JPH11347344A - Method for treating incineration exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make adjustable the amount of a smoke-scrubbing drain which contains highly concentrated impurities and is supplied to an impurity removing installation and thereby reduce the scale of the removing installation and further make effective use of resources by sending the smoke-scrubbing drain to the impurity removing installation and on the other hand, using part of the smoke-scrubbing drain which contains a low concentration of impurities as a cooling water for the interior of a flue gas treatment column and discharging the used drain. SOLUTION: An incineration exhaust gas is supplied to the lower chamber 4 of a flue gas treatment column 1 and a cleaning water is atomized to remove impurities while the exhaust gas ascends sequentially from an intermediate chamber 3 and an upper chamber 2 in that order. After that, the smoke-scrubbing drain generated in the lower chamber 4 is stored in a drain tank 5 and the cleaning drain generated in the intermediate chamber 3 is stored in a circulation tank 6. In this case, the cleaning drain generated in the upper chamber 2 is divided to be supplied to the circulation tank 6 and a receiving tank 7 through water meters 8, 9. Next, the cleaning drain stored in the drain tank 5 is circulated by a pump 10 as a cleaning water for the lower chamber 4, and the cleaning drain supplied to the circulation tank 6 is circulated by a pump 11 as a cleaning liquid for the intermediate chamber 3. On the other hand, the smoke-scrubbing drain supplied to the receiving tank 7 is sent to a cooler 12 by a pump 14 as a cooling water and used to cool the smoke-scrubbing drain to be supplied to the lower chamber 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to low-boiling metal substances such as mercury, cadmium, and arsenic generated from sewage sludge incineration equipment, dust, and acidic substances (hereinafter, these are collectively referred to simply as impurities). The present invention relates to a method for treating contained exhaust gas.

[0002]

2. Description of the Related Art For example, sludge generated from sewage treatment contains various types of impurities, and in some cases, low-boiling metal substances such as mercury (Hg) are contained therein. is there. Sludge disposal methods at sewage sludge treatment plants include incineration and use as compost raw materials. However, the concentration of mercury in the sludge tends to gradually increase, and there has been a situation in which it cannot be used as a compost material.

[0003] This is because the mercury contained in the influent migrates to the sludge, and the mercury vaporized by incineration is captured in the smoke-washing wastewater by the cooling effect of the flue gas treatment tower, and returned to the water treatment facility as return water in the plant. It is considered that this is because, by returning and circulating in the plant, the sludge in the system is circulated and concentrated with the elapse of the incinerator operation time. In order to continue composting, it is necessary to remove mercury in the smoke-washing effluent so that the mercury is not concentrated by circulation in the plant.

FIG. 2 shows a conventional flue gas treatment tower for treating incineration exhaust gas. Usually, the inside of the smoke treatment tower A is divided into three chambers, an upper chamber a, a middle chamber b and a lower chamber c. Has been
The incineration exhaust gas at about 240 ° C. is sent into the lower chamber c.
The exhaust gas passes through a partition plate d provided between the respective chambers and passes through the lower chamber c.
From the upper chamber a to the middle chamber b.

[0005] Since water for cleaning exhaust gas is sprayed downward from above in each room, impurities contained in the exhaust gas are captured by the cleaning water. The washing water trapped in the lower chamber c becomes smoke washing wastewater and is stored in the drainage tank e below the flue gas treatment tower A. Further, the smoke washing drainage generated in the middle chamber b is sent into the circulation tank f through an external path. Further, the smoke washing wastewater in the upper chamber a is also sent into the circulation tank f.

[0006] The smoke washing wastewater stored in the drainage tank e is sent to the lower chamber c via the circulation pump g, and is used as washing water in the lower chamber c.
Sprayed into. Further, the smoke washing drainage accumulated in the circulation tank f is sent to the middle room b via the circulation pump h, and is sprayed into the middle room b as washing water. Therefore, in the middle room b and the lower room c, water after washing, that is, smoke washing wastewater is circulated to be used as washing water. And upper room a
Inside, water from the outside, for example, secondary treatment water generated in a sewage treatment plant is sprayed as washing water, and smoke washing wastewater after washing is sent to the circulation tank f.

[0007]

Smoke washing waste water generated in the lower chamber c and the middle chamber b after being cleaned is sprayed as cleaning water into the respective chambers via the circulation pump g and the circulation pump h. The smoke drainage is circulating. But,
Since external water is supplied as washing water to the upper chamber a,
The smoke washing wastewater generated in the upper chamber a is continuously supplied to the circulation tank f without circulating in the upper chamber a.

Accordingly, the amount of water in the circulation tank f is
Since the amount of smoke washing wastewater circulated to the wastewater is larger than the amount of wastewater, it overflows to the drainage tank e. Then, the overflow water causes the amount of water in the drainage tank e to be larger than the amount of water circulating to the lower chamber c.
Leaked to

[0009] The smoke washing wastewater flowing into the wastewater storage tank i is sent to the facility for removing impurities, and at least the amount of smoke washing wastewater corresponding to the amount of washing water supplied to the upper chamber a is continuously generated. It will be sent to the removal facility. That is, since all of the smoke washing wastewater generated in the smoke exhaust treatment tower A is sent to the impurity removal equipment, the equipment for removing the impurities becomes very large and the supply amount of the smoke washing wastewater is large. Has a problem that the capacity of removing impurities is exceeded.

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 smoke washing waste water 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 drainage tank e, and the like, and serves to prevent the temperature of the circulating smoke washing wastewater from rising.

The present invention has been made in view of the above-mentioned conventional problem of treating incineration exhaust gas, and sends smoke-washing wastewater having a high impurity concentration to a facility for removing impurities, and partially removes the smoke-washing wastewater having a low impurity concentration. It is an object of the present invention to provide a method for treating incineration exhaust gas, in which the amount of smoke washing wastewater supplied to an impurity removing facility can be adjusted by draining water used as cooling water in a processing tower.

[0012]

In order to achieve the above object, the present invention is divided into a plurality of upper and lower chambers, each of which captures impurities in incineration exhaust gas by spraying washing water in each chamber,
In the treatment of incineration exhaust gas, the smoke drainage generated in the lower room circulates as wash water in each room, and the entire amount of the smoke drainage generated in the uppermost room is supplied to the circulation tank and sent to the drainage storage tank, for example. A part of the smoke washing wastewater generated in the uppermost room is supplied to the circulation tank and sent to the wastewater storage tank, and the remaining smokewash wastewater generated in the uppermost room is used as cooling water for the circulating smoke washing wastewater.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 schematically shows an exhaust gas treatment apparatus used in the treatment method of the present invention. Reference numeral 1 denotes a flue gas treatment tower, which is an upper chamber 2 and a middle chamber 3 as in the prior art.
And a lower chamber 4. The incineration exhaust gas is in lower chamber 4
When the water is supplied to the inside and rises in the flue gas treatment tower 1, impurities contained in the exhaust gas are captured by the washing water sprayed in each room. Then, the smoke wash drain generated in the lower chamber 4 is sent to the drain tank 5, and the smoke wash drain generated in the middle chamber 3 is sent to the circulation tank 6, and the water in the drain tank 5 is used as the wash water for the lower chamber 4. It is circulated, and the water in the circulation tank 6 is circulated and used as washing water for the inner chamber 3. The configuration described above and the circulating use of the smoke washing wastewater are the same as those of the conventional smoke exhaust treatment tower.

[0014] Mercury in impurities is a low boiling metal substance,
As shown in Table 1, as compared with the mercury concentration at the outlet of the upper chamber 2, the mercury concentration at the outlet of the drainage tank 5 is very high. 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 3 and the lower room 4. Most of the other impurities are also trapped in the middle chamber 3 and the lower chamber 4.

According to the present invention, the smoked wastewater after washing obtained from the middle chamber 3 and the lower chamber 4 having a high impurity concentration containing mercury is sent to a known impurity removing facility, and the upper chamber 2 having a low impurity concentration containing mercury is removed. A part of the smoke washing wastewater obtained in the above was used as washing water for the middle room 3 and most of the smoke washing wastewater for the upper room 2 was used as cooling water, and then drained as it was without being sent to the impurity removing equipment. Thus, the present invention is characterized in that the amount of smoke washing wastewater to the impurity removing equipment is reduced.

[0016]

The present invention will be described in detail below with reference to an embodiment.
The present invention is not limited to this embodiment. Lower room 4
The exhaust gas supplied therein rises and passes through the respective chambers 3 and 2 in order, and the impurities contained in the exhaust gas are captured by the washing water sprayed into the respective chambers 4, 3 and 2. The smoke washing drainage sprayed into the lower chamber 4 is stored in a drainage tank 5 below the smoke exhaust treatment tower 1. Further, the smoke washing drainage generated in the middle chamber 3 is stored in the circulation tank 6 through an external path. Then, a part of the smoke washing drainage generated in the upper chamber 2, for example, 1 /
3 is supplied into the circulation tank 6 and the remaining 2
Smoke washing wastewater is supplied to the receiving tank 7. Adjustment of the distribution ratio of the smoke washing drainage in the upper room 2 is performed by the water meters 8 and 9.

Table 2 shows an example of the balance between the amounts of water and the temperature of the supply water and the smoke washing wastewater in the conventional method and the present invention. According to the present invention, the amount of smoke washing drainage is reduced to about one third of the conventional method without impairing the function of the smoke exhausting tower.

The wastewater collected in the drain tank 5 is circulated through the pump 10 as washing water for the lower chamber 4, and the wastewater collected in the circulation tank 6 is discharged through the pump 11. Circulated as the washing water in the chamber 3. Thus, the middle room 3,
By circulating and using the smoke washing wastewater as the washing water to the lower chamber 4, the temperature of the smoke washing wastewater passing through the pumps 10, 11 remains high. Therefore, coolers 12 and 13 are installed in the circulation path of the smoke washing wastewater, and the smoke washing wastewater is cooled and sent to the middle room 3 and the lower room 4.

The smoke washing wastewater stored in the receiving tank 7 is
It is sent to the cooler 12 by the pump 14 as cooling water,
The smoke washing wastewater supplied to the lower chamber 4 is cooled. The water used for cooling is discharged through a path to the outside.

In the cooler 13, supply water, for example, secondary treatment water is used as cooling water, and is sent to the cooler 13 by a pump 15 to cool the smoke washing wastewater supplied to the inner chamber 3. Then, the water used for this cooling is discharged to the outside as it is. The water in the receiving tank 7 can be used as cooling water for the cooler 13.

As the coolers 12 and 13, plate heat exchangers can be used, and the amounts of washing water and cooling water, temperature balance, etc. are as shown in Table 3.

The present invention is constructed as described above, and the smoke-washing wastewater generated in the lower chamber 4 and the middle chamber 3 after cleaning is circulated and reused as cleaning water. The impurity concentration including mercury in 6 is high. The smoke washing wastewater in the upper chamber 2 is supplied to the circulation tank 6, but the amount of the water is small. Therefore, the wastewater overflows and flows out in the circulation tank 6 and the drainage tank 5, and is supplied to the impurity removal equipment through the wastewater storage tank 16. The amount of water to be supplied is also regulated. Most of the smoke-wash drainage generated in the upper room 2 is
Used as cooling water for smoke-wash drainage used as cleaning water and discharged to the outside.

[0023]

According to the present invention described above, the middle room 3
Smoke washing wastewater in which exhaust gas has been treated in the lower chamber 4 is circulated and used as washing water, and part of the smoke washing wastewater in the upper chamber 2 is discharged from the circulation tank 6 through the drainage tank 5 so as to have high impurity concentration. Although the water is supplied to the external impurity removing equipment, the amount of the smoke washing wastewater sent to the circulation tank 6 in the upper chamber 2 is smaller than the total amount of the smoke washing wastewater in the upper chamber 2. The amount of smoke washing drainage provided to the equipment is also reduced, and the scale of the impurity removal equipment can be reduced.

Further, a cooler 1 is provided in the circulation path of the smoke washing drainage.
2 and 13 are installed, and most of the smoke-wash wastewater generated in the upper room 2 can be used as cooling water. Therefore, the smoke-wash wastewater used as the wash water is always cooled. Does not impair the function. In addition, the pumps 10, 11 and the like do not break down due to heating, and effective use of resources can be achieved by using the smoke washing drainage as cooling water. Furthermore, the temperature of the gas after the treatment discharged from the outlet of the flue gas treatment tower 1 can be kept constant.

[Brief description of the drawings]

FIG. 1 is a schematic view of equipment used for a method for treating incineration exhaust gas of the present invention.

FIG. 2 is a schematic view of a conventional facility for treating incineration exhaust gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Smoke exhaust tower 2 Upper room 3 Middle room 4 Lower room 5 Drain tank 6 Circulation tank 7 Receiving tank 8 Water meter 9 Water meter 10 Pump 11 Pump 12 Cooler 13 Cooler 14 Pump 15 Pump 16 Drainage storage tank A Smoke exhaust Processing tower a Upper chamber b Middle chamber c Lower chamber d Partition plate e Drain tank f Circulation tank g Pump h Pump i Drainage storage tank

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[Procedure amendment]

[Submission date] June 19, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

As the coolers 12 and 13, plate heat exchangers can be used, and the amounts of washing water and cooling water, temperature balance, and the like are as shown in Table 3.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (1)

[Claims] Claims 1. An upper and lower chamber is divided into a plurality of chambers, and cleaning water is sprayed in each chamber to capture impurities in incineration exhaust gas.
Smoke washing wastewater generated in each lower room circulates as washing water in each room, and the entire amount of smoke washing wastewater generated in the uppermost room is supplied to the circulation tank and sent to the wastewater storage tank. In the treatment, part of the smoke washing wastewater generated in the uppermost room is supplied to the circulation tank and sent to the wastewater storage tank, and the remaining smokewash wastewater generated in the uppermost room is used as cooling water for the circulating smoke washing wastewater. A method for treating incineration exhaust gas, characterized in that: