WO1996032182A1

WO1996032182A1 - Apparatus for the purification of polluted air and related purification process

Info

Publication number: WO1996032182A1
Application number: PCT/IT1996/000067
Authority: WO
Inventors: Francesco Cirillo; Remo Pimpinelli
Original assignee: B.C.P. S.R.L.
Priority date: 1995-04-11
Filing date: 1996-04-10
Publication date: 1996-10-17
Also published as: EP0764044A1; JPH10503126A

Abstract

An apparatus made up of one or more sections, each of which is particularly active in reducing one, or a group, of pollutants characteristic of polluted air, is designed and sized in such a way as to be conveniently installed aboard a moving transport means or in a fixed site. The process carried out by said apparatus allows polluted air to be purified of carbon oxides, nitrogen oxides, sulphur oxides, ozone, unburned hydrocarbons, particulate, dust and in general the exhaust fumes from internal combustion engines, with a negligible energy expenditure when compared with the amount of air treated.

Description

APPARATUS FOR THE PURIFICATION OF POLLUTED AIR AND RELATED PURIFICATION PROCESS

DESCRIPTION The present invention relates to an improved apparatus and process for purification, with a minimum expenditure of energy, of an appreciable amount of air in a metropolitan area suffering from pollution by carbon, nitrogen and sulphur oxides, as well as from unburned particles, dust and exhaust fumes from internal combustion engines in general-

Technical Background The problem of atmospheric pollution in metropolitan areas due to the circulation of vehicles powered by internal combustion engines is universally known. Equally well known are the problems involved in finding a solution to this problem, even if it is only a partial one.

Mechanical filtering is not a suitable solution, because frequent cleaning is necessary and this would be unacceptable.

The use of electrostatic filters to capture ionised particles present in the air has no effect on the gaseous chemical pollutants, and also involves an excessively frequent removal and/or cleaning of the filters. Catalytic systems used for catalytic post-combustion of combustion products and for their purification from unburned elements are applied to gaseous fluids with a high concentration of combustion products, and are only active at temperatures much higher than that of the surrounding environment. This would involve a substantial consumption of energy for the specific purpose, and might result in environmental overheating.

The problem of polluted city air involves the following functions: reduction of dust, reduction of particulate and unburned hydrocarbons, reduction of the concentrations of sulphur, nitrogen, carbon oxides and ozone and possibly reduction of carbon monoxide. To reduce dust, particulate and unburned hydrocarbons, present technology provides systems such as dry filters or viscous filter of varying fineness and thus of varying filter capacities, electrostatic filters, dynamic filters (scrubbers) , damp filters and washing chambers.

None of the systems mentioned above can be used for the purposes indicated in the present invention to give a significant cost/effect relationship. Dry filters, viscous filters and electrostatic filters, in fact, all loose effectiveness as the filtered material accumulates, so that n the application in question, given the limited surface areas available due to reduced size, these systems would require frequent maintenance and cleaning, in the order of once every hour.

Dynamic filters normally used for separation of medium/large particles are of little effectiveness due to the size of the particles present in polluted city air, and in any case, to give the necessary flow rate of air to be treated, involve the use of separator fans, which are of a size unsuitable, for example, for installation on a moving vehicle or in a number of points within a metropolitan area. Damp filters and washing chambers, according to the working flow of air to be treated and the concentration of small dust particles, involve working dimensions that are excessive for the spaces available when installing on a vehicle or in a certain number of fixed points. The same can be said for the amount of washing liquid required, which would make it necessary to load the vehicle with a large amount of liquid if used according to current sizing criteria- International Patent Application No. W095/22395 to the same Applicant describes a mobile apparatus for the purification of polluted air in a metropolitan environment installed on a vehicle, which comprises an inlet section for the air to be purified, an oxidisation section following said inlet section, to oxidise CO into C0₂ and nitrogen oxides N0_X into N0_: by means of the action of nascent oxygen and a catalyst active at room temperature, a washing section following said oxidation section to purify the air from said higher carbon and nitrogen oxides and from S0₂ by reaction in solution in an aqueous washing solution, and a section for reduction of nascent oxygen or residual ozone by means of a catalytic filter, as well as for reduction of particles, dust and unburned substances. The process used in the apparatus described above is also described.

The above mentioned International Application W095/22395 thus provides, in a transportable form, an organic system for the overall purification of polluted air. For this reason the dimensions of the apparatus relate to average possible pollution levels for each of the pollutants, without making the apparatus more effective in the reduction of one particular pollutant or another. The above mentioned international application thus provides an effective solution for the purification of urban air characterised by pollution levels corresponding to ideal average levels, which can be identified in terms of the "warning levels" foreseen by current legislation, or levels higher than these, but always taking into account the polluting agents as a whole and not selectively.

It is not possible to increase the effectiveness of the system in treating one specific pollutant, without changing the sizing of the whole system and thus altering its effectiveness for all the other pollutants. In other words it is not possible to change the units that make up the system in order to eliminate or change certain sections according to the concentration of pollutants and/or on the basis of economic considerations.

Description of the invention Object of the present invention is an apparatus that provides a "selected" purification of air polluted with carbon, nitrogen and sulphur oxides, ozone, unburned hydrocarbons, particulate and dust, that is to say an apparatus that is structured in such a way that each component section is particularly active for the reduction of one, or the other of the above mentioned pollutants. It is therefore possible to size the system according to the specific characteristics of the air to be purified, encouraging reduction of those pollutants that are present in the highest concentrations and reducing (if necessary to zero) the sections destined for reduction of those pollutants whose level can be considered negligible.

The above is all to the advantage of simplicity and economy of production and operation.

