Blanking strips

The fabrication of all trays may be punched or drilled (more expensive) with 1410 holes, and those in the lower section have blank strips placed over the inlet and outlet edge rows until approximately 1223 holes are left open in the top section above the feed tray. 

This number is in the range of acceptable performance for bottom section and should be punched. If performance indicates fewer holes are preferable, blanking strips can be added (or even added before the trays are installed). The top trays definitely require blanking of holes. 

This is satisfactory, because it is less than 50% of the tray spacing of 24-in. Therefore, the tray appears to have adequate liquid handling capacity. No hole blanking strips required. 

For new towers, the designs will usually develop to utilize the entire tower cross-section. However, for existing towers with perforated trays being installed to replace bubble caps or packing, the optimum active tray area may not utilize the entire cross-section. If the number of holes required is small compared to available area, it is better to group the holes on 2.5 dg to 3.5 do than to exceed these limits. Holes separated by more than 3 in. are not considered effective in tray action so necessary for good efficiency. Blanking strips may be used to cover some holes when more than required have been perforated in the tray. 

Make a proof for maximum black using the blank strip and a piece of photographic enlarging paper (Appendix 4, Proofing for Maximum Black). 

When moths were allowed a choice of an untreated paper strip, a strip treated with the extract of Rexoro and another strip treated with the extract of the fTKM6f variety, they oviposited heavily on Rexoro extract-treated strips, none on the TKM6 extract-treated strips, and very few on untreated strips. However, almost an identical number of SSB moths arrived on Rexoro and fTKM6f extract-treated strips, few moths arrived on the blank strips (Figure 1). 

Tray hole area is consistent with the design value. Care should also be taken to ensure that the holes are of consistent diameter, and that blanking strips (Sec. 6.4) are correctly positioned. The author is familiar with a case where one tray with a grossly diminished hole area was enough to prematurely flood an entire column. Hole, riser, and/or weep hole areas should be checked in a similar manner in distributors, redistributors, parting boxes, and chimney trays. 

When it is necessary to decrease the hole area of an existiti sieve tray, small blanking strips can be used these are metal pieces that can be fastened directly to the iflate and that block the vapor flow through the holes that ate coveted by the strips. Care should be taken to distribute these strips thiougbout the tray. 

Because of changing vapor and liquid flows throughout the cohmm. it may be desirable to vary the parameters such as hole area and downcomer area. For the former, a fixed design plus variable blanking strip arrangements is often feasible. Variations in downcomer area usually are limited to cases with very wide-ranging liquid flow rates. 

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