Regulation and control method for coping with accidental overrun of steam pressure at outlet of circulating fluidized bed boiler

Abstract

The invention discloses a regulation and control method for coping with accidental overrun of outlet steam pressure of a circulating fluidized bed boiler, which realizes advanced coping with the overrun of the outlet steam pressure of the circulating fluidized bed boiler and greatly avoids the overrun phenomenon. 0.001 MPa per second is defined as an accidental overrun early warning value of the outlet steam pressure change rate of the circulating fluidized bed boiler; the change rate of the steam pressure at the outlet of the circulating fluidized bed boiler is collected in real time, if the change rate of the steam pressure at the outlet of the circulating fluidized bed boiler collected in real time is larger than 0.001 MPa / s, it is pre-judged that the steam pressure at the outlet of the circulating fluidized bed boiler is about to accidentally exceed the limit, and the coal feeding flow of the boiler is adjusted by changing feedforward of a PI adjusting system of the coal feeding flow of the boiler. The purpose of rapidly adjusting the coal feeding flow of the boiler is achieved, and therefore the situation that the outlet steam pressure is about to exceed the limit accidentally is avoided.

Description

Technical Field

[0001] The present invention relates to a circulating fluidized bed boiler in a cogeneration thermal power plant, and particularly to a method for coping with and regulating accidental overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler. Background Art

[0002] In a cogeneration thermal power plant, the target value of the steam pressure at the outlet of the circulating fluidized bed boiler that supplies steam to the steam turbine is determined according to the steam inlet parameters of the back-pressure steam turbine; during the operation of the unit, the steam pressure at the outlet of the circulating fluidized bed boiler needs to be kept stable under various working conditions to ensure the working efficiency and quality of the steam turbine unit; however, the steam pressure at the outlet of the circulating fluidized bed boiler in the cogeneration thermal power plant will fluctuate due to various factors. There are two main influencing factors: one is the change in the coal fired in the circulating fluidized bed boiler that supplies steam to the steam turbine, that is, the factor of replacement of different coal types and large changes in the coal type ratio of the coal fired. When the coal type and ratio of the coal fired in the circulating fluidized bed boiler change, it will directly affect the steam production capacity of the circulating fluidized bed. The fluctuation of the steam production capacity will directly cause the steam pressure at the boiler outlet to also fluctuate accordingly. This factor is commonly known as "internal disturbance" in the industry; the other is the factor of large fluctuations in the heat load of the heat users in the cogeneration power plant. When the heat load fluctuates, the back-pressure steam turbine needs to adjust the steam inlet valve in a timely manner to meet the requirements of the heat load fluctuation. At this time, it is required that the steam at the outlet of the circulating fluidized bed boiler be adjusted and followed up in a timely manner to ensure the stability of the steam pressure output by the circulating fluidized bed boiler and prevent it from exceeding the adjustment control range of the design pressure; if it exceeds the limit range of the steam pressure at the outlet of the circulating fluidized bed boiler, the steam pressure will be much greater than the design value, directly causing the relevant safety valves in the system to trip and resulting in production safety accidents; if it is much lower than the limit range of the steam pressure at the outlet of the circulating fluidized bed boiler, the steam pressure will be much less than the design value, directly causing the steam turbine to fail to work properly; how to cope with the accidental overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler has become a difficult problem in on-site operation. Summary of the Invention

[0003] The present invention provides a regulation method for coping with accidental overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler, realizing the advanced response to the overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler and greatly avoiding the occurrence of overlimit phenomena.

[0004] The present invention solves the above technical problems through the following technical solutions: Overall concept of the present invention: Define "0.001 megapascals per second" as the accidental overlimit warning value of the change rate of the outlet steam pressure of a circulating fluidized bed boiler; collect in real time the change rate of the outlet steam pressure of the circulating fluidized bed boiler. If the change rate of the outlet steam pressure of the circulating fluidized bed boiler collected in real time is greater than 0.001 MPa / s, it is predicted that the outlet steam pressure of the circulating fluidized bed boiler will accidentally overlimit. By changing the feedforward of the PI regulation system of the coal feeding flow of the boiler, the purpose of quickly adjusting the coal feeding flow of the boiler is achieved, thus avoiding the accidental overlimit of the outlet steam pressure that is about to occur.

[0005] A regulation method for coping with the accidental overlimit of the outlet steam pressure of a circulating fluidized bed boiler, characterized by the following steps: First step: Retrieve the feedforward coefficient K of the change rate of the outlet steam pressure of the circulating fluidized bed boiler obtained during the operation and commissioning of the circulating fluidized bed boiler (generally, the feedforward coefficient K = 10 - 30); Second step: Define the pressure change rate of "0.001 megapascals per second" as the accidental overlimit warning value of the change rate of the outlet steam pressure of the circulating fluidized bed boiler; Third step: Collect in real time the outlet steam flow Q of the circulating fluidized bed boiler during operation; Fourth step: Collect in real time the change rate SL of the outlet steam pressure of the circulating fluidized bed boiler during operation. If the change rate SL of the outlet steam pressure of the circulating fluidized bed boiler is greater than 0.001 megapascals per second, it is predicted that the outlet steam pressure of the circulating fluidized bed boiler will accidentally overlimit; Fifth step: Use the product obtained by multiplying the outlet steam flow Q of the circulating fluidized bed boiler by the change rate SL of the outlet steam pressure of the circulating fluidized bed boiler and then by the feedforward coefficient K as the feedforward increase and decrease value M of the PI regulation system for controlling the coal feeding flow of the circulating fluidized bed boiler, and add the feedforward increase and decrease value M to the feedforward coefficient of the PI regulation system for controlling the coal feeding flow of the circulating fluidized bed boiler; after correcting the change rate SL of the outlet steam pressure of the circulating fluidized bed boiler with the feedforward coefficient and then multiplying it by the outlet steam flow Q of the circulating fluidized bed boiler, a more scientific and reasonable feedforward increase and decrease value M of the PI regulation system for regulating the coal quantity is obtained, realizing the advanced regulation of the coal feeding flow of the coal feeder, thus playing a role in pre-suppressing the accidental overlimit of the outlet steam pressure of the circulating fluidized bed boiler.

[0006] Sixth step: Continue to monitor the change rate SL of the outlet steam pressure of the circulating fluidized bed boiler during operation. If the change rate SL of the outlet steam pressure at the circulating fluidized bed outlet shows a reverse change, remove the feedforward increase and decrease value M added to the feedforward of the PI regulation system for controlling the coal feeding flow of the circulating fluidized bed boiler. This removal is completed instantaneously, so that the feedforward value of the PI regulation system for controlling the coal feeding quantity of the circulating fluidized bed boiler returns to the initial state.

[0007] The sixth step described above can be replaced by the following steps to achieve a reasonable withdrawal of measures after the accidental overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler; retrieve the design value SP of the steam pressure at the outlet of the circulating fluidized bed boiler, collect the steam pressure PV at the outlet of the operating circulating fluidized bed boiler, subtract the design value SP of the steam pressure at the outlet of the circulating fluidized bed boiler from the collected steam pressure PV at the outlet of the circulating fluidized bed boiler to obtain the deviation value ΔPV of the steam pressure at the outlet of the real-time circulating fluidized bed boiler; If the deviation value ΔPV of the steam pressure at the outlet of the circulating fluidized bed boiler is less than 0.1 MPa, start timing when the change rate SL of the steam pressure at the outlet of the circulating fluidized bed shows a reverse change. Within 5 seconds, gradually adjust the feedforward increase and decrease value M added to the feedforward of the PI control system for controlling the coal feeding flow of the circulating fluidized bed boiler to zero, so that the feedforward value of the PI control system for controlling the coal feeding amount of the circulating fluidized bed boiler returns to the initial state; If the deviation value ΔPV of the steam pressure at the outlet of the circulating fluidized bed boiler is greater than or equal to 0.1 MPa, start timing when the change rate SL of the steam pressure at the outlet of the circulating fluidized bed shows a reverse change. Within 50 - 100 seconds, gradually adjust the feedforward increase and decrease value M added to the feedforward of the PI control system for controlling the coal feeding flow of the circulating fluidized bed boiler to zero, so that the feedforward value of the PI control system for controlling the coal feeding amount of the circulating fluidized bed boiler returns to the initial state.

