• Title/Summary/Keyword: Shrinking core model

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A discussion on the application of particle reaction model for iron ore pellet induration process modeling (탄재를 포함한 산화철 펠릿 소성 공정 수치 모델의 입자 반응 모델 적용)

  • Ahn, Hyungjun;Choi, Sangmin
    • 한국연소학회:학술대회논문집
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    • 2014.11a
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    • pp.165-166
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    • 2014
  • The application of particle reaction model in the packed bed process modeling is discussed for iron ore pellet induration process. Combustion of coke breeze in the pellet is estimated by using shrinking unreacted-core model and grain model in which the progress of chemical reaction is described in different concepts. Under the identical inlet gas and solid conditions, the calculation using shrinking core model showed deviated results in terms of temperature profile and conversion fraction, which may imply the significance of selecting proper particle reaction model in consideration of particle characteristics and process operation conditions.

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A new gas-solid reaction model for voloxidation process with spallation

  • Ryu, Je Ir;Woo, Seung Min
    • Nuclear Engineering and Technology
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    • v.50 no.1
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    • pp.145-150
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    • 2018
  • A new methodology, the crack-spallation model, has been developed to analyze gas-solid reactions dominated by crack growth inside of the solid reactant and spallation phenomena. The new model physically represents three processes of the reaction progress: (1) diffusion of gas reactant through pores; (2) growth of product particle in pores; and (3) crack and spallation of solid reactant. The validation of this method has been conducted by comparison of results obtained in an experiment for oxidation of $UO_2$ and the shrinking core model. The reaction progress evaluated by the crack-spallation model shows better agreement with the experimental data than that evaluated by the shrinking core model. To understand the trigger point during the reaction progress, a detailed analysis has been conducted. A parametric study also has been performed to determine mass diffusivities of the gas reactant and volume increase constants of the product particles. This method can be appropriately applied to the gas-solid reaction based on the crack and spallation phenomena such as the voloxidation process.

A kinetic study of pyrite in the lime roasting of a vertical cyclone (수직 싸이클론의 ${Ca(OH)}_{2}$ 배소에서 $FeS_{2}$의 열적반응에 관한 연구)

  • 조종상
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.1
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    • pp.119-125
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    • 1999
  • This research has been studied in terms of investigating the reaction behavior of pyrite with a cyclone reactor. The Mathematical model has developed pyrite oxidation and lime sulfation in this reactor. The model assumes a chemical control shrinking core behavior for the pyrite and a fluid film control shrinking core behavior for the lime. The model was solved and characterized numerically. Experiments have been performed to study the influence of reaction parameters such as reactor temperatures, pyrite particle sizes, air flow rates, feeding rates, and mixing ratio of pyrite and lime. The oxidation and sulfation products were characterized chemically and physically.

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A Study on the Particle Reaction Models for Iron Ore Pellet Induration Process Modeling (철광석 펠릿 소성 공정 모형의 입자 반응 모델 적용에 관한 연구)

  • Ahn, Hyungjun;Choi, Sangmin
    • 한국연소학회:학술대회논문집
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    • 2015.12a
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    • pp.325-326
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    • 2015
  • Combustion of coke grains in a pellet used to be modeled using the shrinking core model in the previous indurator simulations. This leads to the discussions about its propriety due to the fundamental assumptions of the model inconsistent with the particle characteristics. The current study presents the grain model as an improvemen, and the differently used reaction models are compared. In addition, the simulations assuming changed particle conditions are conducted to display the effects of using the grain model.

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Hydrated Lime Roasting of Precious Metal Ores with A Cyclone Reactor

  • Cho, Chong S.
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1997.06a
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    • pp.53-60
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    • 1997
  • The roasting of pyrite with a cyclone reactor have been studied in terms of investigating the reaction behavior of pyrite. The development of a fundamental model for pyrite oxidation and lime sulfation in a vertical cyclone reactor. The model assumes a chemical control shrinking core behavior for the pyrite and a fluid film control shrinking core behavior for the lime. The oxygen and sulphur dioxide concentrations and the energy balance for the gas, pyrite and lime particles are solved. The model was solved and characterized numerically. Experiments have been performed to study the influence of reaction parameters such as reactor temperatures, pyrite particle sizes, air flow rates, feeding rates, and mixing ratio of pyrite and lime. The oxidation and sulfation products were characterized chemically and physically.

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Gasification reactivity of Chinese Shinwha Coal Chars with Steam (스팀을 이용한 중국산 신화 석탄 촤 가스화 반응에 관한 연구)

  • Kang, Min-Woong;Seo, Dong-Kyun;Kim, Yong-Tak;Hwang, Jung-Ho
    • Journal of the Korean Society of Combustion
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    • v.15 no.1
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    • pp.22-29
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    • 2010
  • In this study, carbon conversion was measured using an electronic mass balance. In a lab scale furnace, each coal sample was pyrolyzed in a nitrogen environment and became coal char, which was then gasified with steam under isothermal conditions. The reactivity of coal char was investigated at various temperatures and steam concentrations. The VRM(volume reaction model), SCM(shrinking core model), and RPM(random pore model) were used to interpret experimental data. For each model the activation energy(Ea), pre-exponential factor (A), and reaction order(n) of the coal char-steam reaction were determined by applying the Arrhenius equation into the data obtained with thermo-gravimetric analysis(TGA). According to this study, it was found that experimental data agreed better with the VRM and SCM for 1,000 and $1,100^{\circ}C$, and the RPM for 1,200 and $1,300^{\circ}C$. The reactivity of chars increased with the increase of gasification temperature. The structure parameter(${\psi}$) of the surface area for the RPM was obtained.

