Method for cleaning plates of a plate heat exchanger and device for implementing the method

Abstract

The invention relates to a method for cleaning plates of a plate heat exchanger, which comprises the following steps: - providing the plates (2) to be cleaned; - supplying dry ice granules; - supplying a cryogenic cleaning device (1) capable of generating a flow of cryogenic air (4) containing compressed air and dry ice particles, from the supplied dry ice granules when it is supplied with compressed air; - obtaining a cryogenic air flow by means of the cryogenic cleaning device, from a compressed air supply, the pressure of which is between 7 and 10 bar and the flow rate of which is between 250 and 350 m3 / h, and a dry ice granule consumption of between 60 and 80 kg of dry ice per hour; and - cleaning the plates to be cleaned using the cryogenic air flow obtained.

Description

[0001] METHOD FOR CLEANING PLATES OF A PLATE HEAT EXCHANGER AND DEVICE FOR IMPLEMENTING THIS METHOD

[0002] Technical field

[0003] The present invention relates to the sector of cleaning and maintenance of industrial equipment and more particularly plate heat exchangers.

[0004] More specifically, it relates to a cryogenic process for cleaning the plates of a plate heat exchanger.

[0005] It also relates to a cryogenic cleaning apparatus specially adapted for carrying out this process.

[0006] Prior art

[0007] Plate heat exchangers are widely used in all types of industries, particularly in the food, pharmaceutical, chemical and industrial refrigeration industries. These exchangers allow heat to be transferred from a fluid circulating in a first circuit to another fluid circulating in a second adjacent circuit, without ever mixing them.

[0008] These exchangers typically comprise a large number of plates, generally between 10 and 500, for example made of stainless steel, titanium or Hastelloy™ type nickel alloy, and of substantially rectangular shape. In the exchanger, these plates are arranged parallel to each other and are compressed between the two frames which are brought together by tightening a set of perpendicular tie rods.

[0009] Each of these plates has four through openings which form, by juxtaposition of the plates, a fluid supply duct and a fluid discharge duct for each of the two fluid circuits. Each of the plates of the exchanger is provided with a seal of alternating specific shape, delimiting a sealed intermediate compartment between two successive plates of the exchanger which is alternately placed in communication with the supply duct and the discharge duct of one or other of the fluid circuits. Thus, the heat exchange occurs through each of the plates of the exchanger, between the fluids located in the two compartments located on either side of the plate, without mixing between the two fluid circuits.To improve heat transfer efficiency, the plates of plate heat exchangers are typically grooved in a specific pattern that extends the circulation time of the fluid on the surface of the plate and increases pressure losses to improve heat exchange.

[0010] This type of heat exchanger requires regular maintenance. Over time, the fluids circulating between the plates leave deposits and impurities that gradually accumulate on the roughness and in the hollows of the plates, particularly around the grooves and at the base of the seals. As a result of this fouling, the efficiency of heat exchange gradually decreases, and there is a risk of leaks at the seals.

[0011] In order to restore satisfactory energy performance and prevent any risk of leakage, regular cleaning of these exchanger plates accompanied by replacement of the seals is recommended at regular intervals, for example every five years.

[0012] To carry out such cleaning of the plates of plate heat exchangers, several methods have been proposed in the prior art. However, none of these known methods is entirely satisfactory.

[0013] The most efficient method is to disassemble the exchanger or the complete plate set and send it to the factory for reconditioning. There, the plates are disassembled, their gaskets are removed, and, depending on the nature of the deposits covering them, the plates are immersed for several hours in one or more baths of chemicals capable of loosening or dissolving the encrusted deposits. The plates are then rinsed and dried, before being fitted with new gaskets. The heat exchanger is then reassembled, or the complete plate set is then prepared, before being returned to its place of use.

[0014] Although effective, this cleaning method is particularly time-consuming and expensive. Due to transport and the long duration of the successive soaking, rinsing, and drying steps, several days, and often several weeks, are required to complete such cleaning. The plate heat exchanger therefore remains unavailable for the industrial process in which it is usually installed for a long time. In the field of industrial refrigeration, for example, this is particularly problematic, because without an exchanger, cold production can no longer be ensured. The duration of maintenance interventions must therefore be reduced as much as possible. This type of cleaning process using chemical baths is therefore very difficult to use in this technical field.

[0015] Another disadvantage of this chemical bath cleaning method is that it is likely to leave traces of chemical substances used in the baths on the surface of the exchangers, which can subsequently contaminate the fluids circulating in the exchanger during its use. This contamination is very troublesome when these exchangers are used in sensitive processes, particularly in the pharmaceutical or food industry.

[0016] Another cleaning method known from the prior art, called Clean In Place (CIP), consists of cleaning the exchangers directly at their place of use, without dismantling them. To do this, chemicals are circulated, which are sent directly inside the exchanger in its two fluid circuits, in order to dissolve the deposits on the plates and remove them. While this method, without dismantling or transport, is much faster than the previous one, it is on the other hand much less effective. Indeed, only a portion of the deposits is removed and fouling remains in hard-to-reach areas, particularly in the hollows of the grooves. In addition, the chemicals circulating inside the exchanger can also attack the seals that are not dismantled and changed with this method.The risk of leaks at the joints may therefore increase after cleaning, which defeats the purpose.

[0017] Finally, with this method we find the risks of pollution by chemical contaminants mentioned with the previous cleaning method, which can be particularly troublesome in sensitive technical fields such as the pharmaceutical or food industry.

[0018] To avoid these drawbacks, cleaning of exchanger plates is often carried out manually at the exchanger's use site. After dismantling the exchanger plates and removing the gaskets, an operator rubs them manually using a cloth soaked in a degreasing product, such as acetone for example. Such cleaning, which is tedious for the operator, remains of limited effectiveness. Indeed, with such a method it is very difficult, even almost impossible, to clean very dirty plates. It is indeed very difficult to access the bottom of the plate's grooves or to actually extract the deposits from these grooves, these deposits being most often pushed towards the periphery of the plate where they accumulate, particularly in the gasket mounting grooves. The pushed-out deposits can then hinder the installation of new gaskets and lead to a risk of subsequent leakage.

[0019] Another known cleaning method is to clean the plates with a pressurized water jet, after first dismantling them.

[0020] This method is also not satisfactory because it is of limited effectiveness. It is very difficult to remove all the deposits present on the plates, especially in hard-to-reach areas, with a pressurized water jet.

[0021] Furthermore, after cleaning, the plates must be thoroughly dried before being reassembled, which lengthens the process. The possible presence of residual water can, in fact, be problematic in many industrial sectors, particularly in sensitive areas such as the pharmaceutical, chemical or food industries, where water can be a source of contamination. Furthermore, it is impossible to use such a method in the industrial refrigeration sector, where the plates must absolutely not come into contact with water.

[0022] As none of the previous cleaning methods are truly satisfactory, maintenance of plate heat exchangers is often postponed or even neglected, to the detriment of the energy performance of the exchangers, with interventions being limited to curative operations in the event of a proven leak problem.

[0023] There is therefore a significant need in the prior art, not met until now, for a method of cleaning the plates of a plate heat exchanger, which can be carried out directly on the site of use of the exchanger, which is rapid, non-contaminating, without the need for drying and truly effective.

[0024] Presentation of the invention

[0025] The present invention addresses this need and provides such a cleaning method.

[0026] To this end, the invention teaches a method for cleaning plates of a plate heat exchanger, at least some of which are to be cleaned, which comprises the following steps:

[0027] - provision of plates to be cleaned;

[0028] - supply of dry ice pellets;

[0029] - supply of a cryogenic cleaning device capable of delivering a cryogenic air flow containing compressed air and dry ice particles, from the supplied dry ice pellets when supplied with compressed air; - obtaining a cryogenic air flow by means of the cryogenic cleaning device, from a compressed air supply whose pressure is between 7 and 10 bars and whose flow rate is between 250 and 350 m 3 / h and a consumption of dry ice pellets supplied of between 60 and 80 kg of dry ice per hour;

[0030] - cleaning of the plates to be cleaned using the cryogenic air flow obtained.

[0031] The cleaning method according to the invention is advantageously a cryogenic cleaning method for the exchanger plates. It does not generate any contamination on the surface of the plates, since the cleaning agent is a cryogenic air flow which vaporizes immediately upon contact with the much hotter plate, releasing only air and carbon dioxide in the gaseous state. There is no need for rinsing or drying. This method can therefore be used in any type of industry, even those most sensitive to contamination or the presence of water.

