STEAM TURBINE POWER GENERATING PLANT

Abstract: An object of the present invention is to provide a compact steam turbine operable at a high temperature in a range of 600 to 660°C by use of ferrite based heat resisting steels, to thereby enhance the thermal efficiency, and a steam turbine power-generation plant using the steam turbine. The present invention provides a compact ultrasuper critical pressure steam turbine power-generation plant in which each of a main steam temperature and a reheated steam temperature can be set in a range of 600 to 660°C by making main parts exposed to a high temperature atmosphere such as a rotor shaft from ferrite based forged steels and cast steels and making a final stage blade of a low pressure turbine from a martensite steel. The final stage blade is made from a ferrite based forged steel having a tensile strength of 120 kgf/mm 2 or more; the rotor shaft is made from a ferrite based forged steel having a 10 5 h creep rupture strength (at each service temperature) of 11 kgf/mm 2 or more; and the inner casing is made from a ferrite based cast steel having a 10 5 h creep rupture strength of 10 kgf/mm 2 or more.

Description: Technical Field The invention refers to a steam turbine power-generation plant including a combination of a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine, wherein a value of the length of a blade (inch) x the number of revolution (rpm) of a final stage rotating blade included in said low pressure turbine is at least 125,000. Background Art A rotating blade for a steam turbine is made from a 12Cr-Mo-Ni-V-N steel at the present time. In recent years, the thermal efficiency of a gas turbine is desired to be improved from the viewpoint of energy saving and the equipment of the gas turbine is desired to be made compact from the viewpoint of space saving. To improve the thermal efficiency of a gas turbine and make compact the equipment thereof, it is effective to make longer blades of a steam turbine, and for this purpose, there is a tendency that the length of a final stage blade of a low pressure steam turbine becomes longer every year. With such a tendency, a service condition for blades of a steam turbine becomes strict, as a result of which the 12 Cr-Mo-Ni-V-N steel is no longer sufficient in strength under the above service condition, and therefore, it is expected to develop a new material having a higher strength. As the strength of the material for blades of a steam turbine, there is required a tensile strength which is a basic mechanical characteristic. The material for blades of a steam turbine is also required to exhibit a high toughness in addition to a high strength for ensuring safety against breakage. As a structural material having a tensile strength higher than that of the conventional 12 Cr-Mo-Ni-V-N steel (martensite based steel), there are generally known a Ni based alloy and a Co based alloy; however, such a material is undesirable as a blade material because it is poor in hot working ability, machinability, and periodic damping characteristic. A disk material for a gas turbine is known, for example, from Japanese Patent Laid-open Nos. Sho 63-171856 and Hei 4-120246. In the conventional steam turbine, the maximum steam temperature has been set at 566°C and the maximum steam pressure has been set at 246 atg. However, from the viewpoint of exhaustion of fossil fuel such as mineral oil or coal, energy saving, and prevention of environmental pollution, it is desired to increase the efficiency of a thermal power-generation plant, and to increase the efficiency of power-generation, it is most effective to increase the steam temperature of a steam turbine. CA 2 142 924 A discloses a final stage rotating blade of a low pressure steam turbine which is made of Ti-based alloy. The Ti-based alloy used for the final stage rotating blades shows quite poor machining characteristics, in particular when the material is cutted. Therefore, it is difficult to form the material into a desired blade shape. Further, the Ti-based alloy material is quite expensive so that the use of Ti-based alloy for the final stage rotating blades is not practical. The problem underlying the invention is to provide a steam turbine power-generation plant including a combination of a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine, the low pressure turbine comprising a final stage blade having superior machining characteristics and both high strength and high tenacity. This problem is solved by a steam turbine power-generation plant comprising the features of claim 1. Preferred embodiments are claimed in claims 2 to 10. A method by which the final stage blade of the low pressure steam turbine can be produced is the subject matter of claim 11. The final stage rotating blade of the low pressure turbine according to the present invention is made of stainless steel, so that the machining characteristics thereof are superior and the costs are substantially low in comparison with the costs of the Ti-based alloy. A final stage rotating blade of a low pressure steam turbine is one of the key parts for determining the power of a turbine. To realize a longer blade of the final stage rotating blade of the low pressure steam turbine, it was necessary to develope materials having both high strength and high tenacity. The martensite stainless steel used for the final stage rotating blade of the low pressure steam