JPH06247756A - Production of lightweight aggregate using dehydrated sludge as raw material - Google Patents

Abstract

PURPOSE:To utilize foamability of a sludge itself, to simplify a process and to improve cost effectiveness by cracking a dehydrated sludge, drying and firing at high temp. CONSTITUTION:A filter cake of the dehydrated sludge 50-65% in water content obtained by dehydrating a precipitate settled by a flocculant is cracked to below a prescribed particle size by a cracking machine. The cracked filter cake is dried to about 10% water content by a hot air of 150-200 deg.C in a hot air dryer. The dried sludge from which the fine particle portion if removed by sifting is rapidly heated to 1000-1300 deg.C and fired for 20-40min in a rotary kiln or the like to induce the internal foaming of the sludge due to aluminum in the flocculant, lime, iron or the like and the surface of the particle is fused and solidified. After the fired sludge is cooled, the sludge having an adequate particle size is sorted by a secondary screen. The sludge having below a fixed particle size together with the dust from the processes or the under size of the sorting process are humidified by adding water and granulated to the adequate particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for utilizing sludge generated in a water purification plant, sludge accumulated in a river, a lake or the like, sludge generated in a sewage treatment plant as a construction material and utilizing the sludge.
More specifically, it relates to a method for producing a lightweight aggregate using a dehydrated sludge obtained by dehydrating the above sludge as a raw material.

[0002]

2. Description of the Related Art In a water purification plant, sludge settling in a sedimentation tank or the like has been dehydrated and then most of it has been landfilled. In addition, sludge accumulated in rivers and lakes,
They were collected by mechanical means such as suction by a pump or excavated by a shovel, dried in the sun as they were, or mixed with cement or a coagulant to be solidified and then landfilled. Sewage sludge generated at the sewage treatment plant was also disposed of in landfill after dehydration. In addition, as another disposal method of sludge, after dehydrating it, mechanical drying to a certain water content,
It was used as a soil improver or as an organic fertilizer for green agriculture. On the other hand, in the case of lake sludge,
After drying, dehydrating, pulverizing, adding water, granulating, and sintering at a high temperature of 950 ° C. or higher to obtain a strong aggregate having a large specific gravity (Japanese Patent No. 1452239), For sewage sludge, dewater, dry and incinerate, then pulverize,
Approximately 1.05
There is a method of firing at 0 ° C. to obtain an artificial fine aggregate. Alternatively, a technique has also been proposed in which sewage sludge is mixed and molded with red mud or the like to form a lightweight aggregate (Japanese Patent Publication No. 42-22638).

[0003]

However, in the above-mentioned aggregate forming technique, the raw sludge is dried to the extent that it can be finely pulverized, and after fine pulverization,
Granulate to a certain particle size and calcinate, or further add another substance such as red mud, calcareous substance, clay substance and mold and fire at high temperature (Japanese Patent Publication No. 47-29710, 44-2383).
No. 9). In view of the above points, the present invention provides a method for economically producing a lightweight aggregate having a high strength without adding any substance other than these sludges, without further water addition or granulation operation. With the goal.

[0004]

The method for producing a lightweight aggregate according to the present invention is devised to achieve the above object, and includes a crushing step of crushing foamable dehydrated sludge by high temperature firing. A drying step of drying the crushed sludge to a water content of about 10% or less and a firing step of firing the dried product at a high temperature of 1000 to 1300 ° C.

The fine powder generated in each step can also be used as a cement raw material.

[0006]

EXAMPLES The present invention will be specifically described below based on examples.

In the sedimentation tank of the water purification plant, suspended solids (S
A coagulant is added so that S) easily aggregates and precipitates. Polyaluminum chloride (PA
C), polymer-based coagulants such as polyaluminum sulfate, and lime-based coagulants such as slaked lime are used. This coagulant greatly affects foamability. The precipitate is dehydrated with a gravity dehydrator or a pressure dehydrator to obtain dehydrated sludge.

The sludge dehydrated by the pressure dehydrator has a water content of 50.
~ 65% dewatered sludge, which, when discharged from the dehydrator, generally becomes a palm-sized filter cake.
This is used as a raw material. Do not add anything other than filter cake to the raw materials.

