WO2002032593A1 - Method, device and installation for cleaning contaminated parts, with a dense pressurised fluid - Google Patents

Abstract

The invention concerns a method for cleaning contaminated, polluted, soiled parts, with a dense pressurised fluid, in particular a supercritical fluid, such as supercritical carbon dioxide CO2. The invention also concerns a device and an installation for cleaning contaminated parts, with a dense pressurised fluid, in particular with a supercritical fluid. The cleaning device comprises: a closed chamber under pressure (1), a drum or basket (3) arranged inside the closed chamber and receiving the metal parts to be cleaned, said drum or basket being driven by a shaft (4) directly engaged with driving means (11) located outside the chamber (1); means (12, 13) for subjecting the parts to the action of a high speed jet of the dense fluid; means (15) for continuously separating in the closed chamber the insoluble solid and/or liquid particles in the fluid from the dense pressurised fluid.

Description

_R PROCESS DEVICE AND INSTALLATION

FOR CLEANING CONTAMINATED PARTS,

BY A DENSITY FLUID UNDER PRESSURE

DESCRIPTION

The present invention relates to a method of cleaning contaminated, polluted, soiled parts, by a dense fluid under pressure, in particular by a supercritical fluid, such as carbon dioxide C0 ₂ supercritical.

The invention also relates to a device and an installation for cleaning contaminated parts, by a dense fluid under pressure, in particular by a supercritical fluid.

The technical field of the invention can, in general, be defined as that of cleaning soiled, contaminated, polluted parts.

The cleaning of materials and parts is a fundamental step in the making and development of intermediate or final products in a very large number of diverse and varied industries encompassing sectors, such as the automotive industry, fine mechanics, electronics, watchmaking, connectors, IT, aeronautics, medical equipment, packaging, which use multiple alloys, such as steels, stainless steels, aluminum and copper, and sectors, such as optics and armament, which can use, in addition to these alloys, composite materials, such as polycarbonates and borosilicate glasses, etc.

The cleaning of parts and materials is in particular a necessity, before or during the machining, manufacturing, assembly, assembly, bonding, application of paint, varnish, coating; surface treatment, chromating, physical vapor deposition.

Thus, in particular, whether during or at the end of the assembly, successive cleaning steps are required and require the use of chemicals for degreasing, for example in the case of alloys, preparing a surface or debinding, for example example in the case of composite materials. The cleaning techniques, hitherto commonly used, consist in using organic solvents, or detergents or surfactants in aqueous solutions by soaking, spraying or wiping.

The solvents used differ in particular, depending on the nature of the pollutant, contaminant, to be dispersed.

The most commonly used organic solvents are: hydrocarbons; halogenated alkanes, alkenes and alkynes (chlorinated and / or fluorinated), such as trichlorethylene, dichloromethane and other CFCs and HCFCs; alcohols and ethylene glycol.

These solvents have met the needs of industries in terms of cleaning efficiency or in terms of universality, in particular with regard to numerous formulations of lubricating agents, such as oils for forming, machining, quenching, protections; the water-soluble fluids emulsifiable or used as such and molding agents.

The use of these solvents has, however, many drawbacks, following their implementation: drawbacks all the more serious as this use generates large volumes of waste which must be treated or destroyed. For example, in the United States, the cumulative production of wastes induced by organic cleaning solvents in all industries, namely, cleaning, surface treatment, machine factories, metal treatments, paints, materials plastics, reached, in the early 1990s, more than 340,000 tonnes per year. In addition, these solvents induce nuisances, both for the operators who use them, such as risk of inhalation, obligation to wear a mask, risk of explosion, as well as for the environment. In addition, industrial equipment must be suitable for the use of these solvents, some of which are explosive, which requires atmospheric control, ADF (Explosion Proof) electrical equipment, high ventilation and good sealing.

Furthermore, the cost of these solvents can be relatively high, while they do not always make it possible to reach the so-called “ultra clean” states required for certain materials, in particular in the aerospace industry. As already indicated above, the cleaning operations with these solvents generate large volumes of effluents and there is generally an obligation for the user to provide for recycling of the solvents, as well as aqueous solutions, detergents, or a treatment facility for these, so as to comply with the regulations concerning discharges.

Indeed, in the early 1990s, an awareness of nations, coupled with scientific progress on the role of protecting the atmospheric layers, led to the definition of protocols: Montreal in 1987, Rio in 1995 and Kyoto in 1997, aimed, respectively, at protecting the stratosphere, the troposphere and limiting the greenhouse effect.

In particular, the Montreal Protocol, implemented by most industrial nations, aims to limit the release of VOCs or Volatile Organic Compounds, responsible for the destruction of the ozone layer. The objective is to achieve zero rejection of these VOCs in 2015, whether for old installations in service or for new installations under construction. The Montreal and Rio protocols also provide for a total ban by 2015 for certain solvents, which requires that they be replaced. This is the reason why, in order to remedy the drawbacks of the cleaning processes and products described above, and to meet the legal and regulatory, the use of fluids in the dense state under pressure, gas, liquid or supercritical, for cleaning parts, has been considered and studied. Indeed, these fluids have solvent properties allowing them to replace many common solvents used in cleaning techniques.

In addition, the special qualities of these fluids make it possible to develop processes which respect the environment and generate small quantities of waste.

In particular, cleaning with dense C0 ₂ , gas, liquid or supercritical has been widely studied and developed and has reached the industrial stage. The C0 ₂ cleaning processes have been developed for various components ranging from simple automotive or aeronautical parts, to complex circuits, such as electronic components, optical systems or missile gyroscopes.

Cleaning by supercritical fluid, such as C0 ₂ , can be carried out by simple soaking, immersion in the supercritical fluid, possibly agitated by blades, or else the parts to be cleaned can be subjected to the action of jets of the supercritical fluid .

It has also been proposed to stir the parts to be cleaned by placing them in an internal basket in the autoclave under pressure, this basket being set in motion by a crown fitted with spray nozzles. the fluid at high speed, creating the necessary reaction force.

Documents US-A-5,267,455 and

US-A-5 412 958, relate to a dry cleaning installation, using a supercritical fluid, such as C0 ₂ , in which the parts to be cleaned are placed in a drum or basket rotating inside a autoclave.

The rotating drum or basket is supported by two sets of rollers and is magnetically coupled to a motor, preferably an electric motor. It is indicated, in general, that other drive means are possible, but they are not described.

The autoclave does not include a filter or spraying device.

The existing methods and devices for cleaning with a dense fluid under pressure, in particular supercritical, do not make it possible to obtain sufficient cleaning of the contaminated parts or materials, even if the parts are placed in a rotating basket or else subjected to action. pressure jet.

Furthermore, the methods and devices of the prior art are only capable of cleaning only small quantities of materials and parts of small size and light weight.

In addition, the problem of recontamination of the parts cleaned by the solid particles and / or the liquid particles of contaminant, insoluble in the dense fluid, which are redeposited on the parts clean, is not resolved by any of the methods and devices of the prior art.

There is therefore a need for a method and a device for cleaning with a dense fluid under pressure - which makes it possible to obtain perfect cleaning, even of large and heavy parts and large quantities of materials.

There is, moreover, a need for a method and a device for cleaning with a dense fluid under pressure, which prevents the (re) contamination of the cleaned parts by redeposition of solid and / or liquid particles.

The object of the present invention is to provide a method and a device for cleaning with a dense fluid under pressure, which meets, inter alia, the needs mentioned above.

The object of the present invention is also to provide a method and a device for cleaning with a pressurized fluid, which does not have the drawbacks, limitations, defects and disadvantages of the methods and devices of the prior art and which solves the problems of prior art.

This object and others still are achieved, in accordance with the present invention, by a method of cleaning contaminated parts, by contacting with a dense fluid under pressure, in which:

- the parts to be cleaned are placed in a drum or basket inside a pressure enclosure containing the dense fluid under pressure, said drum or basket being set in motion by a shaft in direct contact with drive means located outside the enclosure; the parts are also subjected, simultaneously, to the action of a high speed jet of the dense fluid; the solid and / or liquid particles, insoluble in the dense fluid, essentially generated by cleaning are, simultaneously, continuously separated from the dense fluid by separation means provided inside the enclosure.

The method according to the invention associates several mechanical effects with the simple contacting, or simple soaking, of the polluted, contaminated parts, with the dense fluid under pressure, these mechanical effects are, respectively, the stirring effect, stirring due to the movement of the basket or the drum in which the parts are located and, on the other hand, the pickling effect due to the impact of the jets of dense fluid at high speed on the parts. This high-speed jet allows perfect cleaning and eliminates any residual contamination of the parts.

In addition, since the basket or drum set in motion by a shaft in direct engagement with drive means, there is no limitation on the quantity and weight of the parts which can be cleaned, as is the case. case when the basket, generally rotating, is actuated by a magnetic system, for example. In other words, the fact that the shaft is in direct contact with the drive means makes it possible to ensure an almost torque unlimited, which only depends on the power of the drive means, such as an electric motor, ensuring the generally rotational movements.

The method according to the invention removes all the torque limitations which one finds oneself in the methods where the agitation is ensured by blades, by magnetic drive or by a system based on reaction forces due to jets of fluid. In addition, the continuous, simultaneous separation, during cleaning, of solid and / or liquid particles insoluble in the dense fluid by separation means provided inside the pressure vessel itself, makes it possible to trap the contaminants and / or pollutants extracted, generated by cleaning, the stirring action, and the effect of high speed jets and to avoid redeposition of contaminants and / or pollutants on the parts being cleaned and already clean. The combination of the action of the jet (s), of agitation due to the movement of the rotating basket, and of the continuous separation of solid and / or liquid particles insoluble in the dense fluid, results in an unexpected increase in cleaning performance by a dense fluid under pressure compared to the processes of the prior art.

