JPH0124968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical multistage furnace, and more particularly to a multistage furnace suitable for incinerating sludge with a large calorific value using a polymer flocculant or the like.

BACKGROUND ART As one method for treating sludge discharged from wastewater treatment equipment, sewage treatment equipment, etc., there is a known method of incinerating sludge in a vertical multi-stage furnace or the like. usually,
Before incineration, an appropriate flocculant is added to the sludge, and it is dehydrated using a dehydrator to create dehydrated sludge with a moisture content of approximately 80%.
Supplied to vertical multistage furnaces, etc. As the above-mentioned flocculant, an inorganic flocculant such as ferric chloride or lime is used. , lime sludge) is obtained. A vertical multi-stage incinerator can be said to be the most suitable incinerator for this kind of sludge. In contrast, recently, polymer compounds have come to be used as coagulants instead of lime etc. for reasons such as reducing the volume of sludge and reducing processing costs.
The dehydrated sludge obtained in this way (hereinafter referred to as polymer sludge) has a solid calorific value of 3000 to 5000 kcal/
Kg solid content), which is quite high, and the moisture content is low at about 75%. When such sludge is incinerated in a multi-stage furnace, it is self-combustible, and the auxiliary fuel that was conventionally required becomes unnecessary or requires only a small amount, which is extremely effective in terms of energy conservation. However, it has been found that if a conventional multistage furnace (hereinafter referred to as a conventional furnace) for incinerating lime sludge is applied to polymer sludge as is, various problems will occur.

FIG. 1 and FIG. 2 are diagrams showing combustion conditions in a conventional furnace when lime sludge and polymer sludge are incinerated, respectively. In the figure, dehydrated sludge 5 is introduced from the top of the furnace 1 through the supply hole 4.
falls sequentially through the hearths 2 and 2A provided on the furnace wall, and goes through the processes of drying, combustion, and cooling.
The incineration ash is discharged from the chute 6 at the bottom of the furnace. A rotating shaft 10 at the center of the furnace is rotationally driven by a motor 11. On the other hand, air 12 is preheated through the rotating shaft 10 and then introduced from the lower stage of the furnace as air 13 for sludge combustion, comes into countercurrent contact with the falling sludge, is used for cooling and combustion, and then is combusted. It becomes exhaust gas and is discharged from the furnace top exhaust gas duct 8. In addition, in the figure, 3 is a stirring blade provided on the rotating shaft 10, and 14 is a hot air generating furnace.

In the case of lime sludge shown in Figure 1, dehydrated sludge and sludge combustion exhaust gas come into contact with each other in the drying stage at the upper part of the furnace (this is the stage where the drying section 15 is located), and efficient drying is performed, resulting in moderate dryness. The sludge falls into a combustion stage (refers to the stage located in the combustion section 16), and combustible volatiles in the sludge are combusted with flame 19. In this case, the combustible volatiles are almost completely combusted in the combustion section 16, become sludge combustion exhaust gas without remaining soot, and ascend through the drying section. After drying the dehydrated sludge, the furnace top exhaust gas 9
The gas is discharged from the furnace top exhaust gas duct 8 at the top. In this way, when lime sludge is incinerated, the boundary between the drying section 15 where water in the sludge is evaporated and the combustion section 16 where combustible volatile matter is burned is clear, and the exhaust gas is also clean. In addition, from the viewpoint of the operability of the furnace, the position of the combustion stage, which is a key point in operability, can be easily fixed by adjusting the amount of auxiliary fuel used in the hot air generating furnace 4.
The technology of incinerating lime sludge using a multistage furnace can be said to be a completed technology in terms of exhaust gas properties and furnace operability.

