Flow Control for

[BigInch]

Why do control engineers insist on using flow controls for liquid pipeline transmission systems, especially at the pump station at the beginning of a pipeline?

 

[hacksaw]

Those moves are typically dictated by the process/mechanical design engineer or customer, who see themselves as having expert knowledge...and frequently consult the controls programming group for their intimate knowledge.

Such issues are pointed out repeatedly during the course of the project by those who understand process dynamics, but there are some things you can only call out and you make sure your design is workable when in startup process is forced to modify the design.
There in lies the whole point, such idiocy manages to make the top dog look smart!

 

[BigInch]

I find FC at the beginning of the pipeline is the worst possible method. It is great for ensuring a pipeline has the best opportunity to run out dry.

 

[BigInch]

Seriously. Liquid transmission pipelines do not actually need flow control anywhere. They operate on a batch volume transfer basis, so are seldom if ever worried about maintaining any specific flow rate at any given point. Just move a volume from point A to B. The faster you can do it, the sooner you can do another one. Running a liquids pipeline to maximum flow rate is the only thing that makes sense.

Gas pipelines on the other hand do everything by flow rate control.

 

[ApStef]

Liquid transmission pipelines do not actually need flow control anywhere.

When you say "liquid transmission pipelines" you do not include i.e. reactor feed pipelines, right? Because flow control is required there.

You mean just moving liquids e.g. from one tank to another?

 

[BigInch]

Sorry. Correct; not including any process feed, such as reactor feeds, cooling and heating systems, lube oil lines. I understand the need for specific rate control of chemical and thermal processes in those types of systems.

Basically tank to tank, cross country transfer of crude oil, gasoline, diesel, kerosene, LPGs.

As these companies do,

http://www.colpipe.com/home/about-colonial/system-map

http://www.transmountain.com/product-shipped-in-pipeline

 

[djs]

Some pipelines have pressure limits which must be observed. In some cases the pumps are capable of producing a discharge pressure higher than that limitation. If the pump is not on a VFD, then a regulating valve must be used.

 

[BigInch]

Absolutely, a relief valve and PCV, which generally at the scales I'm accustomed to, are far cheaper than VFDs, electric motor drives and the electric power generators to run them.

 

[BigInch]

The generators running on crude oil have a fuel to wire efficiency that hit far harder than the measly few % a VFD could ever save on the pumps.

 

[BigInch]

Link to Stanier's VFD presentation,

http://www.eng-tips.com/viewthread.cfm?qid=381648

 

[zamyusuf]

I am working in Tank Farm project now, with total 44 Tank , and there is no flow control here,

customer designing that for process loading/unloading to or from ship/truck/main plant, they just maintain the pressure in the pipe-line.

as far as I know, flow control is not required if the process only for transmission the product,

 

[BigInch]

Excellent. I agree. If you simply keep pressures within high and low limits, you will be able to move far more products much faster. VFDs only slow you down. I'd rather run at the design flow / sweet spot, 24/7, valve wide open, pump at sync speed. If I can't, hopefully it won't be for long, so I don't mind a little inefficiency if I have to close a valve a little bit. What I don't want is somebody deciding to turn the flowrate down, walking off and running for the next couple of months at reduced capacity.