GB1573349A

GB1573349A - Method and apparatus for the adsorptive separation of solvent vapours

Info

Publication number: GB1573349A
Application number: GB5048077A
Authority: GB
Original assignee: SPEZIALMASCHBAU EISENACH VEB
Current assignee: SPEZIALMASCHBAU EISENACH VEB
Priority date: 1976-12-15
Filing date: 1977-12-05
Publication date: 1980-08-20
Also published as: DD129520B1; DE2735568A1; IT1092169B; DD129520A1; JPS5393176A

Description

(54) METHOD AND APPARATUS FOR THE ADSORPTIVE SEPARATION OF SOLVENT VAPOURS (71) We, VEB SPEZIALMAS CHINENBAU EISENACH of Eichrodter Weg 132/144, DDR-59 Eisenach, German Democratic Republic, a Corporation organised under the laws of the German Democratic Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is concerned with a method and an apparatus for the adsorptive separation of solvent vapours from a current of air, particularly for dry cleaning machines, for the purpose of removing from the textiles, during the drying after the condensation phase, the last residues of the organic solvent used for the treatment, such as chlorinated hydrocarbons or fluorochlorinated hydrocarbons, and recovering them.

An activated charcoal adsorber consists essentially of a container having a sieve bottom on which the layer of activated charcoal lies, tube connections for passing a current of air containing solvents from top to bottom or from bottom to top through the container and additional tube connections for conducting the current of drying air in the same direction through the container and of a steam pipe which ends in a nozzle in the vessel and is disposed opposite to the direction of the current of charging air. The adsorber also comprises a condenser cooler for recovering a mixture of solvent and water vapour, a water separator for separating the cooled solvent from the water by the density principle, a fan for producing a current of drying air and an air heater for heating the latter.

It is customary for the container to be made of a high-grade steel alloy, since the action on the walls of the organic solvent, such as tetrachloroethylene, in conjunction with water, is extremely corrosive. Because of the corrosion which, nevertheless, occurs, its durability is inadequate. For this reason, it is known to use plastics materials for the endangered parts of the plant. It is, however, an open question which plastics material is really suitable for this purpose.

The course of the process in an activated charcoal adsorber is, in particular, characterised by the two phases of adsorption and desorption. Because of its property of adsorbing gaseous substances, activated charcoal can take up a certain amount of such substances and thus free the current of air from the substances in question, which is the real purpose, from the ecological and economic point of view, of using activated charcoal adsorbers. When the activated charcoal is completely saturated with such substances, a so-called break-through occurs, i.e. the current of air carrying harmful substances passes through the bed of activated charcoal without the harmful substances being retained: there is an urgent need for the saturation limit to be effectively recognised and indicated in good time.

Predetermination in the usual manner, based on experience, is the simplest method but has the disadvantage that, on the one hand, premature saturation may occur because of excessive loading of the activated charcoal, so that the break-through takes place unnoticed and, on the other hand, when the proportion of harmful substance contained in the current of air is low, the adsorptive capacity of the activated charcoal is not fully utilised which, from the economic point of view, is unacceptable. In an automatic process, it is, therefore, customary for the saturation of the activated charcoal to be determined from the concentration of gas in the outgoing air or by dielectric measurement of the layer of activated charcoal during charging. However, both methods are complicated and require expensive equipment, which is not acceptable for small sizes of adsorber.

After saturation of the activated charcoal has occurred, it is regenerated by desorption, i.e. the adsorbed solvent is driven out of the activated charcoal by means of water vapour.

The steam possesses the necessary desorption heat and serves as carrier for the liberated solvent. The greatest amount of solvent is freed at the commencement of the regeneration. After a short time the amount decreases asymptotically.

It is customary to limit the desorption on a time scale based on experience. Unfortunately, by this means, it is not possible for the true state of discharge of the activated charcoal to be determined and there is a danger that the activated charcoal will be steamed for too long a time, which is uneconomical, or for the activated charcoal to be left too heavily charged, so that its adsorptive capacity is not completely restored. For the limitation of the drying time in dry cleaning machines, it is known to use an apparatus which monitors the recovery flow from the drying system and operates a switch when a predetermined value is reached (see German Democratic Republic Patent Specification No. 41724).

