JPS6365988A - Harmless treatment of ash collected in electrostatic precipitator by utilizing co2 contained in exhaust gas - Google Patents

Abstract

PURPOSE:To reduce the operating cost by dissolving ashes collected in an electrostatic precipitator which are produced in a refuse incinerator in alkaline water and thereafter treating them with CO2 contained in exhaust gas. CONSTITUTION:Ashes collected in an electrostatic precipitator which are produced in a refuse incinerator are dissolved in alkaline water such as draingage of ashes, and alkaline chemicals are added if necessary and pH is regulated to alkalinity. Then gaseous CO2 contained in exhaust gas is blown thereinto and the mixture is treated. Further in order to stabilize produced sludge and to reduce the concn. of heavy metal contained in supernatant liquid, gaseous CO2 is blown into slurry and thereafter slurry is aerated. Thereby the stabilization of sludge can be contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for detoxifying electrostatic precipitator ash (hereinafter abbreviated as EP ash) using CO2 in exhaust gas.
More specifically, the present invention relates to a method for treating EP ash produced in a waste incinerator that employs a wet harmful gas removal process.

Conventional technology Conventionally, EP ash processing technology using CO2 in exhaust gas has been put into practical use as a process for treating ash wastewater, fly ash, etc. using exhaust gas in garbage incinerators that employ a dry harmful gas removal process. There's something I did. This is caused by unreacted Ca(OH)2 and C generated in the dry harmful gas removal process.
When EP ash containing aQ was received in the ash cooling water tank, the ash sewage level rose, causing problems such as elution of heavy metals from the sludge and scaling. It is intended to neutralize the

However, in waste incineration furnaces that employ a wet process to remove harmful gases, there is no example yet of treating the generated EP ash with exhaust gas.

This type of EP ash has properties considerably different from the above-mentioned ash containing unreacted Ca(OH)2 and CaO, and the following points are aerated with air.

1. Contains no unreacted Ca(OH)2 or CaO.

2. The dissolution rate in water is relatively high, and the dissolved slurry often exhibits weak acidity.

3. The content of harmful heavy metals is high.

The present inventors have provided a method that completely reduces and stabilizes the volume of EP ash produced in the wet harmful gas removal process, reduces construction costs and operating costs, and facilitates operational management. We discovered that a method that utilizes CO2 in exhaust gas is effective.
This invention was completed.

DESCRIPTION OF THE INVENTION The method of detoxifying EP ash using CO2 in exhaust gas according to the present invention converts electric concentrator ash generated in a waste incineration furnace that employs a wet harmful gas removal process into exhaust gas. C
Air aeration, treatment with O2.

In order to effectively detoxify EP ash according to this invention, before the electrostatic precipitator ash is treated with GO2 in the exhaust gas, the circular is dissolved in alkaline water such as ash wastewater, and if necessary, It is advisable to adjust the resulting slurry to be alkaline by adding an alkaline agent.

Furthermore, in order to stabilize the generated sludge and reduce the concentration of heavy metals in the supernatant, it is preferable to aerate the slurry with air after blowing CO2-containing exhaust gas into the slurry.

After dissolving EP ash in water or alkaline water, blowing CO2 gas into the resulting slurry or performing air aeration, the slurry is solid-liquid separated into supernatant water and sludge, each of which is charged. Metal concentration measurements and elution tests were conducted.

There are six treatment patterns for EP ash:

a) Dissolve 80 g of EP ash in 2/2 water and stir the resulting slurry for 30 minutes.

b) After a), add CO2 gas to the slurry at a rate of 0.51/
Blow in for several minutes until the liquid becomes stable (keep the liquid temperature at 35℃).

c) Dissolve 80 g of EP ash in 21 g of water, add Na○1 to the resulting slurry, and stir for 30 minutes while adjusting the slurry from 1 to 12.

d) c) +17)l, Co2 gas added to slurry 0,
Blow at a rate of 51/min until DH is stabilized (liquid temperature maintained at 35°C).

0) After C), blow CO2 gas into the slurry at a rate of 0.51/min until the pH is stabilized (liquid temperature is maintained at 35°C).

f) After e), pump air into the slurry at 0.51/min p.
Blow in until H becomes stable.

In addition, after allowing the slurry of each treatment to stand for 1 hour, the supernatant liquid was filtered through Nα5A filter paper, heavy metal analysis was performed, and the remaining sludge was dried at 80 to 90°C until the moisture content was approximately 60%. Then, an elution test was conducted. The measurement items and measurement methods are as follows.

・pH...JIS KO102 glass electrode method, ・r
"b...JIS KO102 atomic absorption method, Cd.
・・JIS KO102 atomic absorption method, -Zn-JIS
KO102 Atomic absorption method,・■−■・・・Environmental Agency Notification No. 59 Atomic absorption method,・Water content...
Sewage test method, elution test...Environmental Agency Notification No. 13.

The measurement results are shown in Table 1. Further, FIG. 2 shows the change in pile due to CO2 gas injection, and FIG. 3 shows the pH change due to air aeration after CO2 gas injection.

(Margin below) The following can be seen from Table 1, FIGS. 1 and 2.

(1) Effects of slurry p11 adjustment and CO2 gas injection■ pb...If the slurry is alkaline, once eluted Pb2+ is carbonated by CO2 injection, reducing its concentration in the supernatant liquid. . In addition, the sludge can be stabilized. When the slurry is acidic, pb is less likely to carbonate.

■Cd... When the slurry is made alkaline, Cd becomes hydroxide and stabilizes, but as the pH of the slurry decreases by blowing CO2 gas, Oma's Cd''# elutes. However, from the elution test results, CO2 It seems that the gas extracts unstable substances and stabilizes the sludge.

When the slurry is acidic, Cd is less likely to become a hydroxide.

■Zn... Simply making the slurry alkaline is not enough to remove Zn.
Although it is not stable, the effect of CO2 gas injection is almost the same as that of Cd.

(2) Effect of air aeration Sludge PL (After adjustment, it was found that the sludge was stabilized by blowing CO2 gas, but the heavy metal concentration in the supernatant liquid was not reduced except for PB.
2 After blowing, air aeration is performed to remove excess CO2 gas (decarbonation), and reduce the pH of the slurry.
When H is adjusted to be slightly alkaline, Pb and C in the supernatant
It was confirmed that both d and Zn were reduced. Similarly, the sludge elution test also gave stable results of 1:1. Note that this operation also helps prevent scaling.

(3) Others As shown in Figures 2 and 3, in this process, C
Even when excessive O2 gas was blown in, all did not fall below 6°5, and even after that, even when air was blown in excessively, the pH did not exceed 8.3. Therefore, there is no need to perform pH adjustment here, and operation management is thought to be easier.

Further, no occurrence of scaling was observed.

Based on the above, the treatment of EP ash will be carried out as shown in Figure 4. In addition, if the EP ash slurry was simply adjusted to pI+=8.3 with alkali, the water quality of the supernatant liquid would be Pb6, 6119//.

Cd9.1ry/I, Zn16.9m9/l, and the sludge elution test results are Pb1.5'/I)9/1
1Cd4.1yty/(/ (water content 63.0%)).

It can be seen that treatment of EP ash by CO2 injection is effective in this respect as well.

Effects of the Invention In the EP ash detoxification treatment method of the present invention, the electrostatic precipitator method generated in a garbage incinerator that employs a wet harmful gas removal process is treated with CO2 in the exhaust gas, so the following effects are achieved. be done.

(+) To dissolve EP ash, alkaline waste liquid such as ash wastewater can be used.

(2) Sludge can be stabilized by using exhaust gas as a CO2 source, and there is no risk of scaling.

(3) Heavy metals in the supernatant liquid can be significantly reduced without adding a coagulant or the like, reducing the load on wastewater treatment equipment.

(4) In exhaust gas blowing and air aeration, there is no need to adjust the pH of the slurry, and operation management is easy.

Thus, according to the method of the present invention, the volume of EP ash can be reduced and stabilized with reduced construction costs and operating costs, and easy operation management.

Example Next, embodiments of the present invention will be specifically described.

Referring to FIG. 1, EP ash dissolution Ifl! In step (1), EP ash is dissolved in ash wastewater, etc. to form a slurry, and EP
Reduces the volume of ash. In order to make the effect of detoxifying EP ash by the exhaust gas in the exhaust gas blowing tank (2) effective, an alkaline agent is added to the EP ash dissolving tank (1) as needed to make the pH of the slurry alkaline. Adjust it.

The dissolved slurry is then transferred from the EP ash dissolution layer (1) to the exhaust gas blowing layer (2), where the slurry is blown with GO2-containing exhaust gas. This carbonates heavy metals in the EP ash and temporarily elutes unstable substances. Note that even if exhaust gas is blown in excessively, the pH value does not fall below about 6.5.

Next, the slurry is transferred from the exhaust gas blowing tank (2) to the aeration tank (3).
) and aerate the slurry. By this, the excessively dissolved CO2 in the slurry is expelled from the slurry,
The pH is adjusted to be slightly alkaline to stabilize the sludge in the slurry and reduce the heavy metal concentration in the supernatant.

This air aeration also helps prevent scaling.

Note that even if air is blown in excessively, pll does not rise above about 8.3.

Finally, the slurry is transferred from the aeration tank (3) to the solid-liquid branch tank (4).
The liquid is then separated into supernatant liquid and sludge.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the invention, and FIG.
Figure 3 is a graph showing the relationship between CO2 gas injection time and pll, Figure 3 is a graph showing the relationship between air flow time and pH, and Figure 4 is a graph showing the relationship between the experimental process and cabinet. . (1)...EP ash dissolution tank, (2)...exhaust gas blowing tank, (3)...aeration tank, (4)...solid-liquid separation tank. that's all

Claims (3)

[Claims] (1) A method for detoxifying electrostatic precipitator ash, which is characterized by treating electrostatic precipitator ash produced in a garbage incinerator that employs a wet harmful gas removal process with CO_2 in exhaust gas. (2) Before treating the electrostatic precipitator ash with CO_2 in the exhaust gas, dissolve the ash in alkaline water such as ash wastewater, add an alkaline agent as necessary, and adjust the pH of the resulting slurry to alkaline. The method according to claim 1, wherein the method is adjusted to: (3) The method according to claim 2, wherein the slurry is aerated with air after blowing CO_2-containing exhaust gas into the slurry.