On the other hand, in the case of the polymer sludge shown in FIG. 2, since the polymer sludge has a low water content and a large calorific value, it can be self-combusted without the need for auxiliary combustion oil or the like. Furthermore, compared to the situation when incinerating lime sludge, the number of drying stages is reduced and the amount of combustible volatile matter in the sludge is large, so the flame generated from the combustion section 16 becomes longer and reaches the drying section 5. In such a situation, the flame 19 is cooled by the sludge in the middle of drying, and a large amount of combustible volatile matter remains in the exhaust gas as unburned matter. Furthermore, the sludge in the drying stage is also heated by the sludge combustion flame, causing localized excessive drying, which not only evaporates water, but also generates flammable volatile matter, which in extreme cases can even ignite instantly. be. In this way, the combustible volatile matter generated in the drying stage passes through the drying stage as unburned matter without being sufficiently burned, and is included in the furnace top exhaust gas 9. That is, when polymer sludge is incinerated in a conventional furnace, the boundary between the drying section and the combustion section is no longer clear, and the unburned matter due to incomplete combustion of the flame 19 generated from the combustion stage and the sludge in the drying stage are generated. Because of the unburned matter, the furnace top exhaust gas 9 contains a large amount of unburned matter. In addition, from the viewpoint of operability of the furnace, there is no effective adjustment method for fixing the combustion stage position during self-combustion of polymer sludge, equivalent to adjusting the amount of auxiliary combustion oil during lime sludge incineration. The combustion stage moves up and down due to various changes, making it difficult to keep the furnace steady. Therefore, when incinerating polymer sludge in a conventional furnace, it is necessary to reduce the throughput and lower the air ratio to suppress combustion and stabilize the situation inside the furnace. However, in this case, since the air ratio is lowered, the amount of unburned matter in the exhaust gas 9 increases more and more.

The problems when incinerating polymer sludge in a conventional furnace can be summarized as follows.

(1) The flame 19 generated from the combustion section 16 flows into the drying section 1.
5, this flame 19 is cooled by the sludge in the middle of drying, and remains in the furnace top exhaust gas 9 as unburned matter, especially soot, without completing combustion.

(2) The sludge in the drying stage is overheated by the sludge combustion flame 19, and the drying progresses too much to generate flammable volatile matter, which is included in the furnace top exhaust gas 9 as unburned matter.

(3) There is no effective method for fixing the combustion stage, and operability is poor. Therefore, in order to maintain a steady state inside the furnace, it is necessary to reduce the amount of treatment compared to lime sludge and lower the air ratio, which further increases the unburned content in the furnace top exhaust gas 8. It turns out.

An object of the present invention is to provide a vertical multistage furnace that generates less unburned matter and has good operability when incinerating dehydrated sludge containing a polymer flocculant and the like and having a high calorific value.

The vertical multi-stage furnace of the present invention is a vertical multi-stage furnace in which the inside of the furnace is divided into multiple stages for incinerating sludge with a high calorific value containing a polymer flocculant, etc. On the hearth of the combustion section in the furnace, It is characterized by providing a space in which unburned components such as combustible volatile components generated from the sludge are sufficiently combusted.

In the present invention, the combustion space preferably has a volume such that its load rate is 250,000 kacl/hr/combustion unit m ³ or less, and the space is provided with a space for extracting part of the combustion exhaust gas. When the load rate of the combustion space is greater than 250,000 Kcal/h/combustion space unit ^m3 , the flame extends to the upper drying stage, where it is cooled and produces unburned matter, which is largely contained in the exhaust gas. It will come. Note that the lower limit of the load factor of the combustion space is not particularly limited as long as combustion can continue.

Further, it is preferable that a baffle plate is provided in the space to promote combustion, and that a communication hole is provided in the center of the baffle plate to guide the sludge to the tapered portion so that the sludge falls smoothly.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIGS. 3, 4, and 5 are cross-sectional views of vertical multi-stage furnaces showing typical embodiments of the present invention, respectively. The differences from the conventional furnaces shown in FIGS. 1 and 2 are as follows.

(1) The combustion section 16 is provided with a combustion space (hereinafter referred to as the combustion chamber 20) of a size necessary and sufficient for the combustible volatiles generated from the sludge 18 during combustion in the combustion stage to complete combustion. (common to all figures).

