EP4727673A1

EP4727673A1 - Plant and method for the recovery of solvents

Info

Publication number: EP4727673A1
Application number: EP25755989.8A
Authority: EP
Inventors: William BOAROLO
Original assignee: Engineering Process Construction Srl
Current assignee: Engineering Process Construction Srl
Priority date: 2024-08-05
Filing date: 2025-07-29
Publication date: 2026-04-22
Also published as: WO2026033318A1

Abstract

Plant for the recovery of solvents, which comprises at least three adsorbers (3), each comprising in turn at least one layer (4) of material suitable for adsorbing at least one solvent, wherein the adsorbers (3) are connected through inlet regeneration ducts (D4) and outlet regeneration ducts (D5) to at least one cooling heat exchanger (15) and to at least one heating heat exchanger (21), wherein the cooling heat exchanger (15) is connected to the inlet side of one or more adsorbers (3) through one or more inlet cooling ducts (D10) provided with inlet valves (32) and the outlet side of one or more adsorbers (3) is connected to the heating heat exchanger (21) through one or more outlet cooling ducts (D11) provided with outlet valves (33), so that the inlet cooling duct(s) (D10) and the outlet cooling duct(s) (D11) connect the cooling heat exchanger (15) with the heating heat exchanger (21) through one or more adsorbers (3). The present invention also relates to a method which can be carried out by this plant.

Description

Plant and method for the recovery of solvents

Technical field

The present invention relates to a plant for the recovery of solvents and a method that can be carry out by this plant.

Background of the description

Known plants for the recovery of solvents use inert gas, for example nitrogen, to regenerate layers of activated carbon in adsorbers that have adsorbed solvents, in order to prevent the release of these solvents into the atmosphere. In the paint, printing, and adhesive tape industries, paint, inks, and glue are dried by evaporating a solvent with hot gas, for example hot air. This solvent-laden gas, typically containing 1-15 grams/Nm³ of organic solvents and 2-60 grams/Nm³ ofwater vapor, is filtered through one or more activated carbon layers in an adsorber. Most of the solvent content and a portion of water in the gas are adsorbed by the activated carbon, while the filtered gas is released into the atmosphere. The solvent adsorbed by the activated carbon may be desorbed by heating with water vapor or an inert gas with a low oxygen content, suitably heated.

Known plants with water vapor regeneration, which have the advantage of a very compact regeneration system but the disadvantage of recovering solvents with a very high water content, are still widespread in the adhesive tape field. The solvents commonly used in this sector are primarily hexane and toluene, which have been recognized as carcinogenic for years. The low efficiency of these known plants is therefore due to the fact that the wastewater separated from the solvent still contains traces of the solvent and must therefore be treated as process wastewater. Therefore, this wastewater cannot be disposed of or collected in cooling tower plants. Thus, this type of plant has high operating costs, primarily due to wastewater disposal.

Organic solvents such as ethyl acetate, ethanol, propyl acetate, butyl acetate, and other solvents that are highly miscible with water are primarily used in the flexible packaging field. Therefore, since plants for the recovery of solvents with water vapor regeneration are inefficient, processes to regenerate layers of activated carbon have been developed over the years, which processes use hot inert gas, particularly nitrogen, to regenerate the layers of activated carbon and recover the solvents, which can then be reused, as they contain much less water than solvents recovered using plants with water vapor regeneration.

The regeneration process with inert gas of the known methods involves a heating phase and a cooling phase of the activated carbon, which phases are carried out in a closed circuit. The inert gas released from one outlet side, in particular the upper side, of a layer of activated carbon contained in an adsorber is heated in a heating heat exchanger and then returned by a fan to the inlet side, in particular the lower side, of the same adsorber.

After the solvent has been desorbed from the layer of activated carbon with the hot inert gas, the solvent contained in the inert gas is recovered by cooling this gas in a cooling heat exchanger. However, the inert gas also contains water vapor, which is desorbed during heating with the hot inert gas, so that the condensate recovered from cooling the inert gas also contains 4-10% water by weight.

A water content greater than 1 % in the recovered solvent poses a problem for the reuse of the recovered solvent, so that known plants with an inert gas regeneration process must also be provided with layers of molecular sieves, for example based on zeolites, which dehydrate the solvents in the gaseous or liquid phase so that they have a water content of no more than 0.5%.

These molecular sieves represent a disadvantage due to the higher manufacturing and operating costs of the plant, as the molecular sieves must also be regenerated after several hours of water absorption. Furthermore, dehydrating the solvents in the gaseous phase at the outlet of the regeneration duct of the activated carbon adsorber requires high zeolite regeneration costs and a large amount of additional space in the plant. Dehydration of liquid-phase solvents, on the other hand, has the disadvantage of returning the dehydrated solvent with a straw-yellow colour, due to the decomposition of the zeolite binder at the end of the dehydration process, since, when the activated carbon layer is regenerated, the residual solvent evaporating from the zeolites contributes to the decomposition of their binder. During subsequent adsorption, this decomposition product colours the raw solvent passing through the zeolite layer.

Another major disadvantage of the known plants is the duration of their adsorption process for each individual adsorber, which is directly proportional to the regeneration time of an adsorber, since adsorber regeneration in the known plants occurs in cycles, one after the other. Therefore, the longer the regeneration process for a single adsorber, the longer the adsorption process will be. Excessively long regeneration times thus correspond to plants with significant amounts of activated carbon in the adsorbers to compensate for the prolonged adsorption process. However, this solution has been abandoned, as has the option of installing larger regeneration equipment to shorten the regeneration process. These modifications have led to a higher flow rate in the inert gas circuit to reduce the regeneration time, which, however, requires more heating, more refrigeration to cool the gas, and thus a larger fan.

Due to the disadvantages described above, the known plants are relatively bulky and expensive to manufacture and operate, due to the relatively high consumption of inert gas, cooling water and electricity.

In an attempt to reduce regeneration times and thus operating costs in the known plants, activated carbon regeneration can be stopped at a temperature of approximately 160°C. However, at this temperature, a relatively large amount of residual solvent remains in the activated carbon at the end of its regeneration, so that, during the activated carbon cooling phase, this substantial amount of solvent cannot be removed by cooling the circulating inert gas. Therefore, the inert gas released from the cooling heat exchanger during the cooling phase, which is at a temperature of approximately -8°C, still contains 30-100 g/m³ of solvent, which is again adsorbed onto the activated carbon, significantly reducing its available adsorption capacity at the end of the regeneration. Due to the reduced adsorption capacity, the adsorption time and consequently the regeneration time must be reduced in this known plant.

Therefore, the known plants and methods that carry out a regeneration process with inert gas have one or more of the following disadvantages: incomplete regeneration of activated carbon due to the high residual load of solvent after cooling at the end of the regeneration; high amount of water content in the recovered raw solvent compared to the maximum water content allowed for its reuse; installation of a molecular sieve dehydration unit to reduce the water content and allow the reuse of the solvent, with consequent additional costs and disadvantageous coloration of the solvent; higher investment costs compared to recovery plants with steam regeneration; higher operating costs due to high consumption of natural gas to heat the regeneration inert gas, electricity to power the regeneration equipment, and cooling water to cool the inert gas in the regeneration process.

Furthermore, the market has recently begun to demand plants for the recovery of solvents mounted on modular frames, known as skids. These modular frames support transportable vertical adsorbers with a downward-facing inlet side for the adsorbed gas and an upward-facing outlet side for the gas to be released, to minimize on-site mechanical assembly work and accelerate plant commissioning.

