Countercurrent packed tower

Process air in sulfur-burning plants is dried by contacting it with 93—98 wt % sulfuric acid in a countercurrent packed tower. Dry process air is used to minimise sulfuric acid mist formation in downstream equipment, thus reducing corrosion problems and stack mist emissions. 

It is demonstrated in the pilot tests that TCE can be removed by 99% for the direct contact exposure route within 3 to 5 yr using the vapor extraction system. The potential for fugitive losses of air contaminants would be minimal under good control conditions. A countercurrent packed tower air stripper (13.72 m tall and 1.22 m in diameter) would be used to treat the extracted groundwater to meet the performance goal of 5 pg/L TCE concentration. The exhaust air would be discharged through carbon beds for adsorption. 

A reactive absorption is done in a countercurrent packed tower. The material balance is made in terms of solute-free quantities. Inlet conditions are X2 = 0, Yx - 0.5 outlet Xx =0.8, Y2 = 0.1. Bottom is 1, top is 2. 

Countercurrent flow capillary electrophoresis, 4 635 Countercurrent packed tower, 25 810, 811 Countercurrent shaft kilns, 15 47-48 Counterdiffusion, 1 41-42 equimolar, 1 39-40 Counterflow heat exchangers... 

Countercurrent packed towers (in their various forms) appear to be the most appropriate equipment configuration for treating contaminated groundwaters for the following reasons ... 

The absorption of ozone by cyanide solutions in stirred reactors is complicated by mass transfer considerations. The presence of ozone gas in the exhaust from such a reactor does not indicate that equilibrium has been obtained between ozone gas bubbles and ozone in solution, but rather that the mass transfer through the individual bubbles is not complete, because of the resistance on the gas side. In other words, mass transfer controls the reaction, as the ozone will react almost instantaneously with the cyanide ion in solution. The presence of some metals, particularly copper, appears to speed up the absorption by acting as oxygen carriers. A solution of ozone in dilute acid decomposes somewhat more quickly when a trace of cupric ion is added. The presence of these metal catalysts, if this be their function, does not appear to be a necessary condition to ozone oxidation. What is important is that adequate mass transfer time and surface be available, as would be found in a countercurrent packed tower. 

Such processes as mechanical surface aeration, diffused aeration, spray fountains, spray or tray towers, open-channel cascades, and countercurrent packed towers are encompassed by the term air stripping. These procedures produce a condition in which a large surface area of the water to be treated is exposed to air, which promotes transfer of the contaminant from the liquid phase to the gaseous phase. This occurs because under normal conditions the concentration of the contaminant in ambient air is much lower than the concentration in contaminated water. 

A countercurrent packed-tower air stripper has two major components (Fig. 1) ... 

Packed Tower.—A conventional countercurrent packed tower is shown Tor comparison. When used Tor flue gas scrubbing, a short section of low-pressure-drop packing (e.g., 3 in. Intalox saddles) is employed with a mist eliminator above the liquid feed point. 

The development of the design equation for a countercurrent packed tower absorber or stripper begins with a differential mass balance of component A in the gas phase, in a manner similar to that of Example 2.12. However, this time we do not restrict the analysis to dilute solutions or to constant molar velocity. If only component A is transferred (4 G = VA[ = 1.0), considering the fact that the gas-phase molar velocity will change along the column, and that F-type mass-transfer coefficients are required for concentrated solutions, the mass balance is... 

Example 8.1.6 A solution of sulfuric acid having a sulfuric acid concentration of 0.6kgmol/m is used to absorb NH3 from an air stream at 25 °C and essentially atmospheric pressure containing 4 mole % NH3 in a countercurrent packed tower via the instantaneous reaction... 

Types of air strippers include packed towers, tray towers, and spray towers. Packed towers are packed or filled with small forms made of polyethylene [9002-88-4] stainless steel, poly(vinyl chloride) (PVC) [9002-86-2] or ceramic that provide large surface area to volume ratios which increase transfer rates into the air stream. Packed towers operate in countercurrent mode, that is, the aqueous stream enters at the top of the tower while air is blown in from the bottom. An example of this type of unit is shown in Figure 1. Channeling or short circuiting of the aqueous stream is minimized by... 

If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

Packed-bed scrubbers m be construc ted for either vertical or horizontal gas flow. Vertical-flow units (packed towers) commonly use countercurrent flow of gas and liquid, although cocurrent flow is sometimes used. Packed scrubbers using horizontal gas flow usually employ cross-flow of liquid. 

In a countercurrent packed column, n-butanol flows down at a rate of 0.25 kg/m2 s and is cooled from 330 to 295 K. Air at 290 K, initially free of n-butanol vapour, is passed up the column at the rate of 0.7 m /m2 s. Calculate the required height of tower and the condition of the exit air. 

Consider the removal of C02 from a gas stream by treatment with an aqueous solution of monoethanolamine (MEA) in a countercurrent-flow, packed tower operating at 25°C and 10 bar. The reaction is... 

An acetone-air mixture containing 0.015 mole fraction of acetone has the mole fraction reduced to 1 per cent of this value by countercurrent absorption with water in a packed tower. The gas flowrate G is 1 kg/m2s of air and the water flowrate entering is 1.6 kg/m2s. For this system, Henry s law holds and ye = 1.75x, where ye is the mole fraction of acetone in the vapour in equilibrium with a mole fraction v in the liquid. How many overall transfer units are required ... 

Acetone is to be recovered from a 5 per cent acetone-air mixture by scrubbing with water in a packed tower using countercurrent flow. The liquid rate is 0.85 kg/m2s and the gas rate is 0.5 kg/m2s. 

Ammonia is to be removed from a 10 per cent ammonia-air mixture by countercurrent scrubbing with water in a packed tower at 293 K so that 99 per cent of the ammonia is removed when working at a total pressure of 101.3 kN/m2. If the gas rate is 0.95 kg/m2s... 

A soluble gas is absorbed from a dilute gas-air mixture by countercurrent scrubbing with a solvent in a packed tower. If the liquid fed to the top of the tower contains no solute, show that the number of transfer units required is given by ... 

Absorption is a commonly applied operation in chemical processing. It is used as a raw material or a product recovery technique in separation and purification of gaseous streams containing high concentrations of organics (e.g., in natural gas purification and coke by-product recovery operations). In absorption, the organics in the gas stream are dissolved in a liquid solvent. The contact between the absorbing liquid and the vent gas is accomplished in countercurrent spray towers, scrubbers, or packed or plate columns. 

Polymerization of propylene was done in a packed tower with the gas flowing countercurrently to 98% liquid phosphoric acid... 

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