BACKGROUND OF THE INVENTION Volatile solvents are used in many industrial processes in which the volatile solvent is used for cleaning purposes. As a result of such use the volatile solvent becomes contaminated with foreign matter. Due to the cost of such volatile solvents, environmental concerns, and the cost of disposing of such contaminated volatile solvents, it is desirable to maximize the use that can be made of the volatile solvent by removing the contamination from it by recycling it into the purified solvent form for further use in the industrial process.

This invention is concerned with the recycling of solvents used in such processes and, although not limited thereto, is particularly concerned with the recycling of solvents used in spray gun washers (hereinafter called"gun-washers"), which are employed in the cleaning of spray guns used in the application of paints, resins, and other coating materials.

A typical environment for a gun-washer would be an automotive paint shop but, of course, spray guns are used to apply solvent-based coating materials in a wide variety of environments.

Figure 1 illustrates a conventional gun-washer [131] having a bowl [132] for accommodating spray guns to be cleaned and spray jets (not shown) for directing solvent onto the dirty guns. Clean solvent is pumped from a drum [1210] by means of a pump [118]. Dirty, paint sludge-containing solvent from the cleaning operation is collected in a used solvent collection container in the form of a drum [141]. Sludge tends to fall and collect at the bottom of the drum [141]. For automatically cleaning the spray jets of the gun-washer, a pump [147] is provided, which will pump essentially sludge-free solvent from the drum [141] through a conduit [148] extending into the drum and thence through a

further conduit (not shown) to the spray jets. For manually cleaning the spray jets, a pump [149] is provided at the top of the drum and the essentially sludge-free solvent is pumped through a conduit [150] to a tap (not shown), by which the flow of solvent to the spray jets is manually regulated. Pump [118] is operated in conventional manner by a foot pedal [FP] or similar device located on the gun-washer.

The conventional gun-washer thus recirculates contaminated solvent from the drum [141] for automatic and manual cleaning of the spray jets. Even though the solvent starts out being essentially sludge-free, it very quickly becomes so dirty as to be unusable. The conventional gun-washer also requires that the drum [141] be emptied periodically into a recycler or the contents sealed and sent for disposal off-site and the drum [1210] must be recharged with clean solvent periodically. The desirability of recycling the spent solvent back to the gun-washer has been recognized and solvent recovery devices which are especially useful for this purpose are known. Such devices take used solvent and recycle the solvent to provide essentially fresh, clean solvent, which may be used in the gun-washer or for other painting or coating operations in the paint shop. One such device is described in my Canadian Patent Application No. 2,277, 449. This recovery apparatus enables contaminated solvent to be processed and clean solvent recovered efficiently and with minimal environmental impact. Contaminated solvent is fed into a distillation module, wherein the solvent fractions are distilled off and the vapour is passed to a condensation module. Contaminants in the form of residues from the cleaning process are left behind in the distillation module for subsequent disposal. The condensed solvent vapours in the condensation module are available for re-use in the cleaning process.

One approach to utilizing a recycler of this kind in combination with a gun-washer is illustrated in Figure 2. The gun-washer is sold by Drester AB of Sweden and, for sake of illustration only, is shown in combination with a recycler as described in the aforementioned Canadian Patent Application No. 2,277, 449. This combination permits recycled solvent to be re-used in the gun-washer, whilst spent solvent is sent to the recycler for recycling, thus providing an essentially closed loop of solvent flow between the recycler and the gun-washer. As in Figure 1, the gun-washer [131] comprises a bowl [132].

However, in the Drester system, the used-solvent collection drum [141] is located within a

large tank T, which is external to the gun-washer. Within the tank T is also located a container [1210] for clean solvent. Tank T provides a recirculation reservoir for solvent for both the automatic and manual cleaning operations of the conventional gun-washer described above in connection with Figure 1, the used solvent being pumped to the gun- washer by means of pump [149]. The recycler comprises a distillation module [10] and a condensation collection drum [110].

