Multistage Bubble Column Research Articles

Investigations on a solar humidification dehumidification desalination system equipped with various packing materials and multi-stage bubble column dehumidifier.

This work presents the theoretical and experimental investigation of a solar-powered humidification dehumidification desalination (HDD) system with different humidifier packing materials and a two-stage bubble column dehumidifier (BCD). Naturally available coconut shells (CS) and coconut shells with drilled holes (CSH) on the surface to improve water permeability were used as packing materials in the humidifier, and their performance was compared with that of commercial-type pall ring (PR) and raschig ring (RR) packings. An in-house developed numerical model of the HDD system in conjunction with a flat plate solar water collector was used in this study. Steady-state experimental results showed that CSH packing exhibited the highest volumetric mass transfer coefficient (0.00852kg/s), resulting in maximum humidifier efficiency (96%) and freshwater yield (2.16kg/hr), followed by PR (0.00841kg/s, 94%, and 2.137kg/hr), CS (0.00831kg/s, 90%, and 2.127kg/hr), and RR (0.0081kg/s, 81%, and 2.087kg/hr) at feedwater mass flow rate of 1.5kg/min and humidifier inlet temperature of 75 [Formula: see text]. Furthermore, transient outdoor test results showed that using a two-stage configuration in a BCD increased the daily average effectiveness to 0.93, as against 0.79 for a single-stage BCD. Employing CSH instead of PR and RR packings in the humidifier reduced freshwater costs by 6.2% and 7.6%, respectively.

The potential of sweeping gas membrane distillation integrated with multistage bubble column dehumidifier in recovering potable water from wastewater contaminated with industrial metalworking fluids

Wastewater treatment is essential as freshwater becomes scarce due to increasing industrialization. However, the current centralized wastewater treatment technologies are suitable for large-scale applications. There is a pressing need to develop small-scale decentralized wastewater treatment techniques. Towards this goal, a new sweeping gas membrane distillation system (SGMD) integrated with a multistage bubble column dehumidifier (BCD) was designed, built and tested to treat metalworking fluid (MWF)-contaminated wastewater. The performance of the SGMD-BCD system was first optimized using deionized water experiments. The results showed that feed water temperature significantly affected permeate flux, while air and feed water mass flow rates of 10kg/hr and 90kg/hr were identified as optimum since permeate flux and gain output ratio were insignificant above these flow rates. The simulation results of the developed system-scale mathematical model revealed that multi-staging is a more preferable option for improving effectiveness compared to increasing the condensing area in a single-stage BCD. Additionally, in long-term experiments, about 35.5% and 47.7% drops in permeate flux were observed when the MWF concentration in wastewater increased from 5 to 25 wt% at feed water temperatures of 70°C and 80°C, respectively.

Thermodynamic and thermoeconomic modeling of humidification-dehumidification desalination systems with bubble column dehumidifier

Humidification-dehumidification (HDH) desalination systems are popular among researchers due to their simple structure, ability to operate with low-grade and renewable energy sources, and the capacity to work with high-concentration water. This paper presents a thermodynamic and thermoeconomic analysis of an HDH system with a multi-stage bubble column dehumidifier. There was a lack of economic studies on bubble column dehumidifier systems in previous literature; also, no research had examined the impact of different geometric and temperature parameters on the entire system's performance. The fixed surface method was used to model the humidifier and dehumidifier, and the effect of mass flow rate ratio, top and bottom temperature, pipe length within each dehumidification stage, and the number of dehumidifier stages on the system's performance was studied. System performance was compared under various conditions, including gain output ratio (GOR), water production, and cost of produced freshwater. The highest GOR is obtained in the highest pipe length and the highest number of dehumidifier stages. Increasing the length of the pipe and the number of dehumidification stages increases the cost, so achieving the lowest cost of produced water is a compromise between higher cost and higher efficiency. The system achieved a GOR of 3.03, the lowest cost price of produced water is 18.29 $m3, and the highest acheived exergy efficiency is 22.4 %.

Enhanced efficiency in CO2-free hydrogen production from methane in a molten liquid alloy bubble column reactor with zirconia beads

The CO2-free production of hydrogen is an important criterion for the development of future hydrogen economy along with environmental protection. In this work, a new and efficient strategy for catalytic methane pyrolysis to hydrogen production was proposed using a multi-stage bubble column reactor containing molten Ni-Bi alloy, zirconia and molten NaBr. Compared to the 2-stage bubble column reactor, the3-stage bubble column reactor was found to enhance the methane conversion rate from 32% to 37%at 985 °C.The analysis of the carbon products revealed that similar kinds of amorphous and graphitic carbon-based materials can be obtained from both reactors. The enhanced methane pyrolysis rates with the use of zirconia beads indicate that they can be employed to control the bubble behavior and to enhance the contact area between bubbles and the liquid catalyst surface for an efficient bubble column reactor with liquid metal alloy catalysts.

