A METHOD FOR REMOVING A PARTICULATE MATTER FROM A GAS STREAM, IN PARTICULAR FROM AN EXHAUST GAS STREAM OF A FOSSIL SOLID FUEL POWER STATION, AND APPARATUS

THAT CARRIES OUT SAID METHOD

DESCRIPTION

Field of the invention

The present invention relates to a method and an apparatus for removing a particulate matter from a gas, in particular, from an exhaust gas stream that is produced in a solid fuel combustion plant, such as a coal power station.

Background of the invention

The need is felt of purifying particulate matter-containing gas streams, for example exhaust gas streams produced by solid fuel combustion plants. In particular, in case of modern coal power stations, the exhaust gas entrains a very fine particulate, which may lead to particulate pollution. This problem is particularly severe when a fossil solid fuel as anthracite is used.

The known systems for treating an exhaust gas are normally designed for an incineration plant exhaust gas, where a particulate matter is present whose composition and size distribution is usually quite different from the exhaust gas of fossil solid fuel power plants. Selective filters and special washing devices such as electrostatic precipitators are normally used to remove particulate matter from exhaust gas of solid waste material incineration plants, which usually involve high investment, operation and maintenance costs, and are affected by unsatisfactory effectiveness and reliability.

In US6479023 a system for converting the particulate matter of an exhaust gas that uses a generator of plasma is described. However, this system is not adapted to coal power plants, but is designed for antiparticulate filters for vehicles.

In WO2008/142441 a filter is described for capturing gas waste water and particulate matter, comprising a scrubber that is combined with an electrostatic filter. However, it is not adapted to work with the particulate matter of coal power systems, but with particulate matter based on S1O2.

In certain cases, to increase the particulate extraction efficiency, wet electrostatic precipitators or filters are used, such as the systems disclosed in US2347709, DE7520512, US6106592, GB1445753, US4360367, US2555216, US 4256468, US 4154585, WO2005099904.

These solid particulate removal devices cannot work efficiently when used to treat an exhaust gas delivered by a coal power station.

Moreover, they would absorb a huge amount of electric power in order to treat the high exhaust gas flow rate of a coal power plant.

A further limit of the existing filter plants is in the high costs of the filters and of the transformers, to achieve high voltages necessary for ionizing the particles.

Summary of the invention

It is therefore an object of the present invention to provide a method and an apparatus for removing a fine particulate matter from a gas, in particular, from a fossil solid fuel exhaust gas stream, which can capture combustion particulate matter in a way that is more effective and reliable than prior art methods.

It is a particular object of the present invention to provide such a method and apparatus that allow investment, operation and maintenance costs reduction, in particular, in the case of coal power stations.

It is another particular object to provide such a gas treatment device that can be installed within a pre-existing exhaust gas passage chamber, in particular, in a pre-existing chimney, with limited employment of materials and of resources.

It is another particular object to provide such a gas treatment device that has a low electric power consumption, and that at the same time can treat effectively a high exhaust gas flow rate of a coal power plant.

It is a further object of the invention to provide such a gas treatment device in which a cost-effective transformer is used, and that can achieve high voltages necessary for ionizing the particles. It is a further object of the invention to provide such a gas treatment device in which a high amount of CO2 can be captured, in order to reduce significantly the dispersion of combustion CO ₂ in the atmosphere.

These and other objects are achieved through a method for removing a particulate matter from a gas stream, in particular, from a fossil solid fuel exhaust gas stream, the method providing the steps of:

- arranging a couple of electrodes in a passage chamber for the gas;

- feeding the particulate matter-containing gas into the passage chamber so that the gas flows between the electrodes;

- spraying through the particulate matter-containing gas a predetermined water flow in a proximity of or within the electrodes;

wherein a treatment zone of the gas is created between the electrodes in which the gas is mixed with the water forming a water-gas cloud within the electrodes;

intermittently applying a discharge voltage between the electrodes, in order to generate between the electrodes intermittent electrical discharges that cross the cloud of gas and water in the treatment zone, such that the electrical discharges turn the gas-water cloud into a ionized status, and a matter redistribution takes place into a lighter purified gas and into a heavier condensate residue that can be removed separately from the passage chamber.

Advantageously, the discharge voltage is applied intermittently with a frequency of at least 10 cycles per second, such that between the electrodes a corresponding number of electrical discharges per second occurs.

Preferably, the discharge voltage is applied intermittently with a frequency of at least 50 cycles per second, and most preferably between 60 and 00 cycles per second.