In operation of the system, the user will initiate a transfer of clean solvent from a condensation/collection drum [110] into the clean solvent tank [1210] when he/she observes that the clean solvent tank [1210] is emptied-i. e. when depressing the gun-washer pump foot pedal [FP] to activate pump [118] ceases to produce clean solvent. The transfer is effected by activating pump P which pumps clean solvent from the condensation/collection drum [110] into the clean solvent tank [1210]. The condensation/collection drum [110] is fed from a distillation module [10], the condensation/collection drum [110] and distillation module [10] forming the recycler component of the sytem. Used solvent is pumped by means of pump [146] into the distillation module [10]. Clean solvent pumped into the tank [1210] overflows and runs into reservoir tank T to form the reservoir of solvent for the automatic and manual cleaning operations. Thus, it will be seen that the amount of solvent in tank [1210] is less than the amount available from the condensation/collection drum [110] by the amount required for the reservoir tank T. For example, if the capacity of the used-solvent collection drum [141] is 5 gallons, then because the system is closed and operates essentially without external addition of solvent, the amount available for transfer from condensation/collection drum [110] is also 5 gallons (less any losses due to evaporation). Typically, at least 2 gallons is required in recirculation tank T. In the Drester device, drum [141] holds 5 gallons and tank [1210] holds 2.5 gallons, thus leaving 2. 5 gallons for recirculation tank T. Thus, the full amount of the capacity of drum [140] is never available for the clean solvent supply, because part of that capacity is required for recirculation in the automatic and manual cleaning of the spray jets. A further problem with this arrangement is that evaporation can occur in relatively small tank [1210], leading to possibly insufficient overflow to recirculation tank T to maintain the necessary reservoir of solvent in tank T for cleaning of the spray jets.

It would therefore be desirable to provide a system wherein the foregoing disadvantages are obviated or mitigated.

SUMMARY OF THE INVENTION Thus, according to the invention, a system for recovering and recycling solvent from a solvent-based cleaning process comprises: a used solvent collection container for collecting used solvent containing sludge and dissolved contaminants from a cleaning apparatus used in said cleaning process, a solvent recovery apparatus for recovering used solvent from said used solvent collection container, an apparatus for feeding used solvent from said used solvent collection container to said solvent recovery apparatus, an apparatus for feeding recovered solvent from said solvent recovery apparatus to a recovered solvent collection container, and an apparatus for recycling recovered solvent from said recovered solvent collection container to said cleaning apparatus, said used solvent collection container comprising a plurality of compartments, a first compartment receiving used solvent directly from said cleaning apparatus and having a lower sludge-containing region communicating with said apparatus for feeding used solvent to said solvent recovery apparatus and at least a second compartment communicating with means for supplying essentially sludge-free used solvent to said cleaning apparatus without passage through said solvent recovery apparatus, said second compartment receiving used solvent from an upper essentially sludge-free region of said first compartment.

Preferably, said used solvent collection container comprises said first compartment and second and third compartments, said second and third compartments communicating with said means for supplying essentially sludge-free used solvent to said cleaning apparatus without passage through said solvent recovery apparatus and said second and third compartments receiving used solvent from said upper essentially sludge-free region of said first compartment.

Preferably, said third compartment receives overflow of used solvent from said first compartment and said second compartment receives overflow of used solvent from said third compartment.

Preferably, said apparatus for feeding used solvent to said solvent recovery apparatus comprises a conduit extending from a lower sludge-containing region of said used solvent collection container beneath the surface of said used solvent in said container to said solvent recovery apparatus and a pump for pumping used solvent containing sludge through said conduit to said solvent recovery apparatus.

Preferably, a one-way valve is provided between the second and first compartments, so that when used solvent is pumped out of the first compartment, the second compartment is also drained but sludge-laden solvent is prevented from flowing from the first compartment into the second compartment through the one-way valve.