An experimental investigation of a novel design air humidifier using direct solar thermal heating

In this study, a novel solar heated multi-stage bubble column humidifier is designed and tested. The overall objective of this work is to investigate the main operating parameters of the new humidifier. The study addresses the significance of the perforated plate geometric features, optimum balance of air superficial velocity and water column height, and the influence of inlet water temperature and inlet air relative humidity on the performance of the humidifier. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configuration, in which each configuration was tested with and without the integration of the Fresnel lens. Findings show that the average day round absolute humidity, without Fresnel lens, increased up to 9% for the two stage configuration and 23% for the three stage configuration as compared to the single stage configuration of the humidifier. The integration of the Fresnel lens further increased the absolute humidity up to 25% as compared to the results obtained without the integration of the Fresnel lens under the same prevailing conditions, which is significant. Moreover, the current humidifier shows a higher humidification efficiency in the climatic conditions that have a lower inlet air relative humidity. Furthermore, the finding demonstrates that the newly developed multi-stage bubble column humidifier has better performance as compared to the conventional single stage bubble column humidifier. The findings from this study are of pivotal importance to understand the optimum operating conditions of the humidifier for its possible integration with the dehumidifier. Consequently, an improved humidification-dehumidification desalination system attained.

The profiles of radial liquid velocity and mixing parameters in multi-stage bubble columns

Liquid circulation flow is one of the important hydrodynamic characteristics of the multi-stage bubble column. In this paper, the radial liquid velocity, axial back-mixing coefficient, and liquid exchange velocity were studied in a multi-stage bubble column with 2,000 mm height and 282 mm diameter using a Pavlov tube and the tracer method. The effects of superficial gas velocity and plate structure on the mixing characteristics are presented. With an increase of the superficial gas velocity, the liquid velocity in the centre of the bubble column increases. With a decrease in the percentage of free area, the hole diameter, and tongue angle, the gas hold-ups below the perforated plate increases greatly. Moreover, the addition of a perforated plate enhances the eddy strength in the bubble column, which increased the coalescence and breakup of bubbles.

Modeling of Multistage Bubble Column Reactors for Oxidation Reaction

AbstractIn this work, a mathematical model based on axial dispersion has been suggested to simulate the behavior of a multistage bubble column reactor. A six‐stage pilot‐scale reactor with an inner diameter of 0.35 m and a height of 12 m was used for hydrogen peroxide production through the direct oxidation of isopropyl alcohol at isothermal condition. Steady‐state and dynamic simulations were performed to predict the concentration of all the reactants in gas and liquid phases. It was observed that for steady state‐conditions the simulation results were consistent with the experimental results. Dynamic models involving liquid back‐mixing can be used for the simulation of start‐up, shut‐down or transition operations in this kind of a rector.

Distribution characteristics of holdups in a multi-stage bubble column using electrical resistance tomography

Based on the principle of chemical reaction engineering, the addition of perforated plates can improve the performance of conventional bubble column and decrease the backmixing behaviors. The distribution characteristics of gas holdup in a multi-stage bubble column embedded with five types of sieve plates and three types of tongue plates were studied using electrical resistance tomography (ERT). The effects of superficial gas velocity and the geometric design of perforated plates on the gas holdup and its radial distribution above and below the plates of the bubble column were discussed. Experimental results show ERT is suitable as an online monitoring tool to provide useful information on the hydrodynamic parameters of multi-stage bubble columns. With increasing superficial gas velocity, local gas holdup increases, and gas holdup below the plate increases with decrease of free area (%FA), hole diameters or angle of tongue plates. ERT technique facilitates noninvasive and nonintrusive visualization of cross-sectional distribution of gas holdup in a bubble column.

Performance of a modified multi-stage bubble column reactor for lead(II) and biological oxygen demand removal from wastewater using activated rice husk

The excessive release of wastewater into the environment is a major concern worldwide. Adsorption is the one of the most effective technique for treatment of wastewater. In this work activated carbon prepared from rice husk has been used as an adsorbent. In the present investigation a three phase modified multi-stage bubble column reactor (MMBCR) has been designed to remove lead and biochemical oxygen demand (BOD) from wastewater by means of its adsorption onto the surface of activated rice husk. The multi-staging has been achieved by hydrodynamically induced continuous bubble generation, breakup and regeneration. Under optimum conditions, maximum lead and BOD reduction achieved using activated rice husk was 77.15% and 19.05%, respectively. Results showed MMBCR offered appreciated potential benefits for lead removal from wastewater and BOD removal, even this extent of removal is encouraging and the MMBCR can be used a pretreatment unit before subjecting the wastewater to biological treatment.

Effects of Gas Redispersion and Liquid Height on Gas–Liquid Hydrodynamics in a Multistage Bubble Column

The influence of staging, superficial gas velocity, u g, and clear liquid height, h, on the values of volumetric mass transfer co-efficient, k L a, gas hold-up, ɛ g and liquid phase axial dispersion co-efficient, D L, of a 14 cm diameter and 98 cm tall bubble column were studied. The mass transfer parameter, k L a, was estimated by using the electrical conductivity method of Panja and Rao (1991) which consists of measuring the changes in electrical conductivity of water as a function of time obtained by absorbing pure carbon dioxide in water and using the measured data to infer the value of the mass transfer parameter with the help of a mathematical model. The parameter, D L, was determined by conducting tracer mixing experiments and fitting the dispersion model. From the results of the present work, the staging of the column was found to cause an increase in the value of k L a by about 60%, an increase in the value of ɛ g by about 5–10%. and a decrease in the value of D L by about 68–78, while the increase in the power input due to staging was found to be only 2.5% over the range of u g equal to 0.3–4.5 cm s −1 It was also found that in the absence of a gas redistributor, the values of k L a and D L decreased with increase in h. For identical values of gas flow rates and h, the values of k L a obtained under desorption conditions were found to be much higher than the values obtained under absorption conditions. Also, experiments were carried out on absorption of pure CO 2 into an aqueous solution of NaOH under batch and continuous co-current up-flow conditions with CO 2 as limiting reactant, and a preliminary mathematical model was proposed to explain the experimental results.

The Effect of Partitioning Plates Packed with Particles in a Multistage Bubble Column to the Mass Transfer

Longitudinal concentration distributions have been measured under various conditions for oxygen absorption in standard bubble columns. The disadvantages of standard bubble columns are considerable because of backmixing in the continuous liquid phase and the decrease of interfacial area due to bubble coalescence in the viscous liquids. To overcome these disadvantages, modified bubble columns, such as multistage bubble columns partitioned with perforated plates, have been used. When the catalytic particles suspended in the slurry bubble column are brittle and easily break down, the packing of the brittle particles into a partitioning plate is considered, which is called the multistage bubble column with a partitioning plate packed with particles (PMBC). The aims of this study are to make experimentally and theoretically clear the effect of operating parameters on the mass transfer characteristics of the PMBC, and to elucidate the concentration distributions of dissolved oxygen in the PMBC by a revised back flow model.

Mass Transfer Characteristics of a Counter Current Multi-Stage Bubble Column Scrubber

This paper reports on the experimental investigation carried out to evaluate mass transfer characteristics of a hydro-dynamically-induced multi-stage bubble column. As conventional normal bubble column could not meet the high mass transfer rate, this novel bubble column has been conceived, designed and fabricated as a wet scrubber for the control of air pollution; in addition it has versatile use as a gas‐ liquid contactor in chemical processing industries. Chemical methods have been used to characterize the mass transfer of the novel multi-stage bubble column. A liquid side mass transfer coefficient and a volumetric mass transfer coefficient have been found to be effective and improved from the previous work for such an improved gas-liquid contactor.

PREDICTION OF ENERGY DISSIPATION IN A CONVERGENT-DIVERGENT MULTISTAGE BUBBLE COLUMN

An experimental investigation was carried out to evaluate energy dissipation of a divergent-convergent multistage bubble column (with convergent and divergent disks), which has been conceived, designed, and fabricated as a wet scrubber for air pollution control. In addition it has versatile use as a gas-liquid contactor in chemical and biochemical process industries. A detailed experimental investigation of pressure drop and energy dissipation has been reported by using a divergent-convergent multistage bubble column. Correlation developed for predicting energy dissipation has been found to be encouraging and highly significant from a statistical point of view. Energy consumption of the present system has been compared with other systems.

Fly-ash removal efficiency in a modified multi-stage bubble column scrubber

Bubble columns are being widely used in chemical process industries for its various advantages and simplicity. A pilot plant novel multi-stage bubble column wet scrubber has been conceived, designed and fabricated. This novel scrubber has been used as dust collecting wet scrubber in presence of other gaseous and vapor pollutants. This paper reports on the detailed experimental investigations carried out on the scrubbing of fly-ash in this novel wet scrubber using water as the scrubbing medium. It has been found that the present system yielded very high efficiency for the scrubbing of fly-ash. In most cases, the fly-ash removal efficiency is more than 95% and many cases approaches 99.5%. A correlation has been developed for prediction of particulate (fly-ash) removal efficiency. The scale-up of this pilot plant in Indian thermal power plant shows excellent performance and meets the stringent pollution control standards. Attempt has also been made to install the above wet scrubber in Indian Thermal Power Plants and Ceramic Industries to combat particulate pollution control and found excellent performance.

Scrubbing of fly‐ash laden SO2 in modified multistage bubble column scrubber

AbstractThe emission of SO2 from various chemical industries is associated with particulate (fly‐ash), mostly concentrations of particulate laden sulfur dioxide in and around these plants overshoot the danger point. Prediction of fly‐ash laden SO2 removal efficiency is very important for the selection of pollution control equipment. Experimental investigations were conducted on the scrubbing of fly‐ash laden SO2 in the modified multistage bubble column scrubber using water. Experimental results show that almost zero penetration (100% removal efficiency) of fly‐ash laden SO2 can be achieved in this system. A correlation was developed for predicting the percentage collection efficiency of sulfur dioxide in the presence of fly‐ash. Experimental results agreed excellently with the correlation. Enhancement of SO2 collection due to the presence of fly‐ash was also quantified.

Prediction of dispersed phase holdup in a modified multi‐stage bubble column scrubber

AbstractThis paper reports on the experimental investigation carried out to evaluate fractional dispersed phase holdup for a gas‐liquid mixture in a modified multi‐stage bubble column (with contraction and expansion disks), which has been conceived, designed and fabricated as a wet scrubber for control of air pollution; in addition it has versatile use as a gas‐liquid contactor in chemical process industries. A correlation developed for predicting fractional dispersed phase holdup has been found to be encouraging and highly significant from statistical analysis.

A NOVEL MODIFIED MULTI-STAGE BUBBLE COLUMN SCRUBBER FOR SO2 REMOVAL FROM INDUSTRIAL OFF GASES1

The emission of SO2 from various chemical industries, always occur in association with particulate and most of the time the concentrations of sulfur dioxide in and around these plants overshoot the danger point. In the present investigation, an attempt has been made for wet flue gas de-sulfurization using water as the absorbing medium in a newly designed scrubber. Prediction of SO2 removal efficiency is very important for selection of a pollution control equipment. The present paper reports on the detailed experimental investigations on the scrubbing of SO2 in the modified multi-stage bubble column scrubber (MMSBCS) using water. Experimental results show that almost 100% removal efficiency of SO2, can be achieved in the present system. A correlation has been developed for predicting the percentage removal efficiency of sulfur dioxide. Experimental results are in excellent agreement with the correlation. *Patent pending.

Prediction of the Interfacial Area of Contact in a Variable-Area Multistage Bubble Column

This paper reports on the experimental investigation carried out to evaluate the interfacial area of contact to characterize a variable-area multistage bubble column (with contraction and expansion disks), which has been conceived, designed, and fabricated as a wet scrubber for control of air pollution; in addition, it has versatile use as a gas−liquid contactor in chemical process industries. Correlations developed for predicting the interfacial area of contact in terms of fractional dispersed-phase holdup have been found to be encouraging and highly significant from statistical analysis.

Modeling of a novel multi-stage bubble column scrubber for flue gas desulfurization

Desulfurization of flue gases from various chemical industries in a techno-econo-enviro manner is a demanding technology. The concentrations of sulfur dioxide in and around these plants overshoot the danger point. In the present investigation, an attempt has been made for wet flue gas desulfurization using water as the absorbing medium in a newly developed scrubber. Prediction of SO 2 removal efficiency is very important for selection of pollution control equipment. The present paper reports on both the modeling and detailed experimental investigations on the scrubbing of SO 2 in the modified multi-stage bubble column scrubber (MMSBCS) using water. Experimental results show that almost 100% removal efficiency of SO 2, can be achieved in the present system without additives or pre-treatment. A comparison has been made between the predicted and experimental percentage removal efficiency of SO 2. Experimental results are in excellent agreement with the predicted values from the model.

Design and optimisation of a multi-stage bubble column slurry reactor for Fischer–Tropsch synthesis

For carrying out the Fischer–Tropsch synthesis of heavy paraffins starting from syngas (CO+H 2), a multi-stage bubble column slurry reactor design is carried out. The advantages of this reactor configuration with respect to a conventional slurry reactor design, consisting of one well-mixed stage, are (a) increased syngas conversion, and (b) increased reactor productivity. The multi-stage bubble column construction requires installation of additional cooling surface area in order to keep the exothermic reaction within the desired temperature limits.