turbine of the invention satisfies these two requirements and allows to use the final stage rotating blade having a value of at least 125,000 of a blade length (inch) X the number of revolution (rpm) of a turbine. According to the present invention, in the steam turbine (number of revolution: 3600 rpm), the length of the final stage blade portion of the low pressure turbine is set at 914 mm (36") or more, preferably, 965 mm (38") or more; and in the steam turbine (number of revolution: 3000 rpm), the length of the final stage blade portion of the low pressure turbine is set at 1092 mm (43") or more, preferably, 1168 mm (46") or more. Further, [the length of a blade portion (inch)] × the number of revolution (rpm)] is set at 125,000 or more, preferably, 138,000 or more. In the 12Cr based heat resisting steel of the present invention, particularly, when used in steam at a temperature of 625°C or more, the material preferably exhibits a 10 5 h creep rupture strength of 10 kgf/mm 2 or more and an impact absorption energy (at room temperature) of 1 kgf-m or more. (1) There will be described the reason for limiting the content of each component of the 12% Cr based steel used for the final stage blade of the low pressure steam turbine according to the present invention. C is required to be added in an amount of 0.08 wt% at minimum for ensuring the tensile strength. When C is added in an excessively large amount, the toughness is reduced. The content of C is, preferably, 0.10 to 0.18 wt%, more preferably, 0.12 to 0.16 wt%. Si and Mn are added upon melting of steel as a deoxidizer and a deoxidizing/desulfurizing agent, respectively. Such an effect can be obtained by addition of the element in a small amount. Si is a δ ferrite generating element, and therefore, the addition of Si in a large amout may cause undesirable δ ferrite which acts to reduce the fatigue and toughness. The content of Si must be 0.25 wt% or less. In the case of adopting a carbon/vacuum deoxidation process or an electroslag melting process, si is not required to be added, and rather si may be not added. In particular, the content of Si may be in a range of 0.10 wt% or less, preferably, in a range of 0.05 wt% or less. The addition of Mn in a large amount reduces the toughness. The content of Mn must be 0.9 wt% or less. In particular, to improve the toughness, the content of Mn, which is effective as a deoxidizer, may in a range of 0.4 wt% or less, preferably, 0.2 wt% or less. Cr is effective to increase the corrosion resistance and tensile strength of the alloy; however, the addition of Cr in an amount of 13 wt% or more may cause a δ ferrite structure. The addition of Cr in an amount of less than 8 wt% is insufficient for Cr to exhibit the effect of increasing the corrosion resistance and tensile strength. The content of Cr may be in a range of 8 to 13 wt%. To improve the strength, the content of Cr is preferably in a range of 10.5 to 12.5 wt%, more preferably, 11 to 12 wt%. Mo is effective to increase the tensile strength of the alloy by its function of promoting solid-solution and precipitation. Such an effect, however, is not large so much, and the addition of Mo in an amount of 3 wt% or more may cause δ ferrite. The content of Mo is limited in a range of 1.5 to 3.0 wt%. In particular, the content of Mo is preferably in a range of 1.8 to 2.7 wt%, more preferably, 2.0 to 2.5 wt%. It is to be noted that W and Co have the same effect as that of Mo. V and Nb are effective to enhance the tensile strength and improve the toughness by the function of precipitating carbides. When the content of V is 0.05 wt% or less and the content of Nb is 0.02 wt% or less, the above effect is insufficient. The addition of V in an amount of 0.35 wt% or more and Nb in an amount of 0.2 wt% or more may cause δ ferrite. In particular, the content of V may be in a range of 0.15 to 0.30 wt%, preferably, 0.25 to 0.30 wt%; and the content of Nb may be in a range of 0.04 to 0.15 wt%, preferably, 0.06 to 0.12 wt%. It is to be noted that Ta may be added in place of or in combination with Nb. Ni is effective to enhance the low temperature toughness and prevent occurrence of δ ferrite. When the content of Ni is 2 wt% or less, the effect cannot be sufficiently obtained. When it is more than 3 wt%, the addition effect is saturated. In particular, the content of Ni is preferably in a range of 2.3 to 2.9 wt%, more preferably, 2.4 to 2.8 wt%. N is effective to improve the tensile strength and prevent occurrence of δ ferrite. When the content of N is less than 0.02 wt%, the effect cannot be sufficiently obtained. When it is more than 0.1 wt%, the toughness is reduced. In particular, the content of N is preferably in a range of 0.04 to 0.08 wt%, more preferably, 0.06 to 0.08 wt%. The reduction in contents of Si, P and S is effective to increase the low temperature toughness while ensuring the tensile. The contents of Si, P and S are desired to be reduced as much as possible. To improve the low temperature toughness, the content of Si may be in a range of 0.1 wt% or less; the content of P may be in a range of 0.015 wt% or less; and the content of S may be in a range of 0.015 wt% or less. In particular, the content of Si is preferably in a range of 0.05 wt% or less; the content of P is preferably in a range of 0.010 wt% or less; and the content of S is preferably in a range of 0.010 wt% or less. The reduction in contents of