A supercritical coal-fired boiler startup system and operation method coupled with molten salt heat storage

Abstract

The present invention discloses a supercritical coal-fired boiler startup system and operation method coupled with molten salt heat storage. The present invention connects a molten salt heat exchange system in parallel between the steam-water separator and the low-temperature superheater outlet of the supercritical coal-fired boiler, thereby establishing a supercritical coal-fired boiler rapid startup system. The system comprises a low-temperature molten salt storage tank, a high-temperature molten salt storage tank, a molten salt pump, a molten salt-steam-water heat exchanger, a molten salt-flue gas heat exchanger, and the like. During the startup process of the unit, the working fluid in the startup steam-water separator is heated by high-temperature molten salt through the molten salt-steam-water heat exchanger, thereby reducing the boiler recirculating water flow rate during the startup process and improving the startup speed. During the load reduction process, the flue gas in the flue gas at the rear of the boiler heats the molten salt through the flue gas-molten salt heat exchanger to store thermal energy. The present invention greatly improves the startup rate of the coal-fired unit, reduces the additional energy consumption during the startup process through the molten salt heat storage device, and realizes the flexible and efficient coordinated improvement of the coal-fired power generation unit.

Description

Technical Field

[0001] The present invention belongs to the field of flexibility technology for coal-fired power plants, and specifically relates to a supercritical coal-fired boiler startup system and operation method coupled with molten salt heat storage, which increases the steam production during the startup process of the unit by increasing the bypass during the startup process and using a molten salt heat exchange device, thereby increasing the unit load change rate. The system can be adopted and used for deep peak regulation, especially for coal-fired units with frequent start and shutdown, or provide a reference. Background Art

[0002] As my country accelerates the development of a new power system, the power grid urgently needs to improve its peak-shaving capabilities to cope with the impact of intermittent renewable energy generation such as wind and solar on the grid's operating load. Coal-fired power generation is the main source of peak-shaving power in my country, and improving operational flexibility is the most pressing technical requirement facing coal-fired power generation.

[0003] Supercritical coal-fired boilers undergo a wet-dry transition during startup and when transitioning from ultra-low to high load. Due to system limitations, existing boiler startup systems are slow to transition from wet to dry, limiting the flexibility of coal-fired power generation units. Existing coal-fired boiler startup systems typically utilize a boiler water circulation pump to transfer unsaturated water from the separator tank to the boiler water wall inlet during startup, conserving energy and the steam-water working medium. During startup, as the load increases, the boiler's thermal load increases, but the amount of coal fed into the boiler is limited by the water wall temperature. To ensure the water wall operates within a safe temperature range, the coal feed rate is restricted, which in turn reduces the load ramp rate. To meet the power grid's demand for rapid peak-shaving of coal-fired power generation and increase boiler startup rates, these technical challenges must be overcome. Developing novel startup system configurations and operational control methods is key to improving the load ramp rate during supercritical boiler startup. Summary of the Invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a supercritical coal-fired boiler startup system and operation method coupled with molten salt heat storage, and to provide a method for improving the load change rate during the startup process of the coal-fired boiler. By coupling a high-temperature molten salt heat storage tank and a molten salt heat exchanger device, the superheated steam flow rate of the coal-fired boiler during the startup process is increased, the dry-wet transition rate during the boiler startup process is increased, the rapid load change capability of the boiler system is improved, and the operating flexibility of the coal-fired power generation system is comprehensively improved.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] A supercritical coal-fired boiler startup system coupled with molten salt heat storage includes a supercritical coal-fired boiler 11, a steam-water separator 12 arranged in the supercritical coal-fired boiler 11, a low-temperature reheater side boiler tail flue gas damper 13, a low-temperature superheater side boiler tail flue gas damper 14 and a flue gas-molten salt heat exchanger side tail flue gas damper 15; also includes a high-temperature molten salt heat storage tank 21, a low-temperature molten salt heat storage tank 22, a low-temperature molten salt pump 23, a flue gas-molten salt heat exchanger 24, a high-temperature molten salt heat storage tank inlet valve 25, a steam-water separator bypass valve 30, a steam-water separator bypass water pump 31, a high-temperature molten salt pump 32, a molten salt-water heat exchanger 33, a low-temperature molten salt heat storage tank inlet valve 26, a low-temperature superheater outlet header 34 and a low-temperature superheater 35, each Part of them are connected by pipelines, the low-temperature molten salt heat storage tank inlet valve 26 is installed between the low-temperature molten salt heat storage tank 22 and the molten salt-water heat exchanger 33, and the high-temperature molten salt heat storage tank inlet valve 25 is installed between the high-temperature molten salt heat storage tank 21 and the flue gas-molten salt heat exchanger 24; the tail of the supercritical coal-fired boiler 11 is a three-flue, the flue gas-molten salt heat exchanger 24 and the flue gas baffle 15 on the flue gas-molten salt heat exchanger side are arranged in the outermost flue, the low-temperature superheater 35 and the low-temperature superheater side boiler tail flue gas baffle 14 are arranged in the middle flue, and the low-temperature reheater side boiler tail flue gas baffle 13 is arranged in the innermost flue; in the startup system, molten salt and steam-water exchange heat through three branches, namely the molten salt heating branch, the molten salt heat release branch and the steam-water heating branch;

