• Tunnel and Underground Space
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• v.27 no.3
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• pp.161-171
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• 2017

Demand for high-grade limestone is increasing, but the production in the domestic mines has been limited due to the lack of systematic development plans and efforts to develop mining technology to improve the recovery ratio, transition to high-cost underground mining due to increasing social awareness of environmental protection, and the smallness of the domestic mining industry, etc. In this study in connection with this issue, an analysis on the recovery change by improvement of mining method was executed. 3D modeling technique was used to construct a 3D model. 3D model includes the geological structure, the limestone ore body and the underground pits and tunnels excavated at the Daepyeong District of Daesung MDI Donghae District. By using the 3D model, measured resources, reserves and ore recovery were evaluated from the results of pilot operation of the room and pillar hybrid mining method, which is a variant of room and pillar mining method. These results were compared with those obtained from the conventional mining method. The ore recovery obtained by hybrid mining method was found to be up to 71.6%, showing about 26%p. increase compared with the case of conventional mining method.

• Tunnel and Underground Space
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• v.26 no.2
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• pp.131-142
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• 2016

Investigation for rock joints, inspection for rock core, and laboratory tests for rock specimens, in this study, have been performed for identification of the extent and properties of Excavation Damaged Zone in a underground limestone mine, which plans to enlarge the size of openings to improve the production rate. Properties of EDZ and surrounding rock masses have been used numerically for discontinuum analysis, and it is concluded that the effect of EDZ can be increased with increasing the opening size and a blasting pattern of high precision can be suggested for the counterplan.

• Explosives and Blasting
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• v.36 no.1
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• pp.12-19
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• 2018

When an underground limestone mine selects room-and-pillar mining method, in which the stability of mine openings is maintained by leaving safety pillars, the stability of safety pillars is always incompatible with their productivity. Therefore, the engineering decision for stability and productivity is essential. In this study, a progress of excavation faces by conventional blasting pattern has been examined in field for investigating over-break and stereo-photogrammetry method has been applied to this field measurement for improvement of accuracy. Also this result has been reflected instantly to composite blasting pattern by feedback, for minimizing overbreak. Field tests showed the relevant results that $3.5m^2$ in over-break out of $70m^2$ in total excavation face has been decreased, that is 5% of reduction rate in maximum.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.587-592
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• 2016

Sodium borohydride, $NaBH_4$, shows a number of advantages as hydrogen source for portable proton exchange membrane fuel cells (PEMFCs). Properties of $NaBH_4$ hydrolysis reaction using unsupported Co-P-B Co-B, catalyst at high concentration $NaBH_4$ solution were studied. In order to enhance the hydrogen generation yield at high concentration of $NaBH_4$, the effect of catalyst type, $NaBH_4$ concentration and recovery of condensing water on the hydrogen yield were measured. The yield of hydrogen evolution increased as the boron ratio increased in preparation process of Co-P-B catalyst. The hydrogen yield decreased as the concentration increased from 20 wt% to 25 wt% in $NaBH_4$ solution during hydrolysis reaction using 1:5 Co-P-B catalyst. Maximum hydrogen yield of 96.4% obtained by recovery of condensing water and thinning of catalyst pack thickness in reactor using Co-P-B with Co-B catalyst and 25 wt% $NaBH_4$ solution.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.5
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• pp.687-694
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• 2015

The purpose of this study was to evaluate the yield, antioxidant content, and antioxidant activity of adzuki beans according to germination time. Cultivated varieties were Vigna angularis var. Nipponensis cv. Chungju-pat (CJP), and Yeonduchae (YDC), and Vigna radiata (L.) R. Wilczek cv. Dahyeon (DH). The moisture, crude protein, calcium, and magnesium contents of YDC significantly changed with increasing germination time, whereas potassium, natrium, and aluminium contents did not significantly change. Sprout yield, total polyphenol, flavonoid, and tannin contents of ethanolic extracts from adzuki and mung beans significantly increased with increasing germination time. Total polyphenol contents of ungerminated CJP, YDC, and DH were 1.96, 2.68, and 2.02 mg/g, and those of CJP and YDC germinated for 144 h were 3.33 and 3.47 mg/g, respectively. Total flavonoid content of adzuki beans substantially decreased with increasing germination time. Total tannin content substantially increased with increasing germination time, and YDC showed higher contents (0.85 mg/g) sample germinated for 120 h. DPPH radical scavenging activities of CJP and YDC substantially decreased with increasing germination time, whereas that of DH increased. ABTS radical scavenging activities of ungerminated CJP, YDC, and DH were 4.57, 6.51, and 2.82 mg/g, respectively, and increased after germination for 72~120 h.

• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.11-15
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• 2016

Proton Exchange Membrane Fuel Cells (PEMFC) instead of batteries is appropriate for long time flight of unmanned aero vehicles (UAV). In this work, $NaBH_4$ hydrolysis system supplying hydrogen to PEMFC was studied. In order to decrease weight of $NaBH_4$ hydrolysis system, enhancement of hydrogen yield, recovery of condensing water and maintenance of stable hydrogen yield were studied. The hydrogen yield of 3.4% was increased by controlling of hydrogen pressure in hydrolysis reactor. Condensing water formed during air cooling of hydrogen was recovered into storage tank of $NaBH_4$ solution. In this process the condensing water dissolved $NaBH_4$ powder and then addition of $NaBH_4$ solution decreased system weight of 14%. $NaBH_4$ hydrolysis system was stably operated with hydrogen yield of 96% by 2.0g Co-P-B catalyst for 10 hours at 2.0L/min hydrogen evolution rate.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.11-15
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• 2015

Sodium borohydride, $NaBH_4$, shows a number of advantages as hydrogen source for portable proton exchange membrane fuel cells(PEMFCs). Properties of $NaBH_4$ hydrolysis reaction using unsupported Co-B, Co-P-B catalyst were studied. BET surface area of catalyst, yield of hydrogen, effect of $NaBH_4$ concentration and durability of catalyst were measured. The BET surface area of unsupported Co-B catalyst was $75.7m^2/g$ and this value was 18 times higher than that of FeCrAlloy supported Co-B catalyst. The hydrogen yield of $NaBH_4$ hydrolysis reaction by unsupported catalysts using 20~25 wt% $NaBH_4$ solution was 97.6~98.5% in batch reactor. The hydrogen yield decrease to 95.3~97.0% as the concentration of $NaBH_4$ solution increase to 30 wt%. The loss of unsupported catalyst was less than that of FeCrAlloy supported catalyst during $NaBH_4$ hydrolysis reaction and the loss increased with increasing of $NaBH_4$ concentration. In continuous reactor, hydrogen yield of $NaBH_4$ hydrolysis was 90% using 1.2 g of unsupported Co-P-B catalyst with $3{\ell}/min$ hydrogen generation rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.601-608
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• 2011

In OFDMA(Orthogonal Frequency Division Multiple Access) based multi-hop networks, the subcarrier-pairing scheme using the SNR(Signal-to-Noise Ratio) has been proposed as the best solution. But, this scheme is not optimal in cognitive radio system, because of the power control due to the interference to the primary user. In this paper, we propose two subcarrier-pairing schemes for OFDMA based 2-hop cognitive radio systems. One is the IT(Interference channel gain) scheme considering only the interference channel gain, and the other is the CI(Channel SNR over interference channel gain) scheme considering the ratio of channel SNR to interference channel gain. The results show that the CI scheme has the best performance in which throughput is improved more than 10% in comparison with other schemes.

• Tunnel and Underground Space
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• v.10 no.1
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• pp.80-91
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• 2000

Open cut mining of limestone is generally considered to be more advantageous than underground mining in recovery, grade control, economics, and safety, but it causes substantial environmental pollutants such as ground vibration, noise, dust. It also changes ground surface and may destroy vegetation. The Halla limestone mine which lies adjacent to Baikdu mountains range is selected for a model study. To reduce environmental hazards, and to conserve original surface and woods, both open cut and underground mining methods must be adopted. In case of sub-level sloping. a unit block of 87m high, 70m wide, and 100∼l20m long is suggested with an estimated overall recovery of 42%. Some suggestions to reduce the environmental hazards are also included. The followings must be considered in determining the degree of fragmentation; the discontinuity conditions in the rock mass and the charge concentration both at the bottom and column of the hole. In addition to adopting a barrier wall for reducing environmental hazards, the probable production from underground mining is also discussed.

• Tunnel and Underground Space
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• v.27 no.6
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• pp.406-421
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• 2017

This study describes a precise numerical analysis process by adopting the real image of mine openings obtained by LIDAR, which can produce a point cloud data by measuring the target surface numerically. Research area is a section of underground limestone mine which is used hybrid room-and-pillar method for improving the production rate. From the application of LIDAR to this section several results were deduced, that is, the central axis of upper and lower vertical safety pillars is distorted to the direction of NW and the section area of lower vertical safety pillar is $34m^2$ smaller than the designed area of $100m^2$. The results of precise measurement in geometrical shape of mine openings and precise simulation in numerical analysis confirms that LIDAR techniques can be suggested as a valuable tool for stability analysis in underground mine by configuring the mine opening shape.