Typical Biogas Composition Research Articles

Intrinsic kinetics of steam methane reforming over a monolithic nickel catalyst in a fixed bed reactor system

The intrinsic kinetics of steam methane reforming were experimentally investigated using a monolithic nickel-based catalyst in a specially designed fixed bed system. All kinetic tests were performed under various operating conditions: steam to carbon ratio of 2 to 5, methane volumetric concentration in feed gas of 3 % to 9 %, temperature of 500 to 650 °C, and typical biogas compositions with N2 dilution (carbon dioxide 35.7–55.6 %, methane 44.4–64.3 %, with 86–91 % nitrogen dilution). A deconvolution process was applied during the rate calculation and the reaction orders with respect to different gases were determined, coupled with thermodynamic system analysis. The reaction mechanism was then proposed and a Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model was established, followed by kinetic parameter estimations for the model and a further model validation with experimental data. Based on the model, the intrinsic kinetic of SMR reaction using monolithic catalysts was described. The validity and feasibility of applying the faster approach for kinetic parameter estimation were demonstrated, and this work is the first demonstration of a complex reaction system. Also, the reaction mechanism appeared to show a suitably high correlation with alternative and more sustainable methane sources (i.e. biogas).

Renewable biomethane production from biogas upgrading via membrane separation: Experimental analysis and multistep configuration design

In this work, we studied the upgrading of a mixed gas stream having a typical biogas composition by membrane gas separation with the aim of producing a purified biomethane stream. A polyetherimide/polyimide (PEI-PI) membrane module with an area of 1500 cm2 was used to evaluate the mass transport properties and the influence of water vapour and H2S on the separation performance. CO2 permeance was depleted by the presence of CH4 contrarily to this latter, whose permeation was enhanced by CO2. The permeances of both CO2 and CH4 were significantly affected by the presence of water vapour, showing a reduction of about 24–27% with respect to dry gas. Long-term analysis lasted about 650 days, showed an overall permeance variation of about 23% for N2 and 14% for CO2.The experimental permeance and selectivity values measured in wet conditions were used to simulate a multistep membrane system able to purify a “clean” biogas stream up to 98% of methane. It was found that the increasing number of steps from 3 to 7 allows a significant saving of membrane area, paired to an increment of CH4 recovery and CO2 purity.

Long-term performance of highly selective carbon hollow fiber membranes for biogas upgrading in the presence of H2S and water vapor

Biogas is an increasingly attractive renewable resource that needs to be upgraded to meet either the natural gas pipeline quality or the biomethane requirement. The use of carbon membranes is a promising alternative to conventional separation technologies, but, up to now, few attempts have been made to systematically investigate their separation performance under real biogas upgrading conditions, for instance, the presence of water vapor and H2S in the feed stream.In this work, for the first time in literature, the separation performances of as-prepared cellulose-based carbon hollow fiber membranes were monitored for 183 days under continuous exposure to a gas stream also containing H2S and/or water vapor. After the evaluation of their CO2 and CH4 sorption (2,98 mmol g−1 and 2,00 mmol g−1, respectively at 298 K and 10 bar), diffusion(2.45 × 10-7 cm2 s−1 for CO2), and permeation properties (120.9 and 2.3 barrer, respectively at 308 K) with single gases, long-term tests were carried out by feeding gas mixtures with typical biogas composition. It was found that the exposure of the membranes to H2S (up to 500 ppm) and water vapor (relative humidity of 90%) provoked a reduction of CO2 and CH4 permeability compared to the “clean and dry” mixed gas, which resulted in an increment of selectivity, which reached a value of more than 200. Overall, after more than 180 days of continuous testing, the membranes exhibited remarkable CO2/CH4 selectivity with endurability of the H2S and water vapor, confirming the fact of being good candidates for biogas upgrading.