[0032] Furthermore, it is universal, unlike previous methods of cleaning plates where a chemical cleaning agent is used (chemical baths, cleaning in place or manual cleaning with a degreasing product) whose nature must be adapted to the composition of the deposit to be removed to be effective. With the cryogenic process of the invention, cleaning is not carried out by chemical attack of the deposits, but by a physical, thermal and thermodynamic process. Its effectiveness therefore does not depend on the chemical composition of the deposits to be cleaned, but only on the physical properties of the cryogenic air flow and therefore on the particular conditions used to create it. The cleaning process of the invention can therefore be used regardless of the nature of the fouling.

[0033] Indeed, with the method according to the invention, cleaning is due to several successive phenomena. The deposit is first broken up under the effect of the physical shock with the dry ice particles projected at high speed against it and the high pressure of the cryogenic air flow. Then, the very low temperature of the cryogenic air flow promotes the detachment and detachment of this deposit which shrinks under the effect of the cold. Finally, the deposit, previously broken up and detached, is ejected away from the plate under the blast effect linked to the sublimation of the dry ice particles which vaporize on contact with the surface of the plate and the ambient air.

[0034] Due to the specific conditions of pressure, compressed air flow rate and dry ice consumption used, the method according to the invention is very effective, while presenting no risk of damaging the exchanger plates. It allows to clean completely and without difficulty, any type of deposit present on the exchanger plates, even when they are very dirty. It is possible to perfectly clean difficult places such as the bottom of the grooves of the ridges or the mounting grooves of the gaskets, from where the deposits are completely removed and not simply pushed away.

[0035] The seal mounting grooves are thus once again completely clear, which limits the risk of leaks later on.

[0036] This process is very fast, as it only takes about a minute to completely clean a medium-sized plate. In addition, this process can be carried out directly at the site of use of the plate heat exchanger, after simple disassembly of the latter and without the need to ship it to a treatment plant.

[0037] According to one embodiment of the invention, the cleaning method can be applied to plates provided with seals, and can be preceded by the following steps:

[0038] - dismantling of the plates to be cleaned from the heat exchanger;

[0039] - removal of the seals from the plates to be cleaned; and following the following steps:

[0040] - installation of new seals on the cleaned plates; and

[0041] - reassembly of the cleaned plates on the heat exchanger.

[0042] According to one embodiment of the method according to the invention, during the step of cleaning the plates to be cleaned, at least one face, and preferably both faces, of each of the plates to be cleaned is or are swept by the cryogenic air flow obtained.

[0043] According to this embodiment of the method according to the invention, the sweeping by the cryogenic air flow obtained is preferably carried out over the entire surface of the face of the plate by means of regular movements in the direction of the length and in the direction of the width of the face of the plate.

[0044] According to one embodiment of the method according to the invention, the supply of compressed air can be obtained by means of at least one compressor and at least one air dryer.

[0045] According to another embodiment of the method according to the invention, the compressed air supply can be obtained by means of two tappings on one or two compressed air networks. Alternatively, the compressed air supply can be obtained by means of a tapping on a compressed air network and a compressor with an air dryer.

[0046] The invention also teaches a device for cleaning plates of a plate heat exchanger, specially adapted for implementing the cleaning method described above.

[0047] This device includes:

[0048] - a compressed air inlet;

[0049] - a storage tank for dry ice pellets;

[0050] - a mixing zone in which dry ice pellets are fragmented into dry ice particles and brought into contact with compressed air, in order to form a cryogenic air stream containing compressed air and dry ice particles; and

[0051] - a cryogenic air outlet;

[0052] - a compressed air regulator which regulates the compressed air inlet at a pressure between 7 and 10 bars and a flow rate between 250 and 350 m 3 / h ; and

[0053] - a dry ice regulator that regulates the amount of dry ice pellets brought into contact with the compressed air to consume between 60 and 80 kg of dry ice pellets per hour.

[0054] According to one embodiment, the cleaning device further comprises at least one compressor and at least one air dryer connected to said compressed air inlet.

