Real Biogas Research Articles

Hydrogen production through dry reforming of biogas using a porous electrochemical cell: Effects of a cobalt catalyst in the electrode and mixing of air with biogas

This paper reports the performance of porous Gd-doped ceria (GDC) electrochemical cells with Co metal in both electrodes (cell No. 1) and with Ni metal in the cathode and Co metal in the anode (cell No. 2) for CO2 decomposition, CH4 decomposition, and the dry reforming reaction of a biogas with CO2 gas (CH4 + CO2 → 2H2 + 2CO) or with O2 gas in air (3CH4 + 1.875CO2 + 1.314O2 → 6H2 + 4.875CO + 0.7515O2). GDC cell No. 1 produced H2 gas at formation rates of 0.055 and 0.33 mL-H2/(min m2-electrode) per 1 mL-supplied gas/(min m2-electrode) at 600 °C and 800 °C, respectively, by the reforming of the biogas with CO2 gas. Similarly, cell No. 2 produced H2 gas at formation rates of 0.40 mL-H2/(min m2) per 1 mL-supplied gas/(min m2) at 800 °C from a mixture of biogas and CO2 gas. The dry reforming of a real biogas with CO2 or O2 gas at 800 °C proceeded thermodynamically over the Co or Ni metal catalyst in the cathode of the porous GDC cell. Faraday's law controlled the dry reforming rate of the biogas at 600 °C in cell No. 2. This paper also clarifies the influence of carbon deposition, which originates from CH4 pyrolysis (CH4 → C + 2H2) and disproportionation of CO gas (2CO → C + CO2), on the cell performance during dry reforming. The dry reforming of a biogas with O2 molecules from air exhibits high durability because of the oxidation of the deposited carbon by supplied air.

Heat loss analysis in the semi-buried anaerobic digester in Northeast Poland

A thermal model was used to compare an actual and a computational heat losses in an existing the semi-buried anaerobic digester (AD) during the winter season in Northeast Poland. This work is an attempt to answer the question whether the cause of the temperature decrease of the manure AD is underestimated the heat exchanger or its low efficiency. The answer to this question is important for manager to take appropriate action. Understanding the heat loss of biogas digester is important to use these technologies to produce the biogas on assumed level in cold environment - like winter in Northeast Poland. From anaerobic digester point of view, the maintaining of optimal fermentation temperature is crucial. In the current study 2-D axisymmetric steady heat transfer model was carried out to calculate heat loss of AD for a real biogas plant located in north-eastern Poland and compared with actual state.

SOFC Operation with Real Biogas

AbstractBiogas is a valuable energy source and will be available in future in systems relying on renewables. It is an attractive fuel for solid oxide fuel cells (SOFC), which are able to utilize the carbon contained in the biogas and which produce electricity with high efficiency. In the current paper, state‐of‐the‐art SOFCs were studied regarding performance and durability in relation to biogas as fuel and considering important contaminants, specifically sulfur. First, the catalytic behavior in relevant synthetic biogas mixtures was studied and the potential of dry reforming was demonstrated. Successful long term operation of an SOFC under both, conditions of steam and dry reforming, i.e., addition of steam or CO2 to avoid carbon formation was shown. For the steam reforming case a remarkable period of 3,500 h, hereof 3,000 h in the presence of H2S was achieved. Finally, a real biogas from a landfill gas unit was used as fuel. The concept of dry reforming was realized. The SOFC was successfully operated with and in one case even without a specific gas cleaning unit.

