JPH0538468A - Disposal method for coal ash - Google Patents

Abstract

PURPOSE:To separate efficiently unburnt coal content in coal ash. CONSTITUTION:The hydrophobic process and flotation process are carried out in a low pH zone formed by adding a pH adjuster 20 into water slurry of coal ash in the disposal method of coal ash consisting of the hydrophobic process for turning unburnt coal content hydrophobic by adding a collecting agent 22 into water slurry of coal ash and the floatation process in which foams are formed by adding a foaming agent 23 into water slurry, having the unburnt coal content attached to said foams and floating the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating coal ash (fly ash) used as a raw material for building materials.

[0002]

2. Description of the Related Art Coal ash is generated from a pulverized coal burning boiler or the like, and the coal ash contains unburned coal. However, this unburned coal content causes the following problems in using coal ash. For example, when using coal ash as a cement admixture, if a large amount of unburned charcoal is contained in the coal ash, an expensive air entraining agent (A
Since the E agent) is absorbed by the unburned coal, a large amount of air entraining agent is required. Further, when using coal ash as a raw material for an artificial lightweight aggregate or the like, if a large amount of unburned carbon content is contained in the raw material, the ignition loss (Ig-Loss) of the aggregate or the like increases.

Therefore, only coal ash containing a small amount of unburned coal is used as a raw material for concrete, etc., and coal ash containing a large amount of unburned coal is not used and is discarded as industrial waste.
However, it is uneconomical to dispose of coal ash that is effective as a raw material for building materials, etc., and a large amount of cost is required for its disposal.

Therefore, conventionally, a flotation method, that is, a hydrophobizing step of adding a collector to a water slurry of coal ash to make unburned carbon content hydrophobic, and adding a foaming agent to the water slurry to generate bubbles The unburned coal content is separated from the coal ash by a method of treating coal ash, which comprises a flotation step of generating the bubbles and attaching the unburned coal content to the bubbles to float.

The conventional method for treating coal ash has an advantage that a large amount can be treated, but on the other hand, it has a problem that unburned coal in the coal ash cannot be efficiently separated.

In view of the above circumstances, an object of the present invention is to make it possible to separate unburned coal in coal ash with high efficiency.

[0007]

Means for Solving the Problems In the flotation method of the present invention, the present inventors have found that the value of the hydrogen ion concentration index pH of the water slurry of coal ash has a significant influence on the separation efficiency of the unburned carbon content in the coal ash. I noticed this and investigated the reason, and obtained the following results.

That is, the electrical properties of the surface of the solid are largely due to the ζ potential of the particles of the solid in the state of the slurry mixed with water. Here, the ζ potential means a slip surface, that is, a potential of a boundary between a part that moves by sticking to a substance when a solid is moved in water and the other part.

In the case of a solid separated in water, if the solid is composed of one kind, all particles are charged to a certain ζ potential by the atmosphere. Moreover, if it is composed of a plurality of substances, the ζ potential will be unique to each substance, and if they have different charges, the ζ potential will be unique to each substance, and will also have different charges. Heteroaggregation may occur. Here, the hetero aggregation will be described. Each substance in water has a zeta potential, and + A comrades, -B comrades, and + C comrades having the same electric potential repel each other. On the other hand, different polarities, + A and −B, and −B and + C, are attracted to each other, resulting in heteroaggregation.
Further, in + A and + C having the same charge, if + A has a higher potential than + C, −B is more likely to cause stronger heteroaggregation with + A than + C.

Here, by adjusting the atmosphere of water around the substance particles to bring a substance closer to the isoelectric point, the repulsive force of the same substance can be weakened. Therefore, the isoelectric point will be described. The ζ-potential of a substance varies depending on the pH value of surrounding water. That is, if a positive (+) potential in the low pH region shifts to a negative (-) potential at a high pH value, a situation occurs in which the ζ potential becomes zero in the process. The pH value at which this ζ potential becomes zero is called the isoelectric point. At this isoelectric point, the substance can be said to be in an ideal state in which it does not lose its electrical repulsive force and aggregates.

