Process Engineering

I assume you are talking about the relief valve to the flare header? So the question is if the relief valve on the new equipment goes off, then what is the pressure on the header. It depends on you assumptions. The main on is, will the new units have exactly the same timing for the relief valve going off as all others in the plant? if so, you'll need a flare header the about 2 meters in diameter.

SO, write up a scenerio of what relief valves will be affected simutaneously and why ie, powerfail, fire in an are of the plant, sunden vale closure. Based on the most reasonable assumptions you can now see how much mas the flare header is designed for.

If you are talking about controlled blowdowns, then put a RO on the line and limit the flowrate to a manageable number. I always use a 1/2 inch RO which limits rates to about 30,000 pounds per hour.

Calculations for and design of the Pressure Relief SYSTEM is not a trivial exercise. The API Recommended Practice 521? provides some guidance. There are several different 'standard calculations' that must be performed for each vessel to determine the maximum relieving load and selecting the proper sized and type of pressure relief valve (PSV). Then the design of the flare header (the piping system into which each PSV discharges) must be properly done. Improperly done, the flare header will not be properly sized and back pressure will build up at the relief valve discharge--causing rapid chatter, low discharge rates, and ultimately vessel failure. Again, this is NOT a simple undertaking and it MUST be performed by someone well skilled in the calculation methods, evaluation criteria, and relief valve hardware designs. It is not a task for the new graduate or unqualified. I would not let the work be performed by any other than a PE with good experience in this specific field.

The plant designer must ensure and the details about this connections to the flare.