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SYSTEM DESCRIPTION

|Circulating Water System |

|HOPKINS REPOWERING PROJECT |

|UNIT HP2A |

TABLE OF CONTENTS

Section Page

1.0 Introduction 1

1.1 Purpose and Scope 1

1.2.1 P&ID 1

1.2.2 Electrical One Line Diagrams 1

1.2.3 Control Diagrams 1

1.2.4 Instrument Loop Diagrams 1

1.2.5 Instruction Manuals 2

1.2.6 Miscellaneous 2

1.3 System Overview 2

1.3.1 Primary System Flow Path 2

1.3.2 Secondary System Flowpath 3

2.0 MAJOR COMPONENTS AND SUBSYSTEMS 4

2.1 Circulating Water Pumps 4

2.1.1 Function 4

2.1.2 Detailed Description 4

2.1.3 Technical Design Data 6

2.1.4 Operation, Control, and Safety 6

2.2 Condenser 7

2.2.1 Function 7

2.2.2 Detailed Description 7

2.2.3 Technical Design Data 9

2.2.4 Operation, Control, and Safety 9

2.3 Cooling Tower 10

2.3.1 Function 10

2.3.2 Detailed Description 10

2.3.3 Technical Design Data 12

2.3.4 Operation, Control, and Safety 13

3.0 List of Instrumentation and Controls 16

4.0 List of Alarms and Setpoints 17

5.0 List of System Constraints 17

TABLE OF FIGURES

Section Page

Figure 1.1 Chart 1

Figure 2.1 Cooling Tower

Figure 2.2 Circulating Water Pumps

Figure 2.3 Condenser

1. Introduction

1. PURPOSE AND SCOPE

The purpose of the Circulating Water System is to provide cooling water to the main condenser to condense turbine exhaust steam in the condenser. Additionally, the Circulating Water System provides cooling water to the condensate cooling water heat exchangers, the steam turbine lube oil coolers, and to the condenser vacuum pumps. The heat absorbed by the circulating water is dissipated to the atmosphere through convection and evaporation in the cooling tower. The system contains the the following major components:

a. Circulating Water Pumps

b. Cooling Tower

2. References

1. P&ID

a. Ebasco Services Incorporated, Circulating Water and Condenser Vacuum System, CTAL-HPK2-M-F-0006, Rev. 0

2. Electrical One Line Diagrams

a. Reynolds, Smith, and Hills, Unit No. 2 Addition, 480 V Unit Substations Single Line and Arrangement Diagram, E-4, Rev. 0

