A method for setting values of a super-supercritical coal-fired unit boiler coordination control system

Abstract

The application discloses a kind of ultra-supercritical coal-fired unit machine furnace coordination control system set value design method, specific steps include determining wide-range variable load ultra-supercritical coal-fired unit machine furnace coordination system nonlinear dynamic model;System open-loop characteristic test is carried out, and system output variable reaches peak time and time constant are obtained;Establish the transfer function model of unit power and main steam pressure and steam-water separator steam temperature;Calculate main steam pressure and steam-water separator steam temperature set value.The dynamic characteristics of unit power and main steam pressure and steam-water separator steam temperature are used to design the set value of main steam pressure and steam-water separator steam enthalpy value in the application, which can improve the variable load tracking performance and operation economy of the unit;The steam-water separator steam temperature change rate is used to design the set value of steam-water separator steam enthalpy value, and when the unit is running in a wide range of variable load, the steam-water separator steam temperature change rate can be reduced, and the operation safety of the unit can be improved.

Description

Technical Field

[0001] This invention relates to the field of design methods for setpoints of the coordinated control system of an ultra-supercritical coal-fired power unit, and specifically to a design method for setpoints of the coordinated control system of an ultra-supercritical coal-fired power unit. Background Technology

[0002] Due to the intermittent and random nature of renewable energy, ultra-supercritical coal-fired power units require wide-range load variation operation to track grid load commands and stabilize grid operating frequency. The coordinated control system of ultra-supercritical coal-fired power units can coordinate and control the boiler and turbine systems, enabling the unit to quickly track load commands and maintain safe and economical operation. The setpoint of the ultra-supercritical coal-fired power unit boiler-turbine coordinated control system represents the requirements of the grid and operators for the current unit operation. Existing research often controls the boiler-turbine coordinated system from one steady-state condition to another, with the setpoint representing a linear relationship between the two operating points. For example, when the unit load increases, the main steam pressure rises accordingly, and the steam enthalpy of the steam separator also changes accordingly, maintaining a fixed ratio. This setpoint design method increases the deviation of the main steam pressure, accelerates the rate of change of steam temperature in the steam separator, increases the thermal stress on the steam separator metal, and affects the safe and economical operation of the unit. Summary of the Invention

[0003] To address the aforementioned technical shortcomings, the purpose of this invention is to provide a design method for the setpoint of the boiler-generator coordinated control system for ultra-supercritical coal-fired power units. This method can improve the load tracking rate during large-scale load changes of the unit, while simultaneously meeting the safety constraints of the steam temperature change rate of the steam-water separator, thereby enhancing the safety and economy of unit operation.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention provides a method for designing setpoints for a coordinated control system of an ultra-supercritical coal-fired power unit.

[0006] Includes the following steps:

[0007] Step 1: Determine the nonlinear dynamic model of the boiler-generator coordination system for large-scale variable load ultra-supercritical coal-fired power units;

[0008] Step 2: Conduct open-loop characteristic tests on the system to obtain the peak time and time constant of the system output variables;

[0009] Step 3: Establish a transfer function model for the unit power, main steam pressure, and steam temperature of the steam-water separator;

[0010] Step 4: Calculate the main steam pressure and the steam temperature setpoint of the steam-water separator.

[0011] Preferably, in step one, the nonlinear state-space model of the ultra-supercritical coal-fired unit boiler-generator coordination system is written as:

[0012]

[0013] In the formula, u1 is the fuel quantity command, kg / s; u2 is the feedwater flow rate, kg / s; u3 is the turbine control valve opening; x1 is the coal feed rate, kg / s; x2 is the steam pressure of the steam-water separator, MPa; x3 is the steam enthalpy of the steam-water separator, kJ / kg; x4 is the unit power, MW. and These are the first derivatives of the coal feed rate, steam pressure in the steam-water separator, steam enthalpy in the steam-water separator, and unit power, respectively.

[0014] y1 is the main steam pressure, MPa; y2 is the enthalpy of the steam-water separator, kJ / kg; y3 is the unit power, MW; τ is the time delay, s; c0 is the inertial time of the pulverizing system, s;

[0015] c1, c2, d1, and d2 are the dynamic identification parameters of the boiler; c3 is the dynamic parameter of the steam turbine system, s;

[0016] h fw The enthalpy value of the feedwater is expressed in kJ / kg; h. st Main steam enthalpy, kJ / kg; D st Q1 is the main steam flow rate, kg / s; Q2 is the boiler heat absorption, kJ / s.

[0017] k1 is the boiler heat absorption per unit amount of coal fed into the furnace, kJ / kg; k2 is the ratio of the effective unit energy entering the turbine to the unit load.

[0018] ΔQ loss Let MW be the energy function for throttling loss; Δp = g(p) m ), Δp=p st -p m Δp is the superheater differential pressure, MPa; l = h st / h m Δu3 represents the change in turbine control valve opening; μ, γ, and η are constants.

[0019] α is the ratio of water supply flow rate to fuel quantity; where h fw k1, l, τ, c0, c1, c2, d1, d2, μ, γ, η, α, g(.), f(.,.) are identified from unit equipment information and operating data;

[0020] The state variables in the model are X = [x1, x2, x3, x4]. T =[r B ,p m ,hm N e ] T Input variable U = [u1, u2, u3] T =[u B D fw ,u t ] T Output variable Y = [y1, y2, y3] T =[p st ,h m N e ] T .

[0021] Preferably, in step two, an open-loop characteristic test of the system is conducted to obtain the peak time and time constant of the system output variable, specifically implemented as follows:

[0022] To obtain the dynamic characteristics of the boiler-generator coordination system model output under varying load conditions, the coordination system simulation process is conducted during unit load increases and decreases. Specifically, under steady-state conditions, an open-loop characteristic test of the system is performed to obtain the dynamic change curve of the model output. The steam temperature of the steam-water separator is obtained by combining the corresponding steam pressure and enthalpy with the thermodynamic properties of steam. Therefore, at each steady-state load point, the above-mentioned open-loop simulation test is performed to obtain the peak time and time constant of the model output during the large-scale load variation process of the unit.

[0023] Preferably, in step three, a transfer function model is established for the unit power, main steam pressure, and steam temperature of the steam-water separator. The specific implementation is as follows:

[0024] Based on the open-loop dynamic characteristics of the system and the unit's operating experience, the transfer function structure of the unit's power with respect to the main steam pressure and the steam temperature of the steam-water separator is determined, and the transfer function coefficients are also determined.

[0025] Preferably, in step four, the main steam pressure and the steam temperature setpoint of the steam-water separator are calculated, specifically as follows:

[0026] By combining the unit's steady-state data and regression analysis methods, the steady-state setpoints of the main steam pressure and the steam temperature of the steam-water separator are calculated. Based on the transfer function model of the unit power with the main steam pressure and the steam temperature of the steam-water separator, and the thermodynamic properties of the unit power setpoint and the steam enthalpy setpoint curves of the main steam pressure and the steam temperature of the steam-water separator are calculated.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention uses the dynamic characteristics of unit power, main steam pressure, and steam temperature of steam separator to design the setpoints for main steam pressure and steam enthalpy of steam separator, which can improve the unit's load-tracking performance and operating economy.

[0029] 2. This invention uses the steam temperature change rate of the steam separator to design the steam enthalpy setpoint of the steam separator. When the unit is operating under a wide range of load changes, it can reduce the steam temperature change rate of the steam separator and improve the operating safety of the unit. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The curves showing the changes in input quantities of the boiler-turbine coordination system model are as follows: (a) is the fuel quantity command, (b) is the feedwater flow rate, and (c) is the turbine control valve opening.

[0032] Figure 2 The output change curves of the boiler-generator coordination system model are shown below ((a) main steam pressure, (b) enthalpy of steam-water separator, (c) steam temperature of steam-water separator, and (d) unit load).

[0033] Figure 3 The setpoints for the boiler-generator coordinated control system of a traditional ultra-supercritical coal-fired unit are ((a) main steam pressure, (b) enthalpy of steam-water separator, and (c) unit power).

[0034] Figure 4 The steam temperature change rate of the steam separator corresponding to the load command of the traditional boiler-machine coordinated control system ((a) is the load increase stage, (b) is the load decrease stage);

[0035] Figure 5 These are the setpoints of the boiler-generator coordination control system for ultra-supercritical coal-fired units ((a) main steam pressure, (b) steam temperature of the steam-water separator, (c) steam enthalpy of the steam-water separator, and (d) unit load).

[0036] Figure 6 The rate of change of steam temperature in the steam-water separator corresponding to the load command of the boiler-turbine coordinated control system ((a) is the load increase stage, (b) is the load decrease stage). Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The following example uses a 1000MW ultra-supercritical coal-fired unit as an example. The boiler is an ultra-supercritical parameter variable pressure operation spiral tube once-through boiler with single furnace single tangential combustion, balanced ventilation, and a fully suspended tower arrangement. The boiler model is SG-3012 / 27.9-M540.

[0039] This embodiment provides a method for designing setpoints for a coordinated control system of an ultra-supercritical coal-fired power unit, including the following main steps:

[0040] Step 1: Determine the nonlinear dynamic model of the boiler-generator coordination system for large-scale variable load ultra-supercritical coal-fired power units.

[0041] The nonlinear state-space model of the coordination system of an ultra-supercritical coal-fired power unit is written as follows:

[0042]

[0043]

[0044] In the formula, u1 is the fuel quantity command, kg / s; u2 is the feedwater flow rate, kg / s; u3 is the turbine control valve opening; x1 is the coal feed rate; x2 is the steam pressure of the steam-water separator; x3 is the enthalpy of the steam-water separator; and x4 is the unit power. It is the first derivative of the amount of coal fed into the furnace. It is the first derivative of the steam pressure in the steam-water separator. It is the first derivative of the steam enthalpy of the steam in the steam-water separator. It is the first derivative of the unit's power;

[0045] y1 is the main steam pressure, MPa; y2 is the enthalpy of the steam-water separator, kJ / kg; y3 is the unit power, MW; τ is the time delay, s;

[0046] c0 is the inertial time of the powder-making system, in seconds;

[0047] c1, c2, d1, and d2 are the dynamic identification parameters of the boiler; c3 is the dynamic parameter of the steam turbine system; s; h fw The enthalpy value of the feedwater is expressed in kJ / kg; h. st The main steam enthalpy, kJ / kg;

[0048] D st Q1 is the main steam flow rate, kg / s; Q1 is the boiler heat absorption, kJ / s; k1 is the boiler heat absorption per unit amount of coal fed into the furnace, kJ / kg.

[0049] k2 is the ratio of the unit load corresponding to the effective unit energy entering the steam turbine; ΔQ loss Let MW be the energy function for throttling loss; Δp = g(p) m), Δp=p st -p m Δp is the superheater differential pressure, MPa; l = h st / h m Δu3 represents the change in turbine control valve opening; μ, γ, and η are constants; α is the ratio of feedwater flow rate to fuel quantity.

[0050] The state variables in the model are X = [x1, x2, x3, x4]. T =[r B ,p m ,h m N e ] T Input variable U = [u1, u2, u3] T =[u B D fw ,u t ] T Output variable Y = [y1, y2, y3] T =[p st ,h m N e ] T .

[0051] The model parameters of the unit were identified using the unit's operating data as follows:

[0052] Static parameters:

[0053]

[0054] Dynamic parameters:

[0055] τ=20, c0=380, c3=40,

[0056]

[0057] c2 = 639(-0.005248p) m h m -0.003204h m +19.7835p m +9.7266),

[0058] c j =0.46kJ / (kg·℃), m j = 700,000 kg.

[0059] Nonlinear functions:

[0060] Δp=g(p m ) = 0.0522p m -0.00281,

[0061]

[0062] ΔQ loss =ηΔu t p st =8(u3-u 30 )p st ,

[0063] In the formula, u 30 This is the initial state of the turbine control valve opening, u3.

[0064] Step 2: Conduct open-loop characteristic tests on the system to obtain the peak time and time constant of the system output variable.

[0065] To obtain the dynamic characteristics of the boiler-turbine coordination system model output under varying load conditions, the load increase / decrease simulation process was simulated. Specifically, under steady-state conditions, the fuel quantity command, feedwater flow rate, and turbine valve opening were increased by a step of 1 kg / s, 7 kg / s, and 0.05 kg / s, respectively, to obtain the dynamic change curves of the model output. Figure 1 and Figure 2 As shown in the figure. During load changes, to meet the safety constraints of the rate of change of the steam-water separator wall temperature, it is necessary to obtain the dynamic characteristics of the steam temperature at that location. The steam temperature of the steam-water separator can be obtained from the corresponding steam pressure and enthalpy, combined with the thermodynamic properties of steam. Therefore, at each steady-state load point, the above-mentioned open-loop simulation test was conducted to obtain the peak time and time constant of the model output during the large-scale load change process of the unit. The results are shown in Tables 1 and 2.

[0066] Table 1. Peak time and time constant of model output in the load increase simulation test.

[0067]

[0068]

[0069] Table 2. Peak time and time constant of model output in load reduction simulation test.

[0070]

[0071] Step 3: Establish a transfer function model for the unit power, main steam pressure, and steam temperature of the steam-water separator.

[0072] Because the output of the boiler-turbine coordination system model exhibits time-dynamic characteristics during unit load changes, this invention uses a first-order inertial element with a pure time delay to describe the dynamic differences between the unit load and the main steam pressure and the enthalpy of the steam-water separator. Due to the increased step size of the model input, the main steam pressure and the enthalpy of the steam-water separator first decrease and then increase, exhibiting an inverse characteristic. Based on unit operating experience, the time delay between this enthalpy, pressure, and unit load is approximately twice the time constant. Let the inertial time be the corresponding time difference. Both the time constant and the inertial time are taken as the average values ​​from Tables 1 and 2. The results are as follows:

[0073] (1) Load increase phase

[0074]

[0075]

[0076] (2) Load reduction phase

[0077] Step 4: Calculate the main steam pressure and the steam temperature setpoint of the steam-water separator.

[0078] The steady-state operating data of the unit are shown in Table 3.

[0079] Table 3 Model Steady-State Operation Data

[0080]

[0081] Based on the steady-state data in Table 3 and linear regression analysis, the steady-state setpoints for the main steam pressure and the steam temperature of the steam-water separator are calculated as follows:

[0082] p str =0.02487N er +0.939, (7)

[0083] T mr =2.145*10 -7 N er 3 -6.63*10 -4 N er 2 +0.747N er +130.915, (8)

[0084] In the formula, p str ,T mr and N er These are the main steam pressure, steam temperature of the steam-water separator, and unit power setting values.

[0085] The unit load command increased from 344MW to 1048MW, with a load change rate of 25MW / min. The setpoints of the traditional boiler-turbine coordinated control system and the rate of change of steam temperature in the steam-water separator are as follows: Figure 3 and Figure 4 As shown, the setpoints of the boiler-machine coordinated control system and the rate of change of steam temperature in the steam-water separator in this invention are as follows: Figure 5 and Figure 6 As shown.

[0086] Conclusion: As can be seen from the above charts, during the large-scale variable load operation of the unit, the setpoints of the boiler-turbine coordinated control system designed in this study, as well as the rate of change of steam temperature in the steam-water separator, are all within the safety limits, improving the operational safety of the unit. The main steam pressure setpoint can reflect the dynamic characteristics of the system operation and reduce the impact on the load tracking rate.

[0087] In summary, the setpoints of the ultra-supercritical coal-fired power unit boiler-generator coordinated control system designed in this invention can utilize the system's dynamic characteristics to design the main steam pressure setpoint during large-scale load changes, thereby improving the unit's load tracking performance. Furthermore, the setpoints can utilize the rate of change of steam temperature in the steam-water separator to design the steam enthalpy setpoint, maintaining the rate of change within safe limits and reducing thermal stress on the boiler metal. This setpoint design method has significant practical implications for improving the safe and economical operation of the unit.

