Table 13 Valve and sieve tray characterization
Design feature
Suggested value
Alternate
values
Comment
1. Valve size and layout
(a) Valve diameter
–
–
Valve diameter is fixed by the
vendor
(b) Percent hole area
A o /A b
12
8–15
Open area should be set by the
designer. In general, the lower the
open area, the higher the efficiency
and flexibility, and the lower the
capacity (due to increased pressure
drop). At values of open area
toward the upper end of the range
(say 15 %), the flexibility and
efficiency are approaching sieve
tray values. At the lower end of the
range, capacity and downcomer
filling become limiting
(c) Valve pitch diam
ratio
–
–
Valve pitch is normally triangular.
However, this variable is usually
fixed by the vendor
(d) Valve distribution
–
–
On trays with flow path length
!5
0 , and for liquid rates >5,000
GPH/ft. (diameter) on trays with
flow path length <5
0 , provide
10 % more valves on the inlet half
of the tray than on the outlet half
(e) Bubble area, A b or
A B
–
–
Bubble area should be maximized
(f) Tray efficiency
–
–
Valve tray efficiency will be about
equal to sieve tray efficiency
provided there is not a blowing or
flooding limitation
(g) Valve blanking
–
–
This should not generally be
necessary unless tower is being
sized for future service at much
higher rates. Blanking strips can
then be used. Blank within bubble
area, not around periphery to
maintain best efficiency
2. Tray spacing
–
12–36
Generally economic to use min.
values which are which are
usually set by maintenance
requirements. Other
considerations are downcomer
filling and flexibility. The use of
variable spacing to accommodate
loading changes from section to
section should be considered
(continued)
Distillation of the ‘‘Light Ends´´ from Crude Oil in Petroleum Processing
219
Design feature
Suggested value
Alternate
values
Comment
1. Valve size and layout
(a) Valve diameter
–
–
Valve diameter is fixed by the
vendor
(b) Percent hole area
A o /A b
12
8–15
Open area should be set by the
designer. In general, the lower the
open area, the higher the efficiency
and flexibility, and the lower the
capacity (due to increased pressure
drop). At values of open area
toward the upper end of the range
(say 15 %), the flexibility and
efficiency are approaching sieve
tray values. At the lower end of the
range, capacity and downcomer
filling become limiting
(c) Valve pitch diam
ratio
–
–
Valve pitch is normally triangular.
However, this variable is usually
fixed by the vendor
(d) Valve distribution
–
–
On trays with flow path length
!5
0 , and for liquid rates >5,000
GPH/ft. (diameter) on trays with
flow path length <5
0 , provide
10 % more valves on the inlet half
of the tray than on the outlet half
(e) Bubble area, A b or
A B
–
–
Bubble area should be maximized
(f) Tray efficiency
–
–
Valve tray efficiency will be about
equal to sieve tray efficiency
provided there is not a blowing or
flooding limitation
(g) Valve blanking
–
–
This should not generally be
necessary unless tower is being
sized for future service at much
higher rates. Blanking strips can
then be used. Blank within bubble
area, not around periphery to
maintain best efficiency
2. Tray spacing
–
12–36
Generally economic to use min.
values which are which are
usually set by maintenance
requirements. Other
considerations are downcomer
filling and flexibility. The use of
variable spacing to accommodate
loading changes from section to
section should be considered
(continued)
Distillation of the ‘‘Light Ends´´ from Crude Oil in Petroleum Processing
219