Sihyun Lee

Characterization of chars made of solvent extracted coals

Thermal extraction of a sub-bituminous coal (Roto south) using 1-methylnaphthalene solvent has produced ash-free coals successfully. The extracted (EC) and residual coal (RC) as well as its parent coal (PC) were pyrolyzed at 300–900 °C and then the carbonized products were characterized. The extracted coal (EC) contained lower molecular weight components than PC and RC, showing much higher fuel ratio after the pyrolysis. EC is expected to be advantageous over PC and RC when applied to coal gasification and reforming, because EC is readily decomposed and volatized. The heating value of EC chars (7,610–8,120 kcal/kg) was independent of the pyrolysis temperature and was higher than those of PC and RC chars, especially for the chars carbonized below 600 °C. The oxygen content of PC chars at T≤600 °C was mostly at least twice that of EC/RC chars, pointing out the difference in the chemical composition. 13CNMR and FT-IR spectra revealed the release of aliphatic hydrocarbons and reactive functional groups with increasing temperature, in agreement with ultimate/proximate analysis results.

Ash-free coal as fuel for direct carbon fuel cell

This work describes the performance of the direct carbon fuel cell (DCFC) fuelled by ash-free coal. Employing coal in the DCFC might be problematic, mainly because of the ash deposition after the cell reactions. In the study, the carbonaceous ash-free component of coal is obtained, which is then evaluated as the DCFC fuel and compared with raw coal, active carbon, carbon black, and graphite. The electrolyte-supported SOFC structure is adapted to build the DCFC. The DCFC based on the ash-free coal fuel exhibits good performance with regard to the maximum power density, day-by-day measurements, and durability at continuous run. When the carbon fuels are internally gasified to H2 and CO, the power density is generally much improved, compared to N2 pyrolysis environment. The power generation is most likely related to the concentration of pyrolyzed gases as well as the electrochemical reactivity of the solid carbon.

A comparison of spontaneous combustion susceptibility of coal according to its rank

This study investigated spontaneous combustion susceptibility of coal according to the rank. To estimate the spontaneous combustion susceptibility of coal, both crossing-point temperature (CPT) measurement and gas analysis by using gas chromatography (GC) were performed. For the experiment, Eco coal and Kideco coal, Indonesian lignite, and Shenhua coal that is Chinese bituminous coal were used. The lignite such as Eco coal and Kideco coal contains more functional groups that easily react to oxygen more so than Shenhua coal. For this reason, the lignite is more easily oxidized than bituminous coal at low temperature, which results in high O2 consumption, increase in CO and CO2 generation, and low CPT. Although the CPT of Eco coal and Kideco coal is identical to each other as they are the lignite, Kideco coal has a lower initial oxidation temperature (IOT) and maximum oxidation temperature (MOT) than those of Eco coal. This means that although each coal has the same rank and CPT, spontaneous combustion susceptibility of coal may vary because the initial temperature of the coal at which oxidation begins may be different due to the substances that participate in oxidation.

Improved Specific Capacitance of Amorphous Vanadium Pentoxide in a Nanoporous Alumina Template

This article investigates the physicochemical properties of vanadium pentoxide (V 2 O 5 ) prepared by anodic electrodeposition onto two nanoporous alumina templates having pore sizes of 50 and 200 nm. V 2 O 5 formed inside the templates was an amorphous structure with flakelike (50 nm) and round (200 nm) shapes. The capacitance of V 2 0 5 was measured using cyclic voltammetry in 1 M KCl electrolyte, and ca. 900 F g -1 of maximum specific capacitance was obtained from V 2 O 5 in 50 nm alumina oxide. Improved specific capacitance of V 2 O 5 is ascribed to the high surface area of the porous structure by the use of the template.

Comparison of spontaneous combustion susceptibility of coal dried by different processes from low-rank coal

We compared the susceptibility to spontaneous combustion of low-rank coals dried by four different processes: flash drying, fluidized bed drying, non-fried carbon briquetting, and coal-oil slurry dewatering. The coals were characterized by FT-IR and XPS analysis. A crossing-point temperature (CPT) was estimated as a comparison criterion of the susceptibility of the coals to spontaneous combustion. O2, CO, and CO2 emissions during the CPT measurement were also compared. The FT-IR and XPS analysis revealed that some of the oxygen functional groups on the surface of the coal were removed when the coal underwent the drying process. This phenomenon was particularly noticeable in the coal dried by oil. Accordingly, the CPT of the coal that went through this drying process was high. Among the samples, the coals dried by oil showed the highest CPT.

