Methane Volume Fraction Research Articles

Burner development for efficient combustion of biogas

Now in metallurgical production energy resources demand is almost completely satisfied by gaseous fuel. Biogas obtained during organic waste processing is considered as an alternative and cheaper type of fuel. The experience of biogas application has shown that in most modern burners decrease of efficiency and limitation of the range of load regulation is observed. To apply biogas in an industrial environment, it is necessary to develop burners and the methods of its combustion, which provide a high combustion efficiency, as well as a higher energy conversion efficiency. The authors have used the results of gas analysis of biogas obtained in the process of anaerobic decomposition process of organic waste in the reactors of a bioenergy plant. Methods of mathematical statistics with the use of regression analysis of experimental data were used to assess the indicators of the energy efficiency of the gas burner. The possibility of using biogas and landfill gas in the process of roasting, blast-furnace smelting, production of rolled products and steel, as well as heat treatment of metal has been experimentally proven. The properties and composition of biogas at the outlet of the methanogenesis reactor of the bioenergy plant “EcoVoltAgro” are described. A new design of a gas burner is proposed. In this model the efficiency of mixture formation and the completeness of combustion of the flow of a methane-containing gas mixture are significantly increased (up to 32 %) due to the effect of rotation of the perforated pipelines of the gas inlet pipe. On the basis of the results of the full-scale experiment, the optimal values of the gas-air mixture supply rate, the temperature of the supplied air, the volume fraction of methane were determined in order to obtain the largest width of the zone of deviations of the permissible concentrations of carbon dioxide. The use of the designed gas burner provides energy-efficient combustion of biogas in metallurgical furnaces, kilns, and dryers, as well as in any steam and hot water boilers.

Insight into a new phenolic-leaching pretreatment on bamboo pyrolysis: Release characteristics of pyrolytic volatiles, upgradation of three phase products, migration of elements, and energy yield

Leaching essentially removes metallic species from biomass and improves the quality of pyrolysis products. However, common acid solutions, such as hydrochloric acid and acetic acid are expensive and difficult to recycle. This paper reports a new leaching pretreatment, using phenol and guaiacol solutions, which are mainly present in liquid by-products from thermal conversion of biomass. The characteristics of releasing of volatiles and upgradation of pyrolytic products of bamboo were investigated. Four key results can be obtained. (i) Phenolic leaching had much higher removal efficiency of metallic species, compared to water leaching. (ii) Pyrolytic behavior of bamboo changed drastically by phenolic leaching. Specifically, it enhanced the release of pyrolytic volatiles, separated the pyrolysis zones of hemicellulose and cellulose, and eliminated pyrolytic peak for extractives. (iii) Phenolic leaching upgraded the three phase pyrolysis products. Specifically, it inhibited the formation of acids, promoted the formation of anhydrosugars in bio-oil, improved the specific surface area of bamboo charcoal, and increased the volume fraction of methane in the gaseous products. (iv) With improved migration of oxygen and carbon from bamboo to bio-oil, the bio-oil replaced bamboo charcoal to become the pyrolysis product with increased energy yield. The above results demonstrated the importance and promise of phenolic-leaching pretreatment in upgradation of products of bamboo pyrolysis. From application perspective, light bamboo vinegar was an alternative for leaching of biomass. The use of bamboo vinegar filtrate containing metallic species had potential benefits for preparation of liquid fertilizer.

Biogas yields during anaerobic co-digestion of corn stover and cattle manure with different proportions

The biogas production characteristics of anaerobic fermentation of cattle manure and corn stover with different proportions were studied to provide basis for improving efficiency. The dry matter mass ratio of corn stover and cattle manure was set as 1:1,1:2,1:3 and 2:1 respectively. The anaerobic co-digestion was carried out under the fermentation conditions of 8% TS and medium temperature (35±1°C), analysing the change rule of each biomethane production index. The results showed that when the mass ratio of corn stover to cattle manure was 2:1, daily biogas production was up to 80 mL; compared with 1:2 and 1:3, the maximum cumulative biomethane production volume of 4540mL increased by 21.67% and 30.12% respectively. The highest volume fraction of methane is 72%.

Performances Analysis of an Upflow Anaerobic Filter for Domestic Sewage Treatment

Upflow anaerobic filter (UAF) with actual domestic wastewater were examined in this study. The Impacts of hydraulic retention time (HRT) on the performance of a UAF and a primary methanogen group were investigated at mesophilic conditions. The chemical oxygen demand (COD) removal rate was more than 75% after 28 days acclimation at 35℃ and HRT of 24 h. With a gradual decrease in the HRT, the COD removal rate first increased and then decreased. When the HRT was 5 h, the COD removal rate was the highest, with an average 81.71% and a maximum of 87.18%. When the HRT decreased to 2.5 h, the average COD removal rate decreased to 75.12%. The methane produced per unit mass of substrate consumed (CH4/CODre) and volume fraction increased with a decrease in HRT. When the HRT was 2.5 h, it reached 0.30 L·g-1, and the volume fraction of methane was maintained at about 73%. The energy generated by the system met the energy demands of the peristaltic pump. Quantitative analysis of the primary methanogen group in the system indicates that Methanosarcinales is the dominant in the system. With a decrease in HRT, the abundances of acetoclastic and hydrogenotrophic methanogens increased significantly.

Use of combined fermentation technology to improve the efficiency of the energy complex of the MSW landfil

The article analyzes the existing problems associated with the degassing of landfill and the use of landfill gas as an energy resource. Issues related to the composition of the landfill gas are considered. The main reasons for the high nitrogen content in landfill gas are shown. The main measures are highlighted that make it possible to increase the economic attractiveness of the use of landfill gas. A fundamentally new technology of combined fermentation has been proposed, combining the fundamentals of the technologies of “dry” and “wet” fermentation of various substrates. The paper presents the results of using the technology of combined fermentation to increase the efficiency of the active decontamination system of the MSW landfill of WSC Vodino LLC. A significant improvement in the composition of landfill gas was noted, first of all, an increase in the volume fraction of methane and an increase in the average daily volume of recoverable landfill gas by 22%. As a result, the daily production of heat and electricity at the site during the experiment increased by 79.6%. As a side effect in the experiment, a decrease in the height of the horizon of the landfill body was noted by 12.5% and, as a consequence, an increase in the useful capacity of the landfill.

The role of carrier gas in cluster formation in methane supersonic jets

The influence of a monatomic carrier gas on cluster formation in supersonic methane jets is studied. The formation of methane clusters in a mixture with condensed argon and non-condensable helium with the same gas-dynamic parameters is then compared. It is shown that the methane clusters’ formation intensity is extremely low both within a jet of pure methane, and in a mixture with carrier argon. The methane condensation process dependence on the properties of a carrier gas and the methane volume fraction in the mixture at the selected gas dynamic parameters of the flow is demonstrated. The effect of dissociative methane ionization and the fragmentation of methane clusters in the mass spectrometer detector on the recorded mass spectrum is established. The cluster methane ions protonation and the increase in their fraction with increasing clusters are recorded. Finally, magic numbers for methane clusters are found.

Cracking mechanism of coal under high-pressure water jet and its applications for enhanced coalbed methane drainage

This paper is concerned with the mechanism of coal breakage under high-pressure water jet (HPWJ) and its applications. A model of HPWJ impinging on coal target was established to study the cracking mechanism of coal under impact load. The characteristic and pressure distribution of HPWJ, the propagation characteristics of stress wave in coal, the mechanical properties of different coal particles, and the fracture characteristics of coal under HPWJ erosion were investigated theoretically and numerically. The results show that the shock wave and water wedge pressure are the main factors that cause coal breakage and crack propagation. The damage to the far-field coal particles affected by HPWJ is primarily caused by tensile stress, and the damage to the near-field coal particles affected by HPWJ is caused by the coupled effects of tensile stress and compressive stress. An erosion cavity is formed in the coal model with diameters of 1.25 to 2.5 times that of the jet at different depths. Meanwhile, the strong quasi-static pressure at the crack discontinuities further promotes the propagation of radial cracks around the erosion cavity to form a fracture zone, and the diameter of the fracture zone at different depths is 3.5 to 4.0 times that of the jet. In addition, the results of field application show that there is a significant difference between the methane parameters in the hydraulic flushing borehole and the conventional borehole; the average methane volume fraction and the average methane flow rate in hydraulic flushing boreholes are 3.85 and 3.67 times, respectively, that in conventional boreholes. Indicating hydraulic flushing can effectively promote the initiation and propagation of coal cracks. These results are of great significance to improve coalbed methane drainage technology and prevent gas disaster accidents in coal mines.

Features of the methane clusters formation in supersonic jets of methane and its mixtures with monatomic gases

This work demonstrates the methane clusters formation in supersonic free jets of methane mixtures with helium and argon. The dependence of the clusterization process properties on the carrier gas, the volume fraction of methane in the mixture at the selected of gas jet parameters is shown. Impact of the methane dissociative ionization, and methane clusters fragmentation in the detector of the mass spectrometer on the process of condensation was demonstrated. The presence of protonated cluster ions of methane and the increase in their proportion with growing size of clusters was established. The formation of cluster ions with an attached methyl, methylene or methylidene was discovered.

Development of an innovative two-stage fermentation process for high-calorific biogas at elevated pressure

The two-stage high-pressure fermentation (HPF) process enables the production of methane at high operating pressure. Pressure significantly reduces the energy needed for injecting the produced biogas into the gas grid by 45–60%. It also allows for incorporating large parts of the necessary biogas upgrading process into the synthesis step. As a result, the two-stage HPF process provides pressurized biogas with methane volume fraction ranging from 0.75 to 0.94. The pressure is not generated by energy intensive gas compression, but in-situ by microbial gas production. In comparison to conventional biomethane production, the overall costs could be reduced up to 20%. HPF is most beneficial when its operating pressure is adapted to that of the gas grid.The article presents briefly the development of the two-stage HPF beginning with tests in batch reactors, followed by experiments on gas solubility, and proof-of-concept in continuously operated methanogenesis reactors (MR) up to 9 bar. It also represents the effect of incorporating microfiltration (MF) of the feed stream, on improving the biogas quality and process stability of a continuously operated lab scale HPF process. By linking the MF with the HPF, methane volume fraction in the MR increases from 0.86 to 0.94 at 25 bar. Finally, the simulation and experimental results show good agreement with each other thereby making them a good basis for further optimization of the HPF process.

Anaerobic digestion of the above ground biomass of Jerusalem Artichoke in a pilot plant: Impact of the preservation method on the biogas yield and microbial community

The biogas production and the composition of the microbial community in a pilot biogas plant fed exclusively with the above ground biomass (AGB) of Jerusalem Artichoke (JA) were assessed. Biochemical methane potential (BMP) tests, carried out with fresh, air-dried and ensiled above ground biomass of JA, showed that air-dried biomass of JA yielded the highest biogas production whereas the ensiled biomass showed the lowest one. Similar results were obtained from the pilot plant as best results in terms of biogas production and methane volume fraction were associated with air-dried JA. The structure and dynamics of the microbial community involved in biogas production were studied using denaturing gradient gel electrophoresis (DGGE) method. The genus Methanoculleus predominated among methanogenic Archaea, indicating that biomethane was mainly produced through the hydrogenotrophic pathway. In general, there are no significant differences in microbial community structure when the reactor is fed either with air-dried or ensiled JA.