Furthermore, the ability to size each active section regardless of the size of the other sections forming the apparatus and operating on other pollutants, allows additional operations to be carried out, a non-limiting example of which might be that of using the same apparatus to purify the exhaust fumes of the motor powering the vehicle that transports the apparatus, as well as the polluted air from the surrounding environment in which the vehicle itself is moving. Furthermore, these characteristics have surprisingly been shown as suited to position the apparatus itself not only on a moving vehicle, but also in fixed positions within the urban environment, so that the liquid discharged from the process can be disposed of in the normal urban drainage system in a continuous anti- pollution process. In effect, by means of the "selectively segmented" apparatus according to the present invention, the washing operation does not require large amounts of liquid, and likewise does not require a large amount of space, thus combining in a single apparatus the advantages of dynamic filters and those typical of washing chambers, without involving the problems mentioned above.

In short, an object of the present invention is an apparatus and the related process for the purification of air polluted by carbon, nitrogen and sulphur oxides, ozone, unburned hydrocarbons, particulate, dust and exhaust fumes from internal combustion engines in general, comprising in combination: a catalysis section to encourage transformation of N0 into NO; and of CO into CO; by means of a catalyst bed active at room temperature, in which in addition to or in exchange for catalysts made up of the oxides of elements from the First Series of Transition Elements in the Periodic Table, Pt or other noble metals are used, or alternatively the oxides and salts of Elements belonging to Groups 6 B, 7 B, 8 B, 1 B or 2 B of the Periodic Table, the apparatus being installed either on a mobile transport vehicle or positioned in a fixed installation within a metropolitan area, and the succession, type, number and size of the sections of the apparatus being selected according to the composition of pollutants in the air to be purified.

It has also surprisingly been found that the catalysts using Pt and/or noble metals from Group 1 B, which in themselves have a high unit cost, can be used at low concentrations on their catalytic support, while still giving a high simultaneous reduction of CO and 0₃ present in low concentrations in the polluted air. This activity can be greatly increased by heating these catalysts to relatively low temperatures, not exceeding 100°C.

Due to the above characteristics, an economic use of these expensive catalysts is possible, with a percentage by weight of the latter between 0.05 and 3% with respect to the total weight of the catalytic support, and a reduction of CO and 0₃ exceeding 40%, at a temperature of around 40°C or more.

In particular, the catalyst might simply be installed on the fins of a radiator in a motor-powered vehicle to provide a catalytic section for reduction of CO and 0₃ without adding the other sections of the apparatus described above, in order to obtain a useful result in terms of air purification.

Brief description of the drawings Figure 1 is a plan view of the version of the apparatus according to the invention destined for use on a moving vehicle; figure 2 is a plan view of the version of the apparatus to be used as a fixed installation; figure 3 is a plan view of an apparatus capable of being installed vertically within a newspaper kiosk; figure 4 is a plan view of an apparatus capable of being installed horizontally in a newspaper kiosk; figure 5 is a plan view of an apparatus installed in a kiosk selling newspapers or the like; figure 6 is a plan view of an apparatus installed in a space under the level of the road; and figure 7 is a plan view of an apparatus suspended in a tunnel.

Modes for carrying out the Invention

A typical application according to the present invention is illustrated in figure 1. The purification apparatus according to the invention is incorporated in a vehicle, or carried on the roof thereof. The vehicle, as a non-limiting example, may be an urban transport vehicle. This type of vehicle travels around the city streets during the whole of its working day, which can be calculated to last around 10 hours. As the apparatus in this example is a unit capable of dealing with a flow rate of around 4000 m³/h, it can be calculated that each vehicle of this type would be able to treat 40000 m³ of air per day for each unit installed. Furthermore, as working tests have shown that the apparatus according to the invention consumes approximately 4 kWh, it can easily be seen that a vehicle equipped as indicated above produces purified air during the day with a minimum energy cost compared with the energy produced by the vehicle to move, and with a positive effect on environmental parameters. The apparatus comprises an inlet section 3 for the air, served by a suction conveyor 16 provided with traps for dead leaves and other foreign bodies, in which a fan 4 conveys the flow of air to be treated, at a relatively low speed, to an oxidation section 5, by means of a catalysing section 18 in which transformation of NO- into NO; and of CO into CO; and of S0_X and SO; into SO_;. is encouraged by means of catalysts.

The catalysts used in this section comprise a base of oxides of a metal chosen from among those belonging to the I Series of the Periodic Table Transition Group, or oxides and salts belonging to Groups 6 B, 7 B, 8 B, I B and 2 B of the Periodic Table of Elements.

The oxidation section 5 serves to emit into the air flow an amount of nascent oxygen proportional to the amount of CO to be oxidised into CO;, of residual NO_x to be oxidised into NO; and generally speaking to the amount of oxygen necessary for oxidation of the pollutants passing through said section.

The air then accelerates inside a washing section 6, passing through a series of labyrinths in which the air is forced to pass through several water barriers, which may be chemically activated. This section has the job of retaining unburned hydrocarbons, particulate and dust by means of inertia and the pull exerted by the washing liquid. It also has the job of absorbing into the solution S0₂, S0₃, NO; and in part C0₂, thanks to the presence of surfaces coated with Zn and acting as a catalyst.

From section 6 the flow of air slows down in an accumulation section or stilling basin, where any water carried in it is separated from the air, which is then finally returned to the outside, after having passed through a catalysis section 15, in which it passes through a catalyst for total elimination of residual ozone and CO.

It can be seen that, as the apparatus object of the present invention is made up of sections, each of which is conceived and sized to carry out a prevailing function, it is possible to alter the embodiment without destroying the validity of the process.

A non-limiting example of this several possible alternative embodiments are described, resulting from the need to treat atmospheres characterised by different concentrations of the various pollutants.

Let us say that the apparatus is to be destined for treatment of air that is principally polluted with O_/. In this case, the size of section 18 must be increased, whereas if CO is only present in negligible quantities t is possible to reduce the size of the oxidation section to the minimum necessary to deal with NO_x, and that of section 15 to the minimum required to eliminate ozone and residual CO. If, on the other hand, it is necessary to purify air that is principally polluted with CO and ozone, without taking into account the other pollutants, the apparatus might be simplified, reducing it to sections 3 and 15 only, in which the catalyst would provide for reduction of the ozone present in the environment, and thus not produced by the special oxidation section, as well as conversion of CO into C0₂.

