Pressure Safety Valve for Coke Drums

[Freddy Martinez]

We are the engineering company involved in Delayed Coker construction in Russia, Volgograd Region.

At the moment we are in the stage of selection of Pressure Relieve Valves (PRV) for the Coke Drums. We have two drums coker with 12 hours cycle, each of the coke drum is equipped with 3 flanged outlets for PRV mounting. Coke feed temperature is +940F, minimum ambient temperature is minus 31F.

Please advise and/or express your experience what PRV design is superior for such service Direct Spring Operated or Pilot Operated Valves?
We want your expert knowledge in order to make right decision for reliable and safe operation.

[antonio saura Cebrian]

In the coker unit that Ive been involved we have installed this kind of safety valve, they are working properly, I dont know if there are some problem with the minimum temperatura for this type of material (bellow), only for reference
 

 
Tag Number
 
 
 
 
 
 
 
 
 
 
 
 

 
P&ID Dwg. No.
 
 
 
 
 
 
 
 
 
 
 

 
Service
 
 
 
 
 
Coke Drum 
 
 

 
Line No. / Equip. No.
 
 
 
 
 
 
 
 
 
 

 
Full / Semi / Base Nozzle
 
Semi
 
 

 
Safety or Relief
 
 
 
Relief
 
 

 
Conv. or Bellows
 
 
 
Balanced Bellows
 
 

 
Bonnet Type
 
 
 
Closed
 
 

 
Size:  Inlet  |Outlet
 
 
 
12 INCH
12 INCH
 
 

 
Flange Rating / Scrwd: In | Out
900#
900#  
 
 

 
Flange Facing
 
 
 
RF
RF
 
 

 
Body and Bonnet
 
 
5 Cr – 1/2 Mo A217 / 304 SS
 
 

 
Seat and Disc
 
 
 
316 SS
 
 

 
Resilient Seat Seal
 
 
N/A
 
 

 
Guide and Rings
 
 
 
ASTM A297 Gr. HE / 316 SS
 
 

 
Spindle
 
 
 
 
 
416 SS
 
 

 
Spring
 
 
 
 
 
Alloy Steel
 
 

 
Bellows
 
 
 
 
 
Inconel 625
 
 

 
 
 
 
 
 
 
 
Note (**)
 
 

 
Cap:  Screwed / Bolted
 
Screwed
 
 

 
Lever:  Plain / Packed
 
 
No
 
 

 
Test Gag
 
 
 
 
No
 
 

 
Vent with Bug Screen
 
 
Yes
 
 

 
Bonnet / Spring Coating
 
Aluminized
 
 

 
Manufacturer
 
 
 
 
 
 
 
 
 
 
 

 
Model No.
 
 
 
 
 
 
 
12 V 12
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
Outline Dimensions
 
 
Certified Dimension Outline
 
 

 
1.
Two relief valves required for adequate capacity
 
 

 

 

Code  |  Stamp
 
 
 
 
ASME VIII,  UV

Fire / P.F. / B.D. / C.W.F.
 
 
B.D. During Max Quench

Other
 
 
 
 
 
 
 
 
 
 
 
 
 

Fluid and State
 
 
 
 
Hydrocarbon Vapor / Steam

Discharges To
 
 
 
 
Coker Blowdown Drum 

Required Capacity
 
 
 
167747 lbs/hr (Note 1)

Mol. Wt. or Oper. Spec. Grav.
 
18.02
 
 
 
 
 

Press.:  Oper.  |  Set
 
 
psig
659660
661662

Temp.:  Oper.  |  Release
 
F
825
825

Design  Press. 
psig
Temp
F
681682
890

 
 
 
Constant
 
 
 
 
 
 

707708
Center Center
713714
Center Center

 
 
 

Back Press.
Variable
 
 
 
13 (Note 2)

 
psig
 
Built-up
 
 
 
749750

 
 
 
Total
 
 
 
28,0

% Blowdown
 
 
 
 
 
779780

% Allowable Overpressure
 
 
787788

Overpressure Factor
 
 
 
1.16

Compressibility Factor
 
 
1.0

Ratio of Specific Heats
 
 
1.28

Oper. Viscosity
 
 
 
cP
0.02

Wt. % Flash  |  MW of Vapor
 
 
 
 
 
 
 
 

Barometric Press.
 
 
psia
14.689

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 

915916
Center Center

 

Calculated Area
 
 
 
in
70.64
 

[Anonymous]

In my experience, the use of a balanced type valve (direct spring operated) is the way to go. Just make sure you do a proper material selection for the bellows (ie. Inco 625) and the spring. In regards to your -31F temperature, this should not be an issue since I imagine your valves will be located inside the winterized cutting deck enclosure.
 
Regards, Canadian Coker.

[Author]

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