After the desorption phase, the activated charcoal has to be dried to remove the accumulated water so that it will once again be adsorptive for the following charging cycle, drying being effected with a current of warm air. It is important to determine the correct degree of dryingiimitation or drying.

It is customary for the limitation of drying to be determined on a time scale based on experience. It is, however, a disadvantage of this method that the correct degree of drying is not achieved by this means, because the amount of water accumulated fluctuates.

Inadequate drying reduces the adsorptive capacity for the following charging, while excessively long drying is uneconomical because of the time wasted and the expense incurred. It has also been proposed to allow the drying air carrying water vapour to pass through a cooler in a closed circuit and to circulate the air until no more water is separated from the cooler (see Federal Republic of Germany Patent Specification No.

2,214,153). A disadvantage of this system is the expense for the cooling power employed solely to condense water.

It is an object of the present invention to provide an activated charcoal adsorption apparatus constructed in such a manner that it can be operated in a fully automated process and that the disadvantages indicated above are avoided.

The problem forming the basis of the pres ent invention is to provide a method and an apparatus for the adsorption of solvent vap ours for the purpose of monitoring the course of the process in machines of this kind and limiting the phases of the process in the optimum manner and also to find a suitable plastics material for the apparatus.

Thus, according to the present invention, there is provided a method of adsorbing solvent vapours from a current of air using a bed of activated charcoal in a container of glass fibre reinforced polyester, which container has inlets for the air containing the solvent, for purging steam and for heated air, and outlets for the cleansed air and for a mixture of desorbed solvent and steam, the air flow through the container being effected in an upward or downward direction and the supply of steam being effected in a direction opposite to that of the air flow, the adsorbtion being followed by regeneration of the activated charcoal which includes desorbing of solvent from the charcoal by steam and drying the charcoal by heated air, wherein during the adsorption phase, the temperature in the bottom and top regions of the bed of activated charcoal is measured and, when the two temperature values are substantially equal, an electric signal is given for terminating the adsorption; the solvent and steam are passed during said desorption to a cooler whence the condensate of solvent and water passes through a flow measuring instrument, the solvent effecting a switching operation for the termination of the desorption when a predetermined flow quantity of solvent is reached; and the temperatures in the container above and below the activated charcoal bed are measured during the drying phase and when the two temperature values are substantially equal a switching operation is effected for terminating the drying of the activated charcoal.

In a modification of the foregoing method, during the drying phase the temperature of the air current is measured after passing out of the bed of activated charcoal and, when a predetermined temperature value is reached, a switching operation is effected for terminating the drying.

The present invention also consists in an apparatus for the adsorption of solvent vapours from a current of air, comprising an adsorption device which includes a bed of activated charcoal in a container of glass fibre reinforced polyester, the container having inlets for the air containing the solvent, for purging steam and for heated air and outlets for cleansed air and for a mixture of solvent and steam, the inlets and outlets for air being so arranged that air flow through the container is effected in an upward or downward direction and the inlet for the steam being so arranged that steam flow is effected in a direction opposite to that of the air flow, the container being in conduit connection with a condenser cooler for the mixture of solvent and steam and with a fan provided with an air heater, a flow measuring measuring instrument being connected to the condenser cooler downstream thereof, which instrument is in turn connected via a control device to a valve in a pipe for the purging steam, temperature sensors being located in the lower and upper region of the activated charcoal bed and connected via a control device to a signal device, and further temperature sensors being located in said container above and below the activated charcoal bed and connected via a control device to a valve of the air heater.

In a modification of the apparatus, instead of said further temperature sensors, there is arranged, in a chamber downstream of the bed of activated charcoal in the direction of flow, a temperature sensor which is connected to the valve of the air heater via a control device.

In order that the invention may be more readily understood, reference is made to the accompanying drawing which illustrates diagrammatically and by way of example, an activated charcoal adsorption device according to the present invention.