The disadvantage of the vertical adsorbers lies in the maximum acceptable height of the layer of activated carbon contained in an adsorber to ensure that even the upper part of the activated carbon remains efficient during the adsorption process, given that the adsorption efficiency of the activated carbon decreases exponentially as the solvent concentration in the gas to be treated decreases.

The loss of performance of the activated carbon in terms of adsorption capacity is due to the fact that the gas with the solvent, entering from the bottom of the layer, always saturates the activated carbon in the lower part first, which drastically reduces the solvent concentration in the gas passing through the upper part of the activated carbon layer. The low concentration limits the adsorption capacity of the activated carbon in the upper part of the layer, and this problem, over time, leads to significant inefficiencies in this known plant.

The problem relating to the layer height also limits the maximum amount of activated carbon that can be placed in a single transportable vertical adsorber, whose maximum diameter is approximately 3 m. The weight limit of activated carbon per adsorption layer, in turn, limits the capacity of the plants mounted on modular frames.

Known plants that regenerate adsorbers with inert gas and can be mounted on modular frames cannot effectively filter gas flows exceeding 50,000 Nm³/h and solvent concentrations exceeding 10 g/Nm³. To treat higher flows and/or concentrations with the known methods, it is therefore necessary to use multiple plants on modular frames. This technical problem causes even higher initial investment costs and operating costs.

Document WO 2019/086128 A1 describes a plant and method for the recovery of solvent, in which activated carbon is regenerated with inert gas by means of a system for regenerating the activated carbon layer with a vacuum process, which however is expensive, is inefficient, does not ensure complete evaporation of the solvent from the carbon during regeneration, and must use inert gas which is continuously pumped, for the entire duration of the regeneration, directly onto the upper side of the preheated layer of activated carbon, in a countercurrent flow, to enable regeneration of the carbon layer. This known plant does not ensure the complete regeneration of the activated carbon layer because the largest amount of solvent in the activated carbon is found in the lower part of the layer, while the hot inert gas enters the layer from the outlet side, where the solvent concentration is lower and where the amount of heat required to evaporate the solvent is less than the amount of heat required to evaporate the solvent from the inlet side of the layer.

Since in said known plant solvent condensation is performed with a cooling heat exchanger installed after the exhaust of a vacuum pump, using solvent cooled to 5°C as the cooling fluid, the gas released from the cooling heat exchanger still contains approximately 70-100 g/Nm³ of solvent and is circulated by a fan used in the adsorption process. This amount of residual solvent coming from the regenerated activated carbon contributes to premature saturation of the activated carbon, reducing the residual adsorption capacity of the entire plant.

At the end of the regeneration of the activated carbon using the vacuum regeneration technology, 30-35% of the activated carbon is still loaded with solvent that has not evaporated from the bottom of the layer, so that the activated carbon layer available for adsorption is relatively low, as is the adsorption efficiency of the plant during the subsequent adsorption cycle.

US 5958109 A, DE 3303423 A1 and DE 3713346 A1 disclose further plants and/or method for the recovery of solvents.

Summary of the description

The object of the present description is therefore to provide a plant and a method that solve these problems. This object is achieved with a plant and a method, the main features of which are specified in the attached claims, to be considered as an integral part of the present description. Thanks to their particular technical features, the plant and the method according to the present description allow obtaining the following advantages: reduction in the quantity of activated carbon used, thanks to its faster regeneration; increased efficiency in solvent recovery from the activated carbon layer; reduction of the total regeneration time of the activated carbon layer; low water content in the recovered solvent; reduction of residual solvent in the adsorber at the end of the regeneration; reduction of the management costs of the plant; reduction of the manufacturing costs of the plant; reduction in the amount of inert gas used; reduction of the CO2 emissions into the atmosphere thanks to further heat recovery in the plant; compliance with stringent regulations on volatile organic compounds (VOC) emissions.

To achieve these advantages, the plant and method according to the present description provide that heating and cooling phases of two different adsorbers overlap with a heat exchange from one adsorber to the other in one or more heat exchange phases during the regeneration process, thus saving approximately 35% of the total regeneration time of an adsorber compared to known plants and methods, in which the heating and cooling of each adsorber are carried out in two distinct and separate phases.

In particular, in at least one heat exchange phase of the present method, the activated carbon layer of an adsorber is heated with inert gas coming directly from a layer of another adsorber, which is cooled at the same time.

The inert gas used to regenerate the layer of an adsorber is then circulated in a closed circuit, bypassing a heating heat exchanger, in a first, relatively hot, adsorber, which is in the final phase of the regeneration process, to recover the heat of the layer, and then in a second, relatively cold, adsorber, which is in the initial phase of the regeneration process, to heat it. The inert gas released from the second adsorber is cooled in at least one cooling heat exchanger to remove the water contained in the recovered solvent and to cool the inert gas, which is sent to the first adsorber, typically at a temperature of 0°- 5°C, and which contains 2-4 g/m³ of solvent and 2-6 g/m³ of water resulting from the condensation of the inert gas released from the second adsorber. The first adsorber, at the beginning of this heat exchange phase, is hot and is essentially free of water, which was desorbed with the solvent during a previous solvent recovery phase.

As the first adsorber layer is cooled, most of the water exiting the cooling heat exchanger from the second adsorber is adsorbed into the layer of the first adsorber. The inert gas released from the first adsorber is at a temperature of approximately 170°C and contains little water vapor but a large amount of residual solvent that was not evaporated during the previous phase of solvent recovery, typically in an amount of 10-50 g/Nm³ of solvent.

Cooling the first adsorber in this way is very efficient because, in addition to the effect of the cold inert gas, there is also a cooling effect due to the large quantities of solvent being desorbed.

The inert gas heated in the first adsorber is used to directly heat the second adsorber. This solution makes adsorption in the second adsorber highly efficient because a significant amount of solvent released from the layer of the first adsorber is adsorbed in the second adsorber due to the high temperature of approximately 170°C of the inert gas exchanged between the two adsorbers. The heat exchange phase is therefore a cooling phase for the first adsorber and a heating phase for the second adsorber.

Experimental tests have shown that, during this heat exchange phase, almost all of the solvent remaining in the first adsorber is conveyed from the first adsorber to the second adsorber, while the water in the second adsorber, which is beginning the regeneration process, is evaporated thanks to the low concentration of water vapor contained in the inert gas coming from the first adsorber. The effect of heating with essentially water-free inert gas contributes to the release of water vapor from the second adsorber before the solvent, so that essentially water-free solvent can be recovered during a subsequent phase of solvent recovery from the second adsorber.

Further experimental tests showed that during the heat exchange phase, with the second adsorber heated from a temperature of approximately 35°C to a temperature of approximately 80°C, the inert gas released by the second adsorber is indeed water-rich and solvent-poor. Thanks to this solution, the solvent can be subsequently recovered without using molecular sieves to separate the water. This heat exchange phase of the regeneration process also ensures better regeneration of the first adsorber layer, since not only is an active heater to heat the second adsorber avoided but solvent with a water content of less than 1% is also recovered.

Partially overlapping the adsorption and regeneration processes of multiple adsorbers allows for a 40-minute saving in regeneration time compared to known plants and methods, resulting in the following experimentally measured savings: less than 45% natural gas heating consumption; less than 40% coolant consumption;

46% lower CO2 emissions into the atmosphere.

