Application of Ultra-Flocculation for Improving Fine Coal Concentrate Dewatering

Geophysical surveys for Civil Engineering deal with shallow targets. So the problem is not in general the depth of penetration but the need of a very high resolution. This is not an easy task as we work exactly in that “weathered layer” that deeper surveys tend to jump out at a l l , because of high frequencies attenuation, high velocity gradients and local heterogeneities. A number of approaches (high resolution shallow reflection techniques, GRM refraction, etc.) are available. Recently we had to deal with particular situations in different fields (tunnel design, landslides in layered rocks, etc.) where these techniques were not applicable. Seismic tomographic techniques were employed but it was necessary to adapt them to the difficult operational conditions. Surface-tohole measurements were performed. A program has been expressly implemented to deal with the very high vertical velocity gradients: it takes into account both curved direct waves and head waves travelling in deeper high velocity layers. The result is similar to a VSP. It was possible to put in evidence low velocity layers as thin as 0.5 m also in complex stratifications in noisy areas. Data were later confirmed with a very good accuracy. The method proved to be fast, reliable and much less costly than the crosshole tomography. Also geoelectrical surveys were tested to study the l ands l ides : the jo in t use (and inversion) of res i s t iv i ty and IP soundings helped to clear some complex situations.

High seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals, such as majorite‐garnet. Here we present Brillouin scattering measurements of the elasticity of polycrystalline Mg‐majorite (Mj100, Mg4Si4O12) and a Mj50Py50 majorite ‐ pyrope solid solution to pressures similar to those at the top of the transition zone (15.1(1) GPa and 12.8(1) GPa, respectively). The pressure derivatives of the adiabatic bulk (KS) and shear (μ) moduli of both Mj50Py50 and Mj100 are 4.2(3) and 1.4(2), respectively, and are equal to those of pyrope within the experimental uncertainties. We conclude that neither the adiabatic compression of majorite‐garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically. High velocity gradients are consistent with gradual transformations between minerals with very different elastic properties. The transformation of ∼25% or more of clinopyroxene into majorite above 520 km, and the formation of Ca silicate perovskite below 520 km could produce the observed seismic gradients.

Reported are the results of an experimental programme to investigate the influence of mud composition, pressure and temperature on the properties of filter cakes formed during static filtration. Three water-based muds were tested at pressures up to 4.2 MPa and temperatures up to 93°C. The spurt loss, cumulative fluid loss, cake thickness and porosity were measured and, using a modified static filtration equation, the cake resistance and compressibility were calculated. The results clearly illustrate the highly compressible nature of filter cakes formed from drilling muds. Also shown is the profound influence of barite and temperature on the cake properties and fluid loss. Using expressions developed in the general field of solid-liquid separation for the variation in porosity within the filter cake, the behaviour of highly compressible cakes under pressure has been illustrated.

Refraction and wide‐angle reflection velocities from the oceanic crust and the overlying sediments in the Norwegian‐Greenland Sea have been analyzed. There is a relatively rapid increase in velocity with depth in the uppermost sediments, whereas a low constant gradient is representative of the main sediment sequence. Two regions, the northeastern Greenland Sea and the oldest parts of the basins, have particularly high velocity gradients, 0.71 and 0.85 s−1 respectively. The high gradient in the northeastern Greenland Sea is associated with the shear‐rifted margin off Svalbard. Relatively high sea floor sediment sound velocities are typical of the Norwegian‐Greenland Sea. The crustal velocities fit the Houtz‐Ewing model which divides layer 2 into layers 2A, 2B and 2C. Average velocities in the Norwegian‐Greenland Sea are: 3.88(2A), 5.18(2B), 6.05(2C), 6.66(3), and 7.80(4) km/s. Layer 2A is age dependent and has not been observed on crust older than 36 m.y. The model is not representative of the uppermost crust near the active spreading axis where one has to introduce additional layers or assume continuous velocity changes with depth.

Large-scale molecular dynamics simulations are performed to study the fragmentation of metallic liquid sheets with high velocity gradient. Dynamic fragmentation of the system involves the formation of a network of fragments due to the growth and coalescence of holes, decomposition of the network into filaments, and further breakup of the filaments into spherical clusters. The final size distribution of the fragmented clusters in the large volume limit is found to obey a bilinear exponential form, which is resulted from the heterogeneous breakup of quasi-cylindrical filaments. The main factors contributing to fragmentation heterogeneity are introduced, including strain rate inhomogeneity and matter distribution nonuniformity of fragments produced during decomposition of the network structure.

Human exposure to airborne ultrafine (≪1 μm) particulate pollution may pose substantial hazards to human health, particularly in urban roadside environments where very large numbers of people are frequently exposed to vehicle-derived ultrafine particles (UFPs). For mitigation purposes, it is timely and important to quantify the deposition of traffic-derived UFPs onto leaves of selected plant species, with particularly efficient particle capture (high deposition velocity), which can be installed curbside, proximal to the emitting vehicular sources. Here, we quantify the size-resolved capture efficiency of UFPs from diesel vehicle exhaust by nine temperate-zone plant species, in wind tunnel experiments. The results show that silver birch (79% UFP removal), yew (71%), and elder (70.5%) have very high capabilities for capture of airborne UFPs. Metal concentrations and metal enrichment ratios in leaf leachates were also highest for the postexposure silver birch leaves; scanning electron microscopy showed that UFPs were concentrated along the hairs of these leaves. For all but two species, magnetic measurements demonstrated substantial increases in the concentration of magnetic particles deposited on the leaves after exposure to the exhaust particulates. Together, these new data show that leaf-deposition of UFPs is chiefly responsible for the substantial reductions in particle numbers measured downwind of the vegetation. It is critical to recognize that the deposition velocity of airborne particulate matter (PM) to leaves is species-specific and often substantially higher (∼10 to 50 times higher) than the "standard" Vd values (e.g., 0.1-0.64 cm s-1 for PM2.5) used in most modeling studies. The use of such low Vd values in models results in a major under-estimation of PM removal by roadside vegetation and thus misrepresents the efficacy of selected vegetation species in the substantial (≫20%) removal of PM. Given the potential hazard to health posed by UFPs and the removal efficiencies shown here (and by previous roadside measurements), roadside planting (maintained at or below head height) of selected species at PM "hotspots" can contribute substantially and quickly to improve in urban air quality and reductions in human exposure. These findings can contribute to the development and implementation of mitigation policies of traffic-derived PM on an international scale.

Stevioside is one of the naturally occurring sweetener, which can be widely applied in food, drinks, medicine, and daily chemicals. Membrane separation has potential application in clarification of stevioside from pretreated stevia extract by ultrafiltration. In the present study, namely 5-, 10-, 30-, and 100-kDa molecular weight cutoff membranes have been used. Quantification of membrane fouling during ultrafiltration is essential for improving the efficiency of such filtration systems. A systematic analysis was carried out to identify the prevailing mechanism of membrane fouling using a batch unstirred filtration cell. It was observed that the flux decline phenomenon was governed by cake filtration in almost all the membranes. For 100 kDa membrane, both internal pore blocking and cake filtration are equally important. Resistance in series analysis shows that the cake resistance is several orders of magnitude higher than the membrane resistance. The cake resistance is almost independent of transmembrane pressure drop, which indicates the incompressible nature of the cake. A response surface analysis was carried out to quantify the development of cake resistance with time during ultrafiltration of various membranes. Quality parameters show that the 30-kDa membrane is better suited for clarification purposes. Identification of the fouling mechanism would aid in the process of design and scaling up of such clarification setup in future.

Bench tests were conducted on ore slurry filtration using the leaf test method, varying scales, pressures, and water/solids ratios. These results were compared with analytical outcomes derived from applying the dimensionless Buckingham pi method to the general equation of slurry filtration with incompressible cakes under constant pressure. The aim was to validate the tests by corroborating experimental findings with calculated parameters for scale-up purposes. Vacuum pressure was employed to facilitate slurry dewatering, forming a cake comprising solids from the slurry. This cake’s thickness evolved over time, introducing specific resistivity that impeded filtering efficiency. Parameters such as cake resistance and filter media resistance were computed. Filtrate volume was measured over time to determine the filtration rate. These values were then adjusted using factors obtained through dimensional analysis. These factors facilitated comparisons to validate the feasibility of employing the Buckingham pi method for predicting slurry filtration results at larger scales. The results indicated lower errors when analyzing the filtrate rate over time with a solids/water ratio of 20/80%. When evaluating cake resistance, the method yielded lower errors at a ratio of 70/30%, while results for medium resistance were inconclusive. It’s important to consider the ratio and associated errors when predicting the behavior of an industrial filter based on bench test results, aiming to achieve theoretical scaled filtration rates and cake resistances. However, it’s not advisable to rely on the Buckingham pi method for scale-up purposes when evaluating medium resistance.

