Efficiencies of olive kernel gasification combined cycle with solid oxide fuel cells (SOFCs)

Opportunities and Challenges in using SOFCs in Waste to Energy Systems An overview of the research activities and on-going multiple projects at Delft University of Technology aimed at the development of Solid Oxide Fuel Cell (SOFC) integrated waste to energy systems are presented in this paper. Resource and energy recovery from waste streams is becoming increasingly attractive. Pyrolysis, gasification, biomethanation, landfill etc lead to the production of combustible gases from waste feedstocks. However, the fuel gas produced is often contaminated when derived from waste- especially with some of the process routes mentioned above. If energy production is attempted, the use of efficient systems, when not expensive, will result in better financial returns on investment. As SOFCs are efficient and SOFC prices are expected to come down in the future, they might become an attractive option for power production from waste streams. Gasification is often considered for waste processing and results in the production of syngas rich in hydrogen and carbon monoxide. Plasma gasification is an emerging choice for municipal solid waste management and supercritical water gasification for wet waste streams. Pyrolysis systems operate at lower temperatures and hydrocarbon rich streams are produced. Biomethenation and landfill results in methane rich gas streams. Lower temperatures lead to incomplete carbon conversion in these systems thus lowering the achievable efficiencies. Different waste process routes result in different fuel mixes. High levels of contaminants in the fuel gases are expected in most of the waste to fuel gas systems. This makes it necessary to develop contaminant resistant fuel cells or complicated fuel processing and cleaning systems. Waste streams are often difficult to handle and hence system integration and heat integration becomes challenging. The research challenges hence vary from understanding the complex electrochemistry of fuel oxidation, understanding contaminant tolerance limits, developing contaminant tolerant cells, stacks and systems. Influence of waste-derived syngas compositions and contaminants on SOFCs will be presented and the removal of a variety of potential contaminants including higher hydrocarbons, particulates, H2S, HCl, alkali compounds, heavy metals etc will be discussed. A wide range of research activities ranging from pattern cell impedance analysis to integrated system development will be presented. Complex approaches required in cleaning the gas to meet the requirements of SOFCs will be explained. Additionally, a brief discussion on the achievable system efficiencies with SOFC integrated waste to energy systems and novel concepts such as gasifier- Reversible SOFC integrated power production cum energy storage systems will be presented. Finally, an overview of a wide range of national, European and international projects that helped or currently helping us to carry out the above mentioned research activities will be presented. These projects include, among others, Bill and Melinda Gates foundation funded reinvent the toilet project, a Dutch National Award winning wastewater to fertilizer and power project, an industry initiated project on Supercritical Water Gasifier-SOFC integration, an Indo-Dutch jointly funded project with activities also on biogas production from waste streams for SOFC applications and European projects on gasifier SOFC integration and reversible SOFCs.

The objective of this paper was to design energy integrated solid oxide fuel cell (SOFC) based microcombined heat and power (micro-CHP) systems using syngas derived from lignocellulosic biomass waste. The novel contributions of this work include (1) integration of syngas between a community-scale biomass gasification plant and SOFC-based micro-CHP systems in buildings; (2) heat integrated designs of SOFC-based micro-CHP systems; and (3) integration between SOFC and other heat-led renewable technologies, such as, syngas boilers, ground source heat pump (GSHP), and air source heat pump (ASHP). Conceptual process design frameworks including detailed heat recovery strategies were developed using Aspen plus. It is demonstrated that increases in heat integration between the SOFC inlet and outlet gases enhance the power-to-heat generation ratio from the SOFC, albeit at a higher cost of heat exchanger area. A straw (14.6 MJ/kg LHV) based community-scale gasification plant can generate 50−100 kWe of electricity at an overall CHP generation efficiency of ∼42%, while if integrated to SOFC-based micro-CHP systems (1 kWe) in individual dwellings via syngas, the overall energy efficiency can be greatly enhanced to ∼85%. It is envisaged that the SOFC should be operated at the highest electrical efficiency based on optimal heat integration; however, this needs to be coupled to other heat-led renewable technologies in order to meet the high residential heat to power demand ratio in the UK. Around 2.2 times more syngas may be required in boilers for supplementing residential heating. In integration with a GSHP loop, the flue gas from SOFC can itself be used as a refrigerant, and energy integration between the two systems can achieve an overall efficiency of ∼90%.

The paper presents the scheme of mini CHP with methane reformer and planar solid oxide fuel cells (SOFC) stack. The mini CHP produces electricity, superheated steam, hot air and methane for the reformer and it also preheats cathode air used in the SOFC stack as an oxidant. Moreover, the scheme’s mathematical model is constructed. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) studied experimentally is the key element in producing synthesis gas – fuel for the SOFC stack. The research indicates that synthesis gas containing 55% of hydrogen can be derived using the reactor. Through mathematical modeling, the entire reactor’s principal dimensions as well as flow rates of air, water and methane were adjusted to the methane reforming for the mini CHP studied. The paper includes the heat balances of the reformer, SOFC stack and waste heat boiler that produces the superheated steam, hot air and methane for the reformer as well as preheated cathode air. These balances were instrumental for calculating the useful product fraction in the reformer, fraction of hydrogen oxidized in the SOFC anode channel, electric gross efficiency, anode temperature, exothermic effect of synthesis gas hydrogen oxidation by air oxygen, excess entropy and Gibbs free energy change at standard conditions, SOFC electromotive force (EMF), specific flow rate of standard fuel for heat, and power generation. The simulation study has shown that the hydrogen oxidation products temperature in the SOFC anode channel is 850ºС, electric gross efficiency 61.0%, single fuel cell EMF 0.985 V, fraction of hydrogen oxidized in the SOFC anode channel 64.6%, specific flow rate of standard fuel for power generation 0.16 kg/(kW·h), for heat generation 44.7 kg/GJ. All the specific parameters are in good agreement with other publications results.

Direct use of propane and butane in Solid Oxide Fuel Cells (SOFCs) is desirable due to the availability of the fuel source, but is challenging due to carbon coking, particularly on the commercially available Ni+YSZ anode. A novel dual chamber Flame-assisted Fuel Cell (FFC) configuration with micro-tubular SOFCs (mT-SOFCs) is proposed for direct use of higher hydrocarbon fuels. Combustion exhaust for propane and butane fuels is analyzed experimentally and compared with chemical equilibrium. mT-SOFC polarization and power density testing in the FFC configuration with propane and butane fuels is discussed. Peak power and electrical efficiency conditions are assessed by varying the fuel-rich combustion equivalence ratio and flow rate. Carbon deposition and soot formation on the Ni+YSZ anode is investigated with a scanning electron microscope. The results indicate that reasonable power density (∼289 mW.cm−2) can be achieved while limiting soot formation in the flame and carbon deposition on the anode. Electrical efficiency based on the higher heating value of the fuels is analyzed and future research is recommended. Possible applications of the technology include small scale power generation, cogeneration and combined cycle power plants.

Solid oxide fuel cells (SOFCs) have garnered significant attention as a promising technology for clean and efficient power generation due to their ability to utilise renewable fuels such as hydrogen and ammonia. As carbon-free energy carriers, hydrogen and ammonia are expected to play a pivotal role in achieving net-zero emissions. However, a critical research question remains: how does the electrochemical performance of SOFCs compare when fuelled by hydrogen vs. ammonia, and what are the implications for their practical application in power generation? This mini-review paper is premised on the hypothesis that while hydrogen-fuelled SOFCs currently demonstrate superior stability and performance at low and high temperatures, ammonia-fuelled SOFCs offer unique advantages, such as higher electrical efficiencies and improved fuel utilisation. These benefits make ammonia a viable alternative fuel source for SOFCs, particularly at elevated temperatures. To address this, the mini-review paper provides a comprehensive comparative analysis of the electrochemical performance of SOFCs under direct hydrogen and ammonia fuels, focusing on key parameters such as open-circuit voltage (OCV), power density, electrochemical impedance spectroscopy, fuel utilisation, stability, and electrical efficiency. Recent advances in electrode materials, electrolytes, fabrication techniques, and cell structures are also highlighted. Through an extensive literature survey, it is found that hydrogen-fuelled SOFCs exhibit higher stability and are less affected by temperature cycling. In contrast, ammonia-fuelled SOFCs achieve higher OCVs (by 7%) and power densities (1880 mW/cm2 vs. 1330 mW/cm2 for hydrogen) at 650 °C, along with 6% higher electrical efficiency. Despite these advantages, ammonia-fuelled SOFCs face challenges such as NOx emissions, nitride formation, environmental impact, and OCV stabilisation, which are discussed alongside potential solutions. This mini review aims to provide insights into the future direction of SOFC research, emphasising the need for further exploration of ammonia as a sustainable fuel alternative.