3. Control Diagrams

a. Reynolds, Smith, and Hills, Circ Water Pump 2A, S-5

b. Reynolds, Smith, and Hills, Circ Water Pump 2B, S-6

c. Reynolds, Smith, and Hills, Cooling Tower Fan 2A, S-12

d. Reynolds, Smith, and Hills, Cooling Tower Fan 2B, S-13

e. Reynolds, Smith, and Hills, Cooling Tower Fan 2C, S-14

f. Reynolds, Smith, and Hills, Cooling Tower Fan 2D, S-15

g. Reynolds, Smith, and Hills, Cooling Tower Fan 2E, S-16

h. Reynolds, Smith, and Hills, Cooling Tower Fan 2F, S-17

i. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2A, S-117

j. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2B, S-118

k. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2C, S-119

l. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2D, S-120

m. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2E, S-121

n. Reynolds, Smith, and Hills, Cooling Tower M.O.V. 2F, S-122

4. Instrument Loop Diagrams

a. Temperature Control - TG Lube Oil Coolers, Loop 38

b. Cooling Tower Blowdown Control, Loop 63

c. Makeup Water Control, Loop 64

d. Cooling Tower Acid Feed Control, Loop 66

e. Inhibitor Pump Control, Loop 68

f. Cooling Tower to Waterbox A, Loop 288

g. Cooling Tower to Waterbox B, Loop 289

h. Cooling Tower from Waterbox A, Loop 290

i. Cooling Tower from Waterbox B, Loop 291

j. Cooling Tower Fan 2A Load Current, Loop 300

k. Cooling Tower Fan 2B Load Current, Loop 301

l. Cooling Tower Fan 2C Load Current, Loop 302

m. Cooling Tower Fan 2D Load Current, Loop 303

n. Cooling Tower Fan 2E Load Current, Loop 329

o. Cooling Tower Fan 2F Load Current, Loop 320

p. Circulating Water Pump 2A Load Current, Loop 323

q. Circulating Water Pump 2B Load Current, Loop 324

r. Circulating Water Pump discharge, Loop 361

s. Cooling Tower Fan 2A Motor Control, Loop 400

t. Cooling Tower Fan 2B Motor Control, Loop 401

u. Cooling Tower Fan 2C Motor Control, Loop 402

v. Cooling Tower Fan 2D Motor Control, Loop 403

w. Circulating Water Pumps Control, Loop 440

x. Cooling Tower Fan 2E Motor Control, Loop 500

y. Cooling Tower Fan 2F Motor Control, Loop 501

z. Cooling Tower Level Alarm, Loop 658

aa. Cooling Tower Return Test Flow, Loop 1242

5. Instruction Manuals

a. Babcock and Wilcox, Boiler Operations Manual, Vols. I & II

b. Hamon Cooling Tower Instruction Manual

c. Johnson Pump company, Citculating Water Pump Installation Manual, TH-1130-31

6. Miscellaneous

a. Reynolds, Smith, and Hills, Connection diagrams, C-1 through c-198

3. System Overview

1. Primary System Flow Path

The Circulating Water System, as illustrated in Figure 1.1, is a closed loop type circulating water system. Flow through the system is maintained by two 50% capacity circulating water pumps. The two circulating water pumps take suction from the cooling tower cold water basin circulating water sump through individual pump suction screens and discharge into a common header. The common header supplies circulating water to the main condenser inlet waterboxes. Circulating water flows from the inlet waterboxes through the condenser tubes. Exhaust steam from the LP turbine passes across the condenser tubes and is condensed. (The condenser shell and vacuum system are discussed in the Condensate System Description.) Circulating water inside the condenser tubes then flows through the outlet waterboxes to cooling tower.

Figure 1.1 Circulating Water System

Relatively hot circulating water returning from the main condenser is directed to the top of the cooling tower. The cooling tower riser directs the hot water throughout the cooling tower. The hot water flows downward through the six individual cells and collects in the cooling tower cold water basin. As water flows down through the cooling tower, it transfers heat to the air that is being drawn countercurrent (upward) across the falling water by the cooling tower fans. Relatively cold circulating water from each cold water basin flows into the common circulating water sump which provides suction to the circulating water pumps.

2. Secondary System Flowpath

The Circulating Water System also contains or interfaces with the following secondary systems and/or components:

a. Makeup Circulating Water Supply - To maintain sufficient water level in the cooling tower cold water basin, makeup water is continuously supplied from the number 3 and 4 well water pumps to make up for water loss due to evaporation, drift, and blowdown. The well water pumps take suction from the deep wells and discharge through the chlorine house and into a common header. The common header supplies makeup water to cooling tower basin through makeup level control valve 2CWLCV064. The makeup level control valve modulates to maintain the cooling tower basin level at setpoint (approximately six inches below the top of the basin wall).

b. Circulating Water Blowdown - During cooling tower operation, water is lost to the atmosphere due to evaporation. This increases the concentration of salts and other solids in the water remaining in the cooling tower basin. To control the concentration of the solids, circulating water is continuously blown down through the blowdown line, located on the circulating water pump 2B discharge line. Typically, a water sample is taken on the outlet of the condenser waterbox from a drain valve. The water sample is analyzed for conductivity using a conductivity meter.

The flow of water through the blowdown line is controlled by 2CWFCV063, located on the southeast side of the cooling tower. Blowdown then gravity flows to the point of discharge (P.O.D.) and on to the Ochlockonee River. The adjustment of the blowdown is performed by chemical laboratory personnel and requires no operator action.

c. Auxiliary Cooling Water Supply - The circulating water system provides sufficient water flow to the steam turbine lube oil coolers, the condenser vacuum system heat exchangers, and the condensate cooling water heat exchangers. After the water passes through the various heat exchangers, the auxiliary circulating water supply combines into a common discharge header. The discharge header combines into the discharge from the main condenser and flows to the cooling tower with the circulating water. Additional information regarding the circulating water supply to the turbine generator lube oil coolers and the condenser vacuum system heat exchangers is provided in the Main Turbine and Condensate System Descriptions respectively.

d. Chemical Injection - The circulating water is tested by the plant laboratory for the following:

• The circulating water conductivity level should be maintained in the range of 950 to 1100 microhms.

• For microbiological control, bottled chlorine gas is injected into the makeup circulating supply using a feeder system at the chlorine house.

• For pH control, both sulfuric and hydrochloric acids are injected using a feeder system at the cooling tower water flume.

