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Abstract A new cause-based approach was used to estimate the change in methane emissions from the natural gas system resulting from a change in throughput. The analysis builds upon prior work (Mac Kinnon et al., 2018) positing that a cause-based, marginal approach to estimating methane emission impacts of reducing or increasing natural gas use was more accurate than assuming that methane emission vary one-for-one with throughput. The goal of this work is to determine the relationship between methane emissions and changes in throughput both over short time horizons where the gas infrastructure is fixed and over time periods where system expansion (or retirement) and technological improvements via component replacement occur. The results show that methane emissions change with throughput but the relative change in emissions is less than the relative change in throughput. There are many components (emissions sources) in the natural gas system that emit the same amount of methane to the atmosphere regardless of their operational mode; meaning some emissions sources have no or only partial dependence on throughput. As a result, reducing natural gas consumption in the future will not yield a directly proportional reduction in the methane emissions. It is believed that the results of this study will help energy policymakers to understand better the effect of policies aimed at reducing natural gas use on greenhouse gas (GHG) emissions and where such policies should be applied (e.g. system operator or end user).

Abstract This paper investigates reactions of mercury (Hg) compounds in effluents of the wet flue gas desulfurization (FGD) process during waste water treatment. Hence, a concept for the controlled desorption and immobilization of Hg is introduced. The aim is to create a highly concentrated sink for Hg for further processing. Experiments are carried out with a continuously operated lab-scale wet FGD system and a batch-wise operated alkalization reactor for the treatment of synthetic and real waste water samples. By aeration of the liquid phase, the controlled desorption of Hg during the alkalization step of the waste water treatment process is enabled. The Hg-rich exhaust air is directed to an activated carbon fixed bed adsorber. It is demonstrated, that Hg is emitted in its elemental form (Hg0). Thus, a chemical reduction of dissolved Hg2+ compounds takes place prior to Hg0 desorption to the gas phase. Mechanisms for the reactions are proposed, identifying SO32− and OH− as electron donors. Linear dependency of Hg0 formation on SO32− and OH− concentration indicate first order dependencies of reaction kinetics. Decreasing concentration of Hg0 in the exhaust air for increasing Cl− concentration is observed. The results show exponential dependence of Hg0 desorption on temperature and stirring speed. The mass flow of desorbed Hg0 remains constant for variation in aeration flow rate. Thus, the application of low air flux is beneficial in terms of energy demand and for the purpose of creating a highly concentrated sink for Hg in the process. The concentration decrease of Hg2+ in the waste water is proportional to the savings in terms of precipitating agent consumption of further processing steps. Finally, the concept developed prevents unnoticed Hg desorption during waste water treatment and increases sustainability and plant safety.

Abstract The oil industry faces economic and environmental challenges due to its energy- and water-intensive processes. Surplus residual feedstocks and the water produced via heavy oil upgrading and processing are among the most challenging problems in the oil industry. Utilization these waste materials and a lack of efficient technologies to treat them are the main challenges causing the industry to consider them as waste materials. Existing technologies only add a small value, require high capital investment, and generate high greenhouse gas emissions. Therefore, in this study, we review and highlight the major findings regarding the oxy-cracking process, which is introduced as an alternative beyond combustion, as an environmentally friendly technique for converting these feedstocks into value-added products and also enhances the recyclability of wastewater. Through these residual feedstocks are partially oxidized in basic aqueous media at mild operational temperatures (150–230 °C) and pressures (3.4–5.2 MPa). Several operating conditions have been reported to optimize the conversion and selectivity of the products, and the results showed that the temperature and residence time have significant impacts on the yield and environmental impact. The experimental findings were validated with theoretical calculations, which provided insights on understanding the kinetic behavior based on the radical mechanism. The characterization findings revealed that the oxy-cracking could be a platform for a wide range of products such as humic acids, clean fuel, and carbon nanomaterials, and to recover valuable metals. Moreover, this process could be implemented for treatment of oil sand processes affected water and for decomposing emerging pharmaceuticals.

Photo-fermentative production of hydrogen (H2) by purple bacterium Rhodobacter sphaeroides MDC6521 from Armenian mineral springs and its regulation by external reducers and oxidizers have been investigated. Reducers such as dl-dithiothreitol (DTT) and dithionite suppress bacterial growth but enhance H2 yield of R. sphaeroides, whereas oxidizer ferricyanide inhibits both processes. The effect of DTT on DCCD-inhibited FoF1-ATPase activity of R. sphaeroides membrane vesicles has been analyzed too. DTT increases the DCCD-inhibited ATPase activity. Thus, more negative values of Eh by addition of DTT might regulate FoF1-ATPase activity. The participation of the ATPase in redox sensing under photo-fermentative H2 production is suggested. This enzyme might be a target, having a significant role in these processes of purple bacteria.

Abstract In this study, the thermodynamic behaviors, cage-specific guest distributions, structural transition, and dissociation enthalpies of sH hydrates with CO2 + N2 gas mixtures were investigated for their potential applications to hydrate-based CO2 capture and sequestration. The stability conditions of the CO2 + N2 + water systems and the CO2 + N2 + neohexane (2,2-dimethylbutane, NH) + water systems indicated that the gas mixtures in the range of flue gas compositions could form sH hydrates, thereby mitigating the pressure and temperature required for gas hydrate formation. Structure identification using powder X-ray diffraction (PXRD) revealed the coexistence of sI and sH hydrates in the CO2 (40%) + N2 (60%) + NH system and the hydrate structure transformed from sH into sI as the CO2 concentration increased. In addition, the Raman analysis clearly demonstrated that CO2 molecules were enclathrated into the cages of sH hydrates in the N2-rich systems. It was found from direct CO2 composition measurements that CO2 selectivity in the sH hydrate phase was slightly lower than that in the corresponding sI hydrate phase. Dissociation enthalpy (ΔHd) measurements using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) indicated that the ΔHd values could also provide valuable information on the structural transition of sH to sI hydrates with respect to the CO2 concentration in the feed gas. This study provides a better understanding of the thermodynamic and physicochemical background for CO2 enclathration in the sH hydrates and its significance in gas hydrate-based CO2 capture and sequestration.

Abstract Flow patterns and temperature profiles, as well as local and overall heat transfer coefficients, were measured for a horizontal, annular cavity, containing air at atmospheric pressure. The radius ratio of the bounding surfaces of the cavity was 1·5, the inner cylinder being heated. The insertion of two horizontal, radial, co-planar spacers bridging the 18·9 mm cavity along its whole length, reduced the convective rate of heat transfer from the surface of the inner cylinder whereas the same co-planar spacers, if vertical, led to an increased rate of convective heat transfer. Flow instabilities, encountered in the plain cavity, were also eliminated by the insertion of the horizontal spacers.

Abstract In this work, chemical oxygen demand (COD) and temperature stress-tests on a microbial fuel cell (MFC) were studied. Regarding the temperature stress-test, its value was cyclically modified between 20 and 40 °C with stepwise increments of 5 °C. The main result was an exponentially increase in the current intensity generated. In these tests, no hysteresis was observed, indicating that the temperature stress-test did not modify the behaviour of the MFC used in this work. To study the response of the system under COD stress conditions, the influent COD concentration was stepwise modified from the steady-state value, 100 mg COD L−1, to 3000 mg COD L−1 and later was reduced stepwise again to 100 mg COD L−1. In these test, it was observed that the higher the COD concentration, the higher the intensity generated. The electricity yield was an almost constant value of 6.7 × 10−6 A mg−1 COD removed per hour. In these tests, hysteresis was observed for the reverse scan, and a hysteresis loop was traced. To study how long the hysteresis lasts, several stress-tests were carried out during one week, and it was observed that the hysteresis was maintained for only 2 days. After that, the system recovered the initial behaviour.

The use of natural gas as fuel for solid oxide fuel cell is one of main potentials of this technology to be exploited as an efficient and profitable future power generation source. However, using direct methane (main component of natural gas) in conventional nickel-based fuel cells leads to carbon deposition problem which causes performance failure even in short period (24 h). According to thermodynamic principles, fuel addition with oxygen carriers is a good solution to prevent carbon deposition problem. Among the different options, a deep investigation is here presented for the air addition case. Through experimental activity under different operating conditions and suitable performance and structural cell characterization, the 1:5 optimal air addition to methane is determined, providing outcomes of interest for SOFC operation optimization in case of direct methane feeding. In fact, through impedance spectroscopy analysis and voltage measurements, as well as ex-post structural analysis, it is proved that in these conditions both carbon deposition and anode layers delamination are avoided, also after 100 h operation; moreover a cell stable operation at 0.6 V is guaranteed. The proposed operation mode, therefore, represents a promising solution, to be deeply investigated in the future at stack level, for SOFCs directly fed with natural gas.