JPS644813B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a malodorous gas removal device that is applied to equipment where the amount of malodorous gas generated varies greatly. In general, hydrogen sulfide,
Mercaptans, thioethers, ammonia,
Substances with unpleasant odors such as amines and lower fatty acids are excreted. To remove these malodorous substances, various methods such as water washing, chemical washing, activated carbon adsorption, catalytic oxidation, and ozone oxidation have been used singly or in combination. However, since bad odors are caused by trace amounts of multiple components, it has not been possible to obtain a satisfactory removal effect even when conventional methods are used alone or in combination.
For example, washing with water can only remove 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 be used as a countermeasure against instantaneous high-concentration odors, such as those generated in a human waste disposal tank at a human waste treatment plant, where several hundred ppm of hydrogen sulfide is generated when it is introduced. is widely used. However, the removal rate of thioethers is low, and since carbon dioxide gas generated from the atmosphere or human waste is absorbed, alkali consumption is significant.Furthermore, the washing waste liquid contains sulfides, so oxidation treatment and neutralization are required. Post-processing such as treatment was required. A chemical cleaning method using an oxidizing agent, for example, a cleaning method using a sodium hypochlorite solution, has a high removal rate of thioethers that are difficult to remove with other methods, including hydrogen sulfide, and also removes ammonia via chloramine. It has the effect of decomposing it into nitrogen.
However, the consumption of chemicals for sub-odor substances is high;
In addition, if the concentration of foul-smelling gas is high or the concentration of oxidizing agent is high, chlorine and chlorine compounds remain in the gas after cleaning, which not only causes chlorine odor but also damages surrounding plants and accelerates corrosion of peripheral equipment. I end up. 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 causes 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 the activated carbon, thioethers can hardly be removed. Furthermore, the odor of the treated gas changes due to the difference in adsorption breakthrough time. 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 furthermore, the replacement and regeneration of activated carbon after adsorption is complicated. 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. Figure 1 shows the changes in exhaust gas over the course of a day at a typical human waste treatment plant. Exhaust gas from the human waste input tank was collected using a syringe, and changes in the concentrations of hydrogen sulfide, ammonia, and carbon dioxide were measured using a Kitagawa gas detection tube. This is what we investigated. The concentration of hydrogen sulfide fluctuates dramatically, and many of the vaquium cars that collected human waste return at 10:00 and 11:00.
It reaches a maximum of 250ppm at around 14:00 and 16:00, and drops to less than 10ppm around 12:00 when work stops. Also, like hydrogen sulfide, carbon dioxide gas, which increases alkali consumption, is released from human waste and can reach up to 1,800 ppm. However, the concentration of ammonia is around 10 to 20 ppm, and it only increases slightly as the temperature rises, indicating that it has little to do with tasks such as adding human waste. In this way, when the amount of gas to be removed varies greatly, in order to always obtain a sufficient removal effect, it is necessary to set the removal equipment according to when the amount of foul-smelling gas generated is large, which requires large equipment. or may require large amounts of chemicals. The purpose of the present invention is to provide a method for removing malodorous gases that can always achieve a sufficient removal effect even if the amount of gas to be removed changes significantly, without increasing the size of equipment or significantly increasing the amount of chemical solution used. The object of the present invention is to provide a removal device. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1 is a blower that sends the waste gas from the human waste input tank to the deodorizing device. Reference numeral 2 denotes a first washing tower, and a packing layer 3 is constructed inside thereof to increase the gas-liquid contact area. 4 sprays the cleaning liquid onto the gas rising through the filler layer 3. 5 is a demister excluding mist. The processing gas amount is 5Nm ³ /min, the gas-liquid ratio is 2.5, and the inner diameter of the filling layer 3 is
It is 30cm long and 120cm high, and the cleaning liquid is 85%. Second, third, and fourth cleaning towers 8, 14, and 15 having substantially the same structure and conditions as the first cleaning tower are provided. A 5% sulfuric acid aqueous solution 6a is used as the cleaning liquid in the first cleaning tower 2, and is circulated and sprayed from the sprayer 4 using a pump 7. Here, ammonia, which is a basic gas component in the exhaust gas, is absorbed and removed, and the exhaust gas is humidified to near the saturated vapor pressure at the gas temperature. The gas coming out from the upper part of the first cleaning tower 2 is
is introduced into the washing tower 8 from the lower part thereof, and rises again through the packing material bed 3. Here, an alkaline activated carbon suspension with a pH of 10 containing 1 wt% of powdered activated carbon in suspension 6
b is circulated and sprayed from the spray 4 to absorb and remove most of the hydrogen sulfide in the gas. The hydrogen sulfide absorbed here is oxidized by the following reaction 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 NaSO ₃ +1/2O ₂ →Na ₂ SO _4In other words, hydrogen sulfide is a sulfide ion S ^-- , hydrosulfide ion It is absorbed into the solution as SH ^-- , and using activated carbon as a catalyst, thiosulfate ions S ₂ O ₃ ^-- , sulfite ions SO ₃ ^-- , and sulfate ions SO ₄ ^-- are sequentially released into the air contained in the substinous gas itself. Oxidized by molecular oxygen. Alkaline activated carbon suspension 6b that is circulated
Because the pH decreases due to the absorption of hydrogen sulfide and carbon dioxide, the necessary amount of concentrated alkaline liquid in the alkali tank 12 is injected using the conduit 13 using the PH sensor 9, PH regulator 10, and alkali injection pump 11. , keep the pH constant. The gas discharged from the upper part of the second cleaning tower 8 is introduced into the next third cleaning tower 14 from its lower part, and ascends through the packing layer 3. Here, PH8.5, effective chlorine concentration
300-400mg/sodium hypochlorite solution 6c
is circulated and dispersed, and while the gas rises, methyl mercaptan, dimethyl sulfide, etc. remaining in the gas are absorbed and oxidized and decomposed as shown in the following equation. For methyl mercaptan, 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 For dimethyl sulfide (CH ₃ ) ₂ S+nNaClO→(CH ₃ ) ₂ SOn + nNaCl n=1, 2, or 3. The oxidizing agent is added in batches in the third washing tower 14, but the pH is adjusted in the second washing tower 8.
You can do the same thing. Next, the gas discharged from the upper part of the third cleaning tower 14 is introduced into the next fourth cleaning tower 15 from the lower part thereof, and ascends through the packing material layer 3. In this fourth washing tower 15, the alkaline activated carbon suspension 6 of the second washing tower 8 is
Cleaning is performed again using pump 16
The water is put into the fourth washing tower 15, and a part of it is returned to the second washing tower 8 using a pump 17. When the concentration of malodorous components in the exhaust gas increases due to the operation of the input tank, hydrogen sulfide, methyl mercaptan, dimethyl sulfide, etc., which were not absorbed and removed even in the second cleaning using a catalytic reaction, increase to about 10 ppm, and the third cleaning increases the concentration of malodorous components. Tower 1
4, the oxidation reaction with sodium hypochlorite progresses and releases oxidizing gases such as chlorine Cl ₂ and chlorine monoxide Cl ₂ O as byproducts. The chlorine odor can be removed by washing with an alkaline activated carbon suspension 6b containing sulfate ions, and the deodorized gas is discharged from the upper part of the fourth washing tower 15. As shown in FIG. 1, if the amount of malodorous gas generated changes significantly, the second cleaning tower 8
Malodorous gases that have not been completely treated by the 4th cleaning tower 15 may enter the fourth cleaning tower 15.
Since the cleaning liquid is used in circulation with the second cleaning tower 8, it is possible to remove the above-mentioned chlorine odor and also treat untreated malodorous components. Therefore, regardless of changes in the amount of malodorous gas generated, it is possible to obtain the amount of malodorous gas treated and removed that corresponds to the change in the magnitude of the generated amount, and a sufficient malodor removal effect can always be obtained. The deodorization results are shown in the table below.

【table】

[Table] Ammonia (NH ₃ ) was analyzed using a detection tube, and other compounds were analyzed using a gas chromatograph analyzer, and odor quality and odor concentration were determined by sensory tests. The original exhaust gas odor, which had an odor concentration of 800 to 50,000, determined by the dilution method, was reduced to a concentration of 30 or less than 30 by using the apparatus of the present invention. In the above example, all ammonia was removed by acid washing in the first washing tower 2, and furthermore, about half of the total amount of water evaporated in the first to fourth washing towers was removed in the first washing tower. The amount evaporates from 2, and although there are seasonal changes, the amount is about 0.4 per hour.
If you supply common water, etc., you can use it until the pH reaches around 5. Four consecutive two-week tests were conducted, but the second
No scale adhesion was observed on the packing material layer 3 after the cleaning tower 8. Furthermore, the acid cleaning of the first cleaning tower 2 is stopped, and the input tank gas is transferred to the second, third, and fourth cleaning towers 8, 14, 15.
After several hours, the concentration at the inlet and outlet of the second washing tower 8 becomes constant, and ammonia is sent to the third washing tower 14, where it is oxidized with sodium hypochlorite. For this reason, the chlorine gas concentration generated from the third cleaning tower 14 increases from 0.4 to 0.6 ppm to 0.7 to 0.8 ppm, and the amount of sodium hypochlorite added increases from 20 to 30 g per hour as available chlorine. It was confirmed that the weight increased to ~50g. In this way, the method for removing foul-smelling gas containing hydrogen sulfide using an alkaline activated carbon suspension has a pH of 9 to
11. Preferably, it can be used at a pH of 10 as in the example, so scale formation is less likely to occur than with the usual alkaline cleaning method that requires a pH of 12 or higher.Furthermore, by adding a water or acid cleaning step beforehand, it is possible to remove ammonia and gas. Humidifying dust and mist can be removed in the first stage, and more stable operation can be achieved without impairing the fluidity and dispersibility of the alkaline activated carbon suspension. As described above, according to the present invention, there is a first cleaning device that cleans foul-smelling gas containing hydrogen sulfide with water or acid, and a second cleaning device that cleans the gas emitted from the first cleaning device with an alkaline activated carbon suspension. a third cleaning device that cleans the gas emitted from the second cleaning device with an oxidizing agent; and a third cleaning device that cleans the gas emitted from the second cleaning device with an oxidizing agent; Since the fourth cleaning device cleans with a cleaning solution that is circulated between the device and the device, the amount of chemical solution used can be minimized, and even if the amount of malodorous gas generated changes significantly, A stable and high odor removal effect can be obtained at all times.

[Brief explanation of the drawing]

Figure 1: Curve diagram showing changes in concentration of hydrogen sulfide, ammonia, and carbon dioxide in the waste gas from the human waste input tank; Figure 2:
The figure is a schematic configuration diagram showing a sub-odor gas purification apparatus of the present invention. 2...First washing tower, 3...Filling material layer, 4...
Spray, 5...Demister, 6a...Sulfuric acid aqueous solution, 6b...Alkaline activated carbon suspension, 6c...
Sodium hypochlorite, 8...Second washing tower, 9
...PH sensor, 10...PH adjustment device, 14...
Third cleaning tower, 15... Fourth cleaning tower.

Claims (1)

[Claims] 1. A first cleaning device that introduces a foul-smelling gas containing hydrogen sulfide and ammonia to perform water cleaning or acid cleaning; and a first cleaning device that introduces a foul-smelling gas containing hydrogen sulfide and ammonia to perform water cleaning or acid cleaning; a second cleaning device that cleans with an oxidizing agent; a third cleaning device that introduces the gas emitted from the second cleaning device and performs cleaning with an oxidizing agent; 2
a fourth cleaning device that cleans the gas with an alkaline activated carbon suspension introduced through a circulation path provided between the cleaning device and the fourth cleaning device; A malodorous gas removal device characterized by obtaining a malodorous gas removal amount that corresponds to changes in size.