A low load extraction heating device and method for a boiler-turbine system

Abstract

The application relates to a low-load steam extraction heat supply device and method for a one-furnace two-machine system, which comprises a boiler device, a first steam turbine unit, a second steam turbine unit, a first feedwater regenerative device and a second feedwater regenerative device. The device supplies two steam turbine units through a single boiler device, and realizes steam centralized delivery to a single steam turbine unit at low load and uniform steam supply to both steam turbine units at non-low load through dynamic regulation of a shunt valve, effectively solving the technical problems of steam distribution imbalance and poor heat supply and power generation synergy of the one-furnace two-machine system at low load. Through load adaptive adjustment of the shunt valve, the low-load adaptability and load regulation flexibility of the system are significantly enhanced, the synergy optimization of power generation and heat supply is realized, and the operation reliability and comprehensive energy efficiency of the system are improved.

Description

Technical Field

[0001] This application relates to the field of steam turbine power generation technology, specifically to a low-load steam extraction heating device and method for a boiler-two-turbine system. Background Technology

[0002] In traditional combined heat and power (CHP) systems employing a single boiler-generator configuration, one boiler typically drives one steam turbine, which extracts a portion of the steam from its intermediate-pressure or low-pressure cylinder for heating. While this configuration has matured considerably over time, its inherent decoupling of heat and electricity is increasingly revealing significant technical shortcomings in the face of new power systems and dynamic heating network demands. This is particularly evident under low-load operating conditions, where the contradiction between heating capacity and operational economy becomes a critical bottleneck hindering technological progress and efficiency improvements.

[0003] In traditional cogeneration systems with a single boiler and turbine, heating steam is typically drawn from the connecting pipe between the intermediate-pressure and low-pressure cylinders or from a specific part of the low-pressure cylinder. To ensure normal heating operation, this relies heavily on stable flow conditions and sufficient steam parameter margins within the turbine. However, when grid dispatch requires the unit to reduce its power generation load to accommodate renewable energy consumption or participate in deep peak shaving, the boiler combustion rate is correspondingly reduced, leading to a comprehensive decrease in main steam flow, pressure, and temperature. Consequently, the steam parameters in each stage of the turbine's flow path simultaneously decline, and the pressure and superheat at the extraction port rapidly approach or even fall below the minimum thresholds necessary for the safe and economical operation of the heating network heaters. In this state, if steam extraction is forcibly maintained, the quality of the heating steam cannot be guaranteed. This may not only cause a sharp drop in the efficiency of the heating network heaters and safety problems such as water hammer in the pipelines, but also lead to serious losses due to the underutilization of the steam's work capacity. If steam extraction is stopped, it means the interruption of external heating, which is unacceptable for thermal power plants that undertake basic heating or stable industrial process heat loads. In addition, it is usually necessary to start the backup electric or gas boilers, resulting in extremely high operating costs.

[0004] Current technologies primarily employ either "capacity expansion" or "source expansion" approaches. For example, during the planning phase, larger capacity units are selected to ensure sufficient steam extraction capacity during low loads, but this leads to long-term inefficient operation and poor economic performance. Alternatively, additional independent heat sources such as gas-fired boilers or power plant boilers are configured as peak-shaving backups, increasing system complexity and investment and operating costs. These solutions are all passive adaptations that fail to fundamentally resolve the contradiction between heating capacity and operational economics in combined heat and power (CHP), and are accompanied by high costs.

[0005] Therefore, in order to address the above problems, there is an urgent need for a low-load extraction steam heating system that can significantly broaden the low-load heating operation window of cogeneration units under the premise of low cost and low complexity, so as to solve the shortcomings of existing technologies. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this application provides a low-load steam extraction heating device and method for a boiler-two-turbine system, specifically adopting the following technical solution:

[0007] A low-load steam extraction heating device for a boiler-two-turbine system, the device comprising a boiler unit, a first steam turbine unit, a second steam turbine unit, a first feedwater regeneration device, and a second feedwater regeneration device. The boiler unit includes a first steam supply passage for providing superheated steam and a second steam supply passage for providing reheated steam; the superheated steam generated by the first steam supply passage is distributed to the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit via a first diverter valve; the exhaust steam of the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit is merged into the second steam supply passage via a first merging valve; The reheat steam generated by the second steam supply passage is distributed to the intermediate pressure cylinder of the first turbine unit and the intermediate pressure cylinder of the second turbine unit via the second diversion valve; The exhaust steam from the intermediate-pressure cylinder of the first turbine unit is distributed to the low-pressure cylinder of the first turbine unit and the first heating user via the first heating extraction valve. The exhaust steam from the low-pressure cylinder of the first turbine unit and the return medium from the first heating user are combined into the first condenser. After being condensed by the first condenser, the steam is introduced into the first feedwater regeneration device. The exhaust steam from the intermediate-pressure cylinder of the second turbine unit is distributed to the low-pressure cylinder of the second turbine unit and the second heating user via the second heating extraction valve. The exhaust steam from the low-pressure cylinder of the second turbine unit and the return medium from the second heating user are combined into the second condenser. After being condensed by the second condenser, the steam is introduced into the second feedwater regeneration device. The return medium from the first feedwater reheating device and the second feedwater reheating device merges through the second confluence valve and enters the first steam supply passage.

[0008] Optionally: The first steam supply passage includes an economizer, a water-cooled wall, a low-temperature superheater, a screen-type superheater, and a high-temperature superheater connected in sequence. The return medium of the first feedwater reheating device and the second feedwater reheating device is combined through the second confluence valve and then fed into the economizer. The return medium passes through the economizer and the water-cooled wall in sequence to absorb heat and evaporate, generating saturated steam. The saturated steam flows through the low-temperature superheater, the screen-type superheater, and the high-temperature superheater in sequence to be heated, generating superheated steam under high temperature and high pressure.

[0009] Optionally: The second steam supply passage includes a low-temperature reheater and a high-temperature reheater. The exhaust steam from the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit is introduced into the low-temperature reheater through the first confluence valve for initial heating, and then introduced into the high-temperature reheater for secondary heating to generate reheated steam.

[0010] Optionally: The first feedwater reheating device includes a first low-pressure heater, a first deaerator, and a first high-pressure heater; the first condenser is connected to the first low-pressure heater, the reflux medium of the first condenser is heated once by the first low-pressure heater, and the heating steam of the first low-pressure heater is extracted through the intermediate-pressure cylinder and low-pressure cylinder of the first turbine unit; the first deaerator heats the reflux medium of the first condenser a second time, and the heating steam of the first deaerator is extracted through the intermediate-pressure cylinder of the first turbine unit; a first feedwater pump is provided between the first deaerator and the first high-pressure heater, the reflux medium of the first condenser is pressurized by the first feedwater pump and then introduced into the first high-pressure heater; the first high-pressure heater heats the reflux medium of the first condenser a third time, and the heating steam of the first high-pressure heater is extracted through the high-pressure cylinder and intermediate-pressure cylinder of the first turbine unit.

[0011] Optionally: The second feedwater reheating device includes a second low-pressure heater, a second deaerator, and a second high-pressure heater; the second condenser is connected to the second low-pressure heater, the reflux medium of the second condenser is heated once by the second low-pressure heater, and the heating steam of the second low-pressure heater is extracted through the intermediate-pressure cylinder and low-pressure cylinder of the second turbine unit; the second deaerator heats the reflux medium of the second condenser a second time, and the heating steam of the second deaerator is extracted through the intermediate-pressure cylinder of the second turbine unit; a second feedwater pump is provided between the second deaerator and the second high-pressure heater, the reflux medium of the second condenser is pressurized by the second feedwater pump and then introduced into the second high-pressure heater; the second high-pressure heater heats the reflux medium of the second condenser a third time, and the heating steam of the second high-pressure heater is extracted through the high-pressure cylinder and intermediate-pressure cylinder of the second turbine unit.

[0012] Optionally, the high-pressure heater and low-pressure heater of the first feedwater reheating device and the second feedwater reheating device both adopt a multi-stage heating structure, and the heating steam temperature of the single-stage heating structure gradually increases along the flow direction of the condenser's return medium.

[0013] Furthermore: the first diversion valve and the second diversion valve respectively allocate the amount of superheated steam and reheated steam entering the first turbine unit and the second turbine unit according to the load operation status of the boiler unit; as the load of the boiler unit decreases, the amount of superheated steam and reheated steam allocated to one of the first turbine unit or the second turbine unit through the first diversion valve and the second diversion valve increases, while the amount of superheated steam and reheated steam entering the other turbine unit decreases.

[0014] Furthermore, this application also discloses a low-load extraction steam heating method for a boiler-two-unit system, which is applied to the aforementioned low-load extraction steam heating device and can control extraction steam heating when the boiler is under low load. The method includes the following steps: Determine whether the boiler unit is in a low-load operation state. The low-load operation state is when the current total load of the boiler unit is lower than a preset evaporation threshold. The preset evaporation threshold is determined based on the rated evaporation capacity of the boiler unit. When it is determined that the boiler unit is operating at low load, steam is concentrated and delivered to one of the first or second turbine units through the first and second diversion valves, while the other turbine unit is shut down or placed in a standby state with extremely low load.

[0015] Furthermore: when it is determined that the boiler unit is not operating at low load, steam is evenly delivered to the first turbine unit and the second turbine unit through the first diversion valve and the second diversion valve.

[0016] Furthermore, the preset evaporation threshold is set to 40%-50% of the rated evaporation capacity of the boiler unit.

