System using steam turbine

Abstract

To maintain a primary air temperature to be supplied to a crusher to a predetermined value and avoid deterioration of turbine thermal efficiency (power generation efficiency) even if heat transfer performance of a hot air cooler deteriorates.SOLUTION: A system 1 includes: a steam turbine 11; a main condensed water supply passage 16 formed by branching a condensed water bypass passage 17; a branched condensed water flow regulating valve 26 provided in the condensed water bypass passage 17; a hot air cooler 15 that heats part of condensed water by using hot air from a GAH 50 and cools the hot air; a cooled hot air passage 22 connected to the hot air cooler 15; a cooled hot air temperature detector 27a provided in the middle of the cooled hot air passage 22; a hot air bypass passage 23a that bypasses the hot air cooler 15; a hot air bypass passage control valve 20D; and a first control section 24a that controls opening / closing of the hot air bypass passage control valve 20D in accordance with a detection result obtained by the cooled hot air temperature detector 27a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system using a steam turbine, such as a power generation system. [Background technology]

[0002] Systems using steam turbines, such as thermal power plants, employ a regenerative cycle system to improve thermal efficiency. This system preheats the condensate obtained by condensing the steam exhausted from the steam turbine in a condenser using steam extracted from the steam turbine and then supplies the condensate to the boiler. It is also common to utilize the heat of boiler exhaust gas as a heat source within the system. For example, in systems using pulverized coal as boiler fuel, the boiler exhaust gas is used as a drying heat source for the pulverizer that crushes the coal, the fuel raw material. The drying heat source for the pulverizer is a mixture of hot air heated by heat exchange with the boiler exhaust gas and cold air, which is supplied as the pulverizer inlet air (primary air). However, when using fuels with high volatile content and a high risk of fire, such as biomass, the temperature of the primary air must be lower than when using pulverized coal.

[0003] However, in existing systems that adjust the primary air temperature by mixing hot and cold air, if a large amount of cold air is used to reduce the primary air temperature, the amount of heat exchanged in the regenerative air heater (GAH), which uses boiler exhaust gas to heat the air and generate hot air, will decrease. As a result, the boiler exhaust gas temperature at the GAH outlet will be higher than the design value, which may cause problems in the operation of equipment downstream of the GAH (for example, electrostatic precipitators, desulfurization equipment, etc.).

[0004] Therefore, it is necessary to install a hot air cooler that cools the hot air at the GAH outlet (hereinafter referred to as hot air) using turbine condensate, thereby cooling the primary air to a predetermined temperature without raising the temperature of the exhaust gas at the GAH outlet.For example, Non-Patent Document 1 describes the installation of a hot air cooler that cools the hot air by heat exchange and supplies it to a pulverizer, and the use of the recovered heat to preheat the boiler feedwater. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Adam Nicholson, “Coal to Biomass Conversion”, Drax, February 19, 2019, P29, <URL: https: / / nearyou.imeche.org / docs / default-source / Power-Industries-Division-NW-Centre / imeche---biomass-conversion-lecture-v1.pdf> Summary of the Invention [Problem to be solved by the invention]

[0006] The hot air being cooled carries with it ash carried in by the boiler exhaust gas and adhering to the GAH, which causes the heat transfer tubes of the hot air cooler to become dirty over time, resulting in a deterioration in heat transfer performance.If the heat transfer area of ​​the hot air cooler is designed with excessive margin to take this dirt into account, the heat transfer performance will be excessive at the beginning of operation, and the hot air temperature will be too low after cooling, making it impossible to ensure the required primary air temperature.

[0007] On the other hand, if the heat transfer performance deteriorates due to a design that does not ensure sufficient heat transfer area, the heat transfer performance can be ensured by setting the turbine condensate flow rate so as to lower the outlet temperature of the turbine condensate, which is the cooling refrigerant, from the hot air cooler.

[0008] A portion of the turbine condensate is branched off from the turbine condensate piping and used for cooling in the hot air cooler, and the piping for the heated turbine condensate is designed to merge with a part of the turbine condensate piping that is close to the design condition temperature of the hot air cooler in order to prevent a decrease in turbine thermal efficiency. In other words, the turbine condensate piping that branches off to supply turbine condensate to the hot air cooler bypasses a number of low-pressure feedwater heaters (LPH) installed in the turbine condensate system, the number of which corresponds to the above-mentioned temperature.

[0009] In the case of conventional design concepts where the piping merging into the turbine condensate system is fixed at one location, and as described above, operation is performed to lower the cooling refrigerant temperature when the heat transfer performance of the hot air cooler deteriorates, and turbine condensate at a temperature lower than the design value is merged, in a system using a steam turbine, the condensate obtained by condensing steam discharged from the steam turbine in a condenser is preheated with steam extracted from the steam turbine and supplied to the boiler, thereby deteriorating the turbine thermal efficiency of the regenerative cycle system, which aims to improve thermal efficiency.

[0010] The present invention aims to maintain the temperature of primary air supplied to a pulverizer at a predetermined value and to avoid a decrease in turbine thermal efficiency (power generation efficiency) in a system using a steam turbine, even if the heat transfer performance of a hot air cooler decreases. [Means for solving the problem]

[0011] The system of the present invention comprises an extraction-condensing steam turbine having multiple extraction stages; a main condensate supply line for supplying condensate from the steam turbine to a boiler; a plurality of heaters provided on the main condensate supply line, the heaters preheating the condensate with steam extracted from two or more of the plurality of extraction stages; A system comprising: a condensate bypass passage branching from the main condensate supply passage and supplying a portion of the condensate to outlet sides of the plurality of heaters; a branch condensate flow rate regulator provided in the condensate bypass path; a hot air cooler that is provided in the condensate bypass path downstream of the branch condensate flow regulator and that heats a portion of the condensate using hot air from an external device of the system and cools the hot air; a post-cooling hot air passage connected to an air outlet of the primary air cooler; a cooled hot air temperature detector provided in the cooled hot air path; a hot air bypass path that branches off from the pre-cooling hot air path midway through the pre-cooling hot air path connecting the external device and the air inlet of the hot air cooler and joins the post-cooling hot air path downstream of the hot air cooler; a hot air bypass path controller provided in the hot air bypass path and configured to open and close the hot air bypass path; a first control unit that controls opening and closing of the hot air bypass path controller in accordance with the detection result of the cooled hot air temperature detector; It has. [Effects of the Invention]

[0012] According to the present invention, even if the heat transfer performance of the hot air cooler is reduced, the temperature of the primary air supplied to the pulverizer can be maintained at a predetermined value and a reduction in turbine thermal efficiency (power generation efficiency) can be avoided. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the operation of the system shown in FIG. 1, showing the flow of condensate and air during normal operation. [Figure 3] FIG. 2 is a diagram for explaining the operation of the system shown in FIG. 1, showing the flow of condensed water and air when the temperature of the hot air drops after cooling. [Figure 4] 2 is a diagram for explaining the operation of the system shown in FIG. 1, showing the flow of condensed water and air when the air temperature detected by the post-cooling hot air temperature detector cannot be adjusted (1). FIG. [Figure 5] FIG. 2 is a diagram for explaining the operation of the system shown in FIG. 1, showing the flow of condensate and air when the air temperature detected by the post-cooling hot air temperature detector cannot be adjusted (2). DETAILED DESCRIPTION OF THE INVENTION

[0014] [Overall system configuration] 1 shows a power generation system 1 according to one embodiment of the present invention, which includes an extraction condensing steam turbine 11 that is driven by steam supplied from a boiler (not shown) and has multiple extraction stages, and a generator 12 that is connected to the steam turbine 11 and driven by the rotation of the steam turbine 11. In FIG. 1, solid lines indicate the flow of condensate and steam, dashed lines indicate the flow of hot air, and dashed lines indicate the flow of electrical signals.