• A scale inhibitor (HEDP Phosphonate) is used to control scaling and a copper corrosion inhibitor (Betz CU-1) is used to control corrosion inside the condenser tubes. The injection amount and intervals are performed by chemical laboratory personnel and require no operator action.

e. Electrical Distribution System - The electrical distribution system is used to supply power and energize all of the circulating water system pumps, fans and slide gates. The MCCs located throughout the plant feed the system pumps provide the required protection and starter functions for the motors.

f. Instrument Air System - Instrument air supplied between 3-27 psig is used as the medium to operate the system controls, including local controllers, control valves, and instrumentation.

2. MAJOR COMPONENTS AND SUBSYSTEMS

1.

1. Circulating Water Pumps

1. Function

The Circulating Water Pumps supply cooling water to the surface condenser for condensing the steam from the steam turbine exhaust. In addition, the circulating water pumps provide cooling water to the steam turbine lube oil coolers, and the condenser vacuum pump, and the condensate cooling water heat exchangers.

2. Detailed Description

Two 50% capacity circulating water pumps, arranged in parallel, are located at the cooling tower. Each circulating water pump, illustrated in Figure 2.1, is a vertically mounted centrifugal, single stage pump manufactured by Johnston Pump Company. The pumps are sized to provide a capacity of 63,000 gpm at 50 foot discharge head. The pumps take suction from the circulating water sump through individual screens.

[pic]

Figure 2.1 Circulating Water Pumps

The circulating water pumps are each driven by a 1250 hp, 395 rpm, 4,160 VAC electric motor manufactured by Allis-Chalmer. The motor is coupled to the pump shaft by means of a rigid, adjustable, flange type coupling which provides for vertical adjustment of the pump shaft.

The pump is equipped with stuffing boxes integral to the pump casing. Seal water is supplied from the discharge of the pump to each seal assembly. The seal water cools and lubricates the packing, and prevents premature wear and damage. A slight leakoff should be allowed to ensure adequate seal water flow to lubricate and cool the packing.

Each circulating water pump is provided with an air eliminator, isolated by a manual valve, to remove the entrained air from the pump during startup.

A thermocouple is installed in the shell of each pump motor bearing for temperature monitoring. A thermocouple is a temperature sensing device composed of two dissimilar metal wires. The wires are welded together at one end to form a measuring junction used to sense bearing temperature. The junction develops a small DC voltage proportional to the bearing temperature. The wires from each thermocouple are routed to a terminal block external of the pump motor. Each thermocouple provides an input signal to the Micromax Data Manager where the DC voltage is interpreted into a corresponding temperature value.

Each circulating water pump motor is equipped with space heaters. The space heaters are energized during periods of motor shutdown. The heaters maintain internal temperature above the dew point; thus, moisture condensation and water accumulation inside the motor is prevented. Particularly in moisture laden atmospheres, space heaters reduce the formation of corrosion and simplify maintenance of the motor windings.

Circulating water pump 2A discharge piping is equipped with a rupture disk to prevent circulating water piping overpressurization. The rupture disk is isolated by a manually operated butterfly valve.

3. Technical Design Data

|Circulating Water Pumps (2A and 2B) |

|Pump Manufacturer |Johnston Pump company |

|Pump Type |Vertical, single stage, open impeller, centrifugal |

|Total Discharge Head |50 feet |

|Rated Discharge Flow |63,000 gpm |

|Motor Manufacturer |Allis-Chalmers |

|Motor Horsepower |1,250 hp |

|Motor Current |184 amps |

|Motor Voltage |4,160 volts |

|Motor Speed |395 rpm |

4. Operation, Control, and Safety

The circulating water system is generally one of the first systems started and one of the last systems shut down. The circulating water pump motors are energized from the station 4 KV switchgear, located in the first floor switchgear room, and are operated and controlled from the control room. Protective relays are incorporated into the operation of each pump motor feeder breaker. The relays are preset to trip the breaker in the event of motor overload or detection of a ground. Each breaker is equipped with the following protective relays:

➢ 51-50 relay (phase A)

➢ 51-50 relay (phase B)

➢ 51-50 relay (phase C)

➢ 51-50 ground relay

➢ 86 Lockout relay

Each feeder breaker is equipped with pistol grip, TRIP/CLOSE control switch, an ammeter and associated four position (OFF/1/2/3) control switch, and a hour meter. Green and red indicating lights are installed above the breaker control switch to provide the Operator with indication of breaker position. In the TRIP position, the breaker control switch can be locked out of service by turning the lockout relay control switch to the LOCKOUT position. When locked out of service, both breaker indicating lights are extinguished. Current flow through each phase of the breaker can be monitored at the ammeter by placing the ammeter control switch in the respective position.

