Absorbent spray droplets

Dense ammonium nitrate crystals are formed by spraying droplets of molten ammonium nitrate solution (>99.6%) down a short tower. The spray produces spherical particles known as prills . These crystals are non-absorbent and used in conjunction with nitroglycerine. An absorbent form of ammonium nitrate can be obtained by spraying a hot, 95% solution of ammonium nitrate down a high tower. The resultant spheres are carefully dried and cooled to prevent breakage during handling. These absorbent spheres are used with fuel oil. 

According to Assumption (4) above, the specific interface area calculated from the Sauter mean diameter of spray droplets, a, is kept constant. Thus, the integral amount of S02 absorbed within the residence time of the gas and droplets in the effective volume of the reactor, t, can be obtained as... 

The data shown in Fig. 7.14 are somewhat different from those by Berman et al. [25] who reported a sulfur-removal efficiency of about 80% under the condition of C02 = 0 and at Ca/S = 1.0 (see Fig. 4 in Ref. [25] or Fig. 7.7 in this book). Possibly, this difference results from different absorber structures. In that used by Berman et al. spray droplets may collide rapidly on the wall, resulting in a significantly decreased effective interfacial area. 

Dilution is attributed to the large amounts of air that are entrained by the spray. As a result of air entrainment, dispersion behavior is altered for materials that exhibit negative buoyancy upon release. This is found to be effective in controlling flammability hazards that are located close to the release source. If an explosion does occur, some of the energy will be absorbed in the breakup of the water spray droplets, thereby mitigating the explosions impact. 

The medium that interacts with radiation may contain particles and gases which absorb and scatter the radiant energy. In combustion chambers, for example, soot, char, fly-ash, coal particles and spray droplets affect the propagation of radiant energy. Among various gases, carbon dioxide and water vapor are the major participants to radiative transfer, both in combustion chambers and in the atmosphere. 

Wet/dry process. Lime slurry absorbs SO2 in vertical spray dryer forming CaSO —CaS, H2O evaporated before droplets reach... 

There are a variety of nozzles that can be provided to hoses and monitors. They are capable of projecting a solid, spray or fog stream of water depending on the requirements and at varying flow rates. Straight stream nozzles have a greater reach and penetration, while fog and water sprays will absorb more heat because the water droplets absorb more heat due to greater surface area availability. Fog and water spray nozzles are sometimes used to assist in the dispersion of vapor releases. 

To estimate inhalation contact exposure, some assumptions must be made which err on the side of conservatism and which should be modified as more complete data become available. It is necessary to know the droplet size spectrum of the spray because the diameter of the droplet influences its movement down the respiratory system (11). The functional unit of the lung is the alveolus, which is the terminal branch in the system. It is presumed that pesticide particles which are soluble in respiratory tract fluid and are 5p or less in diameter will reach the alveolus where they will be readily absorbed through the cells of the alveolar membrane into the pulmonary capillary beds and hence into the circulatory system. A recent review by Lippmann at al. (12) discusses in depth the deposition, retention and clearance of inhaled particles. 

Spray drying has become increasingly important in recent years as an alternative to wet scrubbing for sulfur dioxide control. In the spray dryer the sulfur-containing flue gas is contacted with a fine mist of an aqueous solution or a slurry of an alkali (typically Ca(0H)2 or soda ash). The sulfur dioxide is then absorbed in the water droplets and neutralized by the alkali. Simultaneously, the thermal energy of the gas evaporates the water in the droplets to produce a dry powdered product. After leaving the spray dryer the dry products, including the fly ash, are removed with collection equipment such as fabric filters or electrostatic precipitators. 

There are several other types of apparata used for reactive absorption, though these are less widespread. In mechanically agitated bubble columns it can be assumed that both phases are ideally mixed, whereas in the jet absorber, the gas stream breaks on a liquid surface and is dispersed in the liquid. In spray towers and venturi scrubbers, liquid is sprayed as fine droplets. Thin-jilm contactors, in which liquid film is scrapped from the walls by impellers, are applied for reactive absorption in viscous liquids. Some units, such as wetted-wall columns, contactor, laminar jet absorber and disc (sphere) column are used mainly in laboratory. 

In a spray absorber, a waste gas containing ammonia will be purified with water. The waste gas and water droplets flow countercurrent to each other as shown in Fig. 2.64. The saturated concentration of ammonia (substance A) for a temperature of 10 °C of the spray water and a pressure of 0.11 MPa appears at the surface of the falling water droplets. The mass fraction of ammonia at saturation is a0 = 0.4. The following mass flow rates and mass fractions are given water feed Mw = 2.3 kg/s, waste gas feed Mqi = 4.4 kg/s, mass fraction of ammonia in the waste gas feed ai = 0.12 this should be reduced to a value of = 0.006 in the waste gas exit stream the mass fraction of ammonia in the water outlet is allowed to reach = 0.24. The fraction of water in the waste gas is negligible. 

Spray-dry scrubbers are an alternative to conventional wet scrubbers. In this type of scrubber, an alkaline slurry or solution is sprayed in fine droplets into a reaction vessel, along with the flue gas. The droplefs rapidly react with the sulfur dioxide while drying to a fine powder of sulfite salts. This powder is entrained in the gas stream, and is carried to a dust precipitator where it is collected, as shown in Fig. 7. Most of the sulfur dioxide is collected in liquid-phase reactions while the droplets are drying, but 10-15 /o additional sulfur dioxide can be absorbed in gas/solid reactions, as the absorbent powder is swept through the ductwork and particulate collector. These are cocurrent devices, and so the limestone utilization and sulfur removal efficiency are inherently lower than those of countercurrent devices such as wet scrubbers. Partial recycle of the sorbent is often used to improve the sorbent utilization. 

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