JPH0140680B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating smoke cleaning wastewater generated by cleaning exhaust gas from an incinerator. The exhaust gas of the incinerator contains CO ₂ as combustion products,
In addition to gas components such as H ₂ O, SOx, NOx, HCl, and excess air, various components such as ash and unburned matter are mixed in depending on the properties of the material to be incinerated or combustion conditions. Of these, the harmful components SOx, NOx, and HCl
Various pairing methods have been proposed to remove
Wet or dry scrubbers are often used for SOx, HCl, etc. In particular, in order to improve the removal rate, it is common to use a wet scrubber that uses alkali as the cleaning liquid.In this case, salts are generated in the cleaning liquid as a result of the reaction between the acidic gas and the alkali, and Dust components are also supplemented. When the cleaning product reaches a certain concentration, it must be drawn out of the system as smoke cleaning wastewater and disposed of. The products in the smoke washing wastewater cannot be directly disposed of because they contain salts, which are the main components, and various toxic heavy metals.
Conventionally, disposal has been carried out by solidification treatment using a solidification agent or solidification treatment after heavy metal separation, but it has been difficult to completely prevent elution, making it difficult to dispose of smoke washing wastewater. In addition, as a method for treating smoke washing wastewater, it is known from previous information that when heating and concentrating to crystallize salts, a process for removing heavy metals, Na ₂ SO ₄ , etc. is adopted. In other words, as a method for removing Na ₂ SO ₄ , CaCl ₂ is added and Na ₂ SO ₄ + CaCl ₂ → CaSO ₄ +
Like 2NaCl, it is converted into plaster form and then extracted.
In this method, excess CaCl ₂ or CaSO ₄ remaining within the solubility range precipitates on the evaporator etc. in the system and adheres as so-called scale, which becomes an obstacle to the operation of the processing equipment. It was necessary to perform cleaning work or add a separate step to remove Ca salts. The present invention includes a heavy metal removal process in which heavy metals are removed from the smoke washing wastewater from an incinerator through coagulation sedimentation and chelate resin adsorption treatment, and a heavy metal removal process in which heavy metals are removed from the smoke washing wastewater by heating and concentration to crystallize NaCl in the smoke washing wastewater. The treatment is characterized by a combination of a desalting step in which the salt is removed and separated, and a deawning step in which the separated mother liquor obtained by separation is cooled and Na ₂ SO ₄ in the separated mother liquor is crystallized and separated,
The purpose is to provide a method for treating incinerator smoke wastewater that eliminates the above-mentioned conventional drawbacks, and that also serves as a recovery method for disposing of the smoke wash wastewater and recovering the contained salts as purified salt for effective use. It is something to do. In the present invention configured as described above, heavy metals are removed by coagulation and sedimentation treatment of smoke washing wastewater, and Hg is further removed at a high level by treatment with a heavy metal scavenger, chelate resin, etc., and then combustion and concentration are performed. by
NaCl is crystallized and separated. The separated mother liquor is cooled to 35° C. or below to crystallize and separate Na ₂ SO ₄ to recover selected salt (NaCl) and Glauber's salt (Na ₂ SO ₄ ). As described above, the present invention includes a heavy metal removal step in which heavy metals are removed from the smoke washing wastewater from an incinerator through coagulation sedimentation and chelate resin adsorption treatment, and a heavy metal removal process in which heavy metals are removed from the smoke washing wastewater by burning and concentrating the smoke washing wastewater. The treatment is a combination of a desalting step in which NaCl is crystallized and separated, and a deawning step in which the separated mother liquor obtained by separation is cooled and Na ₂ SO ₄ in the separated mother liquor is crystallized and separated. Salts and various harmful heavy metals in the smoke wastewater are sufficiently removed, and therefore, the smoke washing wastewater treated by the method according to the present invention can be disposed of extremely easily. In addition, the salts contained in the smoke washing waste water are heated and concentrated.
Since NaCl is crystallized and separated and recovered as purified salt, this is an extremely effective method for recovering resources from smoke washing wastewater. Furthermore, in order to recover the salts contained in the smoke washing wastewater, the smoke washing wastewater is heated and concentrated to crystallize and separate NaCl in the smoke washing wastewater, and then the separated mother liquor obtained by separation is obtained. and the solubility of Na ₂ SO ₄ is 35
Utilizing the physical property that decreases rapidly below ℃
To remove Na ₂ SO ₄ , it remains as before.
There is no trouble caused by the precipitation of CaCl ₂ , the number of chemical addition steps is reduced, and the operational management of the device to which the present invention is applied is facilitated, and by-product Glauber's salt can be used. Hereinafter, a preferred embodiment of the present invention will be explained based on the embodiment shown in FIG. 1. In FIG. 1, a chemical liquid mixing tank 1, a coagulation sedimentation tank 2, A filter tower 3, a chelate resin tower 4, an evaporative concentration can 5, and a centrifugal separator 6 are installed, and a cooling tower 7 and a centrifugal separator 8 are provided in the return line 14 for the separated mother liquor 13 from the centrifuge 6. is interposed, and the downstream side 14a of the return line 14 is returned to the smoke washing wastewater supply line 12 on the upstream side of the chemical mixing tank 1. 11a is the smoke _{washing wastewater from which heavy metals have been removed, 13a is the remaining mother liquor from which Na 2 SO 4 has been} separated, and 15 and 16 are the lines. be. In this embodiment, in the flow shown in FIG. 1, the smoke washing waste water 11 of the smoke furnace is subjected to coagulation sedimentation in the coagulation-sedimentation tank 2 and chelate resin adsorption treatment in the chelate resin tower 4 to collect the heavy metals in the smoke washing waste water 11. a heavy metal removal process to remove metals, a desalination process to crystallize and separate NaCl9 in the smoke washing wastewater 11a by burning and concentrating in an evaporative concentrator 5, and a separation mother liquor 13 obtained by separating in a centrifuge 6. This treatment is carried out in combination with a de-awning process in which Na ₂ SO ₄ in the separated mother liquor 13 is crystallized and separated by cooling in a cooling tower 7 . Further, to describe this embodiment in detail, the smoke washing waste water 11 is supplied from the smoke washing waste water supply line 12 to the chemical solution mixing tank 1, and in the same tank 1, FeCl ₃ , Na ₂ S, a heavy metal scavenger, a polymer flocculant, etc. , PH adjuster, etc., and then in a coagulation sedimentation tank 2, heavy metals in the smoke washing waste water 11 are sedimented and removed. Table 1 shows an example of the properties of the smoke washing wastewater to be treated.

【table】

[Table] Next, the smoke washing waste water 11 is led from the coagulation sedimentation tank 2 to the filter tower 3, where the fine suspended matter in the smoke washing waste water 11 is separated, and further led to the chelate resin tower 4. The very small amount of Hg remaining in the smoke washing waste water 11 is adsorbed and removed in the same column 4. The smoke washing wastewater 11a that has been subjected to the above heavy metal removal process is led to the evaporative concentration can 5, where it is heated and concentrated to remove the smoke washing wastewater 11a.
After NaCl 9 is crystallized, it is separated into separated mother liquor 13 and NaCl 9 using a centrifuge 6 and taken out through line 15 as purified salt. An example of the properties of the purified salt taken out from line 15 is shown in Table 2.

[Table] On the other hand, the separated mother liquor 13 is led through the return line 14 to the cooling tank 7, where it is cooled to 35°C or lower to crystallize Na ₂ SO ₄ 10 in the separated mother liquor 13. Centrifuge 8 takes Na ₂ SO ₄ 10 out through line 16. One of the remaining mother liquors 13a is returned to the smoke washing waste water supply line 12 at the entrance of the chemical liquid mixing tank 1, mixed with new smoke washing waste water 11, and subjected to the above-mentioned circulation treatment. In this way, in this embodiment, the incinerator smoke waste water 11
After chemical injection in the chemical injection tank 1, coagulation and sedimentation in the coagulation-sedimentation tank 2, filtering in the filter tower 3, and chelate resin adsorption treatment with the chelate resin 4, resulting in smoke washing wastewater 11.
A heavy metal removal process for removing heavy metals in the smoke cleaning waste water 11a from which heavy metals have been removed is carried out in an evaporation concentrator 5.
After heating and concentrating the NaCl9 in the smoke washing wastewater 11a, the centrifuge 6 separates it and sends it to the line 15.
The separated mother liquor 13 obtained by separation with the centrifuge 6 is led to the cooling tower 7 through the return line 14, and is cooled in the cooling tower 7 to remove Na ₂ SO ₄ 10 of the separated mother liquor 13. Since the treatment is combined with a de-awning process in which Na ₂ SO ₄ 10 is recovered from the line 16 by separating it in a centrifuge 8 after crystallization, the salts and various harmful heavy metals in the smoke washing waste water 11 are sufficiently removed. This makes it extremely easy to dispose of the smoke washing wastewater that has been treated by the method according to this embodiment. In addition, the salts contained in the smoke washing waste water 11 are heated and concentrated in the evaporative concentrator 5 after removing harmful heavy metals.
Since NaCl 9 is crystallized and separated by the centrifuge 6 and recovered as purified salt, this is an extremely effective method for recovering resources from the smoke washing wastewater 11. Further, in recovering the salts contained in the smoke washing wastewater 11, the smoke washing wastewater 11a is heated and concentrated in the evaporative concentrator 5 to crystallize NaCl9 in the smoke washing wastewater 11a, and then separated in the centrifuge 6. Later, centrifuge 6
The separated mother liquor 13 obtained by separation is sent to the return line 1.
4 to the cooling tower 7, cooled in the same cooling furnace tower 7,
Since Na ₂ SO ₄ is removed by utilizing the physical property that the solubility of Na ₂ SO ₄ rapidly decreases below 35°C, there is no trouble caused by the precipitation of residual CaSO ₄ as in the conventional method, and the number of chemical addition steps is also reduced. In addition, it is possible to easily manage the operation of the operation control device to which this embodiment is applied, and to utilize the by-product mirabilite. As described in detail in the above embodiments, the present invention is a recovery method for disposing of smoke washing wastewater and recovering the contained salts as purified salt for effective use. It is suitable for treating smoke cleaning wastewater discharged from waste incineration exhaust gas cleaning equipment and other HCl and SOx-containing exhaust gas cleaning equipment.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of an embodiment according to the present invention. 1... Chemical solution mixing tank, 2... Coagulation sedimentation tank, 3...
Passing tower, 4... Chelate resin tower, 5... Evaporation concentration can, 6... Centrifugal separator, 7... Cooling tower, 8... Centrifugal separator, 9... NaCl, 10... Na ₂ SO ₄ , 1
1, 11a... Smoke washing waste water, 12... Smoke washing waste water supply line, 13... Separated mother liquor, 13a... Residual mother liquor, 14, 14a... Return line, 15, 16...
...line, ...heavy metal removal process, ...desalination process, ...deawning process.

Claims (1)

[Claims] 1 A heavy metal removal process in which heavy metals are removed from the incinerator smoke wastewater through coagulation sedimentation and chelate resin adsorption treatment, and a desorption process in which NaCl in the smoke wash wastewater is crystallized and separated by heating and condensation. salt process,
A method for treating incinerator smoke washing wastewater, characterized in that the treatment is carried out in combination with a de-awning step in which the separated mother liquor obtained by separation is cooled and Na ₂ SO ₄ in the separated mother liquor is crystallized and separated.