This application claims priority to Japanese Patent Application No. 2007-92286 filed on Mar. 30 2007, and the whole description in Application No. 2007-92286 is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a thermal power plant capable of improving a power generation efficiency by increasing a steam temperature and a turbine efficiency.
2. Background Art
Conventional thermal power plants are classified into a conventional-type thermal power plant shown in
As shown in
As shown in
In
As shown in
As shown in
In
In order to improve a power generation efficiency of a thermal power plant, increase in steam temperature and improvement in turbine efficiency are significantly advantageous.
Regarding the steam temperature, a steam temperature exceeding 600° C. has been recently used in the thermal power plants. Since increase in steam temperature can realize a highly effective power generation, a further increase in steam temperature is continuously expected. On the other hand, as an important factor for contributing the improvement in turbine efficiency, there can be taken, by way of example, reduction in exhaust loss, which can be achieved by elongating a length of a last-stage moving blade. At present, in a full speed machine of 60 Hz utilizing a 2-pole generator, a length of the moving blade of the last stage is as large as about 1.0 m when the moving blade is made of a stainless steel, or about 1.1 m when the moving blade is made of a titanium alloy.
However, when employing these arts for improving the power generation efficiency, i.e., increase of a steam temperature or elongation of a length of a last-stage moving blade, there are required not only an advanced design for fluid and strength and a cooling technique, but also a material of a high strength, which greatly increases a developing cost and extends a developing term therefor.
When the steam temperature is increased in order to attain an effective power generation, a strength of a rotational shaft (rotor) of a turbine made of a steel alloy such as stainless steel, which is currently used, cannot withstand. Introduction of a thermal power plant having a steam condition as high as 650° C. is expected in the near future. In such a thermal power plant, use of a super alloy such as a nickel-based alloy as a material for a rotational shaft of a turbine is indispensable, in order to secure the strengths of the rotational shafts of the high pressure turbine and the intermediate pressure turbine which undergo a high temperature. However, it is difficult to manufacture a large super alloy steel ingot, and a large manufacturing cost is required therefor. Thus, it takes a lot of time before such a super alloy can be practically applied.
On the other hand, regarding the elongation of the last-stage turbine moving blade, the length of the moving blade now nearly reaches the limit of withstanding a centrifugal force. Thus, further reduction in exhaust loss achieved by the further elongation of the moving blade also comes near the limit.
It can be considered that, with a view to reducing the exhaust loss, the number of exhaust steams of the low pressure turbines is increased while unchanging the length of last-stage turbine moving blade, i.e., low pressure steams are respectively distributed and introduced to the plurality of pressure turbines. However, since this structure decreases a flowrate per flow, a length of the moving blade of a first half stage of the low pressure turbine, which invites deterioration in performance of the turbine. In addition, since the number of the low pressure turbines is increased, a larger cost is necessary.
It has been conventionally known to reduce a rotating speed of the low pressure turbine to half (to make a half speed machine) as compared with that of a full speed machine, so as to increase a power generation efficiency (JP2004-137912A, for example). However, in the invention described in JP2004-137912A, the high pressure turbine and the low pressure turbine are directly connected to different generators, which is referred to as so-called “cross-compound type”.
Even a current thermal power plant of 1000 MW class sometimes employs the cross-compound type with two rotational shafts. That is, as shown in
However, in the above-described steam turbine system 50 of a cross-compound type, since it is necessary to electrically synchronize the two generators 12 and 13, a complicated control system is required, resulting in deterioration in operability. In addition, since the two shafts are arranged in parallel, a turbine building (not shown) has to be made larger.
Further, the generator directly connected to the high pressure turbine 8 and the intermediate pressure turbine 9 which undergo a high temperature is the 2-pole generator 12 of a higher rotational speed. Thus, when a conventional alloy steel is used as a material for a rotational shaft, it will be difficult to increase the steam temperature in the future, in terms of the strength of the rotational shaft of the turbine 2a.
The present invention has been made in view of these circumstances. The object of the present invention is to provide a thermal power plant capable of easily improving power generation efficiency, by improving turbine efficiency.