Forced oxidation of the above mentioned pollutant oxides, when required by the composition of the air to be treated, is obtained by the action of nascent oxygen. The nascent oxygen is generated by the decomposition of ozone produced in the oxidation section. The ozone is produced during passage of the air over a battery of lamps capable of producing ultra-violet light with a wavelength lower than 250 μ, or by a system generating high-voltage electric charges.

Normally speaking, the concentration of NO is three times lower than that of CO, so that sizing of the ozone production may differ greatly according to the composition of the air to be purified.

The ozone or nascent oxygen may also be produced by means of other physical or chemical processes, such as for example the formation of high-voltage electric charges.

In order to avoid release of the ozone into the atmosphere, it should be noted that the washing chamber and the accumulation chamber following the oxidation section are effective in reducing to oxygen any ozone that may remain after the oxidation process, and in any case the final catalysis section is sized in such a way as to remove all the ozone produced in addition to the amount of ozone that may be present in the air being purified.

With regard to the problem of reducing the concentration of harmful oxides, the state of the art essentially offers catalytic oxidation based on catalysts preferably made of precious metals such as platinum, gold, cobalt and the like, which, however, require high temperatures for activation. The present invention on the contrary makes it possible to use catalysts that are also active at room temperature, and in any case at temperatures of below 100°C.

According to the present invention, for oxidation of NOχ and N0₂, as well as those commonly used in the prior art, it is also possible to use catalysts based on Cr(IV) or NiO, suitably doped. For final elimination of ozone and CO in the apparatus according to the present invention it is possible to use catalysts based on Pt or other noble metals, or on oxides of a metal chosen from among those belonging to the First Series of the Periodic Table Transition Group, or oxides and salts belonging to Groups 6 B, 7 B, 8 B, I B and 2 B of the Periodic Table of Elements. Among these, along with platinum, mentioned above, it is possible to use gold, silver or oxides of iron, cobalt, nickel, manganese, copper, zinc, chrome, particularly cupric chromite. Although catalysis at room temperature using the catalysts mentioned above is in itself particularly effective, the catalytic effect can be still further improved by heating the catalysts, taking the heat from the exhaust gasses or from the cooling system for the engine powering the vehicle, without any additional energy requirement. As a non-limiting example, furthermore, it is possible to provide a section for catalysis of 0₃ and CO made up of a cooling radiator for the motor powering the vehicle, in which the heat exchanger fins are covered with catalyst. The reduction of S0₂, NO; and CO; downstream of the oxidation section 5 takes place mainly in the washing section 6 in which washing takes place by intimate contact with a washing liquid which, according to the composition of the air to be purified, may be water alone or an aqueous solution containing oxygen ions freed from substances such as calcium, sodium bicarbonate or the like, which, by reaction with the pollutant oxides, produce substances that are separated out in the liquid phase by filtration or precipitation. In effect, the following reaction products are produced: calcium nitrate from nitrogen oxide, calcium carbonate from carbon monoxide, and calcium sulphite from sulphur oxides, or the corresponding carbonates obtained from decomposition of bicarbonate to carbonic acid. In a preferred embodiment, the washing section is made up of a labyrinth within which the air follows a route containing a series of rapid 180° inversions of direction, accompanied by an equal number, or double the number, of washing barriers. Section 6 is in fact sub-divided by a series of dividing walls 10 defining a serpentine route, while a battery of delivery nozzles 11 spray the washing liquid against the metal walls, generating a find sub- division of the particles of liquid which encourages contact between the liquid phase and the gaseous phase and also produces a series of liquid barriers to passage of the air. The washing liquid collects on the bottom of section 6 and is sent to a recycling system, which comprises a filter device 12 and subsequently a decanting device 13, where the liquid is picked up by a pump 14 and recycled to the delivery nozzles 11. When chemically activated solutions are used, the decanting device 13 can be served by a delivery device 17 which restores the desired concentration of oxygen ions, measured using a pH-meter.

It should be noted that in the present invention the washing section does not only carry out the process of reducing the concentration of sulphur, nitrogen and carbon oxides, but also acts as a highly effective filter to reduce particulate, dust and unburned hydrocarbons, due to the mechanical pull provided by the washing barriers and by the rapid changes in direction along the route.

However, whereas the amount of washing liquid in circulation and the number of delivery nozzles must be proportionate to the concentrations of gaseous pollutants, the length of the route and the number of changes in direction must be proportionate to the amount of particulate, dust and unburned hydrocarbons to be eliminated.

It is thus also possible to "specialise" this section according to the composition of the air to be treated. For this reason, in figure 1 the section 6 comprises an element represented with a dotted line, indicating that the number of elements forming the section may be determined case by case according to the composition of the air to be treated. At the outlet from the washing section the partially purified air flow, which is still rich in atomised water particles, passes into the accumulation section 7 or stilling basin, where an increase in the cross-section of the flow slows down the mass of air, allowing precipitation of the drops of water, which collect on the bottom of the basin. Passing next through section 15, which contributes by filtering and catalysis to retain the liquid phase within the apparatus, to eliminate any residual CO and ozone, drastically reducing the concentrations thereof, and to protect against the entry of foreign bodies from outside, the purified air is then returned to the atmosphere.

A modular unit of the apparatus according to the present invention has been created for use on a moving vehicle, and the main characteristics thereof are given below as a non-limiting example. For treatment of a flow of polluted air of approximately 1800 mVhour the unit produced is formed by the juxtaposition of a suction section, an initial catalysis section, an oxidation section, a washing section, a stilling basin section and a final catalysis section, the whole contained within the overall dimensions of 550 x 980 x 4220 mm.