By providing such a combustion chamber 20,
The boundary between the drying section 15 and the combustion section 16 becomes clear,
Unburnt components and flames disappear in the sludge combustion exhaust gas rising from the combustion section 16 to the drying section 15. Therefore, unburned matter, especially soot, generated when the flame is cooled in the drying section 15, and the drying section 15
When the sludge is superheated, unburned matter generated is eliminated, and the furnace top exhaust gas 9 is also purified.

(2) In the multi-stage furnace having the combustion chamber 20, in order to adjust the degree of drying of the sludge in the drying section 15, the combustion chamber 2 A duct (hereinafter referred to as the extraction duct 21) for partially extracting the sludge combustion exhaust gas is provided (common to all figures).
The amount of extracted gas 22 is adjusted so that the temperature of drying section 15 is constant.

This prevents the sludge in the drying section 15 from being heated more than necessary and generating unburned matter, and by supplying sludge with a constant degree of dryness to the combustion stage, the combustion stage can be stably fixed and operated. can improve sex. Furthermore, by adding such an adjustment mechanism, it is possible to introduce sufficient combustion air to improve combustion performance.
There is no need to reduce the air ratio as with conventional furnaces.

(3) In order to quickly complete the combustion of flammable volatiles in the combustion chamber 20, it is desirable to provide a baffle plate 23 to promote mixing and stirring with the combustion air (see Figure 4). and Figure 5).

In this way, by providing a combustion chamber with a high combustion chamber load factor, the amount of sludge throughput per unit area of the combustion stage hearth is significantly improved compared to the conventional furnace.

(4) In the multi-stage furnace having the above-mentioned combustion chamber 20, the dried sludge is removed quickly so that it does not come into contact with the sludge combustion flame for a long time while it falls onto the hearth of the combustion stage. It is desirable to have a structure in which the fuel falls onto the hearth of the combustion stage (Figures 4 and 5).

The conditions stated in paragraphs (1) and (3) above are for sludge above the hearth of the combustion stage, and provide a sufficient combustion chamber for the complete combustion of combustible volatiles generated from the sludge. It stipulates that. but,
In this case, if the sludge comes into contact with the combustion flame for a long time before falling onto the hearth of the combustion stage, it will cause
The sludge during drying is heated and generates flammable volatile matter, which may rise to the drying section without being sufficiently combusted, and this section is intended to prevent this from happening.

As an example of such a structure, in FIG. 4, a passage 25 through which sludge falls is formed on the furnace wall of the combustion section 20, and a screw feeder 26 for forcibly feeding sludge into the combustion chamber is provided. A configuration is shown in which the combustion gas is supplied to the combustion chamber without contacting the high-temperature combustion exhaust gas. In addition, FIGS. 5 and 6 show the baffle plate 2.
3. A tapered wall 3 is provided in the central part of the rotating shaft 10 through the penetrating part.
A funnel-shaped opening 31 having a diameter of 0 is provided, and a configuration is shown in which the sludge quickly falls onto the hearth of the combustion chamber while contacting the low-temperature rotating shaft 10 and without coming into contact with high-temperature gas.

Hereinafter, specific flows shown in FIGS. 4 to 6, which are shown as embodiments of the present invention, will be explained.

In FIG. 4, the dried sludge discharged from the lowest stage of the drying section 15 is fed to the hearth of the combustion stage by a feeder 26 through a dried sludge bypass pipe 25. Combustible volatiles generated from the sludge on the combustion stage hearth of the combustion section 16 are completely combusted in the combustion chamber 20, which has a baffle plate 23 to promote combustion. An extraction duct 21 is provided at the top of the combustion chamber 20, and exhaust gas is extracted so that the temperature of the drying section 15 reaches a predetermined temperature.

