• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.19-19
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• 2011

수중방전은 다양한 라디칼을 직접 물 속에서 발생시키기 때문에 수처리 공정에 다양한 응용이 가능하다. 특히, 최근에 선박평형수 등의 살균이 국제적인 이슈가 되고 있고, 2017년까지는 모든 선박에 살균을 위한 수처리 설비가 의무화된다. 본 연구에서는 염분이 있는 수체에서의 방전공정을 연구하고 이를 수처리공정에 적용할 수 있는 방법에 대해 연구하였다. 해수의 경우 전도도가 53mS로 자유로운 전하의 이동이 가능하기 때문에 일반적인 민물방전의 전원과 전극 등으로는 방전을 할 수 없다. 이에 세라믹과 금속의 이중구조로 되어 있는 모세관전극을 개발하여 전도성이 있는 수체에서의 방전을 이루었다. 전원장치로는 60 Hz, 380 V를 1차측에 인가하여 2차측에서 약 3 kV, 10 kW의 파워가 발생하는 12위상차 교류전원장치를 개발하여 사용하였다. 모세관 내부에 전압이 인가되면 전류가 발생하여 joule heating에 의하여 모세관 내부에 기포가 형성된다. 이 때, 전류의 단락이 이루어지면서 고전압쪽에 전하가 축적되며 기포내부의 E-field가 상승한다. 이후 기포 내에서 방전이 개시되며 각종 라디칼을 생성한다. 방전에 의해 생성되는 산화제로는 오존, OH라디칼, 과산화수소 등이 있으며, 해수에서는 Cl-의 결합에 의하여 Cl2 가스가 발생한다. 약 30,000 J/L의 체적에너지에 대하여 생성되는 총염소의 농도는 2.5 mg/L이다. 수중방전의 적용대상으로 선박평형수, 멤브레인과의 결합, 용존기포부상법을 선정하여 적용가능성을 연구하였다. 먼저 선박평형수 살균처리를 위해 해수의 처리유량을 20 lpm으로 유지하고 대장균, 바실러스, 조류(테트라셀미스) 등을 투입하여 전극 12개가 삽입된 12위상차 플라즈마 반응기를 통과시켰더니, 약 30,000 J/L의 체적에너지에 대하여 1일 후의 살균력이 각각 99.99, 99.99, 99.9%의 살균력을 나타내었다. 이는 국제해사기구에서 권장하는 살균수준인 99.9%를 초과하는 수치이다. 플라즈마를 이용한 해수살균공정의 안정적 운전을 위해 후단에 UF멤브레인을 추가하여 잔류생존 미생물을 제거할 수 있다. 이를 위해 플라즈마가 후단의 멤브레인 운전에 미치는 영향을 평가하였다. 카올린과 탄산칼슘을 오염원으로 각각 투입하여 멤브레인으로 처리를 하였을 때, 방전 직후 멤브레인에 걸리는 막간압력차가 약 30% 감소하였는데, 이는 막에 형성된 파울링이 방전에 의해 제거된 것으로 평가할 수 있다. 수중방전은 다양한 산화제를 생성함과 동시에 미세기포를 발생시키는데 이는 수중유기물의 부상분리에 적용될 수 있다. 방전모세관전극의 내부직경을 1 mm로 유지하고, 60 Hz, 교류전원으로 방전한 결과 평균입경 44 um의 기포를 발생시켰고, 이는 일반적으로 용존공기부상법에 사용되는 기포의 크기와 일치한다.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.513-520
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• 2016

It is well known that volatile compounds including disinfection by-products as well as emissive dissolved gas in water can be removed effectively by air stripping. The micro-bubbles of flotation unit are so tiny as microns while the diameter of fine bubbles applied to air stripping is ranged from hundreds to thousands of micrometer. Therefore, the micro-bubbles in flotation can supply very wide specific surface area to transfer volatile matters through gas-liquid boundary. In addition, long emission time also can be gained to emit the volatile compound owing to the slow rise velocity of micro-bubbles in the flotation tank. There was a significant difference of the THMs species removal efficiency between air stripping and flotation experiments in this study. Moreover, the results of comparative experiments on the removal characteristics of THMs between air stripping and flotation revealed that the mass transfer coefficient, $K_La$ showed obvious differences. To overcome the limit of low removal efficiency of dissolved volatile compounds such as THMs in flotation process, the operation range of bubble volume concentration is required to higher than the operation condition of conventional particle separation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1992.11a
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• pp.44-49
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• 1992

액체를 취급하는 기계.장치는 유속 및 회전속도 등이 빠르게 되면 유체충격과 정압의 저하에 따른 국부적 비등으로 인해 캐비테이션(cavitation) 현상이 발생한다. 이러한 캐비테이션현상에 따른 소음과 진동율 초래하고, 또한 기포의 붕괴에 따른 형격압으로 캐비테이션-침식(cavitation-erosion)이 발생하여 기계.장치의 구성재료에 손실이 일어남으로써 이들 기계의 효율을 저하시킴과 아울러 수명을 단종시킬 수 있다. 더욱이 부식성의 액체에 사용되는 기계.장치의 금속재료에는 캐비테이션(erosion-corrosion)이 중첩하여 발생하는 경우는 침식과 부식이 상호간에 가속하는 상승효과 때문에 기계.장치의 수명에 치명적인 영향을 미친다. 따라서 본 연구에서는 초음파 진동장치에 의한 각종 유중에서 베어링 합금 1종, 7종 및 켈-멧 4종에 대한 캐비테이션-침식실험을 실시하여, 침식손상거동및 특성등을 구명하고저 하였다.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1057-1062
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• 2008

To overcome disadvantages of conventional two interconnected fluidized beds system, a novel two-interconnected fluidized bed process has been adopted to 3kW chemical-looping combustor. This system has two bubbling beds, solid injection nozzles, solid conveying lines, and downcomers. In this study, effects of operating variables such as gas velocity through the solid injection nozzle, fluidizing velocity, solid height, geometry of solid intake hole, bed temperature on solid circulation rate have been investigated in a 3kW chemical-looping combustor. The solid circulation rate increased as the solid height and the opening area of solid intake holes increased. The effect of the fluidizing velocity and the bed temperature were negligible. Moreover, long-term operation of continuous solid circulation up to 50 hours has been performed to check feasibility of stable operation. The pressure drop profiles in the bubbling beds and the downcomers were maintained steadily and solid circulation was smooth and stable.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.5
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• pp.531-540
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• 2008

The main advantage of dissolved air flotation (DAF) in water treatment process is the small dimension compared with conventional gravity sedimentation and it can be basically reduced by the separation zone performed with the short solid-liquid separation time. Fine bubbles make such a short time possible to carry out solid from liquid separation as a collector on the course of water treatment. Therefore, the dimension of separation zone in DAF process is practically determined by the rise velocity of the bubble-floc agglomerates, which is a floc attached with several bubbles. To improve flotation velocity and particle removal efficiency in DAF process, many researchers have tried to attach bubbles as much as possible to flocs. Therefore, the maximum number of attached bubble on a floc and the rise velocity of bubble-floc agglomerates considered as the most important factor to design the separation zone of flotation tank in DAF process was simulated based on the population balance theory. According to the simulation results of this study, the size and volume concentration of bubble influenced on the possible number of attached bubble on a floc. The agglomerates attached with smaller bubble was more sensitive to hydraulic loading rate in the separation zone of DAF process. For the design of a high rate DAF process applied over surface loading 40 m/hr. it is required a precise further study on the variation of bubble property and behavior including in terms of bubble size distribution.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.481-487
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• 2009

In this of study, effects of input air velocity(0.05~0.22 m/sec) and molten carbonate salt temperature ($870{\sim}970^{\circ}C$) on flow regime transition have been studied by adopting a drift-flux model of air holdup and a stochastic analysis of differential pressure fluctuations in an air-molten sodium carbonate salt two-phase system(molten salt oxidation process). Air holdup where the flow regime transition begins was determined by air holdup-drift flux plot. The air holdup value which the flow regime transition begins was increased with increasing molten carbonate salt temperature due to the decrease of viscosity and surface tension of molten carbonate salt. To characterize the flow regime transition more quantitatively, differential pressure fluctuation signals have been analyzed by adopting the stochastic method such as phase space portraits and Kolmogorov entropy, The Kolmogorov entropy decreased with an increasing of molten carbonate salt temperature but increased gradually with an increase in an air velocity, however, it exhibited different tendency with the flow regime and the air velocity value which flow regime transition begins was same to the results of drift-flux analysis.

