US20090094983A1

US20090094983A1 - Steam turbine cycle

Info

Publication number: US20090094983A1
Application number: US12/092,796
Authority: US
Inventors: Koichi Goto; Nobuo Okita
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2006-01-20
Filing date: 2006-12-21
Publication date: 2009-04-16
Also published as: CN101300407A; JP4621597B2; EP1965043B1; EP1965043A1; JP2007192152A; WO2007083478A1; KR20080038233A; CN101300407B; EP1965043A4

Abstract

A steam turbine cycle of the present invention comprises a high pressure turbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 for heating a feed water to the boiler 4 by a bleed steam from the turbines 1 and 24, a feed pump 12, and a condenser 10, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle. A steam temperature at an outlet of the boiler is 590° C. or more. A temperature increase ratio between: a feed-water temperature increase in a first feed heater 7 corresponding to a bleed steam (high-pressure turbine exhaust bleed steam) 22 from an exhaust steam of the high pressure turbine 1; and an average of feed-water temperature increases in second feed heaters 8 where a pressure of the feed water is lower than that of the first feed heater 7; falls within 1.9-3.5.

Description

FIELD OF THE INVENTION

The present invention relates to a steam turbine cycle having an improved cycle thermal efficiency.

BACKGROUND ART

An example of a steam turbine cycle used in a heat power plant or the like is described as a conventional art with reference to FIG. 1.
A boiler feed water 14 heated by a boiler 4 with the use of fuel combustion heat so as to generate a superheated steam (hereinafter referred to as “main steam 16”) of a sufficiently high temperature. The superheated steam may be an ultra supercritical pressure fluid.
The main steam 16, which has flown into a high pressure turbine 1, expands and flows therethrough, while a pressure and a temperature thereof are lowered.
Most part of a high-pressure turbine exhaust steam 21, which has flown out from the high pressure turbine 1, flows into a reheater 5, and becomes there a reheated steam 17 of a higher temperature. The reheated steam 17 flows into an intermediate pressure turbine 2.
The steam expands and flows through the intermediate pressure turbine 2, while a pressure and a temperature thereof are lowered. Then, the steam flows into a low pressure turbine 3.
The steam expands and flows through the low pressure turbine 3, while a pressure and a temperature thereof are lowered. A part of the steam often becomes a saturated steam as a liquid water. The saturated steam is cooled by a condenser 10 by using sea water or atmospheric air 23, so that the saturated steam becomes a condensed water 25. The condensed water 25 is sent to a feed heater 6 by a condensing pump 11 to become a boiler feed water 14. The intermediate pressure turbine 2 and the low pressure turbine 3 constitute a reheating turbine 24.
In FIG. 1, eight feed heaters 6 are illustrated. The boiler feed water 14 is heated by a bleed steam 20 bled from bleeding positions 31 in channels of the intermediate pressure turbine 2 and the low pressure turbine 3. A bleed steam of a higher pressure is flown into the feed heater 6 of a higher pressure.
In FIG. 1, the low pressure turbine 3 is illustrated as a double flow pressure turbine, and a steam is bled from only one of the low pressure turbine 3. However, a steam is actually bled from both the low pressure turbines 3 and merged. The merged steam flows into the feed heater 6. It is possible to bleed a steam from one of the low pressure turbines 3, depending on the feed heater 6.
The feed heater 6 is classified into a feed heater of a surface type and a feed heater of a mixing type. In a feed heater of a surface type, the bleed steam 20 is condensed by exchanging heats with a feed water via a heat transmission surface to become a drain water 15. In principle, the drain water 15 sequentially flows from the feed heater 6 of a higher pressure to the feed heater 6 of a lower pressure. The drain water 15 in the feed heater 6 of the lowest pressure flows into the condenser 10. The drain water 15 may be merged into a feed water by a drain water pump 13.
In the feed heater of a mixing type, a bleed steam is directly mixed with a feed water to heat the same. A deaerator 9 for deaerating oxygen or the like which is dissolved in a feed water is included in the feed heater of a mixing type.
In order to send a feed water to a feed heater 6 of a higher pressure, a feed pump 12 is disposed directly downstream of the feed heater of a mixing type. In FIG. 1, although a bleed steam to the feed heater of a mixed type is an intermediate-pressure turbine exhaust bleed steam 32, another steam is possible. The deaerator 9 may be omitted. Even when the deaerator 9 is omitted, the feed pump 12 is disposed on a suitable position between the plurality of feed heaters 6. A feed water sequentially heated in all of the feed heaters 6 flows into the boiler 4.
In FIG. 1, the high pressure turbine 1, the intermediate pressure turbine 2, and the low pressure turbine 3 are connected to each other by a single rotation shaft 19, and are connected to a generator 18. A steam expands in the high pressure turbine 1, the intermediate pressure turbine 2, and the high pressure turbine 3, so that enthalpy of the steam is converted into a shaft power, whereby electric power is generated by the generator 18. It is possible not to connect the respective turbines to the single generator 18 by connecting the turbines by the single rotation shaft 19.
FIG. 1 illustrates the low pressure turbine 3 as a double flow pressure turbine in which a flow-in steam is divided into two and the divided steams flow into the two low pressure turbines 3. The flow-in steam may be divided into four, or may not be divided. In FIG. 1, although the intermediate pressure turbine 2 is illustrated as a single flow pressure turbine, the intermediate pressure turbine 2 may be a double flow pressure turbine. In addition, although FIG. 1 shows that the intermediate pressure turbine 2 and the low pressure turbine 3 are separated turbines, a single reheating turbine 24 is possible.
Both of a regenerative cycle using the bleed steam 20, and a reheating cycle in which the high-pressure exhaust steam 21 heated by the reheater 5 flows into the reheating turbine 24, are modified Rankine cycles, and improve a thermal efficiency from a simple Rankine cycle. In a power generation plant, a thermal efficiency is substantially equal to a value obtained by dividing an amount of generated power by an amount of boiler heat input.
In addition to a cycle structure, a cycle thermal efficiency varies depending on a temperature and a flowrate of each bleed steam 20. In particular, in accordance with advancement of a material against a high temperature, a temperature of steam has been recently more and more increased, whereby a cycle thermal efficiency has been improved. However, there still is a room for approving a cycle structure under high temperature conditions of steam.
The below non-patent document describes that “an optimum performance is obtained when an increase in enthalpy of a certain heater caused by a bleed steam from a reheating point is 1.8 times an average increase in enthalpy in heaters of a pressure lower than that of the certain heater”.
Non-Patent Document: “Steam Turbine Performance and Economics” written by Bartlett