[0015] This power generation system 1 has, as regenerative cycle equipment, a condenser 13 that condenses steam discharged from a steam turbine 11, a main condensate supply passage 16 that supplies the condensate obtained by the condenser 13 to a boiler directly or via a deaerator (not shown), first to third heaters 19a, 19b, 19c that are provided on the main condensate supply passage 16 and preheat the condensate with steam extracted from two or more of the multiple extraction stages, a hot air cooler 15 that heats a portion of the condensate with hot air from the outside, and a condensate bypass passage 17 that branches off from the main condensate supply passage 16 and supplies a portion of the condensate to the outlet sides of the first to third heaters 19a, 19b, 19c via the hot air cooler 15.

[0016] A condensate pump 14 for sending out the condensate obtained by the condenser 13 is provided on the main condensate supply line 16 upstream of the branching position of the condensate bypass line 17. A deaerator liquid level control valve 25 is provided on the main condensate supply line 16, and a branch condensate flow rate control valve 26 is provided on the condensate bypass line 17. By appropriately adjusting the openings of the deaerator liquid level control valve 25 and the branch condensate flow rate control valve 26, the flow rate of the condensate branched into the condensate bypass line 17 can be adjusted.

[0017] The steam turbine 11 may have any number of extraction stages, and may have, for example, six extraction stages, first to sixth extraction stages E1 to E6, as shown in Fig. 1. Steam of different temperatures is extracted from these first to sixth extraction stages E1 to E6, with the first extraction stage E1 having the highest temperature, followed by the second extraction stage E2, the third extraction stage E3, the fourth extraction stage E4, and the fifth extraction stage E5, and finally the sixth extraction stage E6 having the lowest temperature.

[0018] The number of heaters provided on the main condensate supply passage 16 is also arbitrary, and in this embodiment, a first heater 19a, a second heater 19b, and a third heater 19c are arranged in series in this order from the upstream side in the condensate supply direction on the main condensate supply passage 16. These heaters are usually called low-pressure feedwater heaters (LPH).

[0019] The condensate preheating temperature by the first to third heaters 19a to 19c is lowest for the first heater 19a, which is furthest upstream in the condensate flow direction in the main condensate supply passage 16, followed by the second heater 19b and the third heater 19c. Therefore, steam is supplied to the first heater 19a from the sixth extraction stage E6, steam is supplied to the second heater 19b from the fifth extraction stage E5, and steam is supplied to the third heater 19c from the fourth extraction stage E4. The first heater 19a, second heater 19b, and third heater 19c preheat the condensate to their respective predetermined temperatures. In this embodiment, the steam extracted from the first extraction stage E1, second extraction stage E2, and third extraction stage E3 is not used to heat the condensate.

[0020] The main condensate supply line 16 is provided with a first heater outlet temperature detector 21a that detects the outlet temperature T1 of the first heater 19a, a second heater outlet temperature detector 21b that detects the outlet temperature T2 of the second heater 19b, and a third heater outlet temperature detector 21c that detects the outlet temperature T3 of the third heater 19c.

[0021] The hot air cooler 15 is configured as a heat exchanger that cools hot air by exchanging heat between the hot air and condensate, and has an air inlet, an air outlet, a condensate inlet, and a condensate outlet, the condensate inlet and outlet being provided midway through a condensate bypass path 17 that branches off from the main condensate supply path 16. In this embodiment, hot air from a device external to the power generation system 1 is supplied to the air inlet of the hot air cooler 15 via a pre-cooling hot air path 23. An example of the device external to the power generation system 1 is a regenerative air preheater (GAH) 50. The condensate bypass path 17 supplies a portion of the condensate via the hot air cooler 15 to the outlet sides of the first to third heaters 19a to 19c.

[0022] The condensate bypass passage 17 includes an upstream bypass passage 17a connecting the main condensate supply passage 16 and the hot air cooler 15, and a downstream bypass passage 17b connecting the condensate outlet of the hot air cooler 15 and the outlet sides of the first to third heaters 19a to 19c. Furthermore, the downstream bypass passage 17b has a plurality of branch passages 18a to 18c, the same number as the first to third heaters 19a to 19c, which branch toward the first to third heaters 19a to 19c and are individually connected to the outlet sides of the first to third heaters 19a to 19c. Each of the branch passages 18a to 18c is provided with a heat recovery condensate flow control valve 20A, 20B, or 20C.

[0023] The downstream bypass passage 17b is connected to the heat recovery condensate, which is the condensate heated by the hot air cooler 15, and has a temperature TC B A heat recovery condensate temperature detector 27b is provided that detects the temperature at the condensate outlet side of the hot air cooler 15. The position at which the heat recovery condensate temperature detector 27b is provided may be any position on the downstream bypass path 17b between the outlet of the hot air cooler 15 and the positions at which the branch flow paths 18a to 18c branch off, but it is preferable that the detector 27b be provided immediately before the positions at which the branch flow paths 18a to 18c branch off.

[0024] The air outlet of the hot air cooler 15 is connected to a cooled hot air passage 22, which is a passage for primary air supplied to a pulverizer 40. The pulverizer 40 is a facility for pulverizing fuel for a boiler, such as coal fuel or biomass fuel. The fuel pulverized by the pulverizer 40 is supplied to the boiler.

[0025] A hot air bypass path 23a branches off from the pre-cooling hot air path 23 upstream of the air inlet of the hot air cooler 15. A hot air bypass path control valve 20D that controls opening and closing of the hot air bypass path 23a is provided midway along the hot air bypass path 23a. The hot air bypass path 23a merges with the post-cooling hot air path 22 downstream of the air outlet of the hot air cooler 15.

[0026] Downstream of the junction of the cooled hot air passage 22 with the hot air bypass passage 23a, there is a passage for measuring the temperature TC of the cooled hot air discharged from the hot air cooler 15. A The cooled hot air temperature detector 27a is provided to detect the cooled hot air temperature TC A is used to control the opening degree of the branch condensate flow control valve 26. Therefore, the power generation system 1 detects the cooled hot air temperature TC A The first control unit 24a controls the opening of the branch condensate flow control valve 26 using a control signal from the control unit 24a. More specifically, the first control unit 24a compares the temperature of the cooled hot air discharged from the hot air cooler 15 with a preset set value for the cooled hot air temperature, and controls the opening of the branch condensate flow control valve 26 in accordance with the result of the comparison, thereby adjusting the flow rates in the main condensate supply path 16 and the condensate bypass path 17.

[0027] On the other hand, the temperature of the heat recovery condensate mentioned above, TC B The outlet temperatures T1 to T3 of the first to third heaters 19a to 19c are used to control the opening degrees of the heat recovery condensate flow control valves 20A to 20C. Therefore, the power generation system 1 uses the heat recovery condensate temperature TC B and a second control unit 24b that controls the opening degrees of the heat recovery condensate flow control valves 20A to 20C using outlet temperatures T1 to T3 of the first to third heaters 19a to 19c detected by the first to third heater outlet temperature detectors 21a to 21c. Heat recovery condensate temperature TC B and the outlet temperatures T1 to T3 of the first to third heaters 19a to 19c, and the temperature TC B and the temperature of the heat recovery condensate TC B The heat recovery condensate flow rate adjustment valves 20A to 20C are controlled so that a heater having an outlet temperature lower than the selected heater is selected and the heat recovery condensate is supplied to the outlet of the selected heater.

[0028] [System operation example] Next, an example of the operation of the power generation system 1 of this embodiment will be specifically described using an example in which the operating conditions are such that the pre-cooling hot air temperature from the GAH 50 is 310°C, the set value of the air temperature (A-2) detected by the post-cooling hot air temperature detector 27a is preset to 250°C, and the primary air temperature (A-3) at the inlet of the pulverizer 40 is adjusted to 170°C by mixing with cold air upstream of the inlet of the pulverizer 40.

[0029] <During normal operation> In normal operation, as shown in Figure 2, the most upstream heat recovery condensate flow control valve 20C is open, but the other heat recovery condensate flow control valves 20A and 20B are closed. In addition, hot air bypass path control valve 20D is closed. At this time, the temperature (W-1) of the condensate that has exchanged heat with hot air in hot air cooler 15 and flows through condensate bypass path 17 is 124°C, and the flow rate is 10 t / h.

[0030] <When the hot air temperature drops after cooling> In designing the system, the heat transfer area is designed to be larger in consideration of fouling on the heat transfer tubes of the hot air cooler 15. Therefore, at the start of operation, there is no dust adhering to the surface of the heat transfer tubes of the hot air cooler 15, so the heat transfer performance is very high and the temperature (A-1) at the air outlet of the hot air cooler 15 drops too low. If this temperature drops too low, the drying capacity of the pulverizer 40 becomes insufficient and the amount of pulverization decreases.

[0031] A drop in the temperature (A-1) at the air outlet of the hot air cooler 15 can be detected by a drop in the air temperature (A-2) detected by the post-cooling hot air temperature detector 27a. Therefore, when the temperature (A-1) at the air outlet of the hot air cooler 15 drops (for example, to 220°C), the hot air bypass path control valve 20D is opened so that the air temperature (A-2) detected by the post-cooling hot air temperature detector 27a becomes 250°C, and the hot air (temperature: 310°C) that bypassed the hot air cooler 15 is mixed into the post-cooling hot air path 22 (Fig. 3).

[0032] <When the hot air temperature rises after cooling> As operation continues, dust begins to adhere to the heat transfer tubes of the hot air cooler 15, causing a decrease in heat transfer performance. As a result, the temperature (A-1) of the air outlet of the hot air cooler 15 rises slightly (for example, to 240°C). In this case, the opening of the hot air bypass path control valve 20D is operated in the closing direction, and the air temperature (A-2) detected by the hot air temperature detector 27a after cooling is adjusted to 250°C.

[0033] <When the air temperature detected by the hot air temperature detector after cooling cannot be adjusted (1)> If operation continues and the heat transfer performance of the hot air cooler 15 further deteriorates, the air temperature (A-2) detected by the hot air temperature detector 27a after cooling will exceed 250°C even when the hot air bypass path control valve 20D is fully closed.

[0034] In this case, as shown in Figure 4, the opening of the branch condensate flow control valve 26 is operated in the opening direction so that the air temperature (A-2) detected by the post-cooling hot air temperature detector 27a becomes 250°C, and the flow rate of the condensate flowing through the condensate bypass path 17 is increased (10 t / h → 20 t / h). At this time, the temperature (W-1) of the condensate that has been heat exchanged with the hot air in the hot air cooler 15 becomes 94°C ≦ TC B If the temperature is less than 124°C, the heat recovery condensate flow control valves 20A and 20C are closed and the heat recovery condensate flow control valve 20B is opened, so that the condensate is merged with the outlet side of the second heater 19b.

[0035] <When the air temperature detected by the hot air temperature detector after cooling cannot be adjusted (2)> If the heat transfer performance further deteriorates, the opening of the branch condensate flow control valve 26 is operated in the open direction accordingly, as shown in FIG. 4, to further increase the flow rate of the condensate flowing through the condensate bypass path 17 (20 t / h → 50 t / h). As the flow rate of the condensate flowing through the condensate bypass path 17 increases, the temperature of the condensate from the condensate outlet of the hot air cooler 15 gradually decreases. When the temperature of this condensate (W-1) reaches 59°C or less, B If the temperature is less than 94°C, the heat recovery condensate flow control valves 20B and 20C are closed and the heat recovery condensate flow control valve 20A is opened, so that the condensate is merged with the outlet side of the first heater 19a.

[0036] As described above, according to one embodiment of the present invention, the following systems described in [1] to [5] are provided.

