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In this work, a biomethane fuel was obtained from biogas, using a solid matrix of ashes obtained from a central heating plant fed by wood. Biomethane composition was studied in an experimental pilot plant that treats organic waste through dry anaerobic digestion. European limits were considered and respected for the biomethane injection into the gas grid. The process was able to completely remove carbon dioxide (CO2) during its initial phase. After 50 h of test CO2 concentration started to appear in the outlet gas. This behaviour is related to the ash content, reactive phases (e.g., Ca hydroxides) and fine particle size (

Faults and anomalous behavior affect the operation of Heating, Ventilation and Air Conditioning (HVAC) systems. This causes performance loss, energy waste, noncompliance with regulations and discomfort among occupants. To prevent damage, automated, fast identification of faults in HVAC systems is needed. Fault Detection and Diagnosis (FDD) techniques are very effective for these purposes. The best FDD methods, in terms of cost effectiveness and data exploitation, are based on process history; i.e., on sensor data from automation systems. In this work, supervised and semi-supervised models were developed. Other than with regard to outdoor temperature and humidity, the input parameters of an HVAC system have few internal variables. Performance of traditional methods (e.g., VAR, Random Forest) is low, so Artificial Neural Networks (ANNs) were selected, since they can capture nonlinear relationships among features and are easily optimized. ANNs can detect simultaneous faults from different classes. ANN metrics are easily evaluated. The ground truth is obtained from process history (supervised case) and from a mix of deterministic methods and clustering (semi-supervised case). The derivation of the ground truth in the semi-supervised case, and extensive comparison with advanced supervised models, set this work apart from previous studies. The Mean Absolute Error (MAE) of the best supervised model was 0.032 over 15 min and 0.034 over 30 min. The Balanced Accuracy Score (BAS) of the best semi-supervised model was 86%.

In the current context of complexity between climate change, environmental sustainability, resource scarcity, and geopolitical aspects of energy resources, a polygenerative system with a circular approach is considered to generate energy (thermal, electrical, and fuel), contributing to the control of CO2 emissions. A plant for the multiple productions of electrical energy, thermal heat, DME, syngas, and methanol is discussed and analyzed, integrating a chemical cycle for CO2/H2O splitting driven using concentrated solar energy and biomethane. Two-stage chemical looping is the central part of the plant, operating with the CeO2/Ce2O3 redox couple and operating at 1.2 bar and 900 °C. The system is coupled to biomethane reforming. The chemical loop generates fuel for the plant’s secondary units: a DME synthesis and distillation unit and a solid oxide fuel cell (SOFC). The DME synthesis and distillation unit are integrated with a biomethane reforming reactor powered by concentrated solar energy to produce syngas at 800 °C. The technical feasibility in terms of performance is presented in this paper, both with and without solar irradiation, with the following results, respectively: overall efficiencies of 62.56% and 59.08%, electricity production of 6.17 MWe and 28.96 MWe, and heat production of 111.97 MWt and 35.82 MWt. The fuel production, which occurs only at high irradiance, is 0.71 kg/s methanol, 6.18 kg/s DME, and 19.68 kg/s for the syngas. The increase in plant productivity is studied by decoupling the operation of the chemical looping with a biomethane reformer from intermittent solar energy using the heat from the SOFC unit.

Recent interest in hydrogen as an alternative fuel for lowering carbon emissions is funding the exploration of new ways to cleanly produce this molecule. Iron oxides can be used within a process of chemical looping. More specifically, they can lose oxygens at extremely high temperature in an inert atmosphere. An alumina receiver could not stand the extreme thermal stress, while steel (AISI 316 and Inconel Hastelloy c-276) lasted enough for the reaction to start, even if at the end of the process the receiver melted. Operating at a temperature above 1000 K helped the reaction switch from methane chemical looping combustion to chemical looping reforming, thus favouring H2 and CO yields. The gas flow outlet from the reactor reached a percentage up to 45% of H2 and 10% of CO. Carbon dioxide instead reached very low concentrations. While CO and CO2 reached a peak at the beginning of the experiment and then decreased, H2 was oscillating around a stable value. Unreacted methane was detected. The temperatures recorded in the reactor and the gas mixture obtained were used to validate a multiphysical model. The heat transfer and the chemistry of the experiment were simulated.

In the current context of complexity between climate change, environmental sustainability, resource scarcity, and geopolitical aspects of energy resources, a polygenerative system with a circular approach is considered to generate energy (thermal, electrical, and fuel), contributing to the control of CO

The coupling between biomass gasification and Solid Oxide Fuel Cells can represent a sustainable and efficient system for electricity production. This work aims to develop a preliminary model for the operation of a tubular, electrolyte-supported fuel cell (SOFC) fed by a syngas mixture. The fuel required by the SOFC system is produced inside the energy generator box from an integrated biomass gasification system. This study stems from the European DB-SOFC project, that proposed the exploitation of the abundant biomasses deriving from agricultural residues for energetic purposes (as from olive oil and wine production). In this study, the main processes have been simulated to find a possible configuration to obtain a power value of 200 W. 25 cells were used in the model to produce the required power. The results showed that at 0.7 V it is possible to achieve 12.3 W, when the biomass gasification was integrated into the SOFC box, while it was possible to achieve 9.6 W when the system was fed by externally produced syngas.

Nowadays the most important issues for commercial SOFC systems are related to their durability and stability of performance both of which are affected by fuel feeding composition. The trace compounds contained in biogenous fuels can interact with SOFC components causing evident drops in performance and severely reducing the lifetime of the entire system. Due to the significant impact on SOFC performance from widely varying fuel inputs, the influence of trace compounds should be investigated in real case studies and practical applications. Anode deactivation and porous blocking electrodes are the main consequences that occur due to the presence of trace compounds impact. This work shows an experimental case study where the anode supported solid oxide fuel cells short stacks are fed with fuels containing trace compounds. These compounds were selected from the biological decomposition of organic matters. In addition, sulphur compounds were selected chlorine, aromatic compounds, terpenes, and carboxyl compounds were selected. The most deleterious impact on the stack was due to the sulphur action. However, chlorine compounds also affected the external part of the cell causing the stack to break due to the corrosion of the sealant.

Anaerobically digested sewage sludges were used as feedstock in the production of activated carbons through physical activation. These char samples were experimentally tested as adsorbents for the removal of CO2 from a simulated biogas mixture. The CO2 concentration level allowed in biomethane was fixed from the European Standards EN 16723-1 and EN 16723-2. The char yield and the subsequent adsorption capacity values were studied, considering the operating parameters of the process. A physical activation process was considered with the following parameters: the temperature, the dwell time, the activating agent, the heating rate, the flow rate, and the method. Among the adsorption tests, the activating temperature and the agent employed affected the CO2 removal. The maximum adsorption capacity was achieved with nitrogen as an activating agent at 600 °C, with 2 h of dwell time (102.5 mg/g).

The sustainable transition towards renewable energy sources has become increasingly important nowadays. In this work, a microgeneration energy system was investigated. The system is composed of a solar concentrator system coupled with an alpha-type Stirling engine. The aim was to maximize the production of electrical energy. By imposing a mean value of the direct irradiance on the system, the model developed can obtain the temperature of the fluid contained inside the Stirling engine. The heat exchanger of the microgenerator system was analyzed, focusing on the solar coupling with the engine, with a multiphysical approach (COMSOL v5.3). A real Stirling cycle was implemented using two methods for comparison: the first-order empirical Beale equation and the Schmidt isothermal method. Results demonstrated that a concentrator of 2.4 m in diameter can generate, starting from 800 W/m2 of mean irradiance, a value of electrical energy equal to 0.99 kWe.

The energy crisis and the adaptation of the global energy structure promote the development of renewable energies, in particular solar energy, also for syngas production. In this work, attention was focused on solar devices, necessary to provide high-temperature heat for the reduction reaction of metal oxides involved in the chemical looping driven by solar energy. Thermochemical processes for synthetic-gas production and CO2 sequestration were investigated using a concentrating solar thermal system. This paper proposes a useful forecasting model of the receiver temperature to make a realistic estimate of the system’s producibility for the different periods of the year. The model proposed was validated in the winter season, and the predicted temperature varied below 5% considering the real experimental data (442–472 °C). The validated model was used to evaluate the temperature receiver in spring and in summer, when the thermal level is reliable for thermochemical processes. From the spring season until the completion of the summer season, optimum conditions inside the receiver were reached (above 1000 °C). These preliminary findings could be used for the development of large-scale production systems.

The effect of different pre-treatments method on the gasification efficiency of grass biomass have not previously been evaluated. In this study, the effect of three different pre-treatment methods on gasification properties of grass biomass was investigated under CO2 conditions. The pre-treatment methods were dry torrefaction, wet torrefaction, and leaching (chemical). The results obtained showed that the heating values increased by 2,77% in the leached grass, 8,3% in the dry torrefied grass and 13,5% in the wet torrefied grass. However, the wet torrefaction had the highest reactivity index of 0,25 followed by dry torrefaction 0,182, then leaching 0,156. The effect of the different pre-treatment on activation energy showed that the activation energy of raw grass biomass was reduced from 161,7 kJ/mol to 141.5 kJ/mol for leached grass, 124.3 kJ/mol for dry torrefied and 86.97 kJ/mol for wet torrefied grass. These results show that wet torrefaction can improve gasification properties significantly when compared to dry torrefaction and leaching. The pore structure and pore volume effect of treated biomass was likely the predominant reason for the better char reactivity and conversion during gasification of wet torrefied sample. The research supplied an insight into the effect of different pre-treatment methods on grass biomass gasification.

Three waste-derived adsorbent materials (wood-derived biochar, sludge-derived activated carbon and activated ash) were pre-activated at the laboratory scale to apply them for the removal of H2S from a biogas stream. The H2S removal capabilities of each material were measured by a mass spectrometer, to detect the H2S concentration after the adsorption in an ambient environment. The activated ash adsorbent has the highest removal capacity at 3.22 mgH2S g&minus, 1, while wood-derived biochar has slightly lower H2S removal capability (2.2 mgH2S g&minus, 1). The physicochemical properties of pristine and spent materials were characterized by the thermogravimetric analyzer, elemental analysis, X-ray fluorescence spectroscopy and N2 adsorption and desorption. Wood-derived biochar is a highly porous material that adsorbs H2S by physical adsorption of the mesoporous structure. Activated ash is a non-porous material which adsorbs H2S by the reaction between the alkaline compositions and H2S. This study shows the great potential to apply waste-derived adsorbent materials to purify a biogas stream by removing H2S.

Trace compound stability is crucial for real time gas analysis and for high efficiency energy generators, where part per billion concentrations have a high impact. In this context, the container type chosen for the gas analysis becomes important. Several types of containers, such as stainless-steel canisters, glass bulbs, gas tight syringes and sampling bags can be adopted for sampling and storing such samples. Sampling bags are cheap and easy to manage, for these reasons other solutions are rarely used. Literature studies have showed how nalophan™ bags represent the best choice for the collection of samples due to the extremely low cost, the good sample stability and the low background interaction. No studies have considered the biogas trace constituents, especially at an ultra-low concentration level. Most of the studies relating to trace compound detection, use a GC–MS instrument and focus on few compounds of interest. In this paper, one of the most rapid and reliable direct injection mass spectrometry techniques was used. PTR-QMS was adopted to investigate the real biogas mixture stability. The concentration losses were studied continuously during 24 h from the sampling. These losses may be related to the wall adsorption and/or through the wall diffusion phenomena. The most stable compounds detected were acetone, methanol and formaldehyde with a concentration loss below 5%. Terpenes and sulphur compounds had a concentration loss of around 50%, while hydrocarbons and aromatic compounds showed concentration losses around 60%. The stability of the compounds monitored with acceptable losses (below 5%), was achieved within the first 3 h after the sampling was carried out.

Issues related to SOFCs performance and durability are strictly dependent on the feeding fuel quality. SOFC capability to be fed with fuels different from hydrogen opens to scenarios in which a big variety of fuels can be used at the aim. Unfortunately, problems related to anode deactivation due to the contaminants presence can arise. The present work investigates the performance of anode supported solid oxide fuel cells in case of co-feeding of different trace compounds. Electrochemical impedance spectroscopy is the investigation technique used to analyze the impedance spectra. Typical biogas from OFMSW trace contaminants that follow an initial failure in the cleaning system, such as sulphur, aromatic compounds and siloxanes, have been simultaneously tested. Tests showed that the most deleterious impact for the SOFC was due to the H 2 S action. This influences mostly the electrochemical losses respect to diffusion losses, even if this last are not null and can be accounted as a secondary effect. On the contrary, the co-presence of D4 and H 2 S mitigates in the short-term the effect that the only D4 produces when fed with biogas. The most relevant consequence produced by C 7 H 8 was recorded in the low frequency of Nyquist plot, affecting mainly the mass transport phenomena. Experimental tests are accompanied by the implementation of the fuel cell model through COMSOL Multiphysics software to study the effect of pollutants on fuel cell performance.

Biochar obtained from sewage sludges are adopted for biogas cleaning. Sewage sludges are treated considering temperature, dwell time, activating agent, heating, and flow rate. The best performances achieved are registered considering the char produced at 400 °C using CO2 as an activating agent with a dwell time of 2 h. The adsorption capacity for the biogas cleaning CH4/CO2/H2S (20 ppm(v)) increased from 1.3 mg/g to 5.9 mg/g with the bed height. Future research with chemical activation processes will be made to improve the adsorption capacity achieved to produce cheaper sorbents than commercial ones.

Microalgae present promising green economy applications in the energy and biorefinery sectors. The work concerns a pilot study on the integration of anaerobic digestion with microalgae cultivation for managing at the same time emissions and digestate from the dry anaerobic treatment of organic waste. Biogas produced was used to feed Solid Oxide Fuel Cell after a filtering step for removing toxic compounds. The exhausts and digestate were used for providing carbon and nutrients for microalgae growth. The experimental workflow includes the characterization of both for defining their suitability in the microalgal growth (Chlorella vulgaris) tests. The exhausts of Solid Oxide Fuel Cells showed relatively stable concentration of CH4 (4–7%) and CO2 (93–96%) and low concentrations (sub ppm(v)) of sulphur, carbonyl and carboxyl, and aromatic compounds and terpenes, making it particularly suited for algae growing as compared with internal combustion engines. The challenging growing conditions are a compromise between carbon recovery and use of digestate. A good microalgae growth has been obtained (22.31 mm3 mL−1 of biovolume corresponding to 151 dry mg L−1 day−1) exploiting ammonia and phosphate from dilute digestate (removal efficiency 94% and 30% respectively) as well as a good carbon recovering (310 mg CO2 L−1 day−1). Based on our data, the integration of microalgae growth and anaerobic digestion process seems a viable solution to achieve (i) reduced emissions due to carbon recovery; (ii) optimum integrated management of anaerobic digestion waste and (iii) biomass production by low-cost nutrients and carbon.

Biogas production from organic waste could be an option to reduce landfill and pollutant emissions into air, water, and soil. These fuels contain several trace compounds that are crucial for highly efficient energy generators or gas injection into the grid. The ability of adsorbents to physically remove such adsorbates was investigated using adsorption isotherms at a constant temperature. We experimentally modelled isotherms for siloxane removal. Siloxanes were considered due to their high impact on energy generators performance even at low concentrations. Octamethylcyclotetrasiloxane was selected as a model compound and was tested using commercially available carbon and char derived from waste materials. The results show that recyclable material can be used in an energy production site and that char must be activated to improve its removal performance. The adsorption capacity is a function of specific surface area and porous volume rather than the elemental composition. The most common adsorption isotherms were employed to find the most appropriate isotherm to estimate the adsorption capacity and to compare the sorbents. The Dubinin-Radushkevich isotherm coupled with the Langmuir isotherm was found to be the best for estimating the adsorption capacity.

Organic waste exploitation is crucial for waste emissions restraint in air, soil and water. This type of waste can be exploited to produce biogas, a valuable fuel exploitable for energy purposes. A circular approach for energy production is much cleaner and more sustainable than the traditional linear approach. In this work, organic waste was used for biogas production to feed a highly efficient solid oxide fuel cell power generator, which requires an ultra-purified fuel. Commercial sorbents were experimentally studied in conjunction with a dynamic adsorption model to predict the breakthrough time and organize the material change-over. In the presence of 0.1% oxygen in the gas mixture, AirDep&reg, CKC showed a marked increase in the adsorption capacity (from 3.91 to 84.87 mg/g), overcoming SulfaTrap&reg, R8G (49.91 mg/g). The effect of several operating parameters on adsorption capacity was evaluated: inlet H2S concentration, filter geometry and gas mixture velocity. Experimental data revealed that adsorption capacity increases with initial H2S concentration, following the typical trend of the Langmuir isotherm. Model simulations were in good agreement compared to experimental results, with an average relative error lower than 7%. A sensitivity analysis on the adsorption capacity was accomplished considering parameters from operational and empirical correlations.

The coupling of fuel cell technology with wastewater treatment plants (WWTPs) is within the sustainable development imperative for the integration of energy production purposes and recovery of materials, even if research is still under development in this field. The anaerobic digestion process can be used for fuel cell feeding, only if trace contaminants are removed continuously. The most harmful and frequent contaminant is H2S. This article shows the results of H2S adsorption on activated carbon fixed-beds (dry process), since it is one of the best solutions from both the complexity and costs perspectives. Inside the wide range of commercial activated carbons, a specific commercial carbon has been used in test campaigns, since it is also used in the Societ&agrave, Metropolitana Acque Torino (SMAT) real plant. Thermal regeneration of spent carbons was exploited, using different conditions of temperature, treatment time and atmosphere, since it is a better cost-effective and environmentally sound option than immediate carbon disposal after adsorption. Regeneration with CO2 showed the best regeneration ratio values. In particular, the best conditions achieved were 300 &deg, C and 75 min of thermal treatment time, with a regeneration ratio of 30%.

The current study was oriented at analyzing the performance of an anode-supported solid oxide fuel cell produced using high-pressure injection molding. The cell with a total thickness of 550 μm was produced in the Ceramic Department (CEREL) of the Institute of Power Engineering in Poland and experimentally analyzed in the Energy Department (DENERG) of Politecnico di Torino in Italy. The high-pressure injection molding technique was applied to produce a 500 μm thick anode support NiO/8YSZ 66/34 wt% with porosity of 25 vol%. The screen printing method was used to print a 3 μm thick NiO anode contact layer, 7 μm thick NiO/8YSZ 50/50 wt% anode functional layer, 4 μm thick 8YSZ dense electrolyte, 1.5 μm thick Gd 0,1 Ce 0,9 O 2 barrier layer and a 30 μm thick La 0,6 Sr 0,4 Fe 0,8 Co 0,2 O 3–δ cathode with porosity 25 vol%. The experimental characterization was done at two temperature levels: 750 and 800 °C under fixed anodic and cathodic flow and compositions. The preliminary studies on the application of high-pressure injection molding are discussed together with the advantages of the technology. The performance of two generations of anode-supported cells is compared with data of reference cells with supports obtained using tape casting.

High energy efficiency SOFCs generators can be adopted for local and distributed micro-generation systems to promote the reduction of greenhouse gas emissions with their high fuel flexibility, long-term stability also at partial load and low noise. One of the main drawbacks for such generators, fed by biogenous gas is the impact of trace compounds on the anode compartment. For this reason, a gas clean-up section is mandatory. The effect of temperature and gas moisture was investigated through experiments on the removal performance of the tested sorbents. An increase in the operating temperature caused lower values of the maximum capacity of the adsorbent. The decrease of removal performance considering a humidified gas is connected to the interference of water in the pores of activated carbons. Biochar, compared to the other commercial sorbent materials showed the lowest removal performance, even if with activated biochar the adsorption capacity growth to commercially available materials. The highest adsorption capacity at 1% of the initial concentration was showed by commercial carbons with 1.75 mg/g for H2S and 20.4 mg/g for HCl. Experimental data were employed in a porous particle diffusion model to estimate the breakthrough time. Low values of errors validate the model in the first part of the breakthrough curve, even for competitive adsorption case.

The present work investigates the performance of anode supported solid oxide fuel cells under the influence of different trace compounds. EIS (Electrochemical impedance spectroscopy) has been used to deconvolute the impedance spectra of an SOFC (Solid Oxide Fuel Cell) in order to identify the main losses. The impact of single and double contaminants on the SOFC performance has also been investigated. Typical biogas trace contaminants, obtained after a clean-up stage, such as sulfur, chlorine, aromatic compounds and siloxanes, have been taken into consideration. The results show how the ohmic contribution is almost independent of the H2S concentration. H2S acts mainly on the polarization losses and especially on the mass transport resistance. The impact of HCl on the SOFC performance is mainly connected to the charge transfer process. D4, as the model compound for siloxanes, already acts on SOFC performance at ppb(v) levels. The polarization losses have been influenced the most, and the largest increase has been recorded for the low frequency term, Rlow, related to the mass transport resistance for naphthalene and toluene. H2S, introduced with other contaminants, causes the instantaneous deterioration of the SOFC performance and the more the types of contaminants co-fed to the SOFC, the larger the initial anode degradation.

In recent years, research efforts on fuel cells have been addressed on the development of multifuel reformers with particular emphasis toward the potential use of non-traditional fuels. Among these, biogas is considered very promising to be used as syngas source for fuel cell system applications. The interest on this hydrogen source is focused mainly to supply high temperature fuel cells (HTFC). This paper reports a wide experimental research investigation on SOFC device supplied by syngas produced with different biogas reforming processes (steam reforming, autothermal reforming and partial oxidation). Thermodynamic simulations have been performed to determine the reformed gas composition varying process, reaction temperature and steam to carbon – oxygen to carbon ratios. Syngas mixtures obtained were experimentally tested in order to evaluate the performance of a SOFC mono-cell. Furthermore, an analysis of the combination: fuel processor with a SOFC stack has been determined in order to assess the total energy efficiency.

Organic waste collection from local municipal areas with subsequent energy valorization through CHP systems allows for a reduction of waste disposal in landfill. Pollutant emissions released into the atmosphere are also reduced in this way. Solid oxide fuel cell (SOFC) systems are among the most promising energy generators, due to their high electrical efficiency (>50%), even at part loads. In this work, the local organic fraction of municipal solid waste has been digested in a dry anaerobic digester pilot plant and a biogas stream with methane and carbon dioxide concentrations ranging from 60–70 and 30–40% vol., respectively, has been obtained. Trace compounds from the digester and after the gas clean-up section have been detected by means of a new technique that exploits the protonation reactions between the volatile compounds of interest and the ion source. Sulfur, chlorine and siloxane compounds have been removed from as-produced biogas through the use of commercial sorbent materials, such as activated carbons impregnated with metals. A buffer gas cylinder tank has been inserted downstream from the filtering section to compensate for the biogas fluctuations from the digester. The technical feasibility of the dry anaerobic process of the organic fraction of municipal solid waste, coupled with a gas cleaning section and an SOFC system, has been proved experimentally with an electrical efficiency ranging from 32 to 36% for 400 h under POx conditions.

Lifetime and durability issues connected with Solid Oxide Fuel Cell (SOFC) technology are strongly related to the amount of contaminants that reach the stack. In this study the focus is on organic silicon compounds (siloxanes) and their highly detrimental effects on the performance of SOFC Ni-YSZ anodes. The involved mechanism of degradation is clarified and quantified through several test runs and subsequent post-mortem analysis on tested samples. In particular, experiments on both Ni anode-supported single cells and 11-cell-stacks are performed, co-feeding D4-siloxane (octamethylcyclotetrasiloxane, C8H24O4Si4) as model compound for the organic silicon species which are generally found in sewage biogas. High degradation rates are observed already at ppb(v) level of contaminant in the fuel stream. Post-test analysis revealed that Si (as silica) is mostly deposited at the inlet of the fuel channel on both the interconnect and the anode side of the cell suggesting a relatively fast condensation-type process. Deposition of the Si was found on the interconnect and on the anode contact layer, throughout the anode support and the three phase boundary in the anode, correlating with the observed increase of polarization losses from the EIS analysis of tested cells. (C) 2015 Elsevier B.V. All rights reserved.

Trace compounds contained in the produced biogas range from tens to thousands of ppm(v) and the gas cleaning is crucial, as much as it is important the investigation of the trace compounds impact on the reforming section and on the SOFC performance. The catalytic stability of a Ni-catalyst towards biogas reforming in the presence of three types of deactivating compounds (sulfur, siloxanes and aromatic compounds) was investigated. When the biogas is composed of a methane to carbon dioxide ratio >1 under the tested operating conditions, the Ni catalyst stability is achieved. A Ni/Al2O3 catalyst appears suitable for the steam reforming of biogas including contaminants, under the operative conditions adopted. On the contrary, the effect of a biogas stream with composition CH4/CO2 = 50/50 vol % is much more harmful under steam reforming conditions both in terms of activity and stability. This result was due to CO2-promoted Boudouard reaction that leads to extensive carbon formation on the catalyst surface. Under this condition, sulfur and D5 compounds in the biogas have a significant impact on the longevity of the Ni catalyst. Hence, carbon formation rate is affected by the degree of catalyst poisoning due to adsorption and/or deposition of other species on catalytic sites. (C) 2018 Elsevier Ltd. All rights reserved.

Experimental analysis of a planar 100 mm × 100 mm SOFC cell was conducted during operation at 1173 K in direct internal reforming (DIR) mode. In the first phase the rate of direct internal reforming was varied from 0 to 100% what corresponds to complete external reforming and complete DIR, respectively. In the second phase 1.2 ppm(v) of H2S was introduced to the feeding gas and the variation of the rate of direct internal reforming was repeated. Following the experimental analysis the numerical model was proposed to determine the correlation between the presence of the poisoning agent and the electrochemical performance. The effect on the resistance of the cell was studied. The lumped volume model was applied to predict the cell voltage. With the use of the experimental data it was possible to determine the relative change of the model parameters which describe the ionic and electronic conductivity of the SOFC. Model was adopted for predictive modeling of the solid oxide fuel cell, operated in DIR-SOFC mode with and without the presence of hydrogen sulfide. Additionally, literature data measured for a cell operated in complete internal reforming mode with variation of the sulfur content in the feeding gas were analyzed to define the effect of H2S content on the performance drop. Relative change of the resistance of a cell was correlated with the rate of internal reforming and the content of sulfur. Results of the analysis show that the degradation of the performance of SOFC due to sulfur poisoning during operation in DIR mode can be modelled with high fidelity. Change of the ionic and electronic resistance of a cell accounted for the maximum of 34 and 53%, respectively when the rate of DIR was altered between 0 and 100%. The contribution of the sulfur poisoning accounts for 69 and 79% when the H2S content varies in the range of 0.001–5 ppm(v). With average relative prediction error below 3%, the proposed approach finds good application in simulating the performance of a cell exposed to different gas mixtures with different levels of sulfur in the fuel stream.

The research efforts for SOFC plants fed by biogas moved from the prototypal research to the feasibility of pilot plants up to achieve industrial size plants. Siloxanes among the other trace compounds contained in biogas appear to be the most detrimental for the fuel cell performance. Siloxanes are difficult to be detected and monitored continuously in the gas matrix. A direct injection mass spectrometry technique (PTRMS) was adopted for the monitoring of siloxane removal. Commercial and waste derived sorbent materials are experimentally tested for the removal of siloxanes. Waste derived material was selected to implement the circular recovery purposes. A simple parametric investigation study was developed. It was considered the influence of gas velocity and sulphur compounds, as co-vapors. Physical and chemical characteristics were correlated to the adsorption capacity. Results show three separated groups. Group I shows the best performance in terms of siloxane removal. There is a direct and strong relation between active surface area and microporous volume with the adsorption capacity. This direct correlation is not verified for some elements such as Fe and S, while it is respected for Cu and K. Higher performance are registered for not all the commercial carbons. In fact, the physical structure and impregnating agents are crucial for the siloxane removal.

Biogas produced from biomass is carbon neutral. In fact, the carbon feedstock of biomass is converted into gas phase. Biogas use in high efficient energy systems, such as Solid Oxide Fuel Cells is a viable choice. One of the most important drawbacks for such systems is related to the interaction between trace compounds and anode section. Gas cleaning through physical removal mechanisms is the simplest and cheapest method adopted in the literature. Coupled with this solution, the recovery of waste materials is an efficient application of the circular economy approach. In this work, a physical activation process was investigated experimentally for waste-derived materials at a temperature of 700 °C. The removal of H2S was considered as the most abundant trace compound. Activated biochar showed an adsorption capacity comparable to commercial sorbents, while the performance of ashes are still too poor. An important parameter to be considered is the biogas humidity content that enters in competition with trace compounds that must be removed.

The removal of trace compounds contained in a biogas from the dry anaerobic digestion of organic waste was accomplished. The resulting data were monitored online with a direct injection mass spectrometry technique. Biochar from the pyrolysis of recovered wood waste was used as sorbent material. This material was selected to demonstrate the usefulness of recovered waste for the energy production purposes. Biochar withstands the removal of 2-butanone (158.8 mg/g), toluene (140.1 mg/g) and limonene (64 mg/g) better compared to sulfur (H2S 1.05 mg/g) and siloxane (D3, 1.28 mg/g) compounds. Hydrogen sulfide was the most abundant sulfur compound with the average concentration about 24 ppm(v). The tested sorbent material was able to withstand the H2S and siloxane concentration for almost 30 h with the biogas pilot plant conditions before toachieve the limit value for SOFC applications, 1 ppm(v) and 150 ppb(v) respectively. The performance achieved with this material are comparable to some commercial carbons, even if some more optimized and selective materials show better results especially for the removal of sulfur compounds.

Biogas from biological treatments and from the waste degradation in landfills generally contains a wide range of trace impurities (e.g., sulphur compounds, siloxanes, halogens, tar compounds, etc.). This paper describes an experimental analysis performed with SOFC single cells fed by a synthetic gas polluted by H2S, HCl, D4 and a mixture of H2S + C2Cl4. The aim is to detect the threshold tolerance limit on different cell performance parameters. Results show how: hydrogen sulphide has a strong impact on the polarization losses due to the nickel sulphide formation on the electrode that causes a mass transfer resistance. Hydrogen chloride particularly limited the electrochemical processes. Octamethylcyclotetrasiloxane (D4) showed a high impact on SOFC performance even at ultra-low level (78–178 ppb(v)) as a consequence of the formation of silicon dioxide covering the anode porous sites. Sulphur added to C2Cl4, accelerated the deterioration of SOFC performance. In addition, current density variations and operating temperature are studied during sulphur poisoning. An opposite behaviour on SOFC performance was revealed by operating temperature and current density.

In this study, the main sections required to produce electricity in an SOFC short stack starting from biogas were studied and tested at a lab-scale level. A test-rig including a cleaning unit, a reformer and an SOFC stack was built and used to run a test of 500 h. In the plant, an in-house planar SOFC short stack (composed of three nickel based anode-supported cells) was fed by a simulated biogas mixture (60 vol.% CH 4 , 40 vol.% CO 2 ) contaminated by 30 ppmv of H 2 S (the main contaminant found in biogas, and deleterious for both the reformer and fuel cells). In the plant, H 2 S is first removed from the gas stream by adsorption in a fixed bed reactor packed with Na–X zeolites. The mixture was also passed on a ZnO guard bed (heated at 300 °C) before feeding the reformer unit in order to guarantee a durable and stable operation of the same. The reformer uses a Ni-based catalyst, and was operated at ∼700 °C in a mixed steam-/dry-reforming condition to produce a gas mixture suitable for the Ni-based SOFC with CH 4 converted almost entirely to H 2 and CO. The 3-cells short stack was operated at 800 °C and 0.1 A cm −2 for more than 500 h. The gas analysis was performed, via a mass spectrometer, in several points of the plant. These measurements indicated that no sulfur breakthrough takes place from the zeolites bed, and furthermore that the catalyst has a quite stable behavior. Results clearly show how a SOFC stack can be successfully operated with a contaminated biogenous gas mixture as fuel. As a matter of fact the cell stack exhibited a regular behavior, with no signs of degradation in the complete test.

Solid Oxide Fuel Cells (SOFCs) fed by biogenic fuels are a key renewable energy technology. Fuel contaminants, and sulfur compounds in particular, can strongly decrease SOFC performance. For this reason, their accurate, high sensitivity, and rapid monitoring and the development of successful removal strategies are major challenges in SOFC research. In this work the removal efficiency of commercial activated carbon filters for biogas filtering upstream of an SOFC was investigated using a Proton Transfer Reaction-Mass Spectrometry instrument (PTR-MS). In particular, we tested sulfur compounds by focusing on the effect of co-vapor adsorption (aromatic, carbonyl and chloro-compounds which are biogas pollutants) on filter performance. The results demonstrate the applicability of PTR-MS for investigating covapor effects which are of practical relevance for SOFC development.

Fuel cell and hydrogen technologies are re-gaining momentum in a number of sectors including industrial, tertiary and residential ones. Integrated biogas fuel cell plants in wastewater treatment plants and other bioenergy recovery plants are nowadays on the verge of becoming a clear opportunity for the market entry of high-temperature fuel cells in distributed generation (power production from a few kW to the MW scale). High-temperature fuel cell technologies like molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) are especially fit to operate with carbon fuels due to their (direct or indirect) internal reforming capability. Especially, systems based on SOFC technology show the highest conversion efficiency of gaseous carbon fuels (e.g., natural gas, digester gas, and biomass-derived syngas) into electricity when compared to engines or gas turbines. Also, lower CO2 emissions and ultra-low emissions of atmospheric contaminants (SOx, CO, VOC, especially NOx) are generated per unit of electricity output. Nonetheless, stringent requirements apply regarding fuel purity. The presence of contaminants within the anode fuel stream, even at trace levels (sometimes ppb levels) can reduce the lifetime of key components like the fuel cell stack and reformer. In this work, we review the complex matrix (typology and amount) of different contaminants that is found in different biogas types (anaerobic digestion gas and landfill gas). We analyze the impact of contaminants on the fuel reformer and the SOFC stack to identify the threshold limits of the fuel cell system towards specific contaminants. Finally, technological solutions and related adsorbent materials to remove contaminants in a dedicated clean-up unit upstream of the fuel cell plant are also reviewed. (C) 2017 Elsevier Ltd. All rights reserved.

