George Skevis | Centre for Research and Technology, Hellas (Greece) (original) (raw)

Papers by George Skevis

Energies, 2022

Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilien... more Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilient plants that can absorb soil contaminants. The harvested contaminated biomass can be thermochemically converted to energy carriers/chemicals, linking soil decontamination with biomass-to-energy and aligning with circular economy principles. Two thermochemical conversion steps of contaminated biomass, both used for contaminated biomass treatment/exploitation, are considered: Supercritical Water Gasification and Fast Pyrolysis. For the former, the vast majority of contaminants are transferred into liquid and gaseous effluents, and thus the application of purification steps is necessary prior to further processing. In Fast Pyrolysis, contaminants are mainly retained in the solid phase, but a part appears in the liquid phase due to fine solids entrainment. Contaminants include heavy metals, particulate matter, and hydrogen sulfide. The purified streams allow the in-process re-use of water f...

Applied Sciences

Carbon capture on-board ships represents a powerful technological measure in order for the shippi... more Carbon capture on-board ships represents a powerful technological measure in order for the shipping industry to meet the very stringent GHG emission reduction requirements. Operation within the ship environment introduces a number of constraints associated mainly with space, energy supply, and safety which have to be addressed using compact yet efficient solutions. To this end, solvent-based membrane CO2 capture offers several advantages and has the necessary technological maturity for on-board installation. Solvent choice remains a critical issue both for reasons associated with process efficiency as well as on-board safety. In this paper, we present an up-to-date comprehensive review of the different solvents that can be used for post-combustion CO2 capture. Furthermore, we investigated the solvents’ performance as determined by their inherent characteristics, properties, and behavior for a range of operating conditions against the strict shipping requirements. A preliminary quali...

Fuel Cell technologies provide the opportunity for electric power generation in diverse applicati... more Fuel Cell technologies provide the opportunity for electric power generation in diverse applications s uch as recreational yachts, vehicles, etc. where portable, low-cost/volume/weight power sources are required. An LPG Auto Thermal Reformer (ATR) with a High-Temperature Polymer Electrolyte Membrane (HT-PEM) fuel cell lo oks very attractive as an auxiliary power unit because of simple thermal integration efforts and less requ irements concerning the choice of the materials for key syst em components. However, for safety reasons LPG is o dorized by sulfur compounds and even small amounts of sulfur ( higher than 1 ppm) can have detrimental effects in he fuel cell anode, the Water Gas Shift (WGS) catalyst and possi bly to the reforming catalyst. The present paper de scribes work towards downstream reformate desulfurization for a 500 We ATR-HT-PEM system. Besides conventional wet chemistry-based catalyst development technologies, many advanced technologies have been employed inclu d g l...

Membranes

CO2 mineralization is an alternative to conventional geological storage and results in permanent ... more CO2 mineralization is an alternative to conventional geological storage and results in permanent carbon storage as a solid, with no need for long-term monitoring and no requirements for significant energy input. Novel technologies for carbon dioxide capture and mineralization involve the use of gas-liquid membrane contactors for post-combustion capture. The scope of the present study is to investigate the application of hollow fiber membrane contactor technology for combined CO2 capture from energy-intensive industry flue gases and CO2 mineralization, in a single-step multiphase process. The process is also a key enabler of the circular economy for the cement industry, a major contributor in global industrial CO2 emissions, as CaCO3 particles, obtained through the mineralization process, can be directed back into the cement production as fillers for partially substituting cement in high-performance concrete. High CO2 capture efficiency is achieved, as well as CaCO3 particles of cont...

Combustion Science and Technology

Energy & Fuels

The fulfillment of societal energy needs is currently faced with several constrains that are swif... more The fulfillment of societal energy needs is currently faced with several constrains that are swiftly and continuously changing the possible scenarios of the near future energy market. If global warming is accelerating and, in turn, hasten the request of renewable, green energy systems, on the other hand, geopolitical equilibria keep the grid strictly anchored to wellestablished, traditional energy production systems. This hinders the drastic reduction of greenhouse gas emissions, which is needed to meet the strict goals fixed over the years. Energy carriers coupled with advanced combustion technologies are synergistic twin strategies that can satisfy the two apparently antithetic requirements of geo-political and environmental sustainability and security. Indeed, energy carriers represent a wide category of molecules, including both conventional and bio-derived fuels as well as molecules used to store both conventional and renewable source energy surplus as in power to fuel options. At the same time, to efficiently exploit the large class of locally available energy carriers, fuel-flexible advanced combustion technologies are strongly needed. From this standpoint, a smart energy carrier (SEC) identifies with molecules (derived from standard, alternative, or unconventional sources), locally produced or made available, that can be safely and cleanly transformed into energy by means of the best available combustion technologies. SMARTCATs COST Action (www.smartcats.eu) is a collaborative network of research and academic institutions as well as companies from 30 countries, set up within the Cooperation in Science and Technology European framework (www.cost.eu) under the umbrella of the Horizon 2020 Programme. SMARTCATs is focused on the investigation on chemistry and technologies of SECs: the chemistry and kinetics of oxidation/pyrolysis of energy carriers, the potential formation of new noxious species and the tools needed for process study, monitoring, and control, and the technologies needed for SEC practical use are the key topics driving collaborations and share of facilities, tools, and people actively working in the field. This special issue includes a selection of papers, from fundamental to applied research, discussing results presented at the third SMARTCATs general meeting held in Prague at J. HeyrovskýInstitute of Physical Chemistry of the Czech Academy of Sciences. The meeting was organized by Prof.

