WO2006056831A1

WO2006056831A1 - Method and apparatus for removing a pollutant substance from a gaseous fluid

Info

Publication number: WO2006056831A1
Application number: PCT/IB2005/003010
Authority: WO
Inventors: Nico Gualerzi; Danilo Bombardi
Original assignee: Ecociprea S.R.L.
Priority date: 2004-11-29
Filing date: 2005-09-16
Publication date: 2006-06-01
Also published as: ITMI20042296A1

Abstract

It is disclosed an apparatus for removal of at least one polluting substance from an air flow in which the flow containing the polluting substances is caused to pass first through a humidifier (7) designed to selectively transfer a given substance into the flow by coalescence and then through a thermal head device (4) maintained to a lower temperature than that of the flow in a gaseous phase. The device (4) involves condensing and/or frosting of part of the humidity and/or polluting agent present in the air flow which subsequently passes through a drop separator (5) set to remove drops or droplets present in the flow itself. The apparatus comprises at least three of the above mentioned modules and allows a dry air flow to be obtained at the exit which has a low content of polluting substances so that it can be admitted to the atmosphere being in compliance with the regulations in force.

Description

METHOD AND APPARATUS FOR REMOVING A POLLUTANT SUBSTANCE FROM A GASEOUS FLUID

The present invention relates to a method and the concerned process for removal of at least one polluting substance from a gaseous fluid.

In particular, the invention aims at removing polluting substances such as solvents dispersed in the form of vapours, gases, fumes, gaseous phases, and also droplets, from an air flow, so as to obtain an air flow at the apparatus outlet which complies with the regulations in force for admission to the surrounding atmosphere.

It is known that there are regulations both of Italian and international level imposing limits to the presence of polluting substances in the air or gaseous flows that are to be introduced into the surrounding atmosphere . Recently new regulations have been approved according to which said limits have been greatly lowered to conform them to the international provisions .

There are presently systems capable of enabling control of gaseous emissions of pollutants to the atmosphere , and in particular the most widespread systems appear to be the afterburning technologies and activated-carbon technologies .

It is to be pointed out first of all that in a great number of industrial sectors working operations are provided (such as painting of wood, metals and plastic materials, printing processes such as silk-screen, flexographic or rotary-press printing, pickling processes for preparation to painting and even some pharmaceutical processes for extraction of active ingredients) in which large use is done of chemical substances and in particular solvents that, during the 5 process or at the end of it, are dispersed in the air flow that is removed from the working region and must be treated before admission to the atmosphere, to be in compliance with the environmental regulations.

10 The afterburning technology substantially contemplates the presence of one or more incinerators or destructors that shall burn the polluting substances present in the gaseous flow before admission to the atmosphere.

15

This apparatus, in addition to involving a rather high production cost, also has high maintenance costs in particular if it is not possible to make it operate under self-thermal conditions, i.e. if combustion must

20 be constantly fed.

In addition, these apparatus have the further problem of generating secondary polluting agents (CO₂ or NO_x, for example) or also dioxin in the event sufficient 25. temperatures are not reached.

Also the activated-carbon typology enabling absorption of the ^• polluting substances has drawbacks and/or operating limits. In particular it is to be pointed out

30 that carbons generally absorb solvent in an amount of about 1/10 of their weight and therefore where important pollutant flows are present a very quick exhaustion of the depolluting capacity of the activated carbons occurs so that the latter are to be regenerated

35 by means of expensive external-regeneration operations. On the other hand, also use of activated-carbon apparatus with stripping technologies involves the necessity to build rather complicated chemical plants the costs of which can be compared with those of the thermal destructor briefly mentioned above and even higher.

Accordingly/ the present invention aims at substantially solving all the above mentioned drawbacks.

It is a main aim of the invention to make available an apparatus and a method for removal of polluting substances from a gaseous flow, and in particular from an air flow, enabling the apparatus costs as well as those for maintenance of said apparatus to be reduced as much as possible.

Another aim of the invention consists in providing an apparatus that can be used to remove a wide variety of polluting substances and that therefore can be made suitable for different industrial sectors while always ensuring compliance with the regulations in force.

It is a further object of the invention to enable observance of the regulations during all the industrial working steps, i.e. also during possible peaks of pollutant admission to the air.

