• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.443-450
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• 2008

Efficient use of low rank coals (LRC) have been investigated as a method to cope with recent high oil price. Among the coals used in industry, lignite and sub-bituminous coals are belong to the LRC, and have abundant deposit and are distributed worldwide, but high moisture contents and self ignition properties inhibits their utilization. In this paper, chemical coal cleaning to produce ash-free coal from LRC has been investigated. Two technologies, that is, UCC(Ultra Clean Coal) process removing ash from coal and Hyper Coal process extracting combustibles from coal were compared with. UCC process has merits of simple and reliable when it compared with Hyper Coal process, but the remaining ash contents werehigher than Hyper Coal. Hyper Coal has ash contents under the 200ppm when raw coal is treated with appropriate solvent and ion exchange materials to remove alkali materials in extracted solution. The ash-free coal which is similar grade with oil can be used as alternate oil in the industry, and also used as a high grade fuel for IGCC, IGFC and other advanced combustion technology.

• Journal of environmental and Sanitary engineering
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• v.12 no.1
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• pp.49-58
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• 1997

A study on the synthesis of zeolite from bituminous coal ESP fly ash as a raw material, which was emitted from the power plant, was carried out to reduce environmental problems and reuse of the industrial wastes. Bituminous coal fly ash was used as the source of silica and alumina. Zeolite was synthesized by hydrothermal reaction in aqueous NaOH solution with sodium aluminate as additive. The objective of this study is to elucidate the effect of several experimental variables on the synthesis of zeolite. The effects of preroasting temperature, mixing speed, leaching alkalinity, and molar ratio of Na$_{2}$O/SiO$_{2}$ and SiO$_{2}$/Al$_{2}$O of the products were investigated. The synthesized zeolite was proved to be NaA, which is known as 4A type, by comparing with SEM images, and X-ray diffraction analysis. And also we know that the transformation of zeolite A take places into other types of zeolites, i.e. Hydroxysodalite, zeolite P, with the variation of leaching alkalinity.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.231-237
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• 2005

Interruption of good fluidization in a fluidized bed ash cooler(FBAC) for discharging bed materials such as sand or coal ash particles from the CFB combustor is frequently happened because of agglomeration of the particles in the bed. This unstable operation may, in the worst case, result in an unscheduled boiler shut down. In this study, we examined the operation problems of the FBAC of Tonghae CFB boiler and studied and introduced the simple detection and solution techniques with analyzing the mixing property and the occurrence of defluidization in a simulated fluidized bed ash cooler system (0.5m-H x 0.5m-W x 1.0m-L). The bridge of the large particles at the bed surface could be observed, and this caused to form the defluidization area at the entrance of the FBAC. The defluidization was affected not only by airflow rates but also by the particles discharging rates as well as particle size distribution in the FBAC. The local defluidization could be detected by analysis of the accumulated standard deviation error at a given period of time. Also, the regulation of the overall or local airflow rate made clearing up the local defluidization possible.

• International Journal of Concrete Structures and Materials
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• v.9 no.1
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• pp.35-43
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• 2015

The critical element for sustainable growth in the construction industry is the development of alternative cements. A new technological process called geopolymerization provides an innovative solution, and the presence of aluminum and silicon oxides in fly ash has encouraged its use as a source material. Many previous investigations have involved curing the binder in a heated environment. To reduce energy consumption during the synthesis of geopolymers, the present study investigated the properties of ambient cured geopolymer mortar at early ages. An experimental program was executed to establish a relationship between the activator composition and the properties of geopolymer mortar in fresh and hardened states. Concentrations of sodium hydroxide and sodium silicate were ascertained that are advantageous for constructability and mechanical behavior. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques were also used to characterize the material. Test results indicate that there is potential for the concrete industry to use fly ash based geopolymer as an alternative to portland cement.

• Journal of environmental and Sanitary engineering
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• v.17 no.3
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• pp.21-30
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• 2002

This study was Performed to evaluate the effective solidification of Cd sludge using cement and power plant fly ash as cement admixture, to identify the leaching characteristics of the heavy metal Cd sludge solidified, and to develope proper KLT(Korean Leaching Test) of hazardous waste. KLT was compared with EPT(Extraction Procedure Toxicity) and TCLP(Toxicity Characteristics Leaching Procedure). Fly ash contents ranged from 0% to 30% of cement weight. The experimental results showed that the optimum amount of fly ash replaced was 10% to 15% and KLT was less appropriate than EPA and TCLP. Also the purpose of the study was to suggest the modification factors on the leaching test currently used, based on the above mentioned aspects. The effects of pH, leaching time, leaching for agitating intensity, and leaching solvent were investigated. As the result of test, the leaching potential was relatively high when the pH and agitation intensity of leaching solution were 5 and 150rpm, respectively. Leaching time of six hours was found to be sufficient and the use of acetic acid as a leaching solvent is more useful in landfill site particularly.

