Initial Bed Height Research Articles

Performance evaluation of coconut shell originated activated carbon as an adsorbent on the paint factory effluent treatment

The current study was aimed to evaluate the ability of the activated carbon prepared from coconut shell in the decolorization of paint factory effluent (PFE). The studies were performed in the fixed bed adsorption column by optimizing the design variables viz., initial effluent concentration, bed height and low rate. The experimental observations were used to make breakthrough curves and were validated using Adams – Bohart model and Yoon-Nelson model. The results recommended that the encapsulated activated carbon of coconut shell origin showcased its capacity to perform in the process of paint factory effluents decolorization as an adsorbent.

Fixed-Bed Adsorption Column Studies for the Removal of Methyl Orange from Water Using Polyethyleneimine-Graphene Oxide Polymer Nanocomposite Beads

Continuous fixed-bed column studies were performed using nanocomposite beads made up of chitosan, polyethyleneimine, and graphene oxide as adsorbents for the removal of methyl orange (MO) in water. The effects of different operating parameters such as initial MO concentration (5, 10, and 15 ppm), bed height (10, 17.5, and 25 cm), and flow rate (27, 43, and 58 mL/min) were investigated using an upward-flow fixed-bed column set-up. The breakthrough curves generated were fitted with Adams-Bohart, Thomas, Yoon-Nelson, and Yan et al. models. The results showed that Yan et al. model agreed best with the breakthrough curves having an R2 as high as 0.9917. Lastly, design parameters for a large-scale adsorption column were determined via scale-up approach using the parameters obtained from column runs.

Investigation of electrical field effect on the fluidization characteristics in a two-dimensional fluidized bed

Electrostatic charge accumulation in a gas–solid fluidized bed is considered an adverse effect. However, with the presence of an external electrical field, we can take advantage of electrostatic charging to separate charged particles according to their polarity. In this paper, we proposed a bench-scale two-dimensional fluidized bed with an external electrical field. We then systematically investigated the tribo-charging behavior of anthracite-quartz mixture in the fluidized bed at different conditions and the effect of the external electrical field on their fluidization characteristics. Subsequently, an orthogonal design of experiments analysis was implemented to find the optimized parameters of gas velocity, plate voltage, and initial bed height to separate bituminous coal particles. These findings provide a dry method to separate coal particles from their associated minerals using the proposed two-dimensional fluidized bed with an external electrical field and have general implications for the triboelectric separation of various materials.

Immersion Effect on the Anaerobic Degradation and the Rheological Properties of Straw-Cattle Manure (SCM) at 440 L Batch Pilot Scale Reactor

The effects of the solid bed immersion in the anaerobic digestion of straw-cattle manure (SCM) were studied using two batch reactors of 2 m of solid height and 440 L of total volume. The reactors were operated in parallel with total (R1_100%) and partial solid height immersion (R2_74%) and no liquid recirculation. Recovered methane yield was 31.1% higher in R1 than in R2, 33.7 and 23 Nm3 CH4 t−1SCM respectively. The volatile solids (VS) and fiber degradation was studied in layers distributed each 0.5 m of the initial solid bed height profile; VS removal was measured at 16% at 2 m height in contrast to 39.9% at the reactor bottom. VS removal was related with hemicellulose and cellulose biodegradation, maximal hemicellulose and cellulose degradation in the studied layers were 68.2 and 49.5% respectively. Physical and rheological changes of the solid phase were measured between the SCM and the digestate. Macropores volume was reduced from 30.4% to values between 0.82 and 5.57%, this decrease was related to the water content and the fiber degradation state in each layer. Similarly, yield stress values obtained with the slump test depends on total solids content and fiber degradation state, yield stress values ranged from 1.41 and 2.23 kPa for raw and digested SCM. Moreover, values of cohesion and the friction angle were between 1.5 and 2.8 kPa and 15.6 and 47.7° respectively. Physical and rheological properties of digested SCM depends on the solid degradation state and the water availability through the material’s height profile.

CFD Analysis of Phase Holdup Behaviour in a Gas-Liquid Bubble Column

Experimental works on bubble column hydrodynamic are normally carried out on a laboratory scale less than 0.3 m with holes number less than 10. In this paper, we discuss several approaches to bubble column scale-up, relying on variables of parameters. Two spargers with different hole diameters (0.5 mm and 1.25 mm) and superficial gas velocities (0.0125 m/s and 0.0501 m/s) are used to determine the distribution of gas holdup and liquid flow pattern. An Insignificant level of bed heights is investigated for the efficiency of hydrodynamic performance. Computational Fluid Dynamic (CFD) is used as the realistic representation of the actual reactor. The flow of the gas-liquid interface is implemented using the VOF model using the finite volume method by tracking the volume fraction of each of the fluids throughout the domain. It is observed that the initial bed heights, superficial gas velocity, and hole diameter of the sparger influence the overall gas holdup. Although the difference in sparger hole diameter affects overall gas holdup, the results are weak relative to other operating conditions. The simulation work is then compared with experimental data to improve the accuracy in analyzing the hydrodynamics of multiphase system, as well as validated the multidimensional models.

Fluidization behaviors of nanoparticle agglomerates with high initial bed heights

The fluidization behaviors of SiO2 nanoparticles with high initial bed heights of 8–24 cm are investigated experimentally. The effects of the initial bed height and the superficial gas velocity on the minimum fluidization velocity, bed heights, axial solid distributions and the agglomerate diameter are discussed. The results show that the minimum fluidization velocity decreases significantly with the increase of the initial bed height. Over 80% of nanoparticles are fluidized at the bottom dense region of the bed under all fluidization conditions. The high bed expansion arises from a significant increase of the upper dilute region of the bed. The mean diameter of agglomerates measured in the dilute region increases with the initial bed height and the superficial gas velocity. There exists a low-frequency mass transfer between the dense and dilute regions of the bed.

Mixing of nanoparticle agglomerates in fluidization using CFD-DEM at ABF and APF regimes

Mixing of nanoparticle agglomerates in a fluidized bed was investigated by CFD-DEM. A parallel program was used that simultaneously uses the computational resources of GPU and CPU on a single computer. The bed expansion obtained from simulation was compared with experimental and good agreement was observed. Bed expansion in agglomerate particulate fluidization (APF) was 2 to 5 times the initial bed height and final bed expansion in agglomerate bubbling fluidization (ABF) was 1 to 2 times the initial bed height by changing the gas velocity from 2 to 4 and 4 to 8cm/s for APF and ABF regimes respectively. Gas volume fraction distribution was investigated for both APF and ABF regimes, which showed a more uniform distribution in APF. Increasing the gas velocity led to a more homogenous in the APF bed but it did not change the homogeneity of the ABF bed. Besides, the axial and radial dispersion coefficients in ABF were greater than those in APF. Axial dispersion coefficient varied from 2×10−6 to 4×10−5m2/s. Lacey mixing index was investigated in both APF and ABF regimes and it showed that the quality of mixing in ABF was better than APF.

Statistical modeling and optimization of tannery wastewater treatment in a fluidized bed bioreactor with low density biomass support

Treatment of tannery industry effluent is a serious challenge due to the presence of toxic pollutants including dyes and heavy metals. This work is focused on the optimization of bed height and air flow rate for tannery industry wastewater treatment in a fluidized bed reactor with low density biomass support. Response surface methodology was adopted for the optimization of process parameters viz air flow rate, bed height and wastewater dilution ratio and the best operating conditions were identified. The optimum values for the maximum chemical oxygen demand (COD) removal are: air flow rate—233 LPH, Bed height—82 cm and wastewater dilution ratio—1:2. The results from the IFBR showed that a maximum of 90.2% of COD reduction obtained at an airflow rate of 233 LPH and initial bed height of 82 cm. In this research, a maximum colour removal of 83.4% was achieved. A high correlation coefficient (R2) value of more than 0.94 for all the three models indicates that the RSM based models predict the data well. The relative effect of variables on COD removal, colour removal and air hold up were depicted in perturbation plots.

