JPH0462311A - Collected dust disposal method - Google Patents

Abstract

PURPOSE:To make it possible to collect dust collector dust which is generated when sludge is burn-molten efficiently and reduce dust in the final exhaust gas effectively as much as possible by a method wherein dust collector dust which is separated and collected from exhaust gas is mixed in wet sludge prior to drying, and the dust collector dust is collected by making it stick to the wet sludge and returned to a melting furnace. CONSTITUTION:As mentioned before, wet sludge to which dust collector dust is mixed to be adhered is burn-molten by repeating a series of processes such as dry-kneading by a multi-stage dryer 3, crushing by a crusher, 4, burn-melting by a rotary flow melting furnace 5, dust collecting by an electric dust collector 6 and mixing of dust collector dust in wet sludge; and the collected dust is made into slug with high efficiency. In this dust collector dust disposal method, dust in the exhaust gas discharged from the melting furnace is always collected and adhere-mixed in wet sludge, and therefore, the collected dust is not re-mixed in the exhaust gas by flying in the rotary flow melting furnace 5, and the dust can be disposed in the plant system itself. For this reason, the rate of transforming into slug of the dust is increased, and a dust volume in the final exhaust gas can be reduced, and the plant can be made into a closed system.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is directed to the use of collected dust discharged from a melting furnace when sludge produced in the treatment of wastewater such as sewage, human waste, or industrial wastewater is incinerated and melted in a melting furnace. The present invention relates to a dust processing method for collecting and processing dust.

"Prior Art" Conventionally, as one method for treating sludge produced in wastewater treatment such as sewage and human waste treatment, there has been known a treatment method in which dried sludge is incinerated and melted to form a molten solidified product.

In this sludge treatment method by incineration and melting, sludge is dried in a dryer to a moisture content of 10% or less, the dried sludge is sent to a crusher to have a constant particle size, and the sludge is further transferred to a melting furnace such as a swirling flow melting furnace. In this method, the sludge is incinerated and melted, and the volume-reduced sludge is made into a molten solidified product (hereinafter referred to as a slab).

This sludge treatment method by incineration and melting is excellent in reducing the volume of sludge and making it non-polluting, and the slag that is the final residue of the treatment has physical properties similar to crushed stone or gravel.
It is now used in part as a building material, and is an excellent processing method with many advantages.

However, the slagging rate with this treatment method is 90 to 95%.
The remaining 5 to 10% floats as a large amount of dust in the exhaust gas discharged from the melting furnace and is discharged.

If the dust in this exhaust gas is discharged as it is, it will cause air pollution, and in particular, there is a possibility that harmful substances may be mixed in the dust, so it cannot be discharged as it is. Therefore, various measures for processing collected dust are being studied to recover and process the dust in the exhaust gas.

Conventional dust collection methods include the cyclone dust collection method, which gives swirling motion to the dust-containing gas and uses centrifugal force to separate and collect dust from the gas, and the cyclone dust collection method, which uses corona discharge to charge the dust in the dust-containing gas. There is a dry dust collection method in which the charged dust is separated and collected using electric force, such as an electrostatic precipitation method, and then the collected dust is mixed with dry sludge and blown into the swirling flow melting furnace again. Other methods include a wet dust collection method in which exhaust gas is treated using a wet electrostatic precipitator method or a scrubber dust collection method.

``Problem to be solved by the invention'' However, in the dry method described above, since the collected dust is originally fine,
Most of the dust mixed in the dried sludge is scattered again, and there is no hope of recovery as slag, and the dust concentration in the exhaust gas increases on the contrary, and the dust gradually enters the pipes and heat exchangers in the treatment plant. This caused problems such as a decrease in the heat exchange efficiency of the heat exchanger.

In addition, in the wet dust collection method, since water is involved in the dust collection process, the dust will migrate to the drainage side, but in the unlikely event that the dust contains harmful substances such as heavy metals, The harmful substances will be dissolved in the wastewater, and this wastewater must be newly treated.

This invention was made in view of the above circumstances, and it is possible to efficiently collect collected dust generated when sludge is incinerated and melted,
The object of the present invention is to provide a method for treating collected dust that can effectively reduce dust in final exhaust gas to the greatest extent possible.

"Means for Solving the Problems" The present invention provides a dust treatment method for collecting and treating dust in exhaust gas discharged from the melting furnace when dry sludge is incinerated and melted in a melting furnace. The above problem is solved by mixing the collected dust into wet sludge before drying, making the collected dust adhere to the wet sludge, collecting it, and returning it to the melting furnace.

Hereinafter, an example of the dust treatment method according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of an apparatus suitably used to carry out the method of the present invention, in which reference numeral 1 is a wet sludge tank, 2 is a wet sludge tank, 3 is a multi-stage dryer, 4 is a crusher, 5 is a swirling flow melting furnace, and 6 is an electrostatic precipitator.

Wet sludge 2 is stored in the wet sludge 4111, and the wet sludge 2
The screw feeder 7 carries out a certain amount at a time and places it on the conveyor 9. The conveyor 9 conveys the wet sludge 2 to the gravimetric feeder IO, and the gravimetric feeder 10 supplies the wet sludge 2 to the multi-stage dryer 3 in fixed amounts. Next, the wet sludge 2 is dried and kneaded in a multi-stage dryer 3 to obtain dried sludge.

As shown in FIG. 2, this multi-stage dryer 3 includes a wet sludge input port 18, a screw feeder 19 that feeds the input sludge in fixed amounts onto the shelves 20, and stirring blades that stir the sludge on the shelves. 21, heat medium steam supply port 22, steam outlet 23,
It is configured to include a dry sludge outlet 24.

In this multi-stage dryer 3, the stirring blades 21 of each column 20 are rotated, and wet sludge is charged from the wet sludge input port 18 while the heat medium vapor is fed from the heat medium vapor supply port 22. The wet sludge is transferred to the uppermost shelf 20 by the screw feeder I9, and the stirring blades 21 of the shelf 20 stir this sludge while sequentially moving it in the horizontal direction, passing from the upper shelf to the lower shelf through the openings in each column. The sludge is sequentially stirred and transferred toward the target, and the sludge is dried during this time.

The sludge dried and kneaded in this way is carried into a dry sludge storage tank 14 via a screw feeder 12 and a container 13. The dried sludge 11 carried into the dried sludge storage tank 14 is crushed by the crusher 4 into a particle size suitable for combustion and melting. The crushed sludge is blown into the swirling flow melting furnace 5 together with combustion air and is incinerated and melted.

As shown in FIG. 3, the swirling flow melting furnace 5 includes a dry sludge supply port 25, a combustion air supply port 27, a furnace 26, a secondary furnace 28, a secondary air supply port 29, and an exhaust gas outlet 30. It is composed of In the swirling flow melting furnace 5, crushed dry sludge is blown into the one-fire furnace 26 from the dry sludge supply port 25, and at the same time, high-temperature combustion air is blown from the combustion air supply port 27 for swirl combustion. The completely combusted components flow down the furnace wall, and the unburned phosphorus components ride on the swirling flow and reach the secondary furnace 28. In the secondary furnace 28, fresh combustion air is blown into the secondary air supply port 29, and the unburned dry sludge is completely combusted. Further, the completely burned natural material is melted and solidified to become slag 15, which is then taken out. The air sent into the furnace is discharged from the exhaust gas outlet 30, but some of the dried sludge does not become slag, but is mixed in the exhaust gas as dust.

Next, the dust in this exhaust gas is sent to an electrostatic precipitator 6 to be collected. The dust collector used here is preferably an electrostatic precipitator that charges the dust in the dust-containing gas by corona discharge and separates and collects the charged dust by electric force.

The dust collected by the electric precipitator 6 is transferred to wet sludge by the conveyor 16. ! 1 or sent to the receiving hopper 8 of the conveyor 9 and mixed with the wet sludge 2. Here, in order to increase the contact efficiency between the wet sludge and the collected dust, it is desirable to feed the collected dust directly into the wet sludge and knead it to adhering and mixing the collected dust.

As mentioned above, the wet sludge with the collected dust adhering to it is dried and kneaded by the multi-stage dryer 3, crushed by the crusher 4, incinerated and melted by the swirling flow melting furnace 5, and electrostatically collected by I.
! The series of steps of collecting dust and mixing the collected dust with wet sludge in step 6 is repeated to perform incineration and melting treatment, and the collected dust is converted into slag with high efficiency.

In this collected dust treatment method, the dust in the exhaust gas discharged from the melting furnace is constantly collected and mixed into wet sludge, so that the collected dust is scattered in the swirling flow melting furnace 5 and remixed into the exhaust gas. Since the dust can be processed within the plant system without any waste, the rate of dust slab formation is increased, the amount of dust in the final exhaust gas can be reduced, and the plant can be made into a closed system.

In addition, the slagging rate of dust increases and the amount of dust in the exhaust gas is kept low, which prevents dust from adhering to piping and equipment such as the heat exchanger 17 in the sludge treatment plant.
Problems such as a decrease in the heat exchange rate of the heat exchanger are resolved.

Although the present invention is suitable for dust treatment in a swirl flow melting furnace, it can also be applied to other melting furnaces such as surface melting furnaces.

Further, in the method for treating collected dust of the present invention, the collected dust may be returned from any step as long as the sludge to be mixed is in the state of wet sludge before drying.

