JPH03169399A - Granulating and dewatering method of sludge - Google Patents

Abstract

PURPOSE:To lower sludge treatment cost and improve dewatering ratio by using a drying powder with specified particle size in sludge granulating and dewatering processes consisting of granulating sludge into refined sludge granules after primary sludge dewatering while covering it with the dried powder as a dewatering agent and dewatering secondarily. CONSTITUTION:A sludge cake primarily dewatered by a primary dehydrator 1 is supplied to a granulating machine 2. At the same time, incinerated ashes which are discharged from an incinerator 4 and screened by a screening machine 9 to separate fine powder is also supplied to the incinerator via a storage tank 10. 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 incinerated ashes, from which fine powder is separated, and become refined sludge granules and are supplied to a secondary dehydrator 3. Here, the incinerated ashes as drying powder is screened by the screening machine 9 at about 500rpm rotation frequency at which the particles size becomes the highest water permeable size of about 10-100mum.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention involves firstly dewatering sludge generated in sewers, etc., and then granulating it into moist tempered sludge particles coated with dry powder as a dehydration aid. This relates to a method for granulating and dewatering sludge, which is subjected to secondary dewatering after drying. ``Prior art'' As a technology for dewatering sludge generated in sewers, etc. to produce a sludge cake with a low moisture content, a sludge cake that has undergone primary dewatering is Granulate sludge particles with a particle size of 1 to 10 mm while preventing thixotropy (thixotropic change).Dry powders such as diatomaceous earth, slaked lime, and incinerated ash are added to the surface of the sludge particles as a dewatering aid during granulation. Japanese Patent Publication No. 59-48160 describes a technique in which the tempered sludge particles are coated as sludge particles, and the tempered sludge particles are compressed and subjected to secondary dehydration to reduce the water content of the sludge cake to 60% or less. The basic idea of this method is to allow the water contained in the sludge cake to quickly reach the surface of the sludge particles when it is granulated and squeezed, and to take advantage of the high water permeability of the dry powder. A sludge cake with a low water content can be easily obtained in a short time by coating the sludge grains with dry powder to quickly guide the contained water that has reached the surface of the sludge grains to the filter medium. In the above technology, by improving the water permeability of the dry powder, it is possible to improve the drainage of the contained water when the tempered sludge grains are compressed and subjected to secondary dewatering. It is preferable to produce a sludge cake with an even lower water 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 the sludge, there is a strong need to reduce the required cost.6 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. It weighs several tons per day. Therefore, there was a problem in that the cost required for dewatering the sludge did not go down as expected.

The present invention solves the above problems and provides a method for granulating and dewatering sludge that improves the water permeability of dry powder at low cost. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventor has conducted repeated research and has found that the water permeability of dry powder depends on its particle size, thereby completing the present invention.

That is, the present invention supplies a primarily dehydrated sludge cake and dry powder to a granulator, forms tempered sludge particles coated with the dry powder in the granulator, and compresses the tempered sludge particles. In a method for granulating and dewatering sludge for secondary dewatering, dry powder having a particle size of approximately 10 to 10.0 μm is used as the dry powder, or prior to supplying the dry powder to a granulator, e.g. This is a sludge granulation and dewatering method that includes an additional step of removing fine particles less than approximately 15 μm in size. [Example 1 An example of the present invention will be explained using the drawings. FIG. 1 is a flowchart of one embodiment of the present invention. In this embodiment, incineration ash is used as the dry powder, and the sludge is first dehydrated by a
The sludge cake that has undergone primary dewatering is supplied to granulation I12. The granulator 2 is also supplied with incinerated ash discharged from the incinerator 4 and subjected to a classifier 9 to remove fine powder. In the granulator 2, the sludge cake is crushed to an extent that does not destroy the cavities (channels) therein, and is granulated into granules by transfer, and incinerated ash from which fine powder is removed from the surface of the sludge particles during transfer. is covered. The tempered sludge particles granulated by the granulator 2 and coated with incineration ash from which fine powder has been removed are supplied to the next secondary dehydration a3, where the water contained in the tempered sludge particles is further compressed and dehydrated. As the secondary dewatering machine 3 requires a stronger squeezing force, a press type or hydraulic diaphragm type compressing dehydrator is used. 6 After the secondary dehydration, the sludge and cake are fed into the incinerator 4. and incinerated. The incinerator 4 may be a fluidized bed incinerator,
Although a multistage incinerator may be used, a fluidized bed incinerator was used in this practical example.

The incinerated sludge 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 the cyclone 5 and stored in the storage hopper 7. The combustion gas is then electrostatically precipitated a! 6, where the fine incinerated ash is further separated and collected and stored in a storage hopper 8, and the combustion gas is released to the atmosphere.

