8. USC Steam Turbine

Transcription

1 8. USC Steam Turbine SST Steam Turbine (Siemens) Steam Turbine 8. USC Turbine 1 / 93

2 USC Steam Turbine 2 USC Cycle Optimization 24 Representative USC Steam Turbine 39 Advanced USC 52 Reduction of CO 2 Emission 64 USC Materials 83 Steam Turbine 8. USC Turbine 2 / 93

3 Background for the Development of USC Plants 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. Steam Turbine 8. USC Turbine 3 / 93

4 Improvement of Steam Turbine Efficiency 1% increase of efficiency = Fuel save $372,300/year (GE, 1995) = Fuel save \4 billion/year ( 한전, 2010) (for a 500 MW unit with a capacity of 80%) Improvement in Mechanical Efficiency Reduction of Aerodynamic losses Leakage losses Improvement in Thermodynamic Efficiency Increasing of Main steam temperature Main steam pressure Advanced Steam Path Technologies Advanced Steam Cycle and Materials USC Steam Turbine Steam Turbine 8. USC Turbine 4 / 93

5 USC Steam Turbine [1/2] GE Increase in efficiency have been achieved largely through two kinds of advancement: (1) improving expansion efficiency by reducing aerodynamic and leakage losses as the steam expands through the turbine; and (2) improving the thermodynamic efficiency by increasing the temperature and pressure at which heat is added to the power cycle. The later improvement is the core of USC technology. Steam Turbine 8. USC Turbine 5 / 93

6 USC Steam Turbine [2/2] GE The appropriate steam turbine configuration for a given USC application is largely function of the number of reheats selected, the unit rating, the site back pressure conditions. Specific design details will also determine the number of flows in a turbine section, the number of stages, and the LSB length. In particular, the site ambient conditions and the condensing system will play a major role in the selection of the LSB and the number of LP section flows. The 1.5 in.hga would be for a direct cooled condenser, or cooling tower in a cold environment. The 3.5 in.hga would be for cooling towers in an area with warmer environment temperatures. Steam Turbine 8. USC Turbine 6 / 93

7 Classification of Fossil Plants EPRI Nomenclature Steam Conditions Net Plant Efficiency, % Net Plant Heat Rate (HHV), Btu/kWh Subcritical Supercritical (SC) Ultrasupercritical (USC) Advanced Ultrasupercritical (A-USC) 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 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) Steam Turbine 8. USC Turbine 7 / 93

8 Concept of USC Critical point for water : 3208 psia/705 F (22.09 MPa/374.14C) The surface tension property of water becomes zero at the critical point. Therefore, there is no clear distinction between the liquid and the gaseous phase. p T K T E USC T S K SC T O Water Superheated steam Subcritical C E A B D Wet steam o f x g h Steam Turbine 8. USC Turbine 8 / 93

9 Characteristics of Supercritical There is no distinction between water and steam in supercritical units Steam Turbine 8. USC Turbine 9 / 93

10 P-h Diagram Steam Turbine 8. USC Turbine 10 / 93

11 Comparison of Cost Source: Best Practice Brochure (DTI, 2006) Parameter Units Subcritical USC Plant size MW Net plant efficiency % LHV Total investment cost EU/kW Fuel price EU/GJ, bituminous Load factor % Cost of electricity c/kwh UK p/kwh Breakdown of cost of electricity Fuel Capital O&M c/kwh Steam Turbine 8. USC Turbine 11 / 93

12 History of USC [1/7] Steam Turbine 8. USC Turbine 12 / 93

13 History of USC [2/7] Siemens Steam Turbine 8. USC Turbine 13 / 93

14 Thermal Efficiency [%] Temperature [C], Pressure [bar] Max Output Tandem Compound [MW] History of USC [3/7] Siemens Steam Cycle Simple Reheat Supercritical Temperature Power Output Thermal Efficiency Pressure Steam Turbine 8. USC Turbine 14 / 93

15 History of USC [4/7] Experienced Problems in USC Units Higher maintenance cost. Lower operational flexibility, availability and reliability. Control valve wear. Thermal stress. Solid particle erosion of turbine blades. Much more complicated start-up process. Probability of greater potential for turbine water induction through the main steam system compare to drumtype subcritical units. Higher stress corrosion cracking. More sensitive to feedwater quality. Steam Turbine 8. USC Turbine 15 / 93

16 History of USC [5/7] In 1957, the first USC units were put into commercial operation in USA and UK. AEP(American Electric Power) Philo unit MW with steam flow of 675,000 lb/h Steam conditions: 4500 psig/1150f/1050f/1000f (double reheat) 395 MW Drakelow C (UK) In 1959, Eddystone 1 (Philadelphia Electric Co.) was erected and commissioned in MW with steam flow of 2,000,000 lb/h Steam conditions (initial): 5000 psig/1200f/1050f/1050f (double reheat) Steam conditions (later): 4700 psig/1130f/1030f/1030f (double reheat) Net plant efficiency: 40% (HHV, without environmental system auxiliary power) Net plant heat rate: 8534 Btu/kWh Throttle steam conditions were changed because of serious mechanical and metallurgical problems. Most of the problems were due to the use of austenitic steels for thick section components operating at high temperatures. Steam Turbine 8. USC Turbine 16 / 93

17 History of USC [6/7] It is well known that austenitic steels have low thermal conductivity and high thermal expansion resulting in high thermal stresses and fatigue cracking. These problems and initial low availability of many USC power plants temporarily dampened utilities in building USC power plants and consequently most utilities reverted back to subcritical power plants. Additionally, USC plants have another problems compared to subcritical units, such as higher maintenance costs, lower operational flexibility, lower reliability of steam turbines. Many problems were related to the steam turbine control valve wear and tear, to the turbine blade thermal stress, to the solid particle erosion of blades and valves, and to more complicated start-up procedures. USC units are also more sensitive to feedwater quality. Therefore, full-flow condensate polishing is required to protect the turbine from stress corrosion cracking. After that, through more than 45 years of practices, USC technologies have been unceasingly developed and gradually perfected. Operational experience worldwide has brought the evidence, that present availability of USC power plants is equal or even higher than those of subcritical ones. Steam Turbine 8. USC Turbine 17 / 93

18 History of USC [7/7] A-USC study (ongoing project by DOE) 792 MW, 36.2 MPa/735.5C/760C (5250 psig/1356f/1400f) (single reheat) Final feedwater temperature: 332.8C (631F) Estimated net plant heat rate: Btu/kWh (6633 kj/kwh) A net plant efficiency of 44.6 to 45.6% is possible with boiler fuel efficiency of 89 to 90% and auxiliary power between 6.5 to 7.5% of gross generation. For 700C plants, it has been reported that double reheat has an efficiency improvement of only 0.7% (HHV). The double reheat cycle has provided 1.5 to 2.0% of efficiency gain above single reheat at 538C (1000F) throttle conditions. The cost/benefit for double reheat will need more evaluation and the first A-USC plant will more likely be single reheat and employ double reheat when justified later. Steam Turbine 8. USC Turbine 18 / 93

19 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 psig (165 bar) % Sub-Critical Temperature, F Comparison 2400 psig/1000f/1000f versus 4500 psig/1100f/1100f 2.8% + 2.4% + 1.6% = 6.8% Steam Turbine 8. USC Turbine 19 / 93

20 Efficiency Improvement by USC 7% cycle efficiency improvement by steam condition from 160bar / 540C / 540C to 290bar / 600C / 620C Steam Turbine 8. USC Turbine 20 / 93

21 Prediction of Future for Coal Power Plants 100 IGCC + Fuel Cell 80 IGCC 60 Large Coal Unit SC USC Small Coal Unit Steam Turbine 8. USC Turbine 21 / 93

22 Current Situation of Coal Plants in US EPRI The construction of new coal fired power plants has reduced greatly in US. Coal fired power plant being retired in response to tighter environmental regulations. While market for new coal power not favorable now, the past few years have shown how volatile the outlook for power generation can be Is it wise to put all eggs in the natural gas basket? Gas price is volatile: if all new generation is natural gas fired, electricity prices will fluctuate correspondingly. Gas is a fossil fuel and emits CO 2 : evenly CCS will be applied to NGCC. Advanced coal fired USC technology will help stabilize electricity prices and keep them affordable, but if it is to be available in 2025 needed to work on it today. Fuel diversity continues to have value in stabilizing cost of electricity. Steam Turbine 8. USC Turbine 22 / 93

23 USC Technologies 1) Improvement of power density 2) Improvement of mechanical design Increased number of stages Decreased inner ring diameter Optimized stage reaction levels Optimized stage energy level Advanced vortex blades Advanced sealing Integral cover bucket (ICB) Full arc, hook diaphragm first stage Advanced cooling scheme 3) Improved HP/IP/LP shell design 4) Advanced LP design with 45 LSB Advantages Increase the plant efficiency significantly Reduce fuel consumption for a given output Reduce all pollutant and waste, including CO 2 Considerations Higher investment cost Reliability Operational flexibility Steam Turbine 8. USC Turbine 23 / 93

24 USC Steam Turbine USC Cycle Optimization Representative USC Steam Turbine Advanced USC Reduction of CO 2 Emission USC Materials Steam Turbine 8. USC Turbine 24 / 93

25 Cycle Optimization 1 Reduction of condenser pressure larger heat transfer surfaces, and inclusion of an advanced LP exhaust hood 2 Reduction of boiler flue gas reduction of fan power 3 Reduction of boiler pressure losses and leakages water treatment for water/steam side; slagging/fouling/erosion reduction for flue gas side 4 Minimization of combustion air excess 5 Minimization of thermal losses 6 Improvement of boiler and turbine components technical design advanced steam path technologies for turbine side 7 Optimization of main steam parameters advanced steam cycle 8 Application of single or double reheat advanced steam cycle 9 Optimization of feedwater temperature optimized regenerative cycle Steam Turbine 8. USC Turbine 25 / 93

26 Plant Net Efficiency Based on LHV Plant Net Efficiency Based on HHV Efficiency Improvement in PC-Fired Plant Siemens % % in.hga Double reheat 1.9 in.hga 300 bar/600c Single reheat USC 120C 130C 250 bar/540c Excess Air Discharge Flue Gas Temperature Main Steam Condition Reheat Back Pressure Steam Turbine 8. USC Turbine 26 / 93

27 Economic Efficiency Improvement How to best apply the capital funding available on a power plant project is a critical question for the plant designer. The cost basis of technological improvements must be known to make an economic evaluation in today s competitive marketplace. One open literature investigated that the ranking of several technology improvement steps for better plant efficiency. From least cost to highest cost per efficiency improvement, million US$ / % net LHV efficiency, these were. 1) Reducing condenser back pressure, 4.6 2) Increasing to 8 th extraction point feedwater heater, raising feedwater temperature, 5.7 3) Raising main steam temperature and reheat steam temperature, ) Raising main steam temperature, ) Using separate BFPT instead of main turbine driven pump, ) Raising main steam pressure, ) Changing from single to double reheat, ) Using separate BFPT condenser, 60.7 Steam Turbine 8. USC Turbine 27 / 93

28 Available Energy, Btu/lb 1) Main Steam Temperature In the evaluation of steam conditions, the potential cycle efficiency gain by elevating steam pressures and temperatures must be considered. Most of the efficiency increase results from increased temperature, not pressure. Therefore, temperature is the more important factor regarding cycle efficiency than pressure F 1300F 1200F 1100F 1000F Pressure, psia Steam Turbine 8. USC Turbine 28 / 93

29 2) Main Steam Pressure Selection of main steam pressure is of secondary importance in terms of the cycle efficiency. This is because higher main steam pressure results in higher component costs. Thus, the optimum value should be found. The thick pressure parts will require a very limited rate of load change and longer start up times. Therefore, designers should optimize the operating pressure with the design temperature and select materials having optimum properties and cost. Starting with the traditional 2400 psig/1000f single reheat cycle, great improvements in power plant performance can be achieved by raising inlet steam conditions to levels up to 310 bar (4500 psig) and temperatures to levels in excess of 600C (1112F). In a reheat cycle, increasing the main steam pressure will improve the cycle efficiency and this is the incentive for using supercritical steam conditions. However, the thermodynamic benefit of increased main steam pressure at a given temperature is subject to diminishing returns because the significant reduction in volumetric flow at these conditions leads to shorter and wider turbine blade that is subject to higher passage boundary losses and increased steam path leakage. These blade losses act to offset the thermodynamic benefits of elevated steam conditions with increased main steam pressure. It is generally accepted that increasing the main steam pressure above 300 bar with steam temperatures of 600C/620C does not offer any further economic benefits. Steam Turbine 8. USC Turbine 29 / 93

30 3) Reheat Pressure Normally, the cold reheater pressure is a quarter of the main steam pressure. Therefore, the selection of the cold reheat pressure is an integral part of any power plant design. However, it becomes even more important for plants with USC steam conditions. The improvement resulting from the use of a HARP can be about 0.5%. However, economic considerations of the boiler design without a HARP tend to favor a lower reheater pressure at the expense of a slight decrease in cycle performance. Therefore, the resulting net heat rate gain is usually larger, approaching 0.6~0.7%. The use of a HARP results in a lower optimal reheater pressure and a higher optimal feedwater temperature. Both of these considerations significantly impact the design and cost of the boiler. As a result, careful optimization need to be done, in considering the use of a HARP, to ensure an economically optimal cycle selection is made. For double reheat units without HARP, the best performance would be achieved with the first reheat pressure of approximately 1450 psi(100 bar). However, economic considerations associated with the boiler and piping systems would typically favor reducing this to a lower level. The typical outcome is that the first reheat pressure is chosen below the thermodynamic optimum while the second reheat pressure is generally selected slightly above to reduce the LP inlet steam temperature. Steam Turbine 8. USC Turbine 30 / 93

31 3) Reheat Pressure Double Reheat Cycle with HARP Steam Turbine 8. USC Turbine 31 / 93

32 3) Reheat Pressure Four-Casing, Four-Flow, Double-Reheat Steam Turbine RH1 HP RH2 Steam Turbine 8. USC Turbine 32 / 93

33 4) LP Inlet Temperature The use of advanced reheat steam conditions strongly affects the inlet temperature to the LP turbine section. An increase in hot reheat temperature translates into an almost equal increase in crossover temperature for a given crossover pressure. However, the maximum allowable LP inlet temperature is limited by materials associated with the rotor, crossover, and hood stationary components. Of these, the rotor material temperature limits are usually reached first. In addition, the selection of hot reheat temperature (and corresponding effect on LP inlet temperature) impacts the amount of moisture at the LSB which factors into stress corrosion cracking considerations. Once the reheat steam conditions are established, then the LP steam conditions can be determined. If the resulting crossover temperature is too high, the energy ratio between the IP and LP can be changed to lower this temperature. Increasing the energy on the IP section will lower the crossover temperature, but it will also impact the cycle efficiency, increase the number of IP stages, or the loading of the IP stages, increase the height of the final IP bucket, increase the size of the crossover, or increase the pressure drop through the crossover. LP inlet temperature can be adjusted by both reheater pressure and crossover pressure. To lower the crossover temperature, the reheater pressure has to be increased or the crossover pressure has to be decreased. Crossover temperature is increased when a HARP is employed because it choose lower reheater pressure to increase the thermal efficiency of plants. Steam Turbine 8. USC Turbine 33 / 93

34 5) Regenerative Rankine Cycle T Boiler (1) Boiler Turbine G Feedwater heater (m) Condenser (1-m) s pump2 FWH condenser pump1 The Rankine cycle can be used with a feedwater heater to heat the high pressure subcooled water at the pump exit to the saturation temperature. The cycle efficiency can be increased, if the feedwater is heated by extracted steam from turbine. In this case the temperature of the feedwater becomes higher. This cycle is called as a regenerative cycle. Heating of the feedwater is accomplished by using small amounts of extracted steam having high enthalpy at various points in the expansion through the turbine. Steam Turbine 8. USC Turbine 34 / 93

35 5) Regenerative Rankine Cycle The heat input in the boiler decreases as the final feedwater temperature increases and the heat rejected in the condenser getting smaller as the feedwater is heated higher using the extracted steam. The more heaters are used, the higher thermal efficiency. If a large number of heaters is used, the process of feedwater heating is more reversible. For this reason, the regenerative cycle improves the thermal efficiency of the power plant. The feedwater heater arrangement has to be designed to obtain the best heat rate for a given set of USC steam conditions. In general, the selection of higher steam conditions will result in additional feedwater heaters and a higher final feedwater temperature. The higher final feedwater temperature will have an impact on the boiler cost. This then requires a system level optimization to determine the best economical solution for the increase in final feedwater temperature. In many cases, the selection of a heater above reheat point (HARP) is recommended. Employment of a HARP has a strong influence on the design of both turbine and boiler. The use of separate de-superheater ahead of the top heater for unit with a HARP can results in additional performance gain. Steam Turbine 8. USC Turbine 35 / 93

36 5) Regenerative Rankine Cycle In order to maximize the efficiency with USC steam conditions, a HARP is employed for a optimal higher feedwater temperature. Additionally, HARP impact the cost of the boiler significantly. [ Heat rate impact of alternative feedwater heater configurations ] Cycle No. of Feedwater Heaters HARP Heat Rate Benefit Single Reheat (4500 psig, 1100F/ 1100 F) No No Yes Yes Base Case +0.2% +0.6% +0.7% Double Reheat (4500 psig, 1100F/ 1100 F/1100F) No No Yes Yes Base Case +0.3% +0.2% +0.5% Steam Turbine 8. USC Turbine 36 / 93

37 5) Regenerative Rankine Cycle Single Reheat Cycle with HARP HARP: Heater Above Reheat Point SSR: Steam Seal Receiver, SPE: Steam Packing Exhaust Steam Turbine 8. USC Turbine 37 / 93

38 Cycle Optimization - Example Siemens 31.0 MPa / 600 / 610 /610 C Final feedwater temperature = 327C First reheat pressure = 9.5 MPa Second reheat pressure = 3.5 MPa Crossover pressure = 1.0 MPa Steam Turbine 8. USC Turbine 38 / 93

39 USC Steam Turbine USC Cycle Optimization Representative USC Steam Turbine Advanced USC Reduction of CO 2 Emission USC Materials Steam Turbine 8. USC Turbine 39 / 93

40 USC Steam Turbine Siemens [1/5] 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 SST MW ~45.6% (@ design point) 280 bar/600c/610c 4 Flow stages 308C Well below 800 g/kwh Key Technical Features Model Gross power output Main steam conditions SST MW 300 bar/600c/620c Steam Turbine 8. USC Turbine 40 / 93

41 USC Steam Turbine Siemens [2/5] Mixed steam Cooling steam Outer casing inner casing Stage balance piston Steam Turbine 8. USC Turbine 41 / 93

42 USC Steam Turbine Siemens [3/5] The basic design characteristics of HP turbine is the barrel type outer casing design and has an inner casing. This design can enable 300 bar and 600C. This rotation-symmetric design has minimum deformation during steady-state and transient operation and a consequence minimum clearances i.e. minimum leakage losses are achieved. The barrel type outer casing has an axial split casing which can handle highest pressure loadings by adopting the wall thickness. This gives an optimal thermal deformation behavior because there is no horizontal flange. The benefit is small radial clearances between inner casing and blades, that means best turbine efficiency. Advanced sealing technologies such as brush seals and abradable coatings reduce steam leakages even further. USC steam conditions require the use of thick-walled components. In order to remove this restriction, an internal bypass cooling system has been developed. Basically, a small amount of cooling steam passes through radial bores into the small annulus between the inner and outer HP casing. The cooling steam is lead through the inner casing towards the balance piston. Thus, the surface temperature is reduced, creep stresses are reduced, and customers lifetime requirements are met. The internal bypass cooling also effectively protects the inner surface of the outer casing, which would be exposed to main steam temperature without the internal bypass cooling. Steam Turbine 8. USC Turbine 42 / 93

43 USC Steam Turbine Siemens [4/5] As a consequence, it was possible to reduce the wall-thickness of the outer casing and thus enable faster start-up of the casing. An improved starting performance is the main customer benefit of this innovative concept. 3DV technology (3-dimensional design with variable reaction levels) is applied for HP and IP blades. The IP turbine is designed to take reheat steam temperature of 620C. Thus, the first stage blades are made of nickel alloy. The high steam temperature can be handled by reducing the rotor surface temperature by a cooling principle named vortex cooling. This cooling principle enables a temperature decrease due to the reduction of relative steam velocity at the rotor surface. The double flow, double casing turbine has a full arc admission. This first stage has zero flow losses and gives the best transition from a radial flow in the inlet ring to an axial flow in the double flow blade path. Steam Turbine 8. USC Turbine 43 / 93

44 USC Steam Turbine Siemens [5/5] The LP turbine consists of a double flow with a horizontal split casing. The push rod permits parallel axial thermal expansion of LP rotor and inner casing by directly coupling the IP outer casing with the LP inner casing. This reduces clearances between rotor and casing and improves the efficiency. Free-standing 45 LSBs made by steel provide an annular area of 12.5 m 2 per flow. Titanium LSB will be applied in the near future. Frequency control through condensate throttling. Steam Turbine 8. USC Turbine 44 / 93

45 USC Steam Turbine GE [1/5] 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 Steam Turbine 8. USC Turbine 45 / 93

46 USC Steam Turbine GE [2/5] 1) HP Section Design Main steam enters the section through two pipes (top and bottom). A heater above reheat point extraction is taken from the lower half. HP turbine eliminated the partial admission, control stage, and nozzle box. Older steam turbine designs utilized a control valve to control pressure and load during transient conditions. The mechanical design requirements of this stage, having to withstand partial arc stimulus, often result in a very large and inefficient 1st stage design than can be 5-10% lower efficiency than the other HP stages. Therefore, GE chose to implement a full arc 1st stage design, which is much higher reaction and lower aspect ratio to a traditional control stage. This enables the first stage design to rival the efficiency of other stages. Steam Turbine 8. USC Turbine 46 / 93

47 USC Steam Turbine GE [3/5] 1) HP Section Design 1st Stage To allow this, however, changes need to be made to allow the turbine quickly and efficiently respond to load swings. Therefore, GE will utilize an overload valve that will bypass the first stage and allow additional flow/load response. An overload admission was added for frequency control and capacity margin. Elimination of the nozzle box required that two inner shells be used. In this arrangement, the inlet #1 inner casing is subject to adjacent stage steam conditions on its inner surfaces and a downstream stage s steam pressure on its outer surface. The buckets of the first four stages are made of nickel-based material due to the high temperature creep requirements. The remaining buckets are conventional 12Cr material. All 10 stages will utilize integral cover buckets with advanced tip seals. The wheel spaces of the first two stages are cooled using external cooling steam. A combination of brush, variable clearance, and conventional shaft seals are used in the HP section. The corresponding outer casing inner surface is subjected to steam conditions at the same downstream steam pressure. Full admission design alleviated the mechanical challenges associated with partial admission design and the control stage. Steam Turbine 8. USC Turbine 47 / 93

48 USC Steam Turbine GE [4/5] 2) IP Section Design The IP section is designed in a double flow configuration. Two feedwater heater extractions are taken from the lower half. Single casing construction is used. The number of stages is 8. The buckets of the first three stages are made of nickel-based material due to the high temperature creep requirements. The remaining buckets are conventional 12Cr material. All 8 stages will utilize integral cover buckets with advanced tip seals. The wheel spaces of the first two stages are cooled using cooling steam, from HP section. A combination of variable clearance and conventional shaft seals are used in the HP section. Steam Turbine 8. USC Turbine 48 / 93

49 USC Steam Turbine GE [5/5] 3) LP Turbine Design The LP turbine design for the 1000 MW consists of 5 stages with four extractions. Last stages utilize 45 titanium blades. In addition, LSB employs advanced curved axial entry dovetails. The first two LP stages utilize high reaction stage design for optimal efficiency. Advanced brush seals are utilized to reduce leakage losses. Steam Turbine 8. USC Turbine 49 / 93

50 USC Steam Turbine Alstom 700C Steam Turbine Development [ALSTOM] Welding Balance Piston Steam Turbine 8. USC Turbine 50 / 93

51 USC Steam Turbine - Doosan Key Technical Features Max Guarantee Rating 1000 MW 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 Steam Turbine 8. USC Turbine 51 / 93

52 USC Steam Turbine USC Cycle Optimization Representative USC Steam Turbine Advanced USC Reduction of CO 2 Emission USC Materials Steam Turbine 8. USC Turbine 52 / 93

53 Comparison of Parameters Parameters Subcritical Supercritical 1100F USC 1290F A-USC Performance Cost Main steam, F/psia 1005/ / / /5100 Net efficiency, % (HHV) Net heat rate, Btu/kWh (HHV) Coal flow, lb/hr 840, , , ,000 Flue gas, ACFM(actual ft 3 /min) 2,107,000 2,016,000 2,107,000 2,107,000 Make-up water, gpm 4,260 3,750 3,650 3,300 NOx & SOx, lb/mwh CO 2, lb/mwh from plant Fuel cost, $/MBtu (HHV) TPC, $/kw 1,780 1,800 1,840 1,990 Capital, $/MWh Fixed O&M, $/kw-yr Var. O&M, $/MWh (2) Fuel, $/MWh (1) LCOE, $/MWh Dispatch cost, $/MWh (=(1)+(2)) CO 2 adder, $/MWh ($25/ton of CO 2 ) LCOE, $/MWh Dispatch cost, $/MWh (=(1)+(2)) Steam Turbine 8. USC Turbine 53 / 93

54 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 Steam Turbine 8. USC Turbine 54 / 93

55 Generals A-USC (Advanced Ultra Supercritical) means a coal fired power plant design with the inlet steam temperature of 700C to 760C (1292F to 1400F). The higher the inlet steam temperature, the higher the efficiency of a plant. The higher the efficiency of a plant, the less fuel consumption, and fewer emission are produced during electricity generation. Therefore, the purposes of A-USC plants are reducing the emission of CO 2 and its capture cost, and fuel consumption by increasing the efficiency of power plants. When the heat is supplied at 760C, the Carnot cycle efficiency is 69.9%, while the expected A-USC net plant efficiency is 52.7% (6825 kj/kwh, or 6475 Btu/kWh). USC uses ferritic and stainless steels, while A-USC requires nickel alloy materials. The costs of the higher priced nickel alloys must be balanced with the savings in less fuel consumption, lower weight and size of equipment, and cost avoidance for emission allowance requirements. TPC(Total Plant Cost) for 1290F A-USC is 11% higher than for SC unit, but potential to halve the difference because the cost of high temperature materials is getting lower. A-USC plants have the potential for lower cost of electricity especially when combined with the requirements to capture carbon for sequestration (CCS). The plant production costs per megawatt-hour are the lowest for A-USC w/ccs based on plant economic studies for coal firing. Combining CCS with A-USC plants will provide lower cost of electricity generation with 90% CO 2 capture. Currently, A-USC studies have been focused on 50Hz machines. This is because the rotating components of 60Hz machines require reduced steam temperatures by 40F to meet strength requirements. Steam Turbine 8. USC Turbine 55 / 93

56 Selection of Throttle Pressure Throttle pressure for the Rankine cycle is fundamental to the optimum amount of available energy of the working fluid at the specified operating throttle temperature. The optimum throttle pressure increases with throttle temperature. Throttle pressure for the desired throttle temperature of 700 to 760C will most feasible in the range of 5000 to 5500 psi. Considering a single reheat cycle, the optimum available energy peaks at about 2500 psia for 1000F, about 4000 psia for 1200F, and at about 5000 psia for 1400F. Because higher pressure results in higher component costs, the optimum available energy should be investigated. Higher steam pressure can help to reduce the flow path pipe size delivering the energy flow. The more compact plant equipment will help with cost savings as long as pressure vessel thickness and material costs are at the optimum. Due to concerns that very thick parts will require a very limited rate of load change and longer start up times, the throttle pressure should be determined with optimum properties and cost. Temperature is the more important factor regarding cycle efficiency. Selection of pressure is of secondary importance in terms of efficiency. Setting the HP throttle pressure, the IP inlet pressure and the LP exhaust pressure is important for the optimization and meeting acceptable operating conditions. Steam Turbine 8. USC Turbine 56 / 93

57 Double Reheat Cycle The double reheat cycle has normally been considered to provide 1.5% to 2.0% of efficiency above single reheat for throttle temperature of 538C to 593C (1000F to 1100F). It has been reported that the double reheat cycle would only provide 0.7% advantage above single reheat turbine with inlet conditions of 35 MPa/680C/700C (5075 psig /1256F/1292F). High temperature of the second reheat steam requires nickel alloy for its larger diameter piping. Thus, piping cost should be considered. Operation of a double reheat cycle was considered more difficult because of controlling the differential between the HP, IP 1 and IP 2 steam temperatures. The first A-USC plants will more likely be single reheat and double reheat may be adopted later. Double reheat technically feasible, but not economic. Long expensive piping between the boiler and steam turbine. Additional boiler heat transfer surface area. Additional turbine complexity. Steam Turbine 8. USC Turbine 57 / 93

58 Turbine Cycle The capacity of the steam turbine under studying is 750 MW. The steam turbine throttle conditions are 35 MPa/732C/760C (5000 psig /1350F/1400F) with 2 in.hga condenser pressure. An additional new requirement of an A-USC boiler is to deliver cooling steam from a source such as the primary superheater at 1.5% of main steam flow rate to the HP outer casing. 1.5% cold reheat steam is retained at the turbine for IP turbine outer casing cooling. Feedwater temperature to the economizer has ranged from 630F to 649F at MCR. Reducing the economizer gas outlet temperature is a little more difficult because of the higher final feedwater temperature of A-USC. A-USC steam turbine section efficiencies are expected to lie in the following range depending on offered by various vendors; HP: 89.2~93.3%, IP: 90.5~96.6%, LP: 90.6~95.8%. The net plant efficiency is in the range 46~48% based on HHV. CCS will affect net plant efficiency because total auxiliary power for CCS will be about 20.5% of gross power generation. Oxy-combustion A-USC plant efficiency with Ohio coal is estimated to be 38.1% (HHV) with 90% capture of carbon dioxide. Steam Turbine 8. USC Turbine 58 / 93

59 Steam Turbine Major characteristics HP turbine may have two stage because of limited use of nickel alloy Start up time longer because of higher temperature, but frequency control not expected to be affected BFW extractions are similar, but final feedwater temperature will become higher Same availability A-USC steam turbines should have same availability as conventional turbines. Steam Turbine 8. USC Turbine 59 / 93

60 Time Schedule of A-USC EPRI Steam Turbine 8. USC Turbine 60 / 93

61 Time Schedule of A-USC EPRI PCC: post-combustion capture Oxy: oxy-combustion Steam Turbine 8. USC Turbine 61 / 93

62 AD 700 Cycle AD 700 is an advanced 700C PF power plant has being developed in European Union. Steam conditions: 375 bar/700c/ 720C Plant efficiency: 52-55% Fuel saving and CO 2 emission reduction of up to 15% compared with the best available technology of today. Construction and commissioning will be finished in Steam Turbine 8. USC Turbine 62 / 93

63 Time Schedule of AD 700 Cycle Steam Turbine 8. USC Turbine 63 / 93

64 USC Steam Turbine USC Cycle Optimization Representative USC Steam Turbine Advanced USC Reduction of CO 2 Emission USC Materials Steam Turbine 8. USC Turbine 64 / 93

65 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 2 ) 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 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. Steam Turbine 8. USC Turbine 65 / 93

66 CO 2 Emission, g/kwh CO 2 Emission vs. Plant Efficiency Net Plant Efficiency, % (LHV) Steam Turbine 8. USC Turbine 66 / 93

67 CO 2 Emissions, ton/mwh CO 2 Reduction, % CO 2 Emission vs. Net Plant Efficiency CO 2 emissions, ton/mwh Percent CO 2 reduction from subcritical PC plant Subcritical PC plant Ultrasupercritical PC plant range Net Plant Efficiency, % Steam Turbine 8. USC Turbine 67 / 93

68 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%. Steam Turbine 8. USC Turbine 68 / 93

69 Net Plant Efficiency, % (HHV) Efficiency Gain with CCS Incorporated 45 EPRI USC 1300 USC w/pcc 1300 USC w/pcc (1) 1300 USC w/pcc (2) 1400 USC w/pcc (3) USC w/pcc (1) Back-end heat recovery (2) Double reheat (3) 1350F with back-end heat recovery and double reheat 1100F class USC loses efficiency of 7.7% when CCS is incorporated. By going to A-USC conditions of F, plus select other improvements, this loss can be more than recovered. Net efficiency improvements will be enhanced by CCS improvements. Steam Turbine 8. USC Turbine 69 / 93

70 CO 2 Emissions from Different Power Plants Lignite: 980~1,230 Hard coal: 790~1,080 Oil: 890 NG: 640 NG Comb. cycle 410~430 Solar 80~160 Nuclear: 16~23 Wind: 8~16 Unit: g CO 2 /kwh Electricity generation with CCS Hydro power: 4~13 The efficiency penalty associated with CO 2 capture: Rankine cycle: 9.2% (based on Siemens advanced process) Combined cycle: 8% (based on GE 9FB.03 unit with a 3-pressure HRSG) Steam Turbine 8. USC Turbine 70 / 93

71 CO 2 Capture Technologies There are three major technologies for CCS for industrial and power plants applications. Post-combustion separates CO 2 from the flue gases produced by combustion of a fuel in air. Oxy-fuel combustion uses oxygen instead of air for combustion, producing a flue gases that contains mainly H 2 O and CO 2. Therefore, CO 2 is easily separated by condensing the water vapor. Pre-combustion technology processes the primary fuel in a reactor to produce separate stream of CO 2 for storage and H 2, which is used as a fuel. Post-combustion capture chemical absorption process gas-fired power plant in Malaysia constructed by MHI Pre-combustion capture physical solvent process coal gasification plant in US Steam Turbine 8. USC Turbine 71 / 93

72 CO 2 Capture Process and Systems Postcombustion Coal Gas Biomass Air Power & Heat CO 2 Separation N 2,O 2 CO 2 Precombustion Oxycombustion Coal Biomass Gasification Coal Gas Biomass Gas, Oil Air/O 2 Steam Air Reformer +CO 2 Sep. Air Power & Heat O 2 H 2 Air Separation Power & Heat N 2 CO 2 N 2, O 2 CO 2 CO 2 Compression & Dehydration Industrial processes Coal Gas Biomass Air/O 2 Process + CO 2 Sep. CO 2 Raw material Gas, Ammonia, Steel Steam Turbine 8. USC Turbine 72 / 93

73 Post-Combustion Capture Technology [1/3] Remove 85-90% of NOx 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 Steam Turbine 8. USC Turbine 73 / 93

74 Post-Combustion Capture Technology [2/3] Steam Turbine 8. USC Turbine 74 / 93

75 Post-Combustion Capture Technology [3/3] The most common method for separating CO 2 from a gas stream in use today is the chemical absorption using alkaline solvents. The flue gas passes through an aqueous alkaline solvent, and since CO 2 is acidic it is bound to the solvent. The absorption process takes place in the absorption column. The flue gas enters at the bottom of the absorber, while the solvent is pumped to the top of the absorber. After the reaction and CO 2 absorption, the rich- CO 2 solvent drops to the bottom of the absorber and then it is pumped to the separation unit (CO 2 stripper). In CO 2 stripper the rich-co 2 solvent is heated up depending on the solvent type to C. This reverses the absorption process and releases most of the CO 2 in a pure stream for compression and transport. The lean- CO 2 solvent is transported back to the absorber for reuse. A variety of solvents could be used in the absorption/regeneration process and each has its advantages and disadvantages. Choosing the right solvent is important to reduce the energy penalty of the capture process. The most used solvent for CO 2 capture is monoethanolamine. Aqueous ammonia is used as well in capturing CO 2 from flue gases. Steam Turbine 8. USC Turbine 75 / 93

76 Oxy-Fuel Combustion Capture Technology [1/2] Steam Turbine 8. USC Turbine 76 / 93

77 Oxy-Fuel Combustion Capture Technology [2/2] In oxy-fuel combustion capture technology nearly pure oxygen is used for combustion instead of air. Therefore, combustion products are mainly CO 2 and H 2 O. If fuel is burnt in pure oxygen, the flame temperature is exceedingly high. Therefore, CO 2 and /or H 2 O-rich flue gas is recirculated to the combustor to moderate the temperature. The steam can easily be removed by condensation, leaving a rich- CO 2 stream ready for compression and storage. Oxygen is usually produced in cryogenic air separation unit which is the major demanding component in the process. Steam Turbine 8. USC Turbine 77 / 93

78 Pre-Combustion Capture Technology The pre-combustion technology refers to removing of the carbon from the fuel before combustion. Pre-combustion capture involves reacting fuel with oxygen or air and/or steam to give mainly syngas composed of carbon monoxide and hydrogen. The hydrogen can then be used directly as a fuel in the gas turbine. Burning hydrogen emits no CO 2 and primary exhaust gas from hydrogen combustion is water. Both pre- and post-combustion technologies are available at a significant drop in performance. Steam Turbine 8. USC Turbine 78 / 93

79 Carbon Capture Ready Power Plants [1/4] A power plant in the capture ready design will be able to integrate the CO 2 capture unit when the necessary regulatory or economic drivers are in place. In the EU, a capture ready assessment is mandatory for all new fossil power plants 300 MW, in other regions capture ready programs are already implemented or still under discussion. The aim of building power plants that are capture ready is to reduce the risk of space and connections. In the capture ready assessment the following topics have to be addressed. Evaluation of available CO 2 transportation and accessible CO 2 storage options. Siemens Reservation of sufficient area on the site for the later retrofit of the CO 2 capture unit including CO 2 compression and all plant integration measures. Assessment of the economic and technical aspects for the later retrofit and integration of the CO 2 capture unit. The capture process consumes LP steam for solvent regeneration and electrical energy for the solvent pumps and the CO 2 compressors. Cooling water is needed as well. The mass and energy flow rates at the interfaces depend on the capture process. Optimizing the heat integration between the power plant and the CO 2 capture unit including CO 2 compression will be a decisive factor for the competitiveness of a steam power plant with CO 2 capture. Steam Turbine 8. USC Turbine 79 / 93

80 Carbon Capture Ready Power Plants [2/4] Four Main Topics should be Considered 1) Water supply and cooling tower These systems need to be adapted. Later capacity extensions should be considered in civil and in the plant layout from the beginning. 2) Auxiliary power consumption The electrical auxiliary load will be doubled after retrofit of the capture unit, mainly caused by the CO 2 compression. Sufficient space, additional auxiliary transformers, switchyard and cable routes need to be considered. 3) Steam extraction A significant amount of the available LP steam (approx. 40%) needs to be extracted from the steam turbine and has to be supplied to the capture unit for solvent regeneration. (2.7 GJ/ton CO 2 captured, approximately 40% of LP steam) Avoiding thermodynamic inefficiencies associated with throttling at full and partial load as well as keeping the capital costs low are the main challenges. In addition, the different solvents and capture processes under competition vary in demand and properties of LP steam. 4) Flue gas path Additional space need to be reserved for the connection of the flue gas duct with the capture unit (T- Branch), for the installation of the additional flue gas fan and for the adaption of the FGD unit. Steam Turbine 8. USC Turbine 80 / 93

81 Carbon Capture Ready Power Plants [3/4] Capture Ready Requirements [Siemens] Exhaust ducts Consider p from CO 2 absorption unit Later flue gas connection to capture unit (T-branch) Flue gas fan Upgradable design or additional space for installation of second fan downstream of FGD Steam turbine building sufficient space/foundation for Modification of turbines Steam and condensate pipes Installation of heat exchangers Steam turbines Extraction of approximately 40% of LP crossover steam Options for modification of turbines expand on operation modes (part load, full load capability without CO 2 capture other plant and site conditions) Electrical auxiliary load sufficient space for Additional auxiliary transformer(s) Switchyard Cable routes FGD Either consider capacity extension in column design or provide space for enlarged FGD unit Air heating Optional: space for installation of heat exchanger(s) for lowest grade heat utilization Condensate system sufficient space for Heat exchangers for low grade heat utilization Additional piping routes with supporting structure/racks Cooling system sufficient space for Additional circulation pumps Service water system Sufficient cooling capacity of cooling tower Raw water & cooling water supply / Waste water treatment Sufficient space for enlargement Secure water utilization rights Steam Turbine 8. USC Turbine 81 / 93

82 Carbon Capture Ready Power Plants [4/4] Challenges The biggest challenge is the design of LSB. Approximately 40% of LP steam has to be extracted from the cross-over pipe. The varying flow will change the last stage loading and may turn the stage into turn-up mode. In this case, windage heat is generated near the hub region because rotating LSBs feed energy into the trapped steam. Thus, water spray nozzles are installed at the exhaust section to cool the high temperature steam. Typically, large coal-fired power plants have two- or three LP turbines. Therefore, one could be removed from operation when the plant is operated in capture mode. However, plants have one LP turbine may have lower performance when the plant is operated in capture mode because of turn-up loss. Therefore, a true capture ready plant is not feasible in this case, and the plant has to be modified when changed for capture operation. Steam Turbine 8. USC Turbine 82 / 93

83 USC Steam Turbine USC Cycle Optimization Representative USC Steam Turbine Advanced USC Reduction of CO 2 Emission USC Materials Steam Turbine 8. USC Turbine 83 / 93

84 Generals Substantial reduction in emissions from coal-fired power plants can be achieved only by employing most advanced and highly efficient modern power generation technologies. The most direct and economical method for this is the evolutionary advance of increasing steam temperatures and pressures at the steam turbine inlet well beyond the critical point of water. To allow this increases, advanced materials are needed that are able to withstand the higher temperatures and pressures in terms of strength, creep, and oxidation resistance. USC power plants have faced particular challenges for maintaining equipment reliability and flexible operation at more advanced throttle steam conditions. One of most important aspects is the role of pressure on steam-side oxidation. Most of the efficiency increase results from increased temperature, not pressure. As a consequence, material requirements, in terms of high temperature strength and steam side oxidation, could lead to the use of lower pressures (than the goal of 38.5 MPa) to make USC turbine economical, and yet still beneficial in terms of efficiency increases. Since ferritic steels are capable of meeting the strength requirements up to of approximately 620C, there is no obstacle for USC technology within this temperature range. As the steam condition moved to A-USC, ferritic and stainless steels will be replaced by nickel based alloys because those have higher material strength and corrosion resistance. Advanced material application, especially of titanium for LSB with lower density allows longer blades to be used and thus the exhaust annulus area to be increased. Steam Turbine 8. USC Turbine 84 / 93

85 Importance of Fireside Corrosion Steam Turbine 8. USC Turbine 85 / 93

86 Allowable Stress, ksi Austenitic Alloy Strength Ferritic H282 IN740 H230 TP310HCbN IN617 S304H T24 T92 TP347H T22 T Nickel Alloys Temperature, F Steam Turbine 8. USC Turbine 86 / 93

87 Temperature Capability of Materials Alstom Steam Turbine 8. USC Turbine 87 / 93

88 100,000 h Creep Rupture Stress, MPa Creep Rupture Stress Candidates of AD 700 Materials HCM25 7CrMoTiB1010 HCM12 P92 Super 304 Nf Pipe 617 Tube Alloy 263/ Temperature, C Thermal expansion coefficients, hardness, toughness and other mechanical properties are important to the design and fabrication of materials. In addition, welds and weldments for both thick sections and tubes should be tested. To achieve 1400F (760C) steam temperatures, longer creep rupture strength test at higher temperatures is very important to the A-USC design. Steam Turbine 8. USC Turbine 88 / 93

89 Net Efficiency and Materials Steam Turbine 8. USC Turbine 89 / 93

90 Relative Material Cost Relation between Allowable Metal Temperature at the Allowable Stress of 49MPa and the Relative Material Cost Carbon Steel CrMo Low Alloy Steel 9-12% Cr Steel 18%Cr-8%Ni Steel 15%Cr-8%Ni Steel 20-25% Cr Austenitic Steel High Cr-High-Ni Steel Ni-Base Alloys Allowable Temperature at 49 MPa, C Steam Turbine 8. USC Turbine 90 / 93

91 Material Validation Alstom Steam Turbine 8. USC Turbine 91 / 93