Scrubbing liquid

AP is the pressure drop, cm of water p and Pg are the density of the scrubbing liquid and gas respectively, g/cm L/g is the velocity of the gas at the throat inlet, cm/s QtIQg is the volumetric ratio of liquid to gas at the throat inlet, dimensionless It is the length of the throat, cm Coi is the drag coefficient, dimensionless, for the mean liquid diameter, evaluated at the throat inlet and d[ is the Sauter mean diameter, cm, for the atomized liquid. The atomized-liquid mean diameter must be evaluated by the Nuldyama and Tanasawa [Trans. Soc Mech Eng (Japan), 4, 5, 6 (1937-1940)] equation ... 

The effective friction loss, or gas-phase contacting power, is easily determined by direct measurements. However, the liquid-phase contacting power, supplied from the stream of scrubbing liquid, and the mechanical contacting power, supplied by a mechanically driven rotor, are not direc tly measurable the theoretical power inputs can be estimated, but the portions of these quantities effectively converted to contac ting power can only be inferred from comparison with gas-phase contacting power. Such data as are available indicate that the contributions or contacting power from different sources are directly additive in their relation to scrubber performance. 

The principal advantage of self-induced spray scrubbers is the efim-ination of a pump for recirculation of the scrubbing liquid. However, the designs for high-energy service are somewhat more complex and less flexible than those for venturi scrubbers. 

Lucas and Porter (U.S. Patent 3,370,401, 1967) developed a fiber-bed scrubber in which the gas and scrubbing liquid flow vertically upward through a fiber bed (Fig. 17-55). The beds tested were composed of knitted structures made from fibers with diameters ranging From 89 to 406 [Lm. Lucas and Porter reported that the fiber-bed scrubber gave substantially higher efficiencies than did venturi-type scrubbers tested with the same dust at the same gas pressure drop. In similar experiments, Semrau (Semrau and Lunn, op. cit.) also found that a fiber-bed contactor made with random-packed steel-wool fibers gave higher efficiencies than an orifice contactor. However, there... 

The scrubbing liquid must be chosen with specific reference to the gas being removed. The gas solubility in the liquid solvent should be high so that reasonable quantities of solvent are required. The solvent should have a low vapor pressure to reduce losses, be noncorrosive, inexpensive, nontoxic, nonflammable, chemically stable, and have a low freezing point. It is no wonder that water is the most popular solvent used in absorption devices. The water may be treated with an acid or a base to enhance removal of a specific gas. If carbon dioxide is present in the gaseous effluent and water is used as the scrubbing liquid, a solution of carbonic acid will gradually replace the water in the system. 

Available in metal and plastic, used in large and small towers for distillation, absorption, scrubbing, liquid extraction. High efficiency, low HETP, low pressure drop. Limited data available. 

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

A venturi scrubber aeeelerates the waste gas stream to atomize the scrubbing liquid and to improve gas-liquid contact. In a venturi scrubber, a "throat" section is built into the duet that forces the gas stream to accelerate as the duct narrows and then expands (refer to Figure 14). As the gas enters the venturi throat, both gas velocity and turbulence increase. 

Orifice scrubbers generally do not require precleaning, unless the waste gas contains large pieces of debris. Precooling may be necessary for high temperature waste gas flows which increase the evaporation of the scrubbing liquid. 

The scrubbing liquid is fed into the pool at the bottom of the scrubber and later recirculated from the entrainment separator baffles by gravity instead of being circulated by a pump as in venturi scrubbers. Many devices using contactor ducts of various shapes are offered commercially. The principal advantage of this scrubber is the elimination of a pump for recirculation of the scrubbing liquid. 

Another consideration in the application of absorption as a control technique is the treatment or disposal of the material removed from the absorber. In most cases, the scrubbing liquid containing the VOC is regenerated in an operation known as stripping, in which the VOC is desorbed from the absorbent liquid, typically at elevated temperatures and/or under vacuum. The VOC is then recovered as a liquid by a condenser. 

PM Control - An impingement-plate scrubber is a vertical chamber with plates mounted horizontally inside a hollow shell. Impingement-plate scrubbers operate as eountercurrent PM collection devices. The scrubbing liquid flows down the tower while the gas stream flows upward. Contact between the liquid and the particle-laden gas occurs on the plates. The plates are equipped with openings that allow the gas to pass through. Some plates are perforated or slotted, while more complex plates have valve-like openings. 

As stated, gas absorption is a process whereby gas and liquids are brought into intimate contact and a component of the gaseous phase becomes dissolved in the liquid. With the proper selection of scrubbing liquid, the gas contaminant will have... 

Corrosion resistance it is critical to select construction materials such that neither the gas and solute nor the scrubbing liquid will corrode the packing materials. Ceramic and plastic materials, are commonly selected for this reason. 

An impingement scrubber is designed to make the dust particles impinge and adhere to water droplets. Gas is introduced at the bottom and passes up through water-covered perforated trays, where dust is removed by the scrubbing liquid. 

The scmbber is comprised of one or more trays. Each tray contains numerous venturi openings. Each of the MultiVenturi openings is surmounted by a spider cage holding a floating Flexicap (see insert), in addition, each tray is equipped with one or more downcomers" and weir flow baffles that control the scrubbing liquid as it flows across the tray and then to the tray below. 

The direct treatment of the scrubbing liquid from a flue gas desulfurization step could be carried out by using the sulfur-reducing bacterium denoted as KT7 [290], This low-GC Gram-positive bacterium is related to the genus Desulfotomaculum, which is capable of reducing sulfite and sulfate to sulfide. Its optimum growth is observed at a temperature between 48°C and 70°C, at a pH of between 5 and 9 and at a conductivity of the liquid medium between 0 and 40 mS/cm. The treatment was claimed to be favored under anaerobic conditions. 

Depending on the scrubber design, the scrubbing liquid is sprayed into the gas stream before the gas encounters the Venturi throat, or in the throat, or upwards against the gas flow in the throat. The scrubbing liquid is then atomized into small droplets by the turbulence in the throat, and droplet-particle interaction is increased. Some designs use supplemental hydraulically or pneumatically atomized sprays to augment... 

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