the transmitter and valve as a 1oo2 trip architecture query

[hswang2]

I have a transmitter and its signal will be used as a second shutdown input with 1oo2 voting and the control valve will be used as a second shutdown mechanism. (Pls see the attachement Figure 15-3.) common equipment is used, the BPCS cannot be considered an independent layer of protection. It is said that this case only valid that the control valve will have sufficient tight shutoff performance to protect against the against the hazard by itself. If this is not the case, then this design cannot be used.
My query what kind of control valve(ex. Fail close,...) can be suitted for this situation and what kind of process (ex. Pump Min flow path ...)will apply this design?

Thank you very much for your kindly help.

 

[hacksaw]

these questions are largely a function of the degree of hazard. In some cases redundant shut-off is completely inadequate, in others, more than sufficient.

have you performed the HAZOP review?

 

[JLSeagull]

What size valve?
What process conditions?
Flashing?
Cavitating?
...
A triple offset butterfly valve with zero leakage could be a suitable shutdown valve; and might even be an adequate control valve - if suitable.

In my opinion, the typical control valve is not a good shutdown valve.

 

[atayto]

BPCS control valve and its loop can not be considered as layer of protection. And also this arrangement with two transmitters is not good as well, but it depends of hazid and hazop studies. In europe there is leakage rate classification you can find control valves(KKI can supply you valve with leakage class VI)which can be leak tight as well, but I would suggest to use 2oo3 voiting system and totally separate BPCS transmitter.I would even suggest to segregate shut down system(SIS) and BPCS and not feed any BPCS transmitter output to SIS system. This is much safer.