촉매 연소를 열원으로 한 수증기-메탄개질반응 전산유체해석

이정섭,이강훈,유상석,안국영,강상규 한국수소및신에너지학회 2013 한국수소 및 신에너지학회논문집 Vol.24 No.2

A steam reformer is a chemical reactor to produce high purity hydrogen from fossil fuel. In the steam reformer, since endothermic steam reforming is heated by exothermic combustion of fossil fuel, the heat transfer between two reaction zones dominates conversion of fossil fuel to hydrogen. Steam Reforming is complex chemical reaction, mass and heat transfer due to the exothermic methane/air combustion reaction and the endothermic steam reforming reaction. Typically, a steam reformer employs burner to supply appropriate heat for endothermic steam reforming reaction which reduces system efficiency. In this study, the heat of steam reforming reaction is provided by anode-off gas combustion of stationary fuel cell. This paper presents a optimization of heat transfer effect and average temperature of cross-section using two-dimensional models of a coaxial cylindrical reactor, and analysis three-dimensional models of a coaxial cylindrical steam reformer with chemical reaction. Numerical analysis needs to dominant chemical reaction that are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming(DSR) reaction. The major parameters of analysis are temperature, fuel conversion and heat flux in the coaxial reactor.

Development of a stand-alone steam methane reformer for on-site hydrogen production

Yang, Jung-Il,Kim, Tae Wan,Chan Park, Ji,Lim, Tak-Hyoung,Jung, Heon,Chun, Dong Hyun Elsevier 2016 International journal of hydrogen energy Vol.41 No.19

<P><B>Abstract</B></P> <P>A small, stationary reformer designed as a stand-alone and self-sustaining type was developed for on-site hydrogen (H<SUB>2</SUB>) production. We created a compact reformer to produce H<SUB>2</SUB> at a rate of 1 Nm<SUP>3</SUP>/h using the previously reported reaction kinetics of steam methane reforming (SMR). Both catalysts for the compact reformer - i.e., 15 wt% and 20 wt% Ni/γ-Al<SUB>2</SUB>O<SUB>3</SUB> - showed good activity, with CH<SUB>4</SUB> conversion exceeding 90% at 655 °C and a contact time of 3.0 g<SUB>cat</SUB>h/mol, which were considered critical thresholds in the development of a small, compact stationary reformer. At an H<SUB>2</SUB> production rate of 1 Nm<SUP>3</SUP>/h, the catalyst amount was calculated to be 167.8 g and the reformer length required to charge the catalyst was 613 mm, with a diameter of 1 inch. The CH<SUB>4</SUB> conversion and H<SUB>2</SUB> production rates achieved with the compact reformer using the 20 wt% Ni/γ-Al<SUB>2</SUB>O<SUB>3</SUB> catalyst at 738 °C were 97.9% and 1.22 Nm<SUP>3</SUP>/h, respectively. Furthermore, a heat-exchanger type reformer was developed to efficiently carry out the highly endothermic SMR reaction for on-site H<SUB>2</SUB> production. This reformer comprised a tube side (in which the catalysts were charged and the SMR reaction took place by feeding the reactants) and a shell side (in which the heat for the endothermic reaction was supplied by CH<SUB>4</SUB> combustion). Reforming activities were evaluated using the active 20 wt% Ni/γ-Al<SUB>2</SUB>O<SUB>3</SUB> catalyst, depending on the reactants' gas hourly space velocity (GHSV). The H<SUB>2</SUB> production rate increased as the GHSV increased. Finally, the reformer produced a CH<SUB>4</SUB> conversion of 98.0% and an H<SUB>2</SUB> production rate of 1.97 Nm<SUP>3</SUP>/h at 745 °C, as well as a high reactants' GHSV of 10,000 h<SUP>−1</SUP>. Therefore, the heat-exchanger type reformer proved to be an effective system for conducting the highly endothermic SMR reaction with a high reactants' GHSV to yield a high rate of H<SUB>2</SUB> production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Development of the compact reformer for 1 Nm<SUP>3</SUP>/h production rate. </LI> <LI> The heat-exchanger type reformer with CH<SUB>4</SUB> combustion as a stand-alone and self-sustaining type for on-site H<SUB>2</SUB> production. </LI> <LI> 99.7% CH<SUB>4</SUB> conversion and 1.21 Nm<SUP>3</SUP>/h H<SUB>2</SUB> production rate obtained by the heat-exchanger type reformer at 798 °C. </LI> <LI> The H<SUB>2</SUB> production rate was increased with increasing the reactants' GHSV. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Combined thermal characteristics analysis of steam reforming and combustion for 5 kW domestic PEMFC system

Jo, Taehyun,Koo, Bonchan,Lee, Yonghan,Kim, Dowook,Lee, Dohyung Elsevier 2018 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.43 No.31

<P><B>Abstract</B></P> <P>A natural gas-based steam reformer for a domestic polymer electrolyte membrane fuel cell (PEMFC) system is thermodynamically analyzed with a special focus on the heat supply mechanism, which is critical to the endothermic steam reforming process. The interdependence of the reforming and combustion processes is evaluated through a characteristic study of heat transfer from the heat source to the reforming zone. Premixed combustion patterns may be affected by the inclusion of controlling means such as a metal fiber screen or burner placement. In this study, we attempted to enhance reforming performances of a reformer embedded in a 5 kW in-house PEMFC through modification of the combustion pattern by varying the type and placement of the burner and other operating conditions. Reforming input conditions such as steam-carbon ratio (SCR) and fuel distribution ratio (FDR) are also analyzed to quantify the overall performance such as thermal efficiency and fuel conversion rate. In our experiments involving three types of combustors—cylindrical metal fiber burner, flat type metal fiber burner and nozzle-mixing burner—the operating conditions are set so that the SCR and FDR are in the range 3.0–4.0 and 0.4–0.7, respectively. It is found that the cylindrical metal fiber burner at an appropriate location could improve thermal efficiency up to 79% by 10%, compared to other devices. This maximum thermal efficiency output is obtained with 0.63 FDR, which eventually yields 99% hydrogen conversion rate when using a cylindrical metal fiber burner, while the other burners produce 95% conversion. These outputs substantiate that the overall efficiency is strongly affected by an appropriate control for uniform temperature distribution on the catalyst layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The steam reformer is experimentally studied in terms of operation conditions and the heat exchange between three type combustors and reactor. </LI> <LI> The CMFB could enhance the thermal efficiency by 10%, up to 79%, higher than the FMFB and Nozzle burner. </LI> <LI> Various correlations are discovered between SCR, FDR, internal temperature and performances throughout the experiments. </LI> <LI> The optimal fuel distribution ratio is considered as 0.63 that allows appropriate catalyst layer temperature and also best thermal efficiency. </LI> </UL> </P>

Steam reforming of monohydric alcohols and polyalcohols: Influence of single or multiple hydroxyl group(s) on nature of the coke

Yiran Wang,Chao Li,Shu Zhang,Leilei Xu,Xun Hu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.110 No.-

Alcohols like ethanol and glycerol have been extensively investigated as potential feedstock for on-sitehydrogen production by steam reforming. The varied number of hydroxyl group in the alcohols inevitablyaffects the reaction intermediates generated and eventually properties of coke formed. In this study, fouralcohols (ethanol, ethylene glycol, 1-propanol and glycerol) with the single or multiple hydroxyl groupswere steam reformed, focusing on the influence of the hydroxyl group on the properties of the coke. Theresearch results showed that steam reforming of ethanol and glycerol produced more coke than that insteam reforming of 1-propanol or ethylene glycol, while the Ni/SBA-15 catalyst deactivated to a higherextent in steam reforming of ethylene glycol or glycerol with multiple hydroxyl group, due to the cokeof varied properties. The coke produced by steam reforming of ethanol and 1-propanol contained moredefective structures but more aromatic. However, the generated coke from the steam reforming of ethyleneglycol and glycerol had more aliphatic structures, especially in that from ethylene glycol. On theother hand, the carbon nanotubes formed by the steam reforming of ethanol or 1-propanol had thin wallthickness and smooth surface, while that in steam reforming of ethylene glycol and glycerol had thickwall and very rough surface, resulting from the distinct reaction intermediates formed.

