2 replies to this topic

[s0050506]

I have read everywhere that distillation columns are enormously energy consuming process parts. But I don't really understand why?

In this respect I have two questions:

1) What are the main heat inputs and outputs, and what makes them so large?
I guess these are the reboiler and condensor, but then I don't see what would be so energy consuming compared to other process parts. Is it perhaps because of the reboiler must supply the energy to evaporate a liquid, which can be much energy depending on the latent heat of vaporisation? But then with heat integration (despite the control difficulties that it may bring along) condensor heat can be reused in the reboiler, and then I don't see what the enormous energy requirement is.

2) Is there a general method of calculating the energy requirement of a distillation column once it's design is completed in terms of mass flow rates, reflux ratio, number of stages, ...?
Here I guess that a thermodynamic first law analysis is a good start, but maybe there is a standard method?

I would be very greatful for any suggestions, references or short explanations.
Sander

[StealthProg]

The main heat input is the reboiler or the feed furnace, main heat out is the condenser.

Lets take a typical crude oil column distillation column, the energy input in the form of a furnace for feed heating requires for a typical sized one is of the order of 60MW. Pretty big by anybodies standards. It far outweighs the energy requirements for pumping, or instruments etc etc.

Learning how to do a heat and mass balance would be a good place to start.

[Andrei]

s0050506,

Saying just that distillation columns need enormous heat amounts to work is like looking only at one half of the business: the spendings. Look at the other half also: the earnings. Put both of them in an equation and only after that you can draw a conclusion. That's valid not only in distillation columns, but everywhere in life: look at both sides of the equation.
Your questions are extremely fundamental according to my opinion. Some of your questions contain the responses; some denote a misunderstanding or incomplete understanding of the issues, heat integration for example.
You need to complete your training.
You need to take some courses of heat and mass transfer operations. It took me 2 years in university to understand all the aspects involved in a distillation. And still I needed some years of operations to understand how the economics work.

Good Luck