• 한국가스학회지
• /
• 제21권6호
• /
• pp.8-14
• /
• 2017

가스배관 사고의 대표적인 원인 중 하나는 기계적 충격(타공사 등)으로 인한 사고이다. 이는 국내 주요 산업단지에 매설되어 있는 고압가스배관의 대다수가 매설 시기가 20년 이상인 노후 배관이기 때문에 사고 발생 시 별도의 검사 및 보강 시간 없이 대형 사고로 이어질 가능성이 높다. 본 연구에서는 타공사(굴착공사) 실험을 통해 기계적 충격 시 배관에 미치는 결함 정도에 대해 연구하였다. 실제 산업단지에서 굴착공사 시 사용되고 있는 21 ton 굴착기와 ASTM A106 Grade.B와 ASTM A53 Grade.B 배관을 이용해 타격실험을 진행하였다. 그 결과 굴착기 작업에 이용되는 버켓 중 톱니 버켓 일 때 결함의 정도가 더 컷으며, 매설되어 있는 배관의 관경이 작을수록 결함의 깊이 및 길이가 큰 것을 확인하였다. 굴착기 작업 중 타격 높이는 매설 배관의 결함에 아무런 영향을 미치지 않는 것을 확인하였다.

• 한국수소및신에너지학회논문집
• /
• 제24권1호
• /
• pp.12-19
• /
• 2013

A gasification process with pre-combustion $CO_2$ capture process, which converts coal into environment-friendly synthetic gas, might be promising option for sustainable energy conversion. In the coal gasification for power generation, coal is converted into $H_2$, CO and $CO_2$. To reduce the cost of $CO_2$ capture and to maximize hydrogen production, the removal of CO and the additional production of hydrogen might be needed. In this study, a 2l/min water gas shift system for a coal gasifier has been studied. To control the concentration of major components such as $H_2$, CO, and $CO_2$, MFCs were used in experimental apparatus. The gas concentration in these experiments was equal with syngas concentration from dry coal gasifiers ($H_2$: 25-35, CO: 60-65, $CO_2$: 5-15 vol%). The operation conditions of the WGS system were $200-400^{\circ}C$, 1-10bar. Steam/Carbon ratios were between 2.0 and 5.0. The commercial catalysts were used in the high temperature shift reactor and the low temperature shift reactor. As steam/carbon ratio increased, the conversion (1-$CO_{out}/CO_{in}$) increased from 93% to 97% at the condition of CO: 65, $H_2$: 30, $CO_2$: 5%. However the conversion decreased with increasing of gas flow and temperature. The gas concentration from LTS was $H_2$: 54.7-60.0, $CO_2$: 38.8-44.9, CO: 0.3-1%.

• 한국컴퓨터정보학회논문지
• /
• 제25권4호
• /
• pp.19-27
• /
• 2020

본 논문에서는 정압기의 이상 상태 진단을 위한 기계학습 방법을 제안한다. 일반적으로 설비의 이상 상태 탐지를 위한 기계학습 모델 구현에는 관련 센서의 설치와 데이터 수집 과정이 동반되나, 정압기는 설비 특성상 안전문제에 매우 민감하여 추가적인 센서 설치가 매우 까다롭다. 이에 본 논문에서는 센서의 추가 설치 없이 정압기 설비에서 자체 수집되는 유량과 유압 데이터만을 가지고 정압기의 이상 상태를 조기에 판단하는 기계학습 모델을 제안한다. 본 논문에서는 정압기의 비정상데이터가 충분하지 않은 관계로, 모델 학습 시 오버 샘플링(Over-Sampling)을 적용하여 모델이 모든 클래스에 균형적으로 학습하도록 하였다. 또한, 그레이디언트 부스팅(Gradient Boosting), 1차원 합성곱 신경망(1D Convolutional Neural Networks), LSTM(Long Short-Term Memory) 등의 기계학습 알고리즘을 적용하여 정압기의 이상 상태를 판단하는 분류모델을 구현하였고, 실험 결과 그레이디언트 부스팅 알고리즘이 정확도 99.975%로 가장 성능이 우수함을 확인하였다.

