Abstract:
An apparatus and method for deodorizing a gas mixture including air and a malodorous substance having a flow passage for the gas mixture and a fan for inducing air flow in a predetermined direction through the passage. An ultraviolet lamp for generating uv rays below a critical wavelength is in the flow passage for generating ozone from the air in the gas mixture. An ozone-decomposing catalyst layer is in the passage for contacting the gas mixture, and an ozone-decomposing ultraviolet lamp for generating uv rays above critical wavelength is positioned to irradiate the layer directly. The intensity of the radiation of the two layers is controlled to avoid the discharge of ozone from the downstream end of the passage.

Description:
INDUSTRIAL FIELD 
     This invention relates to a novel deodorizing apparatus and method which is capable of decomposing malodorous substances through oxidation by effective use of ozone. 
     BACKGROUND OF THE INVENTION 
     Ozone is produced from oxygen by silent discharge or by the action of ultraviolet rays below a critical wavelength. Above all, ozone is produced by irradiating oxygen with an ultraviolet ray of a wavelength smaller than 200 nm, preferably of a wavelength of 185 nm, according to the following formulas (I) and (II). 
     
         O.sub.2 +hv→20 (I) 
    
     
         O.sub.2 +0+Ml→O.sub.3 +Ml (II) 
    
     wherein hv is an ultraviolet ray and Ml is a third substance such as nitrogen. 
     For deodorization, there has thus far been adopted a method of decomposing malodorous substances in exhaust gases by oxidation with the produced ozone and treating unreacted ozone with activated carbon in consideration of its toxicity to human bodies. In order to improve the efficiency of deodorization by ozone, it has been known to use oxygen of nascent state with extremely strong oxidizing power, which is produced by forcibly decomposing ozone. The means for producing the nascent state oxygen from ozone include catalytic methods, ultraviolet (above a critical wavelength) ray methods, pyrolytic methods, radioactive ray or electron beam irradiation methods and other methods using supersonic or high freguency waves. As deodorizing devices using the radioactive ray or electron beam irradiation or supersonic or high freguency waves are relatively large in scale, it appears practically advantageous to use a catalyst or ultraviolet ray for deodorizers of small sizes which are intended for home use. 
     The decomposition of ozone by a catalyst is generally expressed by the following formula (III). 
     
         O.sub.3 +M.sub.2 →O.sub.2 +(O) +M.sub.2             (III) 
    
     wherein M 2  is a catalyst, (O) is oxygen in nascent state. 
     The decomposition of ozone by ultraviolet ray is generally expressed by the following formula (IV) 
     
         O.sub.3 +hv→O.sub.2 +(O)                            (IV) 
    