Sb, Sn and As is also effective to increase the low temperature toughness, and therefore, the contents of Sb, Sn and As are desired to be reduced as much as possible. However, in consideration of the existing steel-making technical level, the content of Sb may be in a range of 0.0015 wt% or less; the content of Sn may be in a range of 0.01 wt% or less; and the content of As may be in a range of 0.02 wt% or less. In particular, the content of Sb is preferably in a range of 0.001 wt% or less; the content of Sn is preferably in a range of 0.005 wt% or less; and the content of As is preferably in a range of 0.01 wt% or less. According to the present invention, the ratio (Mn/Ni) is preferably in a range of 0.11 or less. The heat-treatment of the inventive material is preferably performed by uniformly heating the material at a temperature allowing perfect austenite transformation, that is, in a range of 1000 to 1100°C, followed by rapid cooling (preferably, oil-cooling) of the material; heating and keeping to and at a temperature of 550 to 570°C, followed by cooling of the material (primary temper); and heating and keeping to and at a temperature of 560 to 680°C, followed by cooling of the material (secondary temper), to thereby obtain a full temper martensite structure. Brief Description of Drawings Fig. 1 is a diagram showing a relationship between a tensile strength and a (Ni-Mo) amount (wt%); Fig. 2 is a diagram showing a relationship between an impact value and a (Ni-Mo) amount (wt%); Fig. 3 is a diagram showing a relationship between a tensile strength and a quenching temperature; Fig. 4 is a diagram showing a relationship between a tensile strength and a temper temperature; Fig. 5 is a diagram showing a relationship between an impact value and a quenching temperature; Fig. 6 is a diagram showing a relationship between an impact value and a temper temperature; Fig. 7 is a diagram showing a relationship between an impact value and a tensile strength; Fig. 8 is a sectional configuration view of a low pressure steam turbine according to the present invention; Fig. 9 is a perspective view of a turbine rotating blade according to the present invention; Fig. 10 is a sectional view of a low pressure steam turbine according to the present invention; Fig. 11 is a sectional view of a rotor shaft for the low pressure steam turbine according to the present invention; and Fig. 12 is a perspective view of a leading end portion of a turbine rotating blade according to the present invention. Best Mode for Carrying Out the Invention [Embodiment 1] Table 1 shows chemical compositions (wt%) of 12% Cr based steels used as long blades materials for steam turbines. Each sample of 150 kg was melted by a vacuum arc melting process, being heated to a temperature less than 1150°C, and forged, to prepare an experimental material. Sample No. 1 was heated at 1000°C for one hour and cooled to room temperature by oil quenching, and then heated to and kept at 570°C for two hours and air-cooled. Sample No. 2 was heated at 1050°C for one hour and cooled to room temperature by oil quenching, and then heated to and kept at 570°C for two hours and air-cooled. Each of Sample Nos. 3 to 6 was heated at 1050°C for one hour and cooled to room temperature by oil quenching, and then heated to and kept at 560°C for two hours and air-cooled (primary temper), and further heated to and kept at 580°C for two hours and furnace-cooled (secondary temper). In Table 1, Sample Nos. 3 and 4 are inventive materials; Samples No. 5 and 6 are comparative materials; and Sample Nos. 1 and 2 are existing long blade materials. Table 2 shows mechanical properties of these samples at room temperature. From the results shown in Table 2, it is revealed that each of the inventive materials (Sample Nos. 3 to 5) sufficiently satisfies a tensile strength (120 kgf/mm 2 or more, or 128.5 kgf/mm 2 or more) and a low temperature toughness (Charpy V-notch impact value (at 20°C): 2.5 kgf-m/cm 2 or more) which are required for a long blade material for a steam turbine. On the contrary, each of Sample Nos. 1 and 6 as the comparative materials exhibits a tensile strength and an impact value which are lower than those required for a long blade for a steam turbine. Sample No. 2 as the comparative material is low in tensile strength and toughness. Sample No. 5 exhibits an impact value of 3.8 kgf-m/cm 2 which is slightly lower than a value of 4 kgf-m/cm 2 or more required for a long blade of 43 inches or more. Sample No. Tensile strength (kgf/mm 2 ) Elongation (%) Reduction of area (%) Impact value (kgf-m/cm 2 ) 1 114.4 19.0 60.1 8.0 2 114.6 18.6 59.7 1.2 3 132.5 21.0 67.1 5.2 4 134.9 20.8 66.8 4.8 5 137.0 18.5 59.8 3.8 6 118.7 21.1 67.3 5.2 7 133.5 20.1 60.4 5.1 Fig. 1 is a diagram showing a relationship between a (Ni-Mo) amount and a tensile strength. In this embodiment, both a strength and toughness at a low temperature are improved by adjusting the contents of Ni and Mo to be substantially equal to each other. As a difference between the contents of Ni and Mo becomes larger, the strength becomes lower. As shown in Fig. 1, when the Ni content is smaller, 0.6% or more, than the Mo content, the strength is rapidly lowered. On the contrary, when the Ni content is larger, 1.0% or more, than the Mo content, the strength is also rapidly lowered. As a result, the (Ni-Mo) amount suitable for enhancing the strength is in a range of -0.6% to 1.0%. Fig. 2 is a diagram showing a relationship between a (Ni-Mo) amount and an impact value. As shown in the figure, the impact value is low near -0.5% of the (Ni-Mo) amount, and is high in regions less than -0.5% and more than 0.5% of the (Ni-Mo) amount. Figs. 4 to 6 are diagrams showing dependences of heat-treatment conditions (quenching temperature and secondary temper temperature) on the tensile strength and impact value for Sample No. 3. The quenching temperature is in a range of 975 to 1125°C, and the primary temper temperature is in a range of 550 to 560°C and the secondary temper temperature is in a range of 560 to 590°C. From the results shown in the figures, it is confirmed that Sample No. 3, which is heat-treated in the above heat-treatment conditions, satisfies characteristics required as a long blade material (tensile strength ≧128.5 kgf/mm 2 , Charpy V-notch impact value (at 20°C) ≧ 4 kgf-m/cm 2 ). In addition, the secondary temper temperature in Figs. 3 and 5 is 575°C, and the quenching temperature in each of Figs. 4 and 6 is 1050°C. Fig. 7 is a diagram showing a relationship between a tensile strength and an impact value. The 12% Cr based steel in this embodiment is, as described above, preferred to exhibit a tensile strength of 120 kgf/mm 2 or more and an impact value of 4 kgf-m/cm 2 or more, and is more preferred to exhibit an impact value (y) which is not less than a value obtained by an equation of [-0.45 × (tensile strength) + 61.5]. The 12% Cr based steel according to the present invention is preferred to have such a composition that the (C + Nb) amount is in a range of 0.18 to 0.35%; the (Nb/C) ratio is in a range of 0.45 to 1.00; and the (Nb/N) ratio is in a range of 0.8 to 3.0. [Embodiment 2] With a sudden rise in cost of fuel after oil crisis as a turning-point, a boiler of a type of direct combustion of pulverized coal at a steam temperature of 600 to 649°C and a steam turbine have been required to be used for the purpose of improving a thermal efficiency by setting high the steam conditions. One example of the boiler used under such high steam conditions is shown in Table 3. Plant output Operating type 1050MW Constant pressure type Specification of boiler Type Radiative reheat type ultrasuper critical pressure once-through boiler Amount of evaporation 3170 t/h Steam pressure 24.12 Mpa[G] Steam temperature 630°C/630°C Performance Combustion characteristic NOx Unburned combustible in ash 120ppm 3.2% Rate of change in load (50 ↔ 100%) 4%/min Minimum load 33% ECR (Wet bank coal) With the increased plant output, the size of a pulverized coal combustion furnace is enlarged. For example, for a plant output of 1050 MW class, the furnace has a width of 31 m and a depth of 16 m; and for a plant output of 1400 MW class, the furnace has a width of 34 m and a depth of 18 m. Table 4 shows a main specification of a steam turbine in which the steam temperature is set at 625°C and the plant output is set at 1050 MW. The steam turbine in this embodiment is of a cross compound/quadruple-flow exhaust type. In this steam turbine, the length of a final stage blade in a low pressure turbine is 43 inches. A turbine configuration A has a turbine combination of [(HP-IP) + 2 × LP] and is operated at the number of revolution of 3000 rpm, and a turbine configuration B has a turbine combination of [(HP-LP) + (IP-LP)] and is operated at the number of revolution of 3000 rpm. Main components in the high pressure portion are made from materials shown in Table 4. In the high temperature portion (HP), the steam temperature is 625°C and the steam pressure is 250 kgf/cm 2 . The steam supplied from the HP portion is heated to 625°C by a re-heater and is supplied to the intermediate pressure portion (IP). The intermediate pressure portion is operated at the steam temperature 625°C and at a steam pressure of 45 to 65 kgf/cm 2 . The steam at a steam temperature of 400°C is supplied in the low pressure portion (LP), and the steam at a steam temperature of 100°C or less and in a vacuum of 722 mm Hg is supplied to a steam condenser. Fig. 8 is a sectional view of two low pressure turbines in tandem with each other, whose structures are substantially identical to each other. Two sets, each being composed of rotating blades 41 of eight stages, are disposed substantially symmetrically right and left, and stationary blades 42 are provided correspondingly to the rotating blades 41. The final rotating blade has a length of 43 inches, and is made from the 12% Cr based steel corresponding to Sample No. 7 shown in Table 1. The final rotating blade is of a double tenon/saddle-dovetail type shown in Fig. 9, and a nozzle box 44 is of a double-flow type. A rotor shaft 43 is made from a super clean forged steel having a full temper bainite structure. To be more specific, the forged steel contains 3.75 wt% of Ni, 1.75 wt% of Cr, 0.4 wt% of Mo, 0.15 wt% of V, 0.25 wt% of C, 0.05 wt% of Si and 0.10 wt% of Mn, the balance being Fe. The rotating blades other than the final one and the stationary blades are made from a 12% Cr based steel containing 0.1 wt% of Mo. The inner and outer casings are made from a cast steel containing 0.25 wt% of C. In this embodiment, the distance between centers of bearings 43 is 7500 mm; the diameter of a portion, of the rotor shaft, corresponding to the stationary blade is about 1280 mm; and the diameter of a rotating blade planted portion of