Low Liquid Loading Research Articles

Use of Air Stripping Technology to Remove Ammonia from Biologically Treated Blue Crab Processing Wastewater

Crab cooker wastewater contains high concentrations of chemical oxygen demand (COD), total suspended solids (TSS), and total Kjeldahl nitrogen (TKN). Anaerobic biological treatment of the wastewater releases high concentrations of ammonia. In this study, the potential for air stripping to remove ammonia from wastewater which was treated biologically under anaerobic conditions was evaluated. An air stripping tower's ammonia removal efficiency increased from 50 to 72 percent as the air flowrate was increased from 9 to 21 m3/min. The average liquid loading rate and liquid temperature were 25 L/m2/min and 14GC, respectively. Ammonia stripping efficiency increased as the stripping factor was increased from one to three; however, under the conditions of this study (2,3 inch LanPac packing and countercurrent tower), stripping factors from two to three were only possible at low liquid loading rates (less than 41 m-Vm2/min) due to pressure drop considerations. At liquid loading rates less than 41 m-Vm2/min, the product of the overall mass transfer coefficient (KL) and the specific interfacial area (a) increased with increasing liquid loading rate, probably because more of the packing surface was wetted at higher liquid loading rates.

Gas-Liquid Stratified-Wavy Flow in Horizontal Pipelines

Gas-liquid stratified-wavy flow with low liquid loading is common in natural gas transmission pipelines and offshore gas pipelines. This specific case of two-phase pipe flow has been studied experimentally and theoretically in the present paper. The interfacial behavior during air-kerosene stratified-wavy flow in a 77.9-mm-dia 420-m-long pipeline was observed carefully. The gas-liquid interface usually exhibits a concave downward curved configuration. The liquid film-wetted wall fraction, liquid holdup, and pressure drop were also measured. A mechanistic “double-circle” model and a correlation for interfacial friction factor, required as a closure relationship in the model, have been developed. The new model gives significantly improved predictions for both liquid holdup and pressure drop during gas-liquid stratified-wavy flow in horizontal pipelines.

An immobilized cell reactor with simultaneous product separation. II. Experimental reactor performance

The simultaneous separation of volatile fermentation products from product-inhibited fermentations can greatly increase the productivity of a bioreactor by reducing the product concentration in the bioreactor, as well as concentrating the product in an output stream free of cells, substrate, or other feed impurities. The Immobilized Cell Reactor-Separator (ICRS) consists of two column reactors: a cocurrent gas-liquid "enricher" followed by a countercurrent "stripper" The columns are four-phase tubular reactors consisting of (1) an inert gas phase, (2) the liquid fermentation broth, (3) the solid column internal packing, and (4) the immobilized biological catalyst or cells. The application of the ICRS to the ethanol-from-whey-lactose fermentation system has been investigated. Operation in the liquid continuous or bubble flow regime allows a high liquid holdup in the reactor and consequent long and controllable liquid residence time but results in a high gas phase pressure drop over the length of the reactor and low gas flow rates. Operation in the gas continuous regime gives high gas flow rates and low pressure drop but also results in short liquid residence time and incomplete column wetting at low liquid loading rates using conventional gas-liquid column packings. Using cells absorbed to conventional ceramic column packing (0.25-in. Intalox saddles), it was found that a good reaction could be obtained in the liquid continuous mode, but little separation, while in the gas continuous mode there was little reaction but good separation. Using cells sorbed to an absorbant matrix allowed operation in the gas continuous regime with a liquid holdup of up to 30% of the total reactor volume. Good reaction rates and product separation were obtained using this matrix. High reaction rates were obtained due to high density cell loading in the reactor. A dry cell density of up to 92 g/L reactor was obtained in the enricher. The enricher ethanol productivity ranged from 50 to 160 g/L h while the stripper productivity varied from 0 to 32 g/L h at different feed rates and concentrations. A separation efficiency of as high as 98% was obtained from the system.

TUBESIDE EXIT CONDITION WITH COMPLETE CONDENSATION IN MULTITUBE CROSS-FLOW HEAT EXCHANGERS

A transition condensate Froude number characterizes the tubeside exit condition or whether condensate fills the tube or is in a stratified flow regime with vapor flowing into the tube exit. The transition Froude number, which defines the boundary between high and low condensate loading conditions, was determined with single-phase water tests and was verified with two-phase tests of large multitube cross-flow heat exchangers. For both cases, the water or condensate is discharged from a tube or tubes into a gas or vapor-filled plenum. With complete condensation and high liquid loading, the flow regimes are progressively annular, slug, and plug followed by the tube running full with subcooled condensate. With complete condensation and low liquid loading, the flow regimes are annular, wavy, and stratified followed by stratified flow with vapor flowing back from the tube exit.