     In the catalytic ozone decomposition, however, it has been difficult to maintain the initial high decomposition capacity since the catalyst life is shortened as it is rapidly deteriorated due to oxidation reaction of the catalyst itself as a result of the ozone decomposition. In case of ozone decomposition by an ultraviolet ray with a wavelength of 254 nm, the decomposition capacity is impractically low as compared with the catalytic method. 
     SUMMARY OF THE INVENTION 
     Under the foregoing circumstances, the present invention contemplates providing a deodorizing apparatus with a high decomposition capacity and a method which can solve the above-mentioned problems in the deodorization of malodorous substances with use of oxygen of nascent state which has high oxidation power. 
     In accordance with the present invention, the aforementioned problems are solved by the provision of a novel deodorizing apparatus, which essentially includes means for inducing air flows in a predetermined direction; an ozone-generating ultraviolet lamp; an air-permeable ozone-decomposing catalyst layer; and an ozone-decomposing ultraviolet lamp; the ozone-decomposing catalyst layer being located in a position where the catalyst layer is directly irradiated by the ozone-decomposing ultraviolet lamp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical section of an embodiment of deodorizing apparatus made according to the invention; 
     FIG. 2 is a transverse sectional view taken on line 2--2 of FIG. 1 with the ozone-decomposing layer removed as indicated by the broken lines; 
     FIG. 3 is a diagrammatic illustration of the procedures used in Experiment I; 
     FIG. 4 is a diagrammatic illustration of the procedures used in Experiment II; 
     FIG. 5 is a diagrammatic illustration of the procedures used in Experiment III; and 
     FIG. 6 is a diagram of hydrogen sulfide removal rates determined in Experiment II. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An example of a deodorizing apparatus made according to the present invention is shown in FIGS. 1 and 2. 
     In FIG. 1 and FIG. 2, the reference character G denotes a gas mixture of a malodorous substance and air and the arrow indicates the flow direction of the gas mixture. The deodorizing apparatus 10 includes a lower 13 and an upper housing 14 on support legs 12. The housings are hollow, and in the present instance are of sguare configuration to provide an upright flow passage 17 therethrough. Upstream in the flow passage 17, in the flow direction of the gas mixture G, the deodorizing apparatus is provided with a diffuser plate 40 of punched metal to provide a uniform distribution and rectification of the gas mixture of the malodorous substance and air throughout the entire cross section of the flow passage 17. Within the flow passage 17 there is an ozone-generating ultraviolet lamp 20, generating uv rays below a critical wavelength for producing ozone from oxygen in the air, an ozone-decomposing ultraviolet lamp 30 generating uv rays above a critical wavelength for producing nascent and molecular oxygen from the oxygen, a catalyst layer support 11 for mounting thereon an air-permeable ozone-decomposing catalyst layer, and an axial flow fan 60 employed as means for inducing air streams in a predetermined direction through the passage 17. 
     At the upper end of the lower housing 13, the wall of the housing is recessed at 11 to provide a support for an air-permeable ozone-decomposing catalyst layer 18 which can be mounted on the support 11 in a position where the catalyst layer is directly irradiated by the ozone-decomposing ultraviolet lamp 30. In the preferred embodiment, the lamps 20 and 30 comprise elongated tubes spanning across the flow passages 17 between and generally parallel to the diffuser plate 40 and the layer 17, the tubes being oriented perpendicular to each as shown. 
     The air-permeable ozone-decomposing catalyst layer 18 consists of, for example, a transition metal oxide, like nickel oxide, a noble metal, like platinum, or a mixture of a transition metal oxide and a noble metal, which is supported on a carrier of cordierite or the like. In the present embodiment, a nickel oxide-base catalyst layer in the form of an air-permeable filter is used. 
     The upper housing 14 is releasably attached to the upper end of the housing 13 to afford ready access to the layer 18 on the support 11 for servicing and/or removal and replacement. 
     The ozone-generating ultraviolet lamp 20 generates an ultraviolet ray of a wavelength smaller than 200 nm, mainly of a wavelength of 185 nm. On the other hand, the ozone-decomposing ultraviolet lamp 30 mainly generates an ultraviolet ray of a wavelength of 254 nm. These two kinds of ultraviolet lamps 20 and 30 each include means for adjusting their intensity as indicated at 25 and 35 in FIG. 2. 
     OPERATION 
     A flow of the gas mixture G which consists of a malodorous substance and air is generated by an air flow generating means, in the present case the fan 60 at the upper end of the housing 14. Ozone is produced by the ozone-generating ultraviolet lamp 20 from oxygen in the air to convert the gas mixture into an ozone-prevailing atmosphere. Thereafter, the ozone which is produced by the lamp 20 is decomposed by the catalyst layer 17 and the ozone-decomposing ultraviolet lamp 30 to generate nascent state oxygen with extremely strong oxidizing power for oxidation/decomposition of the malodorous substance. 
     As the ozone decomposition proceeds, the above-mentioned catalyst gradually loses its decomposing capacity due to a deteriorating reaction of the catalyst itself. However, according to the present invention the ozone-decomposing ultraviolet lamp 30 not only reduces the ozone to reduce the burden on the catalyst in decomposing the ozone, but also generates, by an ultraviolet ray (especially of 254 nm wavelength), nascent state oxygen which reacts inversely to the deteriorating reaction of the catalyst, thereby reactivating the catalyst and preventing its deterioration. 
     Thus, the deodorizing apparatus according to the present invention succeeds in advantageously incorporating the synergistic effects of the catalytic and ultraviolet decomposition systems which have been found to be insufficient in function when applied separately. 
     The illustrated deodorizing apparatus 10 operates as follows: 
     The gas mixture G which is suctioned into the deodorizing apparatus 10 through the plate 40 by the axial flow fan 60 produces ozone as it is irradiated by the ozone-generating ultraviolet lamp 20. The gas mixture G which now consists of ozone and a malodorous substance is then irradiated by the ozone-decomposing ultraviolet lamp 30 and admitted into the ozone-decomposing catalyst layer 17 which is also irradiated by the ozone-decomposing ultraviolet lamp 30. As a result, the ozone is forcibly decomposed, thereby generating nascent state oxygen with extremely strong oxidizing power to decompose the malodorous substance in the gas mixture G. 
     The ozone concentration in the gas mixture which is discharged from this operation is preferably smaller than 0.1 ppm from the standpoint of safety. For this purpose, the intensity of the ozone-generating ultraviolet lamp 20 of the deodorizer 10 is adjusted so as to maintain the ozone concentration in the gas mixture to a value smaller than 0.1 ppm. 
     It is to be understood that the foregoing embodiment of the deodorizing apparatus has been shown and described by way of example, and, needless to say, it should not be construed as limitative of the present invention. 
     EXPERIMENTAL EXAMPLES 
     The present inventors conducted the following experiments in order to confirm the effects of the deodorizing apparatus as disclosed in the foregoing embodiment, in which the catalyst deterioration was accelerated by the use of ozone in a high concentration of 300 ppm in the experiments for observation of the catalyst deterioration as well as in the experiments for observation of the action of the 254 nm ultraviolet ray on the catalyst. 
     Experiment I 
     There was firstly conducted an experiment for measuring the variations in ozone decomposing capacity of the catalyst layer. 
     Shown in FIG. 3 is an experimental apparatus for forcibly deteriorating the ozone-decomposing catalyst layer by means of high concentration ozone, in which indicated at 50 is an air-permeable ozone decomposing catalyst layer for forcibly decomposing ozone; at 21 is an ozone-generating ultraviolet lamp for generating ozone from oxygen by the action of the ultraviolet ray; and at 41 and 42 are diffuser plates of punched metal. A fan 62 is connected to an ozone generating chamber 71 to send air thereinto. The air which has been sent into the ozone generating chamber 71 by the fan 62 is formed into rectified or diffused streams by the diffuser plate 41 and is irradiated by the ozone-generating ultraviolet lamp 21 to generate ozone. The air which contains the generated ozone flows into an ozone-decomposing chamber 72 through a connecting duct 81, in which the ozone-containing air is formed into rectified streams by the rectifier plate 42 and into contact with the ozone-decomposing catalyst layer 50. Indicated at 82 is a sampling pipe upstream of the ozone-decomposing catalyst layer 50; at 83 is a sampling pipe downstream of the ozone-decomposing catalyst layer 50; and at 84 a discharge pipe. 
     In this experimental apparatus, the ozone-decomposing catalyst layer 50 employed as a carrier a ceramic filter with a three-dimensional structure of cordierite, supporting thereon a nickel oxide-base catalyst, and air was fed by the fan 62 at a volumetric flow rate of 2 liters/min. 
     Samples (hereinafter S82 and S83) were taken through the sampling pipes 82 and 83 in an initial stage of the experiment, after a lapse of 50 hours and after a lapse of 100 hours, respectively, to measure the ozone concentration. 
     In this experiment, the intensity of the ozone-generating ultraviolet lamp 21 was adjusted to generate ozone in a concentration of 300 ppm. 
     The results of the experiments are shown in Table 1 below. 
     
                       TABLE 1______________________________________        S 82 (ppm)                S 83 (ppm)______________________________________Initial stage  300       1.050 hours later 300       46100 hours later          300       98______________________________________ 
    
     From these experimental results, it was confirmed that the ozone-decomposing capacity of the catalyst deteriorated with time. 
     Experiment II 
     Next, a comparative experiment was conducted to examine the deodorizing capacity of samples obtained from the layer 50 in the foregoing experiment, namely, a sample I of the ozone-decomposing catalyst layer in the initial stage, a sample II of the ozone-decomposing catalyst layer after a time lapse of 50 hours, and a sample III of the ozone-decomposing catalyst layer after a time lapse of 100 hours. 
     FIG 4 illustrates an apparatus which was used in the aforementioned comparative experiment. A cross-flow fan 61 is provided within a hermetically sealed chamber 70 of 216 litres in volume. The sealed chamber 70 is provided with a measurement hole 80 to be used for gas injection and sampling. 
     The sample I was mounted in the place of layer 17 on the ozone-decomposing catalyst layer support 11 of the deodorizing apparatus 10 of FIGs. 1 and 2 and the apparatus was placed in the sealed chamber 70. Turning on the cross-flow fan 61, hydrogen sulfide was slowly injected by means of an injector 90 while measuring the gas through a gas detector tube (not shown) to hold the hydrogen sulfide concentration at about 100 pp. Thereafter, the ozone-generating ultraviolet lamp 20 and ozone-decomposing ultraviolet lamp 30 of the deodorizer 10 were energized, and at the same time the axial flow fan 60 was started. At predetermined time intervals, the hydrogen sulfide concentration in the sealed chamber 70 was measured by the gas detector tube. 
     The same experimental procedures were repeated for the samples II and III. 
     The results of experiments on the samples I to III are shown in Tables II to IV, respectively. 
     FIG. 6 shows the hydrogen sulfide removal rates which were obtained from the results of these experiments. 
     
                       TABLE II______________________________________(Sample I)Time (hr) H.sub.2 S Concentr&#39;n (ppm)                    Removal Rate (%)______________________________________0         112             01         21             812         7              943         0              100______________________________________ 
    
     
                       TABLE III______________________________________(Sample II)Time (hr) H.sub.2 S Concentr&#39;n (ppm)                    Removal Rate (%)______________________________________0         98              01         38             612         21             793         12             884          5             955          1             99______________________________________ 
    
     
                       TABLE IV______________________________________(Sample III)Time (hr) H.sub.2 S Concentr&#39;n (ppm)                    Removal Rate (%)______________________________________0         108             01         60             442         43             603         28             744         22             805         14             87______________________________________ 
    
     It was confirmed from the results of the foregoing experiments that the capacity for decomposing the malodorous substance dropped with deterioration in the ozone decomposing capacity of the catalyst. Accordingly, in order to carry out the deodorizing operation effectively, it is necessary to prevent the deterioration of the ozone-decomposing catalyst layer which occurs as a result of ozone decomposition. 
     Experiment III 
     The following experiment was conducted next to examine the effects of the ultraviolet ray of 254 nm in wavelength which acts as a means for preventing the catalyst deterioration in the ozone decomposition. 
     FIG. 5 shows the apparatus employed for experiment III, which has a fan 63 attached to one side of an ozone-generating chamber 73 for sending air thereinto. Provided within the ozone-generating chamber 73 are a diffuser plate 43 of punched metal and an ozone-generating ultraviolet lamp 22. Provided in an ozone-decomposing chamber 74 are a diffuser plate 44 of punched metal, an ozone-decomposing ultraviolet lamp 32 adapted to generate an ultraviolet ray mainly of 254 nm wavelength, and an ozone-decomposing catalyst holder 52 located in a position which is directly irradiated by the ozone-decomposing ultraviolet lamp. The ozone-decomposing chamber 74 is communicated with the ozone-generating chamber 73 through a connecting duct 85. Denoted at 86 is a sampling pipe upstream of the ozone-decomposing catalyst layer (not mounted in FIG. 5); at 87 is a sampling pipe downstream of the ozone-decomposing catalyst layer; at 88 is a discharge pipe; and 89 is a sampling pipe downstream of the ozone-generating chamber 73, and upstream of the chamber 74. 
     Firstly, without mounting the catalyst on the ozone-decomposing catalyst holder 52, air was fed by the fan 62 at a volumetric flow rate of 2 liters/min, and simultaneously the ozone-generating ultraviolet lamp 22 was turned on, while adjusting the ozone concentration to 300 ppm. Then, the ozone-decomposing ultraviolet lamp 32 was turned in, measuring the ozone decomposing capacity of the 254 nm wavelength ultraviolet ray alone from the ozone concentration. The results are shown in Table V below. 
     
                       TABLE V______________________________________Downstream of ozone-              Downstream of Ozone-Generating Chamber Decomposing Chamber(at 89)            (at 87)______________________________________Ozone   300            180Concentr&#39;n(ppm)______________________________________ 
    
     Thereafter, a fresh ozone-decomposing catalyst layer (similar to Sample I) was fitted in the catalyst holder 52, measuring the ozone decomposing capacity on the basis of the ozone concentration in an initial stage and after a time lapse of 100 hours with the ozone-decomposing ultraviolet lamp 32 in both on- and off-states. The results are shown in Table VI below. 
     
                       TABLE VI______________________________________OZONE CONCENTRATION (ppm)           Downstream of Catalyst LayerUpstream of     (at 87)  Catalyst Layer               Initial StageLamp 32  (at 89)      of Measurement                           100 hrs later______________________________________ON     300          1.0          34OFF    300          1.2         103______________________________________ 
    
     As a result of this experiment, it has been confirmed that the 254 nm wavelength ultraviolet ray acts not only to reduce the amount of ozone to be treated with the catalyst by decomposing ozone but also to reactivate the catalyst with nascent state oxygen which is produced by the ultraviolet rays, thereby preventing deterioration of the catalyst. 
     EFFECTS OF THE INVENTION 
     According to the present invention, in the deodorization of malodorous substances with nascent state oxygen which occurs as a result of forced decomposition of ozone by an ultraviolet ray, it becomes possible to prevent deterioration of the ozone-decomposing catalyst and conseguently to maintain the deodorizing capacity effectively by irradiating the ozone-decomposing catalyst layer with an ultraviolet ray (especially of 254 nm in wavelength) from an ozone-decomposing ultraviolet lamp in an ozone-prevailing atmosphere to reactive the ozone-decomposing capacity of the catalyst. 
     With regard to the action of the ultraviolet ray on malodorous substances (e.g. sulfides, ammonia, etc.), the photo energization by the 185 nm wavelength ultraviolet ray decomposes the malodorous substances or renders them easily decomposable, so that it has an effect of promoting the oxidative decomposition of the substances by nascent state oxygen in the next stage. Further, since the ozone-generating ultraviolet lamp can generate a 254 nm wavelength ultraviolet ray simultaneously with the 185 nm wavelength ultraviolet ray, the deodorizing capacity can be improved all the more by providing an ozone-generating ultraviolet lamp also in a position which it can directly irradiate the ozone-decomposing catalyst layer. 
     With regard to sterilization, the 254 nm wavelength ultraviolet ray has an excellent sterilizing effect. 
     While a preferred embodiment of the apparatus of the present invention has been illustrated and described, changes and modifications may be made therein and thereto within the scope of the present invention defined in appended claims.