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1

A study on mass transfer modelling in SOFC anode: Comparison of diffusion mass transfer models for estimation of diffusion overpotential

Ramakrishnan P., Sahoo Abanti

Chemical and Process Engineering : New Frontiers

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2023

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Vol. 44, nr 1

art. no. e4

EN

The mathematical approach to SOFC modelling helps to reduce dependence on the experimental approach. In the current study, six different diffusion mass transfer models were compared to more accurately predict the process behavior of fuel and product diffusion for SOFC anode. The prediction accuracy of the models was extensively studied over a range of parameters. New models were included as compared to previous studies. The Knudsen diffusion phenomenon was considered in all the models. The stoichiometric flux ratio approach was used. All the models were validated against experimental data for a binary (CO-CO2) and a ternary fuel system (H2-15 H2O-Ar). For ternary system, the pressure gradient is important for pore radius below 0.6 μm and current density above 0.5 A/cm2. For binary system, the pressure gradient may be ignored. The analysis indicates that the MBFM is identified to be the best performing and versatile model under critical SOFC operating conditions such as fuel composition and cell temperature. The diffusive slip phenomenon included in MBFM is useful in SOFC operating conditions when fuel contains heavy molecules. The DGMFM is a good approximation of DGM for the binary system.

2

Numerical study on control strategy of a single cell proton conducting solid oxide fuel cell

Szczęśniak Arkadiusz

Journal of Power Technologies

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2022

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Vol. 102, nr 4

175--182

EN

The aim of the paper is to examine a control strategy for a single proton conducting solid oxide fuel cell (H+SOFC). The study is based on a dynamic model originating from the steady state reduced order model of H+SOFC. The proposed control strategy is based on a singular PID controller that controls the amount of air delivered to the cathode side of the fuel cell. Additionally, fuel mass flow is correlated with current density to achieve a fixed fuel utilization factor. The concept was tested on typical operating scenarios such as load-follow mode. The study revealed that the singular PID controller is reliable and ensures a safe H+SOFC operation.

3

Sensitivity analysis of main parameters of pressurized SOFC hybrid system

Kupecki Jakub

Journal of Power Technologies

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2019

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Vol. 99, nr 2

115--122

EN

The paper presents a sensitivity analysis of a pressurized SOFC–HS system. The systems are divided into two groups: atmospheric and pressurized. The main parameter of such systems are indicated and commented. The comparison of various configurations is shown in a view of efficiency obtained. The ultra high efficiency (65% HHV, 72% LHV) of electricity production seems to be possible by systems like these.

4

Effects of gas velocity on formation of carbon deposits on AS-SOFC fuel electrodes

Motylinski K., Skrzypkiewicz M., Naumovich Y., Wierzbicki M., Kupecki J.

Journal of Power Technologies

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2018

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Vol. 98, nr 4

322--328

EN

The elevated operating temperatures of solid oxide fuel cells (SOFC) create favorable kinetics for the oxidation of carboncontaining gas mixtures, which may include carbon monoxide and light organic compounds. The presence of carbon-based components in the fuel might result in the formation and deposition of soot on the surface of the anode in a fuel cell. This process depends on and is driven by the prevailing thermodynamic, kinetic and electrochemical conditions. The present study was premised on the following: in addition to the aforementioned parameters providing for the operating conditions, gas velocity also affects the formation of deposits on the anode. The role of fuel gas velocity in the process was studied experimentally using 5 cm x 5 cm anode supported solid oxide fuel cells (AS-SOFC) at 750°C at velocities in the range 0.1 to 0.9 m/s. It was found that carbon deposition was clearly observable approximately 24 hours after the necessary conditions were attained. An intense stage of performance degradation typically lasts for a period of up to 60 hours. An increase in fuel flow velocity leads to an acceleration in the carbon deposition process. The correlation between velocity and cell degradation due to this phenomenon was determined and the corresponding function was proposed.

5

Direct carbon, integrated gasification, and deposited carbon solid oxide fuel cells: a patent-based review of technological status

Skrzypkiewicz M., Obrębowski S.

