Subcritical main pipe feed water system boiler cooling and pressure reduction start-up system and method

Abstract

The invention discloses a subcritical main pipe feed water system boiler cooling and pressure reducing starting system and method. The system comprises a controllable pressure reducing regulating valve, a water spraying and cooling device, a feed water pressure transmitter and a feed water temperature sensor, which are sequentially installed between a boiler drum water level regulating valve and a No. 1 boiler and a No. 2 boiler, a water spraying and cooling device, a feed water pressure transmitter and a feed water temperature sensor, a water spraying and cooling regulating valve installed on a water source pipeline of the water spraying and cooling device, a feed water temperature PID controller connected to the corresponding boiler water spraying and cooling regulating valve and the feed water temperature sensor, and a feed water pressure PID controller connected to the corresponding boiler controllable pressure reducing regulating valve and the feed water pressure transmitter; the feed water pressure PID controller controls the controllable pressure reducing regulating valve to open slowly, so that the boiler feed water pressure is always within the pressure range allowed by the boiler metal material; the feed water temperature PID controller controls the opening of the water spraying and cooling regulating valve to control the feed water temperature to always be within the temperature range allowed by the boiler metal pipe wall; the invention is of great significance for reducing the start-up cost of the unit.

Description

Technical Field

[0001] The invention relates to the technical field of thermal power station automatic control, and in particular to a subcritical main pipe feedwater system boiler cooling and pressure reducing starting system and method. Background Art

[0002] In the existing subcritical main pipe feedwater system with two boilers and one unit, the two boilers share a feedwater system, which has become the preferred solution for thermal power energy companies to reduce initial investment. First, in conventional thermal power generating units, a feedwater system includes a feedwater pump group, a high-pressure heater system, a high-pressure steam extraction system and a high-pressure heater drainage system, while two boilers share a feedwater system, which can greatly reduce the initial investment of the enterprise; secondly, with one less feedwater system, the company's repair and maintenance costs for the feedwater system equipment will also be significantly reduced. However, the main pipe feedwater boiler is started in two ways: either the two boilers are started at the same time; or the first boiler is started first to drive the turbine to run, connect to the grid for power generation, and take the initial load, and then wait for the second boiler to reach the steam quality close to that of the first boiler through the turbine bypass system, and then the steam of the two boilers is merged into the same steam main pipe through the steam equipment, and finally the two boilers synchronize the turbine to achieve full load operation of the unit.

[0003] The main pipe water supply system has brought some restrictions to the flexible operation of the unit. For example, when the second boiler is under maintenance, the first boiler is running at full load with the steam turbine. When the second boiler completes the maintenance task, it needs to be put into operation. The first boiler and steam turbine need to go through load reduction, reduce the output of various auxiliary machines, stop the coal feeder in turn, add oil to assist combustion, put into bypass, decouple the generator, trip the steam turbine, and finally shut down the running boiler. The two boilers are then started synchronously to drive the unit to full output; or the first boiler is reduced from full output to the initial load state of the steam turbine through a series of operations such as load reduction, reduction of the feed system, and oil addition for stable combustion, waiting for the feed water temperature to drop to a temperature suitable for the metal of the maintenance boiler. This process may take several hours or even a whole day. The second boiler is watered from the boiler, cold flushed, ignited and heated, and hot flushed until the steam quality meets the steam connection conditions. This process may take several hours or even a whole day. Then synchronize the steam turbine with the first boiler to full output. In the process of connecting the second boiler, assuming that one layer of oil burners is in operation and burning stably, with four oil guns per layer, and each oil gun uses 500 kg of fuel per hour, and considering that the first boiler is not fully loaded, the company's loss on the power grid. In this way, the economic loss caused to the company in the process of starting and connecting the second boiler is obvious.

[0004] This startup method has the following problems:

[0005] First, when two boilers are started at the same time, the number of devices that operators need to monitor will increase exponentially, and it is inevitable that mistakes will occur during the start-up process, causing unnecessary losses to the company and employees. Also, due to the inconsistency of the equipment materials of the two boilers, the requirements for the water supply system during the start-up process are also different, which is also a great test for the professional quality of operators and the reliability of equipment materials.

[0006] Second, it is a waste for the first boiler to wait for the second boiler to start with the initial load, and it is harmful to the equipment if the unit runs below the steady-fire load for a long time, reducing the service life of the equipment.