Brief description of the drawings

Further advantages and features of the plant and method according to the present description will become apparent to those skilled in the art from the following detailed description of some embodiments, to be considered non-limiting examples of the claims, with reference to the attached drawing, in which figure 1 is a diagram of an embodiment of the plant.

Exemplary embodiments

Figure 1 shows an embodiment of the plant, in which adsorption ventilation means 1 , in particular a fan, are connected through inlet adsorption ducts D1 provided with inlet valves 2 to an inlet side of adsorbers 3 which comprise at least one layer 4 of activated carbon or other material suitable for adsorbing at least one solvent, i.e. a volatile organic compound that can be used as a solvent. An outlet side of the adsorbers 3 is connected through outlet adsorption ducts D2 provided with outlet valves 5 to at least one exhaust device 6, for example a chimney, suitable for discharging gas outside the plant. In the plant, the inlet side of an adsorber 3 is preferably arranged below the outlet side, so that a gas with solvent to be adsorbed by the adsorber 3 enters from a lower side of the layer 4, flows through the layer 4 and exits from an upper side of the layer 4. In other embodiments, an adsorber 3 may comprise multiple inlet sides, multiple outlet sides and/or multiple layers of material suitable for adsorbing one or more solvents.

The method according to the present description comprises at least one adsorption process and at least one regeneration process which are carried out one after the other, for example by the plant according to the present embodiment, one or more times, as explained below.

In the adsorption process, the adsorption ventilation means 1 convey a gas, in particular air, containing at least one solvent and coming for example from an external source 7, through the inlet adsorption ducts D1 to the inlet side of at least one adsorber 3, in which the respective layer 4 retains a quantity of solvent contained in the gas, which is then released with a reduced quantity of solvent, preferably tending to zero, through the outlet adsorption ducts D2 and the discharge device 6. The inlet valve 2 and the outlet valve 5 of each adsorber 3 used in the adsorption process are open. The plant comprises at least three adsorbers 3, preferably at least four adsorbers 3, in which at least two adsorbers 3 are configured to simultaneously carry out the adsorption process and at least two adsorbers 3 are configured to carry out the regeneration process at the same time.

The gas treated by the plant may have a flow rate even greater than 50,000 Nm³/h, a concentration of 2-10 g/Nm³of solvent and a concentration of 5-30 g/Nm³ of water in the gaseous phase. The solvent may in turn comprise different concentrations of solvents depending on the external source 7, for example a flexographic printing press, in which case the solvent may contain 70%-85% by weight of alcohols, 10%-15% by weight of ethyl acetate, and 5%-10% by weight of high-boiling temperature compounds. If the external source 7 is a rotogravure printing press, the solvent may contain 3%-5% by weight of alcohols, 85%-95% by weight of ethyl acetate, and 1 %-3% by weight of high- boiling temperature compounds.

The velocity of the gas with solvent passing through an adsorber 3 in the adsorption process is preferably less than 0.35 m/s to ensure a contact time of at least 3 seconds of the gas in the layer 4, thus optimizing the effectiveness of the activated carbon. The gas with solvent from the external source 7 is preferably cooled to a temperature of approximately 35°C by cooling means (not shown in the figure), again to optimize the effectiveness of the activated carbon.

The adsorbers 3 may comprise containers with a substantially cylindrical shape, in particular with a diameter of 2.8-3.0 m, which are arranged with the longitudinal axis oriented in a substantially vertical manner and contain a layer 4 of activated carbon having a thickness of 0.8-1.3 m, which is substantially less than the height of the adsorber 3 containing it, so as to form two cavities in the adsorber 3, respectively between the layer 4 and the inlet side and between the layer 4 and the outlet side.

The activated carbon of a layer 4 preferably has the following characteristics: pellet diameter: 3-4 mm (ASTM D2862 standard); activity of carbon tetrachloride (CTC): min. 80%; apparent density: 420 ± 20 g/l; ash: max. 15%; humidity: max. 5%; hardness: max. 95%;

BET surface (Brunauer-Emmett-Teller, ASTM 3663 standard): 1050-1250 m²/g.

The layers 4 of activated carbon contained in the adsorbers 3 involved in the adsorption process are gradually saturated by the adsorbed solvent. The adsorption process in an adsorber 3 is interrupted when a sensor in the adsorber 3 or in the outlet adsorption ducts D2 detects and signals to a control unit 8, in particular a programmable electronic control unit, that the layer 4 is almost saturated with solvent, in particular with a percentage of approximately 70% solvent saturation, after which the control unit 8 terminates the adsorption process, thus avoiding solvent emissions into the environment, and starts the regeneration process of the saturated adsorber 3.

Said sensor is preferably an FID (Flame Ionization Detector) detector, which is arranged downstream of a layer 4 and is configured to measure the concentration of the solvent in the gas released from an adsorber 3. In particular, the control unit 8 starts the regeneration process in an adsorber 3 when the concentration of the solvent in the gas released from this adsorber 3 reaches a predetermined value, in particular 10-70 mg/Nm³.

The control unit 8 is also connected to other components of the plant, such as the adsorption ventilation means 1 , to other gas, pressure or temperature sensors and to the valves of the plant, so that the control unit 8 can open and close these valves during the various phases of the adsorption process and the regeneration process to control the correct functioning of the entire plant.

The regeneration process preferably includes an inertization phase, in which an unwanted gas, particularly a comburent such as oxygen, is removed from an adsorber 3 to avoid the risk of combustion in the layer 4 during the regeneration process. For example, the first adsorber 3 from the left in the figure begins the regeneration process, the first adsorber 3 from the right is in a waiting phase, and the remaining two adsorbers 3 carry out the adsorption process.

In the inertization phase an inert gas, for example nitrogen, introduced into the plant from an inert gas source 9 through an inert gas duct provided with an inlet valve 10, is circulated in the plant by regeneration ventilation means 11 , for example a fan controlled by the control unit 8. The inert gas is then circulated through a bypass duct D3 provided with a bypass valve 12 and inlet regeneration ducts D4 provided with inlet valves 13 to at least one adsorber 3 which is starting the regeneration process. The inert gas released from this adsorber 3 is then returned through outlet regeneration ducts D5 provided with outlet valves 14 to the regeneration ventilation means 11. The inert gas preferably flows through the adsorber 3 from the inlet side to the outlet side, i.e. in the same direction of the flow of the solvent gas in the adsorption process, so as to follow the concentration gradient of the solvent in the layer 4, which decreases from the inlet side to the outlet side of the adsorber 3. During the inertization phase, the layer 4 is inerted and, in addition, the concentration gradient of the solvent is distributed from the inlet side of the adsorber 3 to its outlet side thanks to the inert gas passing through the layer 4. Thanks to the low vapor pressure of the highly concentrated solvent contained in the layer 4, the solvent begins to evaporate in the inert gas, which for example has a temperature of around 35°, moving towards the upper part of the layer 4 to be ready to evaporate in a subsequent phase. This arrangement allows for better and faster evaporation of the solvent contained in the layer 4 during its heating.