Struvite precipitation from biogas digestion slurry using a two-chamber electrolysis cell with a magnesium anode

A novel, two-chamber electrolysis cell equipped with an ion exchange membrane and a magnesium anode was proposed in this study to recover phosphate as struvite from both the simulated and real biogas digestion slurry of swine wastewater. In the electrolysis experiments with the simulated slurry, the optimal pH and current density were determined to be 8.5 and 22.2 A m−2, respectively, achieving 95% phosphate removal efficiency and 100% current efficiency. The phosphate removal rate was mainly dependent on the magnesium dissolving rate. In the electrolysis experiments with the real digestion slurry, the pH of slurry increased from 7.4 to around 8.7 after the cathode-anode sub-section electrolysis without adding chemical reagents, achieving 93% phosphate removal efficiency at 22.2 A m−2. The phosphate removal efficiency could be kept constant in three consecutive electrolysis cycles with both the anion exchange membrane and the cation exchange membrane. The cost of the magnesium anode treatment for the real biogas digestion slurry for struvite recovery was estimated to be $81.57 kg−1 P, mainly resulting from the consumption of electricity and magnesium anode. The precipitates collected from all experiments were identified as struvite by the X-ray diffraction analysis.

The Effect of WO3 Modification of ZrO2 Support on the Ni-Catalyzed Dry Reforming of Biogas Reaction for Syngas Production

The time-on-stream catalytic performance and stability of 8wt% Ni catalyst supported on two commercially available catalytic supports, ZrO2 and 15wt% WO3-ZrO2, was investigated under the biogas dry reforming reaction for syngas production, at 750oC and a biogas quality equal to CH4/CO2=1.5, that represents a common concentration of real biogas. A number of analytical techniques such as N2 adsorption/desorption (BET method), X-Ray diffraction (XRD), temperature programmed reduction (H2-TPR), temperature programmed desorption (NH3- and CO2-TPD), scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), thermal analysis (TGA/DTG) and Raman spectroscopy were used in order to determine textural, structural and other physicochemical properties of the catalytic materials, and the type of carbon deposited on the catalytic surface of spent samples. These techniques were used in an attempt to understand better the effects of WO3-induced modifications on the catalyst morphology, physicochemical properties and catalytic performance. Although Ni dispersion and reducibility characteristics were found superior on the modified Ni/WZr sample than that on Ni/Zr, its dry reforming of methane (DRM) performance was inferior; a result attributed to the enhanced acidity and complete loss of the basicity recorded on this catalyst, an effect that competes and finally overshadows the benefits of the other superior properties.

Comparison of the experimental and theoretical production of biogas by monosaccharides, disaccharides, and amino acids

The estimation of biogas production from organic monomers is very important for the optimal design, configuration, and efficient evaluation of the anaerobic digestion processes in a digester. The theoretical estimation of the biogas potential that is most used is that of Buswell and Boyle. In this work, we found that this estimate was much exaggerated compared to the real biogas potential determined in practice. For monosaccharides, we noted that the biogas potential of glucose was very low compared to that of fructose, even though the two substrates have the same chemical composition and molecular mass. The same result was observed for the disaccharides lactose and maltose. The amino acid valine produced more biogas than the amino acid cysteine did. The experimental potential remained lower than the calculated potential. An important difference existed between the experimental biogas potential of the six monomers investigated and the theoretical biogas potential. This indicated that the calculation of the biogas potential by the stereochemical equation of Buswell and Boyle was overstated and did not take into consideration the isometric form, spatial configuration, and intermediate metabolite produced by the monosaccharides in the four steps of anaerobic digestion. For the disaccharides, the theoretical calculations did not take into account the nature of the molecular components in carbohydrate, type of glycosidic bond, and intermediate metabolites of substrates for anaerobic digestion. Finally, for the amino acids, it does not take into account the ramification of the atomic components and the chemical nature of atoms in amino acids.

Biogas Engine Emissions: Standards and On-Site Measurements

The European Union, with 60% of the total global production of biogas, is the world leader. In 2012, the percentage of electrical energy produced by biogas was 6% of the EU-28 electricity generated through renewable sources while, in 2013, the almost 830 biogas units produced 7448 GWh which corresponds to 14% of EU-28 gross electricity production. Germany, U.K. and Italy are the main EU biogas producers with over 78% of the 2013 primary energy production. Electricity production is the main biogas energy recovery form because the engine cooling water is used to maintain the digester required temperature while energy crops and manure are the most used organic matters. Spark-ignition engines with a rated power of 1MWel in which the filtered biogas is burned to produce work is the widely-adopted technology. With the aim of analyzing the emissions of a real biogas engine, in the present work, the authors firstly present an overview of the Italian biogas sector and the most used conversion technologies. Then, the standards which regulate the biogas plant emissions and the emissions data acquired during a one-year monitoring activity on 10 biogas plants are presented and discussed with the aim of assessing the biogas units’ real emissions.

