The theme for this week’s sustainability research is BIOGAS
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Research in Details
Research #1
Biogas combustion with various oxidizers in a nanosecond DBD microplasma burner
Highlights
The flame characteristics of the plasma-assisted biogas combustion were studied using optical emission spectroscopy.
The plasma discharges at 10 kHz repetition rate improved the biogas flame stability.
The use of oxygen-enriched air increased the flammability of biogas mixtures (CH4 with 50-20 vol. % in CO2).
The role of reactive oxygen species in the plasma-assisted combustion process by supplying oxygen-enriched air was determined.
A discussion was given for the mechanism of the plasma-assisted combustion.
Authors: R. Paulauskasa, D. Martuzevičiusa, R. B. Patelbc, J. E. H. Peldersc, S. Nijdamb, N. J. Damc, M. Tichonovasa, N. Striūgasd, K. Zakarauskasd
Date of publication: 4 May, 2020
Summary
This study concerns the effect of non-thermal plasma discharges on simulated biogas (mixture of CH4 with 80-20 vol.% CO2) combustion at atmospheric pressure in synthetic air or synthetic air enriched by oxygen. The plasma-assisted, premixed combustion was performed in a porous-plate burner with dielectric barrier discharge microplasmas driven by nanosecond high-voltage pulses at 3 kHz and 10 kHz repetition rates in the burner holes. The characteristics of the plasma-assisted flames and the role of reactive oxygen species in the plasma-assisted combustion process supplying various oxidizers were determined using a spatial flame chemiluminescence scanning technique acquiring OH*, C2* and CH* emission intensities. From the obtained results, the pathways of combustion enhancement by the plasma were established.
During plasma-assisted combustion, the biogas flame stability has improved. The highest plasma impact on the flame stability was observed for the biogas mixture (CH4-60%/CO2-40%). The flame lift-off for a stoichiometric mixture was reduced by 54% with the discharge at 10 kHz repetition rate, but a decrease of fuel-air ratio φ resulted in reduced effect of plasma and the lift-off was reduced only by 38–10% with 10 kHz discharge and by 22–7% with 3 kHz discharge. The experiments with oxygen-enriched synthetic air showed that the oxygen addition increases the flammability limit of biogas mixtures (CH4 with 50-20 vol.% in CO2), and allowed to burn mixtures which were not able to combust under normal conditions. However, the plasma-assisted combustion with oxygen enrichment showed a lower effect on the combustion enhancement than without. During experiments of plasma-assisted combustion, the plasma impact on NOX emissions was also determined, showing that NOX concentrations increased with increasing plasma power.
Keywords: Biogas, unstable flame, plasma-assisted combustion, oxygen addition, chemiluminescence
Research #2
Biogas recirculation technology: Effect on biogas purification, slurry characteristics, microbial activity and energy consumption
Highlights
Biogas recirculation during the digestion time not only needed little energy but also helped to mix the slurry.
It increased the carbonated compounds of the slurry.
It led to an acidity environment in the digester.
It created a suitable environment for better growing the anaerobic microbes.
It could decrease H2S and increase CH4 without significant changing CO2
Authors: Mahmood Mahmoodi-Eshkaftaki, Ehsan Houshyar
Date of publication: 4 May, 2020
Summary
In the present study, effect of biogas recirculation on slurry characterization, microbial activity and biogas purification were studied. Two digester units, one for control treatment and another equipped with a gas compression system for recirculation treatment, were designed and constructed. Experimental results showed that the recirculation system could improve the mixing process with a little energy consumption. The slurry analysis during the digestion indicated that (i) in the recirculation treatment, TC, TN, COD and BOD had a step up after the first injection and then decreased while they continuously decreased for the control treatment, (ii) amounts of TC/TN appeared that the carbonated compounds increased more than nitrogenous compounds for recirculation treatment, and (iii) the biogas recirculation decreased pH. The biogas analysis showed that the biogas recirculation could create a suitable environment for growing the anaerobic microbes (up to 21%) in the digester that not only decreased some of the harmful compounds like H2S (about 0.21 %VOL) but also increased the CH4 concentration (up to 11 %VOL). Significant correlations between the anaerobic microbial communities and CH4 (r=0.9), CO2 (r=−0.91), H2S (r=−0.89), CO (r=−0.8) and O2 (r=−0.71) for recirculation treatment documented the biogas recirculation can improve the environmental conditions for anaerobic microbial life and is a very convenient way for biogas purification.
Keywords: Biogas purification, Anaerobic digestion efficiency, Methane enrichment, Microbial community, Stirred digester
Research #3
Biogas slurry as an activator for the remediation of petroleum contaminated soils through composting mediated by humic acid
Highlights:
Biogas slurry was added to the compost of hydrocarbon contaminated soil as activator.
Biogas slurry addition increased the degradation of TPH by 12.8% compared to CK.
Biogas slurry addition improved the composting maturity and the humification of HA
Biogas slurry brought estrogen in composting but the products achieved to safe level.
Adding biogas slurry reduced phytotoxin level of composts by regulating TN and HA.
