• Journal of Hydrogen and New Energy
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• v.35 no.1
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• pp.66-74
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• 2024

This study addresses the escalating issue of worldwide hydrogen gas accidents, which has seen a significant increase in occurrences. To comprehensively evaluate the risks associated with hydrogen, a two approach was employed in this study. Firstly, a qualitative risk assessment was conducted using the bow-tie method. Secondly, a quantitative consequence analysis was carried out utilizing the areal locations of hazardous atmospheres (ALOHA) model. The study applied this method to two incidents, the hydrogen explosion accident occurred at the Muskingum River power plant in Ohio, USA, 2007 and the hydrogen storage tank explosion accident occurred at the K Technopark water electrolysis system in Korea, 2019. The results of the risk assessments revealed critical issues such as deterioration of gas pipe, human errors in incident response and the omission of important gas cleaning facility. By analyzing the cause of accidents and assessing risks quantitatively, the effective accident response plans are proposed and the effectiveness is evaluated by comparing the effective distance obtained by ALOHA simulation. Notably, the implementation of these measures led to a significant 54.5% reduction in the risk degree of potential explosions compared to the existing risk levels.

• Journal of Korea Water Resources Association
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• v.55 no.spc1
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• pp.1251-1260
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• 2022

Recently, due to the deterioration of watermains and the detachment of scale which is accumulated on the watermain surface, water quality accidents in a water supply network occur frequently. As scale accumulated on watermains is stabilized, it may not cause water quality accidents under the normal operating condition. However, due to water hammer or transient flow caused by the abrupt velocity and/or direction of flow change, it can be detached from the watermain surface resulting in water quality accidents. To prevent these kinds of water quality accidents, it is required to remove scale by watermain cleaning regularly. Many researches about flushing which is the most popular water cleaning method are focused on the desirable velocity criteria and the cleaning condition to accomplish the effect of flushing whereas less amount of research effort is given to develop a method to consider whether the desirable velocity for flushing can be obtained before flushing is performed. During flushing, the major and minor headloss is occurred when flushing water flows through a hydrant or drain valve. These headloss may slow down the velocity of flushing water so that it can reduce the flushing effect. Thus, in this study, we suggest a method to simulate the flow velocity of flushing water using "MinorLoss Coefficient" and "Emitter Coefficient" in EPANET. The suggested method is applied to a sample network and the water supply network of "A" city in Korea to compare the flushing effect between "flushing through a hydrant" and "flushing through a drain valve". In case of "flushing through a hydrant", if the hydraulic condition ocurring from a watermain pipe connecting to the inlet pipe of a hydrant to the outlet of a hydrant is not considered, the actual flowrate and velocity of a flow is less than the simulated flowrate and velocity of a flow. In case of "flushing through a drain valve", the flushing velocity and flowrate can be easily simulated and the difference between the simulated and the actual velocity and flowrate is not significant. Also, "flushing through a drain valve" is very effective to flushing a long-length pipe section because of its efficiency to obtain the flushing velocity. However, the number and location of a drain valve is limited compared to a hydrant so that "flushing through a drain valve" has a limited application in the field. For this reason, the engineer should consider various field conditions to come up with a proper flushing plan.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.143-154
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• 2016

This study investigated the occurrences, causes, and mitigation of the recent ground subsidence and underground cavity generation events in Korea. Two main causes of ground subsidence are (1) the soil erosion by seepage during tunneling and earth excavation and (2) the damage of underground pipes. The main cause of the soil erosion during tunneling was the uncontrolled groundwater flow. Especially, when excavating soft grounds using a tunnel boring machine (TBM), the ground near TBM operation halt points were found to be the most vulnerable to failure. The damage of underground pipes was mainly caused by poor construction, material deterioration, and differential settlement in soft soils. The ground subsidence during tunneling and earth excavation can be managed by monitoring the outflow of groundwater and eroded soils in construction sites. It is expected that the ground subsidence by the underground pipe damage can be managed or mitigated by life cycle analysis and maintenance of the buried pipes, and by controlling the earth pressure distribution or increasing the bearing capacity at the upper ground of the buried pipes.

• Journal of Korean Society on Water Environment
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• v.23 no.1
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• pp.138-143
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• 2007

This study goes in for the observation of the characteristics of nitrogen removal from swine wastewater by struvite crystallization. In addition, the struvite formation potential in supernatants after struvite crystallization was investigated. In the study for nitrogen removal by struvite crystallization, the effects of pH and molar ratio of magnesium (Mg) injected using bittern as Mg source were investigated. Also, the potential of struvite formation in the supernatant with amount of Mg added was carefully observed. As the results, the optimum pH in the removal of nitrogen was 8.8 and sludge volume was increased as pH was raised from 7 to 12 under the condition that the molar ratio of $Mg^{2+}$ to ${NH_4}^+$-N to ${PO_4}^{3-}$-P was 1:1:1. An optimum removal efficiency of ammonia-N was observed at 1 molar ratio of Mg to ${NH_4}^+$-N, showing no further increase at over 1 molar ratio and dramatical deterioration at under 1 molar ratio. However, the sludge volume was increased by increasing the molar ratio of Mg. In the experiments for the potential of struvite formation in the supernatants, initial -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was much lower than $pK_{sp}$ and gradually reached $pK_{sp}$ at 2 days, as the molar ratio of Mg increased over 1.2. At 31 days, -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was returned to the initial value. In addition, the supernatants had a potential precipitation of hydroxylapatite due to calcium contained in bittern, $K_2Mg(SO_4)_3$ and $K_3Na(SO_4)_2$ resulting from the decrease of sodium and potassium in supernatants formed after struvite crystallization as times go by. Based on the results, it appears that some retention time and proper dosage of Mg may be needed for the prevention of scale in pipe line.

• Korean Journal of Heritage: History & Science
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• v.51 no.4
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• pp.66-83
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• 2018

This article focuses how the materials of hatstrings of the 19th to 20th century gat, the Korean top hat for men among the collections of National Folk Museum of Korea, was transformed after port opening treaties with overseas since 1876. As a result of analyzing the materials of the hatstrings, amber, tortoiseshell, wood and bamboo as the traditional materials were used, and ivory, glass (soda glass, lead glass, alkali mixed glass) and plastics (cellulose nitrate, phenol-formaldehyde, polystyrene, acryl) were newly used for the hatstrings. Bamboo, wood and amber were the most frequently used materials. Bamboo was mainly used for the pipe of hatstring and were combined with beads and central decorations of other materials. This shows the trend of bamboo hatstring according to the simplification of the clothing and the culture by Regent Heungseon Daewongun. Ambers were used in the central decorations and beads and the origin of ambers was baltic amber just like the amber relics found in Korea. Compositions of glass were soda glass and alkali mixed glass which were excavated or handed down in Korea from ancient times to Joseon dynasty. But in the case of lead glass, Na2O was detected and it is considered to be a new type lead glass for crafts which came from overseas after port opening since 1876 because it showed the characteristic that it deviates from the lead glass component found in Korea. Plastics such as cellulose nitrate and phenol-formaldehyde were used as new synthetic materials to replace traditional materials such as tortoiseshell, amber, and coral as in the West. Cracks, crazing, crumbly and yellowing of cellulose nitrate of hatstrings were observed by deterioration. The survey of the materials of the 19th to 20th century hatstrings among the collections of National Folk Museum of Korea showed that the introduction of new materials such as glass and plastics were used to replace natural materials such as tortoiseshell and amber along with the use of traditional materials after port opening since 1876.