JPS623056A - Granulation for coal ash - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for granulating coal ash, and more particularly, it improves the granulation of coal ash by imparting water permeability to the granules formed. The present invention relates to a method for obtaining granulated coal ash that can prevent sludge formation and suppress the basicity of coal ash to a low level.

The invention further relates to an improvement for rapid and low cost granulation of coal ash.

Technical Problems of Prior Art and Invention Coal-fired power plants emit extremely large amounts of coal ash.
Its disposal has become an important issue.

If coal ash is to be disposed of in a landfill, it is stipulated that it must be disposed of in a managed disposal site as industrial waste.

In other words, most of the particles of coal ash, especially fly ash, are spherical, in the form of glass (5AL, O, -2SiO,), and are fine powders with an average particle size of about 20 to 30 μm. Laminated systems have extremely poor water drainage and lack so-called water permeability. For example, if they are used in landfills, there is a problem that they contain large amounts of rainwater and turn into mudslides, and they also have high basicity. Leachate from landfills has a high pH that exceeds wastewater standards, and the leachate has a negative impact on the environment.

Conventionally, many proposals have been made regarding solidifying coal ash so that it can be easily disposed of. A typical method is to mix coal ash with one or more of cement, lime, and gypsum (1-1), add water, and let it harden naturally. It has the disadvantage of being highly basic, with a high value of 11 or more, and also requires a long period of time for curing, requires a large amount of additive components, and has high processing costs.

OBJECT OF INVENTION □ Accordingly, an object of the present invention is to provide a method for granulating coal ash that can impart water permeability to waste granules and suppress the aqueous dispersion pg to a relatively low level. There is something to do.

Another object of the present invention is to provide a method by which coal ash can be solidified into granules quickly and easily at relatively low cost.

Still another object of the present invention is to provide a method for granulating coal ash, which can make coal ash usable as a civil engineering material.

Structure of the Invention According to the present invention, there is provided a method of producing coal ash, which is characterized in that waste acid, lime or slaked lime, and clay, which are by-produced by the sulfuric acid treatment of clay minerals, are blended into coal ash, and the blended composition is granulated. A granulation method is provided.

The blending amount of each component mentioned above differs depending on the use of the obtained granules, but it is based on solid content weight (based on coal ash).
Unless otherwise specified, parts and parts are based on weight), preferably 15 to 60 grams of waste acid, 2 to 8 grams of lime or slaked lime, and 5 to 40 grams of clay.

The present invention will be explained in detail below.

It is known that when coal is burned, 10 to 20% of the amount of coal used is generated as coal ash, and in pulverized coal combustion boilers used in thermal power plants, most of the coal ash is so-called fly ash. It will be done.

Judging from its chemical composition, coal ash belongs to the toepozolan material, and it combines with calcium hydroxide in the presence of water to form a water-insoluble silica-based compound (CaO-5iO,-
Al2O,-nH,0) is produced. Furthermore, it reacts with gypsum or cement to form ettringite (3CaO-
It produces a water-insoluble hydration product called A40s .5Ca S04.52 ``t o ).

Conventionally, the reaction used for curing coal ash is the above-mentioned pozzolan curing and ettringite curing, and the present invention also utilizes these pozzolan curing, gypsum curing, and ettringite curing, but the present invention The method is characterized in that it uses a combination of waste acid, lime or slaked lime, and clay, which are by-products of the sulfuric acid treatment of clay minerals, as raw materials for carrying out the above-mentioned curing reaction with coal ash. If necessary, industrial sulfuric acid may be used instead of the above-mentioned waste acid, and a calcium silicate composition such as cement may be used instead of lime.

The waste acids used in the present invention are those obtained in the process of producing activated clay, color developer for carbonless paper, silica, etc. by treating clay minerals such as acid clay and bentonite with sulfuric acid, and are free acids. In addition to sulfuric acid, it contains soluble sulfates such as aluminum sulfate, iron sulfate, magnesium sulfate, etc. The table below shows typical compositions of such waste acids.

Free sulfuric acid 0 to 57/aluminum sulfate 10 to 25? / iron sulfate
1 to 10? / magnesium sulfate 0.1
Other sulfates 0.1 to 19/
The waste acid used in the present invention is characterized by containing free sulfuric acid and aluminum sulfate in the form of a solution, and the lime used in combination is Alternatively, it has the characteristics of rapidly reacting with quicklime to effect ettringite-type hardening, and suppressing the pH of the granules after the reaction to a relatively low range.

In this sense, it is also important to use lime or slaked lime. However, it is worth noting that the amount of lime or slaked lime used in the method of the invention is considerably lower than that used in conventional methods.

In the present invention, in addition to the above-mentioned components, the use of clay is also important in providing rapid granulation solidification performance. That is, in coal ash, the silica component is vitrified together with AI and 03 components, and basic components include CaO, MfO, and N.
a, 0. However, it contains 0 and has poor rapid reactivity and almost no water retention. When water is mixed with coal ash and conventional curing agent components such as lime and cement, the blended composition does not retain its shape for several hours, but solidifies after being left for several days. state.

