Onda Correlations Research Articles

Process Modeling of CO2 Absorption with Monoethanolamine Aqueous Solutions Using Rotating Packed Beds

A first-principle process simulation model is presented for the chemical absorption of carbon dioxide (CO2) with monoethanolamine (MEA) aqueous solutions using rotating packed beds (RPB). Built on a proven rate-based packed bed absorber model, the RPB model rigorously simulates the phase and chemical equilibria at the vapor–liquid interface, the heat and mass transfer across the gas and liquid films, the fast reactions between MEA and CO2 in the liquid film, and the RPB hydraulics. Estimation of the rate of transfer of mass across the liquid film is central to accurate simulation of the CO2 absorption process with MEA aqueous solutions. We show that the literature lab-scale RPB data for CO2 removal efficiency can be satisfactorily correlated by introducing a correction factor for the effective packing surface area predicted by the Onda correlation. Given the validated RPB model, we further show that, among the gas-phase mass transfer coefficient, the liquid-phase mass transfer coefficient, and the reaction rate constant for the reaction between amine and CO2, the reaction rate constant is the controlling step with the greatest potential to enhance the CO2 absorption performance in RPB.

Harmless Treatment of Sulfuryl Fluoride by Chemical Absorption

Chemical absorption was employed for the harmless treatment of sulfuryl fluoride (SO2F2) in the simulated residual fumigant. SO2F2 was absorbed by sodium hydroxide (NaOH) solution in a packed column. Effects of spray density, gas flow rate, concentration of NaOH solution, and inlet SO2F2 volume concentration on SO2F2 removal efficiency were investigated at room temperature. It was found that SO2F2 could be removed completely when inlet SO2F2 volume concentration, spray density, gas flow rate, and NaOH concentration were 0.50%, 12 m3/(m2 · h), 0.12 m3/h, and 0.68 mol/L, respectively. According to the two-film theory, a mathematical model based on Onda correlations was developed to describe the removal efficiency of SO2F2. Comparison between the experimental data and the calculated data proved that the predictability of the proposed model was within the maximum deviation of 8.0%. Aqueous NaOH solution after absorption was analyzed. It was found that the SO2F2 was fixed and converted to NaF, NaSO3F, and Na2SO4.

Semiempirical Determination of Overall Volumetric Molar Transfer Coefficient for the Scrubbing of Gaseous Tars in Biodiesel

This work contains a description for the determination of the liquid phase molar transfer coefficient (KXa) by a method which is different from that by Onda correlation. The method is different because KXa is for the transfer of the tars which change their phase and size as the temperature and pressure change. In the method, the solubility of the tars in biodiesel was predicted and ultimately the equilibrium coefficient was calculated. The equilibrium coefficient and measured tars compositions in liquid and gas phases at steady state were used to determine KXa. In this way, the determination of KXa for the wet scrubbing of tars into biodiesel was achieved semiempirically. The predicted equilibrium coefficient of the 0.3818 mole ratio at liquid phase temperature of 300 K and atmospheric pressure was used in the calculation. Under these conditions, KXa depended on the liquid to gas flow rate ratio, the inlet and outlet liquid phase compositions, and the exit gas composition. As a result, the measured values of these parameters together with the predicted equilibrium coefficient were fitted into a semiempirical correlation defined as KXa = 0.0143L0.7704G0.0282. This fitting is reasonably satisfactory as it satisfies the conditions cited in the literature and can be effectively applied at liquid to gas flow rate ratios of 36 and 38.

Interfacial mass transfer in randomly packed towers: a confident correlation for environmental applications.