Fluidization of biomass: a correlation to assess the minimum fluidization velocity considering the influence of the sphericity factor

This paper deals with the influence of different definitions for evaluating the sphericity factor on the prediction of minimum fluidization velocity (U mf) of different agro-industrial/forestry biomass residues and sand. Three biowastes (sawdust, grape marc, and grape stalk) and sand were characterized by sieving, and sphericity was calculated using images obtained by scanning electron microscopy (SEM). Two particle size populations (with mean diameters and density corresponding to B and D Geldart groups) were adopted for each biomass. As for sand, particles with a mean diameter of 0.33 mm were used. Tests were carried out in a lab-scale fluidized bed. Bed pressure drop was measured as a function of the superficial velocity of air at two different initial bed heights, for each type of biomass and mixtures with sand. Ratios of 0.50 and 0.75 (v/v) were used for mixtures. For all cases, U mf values were calculated experimentally and were compared against predicted values obtained from Ergun's equation and other correlations. It was found that the methodology adopted for determining sphericity significantly influences the obtained value of U mf. The lowest relative error between predicted and experimental U mf values was obtained using Riley’s sphericity method. Finally, a new correlation for U mf was proposed.

Numerical modeling of a batch fluidized-bed gasifier: Interaction of chemical reaction, particle morphology development and hydrodynamics

The present study aims to analyze the interaction of chemical reactions, particle morphology change and hydrodynamics in fluidized-bed gasifiers. The char gasification in a batch fluidized-bed gasifier was modeled. The two-fluid model approach was coupled with an extended version of the uniform conversion model accounting for inert ash fraction. Model assumptions were confirmed via measurement of char density, porosity and particle size distribution at different stages of conversion in a lab-scale fluidized-bed gasifier. The CFD model correctly predicts the effects of particle structure change on chemical reactions, approved by a first of its kind comprehensive validation against unsteady experiments. Based on the validated CFD model, the interaction of hydrodynamics and local particle density variations due to chemical reactions is analyzed, and the effect of the initial bed height is studied.

Packed bed column adsorption of phenol onto corn cob activated carbon: linear and nonlinear kinetics modeling

In the present study, linear and nonlinear regression analysis for packed bed column adsorption of phenol onto corn cob activated carbon was investigated. The activation of the corn cob provided the activated carbon with enhanced surface area and micropore volume of 903.7 m2/g and 0.389 cm3/g respectively. The analysis of the physical properties of the corn cob activated carbon (CCAC) revealed that it contained 33.47% of fixed carbon, 5.82% of ash content, 18.01% of volatile matter, 0.63 g/mL of bulk density, 5.50% of moisture content, and a pH of 6.30. SEM images indicated the presence of interspatial pores within the matrix of the adsorbent, while the FTIR analysis revealed that the major functional groups in CCAC were alkanol, alkanes, alkyls, carboxylic acids, ethers, esters, and nitro compounds. The effect of the process parameters influencing the dynamic adsorption process was investigated at flow rates (9–18 mg/min), initial phenol concentration (100-300 mg/L), bed height (5–10 cm), and particle size (300-800 µm). The breakthrough time and adsorption capacity increased with an increase in bed height but decreased with an increase in flow rate, initial phenol concentration, and particle size. At optimum conditions of bed height 10 cm, initial phenol concentration, 100 mg/L, flow rate, 9 mL/min, and particle size 300 µm, the adsorption capacity at breakthrough (qb), adsorption capacity at saturation (qs), volume of effluent treated at saturation (Veff,s), length of mass transfer zone (MTZ), adsorbent exhaustion rate (AER), fractional bed utilization (FBU) factor, Reynolds number (Re), Sherwood number (Sh), and the percentage phenol removal (Ys) were 2.143 mg/g, 8.570 mg/g, 12.96 L, 7.50 cm, 30.86 g/L, 0.25, 17.93, 28.85, and 66.13% respectively. The linear and nonlinear regression analysis of the Thomas, Adams-Bohart, and Wolborska models fitted better with the experimental data than the Yoon–Nelson model. Generally, the nonlinear regression proved to be a better tool for dynamic adsorption model analysis as the model parameters generated by the technique have a better correlation with the experimental data when compared to those obtained via linear regression. Conclusively, this study has shown that CCAC can successfully be used for the removal of phenol from aqueous solutions. It also demonstrated that the modeling approach significantly affects the outcome of the analysis of dynamic adsorption systems.

