A SYSTEM FOR DECOMPOSING ODOROUS SUBSTANCES IN THE AIR

The prior art

The invention relates to a system for decomposing smelling substances in air, such as stable air in pig stables, said stable air being sucked out from the stable via an air channel to an air cleaning system, as well as use of the filtered part.

So far, it has been attempted to solve the problem of the pollution of the air, in particular in stables, by simple exhaustion of the stable air. In particular nitrogenous substances from the manure are accumulated in stable air, which may be converted into ammonia. To this should be added hydrogen sulphide, dust and moisture, which necessitates an effective exchange of air owing to the well-being of the animals.

In step with the establishment of large herds of livestock, with a consequent increase in the amount of stable air which is to be discharged, the need for reducing the nuisances of the increased discharge of offensively smelling air has increased.

Systems for the cleaning of air from e.g. stables are known, where the air is conveyed through filters for separating particles in the air and for decom- posing smelling substances. DE G 92 03 062 describes such a system, in which the air is conveyed through a channel having a filter block. This filter block is composed of elements which are suitable for separating particles from the air, each element consisting of profile plates forming chutes which retain the particles. The profile plates have finer and finer chutes in the di- rection of flow of the air. The last ones of the elements of the filter block form biological filters, as they are coated with a bioactive layer which binds

the smelling substances. The lower part and optionally the upper part of the filter block are wetted by means of water nozzles. A water separator having a drop trap is arranged immediately before the outlet.

The object of the invention

It is the object of the invention to provide an air cleaning device of this type, which is more efficient and more reliable in operation, and which requires less maintenance than the known systems.

This is achieved according to the invention by an air cleaning device, which, as stated in claim 1 , comprises a substantially vertical channel in whose lower part a wetting zone having downwardly directed water mist nozzles is provided, and wherein a biological filter zone is provided above the wetting zone, said biological filter zone comprising filter elements disposed after each other with spaces between the individual filter elements, and wherein a centrifugal blower is present at the top in the substantially vertical channel, said centrifugal blower having the suction side facing downwards and forming, together with an expanded upper part of the channel, a separation zone for separating the water from the air, and wherein the channel has a discharge opening for the dried and cleaned air above the centrifugal blower.

This structure of the system completely avoids mechanical filters for the separation of particles, as the particles are removed by suspension in the water mist formed. Accordingly, there are solely biological filters in the system, and not only a more effective removal of the odour is achieved, but also a more effective separation of the particles. Relatively much water is used, since water is employed not only for wetting the faces of the filters, but also for the water mist which suspends the solid particles. This water, however, is separated without problems in the separation zone at the top of

the system, where the centrifugal blower, which ensures the transport of the air through the system, throws the water out against a cylindrical wall. The separated water percolates along the sides in the vertical channel and is collected in a sedimentation system, from which the water is recycled in an ordinary manner to form water mist.

In the biological filter elements, bacteria cultivated in order to "eat" the odour, can reduce the odour nuisances in a simple and effective manner. This biological process results in a growth substance on the biological filter elements which is nitrogenous, and which may advantageously be used as a nitrogenous fertilizer supplement.

This will mean that the nitrogen is utilized in the air, instead of being discharged by direct discharge to the atmosphere.

As stated in claim 2, rows of downwardly directed water mist nozzles are arranged in the spaces between the individual elements of the filter zone. This ensures that particles may be suspended during the entire course of the upward flow of the air. At the same time, these nozzles serve to wet the surfaces on the biological filters.

When, as stated in claim 3, the filter is composed of a plurality of juxtaposed lengths of pipe of a net-like structure and these are assembled into a disc-shaped element, favourable conditions of growth are created on the large growth surface.

When, as stated in claim 4, elements are formed from juxtaposed lengths of pipe, the manufacture of the filter elements may be simplified.

When, as stated in claim 5, the lengths of pipe are inclined, the maximum available net area, cultivation area, is achieved for the individual filter ele-

ments.

When, as stated in claim 6, the inclined lengths of pipe extend in mutually opposite directions of adjacent elements, the direction of flow of the air will be increased to achieve the greatest possible filter effect.

When, as stated in claim 7, a scraper device is mounted above each filter element, the surface may be scraped in an effective manner to maintain the conditions of the growth on the elements.

When, as stated in claim 8, the liquid running away from the system and the biological biomass are treated in a separation system, cleaning system, the liquid may be recycled in the system, while the filtered material may be separated.

Finally, it is expedient, as stated in claim 9, to use this filtered material as a fertilizer, as it will contribute to covering the operational costs of the system when utilized as a nitrogen fertilizer.

The drawing

An example of an air cleaning system according to the invention will be described more fully below with reference to the drawing, in which

fig. 1 shows a partially sectional view of a system seen from the side, and

fig. 2 shows a biological filter element seen from above.

Description of an exemplary embodiment

A system according to the invention for use in the decomposition of smelling substances in air will be described first, and then the mode of operation will be described.

Figure 1 shows a system 1 which is shown mounted outside a building 2, which may e.g. be a pig stable.

An air channel 2a conveys the stable air 3 into a wetting zone 4 at the bottom in the system 1 , where liquid is supplied via nozzles on a pipeline 5 to form a water mist 10.

This water mist 10 serves to suck and trap, respectively, gaseous and solid particles in the air.

Agents for conditioning the air may be added to the liquid, such as acid to regulate the pH value.

A biological cleaning zone in the form of one or more filter elements 6, which are arranged above each other, is established above the wetting zone 4.

A water mist 10 is likewise supplied to this filtration zone via nozzles on supply pipes 5, as shown.

The individual filter elements 6 are shown seen from above in fig. 2. The elements 6 are composed of objects, which are tubular in the example shown. These lengths of pipe 6a typically have the same dimension and are juxtaposed to form a continuous filter element 6. They are made of a net-shaped mesh material to form a large surface.

The net structure means that supplied or added bacteria obtain a large filter face to grow on, and when the individual lengths of pipe 6a are mounted obliquely relative to the filter face, the flow area will be increased. To enhance the efficiency of the filter, the direction of flow 7 of the air up through the filter zone is changed through the individual filter elements, so that the efficiency is maximum owing to the increased contact time of the air.

Bacteria may grow on the surfaces of the filters by "eating" the smelling substances in the air saturated by water mist and thereby produce a growth material 6b, as indicated on a few of the lengths of pipe 6a in fig. 2.

In some cases the liquid mist 10 can flush growth material away from the filter material and thus flush the biological growth material away from the filter element, when the material has reached such an extent that the air flow is reduced.

This material may be collected together with the liquid at the bottom of the system, in which an inclined bottom 13 is mounted, where the material flushed off may be collected in a separation system 15A and 16A, as shown in fig. 1.

A scraper device may be arranged above one or more of the filter elements 6 in the form of a scraper blade 9, which will be able to scrape off the growth material from the elements 6 via a through shaft 8, as shown in fig. 1.

Finally, a liquid separation zone 22 is established at the top of the system 1 , where a centrifugal blower (not shown) is mounted.

This blower sucks the stable air 3 through the system 1 via a funnel 11 at the top and discharges the cleaned air at the top.

The liquid will be precipitated in the separation zone by centrifugation of the air drawn in. The liquid will run down via the openings 12 in the funnel 11 , while the dry and clean air 23 will be discharged at the top.

The cleaning zone comprises a discharge pipe 15 which conveys liquid and material to a sedimentation tank 15A, in which liquid will run via an overflow

16 to a precipitation tank 16A. The clean water is then conveyed via a pipe

17 to a pump 18 and through a filter 19 to the supply pipe 20 for liquid to the nozzles via the individual supply pipes 5.

The material precipitated in the tank 16A is discharged via a channel as a material 21 which, owing to its high content of nitrogen, may be utilized as a fertilizer.

By way of example, the system may be dimensioned for an admitted air amount of 30,000 m ³ per hour. The channel diameter may be about 1 ,500 mm, and the air flow velocity about 4.5 m per second.

The water mist may be derived from about 470 I per hour, while the filter surface in total may be about 320 m ² . By way of example, the total height of the system may be about 8.5 m.

The function of the system will be described now:

Stable air 3 is sucked out by the blower in the separation zone 22 in the system via a channel 2a, which connects the stable 2 with the system 1. The air is conveyed into a wetting zone 4, in which a water mist 10 absorbs the water-soluble parts and binds dust particles, etc.

Then, the wetted air 7 is passed through one or more biological filters 6, which are seeded with or is supplied with bacteria via the liquid 10, which

are capable of "eating" the odour and thereby removing smelling substances from the passing air 7.

Finally, the liquid is separated from the air in a centrifugal separator 22, for the clean air 23 to be discharged. This will be completely without odour.

The growth material on the filters 6 may be flushed or scraped off in order to be removed from the filter surface and drop down to the bottom of the system, from which it may be conveyed to a separation and cleaning sys- tern 15A and 16A at the bottom.

Liquid may be taken from there for re-use in the nozzles, while the residual material is discharged for use as a fertilizer.

The invention is described in connection with a pig stable, but, of course, the system can operate in a quite corresponding manner for the removal of odour from other sources, such as cleaning systems, bone meal factories and similar odour-emitting facilities.

The shown and described exemplary embodiment relates to an upright air cleaner, but, of course, it will also be possible to mount it in an inclined position, where this is appropriate. Access for inspection of the bio-filter will thus be facilitated.