Reciprocating Compressor - Manual Shut down

[planck121]

Hello,
I would require some help and feedback in the following:
We have a H2 recip machine and vendor is proposing some manual shut down operation actions for the recip machines. They claim the settling out pressure of the recip machine is too high so in the case of emergency trip/shutdown, the operator with-in one hour will have to take the following action:

The by pass valves and other vent valve intially close automatically but then the operator will manually have to open the vent valve on 3rd stage to relieve the pressure and the other by pass valves on 2nd and 1st stage to relieve the pressure in those stages.

The essense being the whole process will be manual for depressuring the compressor incase of emergency trip. I feel given the little time operators have in a typiucally running facility this would cause undue stress and issues for operations....

Are there any other ways to depressure the recip machine because of the high settling out conditions. Also, are there any draw back to the above mentioned philosophy.

Thanks much

 

[zdas04]

There are a large number of recips in the world that remain pressurized after a trip. I would say that compressors outside of plant fences are more likely to remain pressurized than there are machines that blow down on an ESD.

But with an H2 machine you are inside a plant fence. The Pressurize/Blowdown decision must be integrated with the rest of the plant PSM and/or LOPA analysis. Making that decision without considering the rest of the equipment in the plant is a good way to do it wrong.

If I had a machine that must be blown down within one hour of a trip, I would automate the isolation/blowdown as part of the trip. The simplest way to do this is with actuated valves. Actuation can be either pneumatic or electric and the valve operating sequence must be controlled by some sort of control logic in a program (just having the block, bypass, and vent valves open is a good way overpressure some component and turn a bad situation into a nightmare). I'd do something like: (1) Once rotations stop, shut inlet; (2) shut outlet; (3) open 3rd stage vent; (4) opent 2nd/3rd bypass; and (5) open 1st/2nd bypass. You'd want to think about it more than the 20 seconds I just thought about it, but the control logic will be something like that.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[planck121]

Thanks David,
I did not understand your point about
(just having the block, bypass, and vent valves open is a good way overpressure some component and turn a bad situation into a nightmare).

wouldn't having the valves open is a good way to not overpressure.

 

[zdas04]

If the bypass valves happen to operate first, third stage pressure can do ugly things to first stage piping. Shutting the discharge valve with the machine rotating can give you some high pressures. The point is that if you just send a shut/open command simultaneously to a list of valves, lets random chance control the sequence. Random chance is never your friend.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[bcs5274]

blowdown to upstream of suction control valve thru a small port valve, if bypass left open the unit will equalize, can be set to reclose at set pressure for strartup