WO2006090954A1

WO2006090954A1 - Cement additive manufacture method for using bottom ash of thermoelectric power plant

Info

Publication number: WO2006090954A1
Application number: PCT/KR2005/001899
Authority: WO
Inventors: Ji-Whan Ahn; Gi-Chun Han; Kwang-Suk You; Young-Hwan Yu; Ki-Suk Han
Original assignee: Korea Institute Of Geoscience And Mineral Resources
Priority date: 2005-02-22
Filing date: 2005-06-18
Publication date: 2006-08-31
Also published as: KR100633781B1; KR20060093566A

Abstract

Disclosed herein is a method for producing a cement additive using bottom ash of a thermoelectric power plant comprising the steps of: cooling bottom ash of a boiler of a thermoelectric power plant with air without a cooling treatment with sea water; pulverizing the cooled bottom ash; screening the pulverized bottom ash to obtain a particle size fraction of 50 mesh or less by particle size classification; grinding the screened bottom ash by means of a ball mill to produce bottom ash powder; and mixing the bottom ash powder with portland cement in a mixing ratio of 5 to 25 wt%. According to the present invention, it is possible to emerge from the conventional method comprising drying of bottom ash of thermoelectric power plants and reclamation under sea water and to utilize the bottom ash as a cement additive to produce cement with improved long-term strength, low hydration heat and chemical resistance.

Description

CEMENT ADDITIVE MANUFACTURE METHOD FOR USING BOTTOM ASH OF THERMOELECTRIC POWER PLANT

Technical Field

[1] The present invention relates to a method for producing a cement additive, and more particularly, a method for producing a cement additive by combining cement with a pozzolan active material screened from bottom ash which is generated in a thermoelectric power plant to improve long term strength, low hydration heat and chemical durability of concrete.

[2]

Background Art

[3] Generally, thermal power generation refers to a method for generating electricity in a power generator by combusting coal to obtain energy, boiling water using the energy to generate steam, spinning a turbine connected to the power generator by the steam.

[4] The facility where the above-described power generation takes place is called "a thermoelectric power plant". Ash generated in a boiler of the thermoelectric power plant is largely divided into fly ash and bottom ash according to positions where they are formed. The fly ash is about 80 wt% and the bottom ash is about 20 wt%.

[5] The fly ash has a Blaine specific surface area of about 3,000 to 5,000 cm /g, which is similar to those of cement particles. The fly ash itself is not water-settable but is pozzolan active. Thus, water-soluble silica and alumina contained in the fly ash can slowly react with calcium hydroxide, produced upon hydration of cement, in an alkali atmosphere at room temperature to form hydrates of calcium silicate and calcium aluminate, which is non- water-soluble and stable compound for a long period of time.

[6] Also, due to its spherical, the fly ash can improve fluidity and thus, is widely used as an admixture of concrete.

[7] In other hand, the bottom ash is generally cooled by sea water and has a particle diameter of about 1 to 2.5 mm. It is collected at the bottom of the boiler and mostly dumped to an ash pond, after pulverization. Thus, though most of the bottom ash is disposed by reclamation, it may be used as an admixture like the fly ash, since it has been rapidly cooled from a high temperature of at least l,500°C. However, owing to high particle size and high salt content, it is not suitably used as an admixture. In addition, its non-uniform unburned carbon content should be addressed.

[8] Since the bottom ash of thermoelectric power plants has non-uniform and large particle size, it is less utilizable and mostly has been dumped into an ash pond furnished in the thermoelectric power plats which are conventionally located in a costal region.

[9] However, the established ash ponds are gradually filled up and there is difficulty in reclamation disposal. Also, it is hard to find a new place to build an ash pond due to opposition of local residents and environmental problems. Therefore, it is highly desired to recycle the bottom ash.

[10] There have been conducted researches to use the bottom ash of thermoelectric power plants as aggregate alternatives or cement additives. However, the prior art is not suitable for application to concrete in terms of economy, process and final product quality, since treatment processes such as drying is complicated chlorine component contained in sea water induces corrosion of steel reinforces.

[11] The bottom ash of thermoelectric power plants is known to have pozzolan reactivity. For use as an additive of concrete, chlorine content is essentially limited to prevent corrosion of steel reinforces. When the bottom ash of thermoelectric power plants is used to prepare a cement additive without any treatment, properties of concrete is deteriorated and thus, the bottom ash is not suitable for use to concrete.

[12]

Disclosure of Invention Technical Problem

[13] Thus, in order to solve the foregoing problems, it is an object of the present invention to provide a method for preparing a cement additive using bottom ash of thermoelectric power plants which is mixed to portland cement to improve long-term strength, low hydration heat and chemical resistance of concrete, while emerging from the conventional method comprising drying of bottom ash of thermoelectric power plants and reclamation under sea water.

