Booster Pumping System, Control Strategy 1

[sam01]

I'm trying to develop the control strategy for a booster pumping sytem. There are 4 booster pumps three operating and one standby, each pump operates at 130 TDH at 3500 gpm. the maximum flow rate for the system would be 10500 gpm. The pumps are controled by a variable frequency drives. The system includes a pressure transducer and a magnetic flow meter. Can someone explain to me the sequence of operation of how pumps come online and offline. Does the system have to maintain a constant pressure where the transducer is located. Does the pressure at my demand point vary as flow varies? Also what happens during periods of low demand, maybe when one pump operates at min. speed?

 

[petern1]

I think one could write a text book on this. I need to get the terminology right as to how you refer to booster pumps.

In our plant, we have slurry pumps (5 in series) pumping into a tailings line, then a set of two booster pumps mid-way along the line. Is this similar to your set-up?

We also have some installations where the 5 pumps in series take suction from a pump box and then pump into a tailings line with no booster pump.

What are the requirements of the downstream destination? Does it need constant flow, pressure, or both? The answer to that can change how you would control the boosters.

In slurry flow, for instance, where you have to maintain a minimum velocity, we control with suction pressure and a low flow limit that will kick-in a suction water flush to maintain supply to the pumps.

 

[KernOily]

It depends on the demand/load/service/customer/whatever you call it. I'd have to know more about your operating strategy and the requirements of the load before you can write a control strategy. Thanks!
Pete
pjchandl@prou.com

 

[sam01]

The pumping system consists of pumping effluent water from the final effluent tanks at a wastewater treatment plant. The largest demands are spray water which I'd like to maintain at 40 psi. Some of the other demands throughout the plant include cooling water, pipe flushing(intermittent), There are four pumps connected to a main header which takes suction from an open channel. The discharge piping is routed through strainers, and then through a piping network to the various demands. A pressure tansducer and a magnetic flowmeter will be provided at one location in the discharge header, these instruments will be used to control both pump operation by VFD (PUMP SPEED)and Pump sequencing (ON/OFF).

 

[ChasBean1]

Hi Sam, opinions are like armpits - everybody's got them and they all stink. Anyway, here's mine:

The pressure is your controlling device and the flow meter is there, nifty to have, and is for your information. You can't control the pump VSDs via input from a flow meter while maintaining a constant pressure. When demand is low, the flow meter will sense the flow reduction and tell the pumps to pick up speed! How sensible would that be?

So specify a 0-60 or 0-80 psig pressure transducer, locate it one-half to three-quarters down the main run of pipe, or at a location where you know you need 40 psig. The automatic control software should take the 40# as an analog in, and stage the speed drives appropriately. (Rough) sample of staging language:

"When the system is enabled via the facility automation system, pump P1 initially starts at minimum VFD setting and ramps up to maintain pressure at transducer PT-1. If P1 operates at greater than 95% for five minutes (adj.), P2 shall start at minimum VFD and slowly ramp up to maintain setpoint. When P1 and P2 operate in parallel, both VFDs shall be synchronized. If P1 and P2 operate at greater than 95% for five minutes (adj.), P3 shall start and run in parallel with P1 and P2..."

Add similar language for unloading each pump at 45% speed (adj.). Add in standby function of P4; note the analog-in reading from the flow meter to provide indication on the facility automation system, but not to perform a control function.

Good luck, -Chas