Critical Review of Correlations for Predicting Two-Phase Flow Pressure Drop across Tube Banks

Published correlations for predicting the two-phase flow pressure drop across ideal tube banks are reviewed and compared with experimental data. No presently available methods can be considered general enough for use under all conditions. The Martinelli-type method used for tube-side pressure drop correlation appears to be a basically usable approach if correspondingly modified. All available data are reasonably well represented in terms of the Martinelli parameters at low liquid loading (Xtt small). At high liquid loading ( Xtt large) there is increasing scatter and additional parameters are needed. Substantial improvement is believed to be possible by adjustment of the Martinelli model through recognition of the different flow regimes.

Mixed retention mechanisms in gas-liquid chromatography : II. Contributions of adsorption and partition to the retention volume in systems with polar solutes and non-polar stationary phase on a silanized support

The contributions from adsorption and partition at infinite and finite solute concentrations have been investigated for a gas-liquid chromatography system with a silanized support, non-polar stationary phase (octadecane) and polar solutes (ethyl methyl ketone and diisopropyl ether). It was found that the contribution from adsorption varied strongly with the sample size. The variation of adsorption with liquid loading at infinite solute concentration showed a rapid decrease between 0 and 1% loading followed by a rapid increase at ca. 5%. To explain this behaviour it is suggested that one part of the stationary phase is blocking the most active sites (dominating at very low liquid loading) and another part is forming droplets on the surface of the support. The variation of adsorption with liquid loading for loadings higher than ca. 2% can be explained by the variation of the gas-liquid interfacial area with liquid loading. It is therefore concluded that the dominant adsorption mechanism for loadings higher than ca. 2% is the adsorption at the gas-liquid interface.

Development of apparatus for separation of liquid mixtures of volatile components by vaporization through semipermeable membranes

1. Laboratory tests of equipment with film flow of the mixture undergoing separation have demonstrated the operating reliability of this equipment and adequate life of the cellophane membrane. 2. An increase in liquid-mixture temperature from 50 to 75°C increased the process rate considerably and also improved the selectivity of separation. 3. Experiments on the separation of an azeotropic isopropanol mixture showed that rather low linear liquid loads and gas velocities are adequate for the drying of water/alcohol mixtures.

Effects of the column length on the HETP in gas chromatography

The effects of varying the length of a gas chromatography column operated under laminar flow conditions on the course of the HETP versus flow velocity curve have been discussed in terms of the mean absolut column pressure. Systems have been considered with both high and low liquid load packings, operated at either a constant outlet and variable inlet pressures or vice versa. An account has been given of the effects of varying the absolute mean column pressure at a constant column length.

Pressure induced turbulence in a packed gas chromatographic column

HETP versus carrier gas flow velocity curves have been measured on a low liquid load packed column operated under two different mean absolute pressures within wide flow velocity limits, using hydrogen as the carrier gas. In the case of the higher column pressure, a fall-off of the HETP occurred at a certain velocity, indicating the onset of turbulence in the flow of the carrier gas, whereas the corresponding curve obtained at the lower pressure displayed all the characteristics of laminar flow. The extent of turbulence was checked by measuring the characteristics of the dynamics of flow under the corresponding conditions.

Phenomena Which Influence the Retention of Metal Fluoroacetylacetonates in Gas-Liquid Chromatography

The influence of support treatment and liquid loading on the retention behavior of volatile metal fluoroacetylacetonates in gas-liquid chromatography has been investigated. The decrease of adsorption activity of the solid support due to the silanization of the column is demonstrated. The relative contributions of solution in the stationary liquid and adsorption on the solid support are determined by investigating the behavior of Cr(tfa)3 and Ru(tfa)3 on columns containing different liquid loadings. A graphical evaluation of the data shows that the retention of these compounds at low liquid loading is governed essentially by adsorption. For more highly loaded columns the solution effect dominates, however, adsorption on the solid surface cannot be neglected.

Theoretical investigation of low liquid load and low temperature operation in gas chromatography

The change in resolution resulting from the simultaneous reduction of liquid load and temperature is theoretically treated. The effects of decreases in load and temperature are formulated in terms of a standard reduction (in which the zone to gas velocity ratio is constant) plus any small changes in temperature required to match the observed changes in zone velocity. Taking the standard reduction as the norm. it is found that both the thcrmodynamic (relative peak clution times) and rate (peak spreading) effects favor the liquid load and temperature decreases. This is discussed specifically in relationship to diatomaccous earth and glass beads as the solid support and also to capillary columns.