JPH0229396B2 - - 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 strong reducing power and is widely used as a boiler feed water deoxidizer, rust preventive, rocket fuel, etc., but water containing hydrazine is a COD component. 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 shut down. 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/as Cl ₂ ) must be added to 1 mg/as N ₂ H ₄ of hydrazine, resulting in high cost. The amount of sodium hypochlorite required for hydrazine decomposition is controlled by detecting the redox potential of the reaction solution, but it is difficult to inject an equivalent amount of sodium hypochlorite because it is easily affected by pH. There are some problems, such as it being quite difficult. 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, 1978/6g p21), but the injection method is extremely complicated. It is becoming. 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. Therefore, 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 for aeration (Japanese Patent Laid-Open 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) Problems to be solved by the invention, namely:
The object is to provide a method for treating hydrazine-containing water having the following characteristics. Does not use expensive chemicals Simple and easy to maintain Continuous processing is possible (means to solve the problem) The present invention involves a process of bringing activated carbon and hydrazine-containing water into contact and adsorbing hydrazine to activated carbon. It consists of a regeneration process in which activated carbon whose adsorption capacity has decreased is forcibly brought into contact with outside air to restore its adsorption capacity. It has been devised so that it can be done. That is, a rotating body or belt containing activated carbon is rotated so that a part of the rotating body or belt comes into contact with hydrazine-containing water and the rest comes into contact with air. Here, the shape of the rotating body containing activated carbon is preferably a disc or a cylinder, and activated carbon is formed into a disc or cylinder, activated carbon is mounted on a disc or cylinder support, and activated carbon is formed into a disc or cylinder. One type or a combination of two or more types can be used by filling the inside of a cylindrical or cylindrical support. Furthermore, a belt containing activated carbon refers to activated carbon formed into a belt shape, attached to and/or carried on a belt-like support, or filled inside a belt-like support. Can be used in combinations of more than one species. The activated carbon used can be in the form of granules, powder, powder supported on a carrier, fibers, cloth-like fibers, honeycomb-like fibers,
It can be used in various shapes, such as in the form of fiber felt, but it is difficult to handle the powder as it is, so it is preferable to have it supported on a carrier. If a rotating body or belt containing activated carbon as described above is rotated so that a part of it comes into contact with hydrazine-containing water and the rest with air, hydrazine will be adsorbed and part of it will be absorbed in the part where activated carbon and hydrazine-containing water are in contact. The decomposition of hydrazine and the adsorption of oxygen on the surface of activated carbon occur in the area that is in contact with air. Hydrazine adsorbed on activated carbon is partially decomposed by dissolved oxygen in water, but in the present invention, the activated carbon is forced into contact with the outside air, so the contact area between the activated carbon surface and oxygen increases dramatically, and the adsorbed hydrazine is decomposed for a short time. It breaks down into The rotating body containing activated carbon may be rotated using a motor or the like, but air may be introduced into the hydrazine-containing water and the stirring force generated by aeration may be used as the motive power. Thus, according to the present invention, adsorption and decomposition of hydrazine can be carried out continuously without using any special chemicals, making continuous treatment possible. (Function) FIG. 1 shows an embodiment in which activated carbon is used by being attached to a disc, and FIG. 2 shows an embodiment in which activated carbon is used by being filled in a cylindrical support. This will be explained in more detail with reference to FIG. Hydrazine-containing water flows into the hydrazine decomposition tank 1 through a raw water inflow pipe 3 and is discharged through a treated water outflow pipe 4. The hydrazine decomposition tank 1 has many rotating disks 2.
is attached to a rotating shaft 5, and the lower part of the disc rotates while being immersed in hydrazine-containing water. The rotating disk 2 may be a disk-shaped support with cloth-like activated carbon fibers, honeycomb-like fibers, or powdered fibers supported on a disk-shaped support. The hydrazine-containing water comes into contact with a large number of discs equipped with activated carbon, and hydrazine is adsorbed and decomposed in sequence, and finally treated water with an extremely low hydrazine concentration is discharged. Figure 2 shows activated carbon filled inside a disc-shaped support, and the activated carbon can be in the form of granules, fibers, cloth-like fibers, honeycomb-like fibers, or powder. It is possible to use granular and/or cloth-like carriers. However, it is necessary to cover the outside of the cylindrical activated carbon with a saran net, wire mesh, etc. to prevent the filled activated carbon from flowing out. One embodiment of the case in which activated carbon is attached to a belt-like support is shown in FIGS. 3 and 4. Hydrazine-containing water flows into the hydrazine decomposition tank 1 through a raw water inflow pipe 3 and is discharged through a treated water outflow pipe 4. In the hydrazine decomposition tank 1, a belt equipped with activated carbon is driven by two rotating shafts while its lower part contacts the hydrazine-containing water. The belt on which the activated carbon is attached may be of any type, but a cloth-like or net-like one that is easy to wear is preferable. Activated carbon can be used in granular or powdered forms, but fibers, felt-like fibers, and honeycomb-like fibers are easier to attach. These activated carbons can also be used as sandwiched between two belts. By rotating the belt equipped with activated carbon, adsorption and decomposition of hydrazine occur continuously, making continuous processing possible. Figure 3 shows an example in which the rotation axis of the belt is installed in the horizontal direction, but in Figure 4, it is installed in the vertical direction, and furthermore, the hydrazine decomposition tank is divided into a number of tanks by a partition plate 8, and each tank is This is an example with a belt attached. This example is effective in reducing the footprint and increasing the removal rate of hydrazine. Example 1 A PVC pipe with an inner diameter of 10 cm was cut into 2 cm width, and the outside was
Five pieces of granular activated carbon (Tsurumicol GL-30 trade name) covered with a wire mesh of 20 mesh were placed in a square tank (width 12 cm, length 20 cm) with partitions every 4 cm.
cm, height 6 cm) as shown in Figure 2. The rotating shaft connecting these five cylinders was rotated at 10 rpm, and 220 mg/as of hydrazine was released from one end of the tank.
Synthetic raw water containing N ₂ H ₄ was passed through for 1/1 hour, and the treated water was discharged from the other end. Note that the lower half of the cylinder was immersed in water. When the hydrazine concentration in the treated water was measured in this way, the results were as shown in Table 1.

[Table] Example 2 A saran net with a width of 10 cm and a length of 40 cm was connected at both ends to form a belt, and a felt-like activated carbon fiber (single fiber diameter 17 μm, basis weight 200 g/m ² ) was attached to the outer periphery. As shown in Figure 3, it was installed in a square tank (width 12 cm, length 20 cm, height 5 cm), and the rotating shaft was rotated so that the belt speed was 5 cm/sec.
Synthetic raw water containing various concentrations of hydrazine was flowed into the tank from one end at a flow rate of 500 ml/h, and the treated water was discharged from the other end. The water level in the tank was 2 cm, and the lower half of the belt was always immersed in water. When the hydrazine concentration in the treated water was measured in this way, the results were as shown in Table 2.

[Table] Comparative example The entire device shown in Example 1 was covered with an airtight container,
Filled with _N2 gas, oxygen in the air is normally (21%)
Tests were conducted under the same conditions as in Example 1 for cases where the amount was reduced to approximately half of 8 to 12% and 2 to 5%.
The results are shown in Table 3.

【table】

[Table] (Effects of the Invention) As described above, according to the present invention, adsorption and decomposition of hydrazine can be carried out continuously without using any special chemicals. Therefore, not only costs are reduced, but maintenance and management are also facilitated, greatly contributing to the safety and health of field workers.

[Brief explanation of drawings]

FIG. 1 shows an embodiment in which the activated carbon of the present invention is mounted on a disk. FIG. 2 shows an embodiment in which the activated carbon of the present invention is used by being filled inside a cylindrical support. FIG. 3 shows an embodiment in which the activated carbon of the present invention is attached to a belt, and FIG. 3 shows an example in which the rotating shaft of the belt is attached in a horizontal direction. FIG. 4 shows an embodiment in which the rotating shaft shown in FIG. 3 is installed vertically, and the decomposition tank is divided into a large number of parts by partition plates. 1... Hydrazine decomposition tank, 2... Disc equipped with activated carbon, 3... Raw water inflow pipe, 4... Treated water discharge pipe, 5, 5'... Rotating shaft, 6... Rotating body filled with activated carbon , 7... Belt equipped with activated carbon, 8...
...Partition board.

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 the activated carbon, which has adsorbed hydrazine and has a reduced adsorption capacity, is drained and then brought into contact with air. 1. A method for treating hydrazine-containing water, characterized in that the treatment is carried out continuously while bringing activated carbon into contact with hydrazine-containing water and air alternately at regular intervals. 2 The activated carbon formed into a disc or cylinder, or mounted on a disc or cylinder support;
One or more selected materials filled inside a disk or columnar support are attached to a rotating shaft, and as the disk or column is rotated, a part of the rotating disk or column is filled with hydrazine-containing water. The method for treating hydrazine-containing water according to claim 1, wherein the other portion is brought into contact with air. 3 One or two selected from the activated carbon formed into a belt shape, attached to a belt-shaped support, and filled inside a belt-shaped support.
A method for treating hydrazine-containing water according to claim 1, which comprises: attaching a seed or more to a rotating shaft, driving a belt, and bringing one end of the belt into contact with the hydrazine-containing water and the other end with air. . 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. A method for treating hydrazine-containing water according to claim 1, 2, or 3, comprising the above.