5. Steam Turbine Wheels and Diaphragms Bearings Packing Head LP Inner Casing LP Casing Packing Head Double Shells Reheat Stop and Intercept Valves 5. Steam Turbine 1 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement 2 Steam Path Parts 10 Valves 48 Rotor 71 Casing 75 Bearing 96 Recent Developmental Trend 110 5. Steam Turbine 2 / 128
Layout of a Steam Turbine [1/3] Generator Gas Cooler Generator LP Turbine Crossover Pipe Journal Bearing Pedestal IP Turbine Thrust Bearing Pedestal HP Turbine Front Bearing Pedestal Lube Oil Unit Lube Oil Cooler Generator Auxiliary Equipment Condenser 5. Steam Turbine 3 / 128
Layout of a Steam Turbine [2/3] Siemens SST5-6000 (Siemens), 280 bar 600C/610C, net plant efficiency above 45% (LHV) The function of the steam turbine is to convert the thermal energy contained in the steam into mechanical energy for turning the generator. 5. Steam Turbine 4 / 128
Layout of a Steam Turbine [3/3] 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. 5. Steam Turbine 5 / 128
Steam Turbine Components 5. Steam Turbine 6 / 128
HP/IP Turbine Components 5. Steam Turbine 7 / 128
LP Turbine Components 5. Steam Turbine 8 / 128
Foundation is decoupled from the overall structure Steam Turbine Foundation Monolitic Concrete Foundation Spring Foundation on Transoms Spring Foundation on Single Supports Spring Supported Foundation 5. Steam Turbine 9 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend 5. Steam Turbine 10 / 128
A Typical 500 MW Class Steam Turbine A Steam Turbine Used to Explain Details Turbine parameters Manufacturer Type Values GE Tandem-compound opposed flow, reheat turbine with two double flow LP turbines Number of stages 18 (6-5-7) Steam conditions Condenser pressure 2400 psig/1000f/1000f 1 in.hga rpm 3600 Steam flow Turbine capacity 3,800,000 lb/h 512,094 kw [ 3 Casing, 4-Flow ST ] 5. Steam Turbine 11 / 128
A Typical 500 MW Class Steam Turbine Steam Flow [1/3] 5. Steam Turbine 12 / 128
Steam Flow [2/3] 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. 5. Steam Turbine 13 / 128
Steam Flow [3/3] 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. 5. Steam Turbine 14 / 128
Steam Path [1/7] HP Turbine Section Diaphragms (Stationary Parts) Steam Flow Nozzle Box Buckets / Blades (Rotating Parts) [ Nozzle Box ] 5. Steam Turbine 15 / 128
HP Turbine Section Steam Path [2/7] 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. 5. Steam Turbine 16 / 128
Steam Path [3/7] IP Turbine Section Steam Flow Diaphragms (Stationary Parts) Nozzle Block Buckets / Blades (Rotating Parts) 5. Steam Turbine 17 / 128
Steam Path [4/7] 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. 5. Steam Turbine 18 / 128
Steam Path [5/7] LP Turbine Section LP - B LP - A 5. Steam Turbine 19 / 128
Steam Path [6/7] LP Turbine A Section Steam Flow Atmosphere Relief Diaphragm (Breakable Diaphragm, or Rupture Disc) Low Pressure Exhaust Inner Casing Bearing No.3 Bearing No.4 5. Steam Turbine 20 / 128
Steam Path [7/7] 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. 5. Steam Turbine 21 / 128
Nozzle Box #3 43 42 #1 Turbine C.W. Number of nozzle 42 43 #4 #2 500 MW (3,500 psig, 1,000F) 5. Steam Turbine 22 / 128
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 5. Steam Turbine 23 / 128
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. 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. 5. Steam Turbine 24 / 128
Diaphragm [2/2] 다이아프램 (Diaphragm) Inner ring 과 outer ring 사이에노즐을조립한하나의열 Outer ring 은터빈케이싱에조립되어고정, inner ring 은축을둘러싸고있으며 labyrinth seal 을설치하여증기누설방지 5. Steam Turbine 25 / 128
Nozzle [1/2] V V+dV 1 Convergent nozzle 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. 5. Steam Turbine 26 / 128
