A thermal system with one furnace and two machines operating at ultra-low load and a switching method thereof

Abstract

The present invention discloses a thermal system and a switching method for ultra-low load operation of two machines with one furnace, the system comprising two unit-type units; the first unit-type unit comprises a first intermediate pressure cylinder exhaust valve, a first temperature reduction and pressure reducing valve, a first intermediate pressure cylinder exhaust regulating valve, a first cylinder cooling steam pipeline, etc., and the second unit-type unit comprises a second intermediate pressure cylinder exhaust valve, a second temperature reduction and pressure reducing valve, a second intermediate pressure cylinder exhaust regulating valve, a second low pressure cylinder cooling steam pipeline, etc.; the outlet of the first intermediate pressure cylinder exhaust valve and the outlet of the second intermediate pressure cylinder exhaust valve are connected by an intermediate pressure cylinder exhaust connecting pipe, and an intermediate pressure cylinder exhaust connecting pipe regulating valve is installed on the intermediate pressure cylinder exhaust connecting pipe; the method realizes flexible switching between the two unit-type units. The present invention does not require technical transformation of the boiler side, makes full use of the difference in the working capacity of the high and medium pressure cylinders and the low pressure cylinders, is flexible in operation, practical in function, and has a certain ability to resist accidents.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy power steam turbine power generation, and specifically relates to a thermal system in which one furnace drives two machines for ultra-low load operation and a switching method thereof. Background Art

[0002] In the power dispatching system, new energy power enjoys priority dispatching rights, but new energy power is often characterized by large fluctuations and instability. In order to absorb more zero-carbon emission electricity, thermal power generating units must have excellent deep peak-shaving capabilities. The introduction of power peak-shaving auxiliary service market policies also encourages more thermal power generating units to participate.

[0003] Due to the limitation of the minimum stable combustion output of coal-fired boilers without auxiliary fuel, the minimum electrical load of existing thermal power units is generally limited to about 30%-40%. Further reduction will have an adverse effect on the safe and continuous operation of the boiler. For unit-type thermal power generating units, under small volume flow conditions such as start-up and shutdown of the steam turbine, ultra-low load operation can be achieved as long as the flutter, blasting and heating problems of the last stage blades of the low-pressure cylinder are properly solved. China's invention patent disclosure specification CN108661726A discloses a low-pressure cylinder cooling system with zero output of the low-pressure cylinder. By sending a small flow of low-pressure steam into the low-pressure cylinder, the low-pressure cylinder can achieve zero output, greatly reducing the power generation capacity of the unit and improving the heating capacity of the unit. At present, there have been many successful cases of zero-output heating transformation of the low-pressure cylinder in my country, which is a powerful solution for the flexibility transformation of thermal power units. Chinese invention patent disclosure specification CN109653810A discloses a thermal system in which one boiler drives two turbines for switchable operation. By adding superheated steam and reheated steam bypass and control valves, the problem of using one boiler to drive two steam turbines to generate electricity is solved when a boiler fails. However, the layout of the system is relatively complex, and the deep peak-shaving capability of the unit needs to be further explored.

[0004] As we all know, when a unit is generating electricity, there are obvious differences in the working capacity of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder. If this feature can be fully utilized, it is possible to break through the impact of the boiler's minimum output limit on the turbine's minimum power generation output and achieve deep peak-shaving operation of two units with one boiler. This can further increase the power plant's deep peak-shaving electricity price income, reduce the unit's idle rate, and enhance the unit's flexibility in adapting to dispatching electricity load instructions. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a thermal system with one furnace and two machines operating at ultra-low load and a switching method thereof, which does not require technical transformation on the boiler side, makes full use of the difference in working capacity between high-pressure, medium-pressure cylinders and low-pressure cylinders, is flexible in operation, practical in function, and has a certain ability to resist accidents.

