GB2036951A

GB2036951A - Air cleaning

Info

Publication number: GB2036951A
Application number: GB7935369A
Authority: GB
Original assignee: SCHMIDT REUTER
Current assignee: SCHMIDT REUTER
Priority date: 1978-10-16
Filing date: 1979-10-11
Publication date: 1980-07-02
Also published as: FR2439365A1; DE2844997A1; SE7908512L; GB2036951B

Abstract

Process for the cleaning of air in air-conditioning and ventilation systems comprises moistening the air by water, exposing the humidified air to ionisation and subsequently feeding the air to a washer 20. An apparatus for the performance of the process comprises an ionisation equipment (18) and/or an arrangement of ultra- violet tubes (19) downstream of a humidifying device, and upstream of a washer which operates either adiabatically or with cooled and cleaned water. The ionisation equipment may comprise an electrostatic precipitator. <IMAGE>

Description

SPECIFICATION Air cleaning The present invention relates to an apparatus and a method for cleaning air.

For cleaning air in an air-conditioning system, apparatus for the precipitation of dust are known.

Precipitation of fine dust by for example electrostatic precipitations or fine liquid drops, as well as absorption on active carbon filters by which a series of gaseous injurious substances can be removed are known.

Further, sterilization of the air or of washing water in air-conditioning systems by the use of ultra-violet tubes, by the addition of steam or the fine atomization of water with centrifugal disc atomizers or by the absorption of sulphur dioxide in washers used for humidifying are known. The sterilizing and smell-reducing effect of the ionization of the air through corona discharges or through ionization by radio-active apparatus or through the Lenard effect are likewise known and are employed particularly for sterilization and smell reduction in for example cold stores.

The disadvantage of known ionization apparatuses is that, although smells and germs are removed and dust is charged up, their subsequent removal on cleaning the apparatus is however omitted. Substances in suspension are likely to get into the lungs and tend to deposit in the breathing passages.

On the employment of apparatuses which yield ultra-violet rays (ultra-violet radiators) alone, sterilization of the air is possible only in part. Even a very high number of ultra-violet lamps provide only incomplete sterilization of the air, although for sterilization, ultra-violet tubes radiating energy having a wavelength of 254 nanometres have been used. These are designed for killing microorganisms.

For the elimination of traces of injurious substances, an active carbon filter is only selectively employable and has a relatively high resistance to air flow. This resistance to air flow also applies to filters of suspended substances.

These have the disadvantage that the air must get past the deposited particles of dust and injurious substances and its smell quality thereby suffers.

Electrostatic precipitators have stopped being used in air-conditioning systems because they produce ozone and nitrous gases. Although the formation of injurious substances has been reduced through positive ionization voltage (Penney), a deficiency of small negative ions in the air was however produced. Further, electrostatic precipitators have the disadvantage that the proportion of fine dust passing through is in the form of large ions in the air, which can be recognised in precipitations on for example suction openings. The electrical conductivity (small ion density) of the air is displaced polariy; this gives flat, unpleasant taste to the air.

A steam supply and spray nozzle washers were hitherto used for humidifying the air. The water exchange in the washer takes place according to the increase in the hardening constituents in the water. However, the washer does not wash but only moistens the air. Most of the washers operating with unprepared water during atomization bring a part of the water residues as well as the water germs into the air. They seldom contribute to a reduction in smell, and may even cause additional smells.

Sprayed surface coolers are likewise known, but work on thermo-dynamic principles are not used for cleaning purposes.

No consideration is given for example to the formation of sulphuric acid through sulphur dioxide absorption during water change. This results in corrosion of the apparatus.

Atomizers, especially centrifugal disc atomizers, are also quite well known in air-conditioning apparatus, but are mostly used only as moisteners.

The germs and residues of the water are particularly strong in the air during fine atomization and lead to deposits and other nuisances. It has recently become known that the distribution of water germs in air can be avoided through ultra-voilet radiation of the washer in centrifugal disc moisteners.

Air-sided resistances of drip separators of washers or of the laminae of coolers must be accepted for the whole year with the, resent mode of construction, although moistening is usually required during only a few months of the year.

