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Primary Treatment Controls
Control Strategies PIDs
 
Primary Clarifier Inlet Gates
Local Manual Control
The primary clarifier inlet gates are manually opened and closed using the manual operator at the end of the headworks channel. The elevation of each gate may be adjusted to increase or decrease the flow volume to each clarifier.
 
Primary Clarifiers
Local Manual Control
The clarifier drive starts when the On/Off switch at the primary clarifier local control panel is in the On position, and stops when the On/Off switch is in the Off position.
Fault Conditions
The torque switch mounted on the clarifier drive unit will shut off the primary clari­fier mechanism in an over-torque situation. An over-torque failure will also result in an alarm signal to the PLC, which will annunciate at the HCP. The RESET button lo­cated on the local control panel will restart the primary clarifier mechanism after an over-torque shutdown.
 
Primary Sludge/Scum Pumps
Local Manual Control
When the primary sludge/scum pump Hand/Off/Auto switch is in the Hand position, the sludge pump is controlled by the Start/Stop switch at the associated scum pit.  The pumps are configured in this manner to allow easy pump control for pumping the scum pits.
SCADA Manual Control
None
SCADA Auto Control
The primary sludge/scum pumps each have an HOA switch at the HCP. In the AUTO mode, these pumps are controlled by the PLC. When the PLC detects that Pri­mary Clarifier No.1 is On, Primary Sludge/Scum Pump No.1 is automatically used to pump sludge.

The PLC will start the pump for an operator selectable amount of time (set through the PCMS). The PLC will start the pump based on time or total plant flow, which­ever occurs first. These set points for flow or time will be operator selectable through the PCMS.

When the PLC detects that Primary Clarifier No. 2 is On, Primary Sludge/Scum Pump No.2 will be used to pump sludge and will operate in the same manner as pump No.1, as described above.

If the PLC detects that both primary clarifiers have an On status, Primary Sludge/Scum Pump No.1 will automatically be used to remove sludge from Primary Clarifier No. 1 and Primary Sludge/Scum Pump No.2 will be used to remove sludge from Pri­mary Clarifier No.2. The automatic sludge removal cycle will be the same as described above. The PLC will not allow both primary sludge/scum pumps to pump sludge from two clarifiers at the same time.

When Primary Clarifier No. 1 is in operation, Primary Sludge/Scum Pump No. 2 is used to pump scum in the HAND mode from a local station at Primary Clarifier No. 1. For the scum pump to be operated from the local push-button station, the HOA switch must be left in the HAND position. (Note that in other applications the HAND position actually starts the equipment.)

Normally, the operator will go to the Clarifier No. 1 scum pit and open the air valve to mix the scum. He will then start Primary Sludge/Scum Pump No. 2 using the Start-Stop buttons at the scum pit. When the scum pit is emptied, the operator will stop the pump and close the air valve.

With only Clarifier No. 2 in operation, Primary Sludge/Scum Pump No. 1 will be used to pump scum, as described above for Clarifier No. 1.

To pump scum with two clarifiers in operation, the operator must first switch the HOA switch at the HCP from AUTO to HAND for one of the pumps. The valving in the pump room must then be changed so that the pump suction is from the scum pit. The operator will then open the air valve at the scum pit to mix the scum. Scum/Sludge Pump No. 1 must be started and stopped at the control panel located at the Clarifier No. 2 scum pit. Sludge/Scum Pump No. 2 must be started and stopped at Clarifier No. 1.

After scum pumping is completed for one clarifier, the valving in the pump room must be changed back so that the pump suction is from the clarifier sludge hopper, and the pump must be placed back in the AUTO mode. This procedure can then be re­peated for the other clarifier.
Fault Conditions
A high-pressure switch on the discharge of each pump will stop the associated pump whether in the AUTO or HAND mode of operation. This situation will result in an alarm signal to the PLC and the control panel failure alarm annunciator. The RESET button on the local control panel will restart the primary sludge/scum pump.

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Last Updated: 9/16/2013 9:09:39 AM
Version 4.0.1