JP2000024640A - Recovering method of high purity condensed water from heavy metal-containing waste water and production of pure water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover the condensed water suitable as the raw water for pure water by adding a heavy metal capturing agent to the waste water containing a heavy metal, evaporatively concentrating the mixture and condensing the steam generated by the evaporative concentration. SOLUTION: The heavy metal-containing waste water to be treated is a stack gas desulfurized waste water, etc., discharged from a thermal power station for example. The heavy metal capturing agent is added to the heavy metal-containing waste water and the mixture is evaporatively concentrated. The heavy metal capturing agent is not limited especially but sulfide based high molecular chelating agent is preferable. The evaporative concentrating means is not limited especially and even horizontal heat transmitting pipe system and vertical thin film system may be used as the evaporative concentrating vessel. Even external heating system and self vapor pressurizing system may be used as a heating system of the evaporative concentrating vessel. The volume of the heavy metal-containing waste water is reduced to about 1/10 to 1/20 by the evaporative concentrating means. Since the condensed water obtained by evaporative concentration is efficiency reduced in heavy metal content, the condensed water can be used as the feed water for a pure water production device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering water free from heavy metals from wastewater containing heavy metals such as flue gas desulfurization wastewater mainly discharged from a coal-fired power plant.

[0002]

2. Description of the Related Art In a thermal power plant using fuel oil or coal containing sulfur as a fuel, a wet limestone-gypsum method flue gas desulfurization apparatus is used to prevent sulfur oxides in a combustion gas from being discharged into the atmosphere. The flue gas desulfurization treatment is performed by such means. From such a device, in addition to a large amount of sulfate ions, flue gas desulfurization wastewater containing fluorine ions and heavy metals corresponding to the wastewater standard items is discharged.

Conventionally, as a method for treating flue gas desulfurization wastewater, a coagulation sedimentation method using a chemical such as a coagulant has been generally used. In recent years, a volume reduction treatment by evaporation and concentration has been incorporated as a part of the treatment. Wastewater treatment is being proposed. In this treatment method, high-purity water is recovered as condensed water from steam generated from flue gas desulfurization wastewater in the process of evaporation and concentration.

[0004] For example, if this high-purity condensed water is used as raw water for a pure water producing apparatus in a power plant, the frequency of regeneration of ion-exchange resin is significantly reduced and turbidity is reduced as compared with the case where industrial water is conventionally used as raw water. The life expectancy of the filtration membrane used is expected to be prolonged. As an example, FIG. 3 shows a schematic flow diagram in the case where the flue gas desulfurization wastewater is evaporated and concentrated, and the condensed water is used as raw water in a pure water production apparatus. As shown in FIG. 3, by condensing the flue gas desulfurization effluent by evaporating and concentrating the vapor generated from the flue gas desulfurization effluent, a condensed water and a concentrate can be obtained. Pure water can be obtained by using the condensed water as raw water in a pure water production apparatus using an ion exchange resin. The ion-exchange resin of the pure water producing apparatus performs a regeneration treatment by periodically passing a regeneration chemical. In addition, as a pure water production apparatus, an electric regeneration type desalination apparatus (EDI) can also be used.

[0005]

However, the flue gas desulfurization effluent often contains a large amount of sulfate ions and heavy metals contained in the fuel. For this reason, the vapor generated in the process of evaporation and concentration is accompanied by droplets (mist) containing heavy metals, so that heavy metals may be mixed into the condensed water.

When condensed water is recovered and used as raw water for a pure water production apparatus, it is not preferable that heavy metal ions are contained in the condensed water. This is because the heavy metal is adsorbed by the ion exchange resin and does not enter the pure water, but enters the regeneration wastewater in the regeneration process of the ion exchange resin, and a heavy metal removal process must be added to the treatment of the regeneration wastewater. Similarly, when an electric regeneration type desalination apparatus (EDI) is used as a pure water producing apparatus, the treatment of EDI concentrated water becomes a problem.

An object of the present invention is to provide a method for collecting condensed water suitable as raw water for pure water and a method for utilizing the collected condensed water in a treatment method for evaporating and condensing wastewater containing heavy metals. It is to be.

[0008]

According to a first aspect of the present invention, there is provided a method for producing a wastewater containing a heavy metal, comprising the steps of: And a method for collecting high-purity condensed water from heavy metal-containing wastewater, wherein the method recovers raw water for producing pure water.

According to a second aspect of the present invention, there is provided a high purity condensed water according to the first aspect, wherein the heavy metal collector is a sulfide polymer chelating agent. It concerns the collection method.

According to a third aspect of the present invention for solving the above-mentioned problems, pure water is characterized in that high-purity condensed water recovered by the method according to the first or second aspect is used as raw water. And a method for producing the same.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The wastewater containing heavy metals to be treated by the method of the present invention is wastewater containing heavy metals, such as flue gas desulfurization wastewater discharged from a thermal power plant. The flue gas desulfurization effluent discharged from the thermal power plant usually contains about 0.001 to 0.1 mg / L of heavy metals such as mercury, cadmium, lead, chromium, arsenic, and selenium.

The method of the present invention is characterized in that a heavy metal-collecting agent is added to a heavy metal-containing wastewater, which is evaporated and concentrated, and the condensed water is recovered as raw water for producing pure water.

The heavy metal collecting agent in the method of the present invention is not particularly limited as long as it can collect and insolubilize heavy metals in wastewater. For example, a sulfide polymer having a functional group such as dithiocarbamic acid and thiol can be used. Although a chelating agent and an inorganic sulfide can be mentioned, a sulfide polymer chelating agent is preferable.

The addition rate of the heavy metal collector varies depending on the heavy metal content in the wastewater. For example, in the case of flue gas desulfurization wastewater discharged from a thermal power plant, the sulfide polymer chelating agent is used in an amount of 0.01 to 0%. What is necessary is just to add 0.5 Wt%.

The means for evaporating and concentrating in the present method is not particularly limited. For example, the evaporating and concentrating apparatus may be a horizontal heat transfer tube system or a vertical thin film system. In addition, the heating method of evaporative concentration may be an external heating method or a self-vapor compression method. The heavy metal-containing wastewater is reduced by 1/10 to 1
The volume may be reduced to about / 20. The heavy metals in the reduced volume concentrate are insolubilized by the heavy metal scavenger.

The concentrated solution needs to be subjected to a further advanced treatment. However, compared with the case where the heavy metal collecting agent is added after the evaporation and concentration, the method of adding the heavy metal collecting agent before the evaporation and concentration is performed with the concentrated solution. Can be simplified. The flow chart shown in FIG. 1 can be exemplified as one embodiment of a method for advanced treatment of the obtained concentrate by the method of the present invention. That is, a heavy metal collector is added to the flue gas desulfurization effluent to insolubilize the heavy metals, and thereafter, evaporation and concentration are performed. A chemical such as a calcium salt is added to the concentrate thus obtained to remove fluorine. In the fluorine removing step, fluorine is recovered as sludge, and at this time, the insoluble metal is also recovered. Next, a chemical such as ferric chloride is added to reduce COD in the concentrated solution to obtain treated water.

On the other hand, when a heavy metal scavenger is added to the concentrated liquid after evaporation and concentration as a comparative example, the process is as shown in FIG. That is, a chemical for removing fluorine in a fluorine removing step is added to the concentrated solution obtained by evaporation and concentration, and the fluorine is settled as sludge. Next, a heavy metal collecting agent is added in the heavy metal removing step to settle heavy metals as sludge. Further, in the COD reduction step, a chemical such as ferric chloride is added to settle the COD component as sludge.

As can be seen from the comparison of the flow charts shown in FIGS. 1 and 2, the method of the present invention in which a heavy metal-collecting agent is added to a heavy metal-containing wastewater to evaporate and concentrate is employed in the concentrated liquid after evaporation and concentration. Can be simplified in the advanced treatment of the concentrated liquid, as compared with the method of adding.

As in the third aspect of the present invention, the condensed water recovered by the method of the first aspect can be used as raw water for producing pure water because the content of heavy metals can be reduced efficiently. Can be. The method for producing pure water is not particularly limited, and a known pure water producing apparatus such as a two-bed three-column type, an electric regeneration type desalination type, a two-stage RO type, or the like may be used.

The condensed water recovered by evaporation and concentration according to the method of claim 1 can be used, for example, as raw water for a pure water production apparatus using a two-bed, three-column ion exchange resin. In actual operation, industrial water will be replenished to meet the required amount of pure water production. Since the condensed water has a smaller ion load than industrial water, the frequency of regeneration of the ion exchange resin is reduced. In the method of the present invention, since heavy metals are prevented from being mixed into the condensed water, the treatment of the ion-exchange resin regenerated wastewater does not require any special treatment. Can meet criteria.

As a pretreatment step of the pure water producing apparatus, M
In the case of providing a turbidity removing step using an F membrane or the like, since the condensed water has a small amount of turbidity, clogging of the MF membrane or the like is less likely to occur, and the frequency of back washing to the MF membrane or the like can be reduced. Compared with the case where water is passed, the amount of water taken can be increased, and the life of the MF membrane and the like also increases.

[0022]

EXAMPLES Examples will be shown below, but the present invention is not limited to these examples. Example 1 A chelating heavy metal collector (trade name “Organite 2050”, Organo Corporation) was added to flue gas desulfurization wastewater shown in Table 1.
) Was added to a concentration of 0.5 g / L, and then a horizontal heating tube type evaporating and concentrating apparatus of a steam heating system was used to obtain -5.
The solution was concentrated under reduced pressure at 50 mmHg and 70 ° C.
0 L of flue gas desulfurization wastewater was concentrated 15 times. The heavy metal concentration of the obtained condensed water and the supernatant of the concentrated liquid was measured, and the results are shown in Table 2.

Comparative Example 1 The flue gas desulfurization effluent shown in Table 1 was evaporated and concentrated under the same conditions using the same evaporation and concentration apparatus as in Example 1. The heavy metal collector was not added. The heavy metal concentrations of the condensed water and the supernatant of the concentrate were measured and are shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

As is evident from the results in Table 2, the amount of heavy metal that migrates to the condensed water side is higher in Example 1 in which a heavy metal collector was added to the flue gas desulfurization effluent and evaporation was performed. The amount was smaller than that of Comparative Example 1 in which evaporation and concentration were performed without adding a heavy metal collector to the smoke desulfurization wastewater. Therefore, the condensed water obtained in Example 1 was suitable as raw water for producing pure water.

Example 2 The condensed water obtained in Example 1 was subjected to an electric regeneration type desalination apparatus (trade name "Super Desaliner", Organo Corporation)
To produce pure water. An electric regeneration type desalination device is a device that produces pure water while applying a direct current to a container having a structure in which ion exchange resin layers and ion exchange membranes are alternately arranged, and is known by an abbreviation such as EDI. It is. In this apparatus, as shown in FIG. 4, the concentrated water is discharged simultaneously with the treated water.
Treated water: concentrated water = 7: 3. EDI treated water and E
The heavy metals contained in the DI concentrated water were measured and are shown in Table 3.

Comparative Example 2 The condensed water obtained in Comparative Example 1 was passed through an electric regeneration type desalination apparatus under the same conditions as in Example 2. At this time, heavy metals contained in the treated water and the concentrated water were measured, and the results are shown in Table 3.

[0029]

[Table 3]

As is clear from the results in Table 3, Example 2
No heavy metal was detected in both the EDI treated water and the EDI concentrated water, and the condensed water of the present invention obtained in Example 1 was suitable as raw water for producing pure water. On the other hand, in Comparative Example 2, EDI
Heavy metals were detected in the treated water and EDI concentrated water. That is, in Comparative Example 2, the EDI-treated water was reused or
In order to discharge the DI concentrated water, it is necessary to further perform a treatment for removing heavy metals, so the condensed water obtained in Comparative Example 1 is not suitable as raw water for producing pure water.

[0031]

According to the method of the present invention, in a method of recovering and using high-purity condensed water by evaporating and concentrating wastewater containing heavy metals, it is possible to prevent heavy metals from being mixed into the condensed water, and to further concentrate. Heavy metals in the liquid can also be insolubilized.
Therefore, when the condensed water obtained by the method of the present invention is used as raw water for producing pure water, it is possible to extend the life of the opaque filtration membrane and reduce the frequency of regenerating the ion exchange resin.

Further, in the advanced treatment of the concentrated liquid, the processing steps can be simplified.

[Brief description of the drawings]

FIG. 1 is a flowchart of an advanced treatment step of a concentrated solution obtained by the method of the present invention according to claim 1.

FIG. 2 is a flow chart of a concentrated liquid advanced treatment step when a heavy metal collecting agent is added after evaporation and concentration as a comparative example.

FIG. 3 is a schematic flow chart when condensed water is used as raw water of a pure water production apparatus.

FIG. 4 is a schematic flow chart of producing raw water using condensed water as raw water and using an electric regeneration type desalination apparatus.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/42 B01D 53/34 125R // C09K 3/00 108 (72) Inventor Hideki Takahashi Koto-ku, Tokyo F-term (reference) in Shinsuna 1-2-8 Organo Corporation 4D002 AA02 BA02 EA07 4D025 AA09 AB21 AB24 AB25 AB27 BA17 DA10 4D034 AA11 BA01 BA03 CA12 4D076 BA01 BA11 BC04 FA03 HA01 HA06

Claims (3)

[Claims] 1. A heavy metal-containing wastewater, characterized in that a heavy metal-collecting agent is added to a heavy metal-containing wastewater and evaporated and concentrated, and steam generated by the evaporation and condensation is condensed and recovered as raw water for producing pure water. High-purity condensed water recovery method. 2. The method for recovering high-purity condensed water according to claim 1, wherein the heavy metal collecting agent is a sulfide polymer chelating agent. 3. A method for producing pure water, wherein high-purity condensed water recovered by the method according to claim 1 or 2 is used as raw water.