Solid Flux Research Articles

Solids backmixing and entrainment in the splash zone of large-scale fluidized bed boilers

This work studies the fluid dynamics of the solids in the splash zone of fluidized bed furnaces, with focus set on solids back-mixing and solids entrainment in order to enhance the understanding and prediction of the solids flow in the bottom region of the furnace. Experimental results show the establishment of a splash zone also for runs in absence of a dense bottom bed. A simple model assuming ballistic trajectories of the ejected solids is shown to satisfactorily estimate the solids back-mixing rate. The flux of non-backmixed solids, which are entrained from the bottom region, is found to be unaffected by the bottom wall configuration (tapered/vertical) for a given gas flow. Finally, an empirical expression is proposed for the solids entrainment from the bottom region which covers wide operational and unit size ranges.

Shallow Calcium Carbonate Cycling in the North Pacific Ocean

AbstractThe cycling of biologically produced calcium carbonate (CaCO3) in the ocean is a fundamental component of the global carbon cycle. Here, we present experimental determinations of in situ coccolith and foraminiferal calcite dissolution rates. We combine these rates with solid phase fluxes, dissolved tracers, and historical data to constrain the alkalinity cycle in the shallow North Pacific Ocean. The in situ dissolution rates of coccolithophores demonstrate a nonlinear dependence on saturation state. Dissolution rates of all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods) are too slow to explain the patterns of both CaCO3 sinking flux and alkalinity regeneration in the North Pacific. Using a combination of dissolved and solid‐phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO3 dissolution with a combination of ambient saturation state and oxygen consumption simultaneously explains solid‐phase CaCO3 flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. We do not need to invoke the presence of carbonate phases with higher solubilities. Instead, biomineralization and metabolic processes intimately associate the acid (CO2) and the base (CaCO3) in the same particles, driving the coupled shallow remineralization of organic carbon and CaCO3. The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration within degrading particle aggregates. The coupling of these cycles acts as a major filter on the export of both organic and inorganic carbon to the deep ocean.

Effect of gelling agent and penetration enhancer on the release rate of ibuprofen-PEG 6000 solid dispersion from gel preparations

Introduction: Ibuprofen is a non-steriodal anti-inflammatory drug which shows low bioavailability. For gel preparations it is important to increase the release rate of ibuprofen by using solid dispersion systems. Objective: To obtain the optimum release rate of ibuprofen-PEG 6000 solid dispersion from gel, by optimising the gelling agent and the penetrating enhancers. Method: Determination of gelling agent was carried out by comparing the ibuprofen release flux. The gel formulation with the best release flux will be used in the determination of penetrating enhancer to obtain the optimum release flux, by using a two-factor factorial design. Result: HPMC showed the highest release flux (339.5 g/cm2min). The results showed an increase in the release flux (489.4 g/cm2min) in the optimum formula with 39.9% propylene glycol and 3.3% isopropyl myristate. Conclusion: The increase in the ibuprofen solid dispersion release flux has been carried out using HPMC, and propylene glycol-isopropyl myristate as a penetrating enhancer.

Nitrogen, Phosphorus and granulometric characterization in nearshore sediments of Guanabara Bay: tentative application of a solid phase diagenetic model

Total nitrogen, phosphorus and organic carbon were measured in sediment profiles, and correlated to granulometric distribution in different depth levels o f nearshore sediments in Guanabara Bay (Brazil). This paper assesses the pool o f these elements and the influence of sedimentary dynamics on it, in five different depositional environments. Textural parameters exhibit vertical changes in three stations. This is an evidence of changes in depositional processes, reflected by anomalous nutrient profiles. However, there was no correlation with granulometry, showing rather an erratic behaviour. Surficial sediment TN and TP ranged from 0.56 to 6.00 mg. g’1 and0.15to 1.62mg.g-1, respectively. Tentative application of solid phase diagenetic model estimates fluxes of about 1.1 - 24.7 g P . m*2 . y'1 and 2.2 - 67.2 g N . m‘2 . y'1. These values correspond to 4 - 82% o f phosphorus and 2 - 45% of nitrogen annual average phytoplanktonic demand.

Nitrogen, Phosphorus and granulometric characterization in nearshore sediments of Guanabara Bay: tentative application of a solid phase diagenetic model

Total nitrogen, phosphorus and organic carbon were measured in sediment profiles, and correlated to granulometric distribution in different depth levels of nearshore sediments in Guanabara Bay (Brazil). This paper assesses the pool of these elements and the influence of sedimentary dynamics on it, in five different depositional environments. Textural parameters exhibit vertical changes in three stations. This is an evidence of changes in depositional processes, reflected by anomalous nutrient profiles. However, there was no correlation with granulometry, showing rather an erratic behaviour. Superficial sediment TN and TP ranged from 0.56 to 6.00 m g. g'1 and 0.15 to 1.62 m g. g'1, respectively. Tentative application of solid phase diagenetic model estimates fluxes of about 1.1- 24.7 g P . m’2 . y’1 and 2.2 - 67.2 g N . m’2 . y’l. These values correspond to 4 - 82% of phosphorus and 2 - 45% of nitrogen annual average phytoplanktonic demand.

Ayurvedic hospital wastewater degradation using electrochemical treatment.

The goal of this research was to remove COD, oil and grease (O&G) and color from raw ayurvedic hospital wastewater (AHWW) using a novel electrochemical coagulation (ECC) process. Cell voltage was initially optimized using iron electrodes in bipolar mode for both raw AHWW and ayurvedic hospital therapy room wastewater (AH-TRWW) for a pre-optimized electrolysis time (ET) of 60 min. O&G, COD and color removals for AHWW at 8 V optimized cell voltage were 96, 61 and 96% respectively. Different electrode materials, copper, aluminum, graphite, were used to evaluate relative performances at 8 V. Iron electrodes showed maximum pollutant removal from raw AHWW. The sludge obtained after the ECC process showed good settling and filterability properties compared to graphite and aluminum electrodes. The low SVI value of 146 mL/g was obtained exercising absolute control on sludge volume. Solids flux values showed assurances of compact settling tank design with least spatial footprint. EDX analysis for ECC sludge of AHWW using iron showed gross elements 40.19% C, 48.63% O and 7.92% Fe redefining the fate of sludge. The XRD pattern of the ECC sludge showed an amorphous nature. Post-ECC filtration effluent showed clear water reclamation of 80-82%, proving the effectiveness of the novel ECC treatment process.

Synthesis, crystal structure and magnetic properties of KLnSe2 (Ln = La, Ce, Pr, Nd) structures: A family of 2D triangular lattice frustrated magnets

We report the detail synthesis, single crystal structure characterization and magnetic properties of KLnSe2 series obtained via solid state molten flux growth method. The crystal structures were characterized using single crystal x-ray diffraction. The KLnSe2 (Ln ​= ​La, Ce, Pr and Nd) series crystallizes in the trigonal crystal system with the space group of R-3m (No. 166). The overall structure contains two-dimensional (2D) layers made from edged shared LnSe6-octahedra. Ln3+ ions form a perfect triangular magnetic lattice which propagates along ab-plane. These triangular lattices are separated by the K+ ions. The magnetic properties confirm that, Ce, Pr and Nd do not show any long-range ordering down to 0.4 ​K indicating frustrated magnetism in the KLnSe2 series.

A dynamic cluster structure-dependent drag coefficient model applied to the riser in high density circulating fluidized bed

A dynamic cluster structure dependent (DCSD) drag model based on energy dissipation minimization using the two-fluid model (TFM) and the kinetic theory of granular flow (KTGF) is applied to the riser in high density circulating fluidized bed (HDCFB). The characteristics of gas and solid are predicted by means of the DCSD drag model with the convective and local accelerations. The law of granular collision energy dissipation and drag energy dissipation are compared and the influence of granular collision energy dissipation to agglomerate structure is researched. The study shows that granular collision energy dissipation has great influence on heterogeneous structure of riser. Simulated solid volume fraction, axial pressure drop and solid mass flux are compared to experimental measurements, numerical analysis suggests that the temporal-spatial heterogeneous structure characteristics and particle collision affect the flow of the riser in the literature.

