For any type of packing, define the material of construction and its thickness (at least to get all quotes on a common basis). You also might wish to specify the type and material of the supports. In addition, the supplier needs to know the diameter and location of loading manways.
Detailed discussion of liquid distributors is beyond the scope of this article. They are expensive and take up space that could be occupied by packing. However, inadequate liquid distribution has long been cited as the reason for packed column failures . Lockett and Billingham provide a good guide for checking the sensitivity of the separation in question . At the RFQ-preparation stage, the key requirement is to specify what is needed in such a way as to obtain comparable quotations. For gravity distributors, the key parameters are the number of distribution points per unit area, the percent open area for vapor flow, possibly a minimum orifice size, a minimum liquid level at reduced flow conditions, the installed level tolerance and whether a shop water test is included in the quotation. For pressurized types, key parameters are the number of nozzles and the pressure drop.
Other important details
Whether the column is trayed or packed, the supplier needs to know the feed condition, particularly if the feed is partially or totally vaporized. You must supply the quantity and density of feed vapor and liquid at the column, both after any control valve and at the feed-point elevation. Many failures have been traced to not properly taking flashing into account.
All vendors should be asked to quote the installation services included or, if not included, the services offered and the rates. They also should detail the installation time required for the base case and for all options.
Many forms are available for specifying distillation-column internals requirements. FRI has compiled and released a set of forms as a service to the industry.
By following the principles we have outlined, you should receive adequate and comparable proposals. In the next article, we will discuss how to evaluate these quotes.
John G. Kunesh is a part-time consultant on distillation based in Red River, N.M. He served as technical director of Fractionation Research Inc., Stillwater, Okla., until his recent retirement. E-mail him at JGKunesh@aol.com. Raymond M. Sowiak is a senior process engineering specialist at Sunoco, Philadelphia. He is Sunoco’s technical representative to FRI and is a member of FRI’s Design
|1. Kister, H.Z., “Troubleshoot Distillation Simulations,” CEP, p. 63 (June 1995).
2. Kister, H.Z, “Can We Believe the Simulation Results?” CEP, p. 52 (Oct. 2002).
3. Kister, H.Z., “Distillation Design,” McGraw-Hill, New York (1992).
4. Stichlmair, J.G. and J.R Fair, “Distillation: Principles and Practices,” Wiley-
VCH, Hoboken, N.J. (1998).
5. Fitz, C.W. and J.G. Kunesh, “Column Hydraulics: System Limit/Ultimate Capacity,” Chem. Eng. J., 88, p. 11 (2002).
6. Stupin, W.J. and H.Z. Kister, “System Limit: The Ultimate Capacity of Fractionators,” presented at Intl. Conf. on Distillation and Absorption, Baden-Baden, Germany (Sept. 2002).
7. Stupin, W.J., “Ultimate Capacity of Fractionators,” Topical Report No. 34, FRI, Special Collections and University Archives, Oklahoma State Univ. Libraries, Stillwater, Okla. (Jan. 1965)
8. “1961 Annual Report,” FRI, Special Collections and University Archives, Oklahoma State Univ. Libraries, Stillwater, Okla. (1962).
9. Robinson, C.S. and E.R. Gilliland, “Elements of Fractional Distillation,” McGraw-Hill, New York (1950).
10. Billingham, J.F. and M.J. Lockett, “A Simple Method to Assess the Sensitivity of Packed Distillation Columns to Maldistribution,” Part 1, Trans. I.Chem.E., 80, Part A, p. 373 (May 2002) and Part 2, 81, Part A, p. 131 (Jan. 2003).