[0006] The present invention is achieved through the following technical solutions:

[0007] A thermal system with one furnace and two machines operating at ultra-low load, comprising a first unit-type unit and a second unit-type unit;

[0008] The first unit system comprises a first intermediate pressure cylinder exhaust valve, a first temperature and pressure reducing valve, a first intermediate pressure cylinder exhaust regulating valve, a first cylinder cooling steam pipeline, a first low pressure cylinder, a first high pressure cylinder and a first intermediate pressure cylinder;

[0009] The second unit system comprises a second intermediate pressure cylinder exhaust valve, a second temperature and pressure reducing valve, a second intermediate pressure cylinder exhaust regulating valve, a second cylinder cooling steam pipeline, a second low pressure cylinder, a second high pressure cylinder and a second intermediate pressure cylinder;

[0010] The outlet of the first intermediate pressure cylinder exhaust valve and the outlet of the second intermediate pressure cylinder exhaust valve are connected through an intermediate pressure cylinder exhaust connecting pipe, and an intermediate pressure cylinder exhaust connecting pipe regulating valve is installed on the intermediate pressure cylinder exhaust connecting pipe;

[0011] A first cylinder cooling steam pipeline is led out in the form of a branch from the intermediate pressure cylinder exhaust connecting pipe at the outlet of the first intermediate pressure cylinder exhaust valve, and is connected to the steam inlets of the first low pressure cylinder, the first high pressure cylinder, and the first intermediate pressure cylinder respectively; a second cylinder cooling steam pipeline is led out in the form of a branch from the intermediate pressure cylinder exhaust connecting pipe at the outlet of the second intermediate pressure cylinder exhaust valve, and is connected to the steam inlets of the second low pressure cylinder, the second high pressure cylinder, and the second intermediate pressure cylinder respectively; a first temperature reducing and pressure reducing valve and a second temperature reducing and pressure reducing valve are installed on the first cylinder cooling steam pipeline and the second cylinder cooling steam pipeline respectively;

[0012] A first intermediate pressure cylinder exhaust regulating valve is provided between the outlet of the first intermediate pressure cylinder exhaust valve and the steam inlet of the first low pressure cylinder, and a second intermediate pressure cylinder exhaust regulating valve is provided between the outlet of the second intermediate pressure cylinder exhaust valve and the steam inlet of the second low pressure cylinder;

[0013] A feedwater connecting pipe is connected between the water side outlets of the No. 7 low-pressure heaters of the two steam turbines, and a feedwater flow regulating valve is installed on the feedwater connecting pipe;

[0014] A drain connecting pipe is connected between the drain inlets of the No. 7 low-pressure heaters of the two steam turbines, and a drain flow regulating gate is installed on the drain connecting pipe.

[0015] A further improvement of the present invention is that the first unit-type unit and the second unit-type unit have the same power generation capacity and capacity, and the equipment type and thermal system design are consistent.

[0016] A further improvement of the present invention is that the operating status of the first unit-type unit and the second unit-type unit is that one boiler is running and the other boiler is stopped for standby, or both steam turbines are in the power generation operation state at the same time.

[0017] A further improvement of the present invention is that the exhaust steam of the first intermediate pressure cylinder of the first unit system unit enters the second low pressure cylinder of the second unit system unit through the intermediate pressure cylinder exhaust steam connecting pipe.

[0018] A further improvement of the present invention is that the steam extraction and drainage of the first high-pressure cylinder and the first medium-pressure cylinder of the first unit-type unit enters the steam extraction and drainage system of the second low-pressure cylinder of the second unit-type unit through the drainage communication pipe.

[0019] A further improvement of the present invention is that the steam extraction heating feed water corresponding to the second low-pressure cylinder of the second unit system unit enters the feed water heat recovery system of the first high-pressure cylinder and the first medium-pressure cylinder of the first unit system unit through the feed water connecting pipe.

[0020] A further improvement of the present invention is that the first cylinder cooling steam pipeline is connected to the intermediate pressure cylinder exhaust communication pipe in the form of a bypass branch pipe, and the steam therein enters the first high pressure cylinder and the first intermediate pressure cylinder through the first temperature reduction and pressure reducing valve.

[0021] A further improvement of the present invention is that the second cylinder cooling steam pipeline is connected to the medium-pressure cylinder exhaust communication pipe in the form of a bypass branch pipe, and the steam therein enters the second low-pressure cylinder through the second temperature and pressure reducing valve.

