Solid Flow Rate Research Articles

Efficiency analysis of citrus waste biomass valorization using rotary dryer

Citrus residue is a large-scale agro-industrial biowaste that can become a source of renewable energy through drying. Drying demands high power consumption due to the low energy efficiency of this process in the industries. In this work, the energy performance of the drying process in a semi-industrial rotary drum of 2.7 m length and 0.45 diameter was analyzed. The main objective was to find the operational condition for the lowest energy consumption and also the highest energy, drying and exergetic efficiencies. The experiments were performed under different solid mass flow rates (0.2 and 0.4 kg/min) inlet air velocities (1 and 2 m/s) and temperatures (135, 145, and 155 °C). The average energy efficiency was 13.1% with 25.1% of drying efficiency, 37291.3 kJ/kg of specific energy consumption, and 37.3% of exergy efficiency. The results showed that the drying technique can be an interesting alternative to add value to the citrus residue.

Particle flow regime in a swirling pneumatic conveying system

Particle fluidization is crucial for pneumatic conveying, combustion, and material drying. In this study, a swirling generator was designed to investigate the effect of the swirling flow on the flow regimes of pebble particles in a vertical pipe, and four different sizes of pebble particles were experimentally evaluated. Experiments were performed to investigate the effect of the axial flow and swirling flow on the flow regime, pressure drop, and suspension height of particles in a vertical pipe. The results indicated that the swirling flow has a significant effect on the particle flow regimes in a vertical pipe when the solid mass flow rate and inlet airflow velocity are constant. The swirling flow reduces the pressure drop and increases the particle fluidization in a vertical pipe, and it lifts the particles only when the inlet airflow velocity is higher than the particle velocity for the choking condition.

Critical Flux and Fouling Analysis of PVDF-Mixed Matrix Membranes for Reclamation of Refinery-Produced Wastewater: Effect of Mixed Liquor Suspended Solids Concentration and Aeration.

Fouling tends to cause a significant increase in hydraulic resistance, decreased permeate flux, or increased transmembrane pressure (TMP) when a process is operated under constant TMP or constant flux conditions. To control membrane fouling and maintain sustainable operation, the concept of critical flux has been discussed by several researchers. Various fouling mechanisms, such as macromolecule adsorption, pore plugging, or cake build-up, as well as hydrodynamic conditions, for example aeration, can take place at the membrane surface. This study aimed to investigate the effects of mixed liquor suspended solid (MLSS) concentration and air bubble flow rate (ABFR) on the critical flux and fouling behavior, when treating refinery-produced wastewater. To determine the critical flux values, the experimental flux-steps were the following: (1) the filtration began with a 30 min step duration at a low flux (10 to 20 L/m2h); (2) at the end of this step (after 30 min), the permeate flux was increased, (3) this step was repeated until the TMP did not remain constant at the constant permeate flux, (4) the critical flux was then achieved. A critical flux model with an R2 of 0.9 was, therefore, derived, which indicates that the particle properties were regulated by the suspended solids. The increase of MLSS concentration, from 3 mg/L to 4.5 mg/L, resulted in a decrease of the permeate flux by 18%. Moreover, an increase in ABFR, from 1.2 mL/min to 2.4 mL/min, increased the permeate flux, but this decreased with a greater flow rate of aeration. To assess the stability and reversibility of fouling during critical flux (Jc) determination using a mixed matrix membrane, flux-step methods were utilized. A step height of 14.3 L/m2h and 30 min duration were arbitrarily chosen. The flux increased to 32.5 L/m2h with a slight increase of trans membrane pressure (TMP), while the rate of increase became significant at a higher flux of 143.6 L/m2h, due to fouling. Overall, this study proved that the response of MLSS concentration and aeration affected the membrane performance, based on the critical flux and fouling behavior.

Characterization of countercurrent liquid-upward and solid-downward fluidized system

Acting as an operating mode of fluidization, the flow characteristics of a countercurrent liquid–solid fluidized bed (CCLSFB) were experimentally investigated using a Plexiglas column of 1.5 m in height. Countercurrent liquid-upward and solid-downward fluidization was achieved under a limited solid flowrate before flooding occurred.The “flooding” phenomena and the flooding velocity were identified by measuring the variations in pressure drop in the axial direction of the column. Two different methods were used to quantify the flooding point that led to the instability of the system. Axial solids holdup profiles were also obtained from the pressure drop data along the column and the influences of device structure and operating conditions on the solids holdup were also studied. Seven types of particles with different diameters and densities were used. An agreement was found between the experimental results and the mathematic prediction derived from the Richardson–Zaki equation on the data of the solids holdup.

Particle flow characteristics in a gas-solid separation fluidized bed based on machine learning

Particles in a gas-solid separation fluidized bed have fluid-like properties in a fluidized state, and particle flow has a great influence on bed uniformity and stability. To study the complex spatial characteristics of particle flow, the macro flow characteristics of particles and the mass flow rate model for solid particle flow were studied with theoretical calculations and machine learning. The results showed that particle flow has obvious nonuniform characteristics in axial space. The theoretical solid mass flow rate model was then modified by introducing a bed expansion ratio. The theoretical calculation error was controlled to within 20%, and the machine learning error was within 15%. Based on these results, the machine learning method was found to be more accurate and comprehensive than the theoretical method. An artificial network model was also proposed to predict the spatial uniformity of a gas-solid fluidization system. The results showed that the accuracy of the training set was 94.9%, and that of the test set was 95.6%. Thus, the ANN model makes it possible to predict the spatial uniformity of a gas-solid fluidization system.

Numerical exploration of the flow regime transition of a novel catalytic cracking reactor and operation mode analysis

The maximizing isoparaffins (MIP) reactor has multiple reaction zones by expanding the diameter of the middle section of the conventional equal-diameter FCC riser to produce high-quality gasoline. This study aimed to probe the flow regime transition and corresponding regulation of such diameter-transformed reactors using multiscale CFD simulations with twelve-lump kinetics. It was found that a choking plateau that appears in a low-velocity, equal-diameter riser was captured at a much higher solid concentration in the new reactor when considering reactions, while the plateau disappears and becomes a slowly ascending slope under cold-model conditions. Using the particle circulating mode instead of the fixed mode gives rise to large fluctuations in solids flow and reaction rate in the first zone, but the formation of fast fluidization in the expanded second zone can help stabilize the flow behaviors and product yield. This finding sheds light on the design and operation of diameter-transformed fluidized beds.

Liquid–Solid Two-Phase Flow Rate Measurement by Electrical and Ultrasound Doppler Sensors

Flow rate measurement in multiphase flow is essential for process control and safety production. As the drawbacks of conventional flowmeter measurement error produced by the heterogeneous phase or velocity distribution, a measurement technique combining an electrical resistance tomography (ERT) and an ultrasound Doppler (UD) sensor is proposed. The UD sensor obtains the dispersed particle velocity distribution, and the ERT acquires the solid phase distribution. An experimental platform is constructed for the liquid-solid two-phase horizontal flow experiments. The dual-plane ERT with the cross-correlation signal analysis compensates for the inaccurate particle velocity measurement at the bottom of the pipe by using UD independently due to the locally high concentration. The liquid-solid two-phase mixed flow rate under different flow regimes is measured with the two sensors. The proposed method has a 6.3% maximum uncertainty for the liquid-solid two-phase flow rate measurement.

Application of the ARMA Model to Describe and Forecast the Flotation Feed Solids Flow Rate

The flow rate of solids is subject to random disturbances of the changing feed and can significantly affect the quantitative and qualitative parameters of the coal flotation products. This quantity can be described as a stochastic process. The paper presents the results of the solids flow rate model for coal flotation identification calculations, treated as a disturbance to the process. This is an innovative approach to modelling those quantitative parameters of the flotation feed that are measurably available and whose random changes have a significant impact on the enhancement process under industrial conditions. These include the volumetric flow rate of the feed and, in particular, concentration of solids in the feed. Therefore, it is suggested that random changes of these two parameters of the feed should be mapped using a model of one quantity—the flow rate of solids. This solution is advantageous because this quantity, as a quantitative parameter of the feed, has a significant impact on the course of the coal flotation process. The model is necessary in the process of designing an automatic control system through simulation tests. It allows us to generate a data string simulating random changes to this quantitative parameter of the feed. On this basis, in the simulation model, the correct functioning of the automatic control system is tested, the task of which is to compensate the influence of this disturbance. To determine the empirical model of the feed solids flow rate, measurement data obtained during the registration of the solids concentration and volumetric flow rate of the feed were used in four consecutive periods of operation of an industrial facility of one of the Polish coal processing plants. The time courses of the solids flow rate in the feed were described by ARMA (autoregressive–moving-average model) means, and the two-stage least squares method was used to estimate the model parameters. The results of the identification and verification of the designated model showed the correctness of adopting the third-order ARMA model, with parameters a1 = −1.0682, a2 = −0.2931, a3 = 0.3807, c1 = −0.1588, c2 = −0.2301, c3 = 0.1037, and variance σ2ε = 0.0891, white noise sequence εt, determined on the basis of a series of residuals described by the fifth-order model. It has been shown that the identified model of the flow rate of solids of the feed to flotation as disturbances can be used to develop a predictive model that allows forecasting the modelled quantity with a prediction horizon equal to the sampling period. One-step forecasting based on the determined predictor equation was found to give results consistent with the recorded values of the solid part flow rate of the feed and the extreme values of the prediction error are within the range from −1.08 to 2.90 kg/s.

Recent advances of hybrid solar - Biomass thermo-chemical conversion systems

Solar biomass hybridization is a promising energy technique for efficient utilization while mitigating the disadvantages associated with both biomass and solar energy source. In conventional concentrating solar power (CSP) systems, the contribution of solar energy is relatively low, merely supplementing the system with low/medium temperature air/steam. This paper aimed to emphasize the improvement of solar heat share, particularly in the topping cycle of the hybrid system. The solar aided processes, either directly generating superheated air/steam or direct gasification are thermodynamically favorable at very high temperatures, in excess of 800 °C. Unfortunately, this temperature is unattainable in conventional CSP systems using molten salt. Accordingly, the integration of solar power tower (SPT) with solid particle fluidized system in a beam down configuration has been proposed for the hybrid solar-biomass systems. Studies of such integration system presented challenges in terms of operating temperature, continuous supply/syngas production and scaling of reactor, particularly for circulating fluidized bed (CFB). The selection of solid particle and gas flow rate are among the governing parameters for high operating temperature and effective utilization of solar heat. The development of high temperature hybrid solar-biomass system is anticipated for higher solar-to-fuel conversion efficiencies, minimizing the direct combustion of biomass and reduce the emission of greenhouse gas (GHG) emissions.

The influence of different fly ash-cement replacement ratios on the pressure drop of a horizontal backfilling pipe

Fly ash (FA) is a kind of harmful by-product in thermal power generation plants, and finding a way to enhance the utility of fly ash has been widely discussed among civil engineering and mining sectors. To investigate the possible optimal ratios of replacing usually used bind agent namely Portland cement (PC) with fly ash, this paper designed different test groups with varying PC-FA replacement ratio. To identify the physical and chemical characteristics of mixing materials used to produce the backfilling slurries, a rheological experiment and X-ray diffraction test have been conducted. Rheological tests show all these three replacement ratio groups (60%, 65%, 70% respectively) are yield pseudoplastic fluid. Computational fluid dynamics as an efficient and money-saving method also has been introduced in the present research to duplicate the flow behaviors and calculate the pressure drop (PD) in the backfilling pipe circuits. The simulation results suggested that all these three RR categories experience an increasing tendency in pressure drop with increasing flow velocity, but in the velocity range of 2 m/s - 2.4 m/s, the increasing tendency is gentle until flow velocity reaches 2.6 m/s, the PD increase evidently. Furthermore, when the RR = 65%, the pressure drop is significantly lower than that of RR = 60% or RR = 70% at all the corresponding investigated flow particle sizes have significant impact on the pressure drop across a pipe and is dependent on solid fraction and flow rate and velocities. Therefore, we can conclude that a proper dosage of FA in mixing backfilling slurries can reduce pressure drop obviously and thereby decrease the expenses in bind agent. Given the FA’s significant effect on pressure drop, and comprehensive considering the backfilling capacity and backfilling cost, the combination of RR = 65% and velocity = 2.6 m/s is optimum.

