contaminant, iii) rinsing the aggregate with water to remove residual solvent containing the hydrocarbon contaminant, iv) separating off the solvent containing the hydrocarbon contaminant and water from the aggregate, and v) recycling the cleaned aggregate. 2. A method as claimed in claim 1 wherein prior to step i) the aggregate is subjected to a dry screen. 3. A method as claimed in claim 1 or 2 wherein the solvent comprises a citrus extract. 4. A method as claimed in claim 3 wherein the citrus extract comprises a folded oil and/or terpene. 5. An apparams for conducting the method of the invention, comprising; i) means for extracting and/or transferring the aggregate to the apparams ii) means for prewashing the aggregate; iii) means for transferring the aggregate to a solvent treatment circuit; iv) means for transferring the aggregate to a water treatment circuit; v) means for transferring the cleaned and decontaminated aggregate for recycling, and vi) means for collecting waste streams from the solvent and water treatment circuits. 6. An apparams as claimed in claim 5 wherein the apparams is a mobile apparams. 7. An apparams as claimed in claim 5 wherein the apparams is a stationed apparams. 8. a n apparams as claimed in claim 5, 6 or 7 wherein the means for extracting and/or transferring the aggregate to the apparams is a hose. 9. An apparams as claimed in any of claims 5 to 8 which comprises three drums. 10. An apparams as claimed in claim 9 wherein the three drums are arranged such that a prewash drum is vertically disposed above a solvent drum which is vertically disposed above a rinse drum. 11. An apparams as claimed in claim 9 or 10 where each drum comprises a spray arm. 12. An apparams as claimed in claim 9 , 10 or 11 wherein each drum comprises a plurality of shaped blades. 13. An apparams as claimed in any of claims 9 to 12 wherein the drums are rotatable in both forward and reverse directions.

Inventors: BROOKES IAN, MONBIOT RICHARD, BROOKES, IAN, MONBIOT, RICHARD
Applicants: BROOKES IAN, MONBIOT RICHARD, PRONATUR PRODUCTS LIMITED, BROOKES, IAN, MONBIOT, RICHARD
Application year: 1998
Main classification: B09C1
IPC codes: B03B5, B03B9, B09C1, E01B27