# Pressure Safety (relief) Valve Sizing

Document Sample

```					Gas PSV Sizing                                                                                                                                                                              Liquid PSV Sizing
A=            (110)(Qg).sqrt[(T1)(MW)(Z)]                            =         0.511 in. 2                                                                    0.518 in. 2
(C1)(K)(P1)(Kb)                                                                     Gas Input Data:                                     Liquid Input Data:
Qg =    21.7   MMSCFD                                    Ql =       450       gpm
where,          A=      PSV orifice area required                                                          T1 =    110    °F                                       P1 =        464       psig
Qg =     Relieving gas rate (MMSCFD)                                                        P1 =   1300    psig                                     P2 =         0        psig
T1 =     Upstream temperature (R)                                                          MW =     19                                              SG =       0.72
C1 =     Coefficient determined by ratio of specific heats (k) - See table below            C1 =    345                                             Kb =        1.00         (best fit)
P1 =     Upstream relieving pressure (psia) - includes overpressure                         Kb =    1.00     (best fit)                              K=         0.9
K=      Coefficient of discharge - from manufacturer - use 0.975 for prelimary design       Z=     0.83   <-- Estimate +/- 0.03
Kb =     Capacity correction factor due to backpressure - See table below                    K=    0.975                                     A=                  (gpm).sqrt(SG)
(38).K.Kb.sqrt(P1-P2)
Air          N2           O2        Nat. Gas         C1           C2         C3       C4        CO2           H2S
k              1.4          1.4          1.4         1.27           1.3          1.22       1.14     1.11       1.28          1.32             gpm            gallons per minute
C1             356          356          356          345           346          339        331      328        345           348              SG             specific gravity
A, K, Kb       same as gas
Back-pressure           <= 50%         70%          80%        90%      100%
Orifice Area                        Kb                     1            0.94         0.83       0.64      0
(in.2)
D          0.110            *             *            *
Method for 2-phase flow
Standard Orifice Designation

E          0.196            *             *            *
F          0.307            *             *            *                                                                                                   Calculate area required for gas portion
G          0.503                                       *            *             *                                                                        Calculate area required for liquid portion
H          0.785                                                    *             *                                                                        Add the two areas
J          1.287                                                                  *            *         *
K          1.838                                                                                         *
L          2.853                                                                                         *         *                                            P2/P1 = 0.011
M           3.60                                                                                                   *                                                    0.031
N           4.34                                                                                                   *
P           6.38                                                                                                   *
Q          11.05                                                                                                              *
R           16.0                                                                                                              *             *
T           26.0                                                                                                                                     *
1x2          1.5 x 2     1.5 x 2.5     1.5 x 3        2x3         2.5 x 4     3x4      4x6        6x8          6 x 10   8 x 10
Valve Body Size (Inlet Diameter x Outlet Diameter), in.

Case Description:

Instructions:
This sheet can be used for conceptual sizing of pressure safety (relief) valves (PSV's). You
can enter the values that are in this color. The results appear in the yellow highlighted cells.
Note that compressibility (Z) factor is estimated for hydrocarbon gases. If other gas, then you
need to unprotect the sheet and adjust Z manually.
You can register by sending an email to hmalmosa@gmail.com. Registration allows you to
receive the first upgrade to this sheet free. Suggestions are also welcome to the same email