Each step until the product is obtained is as shown in FIG. 1, and the method of the present invention comprises a crushing step, a drying step,
It consists of a primary sieving process, a firing process, a secondary sieving process and a fine powder granulating process. (a) Crushing step A palm-sized filter cake is crushed by a crusher into particles having a predetermined particle size or smaller, for example, a diameter of 10 mm or smaller.

(B) Drying step By this drying step, the filter cake has a water content of 50 to 6
Dry until 5% is below about 10%. At this time, the water content of the dried cake greatly affects the strength of the product aggregate, and therefore it is important to reduce the water content as much as possible. As the dryer, a band hot air dryer is used, but a rotary hot air dryer or a vibration swing hot air dryer can also be used. The hot air temperature is preferably higher from the viewpoint of thermo-economical value, but is 150 to 150 due to the properties of sludge, for example, the content and combustibility of combustible substances such as organic substances
200 ° C is desirable.

(C) Primary Sieving Step The dried sludge is sieved before the firing step.

The purpose of the primary sieving is as follows. That is, in the subsequent firing step, the surface of the fired product is melted at a high temperature, so that they are easily welded. In particular, since the fine particles serve as the binder, it becomes difficult to operate the firing process. To avoid this, the dried sludge is sieved before the firing step. In addition, the dried sludge is sieved before the firing step for the purpose of removing fine particles according to the target particle size of the product aggregate after firing.

(D) Firing step The sludge is fired at a firing temperature of 1000 to 1300 ° C. Here, the important points are (1) internal foaming of sludge (filter cake), and (2) melting and solidification of the particle surface. Therefore, it is necessary that the sludge itself has the property of foaming, and the substance used as a coagulant in the sludge,
For example, the content of aluminum, lime or iron and its properties are important. By this foaming, weight reduction of the product is achieved. The strength of the product is ensured by the melt-solidified layer on the surface of the particles together with the foam structure inside.

In order to prevent the inter-particle welding during this time, it is important to perform rapid heating in the firing step, and a residence time of about 20 to 40 minutes is desirable in firing using a rotary kiln. As shown in FIG. 2, the structure of the particles obtained by the firing is composed of a core part (1) having a foamed structure and a melt-solidified layer (2) covering the surface of the core part (1).

As described above, in the method of the present invention, by utilizing the foamability of the sludge itself, it is possible to produce a predetermined lightweight aggregate without crushing the sludge or granulating the sludge before firing. it can.

(E) Secondary sieving step After the calcined product is cooled, it is sent to the secondary sieving step, where it is screened on a secondary screen, and those having an appropriate particle size are selected as products.

Here, the particle size is less than a certain value, for example, a diameter of 0.15.
Those having a size of less than or equal to mm are sent to the fine powder granulation step for treatment together with the dust and dust in the primary sieving step, the drying step and the firing step and the undersize of the primary sieving step.

(F) Fine powder granulation step In this step, water is added to a small amount of fine powder generated in each step to adjust the humidity and granulate to an appropriate particle size. The granulated product may be returned to the drying step or may be directly added to the firing step.

Further, the fine powder generated in each process can be used as a part of cement raw material in a cement manufacturing factory.

[0020]

Since the method for producing a lightweight aggregate according to the present invention is constructed as described above, it is possible to utilize the foamability of sludge itself, and it is not necessary to use an additive such as a foaming agent, which is economical. It is a typical lightweight aggregate manufacturing process.

Further, except for a small amount of fine powder granulating step, no sludge crushing step or granulating step is required, and the process is simple.

Furthermore, the use of fine sludge as a cement raw material can further simplify the process.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the present invention.

FIG. 2 is a cross-sectional view showing the structure of fired particles.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Oshio 3-28 Nishikujo 5-chome, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd.

Claims (2)

[Claims] 1. A crushing step of crushing foamable dewatered sludge by high-temperature calcination, a drying step of drying the crushed sludge to a water content of about 10% or less, and a dried product at a high temperature of 1000 to 1300 ° C. A method for producing a lightweight aggregate using dehydrated sludge as a raw material, which comprises a firing step of firing at. 2. The method according to claim 1, wherein the fine powder generated in each step is used as a cement raw material.