Section 10 - Influent Pumping

This section tells the operator how to interact with the PLC and the SCS, describes each control loop and describes how and where alarm and equipment status is transmitted.

10.03.b.1. Influent Wet Well Gate

Operation:

1. The wall penetration for the incoming 60 inch raw sewage pipe is provided with a motorized sluice gate that allows the operator to isolate the wet well. To open or close influent gate G-01000, use handswitch HS-01000. The influent gate can be opened or closed only at the wet well. There is no remote operational capability available.
   
   
2. Switch ZS-01000 shows the position of the gate (either open/closed). Sensor ZI-01000 monitors the position of ZS-01000 and sends this information to the PLC. If ZI-01000 shows that the gate is closed, the PLC initiates alarm QA-01000 which is displayed on LCP-01 and the SCS located in the Operator Laboratory and in the Administration Building. If this alarm occurs during the period when the plant is unoccupied, the critical alarm dialer will call out this alarm. The gate must be reopened to reset the PLC/SCS.

10.03.b.2. Influent Wet Well

Operation:

1. Ultrasonic level sensor LE-01030 monitors the wet well level. The signal from LE-01030 is sent to LIT-01030 which sends the level reading as an analog input to the PLC. The wet well level is shown on LCP-01 as LED bar graph LI-01030 and on the SCS located in the Operator Laboratory and in the Administration Building.
   
   The PLC uses the wet well level input from LE/LIT-01030 to set the influent pump speed and wet well setpoints (see section 10.03.b.3.).
   
   
2. Level floats LSH-01031 and LSL-01032 send high and low wet well alarms LAH-01031 and LAL-01032 to the PLC. LAH-01031 is displayed on LCP-01 and on the SCS. LAL-01032 is displayed only on the SCS. If the high wet well alarm occurs during the period when the plant is unoccupied, the critical alarm dialer will call out this alarm. To reset the PLC/SCS after alarm LAH-01031, the wet well level must fall below 16.5', To reset after alarm LAL-01032, the wet well must rise above 10.75'.
   
   
3. LEL gas sensor AE-01020 monitors LEL levels in the wet well. Transmitter AIT-01020 sends the LEL signal to the PLC. When the LEL level exceeds 4.5%, LEL alarm module ASM-01020 sends warning alarm AAM-01020 to the SCS located in the Operator Laboratory and in the Administration Building. To reset the PLC/SCS the LEL level in the wet well must fall below 4.5%. If the LEL continues to rise and exceeds 10%, LEL alarm module ASH-01020 sends LEL high level alarm AAH-01020. This alarm is displayed on LCP-01 and on the SCS. In addition, the LEL horn and beacon located at the wet well will be activated. Press the horn alarm silence button HS-01020 located at the wet well to silence the alarm horn. Reset the PLC/SCS by acknowledging the alarm condition at LCP-01.

1. The two small and two large influent pumps function together in a LEAD-LAG configuration. When both pumps of each pair are placed in REMOTE using the HOR handswitch, the first pump placed in REMOTE becomes the LEAD pump. LEAD pump designation can be changed using a SCS CRT handswitch (HS-01040A for pumps P-01041 and P-01042; HS-01040B for pumps P-01043 and P-01044). When all four pumps are placed in the REMOTE mode, influent pump sequencing and control is directed through the PLC/SCS system. The operator uses the SCS CRT to select either AUTO or MANUAL mode. In AUTO mode, the wet well level controller (LIK-01030) controls the level setpoint and pump speed. The setpoint cannot be adjusted through the SCS CRT. One of three wet well setpoints is automatically set based on the number of pumps running (one small; two small; one small and one large). In MANUAL mode, the operator may set the speed of the pumps and individually start and stop pumps through the SCS CRT. The operator may select to run one small pump, one large pump or a maximum of one large and one small pump.
   
   The pumps are sequenced automatically when in the AUTO mode. The operator may choose from one of two modes, SMALL-SMALL and SMALL-LARGE, through the SCS CRT. The PLC starts and stops pumps based on the level in the wet well and the output of the wet well controller (see Tables 1 and 2 in Section 10.04.a. General Operating Strategy). The level controller varies the speed of the pumps to match the plant influent flow.
   
