Bulletin 74.1:Y692
6
tank, product and personnel in cases of equipment
failure,reexposureorotherconditionsthatcould
cause the tank pressure or vacuum to exceed
operating limits.
Sizing can be done by following these steps:
1. Determine the gas ow rate required to replace the
liquid being pumped out (see Table 2).
2. Using the established procedures from the
American Petroleum Institute Standard 2000
(API 2000), determine the gas ow rate due to
“inbreathing” caused by atmospheric thermal
cooling (see Table 4).
3. Add the requirements of 1 and 2 and select the
regulator size, based on total capacity required from
Table 6.
Sample sizing problem for blanketing applications:
Service Conditions:
Vessel Capacity . . . . . . . . . 42,000 gallons / 159,000 L
Pump In/Out Capacity . . 150 gallons/minute / 570 L/m
Inlet Pressure Source . . . . . 20 psig / 1.4 bar Nitrogen
Desired Blanket Setpoint . . . . . . . . 1 in. w.c. / 2 mbar
Sizing and Selection Methodology:
1. From Table 2 the desired air ow rate due to pump
out equals 150 GPM x 8.021 = 1203 SCFH /
32.2 Nm
3
/h air.
2. From Table 4, the required air ow due to thermal
cooling = 1000 SCFH / 26.8 Nm
3
/h air.
3. Total ow required for pump out and thermal
cooling is 1203 + 1000 = 2203 SCFH /
59.0 Nm
3
/h air.
4. Convert to nitrogen by dividing the total air ow by
the square root of the specic gravity of nitrogen:
2203 ÷ 0.97 = 2248 SCFH / 60.2 Nm
3
/h nitrogen
(See Table 3 for the conversion).
5. From Table 5, a Type Y692 in either an NPS 1-1/2
and 2 / DN 40 and 50 body sizes and a 3/8 in. /
9.5 mm orice will ow 3620 SCFH / 97.0 Nm
3
/h
nitrogen at 20 psig / 1.4 bar inlet pressure. This
satises the required ow of 2248 SCFH /
60.2 Nm
3
/h nitrogen.
API 2000
The American Petroleum Institute Standard 2000
(API 2000) sizing method accounts for liquid pump-out
as well as contraction of tank vapors due to cooling.
When using API methods:
Q
total
= Q
pump
+ Q
thermal
where,
Q
total
= Required Flow Rate
Q
pump
= Required Flow Rate to replace pumped out
liquid from Table 1
Q
thermal
= Required Flow Rate due to thermal cooling.
See Thermal Equations 1 to 4 below or
Table 2.
Thermal Equations
For tanks up to 840,000 gallons / 3179 m
3
capacity,
use one of the following equations:
Equation 1:
Q
thermal
[SCFH Air] = V
tank
x 0.0238
Equation 2:
Q
thermal
[SCFH Nitrogen] = V
tank
x 0.0238 x 1.015
Equation 3:
Q
therma
l
[Nm
3
/h Air] = V
tank
x 0.169
Equation 1:
Q
thermal
[Nm
3
/h Nitrogen] = V
tank
x 0.169 x 1.015
where,
For Equations 1 and 2: V
tank
= tank volume, gallons
For Equations 3 and 4: V
tank
= tank volume, m
3
For tanks greater than 840,000 gallons / 3179 m
3
capacity: See Table 2.
Depending on the method, there can be a signicant
difference in the calculated required capacity. No
matter which method is used, the tank must be
equipped with supplemental venting to protect the
(1 pages)
(1 pages)
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Comments to this Manuals