Nozzle [2/2] 노즐 (Nozzle) 증기가속을통해증기의압력에너지를운동에너지로변환시킴 따라서노즐입구와출구사이에압력차이발생하며, 압력차이가클수록다이아프램을튼튼하게제작해야함 노즐을빠져나온증기는큰접선방향속도성분을가지며, 매우큰운동에너지를가짐 p 1 c : absolute velocity of fluid u : tangential velocity of blade w : velocity of fluid relative to blade c 1 1 Nozzle Row r x p 2 2 2 Bucket Row u w 2 c 2 u p 3 w 3 3 c3 3 u Nozzle Row Bucket Row 5. Steam Turbine 27 / 128
Active length Bucket [1/3] Nomenclature Diaphragm Cover 버켓 (Bucket) Rotating blade 를의미 Tip 발전기를구동하기위한회전동력발생 노즐을빠져나온고속의증기에포함되어있는운동에너지, 열에너지, 압력에너지를기계적인일로변환 버켓은로터를회전시키며, 로터의회전동력이발전기를구동하여전기생산 Nozzle row Stage Bucket row Root Dovetail Short bucket Active length is shorter than 10 inches. Long bucket Active length is longer than 10 inches. Bucket vibration should be considered carefully. Radial velocity component is employed in the design stage. 5. Steam Turbine 28 / 128
Bucket [2/3] Dovetail Fir tree type Axial entry dovetail Pine tree type Finger type 5. Steam Turbine 29 / 128
Bucket [3/3] Shrouded vs. Covered Shrouded blade Covered blade 5. Steam Turbine 30 / 128
터빈동력생산원리 [1/6] 유체역학적힘 F = mv = V 2 A m = VA (mass flow rate) Nozzle A, V F R Reaction Action 5. Steam Turbine 31 / 128
터빈동력생산원리 [2/6] 터빈블레이드명칭 Leading Edge Blade Thickness Camber Angle Suction Side Pressure Side Trailing Edge Deflection Stagger Angle Pitch Blade Inlet Angle Blade Outlet Angle Gas Inlet Angle Gas Outlet Angle Direction of Gas Flow Incidence Tangential Deviation Angle Direction of Gas Flow Axial 5. Steam Turbine 32 / 128
유체유동에의해발생하는힘 터빈동력생산원리 [3/6] 1 V 1 m V 1 Tangential m V 1 sin1 V2 sin 2 Axial V 2 m V 2 2 5. Steam Turbine 33 / 128
터빈동력생산원리 [4/6] 유체유동에의해버켓에발생하는힘의크기 배기가스는피치에해당하는면적에경사진형태로버켓통로로유입 따라서유동조건과버켓열이형성하는기하학적데이터를이용하면유입되는배기가스에의해버켓에접선방향으로작용하는힘의크기계산가능 이와같은방법으로버켓을빠져나가는유동조건을이용하면버켓을빠져나가는배기가스의반작용에의해발생하는접선방향힘의크기계산 그리고유입되는배기가스와배출되는배기가스에의해접선방향으로작용하는두힘의크기를합치면버켓에접선방향으로작용하는전체힘의크기가됨 그러나이방법으로는버켓에작용하는힘의크기를정확하게계산하기어려움. 그이유는버켓날개표면에서발생하는경계층때문에버켓을빠져나오는유동이균일하지못하기때문임 버켓에작용하는힘을계산하기위한또다른방법으로날개이론 이방법은버켓표면에작용하는압력분포를이용하여양력을계산하는방법으로써가장정확하면서실제적으로가장많이이용 흡입면압력이압력면에비해서낮으며, 이로인해버켓에양력발생 5. Steam Turbine 34 / 128
터빈동력생산원리 [5/6] 날개주위유체거동 NACA 4412 Velocity distribution p o 1 p1 V 2 2 1 1 p 2 1 2V 2 2 2 Pressure distribution 5. Steam Turbine 35 / 128
터빈동력생산원리 [6/6] 버켓단면에나타나는공기역학적현상을살펴보면, 배기가스가버켓을지나면서압력면 (pressure surface) 에흡입면 (suction surface) 보다높은압력형성 이로인해버켓압력면에서흡입면방향으로, 즉접선방향으로버켓을들어올리는양력발생 그런데버켓은터빈디스크에체결되어있기때문에버켓에발생하는양력은터빈축을회전시키는토크로작용하며, 이토크가압축기와발전기구동에사용되는회전력으로작용 버켓에서생산된양력에버켓이회전한거리를곱하면버켓이한일의크기가되며, 이일의크기가버켓에서생산된기계적인일의크기가됨. 한편, 일을시간으로나누면동력이됨 1 p 2 p 1 p c 1 ½ c 1 2 b Direction of Rotation P S S P c 2 2 P: Pressure Surface S: Suction Surface p 2 ½ c 2 2 p o 5. Steam Turbine 36 / 128
Flow in a Convergent-Divergent Nozzle Last Stage Blade [1/8] da A = (M2 1) dv V Compressor Blades Blade direction Turbine Blades Axial direction M 1 Convergent Nozzle (Nozzle) M 1 M 1 Convergent Nozzle (Nozzle) M 1 M 1 Divergent Nozzle (Diffuser) M 1 M 1 Divergent Nozzle (Diffuser) M M 1 5. Steam Turbine 37 / 128
Flow in a Convergent-Divergent Nozzle Convergent-divergent nozzle Last Stage Blade [2/8] da A = (M2 1) dv V M=1 M1 [ Convergent-Divergent Nozzle ] M1 x Blade Overlap [ Supersonic Converging-Diverging Nozzle, GE ] 5. Steam Turbine 38 / 128
Flow in a Convergent-Divergent Nozzle Last Stage Blade [3/8] 삼천포화력본부 #6 LSB (33.5 /3600 rpm) LSB developed by Siemens (32 /3600 rpm) 5. Steam Turbine 39 / 128
Last Stage Blade [4/8] Mach Number Distribution Siemens 32-LSB/3600rpm (Siemens) 5. Steam Turbine 40 / 128
Last Stage Blade [5/8] LSB Features 1) LSB 는 LP 터빈형상을결정하는중요한요소 2) LSB 길이는사이트대기조건과응축계통에의해서가장큰영향을받음 3) LSB 가길어질수록배기손실이감소하여증기터빈성능향상. 그러나동일한출력을가지는증기터빈의경우 LSB 가길어질수록제작비증가 4) LSB 는큰출력생산. 일반적으로대형화력발전의경우 LSB 는증기터빈전체출력의약 10% 를생산. 복합발전의경우 LSB 는증기터빈출력의 15~17% 정도생산 5) LSB 가길어지면큰회전속도가나타나는 LSB 팁부위에서초음속유동발생. 따라서길이가긴 LSB 팁부위날개형상은초음속유동에적합한수축 - 확산노즐형태를가짐 6) LSB 는습증기영역에서운전되며, 큰회전속도를가지는팁부위에서는물방울과큰속도로충돌하기때문에습분침식발생. 따라서대부분의 LSB 는화염경화나방식막 (erosion shield) 부착등을통해습분침식대비 7) LSB 에는고속회전으로인한큰인장응력발생. 최근에는인장응력을이겨내기위해서비중이철금속의절반정도인티타늄합금을이용하여 LSB 제작. 티타늄합금은습분침식과부식저항성이우수하기때문에 LSB 재료로많이사용되고있음. 그러나티타늄합금은가공성이불량하기때문에 LSB 는고가임 8) LSB 는길어질수록고유진동수가작아지기때문에진동특성불량 5. Steam Turbine 41 / 128
