KR20190080209A - Flowable fill using circulating fluidized bed combustion ash - Google Patents

Abstract

A high flowable filling material comprises circulating fluidized bed combustion ash containing plaster and free lime and sand.

Description

{Flowable fill using circulating fluidized bed combustion ash}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength copper filler, and more particularly, to a high-strength copper filler recycled from a circulating fluidized bed boiler ash.

Fly ash, which is known as a by-product of coal-fired power generation, is actively used as an admixture of concrete. Bottom ash is also used in various fields such as ground-supporting materials. Also, the trend of recycling by using these byproducts is gradually increasing, and related research is increasing in an attempt to improve the engineering performance of construction materials utilizing the environmental preservation.

Prior art 1 discloses an eutectic filler prepared by mixing fly ash, cement and sand as an intrinsic filler. Prior art 2 discloses an intrinsic copper filler to which anthracite bottom ash is applied. It is a mixture of coal ash generated from general chemical power plants and has a certain degree of fluidity, so it can be used as backfill material. However, since there is a disadvantage that the volume stability may be low due to the long condensation time, there is a problem that a large amount of cement must be mixed to maintain the volumetric stability.

The circulating fluidized bed combustion system has a small effect on combustion even when the type of fuel, ash and moisture content are changed, and it uses a wide range of fuels for all combustible materials such as intrinsic carbon, low grade coal, and waste which are not suitable for conventional combustion furnaces such as pulverized coal combustion It is possible. In addition, since the combustion furnace temperature can be maintained at about 800 ° C to suppress the formation of nitrogen oxides and the integrated desulfurization can be performed in the furnace by the limestone, there is an increasing tendency of the thermal power plants of the circulating fluidized bed combustion type.

One of the greatest advantages of the circulating fluidized bed combustion system is that desulfurization in the combustion chamber is possible by reaction with limestone during combustion. When limestone is injected into the combustion chamber and burned together with coal, limestone in the combustion gas reacts in the furnace to remove sulfur in the combustion gas, and gypsum is generated and discharged together with coal ash. As a kind of dry desulfurization concept, the concentration of sulfur oxides in the exhaust gas can be easily controlled by regulating the injection amount of limestone according to the sulfur content of the fuel. With this process control, the coal ash in the circulating fluidized bed combustion system is discharged with a high CaO content, which is completely different from the F-grade coal ash produced in the pulverized coal combustion method of the general thermal power plant.

Coal materials in the circulating fluidized bed combustion system have very different mineral composition, chemical composition and form due to the difference of combustion method from the pulverized coal material. In the circulating fluidized bed combustion method, limestone is artificially added to desulfurize the furnace. In this case, the excess lime component that did not participate in the desulfurization reaction is present in the form of CaO compound in the fly ash. When a material containing a large amount of CaO compound is used as a raw material for a remicon admixture or a cement, the Free-CaO component causes problems such as abnormal condensation of the concrete, loss of slump, increase of the amount of retarder used, durability deterioration, Expansion, cracking, and the like, thereby lowering the physical properties.

In the case of fly ash generated from pulverized coal-fired thermal power plants, more than 80% of them are used as raw materials for remicon admixture and cement. On the contrary, about 1500 tons / year of coal is discharged from 15 power plants in Korea, Boiler coal ash can not be recycled because it does not meet KS standard (KS L 5405). Various recycling technologies are needed.

It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as adhering to the prior art already known to those skilled in the art.

(Prior Art Document 1) Won Jong Pil, Shin Yoo Gil. A Study on the Durability Characteristics of Low Strength Highly Active Copper Filler Using a Large Volume of Fly Ash. Journal of the Concrete Institute 12 (1): Korea Concrete Institute. 2000.2, 113-122. (Prior Art Document 2) Kim Sung Soo, Dong Hyun Kim, Performance Evaluation of Low Strength High-Fluidity Copper Filled with Anthracite Bottom-ash. Proceedings of the Korea Concrete Institute Conference. 2001.11, 109-114.

SUMMARY OF THE INVENTION The present invention has been conceived to solve such problems, and an object of the present invention is to provide a high-strength copper filler which does not require a compaction action by recycling coal ash in a circulating fluidized bed combustion system.