[0017] The technical solution of this application achieves the following beneficial effects: The low-load extraction steam heating device of this application provides superheated or reheated steam through a single boiler unit with a dynamic diversion design. This allows for centralized steam delivery to a single turbine unit during low-load conditions, while the other unit is shut down or on standby at extremely low loads. During non-low-load conditions, both units provide uniform steam supply, effectively solving the technical problems of unbalanced steam distribution and poor coordination between heating and power generation under low-load operation of a single boiler and two turbine units. Simultaneously, the device adopts a closed-loop structure with independent extraction steam heating for both units, independent condensers, and a dual feedwater regeneration system. The return medium is combined and returned to the boiler economizer via a confluence valve. Combined with a multi-stage heating structure to match the steam temperature gradient, this ensures the stability and independence of heating and steam supply under low-load conditions, significantly improves feedwater regeneration efficiency and overall system thermal utilization, and reduces energy loss. Through load adaptation adjustment of the diversion valve, it significantly enhances the system's low-load adaptability and load adjustment flexibility, achieving synergistic optimization of power generation and heating, and improving the system's operational reliability and overall energy efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the low-load extraction steam heating device in the embodiments of this application.

[0019] The specific meanings of the reference numerals in the attached figures: Boiler Unit-1, First Steam Turbine Unit-2, First Feedwater Regeneration Unit-3, Second Steam Turbine Unit-4, Second Feedwater Regeneration Unit-5, Water-Cooled Wall-11, Screen-Type Superheater-12, High-Temperature Superheater-13, High-Temperature Reheater-14, Low-Temperature Reheater-15, Low-Temperature Superheater-16, Economizer-17, Air Preheater-18, High-Pressure Cylinder-21, Intermediate-Pressure Cylinder-22, Low-Pressure Cylinder-23, First Condenser-24, First Generator-25; First High-Pressure Heater-31, First Feedwater Pump-32, ... Deaerator-33, First low-pressure heater-34; High-pressure cylinder-41, Medium-pressure cylinder-42, Low-pressure cylinder-43, Second condenser-44, Second generator-45, Second high-pressure heater-51, Second feedwater pump-52, Second deaerator-53, Second low-pressure heater-54, Second combined valve-60, First combined valve-61, First diverter valve-62, Second diverter valve-63, First heating extraction valve-64, Second heating extraction valve-65, First heating user-66, Second heating user-67. Detailed Implementation

[0020] The present application will now be further described with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application and should not be construed as limiting the scope of protection of the present application. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present application.

[0021] Specifically, such as Figure 1 As shown in the figure, this embodiment discloses a low-load extraction steam heating device for a boiler-two-turbine system. Through the system architecture design of a boiler-two-turbine system and the flexible distribution strategy of steam flow, the device concentrates the total load of the boiler under low load to a single steam turbine unit to maintain the normal flow condition of the single unit, thereby ensuring the stable output of qualified heating steam. At the same time, through an independent and symmetrical feedwater regeneration device, the working fluid is efficiently recovered and reused, further improving the energy utilization efficiency of the device.

[0022] Specifically, the low-load extraction steam heating device in this embodiment includes a boiler unit 1, a first steam turbine unit 2, a second steam turbine unit 4, a first feedwater regeneration device 3, and a second feedwater regeneration device 5.

[0023] Boiler unit 1 serves as the heat source for the entire unit. It is equipped with a first steam supply passage and a second steam supply passage. The first steam supply passage is used to generate high-temperature and high-pressure superheated steam, while the second steam supply passage is used to provide reheated steam that meets the steam inlet requirements of the intermediate and low-pressure cylinders of the turbine unit. The two steam supply passages work together to ensure the stable power generation and heating of the turbine unit.

[0024] In this embodiment, the superheated steam generated in the first steam supply passage is distributed via the first diversion valve 62 to the high-pressure cylinder 21 of the first turbine unit 2 and the high-pressure cylinder 41 of the second turbine unit 4. The exhaust steam from the high-pressure cylinder 21 of the first turbine unit 2 and the high-pressure cylinder 41 of the second turbine unit 4 merges via the first confluence valve 61 and enters the second steam supply passage.

[0025] Specifically, the first steam supply passage includes an economizer 17, a water-cooled wall 11, a low-temperature superheater 16, a screen-type superheater 12, and a high-temperature superheater 13 connected sequentially along the medium flow direction. The return medium from the first feedwater regeneration device 3 and the second feedwater regeneration device 5 is combined via the second confluence valve 60 and then fed into the economizer 17. The economizer 17 is a device installed at the lower part of the flue at the tail end of the boiler unit 1 to recover the waste heat of the exhaust gas. It increases the temperature of the medium returning to the boiler unit 1 by exchanging heat with the low-temperature medium from the feedwater regeneration system, while simultaneously reducing the exhaust gas temperature, thus saving energy and improving efficiency. Subsequently, the return medium after heat exchange in the economizer 17 is fed into the water-cooled wall 11 for heat absorption and evaporation. The water-cooled wall 11 is a structure arranged on the inner wall of the boiler unit 1, mainly used to absorb the radiant heat released by the furnace flame and high-temperature flue gas, and to heat the return medium to generate saturated steam.