These improved performances are obtained without limitation of load on a quantity and / or a weight of parts clearly higher, thanks to the setting in motion of the basket or drum by an axis or shaft in direct connection with drive means, such as a motor.

The drum or basket can be rotated; the direction of rotation possibly being periodically reversed.

The revolving drum or basket can also be moved in a pendulum motion.

The possibility of reversing the direction of rotation or of making a pendulum movement, for example, depending on the type of part to be cleaned, is precisely one of the advantages provided by setting in motion the drum or rotating basket, using of a tree in direct drive.

In the process according to the invention, by high-speed jet, is generally understood a speed of the fluid from 1 to 500 m / sec, which makes it possible to ensure optimal pickling of the part subjected to the action of this jet, c is to say struck by this jet.

When the movement of the rotating basket or drum is a rotational movement, the rotational speed is generally 5 to 500 revolutions per minute.

It is possible, according to the invention, to maintain high speeds, even for large quantities and weights of parts to be cleaned. Continuous separation of the solid and / or insoluble liquid particles generated is generally carried out by a filtration operation, possibly preceded, followed or associated with an absorption operation, which ensures separation and extremely efficient trapping of said solid particles and / or insoluble liquids. According to the invention, the fluid in the dense state under pressure is preferably brought into contact with the parts to be cleaned at a pressure of 100 to 300 bars and at a temperature of 15 to 80 ° C, preferably 40 at 60 ° C. The treatment conditions are much less severe than those of the processes of the prior art using dense fluids under pressure, which results in a considerable energy gain for the process of the invention. In addition, we obtain a cleaning efficiency close to, or even higher, in most cases, with a much shorter treatment time, for example, from 10 to 15 minutes, again this has a positive effect on the energy cost. and financial of the process.

The milder conditions, namely low temperatures, low pressures and short treatment time of the process of the invention, are precisely due to the combination, according to the invention, of the agitation caused by the moving drum or basket, the action of the high speed jet of dense fluid, and of the continuous separation of solid and / or liquid particles insoluble in the fluid, of the dense fluid under pressure. The implementation, according to the invention, of such “soft” conditions is particularly advantageous for the treatment of mechanically and / or thermally fragile parts, such as parts made of polymers or -alloy / polymer composites whose cleaning was not or hardly possible by the methods of the prior art. Finally, the method according to the invention has, of course, all the inherent advantages associated with the use for cleaning a dense fluid under pressure, instead of a conventional solvent, in particular of the halogenated hydrocarbon type.

Preferably, said dense fluid under pressure is a fluid in the liquid and / or supercritical state, that is to say that the dense fluid is under pressure and at a temperature, such that the fluid is in the state liquid and / or supercritical, more preferably the fluid is in the supercritical state.

Thus, more precisely, in the process according to the invention, a gaseous compound is used, for example, under normal conditions of temperature and pressure, and its density is increased by increasing its pressure. By also modifying the temperature, we will thus place ourselves in the domain where the fluid is in the dense state and under pressure, preferably in its liquid and / or supercritical state. This field can be easily determined by a person skilled in the art, in this technical field.

According to the invention, the extractive properties of the fluid can be varied, in a controlled manner, by acting on the two parameters of temperature and pressure, while remaining in the dense range and under pressure, preferably, the liquid and / or supercritical of the fluid in question: thus, the increase in pressure and temperature increases the solubilization capacity, while the decreasing the pressure decreases the viscosity and increases the diffusivity.

These two characteristics make it possible to control a fluid whose solvent power is modular, in terms of solubilization, in particular light polluting compounds, contaminants, which it is sought to eliminate by cleaning, and in terms of extraction kinetics, in particular for pollutants in the porosity of the material, when cleaning porous parts.

Thus, according to the invention, it is possible, during treatment, to carry out compression / decompression cycles, preferably very rapid, with, for example, an amplitude of the pressure variation of 10 to 100 bars, and time intervals. from 10 seconds to a few minutes, for example, 10 minutes, all for example, for one to a few hours, for example, 10 hours.

This increases the penetration of the solvent fluid into the material of the parts to be cleaned, which has the consequence of improving the cleaning performance.

Additional advantages of the process of the invention derive, essentially, from the specific characteristics of fluids in the dense state under pressure, in particular, supercritical. These advantages are added to and are amplified by the combined effects of agitation in the rotating basket or drum, of action of the high speed jet and of separation, extraction, retention of contamination, specific combined effects of the process of the invention. . The fluid used can be chosen, for example, from carbon dioxide, sulfur hexafluoride, nitrous oxide, nitrous oxide, light alkanes having, for example, from 1 to 5 carbon atoms, such as methane, ethane, propane, butane, isobutane, pentane, alkenes, such as ethylene and propylene, as well as certain organic liquids, such as methanol and ethanol, etc.

One can of course use any compound which may have a dense state and under pressure, in particular, supercritical, and the use of which remains compatible with the material or materials constituting the parts to be cleaned.

Carbon dioxide is preferred because it has the advantage of a relatively easy implementation: it is inexpensive, non-toxic, non-flammable and has easily accessible critical conditions (critical pressure: Pc of 7.3 Mpa and critical temperature Te of 31.1 ° C). C0 ₂ , in the dense state under pressure, liquid or supercritical, solubilizes most organic compounds with molar masses less than or equal to 2000 g / mole. It is therefore an excellent solvent, in particular vis-à-vis organic compounds, called "undesirable", forming most of the contaminants and pollutants.

It is precisely these properties that make it an attractive substitute for organic solvents.

The relative chemical inertness of C0 ₂ , in the dense state, makes it particularly suitable for being works in a process aimed at cleaning sensitive or fragile parts.

In addition, the low viscosity of C0 ₂ in the dense state, its high diffusion coefficients and its very low interfacial tension allow the cleaning of complex parts by their forms and their physical characteristics, in particular when one is in the presence of adsorption phenomena, whether on the surface or at the heart of the part. One can also cite, among the advantages, of using C0 ₂ , replacing the processes conventionally implemented, using organic solvents:

- an almost perfect extraction efficiency with respect to organic compounds, thanks to specific physicochemical characteristics;

- an almost zero volume of residual effluent, strictly limited to the recovery of pollutants extracted and the recycling of purified C0 ₂ gas; - A significant saving, for example, whether in terms of solvent, by the absence of treatment or recovery of effluents or by the use of inexpensive C0 ₂ ;

- strict respect for the environment, within the meaning of the Montreal and Rio protocol, since the process does not generate, or very little, aqueous effluents;

- a total absence of toxicity, vis-à-vis users compared to cleaning agents, such as trichlorethylene or others; a modularity of the solvent power of the variable molecule depending on the conditions of use, that is to say the pressure and the temperature, making it possible to adapt to the nature of the pollutants, contaminants, to be eliminated, extract and / or the desired application.

In other words, the two pressure and temperature characteristics make it possible to control a fluid whose solvent power is flexible in terms of solubilization, in particular of contaminating, polluting, undesirable compounds, parts and extraction kinetics.

The high volatility of C0 ₂ under conditions

(pressure and temperature) normal characterizes it as a dry solvent, not requiring a drying step, after cleaning. In addition, C0 ₂ does not leave a residual trace on the treated, cleaned part.

Treatment in a C0 ₂ atmosphere can avoid the risk of oxidation and improve the final surface condition of the part.

Preferably, according to the invention, a compound, called "cosolvent", is added to the dense fluid, under pressure. The addition of such a cosolvent to a dense fluid under pressure, in the specific context of a cleaning treatment, is neither described nor suggested in the prior art.

It has been found, surprisingly, according to the invention, that the addition of a cosolvent to the dense fluid, under pressure, makes it possible to obtain a total extraction of the contaminating organic compounds, pollutants, in other words, undesirable compounds, from the parts to be cleaned.

The addition of the cosolvent ensures a selective extraction, elimination, of undesirable organic compounds, while sparing the constituent components of the parts.

In other words, the addition of an appropriate cosolvent will make it possible to orient the selectivity of the extraction, cleaning, towards the pollutants, contaminants and undesirable organic compounds, which it is desired to eliminate and extract.

According to the invention, said cosolvent is chosen, for example, from water, aqueous solutions, alcohols, for example, aliphatic alcohols of 1 to 5 C, such as ethanol, methanol, butanol, ketones, such as acetone, and mixtures thereof.

Among the aqueous solutions, there may be mentioned solutions of detergents such as anionic and / or cationic surfactants, solutions of complexing agents, chelating agents, buffer solutions, for example of phosphate and / or hydrogen phosphate, etc. ; antioxidant solutions, such as ascorbic acid, to stabilize the material. According to the invention, said cosolvent is added to the dense fluid, under pressure, in an amount of 0.01 to 10% by weight, preferably from 0.02 to 1% by weight, more preferably from 0.02 to 0, 1% by weight.

The cosolvent, if it is water, can be partly already present in the parts to be cleaned, and we will not add in the fluid supercritical than the amount necessary to give the concentrations mentioned above.

