JPH0481692B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for incinerating sludge generated from wastewater treatment equipment such as a sewage treatment plant.

[Conventional technology]

BACKGROUND ART Conventionally, as a technology for incinerating sludge, a dry operation/incineration system that combines a fluidized bed incinerator and a dry operation machine has been known.

In this case, silica sand or the like is generally used as the fluid medium in the fluidized bed incinerator.

Furthermore, Japanese Patent Application Laid-Open No. 61-70314 discloses a technology for melting dry sludge in a swirling flow combustion melting furnace to turn it into slag, but this technique uses the technical concept of pre-combustion and post-combustion. and no fluidized bed was used.

[Problem that the invention seeks to solve]

The conventional drying/incineration system described above has the following disadvantages.

(1) Since sand is generally used as the fluidizing medium in fluidized bed furnaces, a blower with a large static pressure difference is required for fluidization, which increases power costs.

(2) Conventional fluidized beds use combustion air as the fluidizing gas, so when incinerating processed materials with a high calorific value such as dry sludge, the combustion temperature becomes high and sand, which is the fluidizing medium, is used. There was a problem that caused the .

(3) Because the gas flow rate for fluidizing the sand is high, even if dry sludge is supplied to the furnace, it cannot stay in the sand layer for the necessary time, so it cannot be completely combusted and generates harmful gases. The result was that

(4) In this way, conventional fluidized bed furnaces are suitable when there is a considerable amount of sludge drying load, but there are many points that make them unsuitable for exclusively incinerating dry sludge. Even when pre-drying the sludge, the entire volume cannot be dried, resulting in a mediocre heat recovery rate, which limits the ability to create an energy-saving system.

The present invention was made in view of the above points, and an object of the present invention is to provide a sludge incineration treatment method that can significantly reduce the power cost for fluidization and suppress the generation of NOx. That is.

[Means and actions for solving problems]

In order to achieve the above object, the sludge incineration treatment method of the present invention, as shown in the drawings, is a method for thermally processing dry sludge in the form of powder, in which dried sludge is heated in a swirling flow pre-combustion furnace 4. Partial combustion is carried out, and the produced green gas and incinerated ash are introduced into the fluidized bed section 6 of the swirling flow type after-combustion furnace 5. is completely combusted, and the exhaust gas from the after-combustion furnace 5 containing residual oxygen after the complete combustion is heat recovered and brought to a low temperature. A part of the exhaust gas is returned to the bottom of the after-combustion furnace 5 to It is characterized by fluidizing the incinerated ash at the bottom and secondary combustion of the unused gas by the residual oxygen in the exhaust gas.

In addition, the method of the present invention uses a swirling flow pre-melting furnace 23, which is equipped with a baffle 21 at the exhaust gas outlet and a slag discharge port 22 inside the furnace body, in place of the swirling flow pre-combustion furnace 4. By performing a combustion operation, a part of the incinerated ash is turned into molten slag, which is discharged from the swirling flow type pre-melting furnace 23 furnace body. In this case, the dried sludge with a relatively large particle size is not melted in the pre-melting furnace, but is transferred to the post-combustion furnace as incinerated ash, and is used as a fluid medium in the fluidized bed furnace, unlike in the case of total incineration. The same is true.

As mentioned above, the method of the present invention uses the incinerated ash itself as the fluidized medium of the fluidized bed after-combustion furnace, fluidizes it with the combustion exhaust gas after heat recovery, and supplies the materials to be combusted to the fluidized bed section. partial combustion of dried sludge (pyrolysis of combustibles) by carrying out via an installed swirl flow furnace;
The dry sludge is combusted at a temperature below a predetermined temperature of 700 to 1000°C by sequentially performing secondary combustion using the residual oxygen of the combustion exhaust gas itself and complete combustion using excess combustion air.

If the temperature inside the fluidized bed post-combustion furnace 5 is less than 700°C,
Combustible materials no longer thermally decompose, and on the other hand, when the temperature exceeds around 1000°C, incineration ash no longer melts and becomes a fluid medium.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, unless there is a specific description, the shapes of the components described in this example, their relative positions, etc. are not intended to limit the scope of the present invention to these, but are merely illustrative examples. Only.

Example 1 FIG. 1 shows an example of a sludge incineration treatment apparatus for carrying out the method of the present invention, and FIG. 2 shows the main parts thereof.

A dehydrated cake with a moisture content of 80% is supplied to a crusher 1 along with an air stream at approximately 500°C, and introduced into a cyclone 3 via a conveying pipe 2. Moisture content in cyclone 3 is 10
% of dry sludge and exhaust gas are separated, most of the dried sludge is supplied to the swirling flow pre-combustion furnace 4 together with high temperature combustion air, and a part of the dried sludge is supplied to the crusher 1. . As mentioned above, crusher 1
and the conveying pipe 2 constitute a flash dryer.

The inside of the pre-combustion furnace 4 is operated for thermal decomposition at approximately 900°C, and partial combustion is performed at 50 to 90%, preferably 60 to 80%, of the theoretical combustion air amount, and the generated unresolved gas and incineration ash are subjected to fluidized bed post-combustion. It is introduced into the fluidized bed section 6 of the furnace 5. 7 is an air distribution plate. In the post-combustion furnace 5, an air supply port 8 is provided in the rear half, that is, in the freeboard part.
Excessive air is introduced from the tank to completely combust the gas. The total combustion air ratio at this time shall be at least 1.2 times the theoretical combustion air amount.