Rapid evaluation of coke resistance in catalysts for methane reforming using low steam-to-carbon ratio

Jeon, Jiyoon,Nam, Seongju,Ko, Chang Hyun Elsevier 2018 CATALYSIS TODAY - Vol.309 No.-

<P><B>Abstract</B></P> <P>The formation and subsequent accumulation of coke is one of the major reasons for the catalyst deactivation in methane reforming reaction. Although the investigation of coke-resistant catalysts is closely related to their long-term stability of given catalysts, it takes a long time to quantitatively measure the amount of carbon deposition on catalysts under normal reaction operational conditions. To overcome this problem, we used the steam deficient reaction condition, i.e. a low steam-to-carbon ratio (S/C) of 0.5 to accelerate the carbon deposition on catalysts. In this condition, the base catalyst of 10wt.% Ni/alumina rapidly lost its catalytic activity, indicating fast coke deposition. However, adding proper additives, such as Ru among various precious metals (Ru, Rh, Pt, and Pd) and alkaline earth metals (Mg, Ca, Sr, and Ba) with the appropriate loading (5wt.%) effectively suppressed coke formation. The optimized catalyst composition is 0.5wt.% Ru/5wt.% Mg/10wt.% Ni/alumina, which displayed coke resistance in the long-term stability test of steam methane reforming and 40h test of dry reforming of methane. These experimental results indicate that the method developed in this study is useful for the rapid evaluation of given catalysts for their coke resistance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of steam-to-carbon ratio on coke formation during methane reforming studied. </LI> <LI> Coke formation measured within 5h using low steam-to-carbon ratio and high WHSV. </LI> <LI> Quick development of Ru-Mg catalysts with high coke resistance. </LI> <LI> Long-term stability for both steam and dry methane reforming demonstrated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Low Temperature Methane Steam Reforming for Hydrogen Production for Fuel Cells

Roh, Hyun-Seog,Jun, Ki-Won Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.1

Low temperature methane steam reforming to produce $H_2$ for fuel cells has been calculated thermodynamically considering both heat loss of the reformer and unreacted $H_2$ in fuel cell stack. According to the thermodynamic equilibrium analysis, it is possible to operate methane steam reforming at low temperatures. A scheme for the low temperature methane steam reforming to produce $H_2$ for fuel cells by burning both unconverted $CH_4$ and $H_2$ to supply the heat for steam methane reforming has been proposed. The calculated value of the heat balance temperature is strongly dependent upon the amount of unreacted $H_2$ and heat loss of the reformer. If unreacted $H_2$ increases, less methane is required because unreacted $H_2$ can be burned to supply the heat. As a consequence, it is suitable to increase the reaction temperature for getting higher $CH_4$ conversion and more $H_2$ for fuel cell stack. If heat loss increases from the reformer, it is necessary to supply more heat for the endothermic methane steam reforming reaction from burning unconverted $CH_4$, resulting in decreasing the reforming temperature. Experimentally, it has been confirmed that low temperature methane steam reforming is possible with stable activity.

Low Temperature Methane Steam Reforming for Hydrogen Production for Fuel Cells

Hyun-Seog Roh,전기원 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.1

Low temperature methane steam reforming to produce H2 for fuel cells has been calculated thermodynamically considering both heat loss of the reformer and unreacted H2 in fuel cell stack. According to the thermodynamic equilibrium analysis, it is possible to operate methane steam reforming at low temperatures. A scheme for the low temperature methane steam reforming to produce H2 for fuel cells by burning both unconverted CH4 and H2 to supply the heat for steam methane reforming has been proposed. The calculated value of the heat balance temperature is strongly dependent upon the amount of unreacted H2 and heat loss of the reformer. If unreacted H2 increases, less methane is required because unreacted H2 can be burned to supply the heat. As a consequence, it is suitable to increase the reaction temperature for getting higher CH4 conversion and more H2 for fuel cell stack. If heat loss increases from the reformer, it is necessary to supply more heat for the endothermic methane steam reforming reaction from burning unconverted CH4, resulting in decreasing the reforming temperature. Experimentally, it has been confirmed that low temperature methane steam reforming is possible with stable activity.

루테늄 촉매를 이용한 에탄의 수증기 개질 반응 Kinetics와 반응기 Sizing

신미 ( Mi Shin ),성민준 ( Min Jun Seong ),장지수 ( Ji Su Jang ),이경은 ( Kyung Eun Lee ),조정호 ( Jung Ho Cho ),이영철 ( Young Chul Lee ),박영권 ( Young Kwon Park ),전종기 ( Jong Ki Jeon ) 한국공업화학회 2012 공업화학 Vol.23 No.2

상업용 루테늄 촉매 상에서 에탄의 수증기 개질 반응에 대한 kinetics 데이터를 얻기 위하여 반응온도, 에탄의 분압, 수증기/에탄의 비 등을 변화시키면서 반응 실험을 수행하였다. Kinetics 데이터를 사용하여 Power rate law kinetic model과 Langmuir-Hinshelwood model의 parameter를 구하였다. 또한 kinetic model식을 적용하여 PRO/II를 이용한 공정 모사를 통해서 에탄의 수증기 개질 반응기 sizing을 수행하였다. 동일한 전환율을 얻기 위해서는 Power rate law model을 적용하였을 경우가 Langmuir-Hinshelwood model을 적용하였을 경우보다 개질 반응기의 부피가 더 큼을 알 수 있었다. Langmuir-Hinshelwood model에 의해 계산된 반응 속도가 반응 실험 결과에 의해 구해진 반응 속도와 더 잘 일치했기 때문에 Langmuir-Hinshelwood model을 적용하여 계산된 반응기의 크기가 실제 반응기 설계에 더 적절하다고 판단된다. In this study, kinetics data was obtained for steam reforming reaction of ethane over the commercial ruthenium catalyst. The variables of ethane steam reforming were the reaction temperature, partial pressure of ethane, and steam/ethane mole ratio. Parameters for the power rate law kinetic model and the Langmuir-Hinshelwood model were obtained from the kinetic data. Also, sizing of steam reforming reactor was performed by using PRO/II simulator. The reactor size calculated by the power rate law kinetic model was bigger than that of using the Langmuir-Hinshelwood model for the same conversion of ethane. Reactor size calculated by the Langmuir-Hinshelwood model seems to be more suitable for the reactor design because the Langmuir-Hinshelwood model was more consistent with the experimental results.

The effect of time-periodic heat flux oscillations in the steam reformer

Joonguen Park,Shinku Lee,배중면 한국물리학회 2010 Current Applied Physics Vol.10 No.2

The effective method to increase heat transfer in the steam reformer has been investigated in this paper. The heat must be supplied to an endothermic steam reformer. Most of the heat is transferred from the reactor wall. The convective heat transfer rate can be improved according to periodical change of the heat flux of the plate, and the fuel conversion is in proportion to the heat transfer rate. In this work, correlation between the performance of the steam reformer and the time-periodic heat flux oscillation has been investigated. For this analysis, chemical reaction models in porous medium are incorporated under the transient state. Three types of heat flux wave pattern as an operating parameter are compared. However,total fuel conversion is not affected by these parameters although heat flux is time-periodically changed.

Steam reforming of n-dodecane over K₂Ti₂O₅-added Ni-alumina and Ni-zirconia (YSZ) catalysts

Kim, T.,Song, K.H.,Yoon, H.,Chung, J.S. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.40

<P>The steam reforming of n-dodecane over 35 wt% Ni supported on alumina (Ni-Al2O3) and yttrium-stabilized zirconia (Ni-YSZ) at 800 degrees C for 10 h with a steam-to-carbon ratio of 3 was tested in the presence and absence of 10 wt% of K2Ti2O5 (KTO) particles. The suppression of coke formation by KTO was investigated using various characterizations, including BET, TPO, TGA, TEM, and EELS. After the addition of 10 wt% of KTO particles by ball milling, Ni-YSZ exhibited stable performance with negligible coke formation at space velocities of less than 20,000 h(-1). The addition of KTO to Ni-Al2O3 did not yield any improvements because the majority of Ni particles in alumina pores are not directly in contact with the KTO phase. The dispersion of finely divided KTO particles on the surfaces of both Ni and the support effectively suppressed coke formation by steam gasification of the deposited coke into CO and H-2. First, the gradual accumulation of coke during the course of the reaction deactivated the Ni sites, which presented activity for the steam reforming of methane. The Ni and acidic sites, which were effective for the hydrogenolysis of n-dodecane to methane and ethylene (or ethane in the presence of KTO), were eventually deactivated. An overall reaction pathway was then proposed based on the results. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>