In the inertization phase, the solvent-containing inert gas released from an adsorber 3 is conveyed from the outlet regeneration ducts D5, with the outlet valves 14 open, to an inlet side of at least one cooling heat exchanger 15 provided with an inlet valve 16, which is also open. An outlet side of the cooling heat exchanger 15 is connected to the regeneration ventilation means 11 through at least one connecting duct D6 provided with at least one connecting valve 17, which is open. The cooling heat exchanger 15 is also connected to at least one chiller 18 to condense the solvent and water contained in the inert gas. For this purpose, a cooling fluid, for example, water with glycol, is cooled by the chiller 18 and circulated in the cooling heat exchanger 15 to condense the water vapor and solvent contained in the inert gas coming from the adsorber 3. To remove unwanted gas, in particular oxygen, which is not condensed in the cooling heat exchanger 15, a gas removal duct D14 provided with a gas removal valve 19 preferably connects the cooling heat exchanger 15 with one or more inlet adsorption ducts D1. In particular, the inlet of the gas removal duct D14 is connected between the inert gas duct and the regeneration ventilation means 11 and the outlet of the gas removal duct D14 is connected between the external source 7 and the adsorption ventilation means 1. The gas removal duct D14 then allows the unwanted gas to be conveyed to one or more adsorbers 3 which are carrying out the adsorption process until the control unit 8 detects that the concentration of the unwanted gas in the closed regeneration circuit is below a threshold value, for example a concentration lower than 8% in the case of oxygen. The gas removal valve 19 of the gas removal duct D14 is controlled by the control unit 8 by means of a gas sensor, in particular an oxygen sensor, arranged in the gas removal duct D14.

The bypass duct D3 provided with the bypass valve 12 is configured to bypass a heating heat exchanger 21 provided with an inlet valve 22, when the bypass valve 12 is open and the inlet valve 22 is closed. The outlet side of the heating heat exchanger 21 is connected to the inlet regeneration ducts D4. Therefore, in the inertization phase, the inert gas circulates in an open circuit comprising the inert gas source 9, the regeneration ventilation means 11 , at least one adsorber 3 carrying out the regeneration process, the cooling heat exchanger 15, at least one adsorber 3 carrying out the adsorption process, and the exhaust device 6.

The liquid containing water and solvent obtained from the condensation of the inert gas in the cooling heat exchanger 15 can be collected by a collection device 23, in particular a decanter, to be reused later, as will be explained below.

The regeneration process may therefore comprise an initial heat exchange phase, in which heat is drawn from the layer 4 of a first adsorber 3, for example the adsorber 3 on the right in the figure, which is cooling towards the end of its regeneration process, to heat the layer 4 of a second adsorber 3, for example the adsorber 3 on the left in the figure, which has completed the inertization phase and must begin regeneration. The plant and method according to the present description therefore employ at least two adsorbers 3 that exchange heat in their respective regeneration processes. In the first heat exchange phase, inert gas at approximately 10°, in particular from the inert gas source 9, is circulated in a closed circuit in the plant by the regeneration ventilation means 11 in the inlet regeneration ducts D4 with at least one inlet valve 13 open to the first adsorber 3 (on the right), which is relatively hot and is cooling down, and then through at least one exchange duct D7 provided with an exchange valve 24, which is open, to the second adsorber 3 (on the left), which is colder than the first adsorber 3 and is heating up, so as to exchange heat from the first adsorber 3 to the second adsorber 3. For this purpose, the outlet side of at least the first adsorber 3, in particular of each adsorber 3 of the plant, is connected by means of an exchange duct D7 provided with at least one exchange valve 24 to the inlet side of another adsorber 3, in particular of at least the second adsorber 3, and so on from one adsorber 3 to another adsorber 3, so that all the adsorbers 3 of the plant are linked to each other through respective exchange ducts D7 provided with exchange valves 24. Therefore, the inert gas can pass from the first adsorber 3 to the second adsorber 3 without passing through the regeneration ventilation means 11 , the cooling heat exchanger 15 and/or the heating heat exchanger 21 . Preferably, the exchange ducts D7 are connected to the regeneration ducts D4, D5, in particular with a first junction arranged between the outlet side of an adsorber 3 and the respective outlet valve 14 at a point of an outlet regeneration duct D5 and with a second junction arranged between the inlet side of another adsorber 3 and the respective valve inlet 13 at a point of an inlet regeneration duct D4. Thus, the inert gas released from the outlet side of the first adsorber 3, for example at a temperature of approximately 170°C, with the respective outlet valve 14 closed, flows through the second adsorber 3 from the inlet side to the outlet side, with the respective inlet valve 13 closed, thus essentially in the same direction as the flow of gas with solvent that is adsorbed in the adsorption process.

The inert gas released from the outlet side of the second adsorber 3, with the respective outlet valve 14 open, is conveyed through the outlet regeneration ducts D5 to the cooling heat exchanger 15, with the respective inlet valve 16 open. Preferably, the inert gas is cooled in a first cooling stage 15a of the cooling heat exchanger 15 with a first cooling fluid and then further cooled in a subsequent second cooling stage 15b of the cooling heat exchanger 15 using a second cooling fluid cooled to a temperature of approximately -10°C by the chiller 18, so as to condense water vapor contained in the inert gas in the cooling heat exchanger 15. The inert gas is preferably cooled to a temperature of about 40°C in the first cooling stage 15a of the cooling heat exchanger 15, in particular by means of the first cooling fluid, e.g. water at a temperature of about 24°C coming from an inlet duct 15d connected to an external source, e.g. a cooling tower (not shown in the figure). The first cooling fluid is released from the first cooling stage 15a of the cooling heat exchanger 15 at a temperature of approximately 34°C and is collected by a recovery duct 15e to be fed into a heating stage 15c of the cooling heat exchanger 15, following the second cooling stage 15b of the cooling heat exchanger 15. The inert gas passing through the heating stage 15c of the cooling heat exchanger 15 is then heated from a temperature of approximately -5°C to a temperature of approximately 10°C by exchanging heat with the first cooling fluid, which is then cooled from a temperature of approximately 34°C to a temperature of approximately 30°C in the heating stage 15c of the cooling heat exchanger 15. The first cooling fluid may be released from the heating stage 15c of the cooling heat exchanger 15 through an outlet duct 15f to the external source, in particular to be cooled at an ambient temperature, for example a temperature of approximately 24°C, in a cooling tower (not shown in the figure), so that it can be reused in the first cooling stage 15a of the cooling heat exchanger 15. The inert gas released from the outlet side of the cooling heat exchanger 15 is conveyed to the first adsorber 3 by the regeneration ventilation means 11 through the connecting duct D6 with the connecting valve 17 open. The heat exchange between the first cooling stage 15a and the heating stage 15c of the cooling heat exchanger 15 allows the first cooling fluid to be reused to save electrical energy and/or employ a smaller cooling tower.

At the beginning of the first heat exchange phase, the inert gas released from the second adsorber 3 is not very hot because the heat from the first adsorber 3, which is hotter than the second adsorber 3, is mainly absorbed by the layer 4 of the second adsorber 3, which then releases water vapor and solvent into the inert gas at the outlet side of the second adsorber 3. However, the heat recovery with this arrangement increases exponentially as the temperature of the layer 4 of the second adsorber 3 and thus of the inert gas released from the second adsorber 3 increases.