The present invention is a thermal power plant comprising: a boiler that heats a feed water by utilizing a heat caused by combustion of a fossil fuel so as to generate a main steam; a high pressure turbine into which the main steam from the boiler is introduced, the high pressure turbine having a rotational shaft; a reheater that reheats the main steam discharged from the high pressure turbine so as to generate a reheated steam; an intermediate pressure turbine into which the reheated steam generated by the reheater is introduced, the intermediate pressure turbine having a rotational shaft that is coupled with the rotational shaft of the high pressure turbine; a low pressure turbine into which the reheated steam discharged from the intermediate pressure turbine is introduced, the low pressure turbine having a rotational shaft that is coupled with the rotational shafts of the high pressure turbine and the intermediate pressure turbine; and a generator having more than two poles, and having a rotational shaft that is coupled with the rotational shafts of the high pressure turbine, the intermediate pressure turbine, and the turbine.
A thermal power plant in a first embodiment of the present invention is described below with reference to the drawings.
As shown in
The turbine 2 includes the high pressure turbine 8, the first intermediate pressure turbine 9a, and an intermediate and low pressure turbine 15. The main steam A is introduced to high pressure turbine 8. Intermediate and low pressure turbine 15 further includes a second intermediate pressure turbine 9b and a low pressure turbine 11. In this embodiment, the second intermediate pressure turbine 9b and the low pressure turbine 11 are continuously arranged, as intermediate and low pressure turbine 15, without any connection pipe such as a crossover pipe. Namely, in this embodiment, the second intermediate pressure turbine 9b and the low pressure turbine 11 are installed in a single casing. The second intermediate pressure turbine 9b and the low pressure turbine 11 disposed in the single casing constitute the single intermediate and low pressure turbine 15. In this case, the turbine into which the second-stage reheated steam F is introduced can be defined as the second intermediate pressure turbine 9b, and the turbine that discharges a steam as an exhaust steam into the condenser 14 can be defined as the low pressure turbine 11. It is not necessary to strictly define a boundary between the second intermediate pressure turbine 9b and the low pressure turbine 11. Such a strict separation of the second intermediate pressure turbine 9b and the low pressure turbine 11 can be suitably determined by those skilled in the art based on a design condition or the like. The single casing of intermediate and low pressure turbine 15, which disposes the second intermediate pressure turbine 9b and the low pressure turbine 11, may be formed of different kinds of materials that are integrated by welding or are fastened by bolts, as long as the casing has a single (one-piece) structure without pipes between the second intermediate pressure turbine 9b and the low pressure turbine 11.
As shown in
The rotational shaft of the 4-pole generator 13 is connected to the rotational shaft of the high pressure turbine 8, and the 4-pole generator 13 is disposed adjacent to the high pressure turbine 8. The condenser 14 is disposed to be adjacent to the low pressure turbine 11 of the intermediate and low pressure turbine 15. Since the low pressure turbine 11 of the intermediate and low pressure turbine 15 and the condenser 14 are disposed adjacent to each other, a turbine exhaust steam from the low pressure turbine 11 of the intermediate and low pressure turbine 15 is axially discharged, i.e., in an axial direction of the rotational shaft while remaining to be a single flow, and thus can be smoothly introduced into the condenser 14.
The steam turbine system 50 in this embodiment further includes a low-pressure feed water heater 4, a feed water pump 5 and a high-pressure feed water heater 6. Low-pressure feed water heater 4 heats a water supplied from the condenser 14 by utilizing heat extracted from low pressure turbine 11. Feed water pump 5 pressurizes the water heated by the low-pressure feed water heater 4 as a feed water. High-pressure feed water heater 6 further heats the feed water by utilizing heat extracted from high pressure turbine 8. Namely, low-pressure extracted steam from the low pressure turbine 11, as a heating medium, is introduced into the low-pressure feed water heater 4. A high-pressure extracted steam from the high pressure turbine 8, as a heating medium, is introduced into the high-pressure feed water heater 6. So, low-pressure feed water heater 4 and high-pressure feed water heater 6 are serves as regenerative heat exchangers. Here, the regenerative heat exchanger is defined as a heat exchanger that heats feed water by utilizing heat of extracted steam from turbine 2. Therefore, a thermodynamic cycle of the steam turbine plant 50 is a reheat regenerative Rankine cycle because the reheater, such as a first reheater 41 or a second reheater 42, and the regenerative heat exchanger, such as low-pressure feed water heater 4 or high-pressure feed water heater 8, are provided in the steam turbine system 50.