[0008] The present invention effectively overcomes the accidental overlimit of the steam pressure at the outlet of the circulating fluidized bed boiler and avoids the occurrence of boiler safety hazards caused by the accidental overlimit of the outlet steam pressure; combines the change rate of the outlet steam pressure with the coal feeding flow of the boiler through the feedforward coefficient of the PI regulation system, and realizes a scientific and reasonable jump of the coal feeding amount of the boiler. Specific implementation mode

[0009] The present invention will be described in detail below: A regulation method for coping with the accidental overlimit of the steam pressure at the outlet of a circulating fluidized bed boiler, characterized by the following steps: The first step is to retrieve the feedforward coefficient K of the change rate of the steam pressure at the outlet of the circulating fluidized bed boiler obtained during the operation and commissioning of the circulating fluidized bed boiler. According to the statistical data of on-site tests, the general feedforward coefficient K = 10 - 30; The second step is to define the pressure change rate of "0.001 MPa per second" as the accidental overlimit warning value of the change rate of the steam pressure at the outlet of the circulating fluidized bed boiler; this accidental overlimit warning value is an empirical value obtained through statistical prediction during a large number of on-site commissioning processes of circulating fluidized bed boilers; The third step is to collect the steam flow rate Q at the outlet of the operating circulating fluidized bed boiler in real time; Step 4: Real-time collect the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler during operation. If the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler is greater than 0.001 MPa per second, it is pre-judged that the steam pressure at the outlet of the circulating fluidized bed boiler is about to accidentally exceed the limit; Step 5: Multiply the steam flow rate Q at the outlet of the circulating fluidized bed boiler by the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler and then multiply by the feed-forward coefficient K. The obtained product is used as the feed-forward increase and decrease value M of the PI control system for controlling the coal feeding flow rate of the circulating fluidized bed boiler, and the feed-forward increase and decrease value M is added to the feed-forward of the PI control system for controlling the coal feeding flow rate of the circulating fluidized bed boiler; realize the lead regulation of the coal feeding flow rate of the coal feeder, so as to play a role in pre-suppressing the accidental over-limit of the steam pressure at the outlet of the circulating fluidized bed boiler.

[0010] Step 6: Continue to monitor the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler during operation. If the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler shows a reverse change, remove the feed-forward increase and decrease value M added to the feed-forward of the PI control system for controlling the coal feeding flow rate of the circulating fluidized bed boiler, so that the feed-forward value of the PI control system for controlling the coal feeding amount of the circulating fluidized bed boiler returns to the initial state.

[0011] Retrieve the design value SP of the steam pressure at the outlet of the circulating fluidized bed boiler, collect the steam pressure PV at the outlet of the circulating fluidized bed boiler during operation, and subtract the design value SP of the steam pressure at the outlet of the circulating fluidized bed boiler from the collected steam pressure PV at the outlet of the circulating fluidized bed boiler to obtain the deviation value ΔPV of the steam pressure at the outlet of the real-time circulating fluidized bed boiler; If the deviation value ΔPV of the steam pressure at the outlet of the circulating fluidized bed boiler is less than 0.1 MPa, start timing when the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler shows a reverse change. Within 5 seconds, gradually adjust the feed-forward increase and decrease value M added to the feed-forward of the PI control system for controlling the coal feeding flow rate of the circulating fluidized bed boiler to zero, so that the feed-forward value of the PI control system for controlling the coal feeding amount of the circulating fluidized bed boiler returns to the initial state; If the deviation value ΔPV of the steam pressure at the outlet of the circulating fluidized bed boiler is greater than or equal to 0.1 MPa, start timing when the change rate SL of the steam pressure at the outlet of the circulating fluidized bed boiler shows a reverse change. Within 50 - 100 seconds, gradually adjust the feed-forward increase and decrease value M added to the feed-forward of the PI control system for controlling the coal feeding flow rate of the circulating fluidized bed boiler to zero, so that the feed-forward value of the PI control system for controlling the coal feeding amount of the circulating fluidized bed boiler returns to the initial state.