[0055] According to one embodiment, the cleaning device further comprises a connection element comprising an outlet connector connected to said compressed air inlet and two inlet connectors each being connected to a compressor or intended to be connected to a compressed air network.

[0056] According to a variant of this other embodiment of the cleaning device, the inlet connections and the outlet connection are equipped with express connections called “cat head” connections.

[0057] The connections are thus made easily and quickly, while guaranteeing perfect sealing. The device can therefore be installed, connected and put into operation very easily and quickly directly at the site of use of the exchanger to be cleaned.

[0058] According to a variant of this other embodiment of the cleaning device, the inlet connections are equipped with non-return valves which prevent compressed air from escaping from the device. The installation located upstream of the device is thus protected from any involuntary return of compressed air.

[0059] According to a variant of this other embodiment of the cleaning device, the connecting element further comprises a compressed air inlet to which a blowing unit is connected.

[0060] Such a blowing unit provides an easily usable compressed air outlet for the operator using the cleaning machine. For example, he can use it to clean the machine or the work area after the plate cleaning operation is finished or for any other purpose in which blowing a jet of compressed air could be useful.

[0061] This blowing unit includes, for example, a quick-connect means, followed by a flexible hose, then a gun and / or a blowing nozzle.

[0062] According to one embodiment, the cleaning device further comprises a flexible pipe, connected to said cryogenic air outlet, and terminated by a gun provided with an elongated nozzle with a slotted outlet opening.

[0063] The operator can thus easily control the outlet or stop of the cryogenic air flow and direct it precisely towards the plate to be cleaned. The elongated nozzle allows the operator to work comfortably without having to bend down.

[0064] The slotted outlet opening allows for optimized projection of the cryogenic air flow and the dry ice particles it contains, the shape of which is perfectly adapted to that of the grooves, grooves and striations of the plates to be cleaned.

[0065] According to a preferred variant of this embodiment, this elongated nozzle is at least 30 cm long, preferably at least 40 cm, and the slotted outlet opening is rectangular in shape and measures between 2.5 and 4 cm long and between 3 and 5 mm wide.

[0066] Brief description of the figures

[0067] Other characteristics and advantages of the invention will appear on reading the detailed description which follows, a description made with reference to the appended drawings, in which:

[0068] [Fig 1] Figure 1 is a schematic general view of a first example of a cleaning device according to the invention; [Fig 2] Figure 2 is a schematic general view of a second example of a cleaning device according to the invention;

[0069] [Fig 3] Figure 3 is a functional diagram of the connecting element of the cleaning device of Figure 2 and its connection to a compressed air network;

[0070] [Fig 4] Figure 4 is a functional diagram of an example of a cryogenic apparatus of the cleaning device according to the invention;

[0071] [Fig 5] Figure 5 is a comparative photograph of two plates of a plate heat exchanger, one being photographed before and the other after cleaning by means of the cleaning device according to the invention.

[0072] Detailed description of the invention

[0073] The cleaning method and the cleaning device 1 according to the present invention will now be described in detail with reference to Figures 1 to 5. The equivalent elements shown in the different figures will bear the same numerical references.

[0074] In Figure 1, a first embodiment of a cleaning device 1 according to the invention of the plates 2 of a plate exchanger is shown schematically.

[0075] This cleaning device 1 comprises a cryogenic device 3 which makes it possible to produce a cryogenic air flow 4 from compressed air on the one hand and dry ice on the other hand.

[0076] This is a pneumatic or electro-pneumatic device, preferably equipped with wheels 5, rollers or casters so that it can be mobile and easily moved by an operator 6 who carries out the cleaning operation. The cleaning device 1 according to the invention can thus be taken to the industrial site where the exchanger to be cleaned is located and easily moved to the place where the plates 2 are cleaned.

[0077] In this embodiment, the compressed air necessary for this production of the cryogenic air flow 4 is obtained by means of a compressor 7 of sufficient power to be capable of supplying compressed air at a pressure at least equal to 7 bars, with a flow rate at least equal to 250 m 3 / h.

[0078] The cleaning device 1 shown also comprises an air dryer 8, interposed between the compressor 7 and the cryogenic device 3, which makes it possible to purify the compressed air obtained from the compressor 7 by ridding it in particular of the water vapor it contains which would otherwise freeze on contact with the dry ice. The compressor 7 and the air dryer 8 are connected to each other, then connected to a compressed air inlet 9 of the cryogenic device 3 by means of conduits 10 preferably in the form of flexible pipes 11.

