Thermal power generating unit low-load feed water heating system based on steam leakage sensible heat distributed heat storage

Abstract

The invention discloses a thermal power generating unit low-load feed water heating system based on steam leakage sensible heat distributed heat storage. The thermal power generating unit low-load feed water heating system comprises a steam power circulation loop and at least one stage of heat storage circulation loop. Steam leakage sensible heat or steam extraction sensible heat of a steam turbine in the steam power circulation loop is stored in the heat storage circulation loop, when the system is in low-load operation, the heat stored in the heat storage circulation loop is used for heating feed water at the corresponding temperature grade in the steam power circulation loop, and the heat of steam leakage is utilized in a gradient mode according to the temperature grade. The utilization efficiency of the heat of the leaked steam is improved, and the latent heat of the leaked steam of the steam turbine is still utilized by the deaerator in the steam power circulation loop; according to the method, the heat of leaked steam of the steam turbine can be efficiently utilized, the boiler feed water temperature during low-load operation of the unit is increased, the boiler operation working condition is stabilized, the coal consumption rate of boiler operation is reduced, and normal operation of a denitration SCR system is guaranteed, so that the aim of improving the economical efficiency and environmental protection performance of the thermal power unit during low load is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal power generation, and in particular relates to a low-load feedwater heating system for a thermal power unit based on steam leakage sensible heat distributed heat storage. Technical Background

[0002] Currently, many thermal power plants operate at low load, with some units even operating at ultra-low load. However, during low-load operation, the unit's coal consumption rate increases significantly, making stable operation difficult. Therefore, addressing the stability and economic efficiency of low-load operation is a key issue in the current development of thermal power technology. Research on low-load operation in thermal power plants has primarily focused on boiler combustion stability, including technical measures such as boiler modifications and low-load heat storage to indirectly increase boiler load. However, when a unit operates at low load, not only does the boiler's operating conditions significantly deteriorate, but the operation of the steam-water system, represented by the turbine, condenser, and regenerator, also deteriorates. For example, during low-load operation, the turbine inlet steam pressure and extraction pressure at all stages decrease, leading to a decrease in the extraction steam saturation temperature. This in turn reduces the regenerator's ability to adequately heat the feedwater, ultimately causing a drop in boiler inlet water temperature. This reduces the boiler's average heat absorption stability, increases the coal consumption rate, and reduces the boiler's flue gas temperature, causing the denitrification SCR system to malfunction, seriously impacting the boiler's environmental performance.

[0003] Even with sealed structures, significant steam leakage still occurs in thermal power plants, such as at the valve stem and shaft ends of the turbine. Traditionally, this leaked steam is captured and transferred to the deaerator. However, due to the high superheat of this leaked steam, its temperature far exceeds the deaerator's, resulting in a significant heat exchange temperature difference, which means the sensible heat of the leaked steam is not effectively utilized. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to propose a low-load feed water heating system for thermal power units based on distributed heat storage of sensible heat of steam leakage. By storing the sensible heat of steam leakage or extraction steam in a heat storage circulation loop, when the system is in a low-load period, the heat in the heat storage circulation loop is used to heat the feed water of the corresponding temperature level, while the latent heat of steam leakage from the turbine is still utilized by the deaerator; the present invention follows the principle of "temperature matching and cascade utilization" to efficiently utilize the heat of steam leakage from the turbine, thereby increasing the boiler feed water temperature when the unit is running at low load, stabilizing the boiler operating conditions, reducing the coal consumption rate of boiler operation, and ensuring the normal operation of the denitrification SCR system, thereby achieving the purpose of improving the economy and environmental protection of the thermal power unit at low load, and has important engineering practice value.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A low-load feedwater heating system for a thermal power unit based on distributed heat storage of sensible heat from steam leakage, comprising a steam power circulation loop and at least one stage of heat storage circulation loop;

[0007] The steam power cycle loop includes a boiler 1, the steam outlet of the boiler 1 is connected to the inlet of the steam turbine 2, and the extraction steam outlet of the steam turbine 2 is respectively connected to the steam inlets of the high-pressure heater group 9, the deaerator 7, and the low-pressure heater group 6; the power output shaft of the steam turbine 2 is connected to the power input shaft of the generator 3, driving the generator 3 to generate electricity; the exhaust steam outlet of the steam turbine 2 is connected to the hot side inlet of the condenser 4, the hot side outlet of the condenser 4 is connected to the feed water inlet of the low-pressure regenerator group 6 through the condensate pump 5, the feed water outlet of the low-pressure regenerator group 6 is connected to the feed water inlet of the deaerator 7, the feed water outlet of the deaerator 7 is connected to the feed water inlet of the high-pressure regenerator group 9 through the feed water pump 8, and the feed water outlet of the high-pressure regenerator group 9 is connected to the feed water inlet of the boiler 1, realizing a steam power cycle;