• Advances in concrete construction
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• v.13 no.1
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• pp.101-111
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• 2022

The rapid development of the construction industry in the world causes a rapid increase in the consumption of aggregate resources, which leads to the depletion of existing aggregate reserves. The use of recycled aggregate in the production of concrete and mortar may be a good solution to reduce the use of natural raw materials and to reduce demolition waste in the environment. In this study investigating the use of recycled aggregate in mortar production, mortar mixtures were produced by substituting 0%, 25%, 50% and 100% fine recycled aggregate (FRA) instead of natural aggregate. The effect of 20% and 40% fly ash (FA) substitutes on cement mortar performance was also investigated. Compressive and flexural strength, drying shrinkage, abrasion resistance, water absorption and capillary water absorption were investigated on the produced mortars. The increase in the use of FRA reduced the compressive and flexural strengths of mortars. While the capillarity coefficients, water absorption, rapid chloride permeability and drying shrinkage of the mortars increased with the increase in the use of FRA, the effect of the use of fly ash on the rate of increase remained lower. The increased use of FRA has improved abrasion resistance as well.

• Computers and Concrete
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• v.29 no.5
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• pp.335-346
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• 2022

Geopolymers are an important alternative material supporting recycling, sustainability, and waste management. Durability properties are among the most critical parameters to be investigated; in this study, the durability of manufactured geopolymer samples under the attack of 10% magnesium sulfate and 10% sodium sulfate solution was investigated. 180 cycles of freezing and thawing were also tested. The experimentally obtained results investigate the durability of geopolymer mortar prepared with fly ash (class F) and alkali activator. Three different quarry dust wastes replaced the river sand aggregate: limestone, marble, and basalt powder as fine filler aggregate in three different replacement ratios of 25%, 50%, and 75% to produce ten series of geopolymer composites. The geopolymer samples' visual appearance, weight changes, UPV, and strength properties were studied for up to 12 months at different time intervals of exposure to sulfate solutions to investigate sulfate resistance. In addition, Scanning Electron Microscopy (SEM), EDS, and XRD were used to study the microstructure of the samples. It was beneficial to include quarry waste as a filler aggregate in durability and mechanical properties. The compact matrix was demonstrated by microstructural analysis of the manufactured specimens. The geopolymer mortars immersed in sodium sulfate showed less strength reduction and deterioration than magnesium sulfate, indicating that magnesium sulfate is more aggressive than sodium sulfate. Therefore, it is concluded that using waste dust interrogation with partial replacement of river sand with fly ash-based geopolymers has satisfactory results in terms of durability properties of freeze-thaw and sulfate resistance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.1016-1022
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• 2010

An Experimental study of cleaning solution has been performed on a high capacity steam boiler burning heavy fuel oil to on-line cleaning of deposit. The deposit is mixture of soot, slag, ash, metal oxide and clinker. The traditional technology of deposit cleaning was carried hand-crafted. The conventional technology of boiler cleaning method is mechanical removal by the worker while the boiler shut down operation. In this experiment, the deposit of mixture of soot, slag, ash, metal oxide and clinker has been removed by the cleaning agents without shut down of boiler burning. This study found out the optimum cleaning solution composition. The best results have been obtained when the mixture of ammonium nitrate and $MgNO_3$ were used in cleaning solution. The various transition metal effect was investigated for optimum mixing condition. In this research, the metal compound additive of the clean solution compoition was obtained. The combustion efficiency was improved by on-line cleaning with derived clean solution compoition. On-line cleaning method prevents the fouling and corrosion in the boiler and heat exchanger.

• Journal of the Korean earth science society
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• v.32 no.2
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• pp.170-179
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• 2011

Fly ashes derived from coal fired power plants have unique chemical and mineralogical characteristics. The objective of this research was to study how indigenous bacteria affected heavy metal leaching in fly ash slurry during the fly ash-seawater interactions in the ash pond located in Yeongdong seashore, Korea. The in-situ pH of ash pond seawater was 6.3-8.5. For this study, three sites of the ash pond were chosen to collect a sample of fly ash slurry. Three samples that had a mix of fly ash (0.4 L) and seawater (1.6 L) were collected at each site. First sample was autoclaved ($120^{\circ}C$, 2.5 atm), second one was inoculated with glucose to stimulate the microbial activity, and the last sample was kept in the natural condition. Compared with other samples including autoclaved and natural samples, the glucose added sample showed sharp increase in its alkalinity after 15 days, cation concentration change such as Ca, Mg, and K seemed to increase in early stage, and then decrease 15 days later in slurry solution of glucose added sample, and a possibly considerable decrease in $SO_4^{2-}$ in the fly ash slurry samples when glucose was added to stimulate the microbial activity. Geochemical data of this study is likely to be related to the activity of bacteria at the ash pond. The result may be used to understand about the characteristic of bacteria.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.690-696
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• 2001

$TiO_2$ coated coal fly ash has been prepared in order to develop the low price $TiO_2$ photocatalyst and spread out its utilizing field. $TiO_2$ particles is coated on the surface of coal fly ash by precipitation method. In this method, $TiCl_4$ aqueous solution was used as a titanium stock solution and $NH_4HCO_3$ was used as a precipitant. The titanium hydroxide precipitated on the surface of coal fly ash in these neutralizing reaction process was oxidized by heat treatment in temperature ranges of $300~700^{\circ}C$. The crystal structure of the generated titanium dioxide showed anatase type. The crystal size of titanium dioxide increased with raising the temperature of heat treatment, but the removal ability of NO gas decreased. When the titanium dioxide was heated at temperature ranges of $300~ 400^{\circ}C$ for 2 hours, the crystal size of titanium dioxide appeared about 9nm, and the removal rate of NO gas showed 85~ 92%. The whiteness of $TiO_2$ coated coal fly ash increased with raising the coating rate of titanium dioxide and the temperature of heat treatment.