According to a particularly advantageous embodiment of the invention, the dense fluid, under pressure, located in the pressure vessel, and added with a cosolvent, preferably in the proportions mentioned above, is also subjected to the action of ultrasonic waves.

Preferably, in this case, the dense fluid under pressure is C0 ₂ and the co-solvent is water or an aqueous solution.

The frequency of said ultrasonic waves preferably varies from 20 kHz to 100 MHz, more preferably from 20 to 1000 kHz or from 1 to 100 MHz, such ultrasonic waves are also qualified, respectively, as ultrasound or megaons. .

We know, in fact, that sound waves whose frequency is higher than 16 kHz are qualified as ultrasonic waves. From 1 MHz, these are megaons. The areas of application of ultrasound and megaons are generally different. With ultrasound, we find, rather, all applications for cleaning materials. With megaons, we find rather all applications for measurement probe, but also cleaning, "stripping" of silicon materials, such as wafers, in microelectronics.

The duration during which the fluid is subjected to the action of ultrasonic waves (ultrasound or megaons) is generally from 1 to 60 minutes. In most of the works presented in the literature, it is indicated that the coupling of ultrasound and / or megaons to fluids is only of interest when the fluid is in the liquid state. For example, ultrasound was used on liquid C0 ₂ alone, at a temperature of 20 ° C and at a pressure of 50 bars.

It could, however, be observed a phenomenon (of cavitation) similar to that observed in a conventional medium, such as liquid water, in C0 ₂ , alone, without any co-solvent, in the liquid and supercritical state, at know at a temperature of 40 to 65 ° C, and at a pressure less than or equal to 140 bars, in the context of an application for degreasing materials. In all the processes known up to now, the fluid is always used alone with ultrasound, in the absence of any cosolvent.

Surprisingly, it has been found that the simultaneous implementation in a dense fluid under pressure, in accordance with this particularly preferred embodiment of the process of the invention, of a cosolvent, for example at a rate of 0.01 to 10% by weight, and ultrasound or megaons, induced the propagation of an ultrasonic wave leading to the formation of cavitation bubbles, probably formed by the co-solvent in the dense fluid. This phenomenon then generates significant agitation likely to produce an effect favorable to the detachment and detachment of pollutants, contaminants, fixed to the surface of the treated parts, whatever the pressure and temperature conditions of the dense fluid under pressure.

Unexpectedly, there is a real synergistic effect between the ultrasound and the co-solvent in the dense fluid under pressure, which leads to considerably improved cleaning efficiency.

Preferably, the ultrasound is multifrequency ultrasound from 20 to 1000 kHz or multifrequency megaons from 1 to 100 MHz, such ultrasound or megaons are produced either by probes whose emission covers several frequencies, or by the association of single frequency probes whose resulting emission covers several frequencies. Indeed, there are several models of sonotrodes, some not very specific allow the emission of a “bouquet” of frequencies from 20 to 100 kHz, like the one we used for the tests described in example 8 below. There are also sonotrodes whose spectrum is narrower, for example from 20 to 25 kHz. It is then possible to envisage a device comprising two or three or more sonotrodes, which makes it possible to cover a very wide area, by virtue of their couplings, for example: it is possible to associate a sonotrode of 20 kHz and one of 200 kHz, etc.

Any type of part, without any limitation, can be treated by the method of the invention. The material (s) of these parts can (wind) be organic (s), mineral or other. The parts can be parts composites comprising the combination of several materials.

It should be noted that due to the conditions

"Soft" in temperature and pressure of the process of the invention, thermally and / or mechanically fragile parts can be treated by the process of the invention.

Similarly, as already indicated, the method of the invention knows no limitation as to the size and / or weight of the parts to be treated, in particular, thanks to the specific drive mode chosen.

The materials, which can be cleaned by the process of the invention, are generally solid materials, such as metals, metal alloys, possibly coated, such as aluminum, titanium, steel, stainless steel, copper, brass, and any other alloy, or plated metal.

The parts made of these materials will therefore be, for example, aeronautical, automobile parts, timepieces and micromechanics, electrical and electronic connectors, microelectronic silicon components, such as wafers, medical tools. , etc. By “cleaning”, according to the invention, is generally meant the elimination, the extraction of polluting compounds, undesirable contaminants, which are not normally part of the material of which the parts are made. These polluting compounds, contaminants, to be extracted can also be found on the surface of the part, but they can also be inside the material of the part, within, for example, its porosity.

The method according to the invention makes it possible to clean the parts of any polluting, contaminating inorganic and organic compound found in or on the part.

The inorganic and / or organic compounds can be products present accidentally or naturally on the parts, but they can also be, in particular, products introduced into and / or applied to the parts, during previous operations, entering their process. manufacturing and / or assembly. In the case of metals, these may in particular be oils used in working with metals, such as cutting, machining, quenching and dyeing oils.

The extracted inorganic compounds eliminated by the cleaning process according to the invention are, for example, free metals or metalloids or compounds of metals or metalloids.

By compounds of metals or metalloids is meant all the compounds derived from these metals or metalloids, in particular, their oxides or salts, organometallic derivatives, etc. Among the salts, there may be mentioned nitrates, sulfates, chlorides , etc., hydrated or not.

It turned out that the method according to the invention was particularly effective for extract, eliminate, metal salts from materials.

These free metals and metalloids or in the form of their compounds may be present in the form of their radioactive isotopes or not.

The method according to the invention is therefore particularly advantageous in the context of the decontamination of materials contaminated by radioactive products, for example, organic compounds, contaminated by radioelements such as strontium, cesium, iodine, americium, plutonium, uranium, thorium , tritiated organic compounds, etc.

The organic compounds, which can also be eliminated by the process according to the invention, are all the organic compounds liable to be found in or on the material of the parts accidentally, naturally or for other purposes, for example, during incoming treatments in their manufacturing and / or assembly process. These organic compounds include the low viscosity lubricants oil type cuts as Mobil Mobilube ^®, Mobil DTE 24 ^®, Castrol Variocut B27 + ^®, paraffin oils such as Shell Neatcut XF15 ^®, machining oils of water-soluble or in emulsion such as Castrol Alusol B ^® (mineral), Peralube 7000 ^® , Century oils Trancent LM2 ^® (mineral), Cimstar 560 ^® , Ardrox 970-P25E ^® , Renoform MBO 2728 ^® , anticorrosion films such as Shell Ensis Fluid ^® SDC E or G, Brent Ardrox 3961 ^® , Tectyl 800D ^® , BP thermacote ^® , hydraulic oils like Monsanto Skydrol ^® , Texaco Régal oil R & 0-32 ^® , Nynàs P89-44101 ^® , dye oils like Drawsol 2345 N ¹ , Stratus 250 ^® , Uniq DP 101 ^® , Ardrox 3140 ^® , silicone oils like Dow Corning 180 est ^® , fats such as Cetyl alcohol, Molykote Gn + ^® ..., the compounds ensuring the binder during the forming of composite parts such as Freekote 700 NC ^® , paraffins, etc.

Finally, fatty acids from, for example, fingerprints on optical materials can also be mentioned.

The temperature and pressure ranges used during the cleaning operation may vary, provided that the fluid always remains a dense fluid under pressure, preferably in a liquid and / or supercritical state, similarly, as indicated above, compression / decompression cycles can be carried out.

The temperature and pressure ranges depend, in particular, on the nature of the fluid used.

These temperature and pressure ranges have already been mentioned above and apply, in particular, to C0 ₂ .

Such conditions can be maintained throughout the duration of the process, or else only at the start of the cleaning or treatment process, where such conditions correspond to a high density and to a high temperature - the predominant phenomenon being solubilization - allow 25

extract, eliminate, very quickly the compounds outside the matrix forming the part.

Generally, the duration of the cleaning treatment, that is to say the duration during which the part (s) to be cleaned is left in contact with the dense fluid under pressure, is 1 or a few minutes, per example, 10 minutes, one or a few hours, for example, 5 hours, depending on the flow rate of the fluid and the quantity of materials to be treated. Again, according to the invention, this duration is short compared to the duration of the processes comprising neither agitation in the drum or rotating basket, nor action of a jet of fluid at high speed, nor continuous separation. After a few minutes, that is to say, for example, after 5 minutes, once the parts are subjected to the pressure and temperature conditions of the process, the extraction, the elimination, is carried out very quickly, thanks to a very important diffusive regime.

After reaching equilibrium, for example after 5 to 60 minutes, it can be considered that the extraction, the elimination of pollutants, contaminants, is total with an almost total efficiency, for example of more than 99.9%.

The extraction efficiencies of removing contaminants, pollutants and cleaning are, in all cases, very high, whatever the pollutants or contaminants. The level of solvent used, i.e. the weight of dense fluid - solvent, preferably liquid and / or supercritical, implemented with respect to the surface of the part (s) to be cleaned, can vary from 0 to 100 kg of fluid / cm ² of part (s). According to an additional advantage of the invention, the level of solvent used is significantly lower, thanks to the effects of agitation, and of the fluid jets, than that of the prior art.

Advantageously, the method according to the invention comprises, after cleaning, recycling of the fluid, after one or more physico-chemical separation steps making it possible to separate the fluid from the extracts, and the fluid in gaseous form is recycled, reconditioned to the cleaning step, towards the pressure vessel. The separation steps should not be confused with the separation of solid and / or liquid particles insoluble in the fluid, generated by cleaning, which takes place continuously during the cleaning operation itself, and inside even from the pressure vessel. These separation steps relate to fractions soluble in the fluid.