As described above, the steam turbine system 50 of the thermal power plant in this embodiment, rotational shafts of each turbine and generator are coupled as the common and single rotational shaft, and the 4-pole generator 13 serves as a generator. Thus, as compared with a conventional steam turbine system using a 2-pole generator (hereinafter also referred to as “full speed machine”), a rotational speed thereof is reduced to half (hereinafter the steam turbine system 50 of the present invention is also referred to as “half speed machine”).
The rotational speed of the half speed machine is half the rotational speed of the full speed machine. So, a length of the last-stage moving blade of the low pressure turbine 11 can be easily doubled based on the law of similitude from the full speed machine to the half speed machine, without conducting a new development, which requires an enormous work and period.
The law of similitude, as described above, is a principle often applied when designing a gas turbine or the like. For example, applying this principle, a design for a gas turbine for 50 Hz can be obtained by multiplying a design of a gas turbine for 60 Hz by 1.2. A turbine which is designed based on the law of similitude has the same velocity field and the same stress field as those of the original turbine.
Next, an operation of this embodiment is explained below.
At first, a water (feed water), which is supplied from the feed water pump 5 to the boiler 1 via the high-pressure feed water heater 6, is heated in the heater provided in boiler 1, so that a main steam A is generated in boiler 1. The main steam A is introduced into the high pressure turbine 8. The main steam A is expanded in high pressure turbine 8 so as to rotate the rotational shaft (rotor), and is discharged therefrom. The main steam A discharged from the high pressure turbine 8 is introduced to the first reheater 41 provided in the boiler 1 and reheated so as to generate a first-stage reheated steam E. The first-stage reheated steam E then enters into the first intermediate pressure turbine 9a (see,
Then, the first-stage reheated steam E, which is expanded so as to generate work in the first intermediate pressure turbine 9a and discharged therefrom, returns again to the boiler 1. The first-stage reheated steam E, after discharged from first intermediate pressure turbine 9a, is introduced reheated in the second reheater 42 provided in the boiler 1 so as to generate a second-stage reheated steam F. The second-stage reheated steam F then enters into the second intermediate pressure turbine 9b of the intermediate and low pressure turbine 15 (see,
Then, the second-stage reheated steam F, which is expanded so as to generate work in the second intermediate pressure turbine 9b and discharged therefrom, flows into the low pressure turbine 11, which is disposed adjacent to the second intermediate pressure turbine 9b in the same casing, as described above. The second-stage reheated steam F, after discharged from second intermediate pressure turbine 9b, is further expanded so as to generate work in the low pressure turbine 11. Steam discharged form low pressure turbine 11 is introduced to the condenser 14 (see,
In this embodiment, the low pressure turbine 11 of the intermediate and low pressure turbine 15 and the condenser 14 are disposed adjacent to each other. Thus, a turbine exhaust steam from the low pressure turbine 11 of the intermediate and low pressure turbine 15 is axially discharged in a single flow. In other words, discharged steam from the low pressure turbine 11 flows in a one direction having a velocity component of an axial direction of the rotational shaft. Thus, discharged steam from low pressure turbine 11 can be smoothly introduced into the condenser 14. The steam introduced in condenser 14 condenses as a condensate (water).
The water (condensate) discharged from the condenser 14 is heated by the low-pressure feed water heater 4 by using a extracted steam extracted from the low pressure turbine 11 as a heat source (see,
The water heated by the low-pressure feed water heater 4 is then pumped (pressurized)in the feed water pump 5 as a feed water. Subsequently, the feed water from the feed water pump 5 is heated in the high-pressure feed water heater 6 by using a steam extracted from the high pressure turbine 8 as a heat source. The feed water from high-pressure feed water heater 6 is then returned to the boiler 1 (see,
In this manner, while the water (including condensate and feed water) and the steams A, E, and F are circulated in the steam turbine system 50, the rotational shaft of the 4-pole generator 13, which is coupled with the rotational shaft of turbine 2, rotates. Since the 4-pole generator 13 has more than two poles, rotational speeds of the 4-pole generator 13 and the turbine 2 connected thereto are smaller than those of a conventional turbine system having a 2-pole generator. Specifically, with the use of the 4-pole generator 13, the rotational speeds of the 4-pole generator 13 and the turbine 2 are half speeds as compared to the conventional turbine system having the 2-pole generator.
