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5. Steam Turbine 1 / 128Thermal Fluid Techniques in Plants

5. Steam TurbineBearings

LP Casing

LP Inner Casing

Reheat Stop and

Intercept ValvesDouble ShellsPacking

Head

Packing

Head

Wheels and

Diaphragms


Steam Path Parts 102

Casing 755

Bearing 966

Steam Turbine Arrangement 21

Rotor 714

Valves 483

Recent Developmental Trend 1107


Layout of a Steam Turbine [1/3]

Front Bearing Pedestal

Thrust Bearing Pedestal

Journal Bearing Pedestal

Lube Oil Unit

Lube Oil Cooler

Condenser

HP Turbine

IP TurbineLP Turbine

Crossover Pipe

GeneratorGenerator Gas

Cooler

Generator Auxiliary

Equipment


SST5-6000 (Siemens), 280 bar 600C/610C, net plant efficiency above 45% (LHV)

Siemens

The function of the steam turbine is to convert the thermal energy contained in the steam into mechanical

energy for turning the generator.



Steam turbines are one of the most versatile and oldest prime mover

technologies still in general production.

Power generation using steam turbines has been in use for about 100

years due to higher efficiencies and lower costs.

A steam turbine uses a separate heat source and does not directly

convert fuel to electric energy.

This separation of functions enables steam turbines to operate

enormous variety of fuels, nuclear energy, natural gas, oil, coals, wood,

wood waste, and agricultural byproducts.

The energy is transferred from the steam generator to the turbine

through high pressure steam that in turn powers the turbine and

generator.



Steam Turbine Components


HP/IP Turbine Components


LP Turbine Components


Monolitic Concrete Foundation Spring Foundation on Transoms Spring Foundation on Single Supports

Spring Supported Foundation

Steam Turbine Foundation

Foundation is decoupled from the overall structure


Steam Path Parts 2

Casing5

Bearing6

Steam Turbine Arrangement1

Rotor4

Valves 3



A Typical 500 MW Class Steam Turbine

Turbine parameters Values

Manufacturer GE

TypeTandem-compound opposed flow, reheat turbine with two

double flow LP turbines

Number of stages 18 (6-5-7)

Steam conditions 2400 psig/1000F/1000F

Condenser pressure 1 in.Hga

rpm 3600

Steam flow 3,800,000 lb/h

Turbine capacity 512,094 kW

[ 3 Casing, 4-Flow ST ]

A Steam Turbine Used to Explain Details


Steam Flow [1/3]

A Typical 500 MW Class Steam Turbine


High-pressure steam from the secondary superheater outlet is routed through the main steam line to the main

stop valves.

The main steam line splits into two individual lines upstream of the stop valves, passing the steam to the two

main stop valves.

The steam passes through the stop valves to the external control valve chest, where four control valves are

located.

The steam passes through the control valves, and to the main turbine through four lines called steam leads.

Two of these steam leads enter the bottom of the high-pressure turbine, and two enter at the top.

Each of the four steam leads pass steam to an individual 90 degree nozzle box assembly mounted in quarter

segments around the periphery of the first stage of the high pressure turbine.

High-pressure steam enters the turbine near the center of the HP section, flowing through the individual

nozzle boxes and the six-stage HP turbine toward the front-end standard.

The steam then leaves the HP turbine, and returns to the reheat section of the boiler.

The reheated steam returns to the turbine through single hot reheat line, which splits into two individual lines

upstream of the combined reheat intercept valves.

Steam flows through the combined reheat intercept valves, and into the five-stage IP turbine.

Steam Flow [2/3]


The inlet end of the IP turbine is located near the center of the high-pressure section, next to the HP turbine

inlet.

Steam flow in the IP turbine is in the direction of the generator; this is opposite to the direction of flow in the

HP turbine.

Steam is exhausted from the IP turbine into a single crossover pipe, which routes steam from the IP turbine

exhaust to the inlet of the two double-flow LP turbines.

Steam then enters the center of each seven-stage LP turbine.

The LP turbines consist of two identical sets of LP turbine stages.

In each LP turbine; one-half of the steam flows through one set of LP turbine stages in the direction of the

turbine front standard, the other half of the steam flows through the other set of LP turbine stages in the

direction of the generator.

The steam then exits the LP turbines and is exhausted into the condenser.

The main turbine shaft is connected to and rotates the main generator.

Controlling the steam flow to the main turbine controls the generator speed and/or load.

Steam Flow [3/3]


Diaphragms

(Stationary Parts)

Buckets / Blades

(Rotating Parts)

Nozzle

Box

Steam Flow

Steam Path [1/7]

HP Turbine Section

[ Nozzle Box ]


Steam enters the single-flow HP turbine through separately mounted stop valves and control valves. A steam

lead from each of the control valves routes the steam to the center of the high-pressure casing. Two steam

leads are connected to the upper half of the casing and two to the lower half. Steam is admitted to both

casing halves allowing for uniform heating of the casing and thus minimizing distortion.

Each control valve regulates the steam flow to one of four nozzle box-opening sections (nozzles/partitions).

The nozzle boxes are located within the HP casing; thus containing the steam before it passes through the

first stage nozzle openings.

The steel alloy high pressure outer shell is supported on the front standard at the turbine end, and the middle

standard at the generator end.

The high-pressure inner shell is supported in the outer shell on four shims and is located axially by a rabbit fit.

The inner shell is keyed on the upper and lower vertical centerlines to locate it transversely. This arrangement

maintains accurate alignment of the inner shell under all operating conditions. The nozzle box steam inlets

are equipped with slip ring expansion joints that permit the nozzle boxes to move with respect to the shells

and still maintain a steam-tight fit.

Buckets are placed in grooves machined into the rotor. Each bucket is pinned to ensure its position is fixed.

The fixed blades are mounted in interstage diaphragms located between each stage of moving blades. The

interstage diaphragms serve as nozzles to increase the velocity of the steam and to direct the steam flow

onto the next stage of buckets. Each interstage diaphragm is constructed of two halves that are mounted in

grooves in the upper and lower casings. When assembled in the turbine, the diaphragms are sandwiched in

between the rotating wheels.

Steam leaving the nozzle boxes is directed through the HP turbine blading, with the steam flowing toward the

turbine front standard. The expanded steam exhausts through two nozzles at the bottom of the casing and is

routed to the reheat section of the boiler through the cold reheat line.

HP Turbine Section

Steam Path [2/7]


Diaphragms

(Stationary Parts)

Buckets / Blades

(Rotating Parts)

Nozzle

Block

Steam

Flow

IP Turbine Section

Steam Path [3/7]


IP Turbine Section

Steam is routed to the IP turbine through two parallel combined reheat intercept valves. During normal

operation, the reheat stop and intercept valves are fully open.

The outlets of the combined reheat intercept valves are welded directly to the bottom half of the HP turbine

casing, near the center.

Steam enters the IP turbine and passes through a nozzle block, which directs the steam onto the first stage of

IP turbine blades. Throughout the turbine, the turbine stages are numbered sequentially beginning with the

first stage of the HP turbine. Therefore, the first stage of the IP turbine is the seventh turbine stage.

The IP turbine moving blades are attached to the common HP and IP turbine rotor. The blades are placed in

grooves machined into the rotor and held in position by pinning. Interstage diaphragms are located between

each stage of moving blades.

The steam expands as it passes through each of the IP turbine stages and exhausts through a single

crossover pipe in the upper casing. The crossover pipe directs the steam to the LP turbines. The steam flow

through the IP turbine is toward the generator end, which is opposite to the flow in the HP turbine. By

arranging the flows in the HP and IP turbines in opposite directions, the axial thrust caused by the pressure

drop through the turbine stages is reduced.

A portion of the steam flowing through the IP turbine is extracted at the 9th and 11th stages of the turbine and

supplied to feedwater heaters 7-6A, 7-6B and deaerating heater No. 5 respectively. The 11th stage extraction

steam is also the normal low-pressure steam supply to the boiler feed pump turbines and a source of fire

protection to the mills.

Steam Path [4/7]


LP Turbine Section

LP - ALP - B

Steam Path [5/7]


LP Turbine “A” Section

Steam Flow

Atmosphere Relief Diaphragm

(Breakable Diaphragm, or

Rupture Disc)

Inner

Casing

Low Pressure

Exhaust

Bearing

No.3

Bearing

No.4

Steam Path [6/7]


LP Turbine Section

The function of the LP turbines is to convert part of the remaining energy contained in the steam exhausted

from the IP turbine to mechanical energy for rotating the generator.

The LP turbines are double-flow units with seven-stages. IP turbine exhaust steam flows through the

crossover pipe to the LP turbines. This steam enters each LP turbine at the center of the casing. Inside the

turbine, the steam flow is split, flowing across seven stages of blading to each end. The exhaust steam

leaving the LP turbines is then drawn through the exhaust hood to the main condenser.

