Foam Breaker Research Articles

Analysis of Operating Conditions for an Aerodynamic Foam Breaker

Operating conditions of an aerodynamic foam breaker are analyzed. Its performance is considered in relation to the dynamic factors and structural parameters of the foam.

Foam Rupture by Mechanical and Vibrational Methods

The need to destabilize foams and control their formation arises in many industrial processes. Mechanical foam breakers, mechanical vibration and ultrasonic vibration are examples of physical destructive techniques which do not suffer from the drawbacks associated with the use of chemical antifoams and defoamers. This paper reports on recent studies in this area. Two novel designs of mechanical foam breaker are presented which are superior to traditional foam breakers in controlling unwanted foaming in both bubble columns and stirred vessels. The effectiveness of mechanical and ultrasonic vibrations in destabilizing foams is shown to be governed by vibrational amplitude and frequency, and foam structure. A fundamental understanding of foam destabilization by these physical techniques is crucial to further advancement in the design of efficient and robust foam breakers and the development of enhanced non-invasive vibrational destructive techniques.

Estimating the Efficiency of an Aerodynamic Foam Breaker

An expression for the jet outflow velocity (dynamic characteristic of the foam breaker) and the related effective diameter of a destructurized foam bubble is derived from the energy balance in the interaction of the gas jet and foam structure. An analysis of the jet outflow hydrodynamics gives an expression for the volumetric injection rate as a performance characteristic of the aerodynamic foam breaker. Relationships between the structural and geometric parameters of the original and broken foams are derived under the assumption that the foam breaks by a cohesive mechanism. The properties of the foam are related to the bubble reduction ratio and the number of foam destruction stages. The stable operating conditions of the hydrodynamic foam breaker are determined by nomography. These conditions depend on the foam breaker design and on the structure and behavior of the foam.

Mechanical suppression of the dynamic foam head in bubble column reactors

The necessity of suppressing foam formation arises in many industrial operations and in sewage treatment plants. Mechanical foam breakers are used for such a purpose when the use of chemical antifoams and defoaming agents is prohibited by the process. Two new foam breakers were used to control a dynamic foam head generated in a bubble column containing foamable liquid: a comb-type two-blade paddle with three slits, and a brush-type two-blade paddle with 168 needles. In comparison with more conventional foam breakers, both foam breaker designs gave significantly reduced critical speeds for foam control. Their performance was characterised under various experimental conditions including different foam-base liquid properties, gas sparger types, surfactant concentrations, and foam breaker clearances above the liquid surface level. The control of dynamic foams generated continuously in a bubble column was found to depend on the foam characteristics such as bubble size and liquid holdup, and the foamability of the base liquid. Foams generated in stirred tank reactors were found to be have different characteristics and hence different control requirements.

Performance characteristics of novel mechanical foam breakers in a stirred tank reactor

Unlimited foam formation and insufficient foam collapse can have serious effects in an aerated system such as a fermentation process. Mechanical foam breakers are used in foam control to avoid the drawbacks associated with the use of chemical antifoams and defoaming agents. In this paper, two new foam breakers consisting of a two-blade paddle with three slits, and a two-blade paddle with 168 thin needles have been tested. They gave significantly reduced critical speeds and power consumption for foam control in a stirred vessel, compared with some conventional foam breakers. The effects of various parameters, namely the physical properties of the foaming solution, type of gas sparger, surfactant concentration, and foam-breaker clearance above liquid level, have been investigated. The degree of difficulty of controlling dynamic foams generated continuously in a stirred vessel is found to be a function of the nature of the foam, ie its bubble size, its liquid holdup, and the degree of foamability of the system. © 1999 Society of Chemical Industry

Mechanical foam breaking – a physical model for impact effects with high speed rotors

AbstractDuring recent years in chemical engineering processes for instance with aerated stirred tanks containing surface‐active components foams and their mechanical control have become very important. However, there are still no rules for calculating mechanical foam breakers. As a contribution to foam control the present paper discusses the fundamentals of foam breaking by means of foam densities and gives a physical model for the mechanisms of a mechanical foam breaker when the main breaking effect is based on impact. The mechanisms were proved by measuring pressures in a foam breaker box. Diameters of secondary foam bubbles produced by foam breakers are calculated and discussed. Experimental investigations were made with different surfactants in aqueous solutions. The paper points out their influence on the process of foam breaking.

