Sieve trays allowable velocities

An alternate approach for estimating maximum allowable velocities has been presented by Fair (see reference given in footnote for preceding paragraph) which is based on data obtained with sieve-tray and other types of finite-stage columns and takes into account the effect of surface tension of the liquid in the column, the ratio of the liquid flow rate to the gas flow rate, gas and liquid densities, and dimensions and arrangement of the contactor. In this method, the basic equation for the maximum allowable vapor velocity, equiva-... 

Example 1 Determination of distillation-column diameter on basis of allowable vapor velocity. A sieve-tray distillation tower is to be operated under the following conditions ... 

The fractionating unit is a sieve-tray column with a standard type of tray design. The vapor velocity through the tower is about 90 percent of the maximum allowable value. 

The allowable vapor velocity for bubblecap trays is about the same as for sieve trays, and Figure 13.32(b) may be used. The most complete published source of design and performance prediction of these trays is given by W. L. Bolles (in Smith, 1963). 

Sieve tray extractors are popular in the chemical and petrochemical industries. The trays minimize axial mixing, which results in good scale-up from laboratory data. The dispersed phase drops re-form at the each perforation, rise (or fall) near their terminal velocity, and then coalesce underneath (or above) the tray, as shown in Figure 14.14(d). The coalesced layer is important to prevent axial mixing of the continuous phase and to allow re-formation of the drops, which enhances mass transfer. The continuous phase passes... 

Sieve trays, 651-652, 662, 681-686 allowable velocities in, 656-661 cost of 709 efficiency of 661-667 pressure drop over, 667-679 Silicon rubber, 435 Silver, 432... 

Example 18.6. A sieve-plate column operating at atmospheric pressure is to produce nearly pure methanol from an aqueous feed containing 40 mole percent methanol. The distillate product rate is 5800 kg/h. (a) For a reflux ratio of 3.5 and a plate spacing of 18 in., calculate the allowable vapor velocity and the column diameter. b) Calculate the pressure drop per plate if each sieve tray is in, thick with j-in, holes on a -in. triangular spacing and a weir height of 2 in. (c) What is the froth height in the downcomer ... 

Figure 14-31 or Eq. (14-90) may be used for sieve, valve, or bubble-cap trays. The value of the capacity parameter (ordinate term in Fig. 14-31) may be used to calculate the maximum allowable vapor velocity through the net area of the plate ... 

---