• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.6
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• pp.259-265
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• 2011

This research was performed to stabilize heavy metals in mine tailing using fly ash and clay. Fly ash-clay-mine tailing system were investigated using XRD (X-ray diffractometer), XRF (X-ray fluorescence spectrometer), TG-DTA, SEM (Scanning Electron Microscope), Dilatometer and UTM with various mine tailing contents (~15 wt%). The fly ash used in this research was mainly composed of $SiO_2$ (33.01 wt%), $Al_2O_3$ (28.54 wt%), $K_2O$ (3.32 wt%), $Fe_2O_3$ (1.47 wt%), CaO(9.97 wt%). $SiO_2$ and $Al_2O_3$ composition of the clay was over 61 wt%. And the mine tailing have high composition of $SiO_2$ (26.91 wt%), CaO (24.25 wt%), $Fe_2O_3$ (22.97 wt%). Therefore, it was estimated that fly ash-clay-mine tailing have enough sintering characteristics. The shrinkage of specimens started at around $850^{\circ}C$ and changed little up to $1100^{\circ}C$, but increased markedly at above $1100^{\circ}C$. The shrinkage rate is strongly related to the decarbonization amount of coal fly ash. As the result of SEM, structure of the specimens with mine tailing addition showed more close than the one without mine tailing. Compressive strength of the specimens with mine tailing was highly increased to approximately 200~420 kgf/$cm^2$, it satisfied the first grade criterion for clay brick by KS L 4201. The specification of leaching characteristics of the sintered specimens were within the Korean regulation standard.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.3
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• pp.207-213
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• 2018

Nowadays, circulating fluidized bed combustor(CFBC) boilers system that can reduce environmental pollution particles are widely used in electric power plants. But the fly ash generated from CFBC boilers has lower $SiO_2$ and higher MgO and $SO_3$ contents and also has free CaO inducing expansion and abrupt initial setting of concrete. Therefore, revised KSL5405 for CFBC fly-ash as well as pulverized coal combustion(PCC) is introduced in the concrete field. In this study, the chemical properties and mechanical properties of blended cements with PCC and CFBC fly-ash produced in Korea are analyzed. The blended cement with only CFBC fly ash shows a lower length change than OPC but a higher flow change ratio. The compressive strength of blended cement paste with PCC and CFBC fly ash is slightly greater than that of cement paste with only PCC fly-ash. Based on the results, CFBC flyash blended cement products should be used with PCC flyash to ensure the material stability and material properties.

• Journal of the Korean institute of surface engineering
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• v.34 no.6
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• pp.575-584
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• 2001

Erosion due to abrasive particles contained in gas streams from boilers has been emerged as a significant problem in the coal fired power plants. Particle erosion accounted for approximately 50% of boiler failures and especially flyash erosion was responsible for 20~30% of emergency boiler shutdowns. Particularly, because of the high ash loading and high velocity, most erosion occurs in the boiler tubes and economiser tube bank where the direction of the gas stream changes to $180^{\circ}$ .In this study, a high temperature particle erosion tester was used to evaluate erosion rate in a simulated environment. The erosion parameters such as erosion temperature, particle impact angle, particle velocity and various particle size were changed. Flyash is the combustion product of the pulverized coal, where size is ranging from 1 to $200\mu\textrm{m}$. Flyash composed of mainly SiO$_2$, $A1_2$$_O3$, and $Fe_2$$O_3$has dense spherical particles and irregular particles containing numerous pores and cavities. From the erosion tests at various conditions, the maximum erosion was experienced at impact angles of $30^{\circ}$ to $60^{\circ}$ In addition, erosion rate increased in proportional to velocity and temperature. And from the observation of the eroded surfaces, it was also concluded that 304 stainless steel was mainly eroded by extrusion-forging at high impact angle ($90^{\circ}$) and by microcutting mechanism at low impact angles ($30^{\circ}$ and $45^{\circ}$).