The washing section is made up of a parallelogram measuring 480 x 900 mm x 1200 mm, within which a route approximately 5 m long is formed with at least nine 180° changes of direction and at least nine washing barriers. The unit thus formed consumes less than 50 1 of water, with an autonomy of 10 hours continuous operation at 25° C and 60% relative humidity. The corresponding overall power consumption is 2.4 kWh. Suction is powered by a centrifugal fan with the following characteristics: capacity 1960 mVhour; prevalence 195 mm water; absorbed power 1.5 kW.

The oxidation section is sized in such a way as to optimise flow resistance, bearing in mind the presence of the obstacle created by the ozone-producing lamps. The number of lamps in operation, each of which is capable of producing approximately one g/hour of ozone, can vary according to the concentration of pollutants in the air to be treated.

The total flow resistance in the washing circuit is approximately 5.25 Kg/cm², the recycle pump 14 has a prevalence of approximately 10 Kg/cm², giving a flow rate of approximately 10 1/minute, with an absorbed power of approximately 0.4 kW. The washing circuit is sized so as to guarantee an autonomy of over 10 hours continuous operation with a total capacity of 80 1. The apparatus described above underwent experiments as indicated in the following.

Upstream of the apparatus, a chamber was installed, having a volume of approximately 1.5 m³, made of galvanised metal plate, within which, the clean air is mixed, in an adjustable ratio, with the exhaust fumes from two separate internal combustion engines, both kept at a constant speed: a 4000 cm³ diesel engine and a 1500 cm³ controlled ignition engine.

From this chamber the air, polluted to pre-set mixture ratios, was sucked up by the fan, on the outlet of which a sensor was installed to pick up samples of polluted air (upstream of treatment) . A second sensor was installed downstream of the device on the outlet flow of treated air. Over 1200 measurements were taken, using electro-chemical cells sensitive to the various pollutants, as well as colorimetric devices, checking the environmental conditions such as temperature, pressure and relative humidity and the total energy consumption in real time. For environmental conditions of between 10° and 35° C and between 35% and 70% relative humidity, the results obtained can be summarised as follows: CO:

- average value 8 ppm, reduction 70% — average value 14 ppm, reduction 65%

— average value 20 ppm, reduction 60%. NO_x: - average value 1500 ppb, reduction 85%

- average value 5 ppm, reduction 80%

- average value 20 ppm, reduction 75% S0₂: — average value 500 ppb, reduction approximately 100%

- average value 1500 ppb, reduction approximately 100%

C0₂: - average value 2800 ppm, reduction 20%.

Residual ozone on output: traces, below the instrument sensitivity level. Absorbed power: <2.4 kWh.

Duration of bath: >24 h of continuous operation. With reference to the embodiment of the invention installed on a moving vehicle, it is possible to carry out modifications and alterations without departing from the scope of the invention.

For example the suction section may be omitted or modified, if in practice suction can be achieved by making use of dynamic effects resulting from normal operation of the vehicle. Alternatively, an additional washing section can be provided upstream of the oxidation section for preliminary reduction of SO;, dust and particulate, which would result in the improved performance of the catalytic system adjacent to the oxidation section. The catalysis section itself can be installed upstream or downstream of the oxidation section. Furthermore, on the contrary, as mentioned before one or more of the sections described above may be eliminated if it is intended to eliminate one pollutant rather than another.

Furthermore, the apparatus illustrated in the examples has been designed as a separate modular unit to be applied to a vehicle not specifically constructed for the purpose, but it is understood that the apparatus can also be constructed during the manufacturing process of the vehicle itself to form an integral part thereof.

The present invention can also be used on a fixed installation, allowing purification of an appreciable quantity of polluted air, with a minimum consumption of power and without the intervention of operators either to work it or for maintenance purposes.

The apparatus can be sized and designed in such a way as to be suited for various different applications: it can be fitted within small newspaper kiosks, to be installed in metropolitan areas where there is a high level of atmospheric pollution (these kiosks can be designed in such away as to blend perfectly into the surrounding environment without disturbing the scenery) ; it can be installed within a special space formed under the road level; it can be positioned inside existing buildings overlooking or within the area in which the pollution level is to be reduced; or it can conveniently be installed within tunnels.

Using the catalysts described above, it has been found that it is not necessary, although it is of us'e, to activate the washing water with chemical reagents in case of a fixed installation, and that consequently the purification process can be continuous, for an indeterminate length of time, as the concentration of pollutants in the washing liquid is much lower than that allowed for discharge into the normal city drainage systems.

In a practical embodiment, the apparatus has been made in a modular version sized so that a unit can treat a flow rate of around 3600 mVhour; it can be calculated that each installation is capable of purifying up to 86400 m³ of air per day. The sizing can be varied according to specific needs. Furthermore, working tests have shown that the apparatus according to the invention has an energy consumption of approximately 4 kWh and a water flow rate of below 24 1/h, for a flow of treated air of 3600 m³/h. For a general plan of the apparatus, reference can once again be made to figure 1.

In figures 2 to 6, which represent various embodiments to be used as fixed installations, the elements corresponding to those indicated in figure 1 have been marked using the same reference numbers.

What has been stated above for the embodiment destined for use on a moving vehicle also applies to the embodiment for fixed installation, that is to say the various sections of the apparatus can be sized and positioned in a manner suitable for purification of specific pollutants. Furthermore, the fan 4 can be positioned, for instance, downstream of the oxidation section 5 without modifying the process. In all the possible alternative variations destined for installation above ground it is possible to fit the apparatus on a revolving platform, which performs a slow alternating rotation of +0° -360°, so that the suction and discharge ends of the apparatus point in different directions at different moments of time; furthermore in all cases the apparatus can be equipped with a pollution level sensor capable of detecting the mam pollutants (for example CO, N0_X and 0₃) which might control automatic start-up and shut down when environmental conditions return within pre-set limits.