Progress of SOFC/SOEC Development at DTU Energy: From Materials to Systems

DTU Energy has many years of experience in solid oxide fuel cell and electrolysis (SOFC/SOEC) research and development. Currently, the volume of SOFC/SOEC related projects exceeds 40 man-years per year. The main sources of financing are Danish R&D programs, counting for ~½ of all activities. In addition, activities are funded through European projects, commercial partners and finally from internal funds. The presentation will cover highlights from the SOFC/SOEC activities at DTU Energy, which span over a broad range in the value chain, from materials to cells, stacks and analyses at energy system level. These highlights also include progress of method development that supports SOFC/SOEC research such as ceramic processing methods, micro structural analysis, electro chemical characterization, and modelling. Recent achievements involve electrode development on Ni-free fuel electrodes with high carbon tolerance, redox stability, and tolerance towards impurities in the gas. Building on the concept of nanostructured fuel-electrodes, symmetric cells with zirconia based backbones were successfully prepared by freeze-casting and showed a small area specific resistance of ca. 0.012 Ohm cm2 at 650 oC after infiltration of nano sized ceria. DTU Energy has been among leading groups in the area of metal supported SOFCs. Our approach is based on a “co-firing” route utilizing ceramic manufacturing methods such as tape casting for the supporting metal layer. Recently the focus has been on developing a new cell concept that enables long term operation under conditions of high fuel utilization, where previous cell types have failed. Progress was achieved through micro structural optimization and use of an active and stable electrode material, LSFNT. Apart from development and improvement of fuel and electrolysis cells, comprehensive testing with the aim to understand the processes determining performance and durability has been carried out. Specific emphasis has been on matching real application conditions also in the lab. Such realistic conditions comprise both, the operating regimes – such as dynamic profiles (considering SOFC/SOEC applications in an energy system dominated by wind or solar power) – and the fuels – such as biogas. Biogas - a mixture of mainly methane and CO2 – is formed through anaerobic digestion of for example domestic or farming waste and is already produced at large scale throughout the world. SOFC allow for the direct use of biogas as fuel and offer the unique potential to produce electricity with high efficiency. Recently, a successful SOFC test was performed under dry reforming conditions, i.e. a mixture of a real biogas from a landfill unit and added CO2. With the SOFC technology approaching longer life times of thousands and tens of thousands of hours, durability testing for degradation analysis and life time prediction becomes more time consuming. Accelerated aging tests are therefore highly desired. DTU Energy has several activities in this area and has for example applied a new strategy for degradation analysis, recently. It was shown how the steam content determined by the inlet gas composition and the operating conditions current load and fuel utilization is one of the possible accelerating parameters for SOFC degradation. Also in the area of SOEC an extensive test program has been running over the past 10 years, including durability tests of several thousands of hours, both for steam and co-electrolysis of steam and CO2. This has involved test of various generations of cells, all based on a Ni/YSZ-structural support, but with different oxygen electrodes, as well as long term tests at stack level. Recent learnings on the impact of running cells in glavano static or potentio static regime and of the conversion degree will be presented. In electrolysis operation, the oxygen activity on the oxygen electrode will be higher than in fuel cell mode. This has an adverse effect on interconnect corrosion. The impact of oxygen activity on corrosion and performance of recently developed protective coatings will be presented. Finally, the importance of mechanical robustness for reliable operation of stacks shall be discussed based on newly acquired data on the mechanical properties of both cells and interfaces in the stack.

