• Resources Recycling
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• v.29 no.6
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• pp.3-14
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• 2020

This study aims to introduce and review on the recovery technologies of rare earth elements(REEs) from coal ash. Many researchers have been carried out by various beneficiation processes, such as particle size separation, magnetic separation, specific gravity, and flotation to recover rare earth elements from coal ash generated from Pulverized Coal(PC) boiler. Through the beneficiation process, it was confirmed that concentration of rare earth elements was much lower than the 4,700 ppm, and that additional enrichment treatment through wet process was needed for the products recovered after the beneficiation process. It was confirmed that the rare earth elements contained in coal ash were applied to the leaching process after pretreatment such as alkali-fusion to improve leaching efficiency. Although beneficiation and leaching methods have been studied, its optimum recovery technologies for rare earth elements not been confirmed up to now, research on the recovery of rare earth contained in coal ash is reported to continue. In case of Korea, the technology for the recovery of rare earth elements from coal ash and coal by-product could not been confirmed up to present. In these reasons, it is urgent to develop technologies such as beneficiation and leaching process continuously.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.71.1-71.1
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• 2011

석석탄가스화 기술은 고온, 고압 조건에서 미분탄과 산소의 가스화 반응에 의해 CO와 $H_2$가 주성분인 합성가스를 제조하는 기술로서 차세대 화력발전 뿐만아니라 다양한 화학원료 제조를 위한 분야에서 각광을 받고 있다. 또한, 가스화 기술은 향후 CCS기술, CTL(Coal To Liquid, 석탄액화)기술, SNG(Synthetic Natural Gas, 합성천연가스)생산, 수소생산, 각종 화학원료 생산 등과 연계가 가능한 미래 석탄이용 분야의 핵심 기술이라 할 수 있다. 따라서, 고등기술연구원에서는 이러한 석탄가스화를 통해 양질의 합성가스를 제조하기 위한 기술 개발의 일환으로 pilot급 고온, 고압 건식 분류층 가스화기, 기류수송 방식의 미분탄공급장치, 수냉자켓 구조의 합성가스 냉각장치, 합성가스 중 분진제거를 위한 금속필터 장착 집진장치 등을 연계하여 20기압의 고압 조건에서 장시간 연속운전을 진행하였다. 본 연구에서는 미분탄 공급을 위하여 상부공급 버너를 적용하였고 석탄가스화기는 $1,300{\sim}1,350^{\circ}C$ 정도의 온도에서 운전을 진행하였으며 미분탄을 75 kg/h의 조건에서 연속적으로 공급하였다. 그리고, 이러한 조건에서 5.5일 정도의 연속운전을 진행하는 동안 CO 44~48%, $H_2$ 20~21%, $CO_2$ 4~5% 조성의 석탄 합성가스를 $200Nm^3/h$ 안정적으로 제조할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.587-597
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• 2010

Air-staged combustion is known to be one of the techniques of NOx reduction. The objective of this study is to determine the optimal ratio of air flow distributed for CCOFA and SOFA; at this optimal ratio, the combustion and exhaust emission characteristics of a pulverized coal-fired boiler are maintained at a satisfactory level. A numerical investigation was performed at various airflow ratios of 16.7/83.3%, 25/75%, 50/50%, 75/25%, and 83.3/16.7%. An inert gas was considered as a substitute for air to isolate the effects of the cooling process and chemical reaction on NOx reduction; during NOx reduction in air-staged combustion, both the effects typically occur simultaneously. The results of our study show that the optimum condition, under which the maximum NOx reduction and highest boiler efficiency can be obtained, corresponds to the equal splitting of the over-fire air between CCOFA and SOFA.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.10
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• pp.1881-1891
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• 2000

Cenosphere particles of different fly ash formed at the pulverized coal power plant were hollow sphere or filled with small particles inside solid particles. And size was relatively larger than other fly ash particles as well as specific gravity was small to suspend in the water. In this paper, it was demonstrated to contain a variety of morphological particle type, and the physical and chemical properties related to the cenosphere and fly ash particles. Furthermore it was estimated the possibility to reuse the cenosphere particles on the base of cenosphere properties. Cenosphere formation resulted from melting of mineral inclusion in coal, and then gas generation inside the molten droplet. As the aluminosilicate particle was progressively heated, a molten surface layer developed around the solid core. Further heating leaded to cause the formation of fine particles at the core. The mass median diameter(MMD) of cenosphere particles was $123.11{\mu}m$ and the range of size distribution was $100{\sim}200{\mu}m$ with single modal. It was represented that specific density was $0.67g/cm^3$ fineness was $1135g/cm^3$. The chemical components of cenosphere were similar to other fly ash including $SiO_2$, $Al_2O_3$, but the amount of the chemical component was different respectively. In the case of fly ash, $SiO_2$ concentration was 54.75%, and $Al_2O_3$ concentration was 21.96%, so this two components was found in 76.71% of the total concentration. But in the case of cenosphere, it was represented that $SiO_2$ concentration was 59.17% and $Al_2O_3$ concentration was 30.16%, so this two components was found in 89.33% of the total concentration. Glassy component formed by the aluminosilicate was high in the cenosphere, so that it was suitable to use insulating heat material.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.535-537
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• 2004

The flame image processing and it's analysis system has been developed for optimal coal firing of thermal power plant, especially for reducing NOx and safe operations. We aimed at gaining the relationship between burner flame image, emissions of NOx and LOI(Loss on ignition) in furnace by utilizing the flame image processing methods. And the relationship determines quantitatively the conditions of combustion on the individual burners. The test was conducted on Samchonpo thermal power plant #4 unit(560MW) of KOSEP which has 24 burners. The system simplified the burner adjustment works in accordance with the real time trending of flame behavior like NOx profiles and unburned carbon profiles for individual burners. But, This kind of conventional method increases the cost as the number of burner are increased. Also there is a difficulty to measure exhausted gas of each burner because of measurement errors. This paper intends to propose the useful "Flame Monitoring System" that can find Low NOX and LOI at the upper furnace and to compare with the conventional System.

• 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 $45^{\circ}$).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.895-904
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• 2001

Flow fields, temperature distributions, and particle trajectories in a 2-stage entrained-flow gasifier are calculated using a CFD code, FLUENT. Realizable k-$\xi$ model is used as a turbulent model. Because of swirling flow there appear recirculation regions near the burners. The characteristics of flow fields and temperature distributions in the gasifier are dependent on the swirl number of the system. Mean residence time of the particles in the reductor is inversely proportional to particle size, particle density and swirl number. As the swirl number is increasing, the particles injected from the combustor burners approach the wall near the combustor burners, which prevents the particles from entering the reductor and thus attatching the reductor wall. If the lower combustor burner angle is larger than the higher combustor burner angle for a given swirl number, the particles may move toward the reductor and cause ash/slag deposition problem.

• Journal of the Korean Ceramic Society
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• v.54 no.2
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• pp.128-136
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• 2017

Fly ash from a circulating fluidized bed combustion boiler (CFBC fly ash) is very different in mineralogical composition, chemical composition, and morphology from coal ash from traditional pulverized fuel firing because of many differences in their combustion processes. The main minerals of CFBC fly ash are lime and anhydrous gypsum; however, due to the fuel type, the strength development of CFBC fly ash is affected by minor components of active $SiO_2$ and $Al_2O_3$. The initial hydration product of the circulating fluidized bed combustion fly ash (B CFBC ash) using petro coke as a fuel is Portlandite which becomes gypsum after 7 days. Due to the structural features of the portlandite and gypsum, the self-cementitious strength of B CFBC ash was low. While the hydration products of the circulating fluidized bed combustion fly ash (A CFBC ash) using bituminous coal as a fuel were initially portlandite and ettringite, after 7 days the hydration products were gypsum and C-S-H. Due to the structural features of ettringite and C-S-H, A CFBC ash showed a certain degree of self-cementitious strength.

• Journal of Energy Engineering
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• v.24 no.3
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• pp.150-163
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• 2015

Gasification technology is one of the representative next-generation fossil fuel utilization technologies, converting low grade fossil fuels such as coal, heavy residue oil, pet-coke into highly clean and efficient energy sources. Accordingly, related market demand for gasification technology is ever increasing steadily and rapidly. A few years ago, conventional pulverized coal utilization technology had an edge over the gasification technology but the most significant technical barrier of limited capacity and availability has been largely overcome nowadays. Futhermore, it will be more competitive in the future with the advancement of related technologies such as gas turbine, ion transfer membrane and so on. China has recently completed a commercialization-capable large-scale coal gasification technology for its domestic market expansion and foreign export, rapidly becoming a newcomer in the field and competing with existing US and EU technical leadership at comparable terms. Techno-economic aspect deserves intensive attention and steady R&D efforts need to continue in organized, considering that gasification technology is quite attractive combined with $CO_2$ capture process and coal to SNG plant is economically viable in Korea where natural gas is very expensive. In the present paper, recent technology development and commercialization trend of many leading companies with coal gasification expertise have been reviewed with significant portion of literature cited from the recently held '2014 Gasification Technology Conference'.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.81-89
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• 2002

IGCC (Integrated Coal Gasification Combined Cycle) is a technology that generates electric power using coal gasification and gasified fuel. Carbon conversion value of IGCC is higher and the influence on the environment is lower than the pulverized coal power plant. Especially, in the nations where the weight of fossil fuel for power generation is remarkably high like in Korea, IGCC stands out as an alternative plan to cope with sudden limitation for the emissions. In this paper, system design study for the commercial IGCC system which the introduction is imminent to Korea was performed. Two cases of entrained gasification process are adapted, one is FHR(full heat recovery) type IGCC system for high efficiency and the other is Quench type IGCC system for low cost. System simulations using common codes like AspenPlus were performed for each system. In the case of Quench system, system option study and sensitivity analysis of the air extraction rate was performed. Thermal performance result for the FHR system is 42.6% (HHV, Net) and for the quench system is 40% (HHV, net) when 75% air is extracted.