Recirculation Of Particles Research Articles

Effects from Time Dependence of Ice Nucleus Activity for Contrasting Cloud Types

Abstract The role of time-dependent freezing of ice nucleating particles (INPs) is evaluated with the “Aerosol–Cloud” (AC) model in 1) deep convection observed over Oklahoma during the Midlatitude Continental Convective Cloud Experiment (MC3E), 2) orographic clouds observed over North California during the Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX), and 3) supercooled, stratiform clouds over the United Kingdom, observed during the Aerosol Properties, Processes And Influences on the Earth’s climate (APPRAISE) campaign. AC uses the dynamical core of the WRF Model and has hybrid bin–bulk microphysics and a 3D mesoscale domain. AC is validated against coincident aircraft, ground-based, and satellite observations for all three cases. Filtered concentrations of ice (>0.1–0.2 mm) agree with those observed at all sampled levels. AC predicts the INP activity of various types of aerosol particles with an empirical parameterization (EP), which follows a singular approach (no time dependence). Here, the EP is modified to represent time-dependent INP activity by a purely empirical approach, using our published laboratory observations of time-dependent INP activity. In all simulated clouds, the inclusion of time dependence increases the predicted INP activity of mineral dust particles by 0.5–1 order of magnitude. However, there is little impact on the cloud glaciation because the total ice is mostly (80%–90%) from secondary ice production (SIP) at levels warmer than about −36°C. The Hallett–Mossop process and fragmentation in ice–ice collisions together initiate about 70% of the total ice, whereas fragmentation during both raindrop freezing and sublimation contributes <10%. Overall, total ice concentrations and SIP are unaffected by time-dependent INP activity. In the simulated APPRAISE case, the main causes of persistence of long-lived clouds and precipitation are predicted to be SIP in weak embedded convection and reactivation following recirculation of dust particles in supercooled layer cloud.

CFD modelling of infection control in indoor environments: A focus on room-level air recirculation systems

The emergence of viral variants has driven a continuous pandemic with a higher possibility of airborne transmission and a larger scale of infective cases, posing greater demands on indoor risk control. However, the role of room-level air recirculation systems (RRSs) in infection control remains unclear due to insufficient detailed research. There are also fewer analyses of the filtering rating of recirculation filters from the perspective of multi-scale particle size. Thus, a simulation procedure to assess the performance of RRSs on infection control that accounts the transient recirculation of real virus-laden particles in multi-scale sizes was proposed, and focusing on recirculation filter strategies to balance the risk limitation and energy cost. A poorly ventilated winter classroom was selected as a typical environment equipped with RRSs to operate this procedure. Different RRS strategies (i.e., wall-mounted air conditioners (WMAC), floor-standing air conditioners (FSAC) and 4-way cassette air conditioners (WCAC)) were compared. The results show the important contribution of recirculated particles to accumulating the overall infection risk of susceptible occupants towards a high basic reproduction number (Ro > 1). Then, there is a strong correlation of the spatial distributions between high-risk zones and large vortexes at the breathing height of susceptible occupants. Considering rating suitability and filtration effectiveness, the optimization of recirculation filters on energy and cost can be suggested with comparable benefits of infection control.

Controlling bead and cell mobility in a recirculating hanging-drop network.

Integrating flowing cells, such as immune cells or circulating tumour cells, within a microphysiological system is crucial for body-on-a-chip applications. However, ensuring unimpeded recirculation of cells is a significant challenge. Closed microfluidic devices have a no-slip boundary condition along channel walls and a defined chip geometry (laminar flow) that hinders the ability to freely control cell flow. Open microfluidic devices, where the bottom device boundary is an air-liquid interface (ALI), e.g., hanging drop networks (HDNs), offer the advantage of an easily-actuatable fluid-phase geometry, where cells can either flow or stagnate. In this paper, we optimized a hanging-drop-integrated pneumatic-pump system for closed-loop recirculation of particles (i.e., beads or cells). Experiments with both beads and cells in cell culture medium initially resulted in particle stagnation, which was suggestive of a pseudo-no-slip boundary condition at the ALI. Transmission electron microscopy and dynamic light scattering measurements of the ALI suggested that aggregation of submicron-scale cell-culture-medium components is the cause of the pseudo-no-slip boundary condition. We used the finite element method to study the forces on particles at the ALI and to optimize HDN design (drop aperture) and operation (drop height) parameters. Based on this analysis, we report a phase diagram delineating the conditions for free flow or stagnation of particles at the ALI of hanging drops. Using our experimental setup with 3.5 mm drop apertures, we conducted particle flow experiments while actuating drop heights. We confirmed the ability to control the flow or stagnation of particles by actuating the height of hanging drops: a drop height over 300 μm led to particle stagnation and a drop height under 300 μm allowed for particle flow. This particle-flow control, combined with the ease of integrating scaffold-free organ models (microtissues or organoids) in HDNs, constitutes the basis for an experimental setup enabling the control of the residence time of single cells around 3D organ models.