In order to achieve the above object, the high-strength copper filler according to the present invention includes fly ash and sand containing gypsum and free lime.

The high-strength copper filler may further include a reaction stimulant.

The reaction stimulant may be cement or sodium carbonate.

The amount of the reaction stimulant may be 5 to 15 parts by weight based on 100 parts by weight of the circulating fluidized bed boiler fly ash.

The high-strength copper filler may be one which is cured by underwater curing.

The high-strength copper filler may have an expansion ratio of 1% or more by self-decomposition.

The bottom ash of the circulating fluidized bed boiler including the fly ash and the gypsum and the free lime of the circulating fluidized bed boiler including the high-quality copper gypsum and the free lime according to the present invention is included.

The high-strength copper filler may further include a reaction stimulant.

The reaction stimulant may be cement or sodium carbonate.

The amount of the reaction stimulant may be 5 to 15 parts by weight based on 100 parts by weight of the circulating fluidized bed boiler fly ash.

According to the high-strength copper filler according to the present invention, by using the circulating fluidized-bed boiler fly ash which is discharged in a large amount at present, it is possible to expand the recycling method which is limited to concrete.

In addition, it has an expansive auto-degradability, which is effective when it is used in a sinkhole or abandoned mine area that requires expansive autolysis in the long term.

1 is a graph showing particle size distributions of fly ash, bottom ash, cement and sand used in the present invention.
2 is a graph showing the results of X-ray diffraction analysis of fly ash and bottom ash used in the present invention.
3 is a graph showing the flowability measurement results of the high-strength copper filler according to the present invention.
4 is a graph showing the results of intrusion resistance measurement of an intrinsic copper filler according to the present invention.
5 is a graph showing settlement measurement results of the high-strength copper filler according to the present invention.
6 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (specimen B) according to the present invention.
7 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (specimen B-C15) according to the present invention.
8 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (Specimen B-SC15) according to the present invention.
9 is a graph showing the compressive strength of the high-strength copper filler according to the present invention.
10 is a photograph showing the self-decomposition state of the B specimen according to the present invention after 91 days underwater curing.
11 is a graph showing the amount of heavy metal elution of the filler according to the present invention.
12 is a graph showing the pH change for the high-copper filler according to the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified, and that other specific features, regions, integers, steps, operations, elements, components, and / And the like.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Hereinafter, an intrinsic copper filler according to the present invention will be described with reference to the accompanying drawings.

Circulating Fluidized Bed Combustion (CFBC) is capable of suppressing NOx generation by low temperature combustion at 850 ~ 900 ℃ and can use various fuels.

As a result, the generation of circulating fluidized bed boiler ash is also increasing. However, since it contains a large amount of free-CaO and sulfate ions, the initial reactivity is fast and the calorific value is high.

The inventors of the present invention have completed the present invention by studying a method of using free calcium oxide as a high-magnetic filler by using properties of high self-hydraulicity.

Controlled low-strength material (CLSM) is a highly flowable filler that does not require compaction. Controlled low-strength material (CLSM) requires low strength for re-excavation and high fluidity for self-layering. Trenches with abandoned mines, complex trenches with pipes, and waterproofing materials can be used as fillers on the back of underground retaining walls that are difficult to compaction. As a substitute for ground, it should have fluidity to the extent that it does not require compaction basically, and it is designed to have low intention in consideration of re-excavation.

In recent years, sink holes have been issued due to subsidence in urban areas. The cause of subsidence can be classified into two types: natural phenomena such as crustal fluctuation and sea level rise, excessive flooding of underground water, subsidence due to burial load, and artificial phenomenon caused by excavation. Especially, the ground subsidence occurred in the urban area was caused by the soil loss caused by the tunnel excavation, the aged phase, the leakage from the sewage pipe, the ground subsidence due to the erosion and loss of the soil supported by the sewage pipe, Settlement due to soil loss of natural ground, settlement of adjacent ground due to drainage of groundwater due to excavation work, and ache due to failure of excavation work.

In particular, the present invention is a high-strength copper filler capable of performing such sinkhole backwashing. The high-strength copper filler according to the present invention may include a circulating fluidized-bed boiler ash, or may further contain sand or the like as needed. Since the circulating fluidized bed boiler ash itself may be insufficient in hydration reactivity, it is possible to use additional reaction stimulants to control the reaction.