Journal of Power Technologies

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2018

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Vol. 98, nr 1

139--160

EN

This review presents three directions in solid oxide fuel cell (SOFC) technology development involving solid-state carbon in some stage of the fuel-to-electricity conversion process: direct carbon (DC-SOFC), integrated gasification (IG-SOFC) and deposited carbon (rechargeable SOFC). Recent achievements of science and technology were studied in order to identify the most widely developed concepts. In addition, the review contains a statistical approach to published patents and articles, naming the people and institutions active in the field. Simultaneous development of all three technologies could bring synergies and contributed to a major breakthrough in the efficiency of coal-fired power plants.

6

Analiza możliwości wykorzystania ogniwa paliwowego SOFC jako pomocniczej jednostki mocy APU dla współczesnego samolotu pasażerskiego

Jaroszewicz A.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

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2017

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z. 89 [295], nr 1

45--62

PL

Współczesne samoloty pasażerskie należą do czołówki najbardziej niezawodnych i bezpiecznych środków transportu publicznego. Samoloty te certyfikowane są m.in. normą ETOPS (Extended range Twin Operations) zezwalającą dwusilnikowym samolotom pasażerskim operować na trasach długodystansowych, wcześniej niedostępnych dla maszyn o takiej liczbie silników. Norma ETOPS wymaga jednakzastosowania na pokładzie dwusilnikowego samolotu pasażerskiego dodatkowych, awaryjnych źródeł zasilania energią elektryczną, pneumatyczną i hydrauliczną, kompensujących (częściowo) spadek wydajności pokładowych systemów energetycznych przy niesprawności jednego z silników i systemów z nimi powiązanych. W artykule przeprowadzono analizę wykorzystania różnych typów ogniw paliwowych w technice lotniczej oraz przedstawiono projekt wstępny pomocniczej jednostki mocy APU, wykorzystującej ogniwo paliwowe SOFC (Solid Oxide Fuel Cell), przeznaczonej dla (awaryjnego) zasilania energią elektryczną samolotu pasażerskiego w koncepcji „More Electric Aircraft”.

EN

Modern passenger aircrafts belongs to the one of the most reliable and safe means of public transport. These aircrafts are certified according to ETOPS (Extended-range Twin-engine Operational Performance Standards) and they enable the introduction of twin-engine passenger aircraft on transcontinental routes which were earlier unavailable for twin-engine aircrafts. ETOPS standard requires the use aboard of the twin-engine passenger aircraft additional emergency sources of electrical, pneumatic and hydraulic power which partly compensate a decrease in performance on-board power systems at the failure of one of the engines and systems associated with them. The article describes an analysis of the use of different types of fuel cells in the aerospace engineering and presents preliminary design of the auxiliary power unit APU using fuel cell SOFC (Solid Oxide Fuel Cell), intended for emergency power supply of passenger aircraft in the concept of "More Electric Aircraft".

7

Solid Oxide Electrolysis Cell co-methanation supported by Molten Carbonate Fuel Cell - a concept

Milewski J.

Journal of Power Technologies

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2016

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Vol. 96, nr 1

8--14

EN

The paper presents a concept of coupling a Solid Oxide Electrolysis Cell with a Molten Carbonate Fuel Cell for co–electrolysis of H2O with CO2 for generating synthetic fuel (methane based) for an electricity storage application on a larger scale. The concept is focused on coal/natural gas fired power plants for upgrade as peak energy storage. MCFC anode and SOEC cathode are exposed to the same flow, SOEC produces hydrogen for MCFC and MCFC delivers CO2 for methanation processes. Both electrodes have compatible polarity, thus they can be directly connected by the current collector and there is no need to apply bipolar plates. On the other side, SOEC will release oxygen to the flue gases and MCFC will capture oxygen and carbon monoxide, thus at the outlet will be a flow with increased oxygen content and decreased carbon dioxide concentration. The concept requires detailed electrochemical, chemical, and thermal simulations.

