Hi everyone,
I am trying to control a horizontal separator oil box by maintaining steady outflow, and am not too concerned with the level set point. The separator is the second vessel after the slug catcher, which is essentially a surge vessel. The problem we are having is that the way these controllers were tuned originally is to maintain set point.
As an example, the separator oil box level controller 2-LIC-107, has a set point of 2600 mm. There is a flow meter on this oil outlet line that I have converted to an FIC, so we can send a CAS set point. From what I have been reading, the LIC should be proportional only (no integral), so that the response to inflow changes is proportional, and not exaggerated by the integral action trying to maintain set point. Can someone give me some advice as to how we should be controlling this process? Is there other DeltaV functions that could be used in this situation to maintain steady outflow? (I deadband, PIDplus, nonlinear gain etc.)
Thank you!
Jayme
Controls specialist
In reply to controls_wl:
In reply to James Beall:
In reply to LaurentB:
Thank you again James, and everyone who has helped on this issue thus far!
I will be applying the gap tuning to the separator A oil box on Monday. I was able to do some testing with it on Thursday, but operations did not want to leave it over night, so will get back to it next week.
On another note, I applied the gap and lambda tuning to our interface. (I know you said it is not recommend, but I will tell you why I did it, and why it appears to be working in our situation)
The interface probe is an Agar (probe length is very short, around 20") inserted at a 45 degree angle in the interface zone at the back end of the separator. We have always had issues with interface on the separators, as it is the second vessel after the surge vessel (slug catcher or free water KO), and with our thermal oil sands production, we do get a rag layer some times. With that being said, I always felt something was wrong with the way the interface and water dump controlled. The interface probe PV and the water dump output would constantly oscillate, which made me realize that the probe length being so short (and on a 45 degree angle) was causing the controller to constantly oscillate. With the gap tuning, it seems to have calmed down the water dump valve output substantially, and has propagated the affects to the oil box and the next vessel (treater). When the operators run the vessel in manual, they are able to basically flat line everything. to do that, they make smaller moves periodically on the water dump, and then check physically oil/water taps in the vessel to make sure the water level is where they want it. With what you suggested, the controller is now doing this to some extent. We are trusting the direction of the inteface PV, but not trying to maintain a strict set point.
Here are some trends of the progress so far (and we have not even implemented the gap tuning on the oil box yet!!
Before we applied gap and re tuned with lambda (notice the water dump valve output)
After gap tuning and re tune with lambda (output is a lot more steady instead of up down oscillations in phase opposition to the interface PV)
So far, operations has said that oil treating is good, and Separator A water taps etc. seem to be good.
Now on to the Separator A oil box
Before:
After:
Treater oil out (downstream vessel after separator A, at which point goes to spec sales oil)
Before
Here are all of the tuning values:
2-LIC-106 IF control
Range: 0-100%
Typically SP: 62 % currently
Gain: 0.35
Reset: 436
NL_GAP: 5
NL_HYST: 5
NL_MINMOD: 0.15
NL_TBAND: 9
2-LIC-107 Oil box level control
Range: 1676 to 3048 mm
Typical SP: 2600 mm
Max/min for surge capacity: unknown, but think it is around 2400 (anything lower will push gas to next vessel) to around 2900 mm (may be able to go higher as the capillary pad is not at the top of the vessel, so there is some room)
Values when we did the gap trial yesterday
Gain: 3.33
Reset: 553
NL_GAP: 80
NL_HYST: 80
NL_MINMOD: 0.25
NL_TBAND: 230
I will post some trends of the oil box after we leave the gap tuning on for a day or so. If you have any other suggestions on how to smooth it out more, please do share! I was wondering if I should have 2-LIC-106 interface cascade flow set point to 2-FIC-104A (newly created flow controller on interface zone water dump). It is a vortex flow meter and is pretty reliable. We also have a wedge meter on the oil box dump, but it is not very reliable (entrained gas etc.), would it still be worth while making it into an FIC for master/slave control?
Also, could you explain how dynamic reset limit works (does it go on the master or slave loop?)
And also "Use PV for BKCAL" Is the what the slave controller should have?
Thank you again! Appreciate the help so far, I am learning so much.
In reply to Lou Heavner:
In reply to MPHymel: