Hey there,
I have a valve I have linearized on a pipeline inlet into our sour gas plant. Typically this 8" butterfly valve runs wide open, and when it does, the pipeline pressure upstream of the valve is just under 100 kpa above the downstream pressure (plant pressure). When the valve begins to close the pipeline pressure goes up, and then obviously the valve gain goes up. I have a H2S slug controller configured in the DCS to close the valve to 20% when the slug is detected, then control the rate in of the slug, and then disable, and go back to flow control when the slug is over. Depending on the length of the slug, there can be 1000+ kpa differential across the valve when the slug is over, so what was the flowrate with the valve wide open before the slug is now flowing with the valve around 50% open until the pipeline pressure is brought down. So anyway, I figured the way to linearize the valve was to have the valve wide open, with minimum dp across the valve, and move the valve to 10%, let the flow stabilize somewhat and then move to 20%, and keep going that way. By the time I finish, I'm flowing a lot more than at first because I've created line pack in the pipeline, so I just have to kind of figure the best fit for the top numbers.
So my question is, is there a better way to linearize this valve? I did get the valve profile I expected out of a butterfly, and it seems OK. The flow controller is kind of tuned for about a 500 kpa differential, so I spit the difference and get adequate control. Thanks.
Curtis