JPH0690617A - Production of sintered soil from dehydrated sludge - Google Patents

Abstract

PURPOSE:To provide a process for producing a sintered soil useful as a horticultural soil, etc., having high commercial value by dehydrating sludge generated from a water purifying plant or deposited in rivers, lakes, marshes, etc., and using the dehydrated sludge as a raw material. CONSTITUTION:The objective process for producing sintered soil from dehydrated sludge comprises a disintegration step to crush dehydrated sludge to particle size of about 4-5mm, a granulation step to granulate the disintegration product in the form of granular pellet by a stirring granulator, a drying step to dry the pellet to a water-content of about <=10% and a baking step to the dried pellet at about 800-1100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reusing sludge generated from a water purification plant, sludge accumulated in rivers, lakes and marshes, and more specifically, a dehydrated sludge obtained by dehydrating the above sludge. The present invention relates to a method for producing sintered soil as a raw material.

[0002]

2. Description of the Related Art Most of the sludge settled in a sedimentation tank at a water purification plant has been dehydrated and then disposed of in landfill. Sludge (sludge) accumulated in rivers and lakes is collected by mechanical means such as suction with a pump and excavation with a shovel, and cement and coagulant are mixed in the sludge to solidify it before landfill disposal. It had been.
Then, as another disposal method of sludge, there is a method in which fertilizer is mixed with dehydrated sludge and used as field soil.

[0003]

However, the amount of sludge generated from the water purification plant tends to increase, and it is becoming more difficult to secure a landfill site every year. I can't expect. When fertilizer is mixed with dehydrated sludge and used as field soil, it may become a pollution source if the sludge contains harmful substances such as soluble aluminum and arsenic. There were limitations and in practice only very small amounts were used.

The present invention has been made in view of the above circumstances, and is of a product value using dehydrated sludge as a raw material, which is obtained by dehydrating sludge generated from a water purification plant or sludge accumulated in rivers, lakes and marshes. An object of the present invention is to provide a method for producing a sintered soil used for high horticultural soil, etc., and to effectively reuse sludge.

[0005]

Means and Actions for Solving the Problems In order to achieve the above object, a method for producing a sintered soil using dehydrated sludge as a raw material, according to the present invention, is deposited on sludge generated from a water purification plant, a river, a lake or the like. Is a method for producing a sintered soil that uses dehydrated sludge obtained by dewatering treated sludge as a raw material for horticultural soil, and a crushing step of crushing the dehydrated sludge to a particle size of about 5 mm or less and stirring the crushed material. Granulation step of granulating into aggregated pellets by a dry granulator, drying step of drying the pellet to a water content of about 10% or less, and firing step of firing the dried pellet at a firing temperature of about 800 ° C to 1100 ° C. It consists of

In the above crushing step, the degree of crushing of the dehydrated sludge is about 5 mm or less, more preferably about 4 mm or less, and if it exceeds the above particle size, it is granulated by a stirring type granulator in the subsequent step. The grain cannot be done efficiently.

In the granulating step, a stirring type granulator is used, which promotes agglomeration of pellets.

In the drying step, it is preferable that the pellets are dried for a relatively long time by a hot-air heating type dryer using a low temperature (for example, 150 ° C. to 200 ° C.) hot gas as a heat source. Intermolecular force or the like acts on the pellets to form a nodule structure having an excellent binding force, and it is possible to prevent the pellets from exploding or cracking in the subsequent firing step. If the moisture content of the pellets exceeds 10%, the hardness of the product obtained by firing will not be sufficient and the product will be easily deformed. It is preferable to dry to less than or equal to%.

The dried pellets are fired at the required firing temperature in the firing process, whereby the amount of soluble aluminum contained in the raw material is reduced to the target value or less required for the product, and A product with excellent water absorption and hardness can be obtained. The preferred firing temperature is 8
00 ° C to 1100 ° C, more preferably 900 ° C to 950
If the baking temperature is within the range of 0 ° C, the elution amount of soluble aluminum or the like required for the product cannot be sufficiently achieved at a firing temperature outside this range.

Thus, a pollution-free product having excellent water absorption, water permeability, and hardness, and in which the amount of harmful substances such as soluble aluminum eluted is reduced to a target value or less, is obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below.

In this example, a palm-sized filter cake (dehydrated sludge) obtained by dehydrating sludge settled in a settling tank to a water content of about 65% by a dehydrator installed in a water purification plant was used as a raw material. . The filter cake does not contain any additives such as a binder. Each step until a product is obtained is as shown in FIG. 1, and includes a crushing step, a granulating step, a drying step, a firing step and a sieving step.