The most prominent part of the apparatus is an activated charcoal adsorber 10, which comprises a container 11 having a detachable lid 12, a sieve bottom 13 with activated charcoal 14 lying thereon, an upper chamber 15, a lower chamber 16, a pipe 34, which ends in a nozzle 36 in the lower chamber 16, and connections for pipes 37, 38, 66 and 67. By way of the pipes 37 and 38, the adsorber 10 is connected, for example, to a dry cleaning machine 39. A characteristic of the present invention is the provision of temperature sensors 20 and 22, and of resistance thermometers 27 and 28, as well as of appertaining temperature monitors 21 and 23 and a switch relay 29. The temperature monitors 21 and 23 are connected, via a control line 25, to a current source 24 and a signal lamp 26. The resistance thermometers 27 and 28 are also connected via a control line 31 to a current source 30 and to the switch relay 29.

The switch relay is also connected via a control line 33 to a current source 32 and to a valve 64. A condensation device is provided for the adsorber 10. The device comprises a condenser cooler 40 having cooling water connections 41 and 42, a pipe 43 connection to the adsorber 10 and a pipe 44 connection to a flow measuring instrument 45. The flow measuring instrument 45 has outlet connections 46 and 47. In addition, the flow measuring instrument 45 is connected via a control line 48 and a current source 49 to a valve 35 of the pipe 34. A fan unit is also provided for the adsorber 10. This unit consists of a fan 60, a pipe 61 connection to an air heater 62 and a pipe 66 connection to the adsorber 10.

The adsorber 10 has a pipe 67 leading to the outside. The air heater 62 has a steam connection 63 with the valve 64 and a condensate connection 65.

According to the present invention, the vessel 11, the lid 12 and the sieve bottom 13 are made of glass fibre-reinforced polyester.

The choice of this material is of particular importance because it provides an appropriate combination of a number of improtant requirements which arise when operating an activated charcoal adsorber with an organic solvent such as tetrachloroethylene or the like. The polyester is a material which is resistant to the solvents mentioned and the glass fibre reinforcement offers adequate mechanical strength with regard to the loading and stressing of the components. Both component materials have outstandingly good properties for the designing and economical manufacture of the components.

Furthermore, the poor coefficient of thermal conductivity of the glass fibre reinforced polyester wall is advantageous for the necessary thermal insulation of the activated charcoal adsorber. We have, surprisingly, found that, with this choice of material, troublesome corrosion problems are overcome.

The apparatus works in the following manner: adsorption devices are increasingly used to meet the requirements of environment protection. Industrial air carrying harmful substances is passed through activated charcoal adsorbers before being discharged into the atmosphere. In the particular example of this embodiment, reference is made to the application of an activated charcoal adsorption device for a dry cleaning machine for textiles. In the dry cleaning of textiles, it is customary to remove the last traces of solvent from the clothing by adsorption towards the end of the drying phase. For this purpose, the drying air carrying the organic solvent, such as tetrachloroethylene, is passed out of the dry cleaning machine 39 through the pipe 37 to the activated charcoal adsorber 10. The current of air enters the upper chamber 15, is distributed over the entire cross-section thereof and is forced through the bed of activated charcoal 14.

The amount of activated charcoal is such that the solvent from a determined number of cleaning batches can be taken up, for example 25 batches, before it is saturated. When the current of air passes through the bed of activated charcoal 14, the solvent is deposited on the activated charcoal. The air freed from harmful substances collects in the bottom chamber 16 and is returned through the pipe 38 to the cleaning machines 39, where it is passed through the clothing and again charged with solvent vapours, whereupon recycling thereof to the adsorber 10 is commenced again. Two conditions, which the present invention utilises for control purposes, are characteristic of this adsorption process: 1. Given a suitable design of the adsorber, the activated charcoal adsorbs the adsorbate only in a limited layer of the entire activated charcoal bed. This layer passes through the entire activated charcoal bed in the direction of flow of the charged air, i.e. at the commencement of an adsorption cycle, the uppermost layer adsorbs until it is saturated. The adsorption zone is then displaced in the downward direction until, finally, the entire upper region is saturated and only the lowermost layer is then capable of adsorption. Finally, saturation is also reached in the last layer and the current of air containing solvent breaks through the layer of activated charcoal.