[0008] The heat storage circulation loop includes a high-temperature heat exchanger group 10, a high-temperature heat storage tank 11, a high-temperature pump 12, a low-temperature heat exchanger group 13, a low-temperature heat storage tank 14 and a low-temperature pump 15;

[0009] In the energy storage mode, the steam outlet of the steam turbine 2 is connected to the steam inlet of the high-temperature heat exchanger group 10, and the steam outlet of the high-temperature heat exchanger group 10 is connected to the steam inlet of the deaerator 7; the outlet of the low-temperature heat storage tank 14 is connected to the heat storage medium inlet of the high-temperature heat exchanger group 10 through the low-temperature pump 15, and the heat storage medium outlet of the high-temperature heat exchanger group 10 is connected to the inlet of the high-temperature heat storage tank 11; the sensible heat of the steam from the steam turbine 2 is transferred to the heat storage medium of the high-temperature heat exchanger group 10, and the heat storage medium after absorbing heat is stored in the high-temperature heat storage tank 11;

[0010] In the energy release mode, several high-pressure regenerators of the high-pressure regenerator group 9 are connected in parallel with the low-temperature heat exchanger group 13; the outlet of the high-temperature heat storage tank 11 is connected to the heat storage medium inlet of the low-temperature heat exchanger group 13 through the high-temperature pump 12, and the heat storage medium outlet of the low-temperature heat exchanger group 13 is connected to the inlet of the low-temperature heat storage tank 14. The heat in the high-temperature heat storage tank 11 is transferred to the feed water at the inlet of the high-pressure regenerator group 9 through the low-temperature heat exchanger group 13, and then the heat storage medium after heat release is stored in the low-temperature heat storage tank 14 to realize the heat storage cycle.

[0011] The system also includes a heat storage circulation loop as a front heat storage circulation loop, the water feed outlet of the high-pressure heat regenerator group 9 is connected to the water feed inlet of the low-temperature heat exchanger group 13 of the front heat storage circulation loop, and the water feed outlet of the low-temperature heat exchanger group 13 of the front heat storage circulation loop is connected to the water feed inlet of the boiler 1.

[0012] In the heat storage cycle, the steam used is leakage steam from the steam turbine 2 or combined steam from leakage steam from the steam turbine 2 and extraction steam.

[0013] The steam leakage is steam leaking from the valve stem and shaft end of the steam turbine 2.

[0014] In the front heat storage circulation loop, the steam used is the extraction steam of the steam turbine 2.

[0015] The heat storage medium is one of heat-conducting oil, phase change material, and molten salt.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention proposes a low-load feedwater heating system for thermal power generation units based on distributed heat storage of sensible heat from steam leakage. The system consists of a steam power cycle and a heat storage cycle. Based on the characteristics of steam leakage in the steam power cycle, the sensible heat of steam leaking from locations such as the turbine valve stem and shaft end is stored in the heat storage cycle and used to heat the feedwater during low-load operation, thereby improving the low-load performance of the thermal power generation system. The sensible heat of steam or sensible heat of extraction steam leaking from locations such as the turbine valve stem and shaft end is distributedly stored in the heat storage cycle, while its latent heat is utilized by the deaerator. During periods of low system load, the heat in the heat storage cycle is used to heat feedwater of the corresponding temperature level. Therefore, the heat from the steam leakage is utilized in a tiered manner according to the temperature level, improving the efficiency of the heat from the leakage. For thermal power generation systems, the present invention increases the boiler feed water inlet temperature when the unit is running at low load, stabilizes the boiler operating conditions, reduces the coal consumption rate of the boiler, ensures the normal operation of the denitrification SCR system, and thus improves the economy and environmental protection of the thermal power unit at low load, which has important engineering practice value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural schematic diagram of a low-load feedwater heating system for a thermal power unit based on steam leakage sensible heat distributed heat storage in Example 1.

[0019] Figure 2 This is a structural schematic diagram of a low-load feedwater heating system for a thermal power unit based on steam leakage sensible heat distributed heat storage in Example 2.

[0020] Figure 3 This is a structural schematic diagram of a low-load feedwater heating system for a thermal power unit based on steam leakage sensible heat distributed heat storage in Example 3.