It is finally an aim of the invention, to make available an apparatus and a method for removal and recovery of pollutants that can adapt itself to the most different operating requirements without particular structural modifications, i.e. to the presence of flows with great amounts of polluting substances or small amounts of polluting substances, or also to treatment either of important air volumes or smaller air volumes.

The foregoing and further aims that will become more apparent in the course of the present description are substantially achieved by an apparatus and the related process for removal of at least one polluting substance from a fluid in a gaseous phase in accordance with the features recited in the appended claims.

Further features and advantages will be best understood from the detailed description of a preferred but not exclusive embodiment of a process and the related apparatus for removal and recovery of polluting substances in accordance with the present invention.

This description will be taken hereinafter with reference to the accompanying drawings given by way of non-limiting example, in which: - Fig. 1 diagrammatically shows an apparatus for removal of a polluting substance from a gaseous-phase fluid in accordance with the invention;

- Fig. 2 is a block diagram of a further embodiment of the invention; and - Fig. 3 shows the apparatus seen in Fig. 2 in more detail .

In the figures the apparatus enabling purification of the polluted fluid 3 in a gaseous phase or state has been generally identified by reference numeral 1. Said apparatus will be in particular designed to operate on discharged gaseous fluids coming from different working typologies.

In particular it will be adapted for example to treat O

the exhaust flow from painting plants, plants for plastic material working, printing plants, pickling plants, but also plants in the pharmaceutical or cosmetic sector.

Obviously, the above mentioned sectors are only some of those in which air flows containing amounts of polluting substances, such as solvents for example, are generated.

Still by way of example, the apparatus to be described is arranged for removal and recovery of solvents such as alcohols, ketones, esters, aromatic or aliphatic compounds.

Obviously, said removal to which reference is done in the claims is capable of operating not only with the above mentioned solvents, but also with other polluting substances not listed in the following table (given by way of example only) .

Turning back to Fig. 1, the fluid flow in a gaseous phase 1:hat will generally consist of air, and at least one (or more than one) polluting substances present in the form of vapour, droplets and/or fumes within said flow will be forced to enter the apparatus through a suction inlet 2 to pass through the apparatus itself along a flow advancing direction 6.

The apparatus is provided with means 8 to generate an air flow within the apparatus itself. Generally this flow is already created by other sucking systems (different from those of the apparatus in Fig. 1) within the region in which the vapours of the polluting substances are generated, exactly to cause the air to be removed from this environment.

At all events the apparatus is provided with said further means 8 due to the fact that said apparatus causes a strong flow resistance while the flow is passing through and therefore, in order not to reduce suction at the inside of the manufacturing firm, one or more fans are used for complete recovery of the additional flow resistance caused by the apparatus itself.

Generally the air flow entering the apparatus of the embodiment in Fig. 1 will exactly have the same temperature as on its coming out of the working region at the inside of the manufacturing firm.

In the case of flexographic printing processes the air can even reach temperatures of about 50⁰C, as well as in the case of working operations for aluminium rolling; on the contrary, in the presence of mechanical washing an air flow at room temperature could be generated at the inlet.

At all events the apparatus in Fig. 1 is not generally intended for thermal treatment of the air before removal of the polluting substances; in particular it is not set to vary the temperature of the incoming air and it will be therefore necessary to modify the operating power and temperatures of the different devices depending on the temperature of the incoming air. Obviously exceptionally, should it be absolutely necessary to lower the temperature of the air entering the apparatus, an exchanger with well water or similar apparatus of known type could be also used, the costs of which are not very high.

Still with reference to the first embodiment, the incoming air first of all passes through a flow humidifier 7 selectively designed to transfer a given substance into the flow in a gaseous phase passing therethrough.

In particular, the humidifier used is an adiabatic humidifier acting by coalescence, of the type presently known on the market.

The adiabatic humidifier 7 actually is not always of fundamental importance for operation of the apparatus itself and use of same essentially depends on the conditions and type of the incoming air flow.

For instance, in flows with too small amounts of polluting substances, problems arise (also depending on the solvents used) because the solvents themselves have a • vapour pressure curve varying with the temperature variations.

Obviously the apparatus aim is to bring the vapour pressure to values close to zero (i.e. to obtain complete liquefaction of the solvent) .

Actually, observance of the parameters in force for admission to the atmosphere is reached by obtaining very low values of vapour pressure, in the order of 0.001, enabling compliance with the regulations in force even with very volatile solvents (such as some ketones or alcohols) .

It is to be pointed out however that variation of the vapour pressure based on the temperature also depends on the curve of saturation of the product. Therefore, if there are high percentages of pollutants in the flow, greater reductions are obtained; on -the contrary, if the flows have small amounts of pollutant it is necessary to decrease the temperature much more than in situations with higher percentages.

For instance, when working with isopropyl acetate it is sufficient a temperature decrease of about -30⁰C with saturated flows (2000-3000 milligrams per normal cubic metre) ; vice versa in the presence of only 50-100 milligrams per normal cubic metre, a temperature decrease to about -85⁰C would be necessary, which will involve clear energy problems as well as frosting problems and in general the necessity for complicated cryogenic apparatus adapted to reach such temperatures.

Under this situation the adiabatic humidifier 7 can be used to admit further polluting agent to the flow so as to decrease the temperatures as required for removal of same.

Obviously, also when very high amounts of pollutants are present that therefore are able to give rise to difficulties for sufficient drainage of same, introduction of an intermediate medium enabling the necessary reductions to be obtained is required.

Generally an azeotropic mixture will be created in the flow, which will be able to be easily drained. The same situation also occurs in the presence of very volatile or very hot polluting products, of such a nature that the vapour pressure is very high and does not enable frosting of said products. Under this situation use of the adiabatic humidifier 7 can be suitable to introduce substances acting as vehicles such as water or alternatively 2, 2, 4-trimethyl-l, 3- pentanediol monoisobutyrate, enabling the frosting temperatures to be raised, through creation of suitable azeotropic mixtures, to such values that pollutants can be removed.

In the presence of methyl chloride solidifying at -30⁰C generally it is not necessary to add any further substance acting as a vehicle through the adiabatic humidifier.

A further situation in which the adiabatic humidifier can be used is represented by working operations in which pollutant peaks under some work conditions are generated.

In this case the adiabatic humidifier 7 will be used only and exclusively when the air flow contains great amounts of pollutants and will be deactivated when said flow goes back to a smaller percentage of pollutants.

Obviously the adiabatic humidifier will be connected to a pump to wet the shields and cause coalescence of same. Such a pump can be activated through a timer

(i.e. wetting of the shield takes place every given time interval for a given period of time) or can be also connected to a pollutant detector deciding on activation and deactivation of the pump itself in an automatic manner.

Still looking at the apparatus in Fig. 1 and immediately downstream of the adiabatic humidifier 7 there is the presence of a thermal-head device 4 maintained to a lower temperature than the temperature of the fluid flow in a gaseous phase 3 to generate a very important Δt.

The device is passed through by the flow in a gaseous phase and causes condensing and/or frosting of at least part of the humidity and/or part of the polluting agent .

It is apparent that the first thermal head unit 4 passed through will mainly freeze the water as well as the pollutant portion that is mixed with water.

Obviously, this exchanger will also force part of the vapours, fumes or droplets to condense and they will coalesce downwardly and will most help in absorbing part of the pollutants reaching the flow.

It is also apparent that where substances that are very miscible with water (such as acetone) are present, the first unit will also draw out an important part of the polluting agent, while where the solvent is hardly miscible with water (such as methylene chloride) the first unit will be fundamentally used to remarkably lower the humidity of the air flow.

Obviously the geometry and the exchange surfaces of the thermal-head device 4 must be conceived depending on the sizes of the apparatus and the air and pollutant flows passing therethrough; however generally the same must be conceived in such a manner that the flow in a gaseous phase passes through the thermal head device 4 at an average speed between 1 and 2 m/s and preferably at the limit of the thermal exchange between 1.2 and 1.5 m/s.

At this point it is to be noted that obviously ice will tend, over a long period of time, to occlude the units and therefore at each predetermined time interval (30- 50 minutes for example; however this time interval will obviously depend on the operating conditions and sizes of the apparatus) it will be necessary to release the thermal head device 4 from the apparatus to enable defrosting of same using a water jet, for example.

