7 replies to this topic

[Glauco_Tirollo]

Hello Guys.

 

I attached a picture summarizing the process. I receive the project on the basic engineering stage and i'm doing the detail engineering over it. My problem is that I believe this system is overdesigned with too much relief valves.

 

 

 

It is an water electrolisys hydrogen production facility. I have three parallel electrolizers production hydrogen at 0.3 barg and around 1.000 kg/h total. The equipment has a relief valve that will open in case of high pressure inside the electrolizer package.

 

At the compressor suction, I have another pressure control system that I believe is redudant. The only reason there is to install a high pressure relief valve on the suction of the compressor in the case that that the compressor's  bypass valve fails open. 

 

Downstream the compressor there is another relief valve. I believe this  one is well positioned since if something downstrem the compressor  fails, or a valve is closed, I'll need to relieve  the excess product. The  pressure discharge of the compressor is set at 35 barg.

 

My main concern is on the third and forth relief valves, the one after the  purification and the one before mixing hydrogen with nitrogen. The basic engineer developer probably tought he should put a relief valve downstream every automatic block valve. I know this because I've receive two versions of the syngas mixing station and from one version to the other the designer added both the on-off valve and the relief valve.

 

The compressor and purification units are really close together (less than 30 m apart), but the mixing is done in a different site around 1000 meters away.

 

Downstream the syngas mixing there is another pressure control valve, but that one has a different set point and it's purpose is to regulate the pressure one the reformer (out of scope of this project).

 

I would like your experinced opinion on this arrangement (pressure relief before automatic block valve). Is there a reason to keep all of them? Does it add some degree of safety on the process, or are them more points of failure? Could all the flow be relieved from the valve on compressor outlet?

 

Thank you all,

 

Attached Files

•  relief_valve.png   8.21KB   2 downloads
•  HYDROGEN_RELIEF_CONTROL.jpg   45.61KB   1 downloads

Edited by Glauco_Tirollo, 08 December 2023 - 06:12 PM.

[Pilesar]

Pressure relief calcs should have a 'scenario' describing the reason for overpressure. I can imagine possible scenarios for relieving downstream of control valves, especially if the relief setpoint is higher at the compressor.

[latexman]

No attachment.  Edit the OP, click "Use Full Editor", the document attachment functions are below the text window.

[breizh]

Hi,

Like others said, share a PID and extract of the Hazop, with scenarios explaining the need for PSVs.

Breizh 

[Glauco_Tirollo]

Good Night.

 

I attached the missing file. It's a simplified PFD. Also I added a snap of the compressor discharge line, showing the PV that releases to the vent header. Other PVs will follow the same patterb.

 

I haven't received any HAZOP related document. 

 

I'm really trying to come with scenarios that could justify keeping those PVs.

[breizh]

Hi,

What are the set point of the PSV and the position of ON/OFF and PCV valves in case of power/Utilities Failure?

Hazop is a "must have " document to perform the detail engineering.

Good luck.

Breizh

[Pilesar]

I find two relief valves on the PFD you attached. One at the compressor and one at H2 Purification. I saw no relief valves on the P&ID snippet. There are three pressure control valves downstream of the H2 Purification connecting to the vent header. Are these pressure control valves what you are calling relief valves? These may have another purpose than overpressure protection.

[Glauco_Tirollo]

I don't like the fact that all the pressure control valves are set at the same pressure as the process line. For example, the compressor's discharge pressure is 35 barg, and the pressures at the minimum, normal, and maximum pressure of6421PV01004 is 34.91, 34.98 and 35.01 respectively. This is a pretty short interval.

The failure position of these PVs are fail close.

 

Yes Pilesar, I know I'm not using the correct terms, sorry. I'm refering to the pressure control valves that send hidrogen to the stack.

The setpoint of the compressor PSV is 40 barg.

 

I believe the PV at the compressor discharge is a layer of protection for overpressure supposed to operate at a lower set point than the safety valves.

 can't see a reasor the have the valves after the h2 purification and at the N2+H2 mixing.

The PV after those valves is meant to regulate some pressure or consumption inbalances on the syngas sent to ammonia production plant.