Today in Ukraine the generation of electricity increasing is an extremely urgent task, which can be solved in a short period not only by the creation of new power plants, but by the modernization of high-power steam power units of existing thermal power plants. The conceptual solutions for the use of the gas turbine cycle and solid oxide fuel cell (SOFC) technology as an add-on to existing high-power steam turbines to increase the efficiency and environmental friendliness of their operation was developed. The paper considers the ways of complex modernization on the example of power units of CHPP-5 in Kharkiv with T-110/120-130 steam turbines. As an add-on, it is proposed to use the GTE-60 gas turbine unit with a capacity of 60 MW, produced at the Zorya-Mashproekt State Enterprise, Mykolaiv. Also, the integration into the “T-110/120-130–GTE-60” steam-gas circuit of a modular SOFC unit with internal reforming with a total capacity of 20 MW, which is composed of 40 tubular fuel cells with a capacity of 500 kW is considered. In the study of the condensation mode of the steam turbine operation, the following results were obtained: with the standard scheme of parallel connection of the gas turbine unit to the steam turbine with the supply of steam produced in the heat recovery steam generator (HRSG) to the medium-pressure turbine, the electrical efficiency was 42%, and the total electrical power of the installation was 170 MW; when the gas turbine unit was connected in parallel to the steam turbine with the supply of steam produced in the HRSG to the high-pressure turbine, the electrical efficiency reached 44.75%, and the total electrical power was 170 MW (during the operation of such a scheme, the steam is overheated due to additional combustion of gas in the HRSG); the waste circuit for connecting the gas turbine unit to the steam turbine with SOFC and regeneration substitution provided the electrical efficiency of 46% and the total electrical power of 190 MW; in the scheme of parallel connection of the gas turbine unit and SOFC to the steam turbine with the supply of produced steam to the high-pressure turbine, the electrical efficiency was 49.4% with the total electrical power of 190 MW. A comparative energy analysis of various options for combined circuit solutions for the modernization of the existing power unit of CHPP-5 was performed. This analysis showed that the greatest increase in electrical efficiency by 12% compared to the existing T-100/120-130 steam turbine was achieved in the scheme of parallel connection of the GTE-60 gas turbine unit with gas afterburning in the HRSG and SOFC with a total capacity of 20 MW.

Field test results of residential SOFC co-generation system at Tokyo Gas T. Ishikawa, S. Yamashita Product Development Dept., Tokyo Gas Lo., LTD., Tokyo, JAPAN We are developing residential SOFC co-generation system in order to commercialize it. One of our activities is to operate SOFC systems in field tests to make sure effects of installation and find technical issues. The detail is as below. A serious accident at nuclear power plants in Fukushima which was triggered by a huge earthquake on 11th March 2011 forces drastic re-formulation of Japan’s energy policy. In a series of discussions on the new energy policy, promoted use of distributed power generation is demanded more than ever as one of the main power systems, with extremely strong expectations for the fuel cell co-generation system. Tokyo Gas has been conducting research and development of solid oxide fuel cell (SOFC) which is expected to achieve the highest efficiency among all distributed power systems. In parallel with it, to verify the applicability of the SOFC for residential use and to identify technical challenges of SOFC, we have started field tests of SOFC systems of multiple manufacturers in the “Solid Oxide Fuel Cell (SOFC) demonstrative research project” with financial support from NEDO (Figure 1) [1][2]. We have installed a total of 23 units of four manufacturers in the field test of over four years (from 2007 to 2010), of which 14 units are still under operation as of April 30, 2012 (table 1). And the operating time has reached 18,600 hours at the longest, with 268,500 hours in total of 23 units. We have acquired the knowledge as shown below during the field tests conducted at general residences which we selected to reflect a variety of electrical and hot water demands (Figure 2). (1) Residential SOFC co-generation system contributes to the saving the preliminary energy consumptions and CO2 emissions by households in Japan (Figure 3, Figure 4). (2) SOFC system shows high electricity efficiency exceeding 45%LHV, and the transition of efficiency indicates that the durability of SOFC system including cell stack is estimated to be almost practical use (Figure 5). (3) SOFC system shows high reliability because of its simple system configuration. We will report the detailed results of SOFC field tests based on the latest data. Acknowledgments Finally, we would like to express our appreciation to NEDO, as this report is prepared mainly based on the results of the project supported by NEDO. Figure 2 Residential Demand (/Month) References [1] Solid Oxide Fuel Cell demonstrative research project final report (2011) http://www.nef.or.jp/sofc/share/pdf/h22y.pdf [2] Y. KAWABATA, T.SEYAMA, T.SOBUE, International Gas Union Research Conference ( 2011 ) Development and Field Test of Residential SOFC Co-generation System with All-ceramics-segmented Cells

