JPH03169400A - Granulating and dewatering method of sludge - Google Patents

Abstract

PURPOSE:To lower sludge treatment cost and improve dewatering ratio by using incinerated ashes collected by a cyclone as they are or separated from rough particles or using incinerated ashes collected by electric precipitator and separated from fine powder or using both of them as drying powder. CONSTITUTION:A sludge cake primarily dewatered by a primary dehydrator 1 is supplied to a granulating machine 2. As drying powder, incinerated ashes discharged from an incinerator 4 and collected by a cyclone 5 are supplied to the granulating machine 2 as they are or separated from rough particles by screening using a screening machine 9, or incinerated ashes collected by an electric precipitator 6 and separated from fine powder by a screening machine 10 or both of them are supplied. The sludge cake is pulverized by the granulating machine 2 to a degree not to break the water route of the cake, granulated into granules by rotation, and the granules are coated with the drying powder. In this way, sludge treatment cost becomes low and dewatering ratio is heightened with a little amount of the drying powder and the sludge cake become easy to be handled.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention involves firstly dewatering sludge generated in sewage systems, etc., and then granulating it into so-called solid sludge particles coated with dry powder as a dehydration aid. This relates to a method for dehydrating sludge through granulation, which is then subjected to secondary dewatering. ``Prior art'' As a technology for dewatering sludge generated in sewers, etc. to produce a sludge cake with a low moisture content, the sludge cake that has undergone primary dewatering is subjected to thixolysis. (Thixotrobi change) is granulated to form sludge particles with a particle size of 1 to 10 mm. During granulation, the surface of the sludge particles is coated with dry powder such as diatomaceous earth, slaked lime, or incinerated ash as a dewatering aid. A technique is described in Japanese Patent Publication No. 59-48160, in which the tempered sludge particles are compressed and subjected to secondary dehydration to reduce the moisture content of the sludge cake to 60% or less. The basic idea of the method is to allow the water contained in the sludge cake to quickly reach the surface of the sludge particles when it is compressed, and to take advantage of the high water permeability of the dry powder. By coating the sludge grains with dry powder to quickly guide the water that has reached the surface of the sludge grains to the filter media, it is possible to easily obtain a sludge cake with a low water content in a short time. In the above technology, by improving the water permeability of the dry powder, the drainage of the contained water during secondary dewatering by squeezing the conditioned sludge particles is improved, and It is preferable to produce a sludge cake with a low moisture content.As a technique for improving the water permeability of such dry powder, it is possible to
% of aluminum oxide or aluminum hydroxide, or spraying phosphoric acid into the incinerator so that 0.5% or more of phosphorus remains in the incinerated ash (Japanese Patent Application No. 1-5612) (No. 1 and Japanese Patent Application No. 1-21823). “Problems to be Solved by the Invention” Since the purpose of dewatering sludge is to incinerate and dispose of it, there is a strong need to reduce the required cost.However, in the prior art described above, aluminum oxide, aluminum hydroxide, It is necessary to add similar chemicals such as phosphoric acid, and in particular, the amount of primary dewatered sludge cake processed at sewage treatment plants is several hundred tons per day, and as a result, the amount of chemicals added is 1. This amounts to several tons per day.Therefore, there was a problem that the cost required for dewatering sludge did not go down as expected.In order to solve the above problems, the present invention improves the water permeability of dry powder. The object of the present invention is to provide a method for granulating and dewatering sludge that is improved at low cost and forms a closed cycle as much as possible. [Means for Solving the Problems] In order to achieve the above problems, the present inventors have Through repeated research, we discovered that the water permeability of dry powder depends on its particle size, and by taking advantage of the fact that the particle sizes of incinerated ash collected by a cyclone and incinerated ash collected by an electrostatic precipitator are different, The present invention has been completed.That is, the present invention involves feeding a primarily dehydrated sludge cake and dry powder to a granulator, and forming tempered sludge particles coated with the dry powder in the granulator. In the sludge granulation and dehydration method in which the tempered sludge particles are compressed for secondary dehydration, the sludge cake subjected to the secondary dewatering is incinerated in an incinerator, and the incinerated ash discharged from the incinerator is heated in a cyclone and electric The incinerated ash collected by the dust collector and the cyclone is used as the dry powder, or the incinerated ash collected by the electrostatic precipitator is used as the dry powder after removing the coarse powder, or the incinerated ash collected by the electrostatic precipitator is used as the dry powder. This is a method for granulating and dewatering sludge using the dry powder or both as the dry powder. [Example 1] An example of the present invention will be explained with reference to the drawings. Fig. 1 shows an example of the present invention. In this embodiment, sludge is first dehydrated by a primary dehydrator 1, and the primary dewatered sludge cake is supplied to a pelletizer 2.As will be described later, the pelletizer 2 includes: Classifier 9 after discharge from incinerator 4
．． Incineration ash that has been classified over 10 times is also supplied at the same time.

In the granulator 2, the sludge cake is crushed to the extent that it does not destroy the cavities (channels) therein, and is granulated into granules by transfer, and while it is rolling, the classified incineration ash is deposited on the surface of the sludge particles. It is covered. The tempered sludge particles granulated by the granulator 2 and coated with classified incineration ash are supplied to the next secondary dehydration 8!3, where the water contained in the tempered sludge particles is further compressed and dehydrated. As secondary dewatering 113 requires stronger squeezing force, a press type or hydraulic diaphragm type press dehydrator is used. 6 After the secondary dewatering, the sludge cake is put into an incinerator 4 and incinerated. It will be done. The incinerator 4 may be a fluidized bed incinerator or a multistage incinerator, but in this practical example, a fluidized bed incinerator was used.