When the repulsive force of the same substance weakens, the hetero-aggregation of different substances comrades weakens, and a situation where a specific same substance easily aggregates is created. Specifically, the dissimilar substances dispersed in water are ash and unburned coal, but both have their respective ζ potentials, and the same substances other than near the isoelectric point electrically repel each other. is doing. Also, depending on the situation, ash content and unburned coal content cause heterocoagulation. Here, by adjusting the atmosphere of water, which is the solvent of both, by weakening the repulsive force of the unburned coal comrades and weakening the heteroaggregation of ash and unburned coal, the cohesion of the unburned coal comrades and Separation of unburned coal and ash can be promoted.
That is, by keeping the pH value within the low pH range, the ζ potential of the unburned coal can be brought close to zero, and
Heteroaggregation of unburned coal and ash can be weakened.

[0012] The present inventor has made the following research results by noticing that the separation efficiency of the unburned carbon component in the coal ash changes depending on the order of adding the reagents. That is, the reagent is A: pH
In the case of the adjusting agent, B: dispersant, C: collector, D: foaming agent, B and C are allowed to be charged simultaneously as long as reagents that do not react with each other are used. In addition, B and C require a certain amount of time (condition application time) until they exert their effects on minerals, whereas D does not react with minerals, so condition application time is required in principle. Absent. Therefore,
B and C are input at a time different from that of D. Furthermore, if B and C react in the same way as reagents, considering their respective roles (dispersion of particles by B, hydrophobicization of particles by C), it is reasonable to add them in the order of B → C in separate tanks. Target.

For the above reasons, the order is B → C → D in principle, but consider the case where A is further added. The reason why A must be added first is the pH dependence of the scavenger C and the possible reaction of the pH adjuster A (acid or alkali) with other reagents. Since pH dependence is the most important factor controlling the collecting action of the scavenger, the pH adjuster must be added first. Also, regarding A and B, if there is a concern that the reaction of the reagents will be due to their respective roles, the order will be A → B. If there is no such possibility, simultaneous injection is also permitted. In any case, A must be thrown in before C. The present invention has been made based on the above findings.

This invention relates to an aggregating step of adding a collecting agent to a water slurry of coal ash to agglomerate unburned carbon content, and adding a foaming agent to the water slurry to generate bubbles, and the bubbles are the above-mentioned In a method of treating coal ash, which comprises a flotation step in which fuel coal is adhered and floated, in the low pH range by previously adding a pH adjuster to the water slurry of coal ash, the flocculation step, the flotation step The present invention is intended to achieve the above object by a method for treating coal ash characterized by being carried out.

[0015]

Function: A pH adjusting agent is added to the water slurry of coal ash to adjust the water slurry to a low pH range in advance. Thereafter, a collector is added to the water slurry to make the unburned carbon content hydrophobic, and a foaming agent is added to the water slurry to generate foaming, and the unburned carbon content is attached to the surface of the foaming. To surface.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings, in which the same reference numerals have the same names and functions. First, the first embodiment will be described. Ig-Loss 5.11% coal ash (raw material) M generated from a pulverized coal burning boiler or the like is supplied to the raw material charging tank 1 via a dust collector. In the pH adjusting tank 2, 5 g of the raw material M and water 4 in the water tank 5
00 ml is supplied and mixed by stirring to make a water slurry. The pH of this water slurry was 11.3, which was in the so-called high pH range. A pH adjusting agent 20 such as hydrochloric acid is added to this water slurry and mixed by stirring (pH adjusting step). The amount of the pH adjuster 20 added is gradually increased to a pH of 1 as shown in FIG.
Reduce from 1.3 to pH 2.0.

After completion of the pH adjusting step, the slurry is supplied to the hydrophobizing tank 3, a dispersant 21 such as water glass and a collecting agent 22 such as kerosene are added, and the mixture is stirred and mixed for 2 minutes (hydrophobizing step). .. This makes the unburned ash in the coal ash hydrophobic.

