JPS626853B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for reactivating used powdered activated carbon. The invention also relates to a reactivation device suitable for use in carrying out this method. Powdered activated carbon has the advantage of being cheaper and having a much faster adsorption speed than granular or other shaped activated carbon, so it has applications such as adsorption and removal of trace amounts of organic matter in higher-level treatment of wastewater. . However, no suitable method has been established for reactivating used powdered activated carbon so that it can be used repeatedly, and this has placed restrictions on the industrial use of powdered activated carbon. Most of the reactivation technologies for powdered activated carbon that have been implemented or proposed in the past are of the so-called internal heating type, in which activated carbon is directly heated with controlled high-temperature combustion exhaust gas and steam containing a trace amount of oxygen. This is a method in which the adsorbed material is brought into contact with the adsorbent to cause oxidation and thermal decomposition, thereby reactivating it. This method has the disadvantage that the recovery rate is low because combustion loss of activated carbon cannot be avoided, and when implementing it, it is necessary to strictly control the oxygen concentration. As a technique for reactivating powdered activated carbon to avoid such problems, it is thought to use a so-called external heating method, which applies indirect heating from the outside to a high temperature of 600 to 1000℃ and reactivates it with steam. Ta. For example, in Japanese Patent Publication No. 52-19200, a slurry of powdered activated carbon is atomized with water vapor, the water in the sprayed slurry droplets is vaporized by external heating, and the resulting water vapor is combined with the water vapor for spraying. It is disclosed that reactivation can be carried out using the same method. The present inventors took advantage of the external heating method to establish a reactivation technology that does not require a special nozzle for spraying powdered activated carbon slurry with water vapor, and does not require separate preparation of water vapor for spraying. I did a lot of research. In the process, an aqueous slurry is pumped into one end of the heated tube, where the water evaporates to steam, forming a solid-gas mixture with the contained powder suspended in it, and the water evaporates. Due to the rapid volume expansion caused by high temperatures, this solid
It has been found that the gas mixture moves at high speed towards the other end of the tube and is ejected therefrom, and that, at least as far as the slurry of powdered activated carbon is concerned, the above changes can be achieved continuously without causing blockage of the tube. This research aimed not only to eliminate the problems of equipment clogging that often accompany slurry or powder handling, but also to improve thermal efficiency. When carrying out thermal reactivation of activated carbon industrially, the level of thermal efficiency is an important factor that influences the cost. These aims have been achieved by the present invention. The method of reactivating powdered activated carbon of the present invention is to flow an aqueous slurry of powdered activated carbon to be reactivated through an externally heated cylinder while stirring, and dry powdered activated carbon by evaporation of water into steam. This mixture is moved through an activation tube that is heated by combustion gas from the outside, and the temperature is raised to desorb or thermally decompose the adsorbed substance, and the water vapor It consists of reactivating powdered activated carbon and then separating and recovering the reactivated powdered activated carbon from water vapor. The apparatus for reactivating powdered activated carbon of the present invention comprises a means for feeding an aqueous slurry of powdered activated carbon to be reactivated, an internal slurry stirrer, and an external heating jacket. a drying tube for forming a solid-gas mixture suspended in water vapor; an activation tube for receiving this solid-gas mixture and activating powdered activated carbon with the water vapor by heating from the outside; It consists of a separation tank for recovery and a furnace for heating the activation tube with combustion gas. Hereinafter, typical aspects of the present invention will be described with reference to the drawings. In FIG. 1, used powdered activated carbon is made into a slurry 1A of an appropriate concentration in a slurry adjustment tank 2, and is sent to an upper end 4A of a slurry drying cylinder 4 by a slurry pump 3. The particle size of the powdered activated carbon to be treated is typically less than about 60 mesh, and the slurry concentration is within the range of 5 to 50% by weight. If it exceeds 50%, it will be difficult to handle, and if it is thinner than 5%, the thermal energy consumed for reactivation will be excessive, and this will not meet the purpose of the present invention. A range of 10 to 35% is suitable. The slurry drying cylinder is provided with a jacket 5 on the outside, and the slurry is heated by passing the combustion exhaust gas used for activating the powdered activated carbon through the jacket 5.
Inside the cylinder is an agitator with a number of rods mounted on a rotating shaft, which is driven by a variable speed motor (not shown) to push and scrape the slurry against the walls of the cylinder. Avoids sticking and promotes drying. The slurry flows down the drying cylinder 4 little by little while being stirred, and by the time it reaches the lower end 4B, most of the water has evaporated, forming a solid-gas mixture in which powdered activated carbon is suspended in water vapor. This solid-gas mixture enters the activation tube 7 at a temperature above 400°C, preferably above 600°C. The activation tube 7 is placed in a heating furnace 8 and a burner 9
Heated by A, 9B, 9C and 9D. In the illustrated example, this pipe has a double pipe structure, and the above mixture flows down at high speed between the outer pipe 7A and the inner pipe 7B, and the combustion gas heats the outer pipe 7A from the outside, and then passes through the passage 7C. It passes through and rises inside the inner tube 7B and continues to be heated, reaching the jacket 5 of the drying tube described above. The details of the double pipe structure, especially the vicinity of the lower combustion gas passage 7C, are as shown in FIG. While the powdered activated carbon suspended in the steam flows down the activation pipe 7 at high speed, adsorbed substances are desorbed, thermally decomposed, and oxidized, and then reactivated by the action of the steam. The temperature and residence time required in this part vary depending on the suspended powder concentration (in other words, the slurry concentration), the type of substance to be adsorbed, the amount of adsorption, etc., but preferably a temperature of 700°C or higher and 30 seconds at the longest. A residence time of 1 to 10 seconds is appropriate. Activation is faster at high temperatures, but
If the temperature exceeds 1000°C, there will be a lot of loss due to oxidation of the powdered activated carbon, and it is not practical in terms of the durability of the device. Normally, the temperature is preferably 700 to 900°C, especially about 800°C. The operating pressure inside the activation tube is not particularly limited, but it can be operated from normal pressure to several kg/cm ² G, which helps to make the device more compact, or if the residence time is sufficient. It is also useful to obtain The reactivated powdered activated carbon exits the activation tube 7 together with water vapor and the gas generated during the reactivation, consisting of the desorbed adsorbent and its decomposition products, and is preferably supplied with combustion air as shown. After being given heat by a heat exchanger 10, it enters a separation tank 11. Here, the powdered activated carbon is separated by cold water from the spray nozzle 12 provided at the top, and at the same time, a portion of the water vapor is also condensed, forming a slurry again and recovering it. As shown in the figure, the gas generated by the reactivation is sucked in by a blower 13 to prevent it from transferring to the re-formed slurry of powdered activated carbon, and is sent into a heating furnace for combustion treatment. The present invention may have many modifications in addition to the examples described above. For example, a large number of rods 6 as shown in FIG.
It is recommended to use a combination of two shafts 61 planted with 2. If the rods on the two shafts are placed at different angles and rotated in the same direction in close proximity without touching each other, slurry or powder adhering to the rods can be constantly scraped off. Furthermore, the direction of the drying cylinder may be steeper than that shown in the drawings, or even vertical in the extreme, as long as a solid-vapor mixture in which dried powdered activated carbon is suspended in water vapor is formed. This is achieved by making the drying cylinder long enough and rotating the stirrer relatively fast so that the slurry is hit against the wall of the cylinder by centrifugal force.
This is achieved by ensuring efficient heating. The activation tube may also be a single tube in a small-capacity device, especially one formed in a coil shape as shown in FIG. 4, or a multi-tube structure such as a heat exchanger. Including these aspects, it is desirable that the burners of the heating furnace be arranged in the tangential direction to avoid local overheating. Since the jacket of the drying tube only needs to be heated by the combustion exhaust gas from the surrounding area, it is not limited to the structure shown in Figs. 1 and 3.
As shown in the figure, the same effect can be obtained by placing all or part of the drying tube inside the furnace that heats the reactivation tube. In the present invention, the jacket includes such a jacket. Furthermore, the recovery of reactivated powdered activated carbon is also possible.
It is not always necessary to form a slurry; it is possible to cool it to a certain level with cold air and then collect it in a dry state using a bag filter or cyclone, or if all the water used to cool the powdered activated carbon evaporates. It is also possible to use the above-mentioned dry recovery means by adjusting the amount of water sprayed to the extent that the amount of water is removed. According to the present invention, in addition to enjoying all the benefits of external heating type reactivation, there is no need to separately generate steam for regeneration, and no special spraying equipment is used, so slurry concentration fluctuations and flow rate fluctuations The effect is that the device is stable and free from the possibility of clogging the device. Moreover, since the powdered activated carbon moves in a turbulent state within the reactivation tube and is heated, it has good heat conduction, and the entire activated carbon is evenly reactivated, making it easy to obtain a high reactivation rate.
Since high thermal efficiency can be achieved, the cost of reactivation can be reduced and the possibility of industrial use of powdered activated carbon is expanded. The reactivated powdered activated carbon can be recovered in slurry or dry form, if desired. The activity achieved by reactivation is high as shown in the following example. Example 1 A laboratory-scale device was constructed as shown in FIG. 4, in which the slurry drying tube was vertical and most of it was inside the heating furnace, and the activation tube was a coiled single tube. 190 mg/g of paranitrophenol (reagent special grade) was added to 60 to 400 mesh powdered activated carbon.
The adsorbed material was used as a simulated activated carbon, and its reactivation was attempted at various temperatures. The slurry concentration fed to the device was 20% by weight, and the residence time in the activation tube was about 1 second. The iodine adsorption amount and MB (methylene blue) decolorizing power of the reactivated powder activated carbon were measured. The former is JIS K1474 "Test method for granular activated carbon"
The latter was conducted in accordance with the method specified in JIS K1470 "Powdered Activated Carbon Test Method". The results are as follows.

[Table] Example 2 Powdered activated carbon (60 mesh or less) treated with coke oven wastewater and adsorbed up to 200 mg/g of COD _Mo ,
The same equipment was used to deliver and reactivate various slurry concentrations. The activation temperature is 800°C, and the residence time in the tube is about 1 second. The results are shown below.

[Table] Example 3 Comprehensive wastewater treatment from a petrochemical factory was performed using the same powdered activated carbon as in Example 2, and 200 mg/g of COD _Mo was adsorbed, and the waste was reactivated using the same equipment at different activation temperatures. The slurry concentration is 20% by weight and the activation tube residence time is also about 1 second. The results are as follows.

[Table] Example 4 Sodium dodecylbenzenesulfonate 100%
Powdered activated carbon (60 to 400 mesh) adsorbed mg/g was prepared at a slurry concentration of 20% by weight and an activation temperature of 800%.
Reactivation was carried out under conditions of temperature and residence time of about 1 second. As shown below, a higher regeneration rate than fresh coal was obtained.

[Table] Example 5 The same powdered activated carbon as in Example 1, which also had 190 mg/g of paranitrophenol adsorbed, was used at a concentration of 20
800% by weight slurry and fed into the same equipment.
Reactivation was performed at an activation temperature of °C, but with varying residence times. As a result, the following results were obtained.

【table】 [Brief explanation of the drawing]

FIG. 1 is a system diagram showing a typical example of an apparatus for reactivating powdered activated carbon of the present invention. 2A, B, and C are views showing the structure of the main part of the activation tube in FIG. 1, in which A is a longitudinal cross-sectional view, B is a -position of A, and C is a cross-sectional view at a -position. It is. FIGS. 3A and 3B are views showing another embodiment of the slurry drying cylinder, in which A is a longitudinal cross-sectional view and B is a cross-sectional view. FIG. 4 is a cross-sectional view showing another example of the device of the present invention, which was used in an example. 1A...Slurry of used powdered activated carbon, 1B
...Reactivated powdered activated carbon slurry, 4...
... Slurry drying cylinder, 7 ... Activation tube, 8 ... Heating furnace, 11 ... Separation tank.

Claims (1)

[Claims] 1. An aqueous slurry of powdered activated carbon to be reactivated is allowed to flow down an externally heated cylinder with stirring, and the dried powdered activated carbon is formed into solid air suspended in water vapor by evaporation of moisture. A mixture is formed, and this mixture is moved through an activation tube heated by combustion gas from the outside and heated to desorb or thermally decompose the adsorbed substance, and the powdered activated carbon is reactivated by the water vapor. , and then separating and recovering the reactivated powdered activated carbon from water vapor. 2. The method according to claim 1, wherein the drying tube is heated by the combustion waste gas that heated the activation tube. 3. Feed an aqueous slurry of powdered activated carbon into the drying tube at a concentration of 10 to 35% by weight, heat the mixture in the activation tube at a temperature of 700 to 900°C, and set the residence time to 1 to 10%.
The method according to claim 1, wherein the time period is within seconds. 4. The method according to claim 1, in which the reactivated powdered activated carbon is sprayed with water to rapidly cool it and condense water vapor. 5. The reactivated powdered activated carbon rapidly cooled by water spray and the gas containing the desorbed product or its decomposition product separated from the condensed water are treated by combustion for heating the activation tube. Method. 6. Means for delivering an aqueous slurry of powdered activated carbon to be reactivated, with an internal slurry agitator and an external heating jacket to form a solid-gas mixture in which dried powdered activated carbon is suspended in water vapor. a drying tube for receiving this solid-gas mixture and activating the powdered activated carbon with the steam by heating from the outside, a separation tank for recovering the reactivated powdered activated carbon, and a drying tube for receiving the solid-gas mixture and activating the powdered activated carbon with the steam using combustion gas. A device for reactivating powdered activated carbon, consisting of a furnace that heats a tube. 7. The device according to claim 6, which utilizes waste gas from the furnace as a heat medium for the jacket. 8. The device according to claim 6, wherein the slurry agitator has a number of paddles or rods installed on a rotating shaft. 9. The device according to claim 6, wherein the slurry agitator has a large number of rods installed on two shafts that rotate in the same direction in close proximity. 10. The device according to claim 6, wherein the activation tube has a double tube structure, and the combustion gas is heated by flowing outside the outer tube and inside the inner tube. 11. The device according to claim 6, comprising a device for exchanging heat between the solid-gas mixture after the activation of the powdered activated carbon and combustion air. 12. The device according to claim 6, which is configured to send the gas separated from the powdered activated carbon in the separation tank to a combustion device for combustion treatment.