JPS625008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing malodorous gas,
More specifically, the present invention relates to a method for removing hydrogen sulfide, methyl mercaptan, methyl sulfide, ammonia, trimethylamine, etc. as main malodorous components at an extremely high removal rate from a malodorous gas.

In general, human waste treatment plants, sewage treatment plants, stock farms, seafood processing plants, and other manufacturing plants discharge substances with unpleasant odors such as hydrogen sulfide, mercaptans, thioethers, ammonia, amines, and lower fatty acids. Therefore, in order to remove these malodorous substances, various methods such as water washing, chemical washing, activated carbon adsorption, catalytic oxidation method, and ozone oxidation method have been used singly or in combination.

However, conventional methods are not always satisfactory because bad odors are caused by trace amounts and multiple components. For example, washing with water can only remove some ammonia. On the other hand, the alkaline cleaning method, which has a high absorption and removal rate for hydrogen sulfide and sulfur compounds such as mercaptans, can also be used as a countermeasure against instantaneous high-concentration odors, such as those generated in the human waste disposal tank of a human waste treatment plant, where several hundred ppm of hydrogen sulfide is generated when it is introduced. are widely used, but the removal rate of thioethers is low, and
Since the carbon dioxide gas generated from human waste is absorbed, alkali is consumed significantly, and furthermore, since the cleaning waste liquid contains sulfides, post-treatments such as oxidation treatment and neutralization treatment are required.

Regarding chemical cleaning methods using oxidizing agents, for example, cleaning methods using sodium hypochlorite solution have a high removal rate of thioethers that are difficult to remove with other methods, including hydrogen sulfide, and ammonia is also removed by nitrogen via chloramine. However, the amount of chemicals used to treat malodorous substances is large, and chlorine and chlorine compounds remain in the gas after cleaning, which not only produces a chlorine odor but also damages surrounding plants.
There was a problem that accelerated corrosion of peripheral equipment. The ozone oxidation method, which uses gas-phase oxidation, also reacts with malodorous substances relatively slowly, and unless used in the presence of a catalyst, it can only be used as a masking effect to counter malodors. Furthermore, if unreacted ozone remains in the treated gas at a high concentration, the oxidizing gas will cause other problems similar to the chlorine odor when sodium hypochlorite is used.

The method of removing malodorous gases by adsorption on activated carbon has a good initial effect, but it is affected by humidity and moisture, and once moisture adsorption occurs on activated carbon, thioethers can hardly be removed, and due to differences in adsorption breakthrough time, treatment Gas odor changes occur. In addition, a powerful fan is required to pass a large amount of gas through the adsorption layer, which has a large pressure loss, and further disadvantages include the complicated replacement and regeneration of activated carbon after adsorption.

The catalytic oxidation method requires large-scale equipment, which is convenient for gases containing high concentrations of malodorous components, but increases fuel costs for heating thin malodorous gases.

The present inventors have already proposed a method for purifying malodorous gas that makes use of the strong oxidizing power of chemical solutions such as hypochlorite as described above, reduces the amount used, and eliminates the negative impact on the environment. (Patent Application No. 77673 of 1982 (see Japanese Patent Application Laid-Open No. 1983-2824)). That is, the method includes a first cleaning step of cleaning a malodorous gas containing hydrogen sulfide with an alkaline activated carbon suspension in the presence of oxygen, a second cleaning step of cleaning with an oxidizing agent-containing liquid, and a second cleaning step of cleaning with an alkaline solution. This method is characterized by sequentially performing cleaning treatment in three cleaning steps. However, according to this method, hydrogen sulfide in the malodorous gas is absorbed into the cleaning solution in the first step, is efficiently oxidized by molecular oxygen and becomes thiosulfate ions, and in the second step, hydrogen sulfide, which is relatively oxidizable, is absorbed into the cleaning solution. Thioethers, mercaptans, etc. are oxidized, and oxidizing gases such as chlorine generated by decomposition of the oxidizing agent are efficiently absorbed in the third step. Therefore, according to this method, effective purification of malodorous gas can be expected with a small amount of chemical solution used.

The present invention is mainly aimed at improving the third step in the above-mentioned three-stage purification method for malodorous gas. That is, in the above method, it is recommended to use the alkaline activated carbon suspension used in the first step as it is as the alkaline solution in the third step. This is because it has been found that the presence of thiosulfate ions generated by the oxidation of hydrogen sulfide in the first step is effective in absorbing oxidizing gases. However, upon further study by the present inventors, we found that using the alkaline activated carbon suspension used in the first step directly as a cleaning liquid in the third step is not necessarily desirable because a bad odor remains in the exhaust gas. It was discovered that The reason for this is that, according to subsequent research, malodorous components adsorbed unreacted on activated carbon in the cleaning process in the first step are reversely absorbed in the third cleaning step, where the concentration of malodorous components in the gas to be treated is originally low. It was found that this was due to being released into the processing gas, and not in the cleaning solution itself containing thiosulfate ions. For example, this fact can be seen from the fact that when activated carbon is separated from the spent alkaline activated carbon suspension from the first step, the activated carbon has a strong mercaptan-like odor, but the residual liquid has almost no odor. Regarding the effect of removing oxidizing gas from the treated gas from the second step, the presence of activated carbon is not necessarily required if the liquid is alkaline. Therefore, activated carbon is once separated from the cleaning solution from the first step, and this is recycled to the first step and reused as a hydrogen sulfide oxidation catalyst, and the residual solution containing thiosulfate ions is used as the cleaning solution in the third step. If used, the harmful effects associated with the presence of activated carbon can be eliminated while effectively utilizing its oxidizing gas absorption effect. The present invention was completed based on such knowledge. That is, the method for purifying malodorous gas of the present invention uses hydrogen sulfide and ammonia,
Reducing foul-smelling gases containing basic gases such as amines,
A first cleaning step of cleaning with an alkaline activated carbon suspension in the presence of oxygen, a second cleaning step of cleaning with an oxidizing agent-containing liquid, and a third cleaning with an alkaline solution.
When the washing process is performed sequentially in the washing process, activated carbon is separated from the alkaline activated carbon suspension extracted from the first washing process and returned to the first washing process, and the remaining liquid is used as a washing liquid in the third washing process. It is something.

Hereinafter, the present invention will be described in more detail with reference to the drawings showing examples of an apparatus system for carrying out the present invention.

FIG. 1 is a schematic diagram of a typical system for carrying out the invention, in which activated carbon is separated from an alkaline activated carbon suspension by sedimentation.

In FIG. 1, a foul-smelling gas 1 containing components such as hydrogen sulfide, methyl mercaptan, methyl sulfide, ammonia, and methylamine is sent from a human waste treatment plant, a sewage treatment plant, etc., and passes through a blower 2.
It is charged into the lower part of the washing tower 3, and is brought into gas-liquid contact with an alkaline activated carbon suspension having a pH of about 10, which is sprayed from a spray nozzle 5 while rising through a packing material 4 such as a Raschig ring filled in the tower. It will be done. Here, hydrogen sulfide is absorbed and oxidized by the following reactions in the presence of oxygen using activated carbon as a catalyst.

H ₂ S+NaOH→NaHS+H ₂ O H ₂ S+2NaOH→Na ₂ S+2H ₂ O 2Na ₂ S+H ₂ O+2O ₂ →Na ₂ S ₂ O ₃ +2NaOH 2NaHS+2O ₂ →Na ₂ S ₂ O ₃ +H ₂ O NaHS+NaHCO ₃ +3/2O ₂ →Na ₂ SO ₃ +H ₂ O + CO ₂ Na ₂ S ₂ O ₃ +2NaHCO ₃ +2O ₂ →2Na ₂ SO ₄ +H ₂ O+
2CO ₂ Na ₂ SO ₃ +1/2O ₂ →Na ₂ SO ₄ After the gas-liquid contact, the mist is removed by the demister 6, and the gas exits the first cleaning tower 3. The gas flow rate in the cleaning tower is, for example, about 1 m/sec, and the contact time is about 1 second. (Note that the contact conditions for cleaning in the second and third columns may be approximately the same as in the first column.) On the other hand, for example, an alkaline activated carbon suspension containing about 1% by weight of activated carbon with an average particle size of less than 200 mesh 7 is adjusted to pH 9 to 11, preferably about 10, with an alkali such as sodium hydroxide in an adjustment tank 8 provided by partitioning the lower part of the first column, and then passed through a pump 9 and a spray nozzle 5 to remove, for example, a foul-smelling gas. It is sprayed into the tower 3 at a rate of approximately 3/min to 1 m ³ /mm, and while passing through the packing material 4, it mainly absorbs hydrogen sulfide in the foul-smelling gas and becomes the tower bottom liquid 10, which is then sent to the adjustment tank. Returned to 8. The pH of the adjustment tank 8 is detected by a PH meter 11, and depending on the value, a concentrated alkaline solution 13 stored in the tank 12 is supplied through a chemical dosing pump 14, and makeup water is supplied through a control valve 15 and piping 16. A portion of the bottom liquid 42 is further circulated from the third washing tower 39 through the pipe 17 as will be described later. On the other hand, a part of the bottom liquid 10 is sent to a sedimentation tank 18 with an inclined bottom, which is partitioned off at the top and installed on the opposite side of the adjustment tank 8 at the bottom of the first tower, where the flow of the liquid is slowed down and the activated carbon is It is separated by sedimentation. The activated carbon 19 that has been sedimented and separated falls down the inclined bottom by gravity and returns to the bottom of the column, where it is mixed again with the liquid flowing down from the filler 4 to form a uniform suspended state. Activated carbon is essentially used repeatedly in this way, but as the activated carbon wears out or becomes deactivated, it is removed, replenished, and replaced as necessary. On the other hand, the supernatant liquid 20 obtained by sedimentation and separation of activated carbon is passed through a pump 21, a control valve 22, and a pipe 23 to a third column 3.
9.

Next, the foul-smelling gas 24 leaving the first column 3 and from which hydrogen sulfide has been removed is supplied to the bottom of the second column 26 via a pipe 25, and while rising through the packing material 27 is sprayed from the spray nozzle 5, for example, as follows. It comes into gas-liquid contact with a liquid containing an oxidizing agent such as sodium chlorite, and malodorous components such as mercaptans, thioethers, ammonia, and amines are oxidized or washed away using the following reaction formula.

2CH ₃ SH+NaClO→(CH ₃ ) ₂ S ₂ +H ₂ O+NaCl (CH ₃ ) ₂ S ₂ +5NaClO+H ₂ O→2CH ₃ SO ₃ H+
5NaCl (CH ₃ ) ₂ S+nNaClO→(CH ₃ ) ₂ SOn+nNaCl n=1, 2, or 3.

2NH ₃ +3NaClO→N ₂ +3NaCl (CH ₃ ) ₃ N+9NaClO→CH ₃ NO ₂ +9NaCl+2CO ₂
+3H ₂ O The gas that has completed the cleaning process in the second column passes through the demister 6 and is discharged through a pipe 29 as exhaust gas 28 from the second column. On the other hand, the effective chlorine concentration is about 300
mg/sodium hypochlorite solution preferably
The oxidizing agent-containing liquid 30 whose pH is kept approximately neutral is adjusted in an adjustment tank 31 provided by partitioning off the lower part of the second column. That is, the concentrated oxidizing agent solution 33 stored in the tank 32 is supplied to the tank 31 via the chemical dosing pump 14, and the tank 34 is supplied with the measured value of the PH meter 11.
Acid or alkaline PH adjustment solution stored in 3
5 is supplied through the chemical injection pump 14, and the pH of the oxidizing agent-containing liquid 30 is maintained at approximately neutral. Also, makeup water is added through the control valve 15 and piping 16 to adjust the oxidizer concentration, and then the oxidizer-containing liquid 3
0 is sent from the pump 36 to the spray nozzle 5, and the oxidizing agent-containing liquid that has flowed down in the filler 27 is
It is stored as a bottom liquid 37 at the bottom of the tower, a part of it is discharged through a pipe 38, and most of it is returned to the adjustment tank 31.

The exhaust gas 28 from the second tower has had its malodorous components removed, but it is contaminated with oxidizing gas caused by the decomposition of the oxidizing agent, so it is introduced into the bottom of the third tower 39 through the pipe 29 and rises through the packing material 40. During this time, the cleaning liquid sprayed from the spray nozzle 5 comes into contact with the gas-liquid,
The oxidizing gas is absorbed and removed, passes through the demister 6, and is released into the atmosphere as substantially clean exhaust gas 41. On the other hand, this cleaning liquid is a supernatant liquid 20 containing reducing substances such as thiosulfate ions from which activated carbon has been separated from the bottom liquid of the first column 3, and is transferred to the third column through a pump 21 and piping 23. After gas-liquid contact with the exhaust gas 28 of the second column, it is stored as a column bottom liquid 42. This column bottom liquid 42 is then returned to the adjustment tank 8 of the first column 3 by gravity through the piping 17, and a portion is discharged from the piping 43.

As mentioned above, the alkaline activated carbon suspension from the first tower can be used as the cleaning liquid for the third tower to remove the oxidizing gas generated from the second tower, but if the hydrogen sulfide load is high or the activated carbon catalyst When purifying a foul-smelling gas containing a large amount of slow-oxidizing mercaptans, thioethers, etc., gas-liquid contact is carried out in the third tower while they are still contained in the alkaline activated carbon suspension, and the exhaust gas 28 of the second tower is This will cause the odor to be added again. However, as in the above example, activated carbon is sedimented and separated in a settling tank, and the supernatant is transferred to a third tank.
If used as a washing solution for the column, the residence time in the precipitation tank will also be the reaction time for unreacted substances, and most of the activated carbon that has adsorbed slow-reacting mercaptans, thioethers, etc. will be separated.
The cleaning liquid from the tower does not add any odor to the exhaust gas 41, and the thiosulfate ion or sulfite ion, which is the oxidation product of hydrogen sulfide, is used as an alkaline aqueous solution to remove the oxidizing gas contained in the second tower exhaust gas 28. Acts effectively as a remover. It goes without saying that as a method for separating the activated carbon that has adsorbed malodorous substances from the suspension, in addition to using a sedimentation tank, a superseparator, a liquid cyclone, a centrifuge, etc. can be used.

As shown in Figure 2, in order to separate the alkaline activated carbon suspension into a solution containing thiosulfate ions, sulfite ions, etc. necessary for absorption and removal of oxidizing gases, the alkaline activated carbon suspension is separated by means or devices such as porous plates, cloth, membranes, etc. An example of an embodiment of obtaining a cleaning liquid that does not contain activated carbon will be described.

In other words, in FIG. 2, in which the same parts are given the same symbols as in FIG.
In other words, one side of the bottom of the tower is partitioned with a porous plate 45,
A cleaning solution containing no activated carbon is obtained. The gas system for foul-smelling gas, exhaust gas, etc. and the cleaning method for the second column 26 are the same as in FIG. 1, so their explanation will be omitted. In the first column 3a, as in the embodiment shown in FIG.
The bottom liquid 10 that has flowed down enters the adjustment tank 8 and is circulated, while cleaning liquid 44 that does not contain activated carbon in a tank 46 provided at the opposite side of the adjustment tank 8 at the bottom of the first tower and the porous plate 45. I am in touch with you through. Therefore, solid activated carbon contained in the bottom liquid 10 cannot pass through the porous plate 45, but a solution containing ions such as thiosulfate ions and sulfite ions necessary for absorbing and removing oxidizing gases freely passes through the porous plate. Can be spread. The cleaning liquid 44 containing no activated carbon thus obtained in the tank 46 was supplied to the spray nozzle 5 of the third column 39 through the pump 21, the control valve 22, and the pipe 23, and was brought into gas-liquid contact with the second column exhaust gas 28. Thereafter, a part of the liquid is stored as the bottom liquid 42 and discharged from the pipe 43, and most of it passes through the pipe 17a and returns to the tank 46 adjacent to the bottom of the first column 3a by gravity. The cleaning liquid from the third column, which has consumed thiosulfate ions, sulfite ions, etc. by absorbing and removing oxidizing gases, comes into contact with the column bottom liquid 10 again through the porous plate 45. At this time, there is a difference in the concentration of each ion on both sides of the porous plate 45, and the ions are diffused so that the concentration becomes the same as the contact time increases.

In the example shown in FIG. 2, it goes without saying that as the area of the porous plate increases, the time required to reach the same ion concentration becomes faster. Furthermore, in order to separate the activated carbon and diffuse the ions, a cloth or a permeable membrane can be used in addition to the porous plate.
In addition, the bottom liquid 4 of the third column 39 is passed through the pipe 17a.
2 is added to the inside of the porous plate 45, that is, to the bottom liquid 10 of the first column 3a, the movement of thiosulfate ions through the porous plate 45 becomes active, and the cleaning liquid 44
The concentration of thiosulfate ions in the solution can be increased.

As described above, the present invention provides a first cleaning process using an alkaline activated carbon suspension, a second cleaning process using an oxidizing agent-containing liquid, and a third cleaning process using the first cleaning liquid to remove oxidizing gas. , is a method of purifying foul-smelling gas that prevents unreacted hydrogen sulfide, mercaptanic acid, thioethers, etc. from being released from the first cleaning liquid into the third cleaning process, and not only can it improve the optimal deodorizing effect, but also ,1
There is little variation in the concentration of suspended activated carbon, which serves as a catalyst. 2. Activated carbon wear is low, high sedimentation separation properties can be maintained for a long time, and the discharged wastewater is not polluted. 3. Activated carbon is contained in the mist that passes through the third column demister. By employing the present invention, a stable deodorizing effect can be obtained.

It has also been found that since the method of the present invention is carried out at room temperature to low temperature without heating, a large amount of thiosulfate is accumulated in the cleaning solution, which can be effectively used in the third step of cleaning.

The foul-smelling gases targeted in the method of the present invention are gases generated in various public facilities such as human waste, sewage treatment plants, fisheries, and livestock processing plants, and include sulfur compounds such as hydrogen sulfide and mercaptans, as well as ammonia and amines. It also contains nitrogen compounds, and due to its nature, its concentration may fluctuate greatly depending on the season. However, according to the present invention, all of these components can be effectively absorbed regardless of fluctuations in their concentration. It is effective to remove it.

Furthermore, by using a cleaning solution that separates the activated carbon, it is possible to prevent the re-generation of malodorous gas accompanying the activated carbon, and to reduce the deterioration of the equipment due to slurry circulation.
It is also extremely effective in maintaining the shape of activated carbon particles.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram of each device in a typical example of an apparatus system for carrying out the method of the present invention using a settling tank. FIG. 2 is a layout diagram of each device in a typical example of an apparatus system for carrying out the method of the present invention using a porous plate. 1... Original malodorous gas, 3, 3a, 26, 39...
Washing tower, 4, 27, 40... Filling material, 8... Alkaline activated carbon suspension adjustment tank, 30... Cleaning liquid containing oxidizing agent, 18... Sedimentation tank, 45... Porous plate.

Claims (1)

[Claims] 1. A first cleaning step in which reducing malodorous gases containing hydrogen sulfide and basic gas are cleaned with an alkaline activated carbon suspension in the presence of oxygen, and a second cleaning step in which the oxidizing agent-containing liquid is cleaned. , the third to wash with alkaline solution
When the washing process is performed sequentially in the washing process, activated carbon is separated from the alkaline activated carbon suspension extracted from the first washing process and returned to the first washing process, and the remaining liquid is used as a washing liquid in the third washing process. , a method for purifying foul-smelling gas. 2. The method according to claim 1, in which activated carbon is separated by sedimentation separation. 3. The method according to claim 1, in which activated carbon is separated by filtration. 4. The method according to claim 3, wherein the filter material is a porous plate, cloth or membrane.