Coal-fired heat supply unit deep peak regulation system and method based on multi-stage compression reheating

Abstract

The invention belongs to the technical field of peak regulation of thermal generator sets, and provides a coal-fired heat supply unit deep peak regulation system and method based on multistage compression reheating, which comprises a boiler economizer, a boiler superheater, a generator, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a boiler reheater, a heating network heater IV, a condenser, a heat regeneration system and corresponding connecting pipelines, a second electric valve is arranged on a middle-low pressure cylinder communicating pipeline, a bypass cooling steam pipeline is arranged beside the middle-low pressure cylinder communicating pipeline in parallel, and a first electric valve is arranged on the bypass pipeline; the steam exhaust pipeline of the medium-pressure cylinder is further provided with a third branch leading to a fourth heating network heater, and a third electric valve is arranged on the branch. A sensor and a controller. The deep peak regulation bottleneck under the cylinder switching operation condition is broken through, thermoelectric deep decoupling is achieved, the compression power consumption is reduced through low-grade heat supply network heat exchange, and the system economy is improved.

Description

Technical Field

[0001] This invention belongs to the field of peak shaving technology for thermal power generating units, and in particular relates to a deep peak shaving system and method for coal-fired heating units based on multi-stage compression reheat. Background Technology

[0002] 1. Overview of the Thermal System of Traditional Coal-fired Heating Units The core of the thermal system of a coal-fired heating unit is the steam turbine thermal cycle system, which typically consists of a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder coaxially connected to a generator, and integrates the main steam system, reheat steam system, extraction steam system, and regenerative heating system. Its operating characteristics are as follows: Main steam and reheat steam system: The main steam generated by the boiler enters the high-pressure cylinder to expand and do work. The low-temperature reheat steam returns to the boiler reheater for secondary heating through the cold section pipeline. The high-temperature reheat steam enters the intermediate-pressure cylinder to continue doing work and is finally discharged to the low-pressure cylinder.

[0003] Steam extraction heating system: The exhaust steam from the intermediate-pressure cylinder is used to drive the low-pressure cylinder for power generation, while the remaining steam is supplied to the heating network heaters through extraction pipelines to generate heating steam to meet heating demand. The heating steam flow rate needs to be maintained stable to ensure heating quality.

[0004] Regenerative system: Heats condensate and feedwater through multi-stage steam extraction (usually 7-8 stages) to improve the cycle thermal efficiency.

[0005] To alleviate the thermoelectric coupling problem, the LP-bypass technology is widely used: the valves of the connecting pipes between the intermediate and low-pressure cylinders are closed, and more than 90% of the exhaust steam from the intermediate-pressure cylinder is diverted to the heating network heater. Only a small amount of steam bypasses into the low-pressure cylinder to cool the rotor (to prevent overheating of the blower), bringing the output of the low-pressure cylinder close to zero. At this time, the unit's power generation load is borne by the high-pressure and intermediate-pressure cylinders, and the electrical load can be reduced to 40%-50% of the rated capacity.

[0006] 2. The core contradiction of limited deep peak-shaving capability Although cylinder cutting technology partially achieves thermoelectric decoupling, the following bottlenecks still exist in deep peak shaving scenarios (where the load rate needs to be reduced to below 30%): The "heat-driven power generation" operational constraint: To ensure stable steam flow and parameters for heating, the steam turbine's steam intake cannot be further reduced, preventing the power generation load from exceeding the lower limit. For example, heating units in northern regions are limited by the minimum cooling flow requirement of the low-pressure cylinder, and the load rate can only be reduced to a minimum of 35%-40%.

[0007] Equipment adaptability limitations: Under low load conditions, boilers face problems such as unstable combustion, insufficient main steam / reheat steam temperature (more than 50°C below the required temperature), and soaring coal consumption for power supply (increase of more than 30%). In addition, frequent load changes exacerbate metal fatigue in the turbine inlet system, and the DCS system lacks dedicated control logic for deep peak shaving.

[0008] Energy loss: The heat energy of the exhaust steam from the intermediate pressure cylinder is not fully utilized and is directly used for heating, resulting in a waste of the superheated steam's ability to perform work.