In this paper the operation and performance of a high temperature solid oxide fuel cell (SOFC) stack on biomass syn-gas from a demonstration biomass gasification combined heat and power (CHP) plant is investigated. The objective of this work is to develop a computer simulation model of a biomass-SOFC CHP system, flexible enough for use in industry, capable of predicting system performance under various operating conditions and using diverse fuels. The biomass gasifier is of the dual fluidised bed (DFB) type with steam as the gasifying agent and is operated at atmospheric pressure. The tubular SOFC configuration, developed by Siemens Power Generation Inc (SPGI), is selected. It is considered to be the most advanced design and is approaching commercialisation. The SOFC stack model, developed using the chemical process flowsheet simulator Aspen Plus, is of equilibrium type and is based on Gibbs free energy minimisation. The SOFC model performs heat and mass balances and considers the ohmic, activation and concentration losses for the voltage calculation. Data available in the literature on the SPGI SOFC operating on natural gas is used to validate the model. The system model predicts thermodynamic condition and composition of all internal flow streams, the heat generated by the SOFC stack, voltage (V), current (I) and efficiency. Operating parameters are varied over a wide range, parameters such as fuel utilisation factor (Uf), current density (j) and steam to carbon ratio (STCR) have significant influence. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the SOFC stack should be operated at low STCR and high Uf, within certain limits. SOFC stack operation on biomass syn-gas is compared to operation on natural gas and as expected there is a drop in performance, which is attributed to increased input fuel and air flow due to the lower quality of the fuel gas. The optimum realistic operating conditions with regard to SOFC stack performance are identified. High electrical efficiencies are predicted making these systems very attractive for CHP applications.

The solid oxide fuel cell (SOFC) is recognized as one of high efficiency plants of electricity generation for a sustainable future system with low environmental impact. In term of fuel flexibility, SOFC is suitable for direct use of syngas from a coal gasification plant. The application of integrated SOFC in coal gasification based power plant, such as a light integrated gasification fuel cell (L-IGFC) power plant, could be one of the most promising coal energy conversions system providing high electrical efficiency with low CO2 emitted to the atmosphere. The system consists of a coal gasifier and SOFC module on the top of a steam turbine. The sensitivity analyses of major operating parameters were performed using the developed model. The results indicated that the L-IGFC plant could achieve electrical efficiency in the range of 46.35- 60.32% in lower heating value.

This paper investigated the performance of a bioethanol-fed Solid Oxide Fuel Cell (SOFC) system integrated with a distillation column (SOFC-D). Excess heat from the SOFC system was directly utilized in the distillation column where bioethanol (5 mol%) was purified to a desired concentration before feeding to the SOFC system consisting of an air heater, an ethanol/water heater, a reformer, an SOFC preheater, an SOFC stack and an afterburner. The SOFC-D system was simulated using Aspen PlusTM for the distillation portion and MatlabTM for the SOFC portion. The effects of operating parameters; i.e., ethanol concentration, ethanol recovery, fuel utilization and operating voltage on the performance and energy involved in the SOFC-D system (e.g. distillation energy: QD and the net exothermic heat of the SOFC system: QSOFC,Net) were examined. In addition, the performance of the SOFC-D system at the energy sufficient point where QD = QSOFC,Net was considered. The integration of the distillation column with the SOFC system was found to offer superior SOFC performance. The ethanol recovery and fuel utilization significantly influenced the overall electrical efficiency and power density. Quite low performances are obtained when one operated the SOFC-D without an external heat source. The maximum overall efficiency and power density (~35% and 0.22 W cm-2) occured at an ethanol recovery of 80% and Uf of 90%.

