Plant Blowdown Starting Pressure
Plant Blowdown Starting Pressure
(OP)
We've been instructed to blow down the facility to the lesser of either 700 kPag or 1/2 the design stress of the equipment in 15 minutes or less.
Does anyone know if the starting point is system design pressure (i.e., MAWP) or normal operating pressure? API RP521 is somewhat vague in this manner and it's not real clear. It does make a significant difference because of the large margin between normal and MAWP in some of the vessels.
Does anyone know if the starting point is system design pressure (i.e., MAWP) or normal operating pressure? API RP521 is somewhat vague in this manner and it's not real clear. It does make a significant difference because of the large margin between normal and MAWP in some of the vessels.





RE: Plant Blowdown Starting Pressure
There is more concern for rate to me. If you have to blowdown a million Kg in 15 minutes that is one thing versus 1000 Kg. Most chemical plant limit the rate to a point of either a flare limit or if to atmos, 10,000 kg/hr.
RE: Plant Blowdown Starting Pressure
We're still limiting flare tip mach to 0.5 so no concerns there and we still do detailed piping pressure drop calc's to check backpressure on the system.
RE: Plant Blowdown Starting Pressure
I think the clients Design practice should take precedence on this. Exxonmobil, for instance, requires that you start blowing down from the maximum operating pressure. I have encounted clients to prefers PSHH set point, which can be like 90% of the MAWP.
But for compressors, you have to start from the settle out pressure.
Buchi
RE: Plant Blowdown Starting Pressure
Best regards
Morten