Boiler main steam temperature optimization control method

Abstract

The invention relates to the technical field of steam temperature optimization control, and discloses a boiler main steam temperature optimization control method which comprises the following steps: step 1, a main controller calculates a main steam temperature control error according to a main steam temperature given value and a main steam temperature actual value; step 2, control stage calculation: calculating a given increment of the outlet temperature of the desuperheater according to a main controller proportional control coefficient, a main controller integral control coefficient and a main controller differential control coefficient; and step 3, a judgment control stage: judging a transient state or a steady state control stage according to the main steam temperature control error, the sampling time, the main steam temperature and the main steam temperature control error transient state judgment limit value. By means of the boiler main steam temperature optimization control method, when the main steam temperature meets the steady-state condition, a steady-state control stage is started, a desuperheating water valve can be slowly adjusted, abrasion of the desuperheating water valve is reduced, and long-term stable operation can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of steam temperature optimization control, and particularly to an optimization control method for the main steam temperature of a boiler. Background Art

[0002] With the acceleration of the national economic construction pace, the social demand for electricity is increasing. The country's electric energy production mainly relies on thermal power generation. During the thermal power generation process, the boiler is a key device that provides power for the steam turbine. The main steam temperature at the outlet of the final superheater of the boiler is an important control parameter of the boiler unit. If the main steam temperature entering the steam turbine is too high, it will affect the service life of the superheated pipe material. Prolonged overheating will cause the superheated pipe to burst and damage to the steam turbine components, etc.; if the main steam temperature entering the steam turbine is relatively low, the water content in the steam will be relatively high, resulting in equipment wear and failure and economic losses. Therefore, the control quality of the main steam temperature directly affects the overall safety and economic operation of the unit. For the boiler to operate smoothly, the main steam temperature of the boiler must be strictly controlled within a given range.

[0003] Most of the main steam temperature of the boiler is controlled by spraying water for desuperheating, and the desuperheating water valve is adjusted to control the desuperheating water volume. When the boiler operates at low load, the steam temperature is relatively low and the desuperheating water volume required is less; when operating at high load, the steam temperature is relatively high and the desuperheating water volume required is more. Most power plants use valves with equal percentage or parabolic flow characteristics. However, in the actual application of the boiler, the flow characteristic curve of the desuperheating water valve is non-linear.

[0004] At present, most thermal power plants in the country use traditional single-loop or double-loop PID controllers to control the main steam temperature. When using traditional single-loop or double-loop PID controllers to control the main steam temperature, when the load fluctuates, the main steam temperature frequently exceeds the temperature, affecting the safety of the unit and then unable to meet the requirements of the production process. At the same time, due to the non-linear characteristics of the desuperheating water valve, the automatic control of the main steam temperature cannot operate automatically within the full range of the desuperheating water valve, thereby reducing the service life of the desuperheating water valve.

[0005] Therefore, the technical personnel in this field have provided an optimization control method for the main steam temperature of a boiler to solve the problems raised in the above background art. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides an optimization control method for the main steam temperature of a boiler, which solves the problems that when the load fluctuates, the main steam temperature frequently exceeds the temperature, affecting the safety of the unit and then unable to meet the requirements of the production process, and the automatic control of the main steam temperature cannot operate automatically within the full range of the desuperheating water valve, thereby reducing the service life of the desuperheating water valve.

[0007] To achieve the above object, the present invention is realized by the following technical solutions: A method for optimizing the control of the main steam temperature of a boiler, comprising the following steps:

[0008] Step 1, main controller calculation: Calculate the main steam temperature control error according to the main steam temperature set value and the actual main steam temperature.

[0009] Step 2, control stage calculation: Calculate the given increment of the outlet temperature of the desuperheater according to the proportional control coefficient of the main controller, the integral control coefficient of the main controller, and the derivative control coefficient of the main controller.

