Increasing Bed Depth Research Articles

Exploration and practice to improve the kinetic analysis of char-CO2 gasification via thermogravimetric analysis

Kinetic studies of char gasification with CO2 were conducted using thermogravimetric analysis (TGA) under isothermal conditions. A set of improved solutions were proposed to amend the data acquisition and processing in an isothermal TGA mode to reduce the processing error. On this basis, the effects of the external and internal mass transfer limitations on the gasification reactivity and kinetic parameters were investigated. Conventional cylindrical alumina crucibles (CAC) with different sidewall heights and a flat alumina disc (FAD) were used for sample loading. The stagnant gas region in the CAC played an important role in increasing the external mass transfer resistance of CO2 from the bulk flow to the bed surface. The external mass transfer limitation was eliminated in the FAD and, therefore, an abundant provision of CO2 to the surface of char bed was achieved. It was found that the char reactivity decreased linearly with increasing the height of the stagnant gas region but decreased exponentially with increasing bed depth. The mass-independent reactivity can be obtained by carefully striking a balance between the bed thickness and the loading area. The external mass transfers that occurred in the stagnant gas region definitely decreased the reactivity, the activation energy and the frequency factor but had a limited influence on the reaction order. The inter-particle diffusion (bed diffusion) had more significant effects on the reactivity and all the kinetic parameters than the external mass transfers.

Uranium Dynamic Adsorption Breakthrough Curve onto Rice Straw Based Activated Carbon Using Bed Depth Service Time Model

Uranium adsorption was evaluated on rice straw-based carbon (RSK carbon) that had been KOH-oxidized and impregnated with ionic-liquid. Experiments were performed in fixed bed mode using 100 mg/L uranium solution at 3 different bed depths (12, 6, and 3 cm). Uranium adsorption decreased with increasing bed depth. Agreement between column and batch values was judged to be acceptable in light of inherent differences in continuous versus batch operations. Batch mode reaches equilibrium without continuous solution feeding. However, the solution in fixed bed mode was fed constantly without equilibrium. The bed depth service time (BDST) model was used to investigate uranium adsorption. BDST plots were linear, with a high correlation coefficient (R > 0.97), representing its validity when used for fixed bed of RSK carbon. The failure of the 50% breakthrough BDST curve to pass through the origin point may be due to the complex mechanism of uranium removal by RSK carbon. The calculated BDST slopes were in good agreement with the experimental values, while the values of their intercept slightly varied within certain limit of experimental error. These results support the validity of BDST model for designing a fixed bed column for uranium adsorption onto RSK carbon.

Investigation on the fixed-bed column performance of paracetamol from aqueous solution by low cost materials

Over the last fifteen years, pharmaceuticals have been receiving increasing attention as potential bioactive chemicals in the environment. They are considered as emerging pollutants in water bodies. One of such pharmaceutical is paracetamol which show very difficult to remove from water. In this study, fixed-bed column experiments were performed to investigate the biosorption potential of paracetamol by low cost adsorbents egg shell and sugarcane. The adsorbents were characterized by using SEM, XRD and FTIR study. Present finding indicate that this particular pollutant easily removed by egg shell powder and sugar cane charcoal. Results suggest that, sugarcane charcoal is the best for paracetamol removal. The Thomas model data demonstrate that with increasing bed depth Thomas constant (K th ) increase linearly for egg shell, but sugarcane dose not showed such linearity with bed depth. The adsorbent exhaustion rate also showed linearity with bed depth as 3.2 cm (32), 7.5 cm (75) and 11.0 cm (110 ) for egg shell and 2.5 cm (50), 4.3 cm (86) and 6.2 cm (124) for sugarcane.