The LP turbine casing consists of two halves, upper and lower. The casing halves are machined and bolted

together to ensure a steam-tight fit. The upper half is provided with two rupture discs, which relieve to the

turbine room atmosphere if the turbine exhaust pressure exceeds 5 psig. The lower casing half consists of an

inner and outer casing. The inner casing is the exhaust hood. Exhaust steam enters the main condenser

through this hood.

Exhaust hood spray is required to limit exhaust hood temperatures during startup and low loads, since the

steam flow through the turbine is not adequate to remove heat generated by the rotating turbine blades. The

condensate system supplies water to the exhaust hood sprays.

The LP turbine rotor is a single solid forging. The rotating blades are placed in grooves machined in the rotor.

Each blade is pinned to ensure its position is fixed. The fixed blades are placed in grooves machined into the

turbine casing. They are also pinned to ensure their positions are fixed.

Steam Path [7/7]


Nozzle Box

43

43

42

42

#1

#2#4

#3

Number of nozzle

Turbine C.W.

500 MW (3,500 psig, 1,000F)


Stage

Stage = 1 row of nozzle + 1 row of bucket

Nozzle = Stationary blade

Bucket = Rotating blade

Bowl = Entrance of a stage

Shell = Exit of a stage

Dovetail = Lock the bucket with a rotor shaft

Seal = reduce the steam leakage


Diaphragms are fitted into the casing and contain the

nozzles used to convert the pressure energy contained

in the steam into the kinetic energy at each stage of the

turbine.

The rotor shaft passes through each diaphragm and a

seal is created at each stage between the diaphragm

and rotor by a labyrinth seal.

The diaphragms are supported within the casing by rugs

and location keys that allow for expansion as the turbine

heats and cools.

Diaphragm [1/2]

Diaphragm : Partitions between two adjacent

bucket rows in a turbine's casing are called

diaphragms. They hold the nozzles and seals

between the stages. Usually labyrinth-type

seals are used. One-half of the diaphragm is

fitted into the top of the casing, the other half

into the bottom.


다이아프램(Diaphragm)

• Inner ring과 outer ring 사이에 노즐을 조립한하나의 열

• Outer ring은 터빈 케이싱에 조립되어 고정, inner ring은 축을 둘러싸고 있으며 labyrinth seal을 설치하여 증기누설 방지

Diaphragm [2/2]


V V+dV

Convergent nozzle

Nozzle [1/2]

Nozzle is used to accelerate the flow.

On the contrary, diffuser is used to decelerate the flow.

The steam is expanded partially or fully in a nozzle, resulting in the ejection of a high/medium velocity

jet.

This jet of steam impinges on the moving blades, mounted on a shaft.

Here it undergoes a change of direction and/or magnitude of motion which gives rise to a change in

momentum and therefore a force.

1

2


노즐(Nozzle)

• 증기 가속을 통해 증기의 압력에너지를 운동에너지로 변환시킴

• 따라서 노즐 입구와 출구 사이에 압력 차이발생하며, 압력 차이가 클수록 다이아프램을 튼튼하게 제작해야 함

• 노즐을 빠져나온 증기는 큰 접선방향 속도성분을 가지며, 매우 큰 운동에너지를 가짐

Nozzle Row Bucket Row

x

r

Nozzle [2/2]

u

u

c2

w2

w3

p1

p2

p3

u

1

c1

Nozzle Row

Bucket Row

2

2

3c3

3

c : absolute velocity of fluid

u : tangential velocity of blade

w : velocity of fluid relative to blade


Root

Tip

Nozzle row Bucket row

Stage

Active length

Dovetail

Cover

Diaphragm

Short bucket Long bucket

• Active length is shorter

than 10 inches.

• Active length is longer

than 10 inches.

• Bucket vibration should

be considered carefully.

• Radial velocity

component is employed

in the design stage.

Bucket [1/3]

Nomenclature

버켓(Bucket)

• Rotating blade를 의미

• 발전기를 구동하기 위한 회전동력 발생

• 노즐을 빠져나온 고속의 증기에 포함되어 있는 운동에너지, 열에너지, 압력에너지를 기계적인 일로 변환

• 버켓은 로터를 회전시키며, 로터의 회전동력이 발전기를 구동하여 전기 생산


Fir tree type

Finger typePine tree type

Dovetail

Axial entry dovetail

Bucket [2/3]

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=P-C-fheLea3uuM&tbnid=tEPjdfbbsRER_M:&ved=0CAUQjRw&url=http://www.engineeringcapacity.com/news101/sector-news/aerospace-and-defence/churchill-says-yes-to-viper-grinding&ei=FM5EU574B4m5iQewkoDYBg&bvm=bv.64507335,d.b2I&psig=AFQjCNEw_TpKLmbmsPGOBAvGV_hIBKcO8w&ust=1397104115085319

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=P-C-fheLea3uuM&tbnid=OiccGMfI8tESJM:&ved=0CAUQjRw&url=http://www.ppsvcs.com/products/steam-turbine/blades-buckets/&ei=k85EU4WOB6T_iAeX2oCoAw&bvm=bv.64507335,d.b2I&psig=AFQjCNEw_TpKLmbmsPGOBAvGV_hIBKcO8w&ust=1397104115085319

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=P-C-fheLea3uuM&tbnid=I6yW6ybArAE-hM:&ved=0CAUQjRw&url=http://www.ppsvcs.com/products/steam-turbine/blades-buckets/&ei=Ks9EU93XHoe0iQeCj4HgCw&bvm=bv.64507335,d.b2I&psig=AFQjCNEUYIjYEB84WU1K3zOFV1wmJ8DvRQ&ust=1397104782301793


Shrouded vs. Covered

Shrouded blade

Covered blade

Bucket [3/3]

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=P-C-fheLea3uuM&tbnid=OiccGMfI8tESJM:&ved=0CAUQjRw&url=http://www.ppsvcs.com/products/steam-turbine/blades-buckets/&ei=k85EU4WOB6T_iAeX2oCoAw&bvm=bv.64507335,d.b2I&psig=AFQjCNEw_TpKLmbmsPGOBAvGV_hIBKcO8w&ust=1397104115085319


R

ReactionAction

F

V

A

,Nozzle

F = mV = V2A

m = VA (mass flow rate)

유체역학적 힘

터빈 동력생산 원리 [1/6]


Incidence

Blade Inlet

Angle

Gas Inlet

Angle

Direction of

Gas Flow

Stagger Angle

Camber

AngleDeflection

Direction of

Gas Flow

Deviation

Angle

Gas Outlet

Angle

Blade Outlet

Angle

Pitch

Trailing Edge

Leading Edge

Blade Thickness Suction Side

Pressure Side

Axial

Tangential

터빈 블레이드 명칭



유체유동에 의해 발생하는 힘

2

1

Axial

Tangential

1Vm

2211 sinsin VVm

2Vm

1V

2V



유체유동에 의해 버켓에 발생하는 힘의 크기

• 배기가스는 피치에 해당하는 면적에 경사진 형태로 버켓통로로 유입

• 따라서 유동조건과 버켓 열이 형성하는 기하학적 데이터를 이용하면 유입되는 배기가스에 의해 버켓에접선방향으로 작용하는 힘의 크기 계산 가능

• 이와 같은 방법으로 버켓을 빠져나가는 유동조건을 이용하면 버켓을 빠져나가는 배기가스의 반작용에 의해 발생하는 접선방향 힘의 크기 계산

• 그리고 유입되는 배기가스와 배출되는 배기가스에 의해 접선방향으로 작용하는 두 힘의 크기를 합치면버켓에 접선방향으로 작용하는 전체 힘의 크기가 됨

• 그러나 이 방법으로는 버켓에 작용하는 힘의 크기를 정확하게 계산하기 어려움. 그 이유는 버켓 날개 표면에서 발생하는 경계층 때문에 버켓을 빠져나오는 유동이 균일하지 못하기 때문임