Foams as Membrane Systems

Foams are dispersed systems of gas particles. The stability of the foams, however, is determined by the property of foam membrane. Foams should, therefore, be studied as membrane systems. In this paper, fundamental properties of the foams are discussed on the basis of the surface chemical behavior of the membrane systems. Besides very stable foams covered with solid films or bimolecular films, less stable foams as well as unstable foams are stabilized by the adsorbed monolayer of foaming agent. These foams are the more stable if the more of the foaming agent is adsorbed the more tightly. Antifoams are classified into foam breakers and foam inhibitors. The foam breaker acts upon the foams already formed, by spreading on the surface of the foam membrane. On the other hand, the foam inhibitor acts to prevent foaming by driving out the foaming agent from the surface of the foam membrane as the result of preferential adsorption.

Oxygen transfer rates in a mammalian cell culture bioreactor equipped with a cell‐lift impeller

Measurements of k(L)a were carried out in 1. 5- and 5-L New Brunswick Scientific CelliGen bioreactors. The measured k(L)a in water were identical for both vessel sizes operated in similar condition. The mass transfer rate increased with temperature, mixing speed, and aeration rate, with this last parameter being the most significant. Surface aeration alone gave k(L)a values of 0. 4 to 1. 6 h(-1). A 25% decrease in k(L)a was observed above an aeration rate of 1. 6 vvm. This was caused by the particular foam breaker of the CelliGen bioreactor. Measurements of k(L)a using a mammalian cell culture medium supplemented with 5% fetal calf serum (FCS) have confirmed the negative effect of the foam breaker on k(L)a The measured value in this medium was 1. 2 h(-1) for all aeration rates, more than 60% of which was attributed to surface aeration.

Foam breaking by high speed rotors

AbstractThe first part of this paper presents a relationship for the minimum velocity of rotating installations for foam breaking. The derivation is based on equilibrium of inertia and surface forces. Inertia forces occur during the acceleration of foam bubbles and act mainly at the plateau borders. High and definite acceleration can be obtained with a deformer composed of a rotor and a stator. The surface force is due to the dynamic surface tension because surface‐active solutions react to a rapid change in surface area by altering their surface tension. The theoretical relationship is compared with experimental results of minimum velocities needed to break foams produced from aqueous solutions of detergents. The equation presented here explains why measured minimum velocities often range between 10 and 20 m/s. The second part of the paper deals with condensation of continuously generated foam in a closed system. In the process of condensation, foam is not completely separated into liquid and gas phase but turns into foam with small bubbles and high density. The collapse of this condensed foam must be considered for the control of persistent foams in a closed system. The collapse of foams made of aqueous solutions of different surface‐active agents has been investigated. Different highly surface‐active agents show small variations in times of coalescence. A relationship for the lifetime is given, which is based on laminar flow along plateau borders. Recommendations are made with respect to the geometry of the foam breaker, scale‐up and operating variables such as rotational speed of the foam breaker and gas flow rate.

Foam breaking — key process in detoxification of kraft mill effluents by foam separation

AbstractA study was undertaken to demonstrate on pilot plant scale the performance of a turbine foam breaking system and to develop the design parameters for large scale application.Among various configurations a 3‐blade vaned‐disc turbine was found to be optimal for foam breaking. Major process variables controlling foam breaking were system design, tip velocity, rotation speed, and foam load. A foam breaking system with only restricted liquid draw‐off performed 3 ‐ 16 times better than a conventional flow through system. A 38 cm diameter turbine operating at 1800 τ/min (3600 cm/s tip velocity) collapsed up to 1.2 m3/min (42 ft3/min) of foam.Design equations developed for sizing of foam breakers suggest that a 61 cm (2‐ft) diameter 21 kW turbine will collapse 4.7 m3/min of foam. For a 95 × 103m3/d foam separation plant, approximately 12 foam breakers are required. Capital costs are estimated at $108,000.

A mechanical foam breaker

A mechanical foam breaker

Foam columns for countercurrent surface—liquid extraction of surface‐active solutes

AbstractThe foam separation process uses differences in surface activity to separate components of a solution. Stable foams can flow upward countercurrent to liquid to give countercurrent differential separations with stripping, enrichment, or scrubbing similar to solvent extraction.Six‐ and 24‐in. I.D. foam columns were operated with sodium dodecylbenzenesulfonate solutions to measure height of transfer unit (HTU) values and foam densities and to develop satisfactory gas spargers, liquid feed distributors, foam drainage conditions, and foam condensation equipment. The HTU values for stripping of Sr‐89 were about 1 cm. for the best conditions of uniform foams, liquid flows of 100 gal./sq.ft.hr. or less, and uniform liquid feed distribution with low inlet velocities. Variations of countercurrent column lengths within 10 to 28 cm. caused little variation in HTU values. The foams were condensed, with four types of pneumatic or mechanical foam breakers used. A pilot plant was designed for decontamination of a low level radioactive waste.

