Circulating Water System

Circulating Water System
Industrial Resources, Inc. Big Cajun Power Plant Circulating Water System This module contains information pertaining to the Circulating Water System. A typical Circulating Water System and its associated controls are described within this module. This presentation is designed to provide you the information you need to understand and operate the Circulating Water System. You should view all slides and read and study the information presented. The presentation slides are advanced by clicking on the button. You can also advance to a selected section by using the topic buttons..

In this module we will: Describe the function of the Circulating Water System. Describe the flow paths and major components associated with the Circulating Water System. Describe the Circulating Water System process control loops and associated methods of control. Describe the steps required to prepare for and startup the Circulating Water System. Describe the steps taken during normal operation of the Circulating Water System. Describe the steps required to shut down the Circulating Water System. In this module we will: Describe the function of the Circulating Water System. Describe the flow paths and major components associated with the Circulating Water System. Describe the Circulating Water System process control loops and associated methods of control. Describe the steps required to prepare for and startup the Circulating Water System. Describe the steps taken during normal operation of the Circulating Water System. Describe the steps required to shut down the Circulating Water System.

Circulating Water System Function
Here you see the “typical circulating water system. In this section we will discuss the function and flowpath of the Circulating Water System.

The Circulating Water System Condenses Low Pressure Turbine Exhaust Steam.
Main Steam Cold Reheat Steam Hot Reheat Steam LP Turbine Exhaust Condenser Circulating Water Inlet Circulating Water Outlet Condensate Pump Hotwell The Circulating Water System provides the Main Condenser with cooling water to remove latent heat from the LP turbine exhaust steam and condense the Exhaust Steam into water droplets. Circulating Water flows through the tubes of the condenser, while LP Turbine Exhaust flows to the condenser shell. The condensed water droplets collect in the hotwell and provide the suction supply to the Condensate Pump. In some cases the Circulating Water System also supplies cooling water to Auxiliary Condensers and Heat Exchangers for cooling.

After absorbing heat from the LP Turbine Exhaust steam, the heated Circulating Water returns to the Cooling Tower where the heat is released to the atmosphere via evaporation. Cooling Tower

Flow Path Cooling Tower Basin Condenser Circ Water Pump
Here you see a very simplified flow diagram of the Circulating Water System. As you can see, Circulating Water is drawn by the Circulating water pump from the Cooling Tower Basin. The water is pressurized by the pump and discharged through supply piping to the tube-side of the Condenser. After removing heat from the condenser, the circulating water routes through the return line back to the cooling tower where latent heat is removed. The cooled circulating water falls to the basin.

Circulating Water System Flow Path
Here you see a little more detailed version of the flow diagram. In this diagram, you can see that there are some additional components and valves added to the cycle. Once again, the Cooling Tower Basin acts as the suction supply to the Circulating Water Pumps. The suction supply is strained by the inlet screen prior to entering the Circulating Water Pump suction header. The Circulating Water Pump Suction header supplies the inlet demands of two separate Circulating Water Pumps. Each Circulating Water pump draws Circulating Water through its associated motor operated suction valve. The Pump increases the pressure of the Circulating Water. The pump discharges through its associated motor operated discharge valve to its Circulating Water Supply Line. A motor operated Discharge Cross Tie Valve is provided to connect the discharge flows from each pump. The Circulating Water Supply Lines route the circulating water to the motor operated Condenser Waterbox Inlet Valves. This condenser is divided into north and south sides. Each Waterbox Inlet Valve, when open, allows cool circulating water to enter its associated side of the condenser. The Circulating water flows through the tube side of the condenser while LP turbine exhaust steam (at saturation temperature) enters the shell side of the condenser, contacting the tubes. The temperature of the circulating water is approximately 75 degrees Fahrenheit. The temperature of the LP Turbine Exhaust Steam is approximately 110 degrees Fahrenheit. This differential temperature allows for latent heat to transfer from the exhaust steam, through the tube metal, and to the Circulating Water. The Circulating Water exits its associated condenser tube side through the designated motor operated waterbox outlet valves. The Circulating Water Return Lines join to form a single return line, routing the warm circulating water (approximately 90 degrees Fahrenheit) back toward the Cooling Tower. Flow through the return line flows through risers that direct the circulating water to the top of the Cooling Tower.

Cooling Tower Water enters the top of the Cooling Tower as illustrated here. The water entering the top of the tower flows through nozzles and is broken up into droplets by the nozzles and as it falls through cooling tower fill. Large Fans, arranged along the top of the cooling tower, draw air in through the louvered sides of the cooling tower. The air makes direct contact with the water droplets, and by evaporation, cools the circulating water. The cooled circulating water collects in the basin located below the Cooling Tower.

Circulating Water System Data
Here you see a Circulating Water Control System Graphic. This particular graphic provides information pertaining to equipment operating status and indicates the condition of key process variables. Equipment operating status is indicated by the “color” of the equipment displayed on the graphic. The Circulating Water Pumps and Cooling Tower Fans are operating since their component icons are displayed in “red”. Were am equipment icon to be “green”, the associated piece of equipment would be “off”. Motor Operated Valve icons in “red” are OPEN. If a valve icon is “green” , the associated valve is CLOSED.

Review Questions What is the function of the Circulating Water System?
Click to Review What process is used to realease the heat from the Circulating water in the Cooling Tower? Click to Review How is the Circulating Water cooled as it flows through the Cooling Tower? Click to Review When you are sure you can correctly answer these question click the Button to continue

Circulating Water Pumps
Major Components Condenser Circulating Water Pumps Cooling Tower In this section we will cover the major components associated with the Circulating Water System. These include: Circulating water pumps The Condenser, and The Cooling Tower.

The circulating water pumps draw water from the cooling tower basin, pressurize it, and pump it through the Condenser where it removes latent heat from the LP Turbine exhaust steam. Each Circulating Water Pump, shown here, is of the vertical centrifugal type, powered by a 6.9 kV Motor.

After flowing through the Condenser, the Circulating water returns to the top of the cooling tower where it is cooled via evaporation and gravity drains back to the basin. Here you see the flow path as illustrated on a DCS graphic. Note the various pressures, temperatures and flows pertaining to system operation with both pumps in service.

Circulating Water Pumps Valves
Here you see a closer view of the Circ. Water Pumps, and their associated 480 Volt motor operated suction and discharge valves. Motor operated valves have an “M” in their status icon. Additionally, you can see the manually operated, open, discharge cross-tie valve. With the discharge cross tie valve open, a single circulating water pump is able to supply both condenser supply lines. This type arrangement is used during low load operation. However, during full load operation, both pumps must be in service. Remember, OPEN valves and operating pump motors are displayed in “red” .

Circulating Water Pumps Data
Here you see a graphic that focuses strictly on Circulating Water Pumps and their associated data. From this graphic, you can see that both the 1A and 1B pump motors are energized as evidenced by the associated “red” status icons. Information pertaining to the Circulating Water Pumps found on this DCS Graphic/display includes: Intake level (measured in percent) Intake level, before the screen (measured in percent) Intake level, after the screen (measured in percent) Circulating Water Pump “A” Operating Status (Green/Off, Red/Running) Circulating Water Pump “A” Stator Temperatures – A, B, and C Phases (measured in DEGF) Circulating Water Pump “A” Thrust Bearing Temperature (measured in DEGF) Circulating Water Pump “A” Upper Guide Bearing Temperature (measured in DEGF) Circulating Water Pump “A” Lower Guide Bearing Temperature (measured in DEGF) Circulating Water Pump “B” Operating Status (Green/Off, Red/Running) Circulating Water Pump “B” Stator Temperatures – A, B, and C Phases (measured in DEGF) Circulating Water Pump “B” Thrust Bearing Temperature (measured in DEGF) Circulating Water Pump “B” Upper Guide Bearing Temperature (measured in DEGF) Circulating Water Pump “B” Lower Guide Bearing Temperature (measured in DEGF) Incidentally, the intake level percentage indicates a bad quality point since it displays “xxx” percent. When a point’s quality is suspect, it is represented as “xxx’. This point quality discrepancy could be due to a malfunctioning instrument, or because intake level is out of the readable range for the instrument. And, the before screen and after screen levels are currently in an alarm state since they are displayed in red.

Condenser Extraction Piping LP Heater Inlet Waterbox Outlet Waterbox
Waterbox Vent Tubes Here we have the Condenser, our next component. The condenser functions to condense steam exhausted from the low pressure turbines. This condenser is a single-pass, shell and tube heat exchanger divided into two (north and south) tube sections. Each tube section consists of an inlet and an outlet waterbox connected by tube bundles. Tube bundles are supported by the Tube Sheet. Circulating water flows through the tube side of the condenser while LP Turbine exhaust steam flows to the Condenser shell. Manhole covers at each inlet and outlet waterbox allow access for tube maintenance. Each waterbox is equipped with a normally open ball/check vent valve to prevent air from being trapped within the waterbox section. The air vents to atmosphere. Typically on a condenser, though not shown on this drawing, relief valves connect to each waterbox section to vent the waterbox to atmosphere in the event of over pressurization. In most cases Manual valves are positioned just upstream of the waterbox relief valves and are locked open to prevent inadvertent isolation of the relief valves. Circ Water Inlet Circ Water Outlet Tube Sheet Hotwell

Condenser Waterbox Valves
Looking at a close-up of the Circulating Water System Graphic, we see that there are motor operated waterbox inlet and waterbox outlet valves. Since the position of these valves are controlled, locally at the valve, the associated motor operators are displayed in “blue”.

Condenser Data DP Indication Circ Water Inlet Temperatures
Operating Data pertaining to the condenser as affected by the Circulating Water System is displayed on this Circulating Water/Condenser Graphic. Here you see a close-up view of this data. Condenser cleanliness is monitored from inlet and outlet temperature indicators and differential pressure indicators between each outlet and inlet waterbox. The maximum allowable differential pressure for this condenser is 20 psig. Should the condenser tubes become fouled with debris or scale, the differential pressure increases. This results in less heat transfer across the tubes and can result in a decreased Waterbox outlet temperatures while waterbox inlet temperatures remain the same. This condition has the potential to increase the operating condenser backpressure. Condenser Backpressure is measured in Inches of Mercury or INHG. Condenser Backpressure

Cooling Tower Cells Risers
Here we see a typical cooling tower. The cooling tower removes heat transferred to the circulating water from the condenser and any auxiliary heat exchangers. This cooling tower is made up of a series of 12 cells. Each cell is evidenced by its fan stack mounted on top of the tower. Circulating water is routed from the condenser to the cooling tower through a return header. The return header branches into two risers at the base of the cooling tower. Each riser supplies a distribution manifold which distributes the water along the top of the cooling tower. Each manifold distributes the water to one side of the 12 cells. Risers

Cooling Tower Here you see a typical Cooling Tower. This Cooling Tower is of the mechanical induced draft, cross-flow type. Circulating water from distribution manifolds, fed by the risers, is distributed into each Cooling Tower Cell through manually adjusted, flow control valves. The flow control valves distribute water flow evenly to each cell, or can be used to isolate individual cells for maintenance. This Crossflow type tower has a fill configuration through which the air flows horizontally, across the downward fall of water. Water to be cooled flows into hot-water inlet basins located atop the fill areas and is distributed to the fill by gravity through nozzles in the floor of these basins. Air movement is vertically drawn by fans upward through the fill, counter to the downward fall of the water. The cooled circulating water collects in the cooling tower basin.

Cooling Tower Fans Cooling Tower Fans Risers Bypass Intake Screen
There are 12 Cooling Tower Fans. Fans on this unit are numbered 1 through 12 with Fan 1 being closest to the screens and Fan 12 being farthest from the intake screens. Each Cooling Tower Fan draws air into its associated cooling tower cell through plywood louvers on each side of the tower. The air flows upward counter to the water flow and removes heat via evaporation by direct contact with the water droplets. Each Cooling Tower Fan is mounted directly above its associated cell. Each fan is housed within a fiberglass shroud which provides a suction nozzle to ensure maximum fan efficiency. Each fan is driven by an electric motor. Each fan motor has a reversing feature for de-icing the cooling tower inlet louvers. When reversed, the fan pulls ambient air through the shroud and passes it through the fill members in a reverse flow path. The air absorbs heat from the cascading circulating water and melts ice on the louvers as it passes out the sides of the tower. During normal operation Cooling Tower fans are placed in service one at a time to control circulating water temperature to a value of approximately 70 degrees Fahrenheit. Bypass Intake Screen

Cooling Tower Basin Makeup Bypass Screen
The tower basin serves as a storage reservoir for the Circulating Water System. The tower basin covers the entire floor area of the cooling tower and is sloped toward the intake structure. A stop gate located in the channel between the basin and the intake structure allows the pump intake structure to be isolated. A screen mounted in the channel between the stop gate and the intake structure prevents debris from entering the pump suction. Bromination, acid and chemical dispersant diffusers in the intake channel distribute water quality control chemicals into the Circulating Water System. Bromine is used to control microbiological growth, acid is used to control pH,l and dispersant keeps solids in solution. A Cooling Tower Bypass line connects the warm circulating water return header with a perforated distribution header which directs the returning water directly into the tower basin. The bypass valve is normally closed and is opened only during startup and shutdown operation, for initial filling or draining of the circulating water loop. The tower basin water level is controlled automatically by a level control valve located in the makeup header between the makeup pumps and the intake channel. Makeup is supplied from the Raw Water System. The tower basin water level is maintained at 5 feet during normal operation. Water is continually removed from the circulating water return header by the cooling tower blowdown system. This system maintains the desired level of suspended solids in the circulating water system by regulating a control valve in response to a conductivity measurement and sends the high solids waste water to the cooling tower blowdown ponds. Bypass Screen

Cooling Tower Data Information pertaining to the Cooling Tower is found on associated Cooling Tower DCS Graphic/display. Here you see a close-up view of the Cooling Tower Data. Information provided includes: Cooling Tower Basin Level (measured in percent) Intake Screen Upstream Level (measured in percent) Intake Screen Downstream Level (measured in percent) Cooling Tower Fans 1 through 12 Operational Status Indication (Red/Running, Green/Stopped) Cooling Tower Fans 1 through 12 direction (FWD/Forward, REV/Reverse) Cooling Tower Fan A/M Status Button Cooling Tower Bypass Valve Position (Red/OPEN, Green/CLOSED) Circulating Water Temperature to Riser Deviation From Normal (measured in DEGF) Circulating Water Temperature to Pumps Deviation From Normal (measured in DEGF) Cooling Tower Makeup Valve Position (measured in Percent) Cooling Tower Bypass Valve Controls Cooling Tower Fan Auto Controls Cooling Tower Makeup Valve Controls Cooling Tower Alarms are also provided on this screen as follows: Wet Bulb Temperature Deviation (measured in DEGF) Cabinet Power Trouble Vibration monitor Trouble

Cooling Tower Fans Data
Data specific to operation of the Cooling Tower Fans is found on the Cooling Tower Fans Graphic/display. This data includes: Condenser Outlet A Temperature (measured in DEGF) Condenser Outlet B Temperature (measured in DEGF) Basin Temperature (measured in DEGF) Dewpoint Air Temperature (measured in DEGF) Cooling Tower Fans 1-12 Vibration (measured in MILS) Cooling Tower Fans 1-12 Daily Starts (measured in MILS) Cooling Tower Fans 1-12 Daily Run Time (measured in Hours/HRS) Cooling Tower Fans 1-12 Cumulative Run Time (measured in Hours/HRS) Cooling Tower Fans 1-12 Reverse Time (Exceeded/Not Exceeded) NOTE: Alarm conditions are highlighted in RED. Fan No. 6 is in ALARM.

Review Questions What is the function of the Circulating Water Pumps?
Click to Review Which Circulating Water System Valve, when open, allows a single Circulating Water Pump to supply both condenser sides? Click to Review What component mounted in the channel between the stop gate and the intake structure prevents debris from entering the pump suction? Now let’s review the information we’ve just described. Click to Review When you are sure you can correctly answer these question click the Button to continue

Component Controls Circulating Water Pump Controls
Cooling Tower Bypass Valve Controls Cooling Tower Fans Automatic Controls In this section we will cover component controls, digital in nature, as they pertain to Circulating Water pumps The Cooling Tower Bypass Valve And the Cooling Tower Fans (automatic controls)

Circulating Water Pump Suction Valve Controls
B A there are two (2) Circulating Water Pumps: “A” and “B”. Each pump obtains its suction supply through its associated inlet header fed from the Cooling Tower Basin. Each pump is equipped with motor-operated suction and discharge valves. Each motor operated suction valve is locally controlled and is typically positioned by the outside rounds/auxiliary operator. Red (OPEN) and green (CLOSED) lights, located above the suction valve control station, illuminate to indicate the associated suction valve’s position. The DCS graphic identifies the valve position as well with RED indicating the associated valve is OPEN, and Green indicating the valve is CLOSED. Interlocks prevent the associated circulating water pump from starting unless its suction valve is fully open. A B

Circulating Water Pump Discharge Valve Controls
Each Circulating Water Pump discharge valve is controlled automatically by the pump DCS controller. The associated pump discharge valve and the cross-tie valve between pump A and pump B (HCV5646) must be fully closed before the pumps start. When the pump START is selected and the starting contactor is sealed in, the discharge valve begins to open. After the discharge valve is 10 percent open, the pump motor automatically starts. This logic prevents pump damage caused by pumping against a shutoff head and throttles the initial flow to the condenser to prevent water hammer in the circulating water piping and condenser. When the pump STOP Controller button is selected and pressed, the pump discharge valve begins to close. When the discharge valve reaches the 10 percent open position (after approximately 30 seconds), the pump motor stops. This logic prevents backflow through the idle pump following shutdown. B

Pump Cooling Water Supply
Cooling water for each Circulating Water Pump’s motor bearings (upper and lower) is supplied from the service water system via the service water pumps. On this graphic, the thrust bearing, upper and lower guide bearing temperatures are displayed.

Circulating Water Pump Start/Stop Controls
Start/Stop Soft Keys The Circulating Water Pumps are started and stopped from this Circulating Water Pump DCS Display. Each Circulating Water Pump is operated using the START and STOP soft keys from its DCS controller. Pump operating status is indicated by a transfer of the Start or Stop status icon to its operating condition Green/Stopped to Red/Running or vice versa. Motor amps are displayed at the bottom of the display. A vertical bar is also provided as a visual indicator of the operating amperes of the associated pump.

Pump Permits and Process Trips
Permissives and Process Trips associated with each Circulating Water Pump are displayed on the control display. These include: Cross-tie Closed Process Trips: “B” PUMP OFF “B” DISCH NOT CLOSED SUCTION VALVE NOT OPEN BRKR CLOSED AND DISCH PRESS HI NO SOLENOID VOLTAGE Primary Start Permits BREAKER OPEN SUCTION VLV OPEN DISCH VLV CLOSED Secondary Start Permits COOLING WATER FLOW >10 GPH DISCH VLV NOT CLOSED Status is indicated by the small box located to the left of each trip and permit. When the box is “grey”, the condition is “not true”. When the box is “white”, the condition is “true”.

Pump Lockout/Tagout Lockout Tagout
A Lockout/Tagout selection is available for each pump. When in Lockout/Tagout, the pump is unavailable for starting and the Lockout/Tagout button is outlined in Yellow.

Each Circulating Water Pump’s Discharge Valve is normally positioned as part of the control circuit associated with its pump starting sequence. However, provisions are available for Tagout/Lockout, OPEN JOG and CLOSE JOG of the associated Discharge Valve. When OPEN JOG is selected and “pushed” the valve JOGS OPEN and the associated status indicator turns RED. When the CLOSE JOG is selected and “pushed”, the associated status indicator turns GREEN.

Cooling Tower Controls
The Cooling Tower Display has controls associated with opening and closing the cooling Tower Bypass Valve, Cooling Tower Fan Automatic Controls, and Cooling Tower Makeup Valve Controls.

Cooling Tower Bypass Valve Control
After the Circulating Water System is filled, the cooling tower bypass valve is opened and one circulating water pump is started. When minimum flow has been established and the system piping has been vented, the cooling tower bypass valve is closed and the second circulating water pump is started. Bypass Valve

Cooling Tower Bypass Valve Control
The Cooling Tower Bypass Valve Controller is seen here. The Controller has “OPEN JOG” and “CLOSE JOG” Buttons. When OPEN JOG is selected and “pushed” the valve JOGS OPEN and the associated status indicator turns RED. When the CLOSE JOG is selected and pushed, the associated status indicator turns GREEN. Permissives for Opening and Closing the valve when met/true are identified by a “P” encapsulated in a white status box, located next to the OPEN JOG and CLOSE JOG Buttons. Provisions are also available for Tagout/Disable of the 480 VAC Cooling Tower Bypass Valve.

Cooling Tower Fan Controls
During normal operation Cooling Tower fans are placed in service to control circulating water temperature to a value of approximately 70 degrees Fahrenheit. Normally, all 12 cooling tower cells are in service with the fans operating in the AUTO FORWARD mode at full load. Fans may be operated in LOCAL by the Outside Rounds/Auxiliary Operator or in REMOTE which allows operational control from the START AUTO SEQ and STOP AUTO SEQ Control buttons. Deicing may also be initiated from the DE-ICE button.

Fan Remote Start/Stop Controls
Here we see the Start Auto Sequence and Stop Auto Sequence Buttons associated with the Cooling Tower Fans. The START AUTO SEQ allows the controller to sequentially START all fans that are in REMOTE during unit startup. The goal is to maintain the Circulating Water Inlet Temperature to the Condenser at approximately 70 degrees Fahrenheit. Selecting the Stop Sequence allows the controller to sequentially STOP all fans that are in REMOTE during unit shutdown.

De-icing Control De-icing Control is provided for the Cooling Tower.
Each fan is equipped with a reversing feature for de-icing the cooling tower inlet louvers. The DEICE button, when “pressed” allows for cell deicing. The DEICE Button sequentially shuts down each fan, one at a time, then allows that fan to rotate in a reverse rotation for de-icing for a pre-determined period of time. When reversed, the fan pulls ambient air through the shroud and passes it through the fill members in a reverse flow path. The air absorbs heat from the cascading circulating water and melts ice on the louvers as it passes out the sides of the tower. The affected Fan then STOPS and Restarts in the Forward Direction. This occurs cell by cell along the tower.

Review Questions How is each Circulating Water Pump motor operated suction valve typically controlled? How is each Circulating Water Pump motor operated discharge valve typically controlled? How is De-icing of the Cooling Tower performed? Click to Review Click to Review Click to Review When you are sure you can correctly answer these question click the Button to continue

Process Control Circulating Water System Process Controls pertain to the control of the Cooling Tower Basin Level via operation of the Cooling Tower Makeup Valve.

Cooling Tower Makeup Valve Control
Basin Level The Cooling Tower Makeup Valve is pneumatically actuated and controlled through the DCS. It functions to maintain the basin level at setpoint. The normal basin level is approximately 60 inches. The supply of water to the Makeup Valve is provided via operation of one of the two Cooling Tower Makeup Pumps. During initial fill, the outside rounds/auxiliary operator may also open the manually operated makeup bypass valve to accomplish filling of the basin. A level indicating transmitter signals to the Cooling Tower Makeup Valve to open and close as required to maintain the basin level at setpoint when the controller is in AUTO. Level Controller

Cooling Tower Basin Level Controller
“A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint. Brown arrows indicate basin level upper and lower limits. Level Setpoint Measured Flow Valve Output percent The controller is capable of operating in either Automatic/AUTO or Manual/MAN control. This control block allows the operator to view the Basin level setpoint on the Magenta/pink vertical bar, and displays the actual measured variable/level represented by the blue vertical bar. Setpoint (SPT), in the horizontal control block, is the operator desired level setpoint with the value of 87 percent as displayed representing the normal Basin level setpoint of 5 feet. Deviation from this setpoint is the measured variable (MEAS) located above SPT. When Cooling Tower Makeup Level Valve Control is in AUTO, deviation of the measured variable (MEAS) from the setpoint (SPT) drives the Level Control Valve output to respond in the appropriate direction (opening/increasing makeup flow or closing/decreasing makeup flow) to ensure Basin level is maintained at setpoint. Makeup Level Control Valve output is illustrated on the white vertical bar and again as a percentage of valve travel illustrated on the output (OUT) control block.

Auto/Manual Control “A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint. Brown arrows indicate upper and lower Basin Level limits. Level Setpoint Measured Flow Valve Output percent Here you see the AUTO and MANUAL Controls. When in AUTO, the basin level control valve position is driven by the error between the MEASURED VARIABLE and the SETPOINT. If the error signal grows too large, the controller if in AUTO, trips to manual/MAN. In MANUAL control, valve position is controlled by the operator from the controller. When transferring from MAN to AUTO, a minimal deviation may exist to latch into AUTO. When Valve control is in AUTO, its status icon is RED. When valve control is in MANUAL, its status icon is GREEN.

Basin Level Setpoint “A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint. Brown arrows indicate upper and lower valve output limits. Level Setpoint Measured Flow Valve Output percent The Cooling Tower Basin Level setpoint may be input automatically or locally by the operator. “A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint and in this case, the level setpoint is 87 percent. Brown arrows indicate upper and lower Valve Output limits. In this instance our makeup valve is at percent open.

Review Questions How is the Cooling Tower Makeup Valve actuated and controlled? What does the Cooling Tower Makeup Valve Controller Output Control? Where does the Cooling Tower Basin Level setpoint come from? Click to Review Click to Review Click to Review When you are sure you can correctly answer these question click the Button to continue

Circulating Water System Operation
Startup Prerequisites System Startup Normal Operation System Shutdown This section covers operation of the Circulating Water System. It includes the following: Startup Prerequisites System Startup Normal Operation System Shutdown

Startup Prerequisites
Prior to starting up the Circulating Water System, it is necessary to have the following support systems in service. These include: Service Water System (used to cool the circulating water pump motor bearings) Makeup Pumps in service (used to add water to the cooling tower basin) Compressed Air Systems are in service (for positioning of pneumatically actuated valves, e.g. the tower makeup valve) 6.9 kV power supply is available to power the circulating water pumps 480 volt power supply is available to power the various system valves All control and annunciating systems are operating. And the Fire protection system is in service.

CIRCULATING WATER SYSTEM STARTUP
Ensure Basin Level is established and maintained Ensure Circulating Water Pumps are ready for Startup Ensure system valves are properly aligned Ensure support systems are available for service. During preparation for Circulating Water System Startup, there are many operator checks and activities that must be performed in order to ensure a successful startup of the system. The typical focus of these activities involves four steps. These are: Ensure Basin level is established and maintained Ensure Circulating Water Pumps are ready for startup Ensure System Valves are properly aligned Ensure support systems are available for service.

Prepare the Cooling Tower
Have the outside rounds/auxiliary operator: RACK IN and place the cooling tower bypass valve breaker in REMOTE. Verify that a makeup pump is in service so that the basin may be filled.

Establish Basin Level Makeup Valve Basin Level Level Controller
Place the cooling tower level control valve in AUTO and adjust the set point to approximately 87%. Level Controller

Circulating Water Pump
Rack in pump and valve breakers OPEN each pump’s suction valve Verify motor bearing oil level’s are ok. Valve in instrument air and cooling water. CLOSE the circulating water cross-tie Prepare the Circ. Water Pumps for startup. Have the outside rounds operator: Rack in and place circulating water pump 6.9 kV breakers in remote. RACK IN the associated Circulating Water Pump 480 volt suction valve breaker RACK IN and place Circulating Water Pump 480 volt discharge valve breaker in remote. OPEN the Circulating Water Pump suction valve. LINE UP cooling water to circulating water pumps. LINE Up air to cooling tower blowdown control valve and verify valve position. CHECK for proper oil level on circulating water pump motor. CLOSE the circulating water cross-tie (or makeup the closed limit). Circulating Water Pumps

Cooling Tower Fans Prepare the cooling tower fans for startup. Have the Outside Rounds/ Auxiliary Operator: RACK IN and place cooling tower fans in REMOTE. RESET vibration detectors

Align System Valves Waterbox Inlet Valves Waterbox Outlet Valves
Discharge Cross-tie Valve Suction Valves Have the outside rounds/auxiliary operator walk down the system, inspect the system, and align system valves. Typical checks include: CHECK the intake screen for cleanliness Verify Circulating Water Pump Suction Valves are OPEN Verify Circulating Water Pump Discharge Crosstie valve is CLOSED Verify condenser waterbox doors are CLOSED Verify drains on waterboxes are CLOSED Verify waterbox inlets and outlets are OPEN. (If drained, manually vent waterboxes and backfill slowly by cracking in waterbox outlets until all air is vented, then close vents and fully open outlets and inlets) Verify condenser auto vents are valved in

Open the Cooling Tower Bypass
The Control Room Operator then OPENS the Cooling Tower Bypass Valve from the controller OPEN JOG button.

START the “A” circulating water pump
Verify Start Permits are met and Start the “A” Circulating Water Pump. The START Button turns Red, indicating the pump has started. The Discharge Valve opens 10% and after a 3 minute time delay, opens to 100% The Discharge Valve OPEN status icon turns RED

Check Pump Data After the start of the Circulating Water Pump, check its operating data.

A Have the Outside Rounds/Auxiliary Operator:
OPEN the Circulating Water Pump Discharge Cross-tie START the cooling tower acid pump and control pH (7.6 – 8.0) And then SET cooling tower blowdown and chemicals per the Chemical Control Directive (CCD) A

Close the Cooling Tower Bypass
When circulating water temperature increases to approximately 70 degrees Fahrenheit, CLOSE the Cooling Tower Bypass Valve using the CLOSE JOG Button on the Bypass Valve Controller.

Start Cooling Tower Fans
As Circulating Water Temperature as measured entering the Condenser increases, have the Outside Rounds Operator Locally START more Cooling Tower Fans, (OR) if fans are in Remote Press the START AUTO SEQ to start fans in auto as required to maintain a Circulating Water Supply Temperature of approximately 70 degrees Fahrenheit.

At 50 Percent Load, prepare for and start the 2nd Circ Water Pump
Cross-tie Valve M M A M M At 50 percent unit load, prepare for starting the 2nd Circulating Water Pump. Prior to starting the 2nd pump, the outside rounds operator must locally CLOSE the Circulating Water Pump Discharge Cross tie. After the cross-tie valve is closed, the 2nd Circulating Water Pump May be started from its control switch. B

Re-open the Discharge Cross-tie
M B Cross-tie Valve After the 2nd Circulating Water Pump Starts, and its discharge valve is wide open, have the outside rounds/auxiliary operator “OPEN” the Circ. Pump Discharge Cross-tie Valve.

NORMAL OPERATION Verify that Circulating Water chemistry remains within acceptable limits, having outside rounds operator make any adjustments required. Have the Outside Rounds Operator perform the following: Visually inspect the Cooling Tower for blockage of normal flowpaths of air and water. Visually inspect fans and motors for proper oil levels. Check Chemical Feed System for proper operation. Visually inspect the sulfuric acid distribution troughs for proper feed. Inspect Cooling Tower fire protection system. Visually inspect Circulating Water Pump packing glands. Visually inspect pumps and motors for abnormal noise or vibration. Check pumps and motors for proper oil levels.

Monitor Circulating Water System process variables from DCS displays.
Monitor Circulating Water System process variables on associated graphic displays to ensure components and process variables are within normal range Verify that the Cooling Tower basin is at normal operating level. Check Cooling Tower basin screens for differentials. Monitor condenser differential pressure.

Check Cooling Tower Fans
Check Cooling Tower fans for vibration Stop or start fans to maintain the Circulating Water temperatures and condenser backpressure at the expected values based on Unit load and weather conditions.

De-ice Cooling Tower If Required
During Cold Weather Operation initiate the DE-ICE sequence as required.

Monitor data associated with operation of the Circulating Water Pumps. If an alarm is present, have the outside rounds/auxiliary operator inspect the equipment, determine the source of the alarm and eliminate the cause of the alarm or write a work order.

SHUT DOWN The Circulating Water System is shut down after the unit is off-line. Typically, after the turbine steam seal system is taken out of service the Circulating Water System is shut down.

Shut Down One Circ. Pump Cross-tie Valve M M A M M M B
During the unit load reduction, upon decreasing to approximately 50 percent load, prepare for shut down of one operating Circulating Water Pump. Verify that the Circulating Water Discharge Cross-tie Valve is OPEN. Stop the pump by selecting STOP. Verify that discharge valve closes to about 10 percent. Verify that the pump breaker opens. (from the primary start permits) Verify that the pump discharge valve closes fully. B

Select the Cooling Tower Fan Stop Auto Sequence
Cooling Tower fans may be taken out of service as temperature permits by selecting the STOP AUTO SEQUENCE. (All fans whose control breakers are in REMOTE will sequentially stop). Fans may also be locally stopped if desired. The Outside Rounds/Auxiliary Operator would be the one to perform each local fan stop as required.

OPEN the Cooling Tower Bypass Valve
Below 40 degrees Fahrenheit ambient air temperature, OPEN the Cooling Tower Bypass Valve so as not to overcool and ice up the Cooling Tower.

STOP the Operating Circulating Water Pump
Cross-tie Valve M M M A M M After the Unit is off line, cooled down, and turbine steam seals have been removed from service, STOP the operating Circulating Water Pump. B

Secure Cooling Tower Make-up
Makeup Valve Have the Outside Rounds/Auxiliary Operator CLOSE the Cooling Tower Blowdown Valve. When Cooling Tower makeup is no longer needed to maintain the level, place the Cooling Tower Makeup Valve control in MANUAL, change the setpoint to “0” and verify that the output goes to “O”. Level Controller

Review Questions During preparation for Circulating Water
System Startup, what are the four major steps involved? What position must the Circ. Water Discharge Cross-tie valve be in prior to starting the 2nd Circulating Water Pump? During Normal Operation, how is ice removed from the Cooling Tower? Click to Review Click to Review Click to Review When you are sure you can correctly answer these question click the Button to continue

The Circulating Water System Condenses Low Pressure Turbine Exhaust Steam.
Main Steam Cold Reheat Steam Hot Reheat Steam LP Turbine Exhaust Condenser Circulating Water Inlet Circulating Water Outlet Condensate Pump Hotwell The Circulating Water System provides the Main Condenser with cooling water to remove latent heat from the LP turbine exhaust steam and condense the Exhaust Steam into water droplets. Circulating Water flows through the tubes of the condenser, while LP Turbine Exhaust flows to the condenser shell. The condensed water droplets collect in the hotwell and provide the suction supply to the Condensate Pump. In some cases the Circulating Water System also supplies cooling water to Auxiliary Condensers and Heat Exchangers for cooling. Return to Review Questions

Cooling Tower Return to Review Questions
After absorbing heat from the LP Turbine Exhaust steam, the heated Circulating Water returns to the Cooling Tower where the heat is released to the atmosphere via evaporation. Cooling Tower Return to Review Questions

Cooling Tower Return to Review Questions
Water enters the top of the Cooling Tower as illustrated here. The water entering the top of the tower flows through nozzles and is broken up into droplets by the nozzles and as it falls through cooling tower fill. Large Fans, arranged along the top of the cooling tower, draw air in through the louvered sides of the cooling tower. The air makes direct contact with the water droplets, and by evaporation, cools the circulating water. The cooled circulating water collects in the basin located below the Cooling Tower. Return to Review Questions

The circulating water pumps draw water from the cooling tower basin, pressurize it, and pump it through the Condenser where it removes latent heat from the LP Turbine exhaust steam. Each Circulating Water Pump, shown here, is of the vertical centrifugal type, powered by a 6.9 kV Motor. Return to Review Questions

Circulating Water Pumps Valves
Here you see a closer view of the Circ. Water Pumps, and their associated 480 Volt motor operated suction and discharge valves. Motor operated valves have an “M” in their status icon. Additionally, you can see the manually operated, open, discharge cross-tie valve. With the discharge cross tie valve open, a single circulating water pump is able to supply both condenser supply lines. This type arrangement is used during low load operation. However, during full load operation, both pumps must be in service. Remember, OPEN valves and operating pump motors are displayed in “red” . Return to Review Questions

Cooling Tower Basin Makeup Bypass Screen Return to Review Questions
The tower basin serves as a storage reservoir for the Circulating Water System. The tower basin covers the entire floor area of the cooling tower and is sloped toward the intake structure. A stop gate located in the channel between the basin and the intake structure allows the pump intake structure to be isolated. A screen mounted in the channel between the stop gate and the intake structure prevents debris from entering the pump suction. Bromination, acid and chemical dispersant diffusers in the intake channel distribute water quality control chemicals into the Circulating Water System. Bromine is used to control microbiological growth, acid is used to control pH,l and dispersant keeps solids in solution. A Cooling Tower Bypass line connects the warm circulating water return header with a perforated distribution header which directs the returning water directly into the tower basin. The bypass valve is normally closed and is opened only during startup and shutdown operation, for initial filling or draining of the circulating water loop. The tower basin water level is controlled automatically by a level control valve located in the makeup header between the makeup pumps and the intake channel. Makeup is supplied from the Raw Water System. The tower basin water level is maintained at 5 feet during normal operation. Water is continually removed from the circulating water return header by the cooling tower blowdown system. This system maintains the desired level of suspended solids in the circulating water system by regulating a control valve in response to a conductivity measurement and sends the high solids waste water to the cooling tower blowdown ponds. Bypass Screen Return to Review Questions

Circulating Water Pump Suction Valve Controls
B A there are two (2) Circulating Water Pumps: “A” and “B”. Each pump obtains its suction supply through its associated inlet header fed from the Cooling Tower Basin. Each pump is equipped with motor-operated suction and discharge valves. Each motor operated suction valve is locally controlled and is typically positioned by the outside rounds/auxiliary operator. Red (OPEN) and green (CLOSED) lights, located above the suction valve control station, illuminate to indicate the associated suction valve’s position. The DCS graphic identifies the valve position as well with RED indicating the associated valve is OPEN, and Green indicating the valve is CLOSED. Interlocks prevent the associated circulating water pump from starting unless its suction valve is fully open. A B Return to Review Questions

Each Circulating Water Pump discharge valve is controlled automatically by the pump DCS controller. The associated pump discharge valve and the cross-tie valve between pump A and pump B (HCV5646) must be fully closed before the pumps start. When the pump START is selected and the starting contactor is sealed in, the discharge valve begins to open. After the discharge valve is 10 percent open, the pump motor automatically starts. This logic prevents pump damage caused by pumping against a shutoff head and throttles the initial flow to the condenser to prevent water hammer in the circulating water piping and condenser. When the pump STOP Controller button is selected and pressed, the pump discharge valve begins to close. When the discharge valve reaches the 10 percent open position (after approximately 30 seconds), the pump motor stops. This logic prevents backflow through the idle pump following shutdown. B Return to Review Questions

De-icing Control Return to Review Questions
De-icing Control is provided for the Cooling Tower. Each fan is equipped with a reversing feature for de-icing the cooling tower inlet louvers. The DEICE button, when “pressed” allows for cell deicing. The DEICE Button sequentially shuts down each fan, one at a time, then allows that fan to rotate in a reverse rotation for de-icing for a pre-determined period of time. When reversed, the fan pulls ambient air through the shroud and passes it through the fill members in a reverse flow path. The air absorbs heat from the cascading circulating water and melts ice on the louvers as it passes out the sides of the tower. The affected Fan then STOPS and Restarts in the Forward Direction. This occurs cell by cell along the tower. Return to Review Questions

Cooling Tower Makeup Valve Control
Basin Level The Cooling Tower Makeup Valve is pneumatically actuated and controlled through the DCS. It functions to maintain the basin level at setpoint. The normal basin level is approximately 60 inches. The supply of water to the Makeup Valve is provided via operation of one of the two Cooling Tower Makeup Pumps. During initial fill, the outside rounds/auxiliary operator may also open the manually operated makeup bypass valve to accomplish filling of the basin. A level indicating transmitter signals to the Cooling Tower Makeup Valve to open and close as required to maintain the basin level at setpoint when the controller is in AUTO. Level Controller Return to Review Questions

Basin Level Setpoint “A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint. Brown arrows indicate upper and lower valve output limits. Level Setpoint Measured Flow Valve Output percent The Cooling Tower Basin Level setpoint may be input automatically or locally by the operator. “A” in the grey background indicates that the level setpoint is not in automatic. “L” in a white background indicates that the operator has local control over the Basin Level setpoint and in this case, the level setpoint is 87 percent. Brown arrows indicate upper and lower Valve Output limits. In this instance our makeup valve is at percent open. Return to Review Questions

CIRCULATING WATER SYSTEM STARTUP
Ensure Basin Level is established and maintained Ensure Circulating Water Pumps are ready for Startup Ensure system valves are properly aligned Ensure support systems are available for service. During preparation for Circulating Water System Startup, there are many operator checks and activities that must be performed in order to ensure a successful startup of the system. The typical focus of these activities involves four steps. These are: Ensure Basin level is established and maintained Ensure Circulating Water Pumps are ready for startup Ensure System Valves are properly aligned Ensure support systems are available for service. Return to Review Questions

Circulating Water Pump
Rack in pump and valve breakers OPEN each pump’s suction valve Verify motor bearing oil level’s are ok. Valve in instrument air and cooling water. CLOSE the circulating water cross-tie Prepare the Circ. Water Pumps for startup. Have the outside rounds operator: Rack in and place circulating water pump 6.9 kV breakers in remote. RACK IN the associated Circulating Water Pump 480 volt suction valve breaker RACK IN and place Circulating Water Pump 480 volt discharge valve breaker in remote. OPEN the Circulating Water Pump suction valve. LINE UP cooling water to circulating water pumps. LINE Up air to cooling tower blowdown control valve and verify valve position. CHECK for proper oil level on circulating water pump motor. CLOSE the circulating water cross-tie (or makeup the closed limit). Circulating Water Pumps Return to Review Questions

De-ice Cooling Tower If Required
During Cold Weather Operation initiate the DE-ICE sequence as required. Return to Review Questions

Circulating Water System

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