Questions regarding the calculation of the minimum theoretical plate number using the Fenske equation
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Regarding Nmin for the Fenske equation, textbook No. 414 states that it does not include the overhead condenser and the reboiler at the bottom of the tower, while page 29 of the 05th edition of the Chemical Engineering Principles textbook from Tianjin University says that it does not include the reboiler either! Is the tower top condenser included or not? I have calculated a Nmin. If the problem states that a fractional condenser should be used, do I need to subtract 1?
In the principles of chemical engineering, there is a statement below the formula used to calculate the minimum number of theoretical plates required when using a total condenser under full reflux conditions.
Subtract one for the reboiler, and subtract another one for the fractional distiller
Hehe, really, I saw it, thank you!
So this still doesn’t match what the association specifies – the principles of chemical engineering include degasifiers, but the association does not include them
There is no need for reduction if there is a reboiler, because Nmin does not include the reboiler
This post was last edited by rqj001 on 2015-8-20 at 11:10. The meaning of Nmin should be the number of plates. On the left side of the equation, Nmin+1 should represent the total number of theoretical plates in the entire system; if it is a condenser, then the left side of the equation should be Nmin+2. I’m not sure if this is correct.
Based on the comprehensive process design manual and the principles of chemical engineering, the materials published by the association are incorrect; Nmin includes the effects of the degasifier. In the case of a top degasifier, the calculation results should be reduced by 1. The materials provided by the association are really inaccurate, as there are several important errors in them
That’s right; in fact, the process design manual is explained in a reasonable and clear manner, while the textbooks published by the association are rather confusing. If we don’t add 1 to the left side of the Fenske equation, then it becomes clear that Nmin represents the minimum theoretical stage number
There’s no doubt about this; all that’s needed is to understand what the Fensake equation does. The Fensake equation is used to calculate the number of theoretical plates, and this applies whether it’s the plates inside the tower or the condensers and reboilers outside the tower – as long as they serve as theoretical plates, they are included in the calculation
Just take a look at how this formula is derived; it’s on page 31 of the second volume of Principles of Chemical Engineering by Tianjin University (edited by Yao Yuying). First, assume that the top of the tower is a total condenser (without counting it as a theoretical plate), while the reboiler is counted as a theoretical plate, so the value is Nmin + 1. If, instead, it is assumed that the top of the tower is a fractional condenser, then the value becomes Nmin + 2