放射性廃水蒸発濃縮処理装置の除染係数

A study was made to determine the decontamination efficiency of a radiochemical waste evaporator system, which consisted of evaporator, cyclone, mist-separator and condenser. The system was designed to handle the liquid radioaetive waste, which ranged in activity from 10/sup 4/ 10/sup -2/ mu c/ml, at the nate of 200 1/hr and to get a volume reduction ratio of 100 ~ 200. The evaporator is single effect and vertical shell-and-tube type, and is operated for non-foaming liquid by fixing the liquid level above the upper tube sheet of the calandria. For foaming liquid, however, the evaporator is operated by lowering the liquid level below the middle of the calandria. In the latter case, the upper part of the tubes above the liquid surface serves as a foam breaker. The decontamination factors of the evaporator, cyclone, and mist-separator and the over-all decontamination factor were measured for the boil-up rates varying from 50 to 300 1/hr. Lithium chloride and strontium nitrate solutions were used as test liquid. The decontamination characteristic of the evaporator is different for the two test liquids and depends on the liquid level. The over-all decontamination factor was measured to be 10/sup 6/ ~ 10/sup 8/ and it was revealedmore » that the required decontamination efficiency was achieved. Discussion is given on the mechanism of the generation of liquid entrainment. (auth)« less

Effect of antifoam agents on oxygen transfer in deep tank fermentations

AbstractDevelopment of a foam breaker which operates on the principle of rapid acceleration of foam through a nozzle has allowed large‐scale aerobic fermentations to be run without addition of antifoam agents. Fermentations have been investigated over a wide range of aeration levels in which oxygen supplied to the organisms was the limiting growth factor.With Torulopsis utilis grown in a 5 per cent molasses medium. oxygen utilization followed an exponential pattern during the early phase of growth, with carbon dioxide production equal to the consumption of oxygen. At the point where oxygen supply to the organism became limiting, anaerobic fermentation began, and the consumption of oxygen remained constant. The level of oxygen absorption beyond which the respiratory quotient exceeded unity was used as a measure of limiting oxygen supply.Addition of three types of antifoam compounds to T. utilis fermentations resulted in a marked depression of oxygen consumption, and a decrease in cell production. Incremental addition of small quantities of antifoam to maintain a constant foam level in the fermentor depressed the oxygen absorption rate to a lesser extent. Sulphite oxidation rates did not reflect the true value of oxygen absorption rates found for fermentations without addition of antifoam.

MILK SAMPLING AT WEIGH TANKS—I

Summary1. Samples were taken on three consecutive days from twenty‐two suppliers at three creameries. Six samples were taken at different levels and positions in the weigh tanks.2. Details of two dippers for sampling at different depths in the tank are given.3. Maximum differences between the six samples from each tank of milk ranged from 0·05 per cent to 0·61 per cent for fat and 0·07 per cent to 0·56 per cent for S.N.F., with means of 0·22 per cent and 0·21 per cent respectively.4. Coefficients of variation have been calculated for each tank of milk together with mean figures for each supplier and each creamery.5. Estimates have been made of the accuracy of the fat and S.N.F. content of a single sample taken from a tank of milk as a measure of the composition of the whole of the milk within the tank.6. Maximum differences show that very large differences in composition can occur at different points in the weigh tank.7. Comparison of the coefficients of variation for individual herds showed no correlation between variability within the tank with either the gallonage or the fat or S.N.F. content of the milk. A significant difference in variability was shown when the creameries were compared. This was attributed to the presence in one of the tanks of an obstacle in the shape of a foam breaker.8. Single samples of milk taken from an unagitated weigh tank cannot be relied upon to give an accurate assessment of the quality of the milk within the tank. Some form of agitation must be practised if a reliable sample is to be taken.9. The results of a pilot investigation carried out at one creamery in the winter months indicate very much greater variation in composition within unagitated tanks at this time of the year. The results of this investigation show that the variability of fat content can be considerably reduced by a reasonable plunging of the tank contents. The effect of plunging on S.N.F. variability was not so encouraging.

Stability Tube with Foam Breaker

Stability Tube with Foam Breaker

The Role of Surface Transport in the Stability and Breakdown of Foams

A new theory of foam stability is proposed which demonstrates that the transport of substrate. accompanying a movement of the surface of the bubble film, is a dominant factor in the stability of foams and in the action of foam breakers. The surface moves from a region of low surface tension (high surface pressure) to a region of high surface tension. The surface tension gradients arise from disturbances which may be caused by mechanical or thermal shocks, or by the addition to the surface of particles, droplets, or vapour of a surface-active material. When the surface tension is highest at the centre of disturbance the film mill be stable ; when the surface tension is lowest at this point the surface film and hence the substrate will be moved away from this point and the film will rupture.