[0010] Step 3, judgment of the control stage: Judge the transient or steady-state control stage according to the main steam temperature control error, the sampling moment, the main steam temperature, and the transient judgment limit value of the main steam temperature control error.

[0011] Step 4, output of the secondary controller: Output the desuperheating water valve control command U to the desuperheating water valve according to the compensation amount of the secondary feed-forward compensator, the control increment of the secondary controller, and the control command of the desuperheating water valve opening.

[0012] Preferably, the calculation formula for the main steam temperature control error in step 1 is:

[0013] e 1 (k) = SP 1 (k) - T 1 (k)

[0014] Where, e 1 represents the main steam temperature control error; k represents the sampling moment; SP 1 represents the main steam temperature set value; T 1 represents the main steam temperature.

[0015] Preferably, the calculation formula for the given increment of the outlet temperature of the desuperheater in step 2 is:

[0016]

[0017] Where, K p_m represents the proportional control coefficient of the main controller; K i_m represents the integral control coefficient of the main controller; K d_m represents the derivative control coefficient of the main controller; e 1 represents the main steam temperature control error; k represents the sampling moment; SP 0 represents the given value of the outlet temperature of the desuperheater.

[0018] Preferably, the specific value in step 2 is obtained according to the formula;

[0019] Given value of the outlet temperature of the desuperheater:

[0020]

[0021] Among them, SP 0 represents the set value of the desuperheater outlet temperature, and k represents the sampling time;

[0022] Calculation of the compensation amount of the main feed-forward compensator:

[0023] fb 1 (k) = (D 1 (k) - D 1 (k - 1)) T gR 1 (k)

[0024] Among them, fb 1 represents the feed-forward compensation amount of the main controller, D 1 represents the disturbance amount of the main steam temperature, R 1 represents the compensation coefficient, and k represents the sampling time;

[0025] Control error of the desuperheater outlet temperature:

[0026] e 0 (k) = SP 0 (k) + fb 1 (k) - T 0 (k)

[0027] Among them, k represents the sampling time, SP 0 represents the set value of the desuperheater outlet temperature, fb 1 represents the feed-forward compensation amount of the main controller, T 0 represents the desuperheater outlet temperature, and e 0 represents the control error of the desuperheater outlet temperature.

[0028] Preferably, the calculation process for judging the transient or steady-state control stage in step three is as follows:

[0029]

[0030] Among them, S represents the control stage, 0 represents the steady-state control, 1 represents the transient control, e 1 represents the main steam temperature control error, k represents the sampling time, ε represents the transient judgment limit value of the main steam temperature control error, and T 1 represents the main steam temperature.

[0031] Preferably, in step three, the sub-zone serial number of the desuperheater water valve control command can be judged according to the flow characteristics of the desuperheater water valve for zoning:

[0032] a l-1 ≤ U(k - 1) < a l

[0033] Among them, U represents the control command for the desuperheating water valve opening, and k represents the sampling time;

[0034] Preferred sequence number of the sub - controller for the transient - steady - state controller:

[0035]

[0036] Among them, represents the proportional control coefficient of the sub - controller Cs l ; is the integral control coefficient of the sub - controller Cs l ; is the derivative control coefficient of the sub - controller Cs l ; S represents the control stage; 0 represents steady - state control; 1 represents transient control.

[0037] Preferably, the calculation formula for the compensation amount of the sub - feed - forward compensator in step 4 is:

[0038] fb 0 (k)=(D 0 (k)-D 0 (k - 1)) T gR 0 (k)

[0039] Among them, fb 0 represents the feed - forward compensation amount of the sub - controller, k represents the sampling time, D 0 represents the disturbance amount of the desuperheater outlet temperature, R 0 represents the compensation coefficient;

[0040] The calculation formula for the control increment of the sub - controller is:

[0041]

[0042] Among them, represents the proportional control coefficient of the sub - controller Cs l ; is the integral control coefficient of the sub - controller Cs l ; is the derivative control coefficient of the sub - controller Cs l ; du 0 represents the control increment of the desuperheating water valve opening; e 0 represents the control error of the desuperheater outlet temperature; k represents the sampling time;

[0043] Desuperheating water valve opening control command:

[0044] U(k)=U(k - 1)+du 0 (k)+fb 0 (k)

[0045] Among them, U represents the control instruction for the desuperheating water valve opening, k represents the sampling time, and du 0 represents the increment of the desuperheating water valve opening control, and fb 0 represents the feedforward compensation amount of the secondary controller.