버켓에 작용하는 힘을 계산하기 위한 또 다른 방법으로 날개이론

• 이 방법은 버켓 표면에 작용하는 압력분포를 이용하여 양력을 계산하는 방법으로써 가장 정확하면서 실제적으로 가장 많이 이용

• 흡입면 압력이 압력면에 비해서 낮으며, 이로 인해 버켓에 양력 발생



NACA 4412

2

222

2

1112

1

2

1VpVppo

Pressure distribution

Velocity distribution

날개 주위 유체 거동



c1

2c2

P S S P

p2 p1 p

po

½ c12

½ c22

p2

1

bDirection of

Rotation

P: Pressure Surface

S: Suction Surface

버켓 단면에 나타나는 공기역학적 현상을 살펴보면, 배기가스가 버켓을 지나면서 압력면(pressure

surface)에 흡입면(suction surface)보다 높은 압력 형성

이로 인해 버켓 압력면에서 흡입면 방향으로, 즉 접선방향으로 버켓을 들어올리는 양력 발생

그런데 버켓은 터빈 디스크에 체결되어 있기 때문에 버켓에 발생하는 양력은 터빈 축을 회전시키는 토크로

작용하며, 이 토크가 압축기와 발전기 구동에 사용되는 회전력으로 작용

버켓에서 생산된 양력에 버켓이 회전한 거리를 곱하면 버켓이 한 일의 크기가 되며, 이 일의 크기가 버켓에서

생산된 기계적인 일의 크기가 됨. 한편, 일을 시간으로 나누면 동력이 됨



dA= (M21)

dV

VA

M 1

M 1Convergent Nozzle

(Nozzle)

M 1M 1Divergent Nozzle

(Diffuser)

M 1

M 1Convergent Nozzle

(Nozzle)

M 1M M 1Divergent Nozzle

(Diffuser)

Blade

direction

Axial

direction

Turbine

BladesCompressor

Blades

Flow in a Convergent-Divergent Nozzle

Last Stage Blade [1/8]


Convergent-divergent nozzle

x

M1 [ Convergent-Divergent Nozzle ]M1

M=1

dA= (M21)

dV

VA

[ Supersonic Converging-Diverging Nozzle, GE ]

Blade Overlap




삼천포화력본부 #6 LSB(33.5”/3600 rpm)

LSB developed by Siemens(32”/3600 rpm)




Mach Number Distribution Siemens

32-LSB/3600rpm (Siemens)



LSB Features


1) LSB는 LP터빈 형상을 결정하는 중요한 요소

2) LSB 길이는 사이트 대기조건과 응축계통에 의해서 가장 큰 영향을 받음

3) LSB가 길어질수록 배기손실이 감소하여 증기터빈 성능 향상. 그러나 동일한 출력을 가지는 증기터빈의 경우LSB가 길어질수록 제작비 증가

4) LSB는 큰 출력 생산. 일반적으로 대형 화력발전의 경우 LSB는 증기터빈 전체 출력의 약 10%를 생산. 복합발전의 경우 LSB는 증기터빈 출력의 15~17% 정도 생산

5) LSB가 길어지면 큰 회전속도가 나타나는 LSB 팁 부위에서 초음속유동 발생. 따라서 길이가 긴 LSB 팁 부위날개형상은 초음속유동에 적합한 수축-확산노즐 형태를 가짐

6) LSB는 습증기 영역에서 운전되며, 큰 회전속도를 가지는 팁 부위에서는 물방울과 큰 속도로 충돌하기 때문에 습분침식 발생. 따라서 대부분의 LSB는 화염경화나 방식막(erosion shield) 부착 등을 통해 습분침식 대비

7) LSB에는 고속회전으로 인한 큰 인장응력 발생. 최근에는 인장응력을 이겨내기 위해서 비중이 철금속의 절반정도인 티타늄합금을 이용하여 LSB 제작. 티타늄합금은 습분침식과 부식 저항성이 우수하기 때문에 LSB 재료로 많이 사용되고 있음. 그러나 티타늄합금은 가공성이 불량하기 때문에 LSB는 고가임

8) LSB는 길어질수록 고유진동수가 작아지기 때문에 진동특성 불량


57 inch

1.45 m

69 inch

1.75 m

75 inch

1.9 m

[ A typical LSB for Fossil Power Plants ] [ Typical LSBs for Nuclear Power Plants ]



Turbine Output and Annular Exhaust Area

45 LSB results in a 28% increase in annulus area over that of the 40 LSB.

Longer LSB provides reduced leaving velocity, which results in low exhaust losses and improved heat rate.

Increasing the turbine exhaust annular area gives increased capacity and turbine efficiency, but it increases

turbine size and capital and construction costs.

Increasing the LSB length is restricted by centrifugal stresses in blades, and the number of LP flows and LP

cylinders cannot be too great because of the total turbine length.

A way to reduce the centrifugal loads and make the longer LSB is to use titanium materials, which is lighter

and stronger than steel.

Longer blades are more expensive than shorter ones because they have a better resistance to water droplet

erosion.

The longer the blades, the harder vibration control of blades because of lower natural frequency.

A cylinder with too long a rotor has to be designed with increased radial clearances in its steam path because

of weight bowing of the rotor and danger of its increased vibration.



Convergent-Divergent LSB

The convergent-divergent LSB gives higher efficiency than

conventional LSB for higher discharge velocities of Mach

number of 1.4 in the tip section

However, the LSB having flat profile becomes more efficient

below a Mach number of 1.4

Therefore, it should be investigated flow behaviors at the tip

region of LSB during part load operation and changed back

pressure

It was found that, with reduced volumetric flow in the last stage

blade, the steam moves towards tip section, Thus, when the

overall volumetric flow is decreased, the flow distribution over

the blade length changes, resulting in a much larger reduction

of flow in the hub section and little change at the tip section

Typically, discharge velocity at the tip of LSB does not drop

below a Mach number of 1.3, which justifies the application of

the convergent-divergent profile under typically changing

operating conditions of power plants

Siemens

[ Free standing LSB (Siemens) ]


Convergent-divergent nozzle


Typical Turbine Location of Problems

SPE of Valves WDE of LSB

Seal Rubbing Fouling Stress Corrosion CrackingBearing Rubbing

Rotor Bow

due to rubbing

in transient

operation such as

during startup

SPE of Blades


Potential Components Causes

high

LSB • WDE

HP-1 stage

• SPE - high temperature and velocity

• creep (bucket)

• high cycle fatigue - partial arc admission

IP-1 stage• SPE - high temperature

• creep (bucket)

medium

LSB & L1 stage • corrosion

stages with drilled hole in the vane for

lacing wires• corrosion

HP-2, 3 & IP-2, 3 • SPE

HP-1 & IP-1 diaphragm • creep

Nozzle box • SPE

lowAll other components and stages in the

unit

Component Deterioration Potential


Water Droplet

Erosion

Fog Formation

(Condensation Shock)

Dry Steam Wet Steam

Phase

Change

Formation of Wet Steam


Steam Path Parts 2

Casing5

Bearing6


Rotor4

Valves 3



Steam Turbine Flow Diagram

Stop V/V

Control V/V

HP IP LP Gen

Condenser

ReheaterReheat Stop and

Intercept V/V

Main Steam

Hot Reheat

Cold

Reheat

Crossover pipe

Ventilation

V/V

HRH bypass station

(HRH: Hot Reheat)

HP

byp

ass

sta

tio

n LP


Throttling Process [1/8]

유체가 노즐이나 오리피스와 같이 갑자기 유로가 좁아지는 곳을 통과하면 외부와 열량이나 일의 교환 없이

도 압력이 감소하는 교축과정(throttling process) 발생.

교축과정이 발생하면 와류가 생성되어 에너지가 손실되면서 압력손실 발생.

작동유체가 액체인 경우 교축과정이 일어나서 압력이 액체의 포화압력보다 낮아지면 액체의 일부가 증발하

며, 증발에 필요한 열을 액체 자신으로부터 흡수하기 때문에 액체 온도 감소.

Pre

ssu

re P

1 2


열역학 제1법칙:

단순유동에서 교축과정이 일어나면, 벽면에서의 열전달이 없으며, 이루어진 일이나 공급된 일도

없으며, 위치에너지 변화량도 무시할 수 있으므로,

속도가 40m/s 이하인 경우 운동에너지 변화량은 엔탈피 변화량에 비해 매우 작다.

교축과정은 발전설비에서 자주 일어나는 과정인데, 특히 증기가 밸브를 통과할 때 교축과정이 발

생하며, 이때 압력강하가 발생한다.

12 hh (교축과정 = 등엔탈피 과정)

1212

2

1

2

212122

1wzzgcchhq

02

1 2

1

2

212 cchh



작동유체가 이상기체인 경우 교축과정이 발생한 후에 엔탈피는 일정하게 유지됨.

엔탈피는 온도만의 함수이므로 교축과정 발생 후에 온도변화 없음.

그러나 작동유체가 증기인 경우에는 교축과정이 발생하면 압력과 온도가 떨어져서 에너지 수준이 낮아짐.

주울-톰슨 효과(Joule-Thomson effect).

증기터빈 버켓커버 상부에는 증기누설을 방지하기 위해서 seal을 설치하여 증기누설 방지.

Seal을 통해서 누설되는 증기는 seal strips을 통과하면서 교축과정이 발생하기 때문에 실을 빠져나온 증기

는 온도와 압력이 떨어져서 엔탈피가 낮아짐.

따라서 누설증기가 다음 단에서 주유동과 합류하더라도 주유동의 에너지 수준을 높이지 못하기 때문에 손실

발생 누설손실

즉 누설증기가 실을 빠져나오면서 에너지를 잃지 않았다면 다음 단에서 사용할 수 있지만 이미 잃어버렸기

때문에 손실이 됨.

증기 특성



HP Turbine LP Turbine

MS R

100% Power

75% Power

50% Power

25% Power

Pre

ssure

C/V

A Basic Concept for Part Load Operation



Example: 460 MW, supercritical power plant

Output and Efficiency at Part Load

49.0

48.3

47.6

46.9

46.2

45.5

44.8

44.1

43.4

42.7

42.045 50 55 60 65 70 75 80 85 90 95 100

200

500

470

440

410

380

350

320

290

260

230

Load [%]

Effic

iency,

%

Pow

er,

M

W

Power

Efficiency



U100% load

Nozzle Row

25% load

100%

25%

Bucket Row

U

75% load

50% load

Design efficiency of the turbine blades is maintained during part load operations by using the control

valve

Velocity Diagram at Various Loads



A turbine has different expansion lines as

the load is decreased.

But the part load expansion lines are

generally parallel to the full load expansion

line.

This means that the internal efficiency under

part load conditions is very close to that

under full load conditions.

However, the cycle efficiency is reduced

under part load conditions.

Effect of Throttling on Non-Reheat Steam Turbine Expansion Line

p1

Ava

ilab

le E

ne

rgy

pc

p0

T0

h

s

Partial-flow expansion line

Expansion lines are

essentially parallel

Design-flow expansion line

p1’

p0: Inlet pressure

p1: Throttle pressure1 1′

2′

2



The steam has an initial pressure P1 at the entry to the seal

assembly.

After expanding past the first constriction, the pressure will

have been reduced to condition Xo, with pressure P2.

In the chamber formed between the first and second seal

strips, the kinetic energy of the steam is destroyed and

reconverted at constant pressure P2 to condition X.

From point X, there is then a further expansion of the steam

past the second constriction, with the pressure falling to P3 at

condition Yo.

The kinetic energy is again reconverted in the chamber

between the second and third seal strips, raising the thermal

energy level from Yo to Y at constant pressure P3.

This process of expansion and kinetic energy reconversion is

continued throughout the series of seal strips until the final

expansion takes the steam to condition Qo at pressure P5.

The locus of the points Xo….Qo is called the Fanno curve.

h

s

T1

P1 P2P3 P4

P5

Xo YoZo

Qo

X Y Z

Leakage

Flow

P1 P2 P3 P4 P5

X Y Z

Rotation Side

Principle of Labyrinth Seal



Main Steam Valves

Valve 개수(표준화력 500MW 기준) - Stop v/v : 2- Control v/v : 4

Stop valve = on-off valveControl valve = throttle valve라고도 불리며, load 연동

Typical closing time during emergency- Stop v/v : 0.09초 10%- Control v/v : 0.11초 10%

Generals


Typical Individual Stop and Control Valve Assembly

MSV

MCV

Actuator

Actuator

GE

Steam

Inlet

Steam

Strainer

Valve Seat

Valve Stem

Valve Disc

Steam

Outlet

Pressure

Seal Head

Actuator

Closing

Spring

[ Main Stop Valve ]


The main stop valves are located in the main steam piping between the boiler and the turbine control valve

chest.

The primary function of the stop valves is to provide backup protection for the steam turbine during turbine

generator trips in the event the main steam control valves do not close.

The energy contained in the main steam can cause the turbine to reach destructive overspeed quickly when

generator loose the load.

The main stop valves close from full open to full closed in 0.15 to 0.5 s.

The main stop valves are closed on unit normal shutdown after the control valves have closed.

A secondary function of the main stop valves is to provide steam throttling control during startup.

The main stop valve bypass valves are also used for full arc operation during startup and shutdown of the

turbine.

The main stop valves typically have internal bypass valves that allow throttling control of the steam from

initial turbine roll to loads of 15% to 25%.

During this startup time, the main steam control valves are wide open and the bypass valves are used to

control the steam flow.

The main steam stop valves are operated and controlled by the turbines Electro Hydraulic Control System.

Some recent and current designs do not have these bypass valves.

Initial turbine speed runup is controlled by the main stop valves.

Main Stop Valves [1/3]


The bypass valve is held in the valve disk by a

bolted cap. Holes are located in the cap for steam

entrance, and holes in the valve disk pass the

steam when the bypass valve is utilized.

When the stop valve is opened the bypass valve

opens first as the valve stem moves in the open

direction.

When the bypass valve is fully open it contacts a

bushing on the stop valve and pulls it open. When

the stop valve is fully open, a bushing seats on the

inner end of the valve stem bushing and prevents

steam leakage along the valve stem.

Main Stop

Valve Stem

Main Stop

Valve Disc

Seating

Surface

Main Stop

Valve Disc

Bypass

Valve Disc

Bypass

Valve Ports

(8 ea)

[ Stop Valve Bypass ]

Each stop valve has two steam leakoff points where the stop valve stem passes through the stop valve

casing.

The first leakoff point located closest to the stop valve is referred to as the high-pressure leakoff and is

routed to the steam seal header.

During startup or low loads steam is supplied to this leakoff to assure a seal. After the turbine is loaded,

steam is fed through this line from the stop valve stem into the steam seal header.

The second leakoff point is referred to as the low-pressure leakoff and is routed to the gland steam

condenser.

Bypass Valve GE



Bypass Valve



The steam from the stop valves flows to the

main steam control or governor valves.

The primary function of control valves is to

regulate the steam flow to the turbine and thus

control the power output of the steam turbine

generator.

The control valves also serve as the primary

shutoff the steam to the turbine on unit normal

shutdowns and trips.

MHI

Main Steam Control Valves [1/4]

MSV

MCV

Actuator

Actuator

Siemens

Steam from

No.1 C/V

Steam from

No.3 C/V

Steam from

No.4 C/V

Steam from

No.2 C/V

HP

Inner

Shell

HP

Inner

Shell

HP

Inner

Shell

HP

Inner

ShellSnout

Pipe

Seal

Rings

HP

Inner

Shell

HP

Inner

Shell

Snout Pipes

Snout Pipes

180 Degree Nozzle Box

180 Degree Nozzle Box

Upper

Lower

Snout

Pipe

Seal

Rings


Control V/V

(1.5% p @ VWO)

Nozzle

First stage

shell pressure

Fully Open

Stop V/V

(1.5% p)

Partially Open

Closed

Bucket

#1

#2

#3

#4

Steam

Flow

#1

#2Closed



GE

The control valves regulate the steam flow to the turbine to

control the main turbine speed and/or load. The four control

valves are mounted in line on a common external valve chest.

Steam is supplied to the external valve chest through the main

stop valves. The valve chest is separated from the turbine, and

individual steam leads from the valve chest are provided from

each control valve to the inlet of the HP turbine. Each control

valve is operated by a hydraulic power actuator which positions

the control valves in response to signals from the Electro

Hydraulic Control System.

During startup, the control valves are wide open (full arc), and

the stop valves’ internal bypass valves control the steam flow to

the turbine. Under these conditions, steam is admitted through

all four steam leads around the entire periphery of the HP

turbine inlet. The purpose of this full arc admission is to reduce

thermal stresses caused by unequal steam flow through the

nozzle sections. During full arc admission, throttling of the

steam occurs at the stop valve bypass valves only, and there is

uniform steam flow into the HP turbine. This also results in

lower steam velocities at the turbine inlet. Because of the lower

steam velocities the temperatures cannot change as rapidly.

Full arc admission is used until the high transfer point is

reached, at which time transfer to partial arc will occur. [ Main Steam Control Valve ]

Closing

Spring

Balance

Chamber

Valve

Seat Valve

Disc

Steam

Chest



During normal operation, the main stop valves are wide open and the control valves control steam flow to

the turbine. The control valves operate sequentially to control steam flow to the turbine and the unit load.

All four control valves are never open the same amount for any given load up to full load with wide-open

control valves. This is referred to as partial arc admission.

Transfer to partial arc admission is normally automatically performed by the low transfer and high transfer

micro- switches but may also be initiated by the operator when the OK TO TRANSFER light comes on.

The control valves are throttled until they have control of steam flow and the stop valves then automatically

run full open.

Number l and 2 control valves are balanced type, with internal pilot valves. Number 3 and 4 control valves

are unbalanced single disk type.

The balanced type valves are equipped with an internal pilot valve connected to the valve stem. When

opening, the pilot valve is opened first to equalize the pressure across the main valve disk. Further opening

of the stem opens the main disk.

The disk of the unbalanced type valve is directly connected to the stem.

Each control valve is provided with two steam leakoff points where the control valve stem passes through

the external steam chest wall. The first leakoff point located closest to the external steam chest is referred to

as the high-pressure leakoff and is routed to the hot reheat steam line. The second leakoff point is referred

to as the low-pressure leakoff and is routed to the steam seal header.

GE



Reheat Stop and Intercept Valves [1/3]

[ Combined Reheat Stop and Intercept Valve, GE ]


Balance

Chamber

Intercept

DiscReheat

Stop Disc

Steam Out

Steam

In

Intercept

Actuator

Closing

Spring

Reheat Stop

Actuator

Steam

Strainer

GE Two combined reheat stop and intercept

valves are provided, one in each hot

reheat line supplying reheat steam to the

IP turbine.

As the name implies, the combined

reheat intercept valve is actually two

valves, the intercept valve (IV) and the

reheat stop valve (RSV), incorporated in

one valve casing.

Although they utilize a common casing,

these valves have separate operating

mechanisms and controls.

The function of the intercept valves and

reheat stop valves is to protect the

turbine against overspeed from stored

steam in the reheater.

[ Reheat Stop and Intercept Valves (SKODA) ]



The function of the reheat stop and intercept valves is similar to the main steam stop and control valves.

The reheat stop valve offer backup protection for the steam turbine in the event of a unit trip and failure of

the intercept valves to close.

The intercept valves control unit speed during shutdowns and on large load changes, and protect against

destructive overspeeds on unit trips.

The need for these valves is a result of the large amount of energy available in the steam present in the HP

turbine, the hot and cold reheat lines, and the reheater.

On large load changes, the main steam control valves start to close to control speed, however, energy in the

steam present after the main steam control valves may be sufficient to cause the unit to overspeed.

The steam after the main steam control valves could expand through the IP and LP turbines to the

condenser, supplying more power output than is required, causing the turbine to overspeed.

The intercept valves are used to throttle the steam flow to the IP turbine in this situation to control turbine

speed.

During unit shutdowns, a similar situation could occur, and the intercept valves are used to control speed

under these conditions as for the trip condition.

During unit trips, both the reheat stop and the intercept valves close, preventing the reheat-associated steam

from entering the IP turbine.

During normal unit operation, the reheat stop and intercept valves are wide open, and load control is

performed by the main steam valves only.



During unit trips, the closure of the main stop and control valves and of the

reheat stop and intercept valves traps steam in the HP turbine.

During the turbine overspeed and subsequent coastdown, the HP turbine

blades are subject to windage losses from rotating in this trapped steam.

The windage losses cause the blades to be heated.

This heating, in combination with the overspeed stress, can damage the HP

turbine blades.

To prevent this, a ventilation valve is provided to bleed the trapped steam to

the condenser.

On a unit trip, the valve is automatically opened.

The bleeding action causes the trapped steam to flow through the HP turbine,

maintaining the HP turbine temperature within acceptable limits by preventing

heat buildup from the windage losses. [ Ventilation Valve, CCI ]

Ventilation Valve


Steam Path Parts 2

Casing5

Bearing6


Rotor4

Valves 3



LP Rotor Shaft [1/2]

블레이드가 장착되어 있는 로터축은 LP터빈 전체 가격의 약 40% 차지.

로터축 가격은 허브 지름에 의해서 결정. 로터축 가격을 낮추기 위하여 허브 지름을 줄이면 버켓 단 수와 로터축 길이 증가 (h U2). 로터축이 가늘고 길어지면회전체 동력학 측면에서 설계 어려움. 아울러 로터축이 길어지면 터빈빌딩이 커지기 때문에 발전소 건설비용 증가.

단 수와 허브 지름은 LP터빈 구성과 로터축 설계를 결정하는 가장 중요한 요소.

Shrunk-on rotor

Monoblock rotor

Welded rotor


열박음 로터축(shrunk-on rotor)

• 초대형 잉곳을 확보하기 어려울 때 사용.

• 지름이 작은 로터축을 제작한 후에 휠 디스크를 제작하여 열박음을 통하여 일체화.

• 제작이 쉬운 반면에 기동정지 시에 불안정한 진동이 발생하기 쉬우며, 휠 디스크에 응력부식균열이 발생하는 단점 보유.

• 최근에는 거의 채택하지 않고 있음.

일체형 로터축(monoblock rotor)

• 최근 제강기술이 발달하여 가공중량 200톤 정도의 일체형 로터축 제작

• 열박음 로터축에 비해 강도가 한층 높으며, 응력부식균열이 나타나지 않기 때문에 신뢰성이 높음.

• 열박음 로터축에 비해 제작에 많은 시간이 소요.

• 국내 화력발전 LP터빈 로터축은 모두 일체형이며, 원자력발전은 영광 5.6호기와 울진 5.6호기부터 모두일체형으로 설계.

용접 로터축(welded rotor)

• 원자력발전과 같은 대형 LP터빈에 사용. 현재는 용접기술과 열처리기술이 발달하여 몇 개의 로터를 용접으로 연결하여 하나의 로터축으로 제작한 용접 로터축을 많이 사용.

• 가격이 상대적으로 저렴한 작은 잉곳 여러 개를 이용하기 때문에 전체적으로 가격 저렴.

• 제작단계에서 재료결함 검사가 용이하기 때문에 신뢰성 우수. 일반적으로 로터축 내부 빈 공간은 부식 방지를 위해 진공 유지.

• 두 가지 이상의 서로 다른 재료를 용접하여 사용할 수 있기 때문에 로터축 온도분포에 따른 최적의 로터축제작. 초임계압 발전에서 나타나는 고온부식을 줄이기 위해 전통적으로 사용하던 CrMoV에 9Cr과 12Cr강을 용접하여 사용.

LP Rotor Shaft [2/2]


Wheel Type vs. Drum Type

Impulse Reaction

Bucket

Tip

Diaphragm

Root

cylindrical

drum type

rotor

disc wheels

shrunk on to a

rotor shaft


Casing5

Bearing6


Rotor4


Steam Path Parts 2

Valves 3


Casing

HP Inner Casing

HP Outer Casing

IP Inner Casing

IP Outer Casing

LP Inner Casing

LP Outer Casing

Crossover Pipe

Bearing Pedestal

제작

HP/IP Casing Casting

LP Casing Fabrication

구조

Single Casing 저압력 터빈(원자력) & Small turbine

Double Casing High pressure & Large turbine

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=9P2jgMX2Q-3QZM&tbnid=pr_UIxk3RRkvsM:&ved=0CAUQjRw&url=http://www.sandvik.coromant.com/en-gb/industrysolutions/condensing_power/steam_turbines/pages/default.aspx&ei=KgpCU5SVAcnJiAfqgoGADw&bvm=bv.64125504,d.dGI&psig=AFQjCNHcxQr275tUCdEXqm1pAsj_5alpqA&ust=1396923190993408


Generals for Casing

케이싱 특성

• 대형 증기터빈의 경우 고압(HP)/중압(IP)/저압(LP) 케이싱으로 구성

• 분해/조립이 쉽도록 수평면 기준 2분할 구조이며, 볼트로 결합

• 배럴형(barrel type, or cylindrical type)으로도 제작 – 열응력과 강도 측면에서 우수, 터빈을 수직으로 세워 분해/조립해야 하므로 정비 측면에서는 불리

• 저압 케이싱 하부는 복수기와 연결

• Inner casing에는 노즐과 다이아프램(블레이드 링) 장착

• 열팽창이 자유로우며, 일정한 형상 유지

• 케이싱 하부에 배수관(drain tube) 설치 - 터빈 정지 시 케이싱 내부 응축수 생성으로 인한 부식및 열변형 방지

2중 케이싱 특성

• 열응력 감소 – 터빈 출구 증기를 inner casing과 outer casing 사이로 흐르게 하여 각각의 케이싱내면과 외면의 온도차를 감소시켜 열응력 발생 감소

• 기동/정지 시간 단축

• 케이싱 두께 감소 – 케이싱 내면과 외면의 압력차 감소

Barrel type casing (Siemens)

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HP/IP Casing

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=s5Grfi-_4vbUpM&tbnid=Ai-8DBs7CtWuzM:&ved=0CAUQjRw&url=http://www.doosan.com/doosanheavybiz/en/services/power/power_plant/turbine/products/steam_turbine.page&ei=hQxCU8e7Hei3iQfR-4GADQ&bvm=bv.64125504,d.dGI&psig=AFQjCNGKCaBv417kgdW5E9CF-Lhv6m8nVA&ust=1396923770715975

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=s5Grfi-_4vbUpM&tbnid=Ai-8DBs7CtWuzM:&ved=0CAUQjRw&url=http://www.doosan.com/doosanheavybiz/en/services/power/power_plant/turbine/products/steam_turbine.page&ei=ZAxCU5jJFIujiAfwyYGQCw&bvm=bv.64125504,d.dGI&psig=AFQjCNGKCaBv417kgdW5E9CF-Lhv6m8nVA&ust=1396923770715975


IP Casing

Double casing (Siemens)

Single casing (GE)


LP Casing [1/7]

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=5f-RynAm_vf75M&tbnid=jACibBFrZUpbTM:&ved=0CAUQjRw&url=http://www.ge-energy.com/products_and_services/products/steam_turbines/fossil_d_series.jsp&ei=oApCU_OVFaL1iQeT5ICABg&bvm=bv.64125504,d.dGI&psig=AFQjCNHcxQr275tUCdEXqm1pAsj_5alpqA&ust=1396923190993408

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&docid=-2ASYEg78gRSPM&tbnid=FQflhhJWGA372M:&ved=0CAUQjRw&url=http://www.energy.siemens.com/us/en/fossil-power-generation/steam-turbines/sst-500-geo.htm&ei=SwZCU4vGC4mriAeLrYHICw&bvm=bv.64125504,d.dGI&psig=AFQjCNFelGkLH9lwkw287xQvw17NB1QgUQ&ust=1396922195478401


LP Turbine (Siemens) LP Turbine Inner Casing (Siemens)

LP Casing [2/7]


A push rod concept permits parallel axial thermal expansion of LP rotor and inner casing.

This reduces clearances between rotor and casing and improves the efficiency.

Siemens

LP Casing [3/7]


외부케이싱 외부는 대기압, 내부는 복수기 진공압력이 작용하기 때문에 외부케이싱에는 약 500톤의 진공하중이 작용. 외부케이싱은 진공하중 이외에 내부케이싱 중량과 약150톤 정도의 외부케이싱 자중이 작용. 따라서 외부케이싱은 이들 하중에 견딜 수 있도록 강도와 강성을 확보하기위하여 내부 여러 곳에 지지대와 리브 설치.

외부케이싱 상부에는 동판으로 제작된 대기방출판(atmospheric relief diaphragm, or breakable diaphragm, or rupture disc) 설치.

대기방출판은 증기터빈 안전장치로서 복수기에 냉각수 공급이 정지하거나 어떤 다른 원인에 의해서 LP exhaust hood 압력이 대기압보다 높은 압력(130~140 kPa)으로올라가면 외부케이싱 외부로 증기압력이 작용하여 동판이칼날에 의해 절단되면서 증기를 외부로 방출시켜 LP exhaust hood 및 복수기 파손을 방지.

만약 운전 중에 배압이 상승하면 경보가 울리며, 계속해서상승하면 low vacuum trip이 작동하여 증기터빈을 트립시켜 LP exhaust hood와 복수기를 보호하지만 그 이상으로올라가면 최종적으로 대기방출판이 절단되면서 증기터빈보호.

Atmospheric Relief Diaphragm

LP Casing [4/7]


LP Exhaust Hood

LP exhaust hood is a transition structure

between the LSB exit and the condenser.

It consists of a steam guide, bearing cone,

butterfly vane, outer casing, end wall, and

various plates.

It changes the direction of the steam flow

exiting LSB plane from axial to radial of

the downward flow LP exhaust hood.

It supports the main components of LP

turbine, such as inner casing, diaphragms,

bearings etc.

Condenser Flange

Steam

Guide

Collector

Bearing

Cone

Outer Casing

End

Wall

LSB

Inner Casing

Steam Flow

Siemens

LP Casing [5/7]


It is generally employed for small industrial steam turbines.

The steam exiting LSB enters condenser in axial direction.

The flow distribution is uniform on the LSB exit plane along circumferential direction.

It has a lower exhaust loss than downward flow LP exhaust hood.

It requires a larger plant area than downward flow LP exhaust hood.

LP Exhaust Hood - Axial Flow Exhaust

SST-800 (Siemens) SST-600 (Siemens)

Siemens

LP Casing [6/7]


It is generally employed for large steam turbines.

It has a higher exhaust loss than axial flow LP exhaust hood because of the change of flow direction

from axial to radial, and then downward finally.

It requires a smaller plant area than axial flow LP exhaust hood.

LP Exhaust Hood - Downward Flow Exhaust

LP Casing [7/7]


W = Work

HL = Hood Loss

LL = Leaving Loss

EL = Exhaust Loss

EEL = Effective EL

UEEP = Used Energy End Point (or TEP)

ELEP = Expansion Line End Point

SEP = Static End Point

EL = Change in EL

W = Change in Work

EEL = Change in EEL

pc = Static Pressure at Turbine

Exhaust Flange

pTB = Total Pressure at Last Blade Exit

pSB = Static Pressure at Last Blade Exit

Exhaust Loss

Total Expansion LineStatic

Expansion

Line

EEL

W=EEL

ELEPSEP

LL

HL

EL

sB

hT2

W

hS1

EL

hT1

h

s


Typical Exhaust Loss Curve

UEEP = ELEP + Exhaust Loss

The internal efficiency of a

steam turbine does not include

the loss at the turbine exhaust

end.

The exhaust loss includes

(1) actual leaving loss,

(2) gross hood loss,

(3) annulus-restriction loss,

(4) turn-up loss.

Exh

au

st L

oss, B

tu/lb

of d

ry f

low

0

Annulus Velocity, fpsSonic

200 400 600 800 1000 1200 1400 16000

10

20

30

40

50Annulus

Restriction

Loss

Gross Hood

Loss

Actual

Leaving

Loss

Turn-up

Loss

Total

Exhaust

Loss


Annulus Velocity, ft/s

Exh

au

st L

oss, B

tu/lb

of d

ry f

low

200 400 600 800 1000 1200 1400

6

50

46

42

38

34

30

26

22

18

14

10

20

Bucket Pitch Last stage

Curve length diameter annulus area

no. (inches) (inches) single flow (ft2)

1 14.3 52.4 16.3

1 16.5 57.5 20.7

1 17 52 19.3

1 20 60 26.2

2 23 65.5 32.9

3 26 72 41.1

4 30 85 55.6

5 33.5 90.5 66.1

(1) Read the exhaust loss at the annulus velocity obtained from

the following expression:

Van = m(1-0.01Y) / 3600Aan

(2) The enthalpy of steam entering the condenser is the quantity

obtained from the following expression:

UEEP = ELEP + (Exhaust loss)(0.87)(1-0.01Y)(1-0.0065Y)

(3) This exhaust loss includes the loss in internal efficiency

which occurs at light flows as obtained in tests.

Van = Annulus velocity (fps)

m = Condenser flow (lb/hr)

= Saturated dry specific volume (ft3/lb)

Aan = Annulus area (ft2)

Y = Percent moisture at ELEP

ELEP = Expansion line end point at actual

exhaust pressure (Btu/lb)

UEEP = Used energy end point (Btu/lb)

1

1 2345

2 3 4 5

Exhaust Loss [3,600 rpm, GE]


Turn-up

Region

Normal Rating Operation Low Load Operation

Exhaust Hood Spray [1/6]

Turn-up Loss


[ Eroded Trailing Edge of LSB near the Hub ] [ Recirculation in the Exhaust Hood ]

Water supply line

Water running down

casing walls

Recirculating steam

Water

sprayLSB


[ Source: 한전KPS ]


When the relative velocity leaving LSB is very low, LSB acts like a compressor, and this makes the exhaust

loss is getting higher.

Evidence this pumping action can be detected on turbines with an L-1 extraction. That is, the pressure of

extracted steam from L-1 stage is lower than the condenser pressure during part load operations.

The heat produced by the pumping action requires cooling on both LSB and LP exhaust hood.

In order to remove the windage heat that is generated by recirculation occurred in the lower half of last stage

blade, water is sprayed into the exhaust hood.

The spray water cools the LSB and exhaust hood.

The spray water starts at 60C(140F) in LSB exit and turbine is tripped at 107C(225F) in LSB exit or at

260C(500F) in L-1 stage.

Additional evidence can be detected by the slight water droplet erosion occurred near the root on the suction

side of trailing edge of LSB.

This water droplet erosion is caused by the suction of the spray water into the trailing edge of LSB because

of reverse pressure gradient between L-1 and the last stage.

It had also been found that a large recirculation flow is formed near the root of LSB because of reverse

pressure gradient between L-1 and the last stage.

This recirculation flow produces another loss, which is called as “turn-up loss”.



Trailing edge erosion on the

suction side

Crack in the trailing edge

caused by erosion - PT

A crack emanating from a

trailing edge gouge

Trailing Edge Erosion



Turn-up Region에서의 사고사례 [1/2]



Turn-up Region에서의 사고사례 [2/2]



Casing5

Bearing6


Rotor4


Steam Path Parts 2

Valves 3

Type of Steam Turbines8

Recent Developmental Trend9


Journal

(Radial) Force

Thrust Force

베어링과 접촉하고 있는 축 부분을 저널(journal)이라고 하며, 그 접촉상태에 따라 미끄럼베어링(sliding bearing)과 구름베어링(rolling bearing) 두 종류로 분류

미끄럼베어링은 베어링이 저널부의 표면 전부 또는 표면의 일부를 둘러싼 것 같이 되어 있으며, 베어링과저널의 접촉면 사이에는 보통 윤활유 존재. 이 베어링은 면과 면이 접촉하기 때문에 축이 회전할 때 마찰저항이 구름베어링보다 크지만 큰 하중을 지지할 수 있음

구름베어링은 축과 베어링의 볼 또는 롤러가 접촉하며 축이 회전하면 볼 또는 롤러도 같이 회전하기 때문에마찰저항이 작음.

회전하는 기계축에는 하중이 축과 수직으로 걸리는 경우와 축방향으로 걸리는 경우가 있음.

베어링은 하중 방향에 따라 그 구조가 많이 달라지며, 축과 수직으로 하중이 걸리는 경우에 사용하는 것을저널 또는 레이디얼(journal or radial)베어링이라 하고, 축방향으로 하중이 작용하는 경우에 쓰이는 것을 스러스트(thrust)베어링이라 함

Bearing

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=_70wepulFAhBaM&tbnid=kiEopsJlWx0i_M:&ved=0CAUQjRw&url=http://reliabilityweb.com/index.php/print/balancing_of_an_fd_fan_at_a_refinery&ei=Q011U528GcyKuATMroLwAQ&bvm=bv.66917471,d.c2E&psig=AFQjCNE-eJL5fSio1m_3RwA2lY9DKeZ5fA&ust=1400282810526491


Journal Bearing [1/7]

Tilting Pad Journal Bearing

Oil InletOil Discharge

Rotation



[ Typical Forces Acting on Individual Pads ]



Film Pressure

Distribution

Q2

Qs

B

X

Q1h2

h1

U

(P)Q-h2

UQ '

111

(P)Qh2

UQ '

222

s21 QQQ

W mAUB (h1/h2)2

W: Load capacity

m: Oil viscosity

A: Shoe area

U: Runner velocity

h1: Inlet film thickness

h2: Outlet film thickness

Q: Flow rate

Qs: Side flow rate

X/B: Pivot ratio




Elliptical Journal Bearing

Rotation



The journal bearings are numbered 1 through 10 beginning with No. 1 located in the front standard, and

proceeding through No. 6 located at the generator end of No. 2 LP turbine. Journal bearings No. 7 and 8 are

generator bearings, and 9 and 10 are exciter bearings.

Journal bearings No. 1 and 2 are tilting pad, self-aligning bearings consisting of six Babbitt-lined steel pads.

The pads are supported on a straight seal in the bearings shells, three in each half, so as to be free to pivot

in the direction of shaft movement and adapt them to the greatest oil film wedge during operation.

Oil is fed into the bearing at the center joint on the upcoming side of the journal. The oil groove at the

opposite joint contains a drilled hole, which restricts the flow sufficiently to build up a slight pressure on the

discharge side of the bearing. Oil passing through this discharge hole is carried to the oil sight box; most of

the oil, however, discharges through the ends of the bearings.

Journal bearings No. 3 through No. 10 are elliptical bore-type bearings.

The ellipse of the bearing bore is obtained by machining the bore to the larger horizontal diameter, with

shims inserted in the joints of the bearings; the shims are then removed for final assembly. The bore has an

overshot oil groove extending over the top half of the lining.

To facilitate the entrance and discharge of the oil, the bearing has the Babbitt cut away at the horizontal joint.

This forms oil grooves with well rounded edges, which extends to within a short distance of the ends of the

bearing.

The TURBINE BRG TEMP HIGH alarm is energized whenever the exiting oil temperature exceeds 155F.



Elliptical Journal Bearing

정지상태 회전 시작 회전 시작 후 고속 회전

Journal at rest

No oil film

Rotation begins

Oil film forms

Journal pushed

over to left against

direction of rotation

Journal moves to

right in direction of

rotation

Load Rotation Rotation Rotation



Divergent

Cavitated Film

X

Y

Rotation

Minimum Film

Maximum Film

Temperature

Center Line

Maximum Pressure

Hydrodynamic

Pressure Profile

Converging

Oil Wedge

Bearing



Equalizing Thrust Bearing Rotating Thrust CollarPivoted

Shoe

Direction of

Rotation

Thrust

Collar

Oil WedgeLeveling Plates

Base Ring

Thrust

Thrust Bearing [1/4]

[ Tapered Land Oil Wedge ]


Equalizing Thrust Bearing - Kingsbury



Thrust Runner Thrust Runner

Turbine Shaft

Spacer Plates

Copper Backed

Tapered Land

Thrust Plates

Thrust case

Thrust case



The thrust bearing is located on the main shaft of the turbine. Independently mounted inside the middle

standard, the thrust bearing absorbs the axial thrust of the turbine and generator rotors, which are

connected by a solid coupling.

This tapered-land thrust bearing consists of two stationary thrust plates, and two rotating thrust collars on

the turbine shaft, which provide the front and back faces to the bearing. These plates are supported in a

casing so that they may be positioned against the rotating faces of the collars. The thrust collar faces are

machined and lapped, producing smooth, parallel surfaces.

The surfaces of the two thrust plates are babbitted, and have tapered lands of fixed converging surfaces,

permitting a wedge of oil to exist between the rotating thrust collars and the thrust plates. The thrust plates

are constructed as split copper rings, with the babbitted surfaces divided into lands by radial, oil feed

grooves. The surface of each land is tapered, so that it slopes toward the rotating collar, both in the direction

of rotation and from the inner to the outer radius at the leading edge of the land. The radial grooves are

dammed at the outer ends, maintaining an oil pressure in the groove.

Bearing oil, at 25-psi, is fed into the thrust bearing by separate feed pipes to each thrust plate. The proper

amount of oil is metered to the bearing by an orifice in each pipe. The individual oil supplies enter the lower

half of the casing radially, and are carried into the radial oil grooves of each thrust plate.

Most of the oil from the thrust bearing discharges through the casing and into the bottom of the standard,

where it is returned to the oil tank through the drain pipe. A portion of the discharge oil is piped through a

sight box on the standard. This permits a visual inspection of the oil flow and temperature measurement of

the oil.

The temperature of the inlet oil should be 110 to 120F. The normal temperature rise of the oil should not

exceed 45F. The bearing should operate at a fairly constant temperature rise under full-load conditions.

Any sudden increase in the average temperature rise [5F or greater] should be considered abnormal, even

though the total rise may be within 45F. The TURB THRUST BRG TEMP HIGH alarm is energized

whenever the exiting oil temperature exceeds 175F.



Combined Type Bearing

정상운전 상태에서 하중을 담당하는 패드를 active pad라 하며,

반대 편에 있는 것을 inactive pad라 함

Active Thrust

Plate

Inactive

Thrust Plate

Active Thrust

Collar

Inactive Thrust

Collar

Thrust Collars

Integral with

Rotor

Steam

Flow

Oil

ScoopOil

Feed

Rotor

Pin

Shim

Journal

Bearing

[ A Thrust – Journal Bearing ]


Casing5

Bearing6


Rotor4


Steam Path Parts 2

Valves 3


Classification of Fossil Plants

EPRI

Nomenclature Steam ConditionsNet Plant

Efficiency, %

Net Plant Heat Rate

(HHV), Btu/kWh

Subcritical2400 psig (16.5 MPa)

1050F/1050 F (565C/565C)35 9751

Supercritical (SC)3600 psig (24.8 MPa)

1050F/1075F (565C/585C)38 8981

Ultrasupercritical (USC)3600 psig (24.8 MPa)

1100F/1150 F (593C/621C) 42 8126

Advanced

Ultrasupercritical (A-USC)

5000 psig (34.5 MPa)

1292F (700C)

and above

45 7757

Critical point of water = 3208 psia/705°F

(22.09 MPa/374.14C)

Supercritical steam cycles: Operating

pressure is higher than critical pressure of

water. Water to steam without boiling.

Ultra-supercritical steam cycles: Steam

temperatures above 1100°F as defined by

Electric Power Research Institute (EPRI)


Coal-fired power generation is still a fundamental part of energy supply all over the world.

Reliability, security of supply, low fuel costs, and competitive cost of electricity make a good case for coal-

fired power plants.

Requests for sustainable use of existing resources and concerns about the effect of CO2 emissions on global

warming have strengthened the focus of plant engineers and the power industry on higher efficiency of

power plants.

Efficiency has more recently been recognized as a means for reducing the emission of carbon dioxide and

its capture costs, as well as a means to reduce fuel consumption costs.

USC power plant is an option for high-efficiency and low emissions electricity generation.

