Increase In CO2 Content Research Articles

Experimental and numerical study on the laminar burning velocity of hydrogen enriched biogas mixture

The laminar burning velocities of biogas-hydrogen-air mixture at different fuel compositions and equivalence ratios were determined and studied using the spherical flame method. The combined effects of H2 and CO2 on the laminar burning velocity were investigated quantitatively based on the kinetic effects and the thermal effects. The results show that the laminar burning velocities of the BG40, BG50 and BG60 are increased almost linearly with the H2 addition owing to the improved fuel kinetics and the increased adiabatic flame temperature. The dropping trend of laminar burning velocity from the BG60-hydrogen to the BG40-hydrogen is primarily attributed to the decreased adiabatic flame temperature (thermal effects). The GRI 3.0 mechanism can predict the laminar burning velocity of biogas-hydrogen mixture better than the San Diego mechanism in this study. Whereas, the GRI mechanism still needs to be modified properly for the hydrogen-enriched biogas as the CO2 proportion exceeds 50% in the biogas at the fuel-rich condition. The increased CO2 exerts the stronger suppression on the net reaction rate of H + O2=OH + O than that of H + CH3(+M) = CH4(+M), which contributes to that the rich-shift of peak laminar burning velocity of biogas-hydrogen mixture requires higher H2 addition as the CO2 content is enhanced. For the biogas-hydrogen fuel, the H2 addition decreases the flame stability of biogas fuel effectively due to the increased diffusive-thermal instability and hydrodynamic instability. The improved flame stability of biogas-hydrogen fuel with the increased CO2 content is resulted from the combined effects of diffusive-thermal instability and hydrodynamic instability.

An Investigation into the Self-Purging Mechanism of Anion Exchange Membrane Fuel Cells Exposed to Carbon Dioxide

There is still a gap in the current understanding of how carbon dioxide affects the operation of AEMFCs. Dekel et al. recently reported that only 3% of experimental studies included the effects of ambient CO2 on cell performance3, even though several sources have identified the CO2 problem as a key issue to be addressed in AEMFCs3,5,6. Carbon dioxide from ambient air (or other sources, such as flue gases7,8) can degrade AEMFC performance by reacting with the native hydroxide ions to form bicarbonate and carbonate ions (HCO3 -, CO3 2- respectively). These ions are less mobile than the native hydroxide ions (OH-) and therefore increase ohmic losses in the cell. In addition, the presence of (bi)carbonate species may impact electrochemical processes (and hence activation/thermodynamic losses) in the AEMFC, a phenomenon which is still largely unexplored. Although AEMFC performance is worse when operated in the presence of carbon dioxide, this can be mitigated during normal operation through an effect known as the self-purging mechanism. Several recent reviews and papers have noted that there remains a lack of consensus over the exact mechanism of the self-purging phenomenon1,5,6,9. The two leading theories can be described as a chemical mechanism, and an electrochemical mechanism: Chemical Mechanism: The chemical mechanism proposes that local depletion of OH- near the anode due to the hydrogen oxidation reaction (HOR) shifts the equilibrium of (bi)carbonate-producing chemical reactions to favor OH- production, thereby replenishing OH-, reducing the AEM’s (bi)carbonate content, and releasing CO2 into the anode gas stream via desorption. Electrochemical Mechanism: The electrochemical mechanism proposes that (bi)carbonate ions are direct reactants in the HOR, which would predict their removal from the membrane. This theory also accounts for the decrease in (bi)carbonate concentrations and CO2 emission during operation. In this numerical study we present a transient, spatially-varying AEM model to account for the carbonation process under operating conditions. Within this model we individually simulate the chemical and electrochemical self-purging pathways, and compare the results to those observed experimentally (e.g. conductivity increase with increasing current density, emission of CO2 into the anode gas stream, and increasing anode overpotential with increasing CO2 content). Following the determination of an appropriate self-purging model, we present a parametric investigation into this effect, and make suggestions on how it might be facilitated in order to improve AEMFC performance in the presence of CO2. References Arges, C. G. & Zhang, L. Anion Exchange Membranes’ Evolution toward High Hydroxide Ion Conductivity and Alkaline Resiliency. ACS Appl. Energy Mater. 1, 2991–3012 (2018).Varcoe, J. R. & Slade, R. C. T. Prospects for alkaline anion-exchange membranes in low temperature fuel cells. Fuel Cells 5, 187–200 (2005).Dekel, D. R. Review of cell performance in anion exchange membrane fuel cells. J. Power Sources 375, 158–169 (2017).Omasta, T. J. et al. Beyond catalysis and membranes: Visualizing and solving the challenge of electrode water accumulation and flooding in AEMFCs. Energy Environ. Sci. 11, 551–558 (2018).Ziv, N., Mustain, W. E. & Dekel, D. R. The Effect of Ambient Carbon Dioxide on Anion-Exchange Membrane Fuel Cells. ChemSusChem 11, 1136–1150 (2018).Gottesfeld, S. et al. Anion exchange membrane fuel cells: Current status and remaining challenges. J. Power Sources 1–15 (2017). doi:10.1016/j.jpowsour.2017.08.010Rigdon, W. A. et al. Carbonate Dynamics and Opportunities With Low Temperature, Anion Exchange Membrane-Based Electrochemical Carbon Dioxide Separators. J. Electrochem. Energy Convers. Storage 14, 020901 (2017).Landon, J. & Kitchin, J. R. Electrochemical Concentration of Carbon Dioxide from an Oxygen/Carbon Dioxide Containing Gas Stream. J. Electrochem. Soc. 157, B1149 (2010).Shiau, H.-S., Zenyuk, I. V. & Weber, A. Z. Elucidating Performance Limitations in Alkaline-Exchange- Membrane Fuel Cells. J. Electrochem. Soc. 164, E3583–E3591 (2017).

Effects of shielding gases on process stability of 10CrNi3MoV steel in hybrid laser-arc welding

Hybrid laser-arc welding (HLAW) of 10CrNi3MoV steel was carried out with different shielding gas mixtures including 100% Ar, 5% CO2 + Ar, 10% CO2 + Ar, 15% CO2 + Ar, 20% CO2 + Ar, 25% CO2 + Ar and 100% CO2. A CMOS high speed camera and real-time electric signal data were utilized to obtain the high-speed images (HSI) and electric signals of the droplet transfer and weld pool dynamics in real time during the HLAW process. The results showed that the increase of CO2 content increased the synergetic effect, especially the energy density of laser, and improved the penetration. The electric signal and HSI results revealed that, at low CO2 content (5% CO2 + Ar, 10% CO2 + Ar), the process was unstable with spatters and the metal transfer mode was globular mode. But at medium CO2 content (15% CO2 + Ar, 20% CO2 + Ar), the process was stable with less spatters and the metal transfer mode was spray mode. Stable process and accepted sound weld were obtained using 20% CO2 + Ar, which corresponded to the welding current 200 A and welding voltage 29 V. As CO2 content in the shielding gas increased, the increase in the weld current and welding voltage deteriorated the stability of the welding process, and the transfer mode shifted to repelled transfer, leading to the formation of large spatters.

О ЗОНАЛЬНОСТИ ВОДОРАСТВОРЕННЫХ ГАЗОВ НЕФТЕГАЗОНОСНЫХ ОТЛОЖЕНИЙ НАДЫМ-ТАЗОВСКОГО МЕЖДУРЕЧЬЯ

The results presented in the work were obtained in the studies of the features and zonality of water-dissolved gases within the boundaries of the oil-and-gas bearing sediments of the Nadym-Taz interfluve. Methane-containing waters with total gas saturation from 0.3 to 5.7 l/l and average CH4 content from 95.5 vol.% in the Aptian-Albian-Senomanian complex to 83.3 vol.% in the Lower and Middle Jurassic complex are developed in the region. With an increase in the depth, an increase in the content of homologues ΣHС (C2H6, C3H8, C4H10, C5H12 and C6H14) occurs from 1.34 vol.% in the Aptian_Albian-Senomanian complex to 11.67 vol.% in the Lower and Middle Jurassic complex. The maximal concentrations of ΣHС up to 30 vol.% were revealed in the lower part of the Neocomian complex in the marginal waters of oil deposits. An increase in CO2 content and a regular decrease in the ΣHС/N2 ratio from 96 in the Aptian-Albian-Senomanian complex to 52 in the Lower and Middle Jurassic complex are observed with an increase in the depth.