Advantageously, the discharge voltage between the electrodes is at least 15000V.

In particular, the discharge voltage is set between 15000V and 100000V, preferably between 30000 and 50000V.

In a preferred embodiment of the invention, the discharge voltage is obtained by the following steps:

- providing a source of DC supply voltage; - transforming the supply voltage into the discharge voltage;

- intermittently charging a capacitor by the discharge voltage and discharging the capacitor between the electrodes, such that electrical discharges intermittently cross the cloud of gas and water in the treatment zone at each discharge step of the capacitor.

Advantageously, the step of transforming the supply voltage into the discharge voltage is achieved by an autotransformer.

Advantageously, the step of intermittently charging a capacitor by the discharge voltage and discharging the capacitor is obtained by an electronic switch that connects/disconnects the capacitor from one of the electrodes, the electrical discharges occurring when the switch disconnects the capacitor between a phase electrode and a grounded electrode.

The intermittent application of the discharge voltage to the electrodes has the advantage that, since the electrical discharges occur easily, a low power consumption and low amperage are necessary.

Advantageously, a scale removal step is provided of removing the heavier residue deposited on the electrodes. The scale removal step is preferably carried out by causing a sudden movement of the electrodes.

Advantageously, the method comprises forming a plurality of treatment zones between respective couples of electrodes. In particular, the couples of electrodes are interdigitated with respect to one another, i.e. all the electrodes of a first polarity are arranged parallel to one another at a prefixed pitch, and all the electrodes of a second polarity are arranged integral parallel to one another still at such prefixed pitch, such that all the electrodes are parallel to one another and two adjacent oppositely charged electrodes are spaced apart one half of the pitch.

Preferably, the pitch is set between 1 cm and 20 cm.

Preferably, the electrodes comprise conductor wires that are arranged to form a network, i.e. a grid, and the water flow is sprayed in order to cross the conductor wires, in particular, the water flow and the gas stream are transversal to each other.

Preferably, a pack of large grids is provided, each grid representing an electrode. In particular, each grid has sides set between 1 and 10m, such that said pack can fill as far as possible the hollow space within a chimney that forms said passage chamber

In particular, the gas has a temperature adapted to cause an evaporation of the water flow in the treatment zone and the water flow is supplied as a nebulised water flow, preferably it is supplied as a micronized water flow, such that an electrically conductive water mist is formed between the electrodes in order to form said water-gas cloud in the treatment zone.

The presence of a water mist, or of steam, increases the gas ionization rate and assists the production of the electrical discharges. In particular, a substantially continue succession of discharges is generated, according to the frequency, which assists the gas to be turned into a plasma, causing this transformation treatment to be more effective, even at relatively moderate electric field intensity.

Furthermore, the electrical discharge causes droplets of water to be formed that embed possible residual particulate matter. In other words, the presence of fine particulate matter in the gas, such as fine carbonaceous particulate matter produced by fossil solid fuel combustion, assists a droplet coalescence and/or a local new water condensation proximate to the particles, which enhances the formation of a heavier substantially liquid residue; such residue collects upon the electrode surface and finally falls down to a bottom zone of the passage chamber.

In certain thermodynamic conditions, a sudden expansion occurs during the passage of the electric discharges that causes a formation of ice droplets that embed residual particulate matter and quickly precipitate. In particular, the ice droplets entrap most of solid particles and also entrap carbon dioxide in a rate between 30 and 50%.

In particular, the gas is fed at a temperature of or higher than 150°C, which is a typical outlet condition of a of an exhaust gas exiting from a combustor, while the water is supplied at room temperature, for example at 15°C.

In particular, the gas temperature of the gas is higher than the feeding temperature of the supplied liquid water by at least 130°C. Advantageously, the supply voltage is set between 3000 and 10000 V. In particular, the supply voltage is set between 5000 and 7000 V, preferably the supply voltage is about 6000 V.

In particular, the passage chamber is a generally vertical passage chamber and the gas stream flows upwards inside the passage chamber.

Advantageously, a gas cleaning step is provided, preferably for washing the purified gas by further liquid water spraying.