The circulating fluidized bed boiler ash is different from the conventional pulverized coal combustion type coal ash. Compared with the pulverized coal combustion system, the circulating fluidized bed boiler has more coal ash generated by the large amount of limestone introduced during the desulfurization process. Compared to coal ash generated from pulverized coal combustion boiler, the biggest difference in physical properties of coal ash produced in a circulating fluidized bed boiler is in chemical composition. In a circulating fluidized bed boiler, the ratio of calcium to sulfur (Ca / S) is increased to about 2.0 to 2.5 in order to increase desulfurization efficiency. Therefore, unreacted CaO and CaSO ₄ produced in the desulfurization process constitute a large part of the chemical composition in the coal ash, and the content of the crystal phase is higher than that of the coal ash produced in the pulverized coal combustion type boiler.

In particular, the free calcium oxide (CaO) component has self-hardness when mixed with water, and thus affects the coagulation time as a self-hardening agent. Therefore, there is an advantage that less irritant can be used than when coal ash of a pulverized coal combustion type boiler is used.

In addition, since the gypsum (CaSO ₄ ) component has swelling property, it is self-decomposed while expanding from a long-term viewpoint, especially when it is used as a filler in sink holes and the like. Therefore, the present invention can be applied in terms of maintaining the state of charge for the used space without maintaining the strength.

Hereinafter, the present invention will be described in more detail with reference to examples. The flowability and the environmental impact of high flowability filler were measured by using circulating fluidized bed boiler fly ash and bottom ash produced in Korea.

1. Materials used and content

Using the circulating fluidized-bed boiler fly ash and bottom ash from the Gunsan Thermal Power Plant and designing high-permeability filler by using commercial type 1 portland cement, sodium carbonate powder, ordinary sand (specific gravity 2.65, absorption rate 0.27%, granulation rate 2.95) Respectively.

The components and contents of each specimen are shown in Table 1.

division water Fly ash Bottom ash sand cement Sodium carbonate S 1.4 One 0 2.5 0 0 S-C05 1.4 One 0 2.5 0.05 0 S-C10 1.4 One 0 2.5 0.1 0 S-C15 1.4 One 0 2.5 0.15 0 S-SC05 1.4 One 0 2.5 0 0.05 S-SC10 1.4 One 0 2.5 0 0.1 S-SC15 1.4 One 0 2.5 0 0.15 B 1.4 One 2.5 0 0 0 B-C05 1.4 One 2.5 0 0.05 0 B-C10 1.4 One 2.5 0 0.1 0 B-C15 1.4 One 2.5 0 0.15 0 B-SC05 1.4 One 2.5 0 0 0.05 B-SC10 1.4 One 2.5 0 0 0.1 B-SC15 1.4 One 2.5 0 0 0.15

Each component is in a weight ratio, and basically, a test piece was prepared by mixing in a weight ratio based on a circulating fluidized bed boiler fly ash. Basically, specimens using fly ash and sand were classified into S series, and specimens using fly ash and bottom ash were classified into B series. Basically, the water content is 1.4 times as much as the fly ash, and the sand and bottom ash are mixed 2.5 times. Cement mixed with sodium chloride and sodium carbonate were mixed in a ratio of 0.05-0.15.

2. Measurement of particle size distribution

1 is a graph showing particle size distributions of fly ash, bottom ash, cement and sand used in the present invention. Each particle size distribution ranged from a few micrometers to a few hundred micrometers. Fly ash corresponds to coal ash obtained by collecting in a circulating fluidized bed boiler. Unlike fly ash, bottom ash corresponds to coal ash obtained from the bottom of a circulating fluidized bed boiler.

3. Component analysis and X-ray diffraction analysis

Table 2 is an ingredient analysis table for the main components of CFBC ash used in the present invention. Each content is% by weight.

ingredient CaO SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ MgO SO ₃ K ₂ O TiO ₂ P ₂ O ₅ Loss on
Ignition
(Ignition loss) CFBC
Fly ash 23.2 29.7 13.8 6.6 1.6 6.9 1.5 One 1.1 14.7 CFBC
Bottom ash 51.1 11 6.8 4.5 1.3 19.9 0.3 0.5 0.9 3.7

As shown in Table 2, the CFBC fly ash and bottom ash used in the present invention are derived from Gypsum, CaSO ₄ .2H ₂ O and anhydrite (CaSO ₄ ) A large amount of sulfuric acid ion (SO ₃ ) is found.