Generally a thermal head of about 15°C could be sufficient for the first frosting/condensing operation. Actually the thermal head used is greater even if generally due to the water enthalpy the first thermal head unit generally does not go down beyond -5/-10⁰C, but in any case it usually works under 0⁰C.

Immediately downstream of the thermal head device 4 at least one drop separator 5 is present which is set to receive the drops or droplets already present in the flow or created during passage through the adiabatic humidifier and/or the thermal head device 4.

Generally this drop separator 5 is of a turbulence type to enable a better collection of said drops and is maintained to substantially the same temperature as that of the thermal head device to increase efficiency of same.

In this connection the drop separator 5 is made of metal material such as steel and is directly connected to the thermal head device so that it is maintained cold (in other words it acts as a further condensing means) .

Alternatively, use of a drop separator of a nature different from the turbulence type can be envisaged such as ceramic or sintered ceramic drop separators.

Generally the flow humidifier 7, thermal head device 4 and drop separator 5 define a first module A of the apparatus; generally the apparatus itself comprises at least two modules A, B and usually three modules A, B, C in sequential engagement with each other to be passed through by the flow to be treated.

Obviously the modules following the first one are of quite the same structure as the one previously described, the only changes being represented by the conditions of the incoming and outgoing air flow and the operating temperatures.

Generally the second module will have more problems for ice creation. On the contrary the third module will be passed through by substantially dehumidified and already cold air and the third thermal head device 4 will work at temperatures between -25° and -35° for example, also being able to reach temperatures of -100⁰C.

Obviously, refrigerating means 9 is provided which is adapted to generate the appropriate low temperatures in the thermal head devices 4. Generally this means consists of a compressor and a circuit using Freon as the work gas. If the apparatus embodiment shown in Figs. 2 and 3 is now examined, it is possible to see first of all that immediately downstream of the means 8 for generating the air flow within the apparatus itself there is a heat exchange unit 10 generally consisting of an air- air exchanger.

This heat exchange unit 10 can consist, by way of example, of a nest of boiler tubes or be in the form of a finned pack or still in a different form to enable thermal interaction between the incoming polluted fluid flow 3 and part of the low-temperature flow going out of the apparatus after purification.

In this manner the heat exchange unit 10 will act as a heat regenerator to enable energy regeneration to be obtained and will start lowering the temperature and creating the condensate (at least with reference to humidity and steam) of the polluted fluid flow 3 of which treatment is wished.

Immediately downstream of the heat exchanger a flow mixer 11 is further provided. In particular the polluted fluid flow 3 will be physically mixed with part of the cold-air flow coming out of the apparatus as shown in circuit in Fig. 2.

In particular the two flows will be put into contact with each other in a region 12 immediately upstream of the flow mixer 11 and will then pass through a mixing chamber enabling optimal mixing of same.

For instance, said flows can be mixed in a 1 to 1 ratio and the overall flow will pass through a series of baffles or surfaces acting as barriers for the condensate or the humidity/steam frosting as well as for part of the polluting products to be treated.

It is clear that this process will involve creation of ice at the surfaces of mixer 11 and therefore periodical defrosting cycles will be necessary to enable percolation of the solidified products.

It is also to be pointed out that the air flow coming out of the apparatus and to be mixed in the inlet region 12 can even have temperatures in the order of - 70⁰C, -80⁰C. Therefrom the polluted fluid 3 will pass into an air-cooling unit 13 shown in Fig. 2 and detailed in Fig. 3.

This air cooling unit 13 can be equivalent to a module A of the previously described type and will in detail comprise at least said thermal head device 4 and drop separator 5.

However, in the embodiment shown in Fig. 3 different elements will be present along the advancing direction 6 of the air flow.

A first space 14 is in particular provided to be used for possible accessories to be introduced into the apparatus.

Immediately downstream a de-atomiser 15 is provided which is immediately followed by a deflector 16.

Therefrom the flow enters the thermal head devices 4 of the type previously described wherein it encounters the drop separator 5 also of the previously discussed type. Optionally further free space to be used for possible accessories 17 can be provided. By means of the humidity of the heat exchange unit 10 and thanks to the flow mixer 11, in co-operation with the appropriate refrigerating means described in the following, temperatures even of -10O⁰C can be reached in the apparatus.

