Packed strippers

Packed Stripper (plastic random packing) 1.5 ft diam., 15 ft bed depth... 

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. 

In a steam stripper, steam is introduced into a packed tower, which causes volatiles to be removed in the vapor phase. An a2eotropic mixture is formed, resulting in a separation of the volatiles from the water. An effluent recycle is usually employed to reduce volatiles in the Hquid effluent. 

Distillation Columns. Distillation is by far the most common separation technique in the chemical process industries. Tray and packed columns are employed as strippers, absorbers, and their combinations in a wide range of diverse appHcations. Although the components to be separated and distillation equipment may be different, the mathematical model of the material and energy balances and of the vapor—Hquid equiUbria are similar and equally appHcable to all distillation operations. Computation of multicomponent systems are extremely complex. Computers, right from their eadiest avadabihties, have been used for making plate-to-plate calculations. 

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

FIG. 14-3 Nomenclature for material balances in a packed-tower absorber or stripper. 

Mass Transfer Relationships for calculating rates of mass transfer between gas and liquid in packed absorbers, strippers, and distillation columns may be found in Sec. 5 and are summarized in Table, 5-28. The two-resistance approach is used, with rates expressed as transfer units ... 

Some performance data of plants with DEA are shown in Table 23-11. Both the absorbers and strippers have trays or packing. Vessel diameters and allowable gas and liquid flow rates are estabhshed by the same correlations as for physical absorptions. The calciilation of tower heights utilizes data of equilibria and enhanced mass-transfer coeffi-... 

The fixed cost,, of the stripper (including installation and auxiliaries, but excluding packing) is given by... 

Amine strippers use heat and steam to reverse the chemical reactions with CO2 and H2S. The steam acts as a stripping gas to remove the COo and HjS from the liquid solution and to cairy these gases to the overhead. To promote mixing of the solution and the steam, the stripper is a trayed or packed tower with packing normally used for small diameter columns. 

Adsorbers, distillation colunuis, and packed lowers are more complicated vessels and as a result, the potential exists for more serious hazards. These vessels are subject to tlie same potential haz. uds discussed previously in relation to leaks, corrosion, and stress. However, llicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid distributors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of the fluids being passed tlirough tlie tower, potential liazards may result if incompatible materials are used for llie internals. Reactivity with llie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ullinialely, to vessel rupture. Distillation columns may contain internals such as sieve trays, bubble caps, and valve plates, wliicli are also in conlacl with tlie... 

The packed column section contains a stripper pre-column (column 1), which separates the Cg+ fraction by back-flushing all compounds above -pentane in one peak. HjS, CO2, C2, O2, N2 and Cj are trapped in columns 3 and 4, while C3-C5 hydrocarbons elute from column 2 to the TCD. The remaining components are... 

Figure 9-29. LHC plant stripper using packed tower for Example 9-1.

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. 

The gas pressure drop is a function of the gas and liquid flow rates and the size and type of packing. It relates to the overall cost of the air stripper and to its performance. The gas pressure drop through a stripping unit can be determined from the pressure drop curve. 

Figure 9 Steam-stripping flow diagram. The influent is heated by the stripper effluent before entering the stripping column near the top the liquid stream flows downward through the packing, and steam flows upward, carrying volatile compounds the overhead is condensed and liquid returned to the column volatile compounds are either recycled or incinerated (from Ref. 11).

Add packing to top of stripper to insert oil to increase delta coke when processing very low delta coke feeds... 

Catalyst will defluidize and pack in stagnant areas and cool, leading to potential corrosion. This is a common problem in annular strippers with the spent catalyst stripper ontlet on one side of the bottom of the stripper. Catalyst, if not kept hot by flnffing with steam, will settle, cool, and lead to potential corrosion to the disengager shell and riser. 

There are many commercially available air stripper technologies. There are several different types of air strippers, including packed towers, tray-type, spray aerators, mist aerators, diffused aerators, low-profile packed towers, and centrifugal air strippers. According to the U.S. Environmental Protection Agency (EPA), an estimated 1000 air stripping units were operational at sites throughout the United States in 1991 (see Table 1). 

In 1993, it was estimated that low-profile air strippers cost between 4000 and 40,000 and have treatment capacities ranging from 1 to 360 gal/min (gpm). Packed-tower air strippers have capacities ranging from 5 to 10,000 gpm and cost from 2000 to 200,000 (D15445K, p. 28). Cost information from Case Studies 1 and 3 is summarized below ... 

Case Study 1. Pump-and-Treat System with a Packed-Tower Air Stripper, McClellan Air Force Base Superfund Site, California, Operable Units B/C, 1987. The costs associated with pump-and-treat system used at the site were estimated in 1994. Costs were approximately 80 per pound of removed volatile organic compounds (VOCs) based on operating costs alone and approximately 150 per pound when capital costs were included (D141286, p. 135). It should be noted that the operation and maintenance costs for the an air stripper could not be separated from the total cost of the project. Capital cost and operating cost information for this project are summarized in Case Study 1. 

As in sulfuric acid alkylation, the hydrocarbon-acid emulsion passes from the contactor into an acid settler for separation of acid and hydrocarbon phases and the acid layer recirculates to the reactor. Unlike sulfuric acid, however, hydrofluoric acid is appreciably soluble in hydrocarbons, and as much as 1% by weight may be retained in the hydrocarbon layer. The necessity of recovering this acid from the hydrocarbon phase results, in another difference between hydrofluoric and sulfuric acid processing in that a hydrofluoric acid stripper is required. This stripper is ordinarily packed with aluminum rings which serve not only as tower packing but also as a catalyst for the decomposition of organic fluorides into hydrocarbons and free hydrofluoric acid. 

The Chlorex process utilizes simple countercurrent mixing and settling tanks (four to seven stages) or modern vertical packed towers. Solvent recovery involves conventional flash columns and strippers operated under vacuum (26 to 28 inches of mercury) at about 300° to 325° F. Low temperatures are desirable to minimize decomposition and formation of hydrochloric acid. 

The particular problem I encountered is illustrated in Fig. 10.4. The jet fuel product was steam-stripped to remove a lighter naphtha contaminant. But much naphtha was left in the jet fuel. Apparently, the packing in the stripper tower was not working properly. However, a discussion with the unit operator indicated that they were using very little stripping steam. Introduction of a normal amount of steam resulted in a loss of liquid level in the bottom of the stripper. 

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