DESCRIPTION LOW-PRESSURE STEAM TURBINE TECHNICAL FIELD [0001] This inventeon r e l a t e s t o a low-pressure steam t u r b i n e f o r uqe i n thermaL aqd nuclear power p l a n t s . BACKGROUND ART A low-pressure steam t u r b i n e used i n a thermal power p l a n t or nuclear power p l a n t is driven under w e t steam condition i n t h e y i c i p i t y of i t s f i n a l s t a g e . Under the wet steam - condition, t h e r e + occurs wet l o s s , t h a t isthermodynamican~hydrodynamicenergyloss, f a l o n g w i t h g e n e r a t i o n o r growthof d r a i n , a n d t h e t u r b i n e e f f i c i e n c y is d e t e r i o r a t e d . I f t h e d r a i n c o l l i d e s a g a i n s t t u r b i n e moving r blades r o t a t i n g a t a h i g h speed, t h e b l a d e s u r f a c e s w i l l b e possibly subject t o erosion, r e s u l t i n g i n d e t e r i o r a t i o n of r e l i a b i l i t y of t h e t u r b i n e . [0003] .. As a measure f o r reducing wet l o s s and p r e v e n t i n g e r o s i o n i n a low-pressure steam t u r b i n e , a conventional technique is known i n which d r a i n is removed by means of a d r a i n catcher or hollow I s t a t i o n a r y blades. As a technique o f using a d r a i n catcher i n a low-pres'sure steam,. Patent Document 1 l i s t e d below, f o r example, d i s c l o s e s a technique i n which a d r a i n c a t c h e r is provided on a &tionary blade outer r i n g supporting s t a t i o n a r y blades. . According t o the technique d i s c l o s e d i n Patent Document 1, drain c o n t a i n e d i n t u r b i n e d r i v i n g s t e a m i s c a u g h t w i t h t h e d r a i n c a t c h e r , - and the caught d r a i n is discharged outside through a passage. Further, as a technique o f using hollow s t a t i o n a r y blades i n a low-pressure steam t u r b i n e , Patent Document 2, f o r example I d i s c l o s e s steamturbine s t a t i o n a r y b l a d e s , i n w h i c h e a c h s t a tI i o n a r y bl.ade has a c a v i t y passing from an outer shroud t o an inner shroud ,through the i n s i d e of the s t a t i o n a r y blade. The s t a t i o n a r y blade a l s o has a p l u r a l i t y of slits which connect t h e f r o n t - s i d e and back-side s u r f a c e s o f t h e s t a t i o n a r y b l a d e t o t h e c a v i t y a n d extend + v e r t i c a l l y while being spaced from each other by a predetermined ! d i s t a n c e . The s t a t i o n a r y blades of t h e steam t u r b i n e d i s c l o s e d i n - Patent Document 2 a r e able t o intrGduce d r a i n i n t o t h e c a v i t i e s i n s i d e the stationarybladesthroughthe slits a n d c o l l e c t t h e d r a i n from t h e c a v i t i e s . Further, as another measure f o r reducing w e t l o s s and preventing erosion, t h e r e is known a conventional technique i n which s t a t i o n a r y blades a r e heated by introducing steam i n t o the i n s i d e o f t h e s t a t i o n a r y b l a d e s fromthe outside i n o r d e r t o p r e v e n t condensation of steam on t h e s u r f a c e s of the s t a t i o n a r y blades. Patent Document 3, f o r example, d i s c l o s e s a techn- ique of heating s t a t i o n a r y blades, i n which leakage steam a t high temperature and low pressure is e x t r a c t e d from a s h a f t s e a l gasket upstream of a high-pressure stage of the t u r b i n e and is introduced i n t o hollow 2 Jbationary blades. Patent Document 1: Japanese Patent Application Publication Patent Document 2: Japanese Patent Application Publication NO. H11-336503 Patent Document 3: Japanese Patent No. 3617212 [0006] However, even though the technique of using a drajn catcher as disclosed in Patent Document 1 or the technique of using hollow stationary blades as disclosed in Patent Document 2 are able to realize reduction of wet loss andprevention of - erosionby removing - drain, they still have a problem that turbine driving steam may possibly be discharged together with the drain. As for the technique of heating stationary blades as disclosed in Patent Document 3, steam must be introduced from the outside as energy for heating the stationary blades. This means that the system as a whole requires introduction of energy from the outside. It may be also possible to heat the stationary blades with use of a heater instead of externally introducing steam. In this case, however, additional energy is requiredto drive the heater. Therefore, the systemas a whole requires introduction of energy f-romthe outside. DISCLOSURE OF THE INVENTION In view of the foregoing problems inherent to the prior art, 3 b o b j e c t of t h i s i n v e n t i o n is t o provide a low-pressure steam t u r b i n e w h i c h i s capableofreducingwetloss a n d p r e v e n t i n g e r o s i o n by heating a s t a t i o n a r y blade i n t h e v i c i n i t y of a f i n a l s t a g e without d i s c h a r g i n g steam f o r d r i v i n g t o g e t h e r with d r a i n and without t h e need of i n t r o d u c t i o n o f energy from t h e o u t s i d e . [0008] I n o r d e r t o solve t h e aforementionedproblems, t h i s invention s provides a low-pressure steam t u r b i n e i n c l u d i n g an i n n e r casing t h a t houses arotorhavingapluralityofmovingblades f i x e d t h e r e t o and includes a p l u r a l i t y of s t a t i o n a r y blades f i x e d i n t h e i n s i d e A of t h e i n n e r casing, and an o u t e r casing arranged o u t s i d e t h e inner casing so a s t o coyer t h e i n n e r c a s i n g . The low-pressure steam I t u r b i n e of t h e i n v e n t i o n is c h a r a c t e r i z e d by fukther includi.ng: I a hezit c a r r i e r h e a t i n g channel provided between t h e i n n e r casing L and o u t e r casing so t h a t a heat c a r r i e r flows therethrough; a heat c a r r i e r i n l e t passage f o r i n t r o d u c i n g t h e heat c a r r i e r i n t o t h e heat c a r r i e r heating channel; and a heat c a r r i e r 'chamber provided i n t h e i n s i d e of a t l e a s t one of t h e s t a t i o n a r y blades t o receive t h e heat c a r r i e r t h a t has passed through t h e heat c a r r i e r heating channel, and c h a r a c t e r i z e d i n t h a t t h e a t l e a s t one of s t a t i o n a r y blades i n which t h e heat c a r r i e r chamber is provided is heated by ., t h e heat c a r r i e r which has been heated by passing through t h e heat c a r r i e r heating channel. [0009] An exhaust chamber is formed between t h e i n n e r casing and t h e o u t e r casing f o r guiding steam, which has performed work i n 4 t& low-pressure steam t u r b i n e , t o a condenser provided s e p a r a t e l y . ' T h i s m e a q s t h a t t h e r e e x i s t s , between t h e i n n e r casing and t h e o u t e r casing, t h e steamwhichhasperformedworki~thelow-pressures team * t u r b i n e . On t h e o t h e r hand, p a r t of heat possessed by high-temperature steam within t h e i n n e r casing ( e s p e c i a l l y near - t h e steam i n l e t ) is emitted v i a t h e i n n e r casing and t r a n s f e r r e d t o t h e exhaust. Conventionally, t h e heat t r a n s f e r r e d t o t h e exhaust is dischargedtogetherwiththe exhaustwithou,t beingused. In t h i s invention, t h e heat c a r r i e r heating channel is provided between t h e i n n e r casing a n d t h e o u t e r casing s o t h a t a heat c a r r i e r flowing through t h e heat c a r r i e r heating channel is heated by exchanginq heat with steam which has performed work i n t h e low-pressure steam t u r b i n e and obtained thermal energy correspondiqg t o t h e aforementioned emitted h e a t . - The thermal energy correspon&ng t o t h e e m i t t e d h e a t is I c o n v e n t i o n a l l y d i s c h a r g e d t o g e t h e r w i t h e x h a u s t w i t h o u t b e i h g u s e d . According t o t h i s invention, t h e thermal energy corresponding t o t h e e m i t t e d h e a t t h a t h a s conventionallynotbeenusedis u t i l i z e d , whereby t h e heat c a r r i e r can be heated without i n t r o d u c i n g energy from t h e o u t s i d e . The heated heat c a r r i e r is introduced i n t o t h e heat c a r r i e r chamber provided i n a s t a t i o n a r y blade t o heat t h e s t a t i o n a r y blade, whereby condensation of steam on t h e s u r f a c e of t h e s t a t i o n a r y b l a d e c a n b e p r e v e n t e d , making it p o s s i b l e t o reduce wet l o s s and prevent e r o s i o n . This means t h a t t-h e usage of t h e thermal energy corresponding t o t h e emitted heat makes it p o s s i b l e 5 b heat the stationary blade without introducing energy from the outside. In addition, according tothe invention, condensation of steam on the surface of the stationary blade is prevented and occurrence of drain is prevented by heating the stationary blade, andctherefore no steam for driving is discharged. [ OOll] The inner casing may be formed of a wall member, and the stationaryblades maybe supported on the inside ofthe wall member, via blade rings. Known structures for an inner casing foralow-pressure steam ! turbine include a single-wall inner casing structure formed by a wall member paving stationary blades