The starting current to the circulating water pump motors is three to five times the full load current. The heavy current causes increased magnetic forces on the stator coils and heating of the rotor cage and stator winding. Starting limits must be followed to prevent any damage to the motor windings. With the motor cold, no more than two consecutive starts must be attempted. The motor must be allowed to coast to a complete stop between starts. With the motor hot, no more than one start must be attempted within 30 minutes of shutdown. If the hot-start attempt fails, a period of no less than 60 minutes must elapse before a second start may be attempted.

The operation of each pump is monitored and controlled in the Control Room through individual Stop/Normal/Start pump control switches. Indicating lights are located above each control switch to indicate pump status. A red light indicates the pump is operating, a green light indicates the pump is secured, an amber light indicates the pump is in auto, and a white light will indicate a motor trip condition. Above the indicating lights on the BTG Board is a remote motor load indicator (2CWIIB323/4) for each of the circulating water pump motors.

The operation of each circulating water pump is performed by the operator and no safety interlocks are provided other than motor overcurrent protection. Before a pump can be started, the manual inlet valves to the waterboxes must be two turns open and the steam turbine lube oil coolers, condenser vacuum system heat exchangers, and condensate cooling water heat exchangers manual inlet valves must be closed to prevent possible water hammer damage. In addition, the manual isolation valve for the rupture disk must be closed until the circulating system is filled and vented. Each circulating water pump is started by placing the control room individual control switch in the START position. Prior to opening the waterbox inlet valves the motor amperage, as indicated on the gauge above the control switch, must fall below 184 amps. After the circulating return flow to the cooling tower is established the manual inlet valves to the various auxiliary heat exchangers can be opened as required. Once return flow to the cooling tower is established and verified, the manual isolation valve for the system rupture disk is opened to protect the system from overpressurization.

During unit startup, one circulating water pump is placed in service. Once the unit is up to startup load, the second circulating water pump is placed in service. The point at which the second circulating pump is placed in service is dependant on the turbine back pressure and the ambient air temperature. At least one circulating pump should remain in service as long as turbine exhaust steam is entering the condenser. If only one circulating water pump can be used the turbine load must be reduced to allow all of the entering steam to be condensed and the proper turbine back pressure maintained.

2. Condenser

1. Function

The function of the condenser is to decrease the backpressure against which the steam turbine must operate, thereby permitting full utilization of available steam energy at the lowest absolute pressure. The condenser functions as a heat sink, under vacuum, to condense the turbine exhaust steam for reuse in the Condensate System. The condenser also serves as a centralized point of collection for condensate drains and vents of various plant equipment. The Circulating Water System supplies the water to be used to remove the heat.

2. Detailed Description

The main condenser, illustrated in Figure 2.2, is located directly beneath the low pressure turbines. The inlet and outlet waterboxes are located on the first floor and are vertically divided into two sides. The condenser is attached to the steam turbine by a flexible expansion joint. The condenser is a shell and tube type of heat exchanger which transfers heat from the steam turbine exhaust to the circulating water system. The driving force for this heat transfer is the difference in temperature, or thermal energy levels, of the two fluids. The greater the temperature, or energy level, difference the faster the heat transfer, or energy exchange. The heat transfer is enhanced by the large surface area of the condenser tubes.

[pic]

Figure 2.2 Condenser

The condenser tubes are arranged in a two pass, divided flow arrangement. Tube sheets installed on the inlet and outlet waterboxes separate the tube side and steam side of the main condenser. The circulating water is designed to flow through the main condenser at approximately 121,000 gpm during base load conditions. The condenser is equipped with 15,744 parallel tubes extending across the condenser from the inlet waterbox to the outlet waterbox. The tubes are supported by equally spaced support tube plates. The 90/10 Copper Nickel alloy tubes are 32 feet 8.375 inches long and 1.0 inch in diameter. The tubes provide a cooling surface area of 129,670 square feet.

Each condenser waterbox is equipped with a vent line to remove air from the waterbox. Each vent line is equipped with a manual valve which is opened during startup to vent the waterbox while filling the condenser tubes with circulating water. The condenser waterboxes are also equipped with various sample lines used by the laboratory to test the circulating water quality.

The shell side of the condenser is equipped with a pneumatically operated vacuum breaker (2AEPV482) that allows the condenser shell to be brought back to atmospheric pressure.

3. Technical Design Data

|Main Surface Condenser |

|Manufacturer |Westinghouse |

|Cooling Surface Area |129,670 |

|Number of Water Passes |2 |

|Capacity |1.048.384 lb/hr (steam condensed) |

|Cooling Water Supply |121,000 gpm |

|Cooling Water Inlet Temperature |86°F |

|Tube Material |90/10 CuNi Alloy 760 |

|Number of Tubes |15,244 |

|Tube Length |32 ft. 8.375 in. |

|Tube Diameter |1.0 inch O.D. |

|Tube Wall thickness |20 BWG |

4. Operation, Control, and Safety

Operation of the main condenser tube side is controlled by the flow of circulating water through the condenser tubes. At least one circulating water pump must be in service prior to placing one side of the condenser in service. The main condenser waterboxes should be vented during system startup by opening the vent line manual valves.

The condenser is placed into operation by starting the circulating water pumps and opening the circulating water inlet and outlet valves. Circulating water enters the condenser through the inlet waterboxes, flows through the condenser tubes, and exits through the outlet waterboxes into a common header. Circulating water removes the heat of evaporation from the turbine exhaust steam. The steam condenses at the tubes and falls to the bottom of the hotwell. The warm circulating water exits the waterboxes and flows back to the cooling tower.

When the main condenser is removed from service, the condenser tube side remains in service until the condenser vacuum has been decreased to atmospheric conditions and the Turbine Gland Steam System has been secured. The circulating water pumps are then removed from service to stop circulating water flow through the main condenser tubes.

Four thermocouples (2CWTE1231/2/3/4) are installed in the circulating water headers at the inlet and outlet (2 each) of the condenser. Each thermocouple provides an input signal to the Micromax Data Management System, and to the remote indicators located in the control room. Pressure transmitters (2CWPT280/1/2/3) provide input signals to the remote pressure indicators located in the control room. The signals provided by the thermocouples and transmitters, in conjunction with local pressure (2CWPI116/7/8/9) and temperature indicators (2CWTI065/6/7/8), provide a method of monitoring condenser performance.

The thermocouples also provide signals that will initiate the following alarms in the control room:

➢ "Waterbox A Inlet Temp High" at 115F

➢ "Waterbox B Inlet Temp High" at 115F

➢ "Waterbox A Outlet Temp High" at 135F

➢ "Waterbox B Outlet Temp High" at 135F

3. Cooling Tower

1. Function

The function of the cooling tower is to cool the circulating water used as a cooling medium in the surface condenser and the other auxiliary heat exchangers in the generating station.

2. Detailed Description

The cooling tower, illustrated in Figure 2.3, is located outside, to the west of the generating station main building. The cooling tower, manufactured by Hamon (Research Cortell), is a mechanical induced draft, cross flow type cooling tower. The tower is designed according to the counterflow principle and incorporates asbestos-cement heat transfer surface to assure maximum availability for year round operation, to minimize maintenance, and to virtually eliminate any necessity for replacement of parts or material.

[pic]

Figure 2.3 Cooling Tower

The tower consists essentially of the following six major parts:

➢ Basin

➢ Warm Water Inlet and Distribution

➢ Fill

➢ Drift Eliminators

➢ Structure/Enclosure

➢ Mechanical Equipment

Basin

The cold water basin, which is under the entire base of the tower, is 382 feet long by 71.2 feet wide and contains approximately 1,080,000 gallons of water when filled to the operating level (approximately six inches from the top of the basin wall). The water basin feeds water to the circulating water sump and then to the pump suction screens.

Warm Water Inlet and Distribution

Warm water enters the tower from the condenser outlet through a concrete pipe. This concrete pipe supplies water to six risers, or one per cell, which in turn supply the concrete distribution flumes above the fill level.

Each flume is fitted with asbestos-cement distribution pipes which distribute the warm water evenly to all sections of the tower fill. Each segment of pipe is fitted with evenly spaced plastic nozzles which in turn are fitted with splash plates that cause the water to be uniformly distributed over a wide area of fill.

Fill

The fill consists of a variable number of tiers of asbestos-cement sheets. These sheets are supported from prestressed concrete beams, with uniform spacing between the sheets main¬tained by plastic spacers and struts. Water leaving the splash plates falls onto the fill sheets where it runs down the sheets to the cold water basin below. The falling water is opposed by the induced air flow through the fill, and air/water contact is established.

Drift Eliminators

Immediately above the distribution piping network are the drift eliminator waves which are supported by the concrete structure. The drift eliminators reduce moisture entrained in the air from leaving the tower as drift.

Structure/Enclosure

The tower structure and enclosure consists of concrete and asbestos-cement components. Cast in place concrete columns support a combination of precast and cast in place beams. These beams carry the internals of the tower, support the fan stack and diffuser, and brace the asbestos-cement panels used as siding. The manner of casting the beams in the columns, results in a monolithic connection, requiring no future maintenance attention.

To facilitate inspection of the tower components, the tower is equipped with an access system. A walkway and stairway are provided on the north side of the tower. Access is provided to each cell through a door at the drift eliminator level. A ladder is provided on each warm water riser to provide for inspection of the remaining equipment.