Biogas Production from Local Biomass Feedstock in the Mekong Delta and Its Utilization for a Direct Internal Reforming Solid Oxide Fuel Cell

Fuel-flexible solid oxide fuel cell (SOFC) technologies are presently under study in a Vietnam-Japan international joint research project. The purpose of this project is to develop and demonstrate an SOFC-incorporated energy circulation system for the sustainable development of the Mekong Delta region. Lab-scale methane fermentation experiments in this study with a mixture of biomass feedstock collected in the Mekong Delta (shrimp pond sludge, bagasse and molasses from sugar production) recorded biogas production yield over 400 L kgVS-1 with H2S concentration below 50 ppm level. This real biogas was directly supplied to an SOFC without any fuel processing such as desulfurization, methane enrichment and pre-reforming, and stable power generation was achieved by applying paper-structured catalyst (PSC) technology.

The environmental effect of substituting energy crops for food waste as feedstock for biogas production

Assuring environmental sustainable bioenergy production is an international priority nowadays. The objective of this study was to identify the environmental consequences of feedstock selection in biogas production. Two real biogas plants were assessed and compared from a life cycle perspective. Plant A performs the co-digestion of energy crops (78%) and animal waste (22%) while Plant B consumes energy crops (4%), food waste (29%) and animal manure (67%). According to the results, electricity production from biogas implied lower impacts in climate change compared to the existing electric mix. Maize silage (650 Nm3/TVSfed) and food waste (660 Nm3/TVSfed) appeared as an interesting source of bioenergy. However, the cultivation of energy crops was identified as the main hotspot in Plant A. Finally, the use of organic substrates with lower energy potential and high nutrients concentration such as animal manure (450 Nm3/TVSfed) produced higher amounts of digestate, producing impacts in acidification and eutrophication categories. In order to improve the environmental sustainability of bioenergy, specific guideless should be established to achieve harmonised life cycle studies. In addition, environmental policies should promote the use of waste streams and prevent the use of energy crops as well as include goals related with acidification and eutrophication impacts.

Biogas use in high temperature fuel cells: Enhancement of KOH-KI activated carbon performance toward H2S removal

Activated carbons (ACs) treated with KOH-KI are very effective sorbents for deep H2S removal, as required by biogas use in high temperature fuel cell systems. For this application, the performance of a commercial KOH-KI treated AC was investigated through a systematic study based on dynamic adsorption tests. With reference to the composition of a real biogas produced in a wastewater treatment plant located in Barcelona, the present work presents a sensitivity performance analysis on singular and synergetic effects of gas matrix, humidity and oxygen on AC KOH-KI performance.The results revealed a positive role of water (up to 90% of relative humidity (R.H.)) for different gas matrices, enhanced by the simultaneous presence of small percentages of oxygen (2%v). A relevant influence of gas matrix composition was found (except for the case of oxygen addition to dry inlet streams), specifically in terms of a marked negative effect of CO2 and a significant sorption capacity increase for high percentage of methane. Sulfur dioxide was not detected in the outlet gas-phase for the investigated operating parameters (O2 2%v, R.H. 0–90%, H2S 100 ppmv, temperature 45 °C). Therefore, even in the case of further oxidation of adsorbed elemental sulfur to SO2, this product could be completely removed by AC KOH-KI.

Experimental characterization of multi-component absorption in complex liquid: New method and apparatus

The Henry’s law constant is required to size absorption processes. However, its experimental determination for multi-component gases in presence of complex liquids remains problematic in the process industry and research field. This work presents a new experimental setup built to measure Henry’s law constants easily. The apparatus brings gas and liquid phases into contact before and after equilibrium in medium pressure conditions (from 1 to 10bars). Thanks to standard sensors, temperature, pressure and phase concentrations of the components are recorded continuously, permitting to calculate the Henry’s law constant. Three types of water were tested and put in contact with a real biogas mix. Henry’s law constants for carbon dioxide and methane were obtained with good accuracy and were consistent with the values reported in the literature for tap water. Results obtained with the apparatus show that values of Henry’s law constant can differ between tap water and recycled water. Carbon dioxide absorption is strongly reduced when recycled water is used. We can conclude that the proposed apparatus is a convenient experimental set up for determining Henry’s law constants with good accuracy and as it is movable it can be helpful for engineer in charge of biogas upgrading system.

Vacuum swing adsorption on natural zeolites from tuffs in a prototype plant

A vacuum swing adsorption (VSA) prototype plant was developed and tested, based on natural zeolites from tuffs containing Chabazite. The regeneration procedure of natural zeolites was optimized, and the operative pressure resulted to be the most important parameter. The VSA prototype was fed for 3 months with a real biogas, produced by agrozootechnical byproducts in an anaerobic baffled reactor (ABR). Biogas composition from ABR was very stable and allowed to deeply investigate the performances of natural zeolites in real biogas conditions. Biogas was desulfurized and dehydrated before the VSA unit. In our experimental conditions, a biomethane average purity > 98% was achieved, with methane recovery > 95%. CO2 concentration was always lower than 0.3%, while oxygen ranged from 0.2 to 1.5%. A light desulfurization effect was also observed. CH4 concentration was < 0.1% in the VSA off‐gas. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 887–894, 2017

Model of Electric and Heat Balance of Biogas Station

This paper deals with the model of a biogas station. The introduction provides a description of principle employed in this model. The model works with data reflecting the quantity and type of the input biomass to determine the potential energy and offer a selection from various co-generation units. Other important input parameters comprise fermentors and mainly the material composition of their walls to help with determination of heat losses. The input parameters are accompanied by the energetic balance model for a Biogas Station (BPS) concerned. The next section of this paper provides verification of the model with respect to an actual BPS subject to a series of measurements. These measurements focus on electric and heat parameters. The outcome from these measurements was then used to obtain the energetic balance figure. The comparison of measurement results against the model produces slight deviations of the model from the real biogas station only. This paper has been processed pursuant to a long-term research on biogas stations. The biogas station model will be developed further to obtain a more detailed energetic balance for the biogas station.

Hydrogen formation from a real biogas using electrochemical cell with gadolinium-doped ceria porous electrolyte

The electrochemical cell consisting of a gadolinium-doped ceria (GDC, Ce0.9Gd0.1O1.95) porous electrolyte, Ni–GDC cathode and Ru–GDC anode was applied for the dry-reforming (CH4+CO2→2H2+2CO) of a real biogas (CH4 60.0%, CO2 37.5%, N2 2.5%) produced from waste sweet potato. The composition of the supplied gas was adjusted to CH4/CO2=1/1 volume ratio. The supplied gas changed continuously into a H2–CO mixed fuel with H2/CO=1/0.949–1/1.312vol ratios at 800°C for 24h under the applied voltage of 1–2V. The yield of the mixed fuel was higher than 80%. This dry-reforming reaction was thermodynamically controlled at 800°C. The application of external voltage assisted the reduction of NiO and the elimination of solid carbon deposited slightly in the cathode. The decrease of heating temperature to 700°C reduced gradually the fraction of the H2–CO fuel (61.3–18.6%) within 24h. Because the Gibbs free energy change was calculated to be negative values at 700–600°C, the above result at 700–600°C originated from the gradual deposition of carbon over Ni catalyst through the competitive parallel reactions (CH4→C+2H2, 2CO→C+CO2). The application of external voltage decreased the formation temperature of carbon by the disproportionation of CO gas. At 600°C, the H2–CO fuel based on the Faraday's law was produced continuously by the electrochemical reforming of the biogas.