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.808-811
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• 2007

본 연구는 3톤/일급 이하 가스화 용융로에서 $1,400{\sim}1,500^{\cdot}C$, $7.5{\sim}8.0$ kg/$cm^2$의 안정적인 운전조건일 때, 시료로 Kideco 탄을 사용하고 이때 발생한 슬랙의 특성 및 슬랙의 재활용을 위한 벽돌제조 특성을 고찰하였다. 발생된 슬랙은 $Fe_2SiO_4$와 $SiO_2$가 결정상태로 일부 존재하거나, 중금속들이 결합되어 엉킨 구조인 비결정상태의 치밀한 형태로 이루어져 있었으며, 잔존탄소 함량이 0.06%로 미량 존재하였다. 또한 슬랙에는 중금속 농도가 Kideco탄보다 고농도로 존재하지만, 용출되는 중금속의 농도는 매우 낮아 환경적으로 안정한 물질로서 재활용이 가능한 특성을 지니고 있다. 슬랙 첨가 점토벽돌의 적합성을 평가하기위해 슬랙을 0%, 10%, 30% 첨가하여 벽돌을 제조하고 KS 산업규격에 따라 시험을 실시하였다. 분석결과 슬랙을 첨가할수록 제조한 벽돌의 흡수율이 낮아져 기존 제품에 비하여 우수한 것으로 측정되었다. 또한 압축강도와 휨강도는 기존 제품의 $80{\sim}86%$ 정도인 것으로 측정되었지만 KS 산업규격의 기준치보다 높은 수치를 나타내였고, 내산성, 내알칼리성, 열충격강도 또한 양호한 것으로 나타나, 슬랙을 이용하여 벽돌로 재활용하여 충분히 사용 가능한 것으로 확인되었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.876-885
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• 2009

Char oxidation experiments were performed with a sub-bituminous roto-middle coal in the Drop Tube Furnace (DTF) at atmospheric pressure condition. While temperatures varied between 900, 1100, 1400 $^{\circ}C$, particle size, mass, particle temperature, and CO/$CO_2$ concentration were obtained to be used for kinetic analysis of the char oxidation. This study addresses several different methods to analyze the char consumption rate, which are classified as energy balance method, ash-traced mass method, flue-gas based method, and particle size based method. The char consumption rate obtained with such methods was compared with the results of Monson et al.$^{(24)}$ While there are some differences between them because of differences in experimental apparatus and parameters to be measured, the kinetic results seems to be reasonable enough to be incorporated in a numerical modeling of coal combustion.

• Resources Recycling
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• v.23 no.1
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• pp.40-47
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• 2014

Feasibility of utilizing unburned carbon residue in coal ash as a potential precursor for the production of activated carbon was assessed to seek for solution to recycle unburned carbon residue. The unburned carbon concentrate generated from the 4 stages of cleaner flotation has a grade of 87% carbon. The crystalline impurities in the concentrate included quartz and mullite. Unburned carbon had a low specific surface area of $10m^2/g$, which might be related to a high degree of coalification of domestic anthracite coal. Carbon particles were mostly porous and have a turbostratic structure. When 1g of carbon was activated with 6g of KOH powder, the highest specific surface area value of $670m^2/g$ was achieved. Low wettability of unburned carbon particles, which was resulted from high temperature combustion in a boiler, might cause poor pore formation when they were activated by KOH solution. The activated carbon produced in this study developed micropores, with an equivalent quality of general-purpose activated carbon made from coal. Hence, it is concluded that chemically treated unburned carbon can be used for water purification or an alternative to carbon black as it is.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.305-311
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• 2012

In order to recycle the coal bottom ashes (denoted as BA) produced from a thermal power plant, the artificial aggregates (denoted as AAs) containing BA and red clay were manufactured, and the physical properties of AAs were studied as a function of particle size of BA and batch compositions. As-received BA had 38 wt% coarse particles of above 2 mm and many unburned carbon mass and porous slag particles were co-existed. So the two particle sizes of BA, the fine (< 100 ${\mu}m$) and coarse (< 2 mm), were prepared by milling and screening process. The AAs containing fine BA sintered at $1100{\sim}1200^{\circ}C$ had the higher bulk density and lower water absorption compared to the specimen made of coarse BA. The inside core of AAs manufactured by using coarse BA showed nonuniform and porous microstructure, while the AAs made of fine BA had a uniform and dense microstructure. In this research, the AAs containing BA and red clay with various bulk density (1.2~1.7) and water absorption (13~21 %) could be manufactured by controlling the particle size of BA and batch compositions, so the AAs of various physical properties could be applied to the wide fields such as construction/building materials in near future.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.3
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• pp.279-284
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• 1999