RhNi/CeO2 catalytic activation of alumina open cell foams by dip-spin coating for the CO2 methanation of biogas

Production of CH4 by methanation of biogas provides a promising route towards sustainable energy production for the future. Utilization of biogas from biomass as CO2 source combines the advantage of reduction of greenhouse gas emissions producing a fuel with high energy density. In this study we apply a dip-spin coating method for washcoating Ni(7.5 wt%)Rh(0.5 wt%)/CeO2 catalyst on alumina open cell foams with different cell densities (20, 30 and 40 PPI).The catalytic activity of the structured samples was assessed using a gas mixture that simulates a typical biogas composition (CH4 = 60%vol; CO2 = 40%vol). The effects of the reaction temperature (300–600 °C) and H2/CO2 molar ratio in the feed (3–5) on the CO2 conversion and CH4 selectivity were evaluated under a gas hourly space velocity (GHSV) of 5100 h−1.All samples showed appreciable CO2 conversion ranging between 62.5 and 66.7% at reaction temperature of 500–600 °C, and a CH4 productivity of 3.4 molCH4·gMe−1·h−1 was obtained with the catalyst supported on open cell foam with 30 and 20 PPI under a reaction temperature of 400 °C.

Syngas Production From the Reforming of Typical Biogas Compositions in an Inert Porous Media Reactor.

Syngas production by inert porous media combustion of rich biogas–air mixtures was studied experimentally, focusing on carbon dioxide utilization and process efficiency. Different gas mixtures of natural gas and carbon dioxide, which simulated a typical biogas composition of 100:0, 70:30, 55:45, and 40:60 (CH4:CO2), were comparatively analyzed considering combustion waves temperatures and velocities, and chemical concentrations products, at high equivalence ratios of φ = 1.5 and φ = 2.0. Different CO2 concentrations on biogas composition showed higher H2 productions than on pure methane (100:0), mainly due to CO2 reforming reactions. Also, syngas production, hydrogen yields, and process efficiency by means of biogas filtration combustion were higher than under methane filtration combustion. Results of the thermochemical conversion of biogas show an alternative and promising non-catalytic technique to CO2 utilization.

Carbon membranes for bio gas upgrading

Abstract Carbon materials have a lattice plane distance in the range of the kinetic diameter of small gas molecules making them interesting for gas separating membranes. Thin carbon layers ( Because of the mole sieving behavior nearly constant separation performance was found in synthetic CO2/CH4-mixtures over a wide range of variation in pressure (from 0.2 MPa to 1.2 MPa) and gas composition (from 10% to 90% CO2). By only one membrane step a mixture of a typical biogas composition of 0.57 CH4 / 0.43 CO2 was separated in a highly concentrated CH4-stream of 94% at 1.2 MPa and a highly concentrated CO2-stream of 91% at 0.1 MPa. In real biogas treatments on two different biogas plants a robust membrane performance during the testing period of at least one month was observed. CH4 of 94% was produced from the biogas in only one membrane step. Water as well as H2S (up to 180 mg/m³) permeated through the membrane without any damage of the membrane. Both can be also separated from the biogas by the membrane in one single step. Carbon membranes are a robust alternative to polymeric membranes of lower chemical and pressure stability. There are clear advantages in costs, energy consumption, flexibility and convenience of biogas upgrading with carbon membranes in comparison to classical technologies like PSA and scrubbing.

Biogas combustion: Chemiluminescence fingerprint

A numerical and experimental study was conducted, with the purpose of inferring the influence of the CO2 concentration (xCO2) for different equivalence ratios (ϕ) on CH4/CO2/air (biogas) flames chemiluminescence. A thorough analysis on the signals of OH∗, CH∗, C2∗ and CO2∗ was performed. Typical biogas compositions were tested under laminar atmospheric flame conditions, within the unburned equivalence ratio of 0.9 and 1.14 with CO2 concentrations up to 40% in the blend. Experimental measurements of chemiluminescence were done using spectroscopy in the UV–visible region of the spectra. Simulations were performed with the GRI-Mech 3.0 mechanism without accounting for the nitrogen chemistry, extended with a chemiluminescence kinetics of OH∗, CH∗, C2∗ and CO2∗, in a burner-stabilized frame in CANTERA. Experimental measurements and numerical simulations are compared and generally are in good agreement. It was verified that CO2 dilution leads to a regular decrease in the emission intensities of OH∗, CH∗, C2∗ and CO2∗. Relations between chemiluminescence intensity ratios and xCO2 and ϕ were found. It was shown that OH∗/CO2∗ and C2∗/CO2∗ have the potential predict xCO2 in CH4/CO2/air flames. Moreover, it was verified that OH∗/CH∗, OH∗/C2∗ and CH∗/C2∗ are well suited to infer ϕ for the blends tested. It was verified that xCO2 does not cause relevant changes in the chemiluminescence ratios when inferring ϕ.

