In the construction industry, it is the material production phase and the use phase of buildings’ life cycles that represent the greatest environmental burden. The presented research focused on wood constructions during their use phase. The primary objective of the research was to determine the amount of CO2 produced during the operation of specific wood constructions in connection with the energy demand for their heating. A correlation analysis of selected parameters revealed a statistically significant correlation between heating medium type and energy demand for heating (p = −0.5773) and between heating medium type and amount of CO2 produced (p = 0.4796). A more detailed analysis showed that, in terms of the average energy demand for heating, the column constructions were the most efficient among the compared construction systems, regardless of the energy standard. Similar findings were obtained for annual CO2 production in connection with the average energy demand for heating. The... [more]

Molecule radiation can be used as a tool to study colder regions in switching arc plasmas like arc fringes in contact to walls and ranges around current zero (CZ). This is demonstrated in the present study for the first time for the case of ablation-dominated high-current arcs as key elements of self-blast circuit breakers. The arc in a model circuit breaker (MCB) in CO2 with and an arc in a long nozzle under ambient conditions with peak currents between 5 and 10 kA were studied by emission and absorption spectroscopy in the visible spectral range. The nozzle material was polytetrafluoroethylene (PTFE) in both cases. Imaging spectroscopy was carried out either with high-speed cameras or with intensified CCD cameras. A pulsed high-intensity Xe lamp was applied as a background radiator for the broad-band absorption spectroscopy. Emission of Swan bands from carbon dimers was observed at the edge of nozzles only or across the whole nozzle radius with highest intensity in the arc center, de... [more]

Wall-stabilized arcs dominated by nozzle−ablation are key elements of self-blast circuit breakers. In the present study, high-current arcs were investigated using a model circuit breaker (MCB) in CO2 as a gas alternative to SF6 (gas sulfur hexafluoride) and in addition a long polytetrafluoroethylene nozzle under ambient conditions for stronger ablation. The assets of different methods for optical investigation were demonstrated, e.g., high-speed imaging with channel filters and optical emission spectroscopy. Particularly the phase near current zero (CZ) crossing was studied in two steps. In the first step using high-speed cameras, radial temperature profiles have been determined until 0.4 ms before CZ in the nozzle. Broad temperature profiles with a maximum of 9400 K have been obtained from analysis of fluorine lines. In the second step, the spectroscopic sensitivity was increased using an intensified CCD camera, allowing single-shot measurements until few microseconds before CZ in the... [more]

Successful geological sequestration of carbon depends strongly on reservoir seal integrity and storage capacity, including CO2 injection efficiency. Formation of solid hydrates in the near-wellbore area during CO2 injection can cause permeability impairment and, eventually, injectivity loss. In this study, flow remediation in hydrate-plugged sandstone was assessed as function of hydrate morphology and saturation. CO2 and CH4 hydrates formed consistently at elevated pressures and low temperatures, reflecting gas-invaded zones containing residual brine near the injection well. Flow remediation by methanol injection benefited from miscibility with water; the methanol solution contacted and dissociated CO2 hydrates via liquid water channels. Injection of N2 gas did not result in flow remediation of non-porous CO2 and CH4 hydrates, likely due to insufficient gas permeability. In contrast, N2 as a thermodynamic inhibitor dissociated porous CH4 hydrates at lower hydrate saturations (<0.48... [more]

The electric breakdown at single and multiple protrusions in SF6 and CO2 is investigated at 0.4 and 0.6 MPa, respectively. Additionally, the breakdown fields at rough surfaces of two different areas were determined. From the measurements, breakdown probability distributions for single protrusions were determined and fitted by Weibull distributions. This allowed the determination of statistical enlargement laws for the 50% breakdown probability fields E50. Such enlargement laws describe, for example, the scaling of breakdown field with electrode area or number of protrusions. The predictions were compared to the experimental data, and both agreement and discrepancies were observed depending on polarity and number of protrusions and gas. Discharge predictions including first electron, streamer inception and crossing, as well as leader propagation, gave further insight to this. It was found that predictions from enlargement laws based on statistical processes may not describe the measured... [more]