Changes in spontaneous combustion characteristics of low-rank coal through pre-oxidation at low temperatures

This study investigated the changes in spontaneous combustion susceptibility of low-rank coal through preoxidation processing at low temperatures. The pre-oxidation processing on low-rank coal was conducted for a certain time at 60–150 °C in normal atmospheric conditions. The oxidation characteristics of coal at low temperature were investigated by measuring the temperature of coal and consumption of O2 gas during the pre-oxidation processing. Physical properties of coal and changes in crossing-point temperature (CPT) caused by the pre-oxidation processing were also analyzed. Higher the temperature for pre-oxidation, the more consumption of O2 gas in coal, and larger increase in temperature of the coal was observed. There were no significant changes in the weight of coal samples and calorific value in pre-oxidation processing upto 130 °C. It was found, from Fourier Transform Infrared Spectroscopy (FTIR) analysis, that the coal which underwent pre-oxidation processing upto 80 °C showed no significant difference from raw coal in terms of content. However, higher the temperature for preoxidation, larger decrease in aliphatic hydrocarbon and ether in the coal. As a result of CPT measurement, higher the temperature for pre-oxidation, greater the increase in CTP value of the coal. Therefore, it is expected to reduce the risk of spontaneous combustion susceptibility through the pre-oxidation method. From these results, it was confirmed that the spontaneous combustion susceptibility of the coal can be suppressed without a significant reduction in weight and calories through the preoxidation processing of low-rank coal under the proper conditions.

Pilot-Scale Studies on Upgrading of an Indonesian Low-Rank Coal Using Palm Oil Residues

In the present study, a method was developed to upgrade low-rank coal using palm oil residues. The upgrading process consisted of pulverization, mixing, drying, coating, and briquetting. A palm oil residue (palm fatty acid distillate [PFAD]) was used to upgrade an Indonesian low-rank coal. Pores generated in the low-rank coal due to the evaporation of moisture were coated with the PFAD. The inhibitory effect of the PFAD was investigated by measuring the crossing-point temperature (CPT) of the upgraded coal. The amount of moisture re-adsorbed by the upgraded coal was compared to the raw coal with several methods. The CPT of the upgraded coal increased 10°C, and the moisture re-adsorption decreased by less than 60% compared with the raw coal. The upgraded coal briquettes were hydrophobic and had high compressive strength. This makes the upgraded coal sufficiently stable for long-term storage and long-distance transportation.

Evaluation of the effect of a palm acid oil coating on upgrading low rank coal

Indonesian low rank coal (LRC) was upgraded by the addition of palm acid oil (PAO), and the efficiency of the inhibition of spontaneous combustion, as well as the resistance to moisture readsorption, was compared with raw coal. Fluorescence microscopy images revealed that PAO was well distributed in the coal matrix during the drying process. The PAO coating the surface of coal decreased the pore volume and the surface area of the upgraded coal and improved its stability. The upgraded LRCs had higher heat calorimetry values, greater resistance to moisture readsorption, and a reduced tendency toward spontaneous combustion when compared to raw coal. In upgraded coal briquettes, PAO was present in the form of a network-like structure, which led to an increase in the compressive strength by binding the coal particles. The upgraded LRCs showed less susceptibility to isothermal oxidation due to the PAO coating on the coal particles, which suppressed the reaction of active functional groups with oxygen in the air.

Characteristics of coal upgraded with heavy oils

We investigated the ability of an oil coating to upgrade Indonesian low-rank coal, which has a low ash content and a moisture content of approximately 30%. Proximate and ultimate analyses of the characteristics of coal samples containing different amounts of asphalt (ASP) and palm fatty acid distillate (PFAD) were studied, including the samples’ calorific values, crossing-point temperatures (CPT), specific surface areas, pore sizes, structural changes, and moisture readsorption. The results showed that the 0.5% PFAD-coated coal was the highest quality. This coal showed few physical and chemical changes, and it had a low surface area and a high CPT value.

Efficient Use of Low Rank Coal: Current Status of Low Rank Coal Utilization

Despite vast reserves, low rank coals are not used as a main fuel in industry because their high moisture content, potential spontaneous combustion in transportation and storage, and the low thermal efficiency during the combustion in conventional power plants. With a view to secure and strengthen low rank coal’s position as high available energy source, in recent years many attempts have been made to develop technologies for an energy-efficient upgrading process. This paper reviews these technologies mainly categorized as drying for reducing moisture, stabilization for decrease self-heating characteristics and cleaning the coal for reducing mineral content of coal. Drying technologies consist of both evaporate and non-evaporative types. There are also highly advanced coal cleaning technologies that produce ash-free coal. The paper discusses some of the promising upgrading technologies aimed at improving these coals in terms of their moisture, ash and other pollutants. Korea’s activity for the drying and stabilization technologies will be introduced in this paper and the utilization of dried low rank coal also introduced.