As described above, the steam turbine system 50 in this embodiment can be manufactured as a half speed machine, and thus the following benefits can be resulted according to this embodiment.
A first benefit is increase in temperatures of at least one of the main steam A, the first-stage reheated steam E, and the second-stage reheated steam F. Namely, in the conventional thermal power plant with a 2-pole generator (full speed machine), introducing excessively high temperature steam in turbine 2, especially high pressure turbine 8, first intermediate pressure turbine 9a, or second intermediate pressure turbine 9b, may cause a breakage of turbine moving blade. On the other hand, according to this embodiment, a centrifugal force generated on the turbine moving blade can be decreased because the rotational speed becomes a half of the full speed machine. Therefore, as compared with steam used in the full speed machine, the temperatures of the main steam A, the first-stage reheated steam E, and the second-stage reheated steam F can be increased.
The benefit of the centrifugal force decrease is significantly apparent in the high pressure turbine 8, the first intermediate pressure turbine 9a, and the second intermediate pressure turbine 9b to which a high-temperature steam, such as the main steam A, the first-stage reheated steam E, or the second-stage reheated steam F is supplied. Although the temperature of the main steam A, the first-stage reheated steam E, or the second-stage reheated steam F is increased, a conventional material for these turbines can be consistently used in high pressure turbine 8, first intermediate pressure turbine 9a, and second intermediate pressure turbine 9b because centrifugal forces act on turbine moving blades of these turbines are reduced as a half of the conventional turbine plant having a 2-pole generator. Moreover, when applying better material than conventional material, the temperature of main steam A, first-stage reheated steam E, or second-stage reheated steam F is further increased.
Therefore, the conventional rotational shaft material of a high chrome-containing steel alloy containing 8% to 15% of chrome is used as a material for the rotational shafts of the high pressure turbine 8, the first intermediate pressure turbine 9a, and the second intermediate pressure turbine 9b, the main steam A generated in the boiler 1 and the reheated steams E and F generated in the reheaters 41 and 42 are preferably not less than 620° C., and most preferably about 650° C.
As shown in
As a result, the conventional rotational shaft material of a low chrome-containing steel alloy containing not more than 3% of chrome is used as a material for the rotational shafts of the high pressure turbine 8, the first intermediate pressure turbine 9a, and the second intermediate pressure turbine 9b, the main steam A generated by the boiler 1 and the reheated steams E and F generated by the reheaters 41 and 42 are preferably not less than 545° C., and most preferably about 580° C.
As described above, according to the steam turbine system (half speed machine) 50 in this embodiment, a power generation efficiency can be easily improved because steam having higher temperature, as compared to the conventional full speed machine, can be easily applied as the main steam A, the first-stage reheated steam E, and the second-stage reheated steam F.
It is generally known that, in a two-stage reheating cycle shown in
A second benefit according to the embodiment is reduction in pressure loss between the turbines.
In a conventional steam turbine system of a high output such as 250 MW or more, a two-flow exhaust type or four-flow exhaust type is used for a low pressure turbine. This is because a length of a turbine moving blade limited by the centrifugal force. In this type of turbine system having two-flow exhaust type or four-flow exhaust type low pressure turbine, a piping referred to as the crossover pipe (connecting pipe) 10 (see,
On the other hand, since the steam turbine system 50 in this embodiment is rotated at a rotational speed which is one-half a rotational speed of the full speed machine, a centrifugal force applied to the turbine moving blade of the low pressure turbine 11 can be reduced. Thus, even in the steam turbine system 50 of a high output, a single flow exhaust can be used, and there is no need for using the crossover pipe (connecting pipe) 10 between second intermediate pressure turbine 9b and low pressure turbine 11. In addition, it is possible to accommodate the second intermediate pressure turbine 9b and the low pressure turbine 11 in a single casing, so as to constitute the intermediate and low pressure turbine 15 (see,
The last-stage turbine moving blade of the low pressure turbine 11, which is manufactured based on the law of similitude, has an annular surface area that is four times as large as the last-stage turbine moving blade of the low pressure turbine 11 in the full speed machine. Thus, even when a single flow exhaust is used, the turbine moving blade has the annular surface area equivalent to a four-flow exhaust type low pressure turbine is used in the full speed machine.
