[teluap]

I have to prepare some experiments in order to determine the capacity of an absorption column. They will be carried out with water and nitrogen. I will know the size of the column and the packing type and size.
But I'm having some troubles with calculating the gas and liquid flow rates for the column. I just need a rough approximation, it can't be so difficult but I just get more and more confused...

Can someone, please, help me?

Thank you very much!

[Donaldson Tan]

You will need at least the L/G ratio.

[teluap]

Thanks Geodome, but how can I know which L/G ratio I need for this column? 

[Montemayor]

Teluap:

What Geodome advised you is true.  However, he didn’t tell the other half of the story:  You have to be given the L/G ratio (usually based on empirical experience out in industry) or you have to figure it out yourself, based on basic data furnished to you or that you can obtain or calculate.

From a common sense point of view the above is pretty obvious.  You state you want to “determine the capacity of an absorption column”.  But you fail to tell us just exactly what it is that you are proposing to “absorb”.  In other words, you don’t state all your basic data.  Because of this, I’m forced to make some broad assumptions about what you intend to do.  I’m going to assume you intend to absorb nitrogen gas into a counter-current stream of cold water.  Although this doesn’t sound commonplace, I have to assume this because that’s the only basic data I can hang my hat on.

Now that you have identified what is being absorbed (nitrogen) and what is the absorbent liquid fluid (water), you can start to figure out how much of each stream is being used.  You have also failed to tell us how much nitrogen flow rate you are “scrubbing” or absorbing – and this is a pre-requisite.  We can’t go on any further if we don’t know this flow rate.  I’m going to assume you know it and are keeping it a secret.  Knowing the absorption rate of nitrogen in water (which I have to assume you also know or have available – or can obtain), you can then calculate the related amount of water flow rate required to do the desired absorption.  If you don’t have this data you can apply Henry’s Law and by the appropriate Henry’s Constant you can obtain an estimate of the absorption rate of nitrogen in water.

With the above steps completed, you should be in a position to identify the approximate L/G ratio which is a necessary input for calculating the physical size of the absorber.  Of course, you can appreciate that the use of Henry's Law and his constant only gives you theoretical estimates.  You would be wise to apply a contingent factor to these values to reflect a realistic and expected water flow rate instead of an ideal and theoretical value.

I hope this helps you out.

[teluap]

Thank you very much for your answer Montemayor.

I was wondering if there is a way of calculating the L/G ratio, depending on the column size and packing properties, regardless of what is to be absorbed. Kind of studying the hydrodynamics of the equipment, just with water and nitrogen, to see how the gas and liquid streams behave inside the column. In fact, in order to see which amount of gas the column is able to handle. And then apply these results to the absorption process itself. Could be that possible?

Again, thank you for your help.