4 replies to this topic

[R.Alford]

Hello

I am new to the forum so I maybe posting in wrong place but I hope it is ok

I am currently doing some research into random packing in particular Dixon rings

The two main uses of Dixon rings recently has been Tritium separation and CO2 scrubbers in Submarines.

I am struggling to find out exactly how these really random packing actually work

Does a film of water form over the packing and then as the gas flows over the reaction/ mass transfer occurs ?

I have found lots of good papers on packing uses and efficiency etc but not how the process actually works.


Also is there any software that anyone can recommend to simulate a column where I can do pressure drop simulations, etc. There is a good Excel sheet I download but that can only do pressure drops.

Hope you can help

Thank you

Robert Alford

[Art Montemayor]

Robert:

The more area you can distribute a liquid film on and, at the same time, bring a gas into intimate contact with it, the better simultaneous heat and mass transfer you will have between both phases. This is the same principle used in designing and building atmospheric water cooling towers – whether natural, forced, or induced draft. Any packed bed used to effect a mass transfer is going to suffer a pressure drop. The pressure drop is the trade off that you have to pay for achieving successful mass transfer. The more contact area you build into a given packed bed volume, the greater will be the pressure drop – as a general rule.

The way you have described the flow of air over a film of water is exactly what happens in a packed bed – or an atmospheric water cooling tower.

The best way to study the pressure drop across a given packed bed is to simulate it in a pilot plant setup – not in a software package. You have no way of determining the accuracy or results of a computer print out or simulation result. You are subject to “trusting” the credibility of the software – unless you have used it before, applied it to a design, and actually measured the as-built results in the field. Otherwise, I wouldn’t put any faith on the computer simulated results.

Your supplier of Dixon packing should also have available pilot plant data and curves to predict the expected pressure drop with their packing. Contact them with your request.

[djack77494]

Also is there any software that anyone can recommend to simulate a column where I can do pressure drop simulations, etc. There is a good Excel sheet I download but that can only do pressure drops.

Robert,
I don't know what you want. You asked if anyone had software to do pressure drop simulations, then you say that what you have can only do pressure drop simulations?? Please rephrase your question.

Random packing is effective because it provides a large surface area where liquid and gas phases will be in contact with one another. Since mass transfer is proportional to the contact surface area, this is an effective way of increasing mass transfer. There's really nothing mysterious about how packings (random or structured) work. Their effectiveness could be measured by the HETP or Height Equivalent to a Theoretical Plate (or equilibrium stage). Practically speaking, packings present some challenges in that you seek to optimize mass transfer, minimize HETP, minimize pressure drop, and get good liquid and vapor distributions throughout your packed bed so that you can come close to achieving theoretical performance. You should seek some of the manufacturers' websites for good information on packing. A variety of software tools are made available free to potential customers. I am most familiar with the Koch Glitsch; look for it at www.koch-glitsch.com/masstransfer/pages/Products.aspx.

[Zauberberg]

It appears that Dixon packing is used for laboratory-scale applications, according to this information: http://www.laiko.net...ts/7773781.html
This page provides some design data as well, including pressure drop at some imaginary 80% gas speed. I would suggest you to take Art's advice and contact the manufacturer, and present all the details of your particular application.

As for the principle of packed tower operation, you can find it in almost every ChE textbook. The only difference between packed and trayed towers is phase continuity: packed towers have gas/vapor as the continuous phase, whereas trayed towers have liquid as continuous phase. Some basic information is available in Kolmetz's web page: http://kolmetz.com/p...ation-Rev41.pdf

[R.Alford]

Hello Thank you for your replies

I think that as said performing the tests on a pilot plant is the best way to obtain the required data. What I meant by other data is liquid hold up, flow simulation, loading capacity, wetting conditions, HETP, advantage of coatings, etc. However I have since decided that a pilot plant is the best way to proceed.

I am currently working to determine what are the wider applications for Dixon rings due to there superior low pressure drop and high efficiency to then lead me to how efficiency of Dixon rings can be improved to be application specific, i.e. coatings( Catalytic), size, pressure, aperture, diameter+length of column etc.

If anyone has any information or can suggest specific books papers, sources etc. that you think would help me it would be greatly appreciated.

Thank you again for your replies

Robert