5-1-3 火花点火ガス機関の高温ガス化バイオガスによる運転特性

5-1-3 火花点火ガス機関の高温ガス化バイオガスによる運転特性

Biogas Production Modelling: A Control System Engineering Approach

Due to the Renewable Energy Act, in Germany it is planned to increase the amount of renewable energy carriers up to 60%. One of the main problems is the fluctuating supply of wind and solar energy. Here biogas plants provide a solution, because a demand-driven supply is possible. Before running such a plant, it is necessary to simulate and optimize the process feeding strategy. Current simulation models are either very detailed like the ADM 1, which leads to very long optimization runtimes or not accurate enough to handle the biogas production kinetics. Therefore this paper provides a new model of a biogas plant, which is easy to parametrize but also has the needed accuracy for the output prediction. It is based on the control system approach of system identification and validated with laboratory results of a real biogas production testing facility.

Co-fermentation experiments with agricultural main products and liquid pig manure

My research work proposes the study of the impact of the biogas production by the co-fermentation of agricultural products. The basic substance is the dangerous liquid pig manure of the concentrated stock of big pig farms. The energetic utilization of these materials means bigger income for the agricultural enterprises, savings in the replacement of the plant nutrition with the utilization of the bio-manure, increase in the performance of the plant production, making the dung harmless which means a big environmental load. Because of the profitability of bioenergy utilization depends on the local conditions, it is necessary to do experiments to try the available composition of organic wastes in the ratio of the production in advance. I measured the quantity of the methane and CO2 content of the biogas released from the substrate. The experiment simulated real biogas plant conditions, in mesophilic temperature, continuous biodegradation process. It can be considered, as a semi-industrial size.

Biogas cleaning and upgrading with natural zeolites from tuffs

ABSTRACTCO2 adsorption on synthetic zeolites has become a consolidated approach for biogas upgrading to biomethane. As an alternative to synthetic zeolites, tuff waste from building industry was investigated in this study: indeed, this material is available at a low price and contains a high fraction of natural zeolites. A selective adsorption of CO2 and H2S towards CH4 was confirmed, allowing to obtain a high-purity biomethane (CO2 <2 g m−3, i.e. 0.1%; H2S <1.5 mg m−3), suitable for injection in national grids or as vehicle fuel. The loading capacity was found to be 45 g kg−1 and 40 mg kg−1, for CO2 and H2S, respectively. Synthetic gas mixtures and real biogas samples were used, and no significant effects due to biogas impurities (e.g. humidity, dust, moisture, etc.) were observed. Thermal and vacuum regenerations were also optimized and confirmed to be possible, without significant variations in efficiency. Hence, natural zeolites from tuffs may successfully be used in a pressure/vacuum swing adsorption process.

Biogas upgrading from vinasse digesters: a comparison between an anoxic biotrickling filter and an algal‐bacterial photobioreactor

AbstractBACKGROUNDBiological technologies for biogas upgrading such as anoxic biotrickling filters (BTF) and algal–bacterial photobioreactors (PBR) constitute a cost‐effective, environmentally friendly alternative to conventional physical–chemical methods. Nonetheless, there is a lack of studies comparing their performance when treating real biogas.RESULTSA H2S removal efficiency &gt;98% was consistently recorded in both systems, with elimination capacities up to 26 and 12.4 g S‐H2S m−3 h−1 in the BTF and PBR, respectively, at empty bed residence times (EBRTs) of ∼ 30 min. Both bioreactors demonstrated a high robustness towards fluctuations in biogas composition and flowrate, maintaining nearly complete desulfurization despite the variations in sulfur load and EBRT. The BTF also showed an immediate recovery from a 15 days operational shut‐down, and the ability to utilize the nutrients from nitrate‐supplemented digestate during biogas desulfurization. In addition, the PBR supported an average CO2 removal of 23.0 ± 11.8%, increasing to 62% at higher pH of 8.1, with a carbon fixation rate of 285 mg CO2 L−1 d−1.CONCLUSIONSThe BTF was confirmed as a robust technology for the desulfurization of real biogas, even when supplemented with effluent from the digester. High H2S removal was also achieved in the PBR, the CO2 fixation capacity of microalgae enhancing biogas purification. © 2015 Society of Chemical Industry