2 is a graph showing the results of X-ray diffraction analysis of fly ash and bottom ash used in the present invention. As a result, it can be seen that there are more G and G components in bottom ash than fly ash. In addition, it can be seen that the hydration reaction is possible because there are many free calcium oxides (free-CaO) (L) and calcium hydroxide (portlandite, Ca (OH) ₂ ).

4. Flow measurement (ASTM D6103)

The fluidity of each specimen was measured. The fluidity should be a high fluidity filler and satisfy the basic fluidity value. 3 is a graph showing the flowability measurement results of the high-strength copper filler according to the present invention. In all formulations, the minimum fluidity suggested by the ACI R229-13 standard was more than 10 cm in flowability. S series (fly ash + sand) showed a large difference in fluidity at ambient temperature and high flowability of 20cm when measured at 20 ℃. In the case of the B series, it can be seen that the fluidity does not change significantly depending on the temperature. It can be seen that the fluidity change is large depending on the amount of the reaction stimulant incorporated.

5. Condensation time measurement (ASTM C403)

In the case of high-permeability filler, there is no limitation of the condensation time. The intrinsic resistance of the high permeability filler was measured to determine the setting time. 4 is a graph showing the results of intrusion resistance measurement of the high-strength copper filler according to the present invention. In the case of the conventional high-strength copper filler, the coagulation time tends to be long to have fluidity. In the present invention, free calcium oxide contained in CFBC ash acts as a magnetic hardener. Therefore, there is an advantage that the condensation time is shortened. If the settling time is shortened, the penetration resistance is increased.

As a result, it can be seen that when cement is used as a stimulant, condensation is promoted and penetration resistance is increased. On the other hand, as the content of sodium carbonate is increased in the S series, the condensation is delayed and the penetration resistance is reduced.

6. Volumetric stability evaluation (ASTM C232)

The settlement amount was measured to evaluate the volumetric stability of the high - permeability filler. 5 is a graph showing settlement measurement results of the high-strength copper filler according to the present invention. The typical settlement criteria is about 5% of final settlement. In the case of S series, settlement amount was more than 5% in most formulations and the settling amount deviation was large according to the incorporation of reaction stimulant. However, even if the settling amount is higher than the reference value, it can be used as an intrinsic filler because of its high self-expandability. In the case of the B series, the settlement amount was almost the same regardless of the temperature. Also, there was no deviation in settlement due to incorporation of reaction stimulant.

7. Crystallographic analysis

B-C15 and B-SC15 specimens of the B series were analyzed for the effect of the reaction stimulant of the high-permeability filler. In the case of the S series, since the sand is mixed, it is very difficult to analyze the crystal phase. 6 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (specimen B) according to the present invention. 7 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (specimen B-C15) according to the present invention. 8 is a graph showing a crystal phase analysis result (XRD peak analysis) of an intrinsic copper filler (Specimen B-SC15) according to the present invention.

The aging period was 7 days and 28 days, and it was proceeded with underwater curing and curing curing in water. If no stimulant is added, Ettringite is active. Ettringite caused the swelling as acicular hydrate, and it was found that this phenomenon became more active when water was cured. When cement is used, the amount of ettringite is reduced and the expansion can be reduced and stabilized. When sodium carbonate is used, thenartite (Na ₂ SO ₄ ) occurs as well as Ettringite. Since this crystal is an unstable hydrate that is easily dissolved in water, the microstructure may become weaker thereafter.

8. Compressive strength measurement (ASTM C109)

The compressive strength of the high - strength copper filler was measured. The high-strength copper filler should be capable of re-excavation by maintaining low strength. The limit of strength should be less than 10Mpa which can be re-excavated through equipment such as Baek-Ho and the strength to be able to walk by people should be maintained. 9 is a graph showing the compressive strength of the high-strength copper filler according to the present invention. In the case of underwater curing, the S series satisfied the range of compressive strength, but the B series had a low compressive strength and thus difficult to use. In the case of sealing curing, all the samples satisfied the strength range. However, in the case of underwater curing in Fig. 9, it can be seen that there is no intensity value after 91 days. This is because the formation of Ettringite expands and self-decomposes. 10 is a photograph showing the self-decomposition state of the B specimen according to the present invention after 91 days underwater curing. As shown in FIG. 10, it can be decomposed by magnetic expansion after 91 days. In this case, even if it does not have a certain strength, it may be useful when a material such as a sinkhole is needed. Self-expansion can be caused by ettringite produced by the gypsum component contained in the CFBC ash. It is in the form of a needle, which prevents the distance between particles from decreasing. Self-decomposition by expansion can occur when the expansion ratio is 1% or more. In this case, although it does not have strength, expansion is necessary when it is used as a mine tool or sink hole filler material, so that it is possible to use it more efficiently.

  In the case of sealed curing, the strength increased by the use of cement in both S and B series. B-C10 and B-C15 specimens were steadily increased up to 91 days, while specimens B and C were cured. It is stabilized in the long term by the use of cement. The S-SC05 specimen shows longer-term strength than the S specimen without the reaction stimulant in the S-type seal curing. However, if the content is increased, the initial strength is decreased, which is not effective.

9. Measurement of Heavy Metal Elution Characteristics

To ascertain the characteristics of leaching of heavy metals in the high - boiling filler, the amount of heavy metal leaching was measured by TCLP (Toxicity Characteristic Leaching Procedure) test method according to Method 1311 of US Environmental Protection Agency. 10 is a graph showing the amount of heavy metal elution of the filler according to the present invention. In the S-type specimens, the amount of heavy metal elution was all below the reference value. However, in the specimens of B series, the amount of heavy metal leaching was more than the standard value. In the case of arsenic and copper, the amount of elution was decreased by the reaction stimulant.

10. pH Disturbance Characteristics

The pH change in the leach solution (10 mL of distilled water / 1 g sample) was measured for 35 days. 11 is a graph showing the pH change for the high-copper filler according to the present invention. The initial pH was measured at pH 2 and 7, respectively. In the case of S - type specimens with small absolute volume of circulating fluidized bed boiler ash, the pH was shifted to alkali. This is because pH is determined by calcium hydroxide because the amount of sulfate ion is small. In the case of the B series, the content of the circulating fluidized bed boiler ash is higher than that of the S series, and the sulfate ion generated in the gypsum is equilibrated with the calcium hydroxide and the pH is maintained to be slightly acidic.

As described above, all of the blends of the S series of water and the B series that mixes the bottom ash instead of the sand are suitable as the high-flow filler because they meet the fluidity criterion. Both S series and B series can be applied to sinkholes and abandoned mine tools that have long-term swellable auto-degradability and require long-term swellable autolysis. In case of S series, there is a possibility of high pH and in case of B series, heavy metal leaching is large. Therefore, it is preferable to use in small scale field. For these two types of requirements, a combination of sand and bottom ash .

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (10)

Circulating fluidized-bed boiler fly ash containing gypsum and free lime, and high-
The method according to claim 1,
A high-permeability filler further comprising a reaction stimulant.
The method of claim 2,
Wherein the reaction stimulating agent is cement or sodium carbonate.
The method of claim 3,
Wherein the content of the reactive stimulant is 5 to 15 parts by weight relative to 100 parts by weight of the circulating fluidized bed boiler fly ash.
The method according to claim 1 or 4,
Wherein the high-strength copper filler is cured by underwater curing.
The method of claim 5,
Wherein the high-strength copper filler has an expansion ratio of 1% or more by self-decomposition.
Fly ash of a circulating fluidized bed boiler comprising gypsum and free lime, and bottom ash of a circulating fluidized bed boiler comprising gypsum and free lime.
The method of claim 7,
A high-permeability filler further comprising a reaction stimulant.
The method of claim 8,
Wherein the reaction stimulating agent is cement or sodium carbonate.
The method of claim 9,
Wherein the content of the reactive stimulant is 5 to 15 parts by weight relative to 100 parts by weight of the circulating fluidized bed boiler fly ash.

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