Tower operating pressure

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... 

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

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. 

The prior discussion assumes that the feed rate, feed composition, and heat content (enthalpy) are fixed. My purpose in presenting this review of the phase rule is to encourage the routine manipulation of tower operating pressures, in the same sense, and with the same objectives, as adjusting reflux rates. Operators who arbitrarily runs a column, at a fixed tower pressure, discards one-third of the flexibility available to them, to operate the column in the most efficient fashion. And this is true, regardless of whether the objective is to save energy or improve the product split. 

Absorbers and strippers usually involve components that cover a very wide range of volatility, For example, an absorber might have a feed gas that contains methane, while the absorbent might be an oil of 150 molecular weight. For these two separation operations, which frequently do not utilize either a condenser or reboiler, the tower operating pressure cannot be determined from bubble- and/or dew-point calculations because they can be extremely sensitive to assumed product vapor and/or liquid compositions. Instead, the following rules may apply ... 

For exchangers showing lower pressures, reduce the process side pressure and the condensate level in the channel head to a minimum. For example, as long as the overhead product can be condensed, there is nothing sacred in a particular distillation tower operating pressure. 

Tower operating pressure is most often determined by the temperature of the condensing media,... 

Figure 18.10 illustrates a common cause of an erratic tower operating pressure. The condenser effluent is a two-phase mixture of vapor and liquid. In the summer, the tower pressure is steady. But in the winter when the cooling water is cold, pressure control is erratic. 

High feed gas pressure, which requires a high scrubber-tower operating pressure... 

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