3 replies to this topic

[peterliu0206]

Hello, everyone, this is my very first post after joining cheresources=)

 

Just wonder for the relationship between optimum reflux ratio and minimum reflux ratio in a distillation column (e.g., debutanizer), how to decide the coefficient?

 

I have referred to some quite handy books such as coulson and richardson volume 6, sinnott and towler etc, they suggested a coefficient of 1.1-1.5 or so. however, if we plot N vs. R, some examples suggested to use a R which won't decrease N much as R increases. in that case, the coefficient could reach 3 or so.(I am talking about non-azeotropic component distillation) all the books mentioned that it should be determined by a rigorous economic calculation and experience.

 

So generally speaking, should we keep the coefficient between 1.1 to 1.5 for the best compromise? cheers.

[curious_cat]

Its a tradeoff between capital costs & operating costs oftentimes. 

 

Low Reflux, high number of trays tall column, less reboiler ./ condensor duty

 

High Reflux, lower number of trays, shorter column, high duties.

 

Not too high though else column dia. might again increase & drive up capital cost.

 

Precise tradeoff is a function of your particular economics. 

[peterliu0206]

thanks, curious_cat, eventually I chose the turning point from the graph and it lead to R=3Rmin.

[Bobby Strain]

That doesn't look optimum to me. Depending on relative volatility, I would expect the optimum to be in the range of 1.05 to 1.3.

 

Bobby