[0026] In addition, the low-temperature superheater 16 in boiler unit 1 is generally arranged in the horizontal flue, which heats saturated steam into superheated steam, reduces flue gas losses, and improves boiler thermal efficiency. The high-temperature superheater 13 is arranged at the furnace outlet of boiler unit 1, where it further heats the superheated steam into high-temperature and high-pressure superheated steam. The screen-type superheater 12 is arranged above the furnace of boiler unit 1, which also heats saturated steam into superheated steam and reduces the flue gas temperature at the furnace outlet. In this embodiment, saturated steam from the water-cooled wall 11 is sequentially passed through the low-temperature superheater 16, the screen-type superheater 12, and the high-temperature superheater 13 for gradient heating, ultimately generating superheated steam in a high-temperature and high-pressure state. This ensures the parameter stability of the superheated steam and provides a foundation for the efficient operation of the subsequent turbine unit.

[0027] In addition, the boiler unit 1 is equipped with an air preheater 18 at the air inlet channel. The air preheater 18 can exchange heat between the air introduced into the boiler unit 1 and the high-temperature flue gas in the flue, so as to increase the air inlet temperature and improve the boiler efficiency.

[0028] In this embodiment, the reheat steam generated in the second steam supply passage is distributed via the second diversion valve 63 to the intermediate-pressure cylinder 22 of the first turbine unit 2 and the intermediate-pressure cylinder 42 of the second turbine unit 4. The medium in the second steam supply passage originates from the exhaust steam of the high-pressure cylinder 21 of the first turbine unit 2 and the high-pressure cylinder 41 of the second turbine unit 4. After the superheated steam performs work in the high-pressure cylinder of the turbine unit, its temperature decreases to become cold reheat steam. At this time, it is combined and enters the reheater for heating. The exhaust steam of the two turbine units, i.e., the cold reheat steam, can be combined via the first merging valve 61 and enter the second steam supply passage. It is then heated by the reheater and converted into reheat steam with stable parameters, providing a qualified working medium for the subsequent work of the intermediate-pressure cylinder. Specifically, the second steam supply passage includes a low-temperature reheater 15 and a high-temperature reheater 14. The low-temperature reheater 15 is generally located in the tail flue of the boiler unit 1, while the high-temperature reheater 14 is located in the relatively high-temperature horizontal flue within the boiler unit 1. Both reheat the medium by exchanging heat with the high-temperature flue gas through their internal media and absorbing the waste heat of the flue gas. The exhaust steam from the high-pressure cylinder 21 of the first turbine unit 2 and the high-pressure cylinder 41 of the second turbine unit 4 is combined through the first confluence valve 61 and first enters the low-temperature reheater 15 for initial heating. Then, it is reheated in the high-temperature reheater 14 to generate reheated steam suitable for the intermediate and low-pressure cylinders of the turbine unit, thereby realizing the reheat utilization of steam, improving the steam's work capacity in the intermediate and low-pressure cylinders of the turbine unit, and ensuring that the parameters of the exhaust steam from the intermediate-pressure cylinder meet the heating requirements.

[0029] Furthermore, in this embodiment, the first turbine unit 2 and the second turbine unit 4 are the main power generation and heating equipment of the system. They adopt a completely symmetrical structural design and each includes a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder and a condenser. Each is equipped with an independent heating extraction valve. The high-pressure cylinder, intermediate-pressure cylinder and low-pressure cylinder are coaxially connected to jointly drive the generator of the unit to generate electricity. For example, the first turbine unit 2 drives the first generator 25 and the second turbine unit 4 drives the second generator 45, thereby realizing the coordinated operation of power generation and heating, while providing backup protection for the system.

[0030] Specifically, the steam flow and work process within the device in this embodiment is as follows: The first diversion valve 62 can dynamically adjust the distribution ratio of superheated steam from the first steam supply passage to the first turbine unit 2 and the second turbine unit 4 according to the current load of the boiler unit 1, and the steam is fed into the high-pressure cylinder 21 of the first turbine unit 2 and the high-pressure cylinder 41 of the second turbine unit 4. After the superheated steam expands and does work in the high-pressure cylinders of each turbine unit, it forms cold reheated steam, which is then merged through the first confluence valve 61 and enters the second steam supply passage for reheating. The second diversion valve 63 can also dynamically adjust the distribution ratio of reheated steam to the first turbine unit 2 and the second turbine unit 4 according to the current load of the boiler unit 1, and the steam is fed into the intermediate-pressure cylinder 22 of the first turbine unit 2 and the intermediate-pressure cylinder 42 of the second turbine unit 4. The reheated steam continues to expand and do work in the intermediate-pressure cylinder.

[0031] Simultaneously, the exhaust steam from the intermediate-pressure cylinder 22 of the first turbine unit 2 is distributed via the first heating extraction valve 64 to the low-pressure cylinder 23 of the first turbine unit 2 and the first heating user 66. This first heating extraction valve 64 can independently adjust the distribution ratio of the exhaust steam from the intermediate-pressure cylinder to the low-pressure cylinder and the heating user, flexibly adjusting the heating steam volume according to the load demand of the heating user, while ensuring the stability of the internal flow conditions of the turbine unit. At this time, part of the steam drives the low-pressure cylinder to continue working, while the other part of the steam flows to the first heating user 66 for heating. Subsequently, the exhaust steam from the low-pressure cylinder 23 of the first turbine unit 2 and the return medium from the first heating user 66 will converge in the first condenser 24. After condensation in the first condenser 24, the steam is introduced into the first feedwater regeneration device 3 to achieve the recovery of the heating medium.

[0032] Similarly, in this embodiment, the exhaust steam from the intermediate-pressure cylinder 42 of the second turbine unit 4 is distributed via the second heating extraction valve 65 to the low-pressure cylinder 43 of the second turbine unit 4 and the second heating user 67. This second heating extraction valve 65 can also independently adjust the distribution ratio of the exhaust steam from the intermediate-pressure cylinder to the low-pressure cylinder and the heating user, flexibly adjusting the heating steam volume according to the load demand of the heating user, while ensuring the stability of the internal flow conditions of the turbine unit. Subsequently, the exhaust steam from the low-pressure cylinder 43 of the second turbine unit 4 and the return medium from the second heating user 67 will converge in the second condenser 44. After condensation in the second condenser 44, the steam is introduced into the second feedwater regeneration device 5, realizing the recovery of the heating medium.

[0033] In this embodiment, a single boiler unit 1 supplies steam to two turbine units. Due to the symmetrical and independent design of the two turbine units, they can serve as backups for each other. When one unit is unable to operate due to a fault, the other unit can receive all the steam output from the boiler unit 1 through the first diversion valve 62 and the second diversion valve 63, independently completing the tasks of power generation and heating. This effectively avoids the heating interruption problem caused by unit failure in the traditional one-boiler-one-turbine system, improving the reliability of system operation. In addition, in this embodiment, the load of the boiler unit 1 can be dynamically adjusted according to its load status. The adjustment strategies of the first diversion valve 62 and the second diversion valve 63 are deeply correlated with the load of the boiler unit 1. As the load of the boiler unit 1 decreases, the first diversion valve 62 and the second diversion valve 63 simultaneously increase the steam distribution to one turbine unit and decrease the steam distribution to the other unit until most or even all of the steam is concentrated and supplied to a single unit. This adjustment method breaks the rigid binding between the load of the boiler unit 1 and the steam intake of the turbine in the traditional one-boiler-two-turbine system, laying the foundation for stable heating under low load.

[0034] In this embodiment, the first feedwater regeneration device 3 and the second feedwater regeneration device 5 are connected to the condensers of the first turbine unit 2 and the second turbine unit 4, respectively. The return medium of the first feedwater regeneration device 3 and the second feedwater regeneration device 5 enters the first steam supply passage after being combined through the second confluence valve 60. This forms an independent and complete working fluid recovery and reuse loop for the system. Both devices adopt a symmetrical structure design and include a low-pressure heater, a deaerator, a high-pressure heater, and a feedwater pump to achieve stepped heating and pressurization of the condenser return medium, ensuring the feedwater parameters of the boiler unit 1.

[0035] Specifically, in this embodiment, the first feedwater reheating device 3 includes a first low-pressure heater 34, a first deaerator 33, a first high-pressure heater 31, and a first feedwater pump 32. The return medium of the first condenser 24 enters the first low-pressure heater 34, the first deaerator 33, and the first high-pressure heater 31 in sequence along the flow direction to complete the stepped heating, and then enters the first steam supply passage of the boiler device 1 through the second confluence valve 60. It should be noted that in this embodiment, the heating medium of the feedwater reheating device comes from the exhaust steam of the corresponding high, medium, and low pressure cylinders of the turbine unit. The heating steam of the first low-pressure heater 34 is taken from the medium-pressure cylinder 22 and low-pressure cylinder 23 of the first turbine unit 2. The steam temperature at this location is relatively low, which can heat the return medium in the first stage. The heating steam of the first deaerator 33 is taken from the medium-pressure cylinder 22 of the first turbine unit 2. The steam temperature at this location is relatively moderate, which can remove oxygen from the return medium while completing the secondary heating, thus preventing corrosion of the boiler unit 1 and pipelines. The first feedwater pump 32, which is set between the first deaerator 33 and the first high-pressure heater 31, pressurizes the return medium to ensure the pressure requirements of the boiler feedwater. The heating steam of the first high-pressure heater 31 is taken from the high-pressure cylinder 21 and medium-pressure cylinder 22 of the first turbine unit 2. The steam temperature at this location is relatively high, which can complete the tertiary heating of the return medium.