8

Selected aspects of the design and operation of the first Polish residential micro-CHP unit based on solid oxide fuel cells

Kupecki J., Skrzypkiewicz M., Stefański M., Stępień M., Wierzbicki M., Golec T.

Journal of Power Technologies

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2016

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Vol. 96, nr 4

270--275

EN

The first Polish micro-combined heat and power unit (micro-CHP) with solid oxide fuel cells (SOFC) was designed and constructed in the facilities of the Institute of Power Engineering in Warsaw. The system was launched in September 2015 and is under investigation. At the current stage the unit is customized to operate on a pre-treated biogas. Adaptation of the fuel processing system, which is based on a steam reformer, makes it possible to utilize other gaseous and liquid fuels, including natural gas. The electric and thermal output of the system, up to 2 kW and about 2 kW, respectively, corresponds to the typical requirements of a detached dwelling or a small commercial site. Functionality of the system was increased by engaging two separate start-up modules, which are used for preheating the system from a cold state to the nominal working conditions. The first module is based on a set of electric heaters, while the second module relies on an additional start-up burner. The startup of the system from ambient conditions up to a thermally self-sufficient stage takes about 7 hours using the electric preheaters mode. Output residual heat was used to heat water to a temperature of about 50°C. The temperature of the flue gases at the inlet to the hot water tank was measured at approximately 300°C. Steam reforming of the biogas was performed by delivering deionized water to the steam reformer in order to maintain the S/C ratio at a range of 2–3.5. Selected aspects of the design and construction as well the first operational experiences are presented and discussed. The numerical modeling methodology is presented as a complimentary tool for system design and optimization.

9

The influence of fuel composition on Solid Oxide Fuel Cell obtained by using the advanced mathematical model

Milewski J.

Journal of Power Technologies

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2011

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Vol. 91, nr 4

179-185

EN

The advanced mathematical model of Solid Oxide Fuel Cell (SOFC) is presented. The governing equations of the model are presented and described. Based on the model the influence of fuel composition on SOFC performance is shown. Hydrogen is used as the reference fuel.

10

Determination of electronic conductance of solid oxide fuel cells

Nikonowicz Ł., Milewski J.

Journal of Power Technologies

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2011

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Vol. 91, nr 2

82-92

EN

This work considers electronic conductance in solid oxide fuel cells and consequences of its existence. Various types of electrolyte are analyzed. The voltage characteristics of cells show differences between a theoretical maximum circuit voltage and open circuit voltage (OCV). A relationship is assumed between the OCV value and electronic conductance. Based on experimental measurements an appropriate mathematical model was created. The model is used to calculate the temperature dependence of electronic conductance for the most popular types of electrolytes: GDC (Gadolinia-Doped Ceria), ScSZ (Scandia Stabilized Zirconia), LSGMC (Cobalt, Strontium, and Magnesium Doped Lanthanum Gallate), YSZ (Yttria-Stabilized Zirconia). The obtained results point to the possible existence of a very tight relationship between the electronic conductance and the open circuit voltage. This relationship enables OCV to be calculated when electronic conductance is known. Appropriate formulae can be determined. Temperature is one of the factors which influences the value of electronic conductance. Other influencing factors also exist but their impact on OCV is not well know. This article mentions some of them.

11

Comparative analysis of time constants in Solid Oxide Fuel Cell processes - selection of key processes for modeling power systems

Milewski J., Lewandowski J.

Journal of Power Technologies

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2011

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Vol. 91, nr 1

1-5

EN

The article presents a comparative analysis of the time constants of the main processes in the SOFC. The analysis was used to determine those processes most relevant to the modeling of an energy system comprising a fuel cell. The hybrid system, in addition to the fuel cell, has other devices (such as compressors, turbines, heat exchangers, etc.) working with it that may limit permissible ranges of parameter changes during transient processes. On the other hand, fuel cells affect other devices making up the system, including by restricting their operation in terms of dynamic responses. Determination of time constants of the main processes in the cell and their analysis and comparison with time constants of other devices will allow selection of the most important processes from modeling point of vies and simplify the dynamic fuel cell model, so the class of fuel cell will match classes of models of other system elements.