• Energy Research

Abstract In this work, dynamic modelling of a system based on a reversible solid oxide cell (rSOC) is developed so that it can be integrated with the grid for power balancing. The focus of this work is on the dynamic operation of a system, which is investigated using representative profiles of wind electricity production. In addition, the effect and challenges of dynamic operation on the system and stack itself are studied. Detailed operation strategies are defined during the switching process from one operational mode to another and are implemented on the dynamic process model. Simulation results show that when the rSOC system is operated in solid oxide electrolysis (SOE) and solid oxide fuel cell (SOFC) modes alternatively, energy balancing can be implemented on a continuous basis. In this process, the results show that the rSOC system operates in a safe operating range and does not deviate from the pre-defined limits. This is due to the accurate strategies developed for the switching process. It is also observed from the simulation results that the switching time is significantly influenced by the initial power of the first and the final power of the later operational mode. The proposed model of rSOC was validated using experimental data, and good agreement with experimental data was demonstrated.

The concept of direct carbon fuel cell (DCFC) can be realized using different types of fuel cells. The most important advances were achieved for solid oxide fuel cells or molten carbonate fuel cells, DC-SOFC and DC-MCFC, respectively. Utilization of solid fuels, such as coal, char or biochar in high temperature electrochemical reaction offers a great potential in terms of the electric efficiency. While in conventional gas-fed fuel cells the transference number is equal 2, the electrochemical oxidation of solid fuel - in theory - can be realized with ion transfer number of 4. In the current study several configurations of DCFC systems based on SOFCs and MCFCs were analysed. The focus was on determining the efficiency for systems with different methods of delivering the fuel and alternative post-combustion systems. The article presents variant analysis of eight configurations of power plants based on DCFCs. The modified parameters included the cell voltage, effective transference number and the fuel utilization. Each configuration is presented and discussed. The efficiency of the alternative configurations lays in the range from 36 to 64% (LHV-based). Authors explain the methodology of the study and quantify the results as well provide justification concerning the Assumptions. Koncepcja węglowego ogniwa paliwowego (DCFC) może być realizowana wykorzystując różne typy ogniw paliwowych. Największe postępy osiągnięto dla stałotlenkowych ogniw paliwowych (DC-SOFC) oraz dla ogniw paliwowych ze stopionym węglem (DC-MCFC). Wykorzystanie paliw stałych, tj. węgiel, węgiel brunatny lub biowęgiel w wysokotemperaturowej reakcji elektrochemicznej, ma ogromny potencjał pod względem sprawności elektrycznej. Podczas gdy w konwencjonalnych ogniwach paliwowych zasilanych gazem, liczba przenoszenia wynosi 2, to w przypadku elektrochemicznego utleniania paliw stałych, w teorii, liczba przenoszenia jonów wynosi 4. W ramach niniejszej pracy zbadano kilka konfiguracji układów DCFC opartych na SOFC i MCFC. Skoncentrowano się głównie na określeniu sprawności systemów energetycznych dla różnych metod dostarczania paliwa i instalacji dopalania. W artykule przedstawiono analizę wariantową ośmiu konfiguracji elektrowni opartych na DCFC. Modyfikowanymi parametrami były napięcie ogniwa, efektywna liczba przenoszenia oraz wykorzystanie paliwa. Każda z konfiguracji została zaprezentowana i omówiona. Sprawność zbadanych konfiguracji znajduje się w zakresie od 36 do 64% (oparte na LHV). Autorzy wyjaśniają metodologię badania, określają ilościowo wyniki oraz uzasadniają założenia.