[0009] 3. Deficiencies of the prior art and the objectives of this patent Current solutions (such as electric boilers with hot water storage tanks and molten salt thermal storage) can partially improve peak-shaving flexibility, but they suffer from limitations such as high investment costs (e.g., electric boiler retrofitting costs exceed ten million yuan, and molten salt thermal storage retrofitting costs exceed one hundred million yuan) and low energy conversion efficiency (multiple conversions from heat energy to electricity to heat energy). This patent aims to overcome these bottlenecks by innovatively integrating a multi-stage compression reheat system to achieve continuous adjustment of the unit's net output while maintaining constant heating capacity, providing a cost-effective technical path for deep peak-shaving of coal-fired heating units. Summary of the Invention

[0010] This invention aims to solve the above problems, thereby providing a deep peak-shaving system and method for coal-fired heating units based on multi-stage compression reheat, breaking through the limitation of peak-shaving depth, realizing energy cascade utilization efficiency, and having good equipment compatibility and safety.

[0011] To achieve the above-mentioned objectives, this invention provides a deep peak-shaving system for coal-fired heating units based on multi-stage compression reheat, including a boiler economizer, a boiler superheater, a generator, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a boiler reheater, a heating network heater, a condenser, a regenerative system, and corresponding connecting pipes, and further includes: A multi-stage compression reheat circuit, wherein the inlet of the multi-stage compression reheat circuit is connected to the exhaust pipe of the intermediate pressure cylinder through a parallel branch and a fourth electric valve, and its outlet is connected to the pipe between the exhaust pipe of the high pressure cylinder and the boiler reheater. The multi-stage compression reheat circuit includes a first heat network heater, a first-stage compressor, a second heat network heater, a second-stage compressor, a third heat network heater, and a third-stage compressor arranged in series. An electric motor is used to drive the first-stage compressor, the second-stage compressor, and the third-stage compressor; A second electric valve is installed on the medium and low pressure cylinder connecting pipe, and a bypass cooling steam pipe is installed in parallel next to the medium and low pressure cylinder connecting pipe, and a first electric valve is installed on the bypass pipe. The exhaust pipe of the intermediate pressure cylinder is also provided with a third branch leading to the fourth heating network heater, and a third electric valve is provided on this branch. Sensors and controllers are used to monitor and control the inlet and outlet steam temperature and pressure of each stage of the compressor to ensure that the steam entering each stage of the compressor is in a preset superheated state and to maintain the outlet steam pressure of the three-stage compressor higher than the pressure of the high-pressure cylinder exhaust pipe.

[0012] Furthermore, the first-stage compressor, the second-stage compressor, and the third-stage compressor are either driven coaxially by the same electric motor or driven independently by their respective electric motors.

[0013] Furthermore, a fifth electric valve is installed on the connecting pipe between the outlet of the multi-stage compression reheat circuit and the exhaust pipe of the high-pressure cylinder.

[0014] Furthermore, the cold sides of the first, second, and third heating network heaters are all connected to the heating network circulating water system.

[0015] Furthermore, the drain outlet of the heat network heater four and the outlet pipe of the condenser are connected to the condensate system after they merge.

[0016] The present invention also provides a deep peak-shaving method based on the above system, comprising the following steps: S1: When the unit needs to enter the deep peak shaving mode, first switch to the cylinder cutting heating mode: close the second electric valve, open the first electric valve and the third electric valve, so that most of the medium-pressure cylinder exhaust steam enters the heating network heater four for heating, and the low-pressure cylinder is fed into the minimum cooling flow through the bypass cooling steam. S2: If it is necessary to further reduce the net output of the unit based on the cylinder cutting heating mode, the fourth electric valve is opened to divert part of the intermediate pressure cylinder exhaust steam to the multi-stage compression reheat circuit. S3: The steam that is diverted flows sequentially through the first heat network heater, the first stage compressor, the second heat network heater, the second stage compressor, the third heat network heater and the third stage compressor. Each stage heat network heater uses the heat network circulating water to cool the steam to a slightly superheated state before sending it to the next stage compressor. The compressed steam merges with the exhaust steam from the high-pressure cylinder and enters the boiler reheater for reheating, and then returns to the intermediate-pressure cylinder to do work. S4: By adjusting the opening of the fourth electric valve, the steam flow rate entering the multi-stage compression reheat circuit is continuously controlled, thereby changing the total power consumption of the compressor and realizing dynamic and continuous adjustment of the unit's net power generation output. At the same time, the total heat supply is kept stable by adjusting the heating network system.

[0017] Furthermore, in step S3, the superheat of the steam flowing through the first heating network heater, the second heating network heater, and the third heating network heater is controlled to maintain a superheat of 5-15°C based on the saturation temperature corresponding to the current pressure.

[0018] Furthermore, in step S3, the steam pressure at the outlet of the three-stage compressor is controlled to be 0.05-0.15 MPa higher than the pressure of the high-pressure cylinder exhaust pipe.

[0019] Furthermore, in step S4, the unit's net output P 净 According to formula P 净 = P 发 - P耗 To perform control, where P 发 P represents the total power generation of the high-pressure cylinder, intermediate-pressure cylinder, and low-pressure cylinder. 耗 This represents the total power consumption of all compressors in the multi-stage compression reheat circuit.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Overcome the bottleneck of deep peak shaving under cylinder cutting operation conditions and achieve deep decoupling of thermoelectricity: Under cylinder-cut heating conditions, while conventional systems significantly reduce the output of the low-pressure cylinder and increase heating capacity, the unit's electrical load has already dropped to the sum of the minimum stable outputs of the high-pressure and medium-pressure cylinders, making further reduction difficult to meet deep peak-shaving requirements. This invention significantly increases the unit's load reduction capability by adding a bypass to the compression system via a connecting pipe between the medium and low-pressure cylinders and implementing a multi-stage steam treatment process of "compression-intermediate cooling-recompression." By compressing a portion of the steam and consuming the electrical power driving the compressor (this electrical power is output by the main generator), the unit's actual net power output (high-pressure cylinder + low-pressure cylinder work - compressor power consumption) can be further significantly reduced under cylinder-cut conditions. This fundamentally solves the problem of cylinder-cut heating conditions failing to meet extremely low electrical load requirements, achieving a higher degree of decoupling and independent flexible adjustment of thermal and electrical outputs.

[0021] 2. Utilizing low-grade heat exchange networks reduces compression power consumption and improves system economy: This invention installs a heat network heater before the inlet of each compressor stage, using circulating heating water (or other low-temperature heat sources) to cool the intake steam and reduce its superheat (controlling it to a slightly superheated state, such as saturation temperature +10°C), ensuring that the steam is compressed within a safe margin. This process not only recovers and utilizes the sensible heat from the steam compression process for heating, improving energy efficiency, but more importantly, it significantly reduces the specific power consumption required for compressing steam. By effectively transferring the heat of compression to the heating system, although the newly added compression system consumes net power generation, its unit power cost (kW) corresponding to the heating benefit is far lower than the losses caused by traditional electric boilers, peak shaving during start-up and shutdown, or reduced heating capacity. Deep peak shaving is achieved while ensuring heating capacity, significantly improving economic efficiency.

[0022] 3. The system has a simple and reliable structure, reuses existing equipment, and strengthens the protection of key components: Reusing the heating network system: Utilizing the heating network heater to perform the steam cooling function effectively simplifies the system structure and reduces the cost and complexity of modification.

[0023] To prevent blower condensation and wet steam: Regarding low-pressure cylinder protection, the original cylinder-cutting operation mode is retained and strengthened: after the connecting pipe valve is closed, a small amount of cooling steam is introduced into the low-pressure cylinder through its bypass, effectively solving the blower condensation overheating problem. Simultaneously, the steam undergoes precise "saturation temperature + 10℃" superheat control before passing through the compressor. Combined with multi-stage compression cooling, this effectively prevents steam liquefaction during compression, avoiding the risk of droplet erosion of the compressor blades and ensuring the safe and stable operation of the compressor.

[0024] Staged compression and control safety margin: Multi-stage compression combined with intercooling is adopted to reduce the single-stage compression ratio and optimize compression efficiency; the outlet steam pressure of the final stage compressor is set slightly higher than the exhaust pressure of the high-pressure cylinder of the steam turbine to ensure that the compressed steam can be smoothly sent into the reheat cold section pipeline, and after merging, it is uniformly heated to the rated reheat temperature by the boiler reheater, ensuring the steam flow inside the boiler reheater and avoiding "dry burning" that could lead to tube rupture.

[0025] Parallel design ensures heating supply: The multi-stage compression reheat loop serves as a parallel branch of the heating steam flow. Its activation only diverts a portion of the discharged steam (heat source) for internal circulation heat absorption and release within the system, without affecting the overall heating capacity and parameter stability.

[0026] 4. The system adopts a hierarchical control strategy: When heating demand is high but the power grid requires a reduction in electrical load, the conventional cylinder-cutting operation mode should be activated first (closing the valves of the medium and low pressure cylinder connecting pipes, and only supplying cooling steam to the low pressure cylinder).

[0027] If the cylinder switching operation still cannot meet the requirements of the power grid's deep peak shaving range, then the core function of this invention is activated: the electric valve four is opened as needed and its opening degree is controlled to precisely adjust the steam flow rate entering the compression system.

[0028] Core control advantages: By controlling the steam split ratio introduced into the compression system in real time (i.e., controlling the four-way opening of the electric valve or the compressor speed), the power consumption of the unit's compression stage can be dynamically adjusted, thereby changing the unit's net power generation online and continuously. The system has a fast overall load response, a wide adjustment range, and high precision, and can flexibly adapt to the deep peak-shaving needs under grid AGC (Automatic Generation Control) or command modes.

[0029] In summary, this invention innovatively introduces multi-stage compression reheat technology into existing cylinder-cutting heating coal-fired units, utilizing heating network heating to achieve efficient intermediate cooling. Under the premise of ensuring heating capacity, equipment safety, and main system stability, it breaks through the minimum electrical load limitation in cylinder-cutting mode, significantly improving the unit's ability, flexibility, and economy in participating in deep grid peak shaving during the heating season, and has significant engineering application value. Attached Figure Description

[0030] Figure 1This is a schematic diagram of the deep peak-shaving system for coal-fired heating units based on multi-stage compression reheat proposed in this invention. Figure 2 This is a schematic diagram of the thermal system state of a coal-fired heating unit when it is not supplying heat. Figure 3 This is a schematic diagram of the thermal system state during the period of cylinder switching heating of a coal-fired heating unit, in which the generator output power can meet the requirements of deep peak shaving. Figure 4 This is a schematic diagram of the thermal system state when a coal-fired heating unit is in the period of cylinder switching for heating, the generator output power cannot meet the requirements of deep peak shaving, and the technical solution of this invention is applied. The components include: 1. Boiler economizer; 2. Boiler superheater; 3. Generator; 4. High-pressure cylinder; 5. Medium-pressure cylinder; 6. Low-pressure cylinder; 7. Boiler reheater; 8. First electric valve; 9. Second electric valve; 10. Third electric valve; 11. Fourth electric valve; 12. First heating network heater; 13. Fourth heating network heater; 14. Second heating network heater; 15. Third heating network heater; 16. Electric motor; 17. First-stage compressor; 18. Second-stage compressor; 19. Third-stage compressor; 20. Condenser; 21. High-pressure heater; 22. Boiler feedwater pump; 23. Deaerator; 24. Low-pressure heater; 25. Condensate pump; 26. Electric valve 5. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present patent. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present patent.

[0032] Reference Figure 1 The deep peak-shaving system for coal-fired heating units based on multi-stage compression reheat includes conventional core components of coal-fired heating units and newly added multi-stage compression reheat circuits. Specifically, it includes boiler economizer 1, boiler superheater 2, generator 3, high-pressure cylinder 4, medium-pressure cylinder 5, low-pressure cylinder 6, boiler reheater 7, first electric valve 8, second electric valve 9, third electric valve 10, fourth electric valve 11, first heating network heater 12, fourth heating network heater 13, second heating network heater 14, third heating network heater 15, electric motor 16, first-stage compressor 17, second-stage compressor 18, third-stage compressor 19, condenser 20, high-pressure heater 21, boiler feed water pump 22, deaerator 23, low-pressure heater 24, condensate pump 25, fifth electric valve 26, and other pipe connections required by the system.

