JPH0692810B2 - Fluidized bed type sludge combustion furnace - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sludge combustion furnace used for treating sludge discharged from a sewage treatment apparatus or a human waste treatment apparatus.

[Conventional technology]

Among the sludge combustion furnaces that have been put into practical use in the past, the fluidized bed combustion furnace is the mainstream because of its good combustion efficiency, operability, etc. The outline is as follows.

High water content discharged from sewage treatment plants or human waste treatment plants,
The sludge with a low calorific value is once stored in a hopper or the like, then transferred by a pump, a conveyor or the like, and fed into the furnace by overfeed from the upper part (freeboard part) of the furnace by a constant quantity feeder such as a screw feeder. The thrown sludge drops into a high-temperature fluidized sand layer, and undergoes rapid crushing, moisture evaporation, thermal decomposition, and combustion processes, and combustion residues are discharged from the furnace as fly ash.

The general combustion conditions are as follows.

Superficial velocity: 1 m / sec, sand layer temperature: 800 to 850 ℃, excess air ratio: around 1.2 to 1.4 [Problems to be solved by the invention] By the way, the sludge that is incinerated in the conventional sludge incinerator is high. Water content (65% to 85%), which has the advantage of being pumpable, but has low calorific value. Therefore, there is a problem that incineration requires an auxiliary fuel and the treatment cost increases.

So, instead of simply incinerating sludge as waste,
As part of the plan for effective use as resources, sludge fuel conversion research is underway. This is to increase the calorific value by substituting the water contained in the sludge discharged from the human waste treatment equipment and the like with oil by the multiple effect can evaporation method.

However, the sludge with low water content and high calorific value (hereinafter referred to as "high calorific value sludge") thus obtained is a solid (plasticity) composed of a mixture of lumps and fine powder such as fibrous material, and its properties are those of the conventional high water content. It is quite different from sludge. Therefore, when the high calorific value sludge is burned under the conventional sludge incinerator and incineration conditions, the fine powder is discharged outside the furnace as unburned particles,
There is a problem that combustion efficiency is significantly reduced. In order to prevent the scattering of unburned particles, if the gas flow velocity in the furnace is reduced and the retention time is lengthened, in this case, the furnace load will decrease, and the size of the furnace will increase, making the construction cost more expensive. Occurs. Since the conventional sludge combustion technology cannot be applied as it is, development of a combustion furnace suitable for high calorific value sludge is urgently required.

In view of the above circumstances, the present invention seeks to provide a highly efficient and compact fluidized bed combustion furnace for high calorific value sludge.

[Means for solving problems]

The fluidized bed type sludge combustion furnace according to the present invention is a fluidized bed type combustion furnace for sludge having a low moisture content and a high fine powder content, which is generated from a fuel system such as sewage sludge or human waste sludge,
A classifier that classifies the sludge into a fine particle fraction and a lump fraction having a transportable particle size, a crusher that crushes the lump fraction into a transportable particle size, and a fine powder fraction that is classified by the classifier. And a means for directly supplying the crushed aggregate fraction crushed by the crusher into the fluidized sand layer in the furnace, and maintaining high combustion efficiency without reducing the furnace load. It is what

[Action]

High calorific value sludge is composed of fine particles of several microns to lumps of about 20 to 30 mm. Fractionation is carried out, and then the lump fraction is crushed by a crusher until the total amount becomes several millimeters or less. The fine powder fraction and the crushed lump fraction thus classified are not fed into the conventional freeboard of the furnace, but into the sand layer that is actively fluidized at high temperature by means such as air transportation. Supply directly (hereinafter referred to as underfeed).

The sludge directly put into the sand layer as described above is agitated by contact with the fluid medium having a large heat capacity, and the difference in the heat transfer is good, so that the sludge instantly burns. Moreover, since the residence time is long, it is completely burned. Therefore, as compared with the conventional combustion furnace in which the sludge is supplied by the overfeed from the freeboard section, the reduction of the combustion efficiency due to the scattering of unburned particles is prevented, and the high combustion efficiency can be obtained.

In addition, since it is not necessary to reduce the gas flow velocity in the furnace, a high furnace load can be taken, the furnace can be made compact, and it can be developed as a fluidized bed boiler depending on the amount of heat of sludge.

〔Example〕

FIG. 2 is an explanatory view showing a fluidized bed type sludge incinerator according to a reference example of the present invention.

