Dear all,

I'm facing in my office an internal discussion relevant to LS steam header protection, downstream a split range controlled let down station (2 x 100 t/h let-down with desuperheater, both in service but normally closed).

Let's suppose to have a HS header connected to a LS header through let down system made by 2 x 100 t/h pressure control valves (with desuperheater) controlled in split range from LS pressure.

Designing LS steam header PSV I have to suppose that both valves are driven open because the failure of controller ore one is enough???
Consider that LS header has also one vent 100 t/h capacity.

If the LS pressure controller would have high integrity level (e.g. 2oo3 Pressure transmitter) this would be enough?

Regards

Rob

Not very clear with your question. Due to common controller failure, you need to consider two control valve FULL OPEN for PSV relief load on LS header.



2oo3 voting increase reliability / availability of transmitter. However, controller failure remain an issue.

JoeWong

I will appreciate if you briefly explain about:
-"Blow- By gas"
-"Let- Down Station"
-"HS-Header"
-"LS-Header"

Regards

In the context of this thread, I believe LS-Header and HS-Header stand for the low pressure steam header and high pressure steam header, respectively. A let down station is a control valve of some sorts where the sole purpose is to drop the system pressure to some required amount in a very precise controlled fashion. This can be done with either a control loop (pressure transmitter and actuated valve) or a self contained pressure regulator.

As far a -"Blow- By gas" goes, I don't see this term used in this thread.

Dear Rob,
Could you make the drawing of your system and upload here so that it will be easier to analyse the problem.From your query it seems that you have 3 control valves out of which 2 are for let down and one one vent with the single split-range controller.
In case of controller fails and you find your two let down valves stick open fully and vent control valve sticks close then you have 200 Ton/hr of flow may be that would be the relieving load.I am not sure ignore it if it is wrong.
Please check the replies by other Jedies specially Mr Joe ,Mr Art and Mr Phill. After you will furnish the drawing I am sure they will come with the right solution to your query.