The incinerated ash in the storage hopper 7.8 is passed through a classifier 9 and classified. As the classifier 9, in this embodiment, a rotary classifier that performs classification using centrifugal force and air resistance is used. The incinerated ash from which fine powder has been removed is stored in a storage hopper 10 and then supplied to granulation units 1 and 2. Next, Table 1 shows the results of classifying incinerated ash by the classifier 9 in comparison with unclassified incinerated ash. It was measured by size. As shown in the same table, when the rotation speed of the classifier was 5000 rpm, the average particle size of the fine powder used as a dehydration aid was 21.2 μm, but the particle size range was 10 to 100 μm. Further, when the rotation speed of the classifier was 6000 rpm, the average particle size of the fine powder removed was 16.7 μm, but the particle size range was 5 to 80 μm. Turning machine rotation speed 5000rpm and 6000rpm
The difference in Table 1 average particle diameter and classification ratio of the fines removed powder between M and M is due to the fact that a part of what was classified as fines at 5000rpm entered the fines removed powder side at 60QQrpm6. The figure shows the effect of this example compared to the case without classification. 5000rpm and 6000r in the diagram
pm indicates the case where the incinerated ash from which fine powder has been removed by the rotational speed of each classifier is used as a dehydration aid for secondary dehydration, and "unclassified" means that the collected incinerated ash is directly used as a dehydration aid without being classified. This shows the case where secondary dehydration is performed using Therefore, the average particle size of the incinerated ash becomes smaller in the order of 5000 rpm, 6000 rpm, and no classification. The water reduction rate on the vertical axis in Figure 2 is the ratio of the amount of water squeezed out through secondary dewatering to the amount of water contained in the sludge cake after primary dewatering. The moisture content of the primary dehydrated sludge cake used in this experiment was 82%. Further, the ash addition rate on the horizontal axis is the addition rate of incineration ash to the weight of the primary dehydrated sludge cake.

As is clear from Figure 2, in the case of 5000 rpm, 6
In the case of 000 rpm and in the case of no classification, that is, as the average particle size becomes smaller, the ash addition rate necessary to obtain the same water reduction rate increases. In other words, when trying to obtain the required water reduction rate through secondary dehydration, the amount of ash required is smaller if incinerated ash from which fines have been removed is added as a dehydration aid. It goes without saying that if the amount of ash added is small, the volume of the sludge cake after secondary dewatering will be small, making it easier to handle in incineration or landfill. The reasons why fine powder in incinerated ash impairs water permeability are: first, the finer the powder, the more spherical it becomes, making it difficult to form "channels"; and second, coarse powder particles form with each other. It is thought that this is due to the fine powder entering into the waterway 1 and clogging the waterway 1.As mentioned above, the fine powder classified at the rotation speed of the classifier at 5000 rpm, and the fine powder classified at 6000 rpm. Among the removed powder and unclassified powder, the fine removed powder classified at 5000 rpm has excellent water permeability, and its particle size ranges from 10 to 100 tim. It can be seen that it is effective to improve the dewatering efficiency in the secondary dehydration by using It is effective to improve the secondary dehydration efficiency by adding at least a step of removing fine powder from the incinerated ash prior to the step.In the same step, coarse powder from the incinerated ash may be removed at the same time. Furthermore, at least in the step of removing fine powder, if, on the safe side, for example, fine powder with a particle size of less than approximately 15 μm is removed, it is possible to improve the secondary dehydration efficiency. So, to make the cycle as closed as possible,
Although the case where the incinerated ash obtained by incinerating the sludge cake is used as a dehydration aid during secondary dehydration is shown, not only incinerated ash but also other dry powders can be used as the dehydration aid.7 [Effects of the invention] Since the present invention takes advantage of the fact that the water permeability of dry powder depends on its particle size, the cost of sludge treatment is lower than when chemicals are used as dewatering aids. Furthermore, compared to the case where unclassified dry powder is used as a dehydration aid, the same water reduction rate can be obtained with a smaller amount of addition, making the sludge cake easier to handle.

[Brief explanation of the drawing]

Figure 1 shows seven low seats of one embodiment of the present invention, and the second
The figure is a diagram showing the water reduction rate comparing the present invention and the conventional example.

Claims (4)

[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 method for granulating and dewatering sludge to be dehydrated, the dry powder has a particle size of approximately 1
A method for granulating and dewatering sludge, characterized in that dry powder of 0 to 100 μm is used. (2) Supply the primary dewatered sludge cake and dry powder to a granulator, form tempered sludge particles coated with the dry powder in the granulator, and compress the tempered sludge particles to form a secondary A method for granulating and dewatering sludge to be dehydrated, characterized in that a step of removing fine powder from the dry powder is added before the dry powder is supplied to a granulator. (3) The sludge granulation and dewatering method according to claim 2, wherein the step of removing fine powder from the dry powder removes fine powder having a particle size of approximately less than 15 μm. (4) The sludge granulation and dewatering method according to claim 1, 2 or 3, wherein incineration ash is used as the dry powder.