Blowdown Design

Hi all,

I'm wondering if anyone has experience with designing and sizing the blowdown system from very high pressure gas systems.

Options I'm thinking of are:
Orifice and a control valve
Orifice and a on/off valve
Two paraller systems one for the begining and one for the end of the blowdown

Which one do you think is more reasonable?
How can I size the orifice and the control valve? How can I determine the average flow rate?

Thanks for your help
R.H.