Fuel Gas Composition Research Articles

Performance Evaluation of an Anode-Supported SOFC Short-Stack Operating with Different Fuel Blends as Stationary-CHP System

Abstract In the perspective of the transition of gas grids towards hydrogen/natural gas blends or even pure hydrogen, Solid Oxide Fuel Cells “SOFC” could play a crucial role as efficient and clean stationary Combined Heat and Power systems, flexibly operating on different feedstocks. A solid oxide fuel cell short stack is analyzed experimentally under different fuel gas compositions which emulate different gas grid transition scenarios. The testing campaign is defined with the aid of a preliminary system-level simulation which assesses system architecture and operating strategy (off-gas recirculation, external reforming, etc.). Experimental tests (polarization curves and performance/efficiency maps) are run in different operating conditions in terms of fuel utilization and temperature in three gas composition scenarios. 
To assess the efficiency of the SOFC unit under the different feedstock operation, different formulations of stack and system efficiencies are proposed and analyzed, based on the boundary conditions considered for the input/output energy streams. 
Experimental results were key to evaluate the different efficiency definitions proposed; albeit the highest voltage/power is obtained with the 100% H2 scenario, the efficiency may be higher with 100% NG and blend scenarios, due to the lower energy content of the input fuel.

Performance and Electrochemical Behavior of LSM Based Fuel Electrode Materials Under High Temperature Electrolysis Conditions

High-temperature solid oxide electrolysis cells (SOECs) have gained considerable attention due to more favourable thermodynamic and electrochemical kinetic conditions over low-temperature electrolysis. The SOECs can be used for the production of hydrogen from steam electrolysis, syngas (H2 + CO) from co-electrolysis, and carbon mono-oxide from pure CO2 electrolysis. Despite several advantages, the long-term durability of SOECs is still an issue. The long-term durability of SOEC depends on the stability of electrodes as well as on the operational conditions, for example current load, temperature, and fuel gas composition. The conventional cermet-based fuel electrode i.e. Ni-YSZ shows good initial performance, however, it experiences severe degradation during long-term due to Ni- agglomeration and migration away from the electrolyte. Therefore, searching for new electrode materials is crucial in order to enhance the overall performance and durability of SOECs.In this work, we have considered Lanthanum strontium manganite-based perovskite oxides as fuel electrodes i.e. La0.6Sr0.4MnO3 (LSM). LSM is very stable chemically under oxidizing atmosphere, however, it undergoes phase transformation into a Ruddlesden-Popper (La0.6Sr0.4)2MnO4±δ phase under reducing atmosphere. We have first prepared the electrolyte-supported single cells using 8YSZ electrolyte and LSM+YSZ/LSM oxygen electrodes. The single cells were then electrochemically characterized using AC- and DC-techniques under steam electrolysis, co-electrolysis, and CO2-electrolysis conditions in 800-900 °C temperature range. Moreover, the electrochemical behaviour of LSM+GDC (50:50) and LSM+YSZ (50:50) composite electrodes containing single cells were also investigated. The LSM and LSM+GDC fuel electrode containing single cells show good electrochemical performance in all three electrolysis modes. However, lower performance is observed for LSM+YSZ fuel electrode containing single cell. For example, a current density of 997, 1025, and 511 mA.cm-2 at 1.5 V, are obtained for LSM, LSM+GDC, and LSM+YSZ fuel electrode containing single cells respectively, with 50% N2 and 50% H2O feed gas mixture at 900 °C. Furthermore, the impedance spectra were also recorded for all these cells under OCV and polarization conditions, and fitted with an equivalent circuit model using an inductor, a series resistance and 4 R//CPE elements. The impedance spectra vary significantly with the gas compositions. The detailed electrochemical results will be presented and discussed in detail.

Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO2 Electrolysis

The mixed ionic and electronic conductive property of Ni-GDC has ensured that the electrochemical reaction zones of the electrode extend beyond the triple phase boundary of Ni/GDC/fuel gas to the double phase boundary of the GDC and the fuel gas [1, 2]. In addition, ceria has shown good carbon suppression properties when operated in carbon-containing fuels[3, 4]. For these reasons, Ni-GDC has emerged as a possible replacement for the conventional Ni-YSZ electrode. However, a direct comparison of the performance and long-term degradation of Ni-GDC with literature values of the Ni-YSZ would be ambiguous. On one hand, different reports utilize different fuel gas compositions, operating temperatures as well as current densities. On the other hand, the fabrication of fuel electrode-supported Ni-GDC is still a challenge due to the well-known inter-diffusion [5, 6] between the YSZ and the GDC oxide phase at a high sintering temperature (1400 °C) of YSZ electrolytes. Hence, most of the electrode fabrication has remained on electrolyte support. Thus, a direct comparison of electrolyte-supported Ni-GDC with the conventional fuel electrode-supported Ni-YSZ is ineffective due to different degradation behaviour.Therefore, this present study aims to investigate and compare the long-term stability of Ni-GDC and Ni-YSZ under three different electrolysis modes; steam-electrolysis, co-electrolysis and CO2-electrolysis. Firstly, electrolyte-supported single cells of Ni-GDC (NiO-GDC//8YSZ//GDC//LSCF) and Ni-YSZ (NiO-GDC//8YSZ//GDC//LSCF) were fabricated and investigated using electrochemical impedance spectroscopy (EIS) from 750-900 °C temperature range. Furthermore, the impedance data were also recorded under polarization (0.7 to 1.4V) as well as at OCV by varying the partial pressure of steam, CO2 and oxygen (, pH20, pCO2 and pO2). Finally, stability tests of the single cells were carried out under steam electrolysis (H2O: H2, 50:50) and co-electrolysis (H2O: CO2:H2, 40:40:20) conditions at 900 °C with 0.5 A/cm2 current density for 500 h [7]. For the CO2-electrolysis (CO2:CO, 80:20), the stability test was performed up to 1000 h. The post-test characterization of the operated cells was carried out using both SEM-EDX as well as FIB-SEM. The results reveal that Ni-GDC exhibits higher current density than Ni-YSZ in all the electrolysis modes. In the post-test analysis, loss of GDC percolation was observed and the Ni particles were observed to be covered by the GDC oxide phase. Furthermore, both electrodes demonstrate that Ni is migrating away from the electrolyte in all the electrolysis modes. The detailed electrochemical and microstructural properties of the operated cells will be presented and discussed.

Performance Evaluation of an Anode-Supported Solid Oxide Fuel Cell Short-Stack Operating with Different Hydrogen-Natural Gas Blends as Stationary Combined Heat and Power System

In the perspective of the transition of gas grids towards hydrogen/natural gas blends or even pure hydrogen, Solid Oxide Fuel Cells “SOFC” could play a crucial role as efficient and clean stationary Combined Heat and Power (CHP) systems, flexibly operating on different feedstocks. A SOFC short stack is analyzed experimentally under different fuel gas compositions which emulate different gas grid transition scenarios. The testing campaign is defined with the aid of a preliminary system-level simulation which assesses system architecture and operating strategy (off-gas recirculation, external reforming, etc.). Experimental tests (polarization curves and performance/efficiency maps) are run in different operating conditions in terms of fuel utilization, current loading and temperature in three gas composition scenarios. Experimental results show that – albeit the highest voltage/power is obtained with the 100%H2 scenario – the efficiency may be higher with 100%NG and blend scenarios, due to the lower energy content of the input fuel.

Kinetic Study of Carbon Deposition in Solid Oxide Fuel Cells (SOFCs)

Owing to many irreplaceable advances, solid oxide fuel cells (SOFCs) have a promising and competitive potential in the application of green power supply and greenhouse gas reduction. Especially the utilization of biomass-derived syngas shows a high efficiency potential for the overall system. However, carbon deposition at the anode is a major challenge for the practical application. Once carbon deposited at the anode, the degradation of SOFC performance is permanent and irreversible to a certain extent. The carbon deposition is closely associated with the inner temperature distribution and fuel gas composition within the SOFCs, which is determined by complex chemical and electrochemical reactions. In this study, competing kinetic rates for carbon deposition and regasification are analyzed based on CFD methods for typical biomass-derived syngas compositions. Based on this method, reasonable operating conditions and flow field configuration can be recommended, which reduce the kinetic rate of carbon deposition at the SOFC anode. It is also worth mentioning that the specific anode area where carbon deposition occurs firstly will be detected numerically under different fuel gas components, operating temperatures and flow filed configurations. In summary, an effective method is provided to reduce the carbon deposition at the anode and improve the life expectancy of SOFCs, which is meaningful for SOFC design and operation in practical applications.