2. The adsorption is an exothermal process, i.e. thermal energy (the so-called adsorption heat) is liberated when the adsorbate is adsorbed by the activated charcoal.

Due to the heat liberated, the activated charcoal is heated in the layer in which adsorption is effected at the moment in question and in the following layers in the direction of flow.

During the operating state of an activated charcoal adsorber, there is thus always a temperature difference between the saturated and the unsaturated activated charcoal.

When the adsorbate is, for example, tetrach- loroethylene, this difference in temperature can be from 5 to 8"C.

The present invention utilises these temperature conditions in the activated charcoal as a variable for control purposes. Consequently, two temperature sensors 20 and 22 are provided in the activated charcoal bed 14. The temperature sensor 20 is inserted in the upper region and the temperature sensor 22 in the lower region of the activated charcoal bed 14. Temperature monitors 21 and 23 are associated with the two temperature sensors 20 and 22. These monitors are connected in series with the current source 24 and with the signal lamp 26, i.e. current flows and the signal lamp 26 lights up only when the contacts of both temperature monitors 21 and 23 are closed. This requirement is complied with when approximately the same temperature exists throughout the activated charcoal bed 14. The state of approximately equal temperature in the activated charcoal bed 14 is achieved when the entire activated charcoal is unsaturated, when the entire activated charcoal is saturated and when the adsorber has been out of operation for a long time. While the isothermal states when the activated charcoal is unsaturated and when the adsorber is out of operation are without interest for the control process and, for this reason, are blocked out in the control process, the present invention utilises the temperature state when the entire activated charcoal bed 14 is fully saturated for the purpose of producing a signal. In the practical case of application, the control system according to the present invention is arranged as follows: During the operating phase of the activated charcoal adsorber 10, for example when it is associated with a dry cleaning machine 39, when the current of drying air is switched over to adsorption, the current source is switched on at the same time and thus the control circuit (temperature monitors 21 and 23, control line 25 and signal lamp 26) receive voltage. If the activated charcoal is now saturated to some extent, a temperature gradient occurs from the saturated to the unsaturated region and this is detected by the temperature sensors 20 and 22, while the temperature monitors 21 and 23 ensure that the circuit remains broken until the end of the adsorption phase.

The signal lamp does not light up, thus indicating that the activated charcoal adsorber 10 can still be used for adsorption. If, during further adsorption, it now occurs that the adsorption zone has moved into the lowermost activated charcoal layer and that the undesirable break-through would thereupon take place, the temperature sensor 22, which is disposed exactly in the position where the activated charcoal is already saturated in this operating state, detects the saturation temperature of the activated charcoal, this temperature being that also prevailing in the entire saturated activated charcoal, i.e. also detected by the temperature sensor 20. The temperature monitors 21 and 23 assume the value of the saturation temperature. When identical temperature values are detected by the temperature sensors 20 and 22, the contacts of the temperature monitors 21 and 23 are closed. The control circuit is thus closed and the signal lamp 26 lights up to indicate that the entire activated charcoal bed 14 is saturated. The activated charcoal can no longer receive a current of air containing solvent. The signal produced in accordance with the present invention can also be an acoustic signal or can be used in order to interrupt the adsorption operation and initiate regeration.

According to a modification of the present invention, provision is made for the detection of the temperature difference between saturated and unsaturated activated charcoal during the adsorption process or for the detection of uniformity of temperature when the activated charcoal is in the saturated state by means of resistance thermometers disposed in the upper and lower regions of the activated charcoal bed 14. By means of the resistance thermometers, it is possible for the temperature difference to be detected absolutely independently of any predetermined desired value and with the aid of an appropriate switch relay and to produce a corresponding signal when the temperature difference no longer exists.

The present invention also includes a procedure according to which a signal given continuously throughout the entire adsorption phase indicates the complete saturation of the activated charcoal bed 14, while a signal which is given at the commencement of an adsorption phase, which is produced during the remainder of the adsorption process, or which does not occur until the end, indicates further readiness for adsorption.

