JP4583234B2 - Exhaust gas treatment apparatus and treatment method using the same - Google Patents

Description

  The present invention particularly relates to an exhaust gas treatment apparatus suitable for treating exhaust gas containing organic halogen compounds or pollutants generated as by-products when an organic halogen compound is dehalogenated with an alkali metal. It relates to the processing method using.

  Dehalogenation treatment, that is, decomposition treatment of the organic halogen compound, is carried out by reacting an organic halogen compound such as polychlorinated biphenyl (hereinafter referred to as PCB) with an alkali metal dispersion such as a metal sodium dispersion (hereinafter referred to as SD). The method is known. In this treatment method, for example, in the PCB decomposition process, the exhaust gas discharged contains dioxins contained in the PCB or PCB and contaminants such as biphenyl and benzene as reaction byproducts. It is necessary to completely purify the exhaust gas so as not to leak to the outside. And as a method of detoxifying the pollutants in the exhaust gas described above, an activated carbon packed tower filled with activated carbon is installed in the exhaust gas line of the reaction tank, and the exhaust gas passes through the activated carbon to remove the pollutants. A method of removing by adsorption is known (PCB processing technology guidebook). In this activated carbon adsorption method, when the amount of adsorption of activated carbon is saturated, it is necessary to replace the activated carbon with a new one, and also to remove the pollutant from the used activated carbon as a post-treatment and reprocess it. The processing operation of the used activated carbon is complicated, and the operation of processing a large amount of the used activated carbon involves a risk that the operator takes in the pollutant into the body.

From the background as described above, as described in Patent Document 1, the present applicants have adopted an absorbent as a pre-process for adsorbing exhaust gas to activated carbon in order to suppress the load of exhaust gas treatment with activated carbon. Has developed an exhaust gas treatment facility equipped with an absorption process for contacting the exhaust gas and a cooling process for cooling the exhaust gas with a condenser, enabling an extension of the activated carbon replacement period and improving the adsorption efficiency.
JP2003-170021

  The present invention further improves the absorption / purification efficiency of the exhaust gas treatment used in the previous process of the activated carbon adsorption treatment or the treatment of exhaust gas replacing the activated carbon in the dehalogenation treatment step taken up in the above-mentioned literature 1. It is intended to realize a submerged aeration type exhaust gas treatment apparatus and an exhaust gas treatment method using the same, which can simplify the processing operation and reduce the processing cost.

In order to achieve the above object, an invention according to claim 1 is an exhaust gas processing apparatus in which exhaust gas is aerated to a processing liquid stored in an absorption tank, and a contaminant in the exhaust gas is absorbed by the processing liquid in the absorption tank. the absorption vessel made from upper and lower absorber tower multi-stage is disposed in the absorption tower sparge tube for aeration arranged in each absorption tank, the lower end is connected to the gas phase portion above the absorption vessel, the upper end Is bent from a position above the liquid surface portion liquid level in the upper absorption tank of the absorption tank and connected to the aeration tube in the absorption tank to allow the gas in the lower absorption tank to flow to the upper stage a gas transfer pipe to send to the diffuser tube of the absorption vessel, the upper end is connected to the liquid phase lower side of the absorption trough, the lower end is connected to the gas phase portion of the absorption vessel of the bottom row of the absorbent tank a liquid transfer tube to send the processing solution in the absorption chamber of the upper absorption vessel stages thereunder Te, et provided on the outer periphery of said absorbing compartment Together and a jacket to keep a constant and adjusting the temperature of the treatment liquid by passing a coolant tank Te, of the absorption vessel, the bottom plate partitioning the lower absorption vessel and the absorption vessel stages thereon or The partition plate is provided in an inclined shape in which the lower end connection side of the gas transfer pipe is higher and the upper end side of the liquid transfer pipe, which is the opposite side, is lowered, and the lowermost absorption tank constituting the absorption tower Exhaust gas is aerated through the diffuser pipe to the treatment liquid inside, and the exhaust gas after aeration is passed through the gas transfer pipe and the diffuser pipe from the inside of the absorption tank to the treatment liquid in the upper absorption tank. Te is capable aeration in order, and you are characterized in that it is transported through the liquid flow pipe upper processing solution in the absorption chamber in order to absorption trough stage below it.

On the other hand, the invention of claim 2 is a pollution that is produced as a by-product in the process of decomposing the organic halogen compound contained in the electrical insulating oil using the alkali metal dispersion and contained in the exhaust gas. The exhaust gas treatment apparatus according to claim 1, wherein the treatment liquid removes the contaminants by absorbing a substance (including an organic halogen compound itself) in the treatment liquid, and uses the exhaust gas treatment apparatus according to claim 1. Is a saturated hydrocarbon, mineral oil, or a mixture thereof, and the temperature of the treatment liquid is kept in the range of −15 to 10 ° C., and the exhaust gas is first introduced into the treatment liquid in the lowermost absorption tank. After aeration, the exhaust gas after aeration is sequentially aerated from the inside of the absorption tank to the treatment liquid in the upper absorption tank, and the treatment liquid in the lowermost absorption tank is taken out of the tank, and then the upper stage The treatment liquid in the absorption tank Transferred into Osamuso, sequentially transferring the process liquid in the absorption vessel of the upper to the absorber tank emptied, it is characterized by replenishing the new process liquid to the top of the absorption vessel.

-In invention of Claim 1, since the absorption tank is arrange | positioned at upper and lower multistage, the contact area of exhaust gas and a process liquid can be ensured, suppressing a space, and a process liquid is made into a lower stage in order by gravity. Since the exhaust gas can be automatically transferred to the upper stage in order, the equipment can be simplified by minimizing auxiliary equipment. Depending on the control, for example, the treatment liquid moves from the upper absorption tank to the lower absorption tank, thereby narrowing the gas phase space in the lower absorption tank and reducing the exhaust gas in the absorption tank to the upper absorption tank. It is also possible to efficiently pump to the absorption tank.
Moreover, in this invention, the backflow of exhaust gas can be prevented. Even when the pump and valve for transferring the exhaust gas to the next upper absorption tank are omitted, the exhaust gas and the processing liquid flow back from the diffusion pipe of the upper absorption tank to the lower absorption tank through the gas transfer pipe. To eliminate the risk of Moreover, by supplying the processing liquid from the upper part and withdrawing it from the lower part , the processing liquid in which the contaminant is absorbed can be efficiently transferred to the lower stage. In other words, for example, when a new processing liquid supplied to the uppermost absorption tank is extracted into the lower absorption tank by the overflow method, the replenished processing liquid is sufficiently diffused and does not absorb the contaminants. This is to prevent being discharged as it is. Furthermore, in the absorption tower having the upper and lower absorption tanks, further simplification is realized by the bottom plate or the partition plate partitioning the absorption tanks also having the function of collecting the exhaust gas.

In the invention of claim 2, as an exhaust gas treatment method in the dehalogenation treatment, in addition to the simplification of the apparatus as in the case of claim 1, the treatment operation becomes easy. Of these treatment liquids, only the treatment liquid in the lowermost absorption tank containing the largest amount of contaminants is transferred to the outside of the tank, so that, for example, an efficient decomposition process can be performed while suppressing the amount of treatment in the next step.
Further, in this invention, in the most preferred to identify those, and an operation of absorbing the exhaust gas into the processing solution as a processing solution, but usually it is preferable to aeration as low as possible the temperature of the treatment liquid, low too Temperature In this case, the viscosity of the processing solution is high and the fluidity is poor, and even when aerated, the exhaust gas bubbles do not spread and the contact area becomes narrow. Therefore, the temperature range is specified to satisfy a certain degree of fluidity and absorption efficiency. It has significance.

(Apparatus Structure) A preferred embodiment of the present invention will be described with reference to the schematic diagram of FIG. The exhaust gas treatment apparatus of FIG. 1 includes a vertical absorption tower 1 in which absorption tanks 2 </ b> A to 2 </ b> C are provided in multiple upper and lower stages, and a control device 3. The absorption tower 1 has a three-stage absorption tank, but may have two stages or four or more stages. As a tank structure, each absorption tank 2A-2C is provided in the outer periphery, and the jacket 4 for flowing the refrigerant | coolant etc. and adjusting the temperature of the process liquid in a tank or keeping it constant, and the dispersion | distribution arrange | positioned in each tank And a trachea 5. Further, the lower absorption tank and the upper absorption tank, that is, in this example, the lowermost absorption tank 2A and the middle absorption tank 2B, the middle absorption tank 2B and the uppermost absorption tank 2C are the bottom plate of the upper tank. Or it is partitioned off by a partition plate 6. Among these, each aeration pipe 5 is a pipe for injecting exhaust gas from a number of holes (lower holes), and is held substantially horizontally on the lower side in the tank. Each partition plate 6 is provided in an inclined shape with one side being lowered, so that the exhaust gas in the tank easily flows to the higher side along the inclination.

The absorption tanks 2 </ b> A to 2 </ b> C are provided with an exhaust gas path for flowing exhaust gas and a treatment liquid path for flowing treatment liquid. More specifically, the exhaust gas system path includes the gas transfer pipe 7a for the exhaust gas inlet connecting the exhaust gas generation source 10 to be treated and the diffuser pipe 5 disposed in the lowermost absorption tank 2A, and the uppermost gas transfer pipe 7a. A gas transfer pipe 7b for the treated exhaust gas outlet connecting the absorption tank 2C and the gas recovery unit 11 and the like, a lowermost absorption tank 2A, and an aeration pipe 5 arranged in the absorption tank 2B above And a gas transfer pipe 7d connecting the middle absorption tank 2B and the diffuser pipe 5 arranged in the uppermost absorption tank 2C. The lower ends of the gas transfer pipes 7c and 7d are connected to the upper side of the gas phase part in the absorption tanks 2A and 2B, and the upper end is higher than the liquid phase part liquid level in the upper absorption tanks 2B and 2C above the absorption tank. It is bent from the position and connected to the corresponding diffuser pipe 5 arranged in the absorption tank.

  The processing liquid system path includes a liquid transfer pipe 8a for the processing liquid inlet connecting the reservoir 13 storing new processing liquid and the upper part of the uppermost absorption tank 2C, and the lowermost absorption tank. As an outlet for a used processing liquid (this is a processing liquid that absorbs most of the pollutants in the exhaust gas) connecting 2A and the processing section 14 for collecting and processing the used processing liquid. The liquid transfer pipe 8b, the liquid transfer pipe 8c connecting the lower liquid phase part of the uppermost absorption tank 2C and the gas phase part of the lower absorption tank 2B, and the lower liquid phase part of the middle absorption tank 2B And a liquid transfer pipe 8d connecting the gas phase part of the lowermost absorption tank 2A. The upper ends of the liquid transfer pipes 8c and 8d are connected to the lower side of the liquid phase part in the absorption tanks 2C and 2B, and the lower ends are connected to the gas phase part in the absorption tanks 2B and 2A in the lower stage of the absorption tank. . In addition, valves (solenoid valves or the like) 9a to 9d that are automatically controlled to open and close according to commands from the control device 3 are interposed in the liquid transfer pipes 8a to 8d. Preferably, a shower is attached to the discharge port for discharging the liquid among the liquid transfer pipes 8a to 8d, and the treatment liquid is sprayed in the gas phase portion through the shower to improve the gas-liquid contact efficiency. It is.

  Note that a thermometer and a liquid level meter (not shown) are attached to the absorption tanks 2A to 2C. As materials for the absorption tower 1 and the pipes accompanying it, steel (SS), stainless steel (SUS), and the like are appropriately selected according to the temperature of the processing liquid, equipment costs, and the like.

(Exhaust gas treatment method) Next, with reference to FIG. 2, in the course of the dehalogenation treatment, the procedure for removing the contaminants produced as by-products and contained in the exhaust gas by absorbing them into the treatment liquid will be explained. To do. First, as the organic halogen compound to be used in the dehalogenation treatment of the present invention, in addition to PCB, dioxins, polychlorinated dibenzofurans, polychlorinated benzene, chlorofluorocarbon, DDT, BHC and the like hardly persistent organic halogen compounds Can be illustrated. These organohalogen compounds may be used as they are, but can be used as an organohalogen compound solution adjusted to a concentration suitable for treatment by dissolving in a solvent.

  As the solvent for dissolving the organic halogen compound, aliphatic hydrocarbons, aromatic hydrocarbons or cyclic hydrocarbons which are inert or low in activity to alkali metals are preferable. For example, hexane, cyclohexane, benzene, kerosene, decalin, trans As an alternative to oil (trans oil described in JIS C 2320-1993), heavy oil (heavy oil described in JIS K2205), liquid paraffin, or cleaning oil (fluorocarbon, trichloroethane, kerosene, etc., cleaning automobiles, electronic components, precision equipment And the like, which are used mainly for hydrocarbons), and these can be used alone or as a mixture. Among these solvents, trans oil can be particularly preferably used in terms of stabilizing SD.

  Examples of the alkali metal include potassium, lithium, cesium, rubidium, and alloys thereof in addition to sodium. However, sodium is most preferable when considering ease of handling and reactivity, and SD is most preferable when considering reactivity. In particular, SD produced in electrical insulating oil is excellent in stability, dispersibility, and reactivity. The electrical insulating oil is an oil for electrical insulation used for 1 to 7 types of capacitors described in JIS 2380, and among them, the first type electrical insulating oil is preferable. Further, the alkali metal concentration in the alkali metal dispersion can be arbitrarily selected, but is preferably about 1 to 50%. The average particle size of the alkali metal dispersion is 20 μm or less, preferably 10 μm or less. SD is added in an amount of 1 to 200 times mol per mol of halogen atoms in the organic halogen compound.

  In the dehalogenation treatment step for decomposing the organic halogen compound, the case where the PCB contained in the electrical insulating oil is decomposed at a high concentration (content of 1% or more, particularly 10% or more) is taken as an example. An oil to be treated containing PCB is supplied to a reaction tank in which trans oil as a solvent is stored, and is dehalogenated. The reaction temperature here is 150-200 ° C. By the chemical reaction between PCB and metallic sodium, biphenyl is bonded, and PCB is rendered harmless to the polymer. Here, the transformer oil contains trichlorobenzene in addition to PCB, and a large amount of exhaust gas containing benzene and the like is generated by the dehalogenation treatment, so the exhaust gas is sent to the exhaust gas treatment process for purification. Will be processed.

  The exhaust gas treatment process is a place where contaminants contained in the reaction exhaust gas generated by the dehalogenation treatment are removed and purified by means such as adsorption, and these contaminants are purified without being accompanied by the exhaust gas. Released into the atmosphere. Specifically, using an absorption tower in which upper and lower absorption tanks in which treatment liquids excellent in solubility of biphenyl and benzene are stored are used, the exhaust gas sent to the absorption tower is transferred from the lower stage to the upper stage, A so-called submerged aeration type exhaust gas treatment method in which contaminants contained in exhaust gas are absorbed in order into the treatment liquid of each tank by transferring the treatment liquid from the upper stage to the lower stage and aeration of the treatment liquid in each absorption tank It is. In this processing method, exhaust gas is aerated into the processing liquid, so that the exhaust gas rising in the tower, such as a conventional packed tower type or a shelf type, and the falling processing liquid come into contact with each other, so-called countercurrent. It is a completely different method from contact.

  As the treatment liquid, n-hexane, n-heptane, n-octane, n-decane, kerosene, decalin, liquid paraffin, electric insulating oil (for example, electric insulating oil described in JIS C2320-1993), heavy oil (for example, Heavy oils described in JIS K2205), hydrocarbons such as liquid paraffin; aromatic hydrocarbons such as toluene and xylene; aprotic polar solvents such as 1,3-dimethylimidazoline, sulfolane and polyethylene glycol dialkyl ether; and these A mixture; and the like. Among these, since the vapor pressure is relatively low, the flash point is high, and the absorption ability of organic halogen compounds is excellent, saturated hydrocarbons such as n-decane, decalin, liquid paraffin, kerosene, electrical insulating oil, heavy oil, etc. The use of mineral oils; and mixtures thereof is preferred. In the following examples, trans oil is used as the treatment liquid.

  The use temperature of the treatment liquid is set to a temperature range of −15 to 10 ° C. in consideration of the absorption efficiency of contaminants and the thermal efficiency of the treatment liquid. Since the dehalogenation treatment is performed in the temperature range of 90 to 200 ° C. as described earlier, the exhaust gas discharged from the reaction tank is also at a high temperature, and the temperature of the treatment liquid is directly led to the exhaust gas treatment step. Since this increases the absorption efficiency, a cooling step for cooling the exhaust gas is provided at the beginning of the exhaust gas treatment. In addition, the exhaust gas is condensed in the cooling process, so that the pollutant discharged together is cooled and condensed, that is, absorbed and removed. Specifically, the temperature of the exhaust gas is lowered using a condenser or the like, and the temperature of the treatment liquid in the absorption tower is maintained in an optimum range.

  Since the contaminant is absorbed into the processing liquid, the contaminant accumulates in the processing liquid as the purification process proceeds. Therefore, it is necessary to detoxify this treatment liquid. Therefore, the used processing solution is directly transferred to the reaction vessel and used for the dehalogenation reaction, or once transferred to the receiving vessel and stored, and a certain amount is collected and used for the dehalogenation reaction. In this case, if a solvent that can be used for the dehalogenation reaction of the organic halogen compound is used as the treatment liquid, the used treatment liquid can be directly subjected to the dehalogenation reaction. Therefore, the separation process of the treatment liquid and the contaminant is not required, and the work efficiency and the risk of recontamination by the contaminant in the separation process can be avoided.

  In the exhaust gas treatment process, most of the pollutants can be absorbed by the treatment liquid. However, in order to increase the concentration of pollutants in the exhaust gas and to improve safety and purification efficiency, the aeration submerged exhaust gas After the treatment step, a packing type treatment step, an activated carbon adsorption treatment step, and the like can be provided. The packing type processing is a processing method in which a processing liquid is supplied from the upper part of a tower packed with packings such as Raschig ring and sulzer packing, and exhaust gas is passed from the lower part to make gas-liquid contact. Trace amounts of pollutants in the exhaust gas that have not been taken into the liquid aeration-type treatment oil are adsorbed by activated carbon and the like, and the cleanliness of the exhaust gas can be greatly improved. The flow of these exhaust gases is shown in the flow sheet of FIG.

  In this example, SD adjusted to a concentration of 15 wt% and electrical insulating oil adjusted to a PCB concentration of 50 wt% were mixed in a reaction tank, and a dehalogenation treatment was performed. During the reaction treatment, nitrogen as an inert gas was supplied to the reaction tank, and the exhaust gas discharge rate was adjusted to 10 L / min. The exhaust gas discharged from the reaction tank was cooled to 5 ° C. by a heat exchanger, and then the exhaust gas was introduced into an absorption tower similar to the above-described exhaust gas processing apparatus. The absorption tower has a three-stage absorption tank. Transformer oil as a processing liquid was supplied to the uppermost stage, and a predetermined amount (200 ml of each tank) of processing liquid was stored in each absorption tank through a liquid transfer pipe. After storage, all the valves of the liquid transfer pipe were closed, and the exhaust gas was allowed to pass while maintaining the treatment liquid at 0 ° C. The exhaust gas introduced into the absorption tower passed through the treatment liquid in each absorption tank and was discharged from the absorption tower. Tables 1 and 2 are values obtained by measuring the PCB concentration in the exhaust gas discharged from the reaction tank at the entrance and exit of the absorption tower.

  In the above embodiment, a three-stage absorption tower is used. However, the number of stages and the amount of processing liquid are appropriately determined according to the processing capacity of exhaust gas. In the examples, the treatment liquid was not transferred, but it was arbitrarily designed to open the valve during aeration and replenish the treatment liquid in the uppermost stage or to transfer the treatment liquid in each absorption tank to the lower absorption tank. Is done. It is also possible to measure the concentration of contaminants in the treatment liquid in each absorption tank and transfer it when a predetermined concentration is reached, or to transfer the treatment liquid to the reaction tank. As described above, the present invention only needs to satisfy the requirements specified in the claims, and the details can be variously modified and developed with reference to the above embodiments and examples.

It is a schematic block diagram which shows typically the exhaust gas processing apparatus of invention form. It is reference explanatory drawing which shows the whole flow of the waste gas processing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Absorption tower 2A-2C ... Absorption tank 3 ... Control part 4 ... Jacket 5 ... Aeration pipe 6 ... Bottom plate or partition plate 7a-7d ... Gas transfer pipe 8a-8e ... Liquid transfer pipe

Claims (2)

In the exhaust gas treatment apparatus, aeration gas is aerated into the treatment liquid stored in the absorption tank, and the contaminant in the exhaust gas is absorbed by the treatment liquid in the absorption tank.
It consists of an absorption tower in which the absorption tank is arranged in upper and lower stages ,
An aeration pipe for aeration in which the absorption tower is disposed in each absorption tank;
The lower end is connected to the upper side of the gas phase part in the absorption tank, and the upper end is bent from the position above the liquid surface part liquid level in the absorption tank on the upper stage of the absorption tank, and the diffuser tube in the absorption tank a gas transfer tube to send the gas absorption chamber of the lower to the diffuser tube in absorption trough the stage above it is connected to,
The upper end is connected to the lower side of the liquid phase part in the absorption tank, the lower end is connected to the gas phase part in the absorption tank at the lower stage of the absorption tank, and the treatment liquid in the upper absorption tank is passed to the lower stage. A liquid transfer pipe to be sent to the absorption tank;
A jacket provided on the outer periphery of the absorption tank to adjust the temperature of the processing liquid in the tank by flowing a refrigerant or to keep it constant ,
Among the absorption tanks, a bottom plate or a partition plate that partitions the lower absorption tank and the upper absorption tank has a higher lower end connection side of the gas transfer pipe, and an upper end side of the liquid transfer pipe that is the opposite side. It is provided in a lowered slope,
Exhaust gas is aerated through the diffuser pipe to the treatment liquid in the lowermost absorption tank constituting the absorption tower, and the exhaust gas after aeration is discharged from the absorption tank into the upper absorption tank. The treatment liquid can be aerated through the gas transfer pipe and the diffusion pipe in order, and the treatment liquid in the upper absorption tank can be sequentially transferred to the lower absorption tank through the liquid transfer pipe. An exhaust gas treatment apparatus characterized by that. In the process of decomposing the organic halogen compound contained in the electrical insulating oil using the alkali metal dispersion, the pollutant produced as a by-product and contained in the exhaust gas is absorbed by the treatment liquid, In an exhaust gas treatment method for removing pollutants,
The exhaust gas treatment apparatus according to claim 1, wherein the treatment liquid is one of saturated hydrocarbons, mineral oils, and mixtures thereof, and the temperature of the treatment liquid is maintained in a range of −15 to 10 ° C. The exhaust gas is first aerated into the treatment liquid in the lowermost absorption tank, and the exhaust gas after aeration is sequentially aerated from the absorption tank to the treatment liquid in the upper absorption tank. After the treatment liquid in the absorption tank is drawn out of the tank, the treatment liquid in the upper absorption tank is transferred into the lowermost absorption tank, and the treatment liquid in the upper absorption tank is transferred to the empty absorption tank. An exhaust gas treatment method comprising sequentially transferring and replenishing a new treatment liquid into the uppermost absorption tank.

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