CO2 In Biogas Research Articles

Electrochemical hythane production for renewable energy storage and biogas upgrading

This study investigates the feasibility of using an electrochemical process to convert excess renewable electricity and biogas into hythane gas, which has higher value than biogas and can be stored and transported using current natural gas infrastructure. The electrochemical process utilizes the protons generated in water electrolysis to liberate cations in silicate minerals, which in turn forms metal hydroxide and efficiently captures the CO2 present in biogas. The H2 produced in electrolysis is blended with purified biogas to generate mixed hythane product, which has a higher combustion rate in methane fueled vehicles. Results show that under a voltage of 3.5–4.0V, the system reduced CO2 in biogas from the original 40% to less than 15% and increased the heat value of the gas product from 534kJ/mol to over 669kJ/mol. Preliminary techno-economic analysis showed a net profit of $0.28 per thousand ft.cu hythane generated when standard grid electricity is used, and the profit may be increased by orders of magnitude if excess renewable electricity is used. The process offers a new route for renewable energy storage and upgrade.

Photosynthetic CO2 uptake by microalgae for biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photobioreactor under various light wavelengths, light intensities, and photoperiods

Anaerobic digestion not only produces raw biogas which needs to be upgraded, but also nutrient-rich waste stream biogas slurry which needs decontamination. Therefore, this research focused on the effects of various light wavelengths, light intensities, and photoperiods on biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photobioreactor. The microalgae photobioreactor was a transparent polyethylene bag (80cm×60cm×11cm). The results demonstrated that biogas upgrading and simultaneously biogas slurry decontamination was successfully achieved by the use of the photosynthetic CO2 uptake by microalgae photobioreactor. The optimal light wavelength was the mixed LED red:blue=5:5; whereas the optimized lighting control strategy was: low light intensity (300μmolm−2s−1) with long photoperiod (16h light:8h dark) for the time course of 0–48h, moderate light intensity (600μmolm−2s−1) with middle photoperiod (14h light:10h dark) for the time course of 48–96h, and high light intensity (900μmolm−2s−1) with short photoperiod (12h light:12h dark) for the time course of 96–144h. Its biogas CO2 removal efficiency was 85.46±6.25%. Its removal efficiency of chemical oxygen demand, total nitrogen, and total phosphorus were 85.23±8.32%, 87.10±7.55%, and 92.40±3.05%, respectively.

Experimental Studies and the Chemical Kinetics Modelling of Oxidation of Hydrogen Sulfide Contained in Biogas

This paper presents the results of experimental and numerical research on the process of biogas air combustion. The purpose of the study was to determine the effect of biogas CO2 content on: (a) variations in SO2 concentrations in flue gas, (b) variations in the rates of the key reactions of oxidation of H2S to SO2.The subject of investigation were the gas mixtures: CH4/CO2 (of 25; 35 and 45 vol % CO2) with a varying hydrogen sulfide content. The experiments were conducted in a three-zone pipe furnace equipped with a swirl burner (Sg=1.26) with combustion substrate pre-mixing. It was noticed that the consumption of hydrogen sulfide was significantly reduced with the temperature decrease from 1223 K to 1023 K. The increase in the biogas carbon dioxide content inhibited the process of oxidation of H2S to SO2.

Sodium Bicarbonate Pretreatment on Rice Straw for Bioethanol Production and Utilizing the Waste Water of this Process to Absorb CO2 in Biogas.

The concept of small scale biorefinery from lignocellulosic biomass demonstrated the efficiency of energy and environment through research works at a pilot plant of University of Technology, VNU-HCM. The concept focused on studying bioethanol production in which pretreatment is one of key steps to achieve the efficiency. The pretreatment using NaOH solution 1.0 wt % removed lignin effectively but it is not considered as an eco-friendly chemical. Therefore, this study aims to investigate the alkaline pretreatment using Sodium Bicarbonate (NaHCO3), which is argued to be more environment-friendly and quite cheap. A variety of different conditions were investigated to optimize the pretreatment, including concentration of Sodium Bicarbonate (2.0-8.0 wt%), rice straw content (2.5-10.0 wt%), reaction temperatures (from room temperature to 80oC) and soaking time (4h-32h). The optimized condition was also investigated in combination with ultrasound and stirrer. The results showed that sodium bicarbonate is of quite potential to be used in the rice straw pretreatment. In addition, the waste of water from pretreatment was utilized to absorb CO2 in Biogas which was obtained from Thai My Demonstration plant in Cu Chi District.

Selective removal of H 2 S from biogas using a regenerable hybrid TiO 2 /zeolite composite

It is difficult to selectively remove H2S and simultaneously avoid SO2 emission in biogas purification process with a low-cost and efficient method. In this study, an efficient hybrid adsorbent/photocatalytic composite (TiO2/zeolite) was synthesized for the H2S removal and SO2 capture by coating TiO2 on the surface of cheap natural zeolite with an ultrasonic-calcination way. The TiO2/zeolite showed the highest H2S removal capacity and lowest SO2 emission, compared with the single zeolite adsorption and TiO2 photocatalysis. H2S removal capacity and SO2 capture capacity of TiO2/zeolite were affected little by the high level of CO2 in biogas, and were favored with the presence of moisture in the biogas. Moreover, the regeneration of the TiO2/zeolite could be easily achieved by a weakly basic washing and calcination. The results indicated that the TiO2/zeolite was economically promising, sustainable and nontoxic material for the direct elimination of H2S from biogas.

Appropriate structural parameters of biogas SI engine converted from diesel engine

A simulation of effects of combustion chamber shape, compression ratio, and spark timing advance to the performance of a biogas spark-ignition (SI) engine converted from a diesel engine is presented. It is a comparative research which uses computational fluid dynamics (CFD) software FLUENT for identifying basic structural parameters of the diesel engine that could be modified in order to obtain a high performance biogas engine. The presence of CO2 in biogas fuel slows down the burning velocity of the mixture, thus any mechanisms speeding up the combustion would be desirable. Under the same operating conditions of biogas engine, an increase of indicated cycle work is observed as replacing flat combustion chamber shape by omega combustion chamber shape. Optimal spark timing advance of a biogas engine is greater than that of a gasoline engine and it depends on engine speed and/or on CH4 fraction in the biogas. At rated regime of engine fueled with normal biogas, the results pointed out an optimal value of compression ratio. The research is successfully applied to convert a typical ZH1115 diesel engine to a biogas SI engine. The evidence developed from this research can be applied to any other diesel engine.

Biogas Purification Using Natural Zeolite and NaOH

Biogas purification is the most important process to increase the quality of biogas. This research was introduced a continuous system of biogas purification from CO2 impurity using zeolite and NaOH solution. The granular zeolites were varied from 1 to 5 layers on solid purifier. The NaOH solution was varied from 10% to 50 % based on concentration. Contact time of biogas with zeolite and NaOH solution were observed on interval of 15 minutes. The results showed that the ability of NaOH solution to absorb of CO2 is faster than zeolite. On the initial minutes, NaOH solution on the some concentration absorbed the CO2 until less than 10% of volume CO2 in biogas. Furthermore, the five layers of zeolites able to adsorb the CO2 until the 21.3% of volume CO2 in biogas on 60 minutes. For a similiar condition, CH4 levels increased to be 74.7% and 92.4% for zeolite and NaOH solution, respectively. The ability of CO2 absorbsion was influenced by layers number of zeolite purification system and the concentration of NaOH solution for NaOH purification system.

Behavior of Flame Propagation in Biogas Spark Ignited Premix Combustion with Carbon Dioxide Inhibitor