[0036] Similarly, in this embodiment, the second feedwater reheating device 5 includes a second low-pressure heater 54, a second deaerator 53, a second high-pressure heater 51, and a second feedwater pump 52. The return medium of the second condenser 44 enters the second low-pressure heater 54, the second deaerator 53, and the second high-pressure heater 51 in sequence along the flow direction to complete the stepped heating, and then enters the first steam supply passage of the boiler device 1 through the second confluence valve 60. It should be noted that the heating medium of the feedwater reheating device in this embodiment also comes from the exhaust steam of the corresponding high, medium and low pressure cylinders of the turbine unit. The heating steam of the second low pressure heater 54 is taken from the medium pressure cylinder 42 and low pressure cylinder 43 of the second turbine unit 4. The steam temperature at this location is relatively low, which can heat the return medium in the first stage. The heating steam of the second deaerator 53 is taken from the medium pressure cylinder 42 of the second turbine unit 4. The steam temperature at this location is relatively medium, which can remove oxygen from the return medium while completing the secondary heating, thus avoiding corrosion of the boiler unit 1 and pipelines. The second feedwater pump 52, which is set between the second deaerator 53 and the second high pressure heater 51, pressurizes the return medium to ensure the pressure requirements of the boiler feedwater. The heating steam of the second high pressure heater 51 is taken from the high pressure cylinder 41 and medium pressure cylinder 42 of the second turbine unit 4. The steam temperature at this location is relatively high, which can complete the tertiary heating of the return medium.

[0037] Furthermore, in this embodiment, the high-pressure heater and low-pressure heater of the first feedwater regeneration device 3 and the second feedwater regeneration device 5 both adopt a multi-stage heating structure. Along the flow direction of the condenser return medium, the heating steam temperature of the single-stage heating structure gradually increases. This design realizes the priority utilization of low-grade heating steam, reduces the energy loss of high-grade steam, and improves the regeneration efficiency of the working fluid. At the same time, when the system is under low load, the feedwater pump increases the pressure to ensure that the steam pressure, temperature and other parameters at the boiler outlet are maintained at a high level, thus ensuring the stability of the steam parameters.

[0038] Furthermore, this embodiment also discloses a low-load steam extraction heating method for a boiler-two-unit system. This method can be used in the aforementioned low-load steam extraction heating device to control steam extraction heating when the boiler unit 1 is under low load. This method differentiates steam distribution based on the load state of the boiler unit 1, and is divided into two implementation scenarios: normal load operation and low load operation. Generally, the low load operation state is when the current total load of the boiler unit 1 is lower than a preset evaporation threshold, while the normal load operation state is when the current total load of the boiler unit 1 is higher than or equal to the preset evaporation threshold. In this embodiment, the preset evaporation threshold is generally 40%-50% of the rated evaporation capacity of the boiler system. When the current total load of the boiler is lower than this threshold, it is determined to be a low-load operation state. The specific steps include: First, determine whether boiler unit 1 is in a low-load operating state based on the current load status of boiler unit 1.

[0039] When it is determined that the boiler unit 1 is in a low-load operating state, the first diversion valve 62 and the second diversion valve 63 are used for synchronous regulation to concentrate most or even all of the superheated steam generated by the first steam supply passage of the boiler unit 1 and most or even all of the reheated steam generated by the second steam supply passage to either the first turbine unit 2 or the second turbine unit 4, while the other turbine unit is shut down or placed in a very low-load standby state.

[0040] Furthermore, the steam turbine unit receiving centralized steam does not proportionally reduce its steam intake as the total boiler load decreases; instead, it maintains a relatively high level of 70%-80% of the rated steam intake. The internal flow conditions of the unit are stable, and the pressure, temperature, and superheat of the steam discharged from the intermediate-pressure cylinder remain within the acceptable range for heating requirements. This qualified steam is led out to the heating users through the corresponding heating extraction valve, achieving stable heating under low load. At the same time, the high-pressure, intermediate-pressure, and low-pressure cylinders of the unit normally complete the steam work, driving the generator to generate electricity. The power output drops to the low load value of a single unit, meeting the needs of deep peak shaving of the power grid. Meanwhile, the feedwater regeneration device corresponding to the operating steam turbine unit completes the stepped heating and pressurization of the condenser return medium, which enters the first steam supply passage of boiler unit 1 through the second confluence valve 60. Even if another unit is shut down, the working fluid output of a single feedwater regeneration device can still ensure the feedwater flow and parameters of boiler unit 1, maintaining steam production under low boiler load and forming a complete and stable working fluid cycle.

