Solid Flow Rate Research Articles

Hydrodynamics of a multi-stage counter-current fluidized bed reactor with down-comer for amine impregnated activated carbon particle system

In the present investigation, the hydrodynamic study on the four-staged fluidized bed reactor with solid and gas flowing in the counter-current direction has been carried out. The gas phase was air, and the solid phase was amine impregnated activated carbon. By changing the operating condition like weir height, solid flow rate, gas velocity and particle size, pressure drops were determined at the steady and stable operation of the column without loading and flooding. At the low velocity of gas (0.188m/s) with maximum solid flow rate (4.12kg/h) and maximum weir height (70mm), the maximum pressure drop occurred in the column was 220N/m2. The minimum pressure drop occurred in the column was 92.2N/m2 at high velocity of gas (0.353m/s), with minimum flow rate of solids (2.15kg/h) and low weir height of 30mm. The maximum pressure drop occurred for lowest particle size (467μm) at gas velocity (0.309m/s) was 169.1N/m2 at 50mm weir height and the minimum pressure drop occurred at the same condition for highest size particle size (635μm) was 124.8N/m2 at the same weir height.

From a CFB reactor to a CFB boiler – The review of R&D progress of CFB coal combustion technology in China

Circulating fluidized bed (CFB) technology was applied for coal combustion after CFB chemical reactors have been widely used and studied in chemical engineering. However, there were still many special phenomena found in the CFB boiler. In this paper, the main differences between a conventional CFB reactor and a CFB boiler are summarized. A CFB boiler is a special CFB reactor. It is an open circulating system with a wide size distribution feedstock and a low circulating solid flow rate. The CFB boiler behaves as particle selection machine, retaining particles within a certain size range in the furnace. Its fluidization regime is distinguished from a conventional CFB reactor, composing of a bubble or turbulent dense bed in the lower furnace and a fast dilute bed in the upper furnace. A large portion of heat is released in the dilute bed, and there is an oxygen-deficient combustion zone in the center of the upper furnace of a CFB boiler. Based on the theoretical studies and engineering practice, the principles and a guidance map of fluidization state specification for CFB boiler design are presented. In addition, the paper reviews the research and development (R&D) history and important achievements of the Chinese CFB combustion technology.

Numerical simulation of heat transfer during production of rutile titanium dioxide in a rotary kiln

This paper presents a computational heat transfer model of a rotary kiln used for the production of rutile titanium dioxide by the calcination of paste-like hydrous titanium dioxide. The work details the modelling of several chemical reactions occurring in the solid bed region along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. Finite-difference techniques are used and the steady state thermal conditions are assumed. The kiln is divided into axial segments of equal length. The solution is of marching type and proceeds from the solid inlet to the solid outlet. The direction of gas flow is opposite to that of the solids. Mass balance of each species in the solid charge, and mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperatures, and species concentration at the exit of that segment. The kiln length predicted by the present model is 45.75m as compared to 45m of an actual kiln reported by Ginsberg and Modigell (2011). The steady-state axial gas and solid temperature profiles have been also satisfactorily validated with the numerical results of the aforementioned paper. The output data consist of refractory wall temperature distribution, the axial solids and gas temperature profiles, axial solids composition profile, the length required for drying of the solid charge and the total kiln length required to achieve 98% conversion of anatase TiO2 to rutile TiO2. A detailed parametric study with respect to the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and kiln rotational speed lent a good physical insight into the rutile-TiO2 production process in a rotary kiln.

On-sun operation of a 150 kWth pilot solar receiver using dense particle suspension as heat transfer fluid

Previous studies proved the Dense Particle Suspension (DPS) - also called Upward Bubbling Fluidized Bed (UBFB) - could be used as Heat Transfer Fluid (HTF) in a single-tube solar receiver. This article describes the experiments conducted on a 16-tube, 150kWth solar receiver using a dense gas-particle suspension (around 30% solid volume fraction) flowing upward as HTF. The receiver was part of a whole pilot setup that allowed the continuous closed-loop circulation of the SiC particles used as HTF. One hundred hours of on-sun tests were performed at the CNRS 1MW solar furnace in Odeillo. The pilot was tested under various ranges of operating parameters: solid mass flow rate (660–1760kg/h), input solar power (60–142kW), and particle temperature before entering the solar receiver (40–180°C). Steady states were reached during the experiments, with continuous circulation and constant particle temperatures. For the hottest case, the mean particle temperature reached 430°C in the collector fluidized bed, at the receiver outlet, and it went up to 700°C at the outlet of the hottest tube, during steady operation. A temperature difference between tubes is observed that is mainly due to the incident solar flux distribution heterogeneity. The thermal efficiency of the receiver, defined as the ratio of power transmitted to the DPS in the form of heat over solar power entering the receiver cavity, was calculated in the range 50–90% for all the experimental cases. The system transient responses to variations of the solar irradiation and of the solid mass flow rate are also reported.

Electrochemical Performance of Lithium-Ion Batteries As a Function of Linked Influences Originating from the Dispersing and Calendering Step

Lithium ion batteries for PHEV`s, HEV`s and EV`s have to meet different requirements like high energy density, high power density and always low production costs at high durability. As wide-spread standard, electrodes for lithium ion batteries are produced by mixing and dispersing active materials with conductive additives, binder and solvent. In a subsequent step, the coated electrodes are calendered to homogenize the electrode thickness. These two process steps strongly influence the electrode’s electrochemical performance in the battery cell. Thus, high quality mixing, deagglomeration and dispersing of all solid components in the solvent and a high-precision calendering has to be ensured to produce high performance electrodes. One important aspect in the dispersing process is the deagglomeration of carbon black. Modifying the agglomerate size and shape of carbon black has a strong influence on the electrochemical performance due to structural changes of electrode properties like electrode porosity and conductivity. On the other hand, these structural changes also occur in the calendering step, where electrodes are compressed and electrode thickness and density are adjusted. For this reason, our work focuses on experiments regarding the changes in electrochemical performance due to different deagglomeration degrees of carbon black and subsequent calendering process step. The electrodes were processed with a continuously operated twin-screw extruder. Suspensions with differently deagglomerated carbon black were produced by varying the tensile stress acting inside the suspension and the residence time through changes in the tip speed of extruder screws and volumetric flow rate of solids and solvent at constant solids content in the suspension. In order to examine the influence of carbon black on the electrochemical performance, the agglomerate size of different suspensions was identified via laser diffraction analysis using a Horiba LA-960 Laser Particle Size Analyzer with two light sources, a laser diode with 650 nm and a light emitting diode (LED) with 405 nm wavelength. The analysis displayed a strong bimodal distribution with a shifting peak in the single-digit µm-range representing carbon black agglomerates and a stationary peak at a few hundred nanometers representing smaller carbon black aggregates. A pilot-scale coater with a combined reverse-roll comma bar system and a dryer length of 6 meters was used to produce electrodes continuously out of selected suspensions. Afterwards, the electrodes were compressed with a pilot-scale calender. In this step, a density of 2.8 g/cm³ on cathode side and 1.5 g/cm³ on anode side was set as standard. Structural properties of differently produced electrodes were analyzed using mercury porosimetry and electrode conductivity analysis. Mercury porosimetry was used to visualize changes in the pore structure of electrodes, especially in a range of 0.1 to 4 µm pore diameter. In this pore size range the varying agglomerate sizes and the calendaring step have a great impact on the electrode´s pore structure. Changing the size of carbon black agglomerates also significantly influences the properties of the carbon black conductive network which results in a modified electrode conductivity: A finer distribution and better deagglomeration of carbon black lead to higher electrode conductivity. This is beneficial to some degree for the electrochemical performance at higher c-rates. On the other hand, the calendering process also changes the electrodes structure by modifying the electrodes thickness, porosity and, in conclusion, the electrodes density. Of greater significance is the fact, that the calendering step leads to a larger contact surface between active material particles, carbon black and current collector. Within certain limits, this results in a better electrochemical performance. Linking these influences of different process steps reveals possible interactions which lead to an optimized process control. The effect of structural changes on the electrochemical performance of electrodes was examined performing c-rate-tests up to 5 C and long-term cycling at 1C in full cells. The influence of changes in electrode properties became apparent especially at higher c-rates, where limiting effects in ionic and electrode conductivity, influenced by electrode porosity and conductivity, become more important. Good electrochemical performance only is attainable with suitable electrode porosity and well-developed conductivity network of carbon black. Summing up all experimental results we are able to relate process parameters and structure properties of the electrodes and link these structural changes with the resulting electrochemical performance. Significant differences in electrochemical performance were traceable to structural changes in the electrodes, which necessitate distinct process know-how in the different process steps. This process-structure-property-relationship enables a deeper understanding for the continuously operating industrial processes of extrusion and calendering leading to an optimized production of electrodes for lithium ion batteries. Figure 1

Effective thermal conductivity of unary particulate bed

AbstractEffective thermal conductivity of a unary (mono‐sized) pebble bed depends on the physical properties of solid pebbles, physical properties and flow rate of fluid, temperature, coordination number of pebbles, and void fraction. The pebble size also plays an important role on the effective thermal conductivity of a unary pebble bed. To date, no theoretical justification for the same has been reported. In this present study an attempt was made to justify theoretically the dependence of the effective thermal conductivity on pebble size of a unary pebble bed filled with a stagnant fluid. A mathematical model has been developed to determine the effective thermal conductivity of a unary pebble bed with stagnant fluid. Different particle sizes (10 μm to 10 mm) were considered and modes of heat transfer were assumed to be conduction and convention only. Radiation mode of heat transfer was not considered. It was found that the effective thermal conductivity depends on the pebble size and the estimated values of the same were in close agreement with the reported experimental results.

Developing a particle-based process model for unit operations of mineral processing – WLIMS

Process models in mineral processing can be classified based on the level of information required from the ore, i.e. the feed stream to the processing plant. Mineral processing models usually require information on total solid flow rate, mineralogical composition and particle size information. The most comprehensive level of mineral processing models is the particle-based one (liberation level), which gives particle-by-particle information on their mineralogical composition, size, density, shape i.e. all necessary information on the processed material for simulating unit operations. In flowsheet simulation, the major benefit of a particle-based model over other models is that it can be directly linked to any other particle-based unit models in the process simulation. This study aims to develop a unit operation model for a wet low intensity magnetic separator on particle property level. The experimental data was gathered in a plant survey of the KA3 iron ore concentrator of Luossavaara-Kiirunavaara AB in Kiruna. Corresponding feed, concentrate and tailings streams of the primary magnetic separator were sampled, assayed and mass balanced on mineral liberation level. The mass-balanced data showed that the behavior of individual particles in the magnetic separation is depending on their size and composition. The developed model involves a size and composition dependent entrapment parameter and a separation function that depends on the magnetic volume of the particle and the nature of gangue mineral. The model is capable of forecasting the behavior of particles in magnetic separation with the necessary accuracy. This study highlights the benefits that particle-based models in simulation offer whereas lower level process models fail to provide.

Investigation into mean residence time and filling factor in flighted rotary torrefier

Torrefaction can upgrade the properties of biomass, making it similar to coal. This study develops an innovative indirectly heated two‐stage rotating drum‐type torrefier where biomass moves due to the rotation of inclined cylindrical reactors. The rotary reactors consist of three rectangular flights placed axially along the reactor. This paper mainly investigates the mean residence time and filling factor of reactors operated at steady and plug flow conditions. Semi‐empirical expressions using dimensionless correction constants for the mean residence time and the filling factor were proposed. Experiments keeping a constant solid flow rate at the dryer inlet were conducted in order to measure filling factor and mean residence time at different angular speeds and inclinations of reactors (dryer and torrefier). Mean residence times of 5.8 min at 8 rpm and 3°, and of 27.5 min at 4 rpm and 1° were found in the dryer (diameter: 64 mm, length: 610 mm), whereas they were 4.7 and 21.4 min in the torrefier (diameter: 100 mm, length: 762 mm) at respective operating conditions. Filling factors of 3.0 % at 8 rpm and 3°, and 14.3 % at 4 rpm and 1° were found in the dryer, whereas they were 0.8 % and 3.6 % in the torrefier at the corresponding angular speed and inclination. Measured and predicted mean residence times were also compared and validated against those of other investigators. The proposed expressions, which include the effects of different operating and geometrical parameters, have strong predictive power and may be useful in scaling‐up a rotary torrefier.