Hydrate formation from cyclopentane (CP) and carbon dioxide was measured at 281 K by powder X-ray diffraction (PXRD) and macroscopic methods. The effect of initial pressure and CP mass fraction in liquid phase was analyzed. The results showed that hydrate formation was assumed to start with the nucleation of the mixed CP-CO2 hydrate with small fraction of CO2 followed by a large continuous CO2 adsorption. Initial pressure was found to have a positive correlation with the total CO2 consumptions when the initial pressure was below 2.5 MPa. However, the total CO2 consumptions dropped by over a half as the initial pressure was 3.0 MPa. PXRD revealed that all the hydrate samples formed at different initial pressures were structure II. The CO2 consumptions were assumed to be inhibited by the competitive occupation of 51264 cages between CP and CO2 molecules when the initial pressure was above 2.5 MPa. The CO2 consumptions were also found to be reduced as the CP mass fraction was above 0.25.... [more]

Climate change has been recognized as a threatening environmental problem around the world. CO2 is considered to be the main component of greenhouse gas. By using solar energy (light energy) as the energy source, photocatalytic conversion is one of the most effective technologies to reveal the clean utilization of CO2. Herein, using sodium tungstate, nickel nitrate, and selenium powder as the main raw materials, the high absorption and utilization of WSe2 for light energy and the high intrinsic conductivity of NiSe2 were combined by a hydrothermal method to prepare NiSe2/WSe2 and hydrazine hydrate as the reductant. Then, high-performance NiSe2/WSe2 photocatalytic material was prepared. The characterization results of XRD, XPS, SEM, specific surface area, and UV-visible spectroscopy show that the main diffraction peak of synthesized NiSe2/WSe2 is sharp, which basically coincides with the standard card. After doping NiSe2, the morphology of WSe2 was changed from a flake shape to smaller... [more]

The construction industry is responsible for a high percentage of the energy consumed on the planet and the emission of greenhouse gases, therefore it is considered necessary to rethink many of the processes that this industry carries out in order to reduce its environmental impact. For this, one of the paths could take into account the Life Cycle Assessment of the used materials, for which it is necessary to evaluate this aspect through indicators that allow the qualification and quantification of the weight of these environmental impacts. In this context, this article presents a methodological proposal for the quantitative evaluation of the embodied primary energy and CO2 production at each stage of the life cycle of prefabricated structural systems, taking as case studies eight prototypes from the “Solar Decathlon” competition in its editions of Europe (2014), United States (2015) and Latin America (2015), through a Simplified Life Cycle Analysis, using the Eco Audit tool from CES E... [more]

A novel process is proposed whereby wood wastes from forest tree mortalities and improved forest management are co-digested with high in nitrogen content animal manures to yield bio-methane along with nitrogen, phosphorous, and potassium bio-fertilizers. The process mimics the well-known wood conversion to methane process in lower termites but relies on thermophilic fungi, bacteria, and archaea instead. It is based on the modified state-of-the art two-step, hyperthermophilic (70 °C) hydrolysis and thermophilic (55 °C) fermentation, dry (30% TS), anaerobic digestion technology with a high organic loading and shortened retention time. The process is augmented with the thermophilic fermentation of carbon dioxide in the biogas into secondary bio-methane by employing hydrogen produced via wind-powered electrolysis. The entire process comprised of five distinct steps is designated as “Wood to Methane 3 + 2”. An industrial type, standardized plant unit has been developed that can be employed... [more]

The oil and gas industry generates a significant amount of harmful greenhouse gases that cause irreversible environmental impact; this fact is exacerbated by the world’s utter dependence on fossil fuels as a primary energy source and low-efficiency oil and gas operation plants. Integration of solid oxide fuel cells (SOFCs) into natural gas plants can enhance their operational efficiencies and reduce emissions. However, a systematic analysis of the life cycle impacts of SOFC integration in natural gas operations is necessary to quantitatively and comparatively understand the potential benefits. This study presents a systematic cradle-to-grave life cycle assessment (LCA) based on the ISO 14040 and 14044 standards using a planar anode-supported SOFC with a lifespan of ten years and a functional unit of one MW electricity output. The analysis primarily focused on global warming, acidification, eutrophication, and ozone potentials in addition to human health particulate matter and human tox... [more]

Carbon capture and storage is considered an effective mitigation strategy to reduce the most challenging emissions from heavy industries and gas processing. The safe transport of carbon dioxide via pipelines is an important aspect for developing large-scale Carbon Capture and Storage projects. Dispersion modeling for heavy gas such as carbon dioxide is considerably different from natural gas. The set up for modeling simulations is more challenging than conventional natural gas pipeline for several reasons, such as the differences in thermodynamics that must be considered. Moreover, when the carbon dioxide is transported in dense or liquid phase, the rapid phase changing, and possible consequent formation of solids should be considered. Finally, the equation of state required for accurate prediction of parameters is generally different than the ones applicable for natural gas. The main scope of this comprehensive review is to identify the most important parameters, critical events, suit... [more]

The urgent energy transition needs a better penetration of renewable energy in the world’s energy mix. The intermittency of renewables requires the use of longer-term storage. The present system uses water displacement, in a lined rock cavern or in an aerial pressurised vessel, as the virtual piston of compressor and expander functions in a carbon dioxide heat pump cycle (HPC) and in an organic transcritical cycle (OTC). Within an impermeable membrane, carbon dioxide is compressed and expanded by filling and emptying pumped-hydro water. Carbon dioxide exchanges heat with two atmospheric thermal storage pits. The hot fluid and ice pits are charged by the HPC when renewable energy becomes available and discharged by the OTC when electricity is needed. A numerical model was built to replicate the system’s losses and to calculate its round-trip efficiency (RTE). A subsequent parametric study highlights key parameters for sizing and optimisation. With an expected RTE of around 70%, this CO2... [more]

For reliability and safety issues of injection wells, corrosion resistance of materials used needs to be determined. Herein, representative low-cost materials, including carbon steel X70/1.8977 and low alloyed steel 1.7225, were embedded in mortar to mimic the realistic casing-mortar interface. Two types of cement were investigated: (1) Dyckerhoff Variodur commercial Portland cement, representing a highly acidic resistant cement and (2) Wollastonite, which can react with CO2 and become stable under a CO2 stream due to the carbonation process. Exposure tests were performed under 10 MPa and at 333 K in artificial aquifer fluid for up to 20 weeks, revealing crevice corrosion and uniform corrosion instead of expected pitting corrosion. To clarify the role of cement, simulated pore water was made by dispersing cement powder in aquifer fluid and used as a solution to expose steels. Surface analysis, accompanied by element mapping on exposed specimens and their cross-sections, was carried out... [more]

This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon... [more]

Clathrate formation and guest behaviors in hydroquinone (HQ) clathrates were investigated for the first time using ternary (CO + CO2 + H2) gas mixtures. Two gas compositions (low and high CO2 concentrations) were used to simulate synthesis gases generated from various sources. After reaction at 2.0, 4.0, and 6.0 MPa, the conversion yield of pure HQ to the clathrate form reached >90% if the CO2 partial pressure was 0.7 MPa or higher. In addition, CO2 was the most abundant occupant, whereas CO was only detectable at higher CO concentrations and experimental pressures. The separation efficiency values expressed as molar ratios of CO2 to CO in the solid clathrate form were found to be 12.7 and 23.9 MPa at 4.0 and 6.0 MPa, respectively. The experimental and the calculated results in this study provide information useful for the design of a clathrate-based separation process for synthesis gases from various sources (i.e., synthesis gases with various compositions).