[0079] The cryogenic device 3 also comprises a cryogenic air outlet 12 to which another conduit 10 is connected, which is preferably also a flexible pipe 11, on which a gun 13 extended by a nozzle 14 is mounted.

[0080] This gun 13 allows the operator 6 to easily control the exit or stopping of the cryogenic air flow 4, while directing it towards the plate 2 to be cleaned by means of the nozzle 14 which has at its distal end an exit opening 15.

[0081] The nozzle 14 is preferably elongated, preferably at least 30 cm long and for example approximately 40 cm long, so that the operator 6 can work comfortably standing up, without having to bend down, even in the case where the plate 2 to be cleaned is on the ground or on a low support.

[0082] The outlet opening 15 of the nozzle 14 may have any suitable shape. It is preferably in the form of a slot, so that the cryogenic air flow 4 is projected in the form of a flat jet, perfectly suited to cleaning narrow grooves.

[0083] Indeed, as can be seen more particularly in Figure 5, the plates 2 of the plate exchangers conventionally comprise grooves 16 used for mounting the seals and numerous grooves 17 used to improve the heat exchanges, which are all narrow grooves in which the deposits 18 accumulate over time and which it is very important to clean well despite the difficulty of access.

[0084] For this, the outlet opening 15 of the nozzle 14 is for example a rectangular slot, which preferably measures between 2.5 and 4 cm long and between 3 and 5 mm wide.

[0085] A second embodiment of the cleaning device 1 of the invention has been shown schematically in Figure 2.

[0086] This example of cleaning device 1 comprises a cryogenic apparatus 3 similar to that of the embodiment described previously.

[0087] As previously, a conduit 10, preferably in the form of a flexible pipe 11, is connected to its cryogenic air outlet 12 and a gun 13, extended by a nozzle 14 with an outlet opening preferably in the form of a slot, is mounted at the other end of this conduit 10. However, in this embodiment, the compressed air necessary for the production of the cryogenic air flow 4 is not obtained by means of a compressor, but is drawn from the compressed air network 19 of the cleaning site which generally corresponds to the site in which the exchanger is installed.

[0088] As the compressed air circulating in the pipes 20 of the compressed air network 19 of the majority of industrial sites has a maximum pressure of around 6 to 7 bars and a flow rate of around 200m 3 / h, it is not possible to carry out the method according to the invention by directly connecting a pipe 20 of the compressed air network 19 to the compressed air inlet 9 of the cryogenic device 3, the pressure and flow rate of the incoming compressed air being insufficient.

[0089] To solve this technical problem, the cleaning device 1 comprises a connection element 21 inserted between the cryogenic device 3 and the compressed air network 19. This connection element 21 is a part, for example Y-shaped or T-shaped, which comprises two inlet connections 22 and one outlet connection 23.

[0090] The outlet connection 23 is connected to the compressed air inlet 9 of the cryogenic device 3, via a conduit 10 preferably in the form of a flexible pipe 11.

[0091] In the example shown, each of the inlet connections 22 is connected to a valve 24 of a different pipe 20 of the compressed air network 19, via a conduit 10 preferably in the form of a flexible pipe 11, thus creating two tappings on the compressed air network 19.

[0092] By thus taking a portion of the compressed air from each of the pipes 20, it is thus possible to obtain at the compressed air inlet 9 of the cryogenic apparatus 3 a pressure and a flow rate of compressed air sufficient to be able to implement the cleaning method of the invention satisfactorily, that is to say a pressure at least equal to 7 bars and a flow rate at least equal to 250 m 3 / h.

[0093] According to the embodiments, the two inlet connections 22 of the connection element 21 can alternatively be connected to two valves 24 of the same pipe 20 of the compressed air network 19, if the flow rate and pressure of the compressed air circulating in this pipe 20 are sufficiently high so that, despite the pressure loss linked to the withdrawal, it is possible to obtain at the compressed air inlet 9 of the cryogenic apparatus 3 a pressure and a flow rate of compressed air sufficient to implement the cleaning method of the invention in a satisfactory manner, that is to say a pressure at least equal to 7 bars and a flow rate at least equal to 250 m 3 / h.

[0094] Likewise, depending on the variants, the two pipes 20 can belong to the same compressed air network 19, or to two different compressed air networks 19.

[0095] Finally, mixed embodiments of the cleaning device 1 comprising both a connection element 21 and one or more compressors 7 are also conceivable. In this case, the two inlet connections 22 of the connection element 21 are not connected to two valves 24 of the line 20 of the compressed air network 19, but for example to two compressors 7, or for one to a valve 24 of a line 20 of the compressed air network 19 and for the other to a compressor 7.

[0096] Such mixed embodiments advantageously make it possible to use one or more compressors 7 that are less powerful, and therefore less expensive, smaller and more easily transportable than those of the first embodiment described above, while obtaining at the compressed air inlet 9 of the cryogenic apparatus 3 a pressure and a flow rate of compressed air sufficient to implement the cleaning method of the invention.

[0097] Of course, if the cleaning device 1 comprises one or two compressors 7, it also comprises at least one air dryer 8 interposed between the compressor(s) 7 and the cryogenic device 3. This air dryer 8 may be common to two compressors 7, for example if it is located between the outlet connection 23 and the compressed air inlet 9 of the cryogenic device 3, or be dedicated to a single compressor 7 if it is located between the compressor 7 and one of the inlet connections 22 of the connecting element 21.

[0098] An example of a connecting element 21 has been shown in more detail in Figure 3.

[0099] In order to facilitate the connection between the flexible pipes 11 and the various fittings, valves or inlets of the cleaning device 1, while ensuring the sealing of these connections, the cleaning device 1 comprises a set of express fittings called “cat head” fittings 25, in particular as shown in FIG. 3 at the interface between the flexible pipes 11 and the valves 24, the inlet fittings 22 of the connecting element 21 and the outlet fitting 23 of the connecting element 21.

[0100] Non-return valves 26 are provided at the inlet connections 22 of the connecting element 21 in order to prevent the compressed air from returning to the valves 24 and thus protect the compressed air network 19 from any involuntary return of compressed air. The connecting element 21 also comprises a compressed air inlet 27, for example located at the sleeve of the outlet connection 23. As shown in FIG. 2, a blowing unit 28, comprising a flexible pipe 11 and a blowing nozzle 29, can advantageously be connected to this compressed air inlet 27.

[0101] For the sake of completeness of the description, an example of a cryogenic apparatus 3 has been shown schematically in Figure 4.

[0102] It comprises a storage tank 30 which must be previously filled with dry ice granules. This storage tank 30 is preferably refrigerated and / or has isothermal walls 31 to keep the dry ice at a temperature less than or equal to -78°C so that it remains in a solid state.

[0103] The storage tank 30 has in the lower part an opening 32 which can be entirely or partially open, or closed using a movable closure means 33. When the opening 32 is open, the storage tank 30 communicates via a channel 34 with a mixing zone 35 located below, into which the dry ice granules contained in the storage tank 30 fall by gravity.

[0104] In order to facilitate the transfer of dry ice pellets from the storage tank 30 to the mixing zone 35, the bottom 36 of the storage tank can advantageously be made with a converging slope towards the opening 32 in the manner of a hopper.

[0105] In the mixing zone 35, the dry ice granules fall onto a rotating disc 37 on which they fragment into dry ice particles.

[0106] The mixing zone 35 is also in communication with the compressed air inlet 9 via a channel 38 and with the cryogenic air outlet 12 via a channel 39.

[0107] The compressed air entering the cryogenic device 3 therefore enters the mixing zone 35 where it encounters the dry ice particles located on the rotating disc and carries them towards the cryogenic air outlet 12, thus forming the cryogenic air flow 4.

[0108] The cryogenic apparatus 3 also comprises a compressed air regulator 40, which acts for example at the level of the pipe 38, in order to regulate the entry of compressed air into the apparatus at a pressure of between 7 and 10 bars and at a flow rate of between 250 and 350 m 3 / h.

[0109] It also includes a dry ice regulator 41 which regulates the amount of dry ice pellets which fall from the storage tank 30 to be brought into contact with the compressed air in the mixing zone 35, so as to consume between 60 and 80 kg of dry ice pellets per hour. The dry ice regulator 41 may, for example, control the movement of the closure means 33 to adjust the size of the opening 32.

[0110] Thanks to this regulation of the parameters of the compressed air flow which enters the cryogenic device 3, and of the quantity of dry ice which is consumed, the cryogenic air flow 4 generated by the cleaning device 1 has characteristics optimized to obtain effective cleaning of the plate 2 without damaging it.

[0111] Preferably, the cryogenic apparatus 3 also comprises a means 42 for adjusting the compressed air regulator 40 and a means 43 for adjusting the dry ice regulator 41 which the operator 6 can actuate to choose the operating values ​​he wishes for the pressure and flow rate of the compressed air on the one hand and the consumption of ice on the other hand, while remaining within the ranges of parameters indicated above.

[0112] Thanks to this cleaning device 1, the operator 6 can easily implement the cleaning method of the invention, an example of which will be described below.

[0113] The plates 2 to be cleaned from the plate exchanger must first be removed from the exchanger.

[0114] The gaskets inserted between each of the plates 2 are preferably removed before carrying out the cryogenic cleaning. It is thus possible to better clean the groove 16 in which the gasket is mounted on the plate 2. This is also the opportunity to replace the used gasket with a new one after having completed the cleaning, so that the maintenance is complete.

[0115] However, if necessary, it is also possible to carry out the cryogenic cleaning method of the invention by leaving the seal in place on the plate, the latter not being damaged by the cryogenic cleaning according to the invention.

[0116] After being supplied with dry ice pellets and possibly connected to the site's compressed air network 19, the cleaning device 1 is put into operation. It is then capable of delivering a cryogenic air flow 4 whose parameters are optimum for carrying out the cryogenic cleaning of the plates 2.

[0117] The operator 6 then triggers, by means of the gun 13, the emission of a cryogenic air flow 4 which he directs using the nozzle 14 towards the plate 2 to be cleaned. He sweeps the entire surface of a first face of the plate 2, preferably with regular movements in the direction of the length and in the direction of the width of the plate 2. He then turns the plate 2 over to proceed in the same way on the other face of the plate 2. He then moves on to the next plate to clean it in the same way, until all the plates have been cleaned.

[0118] This cleaning is extremely fast, since operator 6 takes between 30 and 50 seconds approximately to clean one side of a plate 2 depending on its size and therefore between one and two minutes approximately to completely clean a plate 2.

[0119] No rinsing or drying of the plates 2 is necessary thereafter, since there is no trace of cleaning agent on the plate and the removed deposit fragments 18 have been carried away from the plate by the vaporization of the CO2 and the flow of compressed air.

[0120] Operator 6 then only has to replace new gaskets on the cleaned plates 2 if necessary, then reassemble the cleaned plates 2 in the heat exchanger.

[0121] To ensure the respiratory safety of operator 6, this process is preferably carried out outdoors and, as a precautionary measure, the operator is equipped with a CO2 sensor indicating whether the CO2 content of the surrounding air is approaching a threshold likely to be dangerous for his breathing. If necessary, the cleaning operation is stopped and appropriate ventilation is organized until the CO2 level returns to an acceptable value. Operator 6 preferably wears other suitable protective equipment, including cold-resistant gloves, a mask, ear defenders and safety glasses.

[0122] As can be seen in the comparative photograph of Figure 5, the cleaning method according to the invention is particularly effective.

[0123] On the left side of the photograph, we can see a plate 2 of a plate exchanger before cleaning and on the right side an identical plate 2, but photographed after the cleaning according to the invention has been carried out.

[0124] These plates 2 are stainless steel parts of substantially rectangular shape, which have at their corners four through openings 44 to form by juxtaposition the conduits for supplying and discharging the fluids of the two fluid circuits of the exchanger. They have grooves 16 for mounting the seals which are substantially perimetric on the periphery of the plate concerned, as well as a multitude of ridges 17 with zig-zag patterns, these ridges 17 and grooves 16 forming a multitude of narrow grooves over the entire surface of the plates 2. On the plate 2 photographed on the left, a whitish deposit 18 covers the entire surface of the plate 2 and completely fills the grooves formed by the ridges 17 and partially those formed by the grooves 16 where the seals were housed.

