Tray tower scrubbers

A plant manufacturing dry ice will bum coke in air to produce a flue gas which, when cleaned and cooled, will contain 15% CO2, 6% O2, 79,0% N2. The gas will be blown into a sieve-tray-tower scrubber at 1.2 std atm, 25 C, to be scrubbed with a 30% ethanolamine solution entering at 25 C. The scrubbing liquid, which is recycled from a stripper, wiD contain 0.058 mol COj/moI solution. 

Plate Towers Plate (tray) towers are countercurrent gas-atomized spray scrubbers using one or more plates for gas-liquid contacting. They are essentially the same as, if not identical to, the devices used for gas absorption and are frequently employed in apphcations in which gases are to be absorbed simultaneously with the removal of dust. Except possibly in cases in which condensation effects are involved, countercurrent operation is not significantly beneficial in dust collection. 

Active scrubbers, which include pumps or other active components. These scrubbers generally circulate chemicals (such as water, acid, caustics, or organics) through a packed or trayed tower to absorb and/or condense hazardous materials from a vapor stream. The active components may run continuously, or only when material is released to the scrubber. This approach is most effective when the circulating fluid reacts with the material being adsorbed or condensed. 

The equipment typically used in absorption are spray towers, tray towers, packed towers, and Venturi scrubbers. The proper equipment is selected on the basis of the acid gases to be removed, initial and final concentration, and... 

Absorption and stripping are technically mature separation operations. Design procedures are well developed for both packed columns and tray towers, and commercial processes are common. In most applications, the solutes are contained in gaseous effluents from chemical reactors. Passage of strict environmental standards with respect to air pollution by emission of noxious gases from industrial sources has greatly increased the use of gas absorbers (also known as scrubbers) in the past decade. 

Impingement-plate-tower scrubbers have a number of horizontal plates or trays mounted in a tower. The gas stream is made to flow upwards, countercurrent against a downward flow of scrubbing liquid against which the desired aerosol particles and/or droplets are made to impact. The scrubbing liquid is usually an absorbent, or reactive, or solvent liquid. 

Benzene vapor in a coke-oven gas is scrubbed from the gas with wash oil in a countercurrent packed scrubber. The resulting benzenc-wash-oil solution is then heated to I25 C and stripped in a tray tower, using steam as the stripping medium. The stripped wash oil is then cooled and recycled to the absorber. Some data relative to the operation follow ... 

The gas and liquid are often placed in contact in a large vertical cylindrical tower. Several tower designs are shown in Fig. 28.3. Packed towers, spray towers, tray towers, and reverse jet-type scrubbers have aU been used to treat acid plant tail gas. They are usually constructed of fiber reinforced plastic with a suitable corrosion-resistant liner. Unlined stainless steel and rubber-lined carbon steel are also used. 

Pultruded profiles have excellent strength/ weight ratios, corrosion resistance, and good electrical resistivity, and are easy to fabricate via drilling, centerless grinding, and so on. Therefore, they have broad application in products such as fishing rods, industrial ladders, electrical switch actuators, cable trays, fume scrubber structural members, farm animal pen slats and electrical tower insulated guy wires. ... 

Commonly, amine absorbers include an integral gas. scrubber section in the bottom of the tower. This scrubber would be the same diameter as required for the tower. The gas entering the tower would have to pass through a mist eliminator and then a chimney tray. The purpose of this scrubber is to remove entrained water and hydrocarbon liquids from the gas to protect the amine solution from contamination. 

The acid gases, usually CO2 and H2S, are removed by scrubbing with diethanolamine or monoethanolamine solutions and possibly an additional caustic treatment. Older processes used caustic solutions of 5-15 wt% NaOH followed by a water wash. Of course, the spent caustic creates a disposal problem it must be neutralized with acid and then properly disposed of according to prevailing pollution and hazard waste standards. Different column configurations have been proposed, but usually large scrubber towers with well over 30 valve-type trays are used. 

In both contact processes the sulfur trioxide is, after the final passage through the final tray and cooling to 180 to 200°(3, absorbed in 98.5 to 99% sulfuric acid. This occurs either in a countercurrent absorber tower or in a jet scrubber in which acid is sprayed from the top in co-current with the reaction gas and is accompanied by conversion of sulfur trioxide into sulfuric acid. 

Of the above parameters, the ability to increase gas/liquid contact will always result in higher absorption efficiency in a wet scrubber. If temperature can be reduced and the liquid-to-air ratio increased, then the absorption efficiency will also be improved in the scrubber. The actual design of the tower (diameter, height, depth of packed bed, etc.) will also depend on the given vapor/liquid equilibrium for the specific pollutant/scrubbing liquor. Additionally, the type of tower (packed vs tray, and so on) used will affect this equilibrium. The design of wet scrubbers is not covered in this chapter, but design examples can be found elsewhere in the literature (14). 

See Section 4.2 for cost guidelines for packed and tray columns or as pressure vessel Section 10.1. See Section 5.2 for gravity spray, baffled tower, atmospheric scrubber, venturi and wet cyclone. Demister, see Section 9.1. 

Possibly the most frequent cause of flooding or foaming in refinery fuel gas scrubbers is high liquid levels in the bottom of the tower. Referring to Figure 4-3, when the liquid level in the bottom of the scrubber rises to the level of the sour-gas inlet, the tower will flood. This occurs because the incoming gas will entrain the bottoms liquid onto the bottom tray. This entrained liquid will cause the bottom tray to flood, and the flooding... 

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