Impact of Argon in Reforming of (CH4 + CO2) in Surface Dielectric Barrier Discharge Reactor to Produce Syngas and Liquid Fuels

The aim of this work is to study the role of argon during plasma reforming of methane and carbon dioxide in order to convert Biogas into liquid fuels. Mixtures of synthetic CH4 and CO2, representing typical biogas compositions, were processed in a surface dielectric barrier discharge reactor in the presence of argon, which is considered to improve the discharge conditions. Our measurements showed that at constant feed flow rate and constant applied power, increasing the argon percentage from 0 to 66% in the feed, leads to increase the electron density up to 60% and the electron mean energy up to 50%. In these conditions, the absolute conversions of CH4 and CO2 are improved respectively from 19 to 43% and from 11 to 25%, the H2/CO ratio enhances up to 0.9. However, despite these improvements, the addition of argon beyond 33% decreases the carbon balance by deposition of black carbon and soot, decreases the selectivity of liquid products and finally lowers the energy efficiency of CH4 + CO2 mixture conversion. Meanwhile the selectivity of 10 liquid fuels principally alcohols, ketones and light organic acids, obtained in a yield of 3 wt%, depends also on the flow rate of argon in the feed mixture.

Methane-hydrogen fuel blends for SI engines in Brazilian public transport: Efficiency and pollutant emissions

Partial load operation of SI engines is conventionally achieved by the use of a throttle to control the airflow or air-fuel mixture into the engine. When the engine operates at partial load the throttle causes high pumping losses which has an effect on decrease of the engine efficiency. One of the possible ways to decrease the pumping losses during partial loads is to operate the engine under lean mixture condition. The limitation in this case can be misfiring of used fuel. The combustion limits can be extended by addition of hydrogen to the regular fuel. This work presents an analysis of use of hydrogen-methane taking into account aspects related to the efficiency and emission of pollutants. To carry out this study an experimental system composed of a SI engine was used. Two important differentials were used. First, the engine was supplied with simulated biofuels according to the typical biogas composition of the Brazilian landfills (Bio60); second, the system was operated in partial load, with the addition of H2, forming the HBio60 blend, in an attempt to increase efficiency and reduce pumping losses by increasing lambda value and variation in trottle position. The same aspects were evaluated with the engine operating with biogas composed of 95% of methane (Bio95) and in mixture with hydrogen (HBio95). The tests were performed at different ignition angles and air/fuel ratio. The results showed that adding H2 allows the combustion limits to be extended, with an effective increase of indicated efficiency. On the other hand, the reduction of NOx emissions was greater than 95% in the lean mixture provided by the presence of H2. The idea is to encourage change in the control algorithm of SI engines typically fueled with natural gas and use the H2-methane blends as fuel. Furthermore, diesel-powered buses in Brazil could be converted to SI gas engines without the loss of efficiency.

Experimental study of the effects of swirl and air dilution on biogas non-premixed flame stability

An experimental investigation of the stability limits of biogas in a swirling non-premixed burner has been carried out. A mixture of 60% methane (CH4) and 40% carbon dioxide (CO2) was used to reach the typical biogas composition. Vane swirlers with 30?, 45? and 60? angles were used to make the swirling air. The biogas stability limits and flame behavior under swirling conditions were tested. Besides, effects of air dilution with nitrogen (N2) and CO2 on biogas stability limits were investigated. The results show that using swirl can enhance the flame stability limits approximately four or five times comparing to non-swirling air stream. Adding N2/CO2 to the air had negative effects on the flame stability but no changes were observed in the flame structure. The maximum air dilution was also obtained when 27% and 15% N2 was added to the swirling air under strong and weak swirl, respectively.