Experimental Investigation of the Effect of EDM Debris Particles Mixed into the Dielectric Fluid on Tool Feed Rate in Drilling-EDM

In this paper the potential of the recirculation of the EDM debris particles of the workpiece material into the dielectric fluid to increase the tool feed rate vf in drilling Electrical Discharge Machining (drilling-EDM) is experimentally investigated. Two-Channel electrodes made of copper (Cu) and brass (CuZn) in the range from 1.0 mm to 2.5 mm were used. The effect of the EDM debris particles in the dielectric fluid was investigated at a discharge current ie of 25 A, a discharge duration te of 50 μs and a duty cycle of 80 % by comparing the EDM pulse characteristics and the feed rate vf of the EDM process with and without debris particles added to the dielectric fluid (particle concentrations C1 = 2.5 g/l and C0 = 0 g/l, respectively). By the recirculation of EDM debris particles the feed rate could be increased up to 36 % depending on the machining conditions. Furthermore, it was observed that the increase in the feed rate is due to the increase of the percentage of discharge pulses and the decrease of short-circuit pulses as well as a more stable machining process.

A 3D numerical study to evaluate optimum collector inclination angle of Manzanares solar updraft tower power plant

In this paper, a three-dimensional turbulent study was carried out on Manzanares (Spain) plant to study the effects of collector inclination angle (θ). Different ranges of θ (30–0°) with more than 15 models were considered for the analysis. An optimized θ has been proposed based on the estimated parameters such as air velocity, pressure drop, absorber and air temperatures, power developed, collector efficiency, and overall efficiency (ηcoll and ηo). At θ = 6°, an increment of 9.16% in theoretical power (Pth) and a 10.68% increase in air velocity were observed at the chimney base (CB) compared to the horizontal collector plant. Any further increase in θ (greater than 7°) resulted in recirculation of air particles within the collector canopy, leading to obstruction of flow. Any value of θ lesser than 6° resulted in a drop in the major outputs such as Pth, ηcoll, and ηo. Eventually, θ = 6° has been proposed as optimized inclination. The dynamic pressure difference was maximum at a chimney height of 2.5 m from CB; therefore, this was the preferred location for turbine fitment. The results were compared with the experimental data of the Manzanares plant, and a very favorable agreement was noticed.

Experimental and numerical investigation on thermal performance of a quartz tube solid particle solar receiver

The thermal performance of a quartz tube solid particle solar receiver (SPSR) with the gravity driven packed particles moving down in a semi-annular particle flow channel has been experimentally and numerically investigated, and the particle flow channel in the quartz tube was shaped by a ceramic fiber insert. The SPSR was heated by a solar simulator with 7 Xenon lamps at 130A electric current which generated a mean irradiant flux of 276 kW/m2 on the 0.26 m irradiated length, grey ceramsite sand with the solar weighted absorptivity of 72.34% was used in the study. The experimental results with a 6 mm particle layer thickness indicated the particle temperature increase of 164 K and the thermal efficiency of 50.25%. A thinner particle layer thickness was shown to improve the thermal performance of the SPSR as verified both in the experiments and simulations. Although the particle temperature increase in a single pass was not high enough in the experiments, compared with other types of SPSR, this design obtained an advantageous particle temperature increase in per unit irradiation length. Moreover, the particle temperature increase in a single pass can be promoted by a longer irradiated length, and therefore the requirement for continuous recirculation of the solid particles will be decreased which can greatly reduce the required parasitic power. Besides, according to the numerical model, the thermal efficiency can be further improved by various means such as improving the solar weighted absorptivity of the solid particles, reducing the particle layer thickness, increasing particle mass flow rate and so on. A sensitive analysis illustrated that the mean particle diameter had the minimal impact on the thermal performance among the various influencing factors, but a value of greater than 700 μm was recommended based on the simulation results.

