Suggest to read the following paper besides a good text-book on separation processes.

Distillation: Revising Some Rules of Thumb, Chemical Engineering, p. 50, September 2004.

The above paper has results for 13 examples (Table 4), wherein optimum reflux ratio varied between 0.08 and 18.6. Besides reflux ratio, suggest to check reboiler duty and its cost.

Reflux ratios depend on the "tightness" of the separation to be performed, usually based on the volatilities of the light key and heavy key components. Reflux ratios can vary from very small numbers (for easy separations) up to infinity (total reflux).

Distillation process is done to achieve a specific level of enrichment. To achieve this enrichment level, one must specify a reflux ratio.

The reflux ratio will modify the slope of operation line. This will alter the number of plates required for a given separation to be achieved.

Decreasing that reflux ratio has an advantage that the duty of condenser and reboiler decreases, since the load in distillation column decreases. In other sense, the operating cost of distillation column decreases. However, it would be at expense of less enrichment achieved than required.

Increasing reflux ratio would act in reverse i.e, it would have a disadvantage of increase in duty of condenser and reboiler as load increases. This increases the operation cost of distillation column, however, more enrichment is achieved.

Brian Hanley and Mounir Bouaifi,

Thank you for your answers. As far as I understand there is no limit for reflux ratio if desired specs and economically feasable operation is achieved. The point is that when I was doing short-cut calculations or simulations for different columns, sometimes I got reflux ratios very high ( for exmaple 3 or 4), and sometimes very low (for example 0.04 ). And I wanted to clearify if in real industry, these figures are usual or not.

There is no typical reflux ratio. There is however a typical percent above minimum reflux. That's usually 10 to 15% unless the column ends up being too tall, like a C3 splitter, then you can use a higher percent above minimum reflux to reduce the number of stages at the expense of a larger diameter.

If you insist on typical reflux ratio, I'll paraphrase what @Brian Hanley. They vary from 0.1 to 35 depending on the separation.

I recommend you to read any text of chemical engineering. That is what good students do.

Between 1.3 to 1.5 times Rmin

Thank you for answers.

1,3 - 1,5

Suggest to read the following paper besides a good text-book on separation processes.

Distillation: Revising Some Rules of Thumb, Chemical Engineering, p. 50, September 2004.

The above paper has results for 13 examples (Table 4), wherein optimum reflux ratio varied between 0.08 and 18.6. Besides reflux ratio, suggest to check reboiler duty and its cost.

As many have responded, the range of reflux ratio is very wide. In my practical experience I have worked with columns which had numbers from 0.3 up to about 20. Please note one important point -- it varies with the amount of the overhead component(s) in the feed stream. For example, separation of iC4 and nC4 can have reflux ratios from about 10 to about 20 with the only change being the amount of iC4 in the feed stream. It's just the math of reflux ratio at work. Sometimes for difficult separations a better measure is reflux to feed ratio. Using my same example, the reflux to feed for the system would be about 4 regardless of the actual reflux ratio. As someone observed, some time with a good text on distillation would be a good place to start.

A typical economical value for R is 1.1 to 1.3 times Rmin.

R has the lower limit Rmin associated with the infinite number of theoretical plates in the column. The upper limit is shaped by a balancing between the number of plates (investment costs) and the volume of fluids being pumped (operating costs). Regards,

Dear all, thank you very much for your comments.

Gade Pandu Rangaiah,

Thank you for reference. It enabled to observe wide range of reflux ratio.

Hi Nigar

You may also check with the distillation column modules available in simulators like HYSYS, AspenPlus. In these simulators there is an option for shortcut distillation column design, you may check using that what is the minimum reflux ratio and then follow some rule of thumb which is Ropt ~ 1.1-1.3 times Rmin. But you must note that the shortcut calculations are reliable mainly for hydrocarbon systems.

hello, your question is generalized, the rate of reflux directly related to the purity of your distillate, according to the product to be purified and the reactional mixture and to avoid asiotrop

The Reflux ration is determined based on Feed Composition and Desired Purity of Product , it also depend on Column Diameter and height you need select the Optimum reflux ration by simulation software Chemcad/Aspen