(Example) As an example of the present invention, a treatment process for collected dust shown by A in FIG. 4 was carried out. The wet sewage sludge in the wet sludge tank was sent to a multistage dryer, where it was dried and kneaded to form dry sludge. Furthermore, each device was adjusted so that the dried sludge, which had been pulverized to about 5 mm or less by the crusher, could be supplied to the swirling flow melting furnace with an ash content of 125 kg/hc (50 to 9/h). The supplied dried sludge was burned and melted in a melting furnace to form slag. The dust in the exhaust gas discharged from the melting furnace is reduced to the dust in the dust-containing gas by corona discharge! The charged dust is collected by an electrostatic precipitator that separates and collects it using electric force, and the collected dust is mixed into wet sludge. After confirming that the above operations are being performed stably, the weight of dust at the outlet of the swirling flow melting furnace (4a), the weight of the generated slag (4b), and the weight of collected dust collected by the dust collector (4C) ) and the amount of dust It(4d) in the exhaust gas were measured at regular intervals, and the average value thereof was calculated.

In addition, the heat exchange rate of the heat exchanger was also measured.

(Comparative Example 1) In Comparative Example 1, the processing steps from the wet sludge drying step to the dust collection step in the exhaust gas are the same as in the example.
As shown by the symbol B in FIG. 4, the collected dust was discarded without being reused.

In this comparative example 1, as in the example, the weight of dust at the outlet of the swirling flow melting furnace (4a), the weight of the generated slag (4b), the weight of collected dust collected by the dust collector (4c), and the weight of dust in the exhaust gas amount of dust! The weight of (4d) was measured at regular intervals, and the average value was calculated. The heat exchange rate of the heat exchanger was also measured in the same manner.

(Comparative Example 2) In Comparative Example 2, the processing steps from the wet sludge drying step to the dust collection step in the exhaust gas are the same as in the example, but
As shown by the symbol C in FIG. 4, the collected dust was mixed into the dried sludge after drying, rather than into the wet sludge before drying.

Regarding Comparative Example 2, as in Examples and Comparative Example 1, the weight of dust at the outlet of the swirling flow melting furnace (4a), the weight of the generated slag (4b), the weight of collected dust collected by the dust collector (4C), ) and the weight of dust in the exhaust gas (4d) were measured at regular intervals, and the average value was calculated. The heat exchange rate of the heat exchanger was also measured in the same manner.

These results are shown in Table 1.

Table 1 (Unit: kg/hour) As is clear from Table 1, when the method of the embodiment according to the present invention is used, the collected dust is mixed with wet sludge before drying, and the dust is disposed of as is in the comparative example. Compared to Comparative Example 2, the amount of slag can be significantly increased, and the mixed dust firmly adheres to the wet sludge and is sufficiently turned into sludge, so that the mixed dust does not swirl as in Comparative Example 2. There is no possibility that it will be scattered again in the flow melting furnace.

Therefore, the amount of dust at the furnace outlet and the amount of dust in the exhaust gas did not increase, and could be suppressed to the same level as Comparative Example 1. Also, regarding the heat exchange rate of the heat exchanger,
In Comparative Example 2, the heat exchange rate decreased by approximately 20%, but in this example, no such decrease was observed, and stable operation was possible.

Although an electric dust collector was used in this embodiment, other dry dust collectors such as a cyclone dust collector may also be used.

"Effects of the Invention" As described above, in the method for treating collected dust according to the present invention, collected dust separated and recovered from exhaust gas is mixed into wet sludge before drying, and the collected dust is attached to the wet sludge. By mixing and collecting the dust, the collected dust can be processed within the plant system without scattering in the melting furnace 5 and re-mixing into the exhaust gas, increasing the slagging rate of the dust and reducing the amount of dust in the final exhaust gas. It is also possible to reduce the amount of energy required, making it possible to create a closed system for the plant.

In addition, the slagging rate of dust increases and the amount of dust in the exhaust gas is kept low, which prevents dust from adhering to equipment such as piping and heat exchangers in sludge treatment plants, and reduces the heat exchange efficiency of heat exchangers. The problem is resolved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for carrying out the collected dust processing method of the present invention, FIG. 2 is a sectional view of a multi-stage dryer used in the apparatus shown in FIG. 1, and FIG. j, a cross-sectional view of the swirling flow melting furnace used in the apparatus shown in Fig. 1, and Fig. 4 is a flow route for explaining the example. l - Wet sludge tank, 2... Wet sludge, 3. ...Multi-stage dryer, 4...Crusher, 5...Swirling flow melting furnace, 6...Electrostatic precipitator.

Claims (1)

[Claims] In a dust treatment method that collects and processes dust in exhaust gas discharged from a melting furnace when dry sludge is incinerated and melted in a melting furnace, the collected dust separated and recovered from the exhaust gas is
A method for treating collected dust, which comprises mixing the collected dust into wet sludge before drying, making the collected dust adhere to the wet sludge, collecting it, and returning it to the melting furnace.