The dry air free of pollutants and at low temperature can be partly bled (through a bleeding and recirculation fan 18, for example) to be sent to the inlet region 12 and then further mixed with the polluted fluid flow 3 entering the apparatus .

The portion of clean air not used for recirculation will be on the contrary sent to the heat exchange unit 10 to perform the above described functions and will then be admitted to the atmosphere.

It is to be pointed out that use of the heat exchanger 10 and mixer 11 will enable an important energy regeneration because much more energy is required by the apparatus when there is a need for great decrease in temperatures.

It is apparent that obtaining a good energy regeneration enables important cost savings and therefore makes the _.apparatus competitive.

In this connection it is to be pointed out that the apparatus shown in Figs. 2 and 3 can operate in the region of the thermal head device 4 at temperatures even reaching -100⁰C with the outgoing clean air flow

(OUTLET) reaching temperatures between -70° and -9O⁰C.

It will be also recognised that in apparatus of the type shown in Figs. 2 and 3 the method of generating cold also appears to be of the greatest importance. Obviously with temperatures reaching -100^CC technologies utilising liquid nitrogen or exploiting cryogenic systems of known type can be used.

In this particular case, refrigerating compressors for medium temperatures (about -50⁰C as the operating temperature) of the screw type or also of the single- or two-stage piston type with use of Freon gas R 507 have been chosen for use.

For obtaining the cold with this type of compressors, a liquid receiver is placed downstream of the compressor to receive the Freon coming out of the compressor at high pressure and very hot.

Due to an inner pipe coil for heat exchanger the Freon coming out is cooled using Freon of the same circuit coming from expansion in the unit in the cold producing cycle (at temperatures of about -70⁰C.

In this manner the following advantages are achieved.

There is a first cooling of the Freon entering the circuit, and also heating of the Freon entering the compressor (in this way the Freon entering the compressor will have temperatures not exceeding -70°C, but temperatures of -30 or -40⁰C) . By operating the compressor (positive-displacement pump) in this manner there will be a differential pressure capable of giving refrigerating power.

Downstream of the liquid receiver the high-pressure hot

Freon starts being cooled to reach the laminating member. In particular, the Freon can be brought from about 70°C to temperatures in the order of 5-10⁰C corresponding to pressures of about 8 bars.

In detail, a phase of pre-expansion with a plate-type heat exchanger is carried out on part of the Freon so that the last-mentioned gas is expanded and mixed with the other gas to cool it in order to reach, during lamination, temperatures of about -20⁰C.

Thus the Freon gas R 507 can be laminated until pressures of about 0.45 bars so as to reach temperatures between -80 and -90⁰C.

It is also to be pointed out that the apparatus will also comprise at least one tank for collection of the polluting substance and the water separated from the flow (not shown) . The tank enables an at least partial possible separation of the water and the polluting substance by decantation.

In particular most of the solvents have a substantial immiscibility with the water and therefore three phases are generated in the tank by decantation, a heavier phase at the bottom of the container consisting of the pure heavier substance, an intermediate phase in which there is a size interference depending on miscibility of the liquids and a third upper phase consisting of the less heavy liquid in a pure form.

For instance, with a mixture of water and isopropyl acetate, the latter that is lighter will be on top in said tank, while the water will gather at the bottom and an intermediate interference region will be generated. At least one outlet will be present at the bottom to enable exhaust of the heavy substance. If a suitable conductivity/electric resistivity sensor applied to the outgoing fluid is used, said sensor or probe can be set on the heavy phase; when conductivity begins changing, it means that part of the interference portion is draining and therefore the outlet can be selectively closed exactly depending on the signal detected by the sensor.

In this way the heavy phase can be separated from the light one and it is necessary to exclusively treat the interference portion.

It is finally to be noted that the air flow coming out of the apparatus will be at low temperature and¹ therefore a completely dry flow. Said dry flow can be suitably heated by for example utilising the heat produced by the refrigerating means for generation of low temperatures and therefore can be re-used for drying artefacts or given closed environments where the working operations take place in such a manner that part of the heat that would be otherwise lost by dissipation can be regenerated.

Alternatively it will be possible to use the heat created by the pump to generate the cold in order to heat the air utilised for heating the internal environment in the manufacturing firm, in this case too being possible to regenerate part of the consumed energy.