[0088] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for setting values of a supercritical coal-fired unit boiler coordination control system, characterized in that, The method comprises the following steps: Step one, determining a nonlinear dynamic model of a boiler-turbine coordination system of a wide-range variable load ultra-supercritical coal-fired unit; Step two, performing an open-loop characteristic test of the system to obtain peak time and time constant of an output variable of the system; Step three, establishing a transfer function model of unit power and main steam pressure and steam temperature of a steam-water separator; Step four, calculating set values of the main steam pressure and the steam temperature of the steam-water separator; In step one, the nonlinear dynamic model of the boiler-turbine coordination system of the ultra-supercritical coal-fired unit is written as: In the formula, u1 is fuel quantity instruction, kg / s; u2 is feed water flow, kg / s; u3 is turbine governing valve opening; x1 is coal quantity into the furnace, kg / s; x2 is steam pressure of the steam-water separator, MPa; x3 is steam enthalpy of the steam-water separator, kJ / kg; x4 is unit power, MW; and are first order derivatives of coal quantity into the furnace, steam pressure of the steam-water separator, steam enthalpy of the steam-water separator and unit power, respectively; y1 is the main steam pressure, MPa; y2 is the enthalpy of the steam-water separator, kJ / kg; y3 is the unit power, MW; τ is the time delay, s; c0 is the inertia time of the pulverizing system, s; c1, c2, d1, d2 are dynamic identification parameters of the boiler; c3 is a dynamic parameter of the steam turbine system, s; h fw h is the enthalpy of the feed water, kJ / kg; h st D is the enthalpy of the main steam, kJ / kg; D st D is the flow rate of the main steam, kg / s; Q1 is the heat absorbed by the boiler, kJ / s; k1 is the boiler heat absorption amount corresponding to a unit amount of coal; k2 is the ratio of unit load corresponding to effective unit energy entering the steam turbine; ΔQ loss is the throttling loss energy function, MW. Δp = g(p m ), Δp = p st -p m , Δp is the superheater differential pressure, MPa; l = h st / h m ; Δu3 is the turbine governing valve opening change; μ, γ, η are constants; a is the ratio of the water flow and the fuel quantity; wherein h fw k1, l, t, c0, c1, c2, d1, d2, m, g(.), f(.,.) are identified from the unit equipment information and the operation data; The state variables in the model are X = [x1, x2, x3, x4] T = [r B , p m , h m , N e ] T ; Input variables U = [u1, u2, u3] T = [u B , D fw , u t ] T ; Output variable Y = [yl, y2, y3] T = [p st , h m , N e ] T .

2. The method of claim 1, wherein the method is characterized in that: In step two, the open-loop characteristic test of the system is performed to obtain the peak time and the time constant of the output variable of the system, and the specific implementation is as follows: In order to obtain the difference in dynamic characteristics of the model output variable of the boiler-turbine coordination system under a variable load condition, a simulation process of the coordination system is simulated when the unit load is raised and lowered, that is, the open-loop characteristic test of the system is performed under a steady state of the unit, and the dynamic change curve of the model output variable is obtained; the steam temperature of the steam-water separator is obtained from the corresponding steam pressure and enthalpy combined with the thermodynamic properties of the steam; therefore, the open-loop simulation test is performed at each steady load point, and the peak time and the time constant of the model output variable are obtained in the process of wide-range variable load of the unit.

3. The method for setting values of a super-supercritical coal-fired unit boiler coordinated control system according to claim 1, characterized in that: In step three, the transfer function model of the unit power and the main steam pressure and the steam temperature of the steam-water separator is established, and the specific implementation is as follows: According to the open-loop dynamic characteristics of the system and the operation experience of the unit, the transfer function structure of the unit power and the main steam pressure and the steam temperature of the steam-water separator is determined, and the transfer function coefficients are determined.

4. The method of claim 1, wherein the method is characterized in that: In step four, the set values of the main steam pressure and the steam temperature of the steam-water separator are calculated, and the specific implementation is as follows: The steady set values of the main steam pressure and the steam temperature of the steam-water separator are calculated combined with the steady state data of the unit and the regression analysis method, and the set value curve of the main steam pressure and the enthalpy of the steam-water separator is calculated according to the transfer function model of the unit power and the main steam pressure and the steam temperature of the steam-water separator, and the set value of the unit power and the thermodynamic properties of the steam.

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