Sangdo Kim

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.

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.

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.

A Study on the Characteristics of Improvement in Filtration Performance by Dust Precharging

A hybrid dust-collector combining electrostatic charging with fabric filtration was developed and its performance characteristics were evaluated. Charged particles build porous dendritic structure on the filter surface by electrostatic attraction, increasing the collection efficiency of dust particles and reducing the pressure drop through the deposited dust layer and filter media. The cleaning performance of the dust layer is improved because the dendritic structured dust layer may be removed more easily by pulse jet cleaning flow. The results of the experiment showed a reduction of fine particle emission by 37% and 13% energy saving by precharging dust particles before filtration.

Physical, Chemical and Electrical Analysis of Dust Generated from Cement Plants for Dust Removal with an Electrostatic Precipitator

The physical, chemical and electrical characteristics of cement dust generated from a cement plant have been investigated by using a dust analyzer and a high voltage conductivity cell based on JIS B 9915. Major constituents of raw material cement dust generated from the first grinding process are CaO (41.77%), SiO2 (11.72%), Al2O3 (3.45%), and Fe2O3 (1.47%), while the cement clinker dust generated from the second grinding process consists of mainly CaO (48.09-65.50%), SiO2 (14.02-21.56%), Al2O3 (2.86-3.76%), and Fe2O3 (1.77-2.66%). Size distribution of the raw material cement dust is bi-modal in shape and the mass median diameter (MMD) is 3.68 μm, whereas the cement clinker dust also displays bi-modal distribution and the MMD of the cement clinker dust is in the range of 7.89-58.78 μm. The resistivity of raw material cement dust is so high as 1014 ohm·cm at 300 °C, that cement dust would not precipitate well by the electrostatic precipitator.

Temperature Fluctuations and Heat Transfer in a Fluidized-Bed Combustor of Waste Oil

Temperature fluctuations and heat transfer characteristics were investigated in a fluidized-bed combustor of 0.102 m ID and 2.5 m in height, which was designed for waste oil combustion. Effects of excess air (AE), injection height (HI) and feeding rate of waste oil (QF) on the mean bed temperature (TB), Kolmogorov entropy (K2) of phase space portraits and heat transfer coefficient (U0) in the fluidized-bed combustor were determined. TB increased, but K2 and U0 decreased with increasingAE. K2 had a local minimum, but TB and U0 had a maximum at HI of 0.4 m. TB increased, but K2 had a minimum and U0 had a maximum with increasing QF in the combustor. TB, K2 and U0 obtained at the optimum operating condition (AE=40%, HI=0.4 m, QF=30 g/min) were about 855 ‡C, 22 bits/s and 382 W/m2K, respectively.

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.

Upgrading and advanced cleaning technologies for low-rank coals

Abstract Low-rank coals–lignite and subbituminous coals–refer to the lowest and second lowest rank of coals. Unlike high-rank coals deposited in specific areas, low-rank coals are evenly distributed around the world and their reserves are approximately 500 billion tons, which is similar with that of high-rank coals. Low-rank coals are high in moisture or ash content and susceptible to spontaneous combustion. Since low-rank coals are high in moisture, using them as fuel in energy-producing facilities like power plants increases coal consumption, emitting more CO2 and lowering power generation efficiency. This chapter introduces upgrading and advanced cleaning technologies, which are low-carbon utilization technologies. Upgrading is necessary to use as a fuel for high efficiency and low emission combustion and conversion technologies. Upgrading is a process of removing moisture or ash from low-rank coals before using the coals to enhance facility efficiency. As such, we would like to introduce existing coal drying technologies and stabilization technologies as well as new drying/stabilization technologies, which are under development. This chapter also introduces the production technology of ash-free coals which is expected to be used for various purposes in the future.

Electrodynamic Behavior of a Charged Particle among Two-Dimensional Quadrupole Electrodes

An inhomogeneous hyperbolic electric field is established among two-dimensional quadrupole electrodes to which an ac voltage is applied. Conditions under which charged particles are focused into a narrow axis region of the plug laminar flow are discussed. The aerodynamic forces influence the behavior of the charged particles in the quadrupole electric field. We derived the dimensionless equations of motion of a charged particle in the alternating quadrupole electric field, and discussed particle trajectories and focusing performance in terms of two dimensionless parameters, which are functions of particle size, operating pressure, and the amplitude and frequency of applied AC voltage, with the results of numerical simulations and experiments.