In this first heat exchange phase, the water vapor and the gaseous solvent released from the second adsorber 3 together with the inert gas are condensed into a liquid phase in the second cooling stage 15b of the cooling heat exchanger 15, so that the condensed liquid can be collected in the collection device 23, preferably together with the water and solvent condensed in the inertization phase. The liquid contained in the collection device 23 can be pumped with a pump 25, in particular a pump with a relative pressure of approximately 7 barG (bar gauge), to at least one nebulizer 26 which is arranged in one or more adsorbers 3, preferably in the cavity between the inlet side and the layer 4, so as to nebulize the liquid collected in the collection device 23 towards the inlet side of the layer 4. The cooling heat exchanger 15, the collection device 23, the pump 25 and the nebulizers 26 are connected to each other through one or more ducts. For simplicity, the ducts between the pump 25 and the nebulizers 26 in each adsorber 3 are shown with a single dashed line. The condensed liquid from the cooling heat exchanger 15 can be nebulized by the nebulizers 26 onto the layer 4 of an adsorber 3 that is carrying out an adsorption process, so that the water contained in the condensed liquid is separated from the solvent before being released into the atmosphere through the exhaust device 6, while the solvent is adsorbed in the layer 4 of the adsorber 3. Furthermore, the nebulization of the liquid containing water and solvent onto the layer 4 of an adsorber 3 cools the gas with solvent coming from the adsorption ventilation means 1 , so as to improve the adsorption performance of this adsorber 3. In fact, the nebulized water in a large flow of solvent gas returns to the vapor phase and releases the solvent into the layer 4, so that in the adsorption process the water vapor without solvent leaves the adsorber 3 to be released into the atmosphere through the exhaust device 6.

When the outlet gas temperature from the hot adsorber 3 reaches a temperature of approximately 80°C, the solvent concentration in the inert gas increases rapidly while the water vapor concentration decreases rapidly, so that the condensed liquid contains only approximately 1% water content relative to the solvent content. The control unit 8 can terminate the first heat exchange phase to allow the second cooling stage 15b of the cooling heat exchanger 15 to be defrosted.

The regeneration process may then comprise a defrosting phase, in which the second cooling stage 15b of the cooling heat exchanger 15 is defrosted to remove frozen water remaining in the second cooling stage 15b during the first heat exchange phase, so as to avoid watering down the solvent that is subsequently condensed.

The defrosting phase is carried out by continuing to circulate inert gas in a closed circuit through the regeneration ventilation means 11 , continuing the cooling phase of the first adsorber 3 with the residual refrigeration of the frozen water present in the cooling heat exchanger 15, which however is deactivated. Therefore, the second cooling fluid from the chiller 18 is not circulated in the cooling heat exchanger 15 during this defrosting phase to allow the fins of the second cooling stage 15b to be defrosted, while the second adsorber 3 is still being heated. After several minutes of defrosting, when the temperature of the inert gas leaving the cooling heat exchanger 15 reaches a temperature of approximately 15°C and no condensate is detected, in particular by a condensation sensor connected to the control unit 8, released from the cooling heat exchanger 15 towards the collection device 23, the control unit 8 interrupts this defrosting phase and the adsorbers 3 move on to the subsequent phase of the regeneration process.

The regeneration process may comprise a second heat exchange phase, substantially the same as the first heat exchange phase but with a lower temperature in the cooling heat exchanger 15, in particular achieved by varying the temperature of the second cooling fluid in the chiller 18.

In the second heat exchange phase, in order to condense the solvent contained in the inert gas and prevent this solvent from flowing back to the adsorbers 3, the chiller 18 is reactivated by lowering the temperature of the second cooling fluid from a temperature of approximately -10° to a temperature of approximately -25°C, so as to condense further solvent in the cooling heat exchanger 15. The solvent condensed in the cooling heat exchanger 15, in particular in its second cooling stage 15b, has a low water content, so it is collected in the collection device 23 to be pumped into a recovery device 27, e.g. a tank, preferably by means of a second pump 28.

The regeneration process may then include a recovery phase, in which the solvent starts to be removed from the second adsorber 3 (on the left in the figure) which has been heated in the previous phases and is substantially free of water, i.e. has a water content of less than approximately 1%.

The first adsorber 3 (on the right in the figure), cooled during the heat exchange phases, is further cooled to a temperature of approximately 40°C during the recovery phase, completing the regeneration process, after which it is ready to begin a new adsorption process. Simultaneously, the inert gas released from the second adsorber 3 (on the left in the figure), heated during the heat exchange phases, reaches a temperature of approximately 105°C, so that the solvent concentration in the inert gas increases rapidly, and therefore the layer 4 of the second adsorber 3 must be heated with inert gas heated to a higher temperature, specifically to a temperature of approximately 210°C. The recovery phase is carried out by circulating inert gas, in particular the same inert gas used in the heat exchange phases, in a closed circuit through the inlet regeneration ducts D4 and the outlet regeneration ducts D5, preferably by means of the regeneration ventilation means 11 , from the heating heat exchanger 21 activated by the control unit 8, with the inlet valve 22 open and the bypass valve 12 closed, through the second adsorber s (on the left in the figure), with its inlet valve 13 open, while the remaining inlet valves 13 of the inlet regeneration ducts D4 are closed, its outlet valve 14 open, while the remaining outlet valves 14 of the outlet regeneration ducts D5 are closed, to the cooling heat exchanger 15.

The inert gas is heated in the heating heat exchanger 21 from a temperature of 105°- 130°C to a temperature of approximately 210°. For this purpose, an exchange stage 21a of the heating heat exchanger 21 can be connected through exchange ducts D8, D9 to an exchange stage 15g, in particular arranged upstream of the stages 15a, 15b and 15c, of the cooling heat exchanger 15, so that a heat exchange fluid can circulate and exchange heat between these two exchange stages 15g and 21a. In particular, in the recovery phase, the heat exchange fluid, preferably water with glycol, is heated from a temperature of approximately 60°C to a temperature of 85°-110°C, so as to cool the inert gas from a temperature of approximately 130°C to a temperature of approximately 100°C in the exchange stage 15g of the cooling heat exchanger 15 and to heat the inert gas in the exchange stage 21a of the heating heat exchanger 21 to a temperature of approximately 80°C, thereby saving cooling fluid otherwise required to cool the inert gas.

This heat exchange fluid at a temperature of approximately 110°C is collected by the exchange stage 15g of the cooling heat exchanger 15 and sent to the exchange stage 21a of the heating heat exchanger 21 through the exchange duct D9, so that the inert gas enters the exchange stage 21a of the heating heat exchanger 21 at a temperature of approximately 50°C and is heated to a temperature of approximately 80°C while the heat exchange fluid is cooled to a temperature of approximately 60°C, and then returned through the exchange duct D8 to the exchange stage 15g of the cooling heat exchanger 15 for further heat exchange.

In the recovery phase, the inert gas released from the exchange stage 21a of the heating heat exchanger 21 passes through a heating stage 21 b of the heating heat exchanger 21 , where the inert gas is heated from a temperature of approximately 80°C to a temperature of approximately 210°C thanks to the heat exchange with a heating fluid, in particular thermal oil, heated to a temperature of approximately 250°C by a heater 31 , in particular a burner fuelled by natural gas.

The inert gas heated to a temperature of approximately 210°C by the heating stage 21b of the heating heat exchanger 21 is sent to the second adsorber 3 (left in the figure) to evaporate the solvent remaining in the respective layer 4. During the heating of the layer 4, the gas released from the second adsorber 3 changes from a temperature of approximately 105°C to a temperature of approximately 130°C, e.g. with a solvent content of approximately 300 g/Nm³, and enters the cooling heat exchanger 15, in particular the exchange stage 15g, to be cooled as described above to a temperature of approximately 100°C, after which it enters the first cooling stage 15a to be cooled to a temperature of approximately 40°C, using the first cooling fluid which has a temperature of approximately 24°C, and then the second cooling stage 15b to be further cooled with the second cooling fluid, which is at a lower temperature than the first coolant. The inert gas enters the cooling heat exchanger 15 at a temperature of approximately 100°C, rather than approximately 190°C as in known plants, thus saving energy and fluid to cool it.