Semifluidized Bed Adsorption Column Studies for Simultaneous Removal of Aqueous Phase Pb2+ and Cd2+ by Composite Adsorbents: an Experimental and Mass Transfer Dynamic Model–Based Approach

In this present work, the performance of a semifluidized bed adsorption column has been evaluated for the removal of Pb2+ and Cd2+ in a semi-continuous mode. The composite adsorbents have been synthesized from waste biomass–based biochar and alginate-based biopolymer. Synthesized adsorbent characterized and finally tested its effectiveness in the removal of both Pb2+ and Cd2+ metal ions by batch and semifluidized bed column adsorption studies. The adsorptive removal efficiencies were found to be dependent on solution pH, initial metal ion concentration, adsorbent dose or initial bed height, static bed height, system temperature and inlet flow rate of semifluidized bed operation. Pseudo-second-order kinetic model was fitted to the batch adsorption experimental data by non-linear and linear regression method and it was found that the non-linear method gives a better way of obtaining the various kinetic parameters and its applicability. A solute phase mass transfer–based dynamic model has been developed to explain the adsorptive behaviour of metal ions onto adsorbents during the semi-continuous mode of operation of a semifluidized bed system. Various mass transfer parameters and degree of dispersion coefficients for the individual packed and fluidized section were obtained from the developed model.

Experimental study on defluidization behaviours and its influence factors during gas switching fluidization

In this work, an investigation on the fluidization behaviour of solid particles was carried out while the fluidizing agent was switched from one gas to another with an equal volumetric flow. Four different gases, namely helium, nitrogen, argon and carbon dioxide (He, N2, Ar and CO2), were adopted as fluidizing agents, and fluid catalytic cracking (FCC) was used as the experimental material. When changing the gas supply a sharp decrease of the bed pressure drop and significant compression of the emulsion phase are observed, as well as the disappearing of the bubbles and the formation of channels inside the bed. However, these disturbances are temporary, and the initial fluidization conditions can be restored after a certain amount of time. Such behaviour is quantitatively described by measuring the maximum relative decrease of bed pressure drop, the time duration and the intensity of the defluidization phase. The effects of the initial powder bed height, the switching gas velocity and the gas properties are analyzed as well. Finally, a semi-empirical model was developed to predict the defluidization time based on the understanding of this physical process and analyzing the experimental data.

Prediction of particle circulation rate in an internally circulating fluidized bed with a central draft tube

Controlling the internal particle circulation rate quantitatively is of great importance to the operation of the internally circulating fluidized bed with a central draft tube used in the biomass gasification field. In this work, the effects of the operating parameters on the internal particle circulation rate were investigated on a laboratory experimental apparatus. The results indicated that the internal particle circulation rate increased with the increasing air velocity in the central draft tube, and gently increased with the air velocity in the annular bubbling bed. The internal particle circulation rate increased with the increasing initial static bed height in the annular bubbling bed and decreased with the increasing particle size. The correlation formula was obtained through the regression of experimental data. Furthermore, a dynamic prediction model was established based on the theory of fluid mechanics, and the matching degree between the predicted values and experimental data was larger than 80%.

