PROCESS COOLING WATER SYSTEM

3.8.4.4 OPC watchdog

In the Fieldbus-end a flexible function block including a watchdog timer will be employed to detect an OPC link failure. The strategy will utilize a scheme where a discrete value is received on one parameter, toggled, and written to another. If the signal being received is not toggled within a certain configurable timeout, the OPC link can be considered broken and failsafe action will be initiated.

3.8.5 Block Access

This application uses standard, custom and fixed-OD flexible function blocks. Therefore no user-selectable parameter sets apply.

3.9 PROCESS COOLING WATER SYSTEM

Pump failure alarm from the frequency drive.

Each of the pump drives has redundant HSE stacks. The two HSE inputs go to a signal selector which selects the first good signal as the cascade input to the drive speed control.

The primary pressure controller is PC-100 is located in PIT-100 or in the linking device, PX-100. Constant PCW discharge header pressure is maintained by varying the pumps speed. Operational pumps should share the load equally. If two pumps are unable to maintain the pressure setpoint, the standby pump will automatically be started by the FFB in the linking devices and an alarm generated to alert the operator.

If PIT-/ PC-100 fails, control automatically switches to end of loop pressure transmitter and controller, PIT-101/PC-101. The pressure at PIT-101 will be different from PIT-100 due to pipe losses and elevation differences. To maintain a stable process, the setpoint of PC-101 will be the pressure at PIT-101 at the time of failure. Each transmitter will monitor each other’s status and initiate the control transfer on bad or uncertain status of the other. An alarm is generated at the time of control switch over to alert the operator.

Local H-O-A switches in the variable frequency drive cabinets allow local control. When the H-O-A is not in the Auto position, an alarm is generated to alert the operator. When the H-O-A is in Hand, the pump speed can be varied locally at the variable frequency drive console. Automatic control is overridden.

The pumps drives have hard wire interlocks from the PCW Receiver Low-Low level switch, LSLL-100, to shutdown the pumps at low-low level whether in automatic or local manual control.

3.9.4 Process Cooling Water Temperature Control

The PCW is cooled by two parallel heat exchangers, HEX-100A and HEX-100B. Both exchangers are normally online. However, each exchanger is sized to maintain the full system load if the other must be taken out of service

The primary temperature controller is TC-100 located in TIT-100 which controls TV-100A and TV-100B so that they are equally open.

Chilled water, CHW, at 40 degrees F is circulated on the tube side. Flow is varied to maintain a discharge PCW temperature of 65 degrees F. The two heat exchangers should share the load equally.

If TIT-100/ TC-100 fails, control is automatically switched to the backup temperature controllers, TC-100A and TC-100B by the input selector switches, TS-100A and TSD-100B. The temperature setpoints will remain at their last value on failure of the primary controller.

An alarm is generated at the time of control switch over to alert the operator.

The system is also able to continue to function on a single heat exchanger control if one of the inner loops fails. The failed loop control valve will maintain its last setting on failure of the transmitter or controller.

Local H-O-A switches allow individual local control of each heat exchanger. When the H-O-A is not in the Auto position, an alarm is generated to alert the operator. When the H-O-A is in Hand, the CHW flow through the heat exchanger can by varied by an adjacent manual loading station. Automatic control is overridden.

3.9.5 Variable Frequency Drives Monitoring

As a minimum, the following points will be visible, on demand, to the operator in the central control room:

• Motor speed (RPM) or Output frequency

• Output Voltage

• Output current

• Run status

• Major fault status

• Minor fault status

• Current fault condition

• Last fault condition

• Second to last fault condition

• Third to last fault condition

• Fourth to last fault condition

• Motor FLA current setting

• H-O-A Not-in Auto

Both a motor fault and the H-O-A switch not in Auto will generate alarms.

Tk-100

Process n Process 3 Process 2 Process 1

100 LSLL 100 LSHH

100 LIT 100

LAHH

100 LALL 100 LV 100 LC

Pretreated Makeup Water

Tk-100 Process Cooling Water Receiver

ON/OFF Level Controller Flexible Function Block

100 LI

Process Cooling Water

101 TIT

101 PIT 101 PC

P-100A

100A1 PI

100A2 PI

M

P-100B

100B1 PI

100B2 PI

M

P-100C

100C1 PI

100C2 PI

M

100 I

HEX-100A

100A TV

100A/2

TI 100A/1

TI

CHWR

CHWS

100/1 TIT

HEX-100B

100B TV

100B/2 TI

100B/1 TI

101 TI 100

TI

100 PIT

100 FIT 100 FI 100

PI

100 PX

100B HIC 100A HIC

100 PC 100/1

TC

PX-100/101 H1/HSE LINK

FLEXIBLE FUNCTION BLOCK FOR PUMP STANDBY/AUTO START AND ROTATION

100C SIC 100B SIC 100A SIC

VARIABLE FREQUENCY DRIVE WITH NATIVE REDUNDANT HSE STACKS AND SIGNAL SELECTOR

100 TIT 100 TC 100A

TIT 100A

TC

100B TIT 100B

TC

101 PX 101

PI

100 HOA

100A TS

100B TS

HSE - 1

HSE-2

VARIABLE FREQUENCY DRIVE WITH NATIVE REDUNDANT HSE STACKS AND SIGNAL SELECTOR

VARIABLE FREQUENCY DRIVE WITH NATIVE REDUNDANT HSE STACKS AND SIGNAL SELECTOR SW1

HSE

SW2 HSE 3 PORTS 1 FOR EACH DRIVE

3 PORTS 1 FOR EACH DRIVE

100A SS

100A TS

100B SS

100C SS