After completion of the hydrophobizing step, the water slurry is supplied to the flotation tank 4 to add a foaming agent 23 such as pine oil,
Stir mix for minutes. After that, air is blown from the bottom of the flotation tank 4 to generate bubbles, and agglomerates of unburned coal are attached to the surface of the bubbles to float (flotation step). The floating bubbles are taken out from the flotation tank 4 as an overflow. The unburned carbon component extracted as the overflow component is dehydrated by the dehydrator 6, sent to the cement firing kiln, etc., and the separated water is returned to the water tank 5. On the other hand, the ash is taken out from the bottom of the flotation tank 4 as a tail, dehydrated by the solid-liquid separator 7, and then used as a cement admixture and the separated water is returned to the water tank 5 (dehydration step). ).

The work for taking out this overflow is 5
Continued for a minute. As a result, the relationship between the yield A of the coal ash remaining in the flotation tank 4 and the Ig-Loss B was as shown in FIG. In this figure, the horizontal axis represents pH, the left vertical axis represents Ig-Loss (%), and the right vertical axis represents coal ash yield (%). As is clear from this FIG.
Is 4 or less, that is, although there is no difference in the yield of coal ash in the low pH range, Ig-Loss is extremely small, which is a value industrially preferable.

The second embodiment will be described. Mixing tank 30
210 g of Ig-Loss 13.69% coal ash in the raw material tank 1 and 750 Ml of water in the water tank 5 are supplied and stirred and mixed to form a water slurry. The pH of this water slurry is 1
It was 1.8. Hydrochloric acid as a pH adjuster 31 is added to this water slurry and mixed by stirring to lower the pH to 2.1 (pH adjusting step). After the completion of the pH adjusting step, 1 g of kerosene as the collector 32 is added to the water slurry, and the mixture is stirred and mixed for 30 seconds (hydrophobizing step).

Then, 0.5 g of pine oil as the foaming agent 32 is added to the water slurry, and the mixture is stirred and mixed for 30 seconds. Thereafter, air is blown from the bottom of the mixing tank 30 to generate bubbles, and at the same time, the generated bubbles are taken out as an overflow. This take-out work is continued for 5 minutes (flotation step). As a result, the coal ash taken out together with the bubbles was 78 g, and the Ig-Loss was 29.4%,
In addition, the coal ash remaining in the tank 30 was 139 g, and its Ig-Loss was 2.83%.

Next, a third embodiment will be described. This embodiment is carried out as follows using the apparatus of the second embodiment. 210 g of coal ash of Ig-Loss 2.18% is mixed with 750 ml of water to form a water slurry. The pH of this water slurry was 4.23, but this pH was lowered to 2.0 by using hydrochloric acid as a scavenger. Then, the second
When the same process as in the example was performed, the amount of coal ash in the overflow portion was 58 g, and the Ig-Loss thereof was 6.7.
%, And the coal ash remaining in the tank was 152 g.
The g-Loss was 0.48%.

[0023]

As described above, according to the present invention, since the pH adjusting agent is previously added to the water slurry of coal ash to bring it to a low pH range, the hydrophobicizing step, the flotation step and the like are carried out. A large amount of unburned coal adheres to the bubbles. Therefore, the unburned coal content in the coal ash can be separated extremely efficiently.

[Brief description of drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing another embodiment.

FIG. 3 is a graph showing the relationship between the amount of coal ash remaining in the floating tank, Ig-Loss, and pH in the first example. 20 pH adjuster 21 Dispersant 22 Scavenger 23 Foaming agent 30 pH adjuster 31 Dispersing agent 32 Scavenger 33 Foaming agent

Claims (2)

[Claims] 1. A hydrophobizing step of adding a collector to a water slurry of coal ash to make unburned carbon content hydrophobic, and adding a foaming agent to the water slurry to generate bubbles. In a method for treating coal ash, which comprises a flotation step in which fuel coal is adhered and floated, in the low pH range by previously adding a pH adjusting agent to water slurry of coal ash, the hydrophobicizing step, the flotation step A method for treating coal ash, which comprises: 2. The method for treating coal ash according to claim 1, wherein the low pH range is pH 4 or less.