Erratum

n the journal Bulletin of the Russian State Medical University (July – August 2018/04, p. 25–31), mistakes were made in the article: https://vestnikrgmu.ru/archive/2018/4/3/abstract?lang=en Akmalov AE, Kotkovskii GE, Stolyarov SV, Verdiev BI, Ovchinnikov RS, Pochtovyy AA, et al. High-performance aerosol sampler with liquid phase recirculation and pre-concentration of particles. Bulletin of RSMU. 2018; (4): 25–31. DOI: 10.24075/brsmu.2018.049 The editors ask for the following changes: Printed by: p. 25, "Funding" This work was supported by the Federal Target Program The National System for Chemical and Biological Security of the Russian Federation (2015-2020), the state contract No. K-27-НИР/148-2 signed by the Ministry of Healthcare of the Russian Federation and the National Research Nuclear University MEPhI. It should be: This work was supported by the Ministry of Education and Science within the framework of the project RFMEFI60117X0018.

CFD-DEM simulation of flow pattern and particle velocity in a fluidized bed with wet particles

Gas-solid fluidized beds with the presence of a few liquid are applied widely in industry, while agglomeration and poor fluidization could happen as a result of inter-particle cohesiveness. In this paper, a hysteresis contact model is applied to consider energy dissipation resulted from both lubrication and liquid bridge during wet particle collision. The model can predict the particle rebound and adhesion behaviors, under influence of collision velocity, liquid content, liquid viscosity and surface tension. The fluidization characteristics of the wet particles under different conditions in a 2D fluidized bed are simulated and compared. Generally, it is found that with the presence of liquid, the particles begin to be agglomerated and the bubbles become gas channels. By increasing the cohesiveness, the fluctuation of pressure increases first and then decreases, the fluctuation of particle velocity decreases generally and the probability density of particle velocity around zero increases. When the cohesiveness is increased further, the internal recirculation of wet particles is restrained and the gas channels become stable.

Recirculating metallic particles for the efficiency enhancement of concentrated solar receivers

The use of Concentrated Solar Power technology for energy generation relies on the heating of fluids to high temperatures. One of the limitations of this technology is the low working efficiency of current solar receivers which hinders its application and utilization as a renewable clean energy source. This paper presents a novel concept to improve concentrated solar receiver efficiency through the recirculation of solid particles laden flow within the receiver. The recirculating characteristic of the fluid and solid particle mixture is expected to generate higher output fluid temperature than conventional solar receivers. This is expected to lead to significant improvements in the working performance of the concentrated solar receiver. The numerical study investigates this concept, using a commercial CFD package, employing the discrete particle model (DPM), a RNG k-ε flow model and a discrete ordinate (DO) radiation model. It is found that the use of recirculating solid particles improves the energy absorption within the receiver and with it the thermal efficiency of the proposed solar receiver reaches to around 70%. Moreover, comparing this with a conventional solar receiver, this new concept exhibits a more uniform temperature distribution inside the cavity, which is mainly due to the recirculating flow characteristic and the well-controlled mixing of air and particles. The advantages of this novel concept of the solar receiver present its potential benefits in further applications in the process of energy conversion providing on enhanced heat transfer medium.

