WO2007003450A1

WO2007003450A1 - Method for purifying gaseous waste containing volatile organic substances and apparatus for performing the method

Info

Publication number: WO2007003450A1
Application number: PCT/EP2006/061541
Authority: WO
Inventors: Stefano Cappellotto; Vitaliano Vidali
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-15
Filing date: 2006-04-12
Publication date: 2007-01-11
Anticipated expiration: 2007-10-15
Also published as: ITPD20050106A1

Abstract

A method for purifying gaseous waste containing volatile organic substances and the like, comprising the steps of: - sending into a scrubbing tower (11) a stream of air containing vapors of volatile organic substances or the like, - atomizing on the vapors of volatile organic substances a degreasing substance based on surfactants; - collecting the residual liquid in a disposal tank (13).

Description

METHOD FOR PURIFYING GASEOUS WASTE CONTAINING VOLATILE ORGANIC SUBSTANCES AND APPARATUS FOR PERFORMING THE METHOD

Technical Field The present invention relates to a method for purifying gaseous waste.

The invention also relates to an apparatus for performing such purification method.

The method and the apparatus according to the invention are particularly suitable for purifying air polluted by volatile organic substances originating from petroleum-derived products, such as solvents. Background Art

Pollution from organic solvent vapors is a problem which is particularly felt in many chemical industries but also in particular in painting apparatuses, such as those used in mechanical workshops, carpentry workshops, and other similar workplaces.

These volatile organic substances are so dangerous that the competent bodies of the various national and supranational governments (such as for example the European Union) have passed laws which are increasingly strict with those who do not provide appropriately for the safety of their apparatuses.

The European directive on environmental responsibility covers two sectors in which this responsibility is regulated with different degrees of strictness: as regards certain hazardous activities, such as for example the activities of a chemical industry, the general responsibility in case of environmental damage falls on the entrepreneur.

The danger posed by volatile organic substances is clearly exemplified by their possible reaction with nitrogen oxide (NOx), which generates terrestrial (tropospheric) ozone. While ozone is an ally of humanity at high altitudes, where it has a protective action against ultraviolet rays, at ground level it becomes a dangerous toxic substance, which destroys plants, irritates the respiratory tract and becomes a greenhouse gas.

Apparatuses with activated-carbon filters are currently known and used extensively to suppress organic solvent vapors.

The air with the polluting vapors is made to pass through said filters, which are constituted by beds of activated carbon.

The activated carbon, thanks to its porous structure with a high adsorption capacity, retains by adhesion to the surface of the pores the substances dispersed in the air, until it is saturated.

Although these apparatuses are widely used and appreciated, they have drawbacks.

The first of these drawbacks relates to the high costs for disposal or regeneration of saturated filters, followed by the high initial and running costs due to the nonetheless limited average absorption capacities of activated carbon and to the support that such an apparatus requires.

As an alternative to activated-carbon filter apparatuses, combustors are also used in which the gaseous pollutants are oxidized thermally within a closed combustion chamber. Although these combustors have advantages such as good efficiency as a function of the combustion temperature and of turbulence, they have important drawbacks, such as the high energy cost and the possible production of further pollutants (NOx, SO₂, sulfurous acids, etcetera), which in turn have to be suppressed and disposed. Disclosure of the Invention

The aim of the present invention is to provide a method for purifying gaseous waste which is capable of obviating the drawbacks of known methods.

Within this aim, an object of the present invention is to provide an apparatus for performing a method according to the invention. Another object of the present invention is to provide an apparatus that is at least as safe and efficient as known types.

Another object of the present invention is to provide a method and an apparatus that are cheaper than known ones. Another object of the present invention is to provide a method that can be performed also with products that are easily commercially available.

Another object of the present invention is to provide an apparatus that can be set up easily and in a small amount of space in rooms and spaces from which it is necessary to purify the air. Another object of the present invention is to provide an apparatus that allows to dispose of the residual waste rapidly and in full safety.

Another object of the present invention is to provide an apparatus and therefore a method for purifying gaseous waste which can be produced economically with known technologies. This aim and these and other objects, which will become better apparent hereinafter, are achieved by a method for purifying gaseous waste containing volatile organic substances and the like, comprising the steps of:

- sending into a scrubbing tower a stream of air containing vapors of volatile organic substances or the like, - atomizing on said vapors of volatile organic substances a degreasing substance based on surfactants;

- obtaining purified air;

- releasing the purified air into the environment or into a subsequent additional scrubbing tower; - collecting the residual liquid in a disposal tank.

Conveniently, an apparatus for performing a method for purifying gaseous waste according to the invention is characterized in that it comprises at least one scrubbing tower, into which air containing vapors of volatile organic substances or the like is injected through an inlet, at least one atomizer being provided on the opposite side with respect to said inlet to spray the air stream with the surfactant-based degreasing substance in order to suppress said volatile organic substances, said at least one atomizer being arranged between said inlet and the outlet. Brief Description of the Drawings Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment thereof, illustrated by way of non- limiting example in the accompanying drawings, wherein:

Figure 1 is a front view of an apparatus according to the invention; Figure 2 is a top view of an apparatus according to the invention.