Suspended sediment transport estimation in Negro River (Amazon Basin) using MSI/Sentinel-2 data

The dynamics of suspended sediment production and transport in large rivers are essential geomorphologicalprocesses that can influence biodiversity. The aim of this work was to analyze the spatio-temporal variation of suspendedsediment transport in the lower Negro River using Sentinel-2 images. The suspended sediment concentration (SSC) wasestimated from the reflectance of band 4 of the MSI sensor onboard the Sentinel-2A and Sentinel-2B. The results indicate thatthe hydrological regime controls the temporal variability of SSC, being higher in the low water period and lower duringflooding, with a mean concentration of 5.28 mg L-1 for the period 2015–2019. Analysis of the spatial variation of SSC inSentinel-2 images indicated a zone of active sediment deposition located downstream of the islands of the AnavilhanasArchipelago. Geology, forest cover, and hydrological variability are the main factors controlling the low sediment yield of thebasin, with an estimated suspended solid flux of 5.76×106 ton∙year-1 and a specific yield of 8 ton∙km-2∙year-1. Despite the lowerquantity of images between February and April, due to high cloud cover, this study showed that Sentinel-2 images could beused to monitor the temporal and spatial dynamics of suspended sediment transport in Amazonian blackwater rivers.

Long Term Operation Performance and Membrane Fouling Mechanisms of Anaerobic Membrane Bioreactor Treating Waste Activated Sludge at High Solid Concentration and High Flux

Long Term Operation Performance and Membrane Fouling Mechanisms of Anaerobic Membrane Bioreactor Treating Waste Activated Sludge at High Solid Concentration and High Flux

Investigation of the Hydrodynamics of Packed-Fluidized Beds: Characterization of Solids Flux

Investigation of the Hydrodynamics of Packed-Fluidized Beds: Characterization of Solids Flux

Potential Impact of Climate Change on the Sediment Fluxes of a Watershed in West Africa: Cas of the Aghien Lagoon, Côte d’Ivoire

The semi-distributed SWAT (Soil and Water Assessment Tools) model was used in this study to model the sediment yield in the watershed of the Aghien lagoon with an area of 365 km2, located in the north of the district of Abidjan (South-East from C?te d’Ivoire). A sensitivity and uncertainty analysis, as well as calibration of the SWAT model, was conducted using the Sequential Uncertainty Adjustment Procedure (SUFI-2) which is one of the programs interfaced with SWAT in the SWAT-Cup package (SWAT-Calibration-Uncertainty Programs). Five parameters of the SWAT model were found to be more sensitive to sediment fluxes. These have been modified (calibration) sparingly in order to improve the reproduction of observed sediments data. Two measures were used to assess the uncertainty analysis of the model: P-factor and R-factor. The R2 and Nash-Sutcliffe (NS) coefficients of determination were used to assess the quality of the calibration. The P-factor obtained is 0.58 and the R-factor is 2.28. The NS and R2 coefficients in calibration over the period from June 2014 to January 2015 are 0.51 and 0.86 respectively. These values indicate correct consideration of uncertainties by the model and satisfactory calibration of the SWAT model for solid fluxes. Then, the model was used to simulate the sediment fluxes at the horizons 2040 (2035-2056), 2060 (2057-2078) and 2080 (2079-2100) in order to assess the impact of climate change on sediments in the watershed of the Aghien lagoon. The results indicate that sediment fluxes could increase in the future under the RCP 4.5 and RCP 8.5 scenarios. With RCP 4.5, sediment fluxes would increase on average by 14.42%. They could increase by 17.95% on average under RCP 8.5.