[0033] The boiler economizer 1 is connected to the boiler superheater 2. The high-pressure cylinder 4, intermediate-pressure cylinder 5, and low-pressure cylinder 6 are coaxially connected to the generator 3. The boiler superheater 2 is connected to the high-pressure cylinder 4 through the intake pipe. The exhaust port of the high-pressure cylinder 4 is connected to the intermediate-pressure cylinder 5 through the boiler reheater 7 pipe. The intermediate-pressure cylinder 5 is connected to the low-pressure cylinder 6 through the intermediate-low-pressure cylinder connecting pipe. The exhaust pipe of the low-pressure cylinder 6 is connected to the condenser 20. The first branch of the exhaust pipe of the intermediate-pressure cylinder 5 is connected to the low-pressure cylinder 6 through the intermediate-low-pressure cylinder connecting pipe. A second electric valve 9 is installed on the intermediate-low-pressure cylinder connecting pipe. A bypass cooling steam pipe is connected in parallel to the intermediate-low-pressure cylinder connecting pipe. A first electric valve 8 is installed on the bypass cooling steam pipe. The second branch of the exhaust pipe of the intermediate-pressure cylinder 5 is connected to the fourth heat network heater 13 through the third electric valve 10. The drain outlet of the fourth heat network heater 13 and the outlet pipe of the condenser 20 merge and are sequentially connected to the condensate pump 25, the low-pressure heater 24, the deaerator 23, the boiler feed water pump 22, the high-pressure heater 21, and the boiler economizer 1. The third branch of the exhaust pipe of the intermediate pressure cylinder 5 is connected to the multi-stage compression reheat circuit through the fourth electric valve 11. The outlet of the multi-stage compression reheat circuit is connected to the pipe between the exhaust pipe of the high pressure cylinder 4 and the boiler reheater 7 through the fifth electric valve 26.

[0034] The multi-stage compression reheat circuit includes a first heat network heater 12, a first-stage compressor 17, a second heat network heater 14, a second-stage compressor 18, a third heat network heater 15, and a third-stage compressor 19 connected in sequence. The cold sides of the first heat network heater 12, the second heat network heater 14, and the third heat network heater 15 are all connected to the heat network circulating water system.

[0035] The electric motor 16 can be a fixed-speed or, more preferably, a variable-frequency speed-regulating motor, used to drive the first-stage compressor 17, the second-stage compressor 18, and the third-stage compressor 19. Each stage of the compressor can be driven coaxially by the same electric motor or independently by its own electric motor (the latter offers greater adjustment flexibility).

[0036] The system of this invention supports conventional operation mode, cylinder-cutting heating mode, and deep peak shaving mode based on multi-stage compression reheat. Specific implementation methods are as follows: 1. Normal operating mode (no heating, see Figure 2 ): The system operates in conventional condensing or small-volume extraction heating mode. The second electric valve 9 on the connecting pipe between the intermediate and low-pressure cylinders is open, allowing most of the exhaust steam from the intermediate-pressure cylinder 5 to enter the low-pressure cylinder 6 for power generation. The first electric valve 8, the third electric valve 10, the fifth electric valve 26, and the fourth electric valve 11 are closed, and the unit operates in pure condensing mode.

[0037] 2. Cylinder-switching heating mode (to meet higher heating demands) Figure 3 ): When heating demand is high: Close the second electric valve 9 on the connecting pipe between the medium and low pressure cylinders to create physical isolation. Open the first electric valve 8, and only a small amount of steam is introduced into the low-pressure cylinder 6 to remove the heat from the blower, ensuring the safety of the low-pressure cylinder. At this time, the low-pressure cylinder 6 does no work.

[0038] When the third electric valve 10 is opened, most of the steam from the intermediate-pressure cylinder 5 enters the fourth heating network heater 13, heating the circulating water of the heating network and supplying heat to the outside. The water after steam condensation enters the condensate system and then enters the regenerative system of the original unit via the condensate pump 25.