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The object of the present invention is to provide a steam turbine cycle of an improved cycle thermal efficiency.

Means for Solving the Problem

The invention according to claim 1 is a steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle, wherein a steam temperature at an outlet of the boiler is 590° C. or more, and a temperature increase ratio between: a feed-water temperature increase in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of feed-water temperature increases in second feed heaters where a pressure of the feed water is lower than that of the first feed heater; falls within 1.9-3.5.
The invention according to claim 2 is a steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle, wherein a steam temperature at an outlet of the boiler is 590° C. or more, and a specific enthalpy increase ratio between: a specific enthalpy increase in a feed water in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of specific enthalpy increases in feed waters in second feed heaters where a pressure of the feed water is lower than that of the first feed heater; falls within 1.9-3.5.
The invention according to claim 3 is a steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle,
wherein a steam temperature at an outlet of the boiler is 590° C. or more, and a temperature increase ratio between: a feed-water temperature increase in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of feed-water temperature increases in feed heaters other than the first feed heater; falls within 1.9-3.5.
The invention according to claim 4 is a steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle, wherein a steam temperature at an outlet of the boiler is 590° C. or more, and a specific enthalpy increase ratio between: a specific enthalpy increase in a feed water in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of specific enthalpy increases in feed heaters other than the first feed heater; falls within 1.9-3.5.

EFFECT OF THE INVENTION

According to the present invention, there can be provided a steam turbine cycle of an improved cycle thermal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of first to eighth embodiments and an eleventh embodiment of a steam turbine cycle of the present invention, and a conventional art;

FIG. 2 is a schematic view of ninth to eleventh embodiments of a steam turbine cycle of the present invention; and

FIG. 3 is a schematic view showing a relationship between a temperature increase ratio and a thermal efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A first embodiment of a steam turbine cycle of the present invention is described below with reference to the drawings. FIG. 1 is a view of the first embodiment of the present invention.
The steam turbine cycle in this embodiment includes a high pressure turbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 for heating a feed water to the boiler 4 by a bleed steam from the high pressure turbine 1 and the reheating turbine 24, a feed pump 12, and a condenser 10. The steam turbine cycle in this embodiment is a single-stage reheating cycle where a working fluid is water and uses a Rankine cycle which is a regenerative cycle.
A steam temperature at an outlet of the boiler 4 is 590° C. or above. A temperature increase ratio between: a feed-water temperature increase in a first feed heater 7 corresponding to a bleed steam (high-pressure turbine exhaust bleed steam) 22 from a high-pressure turbine exhaust steam 21; and an average of feed-water temperature increases in second feed heaters 8 where a pressure of the feed water is lower than that of the first feed heater 7; falls within 1.9-3.5.
By adjusting a flowrate of each bleed steam 20 and each bleed position 31, feed-water temperature increases in the first feed heater 7 and the second feed heaters 8 can be adjusted. In order to vary temperatures of the high-pressure turbine exhaust bleed steam 22 and an intermediate-pressure turbine exhaust bleed steam 32, exhaust specifications of the high pressure turbine 1 and the intermediate pressure turbine 2 have to be changed.
A feed water temperature at an inlet of the boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that the temperature increase ratio falls within 1.9-3.5.
The temperature increase ratio between a feed-water temperature increase in the first feed heater 7 and an average of feed-water temperature increases in the second feed heaters 8 may vary within a certain range, depending on the number of the feed heaters 6, a mechanical difference in a steam turbine such as an exhaust loss, a value corresponding to a power generation output in a power plant, a difference in a minute structure, and so on.
As described above, the non-patent document describes that an optimum specific enthalpy ratio is 1.8. However, in a general power plant, a specific enthalpy increase ratio of 1.8 is not practical as to a range of a temperature increase ratio.
A reason of this phenomenon is presumed as follows.
An output of the steam turbine is a sum of “a heat drop, i.e., a specific enthalpy decrease amount×seam mass flowrate” at each stage of each turbine. Thus, it is more efficient when a steam is bled from a position of a lower specific enthalpy as much as possible, because the boiler feed water 14 is heated after the steam turbine works. On the other hand, an efficiency of a regenerative cycle can be improved, when a temperature at the inlet of the boiler 4 of the boiler feed water 14 is higher. Namely, both the efficiencies have to be considered.
When a temperature of the inlet of the boiler 4 is determined, there is required a steam of a saturated temperature which is substantially the same as the inlet temperature of the boiler 4 of the feed heater 26 of the highest steam pressure. In this manner, a pressure of the bleed steam 20 is determined. Other feed heaters 7 and 8 support stepwise the temperature increase until the temperature reaches the value.
The high-pressure turbine exhaust bleed steam 22 is a steam that has a low specific enthalpy although a pressure thereof is relatively high. In addition, the high-pressure turbine exhaust bleed steam 22 is not a bleed steam bled from a steam which has been heated by the reheater 5. Thus, when heating of the boiler feed water 14 with the use of the enthalpy of the high-pressure exhaust bleed steam 22 is increased, a thermal efficiency of the overall cycle can be improved.
Namely, as schematically shown in FIG. 3, a temperature increase ratio has a certain optimum value at which a thermal efficiency is maximized. This optimum value is preferable when the temperature increase ratio is sufficiently higher than 1. This optimum value varies depending on conditions of the main steam 16, and it is presumed that the value becomes higher as to a steam of a higher temperature.
As described above, when a temperature increase ratio between: a feed-water temperature increase in the first feed heater 7 and; an average of feed-water temperature increases in the second feed heaters 8; is set to fall within 1.9-3.5, a cycle thermal efficiency can be improved.

Second Embodiment

Next, a second embodiment of the present invention is described with reference to FIG. 1.
A steam turbine cycle in this embodiment includes a high pressure a high pressure turbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 for heating a feed water to the boiler 4 by a bleed steam from the high pressure turbine 1 and the reheating turbine 24, a feed pump 12, and a condenser 10. The steam turbine cycle in this embodiment is a single-stage reheating cycle where a working fluid is water and uses a Rankine cycle which is a regenerative cycle.
A steam temperature at an outlet of the boiler 4 is 590° C. or above. A specific enthalpy increase ratio between: a specific enthalpy increase of a feed water in a first feed heater 7 corresponding to a high-pressure turbine exhaust bleed steam 22; and an average of specific enthalpy increases of feed waters in second feed heaters 8 where a pressure of the feed water is lower than that of the first feed heater 7; falls within 1.9-3.5.
By adjusting a flowrate of each bleed steam 20 and each bleed position 31, specific enthalpy increases in the feed waters in the first feed heater 7 and the second feed heaters 8 can be adjusted. In order to vary specific enthalpies of the bleed steam 20 from a high-pressure turbine exhaust bleed steam 22 and an intermediate-pressure turbine exhaust bleed steam 32, exhaust specifications of the high pressure turbine 1 and the intermediate pressure turbine 2 have to be changed.
A feed water temperature at an inlet of the boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a specific enthalpy increase ratio falls within 1.9-3.5.
A specific enthalpy increase ratio may vary within a certain range, depending on the number of the feed heaters 6, a mechanical difference in a steam turbine such as an exhaust loss, a value corresponding to a power generation output in a power plant, a difference in a minute structure, and so on.
As described above, the non-patent document describes that an optimum specific enthalpy ratio is 1.8. However, this document does not refer to a temperature of the main steam 16. Thus, since a different temperature of the main steam 16 is assumed, an optimum value of a specific enthalpy increase ratio is considered to be different.
Also in this embodiment similar to the first embodiment, as schematically shown in FIG. 3, a specific enthalpy increase ratio has a certain optimum value at which a thermal efficiency is optimized. This optimum value is preferable when the specific enthalpy increase ratio is sufficiently higher than 1. This optimum value varies depending on conditions of the main steam 16, and it is presumed that the value becomes higher as to a steam of a higher temperature.
As described above, when a specific enthalpy increase ratio between: a specific enthalpy increase in a feed water in the first feed heater 7 and; an average of specific enthalpy increases in feed waters in the second feed heaters 8; is set to fall within 1.9-3.5, a cycle thermal efficiency can be improved.

Third Embodiment

Next, a third embodiment of the present invention is described with reference to FIG. 1.
The steam turbine cycle in this embodiment includes a high pressure turbine 1, a reheating turbine 24, a boiler 4, a feed heaters 6 for heating a feed water to the boiler 4 by a bleed steam from the high pressure turbine 1 and the reheating turbine 24, a feed pump 12, and a condenser 10. The steam turbine cycle in this embodiment is a single-stage reheating cycle where a working fluid is water and uses a Rankine cycle which is a regenerative cycle.
A steam temperature at an outlet of the boiler 4 is 590° C. or more. A temperature increase ratio between: a feed-water temperature increase in a first feed heater 7 corresponding to a high-pressure turbine exhaust bleed steam 22 and an average of feed-water temperature increases in feed heaters other than the first feed heater 7; falls within 1.9-3.5.
Herein, the feed heaters other than the first heed heater 7 mean the second feed heaters 8 where a pressure of the feed water is lower than that of the first feed heater 7, and a third feed heater 26 where a pressure of the feed water is higher than that of the first feed heater 7. The third feed heater 26 heats a feed water by a bleed steam from the high pressure turbine 1.
By adjusting a flowrate of each bleed steam 20 and each bleed position 31, feed-water temperature increases in the first feed heater 7, the second feed heaters 8, and the third feed heater 26 can be adjusted. In order to vary temperatures of the high-pressure turbine exhaust bleed steam 22 and an intermediate-pressure turbine exhaust bleed steam 32, exhaust specifications of the high pressure turbine 1 and the intermediate pressure turbine 2 have to be changed.
A feed water temperature at an inlet of the boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a temperature increase ratio falls within 1.9-3.5.
A feed temperature increase ratio between: a feed-water temperature increase in the first heater 7; and an average of feed-water temperature increases in the feed heaters 8 and 26 other than the first feed heater 7; may vary within a certain range, depending on the number of the feed heater 6, a mechanical difference in a steam turbine such as an exhaust loss, a value corresponding to a power generation output in a power plant, a difference in a minute structure, and so on.
As described above, when a temperature increase ratio between: a feed-water temperature increase in the first feed heater 7; and an average of feed-water temperature increases in the feed heaters 8 and 26 other than the first feed heater 7; is set to fall within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the first embodiment.

Fourth Embodiment

A fourth embodiment of the present invention is described with reference to FIG. 1.
The steam turbine cycle in this embodiment includes a high pressure turbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 for heating a feed water to the boiler 4 by a bleed steam from the high pressure turbine 1 and the reheating turbine 24, a feed pump 12, and a condenser 10. The steam turbine cycle in this embodiment is a single-stage reheating cycle where a working fluid is water and uses a Rankine cycle which is a regenerative cycle.
A steam temperature at an outlet of the boiler 4 is 590° C. or more. A specific enthalpy increase ratio between: a specific enthalpy increase of a feed water in a first feed heater 7 corresponding to a high-pressure turbine exhaust bleed steam 22; and an average of specific enthalpy increases of feed waters in feed heaters 8 and 26 other than the first feed heater 7; falls within 1.9-3.5.
By adjusting a flowrate of each bleed steam 20 and each bleed position 31, specific enthalpy increases in feed waters in the first feed heater 7, the second feed heaters 8, and the third feed heater 26 can be adjusted. In order to vary specific enthalpies of the high-pressure turbine exhaust bleed steam 22 and an intermediate-pressure turbine exhaust bleed steam 32, exhaust specifications of the high pressure turbine 1 and the intermediate pressure turbine 2 have to be changed.
A feed water temperature at an inlet of the boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a specific enthalpy increase ratio falls within 1.9-3.5.
A specific enthalpy increase ratio between: a specific enthalpy increase of a feed water in the first feed heater 7; and an average of specific enthalpy increases of feed waters in the feed heaters 8 and 26 other than the first feed heater 7 may vary within a certain range, depending on the number of the feed heaters 6, mechanical differences in the steam turbines such as an exhaust loss, a value corresponding to a power generation output in a power plant, differences in minute structures, and so on.
As described above, when a specific enthalpy increase ratio between: a specific enthalpy increase of a feed water in the first feed heater 7; and an average of specific enthalpy increases of feed waters in the feed heaters 8 and 26 other than the first feed heater 7; is set to fall within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the second embodiment.

Fifth Embodiment

Next, a fifth embodiment of the present invention is described with reference to FIG. 1. The fifth embodiment shown in FIG. 1 differs from the first embodiment in that feed-water temperature increases in the second feed heaters 8 are calculated in consideration of a feed-water temperature increase by a feed pump 12. Other structures of the fifth embodiment are substantially the same as those of the first embodiment.
Since the feed pump 12 heats a feed water, a temperature of the feed water is increased. Thus, in consideration of the temperature increase, an average of a temperature increase in each of second feed heaters 8 is calculated.
Alternatively, in the third embodiment, it is possible to calculate feed-water temperature increases in the feed heaters 8 and 26 other than the first feed heater 7, in consideration of a feed-water temperature increase by the feed pump 12.
Also in this case, since the feed pump 12 heats a feed water, a temperature of the feed water is increased. Thus, in consideration of the temperature increase, an average of a temperature increase in each of the feed heaters 8 and 26 is calculated.
A feed water temperature at an inlet of a boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was fond that a cycle thermal efficiency becomes maximum under conditions that a temperature increase ratio falls within 1.9-3.5.
In addition to the reason as described in the first embodiment, a temperature increase ratio may vary within a certain range, under influences of a heat generation difference caused by a mechanical difference in the feed pump 12.
As described above, by calculating feed-water temperature increases in the second feed heaters 8 in consideration of a temperature increase in the feed water by the feed pump 12, and then by determining a temperature increase ratio, a cycle thermal efficiency can be increased, similarly to the first and third embodiments.

Sixth Embodiment

Next, a sixth embodiment of the present invention is described with reference to FIG. 1. The sixth embodiment shown in FIG. 1 differs from the first embodiment in that feed-water specific enthalpy increases in the second feed heaters 8 are calculated in consideration of a feed-water specific enthalpy increase by a feed pump 12. Other structures of the sixth embodiment are substantially the same as those of the first embodiment.
The feed pump 12 increases a pressure of a feed water, and simultaneously heats the feed water, as described in the third embodiment, so that a specific enthalpy of the feed water is increased. In consideration of the specific enthalpy increase, an average specific enthalpy increase in each of the second feed heaters 8 is calculated.
This embodiment can be carried out, in the above-described fourth embodiment, by calculating specific enthalpy increases of feed waters in the feed heaters 8 and 26 other than a first feed heater 7, in consideration of a specific enthalpy increase in a feed water by the feed pump 12.
Also in this case, since the feed pump 12 increases a pressure of a feed water, and simultaneously heats the feed water, so that a specific enthalpy of the feed water is increased. Thus, in consideration of the specific enthalpy increase, an average specific enthalpy increase in each of the feed heaters 8 and 26 other than the first feed heater 7 is calculated.
A feed water temperature at an inlet of a boiler 4 is generally defined by the boiler 4. Thus, with a feed-water temperature value being fixed, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a specific enthalpy increase ratio falls within 1.9-3.5.
In addition to the reason as described in the first embodiment, a specific enthalpy increase ratio may vary within a certain range, under influences of a heat generation difference caused by a mechanical difference in the feed pump 12.
As described above, by calculating a specific enthalpy increase in a feed water in consideration of a specific enthalpy increase in the feed water by the feed pump 12, and then by determining a temperature increase ratio, a cycle thermal efficiency can be increased, similarly to the second and fourth embodiments.

Seventh Embodiment

Next, a seventh embodiment of the present invention is described with reference to FIG. 1.
In the first embodiment, the third embodiment, and the fifth embodiment, the eight feed heaters 6 in total are used and a cycle structure is made such that a temperature increase ratio falls within 1.9-3.5. This is because, in a large heat power plant, the number of the feed heaters 6 is preferably eight from an economical point of view.
In FIG. 1, steam is bled at two positions from the intermediate pressure turbine 2 including exhaust of steam, and steam is bled at four positions from the low pressure turbine 3. However, as long as the total number of the bleed positions is six, the number and the positions are not limited thereto.
In FIG. 1, a bleed steam to the aerator 9 is the intermediate-pressure turbine exhaust bleed steam 32, but is not limited thereto. With the number of the feed heaters 6 being limited to eight, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a temperature increase ratio falls within 1.9-3.5.
As described above, in the first embodiment, the third embodiment, and the fifth embodiment, by using eight feed heaters 6 in total, and by making a cycle structure such that a temperature increase ratio falls within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the first embodiment, third embodiment, and the fifth embodiment.

Eighth Embodiment

Next, an eighth embodiment of the present invention is described with reference to FIG. 1.
In the second embodiment, the fourth embodiment, and the sixth embodiment, the eight feed heaters 6 in total are used and a cycle structure is made such that a specific enthalpy increase ratio falls within 1.9-3.5. This is because, in a large heat power plant, the number of the feed heaters 6 is preferably eight from an economical point of view.
In FIG. 1, steam is bled at two positions from the intermediate pressure turbine 2 including exhaust of steam, and steam is bled at four positions from the low pressure turbine 3. However, as long as the total number of the bleed positions is six, the number and the positions are not limited thereto.
In FIG. 1, a bleed steam to the aerator 9 is the intermediate-pressure turbine exhaust bleed steam 32, but is not limited thereto. With the number of the feed heaters 6 being limited to eight, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a specific enthalpy increase ratio falls within 1.9-3.5.
As described above, in the first embodiment, the third embodiment, and the fifth embodiment, by using eight feed heaters 6 in total, and by making a cycle structure such that a specific enthalpy increase ratio falls within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the second embodiment, fourth embodiment, and the sixth embodiment.

