Operation and Control

Process control for the CAC system is provided primarily by the CP-200 control panel located in the CAC operating area with duplicated remote operation monitoring and control of essential functions at the PCS. The essential functions were set up with the operations staff during plant commissioning but can be modified during the life of the plant since the CP-200 and PCS have an ethernet connection with capability to path additional functions. Individual CAC units may be taken OUT OF SERVICE or placed IN SERVICE at the CP-200 Operator Interface Terminal (OIT) or PCS. Taking a CAC unit OUT OF SERVICE shuts down all of the associated equipment and instrumentation, closes all associated flow control valves, as well as disables all alarms from the selected unit. Conversely, if a CAC unit is placed IN SERVICE, all the equipment, instrumentation, flow control valves and alarms are enabled for operation.

Each CAC unit may be manually placed in service from the CP-200 OIT or PCS as described above. There are three (3) valves for each CAC unit to control operations; RW, TW, and ALP. At the beginning of a clarification cycle with “clean” bead media, the Effluent FCV will open and the Influent FCV will modulate to produce a constant flow into the unit based on a flow rate set point and the individual CAC inlet flow meter. The flow setpoint is the RW flow rate input by the operator or calculated by the RW pump combinations selected by the PCS and then divided by the number of CAC units in service. Pressure control on the RW pipeline entering the plant is the primary variable used to modulate RW valves and ensure that water is allowed to proceed into the CACs. The setpoint for RW pressure control is an operator setpoint. There is an operator variable that can also be input to keep the RW valves 100% open on a timer.

The pressure variable along with a timed holding of RW valves open upon start-up of the RW pipeline is intended to protect against over-pressure in the pipeline. As the bead media removes and accumulates solids during clarification, headloss will increase in the tank. Upon reaching a preset level, the high-pressure switch will close and automatically begin a flush (backwash) cycle or allow the operator to initiate the flush when in semi-automatic mode. A programmed timer is another way of automatically initiating flush cycles. A second high-pressure switch is a safety feature to completely shut down the unit if its pre-set level is reached. During a flush cycle, the CAC control panel will open the RW FCV as needed to provide the minimum required flush flow through the unit and continue dividing RW flow into the remaining on-line CAC units.

Clarification Mode

Local Control:

Manual or HAND operation requires manual initiation of each step of the CAC sequence.  Each of the valves has an (OPEN / CLOSE / AUTO) switch. The RW FCV and TW FCV are utilized in Clarification Mode. When the plant is OFF, and a CAC is selected for IN SERVICE, the RW FCV shall remain open. With no raw water being pumped to the plant, the water in the RW piping will not flow into the CACs. There is a check valve on the RW piping to the CAC to prevent draining of the units if the plant’s raw water line drains back. When a CAC is selected for OUT OF SERVICE, the RW FCV shall close, whether the plant is ON or OFF, preventing water from flowing into the CAC. HAND operation of CAC Clarification Mode is not routinely anticipated and will only be used during an emergency.

• To operate a CAC in HAND mode, the operator shall first switch the CAC to IN SERVICE, opening the RW FCV and TW FCV.
• When the (OPEN / CLOSE / AUTO) switch is in the OPEN position on the RW FCV, the valve shall open slowly.
• When the RW FCV is placed OPEN by HAND, the FCV shall still be automatically controlled by the CP-200 or PCS using RW flowrate and dividing it into the CACs, so as not to overfeed the units or overpressure the RW pipeline.
• When the TW FCV is placed open by HAND, it will be fully open.

CP-200 and PCS Control:

Automatic operation is initiated once a CAC is placed IN SERVICE and the PCS initiates a PLANT RUN sequence. During normal operation, the individual CACs are controlled by the CP-200 PLC. Each CAC is placed either IN SERVICE or OUT OF SERVICE. Upon PLANT RUN, the IN SERVICE CACs already have their RW FCVs open with a timer holding them 100% open initially, allowing RW into the CACs and then shall modulate based on the RW flow rate and number of CAC units in service. The valve position (% open) is continuously monitored by the CP-200 and PCS. The TW FCV shall open fully.