supported on the inside '! thereof via blade rings, and a double-wall inner casing structure in which the inner casing has a double structure consisting of a first linner casing and a second inner casing and an extraction steam chamber is provided between the first inner casing and the second inner casing,. * In the single-wall inner casing structure, the amount of heat . that is possessed by driving steam flowing within the inner casing and is emitted to between the inner casing and the outer casing through the wall of the inner casing is greater in comparison with the double-wall inner casing structure. In other words, more energy is lost. On the other hand, the single-wall inner casing , structure is simplerin structure than the double-wall inner casing stracture, and hence the manufacturing cost and maintenance cost are less expensive. The Bormation of t h e i n n e r casing i n t o a single-wall inner casing s t r u c t u r e m a k e s i t p o s s i b a e t o redbce(themanufacturing c o s t andmaintenancecost o f t h e i n n e r casing. Further, t h e h e a t emitted through t h e wall of t h e i n n e r casing, t h a t h a s c o n v e n t i o n a l l y been discharged, can be reused t o heat t h e heat c a r r i e r i n t h e heat c a r r i e r h e a t i n g c h a n n e l . Therefore, t h e t h e r m a l e n e r g y l o s s o f t h e lowzpressure steam t u r b i n e a s a whole can be reduced. The stationarybladehavingthe heat c a r r i e r c h a m b e r p r o v i d e d t h e r e i n has a s l i t f o r i n j e c t i n g t h e heat c a r r i e r from t h e heat c a r r i e r chamber t o t h e o u t s i d e of t h e s t a t i o n a r y blade, t h e heat c a r r i e r is water, which is t r a n s f o r m e d i n t o steambypassingthrough t h e heat c a r r i e r heating channel and i n t r o d u c e d ' i n t o t h e heat c a r r i e r chamber. The formation o f t h e s l i t t o i n j e c t t h e heat - c a r r i e r from t h e heat c a r r i e r chamber t o t h e o u t s i d e of t h e s t a t i o n a r y blade e l i m i n a t e s t h e need of providing a channel f o r discharging from th'eheat c a r r i e r chamber t h e heat c a r r i e r whichhas been introduced i n t o the heat c a r r i e r chamber. Fuyther, t h e heat c a r r i e r f i n t r o d u c e d i n t o t h e h e a t c a r r i e r chamber is transforme d i n t o steam, whereby t h e heat c a r r i e r can be i n j e c t e d t o t h e o u t s i d e of t h e I stationarybladethroughthe s l i t without t h e heat c a r r i e r forming a contaminant i n t h e i n n e r casing. Furthermore, t h e steam functioning a s t h e heat c a r r i e r i s i n j e c t e d through t h e s l i t , whereby t h e steam is allowed t o perform work on t h e moving blades. The heat c a r r i e r i n l e t passage is a condensate i n l e t passage a f o r ~ i n t r o d u c i n g , i n t o the heat c a , r r i e r heating channel, condensate 1 obtained by condensing vapor which has been used t o generate work s i n the low-pressure steam t u r b i n e , and t h e condensate may be used I as the heat c a r r i e r . The use of the condensate as t h e heat c a r r i e r e l i m i n a t e s the needofpreparingaheatcarrier s e p a r a t e l y i n a d d i t i o n t o a c a r r i e r required f i r ?riving t h e low-pressure steam t u r b i n e . The low-pressure steam t u r b i n e may f u r t h e r include: a s t a t i o n a r y blade surface temperature d e t e c t i o n u n i t which d e t e c t s a surface temperature of t h e a t l e a s t one of s t a t i o n a r y blades i n which the c a v i t y i s provided; a steampressure d e t e c t i o n u n i t which , d e t e c t s a steam pressure on t h e upstream s i d e of t h e a t l e a s t one I of s t a t i o n a r y b l a d e s i n which t h e heat c a r r i e r chamber is provided;. of heat exchanged based on a d i f f e r e n c e between a temperature I ' 4 d e t e c t e d b y , t h e s t a t i o n a r y b l a d e surface temperature d e t e c t i o n u n i t and a s a t u r a t e d steam temperature a t a d e t e c t e d p r e s s u r e by the steam pressure d e t e c t i o n u n i t . , I n o r d e r t o prevent condensation of steam on the surface of LI the s t a t i o n a r y blade by heating t h e s t a t i o n a r y blade, it i s necessary t o maintain the s u r f a c e temperature of the s t a t i o n a r y b l a d e h i g h e r than the s a t u r a t e d steam temperature corresponding t o t h e s t e a m p r e s s u r e a r o u n d t h e s t a t i o n a r y b l a d e . F o r t h i s p u r p o s e , the heat exchange amount r e g u l a t i n g u n i t is provided so t h a t the 8 a t exchange amount by the heat exchange unit is regulated based on a djfference between a temperature detected by the stationary blade surface temperature detection unit and a saturated steam A temperature at a detected pressure by the steampressure detection unit. In this manner, the surface temperature of the stationary blade is maintained higher than the saturated steam temperature corresponding to the steam pressure around the stationary blade, whereby condensationof steamonthe surface ofthe stationaryblade , can be prevented. The heat exchange amount regulating unit may include: a heat carrier flow regulating valve provided in the heat carrier inlet passage; and a regulating valve control unit which regulates opening of the heat carrier flow regulating valve based on the differencebetweenthetemperaturedetectedbythe stationaryblade surface temperatu~e detection unit and the saturated steam temperature at the detected pressure by the steam pressure ! detection unit. This-makes it possible to regulate the heating amount for the heat carrier in the heat carrier heating channel by regulating the opening of the heat carrier flow regulating valve to regulate the amount of the heat carrier introduced into the heat carrier heating channel. [0016] Further, a plurality of the heat carrier heating channels may be provided. The heat carrier inlet passage may be branched 9 h mid5way-into a plurality of branched inlet passages, and the branched inlet passages may be copnected to the plurality of heat carrier heating channels, respectively. The heat exchange amount regulating unit may include: brarfched inlet passage heat carrier 7t flow regulating valves provided in the respective branched inlet passages; and a branched passage regulating valve control unit which regulates opening of the branched inlet passage heat carrier flow regulating valves based on the difference between the temperature detected by the stationary blade surface temperature detection unit and the saturated steam temperature at the detected pressure by the steam pressure detection unit. This configuration makes it possible to regulate the flow rates of the heat carrier to the branched inlet passages by regulating the openings of the branched inlet passage heat carrier flow regulating valves to regulate the amounts of the heat carrier fed to the branched inlet passages. Further, the openings of some of the branched inlet passage heat carrier flow regulating valves canbe reducedto zero sothat the number ofthe heat carrier heating channels used to heat the heat carrier is changed. Thus, the area of heat exchange surface where the heat carrier exchanges heat can - be changed and the heating amount for the heat cakrier in the heat carrier heating channel can be regulatkd. The heat carrier heating channel maybe - provided surrounding - an upper half of the inner casing. In the upper half of the inner casing, the amount of heat 10 Qhtted through the inner casing is greater than in the lower half , of the inner aasing. Therefore, the provis&oh of the heat carrier I I ! .. heating channel surropnding the upper half of tpe inner enables the heat carrier to be heated more efficiently. In addition, the lower half of the inner casing is generally pravided with more accessories including an extraction steam pipe and so on. + .. Therefore, the attachment of the heat carrier heating channel can be made easier when the heat carrier heating channel is attached to,the upper half of the inner casing having fewer accessories attached thereto. The heat carrier heating channel maybe provided surrounding a steam inlet of the inner casing. .. The steam flowing in the inside of the steam inlet is steam .which has not been used to perform work in the low-pressure steam turbine. In other words, the steam flowing in the inside of the steam inlet is steam having the highest temperature in the steam flowingwithin the inner casing. Therefore, a great amount of heat is emitted from the steam inlet to the outside of the inner casing, ' and hence the provision of the heat carrier heating channel surrounding the stea inlet enables the heat carrier to P be heat efficientl+y . Thisinventionisabletoprovidealow-pressure steamturbine which is capable of reducing wet loss and prevpnting erosion by heating the stationary blade in the vicinity of the final stage 11 &hout introducing energy from the outside and without discharging driving steam together with drain. 1 F I G . 