슬라이드 1

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1 7. LP Turbine Wheels and Diaphragms Bearings Packing Head LP Inner Casing LP Casing Packing Head Double Shells Reheat Stop and Intercept Valves Steam Turbine 7. LP Turbine 1 / 53

2 Nomenclature Toshiba Steam Turbine 7. LP Turbine 2 / 53

3 LP Turbine Structure Steam Turbine 7. LP Turbine 3 / 53

4 Characteristics of LP Steam Turbines Longer blades 3D design Titanium blade Wet steam Lower efficiency caused by moisture loss Difficult to predict flow behavior Water droplet erosion Titanium blade Erosion shield (stellite), or flame hardening Vibration control Reduced axial distance Hard to develop a new model Steam Turbine 7. LP Turbine 4 / 53

5 LP Steam Turbine The efficiency of modern HP and IP steam turbines can be predicted very accurately because it is mainly a function of the flow losses in the blade (steam path). The flow losses have been established in systematic experiments in the fluid mechanics laboratories for all geometric dimensions and flow conditions. The economic optimization (availability, efficiency, and capital cost) of the LP turbine design is not always so successful. Wet steam and three-dimensional flow patterns make complete and accurate measurements difficult. The high costs of systematic tests with LP turbines have until now also prevented the accumulation of data which would permit an accurate efficiency analysis of the LP turbine alternatives. In addition, the LP efficiency has hardly been indentified theoretically, so that an empirical evaluation based on a few measuring points was all that was possible. Currently, this kind of problem has being solved with an aid of CFD techniques. However, the problem related to the wet steam is still vague because phase change can not be solved with CFD techniques. In conclusion, in order to optimize the LP turbine, we have to rely on the experience of engineers who are familiar with the complexity of the problem and can bridge the gaps with reasonable assumptions. Steam Turbine 7. LP Turbine 5 / 53

6 LP Steam Turbine The LP turbine efficiency is greatly affected by exhaust loss. Double flow provides smaller annulus area at the LSB exit plane, and it requires shorter LSB. The axial thrust is equalized by the double flow, therefore, no dummy piston is required. Steam Turbine 7. LP Turbine 6 / 53

7 LP Steam Inlet Design Conventional inlet casing (Torous) Axial design Radial-axial design Skoda - Doosan Steam Turbine 7. LP Turbine 7 / 53

8 LP Steam Inlet Design Although the velocities are much lower in the inlets, meaning that less performance is lost than in the exhaust, some improvements can be made. Aside from the basic area rules of crossover to LP inlet to 1st stage used to avoid acceleration, the LP inlet shape can be designed to reduce pressure drop. Figure shows a CFD analysis of an LP inlet before and after aerodynamic optimization. The colors represent areas of different velocity. (red is high, blue is low) Old Design New Design Velocity magnitude contours (GE) Steam Turbine 7. LP Turbine 8 / 53

9 Casing LP 터빈은입구부터배기까지온도차가매우크기때문에케이싱을 2 중구조로제작하여각각의케이싱에서발생하는온도차를적게하여케이싱의열변형방지. 내부케이싱에는노즐과다이아프램 ( 블레이드링 ) 장착. 외부케이싱은 LP 터빈외형형성. 외부케이싱외부는대기압, 내부는복수기진공압력이작용하기때문에외부케이싱에는약 500 톤의진공하중작용. 외부케이싱은진공하중이외에내부케이싱중량과약 150 톤정도의외부케이싱자중작용. 따라서외부케이싱은이들하중에견딜수있도록강도와강성을확보하기위하여내부여러곳에지지대와리브설치. 외부케이싱상부에는동판으로제작된대기방출판 (atmospheric relief diaphragm, or breakable diaphragm, or rupture disc) 설치. 대기방출판은증기터빈안전장치로서복수기에냉각수공급이정지하거나어떤다른원인에의해서 LP exhaust hood 압력이대기압보다높은압력 (130~140 kpa) 으로올라가면외부케이싱외부로증기압력이작용하여동판이칼날에의해절단되면서증기를외부로방출시켜 LP exhaust hood 및복수기파손방지. 만약운전중에배압이상승하면경보가울리며, 계속해서상승하면 low vacuum trip 이작동하여증기터빈을트립시켜 LP exhaust hood 와복수기를보호하지만그이상으로올라가면최종적으로대기방출판이절단되면서증기터빈보호. Inner Casing (GE) Steam Turbine 7. LP Turbine 9 / 53

