Sum-Rates SR Method

The SR method is suitable for modeling absorbers and strippers. For some extremely wide boiling systems, especially those with noncondensables, it is the best method. It has been found to work very well for the side strippers of a refinery fractionator. Absorbers typically have a rich gas bottom stage feed and a lean oil top stage feed. The equations of the SR method do not allow its direct use for reboiled absorbers, absorbers with condensers, or distillation columns. For these columns, other methods like that of Tomich (Sec. 4.2.8) or Russell Sec. 4.2.10) can be used. 

The SR method was first presented by Sujata (35) andMcNeese (36), and was given its name by Friday and Smith (1). The application of the tridiagonal method for solving the material balances was added by Burningham and Otto (34). 

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. 

The enthalpy of a feed, such as the lean oil feed, L0, on the top stage or the rich gas feed, + 1( on the bottom stage will appear in the numerator. An interreboiler duty also appears in the numerator of the stage. The enthalpy for a side product or an intercondenser duty appears in the denominator of the stage, 

The number of independent functions is equal to the number of stages  

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

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].

SR (sum rates) method, 407,409 algorithm flowsheet, 408 Standards and codes, 2, 3 Steam heaters, 45,46 Steam jet ejectors, 143, 162... 

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. 

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... 

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