In-Operando Detection of Carbon Depositions and Carbon Formation Predictions for Industrial-Sized SOFCs Fueled with Synthetic Diesel Reformate

Solid oxide fuel cells (SOFCs) present an attractive and innovative technology for environmentally-friendly electricity and heat generation. Their high operating temperatures and the excellent catalytic performance make SOFCs the most efficient fuel cell type, with a high level of fuel flexibility. Feeding the SOFCs with conventional or alternative carbon-containing fuels carries the risk of carbon formation and its deposition on the anode, which can reduce cell’s activity, cause irreversible cell degradation, and decrease the cell’s lifetime. In order to prolong the cell’s lifetime and to ensure the undisturbed operation of SOFCs, an in-depth understanding of this degradation phenomenon is required. The problematic of carbon deposition phenomenon is detailed explained and supported with numerical and experimental results for planar, industrial-sized, anode-supported solid oxide fuel cells within this study. Possible reactions to carbon build-up are presented and the methods and calculation principles used to predict the carbon formation are demonstrated. The key parameters that enable carbon predictions are: the components involved in a used gas mixture, temperature, the steam/carbon-ratio, equilibrium state, and C-H-O ternary diagram. All of the mentioned carbon prediction methods and analysis of the basic calculation principles are explicitely explained. For the detailed analysis and prediction of coking propensity, various diesel reformate mixtures, containing H2, CO, CO2, CH4, H2O and N2, are used. In order to examine the impact of water vapor on carbon deposition, the amount of H2O in the fuel mixture is varied between 0 vol%, 11.3 vol% and 20 vol%. The operating conditions, under which carbon can be formed and deposited on the anode side can thus be generated. In the course of the experimental analysis of the carbon deposition phenomenon, the polarized single cells were fed with synthetic diesel reformate mixtures, thus representing realistic operating conditions. In order to obtain information about the degradation of cell performance, such as the critical operating time or degradation voltage, the methane volume fraction in the fuel mixture was varied between 2.3 vol% (as expected in APUs), 9 vol%, 14 vol% and 20.3 vol%. The carbon build-up process on the Ni-catalyst, and, in fact, anywhere in the cell’s fuel supply manifold, was detected at an early stage by means of electrochemical impedance spectroscopy, current/voltage measurement, temperature measuremens and gas analysis. In addition to the in-situ characterization techniques used, an ex-situ post-mortem analysis was introduced to support the knowledge gained in the experimental analysis and to confirm the occurrence of the carbon identified via employed in-situ characterization techniques. Methane, including the decreasing steam/carbon ratio, was identified as having a major impact on the degradation rate at the typical operating temperature of 800°C for anode-supported solid oxide fuel cells. The critical operating time for carbon to form and be deposited on the anode was found to be strongly dependent on the amount of methane in the fuel mixture. For lower amounts of methane in the fuel mixture, such as 2.3 vol%, degradation of the cell performance was observed after 44 h. After accelerated carbon deposition process, due to an increase in the methane concentration of the gas mixture in use, the total critical operating time was significantly reduced. The approaches that allow early identification of carbon build-up in order to avoid irreversible deterioration of cell performance and its microstructure were originated and they are provided. A detailed microscopic investigation showed that carbon was uniformly formed over the Ni- and YSZ-sites. Massive carbon deposits not only caused the degradation of the cell performance, but also changed the Ni-YSZ structure. The crushing of YSZ-particles and their deposition on the Ni-catalyst were determined to be degradation phenomenona that occur if the carbon formation process in not interrupted at an early stage.

Experimental Investigation on CO2 Methanation Process for Solar Energy Storage Compared to CO2-Based Methanol Synthesis

The utilization of the captured CO2 as a carbon source for the production of energy storage media offers a technological solution for overcoming crucial issues in current energy systems. Solar energy production generally does not match with energy demand because of its intermittent and non-programmable nature, entailing the adoption of storage technologies. Hydrogen constitutes a chemical storage for renewable electricity if it is produced by water electrolysis and is also the key reactant for CO2 methanation (Sabatier reaction). The utilization of CO2 as a feedstock for producing methane contributes to alleviate global climate changes and sequestration related problems. The produced methane is a carbon neutral gas that fits into existing infrastructure and allows issues related to the aforementioned intermittency and non-programmability of solar energy to be overcome. In this paper, an experimental apparatus, composed of an electrolyzer and a tubular fixed bed reactor, is built and used to produce methane via Sabatier reaction. The objective of the experimental campaign is the evaluation of the process performance and a comparison with other CO2 valorization paths such as methanol production. The investigated pressure range was 2–20 bar, obtaining a methane volume fraction in outlet gaseous mixture of 64.75% at 8 bar and 97.24% at 20 bar, with conversion efficiencies of, respectively, 84.64% and 99.06%. The methanol and methane processes were compared on the basis of an energy parameter defined as the spent energy/stored energy. It is higher for the methanol process (0.45), with respect to the methane production process (0.41–0.43), which has a higher energy storage capability.