Performance of packed bed column using Chara aculeolata biomass for removal of Pb and Cd ions from wastewater

ABSTRACTBiosorption of Pb and Cd from aqueous solution by biomass of Chara aculeolata was studied in a continuous packed bed column. C. aculeolata in the fixed bed column is capable of decreasing Pb and Cd concentrations from 10 mg/L to a value below the detection limit of 0.02 mg/L. Selective uptake of Pb and Cd in a binary solution resulted in Pb having much higher relative affinity than Cd. The experiments were conducted to study the effects of column design parameters, bed depth, and flow rate on the metal biosorption. Pb uptake capacity of C. aculeolata increased with increased bed depth and decreased flow rate, while Cd uptake capacity increased with increased bed depth but remained constant at any flow rate. The Thomas model was found in a suitable fitness with the experiment data for Pb and Cd (R2 > 0.90). The efficiency of biosorbent regeneration achieved by 0.1 M HCl was very high, that was, 98% for Pb and 100% for Cd in the third reused cycle. It can be concluded that C. aculeolata is a good biosorbent for treating wastewater having low concentrations of Pb and Cd contamination.

A study of 4-chlorophenol continuous adsorption on nano graphene oxide column: model comparison and breakthrough behaviors

Removal of 4-chlorophenol in a continuous fixed-bed column was investigated by using nano graphene oxide (NGO) adsorbent in this study. The adsorbent (NGO) was characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy analysis. Variables in the adsorption process were bed depths (5, 10 and 15 cm), flow rate (1, 2 and 4 mL/min), influent 4-chlorophenol concentrations (5, 10, 15, 20 and 30 mg/L) and influent solution pH (6–7). The enhancement of adsorption is favored by decreasing 4-chlorophenol concentration and flow rate and increasing bed depth. Indeed, the best result obtained in this study was 145.2 mg/g of adsorption capacity under 4-chlorophenol concentration of 5 mg/L at a flow rate of 1 mL/min toward a bed depth of 15 cm. The results of the study showed that the ideal 4-chlorophenol adsorption followed well the Thomas and Yoon–Nelson models for predicting breakthrough behavior at different flow rates and bed depths. Finally, increasing flow rate, decreasing bed depth and increasing influent 4-chlorophenol concentration resulted in the breakthrough time and exhaustion time decreasing.

Fixed-bed column studies for the removal of anionic dye from aqueous solution using TiO2@glucose carbon composites and bed regeneration study

Glucose carbon with uniform diameter was successfully anchored by TiO2 nanoparticles via a facile low-temperature hydrothermal process independent of surfactants or external forces. The resultant TiO2@glucose carbon composite (TiO2@GCs) was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The elimination of direct deep blue (DDB) from aqueous solution by adsorption onto TiO2@GCs was investigated in the up-flow fixed-bed columns. The effects of the influent concentration (10–30 mg L−1), flow rate (3–5 mL min−1), bed depth (1.0–2.0 cm) and pH (1.0–9.0) were investigated. Breakthrough time and adsorption capacity of the fixed-bed increased with increasing bed depth, whereas decreased with the increase in initial concentration, bed depth and solution pH values. The experimental data was in good agreement with both Thomas model and Yoon-Nelson model. The employed bed saturated with DDB was readily regenerated through a simple regeneration process with UV irradiation for 1 h. Furthermore, the adsorption–regeneration process was conducted for six cycles and no major decrease of regeneration efficiency was observed for the first three cycles. One possible mechanism for regenerating dye-loaded TiO2@GCs was proposed. The verifying experiment found that hydroxyl radicals and superoxide ions significantly affected the regeneration of employed TiO2@GCs bed.

Efficient static and dynamic removal of Sr(II) from aqueous solution using chitosan ion-imprinted polymer functionalized with dithiocarbamate

A novel chemically modified chitosan Sr(II)-imprinted polymer (Sr(II)-IIP) with dithiocarbamate groups was prepared. The adsorbent was characterized by FT-IR, XPS, SEM and nitrogen adsorption–desorption. Sr(II)-IIP has regular spherical geometry and possesses larger surface area, pore volume and average pore diameter as compared to those of chitosan. Batch adsorption experiments were performed to evaluate the adsorption conditions and selectivity. The results showed that the maximum static adsorption capacity of Sr(II)-IIP for Sr(II) was 86.66mgg−1 at 45°C, which was larger than many other adsorbents. The experimental data were in good agreement with pseudo-second-order and Langmuir isotherm model. A continuous fixed-bed column study on Sr(II)-IIP showed that the adsorption capacity increased with increasing influent concentration, but decreased with increasing bed depth, flow rate and temperature. The mechanism for dynamic adsorption of Sr(II) onto Sr(II)-IIP was found to follow the Thomas model. Sr(II)-IIP was regenerated and found to be suitable for reuse in successive adsorption–desorption cycles seven times without significant loss in adsorption capacity, which showed that this novel adsorbent could be employed as an effective material for the selective removal of Sr(II) from aqueous solutions.

Assessment of Pb2+ ions removal efficiency of nanomagnetite-loaded poly (acrylamide-co-acrylic acid) hydrogel in fixed-bed microcolumn from aqueous solution

The adsorption potential of nanomagnetite-loaded poly (acrylamide-co-acrylic acid) hydrogel, to remove Pb(II) ions from aqueous solution as well as contaminated water, was investigated using fixed-bed adsorption column. The effect of inlet Pb(II) concentration, feed flow rate, and bed depth on the breakthrough characteristics of the adsorption system were determined. The adsorption capacity increased with the increase in initial Pb(II) concentration and flow rate, but decreased with increasing bed depth. The Thomas, Yoon–Nelson, and Adams–Bohart kinetic models were applied to the experimental data to predict the breakthrough curves and to determine the characteristic parameters of the column, useful for process design.

Continuous adsorption of Pb(II) and methylene blue by engineered graphite oxide coated sand in fixed-bed column

The mixture of several effluents, caused by the improper handling and management of effluents, generated multi-component wastewater containing both metals and dyes, leading to the complicated treatment process. In this study, a continuous adsorption of Pb(II) and methylene blue (MB) has been studied in single and binary solutions by using graphite oxide coated sand (GO-sand) as an adsorbent in a fixed-bed column. GO-sand was analyzed by X-ray photoelectron spectroscopy before and after analyte adsorption. Compared with sand filter, adsorption quantity and capacity for Pb(II) and MB by GO-sand filter were greatly increased. In Pb(II) and MB single solutions, the experimental parameters were investigated in detail including initial concentration, flow rate, bed depth and pH. Exhaustion time decreased with increasing initial concentration and flow rate, and increased with increasing bed depth and pH. In the Pb(II)-MB binary solution, exhaustion time significantly decreased for Pb(II) adsorption, but increased for MB adsorption. The reason was explained that the more favorable adsorption for MB onto the surface of GO-sand than that for Pb(II), which was derived from π–π interaction between MB and GO on sand surface in packed filter. The Yoon–Nelson model was applied at different concentration of Pb(II) and MB to predict the breakthrough curves. The experimental data were well fit with the model indicating that it was suitable for this column design.

Recovery of Zn(II) and Ni(II) Binary from Wastewater Using Integrated Biosorption and Electrodeposition

The present study aimed to obtain best operational conditions for biosorption of Zn(II) and Ni(II) binary metal solution in a fixed bed packed with wheat straw as biosorbent. The effects of bed depths, liquid flow rates and mixture metal concentrations on biosorption service time were investigated. The results showed that breakthrough service time of the biosorption columns (Cb = 2 mg/L Zn and Ni) increased with increasing bed depth, while decreased with increasing influent concentrations and flow rates, as expected. This paper further extended the study to investigate the competition of Zn(II) and Ni(II) binary in solution by performing biosorption tests at varied ratio of the metal concentrations. For biomass regeneration, the effect of desorbing agents (hydrochloric acid, nitric acid and sulphuric acid), their concentrations (0.1–0.5 mol/L) and flow rates (0.05–0.1 L/min) on recovery of Zn(II) and Ni(II) binary mixture was investigated. The best performance in desorption of Zn(II) and Ni(II) binary solutions were 0.1 mol/L H2SO4 and a 0.05 L/min inlet flow rate. Moreover, after five sorption/desorption cycles, the biosorbent still maintained its high adsorption capability. Electrodeposition was also used to recover metal ions from concentrated Zn(II) and Ni(II) binary solutions (about 340 mg/L) from the desorption step. It was found that the electrodeposition could reduce the metal concentrations down to wastewater discharge limit of 2 mg/L Zn and Ni ions.

