Theoretical plate or stage

HETP for a 2-in. slotted metal ring in a condensate stabilizer is about 36 in. This is slightly more than a typical tray design, which would require 34 in. (1.4 trays X 24-in. tray spacing) for one theoretical plate or stage. 

The most useful measure of the separating power of packed towers is the HETP, the height equivalent to a theoretical plate or stage. It is evaluated simply as the ratio of packed height used for a certain degree of separation to the theoretical number of stages. Its relation to the fundamental quantity, HTU, or the height of a transfer unit, is... 

Thus, the number and the height of transfer units and equivalent theoretical plates (or stages) can be related by two ratios, defined as ... 

Standart, G. L., Studies on Distillation—V. Generalized Definition of a Theoretical Plate or Stage of Contacting Equipment, Chem. Eng. Sci., 20, 611-622 (1965). 

For a theoretical plate or stage the vapour and liquid streams leaving are in equilibrium, i.e. This represents the best possible separation, never... 

Hatta number, dimensionless height equivalent to a theoretical plate or stage, m height of a transfer unif, m elecfrical currenf, A wafer flux, m /m s fhermal conducfivify, J/m s K k ky, ky mass fransfer coeffidenf, various unifs elimination rafe consfanf, s reaction rafe consfanf, s partition coefficienf, various unifs permeabilify, m/s or m ... 

Standard G (1965) Studies on distillation-V generalized definition of a theoretical plate or stage of contacting equipment. Chem Eng Sci 20(6) 611-622... 

HETP = Height equivalent to a theoretical plate/tray/stage, in. or ft, or possibly mm... 

Various authors [90] and researchers have published factors that influence the magnitude of HETP values. The lower the HETP value (i.e., number of feet (or inches) per theoretical plate/tray/stage) the more efficient is the packing (random or structured) for any particular separation system. Other influences include ... 

Equilibrium data and material-and heat-balances to determine the number of equilibrium stages (theoretical plates or transfer units) required for the desired separation. The required height of the column can be calculated if data are available for the specific rate of transfer of material between the two phases, expressed in terms of the plate-efficiency or the height of one transfer unit. 

HETP Height equivalent to a theoretical plate (or tray). Also called an equilibrium separation stage. 

The initial solvent and feed concentrahons, the desired hnal concentrations, and equilibrium behavior determine the direction of mass transfer, the minimum solvent-to-feed ratio, and the minimum theoretical tray requirements. These theoretical trays (or stages) are analogous in many respects to theoretical plates of a distillation colnmn, and absorption (or stripping) columns discussed by Fair in another chapter. For any particnlar solvent-to-feed ratio, equilibrium relationships and the operating line determine theoretical stage reqnirements. 

Now we have a theoretical basis to predict the alcohol content of the liquid and vapor at any plate or stage along the column. If we want an alcohol content in the final product of 85 percent (moles per mole), then we can read from Figure 5 what liquid concentration would be in equilibrium with the final vapor concentration (Remember, this is the same as the product concentration.)... 

It was not, however, until the concepts of the theoretical stage and the transfer unit had been introduced that it became possible to express in numerical terms the efficiency of a column and the difficulty involved in a separation. A theoretical (or ideal) plate (or stage) is defined to be such a section of a column that the vapour leaving it upwards (towards the next higher theoretical plate) and the liquid leaving it downwards (towards the next lower theoretical plate) are in thermodynamic-equilibrium (Fig. 24). 

The Fenske equation estimates the minimum number of theoretical plates or equilibrium stages at total reflux. 

The Separation Stage. A fundamental quantity, a, exists in all stochastic separation processes, and is an index of the steady-state separation that can be attained in an element of the process equipment. The numerical value of a is developed for each process under consideration in the subsequent sections. The separation stage, which in a continuous separation process is called the transfer unit or equivalent theoretical plate, may be considered as a device separating a feed stream, or streams, into two product streams, often called heads and tails, or product and waste, such that the concentrations of the components in the two effluent streams are related by the quantity, d. For the case of the separation of a binary mixture this relationship is... 

Fig. 1. The analogy between the separation stage and the transfer unit or equivalent theoretical plate (a) ia a stagewise process (b) ia a...

Use of HETP Data for Absorber Design Distillation design methods (see Sec. 13) normally involve determination of the number of theoretical equihbrium stages or plates N. Thus, when packed towers are employed in distillation appRcations, it is common practice to rate the efficiency of tower packings in terms of the height of packing equivalent to one theoretical plate (HETP). 

One way of calculating the number of equilibrium stages (or number of theoretical plates, NTP) for a mass exchanger is the graphical McCabe-Thiele method. To illustrate this procedure, let us assume that over the operating range of compositions, the equilibrium relation governing the transfer of the pollutant from the... 

---