BACKGROUND OF THE INVENTION

The present invention relates to a process for recycling of used or contaminated fluids, either predominately oil-based or predominately water- based, employing a mobil unit. Recycling of the fluid is accomplished using pasteurization in conjunction with certain filtration and centrifugal separation equipment.

Beginning with the U.S. Resources Conservation and Recovery Act (RCRA), laws have been enacted to deal with the accumulation of chemical waste which has become a major health and environmental issue. Many industries have been severally impacted by this legislation including, for example, the metal working industry. These industries rely heavily on the use of lubricating, cooling and other fluids for proper functioning of their equipment. Thousands of fluids, both water-based and oil-based, have been developed to meet the needs of these industries. Inevitably, contamination of these fluids will occur, eventually reaching a point where the fluid no longer is capable of performing its desired function and may cause corrosion, clogging of lines and other problems. The contamination of the fluids may be caused by metal "fines" and debris from the tools and equipment, which accumulate as an abrasive sludge in both oil- and water-based fluids. Lubricating oils and hydraulic fluids from machinery ("tramp oils") frequently find their way into water-based fluids. Moisture frequently finds its way into oil-based fluids. Micro-organisms also present a problem in these fluids. Bacteria including pseudomonas species, molds and fungi can flourish in oil/water mixtures such as water-based metal working fluids contaminated with tramp oils. This results in sludge and deposits, offensive odors, formation of corrosive acids and destruction of additives necessary for proper fluid performance.

Techniques used in the past to revitalize contaminated fluids have proven to be costly or ineffective. Attempts have included techniques such as filtration of metal fines, stemming or suctioning off of tramp oil and addition of biocides to prolong the life of such fluids. Eventually, the fluid becomes contaminated

to the point where such measures are no longer effective. Thus, the fluid is eventually removed from service and disposed of.

Disposal of used and contaminated fluids, however, is no longer simple and has become very expensive. Previously, contaminated fluids were trucked to a convenient dump site for disposal at a minimal cost. Under RCRA and other environmental legislation, most contaminated fluids can be classified as hazardous waste which can only be disposed of at select facilities. These sites are frequently located many miles from the plant generating these fluids. Scrupulous record keeping must be maintained on these wastes and expensive chemical analysis on each shipment is often required. Transportation costs, disposal fees, insurance, taxes, and additional miscellaneous expenses are incurred when disposing of these fluids, such that today it is often more expensive to dispose of the fluid than it originally was to purchase it.

This situation, as serious as it is today, is getting progressively more difficult. Recently enacted legislation calls for the elimination of all chemical waste dumping. The metal working industry, for example, could be faced with billions of gallons of contaminated fluids for which no satisfactory means of disposal exists. Numerous plants are currently faced with the necessity of dealing with considerable quantities of contaminated fluids which are accumulating on the plant site and must be disposed of in a safe and legal manner.

An obvious alternative to dumping of used fluids is recycling. However, problems in recycling metalworking (MW) fluids are complicated by the variety of fluids which serve this market. The three basic types of MW fluids include cutting oils, soluble oils and synthetics. Cutting oils are petroleum oils used with additives to assist lubrication, protect against corrosion and help wet the metal surface. Viscosity of the fluid varies depending on the metal being machined and the type of machine operation. Soluble oils (or more accurately emulsifiable oils) are petroleum oils containing emulsifiers used in the form of dilute emulsions (usually 5-10% oil soluble in water). These oils combine the lubricating properties of an oil with the cooling properties of water. There is an increasing interest in synthetics, water-based lubricants which contain no

petroleum oil but rely on water-soluble additives for their lubrication. Like soluble oils, synthetics are typically diluted with water in use. Soluble oils and synthetics may contain additives such as rust inhibitors, extreme pressure additives and anti-foam agents and biocides, as is well known in the art. Several different fluids may be in use in a given plant at the same time and the degree of contamination may vary from fluid to fluid and from machine to machine. Thus, the problem exists of developing a recycling process that can be used on a multiplicity of contaminated fluids, including soluble oils and synthetics at different concentrations in water- and oil-based fluids of differing viscosities. Applicant's earlier processes provided improvements in the recycling industry; however, significant improvements have been made, as described below. There may also be differences in composition and contamination in a single storage tank or reservoir of a used fluid. For example, a contaminated soluble oil contaimng metal fines, tramp oil and bacterial sludge naturally tends to stratify on standing in an ordinary cylindrical tank. Metal fines settle to the bottom and oil floats to the top. Bacterial sludge frequently forms "lily pads" which float on the surface of oil- or water-based products or "jelly-fish" type globs of neutral buoyancy which circulate throughout the fluid with convection currents. Bacterial sludge also appears as scum and slime on the tank walls and bottom. This material may often time result in substantial part from the growth of mold and fungus within the fluid which has gone unchecked. It is impractical to remix the contents of such a tank before recycling.

Thus, there is an urgent need for a process that will effectively recycle a variety of water- and oil-based fluids. There is a further need for a process capable of adjusting quickly to differences in fluids or to differences in compositions of the same fluid. There is a further need for a process of recycling contaminated fluids that is mobile and capable of being used at different plants or locations within the same plant.

SUMMARY OF THE INVENTION

The process of the present invention provides a method of recycling used or contaminated fluids comprising a predominately oil-based fluid or a

predominately water-based fluid. The method includes pumping the used or contaminated fluid from the storage sites through appropriate piping and valving means to a mobile recycling unit which utilizes pasteurization and includes equipment to separate solids from liquids, and a centrifugation apparatus. Metal fines and suspended solids are removed from the contaminated fluid utilizing equipment to separate solids from liquids and a centrifugal separator. The equipment which separates solids from liquids includes a plurality of parallel filtering devices. The contaminated fluid is passed through a first set of filtering devices. When metal fines and suspended solids clog the filters, the filters become ineffective. A valve control is provided which when actuated, switches the flow from the first bank of filtering devices to a second bank of filtering devices. The first set of filtering devices may then be cleaned while the contaminated fluid flows through the second set of filtering devices.

The contaminated fluid is pasteurized during the process by carefully controlled heat. Since pasteurization is co-dependent on time and temperature, this careful control by an operator highly trained in the method is an important part of the process. The preferred method includes flash pasteurization in which the fluid is quickly cooled after the pasteurization step. Other methods include irradiation with various frequencies of electromagnetic energy to reduce micro- biological activity to undetectable levels. Importantly, pasteurization will occur both before and during the centrifugation step.

The fluid is then separated into an oil stream, an aqueous stream and a residue of fine particles and solids utilizing a centrifugation apparatus. The centrifugation apparatus includes a plurality of ring regulating rings or dams of varying size. The proper selection and application of the ring dam by the operator is important to the efficient separation of the fluid stream into the various aqueous and oil phases. The centrifical forces created during passing the fluid through the rapidly rotating disk bowl and disk stack within the centrifuge drives any solids remaining in the fluid toward a liner. This action, in conjunction with the ring dam and fluid flow rate, as continually adjusted by the operator, causes a separation between the oil and water phases in the fluid stream.

The fluid then passes through the plate and frame type heat exchanger where it is cooled down. The heat from the cleaned fluid stream is transferred to the dirty fluid stream which is entering the pasteurization stage. This transfer of heat allows a significantly higher flow rate within a given energy input. This provides an important economy to the method of the present invention.

A recycled fluid is then recovered and returned to a clean storage tank. Preferably, fresh fluid, biocide or anti-foam agents are added to the recycled fluid to maintain the level of efficacy of the fluid for its desired purpose.

These and other features of the present invention will be best understood from the following specification and drawing, of which the following is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of a process according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

As shown in Figure 1, a mobile unit 20 carries the key elements of the present invention, including equipment to separate solids from liquids 22, 24 and 30, heat exchanger 26, heater 28 and centrifuge 30. Mobile unit 20 transports the equipment from one site to another. Mobile unit 20 can be a truck, trailer, platform or other suitable vehicle capable of handling the weight of filters 22 and 24, heat exchanger 26, heater 28, centrifuge 30 and other accessory equipment, including pumps, tubing and analytical equipment.

