4 replies to this topic

[munirm]

Dear all,

 

We operate a Carbamate Condenser to reduce the temperature of recycle carbamate from 180 C to 158 C. Condensate is fed on the shell side to generate steam at 3.5 kg/cm2.g. There is a PSV installed on shell side with set pressure 5.5 kg/cm2. A process upset caused 20 kg/cm2.g (superheated) to get into the shell side of the exchange and popping of the PSV. The pressure inside the vessel was reduced to 2 kg/cm2 but the seat didn't revert back. It was reverted back manually using a hand jack.

 

I am trying to find the root cause of the SEAT NOT REVERTING BACK. One of the probable causes that we are thing is the probable thermal expansion of seat metal part and getting stuck inside but the clearance between the cylinder and moving seems to be a bit larger that doesnt't justify this reason. What could be the other probable causes of this phenomenon?

 

Info:

Spring Material: CS Phosphatized

Test Spring pressure: 5.5 kg/cm2.g

Max. Overpressure: 10% of set pressure (5.5 kg/cm2.g)

 

Thanks.

[fallah]

munirm,

 

At first, please clarify about the following issues:

 

- Even when the process upset has been removed, the seat will continue not reverting back?

- What is the value of blowdown for mentioned PSV per the relevant vendor data sheet?

-What are the max/normal operating pressure of the shell side?

[munirm]

Here are the answers:

 

- yes, even when the pressure was reduced to 1-2 kg/cm2, the seat didn't revert back. It was done manually with hand jack.

- Exhaust flow rate is 36000 kg/h

- Operating Pressure is 3.5 kg/cm2 and PSV set point is 5.5 kg/cm2.

[fallah]

 

- Exhaust flow rate is 36000 kg/h

 

munirm,

 

By blowdown value, i mean the percent of set pressure below set pressure on which the PSV will be reseated after removing the overpressure cause...not exhaust flow rate...
 

[munirm]

It should revert back just below 5.5 kg/cm2.