Modified Shrinking Core Model for Atomic Layer Deposition of TiO2 on Porous Alumina with Ultrahigh Aspect Ratio

  • Park, Inhye;Leem, Jina;Lee, Hoo-Yong;Min, Yo-Sep
    • Bulletin of the Korean Chemical Society
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    • v.34 no.2
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    • pp.519-523
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    • 2013
  • When atomic layer deposition (ALD) is performed on a porous material by using an organometallic precursor, minimum exposure time of the precursor for complete coverage becomes much longer since the ALD is limited by Knudsen diffusion in the pores. In the previous report by Min et al. (Ref. 23), shrinking core model (SCM) was proposed to predict the minimum exposure time of diethylzinc for ZnO ALD on a porous cylindrical alumina monolith. According to the SCM, the minimum exposure time of the precursor is influenced by volumetric density of adsorption sites, effective diffusion coefficient, precursor concentration in gas phase and size of the porous monolith. Here we modify the SCM in order to consider undesirable adsorption of byproduct molecules. $TiO_2$ ALD was performed on the cylindrical alumina monolith by using titanium tetrachloride ($TiCl_4$) and water. We observed that the byproduct (i.e., HCl) of $TiO_2$ ALD can chemically adsorb on adsorption sites, unlike the behavior of the byproduct (i.e., ethane) of ZnO ALD. Consequently, the minimum exposure time of $TiCl_4$ (~16 min) was significantly much shorter than that (~71 min) of DEZ. The predicted minimum exposure time by the modified SCM well agrees with the observed time. In addition, the modified SCM gives an effective diffusion coefficient of $TiCl_4$ of ${\sim}1.78{\times}10^{-2}\;cm^2/s$ in the porous alumina monolith.

Characteristics of Various Ranks of Coal Gasification with $CO_2$ by Gas Analysis (가스분석을 이용한 석탄 종류별 $CO_2$ 가스화 반응특성 연구)

  • Kim, Yong-Tack;Seo, Dong-Kyun;Hwang, Jung-Ho
    • Journal of the Korean Society of Combustion
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    • v.15 no.2
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    • pp.41-49
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    • 2010
  • Various coals from many countries around the world have been used for pulverized coal boiler in power plants in Korea. In this study, the gasification reactivities of various coal chars with $CO_2$ were investigated. Carbon conversion was measured using a real time gas analyzer with NDIR CO/$CO_2$ sensor. In a lab scale furnace, each coal sample was devolatilized at $950^{\circ}C$ in nitrogen atmosphere and became coal char and then further heated up to reach to a desired temperature. Each char was then gasified with $CO_2$ under isothermal conditions. The reactivities of coal chars were investigated at different temperatures. The shrinking core model (SCM) and volume reaction model(VRM) were used to interpret the experiment data. It was found that the SCM and VRM could describe well the experimental results within the carbon conversion of 0-0.98. The gasification rates for various coals were very different. The gasification rate for any coal increased as the volatile matter content increased.

Kinetic study of high-temperature removal of $H_2S$ by Ca-based sorbents (황화수소 제거를 위한 칼슘계 고온탈황제의 황화반응속도에 관한 연구)

  • 김영식;전지환
    • Proceedings of the Korean Environmental Sciences Society Conference
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    • 1998.04a
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    • pp.144-153
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    • 1998
  • Sorbents of calcined limestone and oyster particles having a diameter of about 0.63mm were exposed to simulate fuel gases containing 5000ppmv H2S for temperatures ranging from 600 to 800C in a TGA. The reaction between CaO and H2S proceds via an unreacted shrinking core mechanism. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. The kinetics of the sorption of H2S by CaO is sensitive to the reaction temperature and particle size, and the reaction rate of oyster was faster than the calcined limestone.

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Kinetic of High-Temperature Removal of $H_2S$ by Ca-based Sorbents (황화수소 제거를 위한 칼슘계 고온 탈황제의 황화반응속도)

  • 김영식;전지환;손병현;정종현;정덕영;오광중
    • Journal of Environmental Science International
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    • v.8 no.1
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    • pp.125-133
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    • 1999
  • Sorbents of calcined limestone and oyster particles having a diameter of about 0.63mm were exposed to simulated fuel gases containing 5000ppm $H_2S$ for temperatures ranging from 600 to 80$0^{\circ}C$ in a TGA (Thermalgravimetric analyzer). The reaction between CaO and $H_2S$ proceeds via an unreacted shrinking core mechanism. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. The kinetics of the sorption of $H_2S$ by CaO is sensitive to the reaction temperature and particle size, and the reaction rate of oyster was faster than the calcined limestone.

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