Rational suitability of low cost activated carbon in removing hexavalent chromium ions from wastewater by uninterrupted mode of adsorption

Heavy metals such as chromium, lead, arsenic and others are dense metals whose contamination of water may exterminate life on earth at the niche in industrial activities, foodstuffs or medicines and so on. Activated carbons are very helpful in removing heavy metal ions from aqueous solutions by adsorption, and have been investigated by many researchers so far. The practical relevance of activated carbon made from de oiled soya in the removal of hexavalent chromium ions through continuous adsorption mode is reported in this paper. A breakthrough plot was plotted in finding the effect of initial concentration and adsorbent bed height in the adsorption of hexavalent chromium through activated carbon of de oiled soya. The breakthrough time and saturation time increased as the concentration of the initial solution shot up from 40 mg/L to 60 mg/L. The saturation time was in an incremental mode when the thickness of the adsorbent bed height in a fixed bed was increased from 5cm to 7cm for 40 mg/L initial concentration of hexavalent chromium. The Adams-Bohart’s model was found to fit perfectly the fixed bed column in the removal of hexavalent chromium from aqueous solutions. The fabricated adsorbent worked well in detoxifying hexavalent chromium metal ion contaminated wastewater.

Rate of CO2 adsorbent attrition induced by gas jets on perforated plate distributors in bubbling fluidized beds

Particle attrition is a major challenge when handling bulk solid materials with fluidized beds due to its ability to cause particle loss. Herein, the particle attrition induced by the gas jets on a perforated plate distributor in a bubbling fluidized bed was investigated for CO2 adsorbent particles. An attrition tube, which used air as the fluidizing gas, was used as the fluidized bed. At a constant fluidizing velocity, the initial static bed height and orifice gas velocity were considered as variables. It was confirmed that abrasion dominated the particle attrition. The trend indicating the change in the maximum size of the particles (dpm,a) formed by attrition followed that of the attrition rate (i.e., the formation rate of fine particles via attrition). A new stirring factor that combined the model developed by Werther and Xi with the original stirring factor adequately explained the effect of the static bed height on both the attrition rate and dpm,a when the initial static bed height was greater than the length of the orifice gas jet that penetrated the bed. The attrition rate increased linearly with the new stirring factor. However, dpm,a increased exponentially with the new stirring factor. Relationships were successfully proposed to enable the estimation of the attrition rate and dpm,a for the CO2 adsorbent particles. This study provided the evidence indicating the significance of the effect of bed height on particle attrition induced by the gas jet on the distributor. Moreover, proper models for correlating the attrition rate and the maximum size of the fine particles formed by attrition in the bubbling fluidized bed were provided.

Removal of Tetracycline from Wastewater Using Circulating Fluidized Bed

In this study, the circulating fluidized bed was used to remove the Tetracycline from wastewater utilizing a pistachio shell coated with ZnO nanoparticles. Several parameters including, Tetracycline solution flowrate, initial static bed height, Tetracycline initial concentration and airflow rate were systematically examined to show their effect on the breakthrough curve and the required time to reach the adsorption capacity and thus draw the fully saturated curve of the adsorbent. Results showed that using ZnO nanoparticles will increase the adsorbent surface area and pores and as a result the adsorption increased, also the required time for adsorbent saturation increased and thus the removal efficiency may be achieved at minimum antibiotic flowrate, maximum bed height, higher antibiotic concentration, and higher airflow rate. Also, a minimum fluidization velocity correlation was developed in this study. This correlation was found to be a function of liquid velocity, bed height, particle size, and particle density. The results showed that circulating fluidized bed has a better performance and last more than two hours before the bed biomass exhausted in comparison with traditional fluidized bed.

Sodium Alginate Microspheres Interspersed with Modified Lignin and Bentonite (SA/ML-BT) as a Green and Highly Effective Adsorbent for Batch and Fixed-Bed Column Adsorption of Hg (II)