Solid particle flow characteristics in the cone valve and its flow rate prediction model

The solid particle flow characteristics inside the cone valve were experimentally and numerically studied. The experiments were conducted at different valve sizes, valve opening positions, pressure drops, and fluidization velocities. Numerical simulation using the computational particle fluid dynamic method was also carried out over broader conditions. It is found that the solid particle flow inside the cone valve demonstrated the three-stage phenomena as the solid particle flew passing through two in-series connected orifice systems. The explanation of the three-stage phenomena of the solid particle flow rate to the valve opening was given according to the double-orifice flow model. Based on the physical nature of the solid particle flow characteristics, a semi-empirical model of the solid particle flow rate inside the cone valve was proposed. The model parameters, such as the saturated solid flow rate, the saturated valve opening, were determined using the experimental data and the existing knowledge of orifice systems. The model was then verified using the experimental data and presented acceptable prediction accuracy.

Effect of oscillation flow induced by lattices on a horizontal gas–solid two-phase flow

This study is focused on reducing the pressure drop, conveying velocity, and power consumption in a horizontal gas–solid flow. Four types of lattice models, which are fixed in the particle inlet, are proposed to easily generate the oscillation of the wake flow to easily convey the gas–solid two-phase flow. A horizontal pipeline with an inner diameter of 80 mm and length of approximately 5 m was used. Polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were employed as conveying solid materials. The experimental ranges of the average gas velocity and solid mass flow rate were 10–16 m/s and 0.10–0.47 kg/s, respectively. Compared to the nonlattice gas–solid flow, reductions in the total pressure drop, conveying gas velocity, power consumption, and additional pressure loss were achieved in the range of lower gas velocity when using the lattice model. The highest reduction rates of the minimum conveying velocity and additional pressure drop were approximately 5.12% and 15.2%, respectively. In the acceleration region, the particle concentration in the flows with the lattice model was larger than that in the nonlattice flow near the upper part of the pipe and lower than those in the nonlattice flows in the lower part of the pipe. The time-mean axial particle velocity and particle fluctuating velocity in all lattice model flows were higher than those in the nonlattice flow, according to particle image velocimetry measurements, particularly in the upper part of the pipe.

A phenomenological model for the pressure drop applicable across both dilute and dense phase pneumatic conveying

Due to their differences, predictive methods suitable for dilute and dense phase pneumatic conveying are rare in the literature. Conveying trials are often required to characterise a given system, where pressure drop measurements are plotted against gas mass flow rate for various solids flow rates. Empirical curves of constant solids flow are overlaid with measurements and resemble a ‘J’ shape. This paper presents a model for these curves based on the assumption that the pressure drop is a sum of two terms relating to the gas only influence and a combined gas and solids term. The model is validated for slug flow capable materials, where excellent agreement is obtained. However, it is concluded that the procedure is suitable for fluidised dense-phase capable materials as well. The developed model has the potential to significantly reduce the number of conveying trials required to characterise a pneumatic conveying system.