Euler-Euler CFD simulation of the fuel reactor of a 1 MWth chemical-looping pilot plant: Influence of the drag models and specularity coefficient

Euler-Euler (two-fluid) model was applied to simulate the hydrodynamics of the fuel reactor of the 1MWth chemical-looping system with Geldart B particles. The drag models of Wen-Yu and Gidaspow were used along with the restitution coefficient of 0.6 and the specularity coefficient of 0 and 1. The results of the numerical simulation were compared with the experimental data from the 1MWth chemical-looping combustion pilot plant at Technische Universitӓt Darmstadt. The volume fraction of methane agrees well with the measurements for all cases, while the predicted volume fractions of CO2, CO and H2 were different from the experimental values due to improper reaction of CO and H2 with ilmenite. Predicted pressure drop values along the height of the fuel reactor were similar to the experimental values for all cases. Nevertheless all cases overestimate the pressure at the bottom of the reactor by about 10 mbar. Keeping the drag model constant, the outgoing mass flow of the ilmenite was higher for the specularity coefficient (ϕ=1) as compared to the specularity coefficient of (ϕ=0). This is due to higher rate of reaction for (ϕ=1), which is increasing the temperature of the outgoing gases and therefore increasing the gas velocity, resulting in a higher entrainment of ilmenite particles..

Mathematical modelling of sparkplug ignition of a coal-dust monodisperse suspension in a methane-air mixture

The paper provides the numerical simulation of a coal-dust monodisperse suspension sparkplug ignition in a methane-air mixture. The methane-air mixture is not stoichiometric. The aim of the research is a design-theoretical determination of the minimum ignition energy of coal-dust-methane-air mixture (CDMAM) depending on the methane volume fraction. Simulation has shown that the increase of the methane volume fraction leads to the decrease of the CDMAM minimum ignition energy, and with the expansion of coal particles the minimum ignition energy rises.

Experimental investigation of corn cob pyrolysis

This paper presents experimental investigation of pyrolysis process of corn cob from Vojvodina (Republic of Serbia). The influence of temperature, reaction time, particle size, and heating rate on pyrolysis products yields was investigated. Studying of biomass pyrolysis kinetics led to the conclusion that thermogravimetry is an appropriate method for explaining decomposition of different biomass types. Experimental research showed that temperature increase leads to decrease in char yield and volatile yield. Mass yield of pyrolysis oil increased with higher heating rate. Methane volume fraction in pyrolysis gas increased with temperature increase, while the volume fraction of carbon dioxide decreased. Particle size affected the methane yield. It was shown that with the increase in particle size, the volume fraction of methane in pyrolysis gas decreased. Based on the char composition obtained after corn cob pyrolysis process, it was determined that char is rich in carbon (74.80%). Lower heating value of char was 26182.09 kJ/kg. High heating value of char contributes to economic justification for applying corn cob pyrolysis.

Detonations in hydrogen-methane-air mixtures in semi confined flat channels

The aim of this work was to determine the influence of methane addition on the critical layer thickness h* and its relation to detonation cell size (λ) for stable detonation propagating in semi-confined, non-obstructed channel filled with uniform, stoichiometric hydrogen-methane-air mixtures. Three types of gaseous mixture composition were used: 0%, 5% and 10% of methane volume fraction in the mixture with hydrogen. The critical height h*, detonation cell size λ and critical relation h*/λ were defined for each investigated mixture showing that detonation in stoichiometric hydrogen-air mixture may propagate in semi-open channel only when the channel height is very close to, or exceeds, 3 cell sizes. Methane addition to the investigated combustible mixture increases the critical h*, however h*/λ ratio increases as well to 3.1 and 3.4 for 5% and 10% methane fraction, respectively.