For storm electrical shock protection the cooling tower structure is provided with a lighting protection system.

Mechanical Equipment

Each cooling tower cell consists of the following mechanical equipment:

➢ Fan

➢ Reduction Gear

➢ Motor

➢ Cell Slide Gates (MOVs)

The cooling tower fans are axial flow type specifically made for cooling tower service, and are manufactured by Hudson Products. Each fan consists of eight glass reinforced epoxy resin blades held by a galvanized steel hub. The 40 foot diameter fans are mounted on top of the output shafts of the gear reducers.

Each reduction gear reducer is manufactured by Nutall, and is a double reduction type. The reduction gear is a parallel shaft, mechanically lubricated type with a speed reduction ratio of 1785/88 rpm.

The reduction gear is directly connected by a flexible, non-lubricated coupling to an electric drive motor. The 200 horsepower totally enclosed fan cooled motor, manufactured by Allis Chalmers, is centrally located inside of each cell.

The motor and gear reducer are mounted to a structural steel frame. This frame is anchored on top of the cast-in-place riser, which provides a massive and rigid support and serves to dampen any vibrations generated by the operation of the equipment.

Each cell can be isolated for maintenance by the two motor operated slide gates (MOVs) provided for each cell. Two 24 x 41 inch Coldwell Wilcox slide gates are driven by two 6 to 1 worm gear boxes driven by a common electric operator. The electric operator is Rotork 14A Syncropak type of actuator. The slide gates isolate each side of the hot water flume for the specific cell.

3. Technical Design Data

|Cooling Tower |

|Manufacturer |Hamon Cooling Tower Division |

|Cooling Tower Type |Counterflow |

|Heat Exchange Direction |Vertical |

|Number of Cells |6 |

|Circulating Water Capacity |127,000 gpm |

|Cooling Tower Fans |

|Manufacturer |Hudson Products |

|Size |40 ft. diameter |

|Model |APT-40B-8 |

|Blade Type |Glass Reinforced Epoxy Resin |

|Number of Blades |8 |

|Speed |88 rpm |

|Cooling Tower Fan Motor |

|Manufacturer |Allis Chalmers |

|Electrical Supply |4KV / 3 phase |

|Horsepower |200 |

|Cooling Tower Fan Reduction Gear |

|Manufacturer |Nutall |

|Type |Double Reduction |

|Speed Ratio |1785:88 |

|Cooling Tower Slide Gate |

|Manufacturer |Coldwell Wilcox |

|Size |24 in. x 41 in. |

|Number Per Cell |2 |

|Electric Operator Manufacturer |Rotork |

|Electric Operator Model |14A Syncropak |

|Electric Supply |480 VAC / 3 phase / 60 Hz |

|Gear Box Type |6 to 1 worm gear |

4. Operation, Control, and Safety

Principle of Operation

The transfer of heat from the circulating water to atmosphere is accomplished in the cooling tower fill by passing the relatively warm circulating water over thin sheets, through a stream of moving air. The object of the cooling tower design is to achieve a maximum area of contact between the water surface and air. This is accomplished by flowing a very thin film of water down the sides of hundreds of thousands of asbestos-cement sheets that provide for maximum contact with the rising air through the sheet spacing.

Heat transfer from the warm water is accomplished primarily through evaporation, which makes it possible to cool the water below the atmospheric dry bulb temperature. In evaporating one pound of water approximately 1,000 BTUs are transferred from the water into the air. Additional heat is also transferred to the air due to the temperature difference between the water and the air.

The warm moist air is then drawn through the drift eliminators by the cell fans. The drift eliminators cause the air to abruptly change direction, thus removing the entrained water droplets. After the entrained moisture is removed from the air in the drift eliminators the fan discharges the slightly moist air to atmosphere.

The cooling tower is operated and controlled based on unit load, ambient temperature, humidity, and condition of the cooling tower equipment. The cooling tower is controlled by operating the cooling tower fans, maintaining basin level, and operating the cell slide gates.

Cooling Tower Fan Control

The cooling tower fan motors are energized from the station 4160 VAC loadcenters and operated and controlled from the control room. Protective relays are incorporated into the operation of each pump motor feeder breaker. The relays are preset to trip the breaker in the event of motor overload or detection of a ground. Each breaker is equipped with the following protective relays:

➢ 51-50 relay (phase A)

➢ 51-50 relay (phase B)

➢ 51-50 relay (phase C)

➢ 51-50 ground relay

➢ 86 Lockout relay

Each feeder breaker is equipped with pistol grip, TRIP/CLOSE control switch, an ammeter and associated four position (OFF/1/2/3) control switch, and a hour meter. Green and red indicating lights are installed above the breaker control switch to provide the Operator with indication of breaker position. In the TRIP position, the breaker control switch can be locked out of service by turning the lockout relay control switch to the LOCKOUT position. When locked out of service, both breaker indicating lights are extinguished. Current flow through each phase of the breaker can be monitored at the ammeter by placing the ammeter control switch in the respective position.

The starting current to the cooling tower fan motors is three to five times the full load current. The heavy current causes increased magnetic forces on the stator coils and heating of the rotor cage and stator winding. Starting limits must be followed to prevent any damage to the motor windings. With the motor cold, no more than two consecutive starts must be attempted. The motor must be allowed to coast to a complete stop between starts. With the motor hot, no more than one start must be attempted within 30 minutes of shutdown. If the hot-start attempt fails, a period of no less than 60 minutes must elapse before a second start may be attempted.

The operation of each cooling tower fan is monitored and controlled in the control room through individual Stop/Normal/Start control switches. Indicating lights are located above each control switch to indicate cooling tower fan status. A red light indicates the cooling tower fan is operating, a green light indicates the cooling tower fan is secured, an amber light indicates the cooling tower fan is in standby, and a white light indicates a motor trip condition. Above the indicating lights on the BTG Board is a remote motor load indicator for the cooling tower fan main drive motor.

The cooling tower fans are operated in conjunction with the Circulating Water Pumps in order to maintain condenser vacuum at approximately 28 inch Hg and a design cooling water temperature of 86°F. To maintain the proper condenser vacuum it may be required to produce a lower circulating water temperature. The cooling tower fans and circulating water pumps are operated to meet these "ideal conditions" which are influenced by ambient conditions. For example, if two circulating water pumps and all six cells on the cooling tower were in service with a rise in circulating water temperature, the condenser backpressure would also begin to rise due to the lack of cooling ability. At this point, an additional fan would be started in order to meet the backpressure and water temperature criteria.

The operation of each cooling tower fan is performed by the operator and no safety interlocks are provided other than motor overcurrent protection. Each cooling tower fan is started by placing its control switch in the START position. Typically, each fan is started and remains running until it is no longer required for operation.

Cooling Tower Level Control

The cooling tower cold water basin level is automatically controlled. A level transmitter (2CWLT064) located in the cooling tower basin sends a signal to a level controller (2CWLIC064) which in turn sends a pneumatic signal to the makeup level control valve (2CWLCV064) to maintain the level at 6 inches below the top of the cold water basin. The cooling tower cold water basin level can be observed on a remote level indicator (2CWLIB064) located in the control room, which is also fed its signal by the basin level transmitter (2CWLT064).

Sufficient water level must be maintained in the cooling tower cold water basin and the circulating water sump to prevent pump cavitation or loss of pump suction. Level switch (2CWLSL658) is installed in the circulating water sump to detect low water level. If the water level decreases to +74", the level switch initiates a "Cooling Tower Basin Level Low" alarm to the control room warning the Operator of the condition. When the level increases to +80", level switch (2CWLSH658) initiates a "Cooling Tower Basin Level High" alarm to the control room warning the Operator of the condition. No trips are associated with the alarms.

Each cooling tower is equipped with manually operated blowdown stations. The amount of blowdown depends on the amount of total dissolved solids in the circulating water. Typically, a water sample is taken on the outlet of the condenser water box from a drain valve. The water sample is analyzed for conductivity using a conductivity meter. The desired level of total dissolved solids (TDS) is between 200 - 700 ppm. The length of the blowdown varies based on the amount of total dissolved solids. Other chemical conditions are tested for and corrected for by the chemical laboratory. These include the following:

|Parameter |Normal Range |

|pH |8.0 - 8.3 S.U. |

|Conductivity |900 - 1100 mmho |

|Hardness (CaCO3 and Total) |360 - 400 ppm |

|P and M Alkalinity |4 - 6 ppm and 100 - 120 ppm |

|Phosphates |1.5 - 1.7 ppm |

|Tolytriazole |n/a |

|Silica |25 - 30 ppm |

|Sulfates |100 - 125 ppm |

|Chlorine |n/a |

|Copper |50 - 100 ppm |

Cooling Tower Cell Slide Gate Control

The cooling tower slide gates 2A through 2F are energized by 480 VAC feeder breakers located on MCC 2-9. Each breaker is equipped with an ON-OFF switch which opens and closes the breaker at the MCC.

At the cooling tower cells, each slide gate is provided with its own OPEN STOP CLOSE push buttons. Green and red indicating lights are provided to give slide gate operational status to the local operator.

The normal operation of each cooling tower slide gate is monitored and controlled in the Control Room through individual Open/Stop/Close control switches. Each slide gate is manually operated and has no automatic operation capabilities. Indicating lights are provided in the control room for each slide gate. A red light indicates the gate is closing or closed. A green light indicates the gate is opening or opened.

3. List of Instrumentation and Controls

|TABLE 1 – LOCAL INDICATING INSTRUMENTS |

|INSTRUMENT |FUNCTION/DESCRIPTION |NORMAL RANGE |

|2CWTI068 |WATERBOX 2A INLET TEMPERATURE |70 - 90 °F |

|2CWPI118 |WATERBOX 2A INLET PRESSURE |15 - 20 PSIG |

|2CWPI116 |WATERBOX 2A OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI066 |WATERBOX 2A OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI065 |WATERBOX 2B INLET TEMPERATURE |70 - 90 °F |

|2CWPI119 |WATERBOX 2B INLET PRESSURE |15 - 20 PSIG |

|2CWPI117 |WATERBOX 2B OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI067 |WATERBOX 2B OUTLET TEMPERATURE |80 - 100 °F |

|N/A |WATERBOX 2A LEVEL |MIDDLE |

|N/A |WATERBOX 2B LEVEL |MIDDLE |

|2CWTI096 |VACUUM COOLER 2A INLET TEMPERATURE |70 - 90 °F |

|2CWPI166 |VACUUM COOLER 2A INLET PRESSURE |15 - 20 PSIG |

|2CWPI164 |VACUUM COOLER 2A OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI098 |VACUUM COOLER 2A OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI097 |VACUUM COOLER 2B INLET TEMPERATURE |70 - 90 °F |

|2CWPI167 |VACUUM COOLER 2B INLET PRESSURE |15 - 20 PSIG |

|2CWPI165 |VACUUM COOLER 2B OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI099 |VACUUM COOLER 2B OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI101 |TURB GEN L/O COOLER 2A INLET TEMPERATURE |70 - 90 °F |

|2CWPI164 |TURB GEN L/O COOLER 2A INLET PRESSURE |15 - 20 PSIG |

|2CWPI172 |TURB GEN L/O COOLER 2A OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI103 |TURB GEN L/O COOLER 2A OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI101 |TURB GEN L/O COOLER 2B INLET TEMPERATURE |70 - 90 °F |

|2CWPI164 |TURB GEN L/O COOLER 2B INLET PRESSURE |15 - 20 PSIG |

|2CWPI172 |TURB GEN L/O COOLER 2B OUTLET PRESSURE |10 - 15 PSIG |

|2CWTI103 |TURB GEN L/O COOLER 2B OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI079 |C.C. WATER COOLER 2A INLET TEMPERATURE |70 - 90 °F |

|2CWPI143 |C.C. WATER COOLER 2A INLET PRESSURE |15 - 20 PSIG |

|2CWTI177 |C.C. WATER COOLER 2A OUTLET TEMPERATURE |80 - 100 °F |

|2CWTI080 |C.C. WATER COOLER 2A INLET TEMPERATURE |70 - 90 °F |

|2CWPI141 |C.C. WATER COOLER 2A INLET PRESSURE |15 - 20 PSIG |

|2CWTI078 |C.C. WATER COOLER 2A OUTLET TEMPERATURE |80 - 100 °F |

|Table 2 - Control Room Indicating Instruments |

|Instrument |Function/Description |Normal Range |

|2CWLT064 |Cooling Tower Level |+75" to +79" |

|2CWFT064 |Circulating Water Blowdown Flow |800 - 1000 gpm |

|2CWTE1232 |Waterbox 2A Inlet Temperature |70 - 90 F |

|2CWPT282 |Waterbox 2A Inlet Pressure |15 - 20 psig |

|2CWPT280 |Waterbox 2A Outlet Pressure |10 - 15 psig |

|2CWTE1233 |Waterbox 2A Outlet Temperature |80 -100 F |

|2CWTE1234 |Waterbox 2B Inlet Temperature |70 - 90 F |

|2CWPT281 |Waterbox 2B Inlet Pressure |15 - 20 psig |

|2CWPT283 |Waterbox 2B Outlet Pressure |10 - 15 psig |

|2CWTE1231 |Waterbox 2B Outlet Temperature |80 -100 F |

|2CWTE1338 |Vacuum Cooler 2A Outlet Temperature |80 - 100 F |

|2CWTE1339 |Vacuum Cooler 2B Outlet Temperature |80 - 100 F |

|2CWIIB323 |Circ Water Motor 2A Motor Load | ................
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