The above-mentioned objects are also achieved by an apparatus for removing a particulate matter from a gas stream, in particular, from a fossil solid fuel exhaust gas stream, the apparatus comprising:

- a couple of electrodes;

- at least one water spraying member that is adapted to spray a predetermined water flow towards a proximity of, or within, the electrodes; wherein the couple of electrodes and the at least one water spraying member are arranged in a passage chamber that is adapted to receive the gas stream, wherein a treatment zone for the gas is created between the electrodes in which the gas is mixed with the water forming a water-gas cloud within the electrodes,

- an intermittent discharge voltage means, for intermittently applying a discharge voltage between the electrodes, in order to generate between the electrodes electrical discharges that cross the cloud of gas and water in the treatment zone, such that the electrical discharges turn the gas-water cloud into a ionized status and a matter redistribution takes place into a lighter purified gas and into a heavier residue that can be removed separately.

Advantageously, the intermittent discharge voltage means is adapted to apply the discharge voltage at a frequency of at least 10 cycles per second, preferably with a frequency of at least 50 cycles per second, and most preferably between 60 and 100 cycles per second, such that between the electrodes a corresponding number of electrical discharges per second occurs.

In a preferred embodiment of the invention, the intermittent discharge voltage means comprises:

- a source of DC supply voltage;

- a voltage transformation means for transforming the supply voltage into the discharge voltage; - a capacitor;

- a switch for intermittently charging said capacitor by said discharge voltage and discharging said capacitor between said electrodes, such that said electrical discharges intermittently cross said cloud of gas and water in said treatment zone.

Advantageously, said transformer is an autotransformer.

Advantageously, said capacitor is an electrolytic capacitor.

Advantageously, said switch is an electronic switch that connects/disconnects said capacitor from one of said electrodes, the electrical discharge occurring when said switch disconnects said capacitor between a phase electrode and a grounded electrode.

Advantageously, said transformer is adapted to transform said discharge voltage into a voltage set between 15000V and 100000V, preferably between 30000 and 50000V.

Advantageously, said source of supply voltage between the electrodes is set between 3000 and 10000 V, in particular between 5000 and 7000 V, preferably the supply voltage is about 6000 V.

Preferably, the apparatus comprises the passage chamber; the passage chamber is preferably a generally vertical passage.

In particular, the passage chamber is a chimney of a fossil solid fuel combustion plant such as a fossil solid fuel power station.

Advantageously, the apparatus comprises at least one water spray member adapted to spray liquid water in/through the gas stream.

Preferably, the apparatus comprises a plurality of couples of electrodes arranged according to mutually aligned surfaces.

In particular, the electrodes have a planar shape. In alternative, but without excluding any other construction, the electrodes may have a concentric closed cross section, for instance the electrodes may have a cylindrical shape.

In a preferred exemplary embodiment, the plurality of couples of electrodes are interdigitated with respect to one another, i.e. all the electrodes of a first polarity are arranged integral to a first support and parallel to one another at a prefixed pitch, and all the electrodes of a second polarity are arranged integral to a second support and parallel to one another still at the above prefixed pitch, the two supports facing each other such that all the electrodes are parallel to one another and two adjacent oppositely charged electrodes are spaced apart one half of the pitch.

The electrodes of such couples are preferably arranged along a gas flow direction within the passage chamber.

Preferably, each electrode comprises conductor wires that are arranged to form a net such as a grid, in particular, a plane or cylindrical grid. This way, a local concentration of force lines is obtained, i.e. a local electric field intensification at the net conductor wires, which assists gas ionization.

Furthermore, the net structure increases the surface available for deposition of the heavier residue.

Preferably, the conductor wires of the network have a linear extension of at least 1 linear meter per electrode surface unit.

Advantageously, the water spray member sprays water orthogonally with respect to the planar shape of the electrodes, such that the water passes through the mesh of the grid electrodes. In particular, the water spray member is arranged proximate to a wall of the passage chamber, and the gas flows towards a central part of the chamber in order to cross as many electrodes as possible.

Advantageously, a residue removal means is provided for removing the heavier residue that settle on the electrode/s. In particular, the residue removal means is adapted to impulsively move the electrode/s. In particular, the apparatus comprises a shake means for shaking each electrode. The shake means assists the heavy residue matter to fall down.

Advantageously, the passage chamber has a base portion adapted to receive the heavier residue and to create a liquid seal between the passage chamber and the outside environment.

Brief description of the drawings

The invention will be made clearer with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings.