Figure 2 shows an embodiment of the apparatus according to the invention suited for installation inside a newspaper kiosk, m which the route taken by the flow of air to be purified develops in a vertical direction. The air entering through the conveyor 16 and the pump 4 descends vertically through the oxidation section 5, including the lamps 8 for production of ozone and the catalyst bed 9.

The flow then passes through the washing section 6 containing the labyrinth dividing walls 10 and the water or washing liquid delivery nozzles 11, with a horizontal direction of flow for collection of the washing liquid on the bottom and its disposal directly into the drainage system (not shown) . In the air accumulation section 7 the flow returns to a vertical direction and passes through the catalytic filter 15 before coming out into the open at the top.

Figure 3 shows the direction taken by the flow of air in a newspaper kiosk made with a horizontal route.

This solution is preferred to the one illustrated above when conditions in the place of installation are more suited to a horizontal layout than to a vertical one.

Figure 4 shows an example of installation of the embodiment of figure 3 on the roof of a kiosk or newspaper stand, which is understood to be situated in an urban environment particularly polluted by the exhaust fumes of vehicles.

Figure 5 shows the possibility of installing the apparatus under the level of the road in order to avoid encumbering the urban environment.

Another possible use of the present invention is its installation in tunnels, as illustrated in figure 6, to reduce the level of pollution that is inevitably created due to vehicles in transit.

Several examples of embodiment will now be described with the process data found during operation of the apparatus.

Example 1

An apparatus was prepared with a suction funnel 16 with a size of 520 x 890 x 500 mm and a centrifugal fan with the following characteristics: capacity: 1960 mVh prevalence: 195 mm of water absorbed power: 1.5 kW three-phase induction motor belt drive arranged on a vertical axis to reduce working dimensions.

The fan discharged into a diffuser sized in such a way as to reduce the air speed on entry into the following oxidation section and to reduce flow resistance.

The oxidation section was sized in such a way as to optimise flow resistance, bearing in mind the presence of the obstacle created by the ozone-producing lamps.

The washing section provided for passage through 5 different water barriers, each of which obtained using 5 spray nozzles of the type hl/4 W11001, allowing a 110° jet aperture at 3 bar with a total flow rate of the 25 nozzles equivalent to approximately 10 1/min.

The total flow resistance within the circuit was approximately 5.25 Kg/cm2. The recycle pump 14 had a prevalence of approximately 10 Kg/cm² to give a flow rate of approximately 10 1/min. at an absorbed power of approximately 0.4 kW.

The UV lamps were 8 in number, each capable of producing approximately 1 g/h of ozone.

The experimental apparatus showed a consumption of washing water of 24 1/h even in the most severe working conditions foreseen for use, corresponding to a surrounding temperature of 35°C and a relative humidity of 30%.

Example 2 The apparatus described in example 1 was made to undergo testing in a similar manner to that described in example 1, but also using a probe installed downstream of the oxidation section in order to pick up samples of the oxidised air before the latter undergoes washing. Over 500 measurements were taken, using electro¬ chemical cells, in a variety of conditions in order to measure the pollution level, the environmental conditions (temperature, relative humidity, pressure) , the oxidation levels and the reagent type. The results obtained can be summarised as follows: with reference to the pollution level corresponding to the so-called "warning level" for urban pollution, it was found that even quite considerable variations in environmental conditions do not cause any notable variation in the effectiveness of the invention, with the exception of the amount of washing water consumed, which in any case is less than 20 1/h; in the conditions indicated above and with an ozone production equivalent to 2 mg/m³, the results obtained when washing with water alone are given below.

- CO: average value 14 ppm, reduction 58% (8.1 ppm); - NOχ (NO + NO;) : average value 5 ppm, reduction 80%

(4 ppm) ;

- S0₂: average value 0.5 ppm, reduction approximately 100%;

- C0₂: average value 2800 ppm, reduction 10% (300 ppm) ;

- residual ozone at outlet: traces <<0.1 mg/m³;

- flow rate of treated air: 1890 rnVh;

- absorbed power: <2.8 kWh;

- water consumption: <20 1/h. Example 3

Some experiments carried out on specially created experimental apparatus will now be described.

Apparatus A

This is made up of a suction funnel 16 with dimensions 520 x 890 x 500 mm and a centrifugal fan with the following characteristics: capacity: 1960 rnVh prevalence: 195 mm of water absorbed power: 1.5 kW three-phase induction motor belt drive arranged on a vertical axis to reduce working dimensions.

The fan discharged into a diffuser sized in such a way as to reduce the air speed on entry into the following oxidation section and to reduce flow resistance. The oxidation section was sized in such a way as to optimise flow resistance, bearing in mind the presence of the obstacle created by the ozone-producing lamps.

The washing section provided for passage through 5 different water barriers, each of which obtained using 5 spray nozzles of the type Hl/4 W11001, allowing a jet aperture at 3 bar with a total flow rate of the 25 nozzles equivalent to approximately 10 1/min.

The total flow resistance within the circuit was approximately 5.25 Kg/cm". The recycle pump 14 had a prevalence of approximately 10 Kg/cm^; to give a flow rate of approximately 10 1/min. at an absorbed power of approximately 0.4 kW.

The experimental apparatus showed a consumption of washing water of 6 1/h even in the most severe working conditions foreseen for use, corresponding to a surrounding temperature of 35°C and a relative humidity of 30%.

Apparatus B

This has the same structure, sizing and functions as apparatus A, but is characterised by the following differences: the oxidation section is equipped with a Cr and NiO based catalyst to accelerate oxidation of NO_x into N0₂; part of the washing water is continually renewed with the addition of a flow of 20 1/h and evacuation of the corresponding excess volume. Experimentation

The two apparatuses (A and B) described above were made to undergo experimentation as follows.

