using pressure control valve as blowdown valve
using pressure control valve as blowdown valve
(OP)
Hi
I need some opinion on the blowdown system for liquid petroleum gas storage. Some designer do not used any BD mechanisme except the PSV. However if I used PCV as BDV for blowdown any restriction from API 521?. or other codes?. Please
I need some opinion on the blowdown system for liquid petroleum gas storage. Some designer do not used any BD mechanisme except the PSV. However if I used PCV as BDV for blowdown any restriction from API 521?. or other codes?. Please





RE: using pressure control valve as blowdown valve
I think that API requirements for the blowdown duration exist in the API 14 series offshore standards. However I did not find it in a quick word search. Perhaps they use depressure or something else in the standards.
RE: using pressure control valve as blowdown valve
I means that the Pressure Control Valves used as Blowdown valve (depressurized). How??
Regards
RE: using pressure control valve as blowdown valve
RE: using pressure control valve as blowdown valve
Anderson Greenwood has a feature that will allow you to dump the pressure on top of the dome remotely causing the PSV to go fully open which would allow the PSV to function effectively as a blowdown valve (they call it a 'remote unloader'). However, blow down valves are usually quite a bit smaller than PSVs in my experience as they aren't typically sized for the same flow rates. A PSV could be sized for a large vapor flow rate as a result of a fire or gas blowby while a depressurizing valve is typically sized for the gas inventory in the unit that needs to be vented as a result of an ESD (emergency shut-down). Common requirements that I've seen for a blowdown valve is to depressure a unit to 100 psig (or 1/2 of design pressure, whichever is lowest) in 15 minutes.
Remember if you use the PSV as a depessurizing valve to consider low temperatures in the system if you have any liquids that will autorefrigerate. That comment also applies to a depressuring valve.
RE: using pressure control valve as blowdown valve
Agree that the PSV cant be used as BDV, but how about the PCV used for BDV?..
RE: using pressure control valve as blowdown valve
Doug
RE: using pressure control valve as blowdown valve
But if the PCV is a "CONTROL VALVE" it will follow any signal sent to it.
Current advanced state of the art control systems accomplish this easily. Just program in a function block to dump the valve open. Slightly more primitive systems may be more simply adapted by inserting a 3-way normally closed solenoid valve between the positioner and the valve actuator. With a fail-open (Air-to-close) control valve, chopping the power to the solenoid will isolate and vent the actuator, blowing the control valve to full open.
Blowdown can be pretty harsh service. High velocity, entrained particles are pretty tough on the valve trim and as cited in an earlier post, the valve may not shut off as tightly as before the blowdown. I remember once seeing a globe valve plug from a digester vent valve-which is not supposed to be as harsha service as blowdown, and it had suffered easily 50% material loss. Moral of this story: Use hardened trim, oversize the actiator for more seating load.
THis is an application where a ball valve can serve well. Use a full-port valve and get it open as quickly as possible. Then the high-velocity flow will not churn around inside the body doing damage, as it can with a globe-style valve with its S-shaped flow path.