[0041] When the current total load of boiler unit 1 is higher than or equal to the preset evaporation threshold, it is determined that boiler unit 1 is in normal load operation. At this time, the superheated steam in the first steam supply passage and the reheated steam in the second steam supply passage of boiler unit 1 are evenly distributed to the first turbine unit 2 and the second turbine unit 4 through the first diversion valve 62 and the second diversion valve 63. Both turbine units are in a high-efficiency operation state near the rated load.

[0042] The exhaust steam from the intermediate-pressure cylinders of the two steam turbine units is proportionally distributed to the low-pressure cylinders and heating users via their respective heating extraction valves, achieving simultaneous power generation and heating. The first feedwater regeneration device 3 and the second feedwater regeneration device 5 respectively complete the cascade heating and pressurization of the corresponding condenser return medium, which then merges through the second confluence valve 60 and enters the first steam supply passage of boiler unit 1, forming a complete working fluid cycle. Under this operating condition, both the power generation and heating loads of the system are at a high level, fully utilizing the capacity advantage of the one-boiler-two-turbine system and achieving efficient energy utilization.

[0043] The method in this embodiment constructs a completely new energy distribution and conversion path at the physical level through a centralized steam distribution operation strategy. Its core mechanism is to change the total low load to the single unit high load and to change the situation where there is no steam to be extracted to the situation where there is steam to be extracted.

[0044] In traditional boiler-turbine systems, the steam turbine's steam intake is strictly tied to the boiler load. When the boiler is under low load, the steam turbine's steam intake decreases proportionally, and the deterioration of the flow conditions leads to the intermediate-pressure cylinder's exhaust parameters failing to meet heating requirements. This is an inherent defect determined by the turbine's flow thermodynamic characteristics. However, this invention, through a boiler-two-turbine architecture and the regulation of the diversion valve, decouples the binding relationship between the total boiler load and the steam intake of a single turbine. The limited steam resources under low boiler load are concentrated and supplied to a single unit, enabling the unit to maintain a high load factor and good flow conditions. As a result, qualified heating steam is produced at the intermediate-pressure cylinder's exhaust port, completely breaking through the technical bottleneck of traditional units being unable to provide heating at low loads and achieving uninterrupted heating at low loads.

[0045] Meanwhile, the method in this embodiment still follows the principle of cascaded heat utilization under low load conditions. The centrally supplied steam first converts high-grade thermal energy into mechanical work for power generation in the high-pressure cylinder and intermediate-pressure cylinder of the steam turbine unit, and then uses the low-grade thermal energy of the exhaust steam from the intermediate-pressure cylinder for heating, thus avoiding the waste of high-grade steam and ensuring the energy utilization efficiency of the system in the low load range.

[0046] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above-described processes do not imply a sequential order of execution; the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The sequence numbers of the above-described embodiments are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0047] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0048] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components may be combined, or integrated into another device, or some features may be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0049] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units. They may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0050] In addition, each functional unit in the various embodiments of this application can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0051] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media that can store program code, such as mobile storage devices, read-only memory (ROM), magnetic disks, or optical disks.

[0052] Alternatively, if the integrated units described above are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this application, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a device (which may be a terminal or platform, etc.) to execute all or part of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROMs, magnetic disks, or optical disks.

[0053] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A low-load steam extraction heating device for a boiler-two-unit system, characterized in that, The device includes a boiler unit, a first steam turbine unit, a second steam turbine unit, a first feedwater regeneration device, and a second feedwater regeneration device; The boiler unit includes a first steam supply passage for providing superheated steam and a second steam supply passage for providing reheated steam; the superheated steam generated by the first steam supply passage is distributed to the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit via a first diverter valve; the exhaust steam of the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit is merged into the second steam supply passage via a first merging valve; The reheat steam generated by the second steam supply passage is distributed to the intermediate pressure cylinder of the first turbine unit and the intermediate pressure cylinder of the second turbine unit via the second diversion valve; The exhaust steam from the intermediate-pressure cylinder of the first turbine unit is distributed to the low-pressure cylinder of the first turbine unit and the first heating user via the first heating extraction valve. The exhaust steam from the low-pressure cylinder of the first turbine unit and the return medium from the first heating user are combined into the first condenser. After being condensed by the first condenser, the steam is introduced into the first feedwater regeneration device. The exhaust steam from the intermediate-pressure cylinder of the second turbine unit is distributed to the low-pressure cylinder of the second turbine unit and the second heating user via the second heating extraction valve. The exhaust steam from the low-pressure cylinder of the second turbine unit and the return medium from the second heating user are combined into the second condenser. After being condensed by the second condenser, the steam is introduced into the second feedwater regeneration device. The return medium from the first feedwater reheating device and the second feedwater reheating device merges through the second confluence valve and enters the first steam supply passage.