the rotor shaft is 2275 mm. The ratio of the between-bearing distance to the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is about 5.9. Fig. 9 is a perspective view of a long blade of a size of 1092 mm (43"). Reference numeral 51 indicates a blade portion with which high speed steam collides; 52 is a portion to be planted in the rotor shaft; 53 is a hole into which a pin for supporting the blade applied with a centrifugal force is to be inserted; 54 is an erosion shield (plate made from stellite which is a Co-based alloy is joined by welding) for preventing erosion caused by water drop in steam; and 57 is a cover. In this embodiment, the long blade is formed by cutting a one-body forged part. It is to be noted that the cover 57 may be mechanically formed in a state being integral with the long blade. The 43" long blade is produced by melting a material by an electroslag re-melting process, followed by forging and heat-treatment. The forging was performed at a temperature in a range of 850 to 1150°C, and the heat-treatment was performed in the condition described in the first embodiment. Sample No. 7 in Table 1 shows a chemical composition (wt%) of the long blade material. The metal structure of the long blade material was a full temper martensite structure. The tensile strength at room temperature and the Charpy V-notch impact value (at 20°C) of Sample No. 7 are shown in Table 1. It is confirmed that the 43" long blade exhibits sufficient mechanical properties over the necessary characteristics, more specifically, a tensile strength of 128.5 kgf/mm 2 or more and a Charpy V-notch impact value (at 20°C) of 4 kgf-m/mm 2 or more. In the low pressure turbine in this embodiment, the axial root width of a rotating blade planted portion of the rotor shaft becomes gradually larger in four steps in the order of the first to third stages, fourth stage, fifth stage, sixth and seventh stages, and eighth stage. The axial root width of the final stage rotating blade planted portion becomes larger about 6.8 times than that of the first stage rotating blade planted portion. The diameters of portions, of the rotor shaft, corresponding to stationary blades are small. The axial root width of the portion corresponding to the stationary blade becomes gradually larger in three steps in the order of fifth stage, sixth stage and seventh stage from the first stage rotating blade side. The axial root width of the portion corresponding to the stationary blade on the final stage side becomes larger about 2.5 times than that of the portion corresponding to the stationary blade between the first and second stage rotating blades. In this embodiment, the number of the rotating blades is six. The length of the blade portion of the rotating blade becomes longer from about 3" at the first stage to 43" at the final stage. Depending on the output of the steam turbine, each of the lengths of the blade portions of the first to final rotating blades is set in a range of 80 to 1100 mm; the number of stages is 8 or 9; and the length of the blade portion of the rotating blade on the downstream side becomes longer than that of the blade portion of the adjacent rotating blade on the upstream side at a ratio of 1.2 to 1.8. The diameter of the rotating blade planted portion is larger than that of the portion corresponding to the stationary blade. The larger the length of blade portion of the rotating blade, the larger the width of the rotating blade planted portion. The ratio of the width of the rotating blade planted portion to the length of the blade portion of the rotating blade is in a range of 0.15 to 0.91 and it becomes smaller stepwise in the order from the first stage to the final stage. The axial root width of the portion, of the rotor shaft, corresponding to the stationary blade becomes smaller stepwise from that between the first stage and second stage rotating blades to that between the final stage rotating blade and the preceding one. The ratio of the axial root width of the portion, of the rotor shaft, corresponding to the stationary blade to the length of the blade portion of the rotating blade is in a range of 0.25 to 1.25 and it becomes smaller from the upstream side to the downstream side. The configuration of this embodiment can be applied to a large capacity (1000 MW class) power-generation plant in which the temperature at a steam inlet to each of a high pressure steam turbine and an intermediate pressure steam turbine is set at 610°C and the temperature at a steam inlet to each of two low pressure steam turbine is set at 385°C. The high temperature/high pressure steam turbine plant in this embodiment mainly includes a coal burning boiler, a high pressure turbine, an intermediate pressure turbine, two low pressure turbines, a steam condenser, a condensate pump, a low pressure feed-water heater system, a deaerator, a booster pump, a feed-water pump, and a high pressure feed-water heater system. In this turbine plant, ultra-high temperature/high pressure steam generated by the boiler flows in the high pressure turbine to generate a power, being re-heated by the boiler, and flows in the intermediate pressure turbine to generate a power. The steam discharged from the intermediate pressure turbine flows in the low pressure turbine to generate a power, and is then condensed by the condenser. The condensed water is fed to the low pressure feed-water heater system and the deaerator by the condensate pump. The water deaerated by the deaerator is fed to the high pressure feed-water heater by the booster pump and the feed-water pump, being heated by the heater, and is then returned into the boiler. In the boiler, the water is converted into high temperature/high pressure steam by way of an economizer, an evaporator, and a superheater. Meanwhile, the combustion gas in the boiler used for heating the steam flows out of the economizer, and enters an air heater. In addition, a turbine operated by bleed steam from the intermediate pressure turbine is used for driving the feed-water pump. In the high temperature/high pressure steam turbine plant having the above configuration, since the temperature of the feed-water discharged from the high pressure feed-water heater system is very higher than the temperature of the feed-water in a conventional thermal power plant, the temperature of the combustion gas discharged from the economizer in the boiler becomes necessarily very higher than that in a conventional boiler. Accordingly, the heat of the exhaust gas of the boiler is recovered to lower the gas temperature. The configuration of this embodiment can be applied to a tandem compound type power-generation plant in which a high pressure turbine, an intermediate pressure turbine, and one or two low pressure turbines are connected in tandem to each other to rotate one generator for power generation. In the generator having an output of 1050 MW class in this embodiment, a generator shaft is made from a material having a high strength. The high pressure turbine shaft has a structure in which nine stages of blades are planted on each multi-stage side centered on a first stage blade planted portion. The intermediate pressure turbine shaft is provided with two sets, each being composed of six stages of blades, disposed substantially symmetrically right and left with respect to an approximately central portion of the turbine shaft. In addition, while the rotor shaft of the low pressure turbine is not shown in any figure, either of the rotor shafts of the high pressure, intermediate pressure and low pressure turbines has a center hole through which the material quality is checked by ultrasonic inspection, visual inspection and fluorescent penetrant inspection. The material quality of the rotor shaft may be checked from the outer surface side thereof by ultrasonic inspection. In this case, the above center hole may be not formed in the rotor shaft. Table 5 shows a main specification of a steam turbine in which the steam temperature is set at 600°C and the plant output is set at 600 MW. In this embodiment, the steam turbine is of a tandem compound/double-flow type, and the length of a final stage blade in a low pressure turbine is 43 inches. A turbine configuration C has a turbine combination of [(HP/IP) integral type + LP] and a turbine configuration D has a turbine combination of [(HP/IP) integral type + 2 × LP], each of which is operated at the number of revolution of 3000 rpm. Main components in the high pressure portion are made from materials shown in Table 9. In the high temperature portion (HP), the steam temperature is 600°C and the steam pressure is 250 kgf/cm 2 . The steam supplied from the HP portion is heated to 600°C by a re-heater and is supplied to the intermediate pressure portion (IP). The intermediate pressure portion is operated at the steam temperature 600°C and at a steam pressure of 45 to 65 kgf/cm 2 . The steam at a steam temperature of 400°C is supplied in the low pressure portion (LP), and the steam at a steam temperature of 100°C or less and in a vacuum of 722 mm Hg is supplied to a steam condenser. Fig. 10 is a sectional view of the low pressure turbine, and Fig. 11 is a sectional view of a rotor shaft of the low pressure turbine shown in Fig. 10. One low pressure turbine is connected in tandem with the high pressure/intermediate pressure sides. Two sets, each being composed of six stages of rotating blades 41, are disposed substantially symmetrically right and left. Stationary blades 42 are disposed in such a manner as to be matched with the rotating blades. The final stage rotating blade has a length of 43 inches, and is made from a 12% Cr based steel shown in Table 1. A rotor shaft 43 is made from a super clean forged steel having a full temper bainite structure. To be more specific, the forged steel contains 3.75 wt% of Ni, 1.75 wt% of Cr, 0.4 wt% of Mo, 0.15 wt% of V, 0.25 wt% of C, 0.05 wt% of Si and 0.10 wt% of Mn, the balance being Fe. The rotating blades other than the final stage one and the preceding stage one and the stationary blades are made from a 12% Cr based steel containing 0.1 wt% of Mo. The inner and outer casings are made from a cast steel containing 0.25 wt% of C. In this embodiment, the distance between centers of bearings 43 is 7000 mm; the diameter of a portion, of the rotor shaft, corresponding to the stationary blade is about 800 mm. The diameter of the rotating blade planted portion of the rotor shaft is not changed at the first to final stages. The ratio of the between-bearing distance to the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is about 8.8. The axial root width of the rotating blade planted portion of the rotor shaft of the low pressure turbine is smallest at the first stage, and becomes gradually larger to the downstream side in four stages. The axial root width