Experimental investigation on blockage boundary for pneumatic conveying of powders in narrow bifurcation slits

ABSTRACTTo investigate the blockage characteristics for dense-phase pneumatic conveying in narrow bifurcation slits, a study on the blockage boundary conditions of powders was undertaken. The results show that the solid mass flow rate for blockage increases with superficial air velocity, and the variation trend can be divided into three typical stages. Besides the relationship between the solid loading ratio and superficial air velocity for blockage in the bifurcation slit displays a “S” shape with the increase of air velocity, the solid loading ratio increases, then decreases, finally increases, and in each stage above, the relationship between the two approximately meets power function, respectively. According to the “S” shape relationship, the formula used for blockage boundary [Setia, Mallick, Wypych, and Pan (2013). Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems, Particuology, 11, 657–663] was modified into piecewise function for bifurcation slits. In addition, with the increase of the bifurcation angle and conveying pressure, the superficial air velocity decreases, while the solid mass flow rate and the critical solid loading ratio increase. The research work could help understand the blockage theory of the dense-phase pneumatic conveying.

Preconcentration and Determination of Copper(II) by Novel Solid-Phase Extraction and High-Resolution Continuum Source Flame Atomic Absorption Spectrometry

ABSTRACTAmberlite XAD-4 modified with N-para-anisidine-3,5-di-tert-butylsalicylaldimine was investigated as a new chealting sorbent for the selective separation and preconcentration of Cu(II). The metal ion was retained by chemical sorption on the modified resin, eluted by hydrochloric acid, and determined by high-resolution continuum source flame atomic absorption spectrometry. The prepared resin was characterized for the solid-phase extraction of Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+, and Zn2+ in a column. The influence of the pH, the mass of solid phase, eluent, flow rate, and sample volume was optimized. Using the optimum conditions, only Cu(II) showed quantitative sorption at the 95% confidence level, and the recoveries of the other metal ions were below 80%. A preconcentration factor 125 was obtained for Cu(II) with a limit of detection of 0.56 µg L−1. The method was used for the determination of Cu(II) in tap water, river water, tomato leaves, and fish. The relative standard deviation and the relative error were lower than 7%.

Removal of CO2 in a multistage fluidized bed reactor by diethanol amine impregnated activated carbon

ABSTRACTTo mitigate the emission of carbon dioxide (CO2), we have developed and designed a four-stage fluidized bed reactor. There is a counter current exchange between solid adsorbent and gas flow. In this present investigation diethanol amine (DEA) impregnated activated carbon made from green coconut shell was used as adsorbent. This type of adsorbent not only adsorbs CO2 due to the presence of pore but also chemically reacts with CO2 and form secondary zwitterions. Sampling and analysis of CO2 was performed using Orsat apparatus. The effect of initial CO2 concentration, gas velocity, solid rate, weir height etc. on removal efficiency of CO2 have been investigated and presented. The percentage removal of CO2 has been found close to 80% under low gas flow rate (0.188 m/s), high solid flow rate (4.12 kg/h) and weir height of 50 mm. From this result it has been found out that multistage fluidized bed reactor may be a suitable equipment for removal of CO2 from flue gas.

Predictive model for corn flour discharge rates through an aerated hopper

The controlled injection of air can increase the flow rate of some bulk solids from bins and hoppers. From a well-consolidated theoretical model, experimental data obtained by material characterization tests and test rig experiments were used to investigate the aerated discharge behavior of ground yellow corn powder. A comparison between experimental discharge flow rate and the model was performed. Corrective functions obtained by a regression of the experimental data were introduced.

Evaluation of the parameters influencing electrostatic charging of powder in a pipe flow

Triboelectric charging of powders during pneumatic transport can lead to hazardous spark discharges. In this study, the charging process was studied numerically by means of large eddy simulations. A range of design parameters was then analyzed statistically applying the Design of Experiments methodology. It is shown that the electric charge of the powder can be significantly decreased by reducing the conveying air velocity. Furthermore, the usage of pipes of a larger diameter and the application of higher solid mass flow rates also reduce the powder charge.

Hydrodynamics and particle motion in upward flowing dense particle suspensions: Application in solar receivers

Dense gas–solid suspensions have the potential to be applied as heat transfer fluids (HTF) for energy collection and storage in concentrated solar power plants. At the heart of these systems is the solar receiver, composed of a bundle of tubes which contain the solid suspension used as the thermal energy carrier. In the design investigated here, the particles form a dense upward-flowing suspension. Both density of the suspension of these particles and their movement have a strong influence on the heat transfer. An apparatus was designed to replicate the hydrodynamic and particle motion in the real solar energy plant at ambient temperature. The governing parameters of the flow were established as the solid feeding flow rate, the fluidisation velocity, the solids holdup, the freeboard pressure and the secondary air injection (aeration) velocity. In the case studied, aeration was applied with air introduced into the uplift transport tube some way up its length. This study finds that the amount of this secondary air injection is the most important parameter for the stability and the uniform distribution of the solids flow in the tubes. Solids motion was measured using the non-invasive positron emission particle tracking (PEPT) technique to follow the movement of a 60µm tracer particle, onto which was adsorbed the positron emitting 18F radioisotope. Analysis of the resulting three-dimensional trajectories provides information on solids flow pattern and solids velocity. Results show the overall behaviour of the bulk material in detail: small step-wise movements associated with bubble motion superimposed on a general trend of upward flow in the centre and downward flow close to the walls. These findings suggest that this particular type of flow is ideal for transporting energy from the walls of the solar receiver tubes.

Design and Development of Operational Diagram for Controlling the Performance of Activated Sludge Process with a Case Study

AbstractThis paper describes the design and development of an operational diagram that was developed based on the solids flux theory and connects the process operational parameters, namely, mixed-liquor suspended solids, flow, volume, area, and recycle ratio in an unified graphical form to facilitate the design and operation of secondary clarifiers for an Indian pulp and paper industry. A control strategy was developed based on steady-state control methods by utilizing the batch settling data generated in stationary phase complimented with artificial neural network models. These diagrams evaluate the operating strategies in response to changes in flow rate or settleability of solids. These operational diagrams developed based on steady-state control analysis, can be used for controlling the performance of the activated sludge process subjected to long term variations in the influent flowrate and substrate concentration. The plant operator can make a rational decision on his own to control the process usin...

Relationship between Solid Flow Rate and Pressure Drop in the Riser of a Pressurized Circulating Fluidized Bed

Relationship between Solid Flow Rate and Pressure Drop in the Riser of a Pressurized Circulating Fluidized Bed

Dynamic modeling of the circulating fluidized bed riser

Dynamic modeling is required to understand hydrodynamics of a circulating fluidized bed (CFB) riser as a function of time. The paper develops a dynamic model of the riser from the conservation of solid mass. Solid mass that flows out of the riser requires particle residence time to close the mass balance equation. The mean residence time of solids was derived as the riser length divided by the superficial riser gas velocity normalized by a ratio of solid concentration in the riser outlet to that in the riser itself. For bed materials including high-density polyethylene beads, glass beads, and cork, the percentage of solid concentration in the horizontal crossover pipe connecting the riser exit and the cyclone inlet was found to be 22% of the average concentration of solids in the riser. Upon finding the particle residence time, we calculated the solid flow rate out of the riser and along with the knowledge of solids flowing into the riser column we determined the riser inventory as a function of time. We used the estimated solid inventory to model overall pressure drop across the riser from the conservation of momentum. The momentum equation included the balance of pressure force by the hydrostatic head of solids, and the wall frictions due to gas and solids in a fully developed zone. The prediction of overall riser pressure drop compared well with its measured values at many dynamic conditions. Therefore, our dynamic model is useful for developing advanced control strategy or for improving existing control systems of the CFB plant. The residence time approach is also useful for the design of a transport reactor. The technique also comes handy when setting up the boundary condition for the overall pressure drop in the CFD modeling that can simulate incremental pressures along the riser height.