10 Casing LP Turbine (Siemens) LP Turbine Inner Casing (Siemens) Steam Turbine 7. LP Turbine 10 / 53

11 Casing 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. SST Steam Turbine (Siemens) Steam Turbine 7. LP Turbine 11 / 53

12 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 in the case of 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 Steam Turbine 7. LP Turbine 12 / 53

13 LP Exhaust Hood Configuration GE Butterfly vane Bearing cone Horizontal joints Side plates Flow plate Steam guide Radial plates Front wall Inner casing Transverse plates Central plate Steam Turbine 7. LP Turbine 13 / 53

14 LP Exhaust Hood 1) Axial Flow Exhaust It is generally employed for small industrial steam turbines. The steam exiting LSB enters condenser in axial direction. The flow distribution is uniform on LSB exit plane along the 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) Steam Turbine 7. LP Turbine 14 / 53

15 Type of LP Exhaust Hood 2) Downward Flow Exhaust 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. Steam Turbine 7. LP Turbine 15 / 53

16 LP Exhaust Hood 3 Major Functions It acts as a diffuser to provide static pressure recovery. The LP exhaust hood must be aerodynamically designed such that it provides a minimal obstruction to the steam flow from the LSB exit plane to the condenser to minimize loss of energy. Pressure loss of 1 in.hg in a LP exhaust hood can result in a 1% increase in plant overall heat rate. It is a supporting structure for the LP rotor bearings. Typically, the LP bearings are supported in a cone shaped structure overhung into the hood at the end walls This arrangement is used to minimize the rotor span, and thus minimize rotor bending from the gravitational force and to optimize critical speeds of the rotor It supports the weight of the inner casing and diaphragms and must provides precise positioning of the inner casing, diaphragms, bearing and packing. Steam Turbine 7. LP Turbine 16 / 53

17 LP Exhaust Hood Function Extremely low back pressure Large volumetric flow rate of working fluid Large annular flow area Faced with strength limit because of Increased active length of blade Increased capital cost High turbine exit velocity Increased leaving loss because of high turbine exit velocity Required advanced LP exhaust hoods The function of LP exhaust hood High kinetic energy leaving LSB Pressure recovery Increased turbine output Decreased cycle heat rate Steam Turbine 7. LP Turbine 17 / 53

18 Flow Behaviors in LP Exhaust Hood LSB annulus plane; Bearing cone; Steam guide; Collector Inner casing; Outer casing; Condenser flange; End wall Flow is highly three-dimensional Geometry is extremely complex Hard to model parametrically Many potential design parameters LP exhaust hood is one of the few steam turbine components having the potential to be improved Steam Turbine 7. LP Turbine 18 / 53

19 Component Losses Related to Turbine Output 600 MW Reheat Steam Turbine Losses of Turbine Components Siemens Steam Turbine Efficiency % 90% HP Turbine IP Turbine LP Turbine 2.0 % 1 Valve and admission 2 Profile 3 Shaft & inter-stage seal 4 Extraction & exhaust 5 Reheat pressure 6 X-over pressure 7 Moisture 8 Mechanical 1.0 Steam Turbine 7. LP Turbine 19 / 53

20 A Typical USC Steam Turbine GE Steam Turbine 7. LP Turbine 20 / 53

21 Steam Path Lines in a LP Exhaust Hood 500 MW Steam Turbine [Example] (a) Started from LSB hub (b) Started from LSB pitch (c) Started from LSB tip Steam Turbine 7. LP Turbine 21 / 53

22 Flow Behavior in a LP Exhaust Hood 500 MW Steam Turbine [Example] 1) Flow distribution should be improved because of the flow concentration on the end wall makes the exhaust loss get higher and the flow distribution on the LSB annulus plane get worse. 2) Exhaust loss is very high because of old style of steam guide. This type of steam guide has never been used recently in the design of advanced steam turbines. 3) The strength of the swirl flow at collector is so strong that contributes higher exhaust loss. Steam Turbine 7. LP Turbine 22 / 53

23 Flow Behavior in a LP Exhaust Hood Condenser Flange [ Velocity Vectors in a LP Exhaust Hood ] Steam Turbine 7. LP Turbine 23 / 53

24 Flow Behavior in a LSB Exit Plane (a) Newly Designed LP Exhaust Hood (a) Conventional 500 MW Steam Turbine [ Velocity Vectors on the LSB Exit Plane ] Steam Turbine 7. LP Turbine 24 / 53

25 Coanda Effect Steam guide 벽면으로의유동부착및집중 방향전환 mechanism (axial radial) Steam Turbine 7. LP Turbine 25 / 53

26 V2 Flow Behavior in a LP Exhaust Hood 1.50 Conventional Design Improved Design E D C B A A B C D E [ Normalized Velocity Magnitude on the LSB Exit Plane ] V1 1) Discuss the flow behavior on the LSB exit plane in terms of power output. 2) LP turbine vibration can be improved? Steam Turbine 7. LP Turbine 26 / 53

27 Some Issues Steam Turbine 7. LP Turbine 27 / 53

28 Some Issues Steam Turbine 7. LP Turbine 28 / 53

29 Some Issues GEA18786 (June/2011) 207D-17 Steam Turbine 109D-14 Steam Turbine Steam Turbine 7. LP Turbine 29 / 53

30 LP Rotor Shaft 블레이드가장착되어있는로터축은 LP 터빈전체가격의약 40% 차지. 로터축가격은허브지름에의해서결정. 로터축가격을낮추기위하여허브지름을줄이면버켓단수와로터축길이증가 (h U 2 ). 로터축이가늘고길어지면회전체동력학측면에서설계어려움. 아울러로터축이길어지면터빈빌딩이커지기때문에발전소건설비용증가. 단수와허브지름은 LP 터빈구성과로터축설계를결정하는가장중요한요소. Shrunk-on rotor Monoblock rotor Welded rotor Steam Turbine 7. LP Turbine 30 / 53

31 LP Rotor Shaft 열박음로터축 (shrunk-on rotor) 초대형잉곳을확보하기어려울때사용. 지름이작은로터축을제작한후에휠디스크를제작하여열박음통하여일체화. 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. 현재는용접기술과열처리기술이발달하여몇개의로터를용접으로연결하여하나의로터축으로제작한용접로터축많이사용. 가격이상대적으로저렴한작은잉곳여러개를이용하기때문에전체적으로가격저렴. 제작단계에서재료결함검사가용이하기때문에신뢰성우수. 일반적으로로터축내부빈공간은부식방지를위해진공유지. 두가지이상의서로다른재료를용접하여사용할수있기때문에로터축온도분포에따른최적의로터축제작. 초임계압발전에서나타나는고온부식을줄이기위해전통적으로사용하던 CrMoV 에 9Cr 과 12Cr 강을용접하여사용. Steam Turbine 7. LP Turbine 31 / 53

32 Last Stage Blade [1/14] LSB Features 1) LSB 는 LP 터빈형상을결정하는중요한요소이다. 2) LSB 길이는사이트대기조건과응축계통에의해서가장큰영향을받는다. 3) LSB 가길어질수록배기손실이감소하여증기터빈성능이향상된다. 그러나동일한출력을가지는증기터빈의경우 LSB 가길어질수록제작비가증가한다. 4) LSB 는큰출력을생산한다. 일반적으로대형화력발전의경우 LSB 는증기터빈전체출력가운데약 10% 를생산한다. 복합발전의경우에는증기터빈출력의 15~17% 정도가 LSB 에서생산된다. 5) LSB 가길어지면큰회전속도가나타나는 LSB 팁부위에서초음속유동이발생한다. 따라서길이가긴 LSB 팁부위날개형상은초음속유동에적합한수축 - 확산노즐형태를가진다. 6) LSB 는습증기영역에서운전되며, 큰회전속도를가지는팁부위에서는물방울과큰속도로충돌하기때문에습분침식이발생한다. 따라서대부분의 LSB 는화염경화나방식막부착등을통해서습분침식에대비하고있다. 7) LSB 에는큰인장응력이발생한다. 최근에는인장응력을이겨내기위해서티타늄합금을이용하여 LSB 를제작하고있다. 티타늄합금은습분침식과부식저항성이우수하기때문에 LSB 재료로많이사용되고있다. 그러나티타늄합금은가공성이불량하기때문에 LSB 가격이비싸진다. 8) LSB 는길어질수록고유진동수가작아지기때문에진동특성이나빠진다. Steam Turbine 7. LP Turbine 32 / 53

33 Last Stage Blade [2/14] 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 ] Steam Turbine 7. LP Turbine 33 / 53

34 Last Stage Blade [3/14] Each LP turbine is characterized by its outlet area. S out = d p2 (h/d p ) where, d p = pitch diameter of LSB, h = active length of blade) If the hub diameter and thus the pitch diameter of LSB is reduced, the blade length/diameter ratio must be increased. However, h/d p is a parameter which greatly influences the three-dimensional flow in the last stage. Today s customary values lie between 0.3 and 0.35, and may reach 0.38 in extreme cases. The larger the h/d p, the harder the sound aerodynamical design of the blade. An increase in the h/d p for a fixed outlet area leads to longer LSB. The risk of blade vibration increases with blade length because the natural frequencies of the blade decrease as the blade length increases. h d p Steam Turbine 7. LP Turbine 34 / 53

35 Last Stage Blade [4/14] Steam Turbine 7. LP Turbine 35 / 53

36 Last Stage Blade [5/14] 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. Steam Turbine 7. LP Turbine 36 / 53

37 Last Stage Blade [6/14] Mach Number Distribution 32-LSB/3600rpm (Siemens) Steam Turbine 7. LP Turbine 37 / 53

38 Last Stage Blade [7/14] LSB Tip Profile [GE] Blade Overlap Supersonic Converging-Diverging Nozzle Blade Overlap Supersonic Converging-Diverging Nozzle Steam Turbine 7. LP Turbine 38 / 53

39 Last Stage Blade [8/14] 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 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) ] Steam Turbine 7. LP Turbine 39 / 53

40 Last Stage Blade [9/14] Advanced LSB Nozzle [ 40 L-0 Nozzle Assembly ] Steam Turbine 7. LP Turbine 40 / 53

41 Last Stage Blade [10/14] Advanced LSB Nozzle Both tangential and axial lean are applied to the L-0 nozzle. Compound tangential lean is utilized to impart an inward radial force on the flow forcing more flow into the hub region and increasing the pressure. Combined with the flow path contouring the L-0 nozzle lean reduces the radial pressure gradient at the nozzle exit, raises the root reaction. Axial lean is used to control the nozzle to bucket spacing while minimizing the potential for erosion. An increased nozzle to bucket distance near the tip reduces the possibility of nozzle induced stimulus, which results in a more robust mechanical design. Advanced LSB nozzle not only reduces losses within its boundaries, but also optimizes the flow conditions for the following moving blades. The advanced forward curved and twisted blade provides an optimal flow distribution with increased flow at the hub avoiding flow separation, and reduced flow at the moving blade tip for minimizing boundary losses. The best performing center section of moving blade receives an increased mass flow. The follow stationary blade is ideally suited to form a thick profile at the outer diameter and to provide suction slots for moisture removal. Steam Turbine 7. LP Turbine 41 / 53

42 Last Stage Blade [11/14] Advanced LSB Nozzle Steam Turbine 7. LP Turbine 42 / 53

43 Last Stage Blade [12/14] Flutter of Turbine Blades During the low load and high exhaust pressure, random vibration or stall flutter occurs in last stage blades of LP turbine. Nozzle W 1,design C 1,design W 1,off C 1,off In such condition the steam inlet flow angle is larger than normal resulting in negative angle of attack. W 1,design W1,off U As a result of large negative angle at the inlet to the blade, steam flow separation causes the blades to vibrate in stall flutter. Stall Bucket U = Wheel speed C 1 = Absolute velocity W 1 = Relative velocity Steam flow during low load and high exhaust pressure operation Steam Turbine 7. LP Turbine 43 / 53

44 Last Stage Blade [13/14] Flutter of Turbine Blades The structural instability is due to the interaction between the unsteady aerodynamics and the structural dynamics of the blades. In the power generation industry, there is a drive to increasingly large exhaust areas of low-pressure steam turbines, leading to longer blades. Under this condition, design of turbine blades is more likely to react to the effects of dynamic loading due to unsteady aerodynamics. The last stage blades, that contribute approximately 10% of the overall output of a modern power plant are surrounded by hostile aerodynamic environment due to the transonic and droplet laden flow. The longest blades of the last row in a LP turbine are always tapered and twisted to accommodate the demands of mechanical integrity and aerodynamic performance. The tip section of freestanding blades in the last row is more flexible, thus it is difficult to control tip vibration and its susceptibility to flutter. Continuously coupled blade row has greater stiffness that helps to resist vibration and bending forces. Steam Turbine 7. LP Turbine 44 / 53

45 Last Stage Blade [14/14] Flutter of Turbine Blades - Sources of Blade Excitation 1 Harmonic excitation Time dependent periodic fluctuating flow By design practice all the long blades are tuned so as to avoid due to harmonic excitation 2 Random or broadband excitation This is primarily due to temporal unsteadiness of the flow over the stationary blades. Sudden changes in the flow path and steam extraction have been observed to initiate flutter in the blade 3 Self excitation It does not need external excitation, but excitation is internally generated. Stall flutter, usually occurred during low load operation and high exhaust pressure, belongs to this. Steam Turbine 7. LP Turbine 45 / 53

46 Cold-end Optimization [1/4] The kinetic energy of the steam leaving the LSB exit plane is assumed to be almost completely lost. m 1 The exhaust volume flow ( ) is fixed approximately by the turbine power output and the condenser conditions. Hence for a given volume flow, this lost kinetic energy will depend only upon exhaust area. It becomes a matter of economic optimization to select the optimum exhaust area and therefore the active length of the LSB. This process is known as cold-end optimization For cold-end optimization, the LP turbine, condenser, lowest LP feedwater heater, and the cooling water system are taken into consideration For this optimization, the condenser pressure cannot be chosen freely because climatic conditions, such as air temperature, humidity, and cooling water temperature, may limit the choice of the pressure. But, within the given limits, the investigation will provide the economic optimum. 1. LP Turbine 2. Condenser 3. Cooling water pump 4. Main condensate control valve 5. Condensate pump 6. LP Feed water heater 1 7. Cooling tower 8. Extracted steam [ Fluid Flow in LP Turbines ] Steam Turbine 7. LP Turbine 46 / 53

47 Cold-end Optimization [2/4] Effect of Condenser Pressure [1/3] 1 Output m h h h o h p 2 p 2 2 m 2 EL p 2 Steam Turbine 7. LP Turbine 47 / 53

48 Power Gain, MW Effect of Condenser Pressure [2/3] Cold-end Optimization [3/4] Siemens 18 The kinetic energy of the steam leaving the LSB exit plane increases as the condenser pressure decreases. However, at a certain condenser pressure, the choking condition is reached at the last stage Choking 6F32" 4F38" 4F32" Any further decrease of the condenser pressure increases exhaust losses, h remaining unchanged F30" in.hga C Cooling Water Inlet Temperature Steam Turbine 7. LP Turbine 48 / 53

49 Cold-end Optimization [4/4] Effect of Condenser Pressure [3/3] h increases as the condenser pressure decreases, but the temperature of the condensate at the inlet to the lowest LP feedwater heater falls. In this case, the extracted steam flow rate increases, and the steam flow through LSB will decreases at the same time. The selected condenser pressure will determine a set of parameters including turbine output, cost of components and operating costs. For given climatic conditions, the condenser pressure can be lowered only by taking measures which increase the cost of the plant and the cooling system, for example by increasing cooling water flow and condenser heat transfer surface. Similarly, the added thermal resistance of dry or wet cooling tower will generally require increased condenser size and result in a higher optimum condenser pressure. Steam Turbine 7. LP Turbine 49 / 53

50 Frequency Control Condensate Throttling [1/3] Modified sliding pressure operation uses control valve reserve so the valves are slightly closed at 90% to 95% and some boiler stored energy can respond more quickly to rapid load change near full load. Condensate throttling is applied when the grid frequency is decreased greatly. If the grid frequency requires high power demand and the unit is in modified sliding pressure operation(hybrid operation), the turbine control valve is opened to raise the load (except if the valves are fully opened already). Simultaneously the main condensate control valve is throttled to a calculated position allowing a reduced condensate mass flow passing through the LP feedwater heaters. Considering a certain time respond, the extraction steam mass flow of the LP feedwater heater and the deaerator / feedwater tank are reduced. The surplus steam remains in the turbine and generates additional power. The resulting load increase depends on the amount of pre-set throttling of main control valve of the turbine, the throttling of the main condensate control valve and the actual unit load. By means of additional fast acting valves in the regarding extraction steam lines the response time behavior can be optimized. This condensate throttling serves as compensator for the transient time behavior of the boiler. Steam Turbine 7. LP Turbine 50 / 53

51 Frequency Control Condensate Throttling [2/3] The accumulated condensate is stored in the condenser hotwell or a separate condensate collecting tank. Parallel to the above mentioned measures the firing rate of the boiler is increased to meet the load requirements. The feeding of the boiler is continued and increased. Thus, the level of the feedwater storage tank is decreased accordingly. During this time the condensate flow reduction is gradually released and has reached steady state condition again. Refilling of the feedwater storage tank is initiated by releasing the condensate control valve to control the level of the hotwell or condensate collecting tank. The maximum allowable condensate mass flow is monitored and the refill flow is limited to a maximum value. Due to the increased condensate flow through the LP feedwater heaters and into the deaerator, the steam extraction from the affected turbine extractions is increased. The generator output decreases correspondingly. To compensate this influence the boiler-firing rate is increased. However, the maximum allowable superheater outlet flow is limited to 100% BMCR(Boiler Maximum Continuous Rating) Steam Turbine 7. LP Turbine 51 / 53

52 Main Steam Pressure, % Frequency Control Condensate Throttling [3/3] Today, modern power plants are operated in natural sliding pressure mode or modified sliding pressure mode. Primary electrical power response (additional electrical power within seconds) is produced by condensate throttling. Fixed Pressure Mode 50 Fixed Pressure Mode 25 At a certain part load, the control valves can to be throttled to improve the primary response capacity Steam Turbine Load, % Steam Turbine 7. LP Turbine 52 / 53

53 질의및응답 작성자 : 이병은 ( 공학박사 ) 작성일 : (Ver.5) 연락처 : ebyeong@daum.net Mobile: 저서 : 실무발전설비열역학 / 증기터빈열유체기술 Steam Turbine 7. LP Turbine 53 / 53