• Clean Technology
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• v.18 no.4
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• pp.426-431
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• 2012

Carbon-rich coal can be utilized as a fuel for direct carbon fuel cell (DCFC). However, left-behind ash after the electrochemical oxidation may hinder the electrochemical reactions. In this study, we produced ash-free coal (AFC) by thermal extraction and then tested it as a fuel for DCFC. DCFC was built based on solid oxide electrolyte and the electrochemical performance of AFC mixed with $K_2CO_3$ was compared with AFC only. Significantly enhanced power density was found by catalytic steam gasification of AFC. However, an increase of the power density by catalytic pyrolysis was negligible. This result indicated that a catalyst activated the steam gasification reactions, producing much more $H_2$ and thus increasing the power density, compared to AFC only. Results of a quantitative analysis showed much improved kinetics in AFC with $K_2CO_3$ in agreement with DCFC results. A secondary phase of potassium on yttria-stabilized zirconia (YSZ) surface was observed after the cell operation. This probably caused poor long-term behavior of AFC with $K_2CO_3$. A thin YSZ (30 ${\mu}m$ thick) was found to be higher in the power density than 0.9 mm of YSZ.

• Clean Technology
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• v.20 no.3
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• pp.218-225
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• 2014

Catalytic gasification of raw coals at mild condition is not realized yet mainly due to deactivation of catalysts via their irreversible interaction with mineral matters in coal. In this work, the gasification behavior of ash-free coal (AFC) was compared with that of the parent raw coal. In order to modify the gasification conditions, the raw coal gasified with fixed variables (water supply, space velocity, temperature, catalysts) in a fixed bed reactor. When catalysts are added by physical mixing method with coal, $K_2CO_3$ was the most effective additives for steam gasification of coal. However, the activity of ash-free coal (AFC) was much less reactive than raw coal due to high temperature extraction in a 1-methylnaphthalene under 30bar at $370^{\circ}C$ for 1 h, almost removed oxygen functional groups, and increased carbonization. The addition of $K_2CO_3$ in AFC achieved higher conversion rate at low temperature ($700^{\circ}C$). At that time, the molar ratio of gases ($H_2/CO$ and $CO_2/CO$) was increased because of water-gas shift reaction (WGSR) by addition of catalysts. This shows that catalytic steam gasification of AFCs is achievable for economic improvement of gasification process at mild temperature.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.89-96
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• 2015

Recently, much research has been put into finding the causes and solutions of slagging/fouling problems that occur at the end of the boiler. This slagging/fouling, caused by low-rank coal's ash, disturbs the thermal power and greatly reduces efficiency. In environmental aspects, such as NOx pollution, governments have been implementing restrictions on the quantity of emission gases that can be released into the atmosphere. To solve these problems, research on Ash Free Coal (AFC), which eliminates ash from low-rank coal, is in progress. AFC has advantages over similar high-rank coals because it increases the heating value of the low grade coal, reduces the contaminants that are emitted, and decreases slagging/fouling problems. In this study, using a DTF, the changes of NOx emissions, unburned carbon, and the characteristics of ash deposition were identified. KCH raw coal, AFC extracted from KCH, residue coal, Glencore, and Mixed Coal (Glencore 85wt% and residue coal 15wt%) were studied. Results showed that AFC had a significantly lower emission of NOx compared to that of the raw coal and residue coal. Also, the residue coal showed a higher reactivity compared to raw coal. And finally, In the case of the residue coal and mixed coal, they showed a lower ash deposition than that of low-rank coal.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.5-12
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• 1995

본 연구에서는 자력 및 정전기 선별법에 의한 발전용 석탄의 연소전 탈황탈회 가능성 조사를 미국 PETC와 공동으로 수행하였다. 정전기 선별법에 의한 석탄의 탈황실험은 국내무연탄 및 미국 유연탄 시료를 대상으로 수행하였으며, 본 선별법은 석탄으로부터 유황을 함유하는 광물은 물론 회분을 제거하는데 매우 효율적임을 확인하였다. 또한 본 연구에서는 고강도 자력선별기를 이용하여 국내무연탄에 대한 건식자력선별 가능성을 검토하였다. 삼척 및 동원탄광 시료에 대한 입도별 2단계 선별실험을 수행하였으며, 본 실험 결과 동원탄광 시료가 삼척탄광 시료보다 회분제거가 용이하였으며 유황분의 경우는 두 시료 모두 40∼50% 제거가 가능하였다. 기초실험을 통하여 향후 발전용 석탄의 연소전 탈황탈회처리시스템 개발에 필요한 기초자료를 제시하였다.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.555-560
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• 2008

Extraction was performed to prepare ash-free coal from low rank coal under the temperature of $200-430^{\circ}C$ and initial pressure of 0.1MPa. Three kinds of coal samples with different rank were used and N-methyl-2-pyrrolidinone(NMP, polar), 1-methyl naphthalene(I-MN, non-polar), Light Cycle Oil(LCO, non-polar) were used as solvents. Results showed that higher extraction yield could be obtained with NMP than with 1-MN and LCO, but the ash concentration shows minimun in the case of 1-MN. Three operation modes were compared, that is, idle, agitation and ultrasonic extraction mode. From the results, it was found that the extraction yield and ash concentration were 70.09% and 1.03% under the agitation mode, 80.7% and 0.76% under the ultrasonic operation mode respectively in the case of NMP used at the temperature of $350^{\circ}C$. Similar results were obtained with 1-MN. Effect of ultrasonic on the extraction was estimated as 15-20% increase in the yields and 26% reduction in the ash concentration.