1 is a schematic configuration diagram illustrating a configuration of alow-pressure steam turbine according to a first I embodiment; - 8 A F I G . 2 is a schematic configuration diagram illustrating surroundings of a heat exchanger panel according to the first embodiment; F I G . 3 is a schematic configuration diagram illustrating Isurroundings of a final stage stationary blade according to the first embodiment; F I G . 4 is a flowchartillustratingprocedures for controlling + introduction of condensate forthe purpose ofheatinga final stage stationary blade according to the first embodiment; 7 F I G . 5 is a schematic configuration diagram illustrating surroundings of a heat exchanger panel according to a second embodiment; and F I G . 6is a flowchartillustratingprocedures for controlling introduction condensate for the purpose of heating a final stage stationary blade according to the second embodiment. BEST MODE FOR CARRYING OUT THE INVENTION * Preferred embodiments of the invention will be described in detail $y way of example with reference to t It should 1 be undgrstood that dimensions, materials, I arrangement of parts and components describdinthese embodiment 1 are provided fof an illustrative purpose only and are not intended ! to limit &he scope of the invention unless otherwise stated. [Embodiments] First Embodiment Referring to FIG. 1, a configuration of a low-pressure Steam turbine will be schematically described. FIG. 1 is a schematic configuration diagram illustrating a configuration of a low-pressure steam turbine according to a first embodiment ofthe invention. The low-pressure steam turbine lhas an inner casing 2, and an outer casing 4 arranged outside the inner casing 2 so as to cover the inner casing 2. A space 14 is formed between the inner casing 2 and the outer casing 4. The inner casing 2 is configured to include an - inner casing body 22 housing a rotor 6, a steam inlet 24 for introducing steam into the inner casing body 22 from the outside, and a flow guide 26 for guiding flow of the steam that has been used to generate work in the inner casing body 22. The inner casing 2 is of a single-wall inner casing structure. [0024] 4 The rotor 6 is rotatably supported by a bearing 12 outside 13 dk outer casing 4. A plurality of moving blades - 8 are implanted in and fixed to the rotor 6. The portion.,o f the rotor 6, where the moving blades are implanted and the moving blades 8, are housed in the inndr casing body 22. In the inner casing body 22, apluralityof stationaryblades 10 are attached via blade rings 11 (not shown in FIG. 1) so as to * face the moving blades 8 arranged on the rotor 6. The configuratio~o fthis invention is further characterized by a heat exchanger panel 16 provided surrounding an upper half .. I - of the inner casing 2. The heat exchanger panel 16 is a channel 1 in which a heat carrier (that is condensate to be described later in the first embodiment) flows, and is made of a material capable i of exchanging heat with the outside of the chapel. This means that 1 flowing within the heat exchanger panel 16 to exchange heat with , the surroundings of the heat exchanger panel 16. [0027] A configuration around the heat exchanger panel 16 and operation thereof will be described with reference to FIGS. 1 to 3. FIG. 2 is a schematic configuration diagram showing surroundings of the heat exchanger panel according to the first. embodiment. FIG. 3 is a schematic configuration diagram showing surroundings of the final stage stationary blade according to the first embodiment. In FIG. 2, reference numeral 38 denotes a condensate pump. The condensate pump 38 is a pump for feeding conderisate to the next stage. The condensate is condensed by a condenser (not shown) isobarically cooling vapor which has been used to generate work in the low-pressure steam turbine 1. The condensate pump'38 is provided outside the low-pressure steam turbine 1. [0029] The condensate fed by the condensate pump 38 - flows through acondensate channel39, being heatedby two low-pressure feedwater heaters 40 and 42 arranged in series on the condensate channel 39, I , and is fed to the next stage. An upstream condensate inlet passage 50 is formed by being branched from the condensate channel 39 downstream of the condensate pump 38 and upstream of the low-pressure feedwater heater 40, while a downstreamcondensate inlet passage 52 is formed by being branched from the condensate channel 39 downstream of the low-pressure feedwater heater 42. The upstream condensate inlet pass.a ge 50 and the downstream condensate inlet passage 52 merge together to form a condensate inlet passage 54, and the condensate inlet