The European Union (EU) energy policy for sustainable development has been the topic of continuous debate, research, and analysis, which frequently focused on objectives and the evaluation of quantitative and qualitative performance. Different approaches can be used for the assessment of sustainable development goals. The authors of the article conducted a literature review of relevant research papers dated 2016−2020. The most common are quantitative methods based on hard data. Some qualitative studies based on soft data are also available but rare. This article proposes hybrid Rough Set Data Envelopment Analysis (DEA) and Rough Set Network DEA models that integrate both approaches. Also, the models allow the inclusion of uncertainty in the underlying data. The article uses hard data of the International Energy Agency (IEA) and the results of the EU survey regarding the influence of the socio-economic environment on CO2 emissions in EU countries. The authors demonstrate that multifacet... [more]

In the last century, the refrigerant R744 (carbon dioxide) has become an environmentally friendly solution in commercial refrigeration despite its particular issues related to the low critical temperature. The use of transcritical cycles in warm and hot countries reveals the necessity of adopting different configurations and technologies to improve this specific cycle. Among these, subcooling methods are well-known techniques to enhance the cooling capacity and the Coefficient of Performance (COP) of the cycle. In this work, an R600a dedicated mechanical subcooling system has been experimentally tested in an R744 transcritical system at different operating conditions. The results have been compared with those obtained using a suction-to-liquid heat exchanger (IHX) to determine the degree of improvement of the mechanical subcooling system. Using the experimental tests, a computational model has been developed and validated to predict the optimal subcooling degree and the cubic capacity... [more]

Adopting a new paradigm for social development implies a transition to a circular economy. The above requires the reduction of greenhouse gas emissions, the utilization of wastes, and the use of renewable energy sources. The most promising way is the use of methanol for industrial and transport applications. China is experiencing a boom in methanol production and its use in almost every sector of the economy. The purpose of this study was to reveal economic benefits, carbon dioxide emissions and the potential production of green methanol. Fuel price history, energy costs and fuel economy were used for economic assessment. Life cycle analysis to evaluate carbon dioxide emissions was applied. It was revealed that only the use of green methanol as a fuel results in decreases in well-to-wheel CO2 emissions compared to fossil fuels. The potential methanol production by using recycled waste and wind power was determined. Its annual production can range from 6.83 to 32.43 million tones. On th... [more]

Up to now, many kinds of deep eutectic solvents (DESs) were investigated for the capture of acidic gases from flue gases. In this review, non-functionalized and functionalized DESs, including binary and ternary DESs, for SO2, CO2 and NO capture, are summarized based on the mechanism of absorption, physical interaction or chemical reaction. New strategies for improving the absorption capacity are introduced in this review. For example, a third component can be introduced to form a ternary DES to suppress the increase in viscosity and improve the CO2 absorption capacity. DESs, synthesized with halogen salt hydrogen bond acceptors (HBAs) and functionalized hydrogen bond donors (HBDs), can be used for the absorption of SO2 and NO with high absorption capacities and low viscosities after absorption, due to physicochemical interaction between gases and DESs. Emphasis is given to introducing the absorption capacities of acidic gases in these DESs, the mechanism of the absorption, and the ways... [more]

Underground geological energy and CO2 storage contribute to mitigation of anthropogenic greenhouse-gas emissions and climate change effects. The present study aims to present specific underground energy and CO2 storage sites in Greece. Thermal capacity calculations from twenty-two studied aquifers (4 × 10−4−25 × 10−3 MJ) indicate that those of Mesohellenic Trough (Northwest Greece), Western Thessaloniki basin and Botsara flysch (Northwestern Greece) exhibit the best performance. Heat capacity was investigated in fourteen aquifers (throughout North and South Greece) and three abandoned mines of Central Greece. Results indicate that aquifers present higher average total heat energy values (up to ~6.05 × 106 MWh(th)), whereas abandoned mines present significantly higher average area heat energy contents (up to ~5.44 × 106 MWh(th)). Estimations indicate that the Sappes, Serres and Komotini aquifers could cover the space heating energy consumption of East Macedonia-Thrace region. Undergroun... [more]

Microbial electrosynthesis (MES) systems can convert CO2 to acetate and other value-added chemicals using electricity as the reducing power. Several electrochemically active redox mediators can enhance interfacial electron transport between bacteria and the electrode in MES systems. In this study, different redox mediators, such as neutral red (NR), 2-hydroxy-1,4-naphthoquinone (HNQ), and hydroquinone (HQ), were compared to facilitate an MES-based CO2 reduction reaction on the cathode. The mediators, NR and HNQ, improved acetate production from CO2 (165 mM and 161 mM, respectively) compared to the control (without a mediator = 149 mM), whereas HQ showed lower acetate production (115 mM). On the other hand, when mediators were used, the electron and carbon recovery efficiency decreased because of the presence of bioelectrochemical reduction pathways other than acetate production. Cyclic voltammetry of an MES with such mediators revealed CO2 reduction to acetate on the cathode surface. T... [more]

All Carbon Capture and Storage (CCS) projects require the transportation of CO2 from a source to a storage location. Although, a compressor and a large diameter pipeline is the normal method used to achieve this, liquefaction, shipping and pumping is sometimes attractive. Identifying the economic optimum is important for all CCS projects, minimizing energy consumption is also important because it corresponds to a resource efficiency in fossil-fuel based projects. This article describes the development and validation of a model that estimates the energy consumption associate with CO2 transportation using the geographic location of the source and the reservoir to incorporate ambient temperature and bathymetry data. The results of the validation work show an average absolute temperature and pressure error less than 1 °C and 1 bar compared to a reference model. The model has been developed using openly accessible data and is made available in a repository for open research data.

To manage greenhouse gas emissions, directives on renewable energy usage have been developed by the European Commission with the objective to reduce overall emissions by 40% by 2030 which presents a significant potential for renewable energy sources. At the same time, it is a challenge for these energy technologies which can only be solved by integrated solutions. Carbon capture and storage combined with geothermal energy could serve as a novel approach to reduce CO2 emissions and at the same time facilitate some of the negative impacts associated with fossil fuel-based power plants. This study focuses on the technical and economic feasibility of combining these technologies based on a published model, data and market research. In the European Union, Germany is the most energy intensive country, and it also has an untapped potential for geothermal energy in the northern as well as the western regions. The CO2 plume geothermal system using supercritical carbon dioxide as the working flu... [more]

Photosynthetic biogas upgrading using two-stage systems allows the absorption of carbon dioxide (CO2) in an absorption unit and its subsequent assimilation by microalgae. The production of microalgae requires large amounts of nutrients, thus making scale-up difficult and reducing economic feasibility. The photosynthetic process produces oxygen (O2) (1 mol per mol of CO2 consumed), which can be desorbed into purified biogas. Two-stage systems reduce its impact but do not eliminate it. In this study, we test the use of landfill leachate as a nutrient source and propose a viable and economical strategy for reducing the O2 concentration. First, the liquid/gas (L/G) ratio and flow mode of the absorber were optimized for 20% and 40% CO2 with COMBO medium, then landfill leachate was used as a nutrient source. Finally, the system was inoculated with nitrifying bacteria. Leachate was found to be suitable as a nutrient source and to result in a significant improvement in CO2 absorption, with out... [more]

An air-independent propulsion system containing fuel cells is applied to improve the operational performance of underwater vehicles in an underwater environment. Fuel-reforming efficiently stores and supplies hydrogen required to operate fuel cells. In this study, the applicability of a fuel-reforming system using various fuels for underwater vehicles was analyzed by calculating the fuel and water consumptions, the amount of CO2 generated as a byproduct, and the amount of water required to dissolve the CO2 using aspen HYSYS (Aspen Technology, Inc., Bedford, MA, USA). In addition, the performance of the fuel-reforming system for methanol, which occupies the smallest volume in the system, was researched by analyzing performance indicators such as methanol conversion rate, hydrogen, yield and selectivity, and reforming efficiency under conditions at which pressure, temperature, steam-to-carbon ratio (SCR), and hydrogen separation efficiency vary. The highest reforming efficiency was 77.7−... [more]