Increasing the discharge pressure should also increase the flow. How about a controller that works with this in mind? It would be pressure controlled but takes into account the flow. For example, you have a pressure setpoint of 130 barg and a flow setpoint of say 1000m3/hr. Both of these go to a calculation block that calculates the opening for the recycle valve. The flow meter first goes to a scaling block that at 50% would result in no change in the pressure change. If the flow drops below 1000m3/hr, it would increase above 50% and send to the calculation block a request to increase the setpoint pressure. The setpoint of 130 barg would then have the increase added to it in the calculation block and result in an actual higher setpoint of say 131barg which is then passed to the recycle valve and requests it to close. This causes the pressure as well the flow to increase as instructed by both setpoints. You would need the size of the valve and pipes to decide how much the scaling should be. Hope its not too complicated and helps you.
Ahh, my bad, your flow meter is not at the discharge but at the recycle, but I think you get the idea.
Which begs the question, what about the discharge pipeline? Do you need to control it too? Also, the line goes to a fuel gas line that has a PCV on it. If the inlet gas can vary between 57 to 125, which is very large, wherever that fuel gas is going to is going to feel the brunt of it. Especially since there would be 2 PCV on the line and coupling would occur resulting in more instability.
Edited by thorium90, 15 January 2013 - 10:54 PM.
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Recycle sketch.pdf 21.2KB
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