Jump to content
ADI Forums


Popular Content

Showing content with the highest reputation on 09/05/2016 in all areas

  1. 1 point
    I know I'm not the first person to build a DIY rig for making SPP (spiral prismatic packing), but I figured I'd share the one I just made entirely from supplies you can get from your local Home Depot. It was a lot of fun to make and even more fun to watch. The system is powered by two drills who's speed is controlled via the immensely complicated ZTC (zip tie control) method. The wire is just standard copper coated steel mig welding wire (which will be replaced by stainless mig welding wire when I run it in a "production" mode). Here is closeup of what the wound wire looks like: Enjoy, and let me know if you have any questions.
  2. 1 point
    I have done a fair amount of experimentation on fractionator packing and made my own informal deduction that the key elements are the total available wetted surface area open to passing gas, per unit of column volume and the rate of mass transfer through it (gas and liquid). Fractionation of course takes place only at the interface between the moving liquid and the moving gas and its rate is proportional to the surface area of that interface and the velocity difference between the phases, at constant mass transfer, pressure and temperature for any and all points within the column. It is the mass transfer element which is easily overlooked when considering factors such as HETP ratings - which do not relate (at all) to throughput mass. Turn "the wick" down enough and you can make almost ANY column packing material look good, in terms of HETP alone. When it comes to "SPP" and the like, the key elements seem to be the diameter of the central hole vs the wetted surface area of the SPP. Calculating the surface area of the wire it is made from is largely irrelevant, because surface tension buries the wire (and the gaps between the spirals) well below the all-important exposed surface.. If you make your SPP too long, for example, there is a lower probability that the open ends of the tube will be close to a neighbouring tube's orifices, thus restricting gas mobility in the system. The system will ultimately "choke" on liquid phase rather than fractionate, for want of gas porosity. Conversely, if your SPP is "all hole and little wetted surface area" (i.e. too short), there will be little molecular migration between the phases and fractionation suffer just as badly! It's well-understood that a working fractionator has a thermal differential (proportional to and generated by the varying gas and liquid composition) over its length. Careful monitoring of that thermal gradient with respect to throughput mass is essential to efficient fractionation management. Which is, as JHeising will tell you, CRUCIAL in the design of continuous fractionating stills (not mere continuous "stripping" stills".) So, in answer to your question, there are far too many variables involved to be able to provide precise advice based purely on the diameter of your column and the size of your SPP's. A test rig or in-still trail with comprehensive fractionator-length temperature monitoring at your target mass throughput rate is in order? (Edit: must have been preoccupied with web-browsing at the time of posting - I'd typed HTTP instead of HETP, now corrected. Apologies!)