11 replies to this topic

[asade abiodun]

Hi all,

am new in writing process control philosophy. Please i need any information that will serve as guide for me to know what i should look for in writing it.

thanks

[pleckner]

You need to have a complete understanding on how the unit is to operate. You must fully understand all the little things that can go wrong. You must have a complete understanding of how the particular unit interacts with other units upstream and downstream.

Is my answer a little general? Yes because you don't give any specific information.

[asade abiodun]

Thanks Pleckner,

i want to write a control philosophy for the control of pipeline pumps (2) taking there suction from 2 surge vessels. The level in the vessels determine the pump flow discharge into the pipeline. Therefore, i was to write on how the pump will be controlled when there's alteration in the liquid level in the vessel. how the pumps will operate.

i hope i have explained.
Hope to hear from you. thanks once again

[djack77494]

asade,
Though you have provided some additional information, you still leave much to the imagination. Are you dealing with 2 identically sized suction (surge) vessels? Are they at the same elevation, same pressure, and symmetrically piped to a common suction header which then feeds both your pumps symmetrically? And do you want to simultaneously feed either one or both your pumps from both surge vessels? If so, do you want the levels in both vessels to be the same? Discussion of all these points should be included in your control philosophy. For any desirable mode of operation, you should indicate how it will be achieved (but not necessarily controlled if natural forces could achieve it). Do you have different modes of operation, such as normally operating with feeding from both surge vessels, but sometimes removing one from service for special operations; e.g. cleaning. If so, all modes of operation must be described. If you find yourself with the vessels having dissimilar levels, how do you want to deal with this? All your control strategies should be included in the control philosophy.

[asade abiodun]

djack,

thanks for your responce.

the two vessels are identically sized, same capacity on the same elevation, same pressure and they are discharging into common header, in which it feeds the two pumps. Its design that the liquid level should be the same in the two vessels.

One of the scenario i need to consider is different in liquid level in the 2 vessels, because the pumps will operate based on the level in the vessels.

i appreciate more information to consider.

[pleckner]

Are these pumps centrifugal or PD? Are both to be operating or is one a spare? Are these pumps on speed control or is there a flow control valve at a common (or individual) discharge line? Is the control cascade (level resets flow)? Is there a recyle line with an orifice or control valve?

As you can see, there are many details that you are still not giving us. Perhaps a P&ID (or some detailed sketch) can be uploaded for us to see.

[asade abiodun]

Pleckner,

Find attached the pfd for the system. the vessels are with SDVs at there inlets. Each of the vessels are equipped with LICs.

The recycle LCV is designed to operate with signal received from the vessels in case theres's change in liquid level in the vessels. Fluid flow into the vessels by gravity.

The LCV is located at the discharge line to the Lact unit.

I hope i have supply info. Hope to hear your responce. thanks once again

Attached Files

•  PFD_Model__1_.pdf   12.07KB   249 downloads

[AA Mishra]

Purpose

Process explanation

Operating conditions






Regards

[pleckner]

@asade:

What you posted doesn't tell us anything. You need a full blown P&ID to work out the control philosophy. The good news is you should have everything you need if you only look at your P&ID and re-read the posts. You know the process and how it works. All you need to do is explain this in terms of what the controllers are doing. You explain the level control function and what it needs to do. You explain the by-pass and what controls it. You explain the alarms and any interlocks.

I hope this and the other posts help. Short of writing it for you, I don't think there is much more we can offer.

[asade abiodun]

Pleckner and others in the forum, thanks .
For the discussion so far as open my understanding and i have been able to bring out the information i needed.

Thanks for helping young engineers to grow.

Regards,

[Wouter]

asade,

as always there have been some very useful postings here for you to write up your control strategy. Also don't forget to add the more tricky details:
- what will be the controller action if your level measurement fails?
- is there any interaction with SIS or interlock systems?
- are there any alarms which are handled by the control module? Is it DCS based?
- does the controller and its I/O need to be redundant? otherwise, what is the criticality of the loop?
- do you need a feedback contact from your pump and generate a discordance alarm?

Good Luck

[jprocess]

Dear Wouter,
Could you please explain more about SIS or interlock systems?