[0007] Third, the greater the temperature difference between the boiler metal tube wall and the feed water, the greater the possibility of brittle failure of the boiler metal tube wall. If the second boiler that has been overhauled needs to be put into use, it must wait for the first boiler to be in the same state as it. In this process, the economic loss to the enterprise is obvious, and the damage to the unit equipment cannot be ignored. Summary of the invention

[0008] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a subcritical main pipe water supply system boiler cooling and pressure reduction starting system and method, which is of great significance to improving the operating reliability of a thermal power plant with two boilers and one machine or multiple boilers and multiple machines main pipe water supply system, extending the life of key boiler equipment, reducing the probability of metal pipe wall damage or even pipe burst accidents, reducing maintenance and repair costs, and reducing unit startup costs.

[0009] In order to achieve the above purpose, the present invention adopts the following technical scheme:

[0010] A subcritical main pipe feed water system boiler cooling and pressure reducing starting system, comprising a No. 1 boiler controllable pressure reducing regulating valve 1, a No. 1 boiler water spraying and cooling device 2, a No. 1 boiler feed water pressure transmitter 5 and a No. 1 boiler feed water temperature sensor 4 which are sequentially installed on the pipeline between the No. 1 boiler drum water level regulating valve 8 and the No. 1 boiler 19, a No. 1 boiler water spraying and cooling regulating valve 3 installed on the water source pipeline of the No. 1 boiler water spraying and cooling device 2, a No. 1 boiler feed water temperature PID controller connected to the No. 1 boiler water spraying and cooling regulating valve 3 and the No. 1 boiler feed water temperature sensor 4, and a No. 1 boiler feed water pressure PID controller connected to the No. 1 boiler controllable pressure reducing regulating valve 1 and the No. 1 boiler feed water pressure transmitter 5;

[0011] It also includes a controllable pressure reducing regulating valve 11 for boiler No. 2, a water spray cooling device 12 for boiler No. 2, a feed water pressure transmitter 15 for boiler No. 2 and a feed water temperature sensor 14 for boiler No. 2, which are installed in sequence on the pipeline between the water level regulating valve 18 for boiler No. 2 and the pipeline 20 for boiler No. 2, a water spray cooling regulating valve 13 for boiler No. 2 installed on the water source pipeline of the water spray cooling device 12 for boiler No. 2, a feed water temperature PID controller 16 for boiler No. 2 connected to the water spray cooling regulating valve 13 for boiler No. 2 and the feed water temperature sensor 14 for boiler No. 2, and a feed water pressure PID controller 17 for boiler No. 2 connected to the controllable pressure reducing regulating valve 11 for boiler No. 2 and the feed water pressure transmitter 15 for boiler No. 2.

[0012] The water source interfaces of the No. 1 boiler water spray cooling device 2 and the No. 2 boiler water spray cooling device 12 are connected to the water supply pipeline between the water supply pump 9 and the high-pressure heater 10.

[0013] The No. 1 boiler drum water level regulating valve 8 and the No. 2 boiler drum water level regulating valve 18 are installed between the high-pressure heater 10 and the No. 1 boiler 18 and the No. 2 boiler 19 respectively.

