Controlling tank level using multiple parallel drum unloader pumps

[levans]

I have an application where we are trying to control level in a reservoir tank based on running of four 55 gal drum unloader pumps. The drum unloader pumps are VFD controlled and we monitor the drum level of each. We currently operate these pumps by sequencing on/off based on the tank level percentage. We would like to control using a level PID control that would also monitor the drum levels and cascade control the pumps on the drum unloaders based on the level of material in the drum. Lowest level would run faster to try and empty the drum, next lowest level would run slightly slower, etc. This is so that we can empty the drum and then have time to change the drum before a second drum empties. All the while maintain the level in the reservoir. Looking for control ideas I can implement in PLC to provide more efficient and reliable control of the drum unloader pumps and better regulate the level control in the reservoir.

 

[LittleInch]

A drawing would always help, but can I asusme you're filling a tank with up to four drums?

So when one drum is empty then you swap it for a full one?

What sort of flows and timescale are we talking here? 1 gal/min or 10 gals/min makes a lot of difference/

But looks like a cascade control to me.
Start point all drums full.
Tank level falls, calls on drum one until it goes max flow. Still falling start drum 2, then 3 then the same in reverse until drum "one" switches to the next drum once the old drum 1 is empty.

then alarms or indicates to an operator that the drum is empty. Rest the controller and this now becomes drum 4.

A bit of PLC logic for sure, but looks pretty standard to me.

all depends how far you can let the level in the reservoir drop before turning ont he second or third pump??

And how accurate your level controllers really are. I would have thought steps of 50mm should be easily possible and maybe less.

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Also: If you get a response it's polite to respond to it.

 

[levans]

Thank you for the information. That's what I was thinking. Just need to figure out the PLC portion.