passage 54 is connected to the heat exchanger panel 16. The upstream condensate inlet passage 50, the downstream condensate inlet passage 52, and the condensate inlet passage 54 are respectively provided with control valves 44, 46 and 48 for 15 a g u l a t i n g t h e f l u i d flow r a t e t h e r e i n . Opening of each of t h e conJrol valves 4 4 , 46 and 48 is r e g u l a t e d by a c o n t r o l device 30 , t o be described l a t e r . FIG. 2 and FIG. 3 i l l u s t r a t e l a fina4 stage s t a t i o n a r y blade 10a t h a t is one of a p l u r a l i t y of s t a t i o n a r y blades provided i n the low-pressure s t e a m t u r b i n e l . The f i n a l stage s t a t i o n a r y b l a d e 10a is located a t the most downstream i n the flow d i r e c t i o n of steam within the inner casing body 22. A s t a t i o n a r y blade surface temperaturegauge 34 is a t t a c h e d t o t h e f i n a l s t a g e s t a t i o n a r y b l a d e a 10a f o r d e t e c t i n g a surface temperature t h e r e o f . Further, a steam pressure gauge 32 f o r d e t e c t i n g a steam pressure is provided upstream i n the steam flow d i r e c t i o n i n t h e f i n a l s t a g e s t a t i o n a r y blade 10a. The detected values by t h e s t a t i o n a r y blade surface a A temperature gauge 34 and t h e steam pressure gauge 32 a r e input t o the c o n t r o l device 30. [0033] The f i n a l stage s t a t i o n a r y blade 10a has a hollow shape as shown i n FIG. 3, and a heat c a r r i e r chamber 12 is formed t h e r e i n . The heat c a r r i e r chamber 12 communicates with t h e heat exchanger p a n e l 1 6 t h r o u g h t h e w a l l o f t h e i n n e r c a s i n g b o d y 2 2 a n d a s t a t i o n a r y blaae i n l e t passage 17 passing through the i n s i d e of t h e blade r i n g 11. This makes it p o s s i b l e t o introduce condensate, which has been heated and evaporated while passing through t h e - h e a t exchanger panel 16, i n t o t h e heat c a r r i e r chamber 12 within t h e f i n a l stage s t a t i o n a r y blade 10a. 16 : It is preferable in terms of heat exchange efficiency to extend the heat exchapgeq pqnel 16 froh tip st ap iplet 24 to a , stationary blade in an inter~ediake stage. , r The final stage stationary blade 10a is provided with slits 13 connecting the heat carrier chamber 12 to the outside of the I stationary blade 10a. The slits 13 are provided downstream of the final stkge>stationary blade 10a in the flow dirhction of steam flowing in the inner casing body 22. Next, operation of the low-pressure steam turbine 1 having the configuration as described above will - be dqs~ribed. In the low-pressure steam turbine 1, stea.rn introduced from the outside is introduced into the inner casing body-22 through the steaminlet24. The s t ; e a m i n t r o d u c e d i n t o t h e i n n e r casingbody 22 is expanded and increased in flow speed while passing through the stationary blade 10, and works on the moving blades 8 to cause the rotor 6 to rotate. [0036] The steam which has performed work in the inner casing body 22 is discharged from the inner casing body 22 into the space 14. Part of the steam discharged into the space 14 flows upward of the inner casing body 22 along the flow guide 26 as indicated by the C flow direction A in FIG. 1, and then flows downward along the periphery of the inner casing body 22. Another part of the steam A id discharged out ofthe outer casing 4 through a discharge portion 17 *ot shown) provided i n a lower p a r t of t h e o u t e r casing 4 , and then fed t o t h e 'condenser (not shown). Oq t h e o t h e r hand, t h e remainder of t h e steam discharged i n t o t h e space 1 4 flows downward i n t h e space 1 4 along t h e flow guide 26 a s i n d i c a t e d by t h e flow d i r e c t i o n B i n FIG. 1, and d i s c h a r g e d o u t of t h e o . u t e r casing 4 through a discharge p o r t i o n (not shown) provided i n a lower p a r t of t h e o u t e r casing 4, and then fed t o t h e condenser (not shown). - i [0037] In t h e meantime, t h e c o n t r o l device 30 c o n t r o l s t h e 8 . i n t r o d u c t i o n of condensate i n t o t h e heat c a r r i e r chamber 12 within t h e f i n a l s t a g e s t a t i o n a r y blade 10a. This c o n t r o l w i l l be . d e s c r i b e d w i t h r e f e r e n c e t o FIG. 4 . FIG. 4 is a flowchart i l l u s t r a t i n g procedures f o r c o n t r o l l i n g t h e i n t r o d u c t i o n of c o n d e n s a t e f o r h e a t i n g t h e f i n a l s t a g e s t a t i o n a r y b l a d e i n t h e f i r s t embodiment of t h e i n