[0007] The molten salt heating branch includes a low-temperature molten salt heat storage tank 22, a low-temperature molten salt pump 23, a flue gas-molten salt heat exchanger 24 and a high-temperature molten salt heat storage tank 21 connected in sequence;

[0008] The molten salt heat release branch includes a high-temperature molten salt heat storage tank 21, a high-temperature molten salt pump 32, a molten salt-water heat exchanger 33 and a low-temperature molten salt heat storage tank 22 connected in sequence;

[0009] The steam-water heating branch includes a steam-water separator 12, a steam-water separator bypass valve 30, a steam-water separator bypass water pump 31, a molten salt-water heat exchanger 33, a low-temperature superheater outlet header 34 and a low-temperature superheater 35 connected in sequence.

[0010] The supercritical coal-fired boiler 11 is a supercritical π-type coal-fired boiler.

[0011] The flue gas-molten salt heat exchanger 24 is a partition-type flue gas-molten salt heat exchanger, and the molten salt-water heat exchanger 33 is a partition-type molten salt-water heat exchanger.

[0012] The operating method of the supercritical coal-fired boiler startup system coupled with molten salt heat storage is as follows:

[0013] 1) When the molten salt in the high-temperature molten salt heat storage tank 21 is insufficient and needs to be heated, the unit is operated to a stable load state, the flue gas damper 15 at the tail end of the flue gas-molten salt heat exchanger is opened, the low-temperature molten salt pump 23 is started, the high-temperature molten salt heat storage tank inlet valve 25 is opened, and the low-temperature molten salt heat storage tank inlet valve 26 is closed to start the molten salt heating process; when the high-temperature molten salt heat storage tank 21 is full of molten salt, the flue gas damper 15 at the tail end of the flue gas-molten salt heat exchanger and the low-temperature molten salt pump 23 are closed at the same time;

[0014] 2) When the supercritical coal-fired boiler 11 is started, ensure that the flue gas damper 15 at the tail end of the flue gas-molten salt heat exchanger is closed, open the steam-water separator bypass valve 30 and the steam-water separator bypass water pump 31, open the low-temperature molten salt heat storage tank inlet valve 26 and close the high-temperature molten salt heat storage tank inlet valve 25, start the high-temperature molten salt pump 32, start the steam-water heating process, increase the steam volume during the startup process, increase the load change rate, and thus quickly increase the startup rate of the supercritical coal-fired boiler.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] (1) The present invention can quickly increase the startup rate of supercritical coal-fired boilers and significantly improve the peak-shaving capacity of coal-fired power generation systems;

[0017] (2) The present invention reduces the recirculating water flow rate during boiler startup by adding a molten salt-water heat exchange bypass, and reduces the drastic change in the working medium flow rate in the water-cooled wall during the dry-wet state conversion process of the boiler, thereby ensuring the safe operation of the boiler water-cooled wall temperature during the rapid startup of the supercritical coal-fired boiler;

[0018] (3) Since the present invention mainly carries out system modification on the outside of the boiler, only the tail flue is involved internally, and there is no change on the turbine side, the entire system is relatively small. It can be used in both newly built units and in-service units, and the operation control method is simple, which is convenient for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the system of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the accompanying drawings and implementation examples.

[0021] like Figure 1As shown, the present invention provides a supercritical coal-fired boiler startup system coupled with molten salt heat storage, comprising a supercritical coal-fired boiler 11, a steam-water separator 12 arranged in the supercritical coal-fired boiler 11, a flue gas damper 13 at the rear of the boiler on the low-temperature reheater side, a flue gas damper 14 at the rear of the boiler on the low-temperature superheater side, and a flue gas-molten salt heat exchanger side tail flue gas damper 15; and further comprising a high-temperature molten salt heat storage tank 21, a low-temperature molten salt heat storage tank 22, a low-temperature molten salt pump 23, a flue gas-molten salt heat exchanger 24, a high-temperature molten salt heat storage tank inlet valve 25, a steam-water separator bypass valve 30, a steam-water separator bypass water pump 31, a high-temperature molten salt pump 32, a molten salt-water heat exchanger 33, a low-temperature molten salt heat storage tank inlet valve 26, a low-temperature superheater outlet header 34, and a low-temperature superheater 3 5. Each part is connected by a pipeline; the low-temperature molten salt heat storage tank inlet valve 26 is installed between the low-temperature molten salt heat storage tank 22 and the molten salt-water heat exchanger 33, and the high-temperature molten salt heat storage tank inlet valve 25 is installed between the high-temperature molten salt heat storage tank 21 and the flue gas-molten salt heat exchanger 24; the tail of the supercritical coal-fired boiler 11 is a three-flue, the flue gas-molten salt heat exchanger 24 and the flue gas-molten salt heat exchanger side tail flue gas baffle 15 are arranged in the outermost flue, the low-temperature superheater 35 and the low-temperature superheater side boiler tail flue gas baffle 14 are arranged in the middle flue, and the low-temperature reheater side boiler tail flue gas baffle 13 is arranged in the innermost flue; in the startup system, molten salt and steam-water exchange heat through three branches, namely, the molten salt heating branch, the molten salt heat release branch and the steam-water heating branch;

[0022] The molten salt heating branch includes a low-temperature molten salt heat storage tank 22, a low-temperature molten salt pump 23, a flue gas-molten salt heat exchanger 24, a high-temperature molten salt heat storage tank inlet valve 25 and a high-temperature molten salt heat storage tank 21 connected in sequence;

[0023] The molten salt heat release branch includes a high-temperature molten salt heat storage tank 21, a high-temperature molten salt pump 32, a molten salt-water heat exchanger 33, a low-temperature molten salt heat storage tank inlet valve 26 and a low-temperature molten salt heat storage tank 22 connected in sequence;

[0024] The steam-water heating branch includes a steam-water separator 12, a steam-water separator bypass valve 30, a steam-water separator bypass water pump 31, a molten salt-water heat exchanger 33, a low-temperature superheater outlet header 34 and a low-temperature superheater 35 connected in sequence.

[0025] The supercritical coal-fired boiler 11 is a supercritical π-type coal-fired boiler, which can ensure that the flue gas-molten salt heat exchanger is spatially arranged with molten salt. Even if the boiler flue is modified, it is only necessary to add a flue gas-molten salt heat exchange flue at the tail flue.

[0026] The flue gas-molten salt heat exchanger 24 is a partition-type flue gas-molten salt heat exchanger, and the molten salt-water heat exchanger 33 is a partition-type molten salt-water heat exchanger, which can ensure that the molten salt only flows between the high and low temperature heat exchange tanks and the changes to the steam-water and flue gas and air systems are relatively small.

[0027] The operating method of the supercritical coal-fired boiler startup system coupled with molten salt heat storage is as follows:

[0028] 1) When the molten salt in the high-temperature molten salt heat storage tank 21 is insufficient and needs to be heated, the molten salt in the low-temperature molten salt heat storage tank is heated by the high-temperature flue gas inside the boiler and transported to the high-temperature molten salt heat storage tank. The unit is operated to a stable load state, the steam-water separator bypass valve 30 is closed, the steam-water separator bypass water pump 31 is closed, and the high-temperature molten salt pump 32 is closed. The flue gas damper 15 at the tail end of the flue gas-molten salt heat exchanger side is opened, the coal supply is appropriately increased, and the openings of the flue gas damper 13 at the tail end of the boiler on the low-temperature reheater side and the flue gas damper 14 at the tail end of the boiler on the low-temperature superheater side remain unchanged. The high-temperature molten salt heat storage tank inlet valve 25 is opened and the low-temperature molten salt heat storage tank inlet valve 26 is closed. The low-temperature molten salt pump 23 is started to start the molten salt heating process. When the high-temperature molten salt heat storage tank 21 is full of molten salt, the flue gas damper 15 at the tail end of the flue gas-molten salt heat exchanger side and the low-temperature molten salt pump 23 are closed at the same time.

[0029] 2) During the startup process of the supercritical coal-fired boiler 11, the working medium in the steam-water separator 12 is heated by high-temperature molten salt, ensuring that the flue gas damper 15 at the tail of the flue gas-molten salt heat exchanger side is closed, and the opening of the flue gas damper 13 at the tail of the boiler on the low-temperature reheater side and the flue gas damper 14 at the tail of the boiler on the low-temperature superheater side are controlled by the unit control system. The steam-water separator bypass valve 30 is opened, the steam-water separator bypass water pump 31 is started, the low-temperature molten salt heat storage tank inlet valve 26 is opened and the high-temperature molten salt heat storage tank inlet valve 25 is closed, and the high-temperature molten salt pump 32 is started. The steam and water in the startup bypass are heated through the molten salt-water heat exchanger 33. The heated steam and water working medium enters the low-temperature superheater outlet header 34, thereby increasing the steam volume during the startup process, improving the load change rate, and thereby rapidly improving the startup rate of the supercritical coal-fired boiler.

Claims

1. A supercritical coal-fired boiler startup system coupled with molten salt heat storage, characterized by: The invention comprises a supercritical coal-fired boiler (11), a steam-water separator (12) arranged in the supercritical coal-fired boiler (11), a flue gas damper (13) at the rear of the boiler on the low-temperature reheater side, a flue gas damper (14) at the rear of the boiler on the low-temperature superheater side, and a flue gas-molten salt heat exchanger side tail flue gas damper (15); and further comprises a high-temperature molten salt heat storage tank (21), a low-temperature molten salt heat storage tank (22), a low-temperature molten salt pump (23), a flue gas-molten salt heat exchanger (24), a steam-water separator bypass valve (30), a steam-water separator bypass water pump (31), a high-temperature molten salt pump (32), a molten salt-water heat exchanger (33), a high-temperature molten salt heat storage tank inlet valve (25), a low-temperature molten salt heat storage tank inlet valve (26), a low-temperature superheater outlet header (34), and a low-temperature superheater (35), each Partially connected by pipelines, the low-temperature molten salt heat storage tank inlet valve 26 is installed between the low-temperature molten salt heat storage tank 22 and the molten salt-water heat exchanger 33, and the high-temperature molten salt heat storage tank inlet valve 25 is installed between the high-temperature molten salt heat storage tank 21 and the flue gas-molten salt heat exchanger 24; the tail of the supercritical coal-fired boiler (11) is a three-flue, the flue gas-molten salt heat exchanger (24) and the flue gas baffle (15) at the tail of the flue gas-molten salt heat exchanger are arranged in the outermost flue, the low-temperature superheater (35) and the flue gas baffle (14) at the tail of the low-temperature superheater side boiler are arranged in the middle flue, and the flue gas baffle (13) at the tail of the low-temperature reheater side boiler is arranged in the innermost flue; in the startup system, molten salt and steam-water exchange heat through three branches, namely, a molten salt heating branch, a molten salt heat release branch and a steam-water heating branch; The molten salt heating branch comprises a low-temperature molten salt heat storage tank (22), a low-temperature molten salt pump (23), a flue gas-molten salt heat exchanger (24), a high-temperature molten salt heat storage tank inlet valve (25) and a high-temperature molten salt heat storage tank (21) which are connected in sequence; The molten salt heat release branch comprises a high-temperature molten salt heat storage tank (21), a high-temperature molten salt pump (32), a molten salt-water heat exchanger (33), a low-temperature molten salt heat storage tank inlet valve (26) and a low-temperature molten salt heat storage tank (22) connected in sequence; The steam-water heating branch comprises a steam-water separator (12), a steam-water separator bypass valve (30), a steam-water separator bypass water pump (31), a molten salt-water heat exchanger (33), a low-temperature superheater outlet header (34) and a low-temperature superheater (35) connected in sequence.

2. The supercritical coal-fired boiler startup system coupled with molten salt heat storage according to claim 1 is characterized in that: The supercritical coal-fired boiler (11) is a supercritical π-type coal-fired boiler.

3. The supercritical coal-fired boiler startup system coupled with molten salt heat storage according to claim 1 is characterized in that: The flue gas-molten salt heat exchanger (24) is a partition-type flue gas-molten salt heat exchanger, and the molten salt-water heat exchanger (33) is a partition-type molten salt-water heat exchanger.

4. The method for operating a supercritical coal-fired boiler startup system coupled with molten salt heat storage according to any one of claims 1 to 3, characterized in that: The details are as follows: 1) When the molten salt in the high-temperature molten salt heat storage tank (21) is insufficient and needs to be heated, the unit is operated to a stable load state, the flue gas damper (15) at the tail end of the flue gas-molten salt heat exchanger side is opened, the low-temperature molten salt pump (23) is started, the high-temperature molten salt heat storage tank inlet valve (25) is opened and the low-temperature molten salt heat storage tank inlet valve (26) is closed to start the molten salt heating process; when the high-temperature molten salt heat storage tank (21) is full of molten salt, the flue gas damper (15) at the tail end of the flue gas-molten salt heat exchanger side and the low-temperature molten salt pump (23) are closed at the same time; 2) When the supercritical coal-fired boiler (11) is started, the flue gas damper (15) at the tail end of the flue gas-molten salt heat exchanger is ensured to be closed, the steam-water separator bypass valve (30) and the steam-water separator bypass water pump (31) are opened, the low-temperature molten salt heat storage tank inlet valve (26) is opened and the high-temperature molten salt heat storage tank inlet valve (25) is closed, and the high-temperature molten salt pump (32) is started to start the steam-water heating process, increase the steam volume of the startup process, increase the load change rate, and thus quickly increase the startup rate of the supercritical coal-fired boiler.

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