Ninth Embodiment

Next, a ninth embodiment of the present invention is described with reference to FIG. 2. In FIG. 2, the same parts as those of FIG. 1 are shown by the same reference numbers, and their detailed description is omitted.
In this embodiment, by adding one feed heater 6 to the eight feed heaters 6 in total as in the above first embodiment, the third embodiment, and the fifth embodiment, the nine feed heaters 6 in total are used, and a cycle structure is made such that a temperature increase ratio falls within 1.9-3.5. This is because, in a large heat power plant, although the number of the feed heaters 6 is preferably eight from an economical point of view, there is a case in which the number of the feed heaters 6 is preferably nine, with a view to more increasing an efficiency, an output, and a temperature of a main steam.
In FIG. 2, steam is bled at three positions from an intermediate pressure turbine 2 including exhaust of steam, and steam is bled at four positions from a low pressure turbine 3. However, as long as the total number of the bleed positions is seven, the number and the positions are not limited thereto.
In FIG. 2, a bleed steam to a deaerator 9 is an intermediate pressure turbine exhaust steam 32, but is not limited thereto. With the number of the feed heaters 6 being limited to nine, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a temperature increase ratio falls within 1.9-3.5.
As described above, in this embodiment, by using the nine feed heaters 6 in total by adding one feed heater 6 to the eight feed heaters 6 in total as in the above first embodiment, the third embodiment, and the fifth embodiment, and by making a cycle structure such that a temperature increase ratio falls within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the first embodiment, the third embodiment, and the fifth embodiment.

Tenth Embodiment

Next, a tenth embodiment of the present invention is described with reference to FIG. 2.
In this embodiment, by adding one feed heater 6 to the eight feed heaters 6 in total as in the above second embodiment, the fourth embodiment, and the sixth embodiment, the nine feed heaters 6 in total are used, and a cycle structure is made such that a specific enthalpy increase ratio falls within 1.9-3.5. This is because, in a large heat power plant, although the number of the feed heaters 6 is preferably eight from an economical point of view, there is a case in which the number of the feed heaters 6 is preferably nine, with a view to more increasing an efficiency, an output, and a temperature of a main steam.
In FIG. 2, steam is bled at three positions from an intermediate pressure turbine 2 including exhaust of steam, and steam is bled at four positions from a low pressure turbine 3. However, as long as the total number of the bleed positions is seven, the number and the positions are not limited thereto.
In FIG. 2, a bleed steam to a deaerator 9 is an intermediate pressure turbine exhaust steam 32, but is not limited thereto. With the number of the feed heaters 6 being limited to nine, an optimization calculation was conducted. Then, it was found that a cycle thermal efficiency becomes maximum under conditions that a specific enthalpy increase ratio falls within 1.9-3.5.
As described above, in this embodiment, by using the nine feed heaters 6 in total by adding one feed heater 6 to the eight feed heaters 6 in total as in the above second embodiment, the fourth embodiment, and the sixth embodiment, and by making a cycle structure such that a specific enthalpy increase ratio falls within 1.9-3.5, a cycle thermal efficiency can be improved, similarly to the second embodiment, the fourth embodiment, and the sixth embodiment.

Eleventh Embodiment

Next, an eleventh embodiment of the present invention is described with reference to FIGS. 1 and 2.
In the first to tenth embodiments, a cycle structure is made such that a steam temperature at an outlet of the boiler 4 is 600° C. or more. This is because, when a temperature of the main steam 16 is 600° C. or above, a more significant effect can be expected. Namely, an effect of improving a cycle thermal efficiency due to an increased temperature of the main steam 16 is not damaged by set conditions of a bleed steam 20 but can be fully exerted.
In the first to tenth embodiments, by making a cycle structure such that a steam temperature at an outlet of the boiler 4 is 600° C. or more, a cycle thermal efficiency can be improved, similarly to the first to tenth embodiments.

Claims

1. A steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle,

wherein a steam temperature at an outlet of the boiler is 590° C. or more, and

a temperature increase ratio between: a feed-water temperature increase in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of feed-water temperature increases in second feed heaters where a pressure of the feed water is lower than that of the first feed heater; falls within 1.9-3.5.

2. A steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle,

wherein a steam temperature at an outlet of the boiler is 590° C. or more, and

a specific enthalpy increase ratio between: a specific enthalpy increase in a feed water in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of specific enthalpy increases in feed waters in second feed heaters where a pressure of the feed water is lower than that of the first feed heater; falls within 1.9-3.5.

3. A steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle,

wherein a steam temperature at an outlet of the boiler is 590° C. or more, and

a temperature increase ratio between: a feed-water temperature increase in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of feed-water temperature increases in feed heaters other than the first feed heater; falls within 1.9-3.5.

4. A steam turbine cycle comprising a high pressure turbine, a reheating turbine, a boiler, feed heaters for heating a feed water to the boiler by a bleed steam from the high pressure turbine and the reheating turbine, a feed pump, and a condenser, the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle,

wherein a steam temperature at an outlet of the boiler is 590° C. or more, and

a specific enthalpy increase ratio between: a specific enthalpy increase in a feed water in a first feed heater corresponding to a bleed steam from an exhaust steam of the high pressure turbine; and an average of specific enthalpy increases in feed heaters other than the first feed heater; falls within 1.9-3.5.

5. The steam turbine cycle according to claim 1, wherein

the feed-water temperature increases in the second feed heaters are calculated, in consideration of a temperature increase in the feed water by the feed pump.

6. The steam turbine cycle according to claim 2, wherein

the specific enthalpy increases in feed waters in the second feed heaters are calculated, in consideration of a specific enthalpy increase in the feed water by the feed pump.

7. The steam turbine cycle according to claim 1, wherein

the total number of the feed heaters is eight, and

the temperature increase ratio falls within 1.9-3.5.

8. The steam turbine cycle according to claim 2, wherein

the total number of the feed heaters is eight, and

the specific enthalpy increase ratio falls within 1.9-3.5.

9. The steam turbine cycle according to claim 1, wherein

the total number of the feed heaters is nine, and

the temperature increase ratio falls within 1.9-3.5.

10. The steam turbine cycle according to claim 2, wherein

the total number of the feed heaters is nine, and

the specific enthalpy increase ratio falls within 1.9-3.5.

11. The steam turbine cycle according to claim 1, wherein

a steam temperature at an outlet of the boiler is 600° C. or above.

12. The steam turbine cycle according to claim 3, wherein

the total number of the feed heaters is eight, and

the temperature increase ratio falls within 1.9-3.5.

13. The steam turbine cycle according to claim 4, wherein

the total number of the feed heaters is eight, and

the specific enthalpy increase ratio falls within 1.9-3.5.

14. The steam turbine cycle according to claim 3, wherein

the total number of the feed heaters is nine, and

the temperature increase ratio falls within 1.9-3.5.

15. The steam turbine cycle according to claim 4, wherein

the total number of the feed heaters is nine, and

the specific enthalpy increase ratio falls within 1.9-3.5.

16. The steam turbine cycle according to claim 2, wherein

a steam temperature at an outlet of the boiler is 600° C. or above.

17. The steam turbine cycle according to claim 3, wherein

a steam temperature at an outlet of the boiler is 600° C. or above.

18. The steam turbine cycle according to claim 4, wherein

a steam temperature at an outlet of the boiler is 600° C. or above.

19. The steam turbine cycle according to claim 3, wherein

the feed-water temperature increases in the other feed heaters are calculated, in consideration of a temperature increase in the feed water by the feed pump.

20. The steam turbine cycle according to claim 4, wherein

the specific enthalpy increases in feed waters in the other feed heaters are calculated, in consideration of a specific enthalpy increase in the feed water by the feed pump.