[0037] [1] An extraction-condensing steam turbine (11) having a plurality of extraction stages; a main condensate supply line (16) for supplying condensate from the steam turbine (11) to a boiler; a plurality of heaters (19a to 19c) provided on the main condensate supply passage (16) and configured to preheat the condensate with steam extracted from two or more of the plurality of extraction stages; A system (1) comprising: a condensate bypass path (17) branching from the main condensate supply path (16) and supplying a portion of the condensate to outlet sides of the plurality of heaters (19a to 19c); a branch condensate flow control valve (26) provided in the condensate bypass passage (17); a hot air cooler (15) provided in the condensate bypass passage (17) downstream of the branch condensate flow control valve (26), for heating a portion of the condensate with hot air from a device (50) external to the system (1) and for cooling the hot air; a post-cooling hot air passage (22) connected to the air outlet of the hot air cooler (15); a cooled hot air temperature detector (27a) provided in the cooled hot air passage (22); a hot air bypass path (23a) branching from the pre-cooling hot air path (23) midway through the pre-cooling hot air path (23) connecting the external device (50) and the air inlet of the hot air cooler (15) and joining the post-cooling hot air path (22) downstream of the hot air cooler (15); a hot air bypass passage control valve (20D) provided in the hot air bypass passage (23a) and opened and closed to control opening and closing of the hot air bypass passage (23a); a first control section (24a) that controls opening and closing of the hot air bypass passage control valve (20D) in accordance with a result of detection by the cooled hot air temperature detector (27a); A system having (1).

[0038] In this manner, the hot air bypass path (23a) is provided in the pre-cooling hot air path (23) connecting the external device (50) and the air inlet of the hot air cooler (15), branching from the pre-cooling hot air path (23) midway and joining the post-cooling hot air path (22) downstream of the hot air cooler (15). The hot air bypass path (23a) is provided with the hot air bypass path control valve (20D). The first control unit (24a) controls the opening and closing of the hot air bypass path control valve (20D) in accordance with the detection result of the post-cooling hot air temperature detector (27a). This makes it possible to maintain the temperature of the primary air at a predetermined value and avoid a decrease in the thermal efficiency of the steam turbine (11) even if the heat transfer performance of the hot air cooler (15) decreases.

[0039] [2] The condensate bypass passage (17) includes an upstream condensate bypass passage (17a) in which the hot air cooler (15) is provided, and a downstream condensate bypass passage (17b) connecting the hot air cooler (15) and outlet sides of the plurality of heaters (19a to 19c), the downstream condensate bypass channel (17b) has a plurality of branch flow channels (18a-18c) branching toward the plurality of heaters (19a-19c) and connected to outlet sides of the plurality of heaters (19a-19c), a heat recovery condensate flow rate control valve (20A-20C) is provided in each of the plurality of branch flow paths (18a-18c), The system (1) a heat recovery condensate temperature detector (27b) for detecting the temperature of the heat recovery condensate at a condensate outlet side of the hot air cooler (15); a plurality of heater outlet temperature detectors (21a to 21c) for detecting outlet temperatures of the plurality of heaters (19a to 19c), respectively; a second control unit (24b) that controls opening and closing of the plurality of heat recovery condensate flow rate control valves (20A to 20C) so that the heat recovery condensate heated by the hot air cooler (15) is supplied to any one of the outlet sides of the plurality of heaters (19a to 19c), The first control section (24a) further controls the aperture of the branch condensate flow control valve (26) so that the temperature of the air discharged from the hot air cooler (15) and detected by the cooled hot air temperature detector (27a) becomes a preset value; The second control unit (24b) compares the detected temperature of the heat recovery condensate with the outlet temperatures of the plurality of heaters (19a to 19c), and, depending on the comparison result, selects a heater from the plurality of heaters (19a to 19c) that has an outlet temperature that is closest to the temperature of the heat recovery condensate and lower than the temperature of the heat recovery condensate, and controls apertures of the plurality of heat recovery condensate control valves (20A to 20C) so as to supply the heat recovery condensate to the outlet of the selected heater.

[0040] According to the invention described in [2] above, even if the heat transfer performance of the hot air cooler (15) is further degraded, it is possible to avoid a decrease in the thermal efficiency of the steam turbine (11).

[0041] [3] The system according to [1] or [2], further comprising a generator (12) connected to the steam turbine (11).

[0042] [4] The system according to [1] or [2], wherein the external device (50) of the system (1) is a regenerative air preheater.

[0043] [5] The system according to [1] or [2], further comprising a pulverizer (40) for pulverizing fuel supplied to the boiler. [Explanation of symbols]

[0044] 1. Power generation system 11 Steam turbine 12. Generator 13 Condenser 14 Condensate pump 15 Hot air cooler 16 Main condensate supply line 17 Condensate bypass 17a Upstream bypass 17b Downstream bypass route 18a~18c Branch flow path 19a~19c 1st~3rd heater 20A~20C Heat recovery condensate flow control valve 20D Hot air bypass control valve 21a to 21c First to third heater outlet temperature detectors 22 Post-cooling hot air path 23 Pre-cooling hot air path 23a Hot air bypass 24a First Control Section 24b Second control section 25 Deaerator liquid level control valve 26 Branch condensate flow control valve 27a Post-cooling hot air temperature detector 27b Heat recovery condensate temperature detector 40 Crusher 50 Regenerative Air Preheater (GAH)

Claims

1. an extraction-condensing steam turbine having a plurality of extraction stages; a main condensate supply line for supplying condensate from the steam turbine to a boiler; a plurality of heaters provided on the main condensate supply line, the heaters preheating the condensate with steam extracted from two or more of the plurality of extraction stages; A system comprising: a condensate bypass passage branching from the main condensate supply passage and supplying a portion of the condensate to outlet sides of the plurality of heaters; a branch condensate flow rate control valve provided in the condensate bypass passage; a hot air cooler that is provided in the condensate bypass path downstream of the branch condensate flow control valve and that heats a portion of the condensate using hot air from an external device of the system and cools the hot air; a post-cooling hot air passage connected to an air outlet of the hot air cooler; a cooled hot air temperature detector provided in the cooled hot air path; a hot air bypass path that branches off from the pre-cooling hot air path midway through the pre-cooling hot air path connecting the external device and the air inlet of the hot air cooler and joins the post-cooling hot air path downstream of the hot air cooler; a hot air bypass passage control valve provided in the hot air bypass passage and opened and closed to control opening and closing of the hot air bypass passage; a first control unit that controls opening and closing of the hot air bypass passage control valve in accordance with a detection result of the cooled hot air temperature detector; A system having:

2. the condensate bypass passage includes an upstream condensate bypass passage in which the hot air cooler is provided, and a downstream condensate bypass passage connecting the hot air cooler and outlet sides of the plurality of heaters, the downstream condensate bypass passage has a plurality of branch flow passages that branch toward the plurality of heaters and are connected to outlet sides of the plurality of heaters, a heat recovery condensate flow rate control valve is provided in each of the plurality of branch flow paths; The system comprises: a heat recovery condensate temperature detector that detects the temperature of the heat recovery condensate at a condensate outlet side of the hot air cooler; a plurality of heater outlet temperature detectors that detect outlet temperatures of the plurality of heaters, respectively; a second control unit that controls opening and closing of the plurality of heat recovery condensate flow rate control valves so as to supply the heat recovery condensate heated by the hot air cooler to any one of the outlet sides of the plurality of heaters; the first control unit further controls an opening degree of the branch condensate flow control valve so that the temperature of the hot air discharged from the hot air cooler and detected by the cooled hot air temperature detector becomes a preset value; 2. The system according to claim 1, wherein the second control unit compares the detected temperature of the heat recovery condensate with the outlet temperatures of the plurality of heaters, and, depending on the comparison result, selects a heater from the plurality of heaters that has an outlet temperature that is closest to the temperature of the heat recovery condensate and lower than the temperature of the heat recovery condensate, and controls the apertures of the plurality of heat recovery condensate control valves so as to supply the heat recovery condensate to the outlet of the selected heater.

3. The system of claim 1 or 2, further comprising a generator connected to the steam turbine.

4. 3. The system of claim 1 or 2, wherein the device external to the system is a regenerative air preheater.

5. 3. The system of claim 1, further comprising a pulverizer for pulverizing fuel supplied to the boiler.

Images