How to implement P&ID for liquid level control? 2

[aegis4048]

I need to model the existing oil and gas upstream facility in P&ID. For now I'm focusing on the vertical 2-phase separator's liquid control system.

The separator has two liquid dump sides, one is usually closed and the other is usually open, but I still need to model both of them in P&ID. Both sides have a floating ball inside the vessel that detects a liquid level, which is connected to the trunnion, and then the receiving fulcrum. The difference is that one is a (1) lever operated, while the other is (2) pneumatic-operated type.

I came up with some preliminary P&ID for the liquid control portion of the 2-ph vertical separator (attached image). I know that this is massively wrong, so I'm looking for feedback.

Q1. To my understanding, the T (transmitter) in P&ID is intended for devices that send electric signals. The way I modeled seems to be wrong because there's no electric line that sends liquid level information. But I don't know how else to connect the floating ball + fulcrum combo to the actual control valve. What should I do?
Q2. On the (1) side with a lever operated valve, I'm not sure what symbol I should use. I used diaphragm-type symbol for both sides, but I think the lever-operated side should be using a different symbol. Any recommendations?
Q3. On the (2) side with the pneumatic-operated valve, I'm not sure if I can use the LC + LY combo for the pneumatic system. I used LC+LY combo because that's what I commonly see on P&ID examples I found from other people, not sure if its applicable in my case too


Any advice is appreciated, I'm really trying to learn the details whenever possible. I have no mentor to teach me this other than here.

++ the (1) lever-operated side looks exactly the same as this Kimray video I found:

https://www.youtube.com/watch?v=uH3nwN3ppaM&t=174s

 

[1503-44]

LS Level switch

https://symbols.radicasoftware.com/229/single-line-symbols/31/level-switch

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Snickster]

On the purely mechanical side a ball will be shown in vessel with lever and mechanism connected directly to valve. On the pnuematic side a ball and with lever will be shown connected to a mechanical/pneumatic relay with pneumatic tube symbol connected to valve diaphram. I will see if I can find some typical P&ID symbology for that. There are no transmitters. Remember that all symbols on a P&ID represent an actual physical item that it really is. A transmitter is a control device which is basically a single control box that takes an input signal from the sensor in the vessel, pipe, etc. and converts this signal into a variable electronic signal or variable pressure signal and sends this signal to the controled device such as a valve.

 

[georgeverghese]

(1) appears to be a total liquid level control, so it manages the total height of liquid in the tank. This exit line must then be located above the oil-water interface
(2)probably is most likely the interface level controller. So the level transmitter is a dp cell(?), and the level control valve dumps water out the next unit operation.

 

[LittleInch]

Just draw it as best you can and don't call things transmitters if they don't transmit anything....

I'm assuming the set point is that one is for "normal" flow/level and the second for "High" flow / level.

Notes on a P&ID are your friend. Use them.

This is something similar. Its an inlet valve but the same symbol would do. For your air controlled one just show the ball cock mechanism entering a pneumatic valve positioner in place of the normal 4-20mA signal.

Si in place of the "Instrument input line" just show a line going to the ball cock and add a note to explain what it is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[aegis4048]

@LittleInch

I think your 2nd image is what I'm looking for. I think I can replace the "Instrument Input" with "Trunnion & Fulcrum" to describe what the input signal really is. For the lever operated side, I guess I can just take out the instrument air supply line and remove cap on the control valve, and just replace with with horizontal line to indicate lever.

While waiting for answers on this post, I came up with a new drawing, wondering if this is acceptable too. Notably, I'm using "LC" to denote the floating ball level detector as a control device that activates the "Trunnion & Fulcrum" line (This would correspond to "Instrument Input" in the 2nd image of @LittleInch's comment). I couldn't find a standard way to describe trunnion and fulcrum so I used that patterned line, not sure if these are acceptable in the eyes of yall P&ID experts (I know my customer probably won't care, but still would like to know yall's opinion). For the pneumatic valve, I put description "PNEUMATIC-CONTROLLED DUMP VALVE", and the other one as "LEVER-OPERATED DUMP VALVE" for clarity in readers' eyes.

 

[LittleInch]

Looks OK to me.

Just add a couple of notes.

Must admit I've never seen anything like this. Is it 100 years old?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[aegis4048]

@LittleInch
It's a fairly new facility built in 2022. I'm curious, what made you think this is an old facility? Is there anything abnormal or outdated about this piping structure? I really have minimal experience so I don't know if this is normal or not.

