JPH049083B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for treating malodorous exhaust gas containing poorly soluble compounds such as reducing sulfur compounds. PRIOR ART In recent years, various odors have come to be perceived as malodors, and it has become necessary to treat them. The emission sources are wide-ranging, including livestock farming, fertilizer and feed manufacturing, food manufacturing, and chemical industry. Bad odors are generally complex odors, in which various components are mixed in the exhaust gas and emit a bad odor. Many compounds are regulated as legal malodorous substances, of which reducing sulfur compounds such as hydrogen sulfide, methyl mercabutane, methyl sulfide, and methyl disulfide are representative malodorous substances. These reducing sulfur compounds are rarely discharged alone, and generally lower fatty acids, amines, nitrogen compounds such as nitriles, alcohols, aldehydes, etc. coexist. In general, the proportion of components other than the reducing sulfur compound is often higher, and this causes problems in the treatment of malodorous gases, as will be described later. Conventionally, foul-smelling exhaust gas has been treated using combustion methods, activated carbon adsorption methods,
It is treated by chemical oxidation method etc. Among these, the activated carbon adsorption method has the problem that the activated carbon must be replaced periodically, and, like the combustion method, has the problem of high running costs. In addition, exhaust gas containing reducing sulfur compounds is
It is generally treated by a chemical oxidation method using sodium hypozincate, potassium permanganate, etc., and this method is compact in terms of equipment and has lower running costs than the above two methods. . On the other hand, there is a method of oxidizing and decomposing malodorous components using the metabolic action of microorganisms, and this method has been used for a long time as a soil deodorizing method, but this method has the disadvantage of requiring a large area. In recent years, a deodorizing method using a washing tower method using activated sludge has been proposed, and this method is characterized by much lower running costs than other methods. However, this method also has the disadvantage of requiring large-scale equipment because the absorption and removal rate is low for poorly soluble substances such as reducing sulfur compounds, and the amount of decomposition per kilogram of microorganisms and a few grams per day is small. be. From this point of view, the chemical oxidation method seems to be the most suitable method for reducing sulfur compounds, but as mentioned earlier, only reducing sulfur compounds exist alone in foul-smelling exhaust gas. is rare. Therefore, there are disadvantages in that the amount of oxidizing agent consumed by other components in the exhaust gas increases, and that they inhibit the reaction, making it impossible to obtain the desired treatment performance. Therefore, in this chemical oxidation method, alkaline components such as ammonia and amines in the exhaust gas are first removed with acidic chemicals such as sulfuric acid, and then acidic components such as lower fatty acids are pretreated with alkaline chemicals such as caustic soda, and then reducing sulfur compounds are removed. A method was taken to remove the . Therefore, the chemical oxidation method not only requires complicated equipment, but also has the disadvantage that it requires post-treatment of components absorbed by acids and alkalis during pretreatment, resulting in high chemical costs. There is a problem in that neutral substances that cannot be treated inhibit the reaction with the oxidizing agent, resulting in unsatisfactory treatment performance. Purpose and Structure of the Invention Therefore, as a result of intensive research to eliminate the problems of the prior art described above, the present inventors have developed a method for converting exhaust gas containing poorly soluble compounds such as reducing sulfur compounds into activated sludge and circulating fluid. Pretreatment is carried out by contacting gas and liquid in a cleaning tower, allowing reducing sulfur compounds that are absorbed and decomposed in small amounts to pass through, ensuring that other odorous components are removed and decomposed, and then eliminating substantially only the reducing sulfur compounds with bad odors. Deodorizing exhaust gas containing reducing sulfur compounds effectively and economically by bringing the exhaust gas as a component into gas-liquid contact with an aqueous solution containing an oxidizing agent to reliably oxidize the reducing sulfur compounds. We have discovered that it is possible to do this, and have come up with the present invention. DETAILED DESCRIPTION OF THE INVENTION According to the present invention, when deodorizing exhaust gas containing a reducing sulfur compound together with a lower fatty acid, an amine, a nitrile, an alcohol, or an aldehyde,
The exhaust gas is pretreated by being brought into gas-liquid contact with a circulating cleaning liquid containing activated sludge in a cleaning tower, and then the pretreated exhaust gas is brought into gas-liquid contact with an aqueous solution containing sodium hypochlorite or potassium permanganate. An exhaust gas treatment method is provided. Hereinafter, the method of the present invention will be specifically explained with reference to the accompanying drawings. The exhaust gas 11 to be treated, which contains malodorous components such as reducing sulfur compounds such as hydrogen sulfide, methyl mercaptan, methyl sulfide, and methyl disulfide, is first passed through a cleaning tower 12.
feed into the bottom inlet of. Exhaust gas 11 is sent to cleaning tower 12
The circulating washing water 13 containing activated sludge (or activated sludge containing activated carbon in some cases) rising inside the column and falling from the top of the column is brought into countercurrent gas-liquid contact, for example, on an appropriate number of trays 14. Then, malodorous components (for example, fatty acids, amines, aldehydes, and alcohols) other than reducing sulfur compounds in the exhaust gas 11 are absorbed into the circulating cleaning water 13. As the cleaning tower 12, any gas-liquid contact device can be used, such as a perforated plate tower, other plate towers, packed towers, and various scrubbers. The exhaust gas thus treated is supplied as a gas from the top of the column to the bottom inlet of the second column 15 through, for example, a mist separator. The circulating cleaning water 13 that has absorbed the malodorous components in the exhaust gas 11 enters the circulating water tank 16, where it undergoes microbial oxidative decomposition by activated sludge, which is a malodorous component, and is completely decomposed into carbon dioxide gas and water. This washing water is circulated to the washing tower (first etc.) 12 by a pump 17. In order to prevent the accumulation of inorganic salts in the circulating water system, a part of the washing water 13 is used, for example, to settle suspended sludge in a settling tank and blow the water as overflow water of the settling tank. The separated settled sludge is extracted from the lower part of the settling tank and returned to the circulation water tank 16. Circulating water tank 1
Makeup water is added continuously or intermittently to 6, and a PH adjuster and nutrients for activated sludge are supplied to keep the PH of circulating water 13 in a range suitable for activated sludge. Next, the gas pretreated in the cleaning tower 12 is transferred to the second
etc. 15 bottom inlet. In the second stage, etc., the oxidant circulating water 18 is brought into countercurrent gas-liquid contact, for example, on an appropriate number of trays 19, to oxidize and decompose residual components such as reducing sulfur compounds in the exhaust gas. etc. 2 towers 15
As with the cleaning tower 12, any gas-liquid contact device can be used. The oxidizing agent circulating water 18 contains, for example, about 0.01% to 3% of general oxidizing agents such as sodium hypozinc oxide and potassium permanganate,
The water is circulated from the circulation tank 20 to the second etc. 15 by the pump 21 . The remaining malodorous components in the exhaust gas are oxidized and decomposed by the oxidizer circulating water, and the exhaust gas 22 from which the malodorous components have been decomposed and removed is discharged to the outside of the system. Note that depending on the composition of the exhaust gas, the order of the microbial treatment and the oxidizing agent treatment may be reversed. EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. Examples 1 to 4 Exhaust gas from an edible oil manufacturing factory containing odor components such as reducing sulfur compounds and organic substances was treated according to the flow shown in the attached Figure 1. As the cleaning tower, both the first tower 12 and the second tower 15 are perforated plate towers (tower diameter 100 mm) with 3 plates, and the processing gas amount is 120 mm.
We conducted experiments and compared the four combinations of treatment methods shown in Table 1 below by changing the circulating cleaning water in each column under the operating conditions of m ³ /min and liquid-gas ratio (L/G) 10/m ³ . investigated.

[Table] Table 2 shows the measurement results of reducing sulfur compound concentration and odor concentration for each treatment method, and Table 3 shows the amount of each chemical used.

【table】

【table】

[Table] The treated gases of Examples 1, 2, and 3 were analyzed by gas chromatography, and the resulting chart is shown in Figure 2 together with the chart of the original exhaust gas. In Figure 2, chart A is the gas chromatography chart of the original exhaust gas. Charts B, C and D are charts of the treated exhaust gases of Examples 2, 1 and 4, respectively.The analysis was conducted under the following conditions: Column: PEG-1000 (2m) Column temperature: 100°C Detection part temperature: 125℃ Nitrogen flow rate: 31ml/min Detection part: FID Chart speed: 40mm/min As shown in Example 1, when using microbial treatment alone without using chemicals, running costs are low, but odor concentration can be removed. The rate was about 60%, which was not satisfactory.This is because, as can be seen from gas chromatography chart C, most of the peaks of hydrocarbon components have been processed compared to the original exhaust gas (chart A); This is because the removal rate of reducing sulfur compounds is only 20 to 70%, which is lower than in Example 1. Next, as shown in Example 2, in the case of sodium hypochlorite treatment alone, almost all reducing sulfur compounds are removed. Even though the odor concentration has been removed, the odor concentration is only about 76% removed.This is because, as shown in chart B in Figure 2, a considerable amount of components have been removed compared to the components in the raw gas. Compared to Chart D in Figure 2, there is a considerable amount of residual components, and it is thought that in the initial components of Chart, different components were generated due to oxidation compared to the original Chart.For these reasons, the odor concentration has decreased. Example 4 is an example in which exhaust gas was first treated with microorganisms and then treated with hypochlorous acid by the method according to the present invention, but the removal rate of reducing sulfur compounds was also the same as in Examples 1 and 2.
The odor concentration removability, which is the objective of the present invention, is not just an additive effect but a synergistic effect that improves the processability by more than one order of magnitude compared to the processability of Examples 1 to 3. This is what brought about this. The reason for this is
It could not be obtained by the methods of Examples 1 and 2. Complete removal of reducible sulfur compounds and chart D in Figure 2
As is clearer, this is due to the almost complete removal of other components. Moreover, in the method of the present invention in Example 4, despite using an oxidizing agent, the amount of caustic soda consumed is 1/3 compared to single chemical treatment.
In addition, the consumption of sodium hypochlorite was significantly reduced to 1/14. These results show that the method for treating exhaust gas containing reducing sulfur of the present invention, which combines microbial treatment and oxidizing agent treatment, can completely reduce odor concentration, which was not possible with each exhaust gas treatment alone. . Example 5 Activated carbon was added to the absorption liquid in the microbial treatment process of Example 4.
Exhaust gas treatment was carried out in the same manner as in Example 4 except that 1000 mg/g was added. The results were as shown in Table 4.

[Table] *See footnote to Table 2

[Brief explanation of drawings]

The first drawing is a drawing showing an example of the flow of the method of the present invention, and the second drawing is a gas chromatograph chart of the original exhaust gas and the treated exhaust gases of Examples 1, 2, and 4. 12...First washing tower, 13...Activated sludge-containing circulating cleaning liquid, 15...Second washing tower, 18... Oxidizing agent-containing circulating cleaning liquid.

Claims (1)

[Claims] 1 Reducing sulfur compounds, lower fatty acids, amines,
When deodorizing exhaust gas containing nitrile, alcohol, or aldehyde, etc., the exhaust gas is pretreated by bringing it into gas-liquid contact with a circulating cleaning solution containing activated sludge in a cleaning tower, and then the pretreated exhaust gas is treated with sodium hypochlorite or filtrate. An exhaust gas treatment method characterized by bringing a gas-liquid into contact with an aqueous solution containing potassium manganate.