An important possible use of the above described apparatus is to be pointed out, in particular in the presence of big flows of polluted fluid 3 (flows beyond 15,000 normal/cubic meter per hour, for example). With flows of this nature the electric consumptions become very high and the apparatus could not be convenient for use and/or the available current could not be sufficient. In this case common machines for removal and filtering could be used, which machines exploit absorption on activated-carbon filters, in particular two or more activated-carbon beds.

Vice versa, the apparatus shown in Figs. 1, 2 or 3 can be used with a reduced air flow (500-2000 normal/cubic metre per hour) to obtain deabsorption of the exhausted activated carbons .

In particular, by removing the activated-carbon bed that is exhausted for the presence of polluting substances, it will be possible to obtain deabsorption of same making an air flow devoid of humidity pass therethrough (in this manner the activated carbons will have a longer residual life because they suffer from humidity) and then using the apparatus in accordance with the invention to remove the polluting substances from the flow coming from the activated carbons.

In addition, by working on the carbons at low temperatures also dangerous isothermal reactions are avoided.

The invention achieves important advantages.

First of all the apparatus made in accordance with the invention is of simpler construction, operation and maintenance as compared with the solutions of the known art involving afterburning or use of activated carbons. The apparatus is adapted for recovery of a wide variety of solvents and polluting substances so that it can be utilised for many types of working.

In addition, it will be possible to contemplate use of one or more of the modules inserted in the apparatus and only and exclusively activate the devices that among the inserted ones are those strictly necessary for complying with the regulations in force. By way of example only, it will be possible to use none, only one, two or more of the adiabatic humidifiers depending on the flows and the requirements.

Finally the apparatus can be worked with simpler and cheaper operations as compared with the apparatus presently on the market.

Claims

C L A I M S

1. An apparatus for removal of at least one polluting substance from a fluid flow in a gaseous phase, characterised in that it comprises:

- a suction inlet (2) for introduction of a fluid flow in a gaseous phase (3) containing at least one polluting substance;

- at least one thermal head device (4) maintained to a lower temperature than that of the flow in a gaseous phase (3) to generate a Δt, said device (4) being passed through by the flow in a gaseous phase and involving condensing and/or frosting of part of the humidity and/or the polluting agent contained therein during passage therethrough; and

- at least one drop separator (5), preferably placed downstream of the thermal head device along an advancing direction (6) of the flow in a gaseous phase (3), set to collect drops or droplets present in the flow passing through.

2. An apparatus as claimed in claim 1, characterised in that it further comprises at least one flow humidifier

(7) designed to selectively transfer, preferably by coalescence, a given substance into the gaseous flow (3) passing through.

3. An apparatus as^' claimed in claim 2, characterised in that said humidifier (7) is an adiabatic humidifier, preferably an adiabatic humidifier operating by coalescence.

4. An apparatus as claimed in claim 2, characterised in that said humidifier (7) is placed upstream of the thermal head device (4) along the advancing direction ( 6 ) of the flow .

5. An apparatus as claimed in anyone of the preceding claims, characterised in that it further comprises means (8) to generate a fluid flow in a gaseous phase through at least the thermal head device (4) and the drop separator (5), said means (8) being preferably defined by one or more fans and being more preferably able to create at least one pressure increase in the flow which is equal to the flow resistance through the apparatus.

6. An apparatus as claimed in anyone of the preceding claims, characterised in that the thermal head device (4) is set to generate a ΔT with the flow of at least 15⁰C, the operating temperature of the device (4) being preferably lower than O⁰C and more preferably included between 0 and -10⁰C.

7. An apparatus as claimed in anyone of the preceding claims, characterised in that the flow in a gaseous phase passes through the thermal head device (4) at an average speed between 1 and 2 metres per second and preferably between 1.2 and 1.5 metres per second.

8. An apparatus as claimed in anyone of the preceding claims, characterised in that the drop separator (5) is of the turbulence type or alternatively of the ceramic type and is in particular maintained to substantially the same operating temperature as that of the thermal head device (4) .

9. An apparatus as claimed in claim 8, characterised in that the drop separator (5) is made of metal material, steel for example, and is directly connected to the thermal head device (4) .