Experimental evaluation and ANN modeling of a recuperative micro gas turbine burning mixtures of natural gas and biogas

Previously published studies have addressed modifications to the engines when operating with biogas, i.e. a low heating value fuel. This study focuses on mapping out the possible biogas share in a fuel mixture of biogas and natural gas in micro combined heat and power (CHP) installations without any engine modifications. This contributes to a reduction in CO2 emissions from existing CHP installations and makes it possible to avoid a costly upgrade of biogas to the natural gas quality as well as engine modifications. Moreover, this approach allows the use of natural gas as a “fallback” solution in the case of eventual variations of the biogas composition and or shortage of biogas, providing improved availability.In this study, the performance and emissions of a commercial 100kW micro gas turbine (MGT) at full and part loads are experimentally evaluated when fed by varying mixtures of natural gas and biogas. The MGT is equipped with additional instrumentation, and a gas mixing station is used to supply the demanded fuel mixtures from zero biogas to the maximum possible level by diluting natural gas with CO2. A typical biogas composition with 0.6 CH4 and 0.4 CO2 (in mole fraction) was used as reference, and corresponding biogas content in the supplied mixtures was computed.This paper presents the test rig setup used for the experimental activities and reports the results, demonstrating the impact of burning a mixture of biogas and natural gas on the performance and emissions of the MGT. The results indicate that the electrical efficiency is almost unchanged and no significant changes were observed in operating parameters, comparing with the natural gas fired case. It was also shown that burning a mixture of natural gas and biogas contributes to a significant reduction in CO2 emissions from the plant by about 19% at full load operation. Given the extensive data obtained during the experimental tests, a data-driven model based on an artificial neural network (ANN) was developed to simulate the performance of the MGT. The mean relative error (MRE) was used to evaluate the prediction accuracy of the developed ANN model with respect to experimental data which were not used during the training. It was demonstrated that the ANN model can predict the performance parameters of the MGT with high accuracy and the error of most samples is less than 1%. A graphical user interface (GUI) was created for the ANN model in Microsoft Visual Basic. The GUI is presented as a user-friendly tool for modeling and condition monitoring of the plant.

Effect of biogas-enriched with hydrogen on the operation and performance of a diesel-biogas dual engine

The effect of hydrogen enrichment was tested for a diesel-biogas dual fuel engine. The operation and performance characteristics, such as thermal efficiency, pollutant emissions and combustion parameters were determined. Experiments have been carried with a stationary compression ignition (CI) engine coupled with a generator in dual mode using a typical biogas composition of 60% vol. CH4 and 40% vol. CO2. For every load engine evaluated, the hydrogen concentration was varied from 5 to 20% H2 v/v. The results showed increases in peak pressure chamber up to 10.7 bar, and diesel substitution levels up to 80% under conditions of steady combustion without knocking. Also, thermal efficiency increases up to 16% and carbon monoxide emissions decreases up to 13% at full load, and 20% of hydrogen in engines operating in diesel-biogas dual mode.

Effects of oxygen enriched air on the operation and performance of a diesel-biogas dual fuel engine

The effect of oxygen enriched air was tested for a diesel-biogas dual fuel engine. The operation and performance characteristics, such as thermal efficiency, pollutant emissions and combustion parameters were determined. Experiments have been carried out with a stationary compression ignition (CI) engine coupled with a generator in dual mode using a typical biogas composition of 60 vol. %CH4 and 40% vol. %CO2. For every engine load evaluated, the oxygen concentration in the intake air engine was varied from 21% to 27% O2 v/v. Ignition delay time and methane emissions were decreased when using oxygen enriched air with respect to normal air (21%O2), whereas the thermal efficiency was increased.

Experimental evaluation of strategies to increase the operating range of a biogas-fueled HCCI engine for power generation