• The Journal of Advanced Prosthodontics
• /
• 제6권1호
• /
• pp.39-45
• /
• 2014

PURPOSE. The aim of the present study was to evaluate the accuracy of three techniques for correction of cast implant bars. MATERIALS AND METHODS. Thirty cast implant bars were fabricated on a metal master model. All cast implant bars were sectioned at 5 mm from the left gold cylinder using a disk of 0.3 mm thickness, and then each group of ten specimens was corrected by gas-air torch soldering, laser welding, and additional casting technique. Three dimensional evaluation including horizontal, vertical, and twisting measurements was based on measurement and comparison of (1) gap distances of the right abutment replica-gold cylinder interface at buccal, distal, lingual side, (2) changes of bar length, and (3) axis angle changes of the right gold cylinders at the step of the post-correction measurements on the three groups with a contact and non-contact coordinate measuring machine. One-way analysis of variance (ANOVA) and paired t-test were performed at the significance level of 5%. RESULTS. Gap distances of the cast implant bars after correction procedure showed no statistically significant difference among groups. Changes in bar length between pre-casting and post-correction measurement were statistically significance among groups. Axis angle changes of the right gold cylinders were not statistically significance among groups. CONCLUSION. There was no statistical significance among three techniques in horizontal, vertical and axial errors. But, gas-air torch soldering technique showed the most consistent and accurate trend in the correction of implant bar error. However, Laser welding technique, showed a large mean and standard deviation in vertical and twisting measurement and might be technique-sensitive method.

• 한국유체기계학회 논문집
• /
• 제12권2호
• /
• pp.8-16
• /
• 2009

The objective of this study is to investigate the three-dimensional turbulence flow characteristics of a rotor passage of an one-stage axial flow gas turbine and to investigate the effects of a boundary layer fence installed on the hub endwall of the rotor passage. Secondary flows occurring within the rotor passage (e.g. horseshoe vortex, passage vortex, and cross flow) cause secondary loss and reduce turbine efficiency. To control these secondary flows, a boundary layer fence measuring half the height of the thickness of the inlet boundary layer was installed on the hub endwall of the rotor passage. This study was performed numerically. The results show that the wake and secondary flows generated by the stator reduced the rotor load to constrain the development of cross flow and secondary flow reinforced by the rotor passage. In addition, the secondary vortices occurring within the rotor passage were reduced by the rotation of the rotor. Although, the boundary layer fence induced additional vortices, giving rise to an additional loss of turbine, its presence was shown to reduce the total pressure loss when compared to effects of the case without fence regardless of the relative position of blades by enervating secondary vortices occurred within the rotor passage.

• 멤브레인
• /
• 제33권6호
• /
• pp.305-314
• /
• 2023

화학 반응의 수율 향상을 위해 부산물을 제거하는 다양한 방법이 연구되고 있다. 특히 산업적으로 중요한 반응에서 주로 부산물로 물이 생성되기 때문에 넓은 범위의 온도에서 안정적으로 물을 분리하는 기술이 필요하다. 흡수제의 사용, 탈수 반응의 도입 등 다양한 방법이 제안되었으나 추가적인 에너지 및 시간 소요, 전환율의 지속 가능성 등의 문제로 한계를 가지고 있다. 그에 반해 운전 및 설치가 용이하고, 낮은 유지비용 등의 장점을 가지고 있는 분리막 기술은 다양한 촉매 반응에 도입되었을 때 안정적으로 부산물을 제거할 수 있어 반응의 효율을 향상시킬 수 있는 좋은 방안이다. 따라서 본 총설에서는 분리막을 이용한 부산물 제거 및 이를 통한 효과에 대해 논의하였다.

• 한국안전학회지
• /
• 제28권3호
• /
• pp.44-50
• /
• 2013

Process gas piping is one of the most basic components frequently used in the refinery and petrochemical plants. Many kinds of by-product gas have been used as fuel in the process plants. In some plants, natural gas is additionally introduced and mixed with the byproduct gas for upgrading the fuel. In this case, safety or design margin of the changed piping system of the plant should be re-evaluated based on a proper design code such as ASME or API codes since internal pressure, temperature and gas compositions are different from the original plant design conditions. In this study, series of piping stress analysis were conducted for a process piping used for transporting the mixed gas of the by-product gas and the natural gas from a mixing drum to a knock-out drum in a refinery plant. The analysed piping section had been actually installed in a domestic industry and needed safety audit since the design condition was changed. Pipe locations of the maximum system stress and displacement were determined, which can be candidate inspection and safety monitoring points during the upcoming operation period. For studying the effects of outside air temperature to safety the additional stress analysis were conducted for various temperatures in $0{\sim}30^{\circ}C$. Effects of the friction coefficient between the pipe and support were also investigated showing a proper choice if the friction coefficient is important. The maximum system stresses were occurred mainly at elbow, tee and support locations, which shows the thermal load contributes considerably to the system stress rather than the internal pressure or the gravity loads.