Ways of carrying out the Invention

With reference to the figures, an apparatus for performing a method for purifying gaseous waste containing volatile organic substances and the like, according to the invention, is generally designated by the reference numeral 10.

The apparatus 10 comprises at least one scrubbing tower 11, into which air containing vapors of volatile organic substances or the like is injected through an inlet 14.

Inside the tower 11, on the opposite side with respect to the inlet 14, there is an atomizer 15, which is suitable to spray the air stream with a surfactant-based degreasing substance in order to remove the volatile organic substances.

In the embodiment of the apparatus 10 according to the invention described here by way of non-limiting example, the atomizer 15 is suitable to spray the air stream in countercurrent.

Atomization in countercurrent facilitates the entrapment of the volatile organic substances by the sprayed degreasing substance.

The atomizer 15 is arranged between the inlet 14 and an outlet 16.

The inlet 14 is open on the lower part of the tower 11, while the outlet 16 is on the upper part, and therefore the air stream rises and the atomizer 15 acts downward, indeed in countercurrent.

Between the atomizer 15 and the outlet 16 there is a drop retention grid 17, which is suitable to limit the escape from the outlet 16 of the droplets of residual liquid generated by the reaction of the volatile organic substances with the atomized degreasing substance.

The bottom 18 of the scrubbing tower 11 is funnel-shaped in order to convey the residual liquid, which falls back into it toward a disposal tank 13.

The degreasing substance is sent to the nozzle of the atomizer 15 by means of a pressurized pipe 19, which in turn is connected to a pump 20 suitable to aspirate said degreasing substance from a supply tank.

In the embodiment of the apparatus 10 described here, the supply tank is constituted by the disposal tank 13 itself.

The residual liquid is collected on the bottom 18 and from there it is circulated by means of a supply tube 21 toward the tank 13.

From the tank 13, the residual liquid is returned into the tower 11 by means of the same atomizer 15.

At each use, the droplets of degreasing substance, by reacting with the volatile organic substances that are present in the air stream, incorporate said organic substances, increasing their own volume.

The same amount of degreasing substance is reused until it is saturated.

The tank 13, which initially is only partially filled with degreasing substance diluted according to requirements, is sent to a suitable disposal facility when it is completely full.

In the present exemplary embodiment, the tower 11 is constituted by a sealed cylinder, the only openings of which are constituted by the inlet 14, the outlet 16 and the hole, on the bottom 18, for the tube 21 for feeding the tank 13, in addition to the passage for the pressurized tube 19 for feeding the atomizer 15. The flow-rate of the air in input and its pressure, as well as the atomization pressure, the type of spray jet and the dimensions of the droplets that compose it (in relation to the shape of the nozzle) are parameters which must be modulated depending on the quantity and type of the volatile organic substance to be suppressed and of the degreasing substance that is used.

The apparatus 10 can comprise a single tower 11 or, as shown in the figures, can be composed of a plurality of towers in series, in order to improve the suppression of volatile organic substances with a sequence of scrubbing operations.

In the example of Figures 1 and 2, the scrubbing tower 11 therefore can be associated in a modular manner with a further identical scrubbing tower 12, by means of a duct 22 which is suitable to draw the air stream that exits from the outlet 16 of the first tower 11 and to divert the stream toward the inlet 23 of the subsequent second tower 12.

In the case of an apparatus with a plurality of towers in series, it is possible to provide, for each tower, a different type of atomization, by using in the one or more towers that follow the first one jets with droplets having smaller average dimensions, so as to achieve a more diffuse spraying and a gradually finer suppression of the volatile organic substances.

The method for purifying gaseous waste containing volatile organic substances and the like that can be performed with the apparatus 10 described above comprises the steps of:

- sending into the scrubbing tower 11 an air stream which contains vapors of volatile organic substances or the like, which arrive for example from an environment in which painting operations are performed;

- atomizing on said vapors of volatile organic substances a degreasing substance based on surfactants; - releasing the purified air into the environment or to a subsequent additional scrubbing tower 12; - collecting the residual liquid in a disposal tank 13. Preferably, and advantageously but not exclusively, atomization is performed in countercurrent. The degreasing substance is diluted according to requirements.

The surfactants of the degreasing substance are of a kind chosen among anionic, cationic, amphionic, nonionic surfactants or a combination of some of said surfactants.

In particular, the anionic surfactants of the degreasing substance are constituted selectively by alkyl benzene sulfonate, alkyl ethoxy sulfate, or a combination thereof.

The nonionic surfactants which, as an alternative, constitute the degreasing substance are constituted by polyethoxylated fatty acids.

The anionic surfactants are present in the degreasing substance in a percentage comprised between 0.5% and 5%.

Likewise, nonionic surfactants also are present in the degreasing substance in a percentage comprised between 0.5% and 5%.

Such anionic or nonionic surfactants react with the volatile organic substances that originate from the environment in which the painting operation has been performed and entrain the compound to the bottom of the tower by means of the droplets that convey them.

In practice it has been found that the invention thus described solves the problems noted in known types of apparatus and method for purifying gaseous waste containing volatile organic substances and the like. In particular, the present invention provides an apparatus which is at least as safe and efficient as known types, since the only energy that it requires to operate is the energy for driving the supply pump of the atomizer.

Moreover, the present invention provides a method and an apparatus which are cheaper than known ones, since there are no filters of any kind to be regenerated or disposed.

Further, the present invention provides a method which can also be performed with products which are easily commercially available.

Moreover, the present invention provides an apparatus which allows to dispose of the residual waste rapidly and in full safety by virtue of the sealed tank described above.

Further, the present invention provides an apparatus and a method which do not emit pollutant waste vapors in turn, differently from known types, since the residual waste is liquid and is accumulated in the disposal tank.

Still further, the present invention provides an apparatus and a method for purifying gaseous waste containing volatile organic substances which can be produced cheaply with known technologies.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. PD2005A000106 from which this application claims priority are incorporated herein by reference.

Claims

1. A method for purifying gaseous waste containing volatile organic substances and the like, comprising the steps of:

- sending into a scrubbing tower (11) a stream of air containing vapors of volatile organic substances or the like,

- atomizing on said vapors of volatile organic substances a degreasing substance based on surfactants;

- obtaining purified air;

- releasing the purified air into the environment or into a subsequent additional scrubbing tower (12);

- collecting residual liquid in a disposal tank (13).

2. The method according to claim 1, characterized in that said surfactants are preferably of a type chosen among anionic, cationic, amphionic, nonionic, or a combination thereof.

3. The method according to claim 1, characterized in that the anionic surfactants of said degreasing substance are constituted selectively by alkyl benzene sulfonate, alkyl ethoxy sulfate, or a combination thereof.

4. The method according to claim 1, characterized in that the nonionic surfactants of said degreasing substance are constituted by polyethoxylated fatty alcohols.

5. The method according to one or more of the preceding claims, characterized in that said anionic surfactants are present in the degreasing substance in a percentage comprised between 0.5% and 5%.

6. The method according to one or more of the preceding claims, characterized in that said nonionic surfactants are present in the degreasing substance in a percentage comprised between 0.5% and 5%.

7. The method according to one or more of the preceding claims, characterized in that the atomization of said surfactant-based degreasing substance on the vapors of volatile organic substances is performed in countercurrent.

8. An apparatus for performing the method for purifying gaseous waste according to one or more of the preceding claims, characterized in that it comprises at least one scrubbing tower (11), inside which air containing vapors of volatile organic substances or the like is injected through an inlet (14), at least one atomizer (15) being provided within said tower (11) to spray the air stream with a degreasing substance based on surfactants chosen among anionic, nonionic, or a combination thereof in order to suppress said volatile organic substances.

9. The apparatus according to claim 8, characterized in that said at least one atomizer (15) is arranged between said inlet (14) and the outlet

(16).

10. The apparatus according to claims 8 and 9, characterized in that said atomizer (15) is positioned and directed so as to spray the incoming air stream in countercurrent.

11. The apparatus according to claim 10, characterized in that a drop retention grid (17) is provided between said atomizer (15) and said outlet (16) and is adapted to limit the escape from the outlet (16) of the residual liquid droplets generated by the reaction of the volatile organic substances with the atomized degreasing substance.

12. The apparatus according to one or more of the preceding claims, characterized in that the bottom (18) of said scrubbing tower (11) is funnel- shaped in order to convey the residual liquid that falls back into it toward a disposal tank (13).

13. The apparatus according to one or more of the preceding claims, characterized in that said degreasing substance is sent to the nozzle of the atomizer (15) by means of a pressurized tube (19), which in turn is connected to a pump (20) which is adapted to draw said degreasing substance from a supply tank (13).

14. The apparatus according to one or more of the preceding claims, characterized in that said supply tank (13) is provided by said disposal tank (13) itself, said residual liquid being recirculated from the bottom (18) of the tower (11) toward said tank (13), from which it is returned into the tower (11) by means of the same atomizer (15).

15. The apparatus according to one or more of the preceding claims, characterized in that said tower (11) is constituted by a sealed cylinder, the only openings of which are constituted by said inlet (14), said outlet (16) and by the hole, on the bottom (18), for a tube (21) for feeding the tank (13), in addition to the passage for the pressurized tube (19) for feeding the atomizer (15).

16. The apparatus according to one or more of the preceding claims, characterized in that a scrubbing tower (11) can be associated in a modular manner with an additional identical scrubbing tower (12) by means of a duct (22) which is suitable to draw the air stream that exits from said outlet (16) of a first tower (11) and divert said stream toward the inlet (23) of a subsequent second tower (12).