On the front shape of an inertial granular flow down a rough incline

Granular material flowing on complex topographies are ubiquitous in industrial and geophysical situations. In this paper, we study the small-scale experiment of a granular layer flowing on a rough incline. The shape of the granular front is solved analytically by using depth-averaged mass and momentum equations with a fractional expression for the frictional rheology μ(I), which is a generalization of Gray and Ancey [“Segregation, recirculation and deposition of coarse particles near two-dimensional avalanche fronts,” J. Fluid Mech. 629, 387 (2009)]. Unlike previous studies where a “plug flow dynamics” is assumed, a free shape factor α describing the vertical velocity profile is taken into account. The effect of inertia and shear rate on the front profile is evidenced through the introduction of the Froude number and the shape factor α. The analytical predictions are compared to experimental results published by Pouliquen [“On the shape of granular fronts down rough inclined planes,” Phys. Fluids 11, 1956 (1999)] and with our new experimental data obtained at higher Froude numbers. A good agreement between theory and experiments is found for α = 5/4, corresponding to a Bagnold-like velocity profile. However, we observe a systematic deviation near the head of the front where the height vanishes: the theory predicts a continuous precursor layer, while a grain-free region is observed experimentally. This suggests that the vertical velocity profile is not uniform inside the front, but the shape factor α tends to 1 near the head of the front. This raises questions about the vertical velocity profile in granular flows and about the expression of the rheological function μ(I) and its calibration from experimental data.

Density currents as a desert dust mobilization mechanism

Abstract. The formation and propagation of density currents are well studied processes in fluid dynamics with many applications in other science fields. In the atmosphere, density currents are usually meso-β/γ phenomena and are often associated with storm downdrafts. These storms are responsible for the formation of severe dust episodes (haboobs) over desert areas. In the present study, the formation of a convective cool pool and the associated dust mobilization are examined for a representative event over the western part of Sahara desert. The physical processes involved in the mobilization of dust are described with the use of the integrated atmospheric-air quality RAMS/ICLAMS model. Dust is effectively produced due to the development of near surface vortices and increased turbulent mixing along the frontal line. Increased dust emissions and recirculation of the elevated particles inside the head of the density current result in the formation of a moving "dust wall". Transport of the dust particles in higher layers – outside of the density current – occurs mainly in three ways: (1) Uplifting of preexisting dust over the frontal line with the aid of the strong updraft (2) Entrainment at the upper part of the density current head due to turbulent mixing (3) Vertical mixing after the dilution of the system. The role of the dust in the associated convective cloud system was found to be limited. Proper representation of convective processes and dust mobilization requires the use of high resolution (cloud resolving) model configuration and online parameterization of dust production. Haboob-type dust storms are effective dust sources and should be treated accordingly in dust modeling applications.

Filtered EGR – a step towards an improved NOX/soot trade-off for DPF regeneration

Download options Please wait... Article information DOI https://doi.org/10.1039/C2RA21109B Article type Paper Submitted 01 Jun 2012 Accepted 05 Sep 2012 First published 06 Sep 2012 Download Citation RSC Adv., 2012,2, 10400-10408 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Filtered EGR – a step towards an improved NOX/soot trade-off for DPF regeneration S.S. Gill, J.M. Herreros, A. Tsolakis, D.M. Turner, E. Miller and A.P.E. York, RSC Adv., 2012, 2, 10400 DOI: 10.1039/C2RA21109B To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author S.S. Gill J.M. Herreros A. Tsolakis D.M. Turner E. Miller A.P.E. York