A third benefit is further improvement in turbine efficiency because of a single flow discharge of steam exhausted from the low pressure turbine 11.
Similar to the conventional full speed machine, when a two-flow exhaust type or four-flow exhaust type is applied as the low pressure turbine 11 (see,
On the other hand, in this embodiment, since an exhaust steam flow discharged from the low pressure turbine 11 can be a single flow, a blade length of an inlet side stage of the low pressure turbine 11 can be sufficiently elongated. As a result, efficiency in the low pressure turbine 11 can be improved.
A fourth benefit is a reduction in exhaust loss because of an axial discharge of stem from low pressure turbine 11. As described above, an axial discharge means that exhaust steam discharged from low pressure turbine 11 has a velocity component in a direction of rotational shaft (rotor).
Namely, as shown in
On the other hand, according to this embodiment, since steam introduced to the low pressure turbine 11 can be made as a single flow, exhaust steam discharged from the last stage of the low pressure turbine 11 can also be as a single flow. Thus, exhaust steam discharged from the last stage of the low pressure turbine 11 can be axially discharged, i.e., in an axial direction of the rotational shaft of the intermediate and the low pressure turbine 15 having a velocity component of the axial direction. As a result, an exhaust loss of the turbine 2 can be decreased.
Accordingly, according to the steam turbine system 50 in this embodiment, even in a thermal power plant of a high output as large as 1000 MW, an exhaust steam discharged from a last stage of a low pressure turbine can be an axial-flow, whereby a power generation efficiency can be improved.
Moreover, by applying an axial-flow exhaust, a height of a turbine building can be reduced.
That is, in a conventional thermal power plant, a height of a turbine building can be reduced only in a low output using a small turbine, by applying an axial-flow exhaust as exhaust steam discharged from the turbine. However, in a conventional thermal power plant of a large output, an exhaust steam discharged from a turbine cannot be the axial-flow, because the exhaust steam is necessarily discharged under the low pressure turbine. Thus, the height of a turbine building is high.
On the other hand, according to this embodiment, since exhaust steam can be axially discharged (axial-flow) as described above, the height of the turbine building can be reduced even in a thermal power plant of a large output because there is no need providing the condenser under the low pressure turbine.
A fifth benefit is that an influence of erosion of the last-stage turbine moving blade of the low pressure turbine 11 can be reduced, which may be caused by condensed water droplets. Serious erosion of the last-stage turbine moving blade may result in an accident of scattering of the turbine moving blade. Thus, reduction of an influence of erosion is very important in terms of reliability.
In general, the faster a rotational speed of an end of a turbine moving blade is, the faster the erosion speed is. In this embodiment, since the turbine moving blade is designed based on the law of similitude, a rotational speed of the end of the turbine moving blade is equal to that of the conventional full speed machine, so that the erosion speed is the same. However, an allowable amount of erosion is in proportion to the size of the turbine moving blade. In other words, the larger the turbine moving blade is, the more resistance to the erosion the turbine moving blade has.
Specifically, since a size of the turbine moving blade in this embodiment is twice as large as that of the turbine moving blade of the conventional full speed machine, the resistance of the turbine moving blade in this embodiment is twice the resistance of the turbine moving blade of the full speed machine. Thus, an influence given by erosion of the last-stage turbine moving blade of the low pressure turbine 11, which is caused by condensed water droplets, can be reduced by half.
A sixth benefit is further improvement of turbine efficiency because of increase of the allowable maximum number of the stages of the respective turbines 8, 9a 9b, and 11.
Generally, the larger the number of stages of the turbines 8, 9a, 9b, and 11, the higher efficiency of turbine can be achieved. When increasing the number of stages in the turbines 8, 9a, 9b or 11, the rotational shafts of the corresponding turbines 8, 9a, 9b, or 11 have to be elongated. However, it is also generally known that the longer a rotational shaft of a turbine becomes, the less stability, as a rotational machine, the turbine has. For this reason, the number of the stages disposed in the turbines 8, 9a, 9b, and 11 is limited to the allowable number of stages that is determined by taking the stability of the turbine into consideration.
With respect to this point, according to this embodiment, the rotational speeds of the turbines 8, 9a, 9b, and 11 are one-half of the rotational speed of the full speed machine. Thus, when the turbines 8, 9a, 9b, and 11 in this embodiment have the same rotational shafts lengths as those of the turbines of the full speed machine, stability as a rotational machine of the turbines 8, 9a, 9b, and 11 can be improved. In other words, even when the lengths of the rotational shafts of the turbines 8, 9a, 9b, and 11 are elongated, stability as a rotational machine can be substantially the same as that of the full speed machine. As a result, the allowable number of stages can be increased, to thereby improve turbine efficiency.
A seventh benefit is reduction in size of the turbine building because of a reduction of the full length of the steam turbine system 50.
Conventionally, a steam turbine system 50 of a 1000 MW class has to be of a cross-compound type as shown in
As shown in
Meanwhile, as shown in
The reason that the low pressure turbines 11 are of four-flow type in total, which comprises two of double flow low pressure turbine 11, is that the size of the last stage is limited by a centrifugal force applied to the turbine moving blade, as described above. The reason that the intermediate pressure turbine 9 is of double flow type is also a strict limitation by a centrifugal force.
On the other hand, in this embodiment, a centrifugal force applied to the turbine 2 can be reduced as described above. Thus, as shown in
It should be noted that the steam turbine system 50 in this embodiment shown in
In the above-described embodiment, temperatures of the main steam A, the first-stage reheated steam E, and the second-stage reheated steam F can be up to 650° C., as described. When using these steams of 650° C. as steam A, E, and F in steam turbine system 50 according to this embodiment, a net thermal efficiency can be expected as 45%. As compared with the existing reheating and regenerative thermal power plant, about 10% of improvement in power generation in relative ratio may be achieved.
In
In this case, it is possible to successively position, without any connecting pipe, at least an intermediate pressure turbine of a last stage, into which a reheated steam of a last stage is introduced, and a low pressure turbine that discharges a steam into a condenser as exhaust steam.
In the above embodiment, 4-pole generator 13, as a generator having more than two poles, is applied to steam turbine system 50. However, the embodiment, generator is not limited to 4-pole generator 13, any generator having more than two poles may be applied.
In addition, in the above embodiment, the low pressure turbine 11 is of an axial-flow exhaust type. However, not limited thereto, an exhaust steam from the low pressure turbine 11 may be discharged downward, as shown in
Similar to the steam turbine system 50 shown in
As shown in
The rotational shaft of the 4-pole generator 13 is connected to the rotational shafts of the low pressure turbines 11, and the 4-pole generator 13 is disposed adjacent to the high pressure turbines 11.