This procedure particularly takes into account periodic adsorption operation necessary in a chronologically varying sequence where, from one charging pahse to the next, the difference in temperature between the regions of the activated charcoal which, for example, are already saturated and still unsaturated may be equalised and during a new charging phase the same temperatures may prevail at the measurement points, these equal temperatures resulting in the closing of the circuit and, consequently, the transmission of a signal to the apparatus of the present invention.

After saturation of the activated charcoal bed 14 with organic solvent vapours has been indicated in the manner according to the present invention, the activated charcoal must be regenerated by desorption and the solvent recovered. For this purpose steam is passed through the pipe 34 into the bottom chamber 16 of the activated charcoal adsorber. The valve 35 is opened by means of a control device (not shown). The steam is sprayed by means of the nozzle 36 and passes through the sieve bottom 13 into the activated charcoal bed 14. The steam supplies the necessary desorption heat and serves as carrier for the liberated solvent. The mixture of solvent and steam collects in the upper chamber 15 of the activated charcoal adsorber 10 and passes through the pipe 43 to the condenser cooler 40. Cooling water passes through the condenser cooler 40 in countercurrent. The mixture condenses in the condenser cooler 40 and, at the same time, is cooled in the bottom region to the necessary temperature.

The recovery flow passes through the pipe 44 into the flow measuring instrument 45. The flow measuring instrument 45 is constructed, for example, in accordance with the principles described in German Democratic Republic Patent Specification No. 41724.

In one compartment, the water is first separated from the organic solvent in accordance with the density principle and discharged through the outlet connection 46.

The solvent is thereupon passed through a measuring beaker of a weighing system and the amount thereof determined in accordance with the principle of constant emptying by means of a predetermined nozzle and of a decreasing inflow. As a result of the asymptotic decrease of the recovery, the measuring beaker is emptied after a period of time which can be determined on the basis of the diameter of the nozzle, the weighing system is there-upon swivelled and an electric switch relay connected thereto opens the control circuit for the valve 35, this circuit being shown in the form of the control line 48 and current source 49. The valve is thus closed, the admission of steam for the steam ing operation is shut off and the steaming of the activated charcoal is terminated in this manner. The solvent passes out of the flow measuring instrument 45 via the outlet connection 47. This method of limiting the desorption of the activated charcoal is highly appropriate for the desired purpose. Independently of any predetermined period of time, the degree of steaming-out is determined in accordance with the state of desorption of the charcoal, measured by the recovery flow which varies in proportion thereto.

With the apparatus of the present invention, there can be no inadequately or excessively steamed-out activated charcoal, the desorption being limited in an optimum manner, while the process can be automated. From the closing signal for the valve 35, it is also possible, at the same time, to obtain a signal for the continuation of the process.

After the desorption phase, the activated charcoal is dried. For this purpose, the fan 60 produces a current of air, which is fed to the air heater 62 through the pipe 61. The air heater 62 receives water vapour coming through the steam connection 63 and the open valve 64 and heats the current of air, which is then passed through the pipe 66 into the upper chamber 15 of the activated charcoal adsorber. In the upper chamber 15, the hot air is distributed over the entire crosssection and passes through the activated charcoal bed 14 from top to bottom. In so doing, it evaporates the water deposited on the activated charcoal and drives it out of the latter. The current of wet air then passes out of the activated charcoal adsorber 10 via the pipe 67.

For this phase of the operation, the present invention seeks to proportion the drying time in such a manner that, under the changing conditions of activated charcoal of varying dampness and with variable steam values, the activated charcoal will not be excessively dried or remain too wet, which would greatly restrict the renewed adsorptivity of the activated charcoal. For this reason, the temperature of the current of air upstream and downstream of the activated charcoal bed 14 is continuously detected during the drying process by means of the two resistance thermometers 27 and 28. The present invention makes use of the condition that, in the drying of the activated charcoal by means of the current of hot air, a difference in temperature upstream and downstream of the activated charcoal will occur because of the extraction of thermal energy from the air current as evaporation heat for the water humidity which is to be driven out. At the commencement of the drying operation, this temperature difference is very great, because the consumption of heat is high for the ini tially large proportion of water and, towards the end of the drying, decreases because no further heat is extracted. The activated charcoal is thus adequately dried if the temperature values of the air current upstream and downstream of the activated charcoal are substantially equal. At the commencement of the drying phase, the valve 64 is opened.

