Valve trays blanking

If the absorber has aceess manways, blank off a portion of the bubble eaps or valve trays. 

To minimize vapor channeling, valve trays are designed to exceed a minimum unit reference (50). A unit reference is the ratio of the vapor rate to the vapor rate at which all the valves are open (Sec. 6.3.2). A minimum unit reference of 40, 60, and 80 percent is recommended for one-, two-, and four-pass trays, respectively (50). If the unit reference falls below the minimum, selected valves can be blanked, valve density can be reduced, or the ratio of light to heavy valves can be varied (7,50). 

A portion of the valves on three pumparound trays was removed and their opening blanked. Ettds of distribution pans and draw pans were seal-welded. Leakage was reduced, sqrara-tion and heat recovery woe improved. 

Vapor load near the column top was three times lower than near tire column bottom, causing turndown problems. Successful resolution was achieved by different modifications to top 40% of trays. Modifications included (a) blanking half the valves, (b) using leak-resistant valve units, each containing a lijditwei t plate located below the normal disk (c) retraying with bubble-cap trays. 

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