Effect of operating conditions on the hydrodynamics in fountain confined conical spouted beds

Spouted bed stability and operation is greatly affected by particle features. Accordingly, the hydrodynamic behaviour of conical spouted beds has been studied for fine particles differing in size and density in a wide range of inlet air flow rates. This knowledge is essential for a successful scaling up and industrial implementation of the spouted bed. Therefore, the effect air velocity and solid properties (density and size) have on local solid velocity has been ascertained in a fountain confined conical spouted bed using a borescope technique (Particle Tracking Velocimetry, PTV) applied to several bed configurations. The results show a close relationship between the inlet air velocity and the local solid velocity, with the gas-solid contact being especially vigorous in the configurations without draft tube and with the open-sided draft tube. The solid circulation flow rate is lowest when a nonporous draft tube is used due to the low solid vertical velocities in the annulus, even at high air flow rates. Nevertheless, vertical velocities in the annular zone increase when particle size and density are increased, although these velocities are lower in the spout and fountain regions due to the higher momentum exchange required for their acceleration.

Modeling study on the dynamic characteristics in the full-loop of a 350 MW supercritical CFB boiler under load regulation

To improve the load regulation ability of the circulating fluidized bed (CFB) unit, investigating the hydrodynamic characteristics of the gas-solid flow in the CFB loop during such processes is of vital importance. In this work, based on the mass and pressure balance in the whole loop, a one-dimensional dynamic model on the gas-solid flow in the full-loop of an industrial CFB was established. In particular, the solid mass flow rate at the dust exit was correlated with the total inventory of the cyclone, and the re-circulating rate to the furnace was depicted by the pressure drop in the loop seal. The model was validated by the field test data of a 350 MW supercritical CFB boiler during a load increasing process. Subsequently, the impact of the load change rate and operating bed pressure on the hydrodynamic performance in the whole loop of the CFB boiler during the load reduction process were analyzed. The results show that the bed pressure in the furnace will fluctuate more violently when the load change rate increases, while the operating bed pressure has a weak effect on the load regulation process. These conclusions can provide theoretical guidance to the variable load operation of the CFB boiler.

Discharge stability analysis of top discharge blow tank in dense-phase pneumatic conveying system

Dense-phase pneumatic conveying is widely applied in large-scale entrained-bed gasification systems for feeding and conveying pulverized coal into the gasifiers. The discharge stability of blow tanks will affect the conveying process of powders in the conveying pipelines, and ultimately influence the long-term safe and stable operation of the gasifiers. In this paper, aiming at the problem of controllable discharge and conveying of powders in dense-phase pneumatic conveying systems, the research on the discharge analysis of a top discharge blow tank was carried out, which improves the understanding of top discharge blow tanks. Shannon entropy analysis and relative standard deviation analysis based on instantaneous solid mass flow rate signals were used as indicators for the discharge stability. The effects of operating conditions, powder external moisture content, and blow tank structural parameters on the discharge stability of a top discharge blow tank were investigated. The results indicate that for a given pneumatic conveying system, there exists an optimal supplementary gas volume flow rate corresponding to the most stable discharge process of the blow tank. With an increase in the external moisture content of pulverized coal, the discharge stability of the blow tank first increases and then decreases. As the riser diameter increases, the discharge process of the blow tank becomes unstable owing to the increase in the randomness of the conveying process.

Depicting the role of gas–solid interactions on the hydrodynamics of converging pneumatic riser

The understanding of the flow characteristics and effect of gas–solid interactions in pneumatic risers is fundamental to investigate to ensure effective design cost-effective operation. Thus, to understand the effect of gas–solid interactions on the hydrodynamics of newly proposed conversing risers, this study mainly focused on predicting pressure drop in the dilute phase pneumatic conveying system. The experiments were conducted in a converging riser having a convergence angle of 0.2693°. Various solid particles such as sago, black mustard, and alumina have been considered to study the effect of particle sizes and density on the pressure drop. The experimental outcomes indicate that the total pressure drop increases with an increase in the solid density and gas mass flow rate. Moreover, smaller particle sizes are also increased the pressure drop. An empirical correlation is developed for the prediction of total pressure drop Δ P T in converging pneumatic riser via dimensional analysis. All dependent variables such as particle and air density, drag force, acceleration due to gravity, the mass flow rate of air and particle, the diameter of particle and converging riser, the height of converging riser were considered to develop the empirical correlation. The established relationship is tested, and experimental data have been fitted for its validation. The estimated relative error of less than 0.05 proved the significance of the developed correlation. Hence, it can be stated that the established relationship is useful in studying the effects of various parameters on the pressure drop across the length of the conversing riser.