As shown in
As described above, the example shown in
Next, a second embodiment of the present invention is described with reference to
In the second embodiment shown in
At first, a part of a water (feed water) supplied from the feed water pump 5 is heated in heat recovery steam generator (HRSG) 20 by utilizing the heat of the exhaust gas C of the gas turbine 33 as a heat source, so that a main steam A is generated (see,
Then, the main steam A is expanded in the high pressure turbine 8 so as to generate work. The exhaust steam discharged from the high pressure turbine 8 is introduced to a first reheater 41 in heat recovery steam generator (HRSG) 20 (see,
Another part of the feed water supplied from the feed water pump 5 is introduced to heat recovery steam generator (HRSG) 20, and is heated there to become steam. Thereafter, the steam is mixed with the exhaust steam discharged from the high pressure turbine 8. Then, the mixed steam enters into the first reheater 41 in heat recovery steam generator (HRSG) 20. In heat recovery steam generator (HRSG) 20, the steam is reheated by utilizing the heat of the exhaust gas C of the gas turbine 33 so as to generate a first-stage reheated steam E (see,
Then, the first-stage reheated steam E is introduced to a first intermediate pressure turbine 9a. In first intermediate pressure turbine 9a, the first-stage reheated steam E is expanded so as to generate work. The first-stage reheated steam E discharged from the first intermediate pressure turbine 9a returns again to heat recovery steam generator (HRSG) 20. The first-stage reheated steam E discharged from first stage intermediate pressure turbine 9a is reheated in a second reheater 42 in heat recovery steam generator (HRSG) 20 by utilizing the heat of the exhaust gas C of the gas turbine 33, so that it becomes a second-stage reheated steam F (see,
Then, the second-stage reheated steam F is introduced into a second intermediate pressure turbine 9b. In second intermediate pressure turbine 9b, the second-stage reheated steam F is expanded so at to generate work. Thereafter, the second-stage reheated steam F discharged from the second intermediate pressure turbine 9b is mixed with a low pressure steam D which has been introduced into second intermediate pressure turbine 9b at a position of a boundary between the second intermediate pressure turbine 9b and the low pressure turbine 11. Here, the boundary between second intermediate pressure turbine 9b and the low pressure turbine 11 can be a position where second intermediate pressure turbine 9b and the low pressure turbine 11 are connected to each other. Accordingly, The mixed steam of the second-stage reheated steam F discharged from second intermediate pressure turbine 9b and the low-pressure steam D enters into the low pressure turbine 11 in which the steam is further expanded to generate work. The low pressure steam D is generated by heating low-pressure feed water in heat recovery steam generator (HRSG) 20. Here, the low-pressure feed water having been supplied to heat recovery steam generator (HRSG) 20 from a branched position on an upstream side of the feed water pump 5 (see,
Then, the steam, which has completed a work in the low pressure turbine, is discharged and introduced into the condenser 14 where the steam is cooled and condensed to become water (condensate) (see,
Subsequently, the water from the condenser 14 (condensate) is branched at an upstream position and a downstream position of the feed water pump 5, so as to become waters of different pressures, namely, a high pressure feed water, an intermediate pressure feed water, and a low pressure feed water, which are then returned to heat recovery steam generator (HRSG) 20 (see,
Also in the combined thermal power plant in this embodiment, which the gas turbine system 30 and the steam turbine system 50 are combined, steam turbine system 50 includes the 4-pole generator (generator having more than two poles) 13. So, a rotational speed of the steam turbine system 50 can be reduced to half (a half speed machine) as compared with the rotational speed of a conventional steam turbine system (full speed machine), similar to the first embodiment. Thus, according also to this embodiment, the same benefits as those in the first embodiment can be resulted.
That is to say, a length of the turbine moving blade of the last stage can be doubled as compared with that of the conventional full speed machine, based on the low of similitude.
In addition, an exhaust steam discharged from the low pressure turbine 11 can be axially discharged as a single flow. The second intermediate pressure turbine 9b and the low pressure turbine 11 are adjacently provided without using a connecting pipe such as the crossover pipe (connecting pipe) 10 (see, FIGS. 9 to 11)in a single casing as an intermediate and low pressure turbine 15. Thus, a pressure loss between the second intermediate pressure turbine 9b and the low pressure turbine 11 can be eliminated.
Further, since the steam turbine system 50 is a half speed machine, a centrifugal force act on the turbine moving blade can be reduced. Thus, even in a two-stage reheating cycle, whose strength condition is generally severe, a steam temperature of steam introduced to first and second intermediate pressure turbine 9a and 9b can be increased, whereby a thermal efficiency can be easily enhanced.
Furthermore, since the steam turbine system 50 is a half speed machine, a length of the turbine moving blade can be elongated. An exhaust loss of the turbine 2 can be further reduced by applying the last stage turbine moving blades having a sufficient annular surface area in low pressure turbine 11, with axial-flow exhaust type configuration of low pressure turbine 11.
Moreover, since the steam turbine system 50 is a half speed machine, stability of the turbines 8, 9a, 9b, and 15 can be increased. Thus, the number of stages disposed in turbines 8, 9a, 9b, and 15 can be increased, so that a turbine efficiency can be improved.
It is not necessary to synchronize the gas turbine generator 35 of the gas turbine system 30 and the 4-pole generator 13 of the steam turbine system 50, because these generators are disposed in the separate systems. A rotational speed of the gas turbine system 30 may be suitably selected, such as a full speed or a half speed. When the gas turbine generator 35 of the gas turbine system 30 is a 4-pole generator, a thermal power plant is possible in which the rotational shafts of the gas turbine system 30 and the steam turbine system 50 are uniaxially connected to each other. In this case, 4-pole generator 13 can be an only generator which is coupled with gas turbine system 30 and steam turbine system 50.
In the above embodiment, the low pressure turbine 11 is of an axial-flow exhaust type. However, not limited thereto, an exhaust steam from the low pressure turbine 11 may be discharged downward, as shown in
As shown in
As shown in
As shown in
A third embodiment of the present invention is described with reference to
In
In the third embodiment shown in
At first, a part of a water (feed water) supplied from a feed water pump 5 to a boiler 1 is heated so that a main steam A is generated. The main steam A, discharged from a high pressure turbine 8, is reheated by the reheater 45 in the boiler 1 so as to generate a reheated steam B. The reheated steam B then enters into the intermediate pressure turbine 9 (see,
Then, the reheated steam B discharged from the intermediate pressure turbine 9 flows into the low pressure turbine 11 disposed adjacent to the intermediate pressure turbine 9. Here, inter mediate pressure turbine 9 and low pressure turbine 11 is provided in a single casing, which constitute as an intermediate and low pressure turbine 15. Thereafter, the reheated steam B expanded in inter mediate pressure turbine 9 and low pressure turbine 11 is discharged from low pressure turbine 11 (intermediate and low pressure turbine 15) into a condenser 14 where the discharged reheated steam B becomes water as a condensate (see,
Then, the water (condensate) supplied from the condenser 14 is heated in a low-pressure feed water heater 4 by utilizing a steam extracted from the low pressure turbine 11 as a heat source. Following thereto, the feed water heated in the low-pressure feed water heater 4 is introduced to a feed water pump 5 and pressurized. Then, the feed water pumped (pressurized) in the feed water pump 5 is introduced into and heated in a high-pressure feed water heater 6 by utilizing a steam extracted from the high pressure turbine 8 as a heat source. Feed water heated in high-pressure feed water heater 8 then returns to the boiler 1 (see,
Also in the thermal power plant in this embodiment, steam turbine system 50 includes a 4-pole generator 13 as a generator having more than two poles. Since the 4-pole generator (generator having more than two poles) 13 is used, a rotational speed of the steam turbine system 50 can be reduced to half (half speed machine) as compared with a full speed machine, similar to the first embodiment. Thus, according also to this embodiment, the same benefits as those in the first embodiment can be resulted.
That is to say, a length of the turbine moving blade of the last stage can be doubled as compared with that of the conventional full speed machine, due to application of the low of similitude.
In addition, an exhaust steam discharged from the low pressure turbine 11 can axially discharged as a single flow. The second intermediate pressure turbine 9b and the low pressure turbine 11 are adjacently provided without using a connecting pipe such as the crossover pipe (connecting pipe) 10 (see,
Further, since the steam turbine system 50 is a half speed machine, a centrifugal force act on the turbine moving blade can be reduced. Thus, a steam temperature can be increased, whereby a thermal efficiency can be easily enhanced.
Furthermore, since the steam turbine system 50 is a half speed machine, a length of the turbine moving blade can be elongated. An exhaust loss of the turbine can be further reduced by applying the last stage turbine moving blades having a sufficient annular surface area in low pressure turbine 11, with axial-flow exhaust type configuration of low pressure turbine 11.
Moreover, since the steam turbine system 50 is a half speed machine, stability of the turbine 8, 9, or 15 can be increased. Thus, the number of stages disposed in turbine 8, 9, or 15 can be increased, so that a turbine efficiency can be improved.
As shown in
Number | Date | Country | Kind |
---|---|---|---|
2007-092286 | Mar 2007 | JP | national |