Pall Rings Research Articles

Enhanced removal of refractory humic- and fulvic-like organics from biotreated landfill leachate by ozonation in packed bubble columns

Biotreated landfill leachate contains much refractory organics such as humic and fulvic acids, which can be degraded by O3. However, the low O3 mass transfer and high energy cost limit its wide application in landfill leachate treatment. Previous studies proved that packed bubble columns could enhance the O3 mass transfer and increase the synthetic humic acids wastewater degradation, but the performance of packed bubble columns in real wastewater treatment has not been investigated. Therefore, this study aims to evaluate the feasibility of application of packed bubble column in the real biotreated landfill leachates treatment and provide insights into the transformation of organic matters in leachates during ozonation. Packed bubble columns with lava rocks or metal pall rings (LBC or MBC) were applied and compared with a non-packed bubble column (BC). At an applied O3 dose of 8.35 mg/(Lwater sample min), the initial COD (400 mg/L) was only removed for 26% in BC and 32% in MBC while this was 46% in LBC, indicating LBC has the best performance. GC–MS analysis shows that raw biotreated leachate contains potential endocrine disruptors such as di(2-ethylhexyl) phthalate (DEHP). 61% of DEHP was removed in LBC and the least intermediate oxidation products from humic- and fulvic-like organics was detected in LBC. The highest O3 utilization efficiency (89%) and hydroxyl radical (OH) exposure rate (3.0 × 10-10 M s) were observed in LBC with lowest energy consumption (EEO) for COD removal of 18 kWh/m3. The enhanced ozonation efficiency in LBC and MBC was attributed to the improved O3 mass transfer. Besides, LBC had additional adsorptive and catalytic activity that promoted the decomposition of O3 to generate OH. This study demonstrates that a packed bubble column increases removal and decreases energy use when treating landfill leachate, thus promoting the application of ozonation.

Biological elimination of a high concentration of hydrogen sulfide from landfill biogas.

Hydrogen sulfide (H2S) is one of the main contaminants found in biogas, which is one of the end products of the anaerobic biodegradation of proteins and other sulfur-containing compounds in solid waste. The presence of H2S is one of the factors limiting the valorization of biogas. To valorize biogas, H2S must be removed. This study evaluated the performance of a pilot-scale biotrickling filter system on H2S removal from landfill biogas. The biotrickling filter system, which was packed with stainless-steel pall rings and inoculated with an H2S-oxidizing consortium, was designed to process 1 SCFM of biogas, which corresponds to an empty bed residence time (EBRT) of 3.9 min and was used to determine the removal efficiency of a high concentration of hydrogen sulfide from landfill biogas. The biofiltration system consisted of two biotrickling filters connected in series. Results indicate that the biofiltration system reduced H2S concentration by 94 to 98% without reducing the methane concentration in the outlet biogas. The inlet concentration of hydrogen sulfide, supplied to the two-phase bioreactor, was in the range of 900 to 1500 ppmv, and the air flow rate was 0.1 CFM. The EBRTs of the two biotrickling filters were 3.9 and 0.9 min, respectively. Approximately 50 ± 15.7 ppmv of H2S gas was detected in the outlet gas. The maximum elimination capacity of the biotrickling filter system was found to be 24 g H2S·m-3·h-1, and the removal efficiency was 94 ± 4.4%. During the biological process, the performance of the biotrickling filter was not affected when the pH of the recirculated liquid decreased to 2-3. The overall performance of the biotrickling filter system was described using a modified Michaelis-Menten equation, and the Ks and Vm values for the biosystem were 34.7 ppmv and 20 g H2S·m-3·h-1, respectively.

Experimental Investigation of the Effect of Random Packings on Heat Transfer and Particle Segregation in Packed-Fluidized Bed

The heat transfer coefficient, pressure drop, and vertical segregation in a bubbling fluidized bed reactor containing random packings were investigated. The bed material was silica sand in the size range of 90–400 μm. Experiments were done for bed temperatures ranging from 400 to 900 °C and superficial gas velocities up to 0.411 m/s. Five different types of packings were evaluated: (i) RMSR (25 mm stainless steel thread saddle ring), (ii) Hiflow (25 mm stainless steel pall ring), (iii) RR6 (6 mm ceramic Raschig ring), (iv) RR10 (10 mm ceramic Raschig ring), and (v) ASB (12.7 mm aluminum silicate balls). The RMSR packing showed an increase in the heat transfer coefficient (up to 1243 W/m2K), as compared to bubbling beds with no packings (up to 1124 W/m2K). Also, beds with RMSR and Hiflow packings had a lower pressure drop and vertical segregation compared to low void factor packings such as RR6, RR10, and ASB.