[14] It is another object of the present invention to provide a method for preparing a cement additive using bottom ash of thermoelectric power plants, so that natural resources are saved, the cost for raw materials of cement is reduced and waste which has been reclaimed, is effectively used, increasing environmental benefit.

[15] It is a further object of the present invention to provide a method for preparing a cement additive using bottom ash of thermoelectric power plants by selectively screening bottom ash particles possessing pozzolan properties by means of particle size classification and grinding so that the bottom ash in ash generated in thermoelectric power plants can be used as a cement additive, thereby solving the conventional problems of bottom ash such as deterioration in pozzolan activity of bottom ash by reclamation under sea water, drying and chlorine in sea water.

[16]

Technical Solution [17] In order to achieve the above objects, the present invention provides a method for producing a cement additive using bottom ash of thermoelectric power plants comprising the steps of: [ 18] cooling bottom ash of a boiler of a thermoelectric power plant with air without a cooling treatment with sea water; [19] pulverizing the cooled bottom ash;

[20] screening the pulverized bottom ash to obtain a particle size fraction of 50 mesh

(0.3 mm) or less by particle size classification; [21] grinding the screened bottom ash by means of a ball mill to produce bottom ash powder; and [22] mixing the bottom ash powder with portland cement in a mixing ratio of 5 to 25 wt%. [23] Here, the bottom ash powder has a Blaine specific surface area of 2,000 to 6,000 cm

²/g.

Brief Description of the Drawings

[24] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: [25] [26] Fig. 1 is a flow chart showing the procedures of the method for producing a cement additive using bottom ash of a thermoelectric power plant according to the present invention; [27] Fig. 2 is a schematic diagram showing the procedures of the method for producing a cement additive using bottom ash of a thermoelectric power plant according to the present invention; and [28] Fig. 3 is a graph showing the XRD analysis result of bottom ash of thermoelectric power plant according to particle size. [29]

Best Mode for Carrying Out the Invention [30] The method for preparing a cement additive using bottom ash of thermoelectric power plants according to the present invention is explained in detail with reference to

Fig. 1 to Fig. 3. [31] Fig. 1 is a flow chart showing the procedures of the method for producing a cement additive using bottom ash of thermoelectric power plants according to the present invention; Fig. 2 is a schematic diagram showing the procedures of the method for producing a cement additive using bottom ash of thermoelectric power plants according to the present invention; and Fig. 3 is a graph showing the XRD analysis result of bottom ash of thermoelectric power plants according to particle size.

[32] Referring to Fig. 1 and Fig. 2, the method for producing a cement additive using bottom ash of thermoelectric power plants according to the present invention comprises the steps of cooling bottom ash 11 by air without using a cooling treatment with sea water, in which the bottom ash 11 in a boiler 10 is transported by means of a conveyer belt and cooled while passing through a cooler 100 (SlOO); pulverizing the bottom ash 11, which has been cooled through the cooler 100 and free fallen therefrom, using a pulverizer (Sl 10); screening the pulverized bottom ash 11 to obtain a particle size fraction of 50 mesh or less by particle size classification (S 120); grinding the screened bottom ash 11 using a ball mill 120 to obtain powder of the bottom ash 11 having a Blaine specific surface area of 2,000 to 6,000 cm /g (S 130); and mixing the bottom ash powder 11 with portland cement in a mixing ratio of 5 to 25 wt% based on the total weight of the cement composition (S 140).

[33] The term "particle size classification" used herein means classification of material according to chemical component, particle diameter, shape, color, density, radioactivity, magnetism and electrostatic property in a broad sense and operation to divide particles having a same density into two or more particle groups according to their particle diameters, also referred to as "classification".

[34] In the first embodiment, the present invention relates to a method for producing a cement additive characterized by screening bottom ash of thermoelectric power plants, which is a waste by-product, not a natural material, by particle size classification.

[35] According to the present invention, the bottom ash generated in thermoelectric power plants is cooled with air, in stead of cooling with sea water and screened to obtain a particle size fraction of 50 mesh or less, which is then ground and mixed with portland cement in a mixing ratio of 5 to 25 wt%.

[36] Table 1 shows the result of chemical analysis of bottom ash generated in thermoelectric power plants, after rapid cooling by air, according to particle size.

[37] As can be seen from Table 1, bottom ash mainly comprises over 90 wt% of SiO , Al

O , Fe O and CaO and has a specific gravity of 2.73.

[38]

[39] Table 1 Chemical composition of bottom ash from thermoelectric power plant according to particle size fraction (wt%)

[41] [42] Table 2 shows the result of the test to examine pozzolan reactivity of bottom ash from thermoelectric power plants, which has been ground to a particle size of 270 mesh or less, according to Korean Industry Standard (KS L 5405). The particle size fraction of bottom ash of 50 mesh or less satisfies over 90% of Korean Industrial Standards and thus is expected to be utilized as an additive for cement and concrete.

