• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.492-498
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• 2012

In this study, hydrodynamics such as solid circulation rate and voidage in the desulfurizer and the reaction characteristics of Zn-based solid sorbents were investigated using lab-scale high pressure and high temperature desulfurization process. The continuous HGD (Hot Gas Desulfurization) process consist of a fast fluidized bed type desulfurizer (6.2 m tall pipe of 0.015 m i.d), a bubbling fluidized bed type regenerator (1.6 m tall bed of 0.053 m i.d), a loop-seal and the pressure control valves. The solid circulation rate was measured by varying the slide-gate opening positions, the gas velocities and temperatures of the desulfurizer and the voidage in the desulfurizer was derived by the same way. At the same gas velocities and the same opening positions of the slide gate, the solid circulation rate, which was similar at the temperature of $300^{\circ}C$ and $550^{\circ}C$, was low at those temperatures compared with a room temperature. The voidage in the desulfurizer showed a fast fluidized bed type when the opening positions of the slide gate were 10~20% while that showed a turbulent fluidized bed type when those of slide gate were 30~40%. The reaction characteristics of Zn-based solid sorbent were investigated by different desulfurization temperatures at 20 atm in the continuous operation. The $H_2S$ removal efficiency tended to decrease below the desulfurization temperature of $450^{\circ}C$. Thus, the 10 hour continuous operation has been performed at the desulfurization temperature of $500^{\circ}C$ in order to maintain the high $H_2S$ removal efficiency. During 10 hour continuous operation, the $H_2S$ removal efficiency was above 99.99% because the $H_2S$ concentration after desulfurization was not detected at the inlet $H_2S$ concentration of 5,000 ppmv condition using UV analyzers (Radas2) and the detector tube (GASTEC) which lower detection limit is 1 ppmv.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.399-408
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• 2010

The characteristics of lifted laminar propane flames diluted with nitrogen have been investigated experimentally to elucidate self-excitation and the effects of flame curvature. Flame oscillation modes are classified as follows: oscillation induced by heat loss, a combination of oscillations induced by heat loss and buoyancy, and a combination of the oscillations induced by heat loss and diffusive thermal instability. It is shown that the oscillation induced only by heat loss is not relevant to the diffusive thermal instability and hydrodynamic instability caused by buoyancy; this oscillation is observed under all lift-off flame conditions irrespective of the fuel Lewis number. These experimental evidences are displayed through the analysis of the power spectrum for the temporal variation of lift-off height. The possible mechanism of the oscillation induced by heat loss is also discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.461-461
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• 2011

강수, 수위 및 유량자료 등의 수문자료는 안정된 물 관리 계획, 홍수조절 및 공급계획, 전력공급 등을 위한 댐의 역할을 원활하게 하기위한 운영의사결정을 위한 매우 중요한 기초자료가 된다. 댐 운영을 위한 다양한 기능을 가진 모델을 가지고 있다고 하더라도 매년 변하고 있는 댐 유역의 수문현상에 대한 관측자료를 이용하여 지속적으로 모델을 보정하여 정확성을 확인하고 향상시키는 노력을 기울여야 하므로 수문자료는 댐 운영에 있어서 필수적인 요소일 수밖에 없다. 본 연구에서는 한국수력원자력(주)의 9개 댐 유역에서 기존 활용 가능한 관측소 현황 및 현장조사를 통해 운영상 목적에 맞는 최적의 수위관측망을 설계하여 제시하였다. 설계 방법으로는 댐 유입량 파악과 개략적인 도달시간 파악을 위해 주요 유입지천인 국가하천과 지류 중 지방하천이라도 유역면적이 $150\;km^2$ 이상인 경우에는 유입량 파악을 위한 수위관측소를 두도록 설계하였다. 관측소 밀도는 각 댐 유역의 수문학적 유역 특성인 유역면적, 유입하천의 지형적 특성, 하천크기 등을 고려하여 결정하였다. 설계된 수위관측소들은 현장의 수위관측 및 유량관측에 대한 적정성을 검토하여 댐 저류지 배수영향 등으로 인해 관측이 부적정할 경우 이설을 통해 적정한 위치에서 수문조사가 이루어지도록 제안하였다. 본 연구에서 제안된 한국수력원자력(주) 관할 댐 유역의 수위관측망은 자체 관할 수위관측소 뿐 아니라 자료의 공동 활용이 가능한 국토해양부 등의 관측소까지 포함하고 있다. 따라서 댐 운영 의사결정을 위한 중요한 기초자료로서의 수위 및 유량자료를 경제적이고 효율적으로 제공할 수 있을 것으로 기대된다.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.853-860
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• 2019

In order to meet more severe environmental regulations, oxy-fuel circulating fluidized bed(CFB) boilers or ultra supercritical CFB boilers, which are a kind of process in that solid particles moves similar to fluid, have been developed in the world. In CFB power generation processes, the method to reduce or remove sulfur dioxide is in-situ desulfurization reaction via limestone directly injected into CFB boilers. However, the desulfurization efficiencies have continuously changed because limestones injected into CFB boilers are affected by various operation conditions (Bed temperature, pressure, solid circulating rate, solid holdup, residence time, and so on). In this study, a prediction method with physical and chemical properties of limestone and operation conditions of CFB boiler for in-situ desulfurization reaction in CFB boilers has developed by integrating desulfurization kinetic equations and hydrodynamics equations for CFB previously published. In particular, the prediction equation for in-situ desulfurization was modified by using experimental results from desulfurization reactions of various domestic limestones.