v e n t i o n . [0038] I O n c e t h e l o w - p r e s s u r e s t e a m t u r b i n e 1 i s d r i v e n f t h e o p e r a t i o n - ' proceeds t o s t e p S1. In s t e p S1, a d e t e c t e d value by t h e s t a t i o n a r y blade s u r f a c e i temperature gauge 34 a t t a c h e d t o t h e f i n a l s t a g e s t a t i o n a r y blade 10a ( h e r e a f t e r , r e f e r r e d t o a s t h e f i n a l s t a g e s t a t i o n a r y blade surface temperature) is i n p u t t o t h e c o n t r o l device 30, while a t t h e same time a d e t e c t e d value by t h e steam pressure gauge 32 attached upstream of t h e f i n a l s t a g e s t a t i o n a r y blade 10a i n t h e steam flow d i r e c t i o n ( h e r e a f t e r , r e f e r r e d t o as t h e f i n a l s t a g e upstream steam p r e s s u r e ) is input t o t h e c o n t r o l device 30. 18 SubsequentLy, t h e operation proceeds t o s t e p S2. In s t e p S2, based on t h e f i n a l s t a g e upstream steam pressure, the c o n t r o l device 30 computes a s a t u r a t e d steam temperature a t t h i s p r e s s u r e . The c o n t r o l device 30then c a l c u l a t e s atemperature d i f f e r e n c e A t between t h e saturatedsteamtemperature and the f i n a l stage s t a t i o n a r y blade surface temperature. It is assumed here t h a t A t denotes a d i f f e r e n c e o b t a i n e d b y s u b t r a c t i n g t h e s a t u r a t e d steam temperature from t h e f i n a l stage s t a t i o n a r y blade surface temperature. [0040] Subsequently, the operation proceeds t o s t e p S3. In s t e p S3, it is determined whether or not t h e value A t is smal'ler than a predetermined t h r e s h o l d tl, The t h r e s h o l d tl is a p o s i t i v e v-a lue. I f it is determined " Y e s " i n s t e p S3, t h a t is, means t h a t t h e f i n a l s t a g e s u r f a c e temperature has not been s u f f i c i e n t l y r a i s e d , and s t e a m i s l i k e l y t o condense on the surface o f t h e f i n a l stage s t a t i o n a r ~ b l a d eIO a. Therefore, t h e operation a proceeds t o s t e p S4. c o n t r a s t , i f it is determined "No" i n s t e p S3, t h a t i s , i f At2t1, it means t h a t t h e f i n a l s t a g e s t a t i o n a r y blade surface temperature is s u f f i c i e n t l y r a i s e d , a n d t h e p o s s i b i l i t y i s low t h a t the steam colndenses on the s u r f a c e of the f i n a l stage s t a t i o n a r y blade 10a. Therefore, t h e operation proceeds t o s t e p S5. - In s t e p S4, based on t h e temperature d i f f e r e n c e A t , t h e c o n t r o l d e v i c e 30 f u l l y o p e n s t h e c o n t r o l v a l v e 48, while i n c r e a s i n g theopening o f t h e c o n t r o l v a l v e 44 o r 46. This i n c r e a s e s t h e a m o u n t of condensate flowing through t h e condensate channel 39 and i n t r o d u c e d i n t o t h e heat exchanger p a n e l 1 6 through t h e condensate i n l e t passage 54. When t h e f i n a l s t a g e s t a t i o n a r y blade s u r f a c e temperature is iower than t h e . s a t u r a t e d steam temperature, l i k e when t h e temperature d i f f e r e n c e A t assumes a negative value, t h e openings of t h e c o n t r o l valves 44 and 46 a r e r e g u l a t e d such t h a t t h e opening , of t h e c o n t r o l valve 46 is g r e a t e r than t h a t of t h e c o n t r o l valve , 44 so t h a t a g r e a t e r amount o f condensate of a higher temperature t h a t has been heated by t h e low-pressure feedwater h e a t e r s 40 and 4 2 i s i n t r o d u c e d i n t o t h e h e a t e x c h a n g e r p a n e l 1 6 . C,onversely, when A t is a value c l o s e t o tl, t h e openings of t h e c o n t r o l valves 44 and 46 a r e - r e g u l a t e d such t h a t t h e opening of t h e c o n t r o l valve 44 is g r e a t e r than t h e opening of t h e c o n t r o l valve 46. [0042] 'The condensate introduced i n t o t h e heat exchanger panel 16 through t h e condensate i n l e t passage 54 exchanges heat - with t h e outside of t h e heat exchanger panel 16, t h a t is, with steam within t h e space 1 4 , while flowingthrough t h e i n s i d e o f t h e h e a t exchanger panel 16, whereby t h e condensate is heated and transformed i n t o steam. The condensate, t h a t has been transformed i n t o steam i n t h e @at exchanger panel 16, is introduced into the heat carrier 7 hamber 12 provided in the final stage stationary blade 10a t h r ~ g hth e 1 stationary blade inlet passage 17. The final stage stataonary . I . blade 1Oa is heated by the evaporated condensate introduced into the