• During Clarification Mode, the CP-200 PLC shall open RW FCVs to maintain the allowable RW pipeline setpoint pressure and continually modulate the RW FCV to maintain an evenly divided RW flowrate over the CAC units. Four individual flow meters on the RW feed to each CAC unit is monitored for feedback information to modulate the RW valves.
• The RW Turbidimeter and pH analyzers shall continually measure the combined CAC influent. A TW Turbidimeter shall continually monitor combined CAC effluent. The instruments are monitored and trended by the PCS.
• The Run Time is continually recorded for IN SERVICE CACs prior to a flush and displayed in HOURS of operation for units during PLANT RUN.
• The individual CAC flow rate is calculated for each IN SERVICE CAC. This is a measure of the RW Flow meter rate (in gpm) from each CAC RW pipe for CACs that are IN SERVICE.
• During PLANT RUN, the PCS shall totalize the flow to each CAC by taking the RW Flow Meter data from each of the CACs IN SERVICE. The Unit CAC Run Volume or accumulated value is calculated for each IN SERVICE CAC at the completion of a CAC run prior to flush of that CAC. This is a measure of the total water treated by the CAC during Clarification Mode.

Flush Mode

Flush Sequence

The following sequence occurs on the initiation of Flush in either manual, semi-automatic, or automatic modes. The same steps should be taken in any mode to complete a CAC flush. In semi-automatic mode, the operators will be notified of the need to flush based on bed loss or the timer and they will need to start the flush. Automatic flush mode will allow the flush to occur when head loss or the timer dictates without any further input. Manufacturer provided timed flush intervals are 0-24 hours and the bed loss setting is 6 feet.

1. Close the RW FCV and TW FCV. Water remaining in trough will drain to waste.
2. Open the ALP FCV and start two Air Blowers. Start timer is programmed in CP-200 PLC. Bed expansion with air can range from 0-180 seconds.
3. Open the RW FCV for bed flush with air and water. Water level rises to overflow into the trough to the BWW discharge. Flow continues for a 0-10 minute setting duration programmed in CP-200 PLC.
4. Close the RW FCV for bed leveling. Allow air to re-level the media for 30-45 seconds.
5. Close the ALP FCV and turn off Air Blowers. Allow an off-line period for the media to return to its normal depth. Keep CAC off-line for another 30-40 seconds.

Monitor the position of the respective CAC valves and alarm after an appropriate time delay if a valve is not in the correct position for the current automatic mode. If at any time during the Flush sequence a control device such as a valve fails to respond to the command of the Flush sequence within a preset time, a FAIL alarm is indicated for that CAC.

The CAC Blowers (B-200-1, B-200-2 and B-200-3) are controlled from the PCS. However, the start/stop commands are initiated by the CP-200 PLC and transferred to the PCS and the MCC where motor starters are located. Likewise, the status of the blowers (run, fault, current) is transferred from the MCC motor starters to the PCS to the CP-200 PLC.

Local Control:

Manual or HAND operation requires manual initiation of each step of the flush sequence. HAND operation of Flush Mode is not routinely anticipated and will only be used during an emergency. Automatic operation is more efficient and has less risk for equipment damage when the manufacturer programming is used.

• The RW FCV, and TW FCV’s are positioned for Flush Mode. Each of the valves has an (OPEN / CLOSE / AUTO) switch on the CP-200 OIT.
• When a CAC is placed OUT OF SERVICE manually, the RW FCV will automatically close.
• To initiate an Air scour of the media, Air Blowers can be manually started and the CAC ALP FCV will also be manually placed in OPEN to route air to the CAC.
• To initiate the water flush, the RW FCV is OPEN and modulates to maintain the required flow setting based on the RW flowmeter for the CAC being flushed.
• After water flushing is complete, the RW FCV is in the CLOSED position.
• Air is continued to be applied to re-level the media.
• Upon completion of those steps the ALP FCV will return to CLOSE and the Air Blowers are OFF.

CP-200 and PCS Control:

During normal operation, Flush Mode is initiated automatically by one of three conditions previously discussed, and the Flush Mode sequence can be accomplished automatically or semi-automatically. All valves for an IN SERVICE CAC must be in AUTO at CP-200. The detailed Flush Mode sequence was described previously in this section. There are additional operator controls available for flushing.

• A START Flush switch on the CP-200 OIT is used for manual initiation of a Flush sequence in each CAC. This switch is used in semi-automatic mode or any time a flush is desired.
• A HOLD Flush switch on the CP-200 OIT is used for manual delaying of a Flush cycle in each CAC. This switch will be off to allow automatic and semi-automatic modes.
• A CANCEL Flush switch on the CP-200 OIT is used for cancelling a Flush cycle in each CAC.

Clarify-to-Waste Mode

Local Control:

Manual or HAND operation requires manual initiation of each step of the waste sequence, and may be used if operators feel a CAC is not performing. Instead of wasting, operators would likely manually initiate a Flush. Each of the valves has an (OPEN / CLOSE / AUTO) switch on the CP-200 OIT. The RW FCV and TW FCV are utilized in waste mode. The RW FCV is OPEN while the TW FCV will CLOSE. HAND operation of waste mode is not routinely anticipated and will only be used during an emergency.