An Integrated Instrumentation System for Velocity, Concentration and Mass Flow Rate Measurement of Solid Particles Based on Electrostatic and Capacitance Sensors.

The online and continuous measurement of velocity, concentration and mass flow rate of pneumatically conveyed solid particles for the high-efficiency utilization of energy and raw materials has become increasingly significant. In this paper, an integrated instrumentation system for the velocity, concentration and mass flow rate measurement of dense phase pneumatically conveyed solid particles based on electrostatic and capacitance sensorsis developed. The electrostatic sensors are used for particle mean velocity measurement in combination with the cross-correlation technique, while the capacitance sensor with helical surface-plate electrodes, which has relatively homogeneous sensitivity distribution, is employed for the measurement of particle concentration and its capacitance is measured by an electrostatic-immune AC-based circuit. The solid mass flow rate can be further calculated from the measured velocity and concentration. The developed instrumentation system for velocity and concentration measurement is verified and calibrated on a pulley rig and through static experiments, respectively. Finally the system is evaluated with glass beads on a gravity-fed rig. The experimental results demonstrate that the system is capable of the accurate solid mass flow rate measurement, and the relative error is within −3%–8% for glass bead mass flow rates ranging from 0.13 kg/s to 0.9 kg/s.

Pneumatic jet-control valve for dual circulating fluidized beds

With the rapid development of circulating fluidized bed (CFB) technology in different fields, the disadvantages of conventional non-mechanical valves are becoming more apparent, and they are not suitable to be used in complex CFB systems. In this paper, a novel non-mechanical valve named the jet-control valve is presented which can avoid the fluidization of solid particles. The feasibility and performance characteristics of the new valve are investigated with a cold-model dual CFB. The results show that compared with the conventional non-mechanical valve, the jet-control valve can transfer solid particles steadily over a larger range, prevent artesian flow, and improve the leakage characteristics. The effects of the operating parameters and structural parameters on the minimum aeration velocity, solid flow rate, and maximum solid flow rate are studied. A two-valve model is proposed to explain the transport capacity of the valve for one jet pipe. A semi-theoretical expression is obtained based on the experimental data with a maximum deviation of 30% providing useful guide for scaling-up the design.

The effect of oscillating flow on a horizontal dilute-phase pneumatic conveying

ABSTRACTA horizontal dilute-phase pneumatic conveying system using vertically oscillating soft fins at the inlet of the gas–particle mixture was studied to reduce the power consumption and conveying velocity in the conveying process. The effect of different fin lengths on horizontal pneumatic conveying was studied in terms of the pressure drop, conveying velocity, power consumption, particle velocity, and intensity of particle fluctuation velocity for the case of a low solid mass flow rate. The conveying pipeline consisted of a horizontal smooth acrylic tube with an inner diameter of 80 mm and a length of approximately 5 m. Two types of polyethylene particles with diameters of 2.3 and 3.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 17 m/s, and the solid mass flow rates were 0.25 and 0.20 kg/s. Compared with conventional pneumatic conveying, the pressure drop, MPD (minimum pressure drop), critical velocities, and power consumption can be reduced by using soft fins in a lower air velocity range, and the efficiency of fins becomes more evident when increasing the length of fins or touching particles stream by the long fins. The maximum reduction rates of the MPD velocity and power consumption when using soft fins are approximately 15% and 26%, respectively. The magnitude of the vertical particle velocity for different lengths of fins is clearly lower than that of the vertical particle velocity for a non-fin conveying system near the bottom of the pipeline, indicating that the particles are easily suspended. The intensities of particle fluctuation velocity of using fins are larger than that of non-fin. The high particle fluctuation energy implies that particles are easily suspended and are easily conveyed and accelerated.