- Figure 1 shows diagrammatically an apparatus according to the invention, mounted within a chimney of a combustion plant;

Figure 2 shows a block diagram of an exemplary embodiment of the method according to the invention;

- Figure 3 is a diagram of the intermittent discharge voltage means according to an exemplary embodiment of the invention;

- Figure 4 is a diagram of the intermittent discharge voltage means according to an exemplary embodiment of the invention;

- Figures 5 shows an arrangement of planar grid electrodes, according to an exemplar embodiments of the invention;

- Figures 6 and 6A show an arrangement of cylindrical grid electrodes, according to an exemplar embodiments of the invention;

- Figure 7 shows an arrangement of rod electrodes, according to an exemplar embodiments of the invention;

- Figure 8 shows an arrangement of planar grid electrodes, according to an exemplar embodiments of the invention with reference to the gas flow direction.

- Figure 9 shows an arrangement the apparatus of figure 1 according to an alternate embodiment of the invention.

Description of preferred exemplary embodiments

With reference to figures 1 and 2, there are described a method and an apparatus 10 according to the invention for removing fine particulate matter from a gas stream 1. In particular the method and apparatus 10 are well suited for removing a coal-containing particulate matter from a fossil solid fuel exhaust gas stream. Apparatus 10 is adapted to be mounted within a passage chamber 5, in particular a vertical passage chamber such as an existing chimney of a coal power plant, not shown.

Apparatus 10 comprises a plurality of couples of electrodes 11 ,12, that are arranged to form a pack 16 of parallel planes. A montage step 110 is provided (figure 2) in which pack 16 is arranged by conventional means, not shown, within a passage chamber 5, at a height H with respect to the axis 6' of a gas inlet duct 6. Pack 16 can be a pack of large grids, each grid representing an electrode. In particular, each grid can have sides set between 1 and 10m, such that pack 6 can fill as far as possible the hollow space within a chimney that forms said passage chamber 5. In particular, the length of pack 16 is obtained by the sum of distances between electrodes, in order to cover all the cross section of passage chamber 5 of the chimney; the width of pack 16 is the length of each grid, and the height of pack 16 is the height of each grid, chosen to maximize the treatment zone necessary to filter the exhaust gas.

In the exemplary embodiment of figure 1 , electrodes pack 16 comprises a plurality of couples of electrodes 1 1 ,12. Electrodes 1 1 ,12 of each couple of electrodes are electrically connected to respective terminals 13 and 14; such connection may be carried out before the montage step 1 10, i.e before arranging pack 16 within passage chamber 5, or may be a part of the montage step 110, in particular, if passageways are not available to introduce pack 16 into passage chamber 5.

Terminals 13 and 14 are electrically connected to a first terminal 30' and to a second terminal 30" of an intermittent discharge voltage means 30. Intermittent discharge voltage means 30 is adapted to apply a discharge voltage V _D preferably of at least 15000 V, preferably a discharge voltage V _D set between 15000 and 100000 V, more preferably between 30000 and 50000 V between terminals 13 and 14 (step 140) and, therefore, between electrodes 11 ,12 of each couple of electrodes.

In the exemplary embodiment of figure 1 , terminal 14 is set to ground by a grounding means 35- So, electrodes 121 are referred to as grounded electrodes 12, and electrodes 1 1 and terminal 13 are referred to as phase electrodes 1 1 and phase terminal 13, respectively. Phase electrodes 1 1 are mounted at a mutual distance or pitch S to a support 18 that can be in turn integral to phase terminal 13 and grounded electrodes 12 are at the same mutual distance S on a support that can be in turn integral to grounded terminal 14. The two supports are arranged such that phase electrodes 11 are parallel to grounded electrodes 12 and, preferably, such that the distance between each phase electrode 11 and at least one grounded electrode is equal to the half of pitch S. Such distance can be comprised between 1 and 50 cm, for example 15-20 cm.

As shown in figures 5 and 6, the couples of electrodes 1 1 , 12 define a treatment zone 3 that comprises a plurality of passage channels; pack 16 is arranged such that the passage channels are parallel to gas stream 1 direction. Gas stream 1 is fed (step 120) to treatment zone 3 (figures 5 and 6), where it is subject to discharge voltage V _D that is applied by intermittent discharge voltage means 30.

Moreover, apparatus 10 comprises a plurality of water spray members 19, adapted to supply a predetermined water flow 4 into passage chamber 5 (step 130), which creates a mixture with gas stream 1. Water spray members 19 are preferably fixed to passage chamber 5 internal walls by conventional means, in particular they are arranged at a portion H of a chimney 5, i.e. they are arranged between inlet duct 6 and the lower portion or support at a height below pack 16, or immediately above pack 16. In the exemplary embodiment of figures 5-7, electrodes 11 ,12 are crossed by water flow 4, and water spray members 19 are preferably arranged at a height which corresponds to the height of pack 16. This way, water flow 4 is directed towards the electrodes and can cross horizontally as many electrodes 11 ,12 as possible, in order to completely spray the inner regions of electrodes pack 16 and to create the most effective contact between gas stream 1 and water stream 4.