Performance improvement of solid oxide fuel cell system using palladium membrane reactor with different operation modes

One potentially attractive application of solid oxide fuel cells (SOFCs) is for combined heat and power (CHP) in light commercial buildings. An SOFC-based CHP system can be employed to efficiently serve building thermal and electric loads, thereby lowering utility bills and offering many distributed generation benefits. It is often desirable to operate SOFCs in a predominately base load manner from a hardware viewpoint. However, systems in practice will experience some load dynamics during their lifetime and furthermore, optimal economic dispatch of CHP systems frequently recommends a load-following strategy. Thus, the present work is motivated by the need to understand the dynamic response capabilities of SOFC-CHP systems. Part-load performance and dynamic load-following capabilities of a 24 kW planar SOFC system for light commercial applications was investigated through computational modeling. The SOFC and balance-of-plant component models were implemented in gPROMS modeling software. The modeling strategy of each system component and associated transients are discussed. A dynamic SOFC channel-level model, which has been verified against experimental cell data, was integrated with additional balance-of-plant (BOP) component models consisting of a fuel reformer, tail gas combustor, turbomachinery, heat exchangers, and bypass valves. The performance of the system at part-load operation displays increases in electrical efficiency and decreases in CHP efficiency, as well as a more uniform PEN temperature profile. Modeling comparisons between the responses of systems consisting of either dynamic or steady-state BOP component models are reported. A fully dynamic system-level model displays anodic fuel depletion effects and waste heat recovery transients not captured by the steady-state models. The dynamics influence the ability of an SOFC system to load follow indicating when thermal and electric storage may be necessary.

Thermodynamic sensitivity analysis of hybrid system based on solid oxide fuel cell

Carbon-neutral fuel fed solid oxide fuel cell (SOFC) system can achieve highly efficient power generation without any greenhouse gas emissions. In this paper, the influence of supplied fuel species on the SOFC performance has been evaluated by heat and mass balance analysis. The electrical efficiency of carbon-neutral fuel fed SOFCs is quantified and compared with that of conventional fuel fed SOFCs. Then, the effect of electrical efficiency increase on CO2 emission is also investigated. Furthermore, the effect of proton-conducting ceramic materials application as an electrolyte is also discussed to evaluate the influence on the electrical efficiency. The carbon-neutral fuel fed protonic ceramic fuel cells (PCFCs) had an advantage to enhance the electrical efficiency compared with the same fuels fed typical SOFCs. Due to the increase in electrical efficiency, the reduction in CO2 emission was clearly appeared as CO2 emission factor.

Solid Oxide Fuel Cell (SOFC) is a developing energy conversion technology featuring high efficiency, power density, durability, and fuel compatibility. With these advantages, SOFCs are combined frequently with heat engines such as gas turbines, for higher system efficiency and power density.In practice, SOFCs are often required to deliver certain power. Considering economical aspects, power generation efficiency is critical to the running cost of energy conversion systems. However, high power and high efficiency are likely reached under different operating conditions. For example, to meet peak power demands, higher operating currents and fuel flowrates are necessary, while SOFCs are generally more energy efficient at lower current densities and fuel flowrates. Hence, the ideal operating condition is the solution to a power-constrained efficiency optimization problem. Moreover, SOFCs degrade as they operate, introducing gradual changes to SOFC characteristics. Thus, the optimization needs to be solved dynamically.To analyze the above-mentioned problem, a 10 cm by 10 cm planar SOFC was repeatedly tested for polarization characterizations and electrochemical impedance spectra. A 2-dimentional multi-physics model was developed and calibrated using both polarization and impedance data. To account for the lower open circuit voltage at lower fuel flowrates, an equivalent leakage current is included in the model. The model was thereafter employed for efficiency optimization given power constraints. At each required power output, the optimal fuel flowrate and the corresponding voltage, current, and efficiency was calculated. The electrical efficiency peaks globally at around 0.1 Standard Liter per Minute (SLM) hydrogen flowrate, while at higher power, the optimal efficiency is reached at fuel utilizations between 65% and 90%. Accounting for degradation in terms of growing ohmic resistance and decreasing electrode exchange current densities, the optimal efficiency is reached at lowering fuel utilization and lowering voltage, which may result in local oxidization of the anode.Moreover, an easy and straight-forward way was proposed to estimate the optimal fuel flowrate given polarization data. Further studies involving the safety constraints will be carried out in the future. Figure 1