At a customer's plant, lubricating, cutting, cleaning or cooling fluid which has been used and/or is contaminated is typically deposited in a storage tank 32. Over time, contaminated soluble oils or synthetic fluids, debris from metal cutting and grinding such as fine metal particles, grinding abrasives and substrates, tramp oil, dirt and micro-biological sludge will stratify on standing in an aqueous process. Lubricating oils, metal chips and fines, water and aqueous

materials, dirt and micro-biological sludge will stratify on standing in an oil- based process. An operator of mobile unit 20 moves mobile unit 20 into position near storage tank 32. Flexible hosing is connected between storage tank 32 and mobile unit 20. Preferably, tramp oil in tank 32 is initially skimmed, particularly if there is a thick layer of tramp oil floating on top.

The contaminated fluid is then introduced to the process within mobile unit 20 using a pump 34. Because mobile unit 20 is used across a wide variety of fluids, appropriate pumping equipment must be selected for the process of the present invention. Positive displacement pumps which provide a minimum of shearing action such as vane or gear pumps are most useful. Care must be taken to insure that the elastomeric materials in the pumps or appendages thereto are properly selected for compatibility with both oil- and water-based fluids. Many pumps exist which handle both oil-based and water-based fluids. However, it may be useful to maintain two pumps in parallel, one selected specifically for oil-, the other selected specifically for water-based fluids. The fluid stream is directed to the appropriate pump by means of suitable piping and valving as would be obvious to one skilled in the art. A suction filter ahead of the pump is desirable to remove large metal chips, "swarf, etc., which might otherwise have an abrasive effect on the moving parts of the pump. Contaminated fluids, as noted hereinabove, inevitably contain large amounts of metal fines and other debris, most of which will not be trapped by the sort of filter recommended above for removal of larger solids from the fluid before it enters the pump. Such fines are normally too small and have to be removed by other means. Although centrifuge 30 is capable of removing fines, additional equipment to separate solids from liquids is necessary upstream of the centrifuge to reduce the time required for centrifuge clean-out and maintain a high process rate.

In the process of the present invention, metal fines and suspended solids are primarily removed from the contaminated fluid stream utilizing solids separation equipment and centrifugal separation. Contaminated fluid is passed through a plurality of wire mesh suction strainers. Filter sets 22 are in parallel and valve 36 regulates the flow between the alternate filter sets. Each filter set

22 may contain one or more filters. Preferably, each filter set includes two wire mesh strainers of differing size to progressively remove smaller particles (e.g., 40 and 60 mesh). Valve 36 is initially set to one of the filter sets. When the filtering capacity of one filter set 22 approaches their capacity for fines or solids, valve 36 is switched to the other filter set while the first filter set is cleaned or replaced. A filter's capacity can be determined when the pressure of the fluid stream across the filter increases above a particular point. The filters are used in this alternating fashion, providing a continuous flow of contaminated fluids through mobile unit 20. The contaminated fluid is then passed through a second set of filters 24 comprising multiple bag filter sets in parallel, which remove metal fines and suspended solids which filters 22 failed to remove. In the process of the present invention, each bag filter set includes two bag filters in series. It is preferable to select filters 22 and 24 such that the filters remove different types of solids or fines. Thus, bag filters 24 remove smaller and finer particles from the contaminated fluid stream. Filters 22 remove coarser, larger solids and metal fines. Valve 38 controls the flow between alternate bag filters 24. Bag filters useful herein include disposable type bag filters and are generally of the type well known in the art. Metal fines and suspended solids collected in filters 22 and 24 are disposed of in a solid disposable waste bin 40 and further processed by the customer.

Hydrocyclones are well known in the art as solid separation means and may be utilized depending on the nature of the solids contained in the fluids. In a typical hydrocyclone, a fluid stream is passed into the top of a closed conical chamber, which imparts a circular motion and centrifugal force to the stream as it passes down from the wide to the narrow portion of the chamber. The solids, being heavier than the liquid, are forced by centrifugal force to the walls of the hydrocyclone, and are gradually washed by the flow of the stream downwards until they are ejected from an opening in the bottom. The liquid, meanwhile, which is now relatively free of solids, is discharged through a center tube running from near the bottom of the cone and back of the top.

In the process of the present invention, the contaminated fluid is freed of micro-biological contaminates using the pasteurization process. In the pasteurization process, the fluid is passed over heating elements which rapidly raise its temperature to about 65 to 85 °C. Since pasteurization is co-dependent on time and temperature, careful control of temperature and flow rate by an operator is important. Flash pasteurization is a highly practical method of addressing the problems of bacterial, mold and fungal contamination when used in combination with the other elements of the invention. Flash pasteurization occurs when the fluid is quickly heated, kept at a desired temperature for only the minimum required time, and then quickly cooled down. Cooling of the fluid occurs when the fluid passes through the plate and frame type heat exchanger. The heat from the cleaned fluid stream is transferred to the dirty fluid stream which is entering the pasteurization stage. This transfer of heat allows a significantly higher flow rate for a given energy input. An alternate method of eliminating micro-biological contamination includes irradiation with electromagnetic energy of various frequencies. Any practical source of irradiation capable of destroying micro-organisms is included within the scope of the invention.

According to the present invention, the contaminated fluid is then passed through heat exchanger 26 which preheats the fluid prior to centrifugation. Heat exchanger 26 may be a conventional heat exchanger known in the art; however, plate and frame type heat exchangers are preferred in the process of the present invention. Heat exchanger 26 uses the fluid recovered from centrifuge 30 to preheat the contaminated fluid passing through heat exchanger 26 on its way to heater 28.

Contaminated fluids are then conveyed to heater 28. Heater 28 heats the contaminated fluids to a desirable temperature prior to centrifugation. In a method of recycling typical coolant fluid, the fluid is heated to approximately 85 °F. Heaters of the type well known in the art are useful herein. The contaminated fluid is then conveyed to a centrifuge apparatus 30 where the fluids are separated into an oil stream, an aqueous stream and a solid residue. Centrifugation is carried out in a high speed disk bowl centrifuge

operating at a speed of from about 8000-14000 φm and capable of handling a fluid stream flow of from about 5 to 50 gallons/minute. Disk bowl centrifuges are well known in the art. See, for example, the article "Disk-Bowl Centrifuges" by James West in Chemical Engineering, January 7, 1985, Pages 69-73. The normal operation of the disk-bowl centrifuge has been modified as follows. In an ordinary disk bowl centrifuge, a rapidly rotatable bowl contains a series of separation disks held apart by spacers arranged around its axis of rotation. The angle between the plane of the disks and the axis is typically 30 to 50 degrees. Each disk contains holes, conventionally four or eight, arranged at 90 degree positions on the disk. The holes will be placed at different distances from the central axis, depending on whether fluid to be processed is predominately oil- based or predominately water-based. Around the walls of the bowl is a removable liner. Periodically the bowl can be stopped for the cleaning of solid fines that have accumulated on this liner. Alternately, the bowl can be momentarily opened while still in motion for ejection of accumulated solids.

In conventional operation, the fluid to be processed enters the top of the centrifuge through an inlet tube from which it is discharged by gravity into the bottom of the bowl. It moves outwardly through a distribution chamber and then begins to move upwards between the disk stack. The centrifugal force created by the rapid rotation of the bowl forces any remaining solids in the fluid to the liner. Meanwhile, a separation between the oil and the water phases in the stream is formed. The heavier water moves closer to the walls of the bowl, the lighter oil remains closer to the center shaft. As fluid continues to enter the centrifuge, a distinct separation line is established between the oil and water phases, which must be located as close as possible to the center of the holes. The holes, the upper portion of the wall of the bowl which tapers inward towards the axis, and an interior conical baffle around the axis above the disk stack combine to keep the oil and water phases separate as they leave the bowl. The oil phase flows between the interior of the baffle and the axis upwards and into a chamber from which it is pumped to storage. The water phase flows between the baffle and the bowl wall, past the gravity disk or ring dam used to

control its flow and into a second chamber where it too is pumped to storage.

