JPH03288598A - Method for granulating and dehydrating sludge - Google Patents

Abstract

PURPOSE:To increase the coefficient of water permeability of incineration ash and to improve dehydration effect by heat-treating a dry powder at 800-1200 deg.C to coat the surfaces of the sludge particles from a sludge cake subjected to primary dehydration with the heat-treated powder and subjecting the obtained conditioned sludge particles to secondary dehydration. CONSTITUTION:A sludge cake subjected to primary dehydration is granulated to form sludge particles and the surfaces of these sludge particles are coated with a dry powder heat-treated at 800-1200 deg.C to prepare conditioned sludge which is, in turn, subjected to secondary dehydration. When incineration ash is heated at 800-1200 deg.C, the fine particles in the incineration ash are fused to be formed into coarse particles and the coarse particles becomes particles increased in unevenness as a whole. These coarse particles have a large specific surface area and, therefore, the capillary suction force thereof, that is, the force drawing out water from sludge particles thereof becomes strong and the secondary dehydration effect thereof becomes large. Further, the yield of incineration ash can be secured different from classification and the replenishment from the outside can be excluded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating sludge generated in sewerage systems, etc., and particularly a method for dewatering sludge to form a sludge cake and incinerating it. Regarding.

[Prior Art] Conventionally, in order to dehydrate sludge generated in sewers and the like to obtain a sludge cake with a low water content, a sludge cake that has been primarily dehydrated has been subjected to secondary dewatering. For example, it is disclosed in the magazine "Recycling and Utilization J 1981. VoL-4. However, in this method, the sludge cake that has undergone primary dewatering is subjected to secondary dehydration as it is, and this alone does not provide sufficient dehydration effect. Therefore, as a method for improving this, as disclosed in Japanese Patent Publication No. 59-48160, a dewatering aid is applied to the dewatered sludge cake, and mainly incinerated ash, diatomaceous earth, and slaked lime are added to the sludge cake. Dry powder with high water permeability such as calcium carbonate, pulverized coal, etc. is added in an amount of 10 to 100% of the dry weight of the sludge cake to form sludge particles while preventing fluctuation changes, and the surface of the sludge particles is dried as described above. The sludge was coated with powder to form tempered sludge particles, which were then compressed and compressed to reduce the moisture content of the sludge cake to 50% or less.

[Problems that Akira is trying to solve] However, in the sludge granulation and dewatering method described above, components such as incineration ash are used in an unadjusted state to create leggy sludge particles, which are then subjected to secondary dehydration. However, as a result of subsequent experiments by the inventors, the following problems were found.

Incineration ash contains a mixture of coarse particles and fine particles, and compared to coating sludge grains with this as-is and performing secondary dehydration, incineration ash is classified and fine particles are removed. It was found that coating and secondary dehydration had a greater dehydration effect. However, when incineration ash is classified to remove fine particles and use only coarse particles,
There has been a problem in that the yield balance is disrupted and there is often a shortage of quantity.

An object of the present invention is to provide a method for granulating and dewatering sludge that eliminates the above-mentioned drawbacks.

[Means for Solving the Problems] The present invention involves granulating a sludge cake that has undergone primary dewatering to form sludge particles, coating the surface of the sludge particles with dry powder to form tempered sludge particles, and This method of granulating and dewatering sludge for secondary dewatering is characterized in that dry powder is heat treated at 800 to 1200°C and then coated on the surface of sludge particles.

When incinerated ash is heated in the temperature range of 800-1200℃,
The fine particles in the incineration ash fuse with the coarse particles, and the entire coarse particles become grains with large irregularities. Such coarse particles have a large specific surface area, and therefore have a strong capillary suction force, that is, a force to draw out water from the sludge particles, and the secondary dewatering effect becomes large.

[Example] The present invention will be described in detail.

Figure 1 shows incineration ash at 900℃, 1000℃, and 1100'C.
It is a diagram showing the relationship between the addition rate of incinerated ash and the water reduction rate when sludge grains are coated with sludge particles heat-treated to various temperatures and subjected to secondary dehydration. FIG. 2 is a diagram showing the relationship between the heating temperature of incinerated ash and the hydraulic conductivity.

Table 1 shows the heating temperature and properties of the incinerated ash when the incinerated ash was heated.

Table 1 Heating temperature ('C) Average particle size (-) Sphericity (-) Raw powder 8.8 10.2Xlo-"90
0 9.5 9.61XIO-”1000
12.6 8.42xtO-”1100
15.3 8.30

This indicates that as the heating temperature increases, the amount of fine particles adhering to the coarse particles increases, and the unevenness of the coarse particles becomes larger. The heat-treated incineration ash was used to prepare tempered sludge grains, and the results of secondary dehydration are shown in the diagram shown in FIG. The incineration ash addition rate in FIG. 1 is the ratio of the added weight of incineration ash to the dry weight of the primary dehydrated cake. When the addition rate of incinerated ash is the same, the higher the heating temperature of incinerated ash, the greater the water reduction rate, and it can be judged that the dehydration effect becomes greater. Next, according to FIG. 2, the higher the heating temperature of the incinerated ash, the greater the hydraulic conductivity coefficient. A large hydraulic conductivity indicates that water can easily pass through the incinerated ash, which supports the results shown in Figure 1.

The incineration ash used this time will melt and solidify if heated above 1,200°C, and will no longer serve as a dehydration aid. Also, if the incineration ash is heated to 1,200°C or higher, no explosion will occur, meaning that heating is meaningless. There wasn't.

[Effects of the Invention] The present invention heats the incinerated ash and fuses the fine particles therein to the coarse particles to produce incinerated ash with large irregularities, so the permeability coefficient of the incinerated ash can be increased, and the dehydration effect can be increased. Moreover, unlike classification, the yield of incinerated ash can be secured and supply from outside can be eliminated.

[Brief explanation of drawings]

Claims (1)

[Scope of Claims] 1) granulating a sludge cake that has undergone primary dewatering to form sludge particles, and coating the surface of the sludge particles with dry powder to form tempered sludge particles;
A method for granulating and dewatering sludge in which the sludge is subjected to secondary dewatering, characterized in that the dried powder is heat-treated at 800 to 1200°C and then coated on the surface of the sludge particles. 2) The sludge granulation and dewatering method according to claim 1, wherein the dry powder is incineration ash.