   
2. In the event a pump fails while the HOR handswitch is in REMOTE, a pump fail signal is sent from the AFD panel to the PLC. The PLC generates a RUN FAIL alarm (QA-0104X) which is displayed on the SCS located in the Operator Laboratory and in the Administration Building. To reset the PLC/SCS, set the HOR handswitch to OFF. In the event that all pumps shut down and cannot be restarted by the PLC, the PLC sounds alarm QA-1040 (all PUMPS OFF). This alarm is displayed on LCP-01 and the SCS. If this alarm occurs during the period when the plant is unoccupied, the critical alarm dialer will call out this alarm. To reset the PLC/SCS, an Influent Pump must be started. If the operator is running a pump in HAND and the pump fails, the PLC will generate a LOCAL FAIL alarm. This alarm is displayed at the AFD panel as well as on the SCS. Set the HOR handswitch to OFF to reset the PLC/SCS system.

The level in the wet well is controlled by a PID type loop controller. The level controller output is used to vary the speed of the influent pumps. The level controller uses proportional only action, since an exact level setpoint does not need to be maintained. This allows the level of the wet well to vary above the level setpoint and absorb changes in influent flow. The level controller has three different gains and setpoints that are automatically set by the PLC depending on which combination of pumps is running. See Tables 10.04.a.1. and 10.04.a.2. for gain settings.

In REMOTE mode, each pump can be started and stopped and pump speed can be adjusted by the PLC/SCS system. The two small influent pumps and the three large influent pumps function in sets in a LEAD, BACKUP or LEAD, LAG, BACKUP configuration. If both or all three pumps in a set are selected to REMOTE, the first pump placed in REMOTE is the LEAD pump. The LEAD pump may be changed by operations using the SCS CRT button on the Influent Pumping screen. If the LEAD pump fails, the LAG pump is started if it is in REMOTE. In LEAD, LAG, BACKUP configuration, if a LEAD or LAG pump fails, the BACKUP pump starts if it is in REMOTE.

There are three modes of REMOTE influent pump sequencing and control; AUTO,MANUAL, and SIMULATE. The mode selected is used for control of all five influent pumps. There is level control information for AUTO control and SMALL/SMALL and SMALL/LARGE sequencing, a MANUAL control screen for each pump, and a SIMULATE mode at the SCS CRT. When in AUTO mode, the level controller will indicate the setpoint and the current pump speed. The setpoint cannot be adjusted through the SCS CRT. One of the three setpoints is automatically set based on the number of pumps running. The manual control screen can be used to adjust individual pump speeds in the MANUAL mode. The SIMULATE mode is available for controlling pump speed based on a simulated wetwell level, such as when level transmitter maintenance is performed. The PLC/SCS is programmed for bumpless transfer between modes. Current pump speed is maintained when modes are changed. The number of pumps running may be changed to satisfy AUTO control requirements when pump control is selected to AUTO.

When selected to MANUAL mode, the operator may set the speed of the pumps and individually start and stop the pumps through the SCS CRT. From the SCS CRT, the operator may start any combination of pumps except those specifically prevented. This software interlock is provided so that the plant capacity is not exceeded.

The pumps are sequenced automatically when selected to AUTO mode. There are two pump sequencing configurations in AUTO; 2 SMALL & 2 LARGE and 1 SMALL & 3 LARGE. The pumps sequences are selected by the PLC based on the level in the wet well and the output of the level controller as indicated in Tables 10.04.a.1. and 10.04.a.2.. The operator may also manually select the sequencing configuration through the SCS CRT. The pump sequencing and control have been set up to use the most efficient speed range of the pumps and minimize flow transients when changing pump combinations.

The speed of the pumps is varied by the level controller to match the influent flow. As mentioned above, the gain and setpoint of the level controller is changed based on which combination of pumps are running.

