Analysis of the effect of H2O content on combustion behaviours of a biogas fuel

The present work deals with the biogas in a combustor with regard to its combustion features under differing conditions of H₂0 content and H₂S. The content of water (H₂O) vapour has been changed from 0% to 10% and a CFD code has been employed while implementing numerical investigations. In modelling, a combustion model (the PDF/Mixture Fraction) along with a turbulence model (the k-Ɛ standard turbulence model) has been utilised. This study also deals with the combustion performances of the biogas by the addition of a different quantity of H₂O into the biogas. The Emissions and the flame temperature of the biogas through the combustor apparently seem to be strikingly affected by the changes in H₂O contents. It is interesting to note that the flame temperature zones change their positions and advance to the burner's downstream. The rise in flame temperatures of the biogas can be attributed to the change in H₂O content caused by a better fuel-air mixture. It is also observed that adding H₂O into the biogas lowers the axial temperature levels.     

High levels of ammonia nitrogen for biological biogas upgrading

This study aimed to propose a novel method for ex-situ biogas upgrading by adding ammonium chloride to increase the concentration of ammonia nitrogen. The results showed that ammonia nitrogen had a significant effect on biogas upgrading. The maximum content of CH₄ reached 94.1% when the concentration of ammonia nitrogen was 5500 mg/L. At the same time, CH₄ yield of increased by 57.5%. High throughput sequencing results showed that the relative abundance of hydrogenotrophic methanogens reached 73.1%, while that of acetotrophic methanogens was only 1.3%, which greatly increased the content and yield of CH₄. For the bacterial community, Clostridium was the dominant bacteria and the ammonia nitrogen concentration had little effect on it. These results demonstrate that upgrading biogas by increasing the concentration of ammonia nitrogen is feasible.     

Hydrogen sulfide removal from biogas using ion-exchanged nanostructured NaA zeolite for fueling solid oxide fuel cells

Hydrogen sulfide is the most abundant sulfur compound in the biogas, and in order to use for fueling the solid oxide fuel cells, its content should be less than 1 ppm. In this work, NaA nano zeolite is synthesized hydrothermally and modified by Ag⁺ ions, and its breakthrough capacity for hydrogen sulfide adsorption was measured using dynamic lab-scale adsorption tests on the experimental set-up for the first time. The results are compared to those of unmodified NaA nano zeolite and micron-sized commercial 4A zeolite. AgNaA nano zeolite showed the highest adsorption capacity (33.24 mg H₂S/g of Sorbent) and the longest breakthrough time (310 min). The regeneration performance of AgNaA nano zeolite and its structural stability are also investigated after five cycles. The results revealed that the AgNaA nano zeolite could be used promisingly for removing hydrogen sulfide from biogas for cleaner energy production.     

Numerical modeling of SOFCs operating on biogas from biodigesters

In this study, numerical predictions of SOFCs performance operating on biogas are performed in order to evaluate the potential use of biogas produced from different organic sources processed in biodigesters as the fuel for SOFCs. The SOFC performance is predicted numerically by using a fully three-dimensional non-commercial CFD code called DREAM-SOFC. The analysis mainly focuses on the effect of biogas composition on the fuel cell performance. Different biogas compositions are used as the fuel supplied to the SOFC and the concentration of the species in the biogas are those measured by means of a gas chromatography system of the biogas produced in biodigesters installed at University of Guanajuato. Particularly, the biogas produced from water lily and cactus was evaluated as potential fuel for SOFCs. It was observed that the SOFC performance is higher when biogas from water lily is supplied to the SOFC when compared with biogas from cactus.     

Economic analysis of hydrogen production from wastewater and wood for municipal bus system

The levelized cost of hydrogen for municipal fuel cell buses has been determined using the DOE H2A model for steam methane reforming (SMR), molten carbonate fuel cell reforming (MCFC), and wood gasification using wastewater biogas and willow wood chips as energy feedstocks. 300 kg H₂/day was chosen as the design capacity. Greenhouse gas emissions were calculated for each for the three processes and compared to diesel bus emissions in order to assess environmental impact. The levelized cost per kilogram for SMR, MCFC, and gasification is $5.12, $8.59, and $10.62, respectively. SMR provided the lowest sensitivity to feedstock price, and lowest levelized cost at various scales, with competitive cost to diesel on a cost/km basis. All three technologies provide a reduction in total greenhouse gases compared to diesel bus emissions, with MCFC providing the largest reduction. These results provide preliminary evidence that small scale distributed hydrogen production for public transportation can be relatively cost-effective and have minimal environmental impact.     