Kaolinite, as a mineral in fine coal, has an important influence on the flotation of coal particles. In this study, the effects of ultrafine kaolinite particles on the flotation recovery of coal particles were investigated. Flotation tests were carried out using a mixture of coal particles and different amounts of ultrafine kaolinite particles. Combined with the Stefan–Reynold theory, the effect of liquid film drainage rate between coal bubbles in a kaolinite suspension was calculated. The yield of flotation clean coal increases quickly with the increasing content of ultrafine kaolinite particles. The ultrafine kaolinite particles can reduce the surface tension of the suspension, weaken the bubble coalescence, and stabilize the structure of the froth layer. In addition, the ultrafine kaolinite particles increase the apparent viscosity of the flotation pulp slightly. It is concluded that the role of ultrafine kaolinite particles on the positive effect of froth properties conceals the negative effect on the liquid film drainage rate between coal particles and bubbles caused by the kaolinite particles, which ultimately leads to an increasing yield of clean coal with an increasing content of kaolinite particles. This study is important for understanding the influence of ultrafine kaolinite on coal particle flotation.

Doppler-derived blood flow velocity and limb blood pressure measurements were used to characterize the hemodynamics of 128 in situ saphenous vein arterial bypasses. The magnitude and configuration of the graft velocity waveform was the best predictor of clinical outcome. Successful bypasses had antegrade flow throughout the pulse cycle and a blood flow velocity above 40 cm/s. A low graft blood flow velocity (less than 40 cm/s) was associated with technical error or early graft failure due to poor runoff. The return of normal limb blood pressure correlated with a technically satisfactory bypass but was measured in only 50% of limbs on the first day after surgery. In 28 bypasses with high blood flow velocity (mean +/- SD) in systole (102 +/- 20 cm/s) and diastole (35 +/- 11 cm/s), postoperative limb blood pressure was initially low (mean ankle-brachial pressure index = 0.68) due to restriction of blood flow through small-diameter (less than 4-mm) venous conduits. As revascularization hyperemia abated, diastolic blood flow velocity decreased and limb blood pressure normalized. Despite the high blood flow velocity and pressure gradient associated with flow-restrictive venous conduits, limb ischemic symptoms resolved, and graft patency was not decreased. An understanding of graft and limb hemodynamics after in situ bypass grafting is critical when noninvasive diagnostic techniques are used to document technical adequacy and for postoperative surveillance.

Advanced approach to modeling of pulverized coal boilers for SNCR process optimization - review and recommendations

Effect of gas mass flux on cryogenic liquid met breakup

Preparation of gas sensitive film by deposition of ultrafine tin dioxide particles

Ultrasonication-assisted fouling control during ceramic membrane filtration of primary wastewater under gravity-driven and constant flux conditions

The laser Doppler velocity profile sensor (LDV-PS) system offers the possibility to measure flow velocities with high spatial resolution and is therefore a promising method for the investigation of flows with high velocity gradients. The present experimental study revolves around the interplay between a broad range of chosen LDV-PS acquisition parameters, the dynamic velocity range within the observed measurement volume, and the accuracy of the velocity and position estimation from an application perspective. In the chosen set-up, thin wires of different diameters rotate at varying velocity levels and are captured instead of tracer particles by the applied system. It is observed that constant sample rate and number for the Fast Fourier Transform (FFT) evaluation of the detected burst signal allow straightforward measurements of unknown velocity profiles, but imply a velocity-dependent spatial measurement uncertainty. In contrast, velocity-adjusted acquisition settings allow to acquire particle bursts with equal signal resolution and length effecting a constant measurement accuracy at all velocity levels when adjusted appropriately. The position standard deviation is furthermore observed to increase with the wire diameter.Hence, the size of the scattering object should be chosen appropriately small during calibration and measurement. The gained knowledge offers the possibility to adapt the evaluation parameters more specifically to a given measurement problem.Consequently, measurements can be conducted in flows with small velocities with a high spacial resolution, when the FFT parameters and processing routines are adjusted accordingly, small particles are chosen and vibrations in the set-up are avoided.