USC steam conditions are characterized by 250 bar and 600C main steam and 600C reheat steam

conditions.

It is based on increased steam temperatures and pressures, beyond those traditionally employed for

subcritical plants.

Every 28C (50F) increase in throttle and reheat temperature results in approximately 1.5% improvement in

heat rate.

Besides increasing the steam parameters, optimizing the combustion process, reducing the condenser

pressure, and improving the internal efficiency of the steam turbines are some of the well known means for

raising the overall plant efficiency.

Due to the efficiency penalties associated with carbon capture and storage, such improvements are more

than ever needed to ensure a sustainable generation of electricity based on coal.

Introduction to USC Steam Turbine


Siemens

Efficiency Improvement in PC-Fired Plant

46

45

44

43

42

41

43

42

41

40

39

% %

1.15

1.25

120C

130C

300 bar/600C

250 bar/540C

Single reheat

Double reheat

1.9 in.Hga

0.88 in.Hga

Excess Air Discharge

Flue Gas

Temperature

Main Steam

Condition

Reheat Back

Pressure

Pla

nt N

et E

ffic

ien

cy B

ase

d o

n L

HV

Pla

nt N

et E

ffic

ien

cy B

ase

d o

n H

HV

Advanced Hood

USC

USC


Parameter Units Subcritical USC

Plant size MW 600 600

Net plant efficiency % LHV 38.0 46.0

Total investment cost EU/kW 874 920

Fuel price EU/GJ, bituminous 1.6 1.6

Load factor % 85 85

Cost of electricityc/kWh

UK p/kWh

3.5

2.3

3.3

2.2

Breakdown of cost

of electricity

Fuel

Capital

O&M

c/kWh

1.5

1.3

0.7

1.2

1.4

0.7

Comparison of Cost

Source: Best Practice Brochure (DTI, 2006)


Te

mp

era

ture

[C

], P

ressu

re [b

ar]

0 1920 1940 1960 1980 2000 2020

700

800

500

600

300

400

100

200

0

10

20

30

40

50

60

1

10

100

1000

10000

Ma

x O

utp

ut Ta

nd

em

Co

mp

ou

nd

[M

W]

Th

erm

al E

ffic

ien

cy [%

]

Pressure

Thermal Efficiency

Temperature

Power Output

History of USC

Steam Cycle

Simple Reheat Supercritical

Siemens


Heat Rate Improvement by USC

1000 1100 1200

Pla

nt N

et H

ea

t R

ate

Im

pro

ve

me

nt,

%

8

7

6

5

4

3

2

1

0

2.8 %

2.4 %

2400 psig/1000F/1000F

versus

4500 psig/1100F/1100F

2400 psig (165 bar)

Sub-Critical

USC 2900 psig (200 bar)

3650 psig (250 bar)

4350 psig (300 bar)

5800 psig (400 bar)5050 psig (350 bar)

Double Reheat vs. Single Reheat:

Heat Rate Improvement = 1.6%

Temperature, F

Comparison

2.8% + 2.4% + 1.6% = 6.8%

Siemens


History of USC Development


USC Steam Turbine – Siemens

Key Technical Features

Model SST5-6000

Gross power output 813 MW

Net plant efficiency (based on

cooling tower)~45.6% (@ design point)

Main steam conditions 280 bar/600C/610C

LP turbine - LSB 4 Flow - 45

Feedwater preheating 9-stages

Final feedwater temperature 308C

Specific CO2 emission Well below 800 g/kWh


Model SST-6000




USC Steam Turbine – GE



Net plant efficiency 48.7% (@ design point)

Main steam conditions250 bar/600C/610C

(3626 psia/1112F/1130F)


Arrangement of rotor shaft Cross-compound



Net plant efficiency ?

Main steam conditions260 bar/610C/621C

(3770 psia/1150F/1180F)


Arrangement of rotor shaft Tandem-compound


700C Steam Turbine Development [ALSTOM]

Welding Balance Piston

USC Steam Turbine – Alstom


USC Steam Turbine - Doosan


Output @ Max Guarantee Rating 1000 MW

Output @ VWO 1100 MW

Net plant efficiency 49% (estimated value)


LSB 4 Flow - 45

Cycle Single reheat regenerative

Bearings

LP Casing

LP Inner Casing

Reheat Stop and

Intercept ValvesDouble ShellsPacking

Head

Packing

Head

Wheels and

Diaphragms


Alloy Strength

H282

IN740

H230

TP310HCbN

IN617

S304H

T24

T92

TP347H

T22

T12

1100 1200 1300 1400 1500 1600700 800 900 1000

Temperature, F

Allo

wa

ble

Str

ess, ksi

50

45

40

35

30

25

20

15

10

5

0

Ferritic Nickel Alloys

Au

ste

nit

ic


A-USC Steam Conditions

Steam Conditions Remark

EPRI 5100 psia/1290F/1330F (347 bar/700C/721C)

Net plant efficiency = 43.4% (HHV)

• Boiler efficiency = 87.2%

• HP/IP/LP effi. = 90/94.2/88.6%

US. DOE 5015 psia/1350F/1400F (341 bar/732C/760C) Materials program objective

EU 5500 psia/1290F/1330F (375 bar/700C/721C) Net plant efficiency = 52-55% (LHV)

Some abbreviations and its definition

TPC: Total Plant Cost.

LCOE: Levelized Cost of Electricity.

Fixed O&M: personnel and insurance costs.

Variable O&M: cost depending upon the operation regime of the plant. Included items are:

• Inspection and overhauls, including labor, parts, and rentals

• Water treatment expenses

• Catalyst replacement

• Major overhaul expences

• Air filter replacements


Clean and cheap power generation is of prime importance to cope with the challenges imposed by an

increasing energy demand throughout the world.

In recent years, costs associated with CO2 emissions have attracted more attention because of global

warming.

Carbon capture and storage (CCS) and capture ready power plant designs are becoming increasingly

important for the evaluation of investments into new power plants and in addition retrofit solutions for the

existing power plants are required.

Efficiency improvement is a means for reducing emission of CO2, the costs of carbon capture, water use,

particulates, sulfur dioxides (SOx) and nitrogen oxides (NOx) emissions, and fuel consumption.

As coal is more abundant in many parts of the world, coal price is more stable than natural gas price.

However, greater CO2 emissions increase the need for more efficient coal-fired power plants.

USC steam power plants meet notably the requirements for high efficiency to reduce both fuel costs and

emissions as well as for a reliable supply of electric energy at low cost.

Recent developments in steam turbine technologies and high-temperature materials allowed for significant

efficiency gains.

Due to CO2 emission limits and corresponding penalties, the conventional coal-fired power plant with the

efficiency lower than 40% become less cost-effective.

NETL and EPRI studies show that current CCS technologies have CO2 removal costs of $50 to 70/ton.

Background for USC Power Plants


CO2 Emission vs. Plant Efficiency

The need of further reduction of environmental emissions from coal combustion is driving growing interest in

high-efficiency and low-emissions coal fired power plants.

Every 28C (50F) increase in throttle and reheat temperature results in approximately 1.5% improvement in

heat rate.

Every 1% improvement in plant efficiency results in approximately 2.5% reduction in CO2 emission.

An increase in plant efficiency from 30% to 50% reduce CO2 emissions about 40%.

A-USC plants having net plant efficiency of 45%, without CCS(Carbon Capture and Sequestration), will

produce about 22% less CO2 than the average subcritical plants that include the majority of units currently in

service and operating at about 35% net plant efficiency.

Combining CCs with A-USC plants will provide lower cost of electricity generation with 90% carbon capture.

A-USC will lower the CO2 per kWh, thus reducing the size of the CCS equipment.

Oxy-combustion CCS plant that achieve 90% carbon capture use about 20.5% auxiliary power which

includes the compression purification unit (CPU), additional cooling tower, air separation unit (ASU), and

polishing scrubber.

The efficiency penalty associated with CO2 capture based on Siemens advanced process is 9.2%.


CO2 Emission vs. Plant Efficiency

CO

2E

mis

sio

n, g

/kW

h

800

600

1200

200

0

400

Net Plant Efficiency, % (LHV)

36 4828 32 40 44 52 56

1000


DeN

Ox

FG

D

EP

CO

2

Cap

ture

Flu

e G

as

Coo

ling

Chim

ne

y

Continuous

Emission

Monitoring

System

Remove

85-90% of

NOx

Remove

99.7% of

Fly Ash

Remove

90-95% of

SO2

Remove

90% of

CO2

Post-Combustion Capture Technology


질의 및 응답

작성자: 이 병 은 (공학박사)작성일: 2016.02.15 (Ver.1)연락처: [email protected]

Mobile: 010-3122-2262저서: 실무 발전설비 열역학/증기터빈 열유체기술

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