Volumetric mass-transfer coefficients (kLa(w), KLa(w), kGa(w), kGa(w)) required for randomly dumped packed tower design were gathered from the literature to generate a working database comprehending 2675 measurements relevant to water and air pollution abatement processes. The cross-examination of two important correlations predicting mass-transfer coefficients was achieved through this database (Onda correlation, 1968; Billet and Schultes correlation, 1993). Some limitations regarding either the level of accuracy or the application range came to light with this investigation. Artificial neural network (ANN) modeling is then proposed allowing all four mass-transfer coefficients predictions. A single ANN correlation was built to predict the dimensionless gas (or liquid) film Sherwood number (ShL/G) as a function of six dimensionless groups, namely, the liquid Reynolds (ReL), Froude (FrL), Eotvös (EoL) numbers, the gas (or liquid) Schmidt number (ScL/G), the Lockhart-Martinelli parameter (chi), and a bed-characterizing number (K). Using the ANN correlation and the two-film theory, a reconciliation procedure was further implemented resulting in better predictions of the gas (or liquid) overall volumetric mass-transfer coefficients. The resulting correlation yielded an absolute average relative error of 22.1% and a standard deviation of 21.1% based on whole database while the ANN predictions remain in accordance with the physical evidence reported in the literature.

Enhanced scrubbing of chlorinated compounds from air streams

This paper addresses an investigation of mass transfer issues associated with an innovative hybrid process to treat air streams containing chlorinated organics. Three target compounds [dichloromethane (DCM), carbon tetrachloride (CT) and tetra chloroethylene (PCE)] we re evaluated to assess a range of chemical and physical properties. Vegetable oil was found to be an effective scrubbing solution in removing the target compounds from the air streams and was employed in continuous flow tests of a bench-scale countercurrent packed co lumn. Removal efficiencies approached 90% for all three target compounds with gas-liquid flow ratios less than 200. A gas-liquid mass transfer model was developed and compared to the existing Onda correlations, to characterize mass transfer under various operating conditions when water and vegetable oil were employed as scrubbing solutions. It was found that the Onda correlations did not fit the experimental data of vegetable oil very well. The existing Onda correlations we re modified by assuming that the gas phase resistance was controlling mass transfer. In order to enhance mass transfer from the oil phase to an aqueous phase a liquid-liquid contacting reactor was proposed. The results of the liquid-liquid reactor suggested that mass transfer could be achieved for compounds that were not highly hydrophobic.

Improved onda correlations for mass transfer in packed towers

A comprehensive database for VOC stripping in packed towers was gathered from 15 field and pilot-scale studies. This database is used to develop a new correlation based on the Onda model. The development of this new correlation addressed the shortcomings of the Onda correlation which were identified in previous studies. The average error in the new correlation was less than 26% for both the development and the validation data.

Stripping and recovery of ammonia from centrate of anaerobically digested biosolids at elevated temperatures

The process of air stripping/absorption was studied at pilot scale at temperatures ranging between 23 and 75°C using ammonia in artificial and natural centrate. The process was more effective at high temperatures and became pH insensitive beyond a critical pH, which was found to drop as the operating temperature increased. Thus, at high temperatures, shorter packing height and lower pH are required to achieve the same ammonia removal. The Onda correlations predicted well the mass‐transfer properties of 25 mm (1 in.) and 32 mm (1.25 in.) nominal size packing in the ranges of 40 to 60°C and 53 to 61°C, respectively. The Norman/Sherwood–Holloway correlations predicted well the mass‐transfer properties for the former and poorly underpredieted the latter packing. The Onda correlations are recommended for preliminary design of stripping/absorption systems within the preceding temperature ranges.

Improved onda correlations for mass transfer in packed towers

A comprehensive database for VOC stripping in packed towers was gathered from 15 field and pilot-scale studies. This database is used to develop a new correlation based on the Onda model. The development of this new correlation addressed the shortcomings of the Onda correlation which were identified in previous studies. The average error in the new correlation was less than 26% for both the development and the validation data.

Air transfer efficiency of packed saturators used in DAF

A mathematical model predicts how saturation pressure, hydraulic loading, and packing depth affect air transfer.A rational model that predicts the air transfer efficiency in the packing layer of dissolved‐air flotation saturators is described. The model is defined in terms of absolute air concentrations, assumes the Lewis‐Whitman two‐film theory, and uses the Onda correlations to estimate the mass transfer coefficient. A comprehensive method is proposed for experimentally determining the overall air transfer efficiency of an operating saturator. A series of experiments was performed to partition the overall transfer efficiency into the contributions of top and bottom end effects, of free fall of the water before it reaches the packing, and of the packing itself. The laboratory data show a close agreement of the theoretical model with the measured performance. The model is used to demonstrate the effects of the most important saturator design parameters on the concentration of precipitable air.