Particularly injurious gaseous substances, for example car exhaust gases and furnaces gases as well as vapours and liquid from aerosols are precipitated out of the air more effectively than was possible with known apparatus. Pressure losses in the air path are also reduced.

Ionization apparatuses may be so employed that several ionization effects are so combined that long-lived and short-lived small ions of different composition arise and the short life of nascent oxygen is taken into consideration by the arrrangement of the ionization sources.

The washing may be effected with cooled and cleaned water. Good air washing results by preferably cleaning the washing tub contents in a special circuit through ultra-violet radiation with subsequent active carbon filtering.

The cooling surface in this circuit should be in the range of action of the ultra-violet radiation.

The ionization of the humidified air may be effected through discharge wires of an electrostatic precipitator or in conjunction with the Lenard effect occurring in the atomization of the water.

Smells together with germs, gaseous and vapourous injurious substances, filterable dusts and breathable aerosol vapours and liquid particles having diameters of less than 0.1 micrometres may be removed. In the removal of the smells and injurious substances, they may be converted by photo-chemical reactions among one another or with the aid of additional substances into less injurious and/or water-soluble substances and these may then be precipitates in a washer and/or wet cooler. The final removal from the water circuit takes place through water cleaning systems or through the exchange of the water.

Process embodying the invention simulates the self-cleaning mechanism of the earth's atmosphere.

According to one aspect of the present invention there is provided an apparatus for cleaning air, comprising at least one of a source of radiant ultra-violet energy and an ionizating device disposed downstream of an air humidifying device and upstream of air washing means.

According to another aspect of the present invention there is provided a process for cleaning air in the apparatus defined in the preceding paragraph, comprising the steps of humidifying the air, exposing the humidified air to ionization and subsequently washing the air.

The source of radiant ultra-violet energy may radiate energy in a wavelength range of the natural ultra-violet radiation at a height of approximately 3000 metres.

A washer and/or wet cooler may be in operation in the air-conditioning system for the whole year.

It can be operated adiabatically in winter and as a cooling washer or wet cooler in summer. It can however be employed for the whole year as a cooling washer, wherein humidifying takes place through an adiabatically operating centrifugal disc atomizer and/or by the addition of steam.

For the reconstruction of older air-conditioning systems, which have a steam humidifying device, steam addition may be provided not after the preheating, but before the preheating of the air to be humidified with a change of state into the mist region.

A A unidirectional field and a high-frequency grid and/or ionization equipment working on the corona principle for negative and/or positive ionization may be arranged in front of the humidifying device.

A nozzle assembly of the washer or the laminae of the wet cooler may be brought to an electrical potential so that a potential difference is produced to the ionization equipments and/or to the collector of the electrostatic percipitator and/or, with the collector electrically switched off, to the potential of the discharge elements of the electrostatic precipitator.

In the particle separation, the oily, liquid, and fatty dust particles, difficult to wet by water, may be precipitated in the electrostatic precipitator and the water-soluble and easily wettable injurious substances in the washer. The advantage of humidifying the air before the entry into the electrostatic precipitator lies in a halving of the ozone development and the downstream connection of the washer in the advantage of washing-out of residual ozone which at the same time contributes to the sterilization in the washer circuit. The combination of the sterilizing effect of ionization sources and ultraviolet rays permits a lower number of ultra-violet tubes to be incorporated.Smell removal is favoured by the combination of ion-producing elements, such as for example a centrifugal disc moistener and/or ion generators-disposed upstream and/or discharge wires of the electrostatic precipitator disposed downstream and the effect of the ultra-violet source disposed downstream to the production of nascent oxygen, as it proceeds at great heights with the shorter ultra-violet wavelengths, as well as of subsequent washing-out of oxidized smell compounds which have become water-soluble.

