JPS6316194B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for removing hydrazine from water containing hydrazine. (Prior art) Hydrazine has a strong reducing power and is widely used as an oxygen scavenger for boiler feed water, a rust preventive agent, and rocket fuel. Therefore, it cannot be released as is and requires some kind of treatment. There are various treatment methods, but we will explain this using wastewater from a thermal power plant as an example. At thermal power plants, it is common practice to add tens to hundreds of milligrams of hydrazine to preserve the boiler when the boiler is stopped. This hydrazine-containing water is discharged as several hundred to several thousand ^m3 of unsteady wastewater when the boiler is restarted. Conventional techniques for removing hydrazine from this wastewater include a method in which an oxidizing agent such as sodium hypochlorite is added to perform oxidative decomposition, and a method in which a heavy metal or the like is added as a catalyst to perform aeration oxidation. Regarding the method, for example, if we take oxidative decomposition using sodium hypochlorite as an example, the reaction between hydrazine and sodium hypochlorite is an equivalent reaction as shown in equation (1), so hydrazine is almost 100% Disassemble. N ₂ H ₄ +2NaOCl→2NaCl+N ₂ +2H ₂ O (1) However, a large amount of sodium hypochlorite (4.4 mg/asCl 2 ₎ must be added to 1 mg/asN ₂ H ₄ of hydrazine, which increases the cost. The amount of sodium hypochlorite required for decomposition of hydrazine is controlled by detecting the redox potential of the reaction solution, but because it is easily affected by pH, an equivalent amount of sodium hypochlorite is injected. There are some problems, such as it being difficult to A method has been proposed in which the injection of sodium hypochlorite is controlled using a residual chlorine meter (for example, Hikoji Tsuchiya, "Hydrazine wastewater treatment at thermal power plants", PPM 1978/6, p. 21), but the injection method is extremely complicated. It's summery. The method is a method in which a heavy metal (for example, copper sulfate) is added as a catalyst and hydrazine is oxidized by aeration, and the reaction formula is shown by equation (2). N ₂ H ₄ +O ₂ →N ₂ +2H ₂ O (2) This reaction is greatly affected by pH, and the more alkaline the region, the faster the hydrazine decomposition rate. However, the added heavy metals are harmful and must be removed before discharge. For this reason, unit operations such as coagulation sedimentation, sand filtration, and ion exchange are required, and the cost of chemicals required for these operations is also considerable. As a modification of the above method, a method is known in which activated carbon or activated carbon and iron salt are added and aeration is carried out. (Japanese Patent Publication No. 54-23071). However, this method also presupposes a solid-liquid separation operation, and especially when powdered activated carbon is used, it is essential to add iron salt or the like as a flocculant. As described above, the conventional treatment technology for hydrazine-containing water has various problems and there are many points to be improved. As a technology related to the present application, there is Japanese Patent Application No. 59-229292 filed by the same applicant as the present application. (Problems to be Solved by the Invention) A problem to be solved by the present invention is to provide a method for treating hydrazine-containing water that is simple and easy to maintain without using expensive chemicals. (Means for Solving the Problems) The present invention includes an adsorption step in which activated carbon and hydrazine-containing water are brought into contact and hydrazine is adsorbed onto the activated carbon, and activated carbon whose adsorption capacity has decreased after adsorbing hydrazine is drained and left in that state. It consists of a regeneration process in which the adsorption capacity is restored by bringing the adsorbent into contact with the outside air or by forcing it into contact with the outside air. Here, the shape of the activated carbon used is not particularly limited,
One or more types of powder, powder supported on a carrier, granules, fibers, cloth-like fibers, honeycomb-like fibers, felt-like fibers, etc. are acceptable. Although they can be used in combination, powdered ones are difficult to handle, so it is preferable to use them as supported on a carrier. To bring activated carbon into contact with hydrazine-containing water, there is a method in which activated carbon is packed in a column (or tank) and hydrazine-containing water is passed through the activated carbon packed bed in a fixed bed state. There is also a method in which a solid-liquid separation mechanism is attached inside or outside the tower and activated carbon is dispersed or fluidized within the tower (or tank). In the case of a fixed bed, suspended substances in the hydrazine-containing water can also be removed, and the liquid can be passed in either a downward flow or an upward flow. Activated carbon that has lost its adsorption capacity needs to be regenerated, but in the past, high-temperature steam, electric current, special chemicals, etc. were used, resulting in enormous costs. Regeneration according to the present invention can be accomplished by an extremely simple operation of leaving activated carbon whose adsorption capacity has decreased in a drained state and blowing air if necessary. Hydrazine adsorbed on activated carbon comes into contact with oxygen in the air,
It decomposes as shown in equation (2), but since the activated carbon is drained, the contact area between the activated carbon and air increases dramatically, and the decomposition reaction ends in a short time. When activated carbon is used in a fixed bed, all that is required is to stop the flow of hydrazine-containing water and draw out the water in the tower (or tank) from a position below the packed bed, allowing gravity to drain the activated carbon. If necessary, air may be introduced from above the packed bed to push out water in the packed bed. When activated carbon is used in a dispersed or fluidized manner, an attached solid-liquid separation mechanism can be used. This also allows water to be drained by gravity from the location where the solid-liquid separation mechanism is installed. In this way, activated carbon regenerated by contact with outside air has an initial adsorption capacity,
Can be reused for adsorption of hydrazine. In other words, hydrazine can be removed by simple operations without using any special chemicals. (Function) An embodiment of the present invention in which a fixed bed of granular activated carbon is used and a method of passing liquid in a downward flow is shown in FIG. 1, and will be described in more detail with reference to FIG. Hydrazine-containing water flows into the activated carbon packed tower 1 through the raw water inflow pipe 4, and after adsorbing and removing hydrazine in the activated carbon packed bed 3, it passes through the treated water outflow pipe 5 and the treated water tank 2, and is discharged from the effluent water outflow pipe 6. . As the water flow continues, the hydrazine concentration in the treated water gradually increases, and when it no longer satisfies the standard value, the water flow is stopped. At this time, if the inflow of raw water is stopped and the treated water outflow pipe 5 and the exhaust pipe 8 are opened, the water in the activated carbon packed tower 1 will directly flow out of the tower by gravity, and the activated carbon layer will be in a drained state. here,
If water is difficult to flow out of the tower, pressurized air (not shown) may be introduced from the upper part of the tower to extrude the water. Next, the treated water outflow pipe 5 is closed, air is introduced through the air inflow pipe 7, and air is exhausted through the exhaust pipe 8. The introduced air passes through the activated carbon layer 3 in an upward flow, and in this process, hydrazine is decomposed according to equation (1). The installation position of the air inflow pipe is at the bottom of the activated carbon packed bed 3,
It can also be on the top. If pressurized air is introduced from the top of the tower to drain water, the air may continue to flow in as is. Although the amount of air depends on the height of the activated carbon layer, it is usually LV10 or higher, preferably LV50 to 500, and an aeration time of 0.5 to 10 hours is sufficient. When the decomposition of hydrazine by aeration is completed, the introduction of air is stopped, and the treated water is introduced into the activated carbon packed tower 1 through the treated water inlet pipe 9, and the activated carbon layer is immersed. The purpose of this is to remove air bubbles from the activated carbon layer, and it is sufficient to introduce water up to the liquid level during the liquid flow treatment. Next, the raw water inflow pipe 4 and the treated water outflow pipe 5 are opened to resume adsorption and removal of hydrazine. Figure 2 shows an example of using a column packed with granular activated carbon. Activated carbon packed tower 1 is adsorption, activated carbon packed tower 1'
indicates that it is being played. If hydrazine-containing water is treated in this manner, continuous treatment is possible. Next, FIG. 3 shows an embodiment in which activated carbon is used in a dispersed manner. The hydrazine decomposition tank 10 is provided with a perforated plate 13 slightly above the bottom and an air introduction pipe 7 further above. When hydrazine-containing water is introduced into the hydrazine decomposition tank 10 through the raw water inflow pipe 4, activated carbon is introduced, and air is introduced through the air introduction pipe 7, the activated carbon 12 is dispersed as shown in FIG. The role of the perforated plate 13 is to separate solid and liquid between activated carbon and water, and the pore diameter is determined by the size, shape, etc. of the activated carbon used, and it is necessary that the pore diameter is such that the activated carbon does not pass through. Third
The figure shows an example in which a perforated plate is installed in the hydrazine decomposition tank 10, but fillers such as sand, anthracite, gravel, plastic, etc. may be laminated, or porous membranes, perforated pipes, etc. may also be used. can. In short, any means that can separate activated carbon and water into solid and liquid may be used. Furthermore, although FIG. 3 shows an example in which hydrazine decomposition and solid-liquid separation are performed in the same tank, activated carbon may be transferred outside the tank and solid-liquid separated there. Further, instead of the air introduction pipe 7, a stirrer may be used for dispersion. Now, the hydrazine-containing water that has flowed into the hydrazine decomposition tank 10 comes into contact with the activated carbon 12, and hydrazine is adsorbed and removed by the activated carbon. When the adsorption step is completed, all of the water in the hydrazine decomposition tank 10 is discharged from the treated water outflow pipe 5 to the treated water tank 2. However, since the activated carbon 12 is prevented from flowing out by the perforated plate 13, the activated carbon 12 is stacked on the perforated plate 13 in a drained state and exposed to the outside air. If you leave it as it is for a certain period of time, the decomposition reaction of equation (2) will occur, but the air introduction pipe 7
It is better to blow air if the
Especially when using a large amount of activated carbon, air introduction pipe 7
If it is located immediately above or below the perforated plate 13, air will flow through the activated carbon layer, and the time for decomposing hydrazine will be shortened. When the decomposition of hydrazine is completed, hydrazine-containing water is again supplied to the hydrazine decomposition tank 10 from the raw water inflow pipe 4.
Just fill it with water and perform adsorption. Activated carbon once added returns to its initial adsorption performance through air regeneration and can be used semi-permanently over and over again. Circulation line 1
4 is installed to return the treated water to the hydrazine decomposition tank 10 and repeat the treatment when the hydrazine concentration in the treated water tank 2 has not reached a predetermined concentration. When the hydrazine concentration of the treated water reaches a predetermined concentration, it is discharged through the discharge pipe 6 or reused. The mechanism for separating water and activated carbon differs depending on the type, shape, particle size, etc. of the activated carbon used, but any type can be applied as long as activated carbon can be separated. Example 1 Granular activated carbon (Tsurumicol HC-30E trade name) 1.5 in an acrylic column with an inner diameter of 50 mm and a height of 1000 mm.
When the tank was filled with synthetic raw water containing 550 mg of hydrazine/asN ₂ H ₄ in a downward flow at a flow rate of 3/h, the results shown in Table 1 were obtained.

[Table] When 15 liquids had passed, the liquid flow was stopped, and the liquid in the column was discharged from the treated water outflow pipe at the bottom of the column, and the activated carbon layer was drained. Next, air was introduced through the treated water outflow pipe and exhausted from the top of the column. The aeration rate was 3/h for 2 hours. After stopping ventilation,
1.5 liters of the treated water was passed through the activated carbon layer in an upward flow to expel air bubbles in the activated carbon layer. Next, the flow of synthetic raw water was started. In this way, the regeneration of the raw water by passing through it and aeration was repeated for 5 to 10 cycles, and the results are shown in Table 2, with no tendency for the quality of the treated water to deteriorate.

[Table] Example 2 Add granular activated carbon (Tsurumicol) to the beaker 2.
HC-30E brand name) 300ml and hydrazine 550mg/
When synthetic raw water 2 containing asN ₂ H ₄ was added and stirred for 2 hours with a stirrer, the hydrazine in the supernatant was 17.6
mg _{/ asN2H4} . Next, add activated carbon and water.
The activated carbon was separated using a 50 mesh sieve and left as it was for one day and night. Then, this activated carbon was transferred to beaker 2 again and brought into contact with hydrazine-containing water in the same manner, and the hydrazine concentration of the supernatant was 20.3 mg/asN ₂ H ₄ . Even after repeating the above operation five times in total, the hydrazine concentration in the supernatant was 19.5 mg/asN ₂ H ₄ with no tendency for deterioration. (Effects of the Invention) As described above, according to the present invention, activated carbon that has adsorbed hydrazine can be left in a drained state and brought into contact with the outside air, or if necessary, forced into contact with the outside air. Can be played in no time. Therefore, since no expensive or special chemicals are used, the cost is extremely low and it not only meets the social background of resource and energy conservation, but also greatly contributes to the health and safety of on-site workers. be.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the method according to the invention using a fixed bed of granular activated carbon with downward flow. FIG. 2 is a diagram showing a case where two granular activated carbon packed columns are used for continuous treatment, where activated carbon packed column 1 shows adsorption, and activated carbon packed column 1' shows regeneration. FIG. 3 shows an embodiment in which activated carbon is dispersed in a decomposition tank. 1, 1'... activated carbon packed tower, 2... treated water tank,
3,3′...Activated carbon packed bed, 4...Raw water inflow pipe,
5... Treated water outflow pipe, 6... Effluent water outflow pipe, 7...
... Air inflow pipe, 8, 8' ... Exhaust pipe, 9 ... Treated water inflow pipe, 10 ... Hydrazine decomposition tank, 12 ...
Activated carbon, 13...perforated plate, 14...circulation line.

Claims (1)

[Scope of Claims] 1. A hydrazine-containing method comprising an adsorption step in which activated carbon and hydrazine-containing water are brought into contact and hydrazine is adsorbed onto the activated carbon, and a regeneration step in which activated carbon whose adsorption capacity has decreased by adsorbing hydrazine is drained and then brought into contact with outside air. How to treat water. 2. The activated carbon is used in a fixed bed packed in a tower or tank, and adsorption is carried out by passing hydrazine-containing water through the activated carbon packed bed in an immersed state.Regeneration is carried out by draining the activated carbon packed tank and removing water if necessary. A method for treating hydrazine-containing water according to claim 1, which is carried out by blowing air. 3 Use a tower or tank equipped with a solid-liquid separation mechanism inside or outside the tower or tank. Adsorption is performed by dispersing or fluidizing activated carbon in hydrazine-containing water, and regeneration is performed using the attached solid-liquid separation mechanism. A method for treating hydrazine-containing water according to claim 1, which comprises using, draining, and blowing air if necessary. 4. The shape of the activated carbon is one or two selected from granules, powder, powder supported on a carrier, fibers, felt fibers, and honeycomb fibers. The method for treating hydrazine-containing water according to claim 1, 2, or 3 above.