2. The low-load steam extraction heating device for a boiler-two-unit system according to claim 1, characterized in that, The first steam supply passage includes an economizer, a water-cooled wall, a low-temperature superheater, a screen-type superheater, and a high-temperature superheater connected in sequence. The return medium of the first feedwater reheating device and the second feedwater reheating device is combined through the second confluence valve and then fed into the economizer. The return medium passes through the economizer and the water-cooled wall in sequence to absorb heat and evaporate, generating saturated steam. The saturated steam flows sequentially through the low-temperature superheater, the screen-type superheater, and the high-temperature superheater for heating, generating superheated steam under high temperature and high pressure.

3. The low-load steam extraction heating device for a boiler-two-unit system according to claim 1, characterized in that, The second steam supply passage includes a low-temperature reheater and a high-temperature reheater. The exhaust steam from the high-pressure cylinder of the first turbine unit and the high-pressure cylinder of the second turbine unit is introduced into the low-temperature reheater through the first confluence valve for initial heating, and then introduced into the high-temperature reheater for secondary heating to generate reheated steam.

4. The low-load steam extraction heating device for a boiler-two-unit system according to claim 1, characterized in that, The first feedwater reheating device includes a first low-pressure heater, a first deaerator, and a first high-pressure heater. The first condenser is connected to the first low-pressure heater, and the reflux medium of the first condenser is heated once by the first low-pressure heater. The heating steam from the first low-pressure heater is drawn through the intermediate-pressure cylinder and the low-pressure cylinder of the first turbine unit. The first deaerator heats the reflux medium of the first condenser a second time, and the heating steam from the first deaerator is drawn through the intermediate-pressure cylinder of the first turbine unit. A first feedwater pump is provided between the first deaerator and the first high-pressure heater. The reflux medium of the first condenser is pressurized by the first feedwater pump and then introduced into the first high-pressure heater. The first high-pressure heater heats the reflux medium of the first condenser a third time, and the heating steam from the first high-pressure heater is drawn through the high-pressure cylinder and the intermediate-pressure cylinder of the first turbine unit.

5. The low-load steam extraction heating device for a boiler-two-unit system according to claim 1, characterized in that, The second feedwater reheating device includes a second low-pressure heater, a second deaerator, and a second high-pressure heater. The second condenser is connected to the second low-pressure heater. The reflux medium of the second condenser is heated once by the second low-pressure heater, and the heating steam from the second low-pressure heater is drawn from the intermediate-pressure cylinder and low-pressure cylinder of the second turbine unit. The second deaerator heats the reflux medium of the second condenser a second time, and the heating steam from the second deaerator is drawn from the intermediate-pressure cylinder of the second turbine unit. A second feedwater pump is provided between the second deaerator and the second high-pressure heater. The reflux medium of the second condenser is pressurized by the second feedwater pump and then introduced into the second high-pressure heater. The second high-pressure heater heats the reflux medium of the second condenser a third time, and the heating steam from the second high-pressure heater is drawn from the high-pressure cylinder and intermediate-pressure cylinder of the second turbine unit.

6. The low-load steam extraction heating device for a boiler-two-unit system according to claim 4 or 5, characterized in that, Both the high-pressure heater and the low-pressure heater of the first feedwater reheating device and the second feedwater reheating device adopt a multi-stage heating structure, and the heating steam temperature of the single-stage heating structure gradually increases along the flow direction of the condenser's return medium.

7. The low-load steam extraction heating device for a boiler-two-unit system according to claim 1, characterized in that, The first diversion valve and the second diversion valve allocate the amount of superheated steam and reheated steam supplied to the first turbine unit and the second turbine unit respectively according to the load operation status of the boiler unit. As the load of the boiler unit decreases, the amount of superheated steam and reheated steam allocated to one of the first turbine unit or the second turbine unit through the first diversion valve and the second diversion valve increases, while the amount of superheated steam and reheated steam supplied to the other turbine unit decreases.

8. A method for low-load steam extraction heating in a boiler-two-unit system, applied to the low-load steam extraction heating device according to any one of claims 1-7, wherein steam extraction heating control is performed when the boiler is under low load, characterized in that... The method includes the following steps: Determine whether the boiler unit is in a low-load operation state. The low-load operation state is when the current total load of the boiler unit is lower than a preset evaporation threshold. The preset evaporation threshold is determined based on the rated evaporation capacity of the boiler unit. When it is determined that the boiler unit is operating at low load, steam is concentrated and delivered to one of the first or second turbine units through the first and second diversion valves, while the other turbine unit is shut down or placed in a standby state with extremely low load.

9. The low-load steam extraction heating method for a boiler-two-turbine system according to claim 8, characterized in that, When it is determined that the boiler unit is not operating at low load, steam is evenly delivered to the first turbine unit and the second turbine unit through the first diversion valve and the second diversion valve.

10. The low-load steam extraction heating method for a boiler-two-unit system according to claim 8, characterized in that, The preset evaporation threshold is set to 40%-50% of the rated evaporation capacity of the boiler unit.

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