Aco Study Guide Week 5

Front 1

Downcomers

Back 1

Six pipes coming from the bottom of the steam drum used to supply feedwater to the boiler circulating pump suction manifold.

Front 2

Waterwall Tubes

Back 2

Gets water supply from the boiler circulating pumps through the mud drums. Transfers heat from the furnace to the Boiler water to produce steam. Feeds into the steam drum.

Front 3

Boiler Circulating Pumps

Back 3

Takes suction from the boiler circulating pump suction manifold through MOVs. Used to provide controlled circulation of the boiler water through the boiler waterwall tubes. All three pumps are normally in service but, if only two are to be used then load can only be at a max of 80%.

Front 4

Steam Drum

Back 4

Supplies suction to the the boiler circulating pumps though six downcomers and a suction manifold. Separates saturated steam from the boiler water by moisture separators inside the drum. Reduces the dissolved solids content of the steam before it leaves the steam drum via boiler blowdown system.

Front 5

Mud Drum

Back 5

Two drums (one in front and one at the rear of the boiler) that receive water from the boiler circulating pumps to feed the waterwall tubes.

Front 6

Furnace

Back 6

The area inside the boiler where the fuel is burned. It is lined with waterwall tubes and is where the heat is generated to turn the boiler water inside the waterwall tubes into steam.

Front 7

Economizer and Economizer Recircs

Back 7

Economizer preheats the Feedwater prior to entering the steam drum to help limit the thermal stresses on the waterwall tubes and improving efficiency.

A pair of 2" lines from the lower rear mud drum enter the economizer inlet header for recirculation of water during startup to prevent steaming in the economizer.

Front 8

Percentage Blowdown

Back 8

Used to control the concentration of solids in the boiler water and as a means of draining the various sections of the boiler.

One 1% and two 2% valves routed to the blowdown tank.

Front 9

Superheater

Back 9

Used to increase the temperature of the steam flowing from the steam drum at 690°F to the high pressure section of the turbine at 1005°F.

Front 10

Reheater

Back 10

Used to reheat the steam leaving to the high pressure section of the turbine back to 1005°F for use in the intermediate section of the turbine.

Front 11

Main Steam Line

Back 11

Used to provide steam from the steam drum through the superheaters to the high pressure section of the turbine.

Front 12

Cold Reheat Line

Back 12

Used to transfer steam exhaust from the high pressure section of the turbine to the reheater.

Front 13

Hot Reheat Line

Back 13

Used to transfer reheated steam at 1005°F from the reheater to the intermediate section of the turbine.

Front 14

Steam Seal Regulator

Back 14

Automatically maintains the steam seal header at a constant 5 psig. This is accomplished by supplying the header with main steam at low loads, and directing excess steam to the diverting valve at high loads.

Front 15

Steam Seal Bypass

Back 15

The high pressure bypass valve is used to supply the steam seal header directly from main steam by passing the regulator. This valve is used during start up with low steam pressure when the regulator itself cannot maintain seal header pressure. The high pressure bypass valve is fully closed during normal operation.

Front 16

Steam Seal Unloader

Back 16

Used to bleed steam from the seal header directly to the diverting valve, bypassing the regulator. This valve is closed during normal operation.

Front 17

Steam Seal Diverting Valve

Back 17

Automatically directs excess steam from the steam seal regulator to the 17th stage feedwater heater extraction line or the main condenser. Excess steam is normally directed to the 17th stage extraction line but, whenever conditions are such that steam could enter the turbine instead of the feed water heater, steam is directed to the condenser.

Front 18

Gland Steam Exhauster

Back 18

Creates a slight vacuum in the shaft packing and condenses the collected sealing steam for reuse by the system.

Front 19

Steam Seal Supply

Back 19

Receives steam from the main steam lines at low loads, or dumps excess steam at higher loads.

Front 20

Gland Steam Exhauster Blower

Back 20

Maintains a negative system pressure and removes air from the gland steam exhauster shell.

Front 21

How is the Gland Steam Exhaster vacuum controlled?

Back 21

By throttling the butterfly valve in the discharge of the gland steam exhauster blower.

Front 22

Steam Seal Packing

Back 22

The packing seals the turbine against leakage to or from atmosphere.

Front 23

Purpose of a Turbine

Back 23

The turbine is a machine which is designed to convert the heat energy of the steam supplied by the boiler into rotating mechanical energy.

Front 24

Thrust Bearing

Back 24

Thrust bearings absorb the axial thrust of the turbine rotor and maintain the axial internal clearances of the turbine.

Front 25

Which steam seals are pressure seals?

Back 25

1 and 3. The HP and IP turbines operate at a pressure greater than atmospheric at higher loads. For this reason there packings are designated as pressure packings.

Front 26

Which steam seals are vacuum seals?

Back 26

4, 5, 6, and 7. The LP turbines operate at pressures below atmospheric, regardless of load. For this reason, these packings are designated vacuum packings.

Front 27

Main Steam Stop Valve

Back 27

During normal operation, the main stop valves add mid steam to the HP Turbine. In an emergency or during shutdowns, the main stop valves shut off the flow of steam; and during startups, they can regulate the rate of steam flow to the HP turbine.