[0046] Preferably, if the amplitude of the main steam temperature control error is large, transient rapid adjustment is required. When the temperature is high and continuously rising or the temperature is low and continuously decreasing, transient rapid adjustment is entered; otherwise, the steady-state slow adjustment stage is entered.

[0047] Preferably, in the steady-state stage, the secondary controller Cs corresponding to the partition serial number l determined by the flow characteristic is l used as the actual secondary controller to achieve slow fine adjustment; in the transient stage, the secondary controllers Cs corresponding to the partition serial numbers l and l + 1 are l 、Cs l+1 and the controller with a large amplitude of the proportional control coefficient in them is used as the actual secondary controller to achieve rapid adjustment.

[0048] Preferably, for the partition of the desuperheating water valve flow characteristic, the form of the sub-partition expression is:

[0049]

[0050] Among them, the value represented by a0 is 0, and the value represented by an is 100.

[0051] The present invention provides an optimized control method for the main steam temperature of a boiler. It has the following beneficial effects:

[0052] 1. Through the optimized control method for the main steam temperature of the boiler, the present invention enables the main steam temperature to enter the steady-state control stage when meeting the steady-state conditions, and the desuperheating water valve can be slowly adjusted, reducing the wear of the desuperheating water valve and enabling long-term stable operation.

[0053] 2. Through the optimized control method for the main steam temperature of the boiler, when the main steam temperature control error is large or the load of the boiler changes greatly, the present invention enables the automatic control of the main steam temperature to enter the transient control, can quickly adjust the desuperheating water valve, ensure that the main steam temperature meets the process requirements, and improve the safety of the unit operation.

[0054] 3. Through the optimized control method for the main steam temperature of the boiler and the control technology of the partition PID control method according to the desuperheating water valve flow characteristic, the present invention enables the desuperheating water valve to be automatically controlled within the full range under different load operating conditions of the boiler. Brief Description of the Drawings

[0055] Figure 1 is the flow chart of the present invention;

[0056] Figure 2 is the system schematic diagram of the present invention;

[0057] Figure 3 Schematic diagram of the flow rate characteristics of the desuperheating water valve of the present invention. Detailed implementation manners

[0058] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0059] Embodiment:

[0060] Please refer to the attached Figure 1 , the embodiment of the present invention provides a method for optimizing the control of the main steam temperature of a boiler, including the following steps:

[0061] Step 1, Main controller calculation: Calculate the main steam temperature control error according to the given value of the main steam temperature and the actual value of the main steam temperature.

[0062] Step 2, Control stage calculation: Calculate the given increment of the outlet temperature of the desuperheater according to the proportional control coefficient, integral control coefficient and derivative control coefficient of the main controller.

[0063] Step 3, Determine the control stage: Determine the transient or steady-state control stage according to the main steam temperature control error, sampling time, main steam temperature and the transient judgment limit value of the main steam temperature control error.

[0064] Step 4, Output of the secondary controller: Output the desuperheating water valve control command U to the desuperheating water valve according to the compensation amount of the secondary feedforward compensator, the control increment of the secondary controller and the control command of the desuperheating water valve opening.

