A control method for the opening degree of the main steam control valve of a steam turbine

Abstract

The present invention relates to a control method for the opening of the main steam control valve of a steam turbine, comprising: conducting tests to obtain the relationship curve between the unit load and the control valve opening corresponding to different main steam control valve pressure margin coefficients; determining the corresponding main steam control valve pressure margin coefficient according to the proportion of external UHV input to the power grid; determining the opening of the main steam control valve and controlling the main steam control valve. The beneficial effects of the present invention are as follows: when the proportion of external UHV in the power grid is high, the present invention increases the main steam control valve pressure margin coefficient of the unit, enhancing the power grid's ability to resist the risk of losing external power; when the proportion of external UHV power in the power grid is low, the present invention reduces the main steam control valve pressure margin coefficient of the unit, enhancing the operating economy of the unit.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power generation, and more specifically, it relates to a method for controlling the opening degree of the main steam control valve of a steam turbine. Background Art

[0002] Grid-source coordination is the general term for the technical field of the interaction and coordinated cooperation between power generation equipment and grid equipment, generally including primary frequency modulation and the response ability of Automatic Generation Control (AGC). Primary frequency modulation refers to the process in which once the frequency of the power grid deviates from the rated value, the control system of the units in the power grid automatically controls the increase or decrease of the active power of the units to limit the change of the power grid frequency and maintain the stability of the power grid frequency. AGC is an important function in the energy management system. It controls the output of the frequency modulation units to meet the continuously changing power demand of users and makes the system operate in an economical state. According to the regulations of the power grid, the frequency error of the primary frequency modulation of the power grid is 0.2 Hz (corresponding to a speed deviation of 12 r / min), and the frequency modulation power requirement of the unit is 6% Pe (Pe is the rated load).

[0003] The throttling technology of the high-pressure main steam control valve has good load regulation ability. Its principle is: when exceeding the dead zone of the power grid frequency, first, the opