JPH06226238A - Treatment of fly ash - Google Patents

Abstract

PURPOSE:To eliminate the danger of explosion by hydrogen by adding water and a pH control agent at need to fly ashes contg. harmful heavy metals and adding a heavy metal fixing agent thereto under kneading, then sucking and discharging gases contg. the hydrogen generated at the time of kneading to the outside of the system through a scrubber. CONSTITUTION:The fly ashes for one batch are fed from an EP ash hopper 1 by a feeder 3 and are injected together with the humidifying water from a liquid chemical injector 6 to a vibration type kneader 5 in order to subject the smoke gases captured by a refuse incineration furnace, etc., to a batch treatment for the purpose of preventing splashing of the cry ashes. The exciting force of the kneader 5 is made smaller so as to suppress the generation of the hydrogen at this time. Ventilation operation is carried out by opening ventilation dampers 16, 17 and actuating a blower 8 for ventilation after calculation of the fly ashes. Simultaneously, the vibration frequency of the kneader 5 is increased to enhance a kneading effect. The gases contg. the hydrogen generated at this time are discharged by the blower 8 to the outside of the system through the scrubber 7. The heavy metal fixing agent and flocculating agent are successively injected from the liquid chemical injector 6 and the pH control agent is injected at need.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ash discharged together with exhaust gas from an incinerator plant such as municipal waste and industrial waste, for example, EP ash which is ash collected by an electric dust collector (EP) and a bag filter. Collected ash, etc. (This kind of ash is referred to as "fly ash" throughout this specification)
More specifically, the present invention relates to a method for rendering fly ash containing a heavy metal harmful to a human body harmless.

[0002]

2. Description of the Related Art This kind of fly ash contains a large amount of chlorides of heavy metals harmful to the human body, especially cadmium,
Lead and mercury tend to exceed the elution standard values stipulated by the "Prime Ministerial Ordinance that sets criteria for determining hazardous industrial waste."

If fly ash containing such harmful heavy metals is directly landfilled, heavy metals in the fly ash may be eluted by rainwater and the like, which may pollute soil and rivers and cause environmental problems. Increasingly, fly ash is treated by the acid extraction method or the carbonation method.

However, in these treatment methods, the cost of the added cement and the chemicals for fixing the extracted heavy metals becomes great, and the operation and maintenance of the treatment equipment is very troublesome.

Under these circumstances, the present inventors first added a chelating agent and an iron salt while adding a required amount of water or the like to fly ash and moistening and kneading the fly ash using a vibrating mixer. Proposed a method for detoxifying fly ash (JP-A-63-
278589).

The present invention is an extension of the invention of the above patent application.

[0007]

Generally, in the method of detoxifying fly ash, a step of dissolving fly ash in water or moistening with water is necessary. At this time, amphoteric metals such as Al, Zn, and Pb contained in the fly ash react with the alkaline components contained in the fly ash, and hydrogen is generated. Furthermore, when an alkali is added to promote the detoxification of heavy metals, the above reaction is promoted and the generation of hydrogen is further promoted. For this reason, there is a risk that hydrogen will accumulate in the apparatus for detoxifying heavy metals and indoors, leading to an increase in hydrogen concentration and an explosion (4 to 75% of hydrogen in the hydrogen-air system is in the explosion concentration range).

Therefore, it is necessary to take measures to avoid the hydrogen concentration in the device or indoors from the danger range of explosion.

In view of the above situation, an object of the present invention is to provide a method for treating fly ash which is free from the danger of explosion due to hydrogen generated by the detoxification reaction of heavy metals.

[0010]

The present invention has been devised to achieve the above object, and as a result of pursuing a more effective fly ash detoxification treatment method, the operation was intentionally made into a batch type, and The inventors have found that a remarkable effect is brought about by sucking the hydrogen-containing gas in the kneader through the scrubber with a blower and discharging it out of the system, and have completed the invention.

That is, the method for treating fly ash according to the present invention is a kneading machine in which a fly ash containing harmful heavy metals is added with water and, if necessary, a pH adjusting agent to knead the fly ash with humidification. A heavy metal fixing agent and, if necessary, a pH adjusting agent, and a gas containing hydrogen generated in the kneader is sucked with a blower through a scrubber and discharged out of the system.
It is characterized in that the used cleaning liquid of the scrubber is sent to the above kneader as humidifying water, and that a series of operations is performed in a batch system.

[0012]

EXAMPLES Next, the processing method of the present invention will be specifically described by way of examples.

1) Outline of processing apparatus The fly ash processing apparatus is, as shown in FIG. 1, an EP ash hopper (1) having a hopper vibrator (2) on the lower end side, and a hopper.
(1) Feeder for EP ash cutting that is installed underneath (3)
And a vibrating kneader (5) installed via a chute (4) below the end of the feeder (3), and a chemical injection device (6) installed in the kneader (5). From the scrubber (7) installed in the ventilation duct (15) installed outdoors from the machine (5), the ventilation blower (8) installed in the downstream of the scrubber (7), and the blower (8). The main components are a combustible gas detector (9) that detects the concentration of combustible gas in the exhaust gas emitted, and a treated ash discharge conveyor (10) installed below the kneading machine (5). .

In the vibration type kneader (5), a kneading machine main body (11) in the shape of a horizontal cylinder is installed on a base (13) via a spring (12), and a plurality of kneading machine main bodies (11) are installed. The rod (14) is built in, and the shaker (18) is provided on both sides of the kneading machine body (11). By the operation of the shaker (18), the kneader body (11)
Fly ash is kneaded therein by being hit by a plurality of rods (14).

The ventilation duct (15) consists of a vinyl hose,
Even if fly ash adheres, it is wiped off by the vibration of the kneading machine (5).

2) Operation of the device Soot dust discharged from the refuse incinerator is captured by the electrostatic precipitator and temporarily stored in the EP ash hopper (1) by the transfer device.
In order to perform batch processing for the purpose of preventing the scattering of dry ash, one batch of fly ash is cut out from the hopper (1) by the feeder (3) and supplied to the vibration type kneader (5) through the chute (4) at the same time. , Inject water for humidification from the chemical injection device (6).
This water is industrial water. At this time, since dry ash is put into the kneading machine (5), it is not possible to ventilate for hydrogen countermeasures. Therefore, the seismic force of the kneading machine (5) should be reduced to minimize hydrogen generation. Specifically, set the vibration frequency of the kneading machine (5) to 2
0 to 30 Hz. By these operating conditions, the hydrogen concentration in the kneader can be suppressed to below the explosion limit (4%).
In addition, fly ash for one batch is divided into two parts and cut out from the hopper (1) to make the humidification condition of the ash uniform and to divide the water for humidification into two parts, one of which is the scrubber (7 Water is supplied to the kneading machine (5) from the lower water tank of () through the exhaust duct (15), and the exhaust duct is washed to prevent the duct from being blocked. Humidification water at the time of ash measurement should be 50% by weight or more of all the humidification water,
Hydrogen generation is suppressed by lowering the fly ash temperature.

After measuring the fly ash, the ventilation dampers (16) (17) are opened, the ventilation blower (8) is operated to perform the ventilation operation, and at the same time, the vibration frequency of the kneading machine (5) is set to 50 to 60 Hz. Raise,
Enhance the kneading effect by increasing the shaking force of the kneading machine. As a result, the gas containing hydrogen generated in the kneader is scrubbered.
After going through (7), it is discharged to the outside by the blower (8). Ventilation duct
The gas flow velocity in (15) shall be 3 m / sec or less. Chemical injection device
From (6), a liquid chelate or a sulfide such as sodium hydrosulfide, and then a coagulant are sequentially injected as a heavy metal fixing agent, and caustic soda is injected as a pH adjuster when the hydrogen concentration starts to reach saturation. As a result, the hydrogen concentration in the kneader can be averaged. The hydrogen gas concentration in the exhaust gas emitted from the blower (8) is detected by the combustible gas detector (9). A signal is sent from the detector (9) to a safety device that stops the kneader at the set concentration. The addition amount of the pH adjusting agent is preset by automatic titration of the fly ash sample.

After the caustic soda is injected, the amount of the humidifying water is finely adjusted while also cleaning the chemical liquid pipe, and the caustic soda is less mixed when the ash of the next batch is measured to suppress the generation of hydrogen.

The kneading is carried out for 10 to 20 minutes. By this kneading, the amount of the heavy metal fixing agent added can be reduced, and the stabilization of the heavy metal in the treated ash can be achieved. The pH of the treated ash during kneading is 3 to 1
It is about 0.

After the kneading is completed, the discharge gate at the bottom of the kneader is opened to discharge the treated ash. At this time, the kneading machine (5) is tilted (tilted forward) to efficiently perform the discharging work. The treated ash is discharged to an ash pit or the like by the discharge conveyor (10). The fly ash in the kneading machine is almost completely removed by the discharging operation for 10 to 20 minutes. After performing a series of operations in a batch manner, the fly ash sludge finally obtained has a water content of 15 to 50% by weight.

When the discharge is completed, the discharge gate of the kneading machine is washed and then closed to start the next batch process. Ventilate until just before the next batch operation.

Attached Table 1 shows the results of the elution test of heavy metals and the like in the raw ash and the treated ash.

Further, FIG. 2 shows changes in the hydrogen concentration in the fly ash processing apparatus during operation.

[0024]

[Table 1]

[0025]

Since the method for treating fly ash according to the present invention is constructed as described above, it is possible to detoxify heavy metals in fly ash without the risk of explosion due to hydrogen generated.

Further, since a series of operations are performed in a batch system,
The amount of chemicals such as heavy metal fixatives can be adjusted, the timing of addition can be controlled, the vibration force of the kneader can be controlled, and during the exhaust of fine powder (fly ash) accompanying ventilation of the kneader. Can be suppressed as much as possible.

Further, since the used cleaning liquid of the scrubber is sent to the above kneader as humidifying water, the water can be used in a closed system and the ventilation duct can be cleaned to prevent clogging trouble.

Further, according to the method of the present invention, since the kneading effect is good and the kneading time can be adjusted, the reaction between the harmful heavy metal and the drug is efficiently carried out, and the amount of the drug required for detoxification is different from other treatment methods. 1/10 or less compared to, chemicals (aqueous solution)
Since no other additives are used, the effect of reducing the volume of treated ash is large, and fly ash is not dissolved in a large amount of water, so no wastewater treatment facility is required.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

FIG. 2 is a graph showing a change in hydrogen concentration in a fly ash processing apparatus during operation.

[Explanation of symbols]

 (5)… Vibration type kneader (6)… Chemical liquid injector (7)… Scrubber (8)… Ventilation blower (9)… Combustible gas detector

Front page continuation (72) Inventor Tadao Murakawa 5-3-28 Nishikujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd. In-house (72) Inventor Nobuhiro Maeda 5-3-8 Nishi-Kujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd.

Claims (1)

[Claims] 1. In a kneading machine, water and a pH adjusting agent are added to fly ash containing harmful heavy metals to moisten and knead the fly ash, and a heavy metal fixing agent and a pH if necessary are added to the kneaded product. A regulator is added, a gas containing hydrogen generated in the kneader is sucked out of the system by a blower through a scrubber, and the used cleaning liquid of the scrubber is sent to the above kneader as humidifying water, and a series of A method for treating fly ash, characterized in that the above operation is performed in a batch system.