The dried sludge bypass pipe 25 is for preventing the sludge discharged from the drying section from coming into contact with the flame in the combustion chamber and generating unburned matter, and the feeder 26 supplies the sludge into the combustion chamber 20. At the same time, it serves to prevent the flame in the combustion chamber from passing through the dried sludge bypass pipe 25 and rising directly to the drying section.

In this way, the sludge combustion exhaust gas discharged from the combustion section 16 becomes sufficiently clean, so that there is no unburned matter in the furnace top exhaust gas, and by adjusting the amount of extracted gas, the combustion stage is fixed. Enables stable driving. In addition, in the above example,
If the calorific value of the sludge is insufficient, a burner 27 for burning auxiliary fuel can be installed to help ensure sufficient combustion within the combustion chamber 20.

The embodiments shown in FIGS. 5 and 6 are for carrying out the present invention more easily than the embodiment shown in FIG.
The sludge discharged from the lowest stage of the drying section 15 and whose degree of dryness has been adjusted immediately passes through the opening 31 and enters the combustion section 1.
It falls onto the combustion stage hearth 26 of No. 6 and burns. By providing the opening 31 having the tapered portion 30 in the baffle plate 23 for promoting combustion within the combustion chamber 20, sludge will not remain in the middle of the combustion chamber 20 for a long time and unburned matter will not be generated. A combustion fire of combustible volatile matter generated from the combustion stage hearth 26 is disturbed by the baffle plate 23 in the combustion chamber 20, combustion is promoted, and complete combustion occurs within the combustion chamber 20. At the top of the combustion section 20, an extraction duct 21 is provided as in FIG. 4. In this way, the sludge combustion exhaust gas discharged from the combustion section 16 becomes clean, but the structure inside the combustion chamber 20 is simplified compared to the case shown in FIG.
While the construction cost is lower, the cleanliness of the exhaust gas is somewhat sacrificed, but in terms of operability of the furnace, stable operation is possible as in the case of FIG. 4.

As mentioned above, according to the vertical multistage furnace of the present invention, the following excellent effects can be obtained.

(1) The gas discharged from the vertical multi-stage furnace does not contain any unburned matter, resulting in clean exhaust gas.

(2) The combustion stage is easy to fix and has good operability.

(3) Sludge treatment can be increased while achieving (1) and (2).

(4) As a side effect of achieving (1), the burden on the exhaust gas treatment device is reduced compared to conventional devices, and related equipment costs and running costs can be reduced.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing the state in which lime sludge and polymer sludge are burned using a conventional vertical multi-stage furnace, respectively, and FIG. 3 is a vertical sectional view showing an embodiment of the present invention. 4 and 5 are partial sectional views of a vertical multistage furnace showing other embodiments of the present invention, and FIG. 6 is a cross-sectional view of a vertical multistage furnace, and FIG.
FIG. The explanation of the symbols is as follows. 1... Furnace, 2, 2A... Hearth, 5... Dehydrated sludge, 7... Incineration ash, 9... Exhaust gas, 10... Rotating shaft, 15... Drying section, 16... Combustion section, 20... …
Combustion chamber, 23... baffle plate.

Claims (1)

[Scope of claims] 1.
In a vertical multi-stage furnace in which the inside of the furnace is divided into multiple stages to incinerate sludge with a solid content of 3000 Kcal/Kg or more, unburned matter such as combustible volatile matter generated from the sludge is placed on the hearth of the combustion section in the furnace. A vertical multi-stage furnace characterized by having a space so that the fuel is sufficiently combusted and the load rate is 250,000 Kcal/h/ ^m3 or less per unit of combustion section. 2. The vertical multistage furnace according to claim 1, characterized in that the combustion space is provided with a duct for extracting part of the combustion exhaust gas. 3. The vertical multi-stage furnace according to claim 1 or 2, characterized in that a baffle plate for promoting combustion is provided in the space of the combustion section. 4. The vertical multi-stage furnace according to claim 3, wherein the baffle plate has a communicating hole in the center that is guided by a tapered part so that the sludge falls smoothly. Vertical multistage furnace.