• 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.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.19-31
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• 1994

The objective of this study is to conduct a thermal-hydraulic analysis on the spent fuel pool and to evaluate a parametric effect for the thermal-hydraulic analysis of spent fuel pool. The selected parameters are the Reynolds Number and the gap flow through the oater gap between fuel cell and fuel bundle. The simplified flow network for a path of fuel cells is used to analyze the natural circulation phenomenon. In the flow network analysis, the pressure drop for each assembly from the entrance of the fuel rack to the exit of the fuel assembly is balanced by the driving head due to the density difference between the pool fluid and the average fluid in each spent fuel assembly. The governing equations ore developed using this relation. But, since the parameters(flow rate, pressure loss coefficient, decay heat, density)are coupled each other, iteration method is used to obtain the solution. For the analysis of the YGN 3&4 spent fuel rack, 12 channels are considered and the inputs such as decay heat and pressure loss coefficient are determined conservatively. The results show the thermal-hydraulic characteristics(void fraction, density, boiling height)of the YGN 3&4 spent fuel rack. There occurs small amount of boiling in the cells. Fuel cladding temperature is lower than 343.3$^{\circ}C$. The evaluation of parametric effect indicates that flow resistances by geometric effect are very sensitive to Reynolds number in the transition region and the gap flow is negligible because of the larger flow resistance in the gap flow path than in the fuel bundle.

• Journal of Korea Water Resources Association
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• v.48 no.3
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• pp.169-183
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• 2015

As a basic work for river restoration, analysis on fluvial geomorphological characteristics is made using past and present data to understand close-to-nature geomorphic status. The Miho and the Naesung Rivers are targets of this study. Fluvial geomorphic variables including valley-floor width, sinuosity, bankfull width, channel gradient, bed material size, bankfull discharge and unit stream power are evaluated with dominant processes. Though common sand-bed rivers with similar catchment area, the Miho and the Naesung Rivers are different in terms of valley-floor width, channel shape variables and dominant processes related with longitudinal location. In addition, analyses on interrelationship among the geomorphological variables are carried. Bankfull width is shown to be proportional to bankfull discharge, as is in a rough agreement with the previous studies. Relationship of bankfull discharge and channel gradient shows meandering and braiding are prevalent in the Miho River, whereas the most of the sub-reaches of the Naesung River fall to braiding. Relationship of channel gradient with width-depth ratio indicates dune-ripple processes are dominant in the Miho River, while the Naesung River shows longitudinal diversity from braiding in the downstream sub-reaches to riffle-pool and plane-bed along the upper ones. Analyses based on the past data on a river in a close-to-nature status are thought to be rather reasonable in comparison with those on the same river in a engineered condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.1031-1039
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• 1999

Electrospraying comprises the generation of liquid droplets by applying a high voltage to the surface of a liquid. By monitoring the current and the flow rate it was possible to obtain a stable cone jet mode in a given condition. In this work the liquid contained NaCl particles resolved in distilled water. The NaCl particles increased concentration of the ionized solution and thus increased electrical conductivity of the liquid, which was inversely proportional to the flow rate in the cone jet mode. A number of sprayed droplets were sampled and dried enough, and then the size of NaCl particles were measured. The measured droplet diameter was a little larger than two theoretical diameters, Rayleigh diameter and mobility diameter.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.535-543
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• 2022

A CPFD (Computational particle fluid dynamics) model of solar fluidized bed receiver of silicon carbide (SiC: average d_p=123 ㎛) particles was established, and the model was verified by comparing the simulation and experimental results to analyze the effect of particle behavior on the performance of the receiver. The relationship between the heat-absorbing performance and the particles behavior in the receiver was analyzed by simulating their behavior near bed surface, which is difficult to access experimentally. The CPFD simulation results showed good agreement with the experimental values on the solids holdup and its standard deviation under experimental condition in bed and freeboard regions. The local solid holdups near the bed surface, where particles primarily absorb solar heat energy and transfer it to the inside of the bed, showed a non-uniform distribution with a relatively low value at the center related with the bubble behavior in the bed. The local solid holdup increased the axial and radial non-uniformity in the freeboard region with the gas velocity, which explains well that the increase in the RSD (Relative standard deviation) of pressure drop across the freeboard region is responsible for the loss of solar energy reflected by the entrained particles in the particle receiver. The simulation results of local gas and particle velocities with gas velocity confirmed that the local particle behavior in the fluidized bed are closely related to the bubble behavior characterized by the properties of the Geldart B particles. The temperature difference of the fluidizing gas passing through the receiver per irradiance (∆T/I_DNI) was highly correlated with the RSD of the pressure drop across the bed surface and the freeboard regions. The CPFD simulation results can be used to improve the performance of the particle receiver through local particle behavior analysis.

• Clean Technology
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• v.19 no.4
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• pp.437-445
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• 2013

To develop SEWGS (sorption enhanced water gas shift) system using dry $CO_2$ absorbent for pre-combustion $CO_2$ capture, hydrodynamic characteristics of $CO_2$ absorbents were measured and investigated. The minimum fluidization velocity of $CO_2$ absorbent was measured and the effects of the operating conditions were investigated to operate the system at bubbling fluidized bed condition. The minimum fluidization velocity decreased as pressure and temperature increased. Moreover, the minimum fluidization velocity decreased as column diameter increased. The effects of operating conditions on the solid circulation rate were measured and investigated to select appropriate operating conditions for continuous $CO_2$ capture and regeneration. The measured solid circulation rates were ranged between 10 and 65 kg/h and increased as the solid injection velocity, gas velocity in the regeneration reactor, and solid height increased.