Fly ash is the fine ash particles that are flying out of chimney of the thermoelectric power plant where coals are used as fuel. There are two kinds of fly ashes from anthracite and bituminous coal. By scanning electron microscope(SEM) morphological feature of fly ash was confirmed to the exact spherical particles with the diameter variation from the fine to the largest about $50{\mu}m$(mainly silty particle). Surface of anthracite ash particle was very smooth but that of bituminous was somewhat coarse. To find the utilization of fly ash for improving soil permeability, soils of 4 kinds of different texture, clay, clay loam, sandy clay loam and sand mere applied with 7 levels of fly ash: 0, 10, 20, 40, 60, 80, 100%(w/w) and their saturated hydraulic conductivity(Ks) were determined at each application by constant head method. In clay soil with low water permeability, Ks value was increased about 10 times from $10^{-8}$ to $10^{-7}m\;s^{-1}$ level with application of 10% fly ash and it was slightly increased with increasing fly ash application from 40 to 80%. In clay loam Ks value was about $10^{-7}m\;s^{-1}$ level and its value was not influenced by the fly ash application. In sandy clay loam with relatively high permeability, Ks value was decreased about 10 times from $10^{-5}$ to $10^{-6}m\;s^{-1}$ level with application of 10% fly ash and also decreased about 50 times from $10^{-5}$ to $5.0{\times}10^{-7}m\;s^{-1}$ with application of more than 20% fly ash. In sand with very high permeability, Ks value was decreased about 10 times from $10^{-4}$ to $10^{-5}m\;s^{-1}$ level with application of 10% fly ash and also decreased about 100 times from $10^{-4}$ to $10^{-6}m\;s^{-1}$ level with application of 20% fly ash and continuously decreased about 500 times from $10^{-4}$ to $5.0{\times}10^{-7}m\;s^{-1}$ level with application of more than 40% fly ash. In conclusion by fly ash application saturated hydraulic conductivity was increased in clay soil, on the contrary it was decreased in sandy soils. Fly ash may be used as a material for amelioration of soil permeability.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.272-277
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• 2009

Three dimensional numerical analysis for the coal fired boiler has been performed to investigate the effect of yaw angle variation of the secondary air nozzles on the combustion characteristics and NOx emission. It was found that the prediction gives a good agreement with plant data. The increase in yaw angle up to $20^{\circ}$ have results in the decrease in NOx emission at furnace exit and recirculation flow intensity, together with the increase of unburned carbon in ash. It also has been recognized the remarkably change in configuration of fire ball with increase in yaw angle. The results from this study would be valuable in the case of the combustion modification of the corner firing coal-fired utility boiler.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.95-106
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• 1998

To reduce the environmental contamination and to utilize fly ash massively produced from the coal power plant every year, we synthesized the artificial zeolite using fly ash treated with alkaline, and then analyzed the mineralogical and morphological properties by X-ray, IR, and SEM. The amount of $NH_4{^+}$, $K^+$, and $H_2PO_4{^-}$ adsorbed by the fly ash and the artificial zeolite were determined with reaction time, amount of adsorbate used, ion concentrations. The results obtained from the pot experiments packed with the top soil, amended with granulated artificial zeolite which was made by treatment of 4% polyvinylalcohol, showed that CEC of the artificial zeolite was $257.7cmol^+kg^{-1}$, that was almost 36 times greater than that of fly ash. The ratio of $SiO_2/Al_2O_3$ decreased but the amount of Na increased. The physico-chemical properties analyzed by X-ray, IT, and SEM represented that the artificial zeolite synthesized had a similar morphological structure to that of the natural zeolite. The structures of the artificial zeolite had a significantly enlarged surface having a lot of pores, while the fly ash looked like spherical smooth shape with having not pores on the surface. Thus, the artificial zeolite was successfully synthesized. The results of adsorption isotherms of fly ash and artificial zeolite showed that the amount of $NH_4{^+}$, $K^+$, and $H_2PO_4{^-}$ adsorbed increased as the equilibrium concentration increased, while $NH_4{^+}$ was strongly adsorbed on the surface of fly ash and artificial zeolite than that of $K^+$. The most distinctive growth of Chinese cabbage was found from the top soil(NPK + soils + 20% of granulated artificial zeolite + 5% of compost). Therefore, we concluded that one of the most effective methods to effectively recycle a fly ash was to make the artificial zeolite as we did in this experiment.