This paper shows the developments of an equivalent circuit model adopted to interpret the deconvoluted electrochemical impedance spectra of an Ni-YSZ/YSZ/GDC/LSCF solid oxide fuel cell obtained by varying the operating temperature and the oxygen partial pressure under a fixed load. This allowed to unfold the physicochemical processes occurring within the anode supported cell and to identify which elements are responsible for major polarization losses. Furthermore, this model has proved to be effective even in the high frequency region, which is often beset by the onset of troublesome artifacts, as underlined by the comparison with the galvanic current interruption technique.

The real-life operation of solid oxide fuel cell (SOFC) system has to deal with fuel contaminants which might reduce even significantly the lifetime of reformer and stack depending on the type and amount of contaminant present in the feed stream. From a system perspective, detecting and correlating observed stack and reformer performance degradation with fuel contamination is fundamental to implement correctional procedures (e.g., change of clean-up vessels catalysts) and/or trigger alarms to prevent a further contamination of the fuel cell. In this work, based on own experiments with several fuel contaminants (H2S, HCl, tars, siloxanes), we have developed empirical degradation models which are able to quantitatively correlate the range of degradation rate resulting from known amounts of a certain contaminant type in the fuel stream. Degradation induced by carbon deposition is also assessed using a simulation model. The techno-economic trade-off of having ultra-stringent purification requirements on the fuel clean-up unit due to additional operating costs (e.g., for frequent catalysts change) or capital costs (e.g., for vessel over-sizing to accommodate a larger amount of catalysts and possibly of different types) versus the lifetime of the fuel cell stacks is eventually analyzed.

In the context of the paradigm of Carbon Recovery and Re-utilization (or CRR), this work investigates the role of electrochemical generators (such as high-temperature fuel cells) to perform CRR as a practical secondary effect. In fact, the solid oxide fuel cell (SOFC) operating principle is inherently beneficial toward CO2 separation from the exhaust gas since the fuel is electrochemically oxidized resulting in no N2 mixing at the anode (fuel) electrode. An oxy-combustor downstream the fuel cell will complete the residual fuel (mostly H2 and CO) oxidation to yield a stream that contains only H2O and CO2. After water condensation and further drying, the captured CO2 is fed to a photobioreactor that can fix carbon into microalgae. In this work, results of the first SOFC-based poly-generation system with complete CO2 recovery in the form of fast-growing biomass (micro-algae) are presented, as developed in the EU-funded project SOFCOM (GA 278798, www.sofcom.eu ). The overall plant layout is described, and results on the performance of the proof-of-concept plant units are provided.

To curtail greenhouse gas emissions local and distributed energy systems should be fed by renewable and high efficiency fuels. Anaerobic digestate of organic waste from biogas production can be adopted as a substrate, coupled to Solid Oxide Fuel Cell (SOFC) exhausts, for biomass culture. This biorefinery concept can be exploited towards the complete integration of a waste treatment plant. The work concern the preliminary tests assessed to identify the condition to obtain microalgal growth on dry digestate from anaerobic digestion of organic waste and CO2 remaining after power and heat production by fuel cells biofixation. The results of digestate pretreatment and dilution, inoculum: digestate ratio and CO2 supply system were reported. Each test was controlling operating temperature and light intensity using a common green alga, Chlorella vulgaris. Different tests were performed for testing digestate dilution (from 1:20 to 1:70) and for defining microalgal inoculum concentration (9%, 20% and 32%). All trials were performed at laboratory scale. The optimal digestate pretreatment and microalgal inoculum concentration was used for achieving CO2 biofixation in an experimental reactor (15 L). The best dilution for the digestate was found to be approximately 1:70 and inoculum percentage equal to 20%.

The most thermodynamically stable sulfur compound in the anode electrode at SOFC temperature is H 2 S, which dissociates on a nickel (Ni) surface according to a chemisorption mechanism. In this study, SOFC performance losses have been quantified in the presence of H 2 S contamination. The deactivation process has been well quantified by correlating it to Ni surface coverage by sulfur through a Temkin-like isotherm adsorption process. The detailed microscopic features of an Ni-based electrode have been taken into account to quantitatively predict atomic sulfur adsorption on the Ni surface. The results show that, in anode-supported cells, the entire available Ni surface is affected by sulfur contamination and not just the three-phase-boundary (TPB) region. Experiments on both commercial single-cells and on a stack have been described in this work. The H 2 S concentration was varied from 0.8 to 6.5 ppm(v) in the single-cell experiments, and between 0.01 and 25 ppm(v) in the stack experiment. The time-to-coverage evaluation has been established on the basis of the relationship between the sulfur capacity of the Ni anode and the sulfur flow rate through the fuel feed.