Preferably, the third compartment receives used solvent from said first compartment through one or more overflow orifices between said first and third compartments, and said second compartment receives overflow from said third compartment and a one-way valve is provided between the second and first compartments, so that when used solvent is pumped out of the first compartment, the second compartment is also drained but sludge-laden solvent is prevented from flowing from the first compartment into the second compartment through the one-way valve.

Preferably, said apparatus for supplying used solvent to said cleaning apparatus from each of said second and third compartments comprises a conduit extending from beneath the surface of said used solvent in each of said second and third compartments to said cleaning apparatus and a pump for pumping used solvent through said conduit.

Preferably, said cleaning apparatus is a spray gun-washer used for washing spray guns used in spraying solvent based coating materials.

In a preferred embodiment of the invention, there is provided a system for recovering and recycling solvent from a solvent-based cleaning process comprising: a used solvent collection container for collecting used solvent containing sludge from a gun-washer used in said cleaning process,

a solvent recovery apparatus for recovering used solvent from said used solvent collection container, an apparatus for feeding used solvent from said used solvent collection container to said solvent recovery apparatus, an apparatus for feeding recovered solvent from said solvent recovery apparatus to a recovered solvent collection container, and an apparatus for recycling recovered solvent from said recovered solvent collection container to said cleaning apparatus, said used solvent collection container comprising a plurality of compartments, a first compartment receiving used solvent directly from said cleaning apparatus and having a lower sludge-containing region communicating with said apparatus for feeding used solvent to said solvent recovery apparatus and second and third compartments communicating with means for supplying essentially sludge-free used solvent to said cleaning apparatus without passage through said solvent recovery apparatus, said second and third compartments receiving used solvent from an upper essentially sludge-free region of said first compartment, said second compartment being located adjacent to said first compartment and receiving used solvent from said first compartment through one or more overflow orifices between said first and second compartments, said one or more overflow orifices located above said lower sludge-containing region of said first compartment in order to supply essentially sludge-free solvent to said second compartment.

Preferably, the solvent recovery apparatus comprises: a distillation chamber for said solvent and heating means for heating said chamber to vaporize the solvent, said means for feeding used solvent from said used solvent collection container to said solvent recovery apparatus being connected to said distillation chamber; a condensation/collection container which holds a heat absorbing mass through which said vapour is passed for condensing the vapour and collecting the solvent in the liquid phase, said apparatus for feeding recovered solvent from said solvent recovery apparatus to said recovered solvent collection container being connected to said condensation/collection container; and

a conduit for directing vapour from said distillation chamber into said heat absorbing mass within said condensation/collection container.

Preferably, the heat absorbing mass comprises the solvent vapour to be recovered in its liquid phase.

Preferably, said apparatus for feeding recovered solvent from said solvent recovery apparatus to said recovered solvent collection container comprises a conduit having a valve provided in said conduit for selectively opening or closing said conduit to solvent flow from said condensation/collection container to said recovered solvent collection container.

Alternatively, said apparatus for feeding recovered solvent from said solvent recovery apparatus to said recovered solvent collection container comprises a conduit having a pump provided in said conduit for selectively subjecting said conduit to solvent flow from said condensation/collection container to said recovered solvent collection container.

Alternatively, said apparatus for feeding recovered solvent from said solvent recovery apparatus to said recovered solvent collection container comprises a conduit and a siphon mechanism for selectively subjecting said conduit to solvent flow from said condensation/collection container to said recovered solvent collection container.

Preferably, the system further comprises a bypass for said valve, pump or siphon, said bypass including an overflow column having a closed upper end and a bypass conduit extending between an upper region of said column and said recovered solvent collection container, the height of said column corresponding to a selected maximum solvent level in said condensation/collection container to enable solvent to overflow through said bypass conduit into said recovered solvent collection container when the selected maximum solvent level in said condensation/collection container is exceeded.