If gas stream 1 is fed at a temperature remarkably larger than 100°C, water spray members 19 are advantageously adapted to supply liquid water. Liquid water flow 4 may be, for instance, at room temperature. The heat exchange between hot gas and water can cause an at least partial evaporation of water flow 4, creating a highly electrically conductive gas-water cloud 15 between each positive or phase electrode 11 and corresponding closest negative or grounded electrodes 12.

Gas stream 1 may be at such a temperature as 150°C, which may be the case, for instance, of a cooled combustion exhaust gas after heat recovery. Water spray members 19 are preferably adapted to supply a water flow 4 consisting of very fine droplets, whose dimension preferably is of about some microns, such that the fraction of water flow 4 that remains in the liquid forms a very conductive water mist between electrodes 11 ,12.

If gas flow 1 is available and/or fed at a temperature equal or less than 100°C, the heat exchange rate may not be able to maintain a suitable evaporation rate. In this case, at least a part of water spray members 19 is adapted to supply steam instead of liquid water; a vapour source is then provided, not shown, which may be a plant steam network or a dedicated steam generator, which may use the same exhaust gas stream cooled before admission into chimney 5.

The thick succession of electrical discharges between the electrodes occurs at a desired intermittence frequency that can be of at least 10 cycles per second, and for example at least 50 cycles per second, and most preferably between 60 and 100 cycles per second,, such that between the electrodes a corresponding number of electrical discharges per second occurs.

The high discharge voltage V _D , and the presence of steam and/or finely dispersed liquid water between electrodes 1 1 ,12, represents a condition adapted for ionizing gas stream 1 by the electrical discharges, i.e. for turning the gas into a plasma. In such condition, a substantially continuous succession of electric discharges may be easily produced between electrodes 11 ,12, which in turn enhances plasma production. Furthermore, the presence of fine particulate matter in gas 1 to purify 1 , in particular, of fine particulate carbonaceous matter that is residue of the combustion of fossil fuel, assists the coalescence and/or the local new water condensation about the solid particles, and assists the formation of a heavier substantially liquid residue, which tends in part to accumulate on the electrodes and in any case falls towards below along the channels of treatment zone 3, advantageously defined between electrodes 11 ,12. Determined thermodynamic conditions can furthermore, assist the production of semisolid or solid aggregates 8 of ice about the particles, which fall below through the treatment zone 3 defined by electrodes 1 1 ,12 and reach a volume of liquid 9.

The electric discharges do not wear the electrodes 11 , 12, since the thick succession of intermittent electric discharge provides high voltage and low amperage electric discharges. Such low power discharges do not increase much the temperature of the cloud, and cause sudden expansion of the cloud, forming microparticles of ice that entrap the particulate matter, other gases and CO2. Such low power electric discharges are similar to those of a sparking plug in an engine, with high voltage generated and low amperage, capable of triggering ignition but consuming low electric power. In the present invention the thick succession of low power/high voltage electric discharges surprisingly lets to achieve all the objects of the invention. In a prototype practical example, V _S =6000V, V _D =45000V; distance between electrodes 17cm, pack formed by 10 electrode grids, having a height of 3500mm, width 1700mm, intermittence frequency 70 cycles per second, obtaining a very clean purified gas, with 50% C02 entrapped in the water and NOx and particles entrapped such that the purified gas of a coal power plant remain below minimum sensibility of detecting instruments.

The selection of water flow rate and temperature, the selection of discharge voltage VD and, secondarily, of the temperature of gas stream 1 feeding the exhaust gas stream 1 assists adjusting relative humidity, temperature and electric field intensity between electrodes 11 ,12. In a typical condition, in which exhaust gas stream 1 is available at about 150°C, water flow 4 is preferably supplied at a temperature close to 15°C; water spray members 19 are associated with a cold water 4 supplying network, comprising a chilling device, not shown.

The plasma state allows a molecular level redistribution of gas flow 1 components. In particular, particulate matter is parted into a lighter air-like purified gas 7, and into a substantially liquid or sludge heavier residue 8. The heavier residue contains water condensed on electrodes 11 and coal material. The coal material derives from coal residues contained in the exhaust gas flow 1 , and from other products of combustion, in particular CO2.

