The SR Sum-Rates Method

Initial temperatures and vapor flow rates are estimated in the same way as in the BP method. 

At this point the x,y are not normalized but their sum is applied to estimate new liquid flow rates from the relation 

The corresponding vapor rates are obtained by the material balance, which is a rearrangement of Eq. (13.187), 

When the depend on the vapor phase compositions, values of yii from the previous iteration are used. 

New values of the stage temperatures Tj are calculated as bubblepoints with the normalized Xg. Initially the effect of vapor compositions yg on Ktj is ignored and the vapor compositions are found with 

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Figure 13.18. Algorithm for the SR (sum rates) method for absorbers and strippers [Birningkam and Otto, Hydrocarbon Processing 46(10), 163-170 (1967) Henley and Seader, 1981].

Separations 404 Specifications 405 The MESH Equations 405 The Wang-Henke Bubblepoint Method 408 The SR (Sum-Rates) Method 409 SC (Simultaneous Correction) Method 410... 

SR (sum-rates) method. The new liquid flow rates are taken... 

SR (sum-rates) method. The new liquid flow rates are taken proportional to the nonnormalized sums of mol fractions, the vapor rates by subsequent material balances, and the new temperatures by enthalpy balances. A flowsketch of the calculation process is in Figure 13.17, and a brief description also is given subsequently. This method is particularly suited to separations involving substances with widely differing volatilities, as in absorbers and strippers, where the bubblepoint method breaks down. 

In the SR method, temperatures are the dominant variables and are found by a Newton-Raphson solution of the stage energy balances. Compositions do not have as great an influence in calculating the temperatures as do heat effects or latent heats of vaporization. The component flow rates are found by the tridiagonal matrix method. These are summed to get the total rates, hence the name sum rates. 

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