A new green composite microsphere (SA/ML-BT) was prepared from sodium alginate by interspersing modified lignin–bentonite clay (ML-BT) and its adsorption performance to Hg (II) from aqueous solution in a batch mode and column mode was systematically investigated. The morphology and structure of the SA/ML-BT were characterized by SEM, XRD and FTIR. BET analysis showed that the pore type of SA/ML-BT is mainly mesoporous. The enlarged surface area of 5.98 m2/g and the insertion of SA improved the attraction of Hg (II) to porous surface. In batch tests, different initial Hg (II) concentration, pH values and contact time were studied, which were fitted with pseudo-first-order, pseudo-second-order kinetic models and Langmuir/Freundlich isotherms. Zeta potential analysis showed that isoelectric point charge of SA/ML-BT was 3.24 and Hg (II) removal rate increased with pH increasing in the range of 1 to 3 then kept the maximum value of 93% in the range of 3 to 9. Likewise, in the fixed-bed column tests, the effects of initial concentration (10–30 mg/L), bed height (1–3 cm) and influent flow rate (0.5–1.5 mL/min) were evaluated, which were fitted with Yoon–Nelson and Bohart–Adam models. The SA/ML-BT remained 85% removal rate after three repeated cycles, which indicated a promising potential in sustainable applications. A removal capacity of 24.4 mg/g in batch and 42.1 mg/g in column tests were obtained respectively. These findings revealed that the proposed SA/ML-BT has great potential for metallic cation remediation.

Activated carbon from a specific plant precursor biomass for hazardous Cr(VI) adsorption and recovery studies in batch and column reactors: Isotherm and kinetic modeling

The main aim of this work was the development of the chemical activated carbon (AC) method from specific wood biomass, i.e., Eucalyptus camaldulensis sawdust (ECS), and this AC is proposed as a promising alternative treatment for hazardous Cr(VI) from aqueous solution. ECS waste sawdust was carbonized in two stages, i.e. 170 °C for 60 min, followed by 500 °C for 120 min under the continuous steam of nitrogen gas, and rated as an efficient method with H3PO4 activation (>80% Cr(VI) removal). Finally, activated carbon-Eucalyptus camaldulensis sawdust (AC-ECS) was selected for batch and column reactor studies and different influencing parameters, such as contact time, pH, temperature, initial Cr(VI) metal concentration, particle size, and bed height were optimized. AC-ECS was characterized through analysis by SEM, EDX, FTIR, and BET. Cr(VI) adsorption was found to be highly pH-dependent, i.e., 87% at pH 3.0. AC-ECS adsorption mechanism for Cr(VI) with experimental and maximum predicted adsorption capacities of 104 and 125 mg g−1, respectively, was best described by the Langmuir isotherm (R2 = 0.999) and pseudo-second-order kinetics (R2 = 0.999). The column study showed an improvement in the breakthrough curve time from 5595 to 12,270 min, with the respective increase of bed height from 5 to 15 cm, respectively. Column breakthrough data was found to be well fitted to the bed depth service time model. Current batch and column studies indicate that freshwater contamination with Cr(VI) can be managed by upscaling the AC-ECS as an efficient treatment solution.

Defluoridation by fluorapatite crystallization in a fluidized bed reactor under alkaline groundwater condition

Fluoride removal using fluidized bed crystallization (FBC) technology with phosphate rock (PR) and calcite as seed particles under an alkaline groundwater condition was investigated. The results indicated that the optimized operating parameters were: upflow velocity = 7.21 m h−1, Ca:P:F molar ratio = 10:4:1, and initial bed height = 120 cm. The turbidity of FBC reactor effluent was 1.5–5.9 NTU at the first phase, and then reduced to less than 1.0 NTU at the second phase, while the effluent fluoride level remained at a constant level (0.4–0.9 mg L−1) during the entire procedure. The exfoliation and dissociation of newly-generated nuclei from the seed particles surfaces after aging and drying for three days could serve as an additional filtration layer (located on the top of the expanded bed with a thickness of 1.0 cm) to intercept the fine particles in the second phase. Consequently, a rational strategy for fluidized bed operation was provided, which focused on turbidity control and fluoride removal. FBC performance can be divided into ripening and running periods according to the evolution of turbidity in effluent. Fluoride removal was achieved by the formation of amorphous calcium phosphate and then recrystallization into fluorapatite and/or FCO3-apatite and induced crystallization of fluorapatite and/or FCO3-apatite. The FBC process with additional filtration function of dissociated newly-generated nuclei could be regarded as a cleaner technology for fluoride removal; additionally, the spent seed particles could be utilized as resources in the phosphatic fertilizer industry. However, the fertilizer industry should continue to recover fluoride for further economic benefits.