Height-equivalent theoretical plate

All separation processes are inherently accompanied by zone broadening, which is due to the dynamic spreading processes dispersing the concentration distribution achieved by the separation [1]. As long as the relative contributions of these dispersive processes decrease, the efficiency of the separation increases. A conventional empirical parameter describing, quantitatively, the efficiency of any separation system is the number of theoretical plates per separation unit, A, or the height equivalent to a theoretical plate (the theoretical plate height) H defined by... 

Table 14 summarizes the data obtained in [59,60]. Here the chromatographic characteristics of the supports modified using the liquid phase method, are compared with those of the Chromaton N-AW support modified with dimethylchlorosilane (DMCS) from the gas phase. The degree of surface deactivation was calculated from the peak asjTnmetry factor As measured at 0.1 peak height. The efficiency of the chromatographic column was estimated from the value of the equivalent theoretical plate height (ETPH). The supports were loaded into the columns without the stationary liquid phase. 

The reciprocal of A is a quantity known as H, or very rarely now as H.E.T.P. These are all now referred to as plate height (H) or theoretical plate height or height equivalent of (or to) a theoretical plate (H.E.T.P.). The reasons for the older nomenclature can be found in the scientific literature dealing with distillation in general and petroleum distillation in particular, as discussed earlier, and now have much less relevance to a deeper understanding of separation science. 

The same units must be used to measure t and W. These parameters are illustrated in Figure 3.1. Column efficiencies may be described in terms of theoretical plates per metre, or as the column length (plate height) equivalent to a single theoretical plate. Ideally, retention volumes rather than times should be used, but the two are obviously related in a given column. 

Same as theoretical plate height. A number characterizing the quality of the column filling. It is expressed as the length of a column that would be equivalent to one theoretical plate determined by the plate theoiy. 

In the case of a plate column the performance of a real plate is related to the performance of a theoretical one by the plate efficiency. In the case of a packed column the height equivalent to a theoretical plate HETP) gives a measure of the contacting efficiency of the packing. 

Sometimes the height equivalent to a theoretical plate (HETP) is employed rather than and to characterize the performance of packed towers. The number of heights equivalent to one theoretical plate required for a specified absorption job is equal to the number of theoretical plates,... 

An alternative to determining packed height is through the use of an empirical term, height equivalent to a theoretical plate (HETP). This term can be measured in a fashion similar to that used for the overall plate efficiency of a column (eq. 44) ... 

Height equivalent to a theoretical plate (HETP) plate tower data ... 

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). 

HETP height equivalent to theoretical plate, m HTU height equivalent to a transfer unit, m... 

Many operating variables, such as sample volume, flow rate, column length, and temperature, must be considered when performing any separation. The relative importance of these variables for Toyopearl HW-55F resin columns has been specifically evaluated. For example. Fig. 4.47 shows the relationship between column efficiency, or height equivalent of a theoretical plate (HETP),... 

Column efficiency (number of theoretical plates) As in batch chromatography, one needs to determine the efficiency of the column in order to evaluate the dispersion of the fronts due to hydrodynamics dispersion or kinetics limitations. The relationship of N proportional to L can be expressed in terms of the equation for height equivalent to a theoretical plate (HETP) as ... 

HETP = height equivalent to a theoretical plate, ft HTU = height of a transfer unit, ft L = liquid mass velocity, Ib/hr-ft m = exponent a 1.0 n = exponent 0.44 Pr = Prandtl number, dimensionless Sc = Schmidt number dimensionless U, = linear velocity of gas based on total column cross-sectional area, ft/sec... 

FP = flow parameter, dimensionless HETP = height equivalent of a theoretical plate, in. 

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... 

Murch, D. R, Height of Equivalent Theoretical Plate in Packed Fractional Columns. Ind. Eng. Chem., 45, 2616 (1953). 

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