 

[Snickster]

One thing are you sure they are drains and not water supply? Normally that type of setup is used for supplying water to a system such as a cooling water system cooling tower makeup. These types of mechanical valves are not that common in use.

In any case the lever operated valve symbols shown are standard symbols used for that type of valve. You can find this symbol in the standard ISA symbols. However as a P&ID developer you have the liberty to modify the symbols when needed to apply to your installation as you see how I have done.

I am not sure if the pneumatic control is just a mechanical to pnuematic relay or if it is a more sophisticated control device. I think it is just a relay with input as the movement of the lever rotation to opening of control air valve to the diaphram but there could be other devices such as positioners and limit switches associated with this valve that keep it in the proper control range.

Also you could show the actual height of the floats in the vessel when the valves are actuated, if a range of levels then you can show levels of on and level of off for each float as upper and lower lines at the floats.

I have also attached some references on how to develop P&IDs.

 

[LittleInch]

'm curious, what made you think this is an old facility? 

Because it looks like something from another age, the piping and tubing and piping look all over the place and very untidy and there are far better ways to control level, even if your in the middle of nowhere. IMHO.

You must have electrical power if you've got air so why have this complex mechanical mechanism which looks like it could jam up and fail at any time??

May be the person that designed it was 100....



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[aegis4048]

@Snicker
Thanks for the detailed sketch, really appreciate it. That M/P symbol and the lever drawing seems useful for future drawings. FYI these are for sure 2-phase separators. The inlet is the pressurized wellhead stream that needs liquid-vapor separation. The separated liquid from the 2-ph separator is then dumped into a 3-ph heater treater for water separation (not shown in my drawing).

@LittleInch
I asked the operators, and even they are unsure why the vessel has mechanical + pneumatical devices at the same time. They are saying that somebody just put the mechanical levers in the first place, and then later put the pneumatic device and just decided to leave the mechanical lever there because idk.

 

[georgeverghese]

Interface level transmitter must be a pneumatic dp cell, with output signal directly operating the ILCV.
And that LG on the tank must be for visual confirmation of interface level.

 

[Snickster]

@aegis4048

You must have not seen the attachment to the post above with the sketch. Here it is again. It has good references for creating P&ID's.

 

[LittleInch]

george,

I think this is just a simple degassing vessel by the look of it, so the ball cock just sits on the liquid level.

Then it goes to a three stage separator.

Think one is normal flow and the second for high liquid level?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[aegis4048]

@Snickster
I did not see that indeed, thanks for noticing and commenting again. It def looks helpful.
@georgeverghesem, LittleInch
Ya this is a 2-ph separator just to take out gas first and then dump the liquid into another 3-ph separator. I'm curious, under what situations would a dp cell be recommended to use? I did a quick google search and it measures differential pressures, I don't see how that's relevant to level control.

Also no one really knows (including the operator themselves) why the vessel has two working liquid outlets. It's hard to see from the images I attached, but in the original video I have, the ball valve on the lever-operated side is closed, and there's no PLC control system tied to it so the vessel always dumps on the pneumatic side with the current setup.

 

[georgeverghese]

@LI, There are 2 level controllers shown, so this must be 3 phase ? And there are 2 liquid exits shown. The light phase crude then goes to heater treater for residual water removal.

It may well be that the original intent of 3phase operation may now have degraded to 2 phase, given the likelihood of poor interface level detection.
Interface level detection in many crude fields ( and many other types of 3phase seps) is troublesome, given the chemicals used for corrosion inhibition often result in crude - water emulsions which blur out the interface level.

For a clear interface to appear to enable 3 phase automated control operation, some prerequisites are (a) no dirt / suspended solids in the incoming liquid (b)no chemicals in the feed that result in emulsion formation (c) low cloud point / low wax point temp (d)low viscosity of the light phase liquid (e)sufficient residence time for the 2 liquid phases (f)remote seals used on the impulse lines leading the interface level dp transmitter.

Prefiltration and heating the liquid often resolve emulsions (and demulsifier injection in to the hot crude helps too). In some upstream facilities, electrostatic separators are used also with limited success, provided water content in the L-L phase is low.

 

[LittleInch]

George,

You maybe right, but we don't know and even though this was apparently built recently, it sounds like the OP doesn't know either!

Both lines now combine so my guess was that one was to deal with a certain flow rate and the second opened if the level got too high.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.