• Journal of Energy Engineering
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• v.12 no.4
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• pp.289-301
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• 2003

To develop a chemical-looping combustion technology, conceptual design of 50 kW thermal chemical-looping combustor, which is composed of two interconnected pressurized circulating fluidized beds, was performed by means of mass and energy balance calculations. A riser type fast fluidized bed was selected as an oxidizer and a bubbling fluidized bed was selected as a reducer by mass balance for the chemical-looping combustor. Calculated values of bed mass, solid circulation flux, and reactor dimension by mass and energy balance calculations were suitable for construction and operation of chemical-looping combustor. It is concluded from the comparison of the design results and operating values of commercial circulating fluidized bed that the process outline is realistic. Moreover, the previous results support that oxygen carrier particle, NiO/bentonite, fulfills the conversion rates needed for the proposed design. The effects of system capacity, metal oxide content in a oxygen carrier particle, amount of steam input, gas velocity, and solid depth on design values were investigated and the changes in the system performance can be estimated by proposed design tool.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1177-1184
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• 2011

Gas-to-Solid (GTS) technology is composed of three stages: hydrate production, transportation, and regasification. For efficient operation of regasification plants, it is crucial to predict the temperature and flow rate of hot water necessary to dissociate the hydrate pellets. Dissociated gas escaping from the pellet surface, when in contact with hot water, will alter the flow field and consequently alter the heat transfer rate. Methane hydrate pellet dissociation characteristics in low- to moderatetemperature water were investigated by taking images of the changes in the hydrate pellets' shapes in a pressurized reactor and measuring the total time required for complete melting of the pellets. The effects of water temperature, hydrate conversion rate, and flow speed on the dissociation completion time were also investigated. Bubbling gas released from the pellet surface induced a secondary flow that enhanced the heat transfer rate and thus decreased the dissociation time. It was also found that a considerable flow rate was needed to significantly decrease the dissociation time.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.499-505
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• 2010

In this study, hydrodynamics and reaction characteristic of K-based solid sorbents for $CO_2$ capture were investigated using a continuous system composed of two bubbling fluidized-bed reactors(1.2 m tall bed with 0.11 m i.d.). Potassium-based dry sorbents manufactured by the Korea Electric Power Research Institute were used, which were composed of $K_2CO_3$ of 35% for $CO_2$ absorption and supporters of 65% for mechanical strength. The continuous system consists of two bubbling fluidized-bed reactors, solid injection nozzle, riser, chiller, analyzer and heater for regeneration reaction. The minimum fluidizing velocity of the continuous system was 0.0088 m/s and the solid circulation rate measured was $10.3kg/m^2{\cdot}s$ at 1.05 m/s velocity of the solid injection nozzle. The $CO_2$ concentration of the simulated gas was about 10 vol% in dry basis. Reaction temperature in carbonator and regenerator were maintained about $70^{\circ}C$ and $200^{\circ}C$, respectively. Differential pressures, which were maintained in carbonator and regenerator, were about $415mmH_2O$ and $350mmH_2O$, respectively. In order to find out reaction characteristics of dry sorbents, several experiments were performed according to various experimental conditions such as $H_2O$ content(7.28~19.66%) in feed gas, velocity (0.053~0.103 m/s) of simulated gas, temperature($60{\sim}80^{\circ}C$) of a carbonator, temperature($150{\sim}200^{\circ}C$) of a regenerator and solid circulation rate($7.0{\sim}10.3kg/m^2{\cdot}s$). The respective data of operating variables were saved and analyzed after maintaining one hour in a stable manner. As a result of continuous operation, $CO_2$ removal tended to increase by increasing $H_2O$ content in feed gas, temperature of a regenerator and solid circulation rate and to decrease by increasing temperature of a carbonator and gas velocity in a carbonator.