Tower Operation

German vinyl ether plants were described in detail at the end of World War II and variations of these processes are stiU in use. Vinylation of alcohols from methyl to butyl was carried out under pressure typically 2—2.3 MPa (20—22 atm) and 160—165°C for methyl, and 0.4—0.5 MPa (4—5 atm) and 150—155°C for isobutyl. An unpacked tower, operating continuously, produced about 300 t/month, with yields of 90—95% (247). 

Not only may the cooling-tower plume be a source of fog, which in some weather conditions can ice roadways, but the plume also carries salts from the cooling water itself. These salts may come from salinity in the water, or may be added by the cooling-tower operator to prevent corrosion and biological attack in the column. 

Acid circulated over SO absorbing towers is maintained at about 98.5% to minimize its vapor pressure. Where lower concentration product acid is desired, it is made either in separate dilution faciUties, or in drying towers operated at 93—96% H2SO4. 

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... 

On the other hand, if the actual commercial tower area is 1110 fr, the cooling equivalent to 1000 fr of standard tower area can be accomphshed with less air and less fan horsepower. From Fig. 12-15, the fan horsepower for a tower operating at 90 percent of standard performance is 0.031 hp/fr of actual tower area, or 34.5 hp. 

Cycles of concentration involved with cooling-tower operation normally range from three to five cycles. Below three cycles of concentration, excessive blowdown quantities are required and the addition of acid to limit scale formation should be considered. 

Example 14 Uttiy Coefficient for a Hyperbolic Tower Determine the duty coefficient for a hyperbolic tower operating with... 

Aside from the lack of an explicitly defined liquid-phase-resistance term, the limitations on the use of Eq. (14-66) are related to the fact that its derivation implicitly assumes that the system is dilute iysM = 1) and that the operating and equilibrium curves are straight lines over the range of tower operation. Also, Eq. (14-66) is strictly vahd only for the temperature and pressure at which the original test was run even though the total pressure pf appears in the denominator. 

The example spreadsheet covers a three-day test. Tests over a period of days provide an opportunity to ensure that the tower operated at steady state for a period of time. Three sets of compositions were measured, recorded, normalized, and averaged. The daily compositions can be compared graphically to the averages to show drift. Scatter-diagram graphs, such as those in the reconciliation section, are developed for this analysis. If no drift is identified, the scatter in the measurements with time can give an estimate of the random error (measurement and fluc tuations) in the measurements. 

Tower Operations. The tower operator can quickly determine which type of flooding will tend to be the limiting one for a particular system. If a rigorous computer run is available for the anticipated or actual operation, the operator can quickly calculate the expected limiting column section. The operator can then provide DP cell recording for the entire column and limiting section(s). As mentioned previously, a DP cell is the best measure of internal traffic and flooding tendency. 

The plate to plate type calculation is a fundamental procedure wherein the tower is assumed to be composed of theoretical equilibrium plates. The actual plates required are determined from the number of theoretical plates using a predicted overall tower efficiency. The starting point for a tower calculation is usually a specified feed composition, feed temperature, and tower operating pressure. The procedure involves defining the compositions and temperamres on each plate in the tower and subsequently the resultant compositions and temperatures of the product streams. The actual computations, which involve trial... 

The typical stripper consists of a tower operating at 10-20 psig w ith 211 trays, a reboiler, and an overhead condenser. The rich amine feed is introduced on the third or fourth tray from the top. The lean amine i.s removed at the bottom of the stripper and acid gases are removed from the top. 

The tower operates in the same manner as a condensate stabilizer with reflux. The inlet liquid stream is heated by exchange with the gas to approximately 30 F and is injected in the tower at about the point in the tower where the temperature is 30 F. By adjusting the pressure, number of trays, and the amount of reboiler duty, the composition of the bottoms liquid can be determined. 

Tower Operating Pressure Static Slot Seal [15], In. Dynanuc Slot Seal [5],In. 

Check the trays for a finishing tower operating under vacuum of 75 mm Hg at the top. The estimated pressure drop for the twenty trays should not exceed 50-60 mm Hg. Fifteen trays are in the rectifying section, five in the stripping section. 

As a general rule packing heights per su V]vort plate should not exceed 12 It lot Raschig rings or l,a-20 It Idr most other packing shapes. Othei tvpes fit within these limits. The mechanical, vibrational and thermal shock loads become important md sometimes affect the tower operation beyond these limits. 

The HETP (Height Equivalent to a Theoretical Plate (stage or plate)) is the tray spacing divided by the fractional overall tray efficiency [82]. The transfer unit concept has been useful for generalized correlations [89]. Because packed towers operate with continuously changing compositions through the packed height, the concept... 

Revised Packed Tower Pressure Drop Correlation Constants for Towers Operating Below Flooding Region... 

Because actual L = 2250 is less than 16,000 this tower operates in the gas continuous region. 

Comparison with Figure 9-21C gives 3 in. water/ft (parameter) or a total of (3) (45) = 135 in. water. Neither of these values represents a condition (flooding) that should be considered for tower operation, except under known experience studies. Distillation operations sometimes operate above flooding, but other types of contacting normally require operations in the loading region (or below) for stable performance. 

Pressure drop for both AS (0.5-in. crimp height) and AS (0.375-in. crimp height) packings is acceptable for the crude tower operation. 

The economics of forced and induced draft cooling tower operation require a study of fan and water pump horsepower and usually dictate a fan static pressure requirement not to exceed 0.75-1.0 in. of water. For atmospheric and natural draft towers the economics of pumping water are still very important. This means that the ground area must be so selected as to keep the height dovm while not dropping the unit rates so low that performance becomes poor. This then, is a balance of ground area versus total deck height. Pritchard [16] presents an... 

Lc = Critical liquid rate for liquid continuous system, at which the packing becomes completely wetted and tower operation is in the liquid continuous range, lb/(hr) (ft )... 

Otake, T. and K. Okada, Liquid Hold-up in Packed Towers, Operating and Holdup Without Gas Flow, Soc. Chem. Engrs. Qapan) 17, No. 7, 176 (1953). 

Zenz, F A., What Every Engineer Should Know About Packed Tower Operations, Chem. Eng., August, p. 176 (1953). 

Water-cooling in towers operates on the evaporative principles, which are a combination of several heat/mass transfer processes. The most important of these is the transfer of liquid into a vapor/air mixture, as, for example, the surface area of a droplet of water. Convective transfer occurs as a result of the difference in temperature between the water and the surrounding air. Both these processes take place at the interface of the water surface and the air. Thus it is considered to behave as a film of saturated air at the same temperature as the bulk of the water droplet. 

The calcium bisulfite acid used in the manufacture of sulfite cellulose is the product of reaction between gaseous sulfur dioxide, liquid water, and limestone. The reaction is normally carried out in trickle-bed reactors by the so-called Jenssen tower operation (E3). The use of gas-liquid fluidized beds has been suggested for this purpose (V7). The process is an example of a noncatalytic process involving three phases. 

Tower operating pressure is determined most often by the temperature of the available condensing medium, 100-120 F if cooling water or by the maximum allowable reboiler temperature, 150 psig steam, 366 F. 

High noise levels associated with tower operation may limit air stripping. 

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... 

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