• 무역학회지
• /
• 제48권1호
• /
• pp.165-191
• /
• 2023

미국과 EU는 우크라이나 사태에 대응하여 러시아의 에너지 부문을 대상으로 제재하고 있다. 특히 대러 경제제재는 러시아의 석유가스 부문에 대한 에너지 제재의 성격을 가지고 있다. 미국과 EU는 모두 제재 부과국이지만, 미국은 천연가스 순수출국인 반면, 대부분의 EU 회원국들은 러시아에 대한 의존도가 높다는 근본적인 차이점이 존재한다. 따라서 미국과 EU의 대러 에너지 제재는 미국을 포함한 기타 석유가스 수출국들이 EU 에너지 시장에서 러시아를 대체할 공급을 확보할 수 있는 경우에 그 효과성이 보장될 수 있다. 즉, 주요 석유가스 수출국들의 러시아 대체 가능성은 대러 에너지 제재의 효과성을 좌우하는 중요한 결정 요인이다. 본 연구는 석유가스 수출국들의 러시아 대체 가능성 평가를 통해 대러 에너지 제재의 효과성을 살펴본다. 본 연구의 분석 결과, 대부분의 석유가스 수출국들의 추가 생산 역량과 인프라 부족 문제로 인해 단기에 러시아를 대체하는 석유가스의 확보는 어려울 것으로 평가되며, 이에따라 미국과 EU의 대러 에너지 제재는 그 효과성이 불분명한 것으로 판단된다. 우크라이나 사태의 해결을 위해서는 직접적인 제재보다 외교 등 다른 수단이 활용되어야 할 것이다.

• 한국연소학회지
• /
• 제13권2호
• /
• pp.33-41
• /
• 2008

The high permeability of the gas in the molten iron of the dripping zone of the blast furnace is a major factor in achieving the stable operation of a furnace with high productivity. Basic studies of the liquid flow behavior in a packed bed are necessary to grasp the effect of various operational changes on conditions in the dropping zone. Molten iron and slag together playa critical role in the lower zone, transporting mass and energy, while impairing and redistributing the gas flow. In turn, molten iron and slag undergo physical and chemical changes, and are redistributed radially as they descend to the hearth. In this research, mathematical formulations are derived for the gas and the liquid. The solid phase is fixed with constant porosity. The information for the molten iron and slag includes the hold-up, velocity, pressure, and information related to the areas of interaction between the gas and the liquid, and the solid and the liquid. Predictable results include the velocity, pressure and temperature distribution. Additional parameters include the packed particle size and the air blast rate.

• International Journal of Automotive Technology
• /
• 제1권1호
• /
• pp.17-25
• /
• 2000

The electromechanical valve train (EMV) technology allows for a reduction in fuel consumption while operating under a stoichiometric air-fuel-ratio and preserves the ability to use conventional exhaust gas aftertreatment technology with a 3-way-catalyst. Compared with an engine with a camshaft-driven valve train, the variable valve timing concept makes possible an additional optimization of cold start, warm-up and transient operation. In contrast with the conventionally throttled engine, optimized control of load and in-cylinder gas movement can be used for each individual cylinder and engine cycle. A load control strategy using a "Late Intake Valve Open" (LIO) provides a reduction in start-up HC emissions of approximately 60%. Due to reduced wall-wetting, the LIO control strategy improves the transition from start to idle. "Late Exhaust Valve Open" (LEO) timing during the exhaust stroke leads to exhaust gas afterburning and, thereby, results in high exhaust gas temperatures and low HC emissions. Vehicle investigations have demonstrated an improved accuracy of the air-fuel-ratio during transient operation. Results in the New European Driving Cycle have confirmed a reduction in fuel consumption of more than 15％ while meeting EURO IV emission limits.