Intensified ozonation in packed bubble columns for water treatment: Focus on mass transfer and humic acids removal

Ozonation has been widely applied for the oxidation of contaminants in wastewater, and the disinfection of water. However, low ozone (O3) mass transfer efficiency in common ozonation reactors requires high O3 doses and causes high energy consumption. In this study, to intensify the O3 mass transfer and oxidation of humic acids (HA) solution, a lava rock packed bubble column (LBC) and a metal pall ring packed bubble column (MBC) were developed and evaluated. In comparison with non-packed bubble column (BC), both LBC and MBC enhanced the O3 mass transfer efficiency and the generation of hydroxyl radicals, thereby increasing the HA removal from an aqueous solution. At applied O3 dose of 33.3 mg/(Lcolumn h), the HA removal efficiency in BC was only 47%. When MBC and LBC were applied, it increased to 66% and 72%, respectively. Meanwhile, the O3 utilization efficiency in LBC reached 68%, which was higher than that in MBC (50%) and BC (21%). Consequently, LBC has the lowest energy consumption (EEO) for HA removal (1.4 kWh/m3), followed by MBC (1.6 kWh/m3) and BC (2.9 kWh/m3). LBC had better performance than MBC due to the adsorptive and catalytic roles of lava rock on the ozonation process. This study demonstrates the advantages of using lava rocks as packed materials in O3 bubble column over metal pall rings in intensifying O3 mass transfer and organic matters removal, which provides some insights into promoting the industrial application of O3.

Application of a wire-mesh sensor for the experimental characterization of liquid distribution in packed columns

Characteristic design parameters for fluid dynamics and mass transfer of packed column internals are usually obtained from laboratory or pilot plant experiments. At this scale, results are often affected by liquid maldistribution. Knowledge of liquid distribution is necessary to quantify the influence of maldistribution on mass transfer efficiency and helps to prevent an overdesign of industrial packed columns. The applicability of a minimally invasive wire-mesh sensor for distribution measurements is investigated and a measuring and evaluation method is developed and applied to investigate liquid distribution for the Pall Ring 25, the Raschig Super Ring 0.6 and the Montz Pak B1.250. The results for both, tracer, and integral liquid distribution, show a high reproducibility and are in good agreement with published liquid distribution behavior. The wire-mesh sensor can provide valuable results as a supplement or alternative to liquid collectors with little additional experimental effort in fluid dynamics and mass transfer measurements.

Moving bed biofilm reactor developed with special microbial seed for denitrification of high nitrate containing wastewater.

Biological denitrification is the most promising alternative approach for the removal of nitrate from wastewater. MBBR inoculated with activated sludge is a widely studied approach, but very few studies have focused on the bioaugmentation of biofilm forming bacteria in MBBR. Our study revealed that the use of special microbial seed of biofilm forming denitrifying bacteria Diaphorobacter sp. R4, Pannonibacter sp. V5, Thauera sp. V9, Pseudomonas sp.V11, and Thauera sp.V14 to form biofilm on carriers enhanced nitrate removal performance of developed MBBR. Various process parameters C/N ratio 0.3, HRT 3h at Nitrate loading 2400mg L-1, Filling ratio 20%, operated with Pall ring carrier were optimized to achieve highest nitrate removal. After 300days of continuous operation results of whole genome metagenomic studies showed that Thauera spp. were the most dominant and key contributor to the denitrification of nitrate containing wastewater and the reactor was totally conditioned for denitrification. Overall, findings suggest that bench-scale MBBR developed with biofilm forming denitrifying microbial seed accelerated the denitrification process; therefore in conclusion it is suggested as one of the best suitable and effective approach for removal of nitrate from wastewater.

On the Phases’ Distribution in Packed Columns

Packed columns are typical apparatuses for industrial separation processes which are important in fuel and energy production and reduction of harmful emissions in the atmosphere. The efficiency of the processes in them is strongly dependent on the regular distribution of phases. The liquid and gas maldistribution has been the subject of long intensive investigations. The formation of a liquid wall flow has been found to be one of the main factors for the large-scale radial irregularity of liquid and gas distribution. The prediction and control of this phenomenon is still unsatisfactory. Our work suggests a new approach for evaluation of the wall flow in countercurrent absorption with random packings. It uses simple mathematical apparatus and is based on experimental data of the wall flow along the column height. It allows gaining knowledge about the liquid flow and evaluating the wall flow volume as a criterion of efficiency for comparison of packings. The model is demonstrated by a case study with data for metal Pall rings.

Anaerobic Filter Treatment of Landfill-Leachate Using Low-Cost Filter Materials

Anaerobic-filters are quite expensive due to the high-cost of artificial filtration media. Hence, introducing alternative low-cost filtration media will make anaerobic-filters more economical. The aim of this study was to investigate the performances of several low-cost/waste materials as filtration media in anaerobic-filters to treat organic compounds, nutrients and heavy metals found in landfill-leachate. The experimental set-up consisted of four down-flow anaerobic-filter columns, two of which were control columns while the others were experimental columns. The control columns were filled with Granular Activated Carbon (GAC) and Plastic Pall Rings (PPR) as single medium. The experimental columns were filled with a mixture of Dewatered Alum Sludge (DAS), Washed Sea Sand (WSS), Firewood Charcoal (FWC), while the other with the same materials as layers. During the application of 10% diluted landfill-leachate within a period of 115 days, the overall removal efficiencies of the filter bed with layered-media were 73%, 84%, 61%, 55%, 76% and 79% for COD, BOD5, TN, Ammonia-N (NH3-N), TP and Orthophosphate-P (PO43- -P), respectively. The filter bed with mixed-media gave the overall removal efficiencies of 59%, 87%, 49%, 26%, 71% and 78% for COD, BOD5, TN, NH3-N, TP and PO43- -P, respectively. The experimental columns showed significant removal efficiencies for heavy metals, namely Pb (40%), Cd (48%), Cu (41%) and Mn (52%) in the mixed-media column and (54%), Cd (37%), Cu (54%) and Mn (57%) in the layered-media column.

Modelling and Simulation Studies of Multiple Packings Distillation Column

Large scale separation of liquid mixtures into their various components is one of the major operations in the process industries. Distillation remains one of the predominant separation techniques that is use for these separations. It accounts for about 90% of product recovery and purification in the process industries. The strength of the distillation technique lies on its simplicity, low capital investment, and low risk as compared to other traditional separation techniques. In the present study, the synergistic effects of multiple packings in binary distillation column operations was investigated. The investigation was done using Aspen HYSYS process simulation software. Specifically, the study was done to establish a packing order that will be required to achieve a reduction in energy consumption and the overall cost of separation processes that involve distillation operation. The packed distillation was simulated using Berl saddles, Intalox saddles, and Pall rings as the column internals. Single, dual and triple packing arrangements were evaluated. The multiple packing arrangement investigated were Berl/Intalox, Berl/Pall, Pall/Intalox, and Berl/Intalox/Pall. Binary mixtures of pentane and hexane was used as feed to the column. The results of this simulation revealed that the use of multiple packing arrangement had a significant effect on the energy consumption, the height of packing and hence the cost of equipment fabrication. For instance, the estimated cost of packings (USD) are 524.89 for Berl, 406.85 for Pall, 303.77 for Intallox, 427.09 for Berl/Intalox, 473.06 for Berl/Pall, 323.51 for Pall/Intalox, and 388.60 for Berl/Intalox/Pall. These results clearly revealed that multiple packing arrangements can be used to reduce the cost of column fabrication without compromising the performance of the equipment.

Coupling dissolved oxygen microsensors measurements and heterogeneous respirometry for monitoring and modeling microbial activity within sulfide-oxidizing biofilms

A heterogeneous respirometer (HR) was coupled for the first time to a microelectrode monitoring system specifically designed for dissolved oxygen (DO) measuring within the biofilm. Monitoring of the oxygen concentration in the gas and liquid phases was complemented with pioneer monitoring of DO performed simultaneously and continuously at multiple biofilm depths in a linear array of eleven gold-disk electrodes of 50 µm-diameter. A set of respirometric tests performed at neutral pH and with initial gas phase concentrations of H2S ranging from 135 to 6720 ppmv were used to assess sulfide-oxidizing activity of a biofilm grown on 15.9 mm plastic Pall rings withdrawn from a biogas desulfurizing biotrickling filter. A mechanistic model for the description of multi-step sulfide oxidation within a biotrickling filter was improved considering heterogeneous biomass concentration and biomass activity distribution along the biofilm depth. A comprehensive description of physical, chemical and biological phenomena occurring throughout gas, liquid and biofilm phases resulted in an accurate prediction of system behavior. Model calibration using experimental data estimated a biomass concentration from 320.5 to 443.0 g VSS·L−1 as well as a decrease in the fraction of active biomass of 0.5, over the 600 µm thick biofilm. Model simulations accurately reproduced experimental respirometric profiles (NRMSE <10%), demonstrating that coupling HR and microelectrodes improved model predictions in comparison to sole gas or liquid phase measurements, thus contributing to a deeper knowledge of biofilms performance in trickled bed biological systems.

Investigation of countercurrent flow profile and liquid holdup in random packed column with local CFD data

Liquid holdup and mass transfer area are critical parameters for packed column design and CO2 capture efficiency prediction. In this paper, a framework was established for modeling the liquid–gas countercurrent flow hydrodynamics in a random packed column with pall rings. Besides the column-averaged information, the radial pall ring distribution, velocity, and liquid holdup profiles are obtained to study the entrance effect and the wall influence in the packed column. With local CFD data, the validated packing specific area ap and liquid velocity uL range for liquid holdup correlation is significantly expanded with respect to existing experimental or column-averaged CFD data. The proposed liquid holdup correlation hL~uL0.44 indicates the random packed column falls in a viscous to turbulent transition regime and it covers a Reynolds Number range of [6.7–40.2]. The derived liquid holdup correlation is in good agreement with existing correlations developed using the column-averaged experimental data.

Absorber Sizing and Costing Required to Control SO2 Emission from A Combustion System

This work was predicated on the design and costing of a packed column absorber required to remove SO2 from an air/SO2 mixture. The absorber is intended to be developed into an already existing combustion system as a retrofit. The gas flow rate basis of the computation was 40,000Kg/h. The Onda Method was used to estimate the column height as 9m and the column diameter as 2.5m while the column wall thickness as well as the domed head thickness was found to be 9mm using the BS 5500 Standard Method. In order to limit expenses, H2O was utilized as the absorber solvent and a flow rate of 29.5Kg/s to limit solvent usage. A pressure drop of 20mmH2O/m was assumed in the design with metal pall rings of diameter 51mm and surface area of 102m2/m3 chosen as the packing material. The study estimated a profound $306,559.87 as the cost of the absorber required to remove 95% SO2 content from the combustion waste stream.

Absorber Sizing and Costing Required to Control SO2 Emission from A Combustion System

This work was predicated on the design and costing of a packed column absorber required to remove SO2 from an air/SO2 mixture. The absorber is intended to be developed into an already existing combustion system as a retrofit. The gas flow rate basis of the computation was 40,000Kg/h. The Onda Method was used to estimate the column height as 9m and the column diameter as 2.5m while the column wall thickness as well as the domed head thickness was found to be 9mm using the BS 5500 Standard Method. In order to limit expenses, H2O was utilized as the absorber solvent and a flow rate of 29.5Kg/s to limit solvent usage. A pressure drop of 20mmH2O/m was assumed in the design with metal pall rings of diameter 51mm and surface area of 102m2/m3 chosen as the packing material. The study estimated a profound $306,559.87 as the cost of the absorber required to remove 95% SO2 content from the combustion waste stream.

A multiobjective experimental based optimization to the CO2 capture process using hybrid solvents of MEA-MeOH and MEA-water

To achieve the reduction of total energy consumption of CO2 capture without the major drawbacks of conventional amine solvents, the superior performance of a blended physical-chemical solvent, MEA-MeOH, was experimentally compared with that of MEA aqueous absorbent in lab-scale absorption/desorption towers, equipped with stainless steel pall ring packings. Considering the typical industrial requirements, the main operating variables accounted for each solvent were the operating temperature (35–55 °C), amine concentration (15–30 wt%), gas flow rate (50–100 l/min), liquid flow rate (0.75–1.25 l/min), CO2 concentration in the inlet gas (5–15 mol %), and the reboiler heat duty (1.4–2.2 kW). Response surface methodology was applied to give a quadratic mathematical model for obtained empirical volumetric overall mass transfer coefficients (KGaV). Based on the drastic increase of the energy requirement for solvent regeneration, a multiobjective optimization framework has been made to achieve the maximum desirable values for the KGaV, and the absorption percentage (Φ) with the minimum energy consumption (Ω). It was suggested that under the optimum operating condition, adding methanol to an aqueous MEA solution, reduces the regeneration energy consumption by 12%, while augmenting the CO2 absorption percentage (Φ) by 9.1%.