Synthesis Gas Production with Gasification Technology from Municipal Solid Waste

This study aims to develop, test performance, and evaluate the environmental pollution of garbage fuel with gasification technology. Heat conduction from municipal solid waste (MSW) burning from the gasification process was studied to dispose of solid waste and produce energy for communities. There were four types of solid waste in the total amount of 5 kg (including 0.5 kg of charcoal and firewood, 1.5 kg of paper, 2.0 kg of leaf litter, 0.5 kg of plastic, and 0.5 kg of others) with 2 tested ranges of average humidity: 10–20% and 50–55%. It was found that all waste could be converted for gas production with different gas amounts. From the experiment, dried MSW with 10–15% moisture content produced synthesis gas compositions (mole percent) that were H2, CO2, N2, O2, and CH4 at 1.9–2.4, 1.8–3.2, 56.5–60.2, 3.4–4.6, and 1.2–1.6, respectively. When fuel gas composition at the equivalent ratio between 0.2–0.34 was obtained from the MSW burning test with 10–15% average humidity, MSW burning in various equivalent ratios resulted in different amounts of synthesis gas. In addition, the optimal amounts of CH4 and the heating value of the gas were in the equivalent ratio of 0.28, and the highest production efficiency of synthetic gas (ηg) was 33.46%.

Steam Electrolysis vs. Co-Electrolysis: Mechanistic Studies of Long-Term Solid Oxide Electrolysis Cells

High-temperature electrolysis using solid oxide electrolysis cells (SOECs) is an innovative technology to temporarily store unused electrical energy from renewable energy sources. However, they show continuous performance loss during long-term operation, which is the main issue preventing their widespread use. In this work, we have performed the long-term stability tests up to 1000 h under steam and co-electrolysis conditions using commercial NiO-YSZ/YSZ/GDC/LSC single cells in order to understand the degradation process. The electrolysis tests were carried out at different temperatures and fuel gas compositions. Intermittent AC- and DC- measurements were performed to characterize the single cells and to determine the responsible electrode processes for the degradation during long-term operation. An increased degradation rate is observed at 800 °C compared to 750 °C under steam electrolysis conditions. Moreover, a lower degradation rate is noticed under co-electrolysis operation in comparison to steam electrolysis operation. Finally, the post-test analyses using SEM-EDX and XRD were carried out in order to understand the degradation mechanism. The delamination of LSC is observed under steam electrolysis conditions at 800 °C, however, such delamination is not observed during co-electrolysis operation. In addition, Ni-depletion and agglomeration are observed on the fuel electrode side for all the cells.

Optimal Operation of an Industrial Natural Gas Fired Natural Draft Heater

In this work, a custom dynamic mathematical model of an industrial vertical-cylindrical type natural gas fired natural draft heater is developed using gPROMS® ProcessBuilder®. The integrated model comprises sub-models for each of the distinct sections of the fired heater which are connected by mass and energy flows. The temperature profiles of the tubular coils and the process fluid, a heat transfer fluid (HTF) are modelled using the distributed parameter system (DPS) in the axial direction (1D). The flue gas temperature in each section is modelled using the lumped parameter approach. Published empirical methods and correlations are used for estimating some unknown model parameters. The resulting model is a system of partial differential-algebraic equations (PDAEs) and serves as a basis for conducting an optimisation study to aid decision-making and to identify the best operating conditions within the specified constraints that minimise the daily operational costs. Through process simulation studies, the model predictions are adjusted to closely approximate collected actual plant data. It is demonstrated through the optimisation study that significant reduction in fuel gas consumption can be achieved compared to the current operating consumption levels. The developed models can be extended for use by other hydrocarbon processing plant operators with slight modifications, by specifying geometric parameters, HTF thermophysical properties, fuel gas composition and properties, among others.

Performance and Degradation of Electrolyte-Supported Single Cell Composed of Mo-Au-Ni/GDC Fuel Electrode and LSCF Oxygen Electrode during High Temperature Steam Electrolysis

Ni-gadolinia-doped ceria (GDC) based electrode materials have drawn significant attention as an alternative fuel electrode for solid oxide cells (SOCs) owing to mixed ionic conductivity of GDC and high electronic and catalytic activity of Ni. Moreover, the catalytic activity and electrochemical performance of the Ni-GDC electrode can be further improved by dispersing small quantities of other metal additives, such as gold or molybdenum. Therefore, herein, we considered gold and molybdenum modified Ni-GDC electrodes and focused on the upscaling; hence, we prepared 5 × 5 cm2 electrolyte-supported single cells. Their electrochemical performance was investigated at different temperatures and fuel gas compositions. The long-term steam electrolysis test, up to 1700 h, was performed at 900 °C with −0.3 A·cm−2 current load. Lastly, post-test analyses of measured cells were carried out to investigate their degradation mechanisms. Sr-segregation and cobalt oxide formation towards the oxygen electrode side, and Ni-particle coarsening and depletion away from the electrolyte towards the fuel electrode side, were observed, and can be considered as a main reason for the degradation. Thus, modification of Ni/GDC with Au and Mo seems to significantly improve the electro-catalytic activity of the electrode; however, it does not significantly mitigate the Ni-migration phenomenon after prolonged operation.

Fuel gas production through waste polyethylene gasification using bauxite residue as the oxygen carrier

In this study, waste polyethylene (PE) was gasified to produce alternative gas fuel using bauxite residue (BR) as an oxygen carrier in a two-stage reactor. PE was pyrolyzed in the first stage, and the volatiles were subsequently gasified with BR. The influences of temperature and mass ratio on the fuel gas composition were determined. The experimental results indicated that a higher temperature benefits gas production. The gas yield was 0.714 Nm3/kg at 850 °C, and the CH4 yield was 0.231 Nm3/kg. Increasing the BR mass ratio (Fe2O3 to fuel) could lead to over-oxidization (combustible gas production values were 0.531 Nm3/kg and 0.503 Nm3/kg at ratios of 1:2 and 1:4, respectively). Compared with the traditional oxygen carrier Fe2O3, BR showed a stronger oxygen release capability. The oxygen efficiency of BR was over 100% higher than that of Fe2O3. Moreover, the three-stage reactor improved the quality of gas (gas yield was 0.771 Nm3/kg and the production of H2, CH4, and CO accounted for 33.425%, 31.349%, and 19.186%, respectively) compared to the two-stage reactor. Furthermore, the Fe contained in the BR was reduced to Fe3O4, which might have contributed to the magnetic separation. Therefore, the results offer a promising method for the efficient utilization of waste plastic and BR.

Removal of hydrogen chloride from simulated coal gasification fuel gases using honeycomb-supported natural soda ash

In this study, we examined the HCl absorption performance of cheap natural soda ash loaded on a honeycomb support as a hot-gas cleanup method. Air-blown and oxygen-blown coal gasification fuel gases were used to simulate the gas composition. The effect of fuel gas composition on the HCl removal performance of the prepared absorbent was studied. It was found that the removal performance in an inert atmosphere was maintained in the presence of H2. On the other hand, the performance deteriorated in the presence of CO due to carbon deposition from the disproportionation reaction of CO. When CO2 was added to the CO, carbon deposition was suppressed in the air-blown gas and the HCl removal performance recovered. The performance recovery for an oxygen-blown gas was smaller than that for an air-blown gas. However, when the amount of CO2 added to the oxygen-blown gas was increased, the removal performance improved. The HCl removal performance of the absorbent was dependent on the initial HCl concentration and treatment temperature in the following order: 2000 ppm < 1000 ppm < 500 ppm, and 400 °C < 600 °C ≈ 500 °C. Recycled absorbents were prepared by loading natural soda ash once again on the recovered honeycomb supports that had been washed with water. Their HCl removal performance was similar to the fresh absorbent regardless of air-blown or oxygen-blown gasification. Thus, honeycomb supports were recyclable.

Towards integrated gasification and fuel cell operation with carbon capture: Impact of fuel gas on anode materials

Integrated gasification fuel cell technology is a promising option for processing solid fuels, which would enable high efficiencies to be reached in small-scale power generation. Among the different fuel cell types, solid oxide fuel cells present a good temperature match with fluidised bed gasification as well as greater versatility in terms of the fuel gas composition they can handle. However, their resistance to impurities in the gas needs to be addressed. The main objective of this work is to assess the impact on typical materials used in fuel cell anodes of the gases produced from a gasifier operating with a N2-free gasification agent, which would make the system carbon-capture ready. A laboratory scale continuous pressurised fluidised bed reactor has been modified to study CO2 and steam (concentration up to 40 mol%.) gasification of lignite at 850 °C. A second stage fixed bed reactor has been specially designed and constructed to study degradation of two SOFC anode materials (nickel/yttrium–stabilised zirconium oxide (Ni/YSZ) and nickel/gadolinium-doped ceria (Ni/CGO)) after exposure to real fuel gas at 765 °C. Under these conditions, which did not involve any gas cleaning/conditioning between stages, carbon deposition on the surface of anode materials was much smaller than in previous studies that used model tar compounds as feeds. Fuel gas from CO2/H2O gasification tended to deposit less carbon and sulphur on tested anode materials, particularly on Ni/CGO, than that from CO2 gasification. The anode materials converted a significant fraction of the fed tar to gas.

Optimized coupling of ammonia decomposition and electrochemical oxidation in a tubular direct ammonia solid oxide fuel cell for high-efficiency power generation

With high energy density both by weight and volume, ammonia (NH3) is a promising hydrogen carrier. Furthemore, NH3 has a mature industrial background, and in liquid form storage and transportation is not a problem. Adding the merit of zero CO2 emission, NH3-to-power by direct ammonia solid oxide fuel cells (DA-SOFCs) is an acceptable strategy to facilitate hydrogen usage. Nonetheless, to achieve efficacy, a high compatibility between operating temperature and catalytic materials for NH3 decomposition is needed. In this work, we developed a tubular DA-SOFC with an output power capability of > 3 W. By combining experimental measurements and multi-physics simulation, we comprehensively studies the related intrinsic processes. Based on experimental data, we developed a two-dimensional multi-scale electro-thermo model of tubular DA-SOFC. Separately we evaluated the effects of inlet fuel gas composition, inlet flow velocity, operating temperature, and operating voltage on the rate of NH3 catalytic decomposition and H2 electrochemical oxidation, as well as on NH3 conversion, H atom utilization, and electrical efficiency of the tubular DA-SOFC. The results suggest that high H atom utilization could be realized by matching the rate of NH3 decomposition with that of H2 electrochemical oxidation. It was observed that with the decrease of temperature, the rate of H2 oxidation decreases more rapidly than that of NH3 decomposition, suggesting that the flow velocity of NH3 should be appropriately lowered to optimize H atom utilization. Finally, we established a correlation between H atom utilization, operating voltage, and electrical efficiency for synergistic optimization of operating conditions. At 0.7 V and 800 ℃, the tubular DA-SOFC fueled with NH3 of 27 mL·min−1 is capable of offering 3.2 W, displaying an efficiency of 60%. Compared to that of a tubular H2-SOFC (only 51% efficiency), the efficiency is significantly higher on the basis of equal voltage and fuel utilization ratio. The outcome of the present study demonstrates the potential of tubular DA-SOFC as a device for high-efficiency power generation.

A Novel Large-Eddy Simulation-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

Abstract This paper presents a new computational fluid dynamics (CFD) approach for the assessment of NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, this work defines the transport equation source terms for NOx basis on a dedicated NOx-Damköhler number. The latter parameter allows to properly distinguish the “in-flame” contribution from the “postflame” one. While the former is a mix of several mechanisms (prompt, N2O-pathway, thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a large-eddy simulation (LES) framework where the extended turbulent flame speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to detailed postprocessing highlighting the role of some key factors on NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

APPLICATION OF WOBBE INDEX ANALYSER FOR ENERGY EFFICIENCY OPTIMISATION OF COMBUSTION PROCESS CONTROL

The increasing needs to optimise the cost of operation for the oil and gas industry has put more significant demand for Engineers to seek innovative technology and enhanced process design application to save energy. One of the key areas to improve energy efficiency is combustion equipment which consumes a significant amount of fuel gas. The conventional method of air-fuel ratio control using excess oxygen at the exhaust stack is the most common mean of combustion control. This method is effective if the fuel gas composition is stable with minimum fluctuation in Gross heating value. In practice, most modern refineries, gas processing plants, and petrochemical plants have multiple fuel gas sources from flash gas or residue off-gas generated by the intermediate process. The composition can vary widely, making it challenging for conventional air-fuel ratio control via access oxygen. A sudden change of the fuel gas composition can potentially result in unpredictability combustion, leading to equipment inefficiency and the possibility of causing damage to the equipment &amp; product quality, thus leading to economic loss.&#x0D; Wobbe index analyser can determine the exact heating value of fuel gas used for combustion and thus eliminate unstable fuel gas composition issues. The Wobbe index analyser provides compensated value to fuel gas control system to enhance the air-fuel ratio control, leading to more efficient energy management of combustion control equipment.

Measurement of transient temperature distribution behavior of a planar solid oxide fuel cell: Effect of instantaneous switching of power generation and direct internal reforming

The transient temperature distribution behavior of a planar, co-flow type anode supported solid oxide fuel cell is experimentally investigated under furnace temperatures of 670 °C, 720 °C, and 770 °C. An in-situ measurement is conducted by using a specially designed cell holder and a high-resolution infrared camera. The single and combined effects of electrochemical reactions and direct internal reforming (DIR) reactions are examined. The transient response of the cell temperature profile to a sudden change in the current density or reforming reaction rate is obtained. The results show the clear increase/decrease in the local temperature owing to the exothermic electrochemical reaction/endothermic reforming reaction. The analysis of the time constant shows that the response of the temperature distribution to a sudden change in the current density is faster than that to a change in the fuel gas composition. The time constant is smaller in the upstream region, indicating that the new steady state is first achieved near the flow inlet and gradually propagates downstream. The maximum temperature gradient along the operating cell is found to be lower under the DIR condition than under the non-DIR condition regardless of the furnace temperature.

Fuel Cell and Electrolysis Operation Solid Oxide Cells Incorporating 3D-Printed Electrode Supports in H2/H2o and CO/CO2 Gas Mixtures

Electrolysis of CO2 using solid oxide cells is important both for renewable energy storage technologies as well as for upcoming, flagship space missions. Nevertheless, the performance of solid oxide cells performing CO2 electrolysis is generally diminished compared to an identical cell performing H2O electrolysis. The reduced performance when electrolyzing CO2 results both from slower reaction kinetics as well as slower gas transport, which manifest in the performance as large activation and concentration polarizations, respectively. The finite diffusivity of both H2/H2O and CO/CO2 gas mixtures leads to concentration losses which limit overall fuel cell or electrolysis performance, particularly at high current densities. Performance can be improved by diminishing the thickness of the porous electrode support layers, hence decreasing the gas diffusion distance between the flow channels and electrochemically active sites, but this also limits the mechanical support provided to the cell. Structured support layers which cover only some of the electrode functional layer potentially allow substantial areas of the cell to be very thin, therefore easing gas transport from the flow channels to the electrochemically active sites, while largely maintaining the mechanical support for the cell. However, fabricating these layers out of SOC-relevant materials (such as Ni-YSZ) and incorporating them with the functional layers of the cell can be challenging.Here, we present an extrusion-based 3D-printing technique capable of fabricating these layers, which are then integrated with tape-cast layers using traditional lamination and a multi-step firing procedure. This strategy has recently been shown to improve H2O electrolysis performance in cells with a Ni-YSZ fuel electrode, YSZ electrolyte, and LSCF oxygen electrode, operating at 800°C in low-steam conditions (3% H2O/97% H2) by a factor of approximately 2.5 compared to cells possessing traditional, monolithic support layers (the cell containing 3D-printed support generated 258 mA/cm2 at 1.3 V and 800°C). Microstructure of the 3D-printed support layers is investigated using scanning electron microscopy. The cells are characterized using current-voltage measurements and impedance spectroscopy between 600 and 800°C with various fuel gas compositions. All tests are performed with air at the oxygen electrode. Mechanical considerations governing the design of 3D-printed electrode supports will also be discussed.Although Ni-based electrodes have long demonstrated excellent performance for fuel cell and electrolysis operation using H2/H2O gas mixtures, their low stability when operating in CO/CO2, in part due to the poor reoxidation stability and coking resistance of Ni, requires the development of more-stable, alternative electrode materials. Besides these considerations, reaction kinetics for CO2 electrolysis are further slowed by the relative weak adsorption of CO2 molecules. Perovskite fuel electrodes with exsolved catalytic nanoparticles have been shown to possess competitive performance compared to conventional Ni-based electrodes, while nevertheless exhibiting higher stability to reoxidation and resistance to coking. Additionally, the vacancies produced in the perovskite as a result of the exsolution of electron donor B-site cations provide additional, stronger adsorption sites for CO2 molecules, making them strong candidates for fuel electrodes for CO2 electrolysis. Here, we utilize two recently reported, A-site deficient perovskite fuel electrode materials Sr0.95(Ti0.3Fe0.63Ni0.07)O3-δ (STFN) and Sr0.95(Ti0.3Fe0.63Ru0.07)O3-δ (STFRu) for electrolysis of CO2. The electrochemical performance of these electrode materials for CO2 electrolysis will be presented for the first time. Current voltage measurements and impedance spectroscopy are carried out across a range of fuel gas compositions and operating temperatures. Finally, initial results for combining these electrode materials with 3D-printed electrode supports to counteract both activation and concentration losses will be presented.

Self-consistent estimates of emission factors of carboncontaining pollutants from a typical gas flare

This study proposes an approach for estimating the emission of soot, carbon monoxide (CO) and carbondioxide (CO ) from a typical gas flare. The estimations depend on the quantity and varying composition of the 2 natural gas, flame dynamics (represented by the fire Froude number, Fr ) and the equivalence ratio, f, of the fuel- f air mixture. Soot emission estimates are presented as a function of fire Froude number for gases used in labbased test in order to validate the scheme and for two real-world fuel gas compositions. The mass-weighted carbon-hydrogen ratio (C:H) of the fuel gas compositions are 0.25 and 0.29 which are two extreme cases in terms of density. The soot yield of the lab-based test case was scaled up to estimate the soot yield of a full scale flare using the Richardson number as the scaling parameter. When all other variables are held constant at values characteristics of real-world flares, a difference of 16 % in the fuel-gas density, as indicated by the carbonhydrogen ratio, results in an increase of the emission factors (EF) of soot, CO and CO by factors of ~3, ~1.4 2 3 and ~1.7, measured in g/m , respectively. For both fuel gas compositions, the ratio of EF to EF at the fuel- soot CO lean region f &lt; 1) is higher. The ratio lies in the range 0.031 – 0.13 and 0.0012 – 0.0055 for the fuel-lean (f &lt; 1) and fuel-rich (f &gt; 1) regions, respectively. The approach proposed and results obtained may be adopted to generate emissions inventories of emission species associated with gas flaring on regional and global scales.&#x0D; Keywords: gas flaring; soot; natural gas; emission factor; black carbon; equivalence ratio

Optimization of the thermodynamic and thermophysical properties of the gas turbine cycle working fluid

A gas turbine cycle working fluids group based on their production technology and application is presented. The energy parameters analysis procedure of unclosed and closed gas turbine cycles is described. The comparison of the effect of the working fluids thermophysical and thermodynamic properties variations on the useful work l0 of both unclosed and closed gas turbine cycles is presented. The effect of the fuel gas composition variation on the useful cycle work l0 is revealed. The effect of the working fluid thermophysical properties variation on the gas turbine cycle optimal combination of thermodynamic properties (T3 and P3 ) is presented.