[43] [44] Table 2 Pozzolan reactivity of bottom ash of thermoelectric power plant according to particle size fraction (%)

[45]

[46] [47] Fig. 3 shows the XRD analysis result of bottom ash of thermoelectric power plants according to particle size. The bottom ash of thermoelectric power plant comprises mullite (Al Si O ) and SiO (quartz, tridymite, crystobalite) as main mineral phases,

6 2 13 2 and in addition, hematite (Fe O ) and anorthite [(Ca₅Na)(Al, Si) Si O ]. Particularly,

2 3 2 2 8

SiO exists as quartz and tridymite in a small particle size fraction of 50 mesh or less and exists as crystobalite in a larger particle size fraction than 50 mesh.

[48] Thus, as bottom ash of thermoelectric power plants has different chemical and min- eralogical properties according to particle size, according to the present invention, particles of 50 mesh or less having excellent pozzolan reactivity are screened and ground to be used as a cement additive.

[49] [50] Now, the present invention will be explained in detail using the following examples.

[51] [52] Example 1 [53] The bottom ash of thermoelectric power plants having the chemical compositions described in Table 1 was screened to obtain a particle size fraction of 50 mesh or less by particle size classification, ground in a ball mill to form powder of the bottom ash having a Blaine specific surface area of 4,000 cm²/g.

[54] The bottom ash powder was mixed with ordinary portland cement in a mixing ratio of 5 to 15 wt% based on the total weight of the composition and examined for compressive strength of mortar according to KS L 5105 (testing method for compressive strength of hydraulic cement mortar). The result is shown in Table 3.

[55] [56] Table 3 Compressive strength of mortar [57]

[58] [59] As a result, it was noted that when the bottom ash was mixed with the portland cement, the expression of compressive strength was increased along with improvement of physical packing property, as compared to the ordinary portland cement as the Comparative Example.

[60] [61] Example 2 [62] Following the same procedures as described in Example 1, bottom ash of thermoelectric power plants was processed into powder and examined for physical properties of cured or non-cured concrete.

[63] Table 4 shows concrete mixing design of the cement compositions according to the present invention, in which the bottom ash (BA) was mixed with ordinary portland cement (OPC) in a mixing ratio of 5, 10 and 15 wt% based on the total weight of the composition, and the ordinary portland cement alone as a comparative example.

[64] [65] Table 4 Mixing design of concrete

(C: Cement, S: Sand, G: Gravel, a: aggregate (S + G))

[67]

[68] The slump of concrete was increased when the bottom ash was mixed with ordinary Portland cement according to the present invention and high performance concrete showed high flowability. Particularly, concrete containing a large amount of a binder showed greatly improved flowability and drying shrinkage.

[69] Also, bottom ash of thermoelectric power plants contains a small amount of unburned carbon and thereby, has a relatively low adsorption of a chemical admixture. Thus, the amount of an admixture needed to obtain a same workability is lower than the amount which is needed when ordinary portland cement is used alone, causing reduction in unit quantity.

[70] The compressive strength of hardened concrete was examined and the result is shown in Table 5.

[71] [72] Table 5 Compressive strength of concretes [73]

[74] [75] As a result, it was noted that the examples according to the present invention showed a compressive strength equal to or better than that of ordinary portland cement.

[76] Therefore, according to the present invention, the bottom ash of thermoelectric power plant which is prepared by screening particles with high pozzolan activity having a diameter of 50 mesh or less and grinding them into fine powder to increase specific surface area can improve early and long-term strength reinforcement.

[77]

Industrial Applicability

[78] As described above, by the method for producing a cement additive using bottom ash of thermoelectric power plants according to the present invention comprising cooling the bottom ash of thermoelectric power plants, which has been dumped under sea water, with air and grinding the cooled ash, followed by mixing with cement, it is possible to improve long-term strength, low hydration heat and chemical durability of concrete, thereby lowering the unit cost of raw materials of cement and recycling waste effectively, otherwise which is buried.

Claims

[1] A method for producing a cement additive using bottom ash of a thermoelectric power plant comprising the steps of: cooling bottom ash of a boiler of a thermoelectric power plant with air without a cooling treatment with sea water; pulverizing the cooled bottom ash; screening the pulverized bottom ash to obtain a particle size fraction of 50 mesh or less by particle size classification; grinding the screened bottom ash by means of a ball mill to produce bottom ash powder; and mixing the bottom ash powder with portland cement in a mixing ratio of 5 to 25 wt%. [2] The method according to claim 1, in which the bottom ash powder has a Blaine specific surface area of 2,000 to 6,000 cm Ig.