The solvent in the inert gas cooled to a temperature of approximately 40°C and with a solvent content of approximately 300 g/Nm³ is condensed in the second cooling stage 15b of the cooling heat exchanger 15 by means of the second cooling fluid which is cooled by the chiller 18 to a temperature of approximately -25°C. The condensed solvent is then collected in the collection device 23 and conveyed to the recovery device 27 by the second pump 28.

The inert gas cooled to a temperature of approximately -10°C in the second cooling stage 15b of the cooling heat exchanger 15 enters the heating stage 15c of the cooling heat exchanger 15, where further heat exchange takes place, in which the first cooling fluid released from the first cooling stage 15a at a temperature of approximately 34°C is cooled to a temperature of approximately 30°C by the inert gas, which in turn is heated to a temperature of approximately 10°C.

The cooling heat exchanger 15 is connected to the inlet side of one or more adsorbers 3 by means of one or more inlet cooling ducts D10 provided with inlet valves 32 and the outlet side of one or more adsorbers 3 is connected to the heating heat exchanger 21 by means of or more outlet cooling ducts D11 provided with outlet valves 33, so that the inert gas released by the cooling heat exchanger 15 in the recovery phase can be sent directly to at least one adsorber 3, in particular the first adsorber 3 (on the right in the figure), to cool it. In this phase, the inlet valve 32 and the outlet valve 33 of the cooling ducts D10, D11 of the first adsorber 3 are open, while the inlet valves 32 and the outlet valves 33 of the cooling ducts D10, D11 of the other adsorbers 3 are closed. In this phase, the connecting valve 17 of the connecting duct D6 is also closed, so that the inert gas is conveyed by means of the regeneration ventilation means 11 from the cooling heat exchanger 15 to the first adsorber 3 through the respective inlet cooling duct D10, then from the first adsorber 3 to the heating heat exchanger 21 through the respective outlet cooling duct D11 , then from the heating heat exchanger 21 to the second adsorber 3 through the respective inlet regeneration duct D4, and then from the second adsorber 3 to the cooling heat exchanger 15 through the respective outlet regeneration duct D5. Therefore, the inlet cooling duct(s) D10 and the outlet cooling duct(s) D11 connect the cooling heat exchanger 15 with the heating heat exchanger 21 through one or more adsorbers 3, preferably with the inert gas flowing from the inlet side, connected to an inlet cooling duct D10, to the outlet side, connected to an outlet cooling duct D11 , of these adsorbers 3 to be cooled.

This solution allows for the recovery of heat corresponding to a temperature difference of approximately 4°C in the circuit of the cooling fluids, which difference in turn allows for a saving of approximately 50% of the first cooling fluid reintegrated in the cooling tower and therefore allows for a cooling tower 50% smaller than the cooling towers of known plants.

The inert gas at a temperature of approximately 10°C then flows through the first adsorber 3, which can be cooled, in particular to a temperature of approximately 40°C, to initiate a new adsorption process. The inert gas released at a temperature of approximately 50°C from the first adsorber 3 is sent by the regeneration ventilation means 11 through the outlet cooling ducts D11 to the heating heat exchanger 21 to heat the inert gas and regenerate the second adsorber 3, as seen above.

The recovery phase ends when the control unit 8 detects that the inert gas exiting the first adsorber 3 reaches a temperature of approximately 40°C and the inert gas exiting the second adsorber 3 reaches a temperature of approximately 130°C. The regeneration process may therefore comprise a first regeneration phase in which at least one adsorber 3, in particular the first adsorber 3 (on the right), is already regenerated, so that it is not used in this first regeneration phase and is ready to start an adsorption process, while at least one adsorber 3, in particular the second adsorber 3, is regenerated by means of the inert gas circulated by the regeneration ventilation means 11 in the closed circuit comprising the cooling heat exchanger 15, the connecting duct D6, the heating heat exchanger 21 , an inlet regeneration duct D4 with the inlet valve 13 open, the relevant adsorber 3 to be regenerated, and the relevant outlet regeneration duct D5 with the outlet valve 14 open. The inlet valves 13 and the outlet valves 14 of the other adsorbers 3 are closed.

In the first regeneration phase, the inert gas preferably flows through a preheating stage 21 c of the heating heat exchanger 21 , where the inert gas is heated from a temperature of approximately 10°C to a temperature of approximately 50°C thanks to the condensation of a refrigerant, in particular propane, coming from the chiller 18 connected to the preheating stage 21 c of the heating heat exchanger 21 through refrigeration ducts D12, D13 to circulate and condense the refrigerant fluid of the chiller 18 in the heating heat exchanger 21. This arrangement saves refrigerant fluids for condensing the refrigerant fluid of the chiller 18 and is therefore substantially different from known plants in which the refrigerant fluid is freon and is condensed using different methods or devices.

In particular, the refrigerant fluid is sent from the chiller 18 through the refrigeration duct D12 in the gaseous phase at a temperature of approximately 80°C and a pressure of approximately 14 barG to be condensed in the preheating stage 21c of the heating heat exchanger 21 using the inert gas which has a temperature of approximately 10°C. The condensed refrigerant fluid at a temperature of approximately 40°C and a pressure of approximately 14 barG returns from the preheating stage 21c of the heating heat exchanger 21 to the chiller 18 through the refrigeration duct D13 and is used in the evaporator heat exchanger of the chiller 18, where a thermostatic valve allows flash evaporation of the refrigerant fluid from approximately 14 barG to approximately 0.5 barG to generate frigories for cooling the second refrigerant fluid used to condense the solvent in the second cooling stage 15b of the cooling heat exchanger 15.

The inert gas exiting the second adsorber 3 enters the exchange stage 15g of the cooling heat exchanger 15 at a temperature of 130°-160°C during the first regeneration phase. Thanks to the exchange ducts D8, D9 between the exchange stage 15g of the cooling heat exchanger 15 and the exchange stage 21a of the heating heat exchanger 21 , the heat exchange fluid is heated from a temperature of approximately 60°C to a temperature of 110°-140°C by means of the heat of the inert gas in the closed circuit for the regeneration, so that: the inert gas is cooled from a temperature of approximately 160°C to a temperature of approximately 110°C in the cooling heat exchanger 15; the heat of the heat exchange fluid is recovered to heat the inert gas in the heating heat exchanger 21 ; the amount of cooling fluid required to cool the inert gas is smaller than in the known plants.

The heat exchange fluid at a temperature of approximately 140°C is collected by exchange stage 15g of the cooling heat exchanger 15 and sent through the exchange duct D9 to the exchange stage 21a of the heating heat exchanger 21 , where the inert gas enters at a temperature of approximately 50°C and is heated to a temperature of approximately 95°C, while the heat exchange fluid is cooled to a temperature of approximately 60°C before being sent through the exchange duct D8 to the exchange stage 15g of the cooling heat exchanger 15 for a subsequent heat recovery cycle.

The inert gas is then heated from a temperature of approximately 95°C to a temperature of approximately 210°C in the heating stage 21 b of the heating heat exchanger 21 by the heating fluid heated to a temperature of approximately 250°C by the heater 31.