Upstream of the two apparatuses a chamber was installed, having a volume of approximately 1.5 m³, made of galvanised metal plate, within which the clean air is mixed, in an adjustable ratio, with the exhaust fumes from a 4000 cm³ diesel engine kept at a constant speed. From this chamber the mixed and polluted air was sucked into each of the apparatuses by the fan with which both are equipped, on the outlet of which a sensor was installed to pick up samples of polluted air (upstream of treatment) . A second sensor was installed downstream of the oxidation section in order to pick up samples of oxidised air before the latter undergoes washing.

A third sensor was installed downstream of each device on the outlet flow of treated air. Over 700 measurements were taken, using electro¬ chemical cells under different conditions to measure the level of pollution, environmental conditions (temperature, relative humidity and pressure) , the oxidation level, etc.. Apparatus A used as a washing liquid a solution of Na(OH) with a pH 12.5, apparatus B used water that was not chemically activated and which, as available at source, had a pH = 7.2.

The results obtained can be used as follows: with reference to the urban pollution level it was found that even extremely significant variations in environmental conditions do not result in significant variations in the effectiveness of the invention: results for apparatus A in the above conditions and with an ozone production level equivalent to 2 mg/m³, the results obtained with a washing liquid using a solution of Na(OH) in water were the following:

- CO: average value 14 ppm, reduction 60% (8.9 ppm); - NO_x (NO + N0₂) : average value 5 ppm, reduction 60%

(3 ppm) ;

- S0₂: average value 0.5 ppm, reduction approximately 85%;

- C0₂: average value 2800 ppm, reduction 10% (300 ppm) ;

- residual ozone at outlet: traces <<0.1 mg/m³;

- flow rate of treated air: 1890 rnVh; - absorbed power: <2.8 kWh;

- water consumption: <6 1/h. results for apparatus B in the above conditions and with an ozone production level equivalent to 2 mg/m³, the results obtained with a washing liquid using pure water were the following:

- CO: average value 14 ppm, reduction 60% (8.9 ppm);

- NO_x (NO + N0 ) : average value 5 ppm, reduction 90%

(4.5 ppm) ; - S0₂: average value 0.5 ppm, reduction approximately 100%;

- C0₂: average value 2800 ppm, reduction 20% (550 ppm) ;

- residual ozone at outlet: traces <<0.1 mg/m³; - flow rate of treated air: 1890 rnVh;

- absorbed power: <2.8 kWh;

- water consumption: <20 1/h.

The results given above confirm that apparatus B object of the present invention is particularly suited for fixed installations, whereas the other is more suitable for mobile installations. Example 4

A test on a prototype apparatus according to the invention as described in Example 1 was conducted by technical staff of ENEA (Italian Authority for New Technologies, Energy and Environment) with a pair of laboratory test apparatuses of their own and with data processed by a pair of Microwax computers. The test apparatuses were of the current mobile type used for tests on environmental pollution and the tests were carried out in a two-day scheduled program.

Upstream of the purification apparatus of the invention a metal chamber with a volume of 4 cubic meters was installed, in which polluted air was produced artificially by dilution into the environmental air of the exhaust from a diesel motor and an operation controlled motor. The dilution was controlled in such a way as to obtain a concentration of pollutants comparative with the characteristics of town smog.

A sensor mounted at the inlet of the purification apparatus took up polluted air continuously before treatment in the purification apparatus. This gas was directed to one test apparatus.

Another sensor identical to the first one mentioned above took up air at the outlet of the purification apparatus, and this was directed to the second test apparatus.

The two test apparatuses were identical and with exactly the same calibration.

For definite control during the first two hours of each day of test the same air was introduced into both the test apparatuses (first hour at air inlet, second hour at air outlet) and it was checked that the values measured in the different conditions were the same.

Two series of test were carried out for a six hour period each. After this time the measured values were automatically taken and processed by the two computers installed on board the test apparatuses.

The results of the second test session fully confirmed those of the first session. The results obtained are reported below.

First day Second day

Inlet Outlet Reduction % Inlet Outlet Reduction %

CO (ppm) 16.20 7.23 55.34 16.42 7.30 55.54

S0₂ (ppb) 107.65 14.55 84.02 184.72 23.55 87.25

N0₂ (ppb) 1422.73 9.85 99.22 1445.82 12.22 99.15

0₃ (ppb) 912.33 154.02 84.52 1092.25 163.32 85.05 Example 5

Tests were carried out to assess the efficiency of mixed catalysts in abatement of pollutants from the exhaust fumes of an internal combustion engine. The catalysts were of Fe oxide/Pt group of catalysts comprising noble metals.

1. Apparatus

Exhaust fumes from a 1300 cm³ motor vehicle diluted with environmental air were directed with a fan into the testing apparatus. Room temperature and flow rate were measured. CO concentration was measured at the inlet of a section in which 0.3 mg ozone per hour was produced. The flow was directed to a catalyst bed 100 mm thick and 100 mm diameter large. A heater was mounted before the catalyst bed. CO concentration was measured at the outlet with a similar instrument (Dragher Polytron, electrochemical cell 0 to 100 ppm CO, precision of 0.1 ppm) .

The outlet temperature Tu of air was measured by a PT 100. The outlet flow rate was measured by an anemometer with sensitivity 0.05 m/second.

2. Method a. Efficiency vs. operation time test This test was planned as follows. The apparatus was started with no catalyst. After 15 minutes for warming the motor, the catalyst was installed and the outlet flow rate controlled. The inlet CO was controlled at 15-20 ppm.

Readings were taken after 30 minutes and every subsequent 60 minutes by determining every 5 seconds the inlet and outlet CO concentration and the room temperature. b. Efficiency vs. outlet temperature test This test was planned as follows. The apparatus was started with no catalyst. The catalyst was installed after 15 minutes, the flow rate was measured and inlet CO was controlled to 15-20 ppm. First reading was taken after 30 minutes in operation and every 15 minutes the room temperature and the outlet temperature Tu were recorded until the CO abatement at room temperature had stabilised. A first 5 heating step was carried out by heating the catalyst for 20 minutes.