The paper presents recent advances in Poland in the field of high temperature fuel cells. The achievements in the materials development, manufacturing of advanced cells, new fabrication techniques, modified electrodes and electrolytes and applications are presented. The work of the Polish teams active in the field of solid oxide fuel cells (SOFC) and molten carbonate fuel cell (MCFC) is presented and discussed. The review is oriented towards presenting key achievements in the technology at the scale from microstructure up to a complete power system based on electrochemical fuel oxidation. National efforts are covering wide range of aspects both in the fundamental research and the applied research. The review present the areas of (i) novel materials for SOFC including ZrO2-based electrolytes, CeO2-based electrolytes, Bi2O3 based electrolytes and proton conducting electrolytes, (ii) cathode materials including thermal shock resistant composite cathode material and silver-containing composites, (iii) anode materials, (iv) metallic interconnects for SOFC, (v) novel fabrication techniques, (vi) pilot scale SOFC, including electrolyte supported SOFC (ES-SOFC) and anode supported SOFC (AS-SOFC), (vii) metallic supported SOFC (MS-SOFC), (viii) direct carbon SOFC (DC-SOFC), (ix) selected application of SOFC, (x) advances in MCFC and their applications, (xi) advances in numerical methods for simulation and optimization of electrochemical systems.

Solid oxide fuel cells (SOFC) o ff er several advantages that are accelerating the research and development of the technology. Recent advances include the improvement of materials and new fabrication techniques, as well as new designs, fl ow con fi gurations, and applications. The large scale implementation of fuel cells, especially in distributed energy generation, is limited by several factors –– one of which is their limited fuel fl exibility. Changing fuel typically requires modifying the fuel processing unit to make it possible to e ff ectively convert raw fuel into hydrogen-rich gas. One potential solution allows for the use of alternative fuels without the need for customization of the fuel processor. This solution requires the adaptation of the stack to operate with direct internal reforming (DIR) of the fuel on the surface of the anodes. The present study explores the potential to internally reform methane in the SOFC stack with electrolyte supported cells. The numerical model that was developed for the simulation of the 1300 W stack was validated using experimental data obtained from partial internal reforming. Later, the model was applied to simulate the operation of the stack with complete internal reforming of methane. It was observed that the strong e ff ects of internal reforming on the temperature in the outlets are visible when the current exceeds 22 A. However, it was proven that the DIR-SOFC mode of operation is possible in the considered stack without exceeding the advised temperature limits in the core, and in the outlets of the anodic and cathodic compartments. The model was found to be accurate and the observed relative prediction error was in the range of 1.51 – 2.38%

Abstract Solid oxide fuel cells operate at high temperature, typically in the range 650–850 °C, utilizing between 50% and 75% of fuel. The remaining fuel can be either burned in a post-combustor located downstream of the solid oxide fuel cells (SOFC) stack or partially recycled. Several of the SOFC-based power systems include recirculation which is used to supply the steam to the fuel processing unit based on steam reforming. In such a system, the recycled stream makes it possible to eliminate the supply of water from the external source. In the same time, recirculation aids in increasing the overall fuel utilization in the power system. As a result the efficiency increases by 5–12% points. The electrochemical reaction in SOFC generates a substantial amount of water by combining the hydrogen molecules with oxygen extracted from the air entering the cathodic compartments. The recycled stream contains water vapor which is circulated in the recycled loop. In the current analysis, the system for recirculation of the anodic off-gas with complete removal of water was proposed and studied. Performance of a planar cell operated with different rates of recycling was studied using the experimental setup with chiller-based recirculation. Quantification of the improvement of the efficiency was based on the analysis of the increase of voltage of cell operated at a given current density. The experimental study demonstrated that the performance of a stand-alone SOFC can be increased by 18–31%. Additionally, the numerical model was proposed to determine the performance in other operating conditions.

Abstract This paper presents a numerical analysis of a 1000 W-class solid oxide fuel cell stack. The study includes simulation of dynamic operation of the unit under conditions which are qualified as faults. The simulation tool was developed to address the effects of oxidant-related faults on the operating parameters of the stack. Additionally, a control system was proposed in order to mitigate the effects of the sudden reduction in the flow of oxidant and passivation of the cells inside a 60-cell stack. In the current study, those occurrences were related to the loss of tightness of the sealants in the stack of planar cells. The model of an adiabatic-stack was used to generate the temperature profiles and was used in two reference cases. In the first case, the control system was activated in order to maintain the key parameters within the safe range, in the second case the simulations with deactivated controls enabled prediction of the temperature, voltage and power in the stack which continues operation without counteractions oriented toward minimizing the negative impacts on the performance due to exceeding the given limiting values of parameters. In the current study, two scenarios were analyzed: partial loss of oxidant and partial failure of stack modules resulting in decrease of the generated electric power. The results of both cases are presented, with and without the fault prevention control modules considered. Adjustment of the operating parameters can effectively limit the rapid increase in thermal gradients inside the stack. To complement the discussion, a classification of the typical faults of SOFC stack is presented.

