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Muller M.,University of Innsbruck | Muller M.,DBFZ Deutsches Biomasseforschungszentrum Gemeinnutzige GmbH | Graus M.,University of Innsbruck | Graus M.,National Oceanic and Atmospheric Administration | And 6 more authors.
Atmospheric Chemistry and Physics | Year: 2012

A series of 1,3,5-trimethylbenzene (TMB) photo-oxidation experiments was performed in the 27-m 3 Paul Scherrer Institute environmental chamber under various NO x conditions. A University of Innsbruck prototype high resolution Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-TOF) was used for measurements of gas and particulate phase organics. The gas phase mass spectrum displayed ∼200 ion signals during the TMB photo-oxidation experiments. Molecular formulas C mH nN oO p were determined and ion signals were separated and grouped according to their C, O and N numbers. This allowed to determine the time evolution of the O:C ratio and of the average carbon oxidation state OS C of the reaction mixture. Both quantities were compared with master chemical mechanism (MCMv3.1) simulations. The O:C ratio in the particle phase was about twice the O:C ratio in the gas phase. Average carbon oxidation states of secondary organic aerosol (SOA) samples OS SOA C were in the range of-0.34 to-0.31, in agreement with expected average carbon oxidation states of fresh SOA (OS C =-0.5-0). © 2012 Author(s). Source

Tabet F.,DBFZ Deutsches Biomasseforschungszentrum Gemeinnutzige GmbH | Gokalp I.,French National Center for Scientific Research
Renewable and Sustainable Energy Reviews | Year: 2015

Abstract Biomass co-firing within the existing infrastructure of pulverized coal utility boilers is viewed as a practical near-term means of encouraging renewable energy while minimizing capital requirements and maintaining the high efficiency of pulverized coal boilers. Coal/biomass co-firing is a complex problem that involves gas and particle phases, along with the effect of turbulence on chemical reactions. Computation Fluid Dynamic (CFD) simulations can provide insight to design and operational issues, such as co-firing percentage, load swings, injection location, excess air and air/fuel staging, and predictions related to heat release, unburned carbon, and NOx emissions. The CFD based co-firing tools consist of models for turbulent flow, gas phase combustion, particles dispersion by turbulent flow, coal/biomass particles devolatilization, heterogeneous char reaction and radiation. Additional models related to slagging and fouling can also be found. This paper presents a review on CFD based modeling approaches used to predict the combustion characteristics of co-firing biomass with pulverized coal under air and oxy-fuel conditions. © 2015 Elsevier Ltd. Source

Seco R.,Autonomous University of Barcelona | Seco R.,U.S. National Center for Atmospheric Research | Penuelas J.,Autonomous University of Barcelona | Filella I.,Autonomous University of Barcelona | And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2011

Atmospheric volatile organic compounds (VOCs) are involved in ozone and aerosol generation, thus having implications for air quality and climate. VOCs and their emissions by vegetation also have important ecological roles as they can protect plants from stresses and act as communication cues between plants and between plants and animals. In spite of these key environmental and biological roles, the reports on seasonal and daily VOC mixing ratios in the literature for Mediterranean natural environments are scarce. We conducted seasonal (winter and summer) measurements of VOC mixing ratios in an elevated (720 m a.s.l.) holm oak Mediterranean forest site near the metropolitan area of Barcelona (NE Iberian Peninsula). Methanol was the most abundant compound among all the VOCs measured in both seasons. While aromatic VOCs showed almost no seasonal variability, short-chain oxygenated VOCs presented higher mixing ratios in summer, presumably due to greater emission by vegetation and increased photochemistry, both enhanced by the high temperatures and solar radiation in summer. Isoprenoid VOCs showed the biggest seasonal change in mixing ratios: they increased by one order of magnitude in summer, as a result of the vegetation's greater physiological activity and emission rates. The maximum diurnal concentrations of ozone increased in summer too, most likely due to more intense photochemical activity and the higher levels of VOCs in the air. The daily variation of VOC mixing ratios was mainly governed by the wind regime of the mountain, as the majority of the VOC species analyzed followed a very similar diel cycle. Mountain and sea breezes that develop after sunrise advect polluted air masses to the mountain. These polluted air masses had previously passed over the urban and industrial areas surrounding the Barcelona metropolitan area, where they were enriched in NO x and in VOCs of biotic and abiotic origin. Moreover, these polluted air masses receive additional biogenic VOCs emitted in the local valley by the vegetation, thus enhancing O 3 formation in this forested site. The only VOC species that showed a somewhat different daily pattern were monoterpenes because of their local biogenic emission. Isoprene also followed in part the daily pattern of monoterpenes, but only in summer when its biotic sources were stronger. The increase by one order of magnitude in the concentrations of these volatile isoprenoids highlights the importance of local biogenic summer emissions in these Mediterranean forested areas which also receive polluted air masses from nearby or distant anthropic sources. © 2011 Author(s). Source

Dahlin J.,University of Rostock | Dahlin J.,Nuertingen-Geislingen University | Herbes C.,Nuertingen-Geislingen University | Nelles M.,University of Rostock | Nelles M.,DBFZ Deutsches Biomasseforschungszentrum Gemeinnutzige GmbH
Resources, Conservation and Recycling | Year: 2015

Managing digestate output and developing a market for the product is a serious challenge for the biogas industry. Without effective strategies for sustainable management, the large volume of digestate produced by biogas plants may cripple the industry and its potential. Through interviews with diverse biogas stakeholders, we examine current approaches to digestate marketing to identify factors that support and those that inhibit its success. We find that marketing to regions with a nutrient demand or into the non-agricultural sector holds promise. Upgraded digestate products offer increased marketability due to their higher nutrient content and lower water content. Fertilizer and soil manufacturers, farmers, horticulturists and private customers all represent markets for digestate. Current disposal prices range from negative to strongly positive, depending on the regional nutrient availability, agricultural structure, season, feedstock and degree of upgrading. Marketers agree that concealing the biogas origin of digestate products is still necessary to avoid negative perceptions by customers. One implication of this is the need for better understanding by marketers of consumer concerns and preferences, and for better education of consumers regarding the safety and benefits of digestate. Overall, we find that opportunities for digestate marketing remain largely unexploited and marketing strategies remain immature. Our findings should prove helpful to current and future digestate marketers. © 2015 Elsevier B.V. All rights reserved. Source

Mameri A.,University of Oum El Bouaghi | Tabet F.,DBFZ Deutsches Biomasseforschungszentrum Gemeinnutzige GmbH
International Journal of Hydrogen Energy | Year: 2016

This study addresses numerically the influence of several operating conditions on the structure and NO emissions of a biogas diffusion flame. The analysis is conducted at atmospheric pressure in counter-flow configuration and mixture fraction space. CO2 volume in biogas is varied from 25% to 60%, H2 enrichment from 0% to 20% and the scalar dissipation rate from near equilibrium to near extinction. Particular attention is paid to CO2 chemical effect. CO2 contained in biogas can have chemical effects when it participates in chemical reactions and thermal effects when it acts like a pure diluent. Chemical effects of CO2 are elucidated by using the inert species technique. Flame structure is characterized by solving flamelet equations with the consideration of radiation and detailed chemistry. It is observed that flame properties are very sensitive to biogas composition, hydrogen addition and scalar dissipation rate. CO2 increment decreases flame temperature, mass fraction of chain carrier radicals and NO emission index. Blending biogas with hydrogen increases the mixture heating value and makes the fuel more reactive. Hence, chain carrier radicals and NO index emission are all increased. The chemical effect of CO2 is found to be present overall scalar dissipation rate values where it reduces the maxima of temperature and OH mass fraction and increases the maxima of CO and NO mass fractions. H2 enrichment has a weak influence on CO2 chemical effect. Hydrogen-rich biogas flames produce less NO at high scalar dissipation rates. © 2015 Hydrogen Energy Publications, LLC. Source

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