10. An apparatus as claimed in anyone of the preceding claims, characterised in that it further comprises a heat exchange unit (10) placed upstream of the thermal head device (4) along an advancing direction (6) of the flow.

11. An apparatus as claimed in anyone of the preceding claims, characterised in that it further comprises a flow mixer (11) located upstream of the thermal head device (4) along an advancing direction (6) of the flow and adapted to mix the fluid flow (3) with a fluid flow at lower temperature.

12. An apparatus as claimed in claim 2, characterised in that the flow humidifier (7), thermal head device (4) and drop separator (5) define a first module (A) of the apparatus (1), the apparatus (1) comprising at least two modules (A, B) and preferably three modules (A, B, C) in sequential engagement with each other.

13. An apparatus as claimed in claim 12, characterised in that the second thermal head device (4) has an operating temperature, when working, which is included between -20 and -30⁰C.

14. An apparatus as claimed in claim 13, characterised in that the third thermal head device (4) has an operating temperature, when working, which is included between -25 and -35°C, and may even reach -100⁰C.

15. An apparatus as claimed in anyone of the preceding claims, characterised in that the inside thereof is thermally insulated from the external environment.

16. An apparatus as claimed in anyone of the preceding claims, characterised in that the fluid flow in a gaseous phase (3) is mainly defined by air.

17. An apparatus as claimed in anyone of the preceding claims, characterised in that the polluting substance is a solvent such as an alcohol and/or a ketone and/or an aromatic and/or an aliphatic compound and/or an ester.

18. An apparatus as claimed in anyone of the preceding claims, characterised in that it further comprises refrigerating means (9) to generate suitable low temperatures in the thermal head devices (4) .

19. An apparatus as claimed in anyone of the preceding claims, characterised in that it comprises at least one tank for collection of the polluting substance and the water separated from the flow, said tank also enabling possible at least partial separation of water and polluting substance by decantation.

20. An apparatus as claimed in claim 19, characterised in that the collection tank comprises at least one outlet for the heavier substance collected, said outlet being disposed at the tank bottom and in that the apparatus further comprises at least one conductivity/electric resistivity sensor for the outgoing fluid which is capable of generating a corresponding signal, and means for selectively closing the outlet depending on the signal detected by the sensor.

21. An apparatus as claimed in anyone of the preceding claims, characterised in that the flow coming out of the apparatus has a relative humidity close to zero.

22. An apparatus as claimed in anyone of the preceding claims, characterised in that the outgoing flow can be heated and used again to dry artefacts or closed environments.

23. An apparatus as claimed in anyone of the preceding claims, characterised in that the refrigerating means (9) generates heat which is used again to heat internal environments and/or the gaseous flow coming out of the apparatus.

24. A method of removing at least one polluting substance from a fluid flow in a gaseous phase, characterised in that it comprises the following steps:

- generating a fluid flow in a gaseous phase (3) containing at least one polluting substance;

- forcing passage of said flow through a thermal head device (4) maintained to a lower temperature than that of the flow in a gaseous phase (3) to generate a ΔT;

- condensing and/or frosting at least part of the humidity and/or the polluting agent during passage;

- separating drops/droplets from a flow in a gaseous phase (3) by use of at least one drop separator (5) , said separating step preferably taking place after said condensing and/or frosting step.

25. A method as claimed in claim 24, characterised in that it further comprises the step of humidifying said fluid flow in a gaseous phase (3) by means of a flow humidifier (7) designed to selectively transfer, preferably by coalescence, a given substance into the flow in a gaseous phase (3) passing therethrough.

26. A method as claimed in claim 25, characterised in that the humidifying step comes before the condensing and/or frosting step.

27. A method as claimed in claim 25, characterised in that the fluid flow in a gaseous phase (3) sequentially passes through at least two modules consisting of a flow humidifier (7), a thermal head device (4) and a drop separator (5) , said flow preferably passing through at least three of said modules.

28. A method as claimed in claim 24, characterised in that it comprises the further step of heating the flow coming out of the apparatus and the step of using the heated flow again to dry artefacts or closed environments .

29. A method as claimed in claim 24, characterised in that it further comprises the step of using again the heat generated by refrigerating means (9) designed to maintain the thermal head device (4) to a low temperature, in order to heat internal environments.