(A) Crushing step In this step, a palm-sized filter cake was crushed by a crusher to a particle size of 4 mm to 5 mm or less.

(B) Granulation step In the granulation step, the crushed filter cake is mixed with an average particle size of 8 mm by using a stirring type granulator to form an aggregate structure required for plant soil. Granulated into pellets of about 15 mm.

(C) Drying Step In the drying step, the pellets are dried at a low temperature for a relatively long period of time so as to have a nodule structure having an excellent binding force. Pellets were put into a packed bed dryer using a water content of 10
% And dried to below.

(D) Firing step In the firing step, the dried pellets were fired at a firing temperature of 900 ° C to 1000 ° C using a rotary kiln.

Experimental data for examining the relationship between the temperature inside the kiln (firing temperature) and the water absorption, hardness and elution amount of soluble aluminum of the fired pellets are shown in FIGS. 2 and 3 also show experimental data obtained by performing the previous drying step in the same rotary kiln as this step and under the same conditions.

FIG. 2 shows the relationship between the water absorption rate of the fired pellets and the temperature inside the kiln. As is clear from the figure, the higher the temperature inside the kiln, the lower the water absorption rate of the fired pellets. There is.

FIG. 3 shows the relationship between the hardness of the fired pellets and the temperature inside the kiln. As is clear from the figure, the higher the temperature inside the kiln, the harder the fired pellets.

FIG. 4 shows the relationship between the amount of soluble aluminum eluted from the fired pellets and the temperature inside the kiln.
(In addition, as the sample for the elution analysis, a fired pellet finely pulverized to a particle size of 0.5 mm or less was used as a test, and pH 4 and sodium acetate N were used as the solvent.) As is clear from the figure, the kiln was The amount of soluble aluminum eluted tends to decrease as the internal temperature increases.

As is apparent from FIGS. 2 to 4, if the firing temperature is maintained at about 950 ° C., a product having a low elution amount of soluble aluminum and excellent water absorption and hardness can be obtained.

Exhaust gas used in the drying step and the firing step is discharged out of the system through a large-sized high-performance dust collector, thereby making the plant pollution-free.

(E) Sieving Step The pellets fired in the firing step are cooled and then screened to select those having an appropriate particle size as the product. On the other hand, oversize and undersize are crushed to an appropriate particle size and then returned to the crushing step. As a result, the product yield can be improved.

[0024]

INDUSTRIAL APPLICABILITY According to the present invention, the dehydrated sludge having a particle size of about 5 is used in the method for producing the sintered soil using the dehydrated sludge as a raw material for horticultural soil.
mm, a crushing step of crushing to less than mm, a granulating step of granulating the crushed material into aggregated pellets by a stirring granulator, a drying step of drying the pellets to a water content of about 10% or less, and a dried step Since it consists of a firing step of firing the pellets at a firing temperature of about 800 ° C to 1100 ° C, the water absorption and water permeability are excellent, the surface hardness is high, and the elution amount of harmful substances such as soluble aluminum is reduced below the target value. , High quality products with no pollution can be obtained. Therefore, according to the present invention,
The sludge generated in the water purification plant can be effectively reused, which in turn can contribute to a reduction in the amount of sludge to be disposed of.

It is needless to say that the sintered soil produced by the present invention may be used for purposes other than horticultural soil, for example, construction materials such as aggregates and soil improving materials.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a water absorption rate of a fired pellet and a firing temperature.

FIG. 3 is a diagram showing the relationship between the hardness of fired pellets and the firing temperature.

FIG. 4 is a diagram showing a relationship between a soluble aluminum elution amount of a fired pellet and a firing temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nishiro Fujita 5-3-28 Nishikujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd. No. Hitachi Shipbuilding Co., Ltd. (72) Hiroyoshi Yamazaki Inventor Hiroyoshi Yamazaki 5-3-8 Nishikujo, Konohana-ku, Osaka City (72) Inventor Hiroshi Okada 5-6 Kitaurawa, Urawa-shi, Saitama Foundation Corporate Saitama Environmental Conservation Public Company

Claims (1)

[Claims] 1. A method for producing a sintered soil to be used as horticultural soil, etc., using dehydrated sludge as a raw material, which is obtained by dehydrating sludge generated from a water purification plant or sludge accumulated in rivers, lakes and marshes.
A crushing step of crushing the dehydrated sludge to a particle size of about 5 mm or less, a granulating step of granulating the crushed material into aggregated pellets by a stirring granulator, and a drying step of drying the pellets to a water content of about 10% or less. And the dried pellets at a firing temperature of about 800
The manufacturing method of the sintered soil which uses a dehydrated sludge as a raw material which consists of a baking process of baking at ℃ -1100 ° C.