Conventionally, the first separation steps consist of a reduction in the density of the fluid by a series of expansion and successive reheating, in order to approach the gaseous state.

The solvent power of the fluid decreases and part of the previously solubilized extracts is thus recovered during the cleaning or extraction step. Thus, the method according to the invention for cleaning parts makes it possible to physically recover at the end of treatment, on the one hand, the cleaned parts, on the other hand, undesirable products, including the handling, treatment or elimination can be done in a specific manner and therefore easily controlled, while the gas or fluid can advantageously be recycled, in order to carry out a new extraction or cleaning. Before recycling, the process can include, among other things, a stage of distillation of the dense fluid allowing an almost total purification, in accordance with the document FR 85 13246 of 06/09/1985 which describes a process and a device for the extraction of constituents by a supercritical fluid.

Therefore, the cleaning or extraction process can be carried out in a closed circuit or in a loop, which advantageously means that thanks to an initial and constant charge of fluid, such as C0 ₂ , it is possible to gradually eliminate parts, contaminating compounds, undesirable pollutants.

More precisely and following the cleaning process proper, the process according to the invention advantageously comprises one or more steps, for example up to 3 physicochemical separation steps, in which the density of the fluid is reduced, by example by a series of detents and successive reheating, preferably 1 to 3, in order to approach the gaseous state. The conditions prevailing in these successive stages will be, for example, the following: 90 bars and 50 ° C, 70 bars and 40 ° C and 50 bars and 40 ° C.

Because the insulating power of the fluid decreases, the extracts previously solubilized are thus recovered during the cleaning or extraction step.

These extracts are in the form of more or less fluid concentrated liquids, and can be specifically treated and, generally, they are destroyed.

The gas obtained at the end of the separation is preferably recycled to the cleaning, extraction stage, where it is reconditioned, in order to put it back under temperature and pressure conditions so that it is in in a supercritical state, the gas can thus be first cooled to atmospheric pressure, stored in liquid form, then reheated and compressed before being sent to the cleaning or extraction process proper.

Before recycling, the fluid is preferably purified by one or more stages of adsorption and / or liquefaction and / or distillation. The adsorption can be carried out, for example, with activated charcoal or other adsorbent, such as zeolite ^® and the (re) distillation is preferably carried out using the specific device described in the document FR 85 131 246 This purification carried out by adsorption, for example, by passage over activated carbon and / or by distillation and / or by liquefaction makes it possible to remove the traces of organic products. volatile and / or insoluble in C0 ₂ and mechanically entrained by it during the previous separation steps.

Indeed, a thorough purification of the gas is generally necessary, under penalty of greatly reducing the extraction and / or cleaning performance.

At the end of the cleaning, that is to say when it is considered that the contaminants, pollutants have been eliminated to the desired degree, we proceed, in a final step, to relax, depressurize or decompress the pressure vessel with the cleaned parts there.

Advantageously, according to the invention, during this expansion, all or part of the dense fluid under pressure (initial fluid) is replaced by another weaker and chemically inert enthalpy fluid. In the case, for example, of C0 ₂ , this other fluid, chemically inert, may be chosen from nitrogen, helium, neon and dry air, etc.

It will be possible, for example, to carry out a first depressurization, expansion, of the dense fluid under pressure from the pressures and temperatures prevailing during cleaning, namely 100 bars and 300 bars and 15 to 80 ° C., up to a pressure and temperature, respectively about 50 bars and 10 at 20 ° C and for a period of 5 minutes for the first expansion, then introduce the other fluid or lower enthalpy replacement fluid into the enclosure, in order to replace all or part, for example from 50% to 100% of the initial fluid, the introduction of the replacement (gaseous and inert) taking place at a temperature of 20 to 60 ° C and at a pressure of 50 to 150 bar.

A regulation can take place between the temperature of the wall (using a probe) and the percentage of opening of the expansion valve.

The expansion is then continued until atmospheric pressure and a temperature of 50 to 10 ° C. It is obvious that we can also observe several stages by reducing the pressure and each time introducing replacement gas.

One thus solves one of the problems encountered hitherto with the methods of cleaning contaminated parts, by a dense fluid under pressure, which is the time necessary to depressurize or relax the enclosure in which the parts cleaning was carried out. . Indeed, during expansion or depressurization, a pressurized fluid has an enthalpy, specific to each body, the effect of which will result in a significant consumption of calories during its change of state (from supercritical to gaseous). Thus, for C0 ₂ whose pressure is between 100 and 300 bars and at a temperature close to 40 ° C, depressurization to atmospheric pressure, if it is carried out very quickly, for example from 2 to 5 ′, will cause a very significant drop in temperature to levels up to -50 ° C. At this temperature, the C0 ₂ will pass to the solid state, via the liquid state, thus forming dry ice which will prove to be very difficult to eliminate quickly. We will find with clean parts trapped in a large "ice cube" which will require several tens of minutes - for example, from twenty minutes to a few hours if we consider an enclosure of several hundred liters - to disappear while sublimating. In addition, these very cold rooms risk causing condensation of the water vapor, contained in the ambient air, on the surface thereof, canceling out one of the advantages of this process which consists in carrying out cleaning without operations of drying. This humidification following too rapid depressurization could prove harmful in the case of parts sensitive to oxidation and corrosion such as aluminum, for example. Finally, an extension of the relaxation time to avoid this problem can harm the advantage of the process insofar as the treatment time is extended by a time as long for the relaxation. Thus, for cleaning times of the order of 15 minutes, it seems unacceptable to subject the parts to more than 15 minutes, at least, of relaxation time, which increases the total duration of the process by at least a factor. 2. Similarly, for longer times, of the order of 20 to 40 minutes for the cleaning operation only, an expansion or depressurization time of more than 15 minutes would bring the overall processing time of the process since loading. until the pieces are unloaded in the autoclave at around one hour or more, which can be detrimental for rhythms generally admitted into an assembly line from the parts thus cleaned.

This problem is therefore solved by substituting, during expansion, another fluid such as nitrogen, helium, neon or dry air, etc. to the fluid initially present in the enclosure, such as C0 ₂ . Indeed, the lower enthalpy of the replacement fluid results in a lower lowering of the temperature during its depressurization under the same conditions as those used for the initial fluid, conditions which are, for example, those described above for C0 ₂ . Thus, for relaxation times of the order of a few minutes or of the same order of magnitude as those applied with the initial fluid, such as C0 ₂ , alone, lowering the temperature in the presence of the replacement fluid, such than nitrogen, is weaker and stays above the solidification temperature of water vapor. The difference in physical property between the two fluids, initial and replacement, such as C0 ₂ and N ₂ , makes it possible to envisage purge times much faster than with the initial fluid, such as C0 ₂ , only , all to reach internal temperatures of the autoclave and parts subject to cleaning always positive. Dry parts are thus obtained in which the water vapor of the ambient air does not condense on their surfaces, this in order to avoid any risk of corrosion. The invention also relates to a device for cleaning contaminated parts with a dense fluid under pressure, comprising:

- a closed enclosure under pressure; - a drum or rotating basket placed inside the closed enclosure receiving the parts to be cleaned and set in motion by a shaft in direct engagement with means for driving means for subjecting the parts to the action of a high speed jet of dense fluid;

- Means for continuously separating in the closed enclosure the soluble solid and / or liquid particles from the dense fluid under pressure.

The invention further relates to a cleaning installation comprising the device.

The invention will be better understood on reading the following description, made with reference to the accompanying drawings, in which: FIG. 1 schematically represents a side view in section of an example of a device for implementing the method of the invention; Figure 2 shows, schematically, a side sectional view of an example of an installation for implementing the method of one invention.

An example of a device according to the invention is described in FIG. 1.

It is obvious that the device shown is given by way of illustration and in no way is limitative and that various variations are possible. from this, concerning, for example, the shape and size of the various elements making up the device.

The device comprises, first of all, a sealed sealed enclosure (1), more commonly called an autoclave, capable of being pressurized and therefore able to withstand the working pressures, implemented according to the invention.

The enclosure or autoclave (1) will therefore be designed to withstand pressures, generally equal to or greater than 120 bars. Likewise, the material used to manufacture the autoclave is preferably a material compatible with contact with a dense fluid under pressure, thus the enclosure will generally be made of stainless steel.

The enclosure or the autoclave generally has, as shown in FIG. 1, a shape of a straight cylinder, with a diameter, preferably, from 1 to a few tens of centimeters, for example 10 cm up to 1 to several meters , for example 20 m; and of a length of a few tens of cm, for example 20 cm to several m, for example, 20 m.

The volume of the autoclave is variable according to the parts to be cleaned and will be, for example, from 1 1 to 10 m ³ , but does not, in principle, have any limitation, in accordance with the invention.

The autoclave or cylindrical enclosure is preferably placed so that its main axis and its generatrices are horizontal. This arrangement allows easy loading of the parts to be cleaned. For this purpose, one of the circular bases of the cylinder, preferably opposite the drive means, forms a loading-unloading door (2), preferably provided with a rapid opening-closing system, allowing rapid and frontal loading and unloading of the parts. For the specific needs of certain users, the autoclave can be positioned vertically, while retaining all of the quick closing opening devices.

The autoclave or enclosure is generally provided with a double envelope (not shown) supplied with heat transfer fluid making it possible to adjust the temperature inside the enclosure within the required temperature ranges, in particular supercritical.

According to the invention, inside the enclosure or autoclave, there is a moving basket or drum (3), in which the parts to be treated are placed.

Generally, this drum or basket (3) is a rotating drum or basket, that is to say that it is rotated.

The rotational speed can range, for example, from 5 to 500 revolutions per minute, the rotational movement can be periodically reversed. The movement can also be pendulum. This revolving drum or basket is, like the autoclave, generally in the form of a straight, horizontal cylinder, the main axis (of rotation) preferably merges with the main axis of the autoclave. . The autoclave and the basket therefore appear as two straight horizontal cylinders with a common horizontal main axis, the cylinder forming the autoclave containing the smaller cylinder forming the basket or drum.

By way of example, the rotating drum or basket has a diameter of 1 to a few tens of cm, for example 10 cm up to several meters, for example, 5 m; and a length of a few tens of cm, for example 20 cm to several meters, for example, 20 m.

Thanks to its drive mode, described in detail below, according to the invention, there is no limitation on the volume and / or the weight of the parts which can be received by the rotating drum. The mass of the loaded parts can thus range, for example, from 1 kg to 10 tonnes. This drum or basket is perforated, with openings of variable shapes, it can be, for example, made of a trellis or a grid and thus defines a "squirrel cage", with more or less loose meshes. This drum or basket is made of a material supporting the conditions prevailing in the enclosure and contact with a dense fluid, under pressure, this material is generally analogous to the material constituting the autoclave. Generally, the part or parts are arranged inside the drum or basket rotating on or in supports, such as tongs, claws, “racks” or racks, fixed or mobile, for example animated by a translational, rotational or other movement. The movement of the support (s) can be printed by a shaft in direct or indirect engagement with the drive means, for example, with the rotor of the electric motor, preferably this shaft is also the drive shaft of the drum.

The basket or drum is generally rotated about its horizontal axis, by means of a horizontal shaft (4) located in the extension of the horizontal axis of the cylindrical basket or drum, and fixed to the circular base (5 ) of the drum, on the side opposite to the loading-unloading door (2) of the autoclave (1).

This shaft passes through the wall (s) of the autoclave, namely the circular base of the cylinder (6) opposite the base forming a door (2) or loading opening, in the center thereof. The tightness at the crossing of the wall of the enclosure or autoclave is ensured by a rotary joint (7) pressure-tight, up to a pressure which can range, for example up to 350 bars.

This shaft or axis (7) which can be defined as a transmission axis or shaft is preferably a hollow shaft or axis, which thus conveniently provides power (8) for the enclosure and the drum in dense fluid under pressure, such as C0 ₂ , as well as its evacuation (9). The shaft is in direct engagement by means of a coupling block (10) with drive means, such as an electric motor (11) of adequate power, located outside the enclosure. Such a mode of setting in motion of the rotating basket (3) makes it possible to maintain a very high torque. important, including for moving very heavy, eg metallic, loads.

The loading / unloading door of the autoclave can itself be provided with an orifice connected by a flexible cord, resistant to pressure and not impeding its movement, which allows the evacuation and / or the supply of the autoclave in dense fluid under pressure.

The device according to the invention further comprises means for subjecting the parts, simultaneously with their contact with the fluid or their immersion in the dense fluid under pressure, to the action of a high speed jet of the dense fluid under pressure. These means consist of one or more nozzle (s) or nozzle (s) for spraying fluid at very high speed, which allow mechanical stripping of the surfaces. This second mechanical effect is added to the first mechanical effect due to the rotating basket and to the solvent effect due to the dense fluid under pressure in contact with the parts. It has, in fact, been shown that during the expansion of the fluid through a restrictor, the fluid, such as C0 ₂ , does not instantly lose its density. This decreases rapidly, but gradually in the jet leaving the restrictor. The speed and the residual kinetic energy prove to be sufficient to create a significant mechanical effect for extracting and pickling the contaminants present on the surface of the parts to be cleaned. We can then take advantage of the extracting qualities of the fluid, such as C0 ₂ , in this short period of time and the jet phenomenon associated with this relaxation to clean or perfect the cleaning of parts.

The supply pressure of the dense fluid under pressure arriving at the nozzle (s) is generally from 10 to 500 bars. In this case, a pressure differential, generally 500 to 10 bars, can be achieved between the upstream part and the downstream part of the restrictor device (s) or nozzles.

The nozzle (s) can (wind) be fixed (s) or mobile (s) and this or these nozzle (s) can (wind), likewise, be placed (s) on one or more support (s) fixed (s) and / or mobile (s).

This or these support (s) can (wind) be, for example, in the form of arms, ramps, crowns or other, fixed or driven by a movement of rotation, translation, for example, back and forth type , or others.

For example, the nozzles could be fixed on an arm or rotating crown. Each of the supports can carry from 1 to 100 nozzles, depending on the size of the autoclave and depending on the geometry of the parts to be cleaned.

Thus, in Figure 1, there is provided a single fixed ramp (12) carrying 4 nozzles (13).

Each nozzle (13) can generate one or more jets (14) of conical or flat shape, thus sweeping the entire basket and the parts to be cleaned. If the nozzle (s) and / or their support is (are) in motion, the latter is printed by a shaft in direct or indirect engagement with the drive means, for example, with the rotor of the electric motor.

The movement of the nozzle (s) and / or their support (s) can be associated, in addition to the movement of the basket or drum, with the movement of the support of the parts, which makes it possible to expose the assembly different faces to be cleaned, for the effect of the jet (s) from one or more angles: this is particularly interesting in the case of cleaning complex parts.

Finally, the nozzle (s) can be supplied with dense fluid under pressure, such as C0 ₂ , either by the main circuit, that is to say by the same circuit which allows the filling of the autoclave by the shaft. hollow (see description of the installation, below) and its compression pump, either by a secondary circuit, in which all or part of the fluid, such as C0 ₂ , is recycled by an annex recirculation pump.

The device according to the invention also comprises means for continuously separating, inside the closed enclosure, the solid and / or liquid particles from the dense fluid under pressure. The purpose of these separation means is to trap the insoluble solid and / or liquid particles of contaminants or other, extracted, entrained, so as to avoid recontamination of the clean cleaned parts, by redeposition of these particles. These means are generally constituted by filtration means, possibly combined with absorption means. The filtration means will take the form of a filter, known as an “anti-redeposition filter” (15) or a “pollution trap”. It is generally a filter of specific shape, preferably removable, and metallic. This filter could thus have a semi-cylindrical shape (see FIG. 1) and be provided with windows or slots judiciously oriented with respect to the direction of rotation of the basket, which makes it possible in particular to trap solid particles, such as metallic particles and the non-soluble fraction of the contaminants removed and to prevent them from being redeposited on clean parts. In other words, the windows or slots must be oriented according to the direction of rotation. The solid particles or “chips” are eliminated in part by the centrifugal force due to the rotation of the basket, depending on whether the basket rotates clockwise or vice versa, and these slots must be rotated so to capture particles that escape from the basket and cleaning parts towards the filter without letting them escape and return to the basket to recontaminate the parts.

The filter could, in other words, be presented as a filter, for example, metallic in the shape of a semicircle perforated by windows of particular shapes, which take account of the direction of rotation, in which an absorbent material, such as absorbent paper or cloth, can be placed if necessary and which makes it possible to collect and trap liquid particles coming from the fraction insoluble in the fluid, such as C0 ₂ , set in motion by circular agitation and / or the mechanical effects induced by the ramp (s) of nozzle (s), as well as the solid particles, “chips” and “microchips” of metal and other, of totally random shapes, produced during the machining of the parts, in particular metallic, being the object of an operation of cleaning. These particles are "peeled off" and set in motion by the agitation and the effect of the jets, in the lower part or the upper part or both parts of the enclosure.

Finally, advantageously, the device according to the invention can comprise means (not shown) for subjecting the dense fluid under pressure located inside the enclosure, to the action of ultrasonic waves.

These means generally include one or more devices, more sonotrode frequency generators, for generating sound waves, ultrasound and / or megaons, for example a mono or multifrequency frequency generator and from one to ten sonotrodes.

These sonotrodes are generally placed at regularly spaced points inside the enclosure, for example in the longitudinal axis of the autoclave (a sonotrode) or in the radial axis of the autoclave (from one to ten sonotrodes spaced a few centimeters (5 cm) to a few tens of centimeters (20 cm) depending on the size of the enclosure. Only the sonotrode can be placed in the enclosure, thanks to a pressure-tight passage which nevertheless allows its vibration. Alternatively, the sonotrode plus the transducer can be placed in the enclosure, which then requires only a sealed passage for the electrical supply cable from the sonotrode to the frequency generator.

The sonotrode (s) is (are) only one block with the transducer part and is (are) connected (s) to the frequency generator by a coaxial cable for the generation of sound waves of adequate frequency (s) (s), etc.

Figure 2 shows, schematically, a side sectional view of the installation according to the invention.

It is obvious that such a figure only represents an example of an installation and that it is given only by way of illustration and not limitation. In this figure are shown means for bringing the part or parts to be cleaned in contact in the form of an extractor or autoclave (21). The autoclave is similar to that described in FIG. 1, but for the sake of simplification, FIG. 2 shows the autoclave, schematically.

In fact, the installation according to the invention is substantially analogous to a conventional installation for the treatment or cleaning of parts by a dense fluid under pressure, for example supercritical, except that it uses instead of autoclaves conventional, a specific autoclave or extractor, as described in Figure 1.

The installation according to the invention therefore has all the advantages inherent in the device and method according to the invention, as already indicated.

Inside the enclosure, the autoclave, is a basket or rotating drum (22) driven by a shaft (23) in direct contact with the drive means, such as an electric motor (24) .

Likewise, possibly, the autoclave can also be driven by a movement, for example, of rotation, preferably, being driven by the same shaft or axis as the basket or rotating drum. The autoclave is capable of withstanding the pressure used in the process of the invention and it is also provided with heating and temperature regulation means in the form, for example, of a thermostated double jacket (not shown ), in which a suitable heat transfer fluid circulates.

The volume of the autoclave is variable, it depends in particular on the volume of the parts to be treated, it can be easily determined by a person skilled in the art. The extractor or autoclave receives the parts to be cleaned (25), which are preferably placed on one or more support (s) or grid (s), inside the basket or rotating drum (22).

In Figure 1, the installation shown has only one extractor or autoclave (21), it is obvious that the installation can include several extractors, for example, from 2 to 10, arranged, for example, in series.

The installation also includes means for bringing a fluid, such as C0 ₂ in the dense state and under pressure, for example in the supercritical state.

Thus, in FIG. 1, the fluid, for example, from C0 ₂ , coming from a recycling pipe (26), and / or possibly from a storage and make-up tank, for example, from C0 ₂ (27) does it enter, by means of a valve (28) in a liquefaction tank (29) provided with temperature regulation means in the form of a thermostated double jacket (210), in which circulates a suitable heat transfer fluid (211, 212). Said fluid, such as C0 ₂ , is thus liquefied and circulates through a flow meter (213), then is pumped and compressed by means of a pump (214), for example, a compression pump of the type diaphragm or piston or, for example, from a compressor to the autoclave (21).

Before being introduced into the extractor (1), by means of a valve (215), the fluid, for example, the pumped C0 ₂ , is heated in an exchanger (216), called "supercritical" exchanger , in which it is heated to be in conditions where it is in the form of a dense fluid and under pressure, in particular, a dense supercritical fluid.

That is to say that the fluid is, in this exchanger heated above its critical temperature which is, for example, 31.1 ° C, in the case of C0 ₂ . The fluid is (see Figure 1) preferably introduced into the autoclave, via the basket drive shaft or rotating drum, which is hollow. Preferably, the same circuit also supplies the nozzles or spray nozzles provided in the autoclave.

FIG. 2 also shows means for injecting a co-solvent in the form of a high pressure pump (217) supplied by a co-solvent tank (218), which allows the gradual supply of a quantity known cosolvent in the compressed fluid, via a line (219) connected to the fluid supply line of the extractor (21), upstream of the exchanger (216) and downstream of the compression pump (214).

It would also be possible to provide for the injection of cosolvent at any other point of the installation, for example directly into the pressure vessel. It is therefore the mixture formed by the compressed fluid and the co-solvent which is brought to working temperature via the exchanger (216).

According to the invention, the fluid or, optionally, the fluid and cosolvent mixture comes into contact with the parts and cleans them in the enclosure of the extractor (21), while this same fluid is projected at high speed onto the parts . Unwanted polluting contaminant compounds are thus extracted.

Depending on the size of the parts to be treated, one or more parts will be treated simultaneously. At the inlet of the extraction autoclave (21), the supercritical fluid will, for example, be a homogeneous solution of fluid, such as C0 ₂ alone or C0 ₂ with cosolvent. The stream of fluid such as C0 ₂ , in which the polluting compounds, contaminants, extracts eliminated from the parts are dissolved, is then preferably sent by the same hollow shaft used for feeding, or by an orifice located at side on the same side or placed opposite to the door allowing the opening of the autoclave for loading - unloading of the parts, towards separation means connected to the extractor or autoclave (21) and comprising, for example , three cyclone type separators (220, 221, 222) connected in series, each of them being preceded by an automatic expansion valve (23, 24, 25).

Three cyclone separators (220, 221, 222) have been shown in Figure 2, but it is obvious that the number, type and succession of separators can vary.

The expansion to which the fluid is subjected takes place at constant temperature.

In each of the separators, separation or demixing takes place, on the one hand, of the extracted organic compounds which are in the form of liquid and, on the other hand, of a gas, for example, C0 ₂ .

The compounds extracted from the parts are drawn off (226, 227, 228), for example, at the base of the separators, and recovered, then possibly subjected to new operations of separation, extraction or purification, for example, centrifugation, decantation or liquid / liquid extraction, or destroyed.

The gas resulting from the separation, such as C0 ₂ is purified, then sent to the means for recycling the fluid, which essentially comprise a pipe (26) and a “cold” exchanger (229) or liquefier, for example, in the form of a thermostatically controlled enclosure, to be directed towards the liquid reserve (29) at low temperature, maintained by means of a cooling bath which cools and liquefies the fluid (211, 212), such as C0 ₂ .

The purification means (230) have been represented in FIG. 1 by a reflux column or an activated carbon column (230) placed on the means for recycling the fluid.

It should be noted that, optionally, the dense fluid under pressure can be made to recirculate continuously, during cleaning, using a recirculation pump (231). Continuously, during the entire cleaning operation, the insoluble particles are trapped on the filter inside the autoclave (not shown). The particles trapped on the filter are generally recovered at the end of the cleaning operation, when the autoclave is opened and eliminated as solid waste or recovered for the purpose of recycling.

The device may further comprise means for introducing another enthalpy fluid weaker than the dense fluid under pressure, inside of the pressure vessel, and replace all or part of it during a final expansion step.

The introduction of the weakest and chemically inert enthalpy fluid takes place from the top or from the bottom of the autoclave according to the respective densities of the weakest and chemically inert enthalpy fluid and of the dense fluid under pressure to be eliminated.

Finally, the installation comprises regulation means (not shown), in particular of the pressure, in the various parts of the process, which include a regulation chain composed of pressure sensors, regulators and pneumatically controlled needle valves. For example, during the final expansion step with the possible introduction of a lower enthalpy replacement fluid, regulation may take place between the temperature of the wall (using a probe) and the percentage of opening of the expansion valve.

According to the invention, the method is implemented in the installation of FIG. 2, according to a succession of steps, which is generally the following:

- arrange the parts in the basket and on their supports;

- pressurization and working temperature;

- rotation;

- optional circulation of the fluid, such as C0 ₂ ; - setting the fluid renewal rate, such as C0 ₂ ; - relaxation / separation, recycling;

- decompression and recovery of parts. The invention will now be described with reference to the following examples, given by way of illustration and not limitation.

Examples

The treatment or cleaning of samples, consisting of parts and / or metal test pieces of complex shape, was carried out by the method of the invention, using an installation similar to that of FIG. 1, the fluid being dense C0 _2. , under pressure. More specifically, this installation includes:

- a reserve of C0 ₂ in the form of a sphere of approximately 300 kg, such a sphere is commercially available; - a liquefier in the form of a steel enclosure of about 2 liters and thermostatically controlled at low temperature, by means of a cooling bath;

- a compression pump from 0 to 300 bar and a maximum flow of 100 kg / h;

- a supercritical exchanger in the form of a thermostated double jacket;

- a specific extractor, in the form of a rotating basket autoclave with a volume of 10 liters and a maximum pressure of 300 bars, fitted with a double jacket, a device for nozzles for spraying and a metal filter system allowing in particular to trap the solid particles and the oily fractions not dissolved by the solvent CO ₂ ;

- three cyclone-type separators with automatic expansion valves.

The samples to be cleaned are test tubes and / or parts of complex aluminum shapes, previously contaminated with various oils used in metalworking, such as a water-soluble machining oil, a cutting oil, a dyeing oil as respectively oils available commercially under the names CIMSTAR 560 ^®, Mobile Mobilube ^®, Drawsol 2345 N ^®.

Example 1

In this example, the effectiveness of the cleaning induced by the joint use of C0 ₂ as a solvent is shown, and of the mechanical effects caused by the passage of said C0 ₂ through restrictors, such as nozzles. The experiment is carried out on rectangular aluminum test pieces (50 x 65 cm), previously tared and one side of which is coated with a contaminant, which is a water-soluble machining oil 20% in water.

The test piece is placed more than 5 cm from the nozzle outlet. The surface mass of the contaminant is determined by weighing before and after cleaning with C0 ₂ . The cleaning efficiency in percentage is obtained by the following formula: areal mass of contaminant after cleaning

Efficiency% = x 100 areal mass of contaminant before cleaning

For comparison purposes, the cleaning of a contaminated test tube is also carried out under the same conditions by simple contact between it and C0 ₂ , example indicated: by soaking in Table 1.

Table 1 presents this comparison, with the nature of the contaminant, the surface contamination and the operating conditions.

Table 1

Comparison of CO cleaning efficiencies? supercritical by soaking and spraying through a nozzle, on a 20% machining oil

This example shows an improvement in the cleaning efficiency induced by the mechanical effects brought about by the use of C0 ₂ sprayed at high speed. In addition, the very higher level of cleaning achieved, it can also be seen that the treatment time and the working pressure are significantly reduced, namely 1 hour instead of 2 hours and 100 bars instead of 300 bars.

Example 2

In this example, the nature of the contaminant is modified, which in this case is a relatively viscous cutting mineral oil.

The procedure for the experiment is the same as in Example 1. For comparison purposes, cleaning is carried out by simple contact, soaking, of identical test pieces coated with the contaminant.