[0039] At this time, the fourth electric valve 11 and the fifth electric valve 26 remain closed, and the multi-stage compression reheat circuit is not engaged.

[0040] The heating load adjustment is achieved by adjusting the steam intake of the high-pressure cylinder 4. At this time, the unit's power generation load and heating load are linked, that is, they rise or fall synchronously.

[0041] This mode can significantly improve heating capacity while appropriately reducing electrical load, but the peak shaving depth is limited by the minimum steam intake of the high and medium pressure cylinders, and it is still in a state of non-decoupling of thermoelectricity.

[0042] 3. Deep peak shaving mode (based on multi-stage compression and reheat): When the unit is operating in cylinder-cut heating mode, but still cannot meet the grid requirements to reduce the electrical load to a lower level, the core control logic of this invention is activated: Maintain the basic operating status of the cylinder-cutting heating mode.

[0043] Gradually open the fourth electric valve 11. Divert a portion of the exhaust steam from the intermediate-pressure cylinder 5, which flows to the fourth heating network heater 13, into the multi-stage compression reheat circuit.

[0044] Steam Processing and Treatment Figure 4 ): The steam discharged from the intermediate-pressure cylinder 5 carries a certain degree of superheat (its conventional flow is to enter the low-pressure cylinder 6 to perform work). It is first cooled by the first heating network heater 12. The control objective is to use the circulating water in the heating network to cool the steam to its saturation temperature at its current pressure plus approximately 10°C of superheat. This ensures that the steam entering the first-stage compressor is in a safe superheated state. This cooling process recovers some of the sensible heat of the steam for heating purposes.

[0045] After leaving the first heating network heater 12, the steam enters a compressor 17 for pressurization. The compressor can be driven by an electric motor 16 (preferably with variable frequency speed control). The compression process consumes electrical power P1.

[0046] The compressed steam is heated and pressurized, and usually becomes superheated steam with a higher degree of superheat.

[0047] The steam then enters the second heat network heater 14 for cooling, with the goal of cooling it to the saturation temperature corresponding to the current new pressure plus a superheat of 10°C, providing safe entry conditions for the second-stage compressor and recovering heat for heating.

[0048] The cooled steam is sent to the second-stage compressor 18, which also consumes electrical power P2.

[0049] Repeat the above process: the steam from the outlet of the second-stage compressor 18 enters the third heating network heater 15 and is cooled to a slightly superheated state; then it is sent to the third-stage compressor 19 for pressurization (consuming electrical power P3).

[0050] Compression endpoint control: The control objective is to ensure that the outlet steam pressure of the three-stage compressor 19 is slightly higher than the pressure of the exhaust pipe (reheat cold section) of the high-pressure cylinder 4 of the steam turbine. This is typically about 0.05–0.15 MPa higher. This ensures that the compressed steam can smoothly and stably flow into the exhaust pipe of the high-pressure cylinder 4.

[0051] Steam recombining and reuse: The compressed and heated steam is combined with the exhaust steam from the high-pressure cylinder 4. The mixed steam flows through the boiler reheater 7 to raise its temperature to the rated reheat temperature, and then is sent to the inlet of the intermediate-pressure cylinder 5 to perform work.

[0052] Power generation is the same as power consumption: the power generation P of the unit at this time. 发 Mainly composed of the output power P of high-pressure cylinder 4 H 5-pressure cylinder output power P M The output power P of low-pressure cylinder 6 L (In cylinder cut-off mode P) L The entire compressor system (17, 18, 19) is composed of components ≈0, and the power P consumed by the entire compressor system is 17, 18, 19. 耗 = Composed of (P1+P2+P3), that is: P 发 =(P H +P M +P L ) Net output control of the unit: The net output of the unit is the power generated minus the power consumed. That is: Control core: By adjusting the opening of the fourth electric valve 11 in real time, the flow rate of compressed steam entering the multi-stage compression circuit can be continuously adjusted. An increase in the compressed flow rate will lead to increased power consumption P of the compressor. 耗 Increase. This increases the actual net power output P of the unit. 净 The heat energy of this steam is recovered and supplied to the heating network through multi-stage heating network heaters. This achieves the goal of increasing heating capacity and reducing the unit's net output.