[0022] A switching method for ultra-low load operation of two units with one furnace is described based on the thermal system of ultra-low load operation of two units with one furnace. The method is described as follows, taking the first unit system unit operating normally and the second unit system unit being shut down for standby as an example:

[0023] Step 1, the first intermediate pressure cylinder exhaust valve, the first intermediate pressure cylinder exhaust regulating valve, and the first temperature reduction and pressure reducing valve of the first unit system are in the open state; the second intermediate pressure cylinder exhaust valve, the second intermediate pressure cylinder exhaust regulating valve, and the second temperature reduction and pressure reducing valve of the second unit system are in the closed state; the intermediate pressure cylinder exhaust connecting pipe regulating valve, the feed water flow regulating valve, the drain flow regulating valve, the first temperature reduction and pressure reducing valve, and the second temperature reduction and pressure reducing valve are all in the closed state;

[0024] Step 2: Fully open the regulating valve of the intermediate pressure cylinder exhaust communication pipe and the exhaust regulating valve of the second intermediate pressure cylinder; slowly close the exhaust regulating valve of the first intermediate pressure cylinder and open the first temperature reduction and pressure reducing valve to allow the cooling steam to enter the first low pressure cylinder through the cooling steam pipeline of the first cylinder;

[0025] Step 3, start the condenser and condensate pump system of the second unit, and gradually shut down the condenser and condensate pump system of the first unit; fully open the feed water flow regulating valve and the drain flow regulating valve; open the second temperature and pressure reducing valve to allow the cooling steam to enter the second high-pressure cylinder and the second medium-pressure cylinder through the second cylinder cooling steam pipeline.

[0026] A further improvement of the present invention is that the boiler of the first unit system unit is in operation, the boiler of the second unit system unit is in hot standby state, both units are in grid-connected power generation state, and the two units jointly bear the electric load instruction of the first unit system unit;

[0027] The method switches from a one-furnace-one-machine operation mode to a one-furnace-two-machine operation mode.

[0028] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0029] The present invention provides a thermal system and a switching method for ultra-low load operation of one furnace with two units. By adding an intermediate pressure cylinder exhaust connecting pipe, a water supply connecting pipe, a drain connecting pipe, and a cylinder cooling steam pipeline, the safe switching of the operation mode of one furnace with one unit and one furnace with two units is realized. In addition, the present invention makes full use of the difference in the working characteristics of the high and medium pressure cylinders and the low pressure cylinders. The high and medium pressure cylinders of the operating unit and the low pressure cylinders of the standby unit work separately. The two sets of generators can respectively generate lower electrical loads. The dispatching electrical load borne by the original one furnace with one unit system is jointly borne by one furnace with two units, achieving a smaller technical output. The deep peak-shaving operation of the one furnace with two units mode can reduce the idle rate of the unit, enhance the flexibility of the unit to adapt to the dispatching electrical load instructions, increase the deep peak-shaving electricity price income of the power plant, and improve the production and operation efficiency of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of a thermal system with one furnace and two machines operating at ultra-low load as described in an example of the present invention.

[0031] Description of reference numerals:

[0032] 1. Exhaust valve of the first intermediate pressure cylinder; 2. The first temperature reduction and pressure reducing valve; 3. Exhaust connecting pipe of the intermediate pressure cylinder; 4. Exhaust regulating valve of the first intermediate pressure cylinder; 5. The cooling steam pipeline of the first cylinder; 6. The regulating valve of the exhaust connecting pipe of the intermediate pressure cylinder; 7. Exhaust valve of the second intermediate pressure cylinder; 8. The second temperature reduction and pressure reducing valve; 9. Exhaust regulating valve of the second intermediate pressure cylinder; 10. The cooling steam pipeline of the second cylinder; 11. Drain connecting pipe; 12. Drain flow regulating valve; 13. Feed water flow regulating valve; 14. Feed water connecting pipe; 15. The first low-pressure cylinder; 16. The second low-pressure cylinder; 17. The first intermediate pressure cylinder; 18. The second intermediate pressure cylinder; 19. The first high-pressure cylinder; 20. The second high-pressure cylinder; 21. The first unit system; 22. The second unit system. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0034] The present invention provides a thermal system for ultra-low load operation of two units with one furnace, including two unit-type units with the same capacity, equipment type and thermal system. The first unit-type unit 21 includes a first intermediate pressure cylinder exhaust valve 1, a first temperature reduction and pressure reducing valve 2, a first intermediate pressure cylinder exhaust regulating valve 4, a first cylinder cooling steam pipeline 5, a first low-pressure cylinder 15, a first intermediate pressure cylinder 17 and a first high-pressure cylinder 19, and the second unit-type unit 22 includes a second intermediate pressure cylinder exhaust valve 7, a second temperature reduction and pressure reducing valve 8, a second intermediate pressure cylinder exhaust regulating valve 9, a second cylinder cooling steam pipeline 10, a second low-pressure cylinder 16, a second intermediate pressure cylinder 18 and a second high-pressure cylinder 19. The outlet of the first intermediate pressure cylinder exhaust valve 1 and the outlet of the second intermediate pressure cylinder exhaust valve 7 are connected through the intermediate pressure cylinder exhaust communication pipe 3, and the intermediate pressure cylinder exhaust communication pipe 3 is installed with an intermediate pressure cylinder exhaust communication pipe regulating valve 6; the first cylinder cooling steam pipeline 5 is led out from the intermediate pressure cylinder exhaust communication pipe 3 at the outlet of the first intermediate pressure cylinder exhaust valve 1 in the form of a branch and is respectively connected to the steam inlet of the first low pressure cylinder 15, the first high pressure cylinder 19, and the first intermediate pressure cylinder 17, and the second intermediate pressure cylinder 18 is connected to the steam inlet of the first intermediate pressure cylinder 17. The second cylinder cooling steam pipeline 10 is led out from the intermediate pressure cylinder exhaust connection pipe 3 at the outlet of the cylinder exhaust valve 7 in the form of a branch and is connected to the steam inlet of the second low pressure cylinder 16, the second high pressure cylinder 20 and the second intermediate pressure cylinder 18 respectively. The first cylinder cooling steam pipeline 5 and the second cylinder cooling steam pipeline 10 are respectively installed with the first temperature reduction and pressure reducing valve 2 and the second temperature reduction and pressure reducing valve 8; a first intermediate pressure cylinder exhaust valve 1 is also arranged between the outlet of the first intermediate pressure cylinder exhaust valve 1 and the steam inlet of the first low pressure cylinder 15. A second intermediate-pressure cylinder exhaust regulating valve 4 is provided between the outlet of the second intermediate-pressure cylinder exhaust valve 7 and the steam inlet of the second low-pressure cylinder 16; a feed water connecting pipe 14 is connected between the water-side outlets of the No. 7 low-pressure heaters of the two steam turbines, and a feed water flow regulating gate 13 is installed on the feed water connecting pipe 14; a drain connecting pipe 11 is connected between the drain inlets of the No. 7 low-pressure heaters of the two steam turbines, and a drain flow regulating gate 12 is installed on the drain connecting pipe 11.

[0035] Preferably, a medium-pressure cylinder exhaust connecting pipe regulating valve 6 is installed on the medium-pressure cylinder exhaust connecting pipe 3 to realize the switching between the single steam turbine power generation operation mode and the two steam turbine power generation operation mode under the low-load operation state.

[0036] Preferably, the exhaust from the intermediate pressure cylinders of the two steam turbines to the low pressure cylinders is controlled by the first intermediate pressure cylinder exhaust valve 1 and the second intermediate pressure cylinder exhaust valve 7, which can realize the removal and commissioning of the low pressure cylinder, that is, to isolate the low pressure cylinder from the high pressure cylinder and the intermediate pressure cylinder;

[0037] Preferably, the first cylinder cooling steam pipeline 5 and the second cylinder cooling steam pipeline 10 are installed with a first temperature reducing and pressure reducing valve 2 and a second temperature reducing and pressure reducing valve 8. The steam source of the pipeline is the exhaust steam of the intermediate pressure cylinder, which is connected to the intermediate pressure cylinder exhaust steam connecting pipe 3 in the form of a bypass branch pipe, and a small amount of steam is sent to the removed cylinder through temperature reduction and pressure reduction to avoid the vibration, blasting and heating of the last stage blades of the cylinder;

[0038] Preferably, an intermediate pressure cylinder exhaust connecting pipe regulating valve 6 is installed on the intermediate pressure cylinder exhaust connecting pipe 3 of the two steam turbines, which is used to adjust the steam inlet flow of the first low pressure cylinder 15 and the second low pressure cylinder 16 during the switching process;

[0039] Preferably, a water supply flow regulating gate 13 is installed on the water supply connection pipe 14 to regulate the water supply flow of the two units during the switching process;

[0040] Preferably, a drain flow regulating gate 12 is installed on the drain communication pipe 11 to regulate the drain flow of the two units during the switching process.

[0041] The present invention provides a method for switching one furnace with two machines to ultra-low load operation, based on the above thermal system, including the following steps, which are described as follows, taking the first unit system unit 21 operating normally and the second unit system unit 22 being shut down for standby as an example:

[0042] Step 1, the first intermediate pressure cylinder exhaust valve 1, the first intermediate pressure cylinder exhaust regulating valve 4, and the first temperature reduction and pressure reducing valve 2 of the first unit system unit 21 are in the open state; the second intermediate pressure cylinder exhaust valve 7, the second intermediate pressure cylinder exhaust regulating valve 9, and the second temperature reduction and pressure reducing valve 8 of the second unit system unit 22 are in the closed state; the intermediate pressure cylinder exhaust communication pipe regulating valve 6, the feed water flow regulating valve 13, the drain flow regulating valve 12, the first temperature reduction and pressure reducing valve 2, and the second temperature reduction and pressure reducing valve 8 are all in the closed state;

[0043] Step 2, fully open the intermediate pressure cylinder exhaust communication pipe regulating valve 6 and the second intermediate pressure cylinder exhaust regulating valve 9; slowly close the first intermediate pressure cylinder exhaust regulating valve 4, open the first temperature reduction and pressure reducing valve 2, so that the cooling steam enters the first low pressure cylinder 15 through the first cylinder cooling steam pipeline 5;

[0044] Step 3, start the condenser and condensate pump system of the second unit 22, and gradually shut down the condenser and condensate pump system of the first unit 21; fully open the feed water flow regulating gate 13 and the drain flow regulating gate 12; open the second temperature and pressure reducing valve 8, so that the cooling steam enters the second high-pressure cylinder 20 and the second medium-pressure cylinder 18 through the second cylinder cooling steam pipeline 10.

[0045] Step 4: Slowly adjust the operating parameters to switch between one furnace and one unit and one furnace and two units. The high and medium pressure cylinders of the operating unit and the low pressure cylinders of the standby unit jointly bear the dispatching power load instructions.

[0046] The above are only preferred embodiments of the present invention. These specific implementations are different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be covered by the protection of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A thermal system with one furnace and two machines operating at ultra-low load, characterized in that: It comprises a first unit machine group (21) and a second unit machine group (22); The first unit system (21) comprises a first intermediate pressure cylinder exhaust valve (1), a first temperature reduction and pressure reducing valve (2), a first intermediate pressure cylinder exhaust regulating valve (4), a first cylinder cooling steam pipeline (5), a first low pressure cylinder (15), a first high pressure cylinder (19) and a first intermediate pressure cylinder (17); The second unit system (22) comprises a second intermediate pressure cylinder exhaust valve (7), a second temperature reduction and pressure reducing valve (8), a second intermediate pressure cylinder exhaust regulating valve (9), a second cylinder cooling steam pipeline (10), a second low pressure cylinder (16), a second high pressure cylinder (20) and a second intermediate pressure cylinder (18); The outlet of the first intermediate pressure cylinder exhaust valve (1) and the outlet of the second intermediate pressure cylinder exhaust valve (7) are connected via an intermediate pressure cylinder exhaust connecting pipe (3), and an intermediate pressure cylinder exhaust connecting pipe regulating valve (6) is installed on the intermediate pressure cylinder exhaust connecting pipe (3); A first cylinder cooling steam pipeline (5) is led out in the form of a branch from the intermediate pressure cylinder exhaust connecting pipe (3) at the outlet of the first intermediate pressure cylinder exhaust valve (1) and is respectively connected to the steam inlets of the first low pressure cylinder (15), the first high pressure cylinder (19) and the first intermediate pressure cylinder (17); a second cylinder cooling steam pipeline (10) is led out in the form of a branch from the intermediate pressure cylinder exhaust connecting pipe (3) at the outlet of the second intermediate pressure cylinder exhaust valve (7) and is respectively connected to the steam inlets of the second low pressure cylinder (16), the second high pressure cylinder (20) and the second intermediate pressure cylinder (18); a first temperature reducing and pressure reducing valve (2) and a second temperature reducing and pressure reducing valve (8) are respectively installed on the first cylinder cooling steam pipeline (5) and the second cylinder cooling steam pipeline (10); A first intermediate-pressure cylinder exhaust regulating valve (4) is provided between the outlet of the first intermediate-pressure cylinder exhaust valve (1) and the steam inlet of the first low-pressure cylinder (15), and a second intermediate-pressure cylinder exhaust regulating valve (9) is provided between the outlet of the second intermediate-pressure cylinder exhaust valve (7) and the steam inlet of the second low-pressure cylinder (16); A feedwater connection pipe (14) is connected between the water side outlets of the No. 7 low-pressure heaters of the two steam turbines, and a feedwater flow regulating valve (13) is installed on the feedwater connection pipe (14); A drain communication pipe (11) is connected between the drain inlets of the No. 7 low-pressure heaters of the two steam turbines, and a drain flow regulating valve (12) is installed on the drain communication pipe (11).

2. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The first unit system unit (21) and the second unit system unit (22) have the same power generation capacity and capacity, and the same equipment type and thermal system design.

3. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The operating states of the first unit system unit (21) and the second unit system unit (22) are that one boiler is in operation and the other boiler is stopped for standby, or both steam turbines are in a power generation operation state at the same time.

4. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: Exhaust steam from the first intermediate pressure cylinder (17) of the first unit system unit (21) enters the second low pressure cylinder (16) of the second unit system unit (22) through the intermediate pressure cylinder exhaust communication pipe (3).

5. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The steam extraction and drainage of the first high-pressure cylinder (19) and the first medium-pressure cylinder (17) of the first unit-type unit (21) enters the steam extraction and drainage system of the second low-pressure cylinder (16) of the second unit-type unit (22) through the drainage communication pipe (11).

6. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The steam extraction heating feed water corresponding to the second low-pressure cylinder (16) of the second unit-type generating set (22) enters the feed water heat recovery system of the first high-pressure cylinder (19) and the first medium-pressure cylinder (17) of the first unit-type generating set (21) through the feed water connecting pipe (14).

7. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The first cylinder cooling steam pipeline (5) is connected to the intermediate pressure cylinder exhaust communication pipe (3) in the form of a bypass branch pipe, and the steam therein enters the first high pressure cylinder (19) and the first intermediate pressure cylinder (17) through the first temperature reduction and pressure reducing valve (2).

8. The thermal system of one furnace with two machines operating at ultra-low load according to claim 1 is characterized in that: The second cylinder cooling steam pipeline (10) is connected to the medium-pressure cylinder exhaust communication pipe (3) in the form of a bypass branch pipe, and the steam therein enters the second low-pressure cylinder (16) through the second temperature reduction and pressure reduction valve (8).

9. A method for switching one furnace to two machines at ultra-low load operation, characterized in that: The method is based on a thermal system with two machines in ultra-low load operation in one furnace according to any one of claims 1 to 8, and is described as follows by taking the first unit system (21) operating normally and the second unit system (22) being shut down for standby as an example: Step 1: The first intermediate pressure cylinder exhaust valve (1), the first intermediate pressure cylinder exhaust regulating valve (4), and the first temperature reduction and pressure reducing valve (2) of the operating first unit system unit (21) are in an open state; the second intermediate pressure cylinder exhaust valve (7), the second intermediate pressure cylinder exhaust regulating valve (9), and the second temperature reduction and pressure reducing valve (8) of the standby second unit system unit (22) are in a closed state; the intermediate pressure cylinder exhaust connecting pipe regulating valve (6), the feed water flow regulating valve (13), the drain flow regulating valve (12), the first temperature reduction and pressure reducing valve (2), and the second temperature reduction and pressure reducing valve (8) are all in a closed state; Step 2, fully open the intermediate pressure cylinder exhaust communication pipe regulating valve (6) and the second intermediate pressure cylinder exhaust regulating valve (9); slowly close the first intermediate pressure cylinder exhaust regulating valve (4), open the first temperature reduction and pressure reducing valve (2), and allow the cooling steam to enter the first low pressure cylinder (15) through the first cylinder cooling steam pipeline (5); Step 3, start the condenser and condensate pump system of the second unit (22), and gradually shut down the condenser and condensate pump system of the first unit (21); fully open the feed water flow regulating valve (13) and the drain flow regulating valve (12); open the second temperature reduction and pressure reducing valve (8), so that the cooling steam enters the second high-pressure cylinder (20) and the second medium-pressure cylinder (18) through the second cylinder cooling steam pipeline (10).

10. The method for switching one furnace with two machines to ultra-low load operation according to claim 9, characterized in that: The boiler of the first unit-type generating unit (21) is in operation, the boiler of the second unit-type generating unit (22) is in hot standby state, both generating units are in grid-connected power generation state, and the two generating units jointly bear the electric load instruction of the first unit-type generating unit (21); The method switches from a one-furnace-one-machine operation mode to a one-furnace-two-machine operation mode.

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