[0065] The function of the main controller calculation is to determine whether the system reaches the desired state and measures need to be taken for adjustment; the control stage calculation calculates the given increment of the outlet temperature of the desuperheater through the proportional, integral and derivative control coefficients, and the proportional, integral and derivative control coefficients affect the response speed, stability and oscillation during the transient process of the control system; the determination of the control stage involves the control error of the main steam temperature, sampling time, the main steam temperature itself and other transient judgment limit values, and helps the system adapt to different operating conditions; the output of the secondary controller involves the compensation amount of the secondary feedforward compensator, the control increment of the secondary controller and the control command of the desuperheating water valve opening, and the command affects the operation of the desuperheating water valve and adjusts the system to maintain the main steam temperature within the desired range.

[0066] The calculation formula of the main steam temperature control error in Step 1 is:

[0067] e1 (k) = SP 1 (k) - T 1 (k)

[0068] Among them, e 1 represents the main steam temperature control error; k represents the sampling time; SP 1 represents the main steam temperature set value; T 1 represents the main steam temperature.

[0069] The calculation formula for the given increment of the desuperheater outlet temperature in step two is:

[0070]

[0071] Among them, K p_m represents the proportional control coefficient of the main controller; K i_m represents the integral control coefficient of the main controller; K d_m represents the derivative control coefficient of the main controller; e 1 represents the main steam temperature control error; k represents the sampling time; SP 0 represents the given value of the desuperheater outlet temperature.

[0072] The specific value in step two is obtained according to the formula;

[0073] Given value of the desuperheater outlet temperature:

[0074]

[0075] Among them, SP 0 represents the given value of the desuperheater outlet temperature, k represents the sampling time;

[0076] Calculation of the main feed-forward compensator compensation amount:

[0077] fb 1 (k) = (D 1 (k) - D 1 (k - 1)) T gR 1 (k)

[0078] Among them, fb 1 represents the main controller feed-forward compensation amount, D 1 represents the main steam temperature disturbance amount, R 1 represents the compensation coefficient, k represents the sampling time;

[0079] Desuperheater outlet temperature control error:

[0080] e 0 (k) = SP 0 (k) + fb 1 (k) - T 0(k)

[0081] Among them, k represents the sampling moment, and SP 0 represents the set value of the outlet temperature of the desuperheater, and fb 1 represents the feedforward compensation amount of the main controller, and T 0 represents the outlet temperature of the desuperheater, and e 0 represents the control error of the outlet temperature of the desuperheater.

[0082] The calculation process for judging the transient or steady-state control stage in step three is as follows:

[0083]

[0084] Among them, S represents the control stage, 0 represents the steady-state control, 1 represents the transient control, and e 1 represents the main steam temperature control error, k represents the sampling moment, ε represents the transient judgment limit value of the main steam temperature control error, and T 1 represents the main steam temperature;

[0085] If the amplitude of the main steam temperature control error is large, transient rapid adjustment is required. When the temperature is high and continuously rising or the temperature is low and continuously decreasing, enter the transient rapid adjustment stage; otherwise, enter the steady-state slow adjustment stage.

[0086] In step three, the sub-zone serial number of the desuperheating water valve control command can be judged according to the flow characteristic partition of the desuperheating water valve:

[0087] a l-1 ≤U(k - 1) < a l

[0088] Among them, U represents the control command of the desuperheating water valve opening, and k represents the sampling moment;

[0089] The preferred serial number of the secondary controller for the transient and steady-state controller:

[0090]

[0091] Among them, represents the proportional control coefficient of the secondary controller Cs l ; is the integral control coefficient of the secondary controller Cs l ; is the differential control coefficient of the secondary controller Cs l ; S represents the control stage; 0 represents the steady-state control; 1 represents the transient control;

[0092] In the steady-state stage, the secondary controller Cs corresponding to the partition serial number l determined by the flow characteristic is used l as the actual secondary controller to achieve slow fine-tuning; in the transient stage, the secondary controllers Cs corresponding to the partition serial numbers l and l + 1 are used l, Cs l+1 The controller with a large amplitude of the proportional control coefficient in l+1 is used as the actual secondary controller to achieve fast adjustment.

[0093] In step four, the calculation formula for the compensation amount of the secondary feed-forward compensator is:

[0094] fb 0 (k) = (D 0 (k) - D 0 (k - 1)) T gR 0 (k)

[0095] where fb 0 represents the feed-forward compensation amount of the secondary controller, k represents the sampling time, D 0 represents the disturbance amount of the outlet temperature of the desuperheater, and R 0 represents the compensation coefficient;

[0096] The calculation formula for the control increment of the secondary controller is:

[0097]

[0098] where represents the proportional control coefficient of the secondary controller Cs l ; is the integral control coefficient of the secondary controller Cs l ; is the differential control coefficient of the secondary controller Cs l ; du 0 represents the control increment of the desuperheating water valve opening; e 0 represents the control error of the outlet temperature of the desuperheater; k represents the sampling time;

[0099] Desuperheating water valve opening control command:

[0100] U(k) = U(k - 1) + du 0 (k) + fb 0 (k)

[0101] where U represents the desuperheating water valve opening control command, k represents the sampling time, du 0 represents the control increment of the desuperheating water valve opening, and fb 0 represents the feed-forward compensation amount of the secondary controller.

[0102] Division of the flow characteristic zones of the desuperheating water valve, and the expression form of the sub-division zones:

[0103]

[0104] where the value represented by a0 is 0, and the value represented by an is 100.

[0105] Please refer to the appendix Figure 2 , in the main steam temperature control system, the main controller Cm and the secondary controller are composed of partition controllers (Cs 1 ~Cs n ) and a selector Cs 0 . Taking the main steam temperature T1 as the main controlled quantity and the outlet temperature T0 of the desuperheater as the secondary controlled quantity, the stable control of the main steam temperature is achieved by adjusting the opening of the desuperheater water valve.

[0106] Please refer to the appendix Figure 3 . The flow characteristic of the desuperheater water valve refers to the relationship between the water flow through the valve and the relative opening of the valve. And in the control system, by adjusting the opening of the desuperheater water valve, the stable main steam temperature is achieved by adjusting the desuperheater water flow.

[0107] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An optimized control method for the main steam temperature of a boiler, characterized in that, it includes the following steps: Step 1, main controller calculation: Calculate the main steam temperature control error according to the given value of the main steam temperature and the actual value of the main steam temperature. Step 2, control stage calculation: Calculate the given increment of the outlet temperature of the desuperheater according to the proportional control coefficient of the main controller, the integral control coefficient of the main controller, and the derivative control coefficient of the main controller. Step 3, judgment of the control stage: Judge the transient or steady-state control stage according to the main steam temperature control error, the sampling time, the main steam temperature, and the transient judgment limit value of the main steam temperature control error. Step 4, output of the secondary controller: Output the desuperheater water valve control command U to the desuperheater water valve according to the compensation amount of the secondary feed-forward compensator, the control increment of the secondary controller, and the control command for the desuperheater water valve opening.

2. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, the formula for calculating the main steam temperature control error in step 1 is: e 1 ψ(k) = SP 1 ψ(k) - T 1 ψ(k) Among them, e 1 represents the main steam temperature control error; k represents the sampling time; SP 1 represents the set value of the main steam temperature; T 1 represents the main steam temperature.

3. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, the formula for calculating the given increment of the outlet temperature of the desuperheater in step 2 is: δ SP0 (k) = Kp_m(e 1 (k) - e 1 (k - 1)) + Ki_m(e 1 (k)) + Kd_m(e 1 (k) - 2e 1 (k - 1) + e 1 (k - 2)) Among them, K p_m represents the proportional control coefficient of the main controller; K i_m represents the integral control coefficient of the main controller; K d_m represents the derivative control coefficient of the main controller; e 1 represents the main steam temperature control error; k represents the sampling time; SP 0 represents the set value of the outlet temperature of the desuperheater.

4. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, the specific values in step 2 are obtained according to the formula; Given value of the outlet temperature of the desuperheater: SP 0 SP(k) = 0 SP(k - 1)+δ SP0 (k) Among them, SP 0 represents the set value of the desuperheater outlet temperature, and k represents the sampling time; Calculation of the compensation amount of the main feed-forward compensator: fb 1 (k) = (D 1 (k) - D 1 (k - 1)) T gR 1 (k) Among them, fb 1 represents the feedforward compensation amount of the main controller, D 1 represents the disturbance amount of the main steam temperature, R 1 represents the compensation coefficient, and k represents the sampling time; Control error of the outlet temperature of the desuperheater: e 0 y(k) = SP 0 y(k) + fb 1 y(k) - T 0 y(k) where k represents the sampling time, and SP 0 represents the set value of the desuperheater outlet temperature, and fb 1 represents the feedforward compensation of the main controller, and T 0 represents the desuperheater outlet temperature, and e 0 represents the control error of the desuperheater outlet temperature.

5. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, the calculation process for judging the transient or steady-state control stage in step 3 is: Among them, S represents the control stage, 0 represents steady-state control, 1 represents transient control, e 1 represents the main steam temperature control error, k represents the sampling time, ε represents the transient judgment limit value of the main steam temperature control error, T 1 represents the main steam temperature.

6. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, in step 3, it is possible to judge the sub-zone serial number of the desuperheater water valve control command according to the flow characteristic partition of the desuperheater water valve; a l-1 ≤U(k - 1) < a l wherein, U represents the control command for the desuperheater water valve opening, and k represents the sampling time; Preferred serial number of the secondary controller for the transient and steady-state controller: Among them, represents the proportional control coefficient of the secondary controller Cs l ; is the integral control coefficient of the secondary controller Cs l ; is the derivative control coefficient of the secondary controller Cs l ; S represents the control stage; 0 represents steady-state control; 1 represents transient control.

7. An optimized control method for the main steam temperature of a boiler according to claim 1, characterized in that, the formula for calculating the compensation amount of the secondary feed-forward compensator in step 4 is: fb 0 (k) = (D 0 (k) - D 0 (k - 1)) T gR 0 (k) Among them, fb 0 represents the feedforward compensation amount of the secondary controller, k represents the sampling time, D 0 represents the disturbance amount of the outlet temperature of the desuperheater, R 0 represents the compensation coefficient; The formula for calculating the control increment of the secondary controller is: Among them, represents the proportional control coefficient of the secondary controller Cs l ; is the integral control coefficient of the secondary controller Cs l ; is the differential control coefficient of the secondary controller Cs l ; du 0 represents the control increment of the desuperheating water valve opening; e 0 represents the control error of the desuperheater outlet temperature; k represents the sampling time; Control command for the desuperheater water valve opening: U(k) = U(k - 1)+du 0 (k)+fb 0 (k) Among them, U represents the control command for the desuperheating water valve opening, k represents the sampling time, and du 0 represents the increment of the desuperheating water valve opening control, and fb 0 represents the feedforward compensation amount of the secondary controller.

8. An optimized control method for the main steam temperature of a boiler according to claim 5, characterized in that, if the amplitude of the main steam temperature control error is large, transient rapid adjustment is required. When the temperature is high and continuously rising or the temperature is low and continuously decreasing, enter the transient rapid adjustment, otherwise enter the steady-state slow adjustment stage.

9. An optimized control method for the main steam temperature of a boiler according to claim 6, characterized in that, The secondary controller Cs corresponding to the partition serial number l determined by the flow characteristics is used in the steady state stage l As the actual secondary controller, slow fine-tuning is realized; in the transient stage, the secondary controllers Cs l and Cs l+1 with a large amplitude of the proportional control coefficient in are used as the actual secondary controller to achieve fast adjustment.

10. An optimized control method for the main steam temperature of a boiler according to claim 6, characterized in that, the partition of the flow characteristic of the desuperheater water valve, the form of the expression for dividing the sub-zones: wherein, the value represented by a0 is 0, and the value represented by an is 100.

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