Table 2

Comparison of CO cleaning efficiencies? supercritical by soaking and spraying through a nozzle on a cutting mineral oil

In this example, the supply of mechanical energy via jets shows that it is possible to maintain very good cleaning performance, while reducing the treatment time by a factor of 2. Thus, for a contaminant of this type, a posteriori easy to clean, the gain, induced by the invention, will be on the quantity of solvent and is therefore of an energy nature. Example 3

In this example, the procedure being identical to the previous examples, the nature of the contaminant is again modified. This time it consists of a fluid of high viscosity, used during dyeing operations (inking) on metals ("drawing oil"). This fluid has the particularity of being difficult to clean, including by conventional methods using solvents and detergents. For comparison purposes, cleaning is also carried out by simple contact, soaking, of identical test pieces coated with the same contaminant. Table 3 shows the conditions and the results of this comparison.

Table 3

Comparison of CO cleaning efficiencies? supercritical by soaking and spraying through a nozzle on a dye oil

This example shows, on the one hand, that for a more difficult to clean contaminant, it is necessary to increase the temperature and the pressure to increase the solvent power of the CO ₂ . Thus, for equivalent surface contaminations, the cleaning efficiency is improved from 87 to 96%, by increasing the pressure / temperature couple from 200 bars, 44 ° C (conditions 1) to 300 bars, 77 ° C (conditions 2) , which is a fairly significant increase in energy demand.

Using the nozzles (supercritical C0 ₂ by jet), it can be seen that the sprayed C0 ₂ increases the efficiency from 87 to 92%, under conditions 1, and

96 to 98%, under conditions 2, without having to increase the energy intake, on the contrary.

The following examples 4 and 5 relate to the cleaning of real parts.

Example 4 (Reference '

This example consists in coating contaminants with real aluminum parts and complex shapes comprising several faces, as well as one or more holes for drilling. The overall size of these pieces does not exceed 10 cm in length and 6 cm in height.

These parts are contaminated, according to a precise soaking and draining procedure; precise procedure which consisted in completely soaking the part in a container containing the contaminant studied, followed by draining the part thus contaminated according to a precise time from a few hours to a few days, according to the viscosity of the contaminant studied and elimination of the excess by absorbent paper, so as to obtain a film as homogeneous as possible on all of the faces of the part. This procedure was implemented in order to guarantee the most comparable level of contamination possible between the different samples tested and in order to allow good repeatability. In this reference example, we therefore proceed to the cleaning of a single part by simple soaking in C0 ₂ and, we repeat the operation several times to verify that the process can be reproduced without problem. As for the previous examples, the evaluation of the effectiveness is carried out by weighing the tare and the contaminant before and after cleaning and the effectiveness is determined by the formula given above. In this case, the overall mass of contaminant is used in this formula and not the surface mass, as in the previous examples, the surface of an actual part being difficult to obtain precisely.

In this example, the contaminants chosen are those of the previous examples: 20% water-soluble machining oil (from Example 1), cutting oil (from Example 2) and dyeing / inking oil (from Example 3).

This example 4 constitutes the reference for a cleaning operation by supercritical C0 ₂ , without any mechanical effect and based on the sole power of dissolution, with respect to the contaminants studied and indicated in Table 4 below.

For each of the contaminants, the tests were carried out on three pieces.

Table 4

Cleaning conditions and efficiencies obtained on real parts contaminated by three different contaminants and treated by simple soaking of CO? supercritical

It is noted, first of all, that the treatment of real parts makes cleaning less effective. Whether for a lubricating oil considered to be easy to clean or for a dyeing oil deemed difficult to clean, the overall performance is generally lower (in terms of% efficiency) compared to tests carried out on test tubes of simple shapes (as in examples 1 to 3).

The complexity of the shapes of the parts induces average to mediocre efficiencies, down compared to the previous examples, which result, consequently, in an extension of the treatment time, therefore an increased amount of solvent.

Example 5

This example consists in treating parts of complex shapes contaminated with different oils identical to example 4. In this case, the parts, 15 in number per test, are treated in the rotating autoclave, but not equipped with the jetting device and the anti-redeposition filter, that is to say that the parts are subjected to agitation due to the only rotary movement of the basket or drum.

Table 5 shows the contaminants, their masses, the treatment conditions and the efficiencies obtained.

Table 5

Cleaning results on real parts contaminated and cleaned with CO? supercritical in a rotating autoclave

rpm: revolutions per minute,

It can be seen that the agitation due to the rotary movement alone induces a very significant improvement in the cleaning performance by C0 ₂ . Thus, for the water-soluble machining oil 20% in water, the cleaning efficiency reaches almost 80% in 1 h, which is substantially close to the 78% obtained in 2 h and in the absence of agitation in reference example 4.

For cutting oil, the efficiency remains optimal at 100%, with a clear saving in the time of treatment, which goes from 1 h, for example 4, to h, for example 5.

In these two cases, the gain turns out to be essentially of an energy order, thanks to a reduction in treatment time, therefore in the rate of solvent C0 ₂ .

In the case of dyeing oil, the efficiency reaches 94, with stirring, in approximately 1 h, against 90% of effectiveness in 2 h of treatment (for example 4 for reference). In this case, therefore, the efficiency is improved while reducing the treatment time.

Example 6

In this example, the real parts are treated under conditions equivalent to those of Example 5.

However, in this example, in accordance with the invention, a nozzle ramp, making it possible to spray C0 ₂ , at very high speed, was implemented, as well as an openwork metal filter provided with absorbent paper, all to allow to trap the insoluble particles of the contaminant detached from the surface of the parts by the jet of C0 ₂ and the rotary movement of the basket.

Table 6 shows all the conditions, as well as the efficiencies obtained. Table 6

Cleaning results on real parts contaminated and cleaned with CO spray? supercritical and anti-redeposition filter in rotating autoclave

This example, in accordance with the invention, shows that for water-soluble machining oil, the use of nozzles and a filter retaining the fraction insoluble in C0 ₂ makes it possible to obtain an efficiency very close to 100% for a treatment time not exceeding h. In this case, a gain is obtained jointly on the efficiency and the time of treatment, but also on the working pressure where one goes from 300 bars (example 5) to 100 bars.

In the case of cutting oil, it was not necessary to implement the jet effects. This contaminant, considered easy to clean, could be removed by simple stirring. On the other hand, we measure the effect of the anti-redeposition filter, through this example, because we maintain an optimal efficiency of 100% with equivalent conditions, but for a treatment time of 15 minutes against 30 minutes, in the example 5, without filter. It seems that the effect of the filter makes it possible to retain, with proven effectiveness, the contamination eliminated by solubilization and by the rotary movement of the drum. As regards the dyeing oil, the cleaning efficiency is maintained at 94%, with an equivalent treatment time of around 70/75 minutes. On the other hand, the treatment conditions with C0 ₂ appear to be significantly different. Indeed, these conditions vary from 300 bars, 80 ° C, for example 5, to 100 bars, 40 ° C, in this example, with nozzles and filter, which constitutes a considerable energy saving.

Example 7

In this example, we show the gain over the duration of the expansion, final decompression obtained by replacing during this, all or part of the initial fluid (C0 ₂ ) by a lower enthalpy fluid (nitrogen). From a pressurized autoclave at around 230/250 bars and between 40 and 60 ° C in supercritical C0 ₂ , rapid expansion is carried out up to atmospheric pressure.

Under the same conditions, a depressurization of the C0 _{2 is carried out} from 230/250 bars to approximately 100/135 bars, then an introduction of nitrogen is carried out to expel the C0 ₂ still present for times varying from 2 to 5 minutes , followed by expansion to atmospheric pressure.

The temperature is monitored using a thermocouple placed inside the enclosure.

The conditions and the results of this comparison are collated in Table 7.

Table 7

Comparison test of relaxation with CO? alone and with C0 _? 4- N _?

Test n ° l shows that during an expansion deemed rapid at 8'15 '', the final temperature at decompression reaches -50 ° C, with the formation of 2/32593

66

dry ice, for a pressurized fluid at 240 bar and 43 ° C.

Under the same conditions, test No. 2, with the introduction of nitrogen, for 2 ', shows that a final temperature of the fluid in the autoclave is obtained of 17 ° C for a total depressurization time of 11' 30. The difference obtained between the two tests is +67 ° C for only 4 '15' 'more relaxation time. Test n ° 3, comparable to tests n ° 1 and n ° 2, shows that by reducing the relaxation time from 11 '30 to 10', the final temperature of the enclosure remains positive, at 2 ° C.

Example 8

In this example, we show the effect obtained by the coupling of ultrasound (200 X _eff , from 40 to 100 kHz) in C0 ₂ pressurized at 20 ° C, 100 bars, 40 ° C, 100 and 300 bars with or without co-solvent on aluminum sheets placed in an autoclave and a distance of a few cm (5 to 25 cm) from the sonotrode located longitudinally at the base of this cylindrical enclosure. For each test, a photograph of the aluminum foil is taken in order to assess its condition.

Table 8 below gives the operating conditions for the various tests carried out. 67

Table 8

The photographs of the aluminum sheet, carried out during the various tests, indicated in table n ° 8, show that there is a significant effect of ultrasound on the aluminum sheet, in the presence of liquid C0 ₂ (test 8 - 1). This results in a screening and a hole a few millimeters in diameter in the aluminum sample. This test, commonly used by experimenters in the ultrasound field, translates, on the one hand, the existence of a wave propagation from the sonotrode to the sample and, on the other hand, the creation of '' a cavitation by the creation of bubbles which implode in the vicinity of the sample, thus creating an alteration of the surface, visualized by the photos.

