Atmospheric spray tower

Figure 9-100. Atmospheric spray tower, air flow aspirated by pressure-spray water distribution system. Usually applied in small sizes. Used by permission of Hensley, John C. (ed), Cooling Tower Funds.-menteUs, 2nd Ed. (1985), The Mariey Cooling Tower Co., a United Dominion Company.

In an atmospheric spray tower the air movement - is dependent on atmospheric conditions and the aspirating effect of the spray nozzles. Natural-draft cooling tower operation depends on a chimney or stack to induce air movement. Mechanical-draft cboling towers utilize fans to move ambient air through the tower. Deck-filled towers contain tiers of splash bars or decks to assist in the breakup of water drops to increase the total water surface and subsequently the evaporation rate. Spray-filled towers depend only on spray nozzles for water breakup. Coil shed towers are comprised of a combination structure of a cooling tower installed on top of a substructure that contains atmospheric section coils. Hyperbolic natural-draft cooling towers are typically large-capacity systems. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Cooling towers are classified according to the method by which air is introduced to the tower. The principal types are atmospheric spray, natural-draft, mechanical-draft, deck-filled, spray-filled, coil shed and hyperbolic towers. Most industrial cooling tower installations are field-erected units designed for specific thermal characteristics. 

The daily output of a cooler measuring 1650 X 610 X 350 mm and an absorber measuring 1650 X 970 X 350 mm equals 7.5 tons of 30 to 35 per cent hydrochloric acid. As a rule, two graphite absorbers are connected in series and the more diluted acid from the second absorber which contains about 20 per cent HC1 is pumped into the first absorber. The rest of the unabsorbed gas is led through a rubber lined steel absorption tower into the atmosphere. The tower is sprayed with water and the diluted acid obtained is employed as an absorption liquid in the second igurite absorber. The flow of the tail gases is aided by a steam-jet ejector. 

Make appropriate assumptions about windage and evaporation losses and set out and solve an equation for blowdown. Windage losses will be about 1.0 to 5.0 percent for spray ponds, 0.3 to 1.0 percent for atmospheric cooling towers, and 0.1 to 0.3 percent for forced-draft cooling towers for the forced-draft towers in this example, 0.1 percent can be assumed. As for evaporation losses, they are 0.85 to 1.25 percent of the circulation for each 10-degree drop in Fahrenheit temperature across the tower it is usually safe to assume 1.0 percent, so E = AT/10, where AT is the temperature drop across the tower. Therefore, in the present case,... 

Manufacture Synthetic hydrated calcium chloride is produced from the calcium chloride containing-residual brines of the Solvay process by evaporation initially in vacuum, then at atmospheric pressure. Calcium chloride is also produced from waste acid by reaction with limestone. Anhydrous calcium chloride is obtained e.g. by evaporation in fluidized bed dryers or spray towers. 

Air pollution control APC units (cyclone, venturi scrubber, tangential spray scrubber, spray tower, ID fans, chimney) This is required to absorb the gases evolved from reactor and den for air pollution control HF will be released into atmosphere and cause air pollution Monitor operation of APC units and exit gases all the time... 

At near atmospheric pressures, oxidation and absorption rates are slow, and earlier atmospheric and low-pressure plants used between five and ten very large towers. Maximum strengths attainable were in the range of 42% to 52% HNO3. To reduce capital investment and to obtain increased operating efficiencies, absorption under pressure was developed, using various types of equipment, e.g., cascade coolers, packed columns, spray towers, and columns incorporatir bubble plates, sieves, and such special devices as the Kuhlman tray. 

Protection from isocyanate vapours liberated during polyurethane manufacture is usually achieved by installing permanent exhaust ventilation units which either exhaust directly to the atmosphere or pass their exhaust fumes through scrubbers which extract the isocyanate vapour through a sodium carbonate spray tower before atmospheric exhaustion occurs. Continuous vertically positioned exhaust hoods are common where continuous conveyor lines are involved for localized extract situations, vertical down-draught or horizontal extract modes are much safer for operatives, being designed to remove all isocyanate vapour away from an operative s face and body. These latter situations apply particularly in the manufacture of cast-moulded and reaction-injection moulded products. 

The spray-filled tower, Figure 9-100, is also an atmospheric type, containing no fill other than the water sprays and no fans. The water-air contact comes about due to the spray distribution system [144], This design is often used where higher water temperatures are allowed, and the situations where excessive contaminants building up in the water would cause fouling of other direct contact heat transfer surfaces. 

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