Feasibility of Greywater Treatment with River Sand and Polypropylene Pall Rings as Filter Media

There is an increase in scarcity of water with rapid population increase in urban areas giving reason for concern and the need for appropriate water management practices. Greywater recycling is emerging as a new trend in water management practices. Initiatives by the Urban Local Bodies (ULBs) have resulted in attempting the greywater recycling in urban areas, flats and apartments and also in individual houses. A rational design is not available for greywater recycling unlike domestic wastewater. Hence, a study was taken in National Institute of Engineering (NIE), Mysuru campus to evaluate the feasibility of treating greywater using river sand and PPPR. The methodology involved designing, fabricating and installing a greywater treatment model in NIE campus. Greywater treatment system installed in NIE campus consisted of anaerobic and aerobic treatment units. The system was monitored over a period of time to check the performance. The sampling of greywater was done weekly and the samples were analyzed for different water quality parameters like pH, TDS, TSS, BOD, COD, turbidity and nutrients. The greywater treatment system with river sand and PPPR as anaerobic and aerobic filter media was effective in removing the turbidity, TSS, COD, BOD and nutrients from the greywater samples to significant extent. It has shown moderate efficiency in removing TDS compared to other parameters.

Anaerobic methane oxidation coupled to sulfate reduction in a biotrickling filter: Reactor performance and microbial community analysis

The aim of this work was to evaluate the performance of a biotrickling filter (BTF) packed with polyurethane foam and pall rings for the enrichment of microorganisms mediating anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) by activity tests and microbial community analysis. A BTF was inoculated with microorganisms from a known AOM active deep sea sediment collected at a depth of 528 m below the sea level (Alpha Mound, Gulf of Cadiz). The microbial community analysis was performed by catalyzed reporter deposition - fluorescence in situ hybridization (CARD-FISH) and 16S rRNA sequence analysis. The AOM occurrence and rates in the BTF were assessed by performing batch activity assays using 13C-labelled methane (13CH4). After an estimated start-up time of ∼20 days, AOM rates of ∼0.3 mmol l−1 day−1 were observed in the BTF, values almost 20 times higher than previously reported in a polyurethane foam packed BTF. The microbial community consisted mainly of anaerobic methanotrophs (ANME-2, 22% of the total number of cells) and sulfate reducing bacteria (SRB, 47% of the total number of cells). This study showed that the BTF is a suitable reactor configuration for the enrichment of microbial communities involved in AOM coupled to SR at ambient pressure and temperature with a relatively short start-up time.

Hydraulic tests of a random helical packing element

A large number of different packing elements are applied in the chemical, oil refining, petrochemical, food and other industries for implementing heat-and-mass transfer processes in columns. The advantage of packed columns consists in their high efficiency, low flow resistance and stable operation. The most important requirements for packing elements include their high specific surface area, large free volume proportion, ease of manufacture and low material consumption. However, few available packing elements meet all of the aforementioned requirements. In this work, we developed a helical packing element for implementing heat-and-mass transfer processes in distillation, absorption and extraction columns, as well as in cooling towers, and carried out a series of respective hydraulic tests. The novel packing element is characterized by a simple design, implying coiling a metal strip into a helix. Such a shape excludes the contact with neighbouring elements, which prevents blocking of the packing surface and formation of stagnant zones. A specific feature of this design consists in the smooth surface of the element, which prevents the formation of drops and streams, thus reducing the mass transfer efficiency. The film-like flow through the packing element ensures high mass transfer characteristics with minimum entrainment, thus contributing to the reduction of flow resistance. On the basis of experimental data, empirical equations were obtained for calculating the flow resistance of dry and wet packing patterns. A comparative analysis of the developed packing element with Pall Rings and Inzhekhim-2000 is provided. It is shown that the developed helical packing element is characterized by a large surface area, significant free volume and low flow resistance. In addition, the simple design of the element significantly reduces its production costs.