Effect of chitosan on reactor performance and population of specific methanogens in a modified CSTR treating raw POME

In this study, chitosan was periodically added to a CSTR treating raw POME in order to retain more working microorganisms at high OLRs. The data indicated that the CSTR with chitosan addition can be operated with reactor stability at an OLR of 26.5 kg m−3 d−1 which is approximately 7.5 kg m−3 d−1 higher than that for the control CSTR without chitosan addition. In the control CSTR, the biogas production did not increase with increased OLR, and the overall process was limited by slow methanogenic rates. For the CSTR with chitosan addition, the biogas production was 9.39 m3 m−3 d−1 with a methane volume fraction of 68% at an OLR of 26.5 kg m−3 d−1. Corresponding to this increase in methane production, it was found that Methanosarcinales numbers were significantly higher (P < 0.05) in the CSTR with chitosan addition than in the control CSTR.

Experimental Studies on Anaerobic Digestion of Straw Stalk Mixed with Pig Dung

A series of anaerobic digestion experiments on straw stalk mixed with pig dung was carried out at mid-temperature (35°C) by using the self-designed continuous stirring tank reactor (CSTR) in different organic load rates (OLR). Anaerobic digestion indexes, such as pH, ammonia-nitrogen, volatile fatty acid (VFA), total alkalinity, quantity of gas production and production rate of methane under the different organic load were studied and the aerogenic capability of the system and its stability were analyzed, so as to find the optimal organic load rate for anaerobic digestion reaction. The results show that: (1) With the OLR increases from 0.5-2.0g VS/(L·d) step by step, the pH value is always maintained 6.7-7.2; the average daily gas-production quantity is 869-3232 mL; the average ammonia-nitrogen concentration in the anaerobic digestion process has kept 522-850mg/L; the VFA concentration has remained between 1520-3420mg/L; the average total alkalinity is among 2152-2441mg/L . (2) The anaerobic digestion system is stable when the OLR increases from 0.5-2.0g VS/(L·d), and the optimal organic load rate is 1.5g VS/(L·d) for volume fraction of methane.

The Numerical Simulation Research on Thermal Flow-Reversal Reactor of Mine Ventilation Gas

The paper uses computational fluid dynamics software FLUENT to build a single-channel numerical simulation model of the mine ventilation gas Thermal Flow-Reversal Reactor (TFRR). Combining with the analysis of orthogonal test, the influences that four factors (Initial temperature distribution, Ventilation gas flow velocity, Volume fraction of methane, Exchange period) act on reactor performance is investigated. An optimal operation condition is proposed by the establishment of the priority sequence of these four factors.

The composition of gaseous products from corn stalk pyrolysis process

This paper describes experimental investigation of corn stalk pyrolysis. The mass of the sample (corn stalk) inside a pyrolytic reactor was 10 g with particle diameter of 5-10 mm. The sample in the reactor was heated in the temperature range of 24-650?C and the gas components generated during corn stalk pyrolysis were measured using gas analyzer G750 POLYTECTOR II. The sample mass before, during and after pyrolysis process was determined by using METTLER P1000 digital scale. Experimental results of the corn stalk pyrolysis indicate that as the temperature in the reactor increases from 300-650?C, the pyrolytic gas yield increases from 60-72%, while the char (coke) yield decreases from 40-28%. In the temperature range mentioned, the CO2 volume fraction in pyrolytic gas decreases, while the volume fraction of methane increases up to 39.5% followed with a constant decrease in the volume fraction of oxygen. The results obtained can represent starting basis for determining material and heat balance of pyrolysis process as well as corn stalk pyrolysis equipment.