During test 8 - 2, carried out under the same conditions as test 8 - 1, but in the presence of co-solvent, it is found that the screening of the sample is more important and results in the appearance of a hole in aluminum foil several centimeters in diameter (4 cm). In this case, the phenomenon is confirmed by a very significant increase in the audible sound level during the test. This proves that the presence of the cosolvent in the dense CO ₂ under pressure reveals the ultrasonic phenomenon by amplifying it.

During tests 8 - 3 and 8 - 5, the sheet is very weakly screened when acting in the presence of C0 ₂ , alone, in the supercritical state. The effects of ultrasound appear qualitatively weaker than those observed in liquid C0 ₂ , alone. This clearly reflects the fact that cavitation is more difficult to obtain when the C0 ₂ is supercritical.

Tests 8 - 4 and 8 - 6, respectively identical to tests 8 - 3 and 8 - 5, but carried out in the presence of a co-solvent shows that the sheets aluminum are more strongly screened with the appearance of holes a few centimeters in diameter (1 to 1.5 cm), as well as a very high noise level outside the pressure vessel, tangible testimony of '' a phenomenon of propagation and / or increased cavitation. This demonstrates that it is the presence of the cosolvent which acts as a developer and an amplifier of ultrasonic phenomena in supercritical CO ₂ . Finally, it is found that the screening is more important with liquid C0 ₂ with cosolvent, compared to the other supercritical tests.

The observations made in this example show that the cosolvent, put in the presence of a dense fluid under pressure and a generator of sound waves, allows, unexpectedly, the revelation and the amplification of the wave propagation phenomena. sound and cavitation.

Claims

1. Method for cleaning contaminated parts by contacting with a dense fluid under pressure, in which:

the parts to be cleaned are placed in a drum or basket inside a pressure enclosure containing the dense fluid under pressure, said drum or basket being set in motion by a shaft in direct engagement with drive means located outside the enclosure; the parts are also subjected, simultaneously, to the action of a high speed jet of the dense fluid; - The solid and / or liquid particles insoluble in the dense fluid, essentially generated by cleaning, are simultaneously continuously separated from the dense fluid by separation means provided inside the enclosure.

2. The method of claim 1, wherein the drum or basket is rotated.

3. Method according to claim 2, wherein the direction of rotation is periodically reversed.

4. The method of claim 1, wherein the drum or basket is driven by a pendulum movement.

5. Method according to claim 1, wherein the speed of the fluid jet is from 1 to 500 m / sec.

6. The method of claim 1, wherein the dense fluid under pressure is at a temperature of 15 to 80 ^C C and at a pressure of 100 to 300 bar.

7. The method of claim 1, wherein said dense fluid under pressure is in the liquid and / or supercritical state.

8. The method of claim 1, wherein said dense fluid under pressure is in the supercritical state.

9. Method according to any one of claims 1 to 8, in which compression / decompression cycles are carried out.

10. The method of claim 9, wherein said compression / decompression cycles are carried out with a pressure variation amplitude of 10 to 100 bars and time intervals of 10 seconds to 10 minutes.

11. The method of claim 1, wherein said fluid is selected from carbon dioxide; sulfur hexafluoride; nitrous oxide; nitrous oxide; light alkanes having, for example, from 1 to 5 carbon atoms, such as methane, propane, butane, isobutane and pentane; alkenes, such as ethylene and propylene; and certain organic liquids, such as methanol and ethanol.

12. Method according to any one of claims 1 to 11, in which a cosolvent is added to the dense fluid under pressure.

13. The method of claim 12, wherein said co-solvent is selected from water; aqueous solutions; alcohols, for example, aliphatic alcohols of 1 to 5 carbon atoms, such as ethanol, methanol, butanol; ketones; hydrofluoroethers; terpenes; cyclohexanes and their mixtures.

14. The method of claim 13, wherein said aqueous solutions are detergent solutions such as anionic and / or cationic surfactants; solutions of complexing agents, chelating agents; buffer solutions, for example phosphate and / or hydrogen phosphate, etc. ; antioxidant solutions, such as ascorbic acid.

15. Method according to any one of claims 12 to 14, wherein said cosolvent is added to the dense fluid, under pressure, in an amount of 0.01 to 10% by weight.

16. Method according to any one of claims 12 to 15, in which the dense fluid, under pressure, located in the pressure vessel, is, in addition, subjected to the action of ultrasonic waves.

17. The method of claim 16, wherein the frequency of said ultrasonic waves varies from 20 kHz to 100 MHz.

18. The method of claim 17, wherein said ultrasonic waves are ultrasound with a frequency of 20 to 1000 kHz or megaons with a frequency of 1 to 100 MHz.

19. Method according to any one of claims 16 to 18, in which the fluid is subjected to the action of ultrasonic waves, for a period of 1 to 60 minutes.

20. Method according to any one of claims 13 to 19, in which the dense fluid, under pressure is C0 ₂ , and the co-solvent is water or an aqueous solution.

21. Method according to any one of claims 1 to 20, in which, following the cleaning by the dense fluid under pressure, the fluid and the extracts are separated by one or more physico-chemical separation steps and the fluid in gaseous form. is recycled.

22. The method of claim 21, wherein, before its recycling, the gaseous fluid is purified by one or more step (s) of adsorption and / or liquefaction and / or (re) distillation.

23. Method according to any one of claims 1 to 22, in which, at the end of the cleaning, a final step of expansion of the pressure vessel in which the cleaned parts are located is carried out, and during this expansion , all or part of the dense fluid under pressure is replaced by another weaker and chemically inert enthalpy fluid.

24. The method of claim 23, wherein the dense fluid under pressure is C0 ₂ and the other lower enthalpy fluid is chosen from nitrogen, helium, neon and dry air.

25. Device for cleaning contaminated parts with a dense fluid under pressure, comprising:

- a closed enclosure under pressure (1); - a drum or basket (3) placed inside the closed enclosure and receiving the parts to be cleaned, said drum or basket being set in motion by a shaft (4) in direct engagement with drive means (11 ) located outside the enclosure (1); means (12, 13) for subjecting the parts to the action of a high speed jet (14) of the dense fluid;

- Means (15) for continuously separating in the closed enclosure the solid and / or liquid particles insoluble in the fluid, from the dense fluid under pressure.

26. Device according to claim 25, in which the closed enclosure (1) has the shape of a straight cylinder, the main axis and the generatrices of which are horizontal.

27. Device according to claim 26, wherein one of the circular bases of the cylinder, preferably opposite the drive means (11) forms a loading-unloading door (2).

28. Device according to claim 25, in which the drum or basket (3) is rotated.

29. Device according to claim 28, in which the drum or basket (3) has the shape of a straight horizontal cylinder whose main axis of rotation merges with the main axis of the closed enclosure.

30. Device according to claim 29, in which the shaft (4) putting the basket or drum in motion around its horizontal axis is located in the extension of the horizontal axis of the basket or drum and is fixed to the circular base ( 5) of the basket or drum on the side opposite to the loading-unloading door of the enclosure.

31. Device according to claim 30, in which the shaft passes through the circular base (6) of the closed enclosure opposite the door (2) for loading and unloading of the enclosure, the seal at the crossing of the wall. of the enclosure being ensured by a pressure-tight rotating joint (7).

32. Device according to any one of claims 25 to 31, in which the shaft (4) setting in motion the drum or rotating basket is a hollow shaft ensuring the supply (8) of the enclosure with dense fluid under pressure , as well as its evacuation (9).

33. Device according to any one of claims 25 to 32, in which the means for subjecting the parts to the action of a high-speed jet of the dense fluid consist of one or more nozzle (s) (13) or fixed or mobile high-speed fluid spray nozzle (s), possibly placed on one or more fixed and / or mobile support (12).

34. Device according to claim 33, wherein each nozzle generates one or more jet (s) (14) of conical or flat shape.

35. Device according to any one of claims 25 to 34, in which the separation means (15) are constituted by filtration means, possibly combined with absorption means.

36. Device according to claim 35, in which the filtration means (15) consist of a perforated semi-cylindrical filter.

37. Device according to any one of claims 25 to 36, in which the closed enclosure (1) is also driven by a movement, for example, of rotation, preferably, being driven by the same shaft or axis as the basket or rotating drum (3).

38. Device according to any one of claims 25 to 37 further comprising means for introducing another enthalpy fluid weaker than the dense fluid under pressure, and chemically inert, inside the enclosure under pressure and replace all or part of it during a final expansion step.

39. Device according to claim 38, in which the introduction of the weaker and chemically inert enthalpy fluid takes place from the top or from the bottom of the autoclave (1) according to the respective densities of the enthalpy replacement fluid. weaker and chemically inert and dense pressurized fluid to be removed.

40. Device according to any one of claims 25 to 39, comprising means for subjecting the dense fluid under pressure located inside the enclosure to the action of ultrasonic waves: megaons or ultrasound.

41. Device according to claim 40, in which said means for subjecting the fluid to the action of ultrasonic waves: megaons or ultrasound are in the form of one or more sonotrodes.

42. Cleaning installation comprising the device according to any one of claims 25 to 41.

43. Installation according to claim 42, comprising means for injecting a cosolvent into the compressed fluid.