Study and Application of Full Tailing Deep Concentration and Rapid Dewatering Technology

The problem of unstable full tailing sand concentration and dewatering in some mine filling systems has led to substandard bottom flow concentration of tailing sand concentration equipment, wide fluctuation ranges of filling concentration, substandard return water concentration at filling stations, and high flocculant addition cost. Through flocculation and sedimentation tests, the effect of the flocculant and sedimentation law and the effect of slurry concentration on sedimentation rate were studied, and the field application of the flocculant addition point model was verified. The results showed that (1) when the dose of the flocculant was added, the F1‐type polyacrylamide as the flocculant made the best settling effect of the whole tailing sand in the test, as judged by comparing the falling rate of the clarified layer and the clarification degree of the supernatant. (2) With the increasing flocculant concentration, the settling speed of tailing sand gradually becomes slower; the range of the best settling concentration was 8%–18% of tailing sand concentration; and the concentration of tailing sand corresponding to the maximum solid flux was 10%–14%. (3) Relying on the site conditions of a domestic copper mine, the feed concentration was diluted from 20%–25% to 10%–12%, and the overflow water clarification test was less than 300 ppm, which verified the flocculant test and the correctness of the flocculant addition point model. The type and dosage of the flocculant as well as the feed concentration of the tailing slurry all have an effect on the flocculation and settling effect. The results of the study can provide some implications for the efficient flocculation and settlement of tailings in other mines.

Study on particle cluster behavior in the multistage circulating fluidized bed

Particle clusters play a significant role in gas-solid flow systems. Cluster motions are experimentally studied in a multistage circulating fluidized bed. Cluster characteristics including spatial distribution, breakup process, and size are discussed. Dynamic parameters (frequency, duration, and time fraction) are also obtained to characterize cluster behavior by employing the digital image analysis method. The results show that cluster motions gradually weaken along radial and axial directions in the enlarged section. Cluster breakup tends to increase in the enlarged section due to gas turbulence and cluster collision. Cluster frequency, duration, and time fraction decrease with the increasing gas velocity but increase with the increasing solid mass flux. Compared with the conventional riser, cluster size reduces in the enlarged section. Furthermore, the analysis results from cluster dynamic parameters indicate that cluster motions are restricted under the low solid loading.

Lowering Synthesis Temperature of BaTiO3-Bi(Zn0.5Zr0.5)O3 Ceramics by Salt Flux Assistance and Dielectric Properties Investigations

Phase formations and dielectric properties of lead free barium titanate bismuth zinc zirconate, BaTiO3-Bi(Zn0.5Zr0.5)O3 (BT-BZZ), were comparatively investigated between two different synthesis routes, solid state reaction and salt flux assistance methods. The perovskite (1-x)BT-(x)BZZ ceramics, where x = 0.02, 0.05 and 0.10, were synthesized by using reagent grade oxides and the NaCl salt was used as a surface active agent to lower the calcination temperature. Phase formations were examined by X-ray diffraction technique (XRD). It was found that the solid solutions of (1-x)BT-(x)BZZ can be obtained with lower temperature at least 200 °C via salt flux assistance method. The NaCl salt addition could result in single phase of perovskite structure at every compositions with the calcination temperature as low as 800 °C. Dielectric measurements revealed that the Curie temperature (Tc) shifted to lower temperature with increase of BZZ concentration. Moreover, the dielectric behavior transformed to diffuse phase transition when x = 0.1. The samples prepared via salt flux assistance method exhibited smaller grain size which were revealed by scanning electron microscope. In addition, P-E hysteresis measurements illustrated the higher high E-field dielectric constant with the narrower P-E loop when the salt flux was applied.

CFD simulation of a cold flow model of inter-connected three fluidized reactors applied to chemical looping hydrogen production

The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen (H2) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

Mesoscale analysis on clusters in conjunction with fast fluidized bed modeling

As a subsequent paper for “type-A-choking-oriented unified model for fast fluidization dynamics”, the present work aims to provide more systematic mesoscale analyses on clusters. Starting from theoretical derivations on idealized flow patterns of gas and solids around a single falling cluster; the momentum consumption due to particle circulation in clouds and the modification of flows by the constraint of driving force available in the bed were addressed. Complete compensation of the pressure-drop driven percolated gas in clusters by the reversely-penetrating particles was used for the ultimate closure of the model. An important finding of the present work, different from most empirical correlations, but verified by Wei and Zhu's latest experimental data and others, is that the cluster diameter does not vary monotonically with the mean solids holdup of the bed, but has a maximum value in between. Demonstrative calculations show that it is easy for Group A particles to enter the flow regime of high-density fast-fluidization as the circulating solids flux increases continuously, while fast fluidization for Group B particles tends to be stopped at Type C choking in advance. Compared with Group A particles, the clusters for Group B particles are less dense, but the penetration velocities of particles are higher, resulting in much larger dimensionless diameters of clusters. Finally, issues of pseudo-2D fast-bed modeling were discussed, and modeling of fast-beds with uneven flow fields was outlook briefly.