Theoretical assessment of integration of CCS in the Mexican electrical sector

This research evaluates the current most advanced and proven Gas Turbine (GT) technologies in a 1 × 1 scheme (400 MW on average) for their application in CO2 capture schemes. It has been demonstrated that the minimum energy required for the separation of CO2 is higher in a Natural Gas Combined Cycle (NGCC) than in a coal-fired power plant. Therefore, existing schemes were evaluated to assess the increased CO2 content in the Exhaust Gases (EG) for a NGCC in order to help reduce the energy penalty and the investment cost in CO2 capture systems. The schemes analyzed were: Exhaust Gas Recirculation (EGR), Evaporative Gas Turbine (EvGT), Supplementary Firing Combustion (SFC), External Firing combustion (EFC) and alternating systems with Selective Exhaust Gas Recycle (S-EGR) and hybridization. The most common GTs used in Mexico: Mitsubishi (15%), Siemens (41%) and General Electric (GE) (44%) including M − 501 GAC, SGT6-8000H and GE7HA.01 models were evaluated in Thermoflex 26®. For these, Levelized Costs of Electricity (LCOE) of 31.46, 31.18 and 31.05 USD/MWh, respectively, were obtained. GE offers the lowest LCOE and the EGR system presented the lowest energy penalty when the CO2 capture system was modeled in HYSYS V8.6®. Implementation of EGR helped to improve the energy efficiency of the NGCC and increased the content of CO2 from 4.2 to 7.1 mol% at 40%EGR. Similarly, EGR helped to reduce the LCOE in the integrated system with CO2 Capture by 10 USD/MWh.

Regeneration of СO2 Physical Solvents at Elevated Pressures in Gas-Liquid Membrane Contactor

In the present work, a membrane contactor with asymmetric flat-sheet poly(vinyltrimethylsilane) (PVTMS) membranes was proposed for the CO2 desorption process from physical solvents at elevated trans-membrane pressures. Different solvents were studied: water, a mixture of polyethylene glycol dimethyl ethers (Genosorb® tradename, Selexol process) and a number of ionic liquids (ILs). The compatibility of PVTMS with physical solvents was evaluated. Thorough sorption and swelling degree tests, FTIR experiments, and solvent permeation study provided insights into PVTMS-solvent interaction and allowed the selection of water, Genosorb® and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) as demo solvents for proof-of-concept. CO2 desorption experiments were successfully realized at elevated trans-membrane pressure (10 bar) and different temperatures (30 and 50oC). Increasing the temperature from 30 tо 50oС allowed obtaining higher CO2 desorption flux for all studied solvents. The combination of such parameters as CO2 flux (up to 4.5 m3 (STP)/(m2.h)) and the pressure difference between gas and liquid phases (up to 10 bar) is the best among the available literature data. The detailed investigation of [Emim][BF4] possessing the highest CO2 flux revealed that an increase of CO2 content in [Emim][BF4] provided by increasing absorption pressure up to 20 bar resulted in a signifcant CO2 desorption flux growth up to 7.5 m3 (STP)/(m2.h). Finally, the SEM and EDXS study of membranes after CO2 desorption tests revealed the deposition of particles containing Na and F elements from ionic liquid [Emim][BF4] on the membrane surface. Nevertheless, the same study proved the stability of the membrane morphology structure at elevated transmembrane pressures even up to 20 bar.

Effects of exhaust gas recirculation composition and temperature on microscopic mechanical properties of particles in a diesel engine

To investigate the microscopic mechanical properties of particles in a diesel engine, the particles generated with various exhaust gas compositions and temperatures are analyzed by a particle size analyzer and atomic force microscope. The results show that as the exhaust gas temperature increases, the quantity and mass concentration of core mode particle is insignificant, while the accumulation mode particle increased significantly; in addition the particle agglomeration force gradually increases, the major form of agglomeration force gradually shifts from liquid bridge force to Van der Waals force. Studies on exhaust gas composition show that N2 in exhaust gas is the main factor leading to the increase of accumulation mode particle; while CO2 in exhaust gas could reduces the quantity and mass concentration of particle emissions by reducing the accumulation mode particle; when N2 is applied, the particle agglomeration force is primarily assumes the form of the Van der Waals force; when CO2 is applied, the particle agglomeration force primarily assumes the form of a liquid bridge force; increasing N2 content in the exhaust gas can significantly increase the agglomeration force in particles; the effect of increasing CO2 content in the exhaust gas is reversed. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13037, 2019

Effects of N2 and CO2 dilution on the combustion characteristics of C3H8/O2 mixture in a swirl tubular flame burner

Premixed C3H8/O2 combustion has been investigated by adopting N2, CO2 and their mixture (50% N2-50% CO2 by volume) as the diluents, respectively. The oxygen content (mole fraction) in the oxidizer is varied from 0.13 to 0.35, which covers the operating conditions of EGR and OEC. The flame structures, temperatures, burning velocities and NOx emissions are examined under various oxygen contents. Detailed observations show that a steady, uniform tubular flame can be obtained over a wide range from lean to rich. By increasing oxygen content, the flame diameter increases slightly; the flame length decreases significantly, which is almost inversely proportional to laminar burning velocity. During decreasing the burning velocity to less than about 20 cm/s, a turning point appears and the flame length becomes extensively large. With the same oxygen content and equivalence ratio, by replacing half or all of the N2 diluent with CO2, the flame temperature and burning velocity decrease significantly. To obtain the same adiabatic flame temperature, the CO2 diluted mixture requires the highest oxygen content among the three diluents, however, its measured flame temperature is also highest. In the N2-CO2 diluted combustion, owing to thermal and chemical effects of CO2, the NOx emission reduces remarkably comparing with N2 dilution; under the same flame temperature, the NOx concentration reduces to almost 1/5 of that diluted by N2. The lean extinction limit raises by increasing CO2 content in the diluent, while the limit decreases with increasing oxygen content.

Effect of modified atmosphere packaging on the growth of spoilage microorganisms and Listeria monocytogenes on fresh cheese

Queso Fresco has a limited shelf life and has been shown to support the rapid growth of Listeria monocytogenes during refrigerated storage. In addition to improving quality and extending shelf life, modified atmosphere packaging (MAP) has been used to control the growth of pathogenic microorganisms in foods. The objectives of this study were to determine the effects of MAP conditions on the survival and growth of spoilage microorganisms and L. monocytogenes during storage of Queso Fresco manufactured without starter cultures. For L. monocytogenes experiments, cheeses were surface inoculated at ∼4 log10 cfu/g before packaging. Inoculated and uninoculated (shelf life experiments) cheeses were placed in 75-µm high-barrier pouches, packaged under 1 of 7 conditions including air, vacuum, or combinations of N2 and CO2 [100% N2 (MAP1), 30% CO2:70% N2 (MAP2), 50% CO2:50% N2 (MAP3), or 70% CO2:30% N2 (MAP4), 100% CO2 (MAP5)], and stored at 7°C. Samples were removed weekly through 35 d of storage. Listeria monocytogenes counts were determined for inoculated samples. Uninoculated samples were assayed for mesophilic and psychrotolerant counts, lactic acid bacteria, coliforms, and yeast and mold. In general, cheeses packaged under conditions consisting of higher contents of CO2 had lower pH levels during storage compared with those stored in conditions with lower levels or no CO2 at all. Similarly, the antimicrobial efficacy of MAP in controlling spoilage microorganisms increased with increasing CO2 content, whereas conditions consisting of 100% N2, vacuum, or air were less effective. Mean L. monocytogenes counts remained near inoculation levels for all treatments at d 1 but increased ∼2 log10 cfu/g on cheeses packaged in air, vacuum, and 100% N2 (MAP1) conditions at d 7 and an additional ∼1.5 log10 cfu/g at d 14 where they remained through 35 d. In contrast, treatments consisting of 70% CO2 (MAP4) and 100% CO2 (MAP5) limited increases in mean L. monocytogenes counts to <1 log10 cfu/g through 14 d and ∼1.5 log10 cfu/g by d 21. Mean L. monocytogenes counts increased to levels significantly higher than inoculation (d 0) on cheeses stored in MAP2 and MAP3 on d 21, on d 28 for MAP4, and on d 35 for cheeses stored under MAP5 conditions. Overall, significant treatment × time interactions were observed between air, vacuum, and MAP1 when each was compared with MAP2, MAP3, MAP4, and MAP5. These data demonstrate that packaging fresh cheese under modified atmospheres containing CO2 may be a promising approach to extend shelf life while limiting L. monocytogenes growth during cold storage.

A coupled model for CO2 & superheated steam flow in full-length concentric dual-tube horizontal wells to predict the thermophysical properties of CO2 & superheated steam mixture considering condensation

The mixture of CO2 and superheated steam (SHS) has been proved effective for heavy oil recovery by field practices. It has been proved that the development effect is closely related to the state parameters (temperature, pressure and superheated degree etc.) of the mixture. As a result, wellbore modeling is an important branch in the study of thermal recovery of heavy oil. In recent years, concentric dual-tube wells (CDTW) coupled with multi-point injection technique (MPIT) is proposed to overcome the fingering phenomenon, induced by serious reservoir heterogeneity, during the steam injection process. In this paper, a wellbore model is developed for simulating CO2 & SHS flow in a full-length CDTW. The model is solved with finite difference method on space. It is found that: (a) An injection pressure, higher than 4.1 MPa, in the integral joint tube (IJT) or an injection pressure, smaller than 4.1 MPa, in annuli are recommended to obtain a uniform steam absorption rate along the horizontal wellbores. (b) The mass injection rate at well-head condition should be close to each other to avoid un-uniform of steam absorption rate along the horizontal wellbores. (c) When phase change occurs in the annuli, the mixture temperature increases with increasing CO2 content. (d) The total length of wet steam flow in the horizontal section of the wellbores increases with increasing CO2 content.

Effects of CO2 gasification reaction on the combustion of pulverized coal char

Although numerous studies on CO2 gasification during coal char combustion have been documented, the effects of CO2 gasification on high-temperature carbon oxidation, which is important for evaluation of carbon conversion during pulverized coal combustion under oxy-fuel and flue gas recirculation conditions, are unclear. Thus, the char conversion characteristics at various contents of O2 and CO2 were studied in a drop-tube furnace at 1373 K. Due to the cumulative effects of CO2 gasification, which can not only suppress carbon conversion due to endothermicity but also consume part of carbon directly, there exists a minimal carbon conversion point around the CO2 content of 9–13 vol%, where the growth of promotion effect with CO2 content catches up with the suppression effect, and an inflection point around the CO2 content of 17–25 vol%, where the promotion effect of the direct gasification reaction on carbon consumption surpasses the suppression effect. Increasing O2 shifts both points towards high CO2 contents, whereas increasing combustion gas temperature decreases the values. A mathematical formula including oxidation, effect of gasification on oxidation, and CO2 gasification, is presented, which gives well prediction on high-temperature carbon conversion. With increasing CO2 content, the reduction degree of CO2 gasification on oxidation rate increases, and the synthesis oxidation rate slightly decreases, whereas there always exists a minimal point for gasification rate, gross carbon conversion rate, and gasification weightiness. With increasing O2 content, the oxidation rate, reduction degree of CO2 gasification on oxidation rate, and gross carbon conversion rate increase; the gasification rate increases below the minimal point, whereas decreases above the minimal point; the gasification weightiness decreases. Combustion gas temperature shows positive effect on all abovementioned parameters. The results derived here provide meaningful guidelines for practical application and kinetics research on pulverized coal combustion.

Climate Change and Drought: a Precipitation and Evaporation Perspective

Many studies have shown that greenhouse gas (GHG)-induced global warming may lead to increased surface aridity and more droughts in the twenty-first century due to decreased precipitation in the subtropics and increased evaporative demand associated with higher vapor pressure deficit under warmer temperatures. Some recent studies argue that increased water use efficiency by plants under elevated CO2 may reduce the evaporative demand and therefore mitigate the drying. Here we first discuss the model-projected changes in precipitation amount and frequency that affect the surface water balance and aridity and then the changes in actual and potential evapotranspiration under GHG-induced warming. The effects of the GHG-induced warming and changes in plants’ physiology under elevated CO2 on precipitation, soil moisture, and runoff are quantified and compared by analyzing different model experiments with and without the physiologic response. The surface drying effect of GHG-induced warming is found to dominate over the wetting effect of plants’ physiology in response to increasing CO2, leading to similar surface drying patterns in climate model simulations with or without the physiologic response in the twenty-first century. Part of the drying comes from increased dry spells (i.e., more dry days) and a flattening of the histograms of drought indices as GHGs increase, with the latter leading to widespread increases in hydrological drought even over areas with increasing mean runoff. Because of this, the change pattern of the mean cannot be used to represent drought changes. Consistent with the projected drying in the twenty-first century, recent analyses of model experiments suggest wetter land surfaces during the last glacial maximum, which implies that dusty air during cold glacial periods may have resulted from other factors, such as stronger winds and more dust sources, rather than drier land surfaces. Finally, the drying in the subtropics does not appear to be just a transient response to increased GHGs, as the warming and precipitation change patterns do not vary significantly over time in 500-year simulations with increased CO2 contents by a fully coupled climate model.

Experimental study on H2S and CO2 generation capacities of the Bohai bay heavy oil

Thermal recovery is a conventional technology for heavy oil development. During thermal oil recovery the reservoir could generate H2S and CO2. They will potentially threat the safety of downhole tubing regarding the sweet or sour corrosion. In some Bohai heavy oil fields CO2 and H2S under thermal recovery conditions lead to some corrosion problems of the tubing and equipment. Therefore, to determine the corrosive gas generation capacity is crucial for anti-corrosion design of downhole tubing and casing. Heavy oil samples from Bohai, China were experimentally studied for their pyrolysis characteristics using high-temperature-high-pressure autoclaves. The gases were collected when autoclaves cooled down to the in situ formation temperature. Effects of temperature, water chemistry and core mineral on corrosive gas generation were investigated. The results show that total pressure increase significantly when temperature reached 250°C-280 °C under the single heavy oil condition. The additional water facilitates the reaction process, after more SO42− added in the mimic formation water, higher H2S content is obtained. Under the condition of multiphase of oil, formation water and cores, both of the H2S and CO2 content increase obviously, and the cores' effect on CO2 is greater than H2S. Anti-corrosion design usually concerns only the highest corrosive gas concentration without further analysis. The highest concentration does not always correspond to the best corrosive gases generation capacities of heavy oil. Comprehensive analysis of both the total pressure of reaction process and the quality of the reaction heavy oil is carried out, then the corrosive gases volume per unit mass of heavy oil is calculated. These can determine the strongest corrosive formation environment and the maximum gases generation capacities of heavy oil.