The liner is periodically removed for cleaning and disposal of collected solids.

A wide variety of contaminated fluids, both oil-based and water-based, can be recovered using the centrifuge of the present invention. Centrifuges are typically supplied with a fixed disk stack, gravity disks or ring dams and accessories, designed and "sized" for a particular separation, e.g., trace water from diesel fuel or tramp oil from a coolant fluid. It is essential that the interface between the oil and water or "separation line" be properly oriented with respect to the holes in the disks, since this determines whether the oil and water phases will properly separate when they flow from the centrifuge. It is difficult to accomplish this when the actual composition of the fluid being processed (the oil/water ratio) will be different at different levels within the same contaminated fluid storage tank as noted above. The result of such a composition change will be a change in the position of the separation line. This can lead to some oil being ejected along with the water or vice versa if proper adjustments are not made. To some extent, adjustment of the position of the separation line can be accomplished by alteration of the flow rate of the fluid stream into the centrifuge; however, this has not been found to eliminate the difficulty entirely. Extreme variation of composition from one contaminated fluid to another can be handled by use of a multiplicity of gravity disks or ring dams, sized to the particular fluid being processed. The ring dam is fitted onto the top of the bowl into the opening through which the water phase is ejected. The ring dam applies an obstruction to the flow of the water phase and creates a back pressure in the bowl which resists the tendency of centrifugal force and inlet flow to move the separation line outwards from the center. By suitable selection of a ring dam of an appropriate diameter, which would be well within the skill of an operator, a far more effective means of controlling the position of the separation line is provided. The centrifuge can be adjusted to fluids of widely varying composition including predominately water-based and predominately oil- based fluids.

In the process of the present invention, as contaminated fluid is pumped to centrifuge 30, water-based coolant and tramp oil fluid streams emerging from centrifuge 30 are examined for completeness of separation. An increase or decrease in a flow rate can be made to improve separation by adjustment of pump 34, or by shunting or bypassing a portion of the flow away from the centrifuge by means of a regulating valve, typically a needle valve (not shown). If this does not improve separation, centrifuge 30 is shutdown, opened and the separation line examined by inspection of the underside of one or more of the separation disks. Adjustment may then be made by substitution of a ring dam of greater or lesser opening, depending on whether the separation line is to be moved further away or closer toward the center of the bowl. Once centrifuge 30 is properly adjusted, distinct fluid streams of recycled coolant and tramp oil are discharged from centrifuge 30.

From the centrifuge 30, the separated water and oil streams are pumped through the heat exchanger and then to final storage. In an aqueous-based coolant recycling process, tramp oil is directed to a contained tank 42. The customer typically provides a waste oil characterization for off-site refining of the oil or has the oil transported for disposal or incineration through a licensed waste oil hauler 43. Solid residue is directed to a bin 44 for further recycling by the customer. The predominate aqueous-based fluid stream is directed back towards heat exchanger 26 to preheat the contaminated fluid stream. In a predominately oil-based lubricant recycling process, water contaminate is directed to a contaminate tank, while the purified oil-based fluid stream is directed back towards heat exchanger 26 and ultimately to final storage. The recycled fluid is then recovered and directed to clean coolant tank

46. In a coolant recycling process, fresh coolant concentrate 48, biocide 50 and water 52 may be added to maintain an efficacious level of these additives. Other additives, such as anti-foam agents, may be also added.

A preferred description of this invention has been disclosed; however, a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following

claims should be studied in order to determine the true scope and content of this invention.