Preferably, an access is provided to said solvent recovery apparatus for supplying used solvent to said solvent recovery apparatus separate from apparatus for feeding used solvent from said used solvent collection container to said solvent recovery apparatus, and a collection apparatus for used solvent from said solvent recovery apparatus is provided separate from said apparatus for feeding recovered solvent from said solvent recovery

apparatus to said recovered solvent collection container, whereby said solvent recovery apparatus may be used in stand-alone mode separate from said cleaning apparatus.

Preferably, said access enables said system to be topped up with solvent or solvent waste when the amount of solvent circulating through the system falls below a desired level.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: Fig. 1 is a schematic diagram of a conventional gun-washer; Fig. 2 is a schematic diagram of a prior art system for recycling solvent from a gun- washer as shown in Figure 1; Fig. 3 is a schematic diagram of a system according to a first embodiment of the invention; Fig. 4 is a schematic diagram of a system according to a second embodiment of the invention; Fig. 5 is an enlarged view of part of the system shown in Figure 4; and Fig. 6 is a schematic diagram of a system according to a second embodiment of the invention.

DETAILED DESCRIPTION One embodiment of a system according to the invention is shown in Figure 3. In this embodiment, the solvent recovery part of the system is similar to that described in the aforementioned Canadian Patent Application No. 2,277, 449 and comprises a recycler in the form of a distillation module [10] containing a distillation chamber for used solvent and a condensation/collection container in the form of a drum [11]. In this embodiment of the invention, the used solvent which is to be recovered is heated in the recycler [10] to

generate solvent vapour. This solvent vapour is then directed through a downwardly inclined conduit [12] to a vapour. inlet [13] to the condensation/collection drum [11]. This downwardly inclined conduit [12] extends into and toward the bottom of the condensation/collection drum [11]. There is substantially no condensation of the vapour in the conduit [12] but any condensate which does form runs down into the condensation/collection drum [11] and, therefore, no back-pressure is created by the condensate formation. The condensation/collection drum [11] is charged with a coolant liquid [14] which is the same solvent as that being distilled. In this example, the capacity of the condensation/collection drum [11] is about 16 gallons (level A in Figure 3). The drum [11] communicates through a spring loaded valve [V1] and a conduit [15] with a recovered (clean) solvent collection tank [21]. Valve [VI] is mounted to the side of the drum [11] at approximately the 10 gallon level (Level B in Figure 3) of the drum. Thus, there is a reservoir of 5-6 gallons above the valve [V1] for transfer through the valve when required. The valve [V1] may be substituted by a pump or siphon, which may be activated to pump or siphon solvent from the condensation/collection drum [11].

A bypass [16] is provided to allow solvent to flow past the valve or pump [V1] when the latter is closed. The bypass comprises a bypass conduit [16a] and an overflow column [16b]. The conduit extends between the upper region of the column and the tank [21]. The upper end of the conduit is at the height of the level A of the solvent in drum [11], so that once the level A is reached, solvent will overflow into the conduit [16a] and thence into tank [21] for a purpose which is explained below. A conduit [17] is provided between tank [21] and a gun-washer [31] to feed clean solvent to the gun-washer, the conduit being provided with a pump [18] to pump solvent from the tank to the gun-washer.

The gun-washer [31] is a conventional gun-washer having a bowl [32] for accommodating spray guns to be cleaned and spray jets (not shown) for directing solvent onto the dirty guns. Pump [18] is operated in conventional manner by a foot pedal [FP] or similar device located on the gun-washer.

Dirty solvent from the gun-washer collects in a used solvent collection container in the form of a tank [41]. In the example shown, tank [41] has a capacity of approximately 7 gallons. The tank [41] is divided into two compartments. The first compartment is formed

by a tube [42] within tank [41], into which dirty solvent is allowed to drain from gun- washer [31]. Tube [42] extends almost to the bottom of tank [41] and is closed at its bottom end. The second compartment is formed by the tank [41] itself. One or more overflow orifices [44] are provided close to the top of tube [42] and these orifices communicate with the interior of tank [41] forming the second compartment. Sludge from the used solvent collects at the bottom of tube [42] and the upper region of the solvent in tube [42] is therefore essentially sludge-free. Therefore, by providing the orifices [44] near the top of the tube, the solvent passing therethrough into the second compartment is essentially sludge-free.