Influence of Mono- and Multilayered Packaging Material on the Quality of Seer Fish (Scomberomorus commerson) During Chilled Storage

Consumers prefer fresh, mildly preserved fishes without added chemicals. Due to increasing awareness among consumers on health aspects, demand for fish is ever increasing. The conventional preservation methods do not offer fresh-like product for longer duration, which limits the availability of fish in distant markets. Hence, the present study was undertaken to assess the effect of mono- and multilayered packaging material on the quality of seer fish steaks during chilled storage. For this, seer fish (Scomberomorus commerson) steaks were packed in LDPE (monolayer) and polyester–polyethylene (multilayer) pouches and the packs were sealed and stored in ice. Sampling was carried out at regular intervals to assess the changes in headspace gas composition, sensory quality, biochemical, physical and microbial quality. Significant reduction in O2 and increase in CO2 content was observed for both the packs. Lower microbial counts were observed for seer fish packed in multilayered pouches as compared to LDPE. Significant (P < 0.05) lower TVB-N values were observed for seer fish packed in multilayered pouches. Reduction in TBA values and TVBN content was observed for samples packed in multilayer compared to monolayer film. No significant variation in flavor, firmness and taste was observed among the samples up to 7th day. Sensorily, seer fish steaks packed in LDPE were acceptable up to ~ 11–12 days compared to ~ 13–14 days in multilayered pouches indicating better quality in multilayered pouches.

Beer foam decay: effect of glass surface quality and CO2 content

The effect of beer glass surface quality and CO2 content in beer on foam decay was investigated using our experimental method. The effect of beer glass surface quality on foam decay was experimentally investigated for: i) cold &amp; clean glass surface, ii) warm &amp; clean glass surface, iii) cold &amp; greasy glass surface, and iv) cold &amp; dusty glass surface. The fastest foam decay was observed for greasy glass surface. It was found that increasing CO2 content in beer: i) the liquid content in the foam decreases, and ii) the foam breaks down faster. The foam decay and growth kinetics of foam-liquid interface were statistically treated using own models.

Structural controls of CO2 on Y, La and Sr incorporation in sodium-rich silicate - carbonate melts by in-situ high P-T EXAFS

Carbonate-rich silicate and carbonate melts play a crucial role in deep Earth magmatic processes and their melt structure is a key parameter, as it controls physical and transport properties. Carbon-rich melts can be strongly enriched in trace elements, but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses. In this contribution we investigate the influence of CO2 on the local environments of trace elements contained in silicate glasses with variable CO2 concentrations and in silicate and carbonate melts. The melts were studied in-situ at high pressure and temperature conditions using the Paris-Edinburgh press (2.2 to 2.6GPa and 1200 to 1500°C). The compositions studied include sodium-rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at Oldoinyo Lengai volcano. The local environments of yttrium (Y), lanthanum (La) and strontium (Sr) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. Main findings of the study suggest: (1) In peralkaline silicate glasses the local structure of Y is unaffected by the CO2 content. Contrary, a slight increase of oxygen bond lengths of Sr and La is inferred with increasing CO2 content in peralkaline glasses, while they remain constant in glasses of even higher peralkalinity independent of the CO2 content. (2) In silicate melts of different CO2 contents Y-O bond lengths are constant, while a slight increase within carbonate melt compositions is deduced. On the other hand, a steady bond lengths increase over the whole compositional range is inferred for La-O and Sr-O. This may well be explained by distinct preferences of these elements for specific local environments. Based on these new data, we suggest potential mechanisms for the structural incorporation of these elements, a key step towards understanding their partitioning behavior in natural magmatic systems.

Study on CO2 Gasification Reaction during the Combustion of Pulverized Coal Char Particle

Although much research on the effect of CO2 gasification on char combustion has been reported, few studies give clear information on the proportion of carbon consumed by the gasification and oxidation respectively. In this work, a drop-tube furnace is used to study the combustion of Huangling bituminous coal char in different oxygen and carbon dioxide concentrations at different residence times. It is found that with increasing CO2 content the carbon conversion ratio decreases first and then goes up in both oxygen content of 21 and 36 vol.%. There always exists a minimal point around CO2 content of 8-15 vol.% along with increased residence time during pulverized coal char combustion. Meanwhile, a preliminary formula is proposed to calculate the overall carbon conversion ratio of char and the proportion of carbon consumed by the gasification and oxidation respectively.

Thermodynamic equilibrium analysis of water-gas shift reaction using syngases-effect of CO2 and H2S contents

Abstract Thermodynamic equilibrium of water-gas shift reaction (WGSR) under various temperatures, pressures and steam-to-CO (S/C) ratios was analyzed by Gibbs free energy minimization method. Coal-derived syngases with various CO2 and H2S contents were used as the feedstock. Based on the obtained results, it was found that CH4 and carbon formations were enhanced when syngas CO2 content increases. Carbon-free WGSR can be resulted using high S/C ratio. However, CH4-free WGSR cannot be resulted even with low S/C ratios. From the H2O conversion and H2 yield variations, the temperature at which reverse WGSR occurs can be identified and found to decrease with the increase in S/C ratio. Solid CaO sorbent was employed for both CO2 and H2S removals in WGSR when sour syngas was used as the feedstock. It was found that WGSR performance was enhanced due to the CO2 and H2S removals by CaO. The H2S concentration can be decreased with decreased S/C ratio while increasing the reaction pressure was not favourable for H2 production and H2S removal in WGSR with CaO. Because WGSR performance enhancement due to CO2 and H2S removals occurred at high temperature, catalysts can be eliminated in sorption-enhanced WGSR.

In-situ visualization of PLA crystallization and crystal effects on foaming in extrusion

We studied poly(lactic acid)’s strain-induced crystallization behavior during a tandem extrusion process using visualization techniques. Our visualization results showed that, despite its inherently slow crystallization kinetics in the quiescent condition, PLA crystallites were quickly formed inside the die at a temperature even above the melting temperature (Tm), as the melt temperature was decreased. Their rapid formation at a high temperature above the Tm peak, was due to the strain-induced crystallization. We also studied how the strain rate and the use of supercritical CO2 affected PLA crystallization. A significant increase in the PLA crystallization kinetics was caused by a sudden increase in the screw speeds of the extruders with a fixed barrel temperature. The crystallization enhancement, which was caused by the increased flow rate, became more pronounced at lower temperatures due to the higher degree of molecular orientation. Adding the CO2 shifted the crystallization temperature to a lower processing temperature due to its plasticization effect, but it accelerated the crystallization kinetics as well. We also observed a correlation between the content of the induced crystallites inside the extruder and the cellular structure of the extruded foams. This clearly explained the decrease in the optimal processing temperature for foaming with an increased CO2 content.

Potential performance of environmental friendly application of ORC and Flash technology in geothermal power plants

The successful exploitation of geothermal energy for power production relies on to the availability of nearly zero emission and efficient technologies, able to provide flexible operation. It can be realized with the binary cycle technology. It consists of a closed power cycle coupled to a closed geothermal loop, whereby the closed power cycle is generally accomplished by means of an organic Rankine cycle (in a few cases the Kalina cycle has been adopted). The confinement of the geothermal fluid in a closed loop is an important advantage from the environmental point of view: possible pollutants contained in the geothermal fluid are not released into the ambient and are directly reinjected underground.Although a well-established technology in the frame of geothermal applications, the adoption of the binary cycle technology is at the moment typically confined to the exploitation of medium-low temperature liquid geothermal reservoirs, generally between 100-170 °C. The important advantages of the binary cycle technology from the environmental point of view suggest nevertheless that it is worthwhile to investigate whether the application range could be extended to higher temperature reservoirs, and up to which extent. Moreover, the paper investigates the effect of an increasing CO2 content in the geothermal fluid. The paper compares in a convenient high temperature range of the geothermal source the performance of a properly optimized geothermal ORC plant, with the performance of a modified flash plant, whereby the geothermal steam enters a turbine, and the CO2 stream is separated, compressed and finally reinjected. An environmentally friendly working fluid, recently introduced in the market, is considered in the ORC optimization process. The performance comparison will involve the assessment of plant net power. As far as the calculations are concerned, the geothermal fluid is assumed to be a mixture of water and possibly CO2. The auxiliary power consumption is properly accounted for: beyond cooling auxiliaries, a submersible well pump for the ORC plant and a gas compressor for the reinjection of the non-condensable gases in the flash plant are considered.