Role of liquid and solid particles in solid-liquid mixed fluxes on sulfur removal from molten iron under centrifugal stirring by an impeller

Process for removal of S from molten iron alloy is successfully established process in these days, e.g. Kanbara Reactor (KR) process. However, its operating mechanism needs to be understood in a more clear manner. A series of laboratory-scale experiments using lime–fluorspar flux, which is a solid particle-liquid mixture at the reaction temperature, were carried out in order to find out effects of composition, total mass, the liquid fraction (fL), order of injection of the flux, and centrifugal stirring on the reaction performance. Theoretical calculations for the phase diagram of the flux system, flux-molten iron reaction equilibria, and the reaction rate considering flux detachment/aggregation in case of the centrifugal stirring were carried out. It was concluded that (1) major S-absorbing phase should be the liquid phase in the flux, (2) increasing the fL enhances the reaction performance when the molten iron was desulfurized without the stirring, (3) the centrifugal mechanical stirring enhances the reaction rate, but it was not effective when fL is high, (4) the centrifugal mechanical stirring for solid particle-liquid mixed flux significantly affects the interfacial reaction area: enlarging the area by the detachment of the flux and contracting the area by aggregation. The fL, therefore, influences not only the volume of the S-absorbing part of the flux, but also the degree of detachment/aggregation, which depends on the physico-chemical properties of the flux. Optimum fL may be determined by the physico-chemical properties and degree of the stirring. An index for assessing DeS performance was used to reveal the role of fL and the mechanical stirring. It shows that the mechanical stirring could enhance the DeS performance without the unnecessary increase of liquid fraction of the flux, by adding fluorspar in the present case.

Kinetic theory of polydisperse gas–solid flow: Navier–Stokes transport coefficients

The particulate phase stress and solid–solid drag force in the multifluid modeling of polydisperse gas–solid flows are usually closed using kinetic theory. This research aims to establish the hydrodynamic equations and constitutive relations of the multifluid model for polydisperse systems via species kinetic theory, in which the non-equipartition of energy and interphase slip velocity between different species are considered. Whereas previous studies have used approximations, such as Taylor series expansions, to simplify the calculation of collision integrals, the present study, for the first time, solves the collision integrals analytically without any approximations to obtain accurate constitutive relations. Explicit expressions for the constitutive laws are obtained, including the particle stress tensor, solid–solid drag force, heat flux, and energy dissipation rate up to the Navier–Stokes order. The present study offers more complete and mathematically rigorous constitutive laws for the multifluid modeling of polydisperse gas–solid flows.

Numerical and experimental investigation on air distributor design of fluidized bed reactor of sawdust pyrolysis

An improved biomass conversion in a lab-scale fluidized bed reactor (FBR) is achieved by optimizing the air distributor orifice size and number. Two approaches for introducing air were numerically and experimentally examined. These included perforated plate and downward orifice sparger. 3 mm and 5 mm orifice diameters, and 7, 9 and 13 holes were simulated at flow velocities of 2, 4, 6, and 8 times the minimum fluidization velocity, Umf. The simulation results revealed that increasing the orifice number has a positive effect on gas holdup, particularly for the perforated plate, which showed a uniform distribution of bubbles. The sparger configuration produced larger bubbles sizes, which could lead to better recirculation of solid flux, while stagnant particle zones were observed at the lower section of both distributors.A pyrolysis unit is also inserted at the top of freeboard of the FBR. For perforated plate with 6Umf, the pyrolysis process achieved thermal and cold gas efficiencies of 82.91% and 52.03%, respectively, while combustible gases with 41.6%mol CO, 8.7%mol CH 4 and 2.17%mol HC, were obtained. For sparger pipe and 6U mf _sp, 35.33 ppm NOx and 111 ppm SO 2 were measured in flue gas from combustion process at bed region.