[0125] On plate 2 photographed on the right, it can be seen that after cleaning by the method according to the invention, this deposit 18 has completely disappeared. Plate 2 has become shiny again and the grooves formed by the striations 17 and the grooves 16 are again completely empty. No residue or trace of deposit 18 remains, even in areas that are difficult to access, such as the bottom of the grooves.

Claims

CLAIMS 1. Method for cleaning plates of a plate heat exchanger, at least some of which are to be cleaned, method characterized in that it comprises the following steps: - provision of plates to be cleaned; - supply of dry ice pellets; - provision of a cryogenic cleaning device capable of delivering a cryogenic air stream containing compressed air and dry ice particles, from the supplied dry ice pellets when supplied with compressed air; - obtaining a cryogenic air flow by means of the cryogenic cleaning device, from a compressed air supply with a pressure between 7 and 10 bars and a flow rate between 250 and 350 m 3 / h and a consumption of dry ice pellets of between 60 and 80 kg of dry ice per hour; - cleaning of the plates to be cleaned using the cryogenic air flow obtained.

2. Cleaning method according to the preceding claim, characterized in that it is applied to plates provided with seals, and in that it is preceded by the following steps: - dismantling of the plates to be cleaned from the heat exchanger; - removal of the seals from the plates to be cleaned; and following the following steps: - installation of new seals on the cleaned plates; and - reassembly of the cleaned plates on the heat exchanger.

3. Cleaning method according to claim 1 or 2, characterized in that during the step of cleaning the plates to be cleaned, at least one face, and preferably both faces, of each of the plates to be cleaned is swept by the cryogenic air flow obtained.

4. Cleaning method according to claim 3, characterized in that the sweeping by the cryogenic air flow obtained is carried out over the entire surface of the face of the plate by means of regular movements in the direction of the length and in the direction of the width of the face of the plate.

5. Cleaning method according to any one of the preceding claims, characterized in that the supply of compressed air is obtained by means of at least one compressor and at least one air dryer.

6. Cleaning method according to any one of claims 1 to 4, characterized in that the compressed air supply is obtained by means of two tappings on one or two compressed air networks, or by means of a tapping on a compressed air network and a compressor with an air dryer.

7. Device for cleaning plates of a plate heat exchanger, suitable for implementing the cleaning method according to any one of the preceding claims, the device comprising: - a compressed air inlet; - a storage tank for dry ice pellets; - a mixing zone in which dry ice pellets are fragmented into dry ice particles and brought into contact with compressed air, in order to form a cryogenic air stream containing compressed air and dry ice particles; and - a cryogenic air outlet; characterized in that the device comprises a compressed air regulator which regulates the compressed air inlet to a pressure of between 7 and 10 bars and a flow rate of between 250 and 350 m 3 / h, and a dry ice regulator that regulates the amount of dry ice pellets brought into contact with the compressed air to consume between 60 and 80 kg of dry ice pellets per hour.

8. Cleaning device according to claim 7, characterized in that it further comprises at least one compressor and at least one air dryer connected to said compressed air inlet.

9. Cleaning device according to claim 7 or 8, characterized in that it further comprises a connection element comprising an outlet connector connected to said compressed air inlet and two inlet connectors each being connected to a compressor or intended to be connected to a compressed air network.

10. Cleaning device according to claim 9, characterized in that the inlet connections and the outlet connection are equipped with express connections called “cat head” connections.

11. Cleaning device according to claim 9 or 10, characterized in that said inlet connections are equipped with non-return valves which prevent compressed air from escaping from the device.

12. Cleaning device according to any one of claims 9 to 11, characterized in that said connecting element further comprises a compressed air intake to which a blowing unit is connected.

13. Cleaning device according to any one of claims 7 to 12, characterized in that it further comprises a flexible pipe, connected to said cryogenic air outlet, and terminated by a gun provided with an elongated nozzle with a slotted outlet opening.

14. Cleaning device according to claim 13, characterized in that the elongated nozzle is at least 30 cm long, preferably 40 cm, and in that the slotted outlet opening is rectangular in shape and measures between 2.5 and 4 cm long and between 3 and 5 mm wide.

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