Development of Household Defluoridation Unit Based on Crushed Burnt Clay Pot as Sorbent Medium: A Case of Keren Community, Eritrea

Fluoride in water in some parts of Eritrea is above the WHO guideline of 1.5 mg/L. One of the communities in Eritrea exposed to drinking water of high fluoride is Keren community and as a result, they suffer dental and skeletal fluorosis. A survey at 16 water sources in 13 villages was made and 87% of the samples exceeded the guideline, having fluoride levels 1.40-3.98 mg/L. Fluoride removal from synthetic water using crushed burnt clay pot as a sorbent medium was studied in a packed column. A preliminary experiment was carried out on a laboratory scale in mini column, with three different packed beds, 15, 20 and 25 cm depth. A flow rate of 2.5, 5, 10, and 15 ml/min having 5 mg/L fluoride was passed through each bed. The results indicated that the breakthrough volume and time increased with increasing bed depth of the column. On the other hand, an increase in flow rate reduced the treated volume at breakthrough and therefore decreased the service time. Ideal breakthrough occurred at 25 cm bed depth at a flow rate of 2.5 ml/min with breakthrough volume 7.3 L, resulted in reduction of fluoride from 5 to 1.48 mg/L. The result of the mini column was scaled up and tested in a pilot scale unit. The pilot scale managed to treat 324 L of water satisfying the WHO standards of fluoride concentration. The performance of the pilot column agreed with that obtained from the mini column and therefore, crushed burnt clay pot is suitable low cost adsorbent to remove fluoride from water.

Analysis and modeling of column operations on reactive dye removal onto alkaline-treated biomass fly ash

The adsorption characteristics of Reactive Black 5 (RB5) dye on alkaline-treated biomass fly ash (TFA) were investigated in aqueous solutions in a fixed-bed column. The breakthrough curves increased with decreasing initial dye concentration and the flow rate, and with increasing bed depth. In this column study, the optimum flow rate and bed depth were 5 ml min−1 and 10 cm, respectively. The Thomas model provided a good prediction of the breakthrough curve of RB5 removal by the TFA. The maximum adsorption capacity from the column study was in accordance with the equilibrium capacity in a batch experiment. The bed-depth service time model was used to describe the effect of bed depth on the breakthrough curves, and it revealed a good fit with the experimental data. These results suggest that the fixed-bed TFA is suitable for treating dye wastewater.

Removal of Ni (II) ions from aqueous solutions using modified rice straw in a fixed bed column

This paper investigates the ability of modified rice straw, an agricultural biomaterial, to remove Ni (II) ions from aqueous solution in a fixed-bed column. The experiments were performed with different bed heights (1.5 and 2.0 cm), influent Ni (II) concentrations (50, 75 and 100 mg/L) using flow rates (500 μl/min) in order to obtain experimental breakthrough curves. The maximum adsorption capacity of rice straw powder (RSP) was 43 mg/L at 75 mg/L influent concentration of divalent Ni (II) ions at 2 cm bed depth. Adams-Bohart model, Thomas model and Yoon and Nelson kinetic models were used to analyze the column performance. The value of rate constant for Adams-Bohart and Yoon and Nelson model decreased with increase of influent concentration, but increased with increasing bed depth. The rate constant for Thomas model increased with initial influent Ni (II) ions concentration, decreased with increase in bed depth.

Physical property and resistance to airflow through bulk and thin-layer lemon fruit

Introduction Physical properties of lemon fruit are important for drying system and Kept in stock. Objective The prediction of airflow resistance is fundamental to the design of efficient drying and aeration systems for lemon fruit. Methods Using a laboratory unit, two sets of experiments were carried out, namely thick and thin layers. In the thick-layer experiments, four bed depths, 11 flow rates and four temperatures 25, 35, 45 and 55 C. In the thin layer (two kernels depth, 3 cm), the kernels were put together in three arrangements: A, B and random; five moisture contents and 11flow rates were studied. Results Results indicated that resistance to airflow through a column of lemon fruit increased with increasing bed depth and airflow rate. In the latter experiment, pressure drop decreased with a decrease in moisture content.Airflow rate was the most significant factor affecting the pressure drop of lemon fruit in both experiments. Conclusion Three applicable models (Shedd, Hukill and Ives, and Ergun) were used to evaluate the pressure drop data. The Ergun model, with higher values for coefficient of determination and lower values for sum of square error and mean relative deviation modulus, is the best model for predicting pressure drop across lemon fruit bed for the conditions studied.

Lignocellulosic jute fiber as a bioadsorbent for the removal of azo dye from its aqueous solution: Batch and column studies

AbstractThe feasibility of the use of jute fiber for the adsorption of azo dye from an aqueous solution was evaluated with batch and fixed‐bed column studies. The batch studies illustrated that dye uptake was highly dependent on different process variables, namely, the pH, initial dye concentration of the solution, adsorbent dosage, contact time, ionic strength, and temperature. The exothermic and spontaneous nature of adsorption was revealed from thermodynamic study. The equilibrium adsorption data were highly consistent with the Langmuir isotherm and yielded an R2 value of 0.999. Kinetic studies divulged that the adsorption followed a pseudo‐second‐order model with regard to the intraparticle diffusion. In the column studies, the total amount of adsorbed dye and the adsorption capacity decreased with increasing flow rate and increased with increasing bed height and initial dye concentration. Also, the breakthrough time and exhaustion time increased with increasing bed depth but decreased with increasing flow rate and influent dye concentration. The column performances were predicted by the application of the bed‐depth service time model and Thomas model to the experimental data. The virgin and dye‐adsorbed jute fiber was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The investigation suggested that jute fiber could be applied as a promising low‐cost adsorbent for dye removal. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Fixed-Bed Column Study for the Removal of Ag(I)and Cr(III) from Aqueous Solutions Using Puffed Rice Husk

Fixed-bed column studies for the removal of Ag(Ⅰ) and Cr(Ⅲ) from individual aqueous solutions using puffed rice husk were investigated in this work. The experiments were conducted to study the effect of important column parameters such as bed height, feed flow rate and feed initial concentration of solution. It was found that increasing bed depth yielded longer service time while increase in influent concentration and flow rate resulted in faster breakthrough. Bed Depth Service Time (BDST) model was applied to analyze the experimental data and the model parameters were evaluated. Good agreement of the experimental breakthrough curves with the model predictions was observed.

Pilot scale evaluation of biofiltration as an innovative pre-treatment for ultrafiltration membranes for drinking water treatment

Fouling remains one of the major constraints on the use of low pressure membranes in drinking water treatment. Work over the last few years has shown the importance of biopolymers (carbohydrates and protein-like material) as foulants for ultrafiltration (UF) membranes. The purpose of this study was to investigate at pilot scale the use of rapid biofiltration (without prior coagulation or ozone addition) as an innovative pretreatment to reduce fouling of UF membranes. The investigation was carried out on a water with a higher than average DOC and significant temperature variation. The biofilters, each operated at a hydraulic loading of 5 m/h, had empty bed contact times of 5, 10 and 15 minutes. The membrane unit was operated at a flux equivalent to 60 LMH at 20°C. The investigation confirmed the encouraging results obtained in an earlier smaller scale study with essentially the same water. Increased biofiltration contact time (i.e. increased bed depth) led to lower rates of hydraulically irreversible fouling. The initial biofiltration backwash procedure, involving air scour as is common in chemically assisted filtration, led in some cases to an increased rate of membrane fouling immediately after the backwash. An alternative backwashing strategy was developed, however the feasibility of operating with this approach over very long periods of time needs to be confirmed. To assist in full-scale implementation of this “green” and simple pretreatment, the design and operating conditions for the biofilters should be optimized for various types of waters. It is expected that biofiltration pretreatment will be of particular interest for small and/or isolated systems where a higher initial capital cost may be acceptable because of operational simplicity and reduced chemical requirements.

The application of theoretical solutions to the differential mass balance equation for modeling of adsorptive desulfurization in a packed bed adsorber

Adsorptive removal of organosulfur compounds, lumped as total sulfur content, from a real diesel fuel was carried out in a packed bed adsorber. A novel approach was taken in the application of theoretical solutions to the differential mass balance equation using modern software tools, and one classic method as point of reference. Adsorptive desulfurization is a perspective downstream process to hydrodesulfurization for achieving sulfur concentration levels of less then 10 mg kg −1. Compared to the conventional hydrodesulfurization process, the deep desulfurization can be accomplished without changing the physical properties of the product and at relatively low temperature and pressure. The adsorber apparatus comprised computer control, enabling completely automated operation. Adsorbent was activated carbon SOLCARB C from Chemviron Carbon, Belgium. The experimental results regarding the influence of flow rate and bed depth on the outlet sulfur concentration were evaluated as well as the models ability to describe the adsorption kinetics and to estimate the breakthrough curves. Ultra deep desulfurization of diesel fuel was achieved and it was determined that outlet sulfur concentration was being lowered by decreasing flow rate and increasing bed depth. The closest fit to the experimental data was achieved for the Bohart–Adams model.

Resistance to airflow through bulk pistachio nuts (Kalleghochi variety) as affected by moisture content, airflow rate, bed depth and fill method

The prediction of airflow resistance is fundamental to the design of efficient drying and aeration systems for pistachio nuts. Using a laboratory unit, the pressure drop across a column of pistachio nuts (Kalleghochi variety) was investigated to determine the effect of moisture content, airflow rate, bed depth and fill method. Five levels of moisture contents (4.80, 14.50, 23.70, 37.60 and 45.60 w.b.%), four bed depths (25, 50, 75 and 100 cm) and two fill methods (loose and dense) were studied with airflow rates ranging from 0.08–1.00 m 3/S m 2. Results indicated that resistance to airflow through a column of pistachio nuts increased with increasing bed depth, moisture content and airflow rate for both dense and loose fill method. Airflow rate was the most significant factor affecting the pressure drop of pistachio nuts followed by fill method and moisture content. The dense fill of pistachio nuts produced higher resistance to airflow compared with the loose fill. Among the three models (Shedd, Hukill and Ives, and Ergun equation) investigated to describe pressure drop data of pistachio nuts, Ergun equation was found to be the most suitable for describing the pressure drop data of pistachio nuts.

Experimental study of the nature of gas streaming in deep fluidized beds of Geldart A particles

The characteristics of gas streaming in a deep gas–solid fluidized bed containing Geldart's Group A powder has been investigated in a 30-cm ID cold flow unit. Four different experimental configurations including forced streaming flow, high and low-velocity jetting and natural streaming flow in deep beds were designed and conducted for bed depths and gas velocities ranging from 0.4 to 1.6 m and from 0.04 to 0.20 m/s, respectively. The range of gas velocities corresponds to 10–50 U mf which covers the bubbling fluidization regime. The effect of fines content was studied using two particle size distributions with Sauter mean diameters of 48 and 84 μm, corresponding to 20% and 3% fines content, respectively. Analysis results using autocorrelation and power spectral density (PSD) indicated that the natural streaming closely resembles the forced streaming flow at the wall in which flow of gas is also present in the remaining regions of the distributor. Application of supporting secondary jet injection in addition to the primary gas flow enhanced the fluidization quality to some extent, but was not sufficient to provide fully bubbling fluidization throughout the entire bed. Increasing the primary gas velocity from 10 to 50 U mf was found to reduce the effect of supporting jets. It was found that higher fines content improved fluidization. Wavelet analysis of pressure fluctuations showed that in deep fluidized beds, bubbling activity with the typical dominant frequency coexists with the streaming flow, however with a minor contribution to the overall fluidized bed behaviour compared to the prevailing streaming flow. Based on the coexistence of several bubble streams in a bubbling fluidized bed as reported in the literature, Wavelet findings suggested that the streaming flow can be considered to form by increasing the relative importance of one of the available streams of bubbles with increasing bed depth.