• Journal of Hydrogen and New Energy
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• v.29 no.6
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• pp.559-569
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• 2018

Catalytic supports made of carbon have many advantages, such as high coking resistance, tailorable pore and surface structures, and ease of recycling of waste catalysts. Moreover, they do not require pre-reduction. In this study, ash-free coal (AFC) was obtained by the thermal extraction of carbonaceous components from raw coal and its performance as a carbon catalytic support was compared with that of well-known activated carbon (AC). Nickel was dispersed on the carbon supports and the resulting catalysts were applied to the steam reforming of toluene (SRT), a model compound of biomass tar. Interestingly, nickel catalysts dispersed on AFC, which has a very small surface area (${\sim}0.13m^2/g$), showed higher activity than those dispersed on AC, which has a large surface area ($1,173A/cm^2$). X-ray diffraction (XRD) analysis showed that the particle size of nickel deposited on AFC was smaller than that deposited on AC, with the average values on AFC ${\approx}11nm$ and on AC ${\approx}23nm$. This proved that heteroatomic functional groups in AFC, such as carboxyls, can provide ion-exchange or adsorption sites for the nano-scale dispersion of nickel. In addition, the pore structure, surface morphology, chemical composition, and chemical state of the prepared catalysts were analyzed using Brunauer-Emmett-Taylor (BET) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and temperature-programmed reduction (TPR).

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.11-31
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• 1999

Removal of hexavalent chromium from artificial groundwater (AGW) by granular activated carbon (GAC) was investigated in batch and continuous-flow column studies. Experimental parameters that were examined included solution pH, presence of dissolved oxygen (DO), and GAC pretreatment with Fe(II). As the solution pH increased from 4 to 7.5, the amount of Cr(VI) removed by both GACs decreased significantly. Exclusion of DO from the experimental systems resulted in greater removal of Cr(VI) from solution, possibly as a result of reduction to Cr(III). However, pretreatment of the GAC with a reductant (Fe(II)) did not improve Cr(VI) removal. Equilibration With 0.01 M $K_2$$HPO_4$[to extract adsorbed Cr(VI)] followed by a wash with 0.02 N $K_2$$HPO_4$[to remove precipitated/sorbed Cr(III)] proved to be a viable approach for the regeneration of carbons whose Cr(VI) removal capacities had been exhausted. The performance of the regenerated carbons exceeded that of the virgin carbons, primarily because of the favorable adsorption of Cr(VI) at lower pH values and the reduction of Cr(VI) to Cr(III), The presence of Cr(III) in acid wash solutions provides direct evidence that Cr(VI) is reduced to Cr(III) in GAC systems under relatively acidic conditions. GAC performance over five complete cycles was consistently high, which suggests that such a system will be able to function over many operation cycles without deleterious effects.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.47-49
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• 2014

발전소에서 설계 규격을 벗어나는 저등급 석탄을 사용하기 시작하면서, 보일러에서의 연소특성을 예측하기 어려운 다양한 성질의 석탄이 들어오게 되어 각종 연소 문제가 증가하고 있다. 이 중 약 점결 특성을 가지는 저등급 석탄의 사용은 대형 클링커로 인한 보일러 하부의 튜브 손상 사고, 재열증기온도 상승으로 인한 출력감발 등의 문제를 발생시켰다. 또한 현재 개발 중인 무회분석탄 역시 점결 특성을 가지고 있는 것으로 알려져 있어 보일러 내부의 다양한 문제를 일으킬 것으로 예상되고 있다. 발전소에서는 강점결탄 수입 규제를 위해 CSN(Crucible Swelling Number)를 이용하여 제철용으로 사용되는 강점결 석탄의 도입을 규제해왔으나, 발전소 운영에 악 영향을 미치는 약 점결탄에 대한 규제 및 대응으로는 그 효과가 미미한 실정이다. 따라서 본 연구에서는 석탄의 점결 특성 중 팽창 특성을 분석할 수 있는 Microdilatometer와 TGA를 이용한 연소반응성 분석을 통해 석탄의 점결 특성이 연소반응성에 미치는 영향을 분석하였다.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.449-454
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• 2012

Economic feasibility of the process for a coal extraction under mild condition, which will produce ash-free coal at a temperature lower than that of coal softening, was analyzed. To this end, the plant of 6000 t/d in capacity was assumed to be constructed near a coal mine in Indonesia, and the IRR, NPV, B/C ratio, and DPP of the plant were calculated based on $96 million investment cost and 15 years service life. The IRR, NPV, B/C ratio, and DPP of the plant were calculated to be 31%, $87 million, 1.08, and 3.9 years, respectively, and which satisfied the evaluation criteria of investment. The economic feasibility of the plant was mainly dependent on the price of the coal initially fed and the residue coal remaining after the extraction, according to sensitivity analysis.