1.4 Tray drainage
Some amount of liquid is usually remains trapped on a bubble cap (positive seal tray) and on certain valve trays when the column is shut down. This liquid is normally drains through weep holes located near the outlet weirs. Weep hole diameter usually ranges from 3 to 15 mm. The recommended weep hole area is 4 inch2 per 100ft2 of tray area with 50 bubble caps and 4 inch weir to drain in about 8 h [3].
1.5 Tray manways
The maintenance workers travel from one tray to another through tray manways (Figure 8.1). The size of the manways should be such that a person can safely travel through a tray manway segment and also it is removable through the column manholes. Manways are usually rectangular and the recommended size is 40 cm×50 cm. Tray manways should be removable from top and as well as from the tray below.
2. Column design specifications
The column specifications and operating conditions appended below are continued from the process design calculations of sieve plate tower given in module #7.
Shell ID (
): 2403 mm ( is denoted as 
in module #7)
Number of trays: 14
Tray spacing ( 
: 600 mm
Hole diameter ( 
: 12 mm
Plate thickness ( 
: 12 mm
Weir height ( 
: 40 mm
Material for trays, down comers and weirs: Stainless steel SS304L
Shell material: Stainless steel (SS304L), double welded bolt joints
Allowable stress for shell material: 108×106 Pa (108 MPa)
Density of shell material ( 
7800 kg/m3
Skirt height: 2 m
Operating pressure = 118825 Pa (bottom tray pressure)
Design pressure ( 
= 1.1×operating pressure = 130708 Pa
Operating temperature =56.3 to 105°C
Design temperature = 1.1×maximum operating temperature = 116°C
Top disengaging space: 600 mm (same as the tray spacing taken)
Bottom separator space: 1000 mm
Insulation material taken: Asbestos
Insulation thickness considered: 50 mm
Density of insulation ( 
: 270 kg/m3 (asbestos)
Minimum shell thickness ( 
=1.81 
2 mm
Use 
8 mm thickness including corrosion allowance of 6 mm. This value is in accordance to IS 2844-1964.
Standard ellipsoidal head with 
= 2:
The minimum thickness required, 
=1.81 mm 
The head thickness of 8 mm is selected with corrosion allowance of 6 mm for uniformity.
Column height ( 
9.6 m
[Head height from the cylindrical portion of the column is neglected)