The incinerated sludge cake becomes combustion gas and incineration ash, but the incineration ash flows together with the combustion gas and is sent to cyclone 5.
Crude incineration ash in the combustion gas is separated and collected in cyclone 5 and stored in storage hopper 7°. The combustion gas is then introduced into the electrostatic precipitator 6, where fine incineration ash is further separated and collected and stored in the storage hopper 8, and the combustion gas is released into the atmosphere. The cyclone-collected ash stored in the storage hopper 7 and the electrostatic precipitator-collected ash stored in the storage hopper 8 are classified by a classifier 9 and a classifier 10, respectively. For classification I19.10, a rotary classifier that uses centrifugal force and air resistance for classification was used in this example. The cyclone-collected ash from which coarse powder has been removed by the classifier 9 and the electrostatic precipitator-collected ash from which fine powder has been removed by the classifier 10 are stored in a storage hopper 11 and then supplied to the granulator 2. Next, Table 1 shows the classification results of the cyclone-collected ash by the classifier 9 (classifier rotation speed 5000 rpm) and the classification results of the electrostatic precipitator-collected ash by the classifier 10 (same as above). This is a table showing a comparison between incinerated ash and ash collected by an electric precipitator without being classified. I measured it. The medium powder in the same table is incinerated ash from which coarse powder or fine powder has been removed, and its particle size range is 10 to 80 μm.

Table 1 and FIG. 2 are diagrams showing the effects of this example in comparison with the case without classification. In the figure, "classified ash addition" means that the cyclone-collected ash from which coarse powder has been removed by the classifier 9 according to this example and the electrostatic precipitator-collected ash from which fine powder has been removed by the classification alio are used as a dehydration aid to secondary ``Unclassified ash addition J'' refers to the case where cyclone-collected ash and electrostatic precipitator-collected ash are used as a dehydration aid without classification for secondary dehydration. Addition”
The average particle size of the incinerated ash is approximately 22 μm according to Table 1, and the average particle size of the unclassified ash added is 11.6 μm. This is the ratio of the amount of water squeezed out through secondary dehydration to the amount of water contained in the sludge cake.The water content of the sludge cake that was subjected to primary dewatering used in this experiment was 82%. The ash addition rate on the horizontal axis is the addition ratio of incinerated ash to the weight of the primary dehydrated sludge cake. The ash addition rate required to obtain the same water reduction rate is higher than when unclassified with a diameter of 11.6 μm.In other words, when trying to obtain the required water reduction rate by secondary dehydration, By adding incineration ash from which fine particles have been removed as a dehydration aid, the required amount of ash can be reduced.
It goes without saying that the volume of the sludge cake produced will be smaller, making it easier to handle when incinerated or landfilled. The reasons why fine powder in incinerated ash impedes water permeability are: first, the finer the powder, the more spherical it becomes, making it difficult to form a "water channel"; It is thought that this is because fine powder enters the waterway J and blocks the waterway 1.As described above, in this example, the coarse powder is removed from the cyclone-collected ash, and the electrolytic collection m Fine powder was removed from the ash collected by the machine and used as a dehydration aid, but the average particle size of the ash collected by the cyclone after removing the coarse powder was 23.2 μm, and the ash collected by the electrostatic precipitator after removing the fine powder was 23.2 μm. Average particle size is 21.6μm
Therefore, even if any one of these is used alone as a dehydration aid, water permeability can be improved. In addition, the reason why coarse powder was removed from the cyclone-collected ash in this example is to remove silica sand and the like from the incinerator 4 when it gets mixed into the cyclone 5. It's not a hindrance. Therefore, cyclone-collected ash can be used as it is as a dehydration aid, or cyclone-collected ash and electrostatic precipitator-collected ash from which fine powder has been removed can be used as a dehydration aid.

"Effects of the Invention" Since the present invention takes advantage of the fact that the water permeability of incinerated ash depends on its particle size, the cost of sludge treatment is lower than when chemicals are used as dewatering aids. In addition, compared to the case where unclassified incineration ash is used as a dehydration aid, the same water reduction rate can be obtained with a smaller amount added, and therefore the sludge cake is easier to handle.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of one embodiment of the present invention;
The figure is a diagram showing the water reduction rate comparing the present invention and the conventional example.

Claims (5)

[Claims] (1) The primary dewatered sludge cake and dry powder are supplied to a granulator, and the granulator forms tempered sludge particles coated with the dry powder, and the tempered sludge particles are compressed to form a secondary powder. In the granulation and dehydration method for sludge to be dehydrated, the secondary dewatered sludge cake is incinerated in an incinerator, the incinerated ash discharged from the incinerator is collected by a cyclone and an electrostatic precipitator, and the incineration ash is collected in the cyclone. A method for granulating and dewatering sludge, characterized in that incineration ash is used as the dry powder. (2) The sludge granulation and dewatering method according to claim 1, wherein the dry powder is obtained by removing coarse powder from the incineration ash collected in the cyclone. (3) The sludge granulation and dewatering method according to claim 1, wherein the dried powder is obtained by removing fine powder from the incineration ash collected in the electrostatic precipitator. (4) The sludge granulation and dewatering method according to claim 1, wherein the incinerated ash collected in the cyclone and the incinerated ash collected in the electrostatic precipitator after removing fine powder are used as the dry powder. (5) The sludge according to claim 1, wherein coarse powder is removed from the incinerated ash collected in the cyclone and fine powder is removed from the incinerated ash collected in the electrostatic precipitator as the dry powder. Granulation dehydration method.