at the second stage is equal to that at the third stage, and the axial root width at the fourth stage is equal to that at the fifth stage. The axial root width at the final stage is larger 6.2-7.0 times than that at the first stage. The axial root width at each of the second and third stages is larger 1.15-1.40 times than that at the first stage; the axial root width at each of the fourth and fifth stages is larger 2.2-2.6 times than that at each of the second and third stages; and the axial root width at the final stage is larger 2.8-3.2 times than that at each of the fourth and fifth stages. In the figure, the width of a rotating blade planted portion is indicated by a distance between two points at which the downward extended lines of the rotating blade planted portion cross the diameter of the rotor shaft. In this embodiment, the length of the blade portion of the rotating blade becomes longer from about 4" at the first stage to 43" at the final stage. Depending on the output of the steam turbine, each of the lengths of the blade portions of the first to final rotating blades is in a range of 100 to 1270 mm; the number of stages is 8 at maximum; and the length of the blade portion of the rotating blade on the downstream side becomes longer than that of the blade portion of the adjacent rotating blade on the upstream side at a ratio of 1.2 to 1.9. As compared with the shape of the portion corresponding to the stationary blade, the shape of the rotating blade planted portion is extended downward. The larger the length of the blade portion of the rotating blade, the larger the width of the rotating blade planted portion. The ratio of the width of the rotating blade planted portion to the length of the blade portion of the rotating blade, which is in a range of 0.30 to 1.5, becomes gradually smaller from the first stage to the stage directly before the final stage. On the downstream side, the ratio at one stage becomes smaller 0.15-0.40 times than that at the preceding stage thereof. The ratio at the final stage is in a range of 0.50 to 0.65. The final stage rotating blade in this embodiment is the same as that described in Embodiment 1. Fig. 12 is a perspective view, with an essential portion cutaway, showing a state in which an erosion shield (stellite alloy) 54 is joined by electron beam welding or TIG welding as indicated by reference numeral 56. As shown in the figure, the shield 54 is welded at two points on the front and back sides. The configuration of this embodiment can be applied to a large capacity (1000 MW class) power-generation plant in which the temperature at a steam inlet to a high pressure/intermediate pressure steam turbine is 610°C or more and temperatures of a steam inlet and a steam outlet to and from a low pressure steam turbine are about 400°C and about 60°C respectively. The high temperature/high pressure steam turbine power-generation plant in this embodiment mainly includes a boiler, a high pressure/intermediate pressure turbine, a low pressure turbine, a steam condenser, a condensate pump, a low pressure feed-water heater system, a deaerator, a booster pump, a feed-water pump, and a high pressure feed-water heater system. Ultra-high temperature/high pressure steam generated by the boiler flows in the high pressure side turbine to generate a power, being re-heated by the boiler, and flows in the intermediate pressure side turbine to generate a power. The steam discharged from the high pressure/intermediate pressure turbine flows in the low pressure turbine to generate a power, and is then condensed by the condenser. The condensed water is fed to the low pressure feed-water heater system and the deaerator by the condensate pump. The water deaerated by the deaerator is fed to the high pressure feed-water heater by the booster pump and the feed-water pump, being heated by the heater, and is then returned into the boiler. In the boiler, the water is converted into high temperature/high pressure steam by way of an economizer, an evaporator, and a superheater. Meanwhile, the combustion gas in the boiler used for heating the steam flows out of the economizer, and enters an air heater. In addition, a turbine operated by bleed steam from the intermediate pressure turbine is used for driving the feed-water pump. In the high temperature/high pressure steam turbine plant having the above configuration, since the temperature at the feed-water discharged from the high pressure feed-water heater system is very higher than the temperature of the feed-water in a conventional thermal power plant, the temperature of the combustion gas discharged from the economizer in the boiler becomes necessarily very higher than that in a conventional boiler. Accordingly, the heat of the exhaust gas of the boiler is recovered to lower the gas temperature. Although in this embodiment, the present invention is applied to the tandem compound/double flow type power-generation plant in which one high pressure/intermediate pressure turbine and one low pressure turbine are connected in tandem with one generator, the present invention can be also applied to the turbine configuration D having a large output of 1050 MW class, shown in Table 5, which is characterized in that two low pressure turbines are connected in tandem with each other. In the generator having an output of 1050 MW class, a generator shaft is made from a material having a high strength.

Claims: A steam turbine power-generation plant including a combination of a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine, wherein a value of the length of a blade (inch) x the number of revolution (rpm) of a final stage rotating blade included in said low pressure turbine is at least 125,000 characterized in that the final stage rotating blade included in said low pressure turbine is comprised of martensite stainless steel containing 0.08 to 0.18 wt% of C, 0.25 wt% or less of Si, 0.90 wt% or less of Mn, 8.0 to 13.0 wt% of Cr, 2 to 3 wt% of Ni, 1.5 to 3.0 wt% of Mo, 0.05 to 0.35 wt% of V, 0.02 to 0.20 wt% in total of at least one kind of Nb and Ta, and 0.02 to 0.10 wt% of N. A steam turbine power-generation plant according to claim 1, characterized in that a tensile strength of said martensite stainless steel at a room temperature is 120 kgf /mm 2 or more. A steam turbine power-generation plant according to claim 1, characterized in that said martensite stainless steel has a full temper martensite structure. A steam turbine power-generation plant according to claim 1, characterized in that said martensite stainless steel does not substantially contain δ ferrite. A steam turbine power-generation plant according to claim 1, characterized in that a ratio between an amount of Mn and an amount of Ni is 0.11 or less in said martensite stainless steel. A steam turbine power-generation plant according to claim 1, characterized in that said martensite stainless steel is made such that an amount of P is restricted to 0.015 wt% or less, an amount of S is restricted to 0.015 wt% or less, an amount of Sb is restricted to 0.0015 wt% or less, an amount of Sn is restricted to 0.01 wt% or less, and an amount of As is restricted to 0.02 wt% or less. A steam turbine power-generation plant according to claim 1, characterized in that the temperature of a steam inlet to a first stage rotating blade of said high pressure turbine is in a range of 600 to 660°C. A steam turbine power-generation plant according to claim 1, characterized in that the temperature of a steam inlet to a first stage rotating blade of said low pressure turbine is in a range of 380 to 475°C. A steam turbine power-generation plant according to claim 1, characterized in that said high pressure turbine and said intermediate pressure turbine are integrally formed. A steam turbine power-generation plant according to claim 1, characterized in that said low pressure turbine includes rotating blades (41) planted in a rotor shaft (43) and stationary blades (42) for guiding flow of steam to said rotating blades (41), said low pressure turbine having five stages or more of said rotating blades (41) symmetrically disposed, and includes a double flow structure in which the first stage rotating blade is disposed at the central part of said rotor shaft. A method of producing a final stage rotating blade of a low pressure turbine, in a steam turbine power-generation plant which includes a high pressure turbine, an intermediate pressure turbine, and said low pressure turbine, wherein a value of a blade length (inch) x the number of revolution (rpm) of the final stage rotating blade included in said low pressure turbine is at least 125,000, characterized by melting a steel material containing 0.08 to 0.18 wt% of C, 0.25 wt% or less of Si, 0.90 wt% or less of Mn, 8.0 to 13.0 wt% of Cr, 2 to 3 wt% of Ni, 1.5 to 3.0 wt% of Mo, 0.05 to 0.35 wt% of V, 0.02 to 0.20 wt% in total of at least one kind of Nb and Ta, and 0.02 to 0.10 wt% of N to prepare an ingot, and forging the ingot; quenching the ingot by heating and keeping the ingot to and at a temperature of 1000 to 1100 °C and rapidly cooling it; primarily tempering the ingot by heating and keeping the ingot to and at a temperature of 550 to 570 ° C and cooling it; and secondarily tempering the ingot by heating and keeping the ingot to and at a temperature of 560 to 590 °C and cooling it so as to form tempered martensite structure.

Inventors: FUKUI YUTAKA, NAKAMURA SHIGEYOSHI, ONODA TAKESHI, SHIGA MASAO, FUKUI, YUTAKA, NAKAMURA, SHIGEYOSHI, ONODA, TAKESHI, SHIGA, MASAO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1996
Main classification: F01D5
IPC codes: C22C38, F01D5