On the other hand, in the blending system of the present invention, the clay mineral itself acts as a binder as an excipient during granulation, and also in conjunction with the aforementioned waste acid and lime,
The blend immediately becomes ready for granulation, and the solidification reaction proceeds in the granulated state.

Clays include acid clay, bentonite, kaolin,
Aluminosilicate clays such as attapulgite, sabonite, halloysite, pyrofilamate, and zeolite can all be used. Generally oil absorption is 40 to 65rnl/1
Clays in the 00g range are preferred.

In the present invention, waste acid is 10 to 60% per coal ash,
In particular, it is preferable to use it in an amount of 25 to 55%; if it is less than the above range, granulation and solidification will be unsatisfactory, and the pH of the resulting granules will become too high. On the other hand, when the above range is exceeded, granulation tends to become difficult as a result of the liquid content being greater than the limit liquid absorption of the blended system. Lime or slaked lime is 2 to 8% per coal ash,
In particular, a relatively small amount such as 6 to 6 inches is sufficient; if the amount is less than the above range, rapid curing performance cannot be obtained.
Moreover, if the amount exceeds the above range, the advantages of the present invention, namely, the advantage of reducing the amount of lime used and lowering the pH of the granules, tend to be lost.

Clays are preferably used in an amount of 5 to 40% by weight, particularly 10 to 60% by weight, based on coal ash; if the amount is less than the above range, the rapid granulation solidification performance tends to be lost, so the above usage amount If it exceeds , with a small amount of compounding agent
The benefits of granulating coal ash will be lost.

In the present invention, the blending and granulation of these components can be carried out by various methods known per se. A suitable example of a blending method is dry mixing of coal ash, lime and clay;-
1 Mixing and granulation are performed while spraying waste acid onto the mixture. At this time, water as a granulation medium can be supplied as water contained in the waste acid, but of course, if necessary, it may be added separately from the water in the waste acid.

The mixing and granulation conditions are such that the whole is mixed relatively uniformly,
Any material that can be granulated to a desired particle size is sufficient, and particularly complicated conditions and operations are not required. For example, room temperature or ambient temperature is sufficient, and the reaction tends to generate heat, but this heat generation further accelerates curing, and waste heat generated at thermal power plants can be used for curing before and after solidification It may be used for. The resulting granules already have sufficient shape retention and strength, but by leaving the granules to stand, curing progresses and further strength, for example an increase in crushing strength, is brought about.

The particle size of granules varies depending on the application, but when used for applications such as landfill or ground improvement agents, generally 1.
It is desirable to have a particle size of from 15 to 15 mm, especially from 0 to 10 mm. The particle shape can also be arbitrary, such as spherical, columnar, or irregular, and depending on the particle shape, for example, a rolling granulation method, an extrusion granulation method, a mixed granulation method, etc. are employed.

Effects of the Invention The coal ash granules obtained by the present invention have a pH of 5.5 to 6.5 immediately after being obtained, and a pH of 6.5 after long-term immersion in water.
It has a pH of z5 to z5, and is characterized in that the pH of the granules is suppressed to a low level. Therefore, the attached Figure 1 is
Coal ash was processed into granules according to Examples and Comparative Examples shown below, and the granules were immersed in water, and the pH of each immersion water was measured over time.

From the results shown in Figure 1, compared to Example (4), in which the soluble basic components in coal ash are neutralized and stably fixed, Comparative Example CB) is more effective at leaching out these components. The fact that the pH of the granular treated coal ash is suppressed to a low level as an effect of the present invention is due to the fact that the pH of the immersion water increases significantly and exhibits a high pE over a long period of time due to the leaching of the components. yo〈understood. Moreover, the granular material according to the present invention has high crushing strength in water, does not disintegrate in water, and has outstanding water permeability.

Furthermore, according to the present invention, the resulting granules have excellent shape retention immediately after mixing and granulation, and the raw materials used are inexpensive and can be incorporated in relatively small amounts. It has the advantages of easy manufacturing operation, low cost, and suitable for processing large amounts of coal ash.

The present invention will be explained with the following examples.0 Example 1 By mixing coal ash with fine powder of acid clay (acid white) and powder of slaked lime as excipients, and then stirring while spraying waste acid, A method for granulating coal ash into granules (sand grains) with reduced water resistance and basicity will be described.

[Coal ash]

The coal ash used in this example was raw powder (FA) obtained from Tohoku Fly Ash. explain.

Clay: Clay, which is the excipient of the present invention, is particularly important for providing shape retention and improving granulation properties for granulating glassy materials such as coal ash, which have low oil absorption and poor water retention. It is an additive. In this example, acid white, which is inexpensive and easily available industrially, was used as the base.