Last Stage Blade [6/8] 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 ] 5. Steam Turbine 42 / 128
Turbine Output and Annular Exhaust Area Last Stage Blade [7/8] 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. 5. Steam Turbine 43 / 128
Last Stage Blade [8/8] Convergent-Divergent LSB Siemens 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 Convergent-divergent nozzle 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 [ Free standing LSB (Siemens) ] 5. Steam Turbine 44 / 128
Typical Turbine Location of Problems SPE of Valves WDE of LSB SPE of Blades Rotor Bow due to rubbing in transient operation such as during startup Bearing Rubbing Seal Rubbing Fouling Stress Corrosion Cracking 5. Steam Turbine 45 / 128
Component Deterioration Potential Potential Components Causes high medium low LSB HP-1 stage IP-1 stage LSB & L1 stage stages with drilled hole in the vane for lacing wires HP-2, 3 & IP-2, 3 HP-1 & IP-1 diaphragm Nozzle box All other components and stages in the unit WDE SPE - high temperature and velocity creep (bucket) high cycle fatigue - partial arc admission SPE - high temperature creep (bucket) corrosion corrosion SPE creep SPE 5. Steam Turbine 46 / 128
Formation of Wet Steam Water Droplet Erosion Fog Formation (Condensation Shock) Dry Steam Phase Change Wet Steam 5. Steam Turbine 47 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend 5. Steam Turbine 48 / 128
HP bypass station Steam Turbine Flow Diagram Main Steam Stop V/V Crossover pipe Control V/V HP IP LP LP Gen Cold Reheat Ventilation V/V Reheater Hot Reheat Reheat Stop and Intercept V/V HRH bypass station (HRH: Hot Reheat) Condenser 5. Steam Turbine 49 / 128
Pressure Throttling Process [1/8] 유체가노즐이나오리피스와같이갑자기유로가좁아지는곳을통과하면외부와열량이나일의교환없이도압력이감소하는교축과정 (throttling process) 발생. 교축과정이발생하면와류가생성되어에너지가손실되면서압력손실발생. 작동유체가액체인경우교축과정이일어나서압력이액체의포화압력보다낮아지면액체의일부가증발하며, 증발에필요한열을액체자신으로부터흡수하기때문에액체온도감소. P 1 2 5. Steam Turbine 50 / 128
Throttling Process [2/8] 열역학제 1 법칙 : q 12 1 2 2 2 h2 h1 c 2 c1 gz2 z1 w12 단순유동에서교축과정이일어나면, 벽면에서의열전달이없으며, 이루어진일이나공급된일도없으며, 위치에너지변화량도무시할수있으므로, 1 2 2 1 2 1 2 h h c c 0 속도가 40m/s 이하인경우운동에너지변화량은엔탈피변화량에비해매우작다. h2 h 1 ( 교축과정 = 등엔탈피과정 ) 2 교축과정은발전설비에서자주일어나는과정인데, 특히증기가밸브를통과할때교축과정이발생하며, 이때압력강하가발생한다. 5. Steam Turbine 51 / 128
Throttling Process [3/8] 증기특성 작동유체가이상기체인경우교축과정이발생한후에엔탈피는일정하게유지됨. 엔탈피는온도만의함수이므로교축과정발생후에온도변화없음. 그러나작동유체가증기인경우에는교축과정이발생하면압력과온도가떨어져서에너지수준이낮아짐. 주울 - 톰슨효과 (Joule-Thomson effect). 증기터빈버켓커버상부에는증기누설을방지하기위해서 seal 을설치하여증기누설방지. Seal 을통해서누설되는증기는 seal strips 을통과하면서교축과정이발생하기때문에실을빠져나온증기는온도와압력이떨어져서엔탈피가낮아짐. 따라서누설증기가다음단에서주유동과합류하더라도주유동의에너지수준을높이지못하기때문에손실발생 누설손실 즉누설증기가실을빠져나오면서에너지를잃지않았다면다음단에서사용할수있지만이미잃어버렸기때문에손실이됨. 5. Steam Turbine 52 / 128
Pressure A Basic Concept for Part Load Operation Throttling Process [4/8] C/V HP Turbine MS R LP Turbine 100% Power 75% Power 50% Power 25% Power 5. Steam Turbine 53 / 128
Power, MW Efficiency, % Output and Efficiency at Part Load Example: 460 MW, supercritical power plant Throttling Process [5/8] 500 49.0 470 48.3 Efficiency 440 47.6 Power 410 46.9 380 46.2 350 45.5 320 44.8 290 44.1 260 43.4 230 42.7 200 42.0 45 50 55 60 65 70 75 80 85 90 95 100 Load [%] 5. Steam Turbine 54 / 128
Velocity Diagram at Various Loads Throttling Process [6/8] Nozzle Row 25% 100% U 25% load 100% load U 75% load 50% load Bucket Row Design efficiency of the turbine blades is maintained during part load operations by using the control valve 5. Steam Turbine 55 / 128
Available Energy Throttling Process [7/8] Effect of Throttling on Non-Reheat Steam Turbine Expansion Line A turbine has different expansion lines as the load is decreased. h p 0 p 1 T 0 1 1 p 1 p 0 : Inlet pressure p 1 : Throttle pressure But the part load expansion lines are generally parallel to the full load expansion line. Design-flow expansion line Partial-flow expansion line This means that the internal efficiency under part load conditions is very close to that under full load conditions. Expansion lines are essentially parallel p c However, the cycle efficiency is reduced under part load conditions. 2 2 s 5. Steam Turbine 56 / 128
Principle of Labyrinth Seal Throttling Process [8/8] The steam has an initial pressure P 1 at the entry to the seal assembly. After expanding past the first constriction, the pressure will have been reduced to condition X o, with pressure P 2. In the chamber formed between the first and second seal strips, the kinetic energy of the steam is destroyed and reconverted at constant pressure P 2 to condition X. From point X, there is then a further expansion of the steam past the second constriction, with the pressure falling to P 3 at condition Y o. The kinetic energy is again reconverted in the chamber between the second and third seal strips, raising the thermal energy level from Y o to Y at constant pressure P 3. 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 Q o at pressure P 5. The locus of the points X o.q o is called the Fanno curve. h P 1 P 2 P 3 P 4 P 5 T 1 X Y Z Rotation Side P 1 P 2 P 3 P 4 X Y Z X o Y o Z o Q o Leakage Flow P 5 s 5. Steam Turbine 57 / 128
Main Steam Valves Generals Valve 개수 ( 표준화력 500MW 기준 ) - Stop v/v : 2 - Control v/v : 4 Stop valve = on-off valve Control valve = throttle valve 라고도불리며, load 연동 Typical closing time during emergency - Stop v/v : 0.09 초 10% - Control v/v : 0.11 초 10% 5. Steam Turbine 58 / 128
Typical Individual Stop and Control Valve Assembly GE Steam Inlet Steam Strainer Valve Disc Valve Seat Pressure Seal Head MSV Actuator Valve Stem Steam Outlet MCV Actuator Actuator Closing Spring [ Main Stop Valve ] 5. Steam Turbine 59 / 128
Main Stop Valves [1/3] 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. 5. Steam Turbine 60 / 128
Main Stop Valves [2/3] Bypass Valve GE 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 Disc Main Stop Valve Disc Seating Surface Main Stop Valve Stem [ Stop Valve Bypass ] Bypass Valve Disc Bypass Valve Ports (8 ea) 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. 5. Steam Turbine 61 / 128
Main Stop Valves [3/3] Bypass Valve 5. Steam Turbine 62 / 128
Main Steam Control Valves [1/4] 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. Steam from No.1 C/V Snout Pipes HP Inner Shell Steam from No.3 C/V Snout Pipe Seal Rings The control valves also serve as the primary shutoff the steam to the turbine on unit normal shutdowns and trips. HP Inner Shell Upper 180 Degree Nozzle Box HP Inner Shell Actuator HP Inner Shell Lower HP Inner Shell MSV 180 Degree Nozzle Box MCV Actuator Snout Pipe Seal Rings HP Inner Shell Siemens MHI Steam from No.2 C/V Snout Pipes Steam from No.4 C/V 5. Steam Turbine 63 / 128
Main Steam Control Valves [2/4] Fully Open #1 #1 Partially Open #2 Steam Flow #2 Closed #3 Closed #4 Stop V/V (1.5% p) Control V/V (1.5% p @ VWO) Nozzle Bucket First stage shell pressure 5. Steam Turbine 64 / 128
Main Steam Control Valves [3/4] 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. Closing Spring GE 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. Balance Chamber Valve Seat Valve Disc [ Main Steam Control Valve ] Steam Chest 5. Steam Turbine 65 / 128
Main Steam Control Valves [4/4] 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. GE 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. 5. Steam Turbine 66 / 128
Reheat Stop and Intercept Valves [1/3] [ Combined Reheat Stop and Intercept Valve, GE ] 5. Steam Turbine 67 / 128