In the figure, 1 is a hopper for storing high calorific value sludge. The hopper is connected to the crusher 3. The high calorific value sludge sent from the hopper 1 to the crusher 2 is crushed into a mass fraction of several millimeters or less and sent to the underfeed device 4. The pulverized sludge sent to the underfeed device 4 is underfed into the combustion furnace main body by the carrying air 5 through the carrying pipe 6. A fluidized sand layer 8 is provided inside the combustion furnace body, and a temperature control heat transfer tube 9 is disposed in the fluidized sand layer. The finely pulverized sludge supplied to the fluidized sand layer 8 is combusted with the combustion air supplied from the air supply line 10, and the produced gas is the freeboard part 6 in the furnace.
Through the exhaust gas line 11 and the exhaust gas treatment device 12 to be discharged to the outside of the system.

FIG. 1 shows an embodiment of the present invention. In the figure,
The same parts as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In comparison with the reference example of FIG. 2, the classifier 2 is used in this embodiment.
Is different in that it is provided. That is, the high calorific value sludge is first sent from the hopper 1 to the classifier 2, and the fine powder fraction separated here is directly sent to the underfeed device 4. Then, only the lump fraction is sent to the crusher 3, pulverized into fine powder, and then sent to the underfeed device 4. Due to this feature, the efficiency of the disintegrator 3 can be improved, and it is particularly suitable for high calorific value sludge having a high content of fine powders.

In addition, in the above-mentioned embodiment, the air feeding is used as the means for the underfeed, but it is also possible to use the means for directly supplying it into the sand layer by the screw feeder or the like.

Next, a combustion test conducted to confirm the effect of the combustion furnace of the present invention will be described. This test is the third
It carried out using the apparatus shown in the figure. In the figure, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals.

First, the high calorific value sludge was classified, and a pretreatment was performed to crush the lump fraction into fine powders of several mm □ or less. By supplying this pulverized sludge to the underfeed device 4 and directly introducing it into the fluidized sand layer 7 through the sludge transfer pipe 6 by the transfer air 5, a combustion test was conducted in the same state as in the combustion furnace of the above-mentioned example. As a result, it is possible to achieve a high combustion efficiency of 98% or more at the superficial velocity of about 1 m / sec, the sand layer temperature of 800 to 850 ℃, and the excess air ratio of 1.2 to 1.4, which are the optimal combustion conditions of the conventional sludge combustion furnace. did it.

On the other hand, for comparison, a high calorific value sludge (10 mm under) without the above pretreatment was put into the furnace with the same overfeed as in the conventional combustion furnace, and a combustion experiment was conducted under the same conditions as above. However, there were many scatterings of unburned fine powder.
Furthermore, the combustion efficiency was 60-80% even when the superficial velocity was reduced to around 0.5 m / sec.

As is clear from the results of this comparative test, the sludge combustion furnace of the present invention is extremely suitable for burning high calorific value sludge having properties different from those of conventional sludge.

〔The invention's effect〕

As described in detail above, according to the fluidized bed type sludge combustion furnace of the present invention, when burning high calorific value sludge, high combustion efficiency can be maintained without impairing the furnace load. Further, it is possible to develop as a fluidized bed boiler, and a remarkable effect can be obtained. Furthermore, by providing a classifier,
Since only the lumps that need to be crushed are sent to the crusher, it is possible to reduce the load on the crusher, reduce the power of the crusher, and improve the efficiency of fine crushing.

[Brief description of drawings]

FIG. 1 is an explanatory view of a fluidized bed type sludge combustion furnace according to an embodiment of the present invention, FIG. 2 is an explanatory view of a fluidized bed type sludge combustion furnace as a reference example of the present invention, and FIG. 3 is according to the present invention. It is explanatory drawing of the combustion furnace used for the combustion test for confirming an effect. 1 ... High calorific value sludge hopper, 2 ... Classifier, 3 ... Crusher, 4
... underfeed device, 5 ... conveying air, 6 ... sludge conveying pipe, 7 ... furnace freeboard section, 8 ... fluidized sand layer, 9 ... temperature control heat transfer pipe, 10 ... combustion air supply line,
11 ... Exhaust gas line, 12 ... Exhaust gas treatment device

Claims (1)

[Claims] 1. A fluidized bed combustion furnace for sludge having a low water content and a high fine powder content, which is generated from a fuel conversion system for sewage sludge, human waste sludge, etc., and has a particle size capable of transporting the sludge. A classifier for classifying into a fraction and a lump fraction, a crusher for crushing the lump fraction into a transportable particle size, and a fine powder fraction classified by the classifier and crushed by the crusher And a means for directly supplying the lump fraction to the fluidized sand layer in the furnace, and maintaining a high combustion efficiency without reducing the furnace load, a fluidized bed sludge combustion furnace.