Authors: Beidou Xi, Qiuling Dang, Yuquan Wei, Xiang Li, Yansi Zheng, Xinyu Zhaoa
Date of publication: 1 May, 2020
Summary
As global population becomes increasingly urban, opportunities for people to experience nature have decreased. Counteracting this trend is a key challenge for future urban development as interactions of urban people with biodiversity support human health and wellbeing, and may also result in positive attitudes towards biodiversity conservation. Collecting edible plants in urban surroundings, especially outside of gardens (“urban foraging”) is a traditional interaction with nature, based on knowledge about multiple uses of plants. Although some studies exist from different cities around the world, urban foraging has been revealed as a critically understudied phenomenon. We now analyze (i) the relevance of this human-nature interaction in Berlin, one of Europe’s metropolises, (ii) how people’s sociocultural background matters in attitudes of urban foragers vs. non-foragers towards this activity, and (iii) whether urban foraging may lead to conflicts with biodiversity conservation. Our survey revealed urban foraging as a relevant human-nature interaction with a high potential to grow: 33% of 535 respondents already collected edible plants outside of gardens and another 38% would be doing so given certain conditions, e.g. when contamination risks can be excluded. Many sociocultural groups (differing, e.g. on gender, age, childhood experience) shared attitudes towards foraging and existing barriers. Risks to biodiversity seem to be manageable as neither native species nor rare species were over-foraged in relation to species’ abundance in the local flora, with more abundant species being collected more frequently. We conclude that urban foraging can be a powerful tool for connecting urban people to nature without putting native biodiversity at risk. We make a claim for integrated approaches towards environmental policy, environmental education and greenspace management: these should aim on keeping potential health risks at a minimum, and should support urban foraging as a biodiversity-friendly and sustainable human-nature interaction in the cities of tomorrow.
Keywords: Edible plants, Biocultural diversity, Gathering activity, Informal green infrastructure, Provisioning ecosystem services, Urban biodiversity
Research #4
Biogas production enhancement using nanocomposites and its combustion characteristics in a concentric flow slot burner
Highlights:
Generation enhancement of biogas by adding Ni-Co-Ferrite or Ni-ferrite nano-additives.
Investigation of Biogas turbulent flames in a slot burner.
The stability limits at different levels of mixture inhomogeneity and different ratios of CO2 from 0% to 40 % in methane.
Higher level of CO2 beyond 30% in Biogas leads to unstable flames.
Higher percentage of CO2 in the mixture decreases the flame size and temperature levels.
Authors: Mohy S. Mansour, Muhammed S. Abdallah, Nageh K. Allam, A.M. Ibrahim, Alaa M. Khedr, Hazem M. Al-Bulqinid, Mohamed F. Zayed
Date of publication: 1 May, 2020
Summary
Biogas combustion is a very essential topic for the development of many industrial combustion systems and engines. This fuel can replace current fossil fuels used in burners, engines, and many other applications. Understanding the combustion characteristics of this fuel and its stability in highly turbulent flames of practical interest is the aim of this work. The percentage of CO2 in Biogas varies between 25% and 45%, which affects the combustion stability and flame structure. The present work shows that the generation of Biogas is improved by adding Ni-Co-Ferrite or Ni-ferrite nano-additives. In this work, we selected 25 flames of mixtures of natural gas and CO2, where the ratio of CO2 varies from 0% to 40%. The flames are generated in a concentric flow slot burner that produces planar two-dimensional flames. The stability characteristics and the flame structure were investigated. The flame structure is presented in the form of temperature profiles in some selected flames using fine wire thermocouple measurements. The stability characteristics are illustrated for two limits of lifted flames and blow out. The production rate of Biogas can be increased by almost 30% using nano-additives of Ni-Co-Ferrite or Ni-ferrite. The data show that the stability of the flames is affected significantly for the 40% CO2 mixture. Therefore, it is recommended to keep CO2 percentage up to 30% for stable turbulent Biogas flames. On the other hand, partially premixed flames are highly stable for a certain level of mixture inhomogeneity at a mixing length ratio of L/D = 16. At this level, the mixture fraction fluctuations are expected to be within the flammability limits range based on previous investigations in round jet configuration.
Keywords: Biogas, Partially premixed, Stability, Mixing, Mixture inhomogeneity
Research #5
Design and analysis of renewable hydrogen production from biogas by integrating a gas turbine system and a solid oxide steam electrolyzer
Highlights
The performance analysis of a biogas GT system integrated with a SOSE for hydrogen production is reported.
Flameless boiler is used in the boiler attached to the GT system to make steam for SOSE.
By purifying biogas, the generated electrical power and produced hydrogen are augmented significantly.
Increasing steam temperature, the rate of hydrogen production in SOSE increases drastically.
Authors: Seyed Ehsan Hosseini
Date of publication: 1 May, 2020
Summary
In this paper, design and performance analysis of a biogas (60%CH4 + 40%CO2) fueled gas turbine (GT) power generation system integrated with a flameless boiler for steam generation for hydrogen production in a solid oxide steam electrolyzer (SOSE) is reported. In this design, the exhaust gas from GT is conducted to a flameless boiler where diluted and preheated exhaust gases are employed as an oxidizer in this process. Using a small amount of biogas in the flameless boiler enables the hybrid system to produce required steam for SOSE process and the whole generated electrical power by GT is employed in SOSE as well to produce hydrogen. The effects of biogas blends and flow rate, turbine inlet temperature (TIT), steam temperature and the electrode characteristics on the performance of the hybrid system are evaluated. The results indicate that by purification of biogas and increasing CH4 concentration up to 80%, the generated electrical power and produced hydrogen of the hybrid system augment 24% and 20% respectively. In GT system, the TIT should be set at the temperatures higher than 1300 K to prepare a desirable circumstance for the operation of flameless mode in the boiler. At the constant electrical power, when steam temperature increases, the overall SOSE potential decreases and consequently the current of the SOSE enhances which result in the enhancement of the overall hydrogen production in high steam temperatures. To increase the steam temperature from 850 K to 1450 K, the rate of overall biogas consumption of the system increases 1% while the amount of overall hydrogen production from SOSE system augments from 0.01 to 0.052 mol/s. The presented analysis in this paper can be employed to perform more analyses to achieve insightful understanding of the green hydrogen production using hybrid systems.
Keywords: Hydrogen, Biogas, Gas turbine, Flameless combustion, Solid oxide steam electrolyzer