The exhaust gas from the post-combustion furnace 5 containing 2 to 8% residual oxygen after complete combustion is introduced into the combustion air heat exchanger 10 to heat the air, and then passed through the dry hot air heat exchanger 11.
After heating the exhaust gas from the cyclone 3, it is introduced into the cyclone 12 as a low-temperature exhaust gas. Incineration ash and exhaust gas are separated by this cyclone 12, and the exhaust gas is introduced into a dry electrostatic precipitator 13 and then discharged from a chimney 14.

A part of the exhaust gas at the outlet of the electrostatic precipitator 13 is returned to the fluidizing gas inlet 15 at the bottom of the after-combustion furnace 5, fluidizing the incinerated ash and secondary combustion of unused gas by the residual oxygen in the exhaust gas. let 16 is a sludge/air inlet, 17 is a burner, 18 is a reduced ash outlet, and 20 is an exhaust gas outlet.

Embodiment 2 FIG. 3 shows another example of a sludge incineration treatment apparatus for carrying out the method of the present invention, and FIG. 4 shows the main parts thereof.

In this example, instead of the pre-combustion furnace 4 in Embodiment 1, a swirl flow type pre-melting furnace 2 is provided which is equipped with a buttful 21 at the exhaust gas outlet and a slag discharge port 22 inside the furnace body.
By burning the dried sludge at a temperature of about 1000° C. or higher using the cyclone 12 and/or the dry electrostatic precipitator 1, a part of the incinerated ash is turned into molten slag and discharged from the pre-melting furnace 23.
An incinerated ash return pipe 24 is provided so that the incinerated ash from No. 3 can be fed into the pre-melting furnace 23. 25
2 is a molten slag dropping means, and 26 is a granulated slag tank. Other configurations and operations are the same as in the first embodiment.

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects.

(1) Since a fluidized bed furnace does not have a drying load, it does not require sand as a heat storage medium, and instead uses a large amount of alkali metal oxides such as CaO, Al ₂ O ₃ , Fe ₂ O ₃ , etc., which are combustion oxidation catalyst components. By using the included incineration ash as a fluidized medium, the combustion rate in the fluidized bed furnace can be increased and the furnace body can be made smaller. Furthermore, since incinerated ash, which has a lighter apparent specific gravity than sand, can be used as a fluidizing medium, the power cost for fluidizing can be significantly reduced.

(2) A high calorific value treated material such as dried sludge is first partially heated in a swirling flow pre-combustion furnace or swirling flow pre-melting furnace using only primary combustion air of 50 to 90% of the theoretical combustion air amount. By burning, it is possible to prevent the combustion temperature from increasing more than necessary and at the same time suppress the generation of NOx.

(3) Since the flammable gas from the swirling flow precombustion furnace or swirling flow premelting furnace is high temperature, supplying more combustion air will result in a further increase in temperature, but in the fluidized bed, heat recovery is possible. By performing secondary combustion using the residual oxygen in the subsequent combustion exhaust gas, it is possible to suppress the rise in combustion temperature and the generation of NOx, similar to a swirl furnace.

(4) In the freeboard part of the fluidized bed furnace, excess air of 20% or more of the total combustion air ratio is supplied for complete combustion, so no harmful gases are entrained in the combustion exhaust gas.

[Brief explanation of drawings]

Fig. 1 is a flow sheet showing an example of an apparatus for carrying out the sludge incineration treatment method of the present invention, and Fig.
3 is a cross-sectional explanatory diagram showing a swirling flow pre-combustion furnace and a fluidized bed post-combustion furnace; FIG. 3 is a flow sheet showing another example of an apparatus for carrying out the method of the present invention;
The figure is an explanatory cross-sectional view showing the swirl flow pre-melting furnace and fluidized bed post-combustion furnace in FIG. 3. 1... Crushing machine, 2... Conveying pipe, 3... Cyclone, 4
...Swirl flow type pre-combustion furnace, 5...Fluidized bed type post-combustion furnace, 6
... Fluidized bed section, 7... Air distribution plate, 8... Air supply port,
10... Heat exchanger for combustion air, 11... Heat exchanger for dry hot air, 12... Cyclone, 13... Dry electrostatic precipitator, 14... Chimney, 15... Fluidization gas inlet, 16...
Sludge/air inlet, 17... Burner, 18... Ring ash removal port, 20... Exhaust gas outlet, 21... Batsuful, 2
2...Slag discharge port, 23...Swirling flow type pre-melting furnace, 2
4... Incineration ash return pipe, 25... Molten slag dropping means, 26... Granulated slag tank.

Claims (1)

[Scope of Claims] 1. In a method for thermally processing dried sludge in the form of powder, the dry sludge is partially combusted in a swirling flow pre-combustion furnace, and the generated green gas and incinerated ash are transferred to a fluidized bed post-combustion furnace. In the after-combustion furnace, excessive air is introduced into the latter half of the furnace to completely burn the unused gas, and the exhaust gas from the after-combustion furnace containing residual oxygen after complete combustion is recovered as heat. After cooling the exhaust gas to a low temperature, a part of the exhaust gas is returned to the bottom of the after-combustion furnace, where the incinerated ash is fluidized, and the residual oxygen in the exhaust gas is used to convert the unused gas into secondary gas. A sludge incineration treatment method characterized by combustion. 2.Instead of the swirling flow pre-combustion furnace, a swirling flow pre-melting furnace equipped with a flute at the exhaust gas outlet and a slag discharge port inside the furnace body is used to burn dry sludge, thereby reducing the amount of incinerated ash. Claim 1: A part of the melted slag is turned into molten slag and discharged from the swirling flow pre-melting furnace body.
The sludge incineration treatment method described.