A means may be provided for shaking pack 16 in order to assist heavier residual 8 to be removed from the surface of electrodes 11 ,12. Such shake means may a conventional one, and therefore will not be described herein.

Heavier residue 8 falls down and collects at a bottom portion of passage chamber 5, creating a residue volume 9 defined by a residue head 9' and by the walls of passage chamber 5. A duct 21 is provided to allow the motion of heavier residue 8 from the bottom of passage chamber 5 towards a liquid seal device 22 where another residue head is formed, which allows removing heavier residual 8 from passage chamber 5 (step 160).

Figure 3 shows an intermittent discharge voltage means 30 according to an embodiment of the present invention. Intermittent discharge voltage means 30 is adapted to apply intermittent discharge voltage V _D to terminals 13,14 and therefore to each couple of terminals 11 ,12. Intermittent discharge voltage means 30 comprises a source (31) of DC supply voltage Vs, a voltage transformation means 32 suitable for transforming the supply voltage Vs into a prefixed discharge voltage V _D, and a capacitor 33 parallely arranged with respect to terminal 13,14. An intermittent switch device 34, in particular an electronic switch, is provided for intermittently connecting/disconnecting capacitor 33 from one of said terminals 13,14, and therefore from said electrodes 1 1 ,12, respectively, such that capacitor 33 is charged/discharged, i.e. the voltage between said couples of electrodes 11 ,12 intermittently rises to discharge voltage V _D and falls to ground voltage. Electrical discharges 26 occur when switching device 34 disconnects capacitor 33 between phase terminal 13 and grounded terminal 14, i.e. between phase electrodes 1 1 and grounded electrodes 12 through gas/water cloud 15 which is established in treatment zone 3.

Supply voltage Vs between the electrodes can be set between 3000 and 10000 V, in particular between 5000 and 7000 V, preferably is about 6000 V. However, it can be also 380V or less, depending on the existing electrical network in the area.

In Figure 3, transformation means 32 is represented as a transformer. As an alternative, Figure 4 shows an intermittent discharge voltage means 30 according to another embodiment, in which the transformation means is an autotransformer 32'. In the latter case, the autotransformer is very lighter than a transformer, and owing to the low amperage it is very effective to raise the voltage from the supply voltage to the discharge voltage, and allows to reduce substantially the investment costs.

Capacitor 33 is advantageously an electrolytic capacitor, which is lighter and provides very effective electrical discharges when the switch opens.

With reference to Figures 5 and 6, each electrode 1 1 ,12 may have a network structure, in particular a grid structure. In other words, each electrode may comprise a net comprising a plurality of conductor wires 25 mutually connected to form respective grid electrodes.

Conductor wires 25 are preferably made in a corrosion resistant metal.

Conductor wires 25 have a linear extension of at least 1 linear meter per surface unit. The grids may have a planar shape, as shown in figure 5, or may have a closed cross sectional: for instance, figure 6 shows a concentric arrangement of cylindrical grid electrodes. The grids can also have a shape different from the one shown in figures 5 and 6, preferably they may extend along a rotational surface, which allows a mutual arrangement forming linear passage channels 3 parallel to a possible direction gas stream 1 has during the passage through treatment zone 3; in case of a chimney, as in figure 1 and 9, a natural draft-induced flow direction.

Such grid-like dividing wall allows spraying water flow 4 across electrodes 1 1 ,12, in particular, water flow 4 and gas stream 1 are at a substantially right angle with respect to each other, as shown in figure 5.

Figure 7 shows an exemplary embodiment of electrodes pack 16, in which electrodes 1 1 ', 12' are conductive rods substantially perpendicularly connected to respective grid-shaped supports 18. As shown in figures 1 and 9, the supports 18 are arranged transversally with respect to gas stream 1 , and the electrodes are therefore aligned with direction 7 of gas flow 1.

In a further exemplary embodiment, shown in figure 9, electrodes pack 16 is arranged according at a lower height with respect to the position shown in figure 1 , so that gas stream 1 laterally impinges pack 16 after entering passage chamber 5 through inlet duct 6. In this case pack 16 has a permeable structure as shown also in figure 8, in order to immediately form a water-gas cloud in combination with water sprayed by nozzles 19 coming from the opposite side.

In a particular exemplary embodiment, as shown in figure 9, a plurality of further water spray members 24 is provided adapted to spray rinsing water 4' are provided within chimney 5 at a height 5' above electrodes pack 16, to wash purified gas 7 before delivering it to atmosphere through an outlet port 29 (step 150).

The foregoing description of an embodiment according to the invention will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.