[0021] In the figure: boiler 1, steam turbine 2, generator 3, condenser 4, condensate pump 5, low-pressure regenerator group 6, deaerator 7, feed water pump 8, high-pressure regenerator group 9, high-temperature heat exchanger group 10, high-temperature heat storage tank 11, high-temperature pump 12, low-temperature heat exchanger group 13, low-temperature heat storage tank 14, low-temperature pump 15. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings, which are intended to explain rather than limit the present invention.

[0023] Example 1

[0024] like Figure 1 As shown, a low-load feedwater heating system for thermal power units based on steam leakage sensible heat distributed heat storage includes a steam power circulation loop and a primary heat storage circulation loop.

[0025] The steam power cycle includes a boiler 1, a steam turbine 2, a generator 3, a condenser 4, a condensate pump 5, a low-pressure regenerator group 6, a deaerator 7, a feed water pump 8, and a high-pressure regenerator group 9; the steam outlet of the boiler 1 is connected to the inlet of the steam turbine 2, and the steam extraction outlet of the steam turbine 2 is respectively connected to the steam inlets of the high-pressure heater group 9, the deaerator 7, and the low-pressure heater group 6; the power output shaft of the steam turbine 2 is connected to the power input shaft of the generator 3 to drive the generator 3 to generate electricity; the exhaust steam of the steam turbine group 2 is connected to the power input shaft of the generator 3 to drive the generator 3 to generate electricity; The outlet is connected to the hot side inlet of the condenser 4, the hot side outlet of the condenser 4 is connected to the feed water inlet of the condensate pump 5, the feed water outlet of the condensate pump 5 is connected to the feed water inlet of the low-pressure regenerator group 6, the feed water outlet of the low-pressure regenerator group 6 is connected to the feed water inlet of the deaerator 7, the feed water outlet of the deaerator 7 is connected to the feed water inlet of the feed water pump 8, the feed water outlet of the feed water pump 8 is connected to the feed water inlet of the high-pressure regenerator group 9, and the feed water outlet of the high-pressure regenerator group 9 is connected to the feed water inlet of the boiler 1, realizing the steam power cycle.

[0026] The heat storage circulation loop includes a high-temperature heat exchanger group 10, a high-temperature heat storage tank 11, a high-temperature pump 12, a low-temperature heat exchanger group 13, a low-temperature heat storage tank 14 and a low-temperature pump 15. In the energy storage mode, the steam outlet of the steam turbine 2 is connected to the steam inlet of the high-temperature heat exchanger group 10, and the steam outlet of the high-temperature heat exchanger group 10 is connected to the steam inlet of the deaerator 7; the outlet of the low-temperature heat storage tank 14 is connected to the inlet of the low-temperature pump 15, and the outlet of the low-temperature pump 15 is connected to the heat storage medium inlet of the high-temperature heat exchanger group 10, and the heat storage medium outlet of the high-temperature heat exchanger group 10 is connected to the inlet of the high-temperature heat storage tank 11. The high-temperature heat storage medium after absorbing heat is stored in the high-temperature heat storage tank 11, and the sensible heat of the steam of the steam turbine 2 is transferred to the high-temperature heat exchanger group 10. and stored in the heat storage medium of the high-temperature heat storage tank 11; in the energy release mode, the high-pressure regenerator group 9 is connected in parallel with the low-temperature heat exchanger group 13, that is, the outlet of the feed water pump 8 is connected to the feed water inlet of the low-temperature heat exchanger group 13, and the feed water outlet of the low-temperature heat exchanger group 13 is connected to the inlet of the boiler 1; the outlet of the high-temperature heat storage tank 11 is connected to the inlet of the high-temperature pump 12, the outlet of the high-temperature pump 12 is connected to the heat storage medium inlet of the low-temperature heat exchanger group 13, and the heat storage medium outlet of the low-temperature heat exchanger group 13 is connected to the inlet of the low-temperature heat storage tank 14, and the heat in the high-temperature heat storage tank 11 is transferred to the feed water at the inlet of the high-pressure regenerator group 9 through the low-temperature heat exchanger group 13, and then the heat storage medium after heat release is stored in the low-temperature heat storage tank 14, realizing a heat storage cycle.

[0027] The working medium flow of the steam power cycle in this embodiment 1 is as follows: the feed water is heated to steam in the boiler 1, and then enters the steam turbine 2 to expand step by step to low-pressure steam; part of the steam in the steam turbine 2 is extracted at different pressure levels and used to heat the feed water in the low-pressure regenerator group 6, the deaerator 7, and the high-pressure regenerator group 9; the steam discharged after the steam turbine 2 completes all the expansion work enters the hot side pipe of the condenser 4, exchanges heat with the circulating cooling water flowing in the cold side pipe of the condenser 4, and is condensed into liquid water; the condensed liquid water is pressurized by the condensate pump 5, enters the low-temperature regenerator group 6 for heating, and then enters the deaerator 7 for heating and deoxygenation, and then the feed water is further pressurized in the feed water pump 8, enters the high-pressure regenerator group 9 for heating, and finally enters the boiler 1 to be heated to steam.

