JPH11347548A - Method for removing mercury in scrubbed exhaust gas waste water and apparatus for treating scrubbed exhaust gas waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contract the whole scale of an apparatus for removing mercury in scrubbed exhaust gas waste water generated from treating combustion exhaust gas and an apparatus treating scrubbed exhaust gas waste water. SOLUTION: Scrubbed exhaust gas waste water containing mercury treated by using an exhaust gas treatment apparatus constituting a combustion exhaust gas treating equipment is sent to a sand filter tower 3 and chelating tower 4 constituting a mercury removing equipment and mercury is collected and removed by a filtering sand and a chelating resin whose particle sizes are set to be the same and SS contained in the scrubbed exhaust gas waste water is removed by an inorg. chemical injection method and the amt. of the scrubbed exhaust gas waste water sent to the exhaust gas treatment tower is regulated to miniaturize the mercury removing equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to low-boiling metal substances such as mercury, cadmium, and arsenic generated mainly from incineration facilities for sewage sludge and industrial waste, and dusts and acidic substances (hereinafter simply referred to collectively). The present invention relates to a method for removing mercury, particularly to a mercury in a smoke wash wastewater containing an impurity (hereinafter referred to as an impurity), and an apparatus for treating mercury in the smoke wash wastewater.

[0002]

2. Description of the Related Art The incineration exhaust gas generated by sewage treatment and incineration of industrial wastes and the like contains the above-mentioned impurities. At the same time, in particular, mercury contained in impurities has an adverse effect on human bodies and nature. Conventionally, impurities contained in incineration exhaust gas are captured by cleaning water in a flue gas treatment tower, and smoke cleaning wastewater containing impurities is sent to a mercury removal facility to capture mercury together with the impurities.
Had to be disposed of.

Conventionally, as a method of removing mercury contained in smoke washing wastewater, mercury is finally captured by a chelating resin through a coagulation sedimentation tank → a sand filtration tower → a chelation tower. That is, in the coagulation sedimentation tank, a coagulant is added to the smoke washing wastewater obtained in the flue gas treatment tower, and solid-liquid is separated by coagulation sedimentation. S in the supernatant obtained by solid-liquid separation
After S was removed by the sand filtration tower, it was sent to the chelating tower, and the mercury contained in the supernatant was captured by the chelating resin.

FIG. 3 shows a conventional flue gas treatment tower A used in a pretreatment stage of a mercury removal facility. The inside of the tower is divided into an upper chamber a, a middle chamber b and a lower chamber c. The incineration exhaust gas at about 240 ° C. is sent into the lower chamber c. Then, the exhaust gas sequentially rises into the upper chamber through the partition plate d provided between the chambers.

[0005] Since water for washing the exhaust gas is sprayed in each room, impurities contained in the exhaust gas are
Captured in the wash water and treated as smoke wash drainage. Lower room c
The smoke washing wastewater generated in the inside is stored in a drainage tank e below the smoke exhaust treatment tower A. Further, the smoke washing drainage generated in the middle chamber b is sent to the circulation tank f through an external path. Furthermore, upper room a
Is also sent to the circulation tank f.

[0006] The smoke washing wastewater stored in the drainage tank e is sent to the lower chamber c via a circulation pump g, and is circulated and used as washing water. Further, the smoke washing drainage accumulated in the circulation tank f is sent to the intermediate chamber b via the circulation pump h, and is used as washing water. Therefore, smoke washing wastewater containing mercury circulates in the middle room b and the lower room c and is used as washing water.

[0007] Water from the outside, for example, secondary treatment water or industrial water generated in a sewage treatment plant is sprayed into the upper chamber a as washing water, and the smoke washing wastewater after washing is sent to a circulation tank f. Will be sent. Since fresh water is continuously sent to the upper chamber a as washing water, the circulation tank f overflows with water, and the overflowed water flows out to the drainage tank e. Then, since the water overflows also in the drainage tank e, the overflowed water flows out to the drainage storage tank i, and is further sent to the mercury removal facility. In addition, besides the above-described removal method, there is also a method of removing mercury via a coagulation filtration method → a chelation tower.

[0008]

In the above-mentioned conventional method for removing mercury, it is necessary to set up a flocculating sedimentation tank as a pretreatment for filtration or to add a flocculant before the filtration tower. As a result, initial costs, running costs, and the like have increased. The particle size of the chelating resin is about 0.3 mm as an effective diameter, whereas the particle size of the sand used in the sand filtration tower is as large as 0.5 to 0.6 mm. And DS (soluble SS) are agglomerated by the residual coagulant, etc.
S and agglomerates were trapped in the chelate tower, which had an adverse effect on the performance of the chelate resin.

This is because, as shown in Table 1, the properties of the smoke washing wastewater are such that the DS (= TS-SS) concentration is high and the SS particle size is very small.

[0010] When the flocculant is used due to the high DS concentration, as shown in Table 2, after the sand filtration, the SS flocculates due to the residual flocculant, and the SS concentration in the filtered water increases. It has been found to adversely affect the performance of the resin.

[0011] Smoke washing wastewater generated in the lower chamber c and the middle chamber b after cleaning is reduced as cleaning water in the respective chambers via the circulation pump g and the circulation pump h and circulated. Then, the amount of smoke washing wastewater corresponding to the amount of washing water supplied to the upper chamber a is continuously sent to the mercury removal equipment. That is, the smoke washing wastewater generated in the smoke exhaust treatment tower A is
Since all of the wastewater is sent to the mercury removal facility, the equipment for removing mercury becomes very large and has a problem that it exceeds the limit of the mercury removal capacity when the supply amount of smoke washing wastewater is large. I was

Further, since the exhaust gas having a high temperature of about 240 ° C. is supplied into the flue gas treatment tower A, the temperature of the flue gas itself after washing the exhaust gas is also high. Here, if the amount of water supplied to the upper chamber a is reduced to reduce the amount of smoke drainage going to the impurity removing equipment, the water temperature in each place remains high, and the circulation tank f and the circulation pumps g, h, etc., fail. Cause you to Further, the outlet gas temperature of the flue gas treatment tower A also rises, and is released to the atmosphere as it is. Therefore, the smoke washing wastewater generated in the upper chamber a is sent to the circulation tank f, the storage tank e, or the like, and serves to prevent the temperature of the circulating smoke washing wastewater from rising.

In view of the above-mentioned various problems of the above-described conventional method for removing mercury in smoke-cleaning wastewater and a device for treating the smoke-cleaning wastewater, the present invention is not affected by SS contained in the smoke-washing wastewater. It is an object of the present invention to provide a method that enables the removal of mercury without the need. In addition, the present invention provides a method for treating smoke-washing wastewater that discharges a portion of the smoke-washing wastewater to the outside, thereby adjusting the supply amount of the smokewashing wastewater to the mercury-removing equipment and reducing the scale of the mercury removing equipment. It is intended to provide a device.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a sand filtration tower and a chelating tower for capturing and removing mercury in smoke washing wastewater captured by washing water in a flue gas treatment tower. In the method, the particle size of the filter sand and the particle size of the chelating resin are made the same,
And mercury is captured by the chelating resin.

Further, according to the present invention, mercury and other impurities in incineration exhaust gas are trapped by spraying washing water in each of the upper and lower chambers 7, 8, and 9, and the washing generated in the lower chamber is performed. Smoke wastewater circulates as washing water in each room,
A part of the smoke washing wastewater generated in the uppermost room is supplied to the circulation tank 11 and sent to the wastewater storage tank 20, and the remaining smokewash wastewater generated in the uppermost room is used as cooling water for the smoke washing wastewater circulating in the lower room. The smoke washing wastewater in the wastewater storage tank 20 is sent to the wastewater storage tank 1 of the mercury removal facility through the supply path, and the sand filtration tower 3 and the chelate tower 4 capture and remove mercury in the smoke washing wastewater.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of an apparatus used in the method for removing mercury according to the present invention. In the figure, reference numeral 1 denotes a smoke washing drainage storage tank, 2 denotes a filtered water pump, 3 denotes a sand filtration tower, Is a chelating tower, and 5 is a cooler.

Smoke washing wastewater sent from the smoke exhaust treatment tower is supplied into the smoke washing wastewater storage tank 1. Then, the smoke washing wastewater in the storage tank 1 is supplied to the sand filtration tower 3 and the chelating tower 4 in order by the pump 2 to perform a filtering operation to remove mercury and other impurities contained in the smoke washing wastewater. Is the same as the conventional method.

In the present invention, as a pretreatment step of filtration, a filtration operation is carried out by using a chemical-free injection method without using a flocculant, and the particle size of the filter sand used in the sand filtration tower 3 is reduced by the particle size of the chelate resin. The diameter of the chelating tower 4
In this method, only mercury is captured without capturing SS.

For this purpose, the sand filtration tower 3 has a pressure-type two-layer filtration structure of sand and anthracite, and has a sand particle size of about 0.3 mm, which is the same as the chelate resin particle size, and a smoke washing drainage. After being filtered by the sand filtration tower 3, it is sent to the chelation tower 4, and mercury is captured by the chelate resin provided in the chelation tower 4.
Table 3 shows the properties of the sand used in the sand filtration tower 3.

As shown in Table 4, by adopting the chemical-free injection method using no flocculant and making the particle size of the sand the same as that of the chelating resin, as shown in Table 4,
It was proved that S was not trapped in the chelate column 4.

Table 5 shows the results of analysis of mercury trapped by the chelating resin. By adopting the method of the present invention, the effluent standard value of 0.005 mg / l or less was sufficiently satisfied. Was.

Since the chelate resin used in the chelate tower 4 does not have heat resistance, the chelate resin is deteriorated when the high-temperature smoke washing wastewater is continuously supplied, and the adsorption capacity is reduced. For this reason, a cooler 5 is provided before the chelating tower 4 so that smoke washing wastewater can be supplied to the chelating tower 4 at 50 ° C. or lower. As the cooling water, for example, secondary treatment water in a sewage treatment plant can be used, and after cooling, it is drained as it is.

Further, although not shown, sodium hypochlorite (N
aClO) may be provided. By adding sodium hypochlorite to raw water (smoke washing wastewater), mercury in the smoke washing wastewater can be ionized, and the mercury adsorption efficiency of the chelating resin can be increased.

Next, a description will be given of an apparatus for treating smoke washing wastewater. FIG. 2 shows a facility for treating incineration exhaust gas, which is connected to the mercury treatment facility and cooperates with the mercury treatment facility. The flue gas treatment tower 6 is divided into an upper chamber 7, a middle chamber 8 and a lower chamber 9 as in the prior art. Have been. The incineration exhaust gas is supplied into the lower chamber 9, and when ascending in the flue gas treatment tower 6, mercury and other impurities contained in the exhaust gas are captured by the washing water sprayed in each chamber. Then, the smoke washing drainage generated in the lower room 9 is
In addition, the wastewater generated in the middle chamber 8 is sent to the circulation tank 11, the water in the drain tank 10 is circulated as washing water to the lower chamber 9, and the water in the circulation tank 11 is discharged to the middle chamber 8. 8
Used as circulation water for washing. The above-mentioned circulating use of the flue gas treatment tower 6 and the sewage drainage is the same as the conventional one.

Mercury in impurities is a low boiling metal substance,
As shown in Table 6, the mercury concentration at the outlet of the drainage tank 10 is much higher than the mercury concentration at the outlet of the upper chamber 7. This is because mercury is a low boiling metal substance,
This is due to the circulating use of the smoke washing drainage of the middle room 8 and the lower room 9. Most other impurities are also trapped in the middle chamber 8 and the lower chamber 9.

According to the present invention, the middle chamber 8 and the lower chamber 9 having a high mercury concentration are used.
Is sent to the above-mentioned mercury removal equipment, and a part of the smoke washing waste water obtained in the lower room 7 having a low mercury concentration is used as washing water for the middle room, and It is characterized in that most of the smoke washing wastewater is drained after being used as cooling water, and the supply amount of treated water to the mercury removal equipment is reduced.

The exhaust gas supplied into the lower chamber 9 ascends and passes through the respective chambers 8 and 7 in order, and the impurities contained in the exhaust gas by the washing water sprayed into the respective chambers 9, 8 and 7. Is captured. The smoke washing wastewater after being washed in the lower chamber 9 is stored in a drainage tank 10 below the smoke exhaust treatment tower 6. Also, Nakamuro 8
Smoke washing wastewater generated inside is stored in the circulation tank 11 through an external path. A part of the washing water, for example, 1/3 of the amount of washing water supplied from the outside into the upper chamber 7 is supplied to the circulation tank 11, and the remaining 2/3 of the smoke washing drainage is supplied to the receiving tank 12. . The distribution ratio of smoke-wash drainage in the upper room 7 is
It is performed by the water meters 13 and 14.

Table 7 shows an example of the balance between the amount of water and the temperature of the supply water and the wastewater of the smoke washer according to the conventional method and the present invention. Is reduced to about 1/3.

The smoke washing waste water stored in the drain tank 10 is circulated through the pump 15 as washing water for the lower chamber 9, and the smoke washing waste water stored in the circulation tank 11 is recycled through the pump 16. Circulated as washing water in the chamber 8. By using the washing water to the middle chamber 8 and the lower chamber 9 in such a manner that the smoke washing wastewater is circulated, the temperature of the smoke washing wastewater passing through the pumps 15 and 16 remains high. Therefore, coolers 17 and 18 are installed in the circulation path of the smoke washing wastewater, and the smoke washing wastewater is cooled and sent to the middle room 8 and the lower room 9.

The smoke washing wastewater stored in the receiving tank 12 is sent to the cooler 17 by a pump 21 as cooling water, and cools the smoke washing wastewater supplied to the lower chamber 9. The water used for cooling is discharged through a path to the outside.

In the cooler 18, external water, for example, secondary treatment water is used as cooling water, and is sent to the cooler 18 by a pump 19 to cool the smoke washing wastewater supplied to the inner chamber 8. . Then, the water used for this cooling is discharged to the outside as it is. The water in the receiving tank 12 can be used as cooling water for the cooler 18.

As the coolers 17 and 18, plate heat exchangers can be used, and the amounts of washing water and cooling water, temperature balance, etc. are as shown in Table 8.

The incineration flue gas treatment equipment used in the present invention has the above-mentioned configuration, and the smoke-cleaning wastewater generated in the lower chamber 9 and the middle chamber 8 after cleaning is circulated and reused as cleaning water. Therefore, the mercury concentration in the drain tank 10 and the circulation tank 11 is high. The smoke washing wastewater in the upper chamber 7 is supplied to the circulation tank 11, but the amount of the water is small. Therefore, it overflows and flows out in the circulation tank 11 and the drainage tank 10, and is supplied to the mercury removal equipment through the wastewater storage tank 20. The amount of water to be supplied is also regulated. Most of the smoke washing wastewater generated in the upper chamber 7 is used as cooling water for the smoke washing wastewater used as the washing water, and is discharged to the outside.

The smoke-washing wastewater containing mercury obtained in the incineration flue gas treatment apparatus as described above is sent to a smoke-washing wastewater storage tank 1 of a mercury removal facility through a supply path, and is subjected to a sand filtration tower 3 and a chelating tower. At 4 the mercury is captured and removed.

[0035]

As described above, according to the present invention, the smoke washing wastewater obtained by the incineration exhaust gas treatment device is sent to the smoke washing wastewater storage tank 1 of the mercury removal equipment, and the chemical-free injection without using a flocculant. The filter sand used in the sand filtration tower 3 was made to have the same particle size as the chelate resin used in the chelation tower 4 by the method, and the SS in the smoke washing wastewater passed through the sand filtration tower was chelated. Only the mercury can be efficiently captured and removed without being captured by the resin.

In the incineration flue gas treatment equipment, the smoke washing wastewater treated in the middle room 8 and the lower room 9 is circulated into the respective rooms and used as washing water. The smoke washing wastewater in the upper room 7 is discharged from the circulation tank 11. Smoke washing wastewater having a high mercury concentration is supplied to the mercury removal equipment through the drainage tank 10.
Since the amount of smoke washing wastewater sent to the upper room 7 sent to 1 is smaller than the total amount of smoke washing wastewater in the upper room 7, the amount of smoke washing wastewater sent to the mercury removal equipment is also reduced, and mercury removal is performed. The size of the equipment can be reduced.

Further, a cooler 1 is provided in the circulation path of the smoke washing drainage.
7 and 18 are installed, and most of the treated water generated in the upper chamber 7 can be used as cooling water for the smoke washing wastewater. Therefore, the smoke washing wastewater used as the washing water is always cooled. , 16 etc. do not break down due to heating,
By using the smoke washing drainage as cooling water, the resources can be effectively used. Furthermore, the temperature of the gas after the treatment discharged from the outlet of the smoke exhaust treatment tower 6 can be kept constant.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of equipment used for a method for removing mercury in smoke-washing wastewater according to the present invention.

FIG. 2 is a schematic diagram of an incineration exhaust gas treatment facility used in the smoke cleaning wastewater treatment apparatus of the present invention.

FIG. 3 is a schematic view of a conventional facility for treating incineration exhaust gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Smoke washing drainage storage tank 2 Filtration water pump 3 Sand filtration tower 4 Chelation tower 5 Cooler 6 Smoke exhaust treatment tower 7 Upper room 8 Middle room 9 Lower room 10 Drainage tank 11 Circulation tank 12 Receiving tank 13 Water meter 14 Water meter 15 Pump 16 Pump 17 Cooler 18 Cooler 19 Pump 20 Drainage storage tank 21 Pump A Smoke exhaust tower a Upper room b Middle room c Lower room d Partition plate e Storage tank f Circulation tank g Pump h Pump i Drainage water storage tank

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 19, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

As the coolers 17 and 18, plate heat exchangers can be used, and the amounts of washing water and cooling water, temperature balance, etc. are as shown in Table 8.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 29/08 540A

Claims (2)

[Claims] 1. A method for trapping and removing mercury in smoke washing wastewater trapped in washing water in a flue gas treatment tower by a sand filtration tower and a chelating tower, wherein the particle size of the filtered sand and the particle size of the chelating resin are determined. SS with the same diameter and contained in smoked wastewater by non-chemical injection method
A method for removing mercury from smoke wash effluent, which comprises removing mercury and capturing mercury with a chelating resin. 2. It is divided into a plurality of upper and lower chambers 7, 8, and 9, and mercury and other impurities in incineration exhaust gas are trapped by spraying washing water in each chamber, and smoke washing wastewater generated in a lower chamber is respectively separated. Is circulated as washing water in each room, and a part of the smoke washing wastewater generated in the uppermost room is supplied to the circulation tank 11 and sent to the wastewater storage tank 20, and the remaining smokewash wastewater generated in the uppermost room is
Used as cooling water for the smoke washing wastewater circulating in the lower room, the smoke washing wastewater in the wastewater storage tank 20 is sent to the wastewater storage tank 1 of the mercury removal equipment through the supply path, and washed in the sand filtration tower 3 and the chelation tower 4. Smoke washing wastewater treatment equipment that captures and removes mercury in smoke wastewater.