2 replies to this topic

[R.Alford]

Hello

I want to make a small scale packed column to do simple mass transfer experiments using counter current air water flow.
As I am starting from absolute basics and have no prior knowledge on this topic could I have some advice on exactly what I need and procedure?
I will of course need a column into which I can have two flows in and two flows out. Would 100cm length 2cm diameter (the packing is only 3mm) be ok?
Packing (Dixon rings 3mm.)
Contaminated water (Ethanol,brine, acetic aicd ?? sorry I really am at total basic),
A method of measuring decontamination (pH meter ?)
A method of measuring pressure drop ?

That is all the equipment I think ......

Could someone help me or direct me to a source that actually details a procedure to use to measure HETP and pressure drop at this stage all the sources I have found discuss the results but the actual experimental procedure is very minimal.
I feel totally dumb here sorry I have absolutely no experience in mass transfer but I really need data for Dixon rings and as there is no reputable source I am going to have to undertake the procedure myself as discussed in this thread
previous thread

I followed Art Montemayors advice but there is little to now technical data from my supplier, and papers on Dixon rings are also minimal and do not agree with HETP values as high as 80 plates/ft !!!
Sorry again for lacking any information


Any help if you have a clue what I am trying to do would really be very very gratefully received.

Thank you in advance

Robert

[kkala]

I had undertaken a few month operation of a pilot horizontal wet scrubber (1979) to retain NH2 and HF from stackgases of a phosphoric fertilizer unit. Scale was much bigger (treated gases ~ 7000 m3/h) and main challenge was to keep operating conditions stable for reproducible results (this can be easier in the lab). Then a similar scrubber was offered with same residence time as of the pilot.
I do not have expertise to clarify all points, you have to be helped by a lab engineer having conducted similar experiments; yet following suggestions might be useful.
1. If necessary, refresh knowledge on packed towers, e.g. through Perry (Continuous contact equipment, packed towers, 5th ed, p. 21-19), Kohl & Riesenfeld (Gas purification), or other. Perry advises tower diameter > 8 * packing size (so diameter should be bigger than 20 mm for 1/8” Dixon rings) and gives an idea of tower configuration. This is supposed to be of glass, so you can see flow, channeling and flooding (if happen). Same size packing as of the actual-to-be tower would be preferable, but is understood not to be realizable.
2. If also necessary, refresh knowledge on scale-up, e.g. by reading Johnstone & Thring (Pilot plants, models and scale-up methods in Chemical Engineering), or something more practical. According to my university book, best time for pilot plants was 1940-1970 (after it modeling has limited their applications).
Every experimental measurement will need serious labor, so objectives had to be clearly defined and arranged according the results. Do you mainly intend to verify some expected performance (based on assumed modeling)? Probably you have to try again to find data on Dixon rings from their suppliers. Recommended scale up factor is 10x for tower diameter (100x for flow rate) according to the university book, plus 15% margin.
3. Attached "labequip.doc" gives a general idea of the scheme and equipment to start, but try to comment / improve it through the help of your teacher. Preliminary capacities had better be estimated in advance, so that pieces match each other (e.g. air pump should not give too high a flow rate to result in flooding conditions in the packed tower). CO2 is assumed to be mixed with air , though numerous pollutants can be introduced in air (try to use the one interested in).
Procedure is following: Polluted air is continuously directed into the tower through an air pump, after being sampled and analysed. Tower is arrogated counter-flow wise by water (or dilute alkali) measured by a flow meter, which catches the pollutant and ends to a pot below tower base. Purified air leaving the tower is cooled (water cooler), its pollutant content is retained in barboteurs and passes through a gas meter (totalizer) before going to ambient air. The experiment can last (say) 2 hours and conditions should be registered every so often. After that selected water in pot is analysed, and so is liquid of barboteurs. Quantities of gas and liquid passed from the tower during the period is also measured.
4. Points of interest / concern in "labequip.doc" and above procedure.
- Consider pshychrometry and base the the results per kg of dry air passing the tower.
- CO2 retained in liquid equals CO2 removed from the polluted air. Check precision of measurements through this balance.
- Pipes of air and liquid can be of rubber and presented valves are just "constrictors" to lessen their section (hence to reduce flow).
- Temperature should be followed for every stream.
- Any condensate from air after cooler should be mixed with barboteurs' liquid for analysis. Barboteurs are small bottles with a porrous diaphragm at gas entrance to diffuse it effectively for the reaction.
- Pressure drop equipment of air side is not shown in labequip.doc. It can be a simple U - tube (filled with water) to measure air ΔP between entrance and exit of the tower.
- Industrial towers have recirculation of liquid, not shown in "labequip.doc". This could make the system more complex. A small pump would transfer liquid from collection pot to the tower top. Try to avoid it by increasing fresh water flow rate.
- Hope above helps, wish good start!

Attached Files

•  labequip.doc   44KB   54 downloads

[R.Alford]

Thank you very much kkala for your help

Robert