Fuel

The present work is a part of a larger experimental campaign which examines the behaviour of vari... more The present work is a part of a larger experimental campaign which examines the behaviour of various fuels on a swirl stabilized flame burner configuration. Overall, detailed speciation measurements and temperature measurements were combined with optical measurements. The work presented here concerns the part of the experimental campaign which deals with the optical characteristics of the examined flames. The work adds to the growing database of experimental measurements assessing engine-relevant reaction environments which shift from traditional ones in order to meet pollutant emission regulations and efficiency standards. Here, the oxidation of several commonly used fuel and fuel surrogates that are subjected to the addition of a bio-derived fuel additive (dimethyl ether) and emulated exhaust gas recirculation (EGR) is studied in a laboratory-scale swirl stabilized burner. The natural flame chemiluminescence has been exploited to selectively measure line of sight CH* and OH* profiles for combinations of these fuels and reaction environments. As a result, the geometry and intensity of the reaction and oxidation zones have been parametrically evaluated for

International Journal of Chemical Kinetics, 2016

Journal of Energy Engineering, 2015

Ethanol is particularly attractive as an alternative fuel for both automotive and stationary appl... more Ethanol is particularly attractive as an alternative fuel for both automotive and stationary applications. Due to its high hydrogen content, ethanol can also be utilized for hydrogen production in SOFC systems. The present study assesses the potential of non-catalytic ethanol reforming process using a detailed kinetic modelling approach. A recently developed comprehensive detailed mechanism for ethanol oxidation, pyrolysis and combustion is used and further validated against data from ethanol reformers. Comparisons between computations and experimental major and intermediate species data are shown to be satisfactory. Chemical aspects of the fuel reforming process are thoroughly investigated through rate of production path and sensitivity analyses with particular emphasis on syngas and potential carbonaceous deposits formation. An assessment of ethanol as a reformate versus conventional fuels with similar hydrogen content is also numerically performed and ethanol is found to feature ...

The pyrolysis and oxidation of benzene occupies a pivotal role in the combustion chemistry of pra... more The pyrolysis and oxidation of benzene occupies a pivotal role in the combustion chemistry of practical fuels. Despite numerous experimental and numerical investigations, significant uncertainties exist regarding even major benzene combustion features, particularly under lean and stoichiometric conditions. Novel benzene premixed flame datasets that have recently appeared in the literature offer a unique possibility for the judicious evaluation of mechanisms developed solely on the basis of a single flame (Bittner and Howard). In this context, a detailed kinetic mechanism for benzene oxidation and combustion has been further developed and validated against available premixed flame data (a total of six flames) and data from shock tubes, stirred and flow reactors. A significant re-evaluation of phenyl radical oxidation, phenol/phenoxy chemistry and the cyclopentadiene sub-mechanism is proposed in view of both new rate data and validation targets. Benzene chemistry is shown to be largel...

Energy Procedia, 2012

Optimum design of SOFC systems requires the development/application of versatile and robust appro... more Optimum design of SOFC systems requires the development/application of versatile and robust approaches able to handle diverse fuel patterns and complex thermochemistry. In the present work a computational methodology based on the reactor network approach is developed, targeting the thermochemical assessment of fuel flexibility in SOFC systems. SOFC operation on methane, biogas, and ethanol is considered. The methodology results in a detailed quantification of the impact of fuel interchangeability on syngas yield, reformer thermal efficiency, and emission levels. The approach saves computational time and resources when compared, for example, to full CFD modelling, thus providing the opportunity for quick parameterisation.

Proceedings of the Combustion Institute, 2015

ABSTRACT The increasing utilization of renewable fuels in the transportation and industrial secto... more ABSTRACT The increasing utilization of renewable fuels in the transportation and industrial sectors has sparked an interest in understanding the combustion of relevant major fuel components. Among them, smaller, oxygenated compounds, are of particular importance, both as neat fuels and as potential blending agents in engines operating on practical fuels. Additionally, oxygenated exhaust species, e.g. small aldehydes, are harmful and are expected to be regulated by future emission standards. The assessment of the effect of specific fuel components on overall engine efficiency and performance, as well as on pollutants formation, needs to be tackled through a detailed kinetics approach that inherently allows such a correlation. In the present work, a single, in-house developed, detailed chemical kinetic mechanism is utilized in order to model and analyze five stoichiometric or near stoichiometric low-pressure laminar premixed flames of C1–C2 oxygenated fuels; flames of the two smallest aldehydes (formaldehyde and acetaldehyde) and the two smallest alcohols (methanol and ethanol) are considered. The mechanism is shown to satisfactorily reproduce fuel decay as well as major and intermediate species profiles. Reaction path analysis is extensively utilized in order to scrutinize the controlling elementary steps. Parts of the mechanism are identified for further model improvement, based on critical evaluation of available specific rate constants. Early branching ratios and reactions between the major carbonyl or alkoxy products with oxygen carriers, and in particular reactions with O2, appear to be pivotal for the overall oxidation process.

Key Engineering Materials, 2013

Marble is a financially important and highly versatile material used extensively in construction,... more Marble is a financially important and highly versatile material used extensively in construction, decoration and art. The marble industry however is generated with low production efficiency, high waste material generation, high production costs and overall lack of sustainable resources management. A step towards improving the energy efficiency and environmental performance of the marble sector would be the adoption of ecological schemes that are already into force both at national and international levels. The most commonly used schemes are Environmental Management Systems that are focused on the general environmental performance of the enterprise, such as the EU EMAS (Eco-Management and Audit Scheme) and the international EN ISO 14001:2004 standard and ecolabelling schemes, such as the EU Ecolabel, focusing on specific products or services. The present work aims to provide a concise summary of the technical requirements and procedures for obtaining such environmental certificates, ...

Online, 2010

... Lower heating value (MJ kg À1 ) 43.4 27.0 32.0 42.8 37 (37.3) Autoignition temperature (K) 53... more ... Lower heating value (MJ kg À1 ) 43.4 27.0 32.0 42.8 37 (37.3) Autoignition temperature (K) 530 696 638 588 ... À1 ) occurred at an equivalence ratio of about φ ¼ 1.1. The above dataset also constitutes the only high-pressure data for ethanolair flame speeds to date. ...

The combustion chemistry of allene and propyne is critical for the breakdown of higher hydrocarbo... more The combustion chemistry of allene and propyne is critical for the breakdown of higher hydrocarbon fuels and for molecular growth processes. Allene and propyne consumption reactions are primary sources of the key propargyl and allyl radicals which are closely linked to benzene, PAH and soot formation paths. Further, allene and propyne are the smallest pair of isomers encountered in combustion studies. However, uncertainties still exist concerning aspects of the C 3 H 4 isomers chemistry and only recently have the first set of neat allene and propyne flame data appeared in the literature. The paper is part of an on-going effort aiming towards the optimization of a comprehensive kinetic mechanism for the high temperature combustion of small (C 1 -C 6) hydrocarbon species. The mechanism has been validated against species data from stoichiometric and fuel-rich laminar premixed allene and propyne flames with considerable success. A critical evaluation of C 3 H 4 consumption pathways has ...

ABSTRACT Laminar premixed planar adiabatic hydrogen-air flames are analyzed with the Computationa... more ABSTRACT Laminar premixed planar adiabatic hydrogen-air flames are analyzed with the Computational Singular Perturbation (CSP) method. The transport-chemistry interaction and the chemistry dynamics in different flame locations are examined, with particular attention in the preheat zone of the flame, where the main attributes of the flammability limits are manifested. Three different stoichiometries, φ=0.4, 1.0 and 6.0 are considered. For all stoichiometries, it is shown that in the preheat zone the fastest chemical time scale dominates transport and establishes steady state for the H radicals. The second fastest time scale dominates transport only in lean and rich flames, establishing steady state for the OH radicals. Such a dominance cannot be achieved in the stoichiometric flame, where OH chemistry interacts with transport, allowing thus a connection between the preheat and the main reaction zones. Since for all stoichiometries none of the slower chemical time scales can dominate in the preheat zone and all activities tend to diminish as the lean and rich limits are approached, the level of interaction between the preheat and main reaction zones indicated by the change of the OH dynamics is shown critical for flammability. Introduction Combustion of hydrogen has recently received particular attention through its links to enhanced efficiency and reduced pollutant emissions. An understanding of hydrogen-air flame structure is thus of great importance, especially near the flammability limits where flow-chemistry interactions become crucial. The chemistry of premixed hydrogen-air flames is fairly well established [e.g., 1, 2] and flame structures near the flammability limits have been obtained [e.g., 3].