Biogas is a mixture of gases which commonly consists of methane (up to 50%) and other inhibitor gases which are dominated by carbon dioxide (up to 50%). Biogas is produced naturally by the decomposition of organic materials such as vegetation or animal manure in the absence of oxygen and it also contributes less greenhouse gases which may lead to global warming or climate change. The presence of carbon dioxide (CO2) in biogas is presumed to have some effects on biogas flame propagation characteristics. This study focuses on the effect of carbon dioxide (CO2) as the biggest inhibitor composition in biogas on flame propagation speed as the important flame propagation characteristic in spark ignited premix combustion. Propagating flames are employed to measure the flame propagation speed as a function of the mixture composition. This parameter was measured using a transparent tube fuel chamber with dimensions of 60 mm inner diameter and 300 mm height based on DIN 51649 standards and recorded by high speed digital photographic technique. The characteristic of biogas-oxygen flames were studied at stoichiometric, room temperature and atmospheric condition from 0% to 50% CO2 biogas inhibitor composition increased by 10% for each experiment. The results showed that the carbon dioxide decreases flame propagation speed of biogas. These indicated that carbon dioxide reduced reaction rate of biogas premixed combustion.

Biocapture of CO2 from biogas by oleaginous microalgae for improving methane content and simultaneously producing lipid

This study aimed to use oleaginous microalgae to capture CO2 from biogas for improving methane content and simultaneously producing lipid. Several microalgae were screened for their ability to grow and produce lipid using CO2 in biogas. A marine Chlorella sp. was the most suitable strain for capturing CO2 and producing lipid using biogas (50% v/v CO2 in methane) as well as using 50% v/v CO2 in air. The medium and operating conditions were optimized through response surface methodology (RSM). The optimal concentrations of KNO3 and K2HPO4 were 0.80gL−1 and 0.06gL−1, respectively. The optimal operating conditions were: initial pH of 7.8, initial cell concentration of 107.5cellsmL−1, light intensity of 4500lux and gas flow rate of 0.03Lmin−1. After optimization, 89.3% of CO2 was removed from biogas and the methane content was increased up to 94.7%. The lipid productivity was 94.7mgL−1day−1.

Performance of photoperiod and light intensity on biogas upgrade and biogas effluent nutrient reduction by the microalgae Chlorella sp.

Biogas is an environment-friendly fuel but that must be upgraded before being utilized. The method about removing CO2 from biogas by microalgal culturing using biogas effluent as nutrient medium in this study could effectively upgrade biogas and simultaneously reduce the biogas effluent nutrient. Results showed that the optimum parameters for microalgal growth and biogas effluent nutrient reduction was moderate light intensity with middle photoperiod. While low light intensity with long photoperiod and moderate light intensity with middle photoperiod obtained the best biogas CO2 removal and biogas upgrade effects. Therefore, the optimal parameters were moderate light intensity 350 μmol m(-2)s(-1) with middle photoperiod 14 h light:10h dark. Under this condition, the microalgal dry weight, CH4 concentration, reduction efficiency of chemical oxygen demand, total nitrogen, and total phosphorus was 615.84 ± 33.07 mg L(-1), 92.16 ± 2.83% (v/v), 88.74 ± 3.45%, 83.94 ± 3.51%, and 80.43 ± 4.17%, respectively.

Experimental Study of Biogas Combustion in a Two-Layer Packed Bed Burner

Biogas is a promising low-calorific fuel composed of 50–80% CH4 and 20–50% CO2 and provides numerous economic and environmental benefits. In this study, biogas combustion in a two-layer porous burner packed with spherical alumina beads was experimentally investigated to provide guidelines for biogas burner design. The equivalence ratios varied from 0.75 to 0.95 at four different CO2 content values (25, 30, 35, and 40%). The flame stability limits at various equivalence ratios and CO2 concentrations were obtained. The range of biogas equivalence ratios for stable flame was at a higher level than the range for pure CH4. The flame tended to move from the upstream to the downstream region as the flame speed increased, resulting in high exhaust gas temperatures. The effects of the biogas CO2 ratio on the flame temperature, pressure drop of reaction flow, and radiation efficiency were also examined in detail. The NOx, CO, and HC emissions and the flame speed at the four CO2 concentrations were also analyzed. Th...