Fuel Cell and Electrolysis Operation of Solid Oxide Cells Containing 3D-Printed Electrode Supports in H2/H2o and CO/CO2 Gas Mixtures

Electrolysis of CO2 using solid oxide cells is important both for renewable energy storage technologies as well as for upcoming, flagship space missions. Nevertheless, the performance of solid oxide cells operating for CO2 electrolysis is generally diminished compared to an identical cell performing H2O electrolysis. The reduced performance when operating in CO2 results both from slower reaction kinetics as well as slower gas transport, which manifest in the performance as large activation and concentration polarizations, respectively. The finite diffusivity of both H2/H2O and CO/CO2 gas mixtures leads to concentration losses which limit overall fuel cell or electrolysis performance, particularly at high current densities. Performance can be improved by diminishing the thickness of the porous electrode support layers, hence decreasing the gas diffusion distance between the flow channels and electrochemically active sites, but this also limits the mechanical support provided to the cell. Structured support layers which cover only some of the electrode functional layer potentially allow substantial areas of the cell to be very thin, hence easing gas transport from the flow channels to the electrochemically active sites, while largely maintaining the mechanical support for the cell. However, fabricating these layers out of SOC-relevant materials (such as Ni-YSZ) and incorporating them with the functional layers of the cell can be challenging.Here, we present an extrusion-based 3D-printing technique capable of fabricating these layers, which are then integrated with tape-cast layers using traditional lamination and a multi-step firing procedure. This strategy has recently been shown to improve H2O electrolysis performance in cells with a Ni-YSZ fuel electrode, YSZ electrolyte, and LSCF oxygen electrode, operating at 800°C in low-steam conditions (3% H2O/97% H2) by a factor of approximately 2.5 compared to cells possessing traditional, monolithic support layers (the cell containing 3D-printed support generated 258 mA/cm2 at 1.3 V and 800°C). Microstructure of the 3D-printed support layers is investigated using scanning electron microscopy. The cells are characterized using current-voltage measurements and impedance spectroscopy between 600 and 800°C with various fuel gas compositions. All tests are performed with air at the oxygen electrode. Mechanical considerations governing the design of 3D-printed electrode supports will also be discussed.Although Ni-based electrodes have long demonstrated excellent performance for fuel cell and electrolysis operation using H2/H2O gas mixtures, their low stability when operating in CO/CO2, in part due to the poor reoxidation stability and coking resistance of Ni, requires the development of more-stable, alternative electrode materials. Besides these considerations, reaction kinetics for CO2 electrolysis are further slowed by the relative weak adsorption of CO2 molecules. Perovskite fuel electrodes with exsolved catalytic nanoparticles have been shown to possess competitive performance compared to conventional Ni-based electrodes, while nevertheless exhibiting higher stability to reoxidation and resistance to coking. Additionally, the vacancies produced in the perovskite as a result of the exsolution of electron donor B-site cations provide additional, stronger adsorption sites for CO2 molecules, making them strong candidates for fuel electrodes for CO2 electrolysis. Here, we utilize two recently reported, A-site deficient perovskite fuel electrode materials Sr0.95(Ti0.3Fe0.63Ni0.07)O3-δ (STFN) and Sr0.95(Ti0.3Fe0.63Ru0.07)O3-δ (STFRu) for electrolysis of CO2. The electrochemical performance of these electrode materials for CO2 electrolysis, will be presented for the first time. Current voltage measurements and impedance spectroscopy are carried out across a range of fuel gas compositions and operating temperatures. Finally, initial results for combining these electrode materials with 3D-printed electrode supports to counteract both activation and concentration losses will be presented.