The inert gas heated by the heating stage 21 b of the heating heat exchanger 21 is used in the second adsorber 3 to evaporate a further quantity of solvent and thus regenerate the respective layer 4. In this first regeneration phase, the inert gas released by the second adsorber 3, at a temperature increasing from approximately 130°C to approximately 160°C and with a content of approximately 230 g/Nm³ of solvent, first enters the exchange stage 15g of the cooling heat exchanger 15 to be cooled as described above to a temperature of approximately 110°C, then into the first cooling stage 15a of the cooling heat exchanger 15, where it is further cooled to a temperature of approximately 40°C and then into the second cooling stage 15b of the cooling heat exchanger 15, where the inert gas is cooled to a temperature of approximately -10°C and the solvent is condensed to be recovered in the recovery device 27, thanks to the second cooling fluid cooled to a temperature of approximately -25°C by the chiller 18.

The inert gas, without the condensed solvent, is then conveyed to the heating stage 15c of the cooling heat exchanger 15, where the final heat recovery takes place by means of the first cooling fluid which is released from the first cooling stage 15a of the cooling heat exchanger 15 at a temperature of approximately 34°C and is fed into the heating stage 15c of the cooling heat exchanger 15 to be cooled to a temperature of approximately 30°C by the inert gas which is at a temperature of approximately -10°C. The inert gas heated by the heating stage 15c of the cooling heat exchanger 15 to a temperature of approximately 10°C is then conveyed through the connecting duct D6 with the connecting valve 17 open to the regeneration ventilation means 11 to start a new closed- circuit cycle for the regeneration of the second adsorber 3.

This first regeneration phase ends when the control unit 8 detects that the inert gas released by the second adsorber 3 reaches a temperature of approximately 160°C.

The regeneration process may comprise a second regeneration phase, similar to the first regeneration phase, in which the inert gas passes through the preheating stage 21c of the heating heat exchanger 21 , where it is heated from a temperature of approximately 10°C to a temperature of approximately 50°C thanks to the condensation of the chiller refrigerant 18 in the preheating stage 21c of the heating heat exchanger 21.

For this purpose, the inert gas exiting the second adsorber 3 that is regenerated enters the exchange stage 15g of the cooling heat exchanger 15 at a temperature of 130°- 190°C during the second regeneration phase. Thanks to the exchange ducts D8, D9 between the exchange stage 15g of the cooling heat exchanger 15 and the exchange stage 21a of the heating heat exchanger 21 , the heat exchange fluid is heated from a temperature of approximately 60°C to a temperature of 110°-170°C by the heat of the inert gas in the closed regeneration circuit, so that: the inert gas is cooled from a temperature of approximately 190°C to a temperature of approximately 120°C in the cooling heat exchanger 15; the heat of the heat exchange fluid is recovered to heat the inert gas in the heating heat exchanger 21 ; the amount of cooling fluid required to cool the inert gas is smaller than in the known plants. The heat exchange fluid at a temperature of approximately 170°C is collected by exchange stage 15g of the cooling heat exchanger 15 and sent through the exchange duct D9 to the exchange stage 21a of the heating heat exchanger 21 , where the inert gas enters at a temperature of approximately 50°C and is heated to a temperature of approximately 115°C, while the heat exchange fluid is cooled to a temperature of approximately 60°C before being sent through the exchange duct D8 to the exchange stage 15g of the cooling heat exchanger 15 for a subsequent heat recovery cycle.

The inert gas is then heated from a temperature of approximately 115°C to a temperature of approximately 210°C in the heating stage 21 b of the heating heat exchanger 21 by the heating fluid heated to a temperature of approximately 250°C by the heater 31.

The heated inert gas is used in the second adsorber 3 to evaporate a further quantity of solvent and thus regenerate the respective layer 4. In this second regeneration phase, the inert gas released from the second adsorber 3, at a temperature increasing from approximately 160°C to 190°C and with a content of approximately 180 g/Nm³ of solvent, passes first into the exchange stage 15g of the cooling heat exchanger 15 to be cooled to a temperature of approximately 120°C, then into the first cooling stage 15a of the cooling heat exchanger 15, where it is further cooled to a temperature of approximately 40°C, and then into the second cooling stage 15b of the cooling heat exchanger 15, where the inert gas is cooled to a temperature of approximately -10°C and the solvent is condensed to be recovered in the recovery device 27, thanks to the second cooling fluid cooled to a temperature of about -25°C by the chiller 18.

The inert gas, without the condensed solvent, enters the heating stage 15c of the cooling heat exchanger 15, where the final heat recovery takes place by means of the first cooling fluid which is released from the first cooling stage 15a of the cooling heat exchanger 15 at a temperature of approximately 34°C and is fed into the heating stage 15c of the cooling heat exchanger 15 to be cooled to a temperature of approximately 30°C by the inert gas which is at a temperature of approximately -10°C. The inert gas released from the heating stage 15c of the cooling heat exchanger 15 at a temperature of approximately 10°C is sent through the connecting duct D6 with the connecting valve 17 open to the regeneration ventilation means 11 to start a new closed-circuit cycle for the regeneration of the second adsorber 3. This second regeneration phase ends when the control unit 8 detects that the temperature of the inert gas released from the second adsorber 3 reaches a temperature of approximately 190°C. In this phase, the solvent concentration in the inert gas is preferably 30-80 g/Nm³.

As explained above, during the first heat exchange phase the residual solvent contained in the layer 4 of the adsorber 3 which is finishing the regeneration process, i.e. the first adsorber 3 in the first heat exchange phase mentioned above or the second adsorber 3 in the present second regeneration phase, is evaporated to complete the regeneration process of the layer 4.

The regeneration process may also include a waiting phase, in which at least one adsorber 3, in particular the second adsorber 3 (on the left in the figure), has been regenerated and is at a temperature of approximately 190°C, awaiting the regeneration of another adsorber 3, for example the second adsorber 3 from the left in the figure, to exchange heat with this last adsorber 3 during its first heat exchange phase.

The following table shows a non-limiting example of a complete cycle, which can be carried out one or more times, of the present embodiment of the method, with the execution times in minutes of the adsorption process and the phases of the regeneration process of the four adsorbers 3 of the present embodiment of the plant, in which the first adsorber 3 is the first from the right, the second adsorber 3 is the first from the left, the third adsorber 3 is the second from the left, and the fourth adsorber 3 is the second from the right.

Therefore, a complete cycle of the present embodiment of the method lasts approximately 396 minutes and includes four adsorption processes of approximately 243 minutes and four regeneration processes of approximately 153 minutes, carried out in parallel but with phases staggered in time in each of the four adsorbers 4. In the regeneration processes two adsorbers 3 cooperate to exchange heat for approximately 45 minutes (or 54 minutes considering the waiting phase of one of the two adsorbers 3).

Variations or additions may be made by those skilled in the art to the embodiments described and illustrated herein, while remaining within the scope of the following claims. In particular, further embodiments may include the technical features of one of the following claims with the addition of one or more technical features described in the text or illustrated in the drawings, taken individually or in any mutual combination, and including equivalent characteristics thereof.

For example, the plant according to the present description may also include additional ducts, sensors, and/or valves. The stages of the heat exchangers may also be replaced by separate heat exchangers, although this results in a reduction in plant efficiency. Ducts that are to be connected to the inlet and outlet sides of an adsorber may be connected to each other upstream and downstream of this adsorber, respectively, so that they are grouped into a smaller number of ducts connected to the inlet side and/or a single duct connected to the outlet side.

Furthermore, terms used in the text and/or drawings are to be understood as inclusive terms, unless otherwise specified, so that for example the terms “a/an/one”, “comprising”, “including a”, “having two” or “provided with” mean respectively “at least one”, “comprising, but not limited to”, “including at least one”, “having two or more” or “provided with at least one”.

The values ited in the text include a tolerance of at least 5%, unless otherwise specified.