Application of polyimide membranes for biogas purification and enrichment

Biogas is a clean environment friendly fuel that is produced by bacterial conversion of organic matter under anaerobic (oxygen-free) conditions. Raw biogas contains about 55-65% methane (CH(4)), 30-45% carbon dioxide (CO(2)), traces of hydrogen sulphide (H(2)S) and fractions of water vapour. Pure methane has a calorific value of 9100 kcal/m(3) at 15.5 degrees C and 1 atm; the calorific value of biogas varies from 4800 to 6900 kcal/m(3). To achieve the standard composition of the biogas and calorific value of 5500 kcal/m(3) the treatment techniques like absorption or membrane separation should be applied. In the paper the results of the tests of the CH(4) enrichment in simulated biogas mixture consisted of methane, carbon dioxide and hydrogen sulphide were presented. It was showed that using the capillary module with polyimide membranes it was possible to achieve the enrichment of CH(4) from the concentrations of 55-85% up to 91-94.4%. The membrane material was resistant to the small concentrations of sour gases and assured the reduction of H(2)S and water vapour concentrations, as well. The required enrichment was achieved in the single module, however to prevent CH(4) losses the multistage or hybrid systems should be used to improve process efficiency.     

Catalytic decomposition of methane and methane/CO2 mixtures to produce synthesis gas and nanostructured carbonaceous material

Methane and CO₂ are the main components of biogas; therefore its direct conversion into a higher added value gas as syn-gas (mixture of CO and H₂) is a very interesting alternative for the valorisation of such renewable resource. In this work, firstly a thermodynamic analysis of the decomposition of CH₄:CO₂ mixtures at different temperatures and CH₄:CO₂ ratios simulating the biogas composition, has been carried out. Secondly, the decomposition of a mixture with a molar ratio of 1:1 has been studied in a fixed-bed reactor by using a Ni/Al₂O₃ based catalyst, at the temperature range in which according to the thermodynamic study, carbon formation is favoured. Results obtained have been compared to those of methane decomposition carried out under the same experimental conditions. Co-feeding of CO₂ and CH₄ avoids catalyst deactivation substantially, allowing to obtain a syn-gas with H₂:CO ratio close to 1. Moreover, the carbon obtained from mixtures of CH₄ and CO₂ is deposited as fishbone carbon nanofibres at 600 °C and ribbon carbon nanofibers at 700 °C, both being materials with high added value which can be used in multiple applications.     

Simulation des anaeroben Prozesses bei der Biogaserzeugung

A simulation of the anaerobic process of a biogas production for different substrates was realized. The simulation was based on the Anaerobic Digestion Model No. 1 (ADM1). The experimental work comprehends batch‐experiments and experiments in a continuous stirred‐tank reactor at lab scale with different substrates used in a biogas production. The comparison between the experiments and the simulations of the process leads to a modification in ADM1. Furthermore a classification of substrates was developed according to their biodegradability to meet the fractions of the ADM1 simulation. The simulations for the different substrates showed a satisfactory agreement with the measured values.     

沼气发电机组的开发利用

沼气机组发电符合当今发展循环经济,节约能源的时代要求,也会对缓解国内区域性能源紧张发挥重要作用。本文介绍了当前我国沼气生产、利用的现状,阐明了沼气的组成及其燃烧特性,论述了沼气发电机组的结构原理及其创新技术。     

Enhancement in daily production of biogas system

In this communication, a straightforward analysis of a conventional biogas system (KVIC) integrated with a greenhouse at the top of the dome has been presented. The effect of the use of movable insulation during off-sunshine hours has been included in the analysis. The use of night insulation reduces the heat losses from the top of the system, which causes an appreciable increase in the production of the biogas system. Numerical calculations have been made for a typical winter day in Delhi.