Claims

1. A control method for dealing with occasional over-limit of outlet steam pressure of a circulating fluidized bed boiler, characterized by the following steps: The first step is to retrieve the feedforward coefficient K of the circulating fluidized bed boiler outlet steam pressure change rate obtained during the operation and commissioning of the circulating fluidized bed boiler (generally the feedforward coefficient K = 10-30); The second step is to define the pressure change rate of "0.001 MPa per second" as the occasional over-limit warning value of the steam pressure change rate at the outlet of the circulating fluidized bed boiler; The third step is to collect the outlet steam flow rate Q of the circulating fluidized bed boiler in real time; Step 4: Real-time collection of the outlet steam pressure change rate SL of the circulating fluidized bed boiler in operation. If the outlet steam pressure change rate SL of the circulating fluidized bed boiler is greater than 0.001 MPa per second, it is predicted that the outlet steam pressure of the circulating fluidized bed boiler is about to exceed the limit occasionally. Step 5: Multiply the circulating fluidized bed boiler outlet steam flow rate Q by the circulating fluidized bed boiler outlet steam pressure change rate SL and then multiply by the feedforward coefficient K to obtain the product as the feedforward increase / decrease value M of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler, and add the feedforward increase / decrease value M to the feedforward of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler; The coal feeder's coal flow rate can be controlled in advance, thereby preventing the occasional over-limit of the circulating fluidized bed boiler's outlet steam pressure.

2. A control method for dealing with occasional over-limit of outlet steam pressure of a circulating fluidized bed boiler according to claim 1, characterized in that: Step 6. Continue to monitor the outlet steam pressure change rate SL of the circulating fluidized bed boiler in operation. If the outlet steam pressure change rate SL of the circulating fluidized bed changes in the opposite direction, remove the feedforward increase or decrease value M added to the feedforward of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler, so that the feedforward value of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler is restored to the initial state.

3. A control method for dealing with occasional over-limit of outlet steam pressure of a circulating fluidized bed boiler according to claim 1, characterized in that: Retrieving the design value SP of the circulating fluidized bed boiler outlet steam pressure, collecting the outlet steam pressure PV of the circulating fluidized bed boiler in operation, and subtracting the design value SP of the circulating fluidized bed boiler outlet steam pressure from the collected circulating fluidized bed boiler outlet steam pressure PV to obtain the real-time circulating fluidized bed boiler outlet steam pressure deviation value ΔPV; If the outlet steam pressure deviation value ΔPV of the circulating fluidized bed boiler is less than 0.1 MPa, the timing starts when the outlet steam pressure change rate SL of the circulating fluidized bed changes in the opposite direction, and within 5 seconds, the feedforward increase and decrease value M added to the feedforward of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler is gradually adjusted to zero, so that the feedforward value of the PI control system for controlling the coal flow rate of the circulating fluidized bed boiler is restored to the initial state; If the outlet steam pressure deviation value ΔPV of the circulating fluidized bed boiler is greater than or equal to 0.1 MPa, the timing starts when the outlet steam pressure change rate SL of the circulating fluidized bed changes in the opposite direction. Within 50-100 seconds, the feedforward increase and decrease value M added to the feedforward of the PI control system for controlling the coal feed rate of the circulating fluidized bed boiler is gradually adjusted to zero, so that the feedforward value of the PI control system for controlling the coal feed rate of the circulating fluidized bed boiler is restored to the initial state.