Reading was effected by taking 120 successive measurements, one every 5 seconds, of outlet and inlet CO and recording the outlet temperature Tu. 10 c. The following catalysts were tested.

Catalyst 1 Fe oxide/Pt, alumina tablets 3 mm Catalyst 2 Pt alumina tablets 3 mm Catalyst 3 Fe oxide/Pt alumina spheres, d = 3 mm Catalyst 4: Fe oxide (triple concentration) /Pt alumina 15 spheres, d = 3 mm

Catalyst 5 : Fe oxide/Pt granular coal Catalyst 6: Pt/Pd honeycomb.

The results of the tests for efficiency vs. operation time are shown on Table 1. 20

Table 1 Efficiency vs. operation time Catalyst 1 2 3 4 5 6 room temperature °C 30 to 40 - 26 to 35 25 to 30 33 to 40 18 to 22 operations time, hours 33 - 20 20 19 30 bed thickness, mm 100 - 100 100 100 75 flow speed, m/s 0.45 - 0.45 0.45 0.45 0.45 space velocity, hour-1 16200 - 16200 16200 16200 24,000 inlet CO, ppm 18 - 20 18 15 16 average CO abatement, % 33.5 - 26 24.7 36 21

The results of the tests for efficiency vs. temperature 25 are shown on Table 2. Table 2 Efficiency vs. operation time

Catalyst 1 2 5

Outlet temperature Tu, °^"CC CO abatement, %

15 17 15 15 15 15

20 17.5 16 15 17.5 21

25 17.5 18 17 21 29

30 18 21 18 25 34

35 22 25 18 27 40

40 30 27 19 30 48

45 37 33 21 34 58

50 50 48 30 43 68 CO average inlet cone, (ppm) 15 20 - - 15 bed thickness, mm 100 100 100 130 75 flow speed, m/s 0.45 0.45 0.45 0.35 0.50 space velocity, hour-1 16200 16200 16200 9700 24000 The space velocity is referrrreedd to the total mass of catalyst including the support

The results of the tests are discussed hereinbelow. The operational requirement of an apparatus according to the invention in environmental conditions is to abate about 8 over 16 ppm of inlet CO dispersed in the environment air, with an efficiency as constant as possible over a period of time even at low environmental temperatures and with as low a heat supply as possible.

Catalysts 1 and 3 show a good constancy over time, however they require a heat supply that is not negligible and appear to be sensitive to humidity. They can be considered as equivalent, with some minor differences in pressure drop in the air flow.

Catalyst 4 also requires some heat supply. The efficiency vs. temperature test on catalyst 2, compared to catalyst 1, shows an improved efficiency between 30 and 35°C. However a sufficient abatement is obtained only above a temperature of 45°C of the outlet air.

Catalyst 5 shows a performance superior to the preceding catalysts. The durability test (efficiency vs. time) carried out at a room temperature of 33 to 40°C shows an average abatement of 36%, whereas catalyst 1 shows an abatement of 33.5% at room temperature of 30 to 40°C.

Catalyst 5, however, is less dense than catalyst 1, so that it appears that a lighter mass thereof performs the same abatement as a heavier mass of catalyst 1.

The tests indicate that catalyst 6 shows a superior performance as to the amount of abatement (21% average from 18 to 22°C), particularly in the temperature test.

An acceptable amount of abatement is obtained already at a temperature of 35°C of the outlet air.

Moreover, the honeycomb structure can make it easier to solve some construction problems, and enables the available heat to be used for directly heating the catalyst rather than using the air flow for the same purpose.

Although the invention has been described in considerable detail, it will be evident to experts in the field that modifications and alterations can be made thereto without departing from the scope of the invention.

For example, the apparatus illustrated in the examples has been designed as an independent modular unit, more than one unit of which can be installed in the same place.

Claims

1. An apparatus for purification of air polluted by carbon, nitrogen and sulphur oxides, ozone, unburned hydrocarbons, particulate, dust and exhaust fumes from internal combustion engines in general, comprising in combination a catalysis section (18) to encourage transformation of NO_* into NO; and of CO into C0_; by means of a catalyst bed (9) active at room temperature, made up of the oxides of elements from the First Series of Transition Elements in the Periodic Table or CuCr_:0;;, an oxidation section (5) for the production of nascent oxygen, a washing section (6) for purification of the air from said superior carbon and nitrogen oxides and from S0₂, an accumulation section (7) in which the partially treated air travels at a low speed for separation of any particles of water that it may contain, a catalysis section (15) to complete elimination of 0₃ and CO by oxidation into CO; by means of catalysts of the type mentioned above, characterised in that: in addition to or in exchange for the catalysts mentioned above, Pt or other noble metals are used, or alternatively the oxides and salts of elements belonging to Groups 6 B, 7 B, 8 B, 1 B or 2 B of the Periodic Table or a mixture thereof, that are also active at room temperature; said apparatus is installed on a moving transport vehicle or is positioned in a fixed installation; said sections are selected as to their succession, type, number and size according to the composition of the pollution in the air to be purified.

2 . An apparatus according to claim 1, in which said catalyst is a metal or oxide or salt of an element of Group 8 B or 1 B of the Periodic Table or a mixture thereof having a concentration by weight lower than 3% with respect to the weight of the catalytic support and a temperature lower than 100°C, for the reduction of CO and 0₃ present in low concentrations in the air to be purified.

3. An apparatus according to claim 1 or 2, comprising an apparatus (12, 13) for separation of the pollutants collected in the form of a solution by the washing liquid and recovery and recycling of said liquid to said washing station.

4. An apparatus according to claim 1 or 2, in which said sections are contained within a container installed as a modular unit.

5. An apparatus according to any one of the preceding claims, in which said accumulation section is an accumulation chamber (7) with a collection basin that has an increased flow section in order to slow down the speed of the mass of air and separate out from said air the drops of washing liquid that are carried therein, which feeds a catalytic filter for final elimination of residual CO and ozone.

6. An apparatus according to any one of the preceding claims, in which said oxidation section comprises a battery of ultraviolet lamps (8) with a wavelength of below 250 millimicron for production of ozone in the air and formation of nascent oxygen, or a system for production of ozone by means of high voltage electrical charges.

7. An apparatus according to any one of the preceding claims, in which said washing section (6) comprises a series of dividing walls (10) that create a labyrinth type route to be followed by the air being treated, and a series of nozzles (11) to direct said washing liquid, under pressure, against the surfaces of said walls and create a barrier of finely dispersed liquid obstructing the passing flow of air.

8. An apparatus according to any one of the preceding claims, further comprising for purification and return of said washing liquid a washing liquid recycling circuit comprising a pump (14), a filter (12) and a decanting basin (13) for separation of the solid impurities and precipitate.

9. An apparatus according to claim 8, in which a pH- eter and a delivery device (17) are installed on the washing circuit tank to deliver fresh reagent and restore the pH concentrations.

10. An apparatus according to any one of the preceding claims, in which in the washing or accumulation sections, or in both of these sections, the walls are coated with one or more of the catalysts defined in claim 1, to eliminate residual ozone.

11. An apparatus according to claim 1 or 2, in which the catalyst is directly supported on the surfaces of the radiator of an internal combustion engine present in the apparatus.

12. An apparatus according to claim 1 or 2 and 11 for purification of CO and ozone from city air, in which said radiator is an ordinary radiator of the type normally installed in motorised vehicles, said radiator being used as a support and heat exchanger for said catalyst in said catalytic section for oxidation of CO and decomposition of 0₃ into 0;.

13. An apparatus according to claim 1 or 2 installed on a moving transport vehicle, in which the exhaust fumes from the motor of the vehicle are made to pass in heat transmission contact with catalysts in any one of the catalyst sections in order to heat them.

14. An apparatus according to claim 1 or 2 and 13, installed on a moving transport vehicle, in which the liquid in the motor cooling system is made to pass in heat transmission contact with the catalysts in any one of the catalyst sections in order to heat them.

15. An apparatus according to any one of claims 1, 13 or 14, in which due to the ability to size the various component sections selectively, it is also possible to purify the exhaust fumes from the motor of the transport vehicle, as well as the polluted air from the surrounding environment.

16. An apparatus according to claim 1 or 2, fitted as a fixed installation, in which said catalysts are ZnO,

Mn0₂, CuO or CuCr₂0₄.

17. An apparatus according to claim 1 or 2 and 16, fitted as a fixed installation, in which in said washing section a washing liquid is used made up of water or an aqueous solution containing oxygen ions freed from calcium, sodium bicarbonate and the like.

18. An apparatus according to any one of claims 1,

2, 16 or 17, in which said input section and said oxidation section are arranged in succession with the flow of said air to be purified following a vertical route, said washing section being arranged with an horizontal air flow and said accumulation and outlet sections being arranged with a vertical route.

19. An apparatus according to any one of claims 1,

2, 16 or 17, in which said sections are arranged in succession with an horizontal air flow.

20. An apparatus according to claim 19, in which said sections have angular turns in said horizontal route taken by the flow of air.

21. An apparatus according to any one of claims 1 or 2 and 16 to 20, characterised in that it is positioned under the level of the road.

22. An apparatus according to any one of claims 1 or 2 and 16 to 20, characterised in that it is installed inside a tunnel used by motor traffic.

23. An apparatus according to any one of the preceding claims, in which one or more of the sections can be omitted, according to the type of pollutant to be dealt with on the basis of economic or practical considerations.

24. A process for the purification of air polluted by carbon, nitrogen and sulphur oxides, ozone, unburned hydrocarbons, particulate, dust and exhaust fumes from internal combustion engines in general, comprising in combination the operations of: producing nascent oxygen within the polluted air to be purified, oxidising the pollutants CO, N0_X to form their oxides CO; and NO_. by means of reaction with the nascent oxygen and by passing the polluted air in contact with catalysts that are active at room temperature, made up of the oxides of elements from the First Series of Transition Elements in the Periodic Table or CuCr₂0 , subjecting the flow of air to washing by means of jets of washing water, optionally activated using calcium, calcium bicarbonate, soda, sodium bicarbonate, or other reagents capable of increasing the pH of the solution, in a serpentine-shaped route in order to absorb the polluting gasses and reduce the particulate and unburned materials, filtering and decanting the washing liquid to collect insoluble matter and impurities, recovering the washing liquid, restoring it and recycling it to the washing operation, discharging the purified air into the external environment after final catalytic elimination of gaseous pollutants and in particular CO and 0₃, characterised in that: in addition to or in exchange for the catalysts mentioned above, Pt or other noble metals are used, or alternatively the oxides and salts of elements belonging to Groups 6 B, 7 B, 8 B, 1 B or 2 B of the Periodic Table or a mixture thereof, that are also active at room temperature; said operations are carried out in an apparatus installed on a moving transport vehicle or positioned in a fixed installation; and said operations are selected as to their succession, type and number according to the composition of the pollutants in the air to be purified.

25. A process according to claim 24, in which said nascent oxygen is produced by decomposition of ozone.

26. A process according to claim 24 or 25 carried out on a moving vehicle, in which said catalyst bed is heated by means of heat exchange with the exhaust fumes or with the cooling liquid, or with another heat source dissipated by the motor of said vehicle.

27. A process according to claim 24 or 25 carried out in a fixed installation, in which the aqueous washing liquid with a low content of transformation products from said pollutants is discharged directly into the drainage system of the urban environment.

28. A process according to claim 27 in which said washing liquid is water or an aqueous solution containing oxygen ions freed from calcium, sodium bicarbonate and the like.