Reheat Stop and Intercept Valves [2/3] 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. Balance Chamber Steam In Steam Strainer GE 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. Intercept Disc Reheat Stop Disc Steam Out Intercept Actuator Closing Spring [ Reheat Stop and Intercept Valves (SKODA) ] Reheat Stop Actuator 5. Steam Turbine 68 / 128
Reheat Stop and Intercept Valves [3/3] 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. 5. Steam Turbine 69 / 128
Ventilation Valve 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 ] 5. Steam Turbine 70 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend 5. Steam Turbine 71 / 128
LP Rotor Shaft [1/2] 블레이드가장착되어있는로터축은 LP 터빈전체가격의약 40% 차지. 로터축가격은허브지름에의해서결정. 로터축가격을낮추기위하여허브지름을줄이면버켓단수와로터축길이증가 (h U 2 ). 로터축이가늘고길어지면회전체동력학측면에서설계어려움. 아울러로터축이길어지면터빈빌딩이커지기때문에발전소건설비용증가. 단수와허브지름은 LP 터빈구성과로터축설계를결정하는가장중요한요소. Shrunk-on rotor Monoblock rotor Welded rotor 5. Steam Turbine 72 / 128
LP Rotor Shaft [2/2] 열박음로터축 (shrunk-on rotor) 초대형잉곳을확보하기어려울때사용. 지름이작은로터축을제작한후에휠디스크를제작하여열박음을통하여일체화. 제작이쉬운반면에기동정지시에불안정한진동이발생하기쉬우며, 휠디스크에응력부식균열이발생하는단점보유. 최근에는거의채택하지않고있음. 일체형로터축 (monoblock rotor) 최근제강기술이발달하여가공중량 200 톤정도의일체형로터축제작 열박음로터축에비해강도가한층높으며, 응력부식균열이나타나지않기때문에신뢰성이높음. 열박음로터축에비해제작에많은시간이소요. 국내화력발전 LP 터빈로터축은모두일체형이며, 원자력발전은영광 5.6 호기와울진 5.6 호기부터모두일체형으로설계. 용접로터축 (welded rotor) 원자력발전과같은대형 LP 터빈에사용. 현재는용접기술과열처리기술이발달하여몇개의로터를용접으로연결하여하나의로터축으로제작한용접로터축을많이사용. 가격이상대적으로저렴한작은잉곳여러개를이용하기때문에전체적으로가격저렴. 제작단계에서재료결함검사가용이하기때문에신뢰성우수. 일반적으로로터축내부빈공간은부식방지를위해진공유지. 두가지이상의서로다른재료를용접하여사용할수있기때문에로터축온도분포에따른최적의로터축제작. 초임계압발전에서나타나는고온부식을줄이기위해전통적으로사용하던 CrMoV 에 9Cr 과 12Cr 강을용접하여사용. 5. Steam Turbine 73 / 128
Wheel Type vs. Drum Type Bucket Tip Impulse Reaction disc wheels shrunk on to a rotor shaft Diaphragm Root cylindrical drum type rotor 5. Steam Turbine 74 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend 5. Steam Turbine 75 / 128
Casing 제작 구조 HP/IP Casing Casting Single Casing 저압력터빈 ( 원자력 ) & Small turbine LP Casing Fabrication Double Casing High pressure & Large turbine Crossover Pipe HP Outer Casing HP Inner Casing Bearing Pedestal IP Inner Casing IP Outer Casing LP Inner Casing LP Outer Casing 5. Steam Turbine 76 / 128
Generals for Casing 케이싱특성 대형증기터빈의경우고압 (HP)/ 중압 (IP)/ 저압 (LP) 케이싱으로구성 분해 / 조립이쉽도록수평면기준 2 분할구조이며, 볼트로결합 배럴형 (barrel type, or cylindrical type) 으로도제작 열응력과강도측면에서우수, 터빈을수직으로세워분해 / 조립해야하므로정비측면에서는불리 저압케이싱하부는복수기와연결 Inner casing 에는노즐과다이아프램 ( 블레이드링 ) 장착 열팽창이자유로우며, 일정한형상유지 케이싱하부에배수관 (drain tube) 설치 - 터빈정지시케이싱내부응축수생성으로인한부식및열변형방지 2 중케이싱특성 열응력감소 터빈출구증기를 inner casing 과 outer casing 사이로흐르게하여각각의케이싱내면과외면의온도차를감소시켜열응력발생감소 기동 / 정지시간단축 케이싱두께감소 케이싱내면과외면의압력차감소 Barrel type casing (Siemens) 5. Steam Turbine 77 / 128
HP/IP Casing 5. Steam Turbine 78 / 128
IP Casing Single casing (GE) Double casing (Siemens) 5. Steam Turbine 79 / 128
LP Casing [1/7] 5. Steam Turbine 80 / 128
LP Casing [2/7] LP Turbine (Siemens) LP Turbine Inner Casing (Siemens) 5. Steam Turbine 81 / 128
LP Casing [3/7] 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 5. Steam Turbine 82 / 128
LP Casing [4/7] Atmospheric Relief Diaphragm 외부케이싱외부는대기압, 내부는복수기진공압력이작용하기때문에외부케이싱에는약 500 톤의진공하중이작용. 외부케이싱은진공하중이외에내부케이싱중량과약 150 톤정도의외부케이싱자중이작용. 따라서외부케이싱은이들하중에견딜수있도록강도와강성을확보하기위하여내부여러곳에지지대와리브설치. 외부케이싱상부에는동판으로제작된대기방출판 (atmospheric relief diaphragm, or breakable diaphragm, or rupture disc) 설치. 대기방출판은증기터빈안전장치로서복수기에냉각수공급이정지하거나어떤다른원인에의해서 LP exhaust hood 압력이대기압보다높은압력 (130~140 kpa) 으로올라가면외부케이싱외부로증기압력이작용하여동판이칼날에의해절단되면서증기를외부로방출시켜 LP exhaust hood 및복수기파손을방지. 만약운전중에배압이상승하면경보가울리며, 계속해서상승하면 low vacuum trip 이작동하여증기터빈을트립시켜 LP exhaust hood 와복수기를보호하지만그이상으로올라가면최종적으로대기방출판이절단되면서증기터빈보호. 5. Steam Turbine 83 / 128
LP Casing [5/7] LP Exhaust Hood Siemens 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. Outer Casing Bearing Cone Inner Casing Collector Steam Guide End Wall 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. LSB Steam Flow Condenser Flange 5. Steam Turbine 84 / 128
LP Casing [6/7] LP Exhaust Hood - Axial Flow Exhaust It is generally employed for small industrial steam turbines. Siemens 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. SST-800 (Siemens) SST-600 (Siemens) 5. Steam Turbine 85 / 128
LP Exhaust Hood - Downward Flow Exhaust LP Casing [7/7] 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. 5. Steam Turbine 86 / 128
Exhaust Loss h h T1 W = Work h S1 HL = Hood Loss LL = Leaving Loss EL = Exhaust Loss Static Expansion Line Total Expansion Line W EEL UEEP ELEP = Effective EL = Used Energy End Point (or TEP) = Expansion Line End Point SEP = Static End Point s B EL = Change in EL W = Change in Work h T2 EEL = Change in EEL EL LL EL W=EEL EEL p c p TB = Static Pressure at Turbine Exhaust Flange = Total Pressure at Last Blade Exit HL SEP ELEP p SB = Static Pressure at Last Blade Exit s 5. Steam Turbine 87 / 128
Exhaust Loss, Btu/lb of dry flow 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. 50 40 30 20 Turn-up Loss Total Exhaust Loss Annulus Restriction Loss Gross Hood Loss 10 Actual Leaving Loss 0 0 200 400 600 800 1000 1200 1400 1600 Sonic Annulus Velocity, fps 5. Steam Turbine 88 / 128
Exhaust Loss, Btu/lb of dry flow Exhaust Loss [3,600 rpm, GE] 50 46 42 38 34 30 26 22 18 14 2 3 4 5 1 Bucket Pitch Last stage Curve length diameter annulus area no. (inches) (inches) single flow (ft 2 ) 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 2 3 4 5 Van = Annulus velocity (fps) m = Condenser flow (lb/hr) = Saturated dry specific volume (ft 3 /lb) Aan = Annulus area (ft 2 ) Y = Percent moisture at ELEP ELEP = Expansion line end point at actual exhaust pressure (Btu/lb) UEEP = Used energy end point (Btu/lb) (1) Read the exhaust loss at the annulus velocity obtained from the following expression: Van = m(1-0.01y) / 3600Aan 10 (2) The enthalpy of steam entering the condenser is the quantity obtained from the following expression: 6 2 0 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. 200 400 600 800 1000 1200 1400 Annulus Velocity, ft/s 5. Steam Turbine 89 / 128
Exhaust Hood Spray [1/6] Turn-up Loss Turn-up Region Normal Rating Operation Low Load Operation 5. Steam Turbine 90 / 128
Exhaust Hood Spray [2/6] Water supply line LSB Water spray [ Source: 한전 KPS ] Recirculating steam Water running down casing walls [ Eroded Trailing Edge of LSB near the Hub ] [ Recirculation in the Exhaust Hood ] 5. Steam Turbine 91 / 128
Exhaust Hood Spray [3/6] 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. 5. Steam Turbine 92 / 128
Exhaust Hood Spray [4/6] Trailing Edge Erosion A crack emanating from a trailing edge gouge Trailing edge erosion on the suction side Crack in the trailing edge caused by erosion - PT 5. Steam Turbine 93 / 128
Turn-up Region 에서의사고사례 [1/2] Exhaust Hood Spray [5/6] 5. Steam Turbine 94 / 128
Turn-up Region 에서의사고사례 [2/2] Exhaust Hood Spray [6/6] 5. Steam Turbine 95 / 128
1 2 3 4 5 6 7 8 9 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend Type of Steam Turbines Recent Developmental Trend 5. Steam Turbine 96 / 128
베어링과접촉하고있는축부분을저널 (journal) 이라고하며, 그접촉상태에따라미끄럼베어링 (sliding bearing) 과구름베어링 (rolling bearing) 두종류로분류 미끄럼베어링은베어링이저널부의표면전부또는표면의일부를둘러싼것같이되어있으며, 베어링과저널의접촉면사이에는보통윤활유존재. 이베어링은면과면이접촉하기때문에축이회전할때마찰저항이구름베어링보다크지만큰하중을지지할수있음 구름베어링은축과베어링의볼또는롤러가접촉하며축이회전하면볼또는롤러도같이회전하기때문에마찰저항이작음. 회전하는기계축에는하중이축과수직으로걸리는경우와축방향으로걸리는경우가있음. Bearing 베어링은하중방향에따라그구조가많이달라지며, 축과수직으로하중이걸리는경우에사용하는것을저널또는레이디얼 (journal or radial) 베어링이라하고, 축방향으로하중이작용하는경우에쓰이는것을스러스트 (thrust) 베어링이라함 Journal (Radial) Force Thrust Force 5. Steam Turbine 97 / 128
Journal Bearing [1/7] Tilting Pad Journal Bearing Rotation Oil Discharge Oil Inlet 5. Steam Turbine 98 / 128
Journal Bearing [2/7] Tilting Pad Journal Bearing [ Typical Forces Acting on Individual Pads ] 5. Steam Turbine 99 / 128
Journal Bearing [3/7] Tilting Pad Journal Bearing Film Pressure Distribution U Q ' 1 h1 - Q 1(P) 2 U ' Q2 h2 Q2(P) 2 Q Q 1 2 Qs W maub (h 1 /h 2 ) 2 W: Load capacity m: Oil viscosity A: Shoe area U: Runner velocity h1 Q 1 U Q 2 h2 h 1 : Inlet film thickness h 2 : Outlet film thickness Q: Flow rate X B Qs Qs: X/B: Side flow rate Pivot ratio 5. Steam Turbine 100 / 128
Journal Bearing [4/7] Elliptical Journal Bearing Rotation 5. Steam Turbine 101 / 128
Journal Bearing [5/7] 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. 5. Steam Turbine 102 / 128
Journal Bearing [6/7] Elliptical Journal Bearing 정지상태회전시작회전시작후고속회전 Load Rotation Rotation Rotation 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 5. Steam Turbine 103 / 128
Journal Bearing [7/7] Y Divergent Cavitated Film Bearing Converging Oil Wedge Rotation X Hydrodynamic Pressure Profile Minimum Film Maximum Film Temperature Center Line Maximum Pressure 5. Steam Turbine 104 / 128
Thrust Bearing [1/4] Leveling Plates Oil Wedge Base Ring Thrust Collar Equalizing Thrust Bearing Rotating Thrust Collar Thrust Pivoted Shoe Direction of Rotation [ Tapered Land Oil Wedge ] 5. Steam Turbine 105 / 128
Equalizing Thrust Bearing - Kingsbury Thrust Bearing [2/4] 5. Steam Turbine 106 / 128
Thrust Bearing [3/4] Copper Backed Tapered Land Thrust Plates Thrust Runner Thrust Runner Thrust case Turbine Shaft Thrust case Spacer Plates 5. Steam Turbine 107 / 128
Thrust Bearing [4/4] 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. 5. Steam Turbine 108 / 128
Combined Type Bearing 정상운전상태에서하중을담당하는패드를 active pad 라하며, 반대편에있는것을 inactive pad 라함 Active Thrust Plate Active Thrust Collar Pin Shim Journal Bearing Inactive Thrust Plate Inactive Thrust Collar Steam Flow Rotor Thrust Collars Integral with Rotor [ A Thrust Journal Bearing ] Oil Scoop Oil Feed 5. Steam Turbine 109 / 128
1 2 3 4 5 6 7 Steam Turbine Arrangement Steam Path Parts Valves Rotor Casing Bearing Recent Developmental Trend 5. Steam Turbine 110 / 128
Classification of Fossil Plants EPRI Nomenclature Subcritical Supercritical (SC) Ultrasupercritical (USC) Advanced Ultrasupercritical (A-USC) Steam Conditions 2400 psig (16.5 MPa) 1050F/1050 F (565C/565C) 3600 psig (24.8 MPa) 1050F/1075F (565C/585C) 3600 psig (24.8 MPa) 1100F/1150 F (593C/621C) 5000 psig (34.5 MPa) 1292F (700C) and above Net Plant Efficiency, % Net Plant Heat Rate (HHV), Btu/kWh 35 9751 38 8981 42 8126 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) 5. Steam Turbine 111 / 128
Introduction to USC Steam Turbine 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 coalfired power plants. Requests for sustainable use of existing resources and concerns about the effect of CO 2 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. 5. Steam Turbine 112 / 128
Plant Net Efficiency Based on LHV Plant Net Efficiency Based on HHV Efficiency Improvement in PC-Fired Plant Siemens % % 46 0.88 in.hga 45 43 Advanced Hood 44 42 USC Double reheat 1.9 in.hga 43 41 300 bar/600c Single reheat 42 41 40 39 1.15 1.25 USC 120C 130C 250 bar/540c Excess Air Discharge Flue Gas Temperature Main Steam Condition Reheat Back Pressure 5. Steam Turbine 113 / 128
Comparison of Cost Source: Best Practice Brochure (DTI, 2006) 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 electricity c/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 5. Steam Turbine 114 / 128
Thermal Efficiency [%] Temperature [C], Pressure [bar] Max Output Tandem Compound [MW] History of USC Siemens Steam Cycle Simple Reheat Supercritical 800 10000 700 60 50 600 500 Temperature Power Output 1000 40 30 400 300 Thermal Efficiency 100 20 10 200 100 0 10 Pressure 1 0 1920 1940 1960 1980 2000 2020 5. Steam Turbine 115 / 128
Plant Net Heat Rate Improvement, % Heat Rate Improvement by USC 8 7 Double Reheat vs. Single Reheat: Heat Rate Improvement = 1.6% 2.4 % USC 5800 psig (400 bar) 5050 psig (350 bar) 4350 psig (300 bar) 3650 psig (250 bar) 2900 psig (200 bar) Siemens 6 2400 psig (165 bar) 5 4 3 2 1 0 2.8 % Sub-Critical 1000 1100 1200 Temperature, F Comparison 2400 psig/1000f/1000f versus 4500 psig/1100f/1100f 2.8% + 2.4% + 1.6% = 6.8% 5. Steam Turbine 116 / 128
History of USC Development 5. Steam Turbine 117 / 128
USC Steam Turbine Siemens Key Technical Features Model Gross power output Net plant efficiency (based on cooling tower) Main steam conditions LP turbine - LSB Feedwater preheating Final feedwater temperature Specific CO 2 emission SST5-6000 813 MW ~45.6% (@ design point) 280 bar/600c/610c 4 Flow - 45 9-stages 308C Well below 800 g/kwh Key Technical Features Model Gross power output Main steam conditions SST-6000 1200 MW 300 bar/600c/620c 5. Steam Turbine 118 / 128
USC Steam Turbine GE Key Technical Features Gross power output Net plant efficiency Main steam conditions LP turbine - LSB Arrangement of rotor shaft 1050 MW 48.7% (@ design point) 250 bar/600c/610c (3626 psia/1112f/1130f) 4 Flow - 48 Cross-compound Key Technical Features Gross power output 1000 MW Net plant efficiency? Main steam conditions 260 bar/610c/621c (3770 psia/1150f/1180f) LP turbine - LSB 4 Flow - 45 Arrangement of rotor shaft Tandem-compound 5. Steam Turbine 119 / 128
USC Steam Turbine Alstom 700C Steam Turbine Development [ALSTOM] Welding Balance Piston 5. Steam Turbine 120 / 128
USC Steam Turbine - Doosan Key Technical Features Output @ Max Guarantee Rating 1000 MW Output @ VWO 1100 MW Net plant efficiency 49% (estimated value) Main steam conditions 260 bar/610c/621c LSB 4 Flow - 45 Cycle Single reheat regenerative Wheels and Diaphragms Bearings Packing Head LP Inner Casing LP Casing Packing Head Double Shells Reheat Stop and Intercept Valves 5. Steam Turbine 121 / 128
Allowable Stress, ksi Austenitic Alloy Strength 50 45 40 35 30 25 20 15 10 5 0 Ferritic H282 IN740 H230 TP310HCbN IN617 S304H T24 T92 TP347H T22 T12 700 800 900 1000 Nickel Alloys 1100 1200 1300 1400 1500 1600 Temperature, F 5. Steam Turbine 122 / 128
A-USC Steam Conditions EPRI Steam Conditions 5100 psia/1290f/1330f (347 bar/700c/721c) Remark 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 5. Steam Turbine 123 / 128
Background for USC Power Plants 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 CO 2 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 CO 2, the costs of carbon capture, water use, particulates, sulfur dioxides (SO x ) and nitrogen oxides (NO x ) 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 CO 2 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 CO 2 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 CO 2 removal costs of $50 to 70/ton. 5. Steam Turbine 124 / 128
CO 2 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 CO 2 emission. An increase in plant efficiency from 30% to 50% reduce CO 2 emissions about 40%. A-USC plants having net plant efficiency of 45%, without CCS(Carbon Capture and Sequestration), will produce about 22% less CO 2 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 CO 2 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 CO 2 capture based on Siemens advanced process is 9.2%. 5. Steam Turbine 125 / 128
CO 2 Emission, g/kwh CO 2 Emission vs. Plant Efficiency 1200 1000 800 600 400 200 0 28 32 36 40 44 48 52 56 Net Plant Efficiency, % (LHV) 5. Steam Turbine 126 / 128
Post-Combustion Capture Technology Remove 85-90% of NO x DeNOx Remove 99.7% of Fly Ash EP Remove 90-95% of SO 2 FGD Flue Gas Cooling Remove 90% of CO 2 CO 2 Capture Chimney Continuous Emission Monitoring System 5. Steam Turbine 127 / 128