When operating in the 2 SMALL & 2 LARGE sequencing configuration, if one of the small influent pumps fail or is taken out of REMOTE mode, the sequencing mode will automatically switch to the 1 SMALL & 3 LARGE sequencing mode.

If the pumps are running in either MANUAL or AUTO mode and the level decreases to the low-level float, the pumps will stop. This interlock automatically resets when the level in the wet well rises to the "start SMALL lead pump level". If the pumps are not running or if the pump speed is not adequate to keep up with the influent flows and the level increases to the high level float, one large and one small pump in REMOTE will start at maximum flow capacity. The pumps will again stop at the low float level.

Note: Normal plant operations will use the PLC and the SCS CRT to enter setpoints, select equipment operating modes and monitor equipment status. If a process can be controlled manually through the SCS CRT then this will also be included in this section. Local control of equipment will be covered under section 10.04.c. Alternate Operating Conditions.

10.04.b.1. Influent Wet Well Gate (also see Section 10.03.b.1.)

The operator can open and close the Influent Wet Well Gate only at the wet well. This gate cannot be opened or closed using the SCS CRT. However, the position of the gate, either opened or closed, is monitored by the PLC and this information can be called up on the Influent Pumping Overview screen. Except when cleaning the trash rack or inspecting the wet well, the gate will be left open. If the gate is closed for any reason, an alarm will sound. Equipment Status Table 10.04.b.1. summarizes the proper equipment configuration for normal plant operation.

10.04.b.2. Influent Pumps (also see Section 10.03.b.3.)

The influent pumps can be run either in MANUAL, SIMULATE or AUTO through the PLC/SCS system. These SCS CRT controls are located on the Influent Pump Controller screen. From this screen, the operator can select either AUTO, MANUAL or SIMULATE modes, the pump configuration (2 SMALL & 2 SMALL or 1 SMALL & 3 LARGE) and the LEAD, LAG, BACKUP pump for each set of pumps. In AUTO the PLC controls the speed of the influent pumps based on the Wet Well level. In MANUAL the operator sets the pump speed and must monitor the Wet Well level. In SIMULATE, the operator sets a simulated wetwell level to maintain a pump speed and configuration while the level transmitters are being serviced. The operator uses the SCS CRT controls located on the Influent Pump Control screen for manual control of pumps and Wet Well level information. Equipment Status Table 10.04.b.2. summarizes the proper equipment configuration for normal plant operation.

Note: This section covers plant operations when the PLC has failed and the SCS CRT cannot be used as described in section 10.04.b. All equipment control and monitoring is done locally either at the MCC, the AFD panel or the local panel.

10.04.d. Startup/Shutdown Conditions

• Influent Wet Well
• Influent Pumps

10.04.e. Key Control Data and 4 Level Alarm Table

10.04.f. Contingency Plans

A contingency Plan is written to handle an unpredictable occurrence that has a reasonable chance of happening. Most Contingency Plans deal with situations where having a written procedure can help prevent loss of a unit process, handle a process upset or respond to a hazardous situation. The following is a list of Contingency Plans developed for the Influent Pumping process. The plans are kept in the Contingency Plan Notebook located in the Operator Laboratory and the Shift Supervisor Office.

• High LEL Level Measured in the Influent Wet Well
• Loss of ATS Odor Removal from the Influent Wet Well

10.04.g. Standard Operating Procedures

A Standard Operating Procedure (SOP) is written to handle operator activities performed on a regular but not necessarily daily basis. Most SOPs deal with potentially hazardous activities making it important that a written, step-by-step procedure be available. The following is a list of SOPs developed for the Influent Pumping process. The procedures are kept in the SOP Notebook located in the Operator Laboratory and the Shift Supervisor Office.

• Cleaning the Influent Wet Well Trash Rack

10.05. Troubleshooting

See Section 75 Maintenance Plan for troubleshooting dealing with the operation of the influent pumps, influent wet well gate valve and the level sensors located in the influent wet well.

10.06. Safety

Proper lockout procedures are to be followed any time the influent pumps are serviced.

10.07 Records/Sampling