JPH08281064A - Ozone removing method - Google Patents

Abstract

PURPOSE: To efficiently remove ozone from an ozone-contg. waste gas with a relatively simple method by bringing the ozone-contg. gas into contact with an aq. soln. wherein hydrogen sulfide and/or metal sulfide are dissolved. CONSTITUTION: The yield of ozone of the ozonizer 1 is controlled by applying a silent discharge to dry air and adjusting the voltage at this time, and an optional amt. of ozone is mixed in the air to be supplied to an ozonation device by a motor-driven fan 2. Meanwhile, a motor-driven pump 4 is used to circulate an alkaline cleaning soln. and constitutes a cleaning soln. circulating line with a valve 5, flowmeter 6, pressure gage 7, spray nozzle 8, etc., and the circulation of the cleaning soln. is optionally adjusted by the valve 5 and flowmeter 6. When ozone is removed by using this device, an aq. alkaline soln. of hydrogen sulfide and/or a metal sulfide is used as the cleaning soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently removes excess ozone released from ozone sterilization equipment, ozone treatment equipment such as sewage, ozone bleaching equipment, ozone oxidation treatment equipment, etc. with simple equipment. It is about the method that can be done.

[0002]

BACKGROUND OF THE INVENTION As is well known, ozone is used for sterilization, bleaching, disinfection, etc. because it has an excellent oxidizing action and bleaching action and sterilizing action accompanying it. It is also used in a method of adsorbing and collecting dust on an electrode plate such as a wire net charged with positive ions by utilizing the effect that fine dust in the air is charged with negative ions.

Furthermore, exhaust from sewage / sewage treatment plants and deodorization of toilets, deodorization / sterilization of refrigerators, sterilization of clean rooms, deodorization / sterilization of factories, deodorization / sterilization of semiconductor manufacturing facilities and hospitals, sterilization of food storage, air purifiers (For indoor use, automobile use, etc.)
In addition to being used for deodorization and sterilization, it is also widely used for aging of food ingredients and promotion of plant growth.

In these applications, the higher the ozone concentration is, the more effective it is.
Used at concentrations higher than (0.2 mg / m ³ ). Ozone spontaneously decomposes in the air to oxygen, but if there are few impurities and moisture that should be subjected to the oxidizing action of ozone, it will take dozens of minutes for the ozone to decrease to half, so in most cases residual ozone will be removed. Equipment is required.

By the way, ozone is more easily decomposed in water than in air, which is supported by the fact that sterilization, deodorization, decolorization, etc. by ozone are more likely in water than in air. Therefore, ozone water is used for sterilization of water supply, pool purification, cooling tower purification, elevated water tank purification, well water sterilization, ultrapure water production, sterilization / decolorization of liquor, beer, juice, etc. Deodorization, transparency of aquarium tank, purification of rivers, advanced treatment of sewage,
COD reduction and decolorization of factory wastewater, decolorization of dyeing wastewater, bleaching of pulp, algae killing and shellfish killing of power plant cooling water pipes and factory water pipes,
It is widely used for sterilization, disinfection, freshness maintenance, decolorization of food, and sterilization of sanitary equipment.

In order to dissolve ozone generated in air or oxygen in water, ozone on the air side needs to have a high concentration and a high pressure, and it is also necessary to treat ozone remaining in the air after water is dissolved. Become.

Therefore, various methods have been proposed as a method for removing the residual ozone discharged from the ozone treatment equipment as described above, but a typical method currently in practical use is as follows.
It is a method of adsorbing and removing using activated carbon, and a method of decomposing and removing using an ozone decomposition catalyst. However, in the former method of adsorptive removal of activated carbon, the activated carbon reacts with ozone and the activated carbon is rapidly oxidized and consumed.Therefore, the activated carbon must be frequently regenerated or replaced, and there is a risk of ignition depending on the processing conditions. Come on. The latter method of decomposing / removing ozone has an advantage that ozone can be efficiently removed even with a small capacity, but on the other hand, it has a drawback that the decomposition catalyst is very expensive. Furthermore, in order to exert their effects effectively, whether it is activated carbon or a catalyst, the humidity of the gas to be treated must be maintained at about 80% or less, and moreover the dust and impurities in the gas to be treated can cause the humidity to deteriorate. It is easy to cause clogging and decrease in activity.

Another method for removing excess ozone used in ozone treatment equipment that uses ozone for waste treatment and sludge treatment is to pass ozone-containing exhaust gas through an alkaline aqueous solution or ozone in a room where the aqueous solution is sprayed. A method of absorbing ozone by an alkaline aqueous solution to remove it by passing the contained exhaust gas has been put into practical use, but in this method, about 50% of ozone in the exhaust gas is absorbed and removed at most.

Further, in order to remove ozone that cannot be completely removed by the alkali washing tower, there is a method in which an activated carbon adsorption method or an ozone deodorizing catalyst method is additionally provided as described above. It is necessary to keep the humidity of the gas to be treated at about 80% or less, and the pre-alkaline cleaning method performed to maintain the activity raises the humidity and causes an adverse effect. Installation is not preferable because it causes increase in equipment cost and operating cost.

Further, a method of decomposing residual ozone by using an aqueous solution of sodium thiosulfate as a cleaning solution is also known, but this method has a problem that sulfide is generated due to decomposition of sodium thiosulfate, However, it is essential to remove ozone by an adsorption or decomposition tower that requires dehumidification treatment in advance.

[0011]

The present invention has been made in view of the above circumstances, and an object thereof is to efficiently remove ozone from ozone-containing exhaust gas by a relatively simple method. It seeks to provide a way to do it.

[0012]

The constitution of the ozone removing method according to the present invention which was able to solve the above-mentioned problems is as follows: (1) An ozone-containing gas is an aqueous alkaline solution in which hydrogen sulfide and / or metal sulfide is dissolved. To remove ozone, or (2) treat ozone-containing gas with hydrogen sulfide and / or
Alternatively, an alkaline aqueous solution containing a metal salt that absorbs and removes ozone by contacting it with an alkaline aqueous solution in which a metal sulfide is dissolved, and reacts the produced hydrogen sulfide-containing gas with hydrogen sulfide to produce a precipitate of the metal sulfide. The present invention has a gist in that the hydrogen sulfide in the hydrogen sulfide-containing gas is removed as a precipitate of metal sulfide by contacting with.

In carrying out the above methods (1) and (2), sodium sulfide and / or potassium sulfide is used as the metal sulfide, and the concentration of hydrogen sulfide and / or metal sulfide in the alkaline aqueous solution is adjusted. By maintaining the sodium sulfide conversion concentration at 100 to 300 ppm, ozone can be removed more efficiently. Further, as the alkaline component that constitutes the alkaline aqueous solution used when carrying out this method, ozone removal efficiency and handleability,
Sodium carbonate is the most effective in consideration of cost, etc., and zinc salt is used as the metal salt, and the content of the zinc salt in the alkaline aqueous solution is adjusted to include the suspension and precipitate in the liquid. The removal of ozone and the removal of sulfur compounds that may be produced during the ozone removal by maintaining the equivalence ratio to 3 times or more with respect to the sulfide absorbed and accumulated in the alkaline aqueous solution and as a suspension or a precipitate. Can be carried out more efficiently.

[0014]

The inventors of the present invention use the double cleaning type ozone treatment apparatus as shown in FIGS. 1 to 3 below, and use the sodium carbonate aqueous solution or the cleaning solution in which various substances are added as the cleaning solution. The ozone removal efficiency, and further the removal efficiency of hydrogen sulfide contained in the exhaust gas in the ozone removal step were examined. As a result, although the absorption and removal of ozone was insufficient with an alkaline aqueous solution such as sodium carbonate, the following surprising facts were revealed.

When the ozone-containing gas is treated with a cleaning liquid in which hydrogen sulfide and / or metal sulfide is dissolved in an alkaline aqueous solution, ozone can be absorbed and removed very efficiently. If the concentration of hydrogen sulfide and / or metal sulfide dissolved in an alkaline aqueous solution is maintained at 100 to 300 ppm, ozone can be removed by 99.9% or more (up to 0.002 ppm or less). When the ozone-containing gas and the hydrogen sulfide-containing gas are introduced into separate cleaning towers for cleaning, and the ozone-containing gas is cleaned with an alkaline cleaning liquid in which hydrogen sulfide is dissolved, the
Can be removed by 9.9% or more (up to 0.002 ppm or less).

When carrying out the ozone removal methods (1) to (3) above, hydrogen sulfide may be mixed in the ozone-removed exhaust gas, and the hydrogen sulfide reacts with hydrogen sulfide to form a precipitate of metal sulfide. When it is brought into contact with an alkaline aqueous solution containing a metal salt, preferably a zinc salt, the hydrogen sulfide in the hydrogen sulfide-containing gas can be efficiently removed as a precipitate of metal sulfide.

The configuration of FIGS. 1 to 3 used in the above test will be described. FIG. 1 is a schematic view of an apparatus used in the ozone removal test and the examples. In the figure, 1 is an ozone generator, which discharges dry air silently and adjusts the voltage at this time to generate ozone. It has a function of controlling the amount of generation, and allows the ozone to be mixed in an arbitrary amount into the air sent to the ozone processing device by the electric fan 2. The electric fan 2 has a turbo type structure and is configured so that the air volume can be arbitrarily controlled by an inverter. Reference numeral 4 denotes an electric pump for circulating the alkaline cleaning liquid, which constitutes a cleaning liquid circulation path together with a valve 5, a flow meter 6, a pressure gauge 7, a spray nozzle 8 and the like, and the valve 5 and the flow meter 6 circulate the cleaning liquid. It is configured to allow the amount to be adjusted arbitrarily. 9 is a main body of the washing tower, an air flow measuring pipe 10 is connected to the upper part of the main body, and a wind speed sensor is arranged inside the main body 9. The inside of the main body 9 of the washing tower is made of synthetic resin as shown in FIG. A twin-wave structure gas-liquid contact promoting filler 11 and a mist separator 12 in which a three-dimensional knitted fabric and a mesh wire are combined are provided. When ozone is removed using this apparatus, an alkaline aqueous solution in which hydrogen sulfide and / or metal sulfide is dissolved is used as a cleaning liquid as described later in detail.

FIG. 2 is a schematic explanatory view showing a double-cleaning tower ozone removing apparatus used in other ozone removing tests and examples. 9 is a double-cleaning tower, which is made of transparent hard vinyl chloride resin. The lower washing tower 9a and the upper washing tower 9
It has b and the mist separator 12. The gas-liquid contact promoting fillers 11a and 11b arranged in the lower cleaning tower 9a and the upper cleaning tower 9b are constituted by a twill wave structure as described above. Reference numeral 13 is a perforated plate for lowering a part of the cleaning liquid used in the upper cleaning tower 9b to the lower cleaning tower 9a, and is provided with a large number of holes. A cleaning liquid circulation line is formed between the electric pump 4, the valve 5, the flow meter 6, the spray nozzle 8 and the cleaning liquid storage tank 14, and a part of the cleaning liquid passes through a tube (not shown) connected to the bypass 15. A circulation line that directly returns to the cleaning liquid storage tank 14 is configured. The ratio between the regular circulation amount and the bypass circulation amount is the number and size of the holes formed in the perforated plate 13,
Further, it is constructed so that it can be arbitrarily adjusted by operating the valve. When removing ozone using such an apparatus, an alkaline aqueous solution in which hydrogen sulfide and / or metal sulfide is dissolved is used as a cleaning liquid.

Reference numeral 16 is a fan base, 17 is a lower electric fan, 18 is an upper electric fan, 19 is a lower fan damper, and 20 is an upper fan damper. It is designed so that it can be tested with the air volume. Reference numeral 21a is an exhaust pipe for both wind velocity measurement and gas analysis, and the air sucked from the duct 22a is supplied with ozone sent from the ozone generator and then enters the lower cleaning tower 9a to fill the lower part. Material 11
After coming into contact with the cleaning liquid when ascending a, the exhaust pipe 21a
Is discharged as a processing gas. Further, the air sucked by the electric fan 18 from the duct 22b enters the upper washing tower 9b to be washed, and then is discharged through the exhaust pipe 21b for both wind speed measurement and gas analysis.

Reference numeral 23 is an ozonizer mount, and 24 is an ozonizer made of ceramics. Ozone is generated by silently discharging the air sucked by the air pump 25 and passing through the desiccant filling tube 26. Reference numeral 27 denotes an ozonizer power supply, which is configured to control the amount of ozone generated by adjusting the inlet voltage with a bolt slider 28, and the generated ozone can be supplied to the inlet side of the upper electric fan 18 at an arbitrary flow rate. .

FIG. 3 is a schematic explanatory view showing a two-column in-line type ozone removing apparatus used in other ozone removing tests and examples. 9a and 9b are washing towers, each of which is as described above. Twin-ave structure filler 11a for promoting gas-liquid contact,
11b is arranged and the mist separator 1 is provided above.
2a and 12b are provided, and electric pumps 4a and 4b (valves 5a and 5b, flowmeters 6a and 6b, pressure gauges 7a and 7b are omitted) and spray nozzles 8a are provided in the same manner as shown in FIG. 1, respectively. , 8b constitute a circulation path of the cleaning liquid, and the circulation amount of the cleaning liquid can be arbitrarily adjusted by a valve and a flow meter as in FIG. When removing ozone using this apparatus, the cleaning tower 9a,
While charging and circulating an alkaline aqueous solution in each of 9b,
In the cleaning tower 9a, the alkali aqueous solution of metal sulfide is stored in the storage tank 14
In the cleaning tower 9b, an alkaline aqueous solution of a metal salt that reacts with hydrogen sulfide to form a precipitate of sulfide is supplied from the storage tank 14b by the pump Pb in the cleaning tower 9b.

First, a double-cleaning tower ozone removing apparatus as shown in FIG. 2 was used, a 5% aqueous solution of sodium carbonate was used as a cleaning solution, and sodium sulfide (N) was added to the aqueous solution.
The case of variously changing the addition amount of _{a 2 S · 9H 2 O)} , was subjected to a ozone removal test, such results as shown in Table 1 were obtained.

[0023]

[Table 1]

As is clear from Table 1, the concentration of ozone at the outlet cannot be reduced to 1 ppm or less when a cleaning solution consisting of a single aqueous solution of sodium carbonate is used. However, when an appropriate amount of sodium sulfide is contained in the cleaning liquid, the ozone removal rate is dramatically improved, especially at 200 p
When an alkaline cleaning solution in which sodium sulfide of pm or more, more preferably 250 ppm or more is dissolved is used, 90
% Or more, or 95% or more, a high level ozone removal rate is obtained, and the outlet ozone concentration is 0.05 p
It can be seen that it can be reduced to pm or less. Further, it can be seen that such ozone removal efficiency can be further enhanced by setting the gas-liquid contact time at the filler portion longer.

According to another confirmation by the present inventors, Na ₂ S · x, which is the most common sodium sulfide,
Not only when using H ₂ O (hexahydrate, 9-hydrate),
When an anhydride is used or sodium polysulfide (N
a ₂ S ₅ etc.) and sodium hydrosulfide (NaSH ・ 2H ₂
It was confirmed that the same ozone removing effect can be obtained even when O) or the like is used.

Further, even when a cleaning liquid in which hydrogen sulfide is blown into an alkaline aqueous solution to generate sodium sulfide is used, the same effect can be obtained. Considering these facts, for example, a method of absorbing sulfide by treating an exhaust gas containing sulfide such as hydrogen sulfide with an alkali cleaning liquid and absorbing ozone by using the alkali cleaning liquid absorbing the sulfide as sodium sulfide. Is also considered to be effective.

Therefore, using the double-cleaning tower ozone removing device shown in FIG. 2 and using a 5% aqueous solution of sodium carbonate as a cleaning liquid, ozone is mixed with the air sucked from the duct 22a and sucked from the duct 22b. An attempt was made to mix hydrogen sulfide into the air to make the alkali cleaning liquid circulating in the cleaning towers 9a and 9b absorb hydrogen sulfide, and at the same time to make the alkali cleaning liquid absorbing the hydrogen sulfide absorb ozone.

The results are shown in FIG. 5, in which hydrogen sulfide was not substantially absorbed in the alkaline cleaning liquid at the initial stage of the treatment and the concentration of sodium sulfide in the cleaning liquid was low, so that ozone was almost removed. However, as the treatment time elapses and hydrogen sulfide is absorbed in the cleaning liquid, and the concentration of sodium sulfide in the cleaning liquid increases, the ozone removal rate increases proportionally, and the hydrogen sulfide conversion rate is almost saturated. 100% after the concentration reached 200 ppm
It was confirmed that an ozone removal rate close to the above was obtained. From this, as the alkaline cleaning liquid used for ozone absorption, for example, the sulfide-absorbed alkaline cleaning liquid used to remove hydrogen sulfide, which is the main malodorous component discharged from sludge treatment equipment, waste treatment equipment, etc. It is understood that it can be effectively used for ozone treatment.

FIG. 6 is a graph showing the results of examining the ozone removal rate when various ratios of ozone and hydrogen sulfide supplied to the alkali washing tower were examined in the ozone removal experiment. From this graph, It can be seen that in order to remove ozone efficiently, hydrogen sulfide should be supplied in an amount about 5 times the molar equivalent of ozone or more.

As is clear from the above experiment, when a cleaning liquid in which an appropriate amount of hydrogen sulfide or sodium sulfide is dissolved in an alkaline cleaning liquid is used, ozone in the air can be efficiently absorbed and removed. In order to improve the ozone removal efficiency, it is necessary to dissolve a considerable amount (about 200 ppm in terms of sodium sulfide) of sulfide in the cleaning liquid, and a considerable amount of hydrogen sulfide gas is mixed in the ozone removal exhaust gas. . It is considered that this is because the following reactions occur in the ozone removal step. O ₃ + Na ₂ S → Na ₂ SO ₃ O ₃ + Na ₂ SO ₃ → Na ₂ SO ₄ + O ₂ ↑ Na ₂ S + 2H ₂ O → 2NaOH + H ₂ S ↑

Therefore, as a result of conducting research to efficiently remove hydrogen sulfide mixed in the ozone-removing exhaust gas, the ozone-removing exhaust gas is reacted with hydrogen sulfide as described in detail below. By contacting it with an alkaline aqueous solution containing a metal salt that produces a metal sulfide precipitate (for example, an aqueous solution of sodium carbonate), hydrogen sulfide in the ozone-removing exhaust gas can be efficiently removed as a metal sulfide precipitate. Was confirmed.

Generally speaking, it is not easy to efficiently remove hydrogen sulfide in exhaust gas by the usual cleaning method using an alkaline aqueous solution. This is considered as follows.
That is, since hydrogen sulfide is dissolved in the alkaline aqueous solution in the form of S ²⁻ , Na ₂ S is produced in the alkaline aqueous solution.
Since this reaction is a reversible reaction, it is only in equilibrium due to the relationship between the hydrogen sulfide concentration ratio determined by Henry's law between the gas and liquid phases and the solubility of Na ₂ S in the liquid, and If the concentration of hydrogen sulfide becomes low, Na ₂ S accumulated in the liquid returns to hydrogen sulfide, so that hydrogen sulfide cannot be completely removed by a washing tower using an aqueous solution of sodium carbonate. Therefore, in order to continue to completely remove hydrogen sulfide, some substance is added to the sodium carbonate aqueous solution and the dissolved hydrogen sulfide is dissolved in Na ₂ S.
It is necessary to convert to other non-reversible substances. As a means for this, a method of removing sulfide as a metal salt by precipitation can be considered.

There are various metal sulfides having low solubility, but practical ones are almost limited to lead and zinc in view of cost. However, both of them will precipitate as lead carbonate or zinc carbonate, which have very low solubility in an alkaline aqueous solution such as sodium carbonate, so even if they are added to the sodium carbonate aqueous solution in the form of lead chloride or zinc chloride, the ion form It is considered that it is very difficult to efficiently produce metal sulfides in a washing tower having a short gas-liquid contact time.

However, when the solubilities of lead and zinc sulfides are compared, the solubility of zinc carbonate in 100 g of water (15 ° C.) is 0.001 g, whereas the solubility of 100 g of water (1
The solubility of zinc sulfide in 8 ° C.) is 0.00069 g, which is much smaller than that of zinc carbonate. Therefore, the zinc sulfide in the cleaning liquid storage tank is absorbed against the absorption rate of hydrogen sulfide in the sodium carbonate aqueous solution. If the residence time necessary for the formation of is sufficient, the amount of S ²⁻ is very small relative to CO ₃ ²⁻ and most of the zinc compounds added to the sodium carbonate solution are carbonated in the form of solid zinc carbonate. Even if suspended in an aqueous solution of soda, the reaction of ZnCO ₃ → Zn ²⁺ + CO ₃ ²⁻ , Zn ²⁺ + S ² →→ ZnS ↓ may proceed and hydrogen sulfide dissolved in the cleaning solution may be fixed as zinc sulfide. It cannot be said that there is no.

Therefore, when the ozone-removing exhaust gas was washed with an aqueous solution of sodium carbonate in which zinc chloride was dissolved, hydrogen sulfide in the ozone-removing exhaust gas was efficiently removed as a precipitate consisting of a mixture of zinc carbonate and zinc sulfide. What is possible, and with respect to zinc sulfide that absorbs hydrogen sulfide in the exhaust gas and accumulates in the cleaning liquid, the amount of zinc chloride present in the cleaning liquid in a dissolved state and a suspended state or as a precipitate is three times the equivalent ratio. It was proved that hydrogen sulfide can be completely removed by maintaining the above conditions even when using a washing tower using a sodium carbonate aqueous solution as a washing liquid. This is because the dissolved zinc chloride consumed by the reaction to produce zinc sulfide is
It is considered that this is because zinc chloride existing in suspension or as a precipitate in the alkaline washing solution is immediately replenished, and it efficiently acts on the absorption of hydrogen sulfide. Moreover, the precipitate formed of a mixture of zinc carbonate and zinc sulfide generated in this treatment step can be reused as an aqueous zinc chloride solution as an additive to the alkaline cleaning liquid by dissolving in hydrochloric acid, filtering and neutralizing. .

On the other hand, a lead salt is used instead of zinc chloride,
In the method of fixing hydrogen sulfide as lead sulfide in the cleaning liquid,
The solubility of lead carbonate in 100 g of water (20 ° C.) is 0.
10011g of water, while 00001g (18 ° C)
Since the solubility of lead sulfide with respect to is 0.00009 g, it seems to be possible by increasing the amount of the lead compound added relative to the lead sulfide production rate in the cleaning liquid as compared with the case of the zinc compound.

However, since the environmental standard for the amount of lead ions in the waste water is far stricter than the value for the amount of zinc ions, when a lead salt is used, it is necessary to pay close attention to the waste liquid treatment after using the cleaning liquid. On the other hand, the treatment of wastewater containing zinc ions is generally carried out by the precipitation removal method as zinc carbonate by the addition of sodium carbonate. Therefore, in the treatment of the cleaning liquid in the above treatment, it is assumed that the zinc ion precipitation operation has been completed. Since it is possible to discharge by simply separating the precipitate and neutralizing the liquid, it can be said to be extremely practical. Incidentally, the zinc carbonate / zinc sulfide mixture suspended in the washing solution easily precipitates when left standing for a whole day and night, and the supernatant becomes a completely transparent liquid.

Therefore, when the cleaning tower is operated for a long period of time by adopting this method, a zinc compound is continuously or intermittently added to the cleaning liquid by providing a precipitation separation portion in the cleaning liquid circulation line or the storage part. A method may be adopted in which an equivalent amount of precipitate (zinc chloride, etc.) is withdrawn from the line continuously or intermittently. An apparatus that combines the above ozone removal and the removal of hydrogen sulfide generated in the ozone removal step will be described in detail with reference to FIG.

That is, as shown in FIG. 3, a sodium carbonate aqueous solution in which sodium sulfide is dissolved is used as the cleaning liquid in the ozone absorption tower 9a in the first stage, and a sodium carbonate solution in which zinc chloride is dissolved is used as the cleaning liquid in the hydrogen sulfide absorption column 9b in the second stage. 20m ³ of exhaust gas with an ozone content of 1ppm using an aqueous solution
While flowing at a flow rate of min, ozone was removed and hydrogen sulfide produced was removed. In addition, in each absorption tower 9a, 9b,
The twin-wave filler as described above was used for promoting gas-liquid contact. As a result, in the washing tower 9a in the first stage, 2.0 g of a 5% aqueous solution of sodium sulfide was added to the sodium carbonate aqueous solution.
The ozone in the gas to be treated can be almost completely removed (0.03 ppm or less) by quantitatively supplying at a rate of / min, and hydrogen sulfide is 0.03 to 0.5 ppm in the ozone-removed exhaust gas. It was confirmed that it was mixed.

The reaction occurring between ozone and sodium sulfide in the ozone removal step is as shown in the above chemical formula, and sodium sulfite and sodium sulfate are dissolved and accumulated in the cleaning solution in very small amounts. According to the confirmation by the people, the accumulated amount when the total amount of the cleaning liquid is 1 m ³ is only about 1.7% in terms of sodium sulfite conversion concentration in the continuous operation for 3 years, and therefore the cleaning liquid is used in 3 years. It may be neutralized and discarded or replaced about once. When the flow rate of the gas to be treated or the ozone concentration changes, those concentrations are measured over time and the sodium sulfide concentration in the cleaning liquid is 16%.
It is most preferable to control in conjunction with a sodium sulfide aqueous solution supply pump so that the concentration does not become 0 ppm or less, but in addition to this, the sodium sulfide aqueous solution which is slightly overbased on the basis of regular measurement results is supplied to the sodium sulfide aqueous solution supply pump. By maintaining the concentration, it is possible to maintain a stable ozone removal rate.

However, when the concentration of sodium sulfide in the cleaning liquid in the first stage is increased, the hydrogen sulfide generation reaction in the ozone removal step is likely to proceed, so that the required amount of zinc chloride to be supplied to the second stage hydrogen sulfide absorption tower 9b is increased. However, there is no other inconvenience, and the sodium sulfide concentration in the pre-stage cleaning liquid is maintained in a substantially constant range. Further, although the above-mentioned reaction and the supplied sodium sulfide aqueous solution increase the calculated cleaning liquid (water), the humidity of the exhaust gas to be normally treated is not 100%, and the cleaning liquid water is not stored in the ozone absorption tower 9a. However, the amount of water tends to decrease on the evaporation side, so that it is often the case that a ball tap or the like needs to be provided to supply water.

The ozone-removed exhaust gas from which ozone has been removed by the ozone absorption tower 9a and hydrogen sulfide gas has been mixed in as described above,
Subsequently, in the hydrogen sulfide absorption tower 9b, by washing with an aqueous sodium carbonate solution in which zinc chloride is dissolved,
Hydrogen sulfide in the exhaust gas is also absorbed and removed almost completely (0.01 ppm or less), but the amount of 10% zinc chloride aqueous solution corresponding to the amount of hydrogen sulfide mixed is about 0.6 g / min.
As it is very small, for example, 1 zinc chloride per month
By adding about 25 kg of a 0% aqueous solution to the cleaning liquid, it is possible to secure a substantially complete hydrogen sulfide removal rate.

Further, the concentration of zinc sulfide in the cleaning liquid in the hydrogen sulfide absorption tower 9b is about 4.3% after one year of continuous operation when the total amount of the cleaning liquid is 500 liters, and most of it remains as a cleaning liquid as a suspension. Since there is a risk of floating inside and clogging the cleaning liquid circulation line, a zinc sulfide precipitation / deposition portion is formed at an appropriate place in the circulation line, and the accumulated zinc sulfide is regularly discharged to the outside of the system, or It is desirable to change the cleaning solution every 6 months to 1 year. Although not shown in FIG. 3, if a cleaning liquid storage tank is separately provided in the hydrogen sulfide absorption tower 9b and is circulated to increase the total amount of the cleaning liquid, the replacement period of the cleaning liquid can be extended.

When the cleaning liquid circulated in the hydrogen sulfide absorption tower 9b is to be replaced, the cleaning liquid is transferred to a separately prepared storage tank and left to stand for a whole day and night to precipitate and separate zinc sulfide and zinc carbonate, and then the supernatant liquid is sulfuric acid. It may be neutralized with an acid such as sodium chloride or hydrochloric acid, and then discharged. Alternatively, the precipitate may be neutralized with hydrochloric acid in a tank equipped with a hydrogen sulfide gas absorption device and then concentrated to be regenerated as zinc chloride crystals. It is possible.

Further, when the cleaning liquid for the ozone absorption tower 9a and the cleaning liquid for the hydrogen sulfide absorption tower 9b are simultaneously replaced, both towers 9a, 9b and the fan F are operated while the ozone absorption tower 9 is being operated.
The acid is supplied from the sodium sulfide aqueous solution supply line of a.
If all sodium sulfide in the cleaning liquid is discharged as hydrogen sulfide and treated in the hydrogen sulfide absorption tower 9b, the neutralized cleaning liquid of the ozone absorption tower 9a can be discharged as it is. After that, the cleaning liquid for the hydrogen sulfide absorption tower 9b may be treated by the method as described above.

The annual required amount of chemicals consumed when performing the above treatment is about 35 kg of sodium sulfide and about 30 kg of zinc chloride. Sodium carbonate at the time of exchanging the cleaning solution and the acid used for neutralization are added. However, the annual cost required for consuming chemicals is about tens of thousands of yen, and it is possible to significantly reduce the cost as compared with the conventional ozone decomposition catalyst method. By the way, with the ozone decomposition catalyst method currently in practical use, even if the useful life of ozone is set to several years, the annual cost is hundreds of thousands of yen, and the gas to be treated is essential to suppress catalyst deterioration. The total cost including the installation cost of the drying equipment (heater etc.) and the running cost will become higher. Therefore, as an extremely small-scale residual ozone treatment apparatus, the catalytic decomposition method may be preferred in terms of equipment compactness and ease of operation / operation.
^It can be said that the method of the present invention is a very advantageous method for a practical scale facility for treating residual ozone of medium scale or large scale exceeding ³ / min.

The results of the above series of tests and the concentration of the sodium carbonate aqueous solution in the examples were all performed at 5%, but in another experiment, substantially the same effect was obtained in the sodium carbonate concentration range of 1 to 6%. It was confirmed that the higher the concentration, the better the removal performance for both ozone and hydrogen sulfide.

In the above test and examples, sodium carbonate was used as the alkali. This is because most of the gas to be treated is air, and when caustic soda is used, it absorbs carbon dioxide in the air and is transformed into sodium carbonate within a short period of time, so a large amount of it is always required to obtain a stable treatment effect. While caustic soda must be added, this is because sodium carbonate does not cause such deterioration and the stable treatment effect is easily maintained.However, if there is no problem of deterioration due to carbon dioxide, caustic soda can be used. Since the aqueous solution has a better removal performance, caustic soda can be used as an alkali, and substantially a caustic soda / sodium carbonate mixture can also be used.

It is also possible to use another inorganic alkaline aqueous solution such as sodium hydrogen carbonate or caustic potash, or an organic alkaline aqueous solution such as amine or phenol as a cleaning liquid. Among these alkaline chemicals, sodium carbonate is
It has the advantages of being inexpensive and easy to handle and store, and is recommended as the most preferable alkaline drug. In addition, caustic soda is most widely used as an alkaline chemical used in a normal alkaline cleaning liquid, but sodium carbonate can enjoy the advantage that handling risk is very small and safety is enhanced.

Sodium sulfide (sodium sulfide) was used as the metal sulfide added to the alkaline aqueous solution in the ozone absorption tower 9a in the above-mentioned tests and examples. As the sodium sulfide, other than anhydrous substance, Na ₂ O · xH was used. ₂ O (6
It is also possible to use hydrate or nonahydrate, etc., and sodium polysulfide (Na ₂ S ₅ ), sodium hydrogen sulfide (NaSH · 2H ₂ O, etc.) can be used as well. Although it is possible to use metal sulfides other than sodium salts, such as potassium sulfide, sodium sulfide is most preferred in view of cost, solubility in alkaline aqueous solution and the like.

As the zinc salt to be added to the alkaline cleaning liquid of the hydrogen sulfide absorption tower 9b, zinc chloride was used in the above-mentioned tests and examples, but other than this, it reacts with hydrogen sulfide such as zinc sulfate and zinc bromide. It is clear that the same effect can be obtained even with a zinc salt that produces water-soluble zinc sulfide, and it is also possible to add zinc carbonate in a suspended state.

Regarding the type and structure of the cleaning tower, in both the above-mentioned test and examples, the cleaning tower using the twin-wave type filler as shown in FIG. 4 developed by the applicant of the present invention for promoting gas-liquid contact. However, if the gas-liquid contact time is appropriately selected, other gas-liquid contacting devices such as a packed column using a granular packing or Raschig ring or a saddle-shaped packing, a tray column, or the like can also be used. It is clear that the results will be obtained, and the present invention does not exclude their use.

As described above, according to the method of the present invention, ozone can be efficiently removed from the ozone-containing gas, and
Hydrogen sulfide generated in the ozone removing step can be efficiently removed, and an excellent gas cleaning effect can be obtained.

[0054]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately applied within a range compatible with the gist of the above and the following. Modifications can be made and they are all included in the technical scope of the present invention.

Example 1 Using the apparatus shown in FIG. 1, a 3% aqueous solution of sodium carbonate was used as an alkaline cleaning liquid, and this was used at 18 liters / min.
Air with various amounts of ozone and hydrogen sulfide mixed as the gas to be treated and a flow rate of 3.7 m ³ / mi.
n is blown, and hydrogen sulfide is absorbed in the sodium carbonate aqueous solution in the washing tower 9, and ozone is absorbed by the sodium carbonate aqueous solution in which hydrogen sulfide is absorbed, and ozone of the treated gas discharged from the washing tower 9 and The ozone removal rate and hydrogen sulfide removal rate were investigated by measuring the concentration of hydrogen sulfide.

The results are shown in Table 2, and when a cleaning liquid prepared by mixing about 1 ppm or more of hydrogen sulfide in the air supplied to the cleaning tower 9 and absorbing it in an aqueous solution of sodium carbonate is used, It can be confirmed that the ozone removal rate can be increased to about 98% or more.

[0057]

[Table 2]

Example 2 Using the double cleaning tower ozone removing device shown in FIG. 2, 150 liters of a 5% aqueous solution of sodium carbonate as an alkali cleaning liquid was prepared and circulated at a flow rate of 20 liters / min, and the lower cleaning tower 9a was used. The air volume is 0.40 to 0.69 m ³ /
0 to 5.5 ppm of ozone is blown in at the same time, while the upper cleaning tower 9b has an air flow rate of 3.3 from the upstream side of the upper fan 18.
〜3.4m ³ / min Hydrogen sulfide 0〜13.9ppm
Blow-in, ozone and hydrogen sulfide removal rates were investigated.

The results are as shown in FIG. Assuming that the hydrogen sulfide absorbed in the sodium carbonate aqueous solution in the upper washing tower 9b is uniformly dissolved as sodium sulfide, the hydrogen sulfide concentration in the washing liquid at each operating time is calculated as follows:
The removal rate of ozone introduced into the lower cleaning tower 9b is increased almost in proportion to the value, and when the sodium sulfide concentration in the cleaning liquid is 160 ppm or more, the ozone concentration at the outlet of the lower cleaning tower 9a is 0.002 ppm or less, An ozone removal rate of 99.9% or more can be obtained. Further, when the concentration of sodium sulfide in the cleaning liquid becomes 130 ppm or more, hydrogen sulfide will be detected at the outlet side of the lower cleaning tower 9a. Therefore, in order to remove 70% or more of ozone by this method, It is understood that a device for removing hydrogen sulfide mixed in the process gas should be attached downstream of the ozone removing device.

Example 3 A double cleaning ozone removing device as shown in FIG. 2 (however, the ozone supply pipe was connected to the upstream side of the upper fan 18) was used, and a 5% aqueous solution of sodium carbonate was used as an alkaline cleaning liquid.
0 liter was adjusted and circulated at a flow rate of 20 liter / min, and ozone-containing air was introduced into the upper washing tower 9b to start the operation, and sodium sulfide 5 was added to the alkali washing liquid.
% Aqueous solution was further supplemented as needed so as to have the concentrations shown in Table 1, and the operation was continued to examine the relationship between the concentration of sodium sulfide in the cleaning liquid and the ozone removal rate.

The results are shown in Table 1 above. If the sodium sulfide concentration in the alkaline cleaning liquid is maintained at 200 ppm or more, and the gas-liquid contact time at the packing material portion in the cleaning tower is set to be sufficiently long. It can be seen that an ozone removal rate of 95% or more, or 98% or more can be secured.

Example 4 Exhaust gas containing 0.7 to 1.3 ppm of ozone was treated with an air flow rate of 20 m ³ / min using a two-column in-line ozone removing apparatus as shown in FIG. At this time, the washing tower 9 in the previous stage
In a, a 5% aqueous solution of sodium carbonate in which 250 ppm of sodium sulfide is dissolved is circulated at 400 liter / min,
In the latter-stage cleaning tower 9b, operation was started while circulating a 5% aqueous solution of sodium carbonate to which 0.1% of zinc chloride was circulated at 40 liters / min, and for the first-stage cleaning liquid, a 5% aqueous solution of sodium sulfide was used with a metering pump. Was added to the washing liquid in the subsequent stage and 500 g of a 10% aqueous solution of zinc chloride was added once a day to the washing liquid in the latter stage so that the amount of zinc chloride in the washing liquid was equivalent to that of sodium sulfide accumulated in the washing liquid. The ratio was maintained at 3 times or more. As a result, it was confirmed that the ozone concentration in the exhaust gas from the outlet of the fan F was reduced to 0.02 ppm or less and the hydrogen sulfide concentration was reduced to 0.01 ppm or less.

[0063]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and ozone can be efficiently and economically removed from ozone-containing exhaust gas, and hydrogen sulfide gas produced in the ozone removal step can be almost eliminated. It was possible to completely remove it, and it was possible to achieve almost complete purification treatment of ozone-containing exhaust gas.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a simplest ozone removing device used in the present invention.

FIG. 2 is an explanatory view showing a double tower type ozone removing device used in the present invention.

FIG. 3 is an explanatory view showing a two-column serial purification apparatus capable of achieving removal of hydrogen sulfide as well as removal of ozone according to the present invention.

FIG. 4 is a schematic diagram showing a gas-liquid contact filler which is advantageously used in the present invention.

FIG. 5 is a graph showing the results of examining the relationship between the concentration of sodium sulfide in the cleaning liquid and the ozone removal rate.

FIG. 6 is a graph of experimental results showing the relationship between the ozone removal rate and the ratio of ozone in the exhaust gas to hydrogen sulfide absorbed in the cleaning liquid.

[Explanation of symbols]

 4,4a, 4b Cleaning liquid circulation pump 6,6a, 6b Flowmeter 7,7a, 7b Pressure gauge 8,8a, 8b Spray nozzle 9,9a, 9b Cleaning tower 11,11a, 11b Gas-liquid contact filler 12,12a , 12b Mist separator 14, 14a, 14b Cleaning liquid storage tank 24 Ozonizer

Claims (4)

[Claims] 1. A method for removing ozone, which comprises contacting an ozone-containing gas with an aqueous alkaline solution in which hydrogen sulfide and / or metal sulfide is dissolved to absorb and remove ozone. 2. The ozone-containing gas is brought into contact with an alkaline aqueous solution in which hydrogen sulfide and / or metal sulfide is dissolved to absorb and remove ozone, and the produced hydrogen sulfide-containing gas is reacted with hydrogen sulfide to produce a metal. A method for removing ozone, which comprises contacting with an alkaline aqueous solution containing a metal salt that forms a precipitate of sulfide to remove hydrogen sulfide in the hydrogen sulfide-containing gas as a precipitate of metal sulfide. 3. Sodium carbonate is used as an alkaline component constituting an alkaline aqueous solution, and sodium sulfide and / or potassium sulfide is used as a metal sulfide,
The concentration of hydrogen sulfide and / or metal sulfide in the alkaline aqueous solution is 100 to 300 pp in terms of sodium sulfide conversion concentration.
The method for removing ozone according to claim 1 or 2, wherein the ozone is maintained at m. 4. Sodium carbonate is used as an alkaline component constituting an alkaline aqueous solution, and a zinc salt is used as a metal salt, and the content of the zinc salt in the alkaline aqueous solution includes suspensions and precipitates in the solution. 4. The method for removing ozone according to claim 2 or 3, wherein the sulfide is absorbed and accumulated in the alkaline aqueous solution and as a suspension or a precipitate at an equivalent ratio of 3 times or more.