The admission of steam into the air heater 62 permits the heating of the drying air to about 100"C. When drying has been achieved, i.e.

the same temperature of about 100"C.

approximately prevails in the upper chamber 15 and in the lower chamber 16, the valve 64 is closed. Thus, the supply of thermal energy for the air heater 62 is interrupted and the current of air is no longer heated. In order to effect this switching operation at the desired moment of time, the resistance thermometers 27 and 28 are selected in conjunction with the current source 30, the control line 31 and the switch relay 29. If the temperature in the upper chamber 15 is different from that in the lower chamber 16, as is the case at the beginning, with temperature values of, for example, 100"C. and 50"C., and during the entire drying phase, in this control system a determined current flows because of the resistance values which vary analogously to the different temperature values.

This current flux produces, in the switch relay 29, the opening signal for the valve 64.

As the drying is achieved in the activated charcoal bed 14 and the temperature values upstream and downstream of the bed come close to one another, the current flowing varies, in the switch relay the contact is opened and, at the same time, the valve 64 is closed via the control line 33 connected to the current source 32.

As another possibility for the automatic termination of the drying process, the present invention provides for the arrangement of a temperature sensor with temperature monitor downstream of the activated charcoal bed 14 in the direction of flow. If constant conditions in respect of the pressure and temperature of the steam exist, there is selected for the temperature monitor a desired value which corresponds to the temperature when the desired state of drying of the activated charcoal is achieved. For this purpose, use is once again made of the know ledge that, at the commencement of the drying, with a constant inlet temperature of the current of hot air, the temperature downstream of the activated charcoal bed 14 will lie below the adjusted desired value in consequence of the heat of evaporation required in the activated charcoal and will reach the desired value in the course of the drying as the desired result is achieved. The temperature sensor measures the temperature variation during the drying process and, when the predetermined desired value is reached, a contact in the temperature monitor is opened and the valve 64 is closed. With the method and apparatus of the present invention, the process of drying the activated charcoal in adsorbers is also optimised and is automated in a reliable manner and with simple means.

After the valve 64 has been closed, the current of air is no longer heated. It is customary for the activated charcoal to be further cooled for a time with cold air. The regeneration of the activated charcoal is thus completed and the charcoal can be used again for adsorption

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tially large proportion of water and, towards the end of the drying, decreases because no further heat is extracted. The activated charcoal is thus adequately dried if the temperature values of the air current upstream and downstream of the activated charcoal are substantially equal. At the commencement of the drying phase, the valve 64 is opened. The admission of steam into the air heater 62 permits the heating of the drying air to about 100"C. When drying has been achieved, i.e. the same temperature of about 100"C. approximately prevails in the upper chamber 15 and in the lower chamber 16, the valve 64 is closed. Thus, the supply of thermal energy for the air heater 62 is interrupted and the current of air is no longer heated. In order to effect this switching operation at the desired moment of time, the resistance thermometers 27 and 28 are selected in conjunction with the current source 30, the control line 31 and the switch relay 29. If the temperature in the upper chamber 15 is different from that in the lower chamber 16, as is the case at the beginning, with temperature values of, for example, 100"C. and 50"C., and during the entire drying phase, in this control system a determined current flows because of the resistance values which vary analogously to the different temperature values. This current flux produces, in the switch relay 29, the opening signal for the valve 64. As the drying is achieved in the activated charcoal bed 14 and the temperature values upstream and downstream of the bed come close to one another, the current flowing varies, in the switch relay the contact is opened and, at the same time, the valve 64 is closed via the control line 33 connected to the current source 32. As another possibility for the automatic termination of the drying process, the present invention provides for the arrangement of a temperature sensor with temperature monitor downstream of the activated charcoal bed 14 in the direction of flow. If constant conditions in respect of the pressure and temperature of the steam exist, there is selected for the temperature monitor a desired value which corresponds to the temperature when the desired state of drying of the activated charcoal is achieved. For this purpose, use is once again made of the know ledge that, at the commencement of the drying, with a constant inlet temperature of the current of hot air, the temperature downstream of the activated charcoal bed 14 will lie below the adjusted desired value in consequence of the heat of evaporation required in the activated charcoal and will reach the desired value in the course of the drying as the desired result is achieved. The temperature sensor measures the temperature variation during the drying process and, when the predetermined desired value is reached, a contact in the temperature monitor is opened and the valve 64 is closed. With the method and apparatus of the present invention, the process of drying the activated charcoal in adsorbers is also optimised and is automated in a reliable manner and with simple means. After the valve 64 has been closed, the current of air is no longer heated. It is customary for the activated charcoal to be further cooled for a time with cold air. The regeneration of the activated charcoal is thus completed and the charcoal can be used again for adsorption purposes. The present invention has been explained in connection with an adsorption apparatus for a dry cleaning machine. However, it is not restricted solely to this field of application but can also be used for activated charcoal adsorbers for all fields of application. WHAT WE CLAIM IS:

1. A method of adsorbing solvent vapours from a current of air using a bed of activated charcoal in a container of glass fibre-reinforced polyester, which container has inlets for the air containing the solvent, for purging steam and for heated air, and outlets for the cleansed air and for a mixture of desorbed solvent and steam, the air flow through the container being effected in an upward or downward direction and the supply of steam being effected in a direction opposite to that of the air flow, the adsorbtion being followed by regeneration of the activated charcoal which includes desorbing of solvent from the charcoal by steam and drying the charcoal by heated air, wherein during the adsorption phase, the temperature in the bottom and top regions of the bed of activated charcoal is measured and, when the two temperature values are substantially equal, an electric signal is given for terminating the adsorption; the solvent and steam are passed during said desorption to a cooler whence the condensate of solvent and water passes through a flow measuring instrument, the solvent effecting a switching operation for the termination of the desorption when a predetermined flow quantity of solvent is reached; and the temperatures in the container above and below the activated charcoal bed are measured during the drying phase and when the two temperature values are substantially equal a switching operation is effected for terminating the drying of the activated charcoal.

2. A modification of the method claimed in claim 1, wherein, during the drying phase, the temperature of the air current after passing out of the activated charcoal bed is measured and, when a predetermined temperature value is reached, a switching operation is effected for the termination of the drying.

3. A method according to claim 1 of adsorbing solvent vapours from a current of

air, substantially as hereinbefore described and with reference to the accompanying drawing.

4. An apparatus for the adsorption of solvent vapours from a current of air, comprising an adsorption device which includes a bed of activated charcoal in a container of glass fibre reinforced polyester, the container having inlets for the air containing the solvent, for purging steam and for heated air and outlets for cleansed air and for a mixture of solvent and steam, the inlets and outlets for air being so arranged that air flow through the container is effected in an upward or downward direction and the inlet for the steam being so arranged that steam flow is effected in a direction opposite to that of the air flow, the container being in conduit connection with a condenser cooler for the mixture of solvent and steam and with a fan provided with an air heater, a flow measuring instrument being connected to the condenser cooler downstream thereof, which instrument is in turn connected via a control device to a valve in a pipe for the purging steam, temperature sensors being located in the lower and upper region of the activated charcoal bed and connected via a control device to a signal device, and further temperature sensors being located in said container above and below the activated charcoal bed and connected via a control device to a valve of the air heater.

5. A modification of the apparatus claimed in claim 4, wherein instead of said further temperature sensors, there is arranged, in a chamber downstream of the activated charcoal bed in the direction of air flow, a temperature sensor which is connected via a control device to the valve of the air heater.

6. An apparatus according to claim 4 for the adsorption of solvent vapours from a current of air, substantially as hereinbefore described and exemplified.