Start-Up Procedures and Analysis of Microbial Segregation in HABR Using Synthetic Brewery Wastewater

A laboratory-scale hybrid anaerobic baffled reactor (HABR) with five compartments using synthetic brewery wastewater as organic loading rates (OLRs) was investigated for the start-up performance and the effects of microbial community segregation on reactor start-up. Experimental results demonstrated that it was found that the COD removal efficiencies were 92~96% at 1.2 kgCOD/(m3•d) feeding over a period of 33 d, after which the reactors then successfully started. The highest percentage of CO2 in biogas was found in Compartment 1, thereafter decreased from Compartment 2 to Compartment 5 which corresponded to the increased of the percentage of CH4. It indicated that the proper anaerobic consortium in each separate compartment was developed along with specific environmental conditions, which offers the explanations that high treatment efficiency of HABR accompanied by high process stability and low operational requirements in start-up period.

Thermal and Chemical Structure of Biogas Counterflow Diffusion Flames

A modeling study is conducted on blends of CH4 and CO2 simulating biogas from digestion plants or landfills to compare predictions from four nonsooting counterflow diffusion flames and to examine their thermal and chemical structure. Four flames, involving simulated biogas highly diluted with N2 in the fuel stream, have nearly identical strain rates (a ∼ 134 s−1) and stoichiometric mixture fractions (zf ∼ 0.76) but different CO2 mole fractions (0, 0.069, and 0.15). Profiles of major and critical minor species as well as some radical species are compared. Chemical and thermal influences of biogas CO2 content are evaluated. Quantification of the chemical influences of biogas CO2 content is vital because results demonstrate that through these effects CO2 dilution reduces emissions of NOx and greenhouse gases even without flame temperature reduction. CO2 dilution produces a reduction in the peak of acetylene, which is an important soot precursor. Without any flame temperature reduction, a typical digestion pl...

Integration of solid oxide fuel cell and palladium membrane reactor: Technical and economic analysis

This paper presents a technical and economic analysis of a solid oxide fuel cell system equipped with a palladium membrane reactor (PMR–SOFC) with the aim of determining the benefits of such an integrated unit over the conventional reformer module (CON-SOFC). The performance of both SOFC systems under the conditions for energetically self-sustaining operation (QNET = 0) was achieved by varying the fuel utilization for each operating voltage. Two types of fuels, i.e., methane and desulphurized biogas, are considered. The simulation results show that the maximum power density of the CON-SOFC fuelled by methane (0.423 W/cm2) is higher than that of the CON-SOFC fuelled by biogas (0.399 W/cm2) due to the presence of CO2 in biogas. For the PMR–SOFC, it is found that the operation at a higher permeation pressure offers higher power density because lower fuel utilization is required when operating the SOFC at the energy self-sustained condition. When the membrane reactor is operated at the permeation pressure of 1 bar, the methane-fuelled and biogas-fuelled PMR–SOFCs can achieve the maximum power density of 0.4398 and 0.4213 W/cm2, respectively. Although the PMR–SOFC can offer higher power density, compared with the CON-SOFC, the capital costs of supporting units, i.e., palladium membrane reactor, high-pressure compressor, and vacuum pump, for PMR–SOFC need to be taken into account. The economic analysis shows that the PMR–SOFC is not a good choice from an economic viewpoint because of the requirement of a large high-pressure compressor for feeding gas to the membrane reactor.

Confecção e avaliação de um sistema de remoção do CO2 contido no biogás

The biogas is an alternative fuel produced by the biomass anaerobic digestion (organic waste) and is composed by methane and carbon dioxide. The shift in the composition of biogas is very important because it increases its use viability as biofuel. The remotion of carbon dioxide (CO2) increases the methane (CH4) concentration in biogas composition, making its heating value higher. A decrease of acid hydrosulphide (H2S) concentration reduces the corrosion produced during the use of biogas in thermal systems for the secondary energy production. This work aimed to develop a physical and chemical mechanism for biogas CO2 remotion. The device developed was an absorption column stuffed of 250 cm high and 30 cm of diameter, using pipe of PVC rigid of 20 mm of diameter as stuff and water as solvent. Tests were done with inside pressure and gas flow in the column between 300 and 500 kPa and 190 and 670 cm3/s. The original biogas has a concentration of 33% CO2. With the utilization of the column absorption a reduction in CO2 concentration of 15% was obtained, which showed an increasing of 57% in the lower heating value of biogas per unit of mass