In this research oxygen enrichment, gasoline pilot port injection, and delayed time of 50% cumulative heat release (CA50) are evaluated to expand the range for stable and safe combustion of a lean-burning biogas-fueled HCCI engine. A 4-cylinder 1.9L Volkswagen TDI engine was modified to run in HCCI mode at 1800rpm, and boost pressures and charge heating are used to promote autoignition of the biogas-in-air mixture at desired combustion timings. A typical biogas composition of 60% CH4 and 40% CO2 in a volumetric basis was simulated by controlling the CH4 and CO2 flow rates. A range of 2–2.2bar absolute intake pressure and 473–483K initial charge temperatures allowed HCCI operation. At lowest equivalence ratio (0.25) excessive cycle-to-cycle variations were observed and at highest equivalence ratio (0.4) unacceptable ringing intensities were observed. To reduce cycle-to-cycle variability at low equivalence ratios, two strategies were used in enhancing the autoignition behavior of biogas: (1) oxygen enrichment of the inducted charge, and (2) gasoline pilot port injection. To increase gross Indicated Mean Effective Pressure (IMEPg) without excessive ringing intensities at high equivalence ratios, delayed CA50 was used. Oxygen enrichment increased cycle-to-cycle variability and total hydrocarbon emissions because of decreased burning rates and delayed CA50. Gasoline pilot port injection lowered cycle-to-cycle variability, CO and THC emissions, and increased IMEPg at low loads. Higher IMEPg was achieved with high equivalence ratios (above 0.4) and ringing intensities were kept within acceptable limits using delayed CA50, however NOx emission was increased also.HCCI combustion of biogas enables high overall efficiency, and the strategies explored in this research allow higher power output, and more stabilized combustion.

SOFC Power Generation from Biogas: Improved System Efficiency with Combined Dry and Steam Reforming

Solid oxide fuel cell systems (SOFC) can improve the efficiency of electrical power generation from biogas compared to small scale CHP units. The SOFC requires a reforming step converting biogas into synthesis gas (hydrogen and carbon monoxide). . Dry reforming of methane with the carbon dioxide contained in biogas is a promising approach to produce high caloric SOFC fuel gas, but carbon formation is predicted for all typical biogas compositions. To avoid carbon formation and to compensate fluctuating biogas compositions additional supply of steam is essential leading to a combined dry and steam reforming. The paper describes the system approach, upfront analysis, biogas monitoring results, process unit design and evaluation as well as the system setup to demonstrate a biogas to electricity route with a gross efficiency of 45 % using a commercial 1 kW SOFC stack.

An analysis of CH4/N2 rich biogas production, fuel treatment process and microturbine application

Biogas usually contains CH4 and CO2 as main components with the ratio of 6 : 4, and its composition varies with wide range depending on digester conditions. In addition to concentration change of each constituent, biogas com- position could be changed due to the variations in the organic matter treatment process. The aim of the study is to analyze the production and application to a microturbine system of CH4/N2 rich biogas produced from Gong-Ju wastewater treatment plant. CH4/N2 rich biogas is produced due to the internal wastewater recirculation. The internal wastewater recirculation is intended to enhance NO3 − removal without additional carbon source input. As a result, the digester was shown to be the highest contributor for nitrogen removal and average CH4 concentration was lowered compared to the typical biogas composition. Nitrate removal rate was influenced by the internal recirculation ratio. Content of N2 has no effect on biogas clean-up system performance. Besides, adaptability of CH4/N2 rich biogas to microturbine was satisfactory with very low NOx and SO2 concentration in microturbine exhaust gas. Influence of high N2 concentra- tion of biogas on NOx concentration was limited due to the low combustion temperature.

The effect of hydrogen addition on biogas non-premixed jet flame stability in a co-flowing air stream

An investigation of the stability limits of biogas jet non-premixed (diffusion) flames in a co-flowing air stream was conducted. The stability limits were determined experimentally for two different methane–carbon dioxide mixtures that represent the typical biogas composition. Moreover, the effect of jet nozzle diameter was also investigated. It was found that with the presence of a significant amount of CO 2 in the fuel, the stability limits were very low and the flames can only be stabilized over a very small range of co-flowing air velocities. As expected, an increase in carbon dioxide concentration resulted in the narrowing of the region for stable flames. However, it was shown that the flame stability of such mixtures can be enhanced very significantly over a much wider range of co-flowing air velocities by introducing a small amount of hydrogen into the fuel. Results obtained in the current experimental setup indicate that an increase in the stability limits by approximately four-fold when 10% (by vol.) of hydrogen is added under the same operating conditions. The effect of the addition of hydrogen on the enhancement of biogas stability is most significant with a 10% initial addition. The degree of enhancement diminishes with further increases in hydrogen addition from 10% to 30%.