Effect of moisture content on flow behavior and resistance characteristics of dense-phase pneumatic conveying

The flow characteristic of high pressure dense-phase pneumatic conveying of pulverized coal is essential to the safe and stable operation of the gasifier. In this paper, the effects of coal moisture content on conveying behavior and resistance characteristics of dense-phase pneumatic conveying were explored. Meanwhile, a model of the additional pressure drop of particles was proposed and compared with the experimental data. The results show that though the resistance and cohesiveness increase with increasing moisture content, its influence is different in dense and dilute phase. In the dense-phase region, the coal with lower moisture content shows a larger solid mass flow rate and solid concentration; while in the dilute-phase region, the moisture content has minor effect on conveying characteristics. For the coal with lower moisture content in dense-phase region, the solid mass flow rate and solid concentration are larger, and the gas velocity has a small effect on solid friction factor, due to its smaller cohesiveness and resistance, which is showed in our experiments and inferred from our model. The additional pressure drop model was proposed for straight pipes and bends, whose parameters are probably effective than the existing parameters in this kind of model, as the deviation in the vertical rise pipe, horizontal pipe and bend pipe is controlled within ±30%, and the corresponding vertical down pipe are controlled within ±40%.

Flow regime transition and liquid distribution in a 3D concurrent downflow three-phase moving bed

Based on a cold-flow experimental setup, the transition between trickle flow and pulse flow in a 3D concurrent downflow three-phase moving bed is investigated by the standard deviation of pressure drop and visual observations. Results show that at a constant gas flow rate, the trickle-to-pulse transition shifts to a higher liquid flow rate with the increasing solid flow rate because the particle moving inhibits the formation of local liquid blockage. Furthermore, an empirical model is proposed to fit the trickle-to-pulse transition boundary by correlating the dynamic liquid holdup at the boundary with the gas Reynolds number, the particle velocity, and the relative viscosity. Finally, the effects of the particle moving on the liquid distribution are investigated, which shows that the particle moving makes the liquid distribution more uniform when the solid flow rate is smaller than a certain value. But further increasing the solid flow rate, the liquid distribution becomes uneven.

Analysis of the Suspended solids transport in a stream located in the southwest of the Buenos Aires province, Argentina

The total suspended solids (TSS) concentration is a relevant parameter for stream management. A high content of TSS has a negative impact on the ecological habitats and the aquatic environment, and could also be a limitation for the exploitation of surface water. The determination of TSS concentration through water sampling and posterior laboratory analysis is a complex and economically expensive procedure. In this regard, turbidity arises as a useful surrogate measure that allows the indirect estimation of the TSS concentration in a simple and economically convenient way. In the context of a severely deteriorated water supply system, the Napostá Grande stream constitutes a valuable resource for human and industrial consumption in the City of Bahía Blanca. The general objective of the present investigation is to develop statistically based relations between the parameters involved in the suspended solids transport, in order to characterize this phenomenon through the measurement of variables of simple and straightforward field determination. The statistical relationship between the TSS concentration and turbidity and between discharge and solid flow rate was explored. In both regression analyses, the statistical correlation resulted highly significant, and therefore represent valid calibration tools for future solids transport modelling analysis and prediction as well as for sedimentological balances. A comparative analysis of the solids transport between the closure of the medium drainage basin and at the outer limit of the suburban area of Bahía Blanca City, suggests the existence of erosive processes affecting the stream bed and its margins at the section between both sites.