Influence of trickling liquid velocity, low molar ratio of nitrogen/sulfur and gas-liquid flow pattern in anoxic biotrickling filters for biogas desulfurization

Hydrogen sulfide has been successfully removed from biogas using anoxic biotrickling filters but an in-depth study of the main operational variables has not yet been carried out. The effect of (i) the empty bed residence time (32–164 s) at a hydrogen sulfide concentration of 2,000 ppmv, (ii) the inlet hydrogen sulfide concentration (2,000–10,000 ppmv), (iii) the trickling liquid velocity (4.8–20.9 m h−1) and (iv) the feed of low nitrogen/sulfur molar ratio (0.334–0.409 mol N-NO3– mol−1 S-H2S) on the hydrogen sulfide removal efficiency have been studied. The BTF (total packed volume of 2.8 L, height/diameter ratio of 9.8) was filled with polypropylene Pall rings (5/8″) and fed continuously with nitrate and a biogas mimic operating in counter-current and co-current flow modes.The maximum elimination capacity was 282.0 gS-H2S m–3 h–1 (RE 97 ± 0.5%) for counter-current flow and 287.5 gS-H2S m–3 h–1 (RE 99 ± 0.4%) for co-current flow mode for an EBRT of 164 s. In addition, in terms of the nitrogen/sulfur molar ratio a higher elemental sulfur production was found in counter-current flow (97.6 ± 2.0%) when compared to co-current flow (87.6±2.8%) since a better depletion of nitrate occurred in co-current flow mode.Finally, three different nitrogen/sulfur molar ratios (0.4, 1.0 and 1.6 mol N-NO3– mol–1 S-H2S) were compared economically. The low and high ratios would involve a nitrate cost of 0.54 and 2.15 € per kg of treated of S-H2S and an elemental sulfur production of 21.5 metric tons and zero production, respectively.

A comparative study of different mass transfer and liquid hold-up correlations in modeling CO2 absorption with MEA

Although CO2 absorption processes have been widely studied in both laboratory and industrial scales, the viability of different relations for the estimation of mass transfer coefficients has not been studied for industrial units. In this paper, the accuracy of different various equations for the estimation of mass transfer coefficients were are evaluated and compared, on the basis of according to the results of an industrial CO2 absorption unit. Therefore, the relations proposed by Onda, Bravo and Billet-Schules were are selected. Also, in some parts of the column pall ring packing was is used. in these parts the Hanley mass transfer coefficients were also used. In addition, Hanley mass transfer coefficients are used for those parts of the column in which pall ring packing is used. Based on the results of rate-based modeling of the column, obtained results show that the Onda equations show have higher accuracy compared to the other mass transfer equations. The comparison was is carried out based on CO2 absorption capacity, temperature profile and rich solvent concentration. The average errors of Onda's mass transfer correlations and Billet & Schultes's liquid holdup correlations in estimating CO2 absorption (%), temperature of rich solvent's temperature, temperature of outlet water's temperature and loading of rich solvent's loading were are 1.153, 2.923, 6.99 and 1.163% respectively. Onda and Billet & Schultes correlations exhibited the most accurate results. Also additionally, liquid film discretization shows indicates that the reaction occurs almost rather instantaneously at liquid-vapor interface and diffusion is the controlling step in the absorption process.

Quantification of Gas Distribution and Void Fraction in Packed Bubble Column Using Electrical Resistance Tomography

Random or structured packing is typically used in the chemical reactors to increase the contact area between the gas and liquid phases, and thus improve reaction efficiency. Knowledge of how packing types and sizes affect the gas distribution and the overall gas void fraction is critical for the optimal design and operation of industrial processes. In this paper, a method of in situ quantifying the gas distribution and void fraction in a packed bubble column using electrical resistance tomo-graphy (ERT) is proposed. A 3-D simulation validation shows that the ERT is able to quantitatively determine the gas void fraction within 4% relative error against the theoretical value. The experiment was conducted in a bubble column, packed with 6-mm glass beads and 16-mm plastic pall rings. The results demonstrate that the gas distribution and the void fraction are considerably changed by different packing materials. All of these facts suggest that ERT is a reliable imaging tool for the real-time measurement of complex two-phase flows in the packed bubble column reactors.