Front 28

Control Valves

Back 28

The control valves regulate the rate of steam flow to the HP turbine during normal operation to control the turbines speed. During emergencies or shutdowns, they serve as a backup to the main stop valves to shut off the flow of steam to the HP turbine.

Front 29

Combined Reheat Valves

Back 29

The reheat stop valves admit reheated steam to the IP turbine during normal operation. They shut off the flow of steam to the IP turbine during emergencies or shutdowns.

Front 30

Rupture Diaphragm

Back 30

To prevent the compromise of the turbine casing from overpressurization. They are located on top of the LP turbine casings.

Front 31

Main Steam Stop Valve Bypass

Back 31

Used to regulate the rate of steam flow during startup through the main steam stop valve. Normally on the "B" MSSV.

Front 32

Intercept Valves

Back 32

Minimizes a turbine overspeed during a load rejection by gradually closing down when the turbine reaches a certain percent of speed above it's normal operating speed. Starts to close when turbine hits approximately 101% of its operating speed. At 105% the valve is fully closed and steam flow to the IP turbine is stopped and the rotor slows down.

Front 33

Ventilator Valve

Back 33

In the event of a load rejection or following a trip out after carrying load, the high pressure turbine section may overheat due to windage losses if allowed to spin in high pressure bottled up steam. To alleviate this, a ventilator valve is applied to the high pressure turbine section and is connected so as to draw steam from the down stream side of the reheater backwards through the high pressure turbine rotating buckets, through the valve and then exhausted to the condenser. It provides a relatively small cooling flow through the high pressure section of the turbine.

Front 34

Packing Blowdown Valve

Back 34

Prevents the turbine from overspeeding by redirecting the steam from the mid-span seal to the condenser during a turbine trip. Steam leaking from the mid-span seal would travel to the IP and LP sections of the turbine causing it to overspeed on a turbine trip.

Front 35

Hood Sprays

Back 35

Used to cool the turbine hoods.

Front 36

First Stage Drain

Back 36

Used to drain water from the 1st stage line during startup to prevent hammering.

Front 37

First Phase of Turbine Startup

Back 37

Starting the lubricating oil system, engaging the turning year, opening the turbine drains, putting the steam sealing system and service, creating a vacuum in the condenser, and resetting the turbine steam valves.

Front 38

Turning Gear

Back 38

Runs at 2 rpm. Functions to turn the turbine rotor slowly to promote even shaft heat up and even shaft cooldown during start up and shut down.

Front 39

Needed before drawing vacuum

Back 39

1. The lubricating oil systems must be started.

2. The main turbine must be placed on the turning gear.

3. Shaft sealing must be applied and then the vacuum can be drawn.

Front 40

Purpose of steam seals in the turbine

Back 40

Prevents leakage of steam out of the HP and IP turbines and in leakage into the LP turbine.

Front 41

Function of labyrinth seals

Back 41

Prevent the excessive out leaguists of steam or in leakage of air along the turbine rotor shaft.

Front 42

Theory of operation of labyrinth seals

Back 42

Steam has to travel I very torturous path while trying to leak along the shaft. A pressure drop occurs at each direction change, minimizing leakage out.

Front 43

Purpose of turbine bearings

Back 43

Support road or wait, absorb radial and axial forces, and maintain radial and axial clearances.

Front 44

Operation of a rupture diaphragm

Back 44

As pressure increases in the turbine exhaust line, a positive pressure develops in the casing. When casing pressure increases to the rupture set point, the diaphragm separates, relieving pressure.

Front 45

Reheat stop valves

Back 45

Admit re heated steam to the ip turbine and isolate flow to the ip turbine during emergency or shut down

Front 46

Heating steam blocking valve

Back 46

Installed in the number 1 packing 1st leak offline to the 12th stage extraction line. Its primary function is to block heating steam flow from the high pressure turbine to the 12th stage extraction line when pre warming the turbine prior to placing it on the line.

Front 47

H2 System

Back 47

Hydrogen is used as a cooling medium within the generator because of its high thermal conductivity and low density compared with other calling mediums. Hydrogen provides 14 times the heat transfer of air with little windage losses. Hydrogen cooling greatly reduces the size of a generator for a given output. A hydrogen cooling system consists of circulation fans, coolers and associated piping, pressure vessels and instrumentation required to maintain the proper hydrogen pressures and purity and efficient and safe generator operation.

Front 48

CO2 System

Back 48

Carbon dioxide is used as an innerting gas for adding and when removing hydrogen from the generator. Concentrations of hydrogen and air between 5 and 70% will cause a fire or explosive hazard. Therefor, the hydrogen cannot be added to a generator full of air and air cannot be added to a generator full of hydrogen. The CO2 to is used to push out the hydrogen or air in the generator when emptying or filling the generator with hydrogen as to not mix with air.

Front 49

Front Standard

Back 49

Houses the thrust bearing.

Front 50

Where do the after seat drains go from the MSSV?

Back 50

To the condenser

Front 51

Where do the before seat drains go from the MSSV?

Back 51

To the blowdown tank