This applies also to photo-chemical reactions which occur through the co-operation of the discharge electrodes of the electrical cleaners with simultaneous ultra-violet radiation having wavelengths, which especially correspond to the absorption spectra of oxygen, for the conversion of compounds of injurious substances which are soluble in water only with difficulty, into compounds which are more soluble in water and the subsequent washing-out.The ozone occurring in the electrostatic precipitator converts the simuitaneously present nitrous oxides-under ultra violet irradiation (E) approximately according to the following reactions: 203+E 202+20+e3 2 NO + 03o NO2 + O2 and with an excess of O3 2 NO2 + O3N205 + 0,; N205 is already well soluble in water and in moist air forms N205 + H2Qo2 HNO3, which is unlimitedly soluble in water.

An electrostatic precipitator may be used in which the ionization voltage is regulable and is so adjusted that a certain ozone production takes place, but ensuring that the prevailing ozone content is not exceeded after the abovementioned transformations and the subsequent washing-out process.

A washer, which is present in an existing - system, intended for winter moistening and which is not in operation for the rest of the year, may be converted into a cooling washer by the addition of a cooler in the water circuit and so is able to run for the entire year and during the whole year absorbs gaseous injurious substances.

To save energy, it is advantageous to bypass the cleaning equipment when the external air is clean, for example on good ventilation with sufficient wind speeds.

In climatic situations which for example are mostly characterised by lack of wind, the cleaning equipments may again be switched on.

Simultaneous cleaning of added and circulating water may be affected by a reversing osmosis process. In this process a washer operating with rain water is in operation for the whole year and operates with cold water during the summer and transition months in order not to moisten the air during the washing process, but possibly to dehumidify it. The water-air ratio is preferably increased because a greater surface is required for the cooling in the washer than for the moistening.

In motor vehicles, the cleaning circuit would need to be switched on only in case of need and separately from or together with the cooling or heating of the air. When travelling in the country, one can switch the cleaning process off and when travelling in conurbations with greater traffic density the cleaning process on.

Assemblies that cost different amounts may be selectably used according to the demanded comfort and according to whether energy saving or extremely high air quality, such as for example in hospitals, matters.

When energy saving matters, the resistance to air flow also plays a part. The humidifying may then be performed with an adiabatically operating centrifugal disc humidifier only in so far that a subsequent drip separation is unnecessary.

To save pump energy for a washer, a sprayed surface cooler may be employed which uses less water applied with energy-saving distributor devices. One has to determine whether the energy consumption for a washer with low pressure losses in the air path, but corresponding energy effort for pump energy, is better than the reverse conditions with a sprayed cooler. For the separation of gaseous injurious substances, the film-like surface with sprayed coolers is preferably to very small drop diameters in washers. The ingress of gaseous injurious substances in a nonchemical solution reaction results in too great a resistance through the surface tension of the phase boundary layer with small drop diameters.

However, in absorption processes the increase in the surface with small drops is favourable. If fine dust particles of solid consistency are to be removed, the use of a washer is preferable when one predominantly wants to remove gaseous injurious substances, the wet surface cooler is preferable. The combination of both elements is worthwhile for the attainment of an extremely high air quality.

Embodiments of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings in which: Figures 1 to 4 show different arrangements of humidifying devices, ionization equipments and washers.

Fig. 1 shows an apparatus comprising a housing 10 in which is disposed a water atomizer 11 comprising a disc 13 which is arranged on the shaft 12 and which rotates at high speed in the direction of the arrow around the shaft 1 2. Water is formed into fine droplets by the centrifugal disc atomizer. This is symbolically represented by the arrows 14. In place of or together with the centrifugal disc atomizer 11, 12, steam can be fed through a regulating valve 1 5. The steam issues through the nozzles 1 6 and 1 6a.

An ionization equipment, which comprises discharge wires 18, 1 8a etc., is disposed downstream of the air humidifying equipment (the air flow direction being indicated by arrow 1 7).

Tubes 1 9 and 1 9a which give off ultra-violet rays can be disposed downstream of the ionization equipment. The discharge wires 1 8 and/or the ultra-violet tubes 1 9 may be present. Downstream of the discharge wires or the ultra-voilet tubes a wet-washer 20 provided with spray nozzles 21 and a circulating pump 22 is provided. Air is conducted within the housing 10 by a blower 23.