Figures 4 and 5 show an alternative embodiment, wherein tank [41] is divided into three compartments. The first compartment is formed by the tube [42] and, again, the second compartment is formed by the tank [41] itself. The third compartment is formed by a reservoir tank [43] welded or otherwise fastened to tube [42]. The tank [43] could also be fastened to the wall of the tank [41] and communicate with the tube [42] by means of a hose or the like. In the example shown, tank [43] has a capacity of approximately 1 gallon. One or more overflow orifices [44] are again provided close to the top of tube [42] and these orifices communicate with the interior of reservoir tank [43] forming the third compartment. The tank [43] is open and overflows into the tank [41]. Alternatively, the solvent could be allowed to overflow directly into tank [41] through further orifices [44a] without first passing through tank [43].

In both Figures 3 and 4, extending downwardly into and almost to the bottom of chamber [42] is a conduit [45], which communicates via a pump [46] with the recycler [10]. Extending from the tube [42] close to its bottom end is a short extension having a one- way valve [V2], through which solvent in the tank [41] can drain into the tube [42] so that when the tube [42] is pumped out as described below, tank [41] is also drained. The one- way valve ensures that sludge-laden solvent from the bottom of tube [42] is prevented from flowing into tank [41].

For automatically cleaning the spray jets of the gun-washer, a pump [47] is provided, which will pump essentially sludge-free solvent from the solvent reservoir within the tank [41] through a conduit [48] extending into the reservoir and thence through a

further conduit (not shown) to the spray jets. For manually cleaning the spray jets, a pump [49] is provided at the top of reservoir tank [43] and the essentially sludge-free solvent is pumped through a conduit [50] to a tap (not shown), by which the flow of solvent to the spray jets is manually regulated.

In operation of the system, the user will initiate a transfer of clean solvent from condensation/collection drum [11] into the clean solvent tank [21] when he/she observes that the clean solvent tank [21] is emptied-i. e. when depressing the gun-washer pump foot pedal [FP] to activate pump [18] ceases to produce clean solvent. The transfer is effected by opening valve [V1] (or, where [VI] is a pump or siphon, by activating pump or siphon [V1]) and the user has the option to drain from 0 to 5 gallons from the condensation/collection drum [11] into the clean solvent tank [21] -i. e. the 5 gallons residing between levels A and B of Figure 3. Any solvent not initially transferred will be later transferred during the recycling process via the bypass [16]. For example, if the user knows that he/she will only need about 2 gallons of clean solvent for the duration of the recycling process, only that amount need be drained via the valve [V1]. Subsequently, as the condensation/collection drum [11] refills with a further 5 gallons of recycled solvent, the remaining 3 gallons will enter the system via the overflow conduit [16].

To transfer dirty solvent from the tube [42] into the recycler, either the user will actuate the transfer pump [46] or the pump is arranged to actuate automatically upon opening of valve or actuation of pump or siphon [V1]. This pump [46] will drain all 5 gallons (i. e. the 7 gallons within tank [41] minus the sum of the 1 gallon reservoir and the 1 gallon within reservoir tank [43] ) less any losses from evaporation in the gun washing station, into the recycler [1] from the lower region of the tube [42], which contains the settled sludge from the used solvent. Thus, by pumping from the bottom of the tube, the sludge is pumped to the recycler for removal. The system will be topped up to replace the losses from evaporation directly into the recycling chamber using miscellaneous solvent used from other parts of the shop.

As can be appreciated from the foregoing, in the example shown, a 5 gallon reservoir of clean solvent is always available in the clean solvent tank [21] for use in the gun-washer and a 5 gallon reservoir of dirty solvent is always available in the recirculated

solvent tank [41] for recycling. Also, a 5 gallon reservoir of clean solvent is always available above the valve [V1] in the condensation/collection drum [11] for transfer to the clean solvent tank [21]. This reservoir ensures that the entire system is always ahead by one full transfer and thus there is no down time during the recycling process. Additionally, there is always a reserve of 1 gallon for each of the manual and automatic wash functions supplied by reservoir tank [43] and the reservoir within tank [41], respectively. The recirculation efficiency is also optimized by having the solid waste (sludge) essentially confined to the bottom of the tube [42], from which it is pumped to the recycler [10].

The system can readily be switched to a stand-alone recycling system separate from the gun-washer, simply by providing a separate collection spout [111] on the condensation/collection drum [11] to collect clean solvent from the recycler and providing the distillation chamber [10] with an access cover [lOa] for charging the recycler with dirty solvent as required. This feature also allows for the system to be topped up periodically with solvent or solvent waste to compensate for solvent losses due to evaporation. Also, by opening the cover, the amount by which the solvent level is down can readily be seen and the amount of topping up required is accurately controlled.

Also, in the stand-alone mode, the overflow could be diverted from draining into the tank [21] to draining into a separate container [21a], as shown in broken lines in Figure 3.

This would allow a further 5 gallons (i. e. the difference between levels B and A) to always be present in the condensation/collection drum [11], which assists in cooling the drum [11] and provides more efficient condensation.

A further embodiment of the invention is shown in Figure 6. This embodiment is identical to that of Figures 3 or 4, with the exception that the condensation/collection drum [110] and the clean solvent tank [210] are interchangeable. Thus, when clean solvent tank [210] is empty, the tanks are switched and tank [210] is connected to the outlet from recycler [10] and fills with clean solvent. In the meantime, the clean solvent from the previous fill is pumped from drum [110] to the gun-washer. In this case, it is preferred that the condensation/collection drum [110] and the clean solvent tank [210] be of similar capacity, for example, 5 gallons. Whilst not providing the same degree of automation as

Figures 3 or 4, this embodiment is quite practical in that the tanks (or the conduits thereto) can be changed very quickly and easily by hand.

In the foregoing examples, the separate pump [46] is provided to pump used solvent to the recycler. If desired, the pump [47], which is an existing feature of typical gun- washers may be used as a dual purpose pump-namely, for supplying solvent for the automatic cleaning operation as described above or for pumping used solvent to the recycler, instead of using separate pump [46]. This would be effected by providing a suitable valving system between pump [47] and conduits [45] and [48] which would selectively place pump [47] in line with one or other of these conduits, as required.

A further possibility in the practice of this invention is that solvent vapours may be drawn by vacuum pump from the gun washing or spray jet cleaning processes into the system for subsequent recovery or venting to atmosphere through a suitable filter (such as a charcoal filter). In a conventional gun-washer, vapours are sucked through an exhaust tube and vented to the outside of the building containing the equipment. In the present invention, the exhaust tube could be diverted to exit at the bottom of the tank [41]. The vapours would then bubble through the tank and some would condense during passage through the solvent within the tank. Uncondensed solvents would then be passed through a charcoal filter or the like before entering the atmosphere.

Thus, the system of this invention has a number of advantages, as will be apparent from the foregoing description. These include but are not limited to the following: All of the recycled solvent is available for re-use in the gun washing operation, compared with only 50 % (typically) in the prior art system.

The present system will never run out of solvent for the spray jet cleaning operations before running out of clean and dirty solvent.

The amount of topping up of solvent required to compensate for evaporation losses can be accurately controlled.

It is not necessary for each transfer of clean solvent to transfer the full amount of clean solvent available in the condensation/collection drum, which saves time when only a partial amount of the available clean solvent is needed.

The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.