9 replies to this topic

[Novice Instrum]

Hi
This is my first post :-) Hope you all doing good.
I am pretty new to instrumentation.
Perhaps this is already discussed in this forum and I tried to put my post there, but couldn't.

I have desalter package 1st & 2nd stage with upstream separator. The flow from separator is fed to dalter by using level controllerr and level control valve. Vendor requires inlet pressure to his package to be maintained with in limits say 7 barg (My range is 6.5 to 8.2 barg). For meeting his requirement do I need to install a PCV also??
I believe it is possible to install level & pressure control valves in series. Before I go ahead, I need to have an opinion.

I am attaching a simple P&ID scheme, if you require any additional info, please let me know.

I couldn't see the attachment, but please find the process requirements or P&ID and scope of supply from vendor's documents, while the PCV is defined, you should consider it.

I am a chinese, my english is poor, please try your effort to understand my means. And could you send some photoes of your equipment by email with your accommodating? thanks.

[Novice Instrum]

I am attaching the scheme again. Please have a look and suggest, how this scheme can be made working..
Since the pumps are of different characteristics, I believe flow from the pump which have less head will not flow into my down stream equipments.

With I limited knowledge, I think I need to install a pressure control valve, but not sure that it can be in series with level control valve.

 P&I Scheme.jpg   27.57KB   94 downloads

[fallah]

Seems you have two, different parallel pumps. Therefore, the pumps system follows parallel pumps rules and working point of the pumps combination would be intersection of the pumps combination curve and system curve. Thus, each pump has its own flow with same head in the case of parallel working. It is obvious small pump having lower flow with same head.

For maintaining pressure at the inlet of downstream package:

1-The discharge pressure of the pumps combination should be such that you have adequate positive pressure at the package inlet with respect to vendor requirement (7 barg).

2-You should install a PCV on a take-off point at the package inlet.Set point of the mentioned PCV should be around 7 barg to prevent overpressure at the package inlet. Therefore, you haven't to install PCV as inline in discharge line. The outlet of the PCV may routed to upstream separator(s). Of course, at the above situation you cannot account on a fixed and stable flow may should be provided at the downstream.

Hope your problem has been understood well and above helps you out.

[shan]

If you put PCV and LCV in series on the pump discharge line, they will fight each other. The pressure of desalter is controlled by the PCV on the top of desalter (flash gas/blanket gas control). The pump discharge pressure will be converged with the system curve. You may install a PSV (pressure safety valve) on the pump discharge line to satisfy the vendor's requirement.

[cea]

Dear Def110 -

Please find attached my proposed scheme. The scheme is self explainatory, wherein I have consider same pump discharge head for both the pumps. Please note that level & pressure control shall be done separately. Two control valves in same line is not at all recommended.

Hope, this will serve your purpose.

Regards,

Attached Files

•  Book1.xls   56KB   75 downloads

[shan]

Good attempt. However:

1. Make up your mind your PIC is for vapor or liquid?
2. How do you control your release distribution to the separator trains?
3. You release will recycle back to the desalter tank.

Therefore, my friend, your idea does not work.

[cea]

It could be possible that my interpretation of problem may be different. However, I would like to answer your queries.

1. As I understand, it is required to have desalter pressure about 7-8 kg/cm2. Hence, pump discharge head will be back pressure in desalter tank + losses. In short, controlling desalter pressure will automatically control pump discharge head. Further, I have assumed that PIC will control vapors. You may further clarify desalting tank operation. I guess, desalter tank is not pressurised with liquid. However, you can elaborate the operation of desalter tank. Accordingly, I will do necessary changes, if required.

2.In order to have same pump charectaristics, I understand that pump suction conditions need to be same. Hence the vapors are considered to be distrubuted equally to both separator tanks to keep the separator pressure same. If it is not so desired, these vapors can be taken to some other location (outside B.L.).

3. Refer my answer of point 2.

If you still feel the scheme is nonworkable, you may suggest your idea. This may be a good acadamic exercise.

Regards

[Dacs]

Well I'm saying this without the benefit of a more detailed scheme for the desalter.

But I'm just thinking that if the tank has a PCV that controls the pressure in the tank, should this be enough to maintain pressure in the tank?

Just design the circuit so that you'll supply the fluid at 7 barG. Let the PCV (in the desalter) does its job in regulating the desalter tank pressure.

Or am I missing something?