Nonparametric modeling of mass transfer coefficients for air stripping packed towers

Existing parametric correlations have been found to have difficulties in predicting the removal of trace levels of volatile organic chemicals by modern air stripping towers. In this study, a new approach using a nonparametric kernel regression method was used to predict the mass transfer coefficient, KLa, of air stripping towers. Although only four variables were used, the predictions are already improved more than 50% as compared with Onda correlation, the best existing parametric correlation. The proposed technique shows a dependency of KLa on the liquid flow rate which is in good agreement with established theory. Previous parametric approaches were unable to model this relationship correctly. Key words: mass transfer coefficient, air stripping tower, volatile organic compound, nonparametric kernel regression.

Evaluation of the Onda Correlations for Mass Transfer with Large Random Packings

Although large (≥5 cm) polypropylene packings are frequently used in air stripping towers for environmental applications, few fundamental studies of the mass transfer on these large packing designs have been performed. For small packings, previous research has verified that the Onda correlations are valid for environmental applications. In this research, experimental data for air stripping were obtained using a pilot-scale stripping tower, three test compounds, and four polypropylene packings. Results showed that, in general, Onda is a good predictor of mass transfer for large random packings. However, Onda tended to underpredict mass transfer, with 90% of the data falling between a 16.5% overprediction and a 34.0% underprediction of the observed mass transfer. The underpredictions tended to occur at high gas flow rates and when the gas-film resistance predicted by Onda is large. Further analysis revealed that the functionality of the volumetric gas loading rate is incorrect in the Onda correlations.

On the Performance of a Cascade Crossflow Air Stripping Column

The cascade crossflow packed column is an innovative design that offers the separation advantages of countercurrent flow while avoiding flooding limitations. Liquid and gas cross-sectional flow areas and path length in contact with packing may be controlled independently. These features are illustrated by studying the air stripping of methylene chloride (MeCl), 1,2-dichloroethane (1,2-DCA), and methyl ethyl ketone (MEK). Stripping efficiencies in the cascade crossflow column were generally slightly smaller than in countercurrent flow at equal liquid and gas flow rates. However larger gas-to-liquid ratios were possible in crossflow, permitting larger maximum stripping efficiencies to be attained. The experimental mass transfer coefficients were smaller than predicted by the Onda correlation. Modifications to the gas-phase Onda correlation are proposed that reduce the magnitude of the average deviation between experiment and prediction for 40 tests to about 12%. Experimental values of 38 of 40 tests were wi...

Mass transfer correlations for air stripping towers

AbstractThe overall system‐specific liquid phase mass transfer coefficient, KL a, is the most important parameter in the design of air strippers. Designers frequently estimate KL a using a mass transfer correlations to avoid the cost of pilot tests. This paper evaluates the well‐accepted Onda correlations using a newly developed data base. Predictions based on the Onda correlations systematically overestimated KL a for packings typically used in full‐scale applications. They had an average error of ±40% and an average standard deviation of ±47%. The overestimation was a function of the packing diameter. A simple equation was developed to correct the Onda overestimation for packings larger than 1 inch (2.54 cm) in diameter, and it yielded predictions within ±20% range. The experimental KL a values obtained in this study varied with packing depth contradicting a basic assumption of the mass transfer theory, i.e., that KL a spatially is constant. Also, the effect of measurement errors of the variables involved in the calculation of both the experimental and the predicted KL a values were investigated. A large part of the observed difference between experimental and Onda predictions was attributed to a lack of fit of the Onda model. Thus, the quality of the predictive correlations can be improved.