The aforementioned units can be arranged in the housing 10 but they may be disposed in respective associated housings which are then connected with one another for the air guidance.

Figure 2 shows an electrostatic precipitator comprising the discharge wires 1 8 and 1 8a and dust precipitation plates 24, 24a, 24b disposed downstream of the centrifugal disc atomizer.

The ultra-violet tubes 1 9 and 1 9a are disposed downstream of the ultra-violet tubes and a hydroculture 25, 25a and 25b for micro-organisms or plants is disposed downstream of the ultraviolet tubes. Downstream of the hydroculture the apparatus is similar to that shown in Figure 1, the washer being provided with cooling equipment 31 Figure 3 shows an apparatus in which the ultraviolet tubes 1 9 and 1 9a at the inlet of the housing are provided with reflectors 26, in order to direct the rays against the direction of flow of the air.

The wet washer 20 comprises spray equipment 27 provided with spray nozzles 28, 28a etc., a regulating valve 29 and a cooling surface 30.

Figure 4 shows an apparatus in which part of the cleaned air passing out of the housing 10, is fed through a branching 31, back to the cleaning apparatus or arrangement in the housing 10 or to the individual housings connected one behind the other. The cleaning apparatus in this case has greater dimensions than is required for a single pass of space air.

Claims

1. An apparatus for cleaning air, comprising at least one of a source of radiant ultra-violet energy and an ionisating device disposed downstream of an air humidifying device and upstream of air washing means.

2. An apparatus as claimed in claim 1, wherein the ionisating device comprises an electrostatic precipitator.

3. An apparatus as claimed in claim 2, wherein the electrostatic precipitator is provided with discharge wires selectably operable at either a positive or a negative ionising voltage.

4. An apparatus as claimed in any one of the preceding claims, wherein the source of radiant energy comprises ultra-violet tubes adapted to radiate energy at a wavelength of approximately 254 nanometers and provided with reflectors arranged to reflect against the direction of air flow, the source being upstream of the ionisating device when present.

5. An apparatus as claimed in any one of claims 1 to 4, wherein the source of radiant energy comprises ultra-violet tubes adapted to radiate energy at a wavelength of approximately 254 nanometers, the source being downstream of the ionisating device when present.

6. An apparatus as claimed in any one of the preceding claims, wherein the humidifying device comprises an atomiser.

7. An apparatus as claimed in any one of the preceding claims, wherein the humidifying device comprises steam applying means.

8. An apparatus as claimed in claim 6 and claim 7, wherein the steam applying means is disposed downstream of the atomiser.

9. An apparatus as claimed in any one of the preceding claims, comprising a hydroculture device provided with strongly metabolic microorganisms or plants and disposed downstream of the ultra-violet tubes and the ionisating device.

10. An apparatus as claimed in claim 9, wherein the hydroculture device is provided with blue algae.

11. An apparatus as claimed in any one of the preceding claims, wherein the air washing means comprises a scrubber and a sprayed surface cooler disposed downstream of the scrubber.

12. An apparatus as claimed in any one of the preceding claims, comprising means to feed back and recirculate some of the cleaned air through the apparatus, the apparatus being larger than necessary for a single pass of the same quantity of air.

13. An apparatus as claimed in either claim 2 or claim 3, comprising means to regulate the ionisation voltage of the electrostatic precipitator in response to residual ozone content of the air passing through the apparatus.

14. An apparatus for cleaning air, substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawing.

1 5. An apparatus for cleaning air, substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawing.

16. An apparatus for cleaning air, substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawing.

17. An apparatus for cleaning air, substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawing.

18. A process for cleaning air in an apparatus as claimed in any one of claims 1 to 16, comprising the steps of humidifying the air, exposing the humidified air to ionisation and subsequently washing the air.

19. A process as claimed in claim 18, wherein the washing step is performed by cool clean water.

20. A process as claimed in either claim 18 or claim 19, wherein the ionisating step is performed with the aid of discharge wires of an electrostatic precipitator.

21. A process as claimed in any one of claims 1 8 to 20, comprising passing the air between ultra-violet tubes which radiate energy a wavelength of approximately 254 nanometres.