CP-200 and PCS Control:

Upon completion of a flush, the normal CAC operation will utilized a timed waste sequence to allow initial higher turbidity to decrease as the bed returns to a normal service condition. The waste sequence setpoints and timers are available at CP-200.

1. Open the RW FCV and maintain the TW FCV closed. Water proceeding through the CAC will overflow into the trough and out through the BWW pipe. Operator setpoint range for this mode is 0-10 minutes
2. Open the TW FCV and return to clarification service.

CP-200 / HMI Configuration:

• Status Display:
  • CAC IN SERVICE / OUT OF SERVICE switch indication (each).
  • Unit mode AUTO / SEMI-AUTO / MANUAL switch indication (each)
  • Unit Status IN SERVICE / FLUSH DELAY / FLUIDIZATION / BED LEVELING / BED SETTLING / RINSE TO WASTE / OUT OF SERVICE.
  • FLUSH INHIBIT switch indication (each)
  • CAC HIGH pressure switch position (CLOSED) (each).
  • CAC HIGH-HIGH pressure switch position (CLOSED) (each).
  • RW FCV position (% OPEN) (each).
  • Air inlet valve OPEN / CLOSED switch position (each).
  • Effluent valve OPEN / CLOSED switch position (each).
  • CAC Run Time (each).
  • CAC RW Flowrate (each).
• Operator Entries:
  • Number of units to run setpoint.
  • Minutes to hold the CAC valves at 100%.
  • Flush Interval duration timer setpoint.
  • Flush Start delay timer setpoint.
  • Flush Start.
  • Flush Cancel.
  • Blower START/STOP selection.
  • Bed Expansion duration timer setpoint.
  • Flush duration timer setpoint.
  • Bed Level duration setpoint.
  • Bed Settle duration setpoint.
  • Rinse to Waste duration setpoint.
  • Flush Flow setpoint.
  • CAC AUTO / SEMI-AUTO / MANUAL switch (each).
  • RW FCV switch (% OPEN / AUTO) (each).
  • TW FCV switch (OPEN / CLOSED / AUTO) (each).
  • ALP FCV switch (OPEN / CLOSED / AUTO) (each).
• Alarms:
  • Backwash Required (each).
  • CAC High Pressure (each).
  • CAC High-High Pressure (each).
  • CAC Flush Cancelled (each).
  • Flush INHIBIT (switch position, when other CAC is flushing, or low RW flow) (each).
  • RW FCV FAIL (each).
  • TW FCV FAIL (each).
  • ALP FCV FAIL (each).
  • Air Blower FAIL (each).
• Historical Trending:
  • RW pipeline Pressure
  • RW FCV position (each).
  • TW FCV Open Time (each).
  • CAC Run Time (each).
  • CAC Flushing Flow Rate (each).
  • CAC Clarifying Flow Rate (each).

PCS / HMI Configuration:

• Status Display
  • CAC IN SERVICE / OUT OF SERVICE switch indication (each).
  • Call to Run indication (each).
  • Setpoint based RW flow.
  • CAC HIGH pressure switch position (CLOSED) (each).
  • CAC HIGH-HIGH pressure switch position (CLOSED) (each).
  • RW valve %OPEN / CLOSED switch position (each).
  • Air inlet valve OPEN / CLOSED switch position (each).
  • TW valve OPEN / CLOSED switch position (each).
  • CAC Run Time since last flush (each).
  • CAC RW Flowrate (each).
  • Plant RW Flowrate (from Raw Water Pumping Process Control Narrative)
  • RW Turbidity indication (from Raw Water Pumping Process Control Narrative).
  • RW pH 1 indication (from Raw Water Pumping Process Control Narrative).
  • Air Blower status (RUN / OFF).

• Operator Entries:
  • Number of units to run.
  • Minutes to hold the CAC valves at 100%.
  • Setpoint based RW flow.
  • CAC IN SERVICE / OUT OF SERVICE switch (each).
• Alarms:
  • Common Alarm CP-200
• Historical Trending:
  • RW FCV position (each).
  • TW FCV Open Time (each).
  • CAC Run Time (each).
  • CAC Flushing Flow Rate (each).
  • CAC Clarifying Flow Rate (each).
  • RW Turbidity (from Raw Water Pumping Process Control Narrative).
  • RW pH 1 (from Raw Water Pumping Process Control Narrative).
  • RW pH 2 (after chemical addition).
  • Plant RW Flow (from Raw Water Pumping Process Control Narrative).
  • TW Turbidity.