[0053] Conversely, reducing the compressed steam flow rate will increase the unit's net output.

[0054] Therefore, by controlling the opening degree of electric valve four in a closed loop, the net power output P of the unit can be controlled. 净 The online, continuous, and dynamic regulation meets the power grid's AGC load command requirements for deep peak shaving. This regulation method, combined with adjusting the steam inlet flow of the high-pressure cylinder 4, can achieve thermo-electric decoupling.

[0055] Heating Supply Guarantee: The sensible heat portion of the diverted compressed steam (originally intended for heating) is recovered as it flows through the first heating network heater 12, the second heating network heater 14, and the third heating network heater 15. Simultaneously, the system compensates for the impact of the diversion by adjusting the heating output of the main heater (or the fourth heating network heater 13 or others), or by adjusting the overall flow rate / temperature of the heating network water, ensuring that the total heating flow rate and parameters remain stable. This allows for a significant reduction in electrical load without affecting heating capacity.

[0056] 4. Safety and Control Points Low-pressure cylinder protection: In deep peak shaving mode, the first electric valve 8 in cylinder cutting mode maintains an appropriate opening to ensure a constant minimum cooling steam flow through the low-pressure cylinder 6, carrying away the frictional heat of the blower and preventing the blades from overheating.

[0057] Steam superheating and drying: By precisely controlling the steam outlet temperature flowing through the first heat network heater 12, the second heat network heater 14, and the third heat network heater 15, the steam entering each stage of the compressor is always kept in a slightly superheated state (saturation temperature +10°C). Combined with the step-by-step cooling between the multi-stage compressors, the generation of wet steam is effectively avoided, protecting the compressor blades from the risk of droplet erosion.

[0058] Pressure matching and stable operation: Maintaining the outlet pressure of the three-stage compressor slightly higher than the exhaust pressure of the high-pressure cylinder ensures that the compressed steam can be smoothly connected to the steam pipeline at the outlet of the high-pressure cylinder 4, avoiding compressor surge. At the same time, it can ensure that the boiler reheater 7 has sufficient steam flow when the boiler load is reduced, avoiding dry burning of the boiler reheater 7 and tube rupture.

[0059] Load response: The system adopts a hierarchical control strategy: priority is given to starting the cylinder cut-off mode; the fourth electric valve 11 of the multi-stage compression reheat circuit is only opened when cylinder cut-off cannot meet the deep peak shaving requirements. By adjusting the opening of the fourth electric valve 11, the net output of the unit can be changed rapidly and continuously to meet the grid AGC load command requirements, with a wide adjustment range and high precision.

[0060] Redundant design: Necessary temperature and pressure sensors and controllers are installed at critical locations, such as the inlets and outlets of each compressor stage, to provide real-time feedback signals for the control strategy. Safety release devices can be installed at the compressor system inlet or outlet.

[0061] The technical solution of this specific implementation method, while maintaining the original heating capacity, achieves a significant reduction in the net output depth of coal-fired heating units based on cylinder cut-off by controllably introducing a multi-stage compression reheat circuit and utilizing heating network heating for efficient and safe cooling. This fundamentally breaks through the limitations of "heat-driven power generation" on deep peak shaving, enhancing the unit's ability and flexibility to participate in deep peak shaving of the power grid during the heating season, while also possessing high energy utilization efficiency and economic viability for retrofitting.

