Tray diagram

Figure 2-80 shows a typical absorber tray diagram for the absorption of CO2 in MEA solution. Ibis figure is based on actual plant data from a 16 bubble-cap tray absorber treating atmospheric pressure flue gas for CO2 recovery. Because of the low values of solution loading involved, the equilibrium line is almost coincident with the x-axis and is not shown. A pseudo-equilibrium line (dashed) has been drawn to represent actual gas and liquid compositions from each tray. The plate efficiencies in this column vaiy from about 14% in the bottom of the column to slightly over 16% at the top. 

With the operating and equilibrium lines drawn on the chart as indicated, it can be seen that about 1.5 theoretical stages are required. Assuming an individual Murphree tray efficiency of 40%, the number of actual trays can be estimated by using vertical steps on the tray diagram that extend 40% of the distance from the operating line to the equilibrium line at each tray point. The use of this procedure indicates that at least six actual trays should be used. The... 

Figure 11-32. Tray diagram for absortwr design high-ptessure natural gas dehydration...

Fig. 3. Flow diagram for a chemical absorption process where the horizontal lines within the towers represent trays or packing.

Operating Lines The McCabe-Thiele method is based upon representation of the material-balance equations as operating lines on the y-x diagram. The lines are made straight (and the need for the energy balance obviated) by the assumption of constant molar overflow. The liqmd-phase flow rate is assumed to be constant from tray to tray in each sec tiou of the column between addition (feed) and withdrawal (produc t) points. If the liquid rate is constant, the vapor rate must also be constant. 

Preliminary Process Flowsheet. This will show major equipment and lines, preliminary equipment details (vessel diameter, number of trays, pump flow and driver horsepower, etc.), major instrumentation, and, it is hoped, have a material balance at the bottom of each drawing with flows keyed to a numbering system on the diagram. The process flowsheets should cover both the process and utility sides of the plant. 

The design of a distillation column is based on information derived from the VLE diagram describing the mixtures to be separated. The vapor-liquid equilibrium characteristics are indicated by the characteristic shapes of the equilibrium curves. This is what determines the number of stages, and hence the number of trays needed for a separation. Although column designs are often proprietary, the classical method of McCabe-Thiele for binary columns is instructive on the principles of design. 

Simple Batch Distillation Constant a, with Trays or Packing, Constant BoUup, and with Reflux [129] Using x-y Diagram... 

After filling the receiver, reflux runs down the column at the same molar rate as the vapor back up (L = G). The operating line has a slope of 1.0. Then there are n plates/trays between composition Xp and xj (the mol fraction in distillate). As the distillation continues, the operating line moves closer to the 45° line of the diagram, and x and Xp (and Xj) become richer and leaner, respectively, until at the end xj becomes Xq and x becomes x. The required time is 02. 

For the stripping section consider top seven trays, vapor entering tray No. 6, yy = 0.02, m = tray 7, m + 1 = tray 6, reading from diagram. 

Total trays = 7 (from diagram plus (1.71 - 1) = 7.7 theoretical, plus a reboUer or 8.7 including a reboiler. 

Note that if the problem of accurate graphical representation occurs in the rectification end of the diagram, the corresponding relation to use to calculate the balance of the trays, assuming straight line operating and equilibrium lines in the region is [59] ... 

Figure 8-124 illustrates a typical pressure drop diagram for a sieve tray. Note that the figure is for liquid flowing... 

Figure 8-125. Performance diagram of sieve trays (note article reference No. 18) used by permission. Chase, J. D., Chem. Eng., July 31 (1969), p. 105.

Kister et al. [213] have concluded from examining reported cases of cross-flow channeling related to poor sieve tray column performance that under specific conditions the cross-flow channeling does occur. See Figure 8-142 [213] for diagram of the postulated vapor flow across a tray. It is known to occur for valve trays and bubble cap trays. This condition has not been studied very much in the open literature however, several investigators including myself have observed in industrial practice the... 

The pressure drop remains essentially constant as long as the liquid flow on tray remains steady during the period point A to point B on the diagram (the open balance point) [201]. At point B all valves are completely open off their seats, but are on the verge of closing and may be oscillating from open to closed. At point B the vapor velocity through the holes, opened balance point is ... 

Beyond point B on the diagram, the pressure drop for the tray increases as the vapor rate increases. Use Equation 8-314 or 8-315 to determine the dry tray pressure drop, AP, in. liquid, Bolles [205] per Klein [201] ... 

Refer to Figure 9-29 for diagram of loading. From a material balance using (L/D) = 6.0 theoretical trays = 20... 

FIGURE 18.9 Schematic diagram of Redwood slatted tray aerator. 

The next thing that is needed is a program that keeps track of all the process and utility streams, and determines the order in which the individual equipment calculations will be performed. This is sometimes referred to as the executive program. The user of this system has merely to put into computer language the flow diagram, which identifies the units (areas of heat exchangers, number of trays in a distillation column) and their interrelations, and to list the operating characteristics of each unit (the pressures, temperatures, exit compositions), the input variables to the plant... 

Figure 1.2. Schematic flow diagram of SCR process and of the trays and monoliths of the SCR reactor.

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