Claims

1. A plant for the recovery of solvents, which comprises at least three adsorbers (3), each comprising in turn at least one layer (4) of material suitable for adsorbing at least one solvent, wherein the layer (4) is arranged between at least one inlet side and at least one outlet side of an adsorber (3), wherein the inlet side of an adsorber (3) is connected to at least one inlet duct (D1) configured to introduce a gas with solvent to be adsorbed into the adsorber (3) and the outlet side of an adsorber (3) is connected to at least one outlet duct (D2) configured to release said gas from the adsorber (3) with a reduced quantity of solvent, wherein the adsorbers (3) are connected through inlet regeneration ducts (D4) and outlet regeneration ducts (D5) to at least one cooling heat exchanger (15), to at least one heating heat exchanger (21), to regeneration ventilation means (11) and to at least one inert gas source (9), so that inert gas released from the inert gas source (9) can be circulated by the regeneration ventilation means (11) from the outlet side of an adsorber (3) to the cooling heat exchanger (15) through at least one outlet regeneration duct (D5), from the cooling heat exchanger (15) to the heating heat exchanger (21) through at least one connecting duct (D6) and from the heating heat exchanger (21) to the inlet side of an adsorber (3) through at least one inlet regeneration duct (D4), characterised in that the cooling heat exchanger (15) is connected to the inlet side of one or more adsorbers (3) by one or more inlet cooling ducts (D10) provided with inlet valves (32) and the outlet side of one or more adsorbers (3) is connected to the heating heat exchanger (21) through one or more outlet cooling ducts (D11) provided with outlet valves (33), so that the inlet cooling duct(s) (D10) and the outlet cooling duct(s) (D11) connect the cooling heat exchanger (15) with the heating heat exchanger (21) through one or more adsorbers (3).

2. The plant for the recovery of solvents according to the preceding claim, wherein the outlet side of each adsorber (3) is connected by means of an exchange duct (D7) provided with at least one exchange valve (24) to the inlet side of another adsorber (3), so that all the adsorbers (3) of the plant are linked to each other through respective exchange ducts (D7) provided with exchange valves (24).

3. The plant for the recovery of solvents according to one of the preceding claims, wherein the heating heat exchanger (21) is connected through exchange ducts (D8, D9) to the cooling heat exchanger (15), so that a heat exchange fluid can circulate and exchange heat between these two heat exchangers (15, 21).

4. The plant for the recovery of solvents according to one of the preceding claims, wherein the cooling heat exchanger (15) is connected to at least one chiller (18) configured to cool a cooling fluid and circulate it in the cooling heat exchanger (15), wherein the chiller (18) is also connected to the heating heat exchanger (21) by means of cooling ducts (D12, D13), so that a cooling fluid of the chiller (18) can be circulated in the heating heat exchanger (21).

5. The plant for the recovery of solvents according to one of the preceding claims, wherein the cooling heat exchanger (15) comprises a first cooling stage (15a) configured to cool gas by means of a first cooling fluid, a second cooling stage (15b) configured to further cool this gas by a second cooling fluid colder than the first cooling fluid, and a heating stage (15c) configured to heat this gas by means of the first cooling fluid released from the first cooling stage (15a).

6. The plant for the recovery of solvents according to one of the preceding claims, wherein the heating heat exchanger (21) comprises a preheating stage (21c) configured to heat gas by means of a cooling fluid heated by a chiller (18), an exchange stage (21a) configured to further heat this gas by means of a heat exchange fluid heated by the cooling heat exchanger (15), and a heating stage (21b) configured to further heat this gas by means of a heating fluid heated by a heater (31).

7. The plant for the recovery of solvents according to one of the preceding claims, wherein the cooling heat exchanger (15) is connected to at least one collection device (23) configured to collect liquids condensed in the cooling heat exchanger (15), wherein the collection device (23) is connected through one or more ducts to at least one nebulizer (26) arranged in at least one adsorber (3) to nebulize these liquids onto the layer (4) of this adsorber (3).

8. A method for the recovery of solvents by means of a plant comprising at least three adsorbers (3), each comprising in turn at least one layer (4) of material suitable for adsorbing at least one solvent, wherein the layer (4) is arranged between at least one inlet side and at least one outlet side of an adsorber (3), wherein the inlet side of an adsorber (3) is connected to at least one inlet duct (D1) and the outlet side of an adsorber (3) is connected to at least one outlet duct (D2), wherein the adsorbers (3) are configured to carry out one or more times at least one adsorption process and at least one regeneration process one after the other, wherein in the adsorption process of an adsorber (3) a gas with solvent is introduced into the inlet side of the adsorber (3) through the inlet duct (D 1 ), a quantity of solvent contained in the gas is adsorbed in the adsorber (3) from the respective layer (4) and the remaining gas is released from the outlet side of the adsorber (3) through the outlet duct (D2), wherein in the regeneration process of an adsorber (3) inert gas is fed into the adsorber (3) and released from the adsorber (3) with a quantity of solvent desorbed from the layer (4) of the adsorber (3), characterised in that the regeneration process comprises a solvent recovery step, in which a first adsorber (3) of said at least three adsorbers (3) is cooled and solvent is removed from a second adsorber (3) of said at least three adsorbers (3), wherein inert gas is heated by a heating heat exchanger (21), is fed into the second adsorber (3), flows through the respective layer (4), is released from the second adsorber (3), is cooled by a cooling heat exchanger (15), is fed into the first adsorber (3), flows through the respective layer (4), is released from the first adsorber (3), and is fed into the heating heat exchanger (21).

9. The method according to the preceding claim, wherein the regeneration process comprises at least one heat exchange phase, in which inert gas released from the outlet side of the first adsorber (3) is fed into the inlet side of the second adsorber (3), flows through the respective layer (4), is released from the second adsorber (3), is cooled by the cooling heat exchanger (15), and is fed into the first adsorber (3).

10. The method according to the preceding claim, wherein the regeneration process comprises a first heat exchange phase and a second heat exchange phase, wherein the temperature of the cooling heat exchanger (15) in the first heat exchange phase is higher than the temperature of the cooling heat exchanger (15) in the second heat exchange phase.

11. The method according to the preceding claim, wherein the regeneration process comprises a defrosting phase, in which the cooling heat exchanger (15) cooling the inert gas is deactivated, between the first heat exchange phase and the second heat exchange phase.

12. The method according to one of claims 9 to 11 , wherein the regeneration process comprises an inertization phase of the second adsorber (3) which is carried out before the heat exchange phase and in which inert gas is fed into the second adsorber (3), flows through the respective layer (4), is released from the second adsorber (3), is cooled by a cooling heat exchanger (15), and is released in at least one adsorber (3) which is carrying out the adsorption process.

13. The method according to one of claims 8 to 12, wherein liquids condensed in the cooling heat exchanger (15) are collected by at least one collection device (23) and nebulized by at least one nebulizer (26) onto the layer (4) of an adsorber (3) which is carrying out the adsorption process.

14. The method according to one of claims 8 to 13, wherein the regeneration process comprises at least one regeneration phase in which the first adsorber (3) is not employed in this regeneration phase, while inert gas is heated by the heating heat exchanger (21), is fed into the second adsorber (3), flows through the respective layer (4), is released from the second adsorber (3), is cooled by the cooling heat exchanger (15), and is fed into the heating heat exchanger (21).

15. The method according to one of claims 8 to 14, wherein the phases of the adsorption process and the regeneration process are carried out by the plant according to one of claims 1 to 7.