Advanced Automated Controls

Turn-key Automation Solutions in "3D"

Conceptual Design • Project Management • Automation • Controls
Electrical Construction • Mechanical Fabrication

Industry: Wastewater - SCADA Control System

1. System Overview

This system was designed to extend the life of the Clarifier and Booster Pumps in the Water Treatment facility. This is achieved by maintaining a flow in the system at all times. This prevents the introduction of air into the system, thus eliminating cavitation due to low flow or stopping of the system. Under normal running conditions, the Water Treatment system will maintain 50% level in the Sludge Chest. If the Sludge Belt is shut down for a period of time, or if the sludge flow is drastically reduced, the Water Treatment system will integrate down and remain at a minimum speed until the Sludge Tank level reaches 90%. At this point, the Water Treatment system will shut off and need to be restarted manually. If the Sludge system is restarted prior to the Sludge Tank level reaching 90%, the system will remain running and continue adjusting the system to maintain the 50% level.

To accomplish this, the Clarifier Center Well pump and the sludge booster pump have been placed on variable speed drives.  By regulating the speed of the drives we are able to 1. Maintain a constant pressure and flow on the system, 2. Reduce air introduction, thus eliminating cavitation, and 3.Maintain a 50% Sludge Tank level at all times.

This was an initial reading of the flow compared to the actual pump speed. 

This was with some initial tuning.

And finally with the tuning process complete.

The system is fully automatic and should require minimum operator adjustments under normal operating circumstances. The only adjustments that may need to be made will be to regulate the dilution valve before the Booster pump.

2. Hardware

Clarifier Center Well Pump:
In order to maintain consistent flow, the Center Well Clarifier Pump is designed to follow the speed of the Booster Pump while  also maintaining 4PSI pressure between itself and the booster pump. This sustains adequate head pressure at the Booster Pump which is essential for maintaining good flow in the system and prevent pump cavitations. It will follow the speed of the Booster Pump and then be trimmed (adjusted) by the differential pressure between the 4 PSI set point and actual system pressure.  As the Booster pump increases in speed the Clarifier pump will follow assuming the pressure is not above the set point. (currently at 4PSI )  
During initial startup of the system or if the pumps have been stopped and restarted, the Booster Pump will open the Bleeder Valve (XV103) for 5 minutes to bleed off any air introduced into the system. It will also change the pressure set point to 8PSI for the first 5 minutes to assist in purging the lines and discharging any air that may have been introduced into the system. It will then automatically revert back to maintaining 4 PSI after this 5 minute period.
It is identified on the screen as PUMP-020

Sludge Booster Pump:
The Sludge Booster Pump’s purpose is to maintain a 50% level in the Sludge Chest. This is accomplished by monitoring the level of the Sludge Chest (level transmitter LT-034) and adjusting the speed of the Booster Pump accordingly.  As the level decreases, the speed of the Booster Pump increases proportionately .  As the level increases, the speed decreases. 
It is identified on the screen as PUMP-021

Center Well Dilution Valve:
This is a manual valve that is used to flush water into the system in the event flow can not be established between the Clarifier Pump and The Booster Pump.
This valve can be operated manually at the operator screen.  IT DOES NOT OPERATE AUTOMATICALLY.When you turn it on, it will remain on till you turn it off.
When it is manually turned on it will turn green on the screen and red when it is off.
This valve is located in the Center Well pit. 
It is identified on the screen as XV-101.

Sludge Booster Dilution Valve:
This is a variable position valve that is located upstairs before the Booster Pump.  The position of this valve is based on the speed of the Booster Pump and a set point from the operator.  This is used to maintain good flow and consistency to the Sludge Chest from the Water Treatment system.
The operator sets a high limit for the valve that represents the valve position at full Booster Pump Speed. The system will then regulate water flow between 0 and this operator set point, following the Booster Pump speed proportionally. A set point of 40% for example, means that when the Booster Pump is running at 100% speed, the dilution valve will be opened 40%. If the Booster Pump is running at 50%, the Dilution Valve will be opened 20%.
When the valve is open at all the valve will turn green on the operator station and will turn red only when it is completely closed (set to 0%).
This valve is identified on the screen as FCV-102

Booster Bleeder Valve:
The Bleeder Valve is used to bleed off air after the system has been down.  This valve is located after the Booster Pump and will operate only during the starting of the system.
We found that after only a few seconds of down time, sludge would bleed back through the system to the Clarifier causing air to be introduced into the system. This air would then cause the pumps to cavitate during startup and prevent any flow of material into the system. In the past the operator would manually open a dilution valve to start flow.
This is an automatic valve with no manual control.  There is a manual valve in parallel with this one that can be operated at the valve in the water treatment plant.
It is identified on the screen as SV-103