heat carrief chamber 12. Once step S4 is finished, operation returns to step S1. The steam introduced into the heat carrier chamber 12 is injected into the outside, that is, into the inner casing body 22 through the slit13. his eliminatesthe need of providing a system - for discharging the evaporated condensate. Furthermore, the evaporated and injected condensate can perform work on the moving - blades. [0044] On the other hand, in step S5, it is determined whether or notdt'is s m a l l e r t h a n a p r e d e t e r m i n e d t h r e s h o l d t 2 . The threshold t2 is set to a greater value than tl. If it is determined "Yes" in step S5, that is, if t2 In step S6, the opening of the control valve 44 or 46 is decreased to reduce the amount of the condensate introduced into B e heat exchanger panel 16. Once step S6 is finisheGI the operation returng to step S1. During operatiqn of the low-pressure steam turbine 1, the $ I foregoing steps S1 to S6 are repeatsd so that the amount - of heat carrier (evaporated condensate) introduced into the heat carrier chamber 12 is regulated. This makes it possible to maintain the condition in, which tllAtSt2, that is, the condition in which the final stage stationary blade surface temperature is higher than the saturated steam temperature by tl to t2. In this manner, the condensation of steam on the surface of the3 inal stage stationary blade 10a can be prevented, which makes it possible to reduce wet loss and prevent erosion. The stationary blade which is provided with the heat carrier chamber 12 and into which the condensate that has been evaporated by being heated in the heat exchanger panel 16 is introduced is not limited to the final stage stationary blade like in the first , embodiment. The heat carrier chamber can be pr,ovided in each of a plurality of the stationary blades including the final stage , = stationaryblade, and evaporated condensate canbe introducedinto the plurality of heat carrier chambers. Second Embodiment 7 . FIG. 5 is a schematic configuration diagram illustrating arroundings of a heat exchanger panel according to a seconql embodiment of the inyention. In FIG. 5, the save components as I those of FIG'. 1 to FIC. 3 are assigned with the same reference numerals, and description thereof will be omitted. I' [0049] As shown in FIG. 5, a first heat exchanger panel 16a is A provided surrounding a steam inlet 24 forming an inner casing 2, and a second heat exchanger panel 16b is provided surrounding an upper half of the inner casing body 22. Both of the heat exchanger panels 16a and 16b are channels for passing a heat carrier (condensate to be described later, according to the second embodiment) through, and are formed of a material which is able to exchange heat with the outside of the channel. A condensate inlet passage 55 is formed by being branched from the condensate channel 39 on the downstream side of the condensate pump 38. The condensate inlet passage 55 is branched, in its midway, into two branched inlet passages 55a and 55b. These two branched inlet passages 55a and 55b are connected to the heat exchanger panels 16a and 16b, respectively. The branched inlet passages 55a and 55b are respectively - provided with control valves 45a and 45b for regulating the flow rate of fluid flowing therethrough. Openings ofthe control valves 4 5 a a n d 4 5 b a r e b o t h r e g u l a t e d b y a control device 31tobedescribed later. Detected values by a stationary blade surface temperature @hge 34 and a steam pressure gauge 32 are transmitted to the control device 31. [0052] Operation of a low-pressure steam turbine 1' configured as - described above will be described with reference to FIG. 6. In step S11, the control device 31 receives a final stage stationaryblade surface temperaturevalue that is adetectedvalue by the stationary blade surface temperature gauge 34, while . receiving a final stage upstream steam pressure value that is a detected value by the steam pressure gauge 32. I The operation then proceeds to step S12. In step S12, the control device 31 computes, based on the, final stage upstream steampressure, a saturated steam temperature at this pressure. The control device 31.then calculates a + temperature difference At between the saturated steam temperature and the final stage stationary blade surface temperature. The operation proceeds to step S13. In step S13, it is determined whether or not the temperature difference At is smaller than a predetermined threshold tl. The threshold tl is a positive value. If it is determined "Yes", that is, if it is determined that At