[0028] When the system is under high load, steam leaking from the valve stem, shaft end and other positions of the steam turbine 2 is transported to the high-temperature heat exchanger group 10, and the sensible heat of the leaking steam is transferred to the heat storage medium of the high-temperature heat exchanger group 10. The steam after the leaking steam is cooled enters the deaerator 7; when the system is under low load, part of the feed water entering the high-pressure regenerator group 9 is transported to the low-temperature heat exchanger group 13 to be heated, and then enters the boiler 1 to be heated into steam; when the amount of steam leaking from the valve stem, shaft end and other positions of the steam turbine 2 is insufficient, energy storage can be achieved by combining the extraction and leakage of the steam turbine 2; the valve stem of the steam turbine 2 is the main steam valve and the regulating valve, and its shaft end can be the high and low pressure shaft seals of the steam turbine 2.

[0029] The working medium flow of the heat storage cycle in this embodiment 1 is as follows: in the energy storage mode, the heat storage medium stored in the low-temperature heat storage tank 14 is pressurized by the low-temperature pump 15 and enters the high-temperature heat exchanger group 10, where it exchanges heat with the sensible heat of the leakage steam in the high-temperature heat exchanger group 10. The heat storage medium after absorbing heat is stored in the high-temperature heat storage tank 11; in the energy release mode, the heat storage medium stored in the high-temperature heat storage tank 11 is pressurized by the high-temperature pump 12 and enters the low-temperature heat exchanger group 13, where it exchanges heat with the feed water in the low-temperature heat exchanger group 13. The heat storage medium after releasing heat is stored in the low-temperature heat storage tank 14.

[0030] The heat storage medium can be selected from different substances such as heat transfer oil, phase change material, molten salt, etc. according to specific operating parameters; the phase change material can be water;

[0031] Example 2

[0032] This embodiment adds at least one stage of heat storage circulation loop on the basis of Embodiment 1 to form a multi-stage heat storage circulation loop; in the energy release mode, the several high-pressure regenerators of the high-pressure regenerator group 9 are connected in parallel with the low-temperature heat exchanger group 13 in the multi-stage heat storage circulation loop.

[0033] In this embodiment, any number of heat storage stages can be set according to engineering needs. Here, only a two-stage heat storage cycle loop is used as an example for description.

[0034] like Figure 2 As shown, the two-stage heat storage loop is connected in parallel to the two high-pressure regenerators in the high-pressure regenerator group 9. When the system is at low load, according to the principle of "temperature matching and cascade utilization," the feed water temperature level is higher the closer to the boiler 1. Therefore, the first-stage heat storage loop is connected in parallel to the high-pressure regenerator of the high-pressure regenerator group 9 close to the boiler 1, and the second-stage heat storage loop is connected in parallel to the high-pressure regenerator of the high-pressure regenerator group 9 farthest from the boiler 1.

[0035] When sufficient steam is leaking from the valve stem, shaft end, and other locations of steam turbine 2, the first-stage heat storage loop utilizes the sensible heat of steam leakage from the valve stem of the higher-pressure turbine 2 to heat feedwater at a higher temperature. The second-stage heat storage loop utilizes the sensible heat of steam leakage from the shaft end of the lower-pressure turbine 2 to heat feedwater at a lower temperature. The heat from steam leakage from steam turbine 2 is utilized in a tiered manner, based on temperature level. When insufficient steam is leaking from the valve stem, shaft end, and other locations of steam turbine 2, energy storage can be achieved through a combination of steam extraction and leakage from steam turbine 2.

[0036] The use of a multi-stage heat storage circulation loop can more reasonably utilize the sensible heat of the steam leakage from the turbine, and more fully heat the feed water, reduce the heat exchange temperature difference of the system, and improve the economy of the system.

[0037] Example 3

[0038] like Figure 3 As shown, this embodiment adds a heat storage circulation loop as a front heat storage circulation loop on the basis of Example 2; in the energy release mode, the water outlet of the high-pressure regenerator group 9 is connected to the water inlet of the low-temperature heat exchanger group 13 of the front heat storage circulation loop, and the water outlet of the low-temperature heat exchanger group 13 of the front heat storage circulation loop is connected to the water inlet of the boiler 1.

[0039] When the system is under low load, the high-pressure regenerator group 9 and its parallel heat storage circuit may not be able to heat the feed water to the set temperature. Therefore, a preheat storage circuit is set up between the outlet of the high-pressure regenerator group 9 and the inlet of the boiler 1, connected in cascade. This preheat storage circuit uses the sensible heat of the steam extraction from the steam turbine 2 to further heat the feed water of the boiler 1, thereby increasing the feed water inlet temperature of the boiler 1, reducing the coal consumption rate of the boiler 1, and ensuring the normal operation of the denitration SCR system.

Claims

1. A low-load feedwater heating system for thermal power units based on steam leakage sensible heat distributed heat storage, characterized in that: It includes a steam power cycle loop and at least one heat storage cycle loop; The steam power cycle loop comprises a boiler (1), the steam outlet of the boiler (1) is connected to the inlet of the steam turbine (2), the extraction steam outlet of the steam turbine (2) is respectively connected to the steam inlets of the high-pressure heater group (9), the deaerator (7), and the low-pressure heater group (6); the power output shaft of the steam turbine (2) is connected to the power input shaft of the generator (3), driving the generator (3) to generate electricity; the exhaust steam outlet of the steam turbine (2) is connected to the hot side inlet of the condenser (4), the hot side outlet of the condenser (4) is connected to the feed water inlet of the low-pressure regenerator group (6) through a condensate pump (5), the feed water outlet of the low-pressure regenerator group (6) is connected to the feed water inlet of the deaerator (7), the feed water outlet of the deaerator (7) is connected to the feed water inlet of the high-pressure regenerator group (9) through a feed water pump (8), and the feed water outlet of the high-pressure regenerator group (9) is connected to the feed water inlet of the boiler (1), thereby realizing a steam power cycle; The heat storage circulation loop comprises a high-temperature heat exchanger group (10), a high-temperature heat storage tank (11), a high-temperature pump (12), a low-temperature heat exchanger group (13), a low-temperature heat storage tank (14) and a low-temperature pump (15); In the energy storage mode, the steam outlet of the steam turbine (2) is connected to the steam inlet of the high-temperature heat exchanger group (10), and the steam outlet of the high-temperature heat exchanger group (10) is connected to the steam inlet of the deaerator (7); the outlet of the low-temperature heat storage tank (14) is connected to the heat storage medium inlet of the high-temperature heat exchanger group (10) through a low-temperature pump (15), and the heat storage medium outlet of the high-temperature heat exchanger group (10) is connected to the inlet of the high-temperature heat storage tank (11); the sensible heat of the steam of the steam turbine (2) is transferred to the heat storage medium of the high-temperature heat exchanger group (10), and the heat storage medium after absorbing heat is stored in the high-temperature heat storage tank (11); In the energy release mode, several high-pressure regenerators of the high-pressure regenerator group (9) are connected in parallel with the low-temperature heat exchanger group (13); the outlet of the high-temperature heat storage tank (11) is connected to the heat storage medium inlet of the low-temperature heat exchanger group (13) through the high-temperature pump (12), and the heat storage medium outlet of the low-temperature heat exchanger group (13) is connected to the inlet of the low-temperature heat storage tank (14), and the heat in the high-temperature heat storage tank (11) is transferred to the feed water at the inlet of the high-pressure regenerator group (9) through the low-temperature heat exchanger group (13), and then the heat storage medium after heat release is stored in the low-temperature heat storage tank (14), thereby realizing a heat storage cycle.

2. The low-load feedwater heating system for thermal power units according to claim 1, characterized in that: The system also includes a primary heat storage circulation loop, which serves as a front heat storage circulation loop. The water outlet of the high-pressure regenerator group (9) is connected to the water inlet of the low-temperature heat exchanger group (13) of the front heat storage circulation loop, and the water outlet of the low-temperature heat exchanger group (13) of the front heat storage circulation loop is connected to the water inlet of the boiler (1).

3. The low-load feedwater heating system for a thermal power plant according to claim 1, characterized in that: In the heat storage circulation loop, the steam used is leakage steam from the steam turbine (2) or combined steam from leakage steam and extraction steam from the steam turbine (2).

4. The low-load feedwater heating system for a thermal power unit according to claim 3, characterized in that: The steam leakage is steam leaking from the valve stem and shaft end of the steam turbine (2).

5. The low-load feedwater heating system for a thermal power plant according to claim 2, characterized in that: In the front heat storage circulation loop, the steam used is the extraction steam of the steam turbine (2).

6. The low-load feedwater heating system for a thermal power plant according to claim 1, characterized in that: The heat storage medium is one of heat-conducting oil, phase change material, and molten salt.

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