One of the key issues in the energy production sector worldwide is the efficient way to storage energy. Currently- more and more attention is focused on Power-to-Gas (P2G) installations- where excess electric power from the grid or various renewable energy sources is used to produce different kind of fuels- such as hydrogen. In such cases- generated fuels are treated as energy carriers which- in contrast to electricity- can be easy stored and transported. Currently- high temperature electrolysers- based solid oxide cells (SOC)- are treated as an interesting alternative for P2G systems. Solid oxide electrolysers (SOE) are characterized as highly efficient (~90%) and long-term stable technologies- which can be coupled with stationary power plants. In the current work- the solid oxide cell stack was operated in electrolysis mode in the endothermic conditions. Based on the gathered experimental data- the numerical model of the SOC stack was created and validated. The prepared and calibrated model was used for generation of stack performance maps for different operating conditions. The results allowed to determine optimal working conditions for the tested stack in the electrolysis mode- thus reducing potential costs of expensive experimental analysis and test campaigns.

This work aims at the development of a simulation tool to optimize the design of a hybrid fuel cell/battery system to supply ICT equipment. In the framework of the ONSITE European project, which deals with a hybrid (fuel cell and batteries) RBS (Radio Base Stations) supply system, a modeling activity is carried out to optimize the system operations. The developed algorithms separately implement a Solid Oxide Fuel Cell system and a high temperature Sodium Nickel Chloride battery for design purpose and collect them in a unique model for devices interaction (i.e. power production, storage, and control). Moreover, a Computational Fluid Dynamics battery model is developed to analyse the heat transfer while the SOFC stack generates excessive heat during operation and outlet hot gases can be effectively used. Since the SNC batteries need heat during charging process (to maintain their operating temperature) and, conversely, the reactions are exothermic in discharge mode, the described approach aims at combining SNC batteries with micro-CHP unit to optimize the energy flows. The implementation requires several alternative designs and variant analysis to secure proper operation of battery and power generation unit. The model developed and shown in this paper is a dedicated tool for the simulation of the hybrid system proposed and for the optimal designing of each main sub component. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Abstract This article presents a conceptual power-to-gas system based on a high temperature electrolysis unit. The solid oxide electrolyzer (SOE) delivers highly efficient conversion of intermittent electricity from wind and solar into hydrogen, which can then be directly injected into the gas grid or used to synthesize methane in a Sabatier reactor. Due to the unpredictable character of these sources, the grid experiences imbalances, which destabilize the energy system. The solution, in the form of a high temperature electrolyzer, mitigates the problem by coupling the electric and gas grids. The advantages of solid oxide electrolysis over conventional electrolyzers are as follows: (i) SOEC offers outstanding efficiency, exceeding 70–80%, (ii) no noble metals are needed for catalytic reactions – the ceramic materials of electrodes and the high temperature substitute noble metal loading, (iii) SOEC mode can be switched to SOFC and the interchange supports the unique self-healing of the cells, (iv) modular design makes it easy to scale up the system based on the SOEC stack, (v) absence of any liquid electrolyte that has to be replaced on a regular basis. The 10 kW-class power-to-gas system is presented and the efficiency of the system assessed and discussed from an energy point of view. Accepting the current assumptions related to the performance of cells making up the electrolysis unit, the system can achieve efficiency in excess of 74%. The modeling approach is given and the performance map of the system is analyzed with respect to the variation of voltage and steam utilization in the electrolyzer.