Lipoprotein Subfractions and Particle Size in End-Stage Renal Disease

It is interesting to note that the most heavily relied upon measures in nephrology and cardiology are both derived from calculations based on laboratory and clinical values, that is, the estimated GFR and the estimated concentration of low-density lipoprotein cholesterol (LDL-C). The actual particles of LDL in the bloodstream represent the end product of multiple hydrolysis steps that allow the initial nutritional packet, very low-density lipoprotein (VLDL), to deliver fatty acids, as well as cholesterol esters, to tissues for cellular metabolism and maintenance. The half-life of LDL is approximately 3 days, and it is believed that LDL itself has no nutritional value (1). In an ideal situation, LDL would meet its catabolic fate by docking with the LDL receptor and clearance from the circulation. However, in most adults, there is an age-related increase in LDL-C due to impaired clearance and perhaps recirculation of particles via cholesteryl esterase transfer protein. Smaller LDL particles have a longer clearance time and are more densely packed with cholesterol ester than larger particles, giving them more opportunity for tissue deposition (Figure 1) (1). While LDL-C has served reasonably well as an estimate and a proxy for the pathogenic LDL particles, many have believed that measurement of either the number or concentration of particles according to size, or determination of the apolipoprotein B concentration (1:1 with the number of LDL particles) should bring us closer to appreciating ongoing deposition of LDL into the vessel wall, advancing atherosclerosis, and translation into binary events such as myocardial infarction and cardiovascular death (2,3). Figure 1. Depiction of smaller dense LDL particles with ingress into the subintimal space initiating the pathogenesis of atherosclerosis. HSPG, heparin sulfate proteoglycans. In this issue of the journal, Noori and colleagues performed detailed LDL particle analysis on a random sample (n = 235) of hemodialysis patients who were part of a well established cohort followed for all-cause mortality (4). One of the most striking findings in this study is the influence of obesity, as stratified above and below a body mass index of 27 kg/m2, which was associated with an approximately 20 to 40% increase in triglycerides, and statistically significantly higher LDL-C, total LDL particles, and very small to medium LDL particles. The very small LDL particles were only significantly correlated (R = 0.21) with one nonlaboratory measure: fat mass percent. This influence of excess adiposity on lipid subfractions in end-stage renal disease (ESRD) appear to be greater than those observed in the general population (5). These relationships are important to remember, as the detailed tables and figures in this article suggest that there are modest relationships between small LDL particle number and concentration with all-cause mortality, which is a relatively crude and diluted proxy for translated atherosclerotic events. Thus, this article indirectly brings into focus, perhaps, a special pathogenicity of excess adiposity in patients with chronic uremia that is related, in part, to greater numbers of smaller LDL particles. These nuances are fairly well concealed in the standard lipid profile, which features the calculated LDL-C. Many articles suggest that chronic kidney disease (CKD), independent of other risk factors, appears to accelerate the atherosclerotic process, including the gradient dependent deposition of LDL particles, recruitment of monocytes, upregulation of adhesion molecules, ingress of monocytes and conversion to macrophages and foam cells, oxidation of lipid material, mobilization of vascular smooth muscle cells, breakdown of the elastic lamina, and development of an atheroma, which expands both toward the lumen and outward toward the adventitia (6–8). The most prominent component of atherosclerosis influenced by CKD is calcification, which, interestingly, is not associated with LDL particle size or number, nor is it influenced by lipid-lowering therapy (9,10). The present article by Noori and coworkers suggests that, beyond calcification, an atherogenic dyslipidemia is more prominently related to excess adiposity and is in the causal for pathway for earlier, more severe, and consequential atherosclerosis in patients with ESRD (11–13). Future research in ESRD using advanced clinical lipidology measures, including oxidized lipids and quantity, size, content, and circulatory time of particles, is warranted. More detail will be needed on the effects of adiposity, concurrent medications, and state of vascular disease determined by imaging. Finally, the end points of future studies will deserve to be more focused on atherosclerotic vascular events that experts can adjudicate and agree upon, including unstable angina, acute myocardial infarction, and ischemic stroke. The clinical use of commercially available lipoprotein subfractionation or particle tests in patients with ESRD is premature at the present time, due to the complexity of the biologic relationships in uremia, degree of uncontrolled confounding, lack of harmony between testing methodologies on the market, and the absence of a clear therapeutic mandate above and beyond what we currently have in the conventional lipid profile (14).

Experimental investigation on hydrogen production from biomass gasification in interconnected fluidized beds

Hydrogen production from biomass gasification was performed in a laboratory scale apparatus of interconnected fluidized beds in this paper. It resembles a high velocity fluidized bed with a spout-fluid bed after a cyclone. The high velocity fluidized bed is designed for a combustor, the spout-fluid bed for a gasifier. Biomass particles with steam are introduced into the bottom of the spout-fluid bed. It favors the process of hydrogen production from biomass gasification, as well as tar decomposition. The gasification-required heat was achieved by means of the external recirculation of bed particles in interconnected fluidized beds. Direct contact between the gasification and combustion processes is avoided. The effects of gasifier temperature and steam/biomass ratio on the composition of hydrogen-rich gas, carbon gasification of biomass, carbon combustion of biomass, carbon utilization of biomass, tar content and hydrocarbons were discussed. The results indicated that both a relatively high hydrogen content and a great hydrogen yield were obtained from biomass gasification in interconnected fluidized beds. With the increase of gasifier temperature, H 2 content decreased, CO increased evidently with the gasifier temperature. The steam/biomass ratio has a weak effect on the syngas composition. There was an optimal value of steam/biomass ratio corresponding to maximal hydrogen yield. For the gasifier temperature of 820 °C, hydrogen yield and carbon gasification of biomass reached its maximum values of 0.553 Nm 3 kg −1 biomass and 50.02% at the steam/biomass of 1.4, and then decreased with the further increase of steam/biomass ratio. ► Biomass gasification in interconnected fluidized beds. ► Hydrogen production performance with steam/biomass ratio and temperature. ► Tar measurement in syngas. ► Hydrogen yield and carbon gasification of biomass reach its maximum values of 0.553 Nm 3 kg −1 biomass and 50.02%.

Face-Down Solid Particle Receiver Using Recirculation

Solar thermal energy generation needs receiver technologies which can drive highly efficient turbines and decouple the collection of energy from its use by an economic storage technology. High-temperature solid particle receivers for solar tower systems with particle storage are one option. Important issues regarding high-temperature particle receivers are minimization of convective losses, no particle loss due to susceptibility to wind, and high efficiency also in part-load operation. A design approach facing these challenges is the face-down receiver using recirculation of particles. A screening performance analysis studying different recirculation patterns is presented. Using smart recirculation schemes, high receiver efficiencies can be maintained also at part-load operation (100% load ∼90%; 50% load ∼86%; 20% load ∼67%). Simulations of the face-down geometry yield total annual solar-to-electric efficiencies of 24% using a surround field. From the analyses, it can be concluded that solid particle receivers using smart recirculation patterns are a viable receiver option for storage and high-temperature high-efficiency turbine processes.

Simulation study of production of fine ceramic powders in a cyclone reactor

A numerical simulation study of production of fine ceramic powders in an innovative vapor-phase aerosol reactor is described. Arrangement is typical of reverse-flow cyclone equipment; no similar device is present in current scientific literature and industrial technology. The cyclone reactor has a potential technological application as it realizes process intensification by two simultaneous operating advantages: (i) curly flow reduces recirculation of as-synthesized particles towards flame region, and (ii) cyclone arrangement segregates large particles. As a result, ceramic powders with narrower particle size distribution can be produced with regard to traditional equipment. The study is based on the re-modeling of an existing industrial reactor for production of fine TiO 2 according to a cyclone configuration; particle size distributions from simulation and plant are compared.

A Microchemical System with Continuous Recovery and Recirculation of Catalyst‐Immobilized Magnetic Particles

A microchemical system for continuous flow catalytic reactions with magnetic catalyst is presented. The automatic separation of catalyst particles and recirculation by the microchemical system makes it possible to realize fully the advantages a catalytic microreactor can offer. It would be applicable to various catalytic reactions with aid of already reported magnetic catalyst or new magnetic catalyst.

Segregation, recirculation and deposition of coarse particles near two-dimensional avalanche fronts

Stratification patterns are formed when a bidisperse mixture of large rough grains and smaller more mobile particles is poured between parallel plates to form a heap. At low flow rates discrete avalanches flow down the free surface and are brought to rest by the propagation of shock waves. Experiments performed in this paper show that the larger particles are segregated to the top of the avalanche, where the velocity is greatest, and are transported to the flow front. Here the particles are overrun but may rise to the free surface again by size segregation to create a recirculating coarse-grained front. Once the front is established composite images show that there is a steady regime in which any additional large grains that reach the front are deposited. This flow is therefore analogous to finger formation in geophysical mass flows, where the larger less mobile particles are shouldered aside to spontaneously form static lateral levees rather than being removed by basal deposition in two dimensions. At the heart of all these phenomena is a dynamic feedback between the bulk flow and the evolving particle-size distribution within the avalanche. A fully coupled theory for such segregation–mobility feedback effects is beyond the scope of this paper. However, it is shown how to derive a simplified uncoupled travelling-wave solution for the avalanche motion and reconstruct the bulk two-dimensional flow field using assumed velocity profiles through the avalanche depth. This allows a simple hyperbolic segregation theory to be used to construct exact solutions for the particle concentration and for the recirculation within the bulk flow. Depending on the material composition and the strength of the segregation and deposition, there are three types of solution. The coarse-particle front grows in length if more large particles arrive than can be deposited. If there are fewer large grains and if the segregation is strong enough, a breaking size-segregation wave forms at a unique position behind the front. It consists of two expansion fans, two shocks and a central ‘eye’ of constant concentration that are arranged in a ‘lens-like’ structure. Coarse grains just behind the front are recirculated, while those reaching the head are overrun and deposited. Upstream of the wave, the size distribution resembles a small-particle ‘sandwich’ with a raft of rapidly flowing large particles on top and a coarse deposited layer at the bottom, consistent with the experimental observations made here. If the segregation is weak, the central eye degenerates, and all the large particles are deposited without recirculation.

Simulation of hydrogen production from biomass gasification in interconnected fluidized beds

Abstract Hydrogen production from biomass gasification in interconnected fluidized beds is proposed in this paper. It resembles a circulating fluidized bed with the extra bubbling fluidized bed after the cyclone. The circulating fluidized bed is designed for combustion fed with air, the bubbling fluidized bed for biomass gasification fed with steam. Direct contact between the gasification and combustion processes is avoided; the gasification-required heat is achieved by means of the circulation of bed particles. Hydrogen-rich gas is produced free of N2 dilution. The paper intends to provide some process fundamentals about hydrogen production from biomass gasification in interconnected fluidized beds. Simulation of the processes, including chemical reactions and heat/mass balance, is carried out with Aspen Plus software. The effects of gasifier temperature and steam/biomass ratio on the composition of fuel gas, hydrogen yield, carbon conversion of biomass, recirculation of bed particles, etc., are discussed. Some useful results are achieved. The results indicate that both a high hydrogen content and a relatively great hydrogen yield are obtained from biomass gasification in interconnected fluidized beds. The favorable temperature of the gasifier should be between 750 and 800 °C, the combustor temperature should be 920 °C, and the ratio of the steam/biomass should be between 0.6 and 0.7. The increment of hydrogen yield is distinct with the increase of steam/biomass ratio at the lower gasifier temperatures (below 750 °C). The steam/biomass ratio corresponding to maximal hydrogen yield declines with the increase of gasifier temperature. To maintain the gasifier temperature, the recirculation of bed particles increased exponentially with an increase in the gasifier temperature.

Chemical looping combustion of coal in interconnected fluidized beds

Chemical looping combustion is the indirect combustion by use of oxygen carrier. It can be used for CO2 capture in power generating processes. In this paper, chemical looping combustion of coal in interconnected fluidized beds with inherent separation of CO2 is proposed. It consists of a high velocity fluidized bed as an air reactor in which oxygen carrier is oxidized, a cyclone, and a bubbling fluidized bed as a fuel reactor in which oxygen carrier is reduced by direct and indirect reactions with coal. The air reactor is connected to the fuel reactor through the cyclone. To raise the high carbon conversion efficiency and separate oxygen carrier particle from ash, coal slurry instead of coal particle is introduced into the bottom of the bubbling fluidized bed. Coal gasification and the reduction of oxygen carrier with the water gas take place simultaneously in the fuel reactor. The flue gas from the fuel reactor is CO2 and water. Almost pure CO2 could be obtained after the condensation of water. The reduced oxygen carrier is then returned back to the air reactor, where it is oxidized with air. Thermodynamics analysis indicates that NiO/Ni oxygen carrier is the optimal one for chemical looping combustion of coal. Simulation of the processes for chemical looping combustion of coal, including coal gasification and reduction of oxygen carrier, is carried out with Aspen Plus software. The effects of air reactor temperature, fuel reactor temperature, and ratio of water to coal on the composition of fuel gas, recirculation of oxygen carrier particles, etc., are discussed. Some useful results are achieved. The suitable temperature of air reactor should be between 1050–1150°C and the optimal temperature of the fuel reactor be between 900–950°C.