[0014] The working method of the subcritical mother pipe feed water system boiler cooling and pressure reduction starting system is that if the No. 2 boiler 20 is used as the starting boiler, during the startup process from ignition of the No. 2 boiler 20 to merging with the main steam of the No. 1 boiler 19, the temperature of the metal material of the tube wall of the No. 2 boiler 20 changes, and the temperature and pressure of the feed water entering the No. 2 boiler 20 should also change accordingly. In order to reduce the possibility of brittle damage to the metal tube wall of the No. 2 boiler 20 due to the mismatch between the metal temperature of the No. 2 boiler 20 and the temperature and pressure of the feed water, the No. 2 boiler feed water pressure PID controller 17 controls the controllable pressure reduction of the No. 2 boiler. The regulating valve 11 is opened slowly at a preset rate so that the feed water pressure measured by the feed water pressure transmitter 15 of boiler No. 2 is always within the allowable feed water pressure range of the metal material of boiler No. 2 during the load increase stage during the rising process; the feed water temperature PID controller 16 of boiler No. 2 reduces the opening of the water spray cooling regulating valve 13 of boiler No. 2 to reduce the amount of low-temperature feed water sprayed into the water spray cooling device 12 of boiler No. 2, thereby controlling the feed water temperature measured by the feed water temperature sensor 14 of boiler No. 2 to be within the allowable temperature range of the metal pipe wall of boiler No. 2 during the heating process. As the load of boiler No. 2 20 continues to increase, the temperature of the metal tube wall of boiler No. 2 20 also continues to increase, and the required feed water pressure and temperature are also controlled to increase continuously according to the rising speed allowed by the metal tube wall of boiler No. 2 20, until the main steam of boiler No. 2 20 is successfully merged into boiler No. 1 19; at this moment, the controllable pressure reducing regulating valve 11 of boiler No. 2 20 is already in a fully open state, and the water spraying and cooling regulating valve 13 of boiler No. 2 20 is already in a fully closed state, indicating that this invention successfully helps boiler No. 2 20 to complete the startup process; if boiler No. 1 19 is used as the startup boiler, the startup process of boiler No. 1 19 from ignition to merging with the main steam of boiler No. 2 20 is the same as the startup process of boiler No. 2 20 from ignition to merging with the main steam of boiler No. 1 19.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The present invention enriches the startup methods of a unit with two boilers (including multiple boilers) in a main pipe water supply system. The No. 1 boiler 19 that is running first does not have to be below the stable combustion load to wait for the other No. 2 boiler 20 to complete the startup process. The two boilers can wait for the other boiler to join in any state. The economic cost of the power generation enterprise during the unit startup process is reduced; the metal pipe wall of the boiler is protected to the greatest extent; the labor intensity of the operating personnel is also reduced; and even the unnecessary misoperation caused by the operating personnel monitoring two boilers in an unstable combustion state at the same time is reduced.

[0017] (2) Based on the existing thermal power plant system hardware structure, there is no need for complex hardware equipment modification. Only one set of pressure reducing regulating valves, one set of water spraying and cooling device, one pressure transmitter and one temperature sensor are needed. Real-time control of boiler feed water pressure and temperature can be achieved, optimizing the startup method of multiple boiler units with main pipe feed water.

[0018] (3) The existing technology cannot achieve precise control over the boiler feed water temperature. When the feed water temperature alarm appears to be over-temperature, the present invention uses the low-temperature feed water in front of the high-pressure heater 10 to merge into the high-temperature feed water in a short time, thereby achieving the purpose of precisely controlling the feed water temperature as the boiler metal temperature changes, and optimizing the start-up method of multiple boilers in the main pipe feed water system. Furthermore, the process feed water in front of the high-pressure heater 10 is selected as the refrigerant for the water spray cooling device, considering that the quality of the process water is the same, and the water quality will not change during the process of controlling the feed water temperature. The purpose is to make the process simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0020] 1—Controllable pressure reducing regulating valve for boiler No. 1; 2—Water spray cooling device for boiler No. 1; 3—Water spray cooling regulating valve for boiler No. 1; 4—Feed water temperature sensor for boiler No. 1; 5—Feed water pressure transmitter for boiler No. 1; 6—Feed water temperature PID controller for boiler No. 1; 7—Feed water pressure PID controller for boiler No. 1; 8—Drum water level regulating valve for boiler No. 1; 9—Feed water pump; 10—High-pressure heater; 11—Controllable pressure reducing regulating valve for boiler No. 2; 12—Water spray cooling device for boiler No. 2; 13—Water spray cooling regulating valve for boiler No. 2; 14—Feed water temperature sensor for boiler No. 2; 15—Feed water pressure transmitter for boiler No. 2; 16—Feed water temperature PID controller for boiler No. 2; 17—Feed water pressure PID controller for boiler No. 2; 18—Drum water level regulating valve for boiler No. 2; 19—Boiler No. 1; 20—Boiler No. 2. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] like Figure 1As shown, a subcritical main pipe feed water system boiler cooling and pressure reducing starting system of the present invention comprises a No. 1 boiler controllable pressure reducing regulating valve 1, a No. 1 boiler water spraying and cooling device 2, a No. 1 boiler feed water pressure transmitter 5 and a No. 1 boiler feed water temperature sensor 4 which are sequentially installed on the pipeline between the No. 1 boiler drum water level regulating valve 8 and the No. 1 boiler 19, a No. 1 boiler water spraying and cooling regulating valve 3 installed on the water source pipeline of the No. 1 boiler water spraying and cooling device 2, a No. 1 boiler feed water temperature PID controller connected to the No. 1 boiler water spraying and cooling regulating valve 3 and the No. 1 boiler feed water temperature sensor 4, and a No. 1 boiler feed water pressure PID controller connected to the No. 1 boiler controllable pressure reducing regulating valve 1 and the No. 1 boiler feed water pressure transmitter 5;

[0023] It also includes a controllable pressure reducing regulating valve 11 for boiler No. 2, a water spray cooling device 12 for boiler No. 2, a feed water pressure transmitter 15 for boiler No. 2 and a feed water temperature sensor 14 for boiler No. 2, which are installed in sequence on the pipeline between the water level regulating valve 18 for boiler No. 2 and the pipeline 20 for boiler No. 2, a water spray cooling regulating valve 13 for boiler No. 2 installed on the water source pipeline of the water spray cooling device 12 for boiler No. 2, a feed water temperature PID controller 16 for boiler No. 2 connected to the water spray cooling regulating valve 13 for boiler No. 2 and the feed water temperature sensor 14 for boiler No. 2, and a feed water pressure PID controller 17 for boiler No. 2 connected to the controllable pressure reducing regulating valve 11 for boiler No. 2 and the feed water pressure transmitter 15 for boiler No. 2.

[0024] The boiler drum water level regulating valve is located between the high-pressure heater 10 and the boiler. It is the main means of regulating the water supply to the boiler and the only way to supply water to the boiler. Before the boiler is started, the boiler drum water level regulating valve is used to provide the boiler with process water of suitable pressure and temperature. The greater the temperature difference between the process water and the metal of the tube wall in the boiler metal tube wall, the greater the possibility of brittle failure of the boiler metal tube wall. Therefore, the pressure and temperature of the boiler process feed water cannot exceed the range allowed by the temperature of the boiler metal tube wall. In the unit with a main tube feed water system of two boilers (including multiple boilers), during the startup process, the metal tube of the second boiler to be started has the possibility of brittle failure. Under the existing technical conditions, when the second boiler needs to be started, in order to reduce the possibility of brittle failure of the boiler metal tube, the first boiler must be stopped and started together; or the load of the first boiler must be reduced, waiting for the appropriate feed water temperature and feed water pressure, and then the second boiler is put into use. In this process, the labor intensity of the operating personnel will increase exponentially, and the possibility of misoperation at this stage will also increase greatly, which will bring unnecessary economic losses to the enterprise.

[0025] like Figure 1As shown, taking the No. 2 boiler 20 as the second startup boiler as an example, the role of the present invention in the startup process of the No. 2 boiler 20 is specifically described. In the startup process of the No. 2 boiler 20 from ignition to merging with the main steam of the No. 1 boiler 19, the temperature of the metal material of the tube wall of the No. 2 boiler 20 changes, and the temperature and pressure of the feed water entering the No. 2 boiler 20 should also change accordingly. In order to reduce the possibility of brittle damage of the metal tube wall of the No. 2 boiler 20 due to the mismatch between the metal temperature of the No. 2 boiler 20 and the temperature and pressure of the feed water, in the process of the No. 2 boiler 20 from ignition to merging with the main steam of the No. 1 boiler 19, the No. 2 boiler feed water pressure PID controller 17 controls the No. 2 boiler controllable pressure reducing regulating valve 11 in front of the No. 2 boiler 20 to slowly open at a rate of 5% / h. To 100%, so that the feed water pressure measured by the feed water pressure transmitter 15 of the No. 2 boiler 20 is always within the feed water pressure range allowed by the metal material of the No. 2 boiler 20 during the load increase stage in the process of slowly approaching the feed water main pipe pressure from 0MPa; the No. 2 boiler feed water temperature PID controller 16 gradually closes the spray water cooling regulating valve 13 at a rate of 2% / h to gradually reduce the amount of low-temperature feed water sprayed into the No. 2 boiler spray water cooling device 12 to 0t / h, thereby achieving the control of the feed water temperature measured by the No. 2 boiler feed water temperature sensor 14 in the process of heating, which is always within the temperature range allowed by the metal pipe wall of the No. 2 boiler 20. As the load of the No. 2 boiler 20 continues to increase, the temperature of the metal pipe wall of the No. 2 boiler 20 also continues to increase. The required feed water pressure and temperature are also under the control of the system of the present invention, and are continuously increased at 2 degrees / min within the range allowed by the metal pipe wall of the No. 2 boiler 20 until the main steam of the No. 2 boiler 20 is successfully incorporated into the No. 1 boiler 19.

Claims

1. A working method for a subcritical main pipe feedwater system boiler cooling and pressure reduction starting system, characterized in that: The system comprises a controllable pressure reducing regulating valve (1) for a boiler (1), a water spraying cooling device (2) for a boiler (1), a feed water pressure transmitter (5) for a boiler (1) and a feed water temperature sensor (4) for a boiler (1) which are sequentially installed on a pipeline between a water level regulating valve (8) for a boiler (1) and a boiler (19); a water spraying cooling regulating valve (3) for a boiler (1) installed on a water source pipeline of the water spraying cooling device (2); a feed water temperature PID controller (6) for a boiler (1) connected to the water spraying cooling regulating valve (3) and the feed water temperature sensor (4); and a feed water pressure PID controller (7) for a boiler (1) connected to the controllable pressure reducing regulating valve (1) and the feed water pressure transmitter (5); It also includes a No. 2 boiler controllable pressure reducing regulating valve (11), a No. 2 boiler water spraying cooling device (12), a No. 2 boiler feed water pressure transmitter (15) and a No. 2 boiler feed water temperature sensor (14) installed in sequence on the pipeline between the No. 2 boiler drum water level regulating valve (18) and the No. 2 boiler (20); a No. 2 boiler water spraying cooling regulating valve (13) installed on the water source pipeline of the No. 2 boiler water spraying cooling device (12); a No. 2 boiler feed water temperature PID controller (16) connected to the No. 2 boiler water spraying cooling regulating valve (13) and the No. 2 boiler feed water temperature sensor (14); and a No. 2 boiler feed water pressure PID controller (17) connected to the No. 2 boiler controllable pressure reducing regulating valve (11) and the No. 2 boiler feed water pressure transmitter (15); The working method is as follows: if the No. 2 boiler (20) is used as the starting boiler, during the starting process from ignition of the No. 2 boiler (20) to merging with the main steam of the No. 1 boiler (19), the temperature of the metal material of the tube wall of the No. 2 boiler (20) changes, and the temperature and pressure of the feed water entering the No. 2 boiler (20) also change accordingly. In order to reduce the possibility of brittle failure of the metal tube wall of the No. 2 boiler (20) due to the mismatch between the metal temperature of the No. 2 boiler (20) and the temperature and pressure of the feed water, the feed water pressure P of the No. 2 boiler is set to The ID controller (17) controls the controllable pressure reducing regulating valve (11) of the No. 2 boiler to open slowly at a preset rate, so that the feed water pressure measured by the feed water pressure transmitter (15) of the No. 2 boiler is always within the feed water pressure range allowed by the metal material of the No. 2 boiler (20) during the load increase stage. The feed water temperature PID controller (16) of the No. 2 boiler reduces the opening of the No. 2 boiler spray water cooling regulating valve (13) to reduce the amount of low-temperature feed water sprayed into the No. 2 boiler spray water cooling device (12), thereby controlling the feed water temperature measured by the No. 2 boiler feed water temperature sensor (14) to be within the temperature range allowed by the metal pipe wall of the No. 2 boiler (20) during the temperature increase process. As the load of the No. 2 boiler (20) continues to increase, the temperature of the metal pipe wall of the No. 2 boiler (20) also continues to increase, and the required feed water pressure and temperature are also controlled to increase continuously according to the rising speed allowed by the metal pipe wall of the No. 2 boiler (20) until the main steam of the No. 2 boiler (20) is successfully merged into the No. 1 boiler (19). At this moment, the No. 2 boiler controllable pressure reducing regulating valve (11) of the No. 2 boiler (20) is in a fully open state, and the No. 2 boiler water spraying temperature reducing regulating valve (13) of the No. 2 boiler (20) is in a fully closed state, indicating that the No. 2 boiler (20) has completed the startup process; if the No. 1 boiler (19) is used as the startup boiler, the startup process of the No. 1 boiler (19) from ignition to merging with the main steam of the No. 2 boiler (20) is the same as the startup process of the No. 2 boiler (20) from ignition to merging with the main steam of the No. 1 boiler (19).

2. The working method of a subcritical main pipe feedwater system boiler cooling and decompression starting system according to claim 1, characterized in that: The water source interfaces of the No. 1 boiler water spray cooling device (2) and the No. 2 boiler water spray cooling device (12) are connected to the water supply pipeline between the water supply pump (9) and the high-pressure heater (10).

3. The working method of a subcritical main pipe feedwater system boiler cooling and decompression starting system according to claim 1, characterized in that: The No. 1 boiler drum water level regulating valve (8) and the No. 2 boiler drum water level regulating valve (18) are respectively installed between the high-pressure heater (10) and the No. 1 boiler (19) and the No. 2 boiler (20).

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