Removal of Hydrogen Sulfide (H2S) Using MOFs: A Review of the Latest Developments

The removal of hydrogen sulfide (H2S) from gas streams with varying overall pressure and H2S concentrations is a long-standing challenge faced by the oil and gas industries. The present work focuses on H2S capture using metal–organic frameworks (MOFs), in an effort to shed light on their potential as adsorbents in the field of gas storage and separation. MOFs hold great promise as they make possible the design of structures from organic and inorganic units, but also, they have provided an answer to a long-time challenging issue, i.e., how to design extended structures of materials. Moreover, the functionalization of the MOF’s surface can result in increased H2S uptake. For example, the insertion of 1% of a fluorinated linker in MIL-101(Cr)-4F(1%) allows for enhanced H2S capture. Although noticeable efforts have been made in studying the adsorption capacity of H2S using MOFs, there is a clear need for gaining a deeper understanding in terms of their thermal conductivities and specific heats in order to design more stable adsorption beds, experiencing high exothermicity. Simply put, the exothermic nature of adsorption means that sharp rises in temperature can negatively affect the bed stability in the absence of sufficient heat transfer. The work presented herein provides a detailed discussion by thoroughly combining the existing literature on new developments in MOFs for H2S removal, and tries to provide insight into new areas for further research.

COMPARATIVE HYDRO-MORPHOLOGICAL ANALYSIS OF THE ISLANDS OF DIFFERENTLY BRANCHED UPPER OB AND MIDDLE LENA RIVER CHANNELS

This article is devoted to the formation conditions and morphometric features of the river islands. Also it considers the rate of branching of the Upper Ob and Middle Lena river channels. They are the largest rivers, but the Middle Lena River is bigger than the Upper Ob River by 6.15 times of total runoff and 2.5 times of width. However, both of them have unstable or weakly stable channels, characterized by parallel-sleeve, alternating, one-sided and single branchings, formed by numerous islands. Their comparison makes it possible to establish the dependence of the conditions of islands formation, their parameters (length - L , width - B , shape - L / B ), types and number on the indicators of stability, total runoff, branching types and location in the channel (active or peripheral part). These correlations based on hydro-morphological analysis show that the shape of islands L / B and the branching rate of the channel - n / x depend on the degree of stability. It is a common feature of all branching types and stages of island evolution (elementary, small, large islands and island massifs). Uniform dependencies of island parameters on river bed stability for both rivers, despite their large-scale distortions, were obtained by taking into account the connection of channel width ( b ) with its runoff ( Q ) by introducing a correction factor of 2.5 for the river size. Also the formation conditions of elongated islands ( L / B > 5), were determined. Their shape does not correspond to the optimal ratio L / B = 3...4. The revealed patterns give an opportunity to clarify the previously proposed classification of the islands.

Case Study of Transient Dynamics in a Bypass Reach

The operating conditions of Nordic hydropower plants are expected to change in the coming years to work more in conjunction with intermittent power production, causing more frequent hydropeaking events. Hydropeaking has been shown to be detrimental to wildlife in the river reaches downstream of hydropower plants. In this work, we investigate how different possible future hydropeaking scenarios affect the water surface elevation dynamics in a bypass reach in the Ume River in northern Sweden. The river dynamics has been modeled using the open-source solver Delft3D. The numerical model was validated and calibrated with water-surface-elevation measurements. A hysteresis effect on the water surface elevation, varying with the downstream distance from the spillways, was seen in both the simulated and the measured data. Increasing the hydropeaking rate is shown to dampen the variation in water surface elevation and wetted area in the most downstream parts of the reach, which could have positive effects on habitat and bed stability compared to slower rates in that region.

X-ray computed tomography reveals that grain protrusion controls critical shear stress for entrainment of fluvial gravels

The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobility. We suggest that grain protrusion is a suitable proxy for assessing gravel-bed stability.

Quantifying the restoration success of wood introductions to increase coho salmon winter habitat

Large wood (LW) addition is often part of fish habitat restoration projects. However, there is limited information about the spatial–temporal variability in hydraulic changes after LW additions. We investigated reach-scale hydraulic changes triggered after the addition of LW that are relevant to juvenile coho salmon survival. We used Nays2DH, an unsteady two-dimensional flow model, to quantify the patterns and magnitudes of changes of stream velocity and shear stress in three alluvial gravel reaches. The study sites are located in low-gradient reaches draining 5 to 16 km2 in the Oregon Coast Range. Survivable habitat was characterized in terms of critical swim speed for juvenile coho and bed stability considering the critical shear stress required to mobilize the median bed particle size. Model predictions indicated that survivable habitat during bankfull conditions, measured as the area with velocity below the critical swim speed for juvenile coho, increased by 95 %–113 % after the LW restoration. Bed stability also increased between 86 % and 128 % considering the shear stress required to mobilize the median bed particle size. Model predictions indicated more habitat created in the larger site; however, considering that wood would move more frequently in this site there appears to be a trade-off between the timing and the resilience of restoration benefits. Overall, this study quantifies how the addition of LW potentially changes stream hydraulics to provide a net benefit to juvenile salmonid habitat. Our findings are applicable to stream restoration efforts throughout the Pacific Northwest.