Rational design of packed saturators

The paper describes the development of a mathematical model for predicting the mass transfer efficiency of packed saturators used for dissolved air flotation. The first part of the paper deals with the equilibrium condition, i.e. the maximum attainable air concentration with a packed saturator at 100% transfer efficiency. The second part derives a kinetic model based on concentration-driven diffusion and the Lewis-Whitman two-film theory. The transfer rate constant across the laminar liquid film and the wetted packing area are estimated with the Onda correlations. The model is finally used to demonstrate the effects of hydraulic loading, packing depth, packing size and temperature on saturator efficiency.

Rational design of packed saturators

The paper describes the development of a mathematical model for predicting the mass transfer efficiency of packed saturators used for dissolved air flotation. The first part of the paper deals with the equilibrium condition, i.e. the maximum attainable air concentration with a packed saturator at 100% transfer efficiency. The second part derives a kinetic model based on concentration-driven diffusion and the Lewis-Whitman two-film theory. The transfer rate constant across the laminar liquid film and the wetted packing area are estimated with the Onda correlations. The model is finally used to demonstrate the effects of hydraulic loading, packing depth, packing size and temperature on saturator efficiency.

Mass Transfer in Cryogenic Distillation Column Separating Hydrogen Isotopes.

A simulation model was proposed to study the mass and heat transfer rates in hydrogen isotope distillation columns. The model is on the basis of the analogy: the mass transfer coefficients and effective surface area within the column were estimated by Kosuge's and Onda's correlation in the model. The calculated results by the present model agreed approximately with the experimental observations. The model had a tendency to give slightly higher separation performance. This tendency is due to that the estimated effective surface area might be larger than actual values. The calculated results by the proposed model were compared with those by the stage model also to discuss relationship between the mass transfer rate and the HETP value. The estimated mass transfer rates were almost the same for H-D and D-T systems. This calculated results give a reason why the HETP values were not varied for the difference in physical properties of hydrogen isotopes. The proposed model does not have the parameter that fit the calculated results to the experimental observations. Comparing the calculated results by the proposed model with those by the stage model, we can estimate the HETP value.

Air stripping VOCs from groundwater: Process design considerations

AbstractConsiderations for evaluating and designing the air stripping process are presented by case study. The case study involves the design of an air stripping process to remediate groundwater contaminated with volatile organic compounds (VOCs) at a National Priorities List site in Tacoma, WA. Design objectives included developing a tower with minimum volume and energy requirements while complying with discharge air and water quality standards. A two‐phase resistance model using Onda correlations to determine liquid‐ and gas‐phase resistance model using Onda correlations to determine liquid‐ and gas‐phase mass transfer coefficients was used to assist in the evaluation and design.Considerations for applying the two‐phase resistance model to air stripping tower design are presented. The ability of the model to simulate process performance is demonstrated by comparison with actual data for 11 priority pollutant list VOCs evaluated during an onsite pilot study. Design procedures with which to develop a tower with minimum volume and energy requirements are described. Other considerations involving the evaluation of VOC emissions and the precipitation and buildup of inorganic constituents within the internal packing media are described.

Evaluating the Onda Mass Transfer Correlation for the Design of Packed‐Column Air Stripping

A crucial parameter for predictive modeling of the performance of packed columns is the mass transfer rate. An initial screening identified the Onda mass transfer correlation as the most promising predictive model available. The study described here sought to quantify the accuracy that can be expected with the Onda correlation, based on a test data base that was established using 10 literature‐reported, pilot‐scale investigations and that involved 11 different volatile organic chemicals and 4 basic packing types. The correlation predicted the transfer rate constants within an average standard deviation of 17 percent (437 data points), corresponding to a ±30 percent accuracy value for design purposes based on 90 percent confidence limits.

Designing a Cost‐Efficient Air‐Stripping Process

The air stripping of volatile organic chemicals (VOCs) from water was optimized by taking into account both capital and operating costs. By using Onda's correlation for mass transfer coefficient and computer simulations, optimal water loading rates and air‐to‐water ratios were established for five representative VOCs. The overall treatment cost appeared to be relatively insensitive to changes in the operating variables in the vicinity of the optimum region but increased rapidly as the conditions deviated from the optimum region. It was also observed that the overall treatment cost was very sensitive to capital cost but not significantly affected by power costs. The treatment cost dropped almost linearly as temperature increased.