Claims

1. A deep peak-shaving system for a coal-fired heating unit based on multi-stage compression reheat, comprising a boiler economizer (1), a boiler superheater (2), a generator (3), a high-pressure cylinder (4), a medium-pressure cylinder (5), a low-pressure cylinder (6), a boiler reheater (7), a heating network heater (13), a condenser (20), a regenerative system, and corresponding connecting pipes, characterized in that, Also includes: The multi-stage compression reheat circuit has its inlet connected to the exhaust pipe of the intermediate pressure cylinder (5) via a parallel branch and the fourth electric valve (11), and its outlet connected to the pipe between the exhaust pipe of the high pressure cylinder (4) and the boiler reheater (7). The multi-stage compression reheat circuit includes a first heat network heater (12), a first-stage compressor (17), a second heat network heater (14), a second-stage compressor (18), a third heat network heater (15), and a third-stage compressor (19) arranged in series. An electric motor (16) is used to drive the first-stage compressor (17), the second-stage compressor (18), and the third-stage compressor (19). A second electric valve (9) is provided on the medium and low pressure cylinder connecting pipe, and a bypass cooling steam pipe is provided in parallel next to the medium and low pressure cylinder connecting pipe, and a first electric valve (8) is provided on the bypass pipe. The exhaust pipe of the intermediate pressure cylinder (5) is also provided with a third branch leading to the fourth (13) of the heating network heater, and a third electric valve (10) is provided on the branch. Sensors and controllers are used to monitor and control the inlet and outlet steam temperature and pressure of each stage of the compressor to ensure that the steam entering each stage of the compressor is in a preset superheat state and to maintain the outlet steam pressure of the three-stage compressor (19) higher than the exhaust pipe pressure of the high-pressure cylinder (4).

2. The system according to claim 1, characterized in that, The first-stage compressor (17), the second-stage compressor (18), and the third-stage compressor (19) are either driven coaxially by the same electric motor or driven independently by their respective electric motors.

3. The system according to claim 1, characterized in that, A fifth electric valve (26) is installed on the connecting pipe between the outlet of the multi-stage compression reheat circuit and the exhaust pipe of the high-pressure cylinder (4).

4. The system according to claim 1, characterized in that, The cold sides of the first heat network heater (12), the second heat network heater (14) and the third heat network heater (15) are all connected to the heat network circulating water system.

5. The system according to claim 4, characterized in that, The drain outlet of the heat network heater four (13) and the outlet pipe of the condenser (20) are connected to the condensate system after they merge.

6. A deep peak-shaving method based on the system according to any one of claims 1-5, characterized in that, Includes the following steps: S1: When the unit needs to enter the deep peak shaving mode, first switch to the cylinder cutting heating mode: close the second electric valve (9), open the first electric valve (8) and the third electric valve (10), so that most of the medium pressure cylinder (5) exhaust steam into the heating network heater four (13) for heating, and the low pressure cylinder (6) is fed into the minimum cooling flow through the bypass cooling steam. S2: On the basis of cylinder cutting heating mode, if it is necessary to further reduce the net output of the unit, the fourth electric valve (11) is opened to divert part of the exhaust steam of the intermediate pressure cylinder (5) to the multi-stage compression reheat circuit. S3: The steam that is diverted flows through the first heat network heater (12), the first stage compressor (17), the second heat network heater (14), the second stage compressor (18), the third heat network heater (15) and the third stage compressor (19) in sequence. Each stage heat network heater uses the heat network circulating water to cool the steam to a slightly superheated state and then sends it to the next stage compressor. The compressed steam merges with the exhaust steam of the high pressure cylinder (4) and enters the boiler reheater (7) for reheating, and then returns to the intermediate pressure cylinder (5) to do work. S4: By adjusting the opening of the fourth electric valve (11), the steam flow rate entering the multi-stage compression reheat circuit is continuously controlled, thereby changing the total power consumption of the compressor and realizing dynamic and continuous adjustment of the net power output of the unit. At the same time, the total heat supply is kept stable by adjusting the heat network system.

7. The method according to claim 6, characterized in that, In step S3, the superheat of the steam flowing through the first heating network heater (12), the second heating network heater (14) and the third heating network heater (15) is controlled so that it maintains a superheat of 5-15°C based on the saturation temperature corresponding to the current pressure.

8. The method according to claim 6, characterized in that, In step S3, the steam pressure at the outlet of the three-stage compressor (19) is controlled to be 0.05-0.15 MPa higher than the exhaust pipe pressure of the high-pressure cylinder (4).

9. The method according to claim 6, characterized in that, In step S4, the unit's net output P 净 According to formula P 净 = P 发 -P 耗 To perform control, where P 发 P represents the total power generation of the high-pressure cylinder (4), the medium-pressure cylinder (5), and the low-pressure cylinder (6). 耗 This represents the total power consumption of all compressors in the multi-stage compression reheat circuit.

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