Table 2: Calcareous material Calcareous material, which is also an excipient, is used as a reaction related to the granulation and hardening of coal ash) IJ ingite hardening, gypsum hardening,
It also acts as a reaction medium for pozzolan curing, and is important for accelerating the curing of granules.

As the limestone, slaked lime, Portland cement, and aurastonite which is a natural calcium silicate, which are industrially inexpensive and easily available, are used, but in this example, the oil absorption was 44.5 ml/100r.

Industrial slaked lime with an average particle size of 15 μm was mainly used as the excipient (/?).

Same as waste acid. Waste acid, which is an excipient, is sprayed onto a mixture of coal ash, acid white, and slaked lime. Stirring acts as a primary binder in the granulation of the formulation and at the same time as a reaction initiator for etho+Jnggite, gypsum and pozzolanic reactions to take place between the coal ash, calcareous and acid white, and thus the present invention. As excipient CC), it is an important additive as well as acid white. The excipient (C) used is
We mainly used waste acid, which is a by-product when treating acid white with sulfuric acid to produce activated clay and activated silica, which are refining agents for oils and fats. Note that this waste acid is ferrous sulfuric acid band (trade name: MIC5).
) is an industrially inexpensive product that is used in large quantities as a coagulant for water and sewage systems.

Table 6 [Granulation Method] Typical examples of the granulation method in this example will be explained. Into a mortar mixer with a capacity of 1157 tons (manufactured by Wakita, model KM-3T), coal ash primordial (FA), 2 DKy of commercially available industrial slaked lime, 1.1 Kq, and acid white 2.4 to 4 were added. After stirring and mixing thoroughly, remove the waste acid from the stirring system.
．． 5tC9BKo) was gradually pressurized and then stirred for 6 to 5 minutes to recover 66 kg of coal ash sand grains with a diameter of 2 to 10X.

The temperature of the recovered sand grains is raised to 40 to 60C by the heat of reaction.

Next, some of the recovered sand grains were left at room temperature for 6 to 6 hours, and after being left at room temperature for 6 days, they were immersed in water and visually observed to evaluate the presence or absence of disintegration and mudflow.

Note that the I series listed in Table 4 is a comparative example for clarifying the effects of this example.

[Physical property test]

■ Take the oil absorption sample powder 51, drop boiled linseed oil onto it, and set the end point when the whole becomes like a hard putty and can be rolled up into a spiral shape when mixed with a spatula. Calculate the amount of boiled linseed oil added per 1002 samples and calculate the oil absorption (
y+//100S').

Example 2 The sand grains prepared in Example 1 were evaluated for water resistance and basicity suppression effect.

Water Resistance Among the collected sand grains, in order to evaluate the water resistance of the granules that do not disintegrate when immersed in water over a long period of time when they come into contact with water, they were placed in a 20φ x 1200X glass column at approximately 800×. Filled with sand grains at a bed height of 1,000 ml, then pressurized water so that about 150 ml of water remained at the top of the packed bed, and then heated for 1 day, 6 days, 7 days, 60 days, 180 days and 36 days, respectively.
After immersion for 0 days, 150-immersion water was discharged from the bottom of each tube and its speed was measured. From this, the water flow rate (td / yprii) was calculated over time depending on the number of days of immersion. The water resistance required when the granules come into contact with water was evaluated.〇Basicity As a countermeasure against alkalinity in coal ash, when reusing coal ash and its processed materials in landfills, etc., the alkaline substances from coal ash elution is a problem.

Therefore, in addition to the water resistance evaluation test, the pH of the immersion liquid was measured to evaluate the basicity suppressing effect of coal ash according to the present invention.

The results of the water flow rate are shown in Table 5, and a typical example of the basicity suppression effect is shown in Figure 1.0 As is clear from the results in Table 5 and Examples 1 and 2, this According to the invention, by processing finely powdered coal ash into sand grains, it is possible to create sand grains with excellent water resistance that will not disintegrate or turn into mudslides even if immersed in water for a long period of time. It is well understood that the problematic basicity is also suppressed over a long period of time.

[Brief explanation of the drawing]

Figure 981 shows the change in basicity over time when sand grains obtained under the conditions of experiment number 1-1 of Example 1 and coal ash as a comparative example were immersed in water. The symbol (A) in the figure represents an example 12, and the symbol (B) represents a comparative example. Patent Applicant: Mizusawa Chemical Industry Co., Ltd. → Summary (5) Procedural Amendment Form December 11, 1985

Claims (2)

[Claims] (1) A method for granulating coal ash, which comprises blending waste acid, lime or slaked lime, and clay, which are by-produced by the sulfuric acid treatment of clay minerals, into coal ash, and granulating this blended composition. (2) Granulation according to claim 1, wherein 15 to 60% by weight of waste acid, 2 to 8% by weight of lime or slaked lime, and 5 to 40% by weight of clay are blended with coal ash on a solid content basis. Law.