Foam Scrubbing

The foam scrubbing technique is effective because it brings the hazardous material into close contact with the foam by getting it into the bubbles. This is different from using a foam blanket as a cover for spills (see Chapter 3). With the large internal surface area of the foam available for absorption or mass transfer, an equilibrium concentration between the contaminated air inside the bubble and the foam cell wall liquid can be developed rapidly. Unabsorbed gas that is still in the foam bubbles when they collapse is released. This results in the slower release of a smaller quantity of hazardous material, which should result in a reduced hazard zone downfield. 

Data from Brown et al. (1990) show that if the foam contains reactive materials, these materials react to form a neutralized compound as they are absorbed into the liquid bubble. The data indicate that in this situation, the foam may completely recover the released material if adequate amounts of the reactant are contained in the foam when it is generated. The reported work also indicates that heat effects from neutralization reactions do not weaken the stability of the foam. 

The foam technique requires two main components a foam generator, and a pressure source which feeds the contaminated air or vapors to the foam generator. Three applications of this technique for controlling releases are described in Brown et al. (1990). The first works with releases that occur 

The foam-scrubbing technique has been studied for a variety of gases, including ammonia, sulfur dioxide, hydrogen sulfide, formaldehyde, and nitrogen oxides. Liquid and solid streams that have been experimented with include sulfuric acid fog and mist, dust, fly ash, and methylene blue. 

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This section describes four additional techniques for mitigating releases of hazardous substances into the atmosphere. In addition to water, both steam and compressed air can be used to promote the movement of air to dilute a hazardous material. Foam can be used as a scrubbing medium to entrap a hazardous material in its structure. Foam scrubbing is often effective for materials that are soluble in water, or that are highly reactive with an additive contained in the foam. Lastly, dry powders can be used to capture a reactive chemical released into the air. 

The silver coating on old mirrors is dissolved with nitric acid and the surface is rinsed with water. The hands are scrubbed with soap, and the soap foam is transferred to the surface, which is then scrubbed for some time with the foam. Scrubbing is continued while the surface is rinsed, first with tap water, then with distilled water. In the end, the units surface must be perfectly wetted by the water. If any greasy, water-repellent area remains, the entire operation must be repeated. After rinsing, the piece to be mirrored is placed in a dish of distilled water. 

Liquid Liquid Liquid-gas Liquid-liquid Liquid-solid Solution Foam Emulsions Slurry Suspension Metal plating effluent spent acids wash-waters Detergent foam Oil-in-water (e.g. suds) water-in-oil Aqueous effluent from fume scrubbing... 

When a sucrose- or other simple carbohydrate-based solution is mixed with yeast and oxygen in a fermenter, carbon dioxide vapour and alcohol are produced. The carbon dioxide can then be passed through a separator to remove any trace cany-over of foam. Once the foam has been removed the carbon dioxide is compressed. It is then scrubbed with water in a packed tower, removing water-soluble impurities such as alcohol, ketones and other aroma chemicals produced during fermentation. 

Air-oil Solvent-based coating and leveling aid Foam control in gas scrubbing at petrochemical plants... 

There are many methods for the desulfurization of nature gas, which can be classified into dry desulfurization, wet desulfurization, and catalytic adsorption. In the dry desulfurization, some solid sorbents, such as iron oxide, zinc oxide, activated carbon (AC), zeolites, and molecular sieves, are used. In wet desulfurization method, liquid-phase chemical/physical solvent absorption systems are usually used for scrubbing H2S amine-based processes are subject to equipment corrosion, foaming, amine-solution degradation, and evaporation, and require extensive wastewater treatment. As a result, this sulfur removal technology is complex and capital intensive,44 although the processes are still employed widely in the industry. The desulfurization of coal gasification gas will be reviewed in detail in Section 5.5. In the catalytic-adsorption method, the sulfur compounds are transformed into H2S by catalytic HDS or into elemental sulfur or SOx by selective catalytic oxidation (SCO), and then, the reformed H2S and SOx are removed by the subsequent adsorption. 

Ease of rinsing is another test that can be performed. In one case, this is described as scrubbing a sink with a set amount of product to generate foam. This is then rinsed with moderately hard water, collecting the rinse water under the sink to quantify the amount needed until no foam is visible in the sink [357],... 

Contained within Figure 12 is a schematic of a typical four-stage compressor. Between the third and fourth stage is the caustic tower. It is used to scrub acids gases, and C02, from the cracked gas stream. Polymer formation in this tower arises from self-condensation of acetaldehyde that may have been formed in the furnace by partial oxidation of ethylene. This polymer has been held responsible for inducing foam formation in this tower. 

Ninol 5024 coupled with Stepanate SXS shows good builder tolerance. An excellent formulation for use in manual or completely automated scrub machines because of moderate, fastbreaking foam which does not interfere with machine operation. Formulation No. 430... 

This formulation has excellent wetting, detergent, rinsing and foaming properties. It is recommended as a medium duty cleaner for truck bodies, floor scrubs, wax strippers, etc. This product is clear from -5C to 70C. This formula would require approximately 4 times as much sodium xylene sulfonate as the amount of Monateric CEM-36 used to achieve clarity. Other nonionic ethoxy-lates, such as those based on primary alcohol or alkyl phenol may... 

MonaNF. [Mona Industries] Low foaming anionic surfactants fcu use in spray, soak tank, in-place p Une cletuim, floor scrubbing fomuilations. 

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