fig1 shows the cross section and a perspective view of an air conduit according to the invention . as may be seen from the cross section of the plane a - b , the air conduit 101 has the cross section of a regular hexagon . a tubular uv emitter 102 is arranged centrally in the air conduit 101 . the used air , which is contaminated with harmful substances , enters into the inlet 103 and is re - emitted from the outlet 104 . in order to achieve a catalyst effect within the air conduit 101 , the internal walls 105 are coated with a broadband semiconductor material , for example titanium dioxide or doped titanium dioxide . fig2 is a perspective view of a reaction stage according to the invention comprising a plurality of parallel air conduits . the individual air conduits 101 correspond to the air conduit illustrated in fig1 and are arranged in parallel in a honeycombed configuration . a respective tubular uv emitter is arranged , in a corresponding manner , in each air conduit 101 . the air conduits 101 , which are thus interconnected , are surrounded by a metallic housing and thus form the reaction stage 201 . respective contact rails 202 , which , on the one hand , act as cable ducts for the electrical feeds to the uv emitters and , on the other hand , mechanically hold the uv emitters in the air conduits 101 , are provided on the air inlet 203 and the air outlet 204 . laterally corresponding series connection units 205 are provided for the electrical activation of the uv emitters . slide rails 206 and 207 are provided on the lower sides of the reaction stage 201 , so the reaction stage 201 in the overall system may be introduced or removed on corresponding rollers for maintenance purposes . a further improvement in the decomposition rate may be achieved if the internal walls of the air conduit are coated with a catalyst material . as a result of the honeycombed construction of the reaction stage , which comprises a plurality of air conduits , large catalyst surfaces may be provided , with little loss in pressure , in direct proximity to the uv radiation . the direct irradiation of the catalyst surface allows broadband semiconductor materials to be used effectively for photocatalysis . titanium dioxide has proven particularly suitable as a catalyst material . as a result of the irradiation of the titanium dioxide with uv light , the energy of which is greater than or equal to the energy differential between the valence and conduction bands of the semiconductor , electron - hole pairs are firstly generated in the semiconductor material . o 2 — species , which effectively assist the process of the oxidation of harmful substances , are then formed . uv emitters having wavelengths in the range between 340 nm and 420 nm are used for initiating this process . gas molecules are then adsorbed on the generated charges of electron - hole pairs formed by light irradiation . the molecules , which are then co - adsorbed , are activated and form a transition state , from which they react to form the end products , while at the same time forming intermediate products . the harmless reaction products desorb and may be emitted to the environment . by means of heterogeneous photocatalysis , it is , for example , possible to combust compounds such as ammonia , formaldehyde or lower alcohols , which are difficult to oxidise by means of photo - oxidation , with atmospheric oxygen , with a high degree of effectiveness at ambient temperature , to form nitrogen or co 2 and water . the course of the reaction , which has already been described in general terms , is in this case as follows : the used air is directed into a reaction duct , in which titanium dioxide , which is activated by uv light , is located . the irradiation of the photosemiconductor results in the generation of electron / hole pairs . gas molecules are then adsorbed on the generated charges , wherein the gain in energy during the adsorption process determines which molecules preferably interact with the electrons and which with the holes . in the case of the reaction partners , ammonia and oxygen , ammonia reacts , owing to the respective molecule characteristics , with the holes and oxygen with the electrons . the molecules , which are then co - adsorbed , are activated and form a transition state , from which they react to form the end products , while at the same time forming intermediate products . the harmless reaction products , nitrogen and water , desorb and may be emitted to the environment . fig3 is a perspective view of a used air purification system 301 comprising reaction stages 306 and 307 according to the invention . the reaction stages 306 and 307 correspond , in each case , to the reaction stage 201 illustrated in fig2 . the used air , which contains harmful substances , is supplied to the used air purification system 301 via a supply pipe 302 . two systems 303 and 304 , which are identical in construction and are arranged , in the illustration according to fig3 , one above the other , may optionally be provided to increase the quantities of air to be purified . for the sake of simplicity , only the system 304 , the individual components of which are illustrated in greater detail by means of a cut - away view , will be described below . a distributor stage 305 , which uniformly distributes the arriving air and optionally filters out relatively large harmful substance particles , is accordingly first of all connected to the supply pipe 302 . the air forwarded from the distributor stage 305 enters the reaction stages 306 and 307 according to the invention . two reaction stages 306 and 307 , which are identical in the construction , are arranged one behind the other to increase the decomposition rate . however , the used air purification system 301 may , of course , also be constructed with only one reaction stage 306 . a catalyst unit 308 , which may consist , for example , in the above - described manner of poured , highly porous activated carbon material having an internal surface area of approximately 1 , 200 m 2 / g , which may be used as the reaction surface , is connected to the two reaction stages 306 and 307 . the air emitted from the catalyst unit 308 also enters the fan unit 309 , which ensures that a suitable difference in pressure is maintained between the supply pipe 302 and the discharge pipe 310 . the used air purification system 301 is , in principle , operated using this method according to ep 0 778 070 b1 , although it is , according to the invention , distinguished by one or more reaction stages 306 , 307 , as is illustrated in fig2 . the used air , which is contaminated with harmful substances , accordingly passes from the supply pipe 302 , via the distributor stage 304 , into the reaction stages 306 307 , in which short - wave uvc light initiates a chemical reaction . odorous substance and harmful substance molecules are broken up . at the same time , harmful substance radicals and ozone are produced as oxidants . the oxidation of the harmful substances produces the environmentally acceptable products co 2 and h 2 o . compounds that are difficult to oxidise and excess ozone are broken down in the subsequent catalyst unit 308 . the purified and non - odorous air is emitted to the environment via the fan unit 309 and the discharge pipe 310 . for the effective treatment of non - uniform harmful substance contaminations , an additional catalyst unit may be interposed in the above - described manner at location 311 . the additional , interposed catalyst unit allows even harmful substances that occur briefly , at very high concentrations , to be broken down .
the invention relates to a device for purifying used air containing harmful substances , comprising a reaction stage according to the photooxidation principle . the reaction stage encompasses at least one air conduit inside which a tubular uv emitter is disposed along the direction of flow of the used air . in order to increase the decomposition rate within the used air conduit in a simple manner , the cross section of the at least one air conduit is embodied as a regular polygon having at least five sides .