JPS5925634B2 - Waste incinerator ash sewage treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating ash wastewater which is an improved method for neutralizing ash wastewater generated in a waste incineration process.

In the garbage incineration process, as shown in FIG. 1, ash is generated from the garbage incinerator 1 and the dust collector 2, and this ash is put into the water washing tank 3 and cooled with water.

Therefore, ash wastewater is generated in this process, but since it contains harmful heavy metals and is alkaline, it cannot be disposed of as is and requires wastewater treatment such as neutralization.

Conventionally, in order to neutralize alkaline ash wastewater, as shown in Fig. 1, the ash wastewater passes through an ash settling tank 4 and an overflow tank 5, and then enters a neutralization tank 6, where it is poured into a sulfuric acid etc. from a chemical tank. A Japanese chemical solution is added for neutralization, and the product is further separated by precipitation in a settling tank 8, after which the supernatant liquid is reused in the washing tank 3.

However, ash wastewater has a high alkalinity, and usually 1 m° of ash wastewater
For this purpose, approximately 2 kg of concentrated sulfuric acid must be added.

For example, in a city with a population of 10 million people, approximately 9,000 m/day of ash wastewater is generated, so the amount of chemical solution to be input is also 18 in terms of concentrated sulfuric acid.
The number of tons per day increases, and the cost becomes enormous.

In addition, the alkalinity of ash wastewater is mainly caused by calcium hydroxide, and when this comes into contact with carbon dioxide gas in the air during the ash wastewater treatment process, it gradually deposits in pipes and causes scaling in a short period of time. It occurs in

Also, this scaling is hard and difficult to clean.

Based on this, the present inventor noticed that the exhaust gas generated in the garbage incineration process contains 8 to 12% carbon dioxide gas, and that this carbon dioxide gas has the effect of neutralizing alkali.

The present invention was made by taking advantage of the above-mentioned characteristics of exhaust gas, and its purpose is to neutralize it efficiently without incurring high chemical costs, to prevent scaling, and to prevent heavy metals from being precipitated. The present invention provides a method for treating ash wastewater from a garbage incinerator.

That is, the present invention brings ash sewage generated in the garbage incineration process and collected ash directly charged into a gas-liquid contact device into gas-liquid contact with the exhaust gas generated in the process, and converts the ash sewage and ash slurry into carbon dioxide gas in the exhaust gas. This is a method for treating ash sewage for a garbage incinerator, which is characterized in that the ash is washed with water using a supernatant liquid of the treated ash sewage.

The present invention will be explained below with reference to the drawings.

- In the method of the present invention, as shown in FIG. 2, the ash generated in the garbage incinerator 11 is put into a rainwater washing tank 13, and cooling water is added thereto to generate ash wastewater.

The ash wastewater enters an ash settling tank 14 to precipitate ash, and then enters an overflow tank 15.

A fixed amount of the ash wastewater in the overflow tank 15 is fed into the gas-liquid contact device 17 by the action of the pump 160.

Further, the ash generated in the dust collector 12 is not put into the rainwater washing tank 13 but directly into the gas-liquid contact device 17.

On the other hand, part of the exhaust gas that has passed through the dust collector 12 is input into the gas-liquid contact device 17, and the rest is discharged to the outside.

This gas-liquid contact device 17 has a structure in which, for example, a disk 18 provided with a plurality of protrusions is rotated in the horizontal direction, and exhaust gas is introduced from below, and ash wastewater and ash are introduced from above to bring them into gas-liquid contact. Carbon dioxide gas in the exhaust gas neutralizes calcium hydroxide, etc. in the ash wastewater.

The products after neutralization (mainly calcium carbonate) and wastewater are
The sludge ash enters Shirafuna 19 and is separated from the supernatant liquid.

The sludge ash enters the sludge ash pit 20, and the supernatant liquid is fed into the rainwater washing tank 13 as cooling water.

According to this method, the ash wastewater is neutralized using carbon dioxide gas in the exhaust gas, which was conventionally discharged as is, so that the ash wastewater can be efficiently neutralized without incurring the cost of chemicals.

In addition, carbon dioxide gas does not dissolve in ash wastewater in excess of the saturated amount, so
The exhaust gas can be sufficiently blown into the gas-liquid contact device 17, and the amount of blown gas can be easily controlled.

In addition, carbon dioxide gas is dissolved in the supernatant liquid separated by Shirafuna 19, so when it is put into the rainwater washing tank 13, a partial neutralization reaction occurs, and the water dissolved in the ash wastewater is Since the amount of calcium oxide can be reduced, scaling in the piping can be prevented.

In addition, since the exhaust gas contains a large amount of carbon dioxide (8-12%), it can be neutralized by just adding a small amount. Therefore, the gas-liquid contact device 17 can also be small, and the existing garbage incineration equipment It is easy to modify and requires only a small amount of installation space.

Calcium carbonate, which is a product after neutralization, acts as a flocculant and precipitates containing heavy metals in the ash wastewater.

Therefore, it has the advantage of purifying ash wastewater, reducing the scale of various sewage treatment facilities, and even making them unnecessary.

That is, the main plate generated in the garbage incinerator 11 hardly elutes heavy metals in water, whereas the collected ash generated in the dust collector 12 elutes heavy metals in water.

Therefore, when the collected dust ash is put into the rainwater washing tank 13, most of the heavy metals are transferred to the ash sludge, but some of the heavy metals remain in the ash sludge in a state dissolved in water.

This ash sludge is drawn into the sludge ash bit 20, but cannot be discarded as it is because it contains heavy metals dissolved in water.

In contrast, in the present invention, since the collected dust ash is directly fed into the gas-liquid contact device 17, the heavy metals in the collected dust ash are aggregated by calcium carbonate and solidified in a form that cannot be eluted.
This can be abandoned as is.

Therefore, it has the advantages described above.

Next, experimental examples and examples conducted to confirm the effects of the present invention will be explained.

Experimental example As shown in FIG. 3, as a gas-liquid contact device 17, a disk 18 with protrusions is provided in a tank and rotated, and a mixed gas of air 21, carbon dioxide gas 22, and nitrogen gas 23 is supplied from below. was blown in as exhaust gas, and the ash wastewater was introduced from above through the cooling pipe 24 to neutralize the ash wastewater.

In the figure, 25 is a gas meter, 26 is a heater, 27 is a thermometer, 28 is a pH meter, 29 is a drive motor, and 30 is a recorder.

The experimental conditions are as follows.

Ash sewage capacity 31 Ash wastewater pH 12.6 (slaked lime in ash) by) Ash wastewater alkalinity 100 e, p, m.

Ash concentration in ash sewage 5% Ash sewage temperature 40'C Carbonic acid in synthetic flue gas 9% Gas concentration Synthetic flue gas/ash sewage 3.51/sec) Linear velocity of 71 disk 6 m/sec Based on this experiment,
The reaction time, pH value, alkalinity and carbon dioxide absorption efficiency were measured and the results are shown in Table 1.

According to the above table, the neutralization treatment was carried out in a short period of time, the treatment liquid was neutralized, and since the alkalinity was 0, it was confirmed that no residual slaked lime was contained in the solids.

Example 1 In the processing apparatus shown in FIG. 2, the ash from the dust collector 12 was directly charged into the gas-liquid contacting device 17, and the ash wastewater and ash slurry were neutralized.

The implementation conditions are as follows.

Implementation conditions Dust collection ash input amount 180klliI/H * Ash wastewater flow rate 15 m/H Ash wastewater pH (before neutralization) 12°6 Ash wastewater alkalinity (before neutralization) 20°10"p, m Ash wastewater temperature 39 ° C Carbonic acid in flue gas 1□ % Gas concentration flue gas/ash sewage 3,5 (771”/4()/
(Main) Disk linear velocity: 6 m/sec The results of neutralization of ash wastewater carried out under these conditions are shown below.

Results: pH of ash sewage (after neutralization): 7.0 Carbon dioxide absorption efficiency: 61% Alkalinity of ash sewage (after neutralization): 00□p°m From these implementation results, it is clear that ash sewage is effectively neutralized. was confirmed.

Furthermore, when this neutralization treatment was continued, no clogging of the ash wastewater pipe occurred even after a period twice as long as the period in which clogging occurred due to scaling in the conventional method.

Furthermore, the ash wastewater slurry after neutralization was separated into solid and liquid using Shirafuna, and the heavy metals in the supernatant liquid were measured. The heavy metal aggregation effect of calcium carbonate was observed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional ash wastewater treatment method, FIG. 2 is an explanatory diagram of an ash wastewater treatment method showing an example of the present invention, and FIG. 3 is an explanatory diagram showing an experimental example of the present invention. 1.11... Garbage incinerator, 2,12...
・Dust collector, 3.13...Water wash tank, 4,14・
... Ash settling tank, 5.15 ... Overflow tank, 6 ... Neutralization tank, 7 ... Chemical tank, 8 ... Sedimentation tank, 16...pump,
17... Gas-liquid contact device, 18... Disk, 19... Shirafuna, 20... Sludge ash pit.

Claims (1)

[Claims] 1 Bringing the ash wastewater generated in the garbage incineration process and the collected dust directly charged into the gas-liquid contact device into gas-liquid contact with the exhaust gas generated in the process, the ash wastewater and ash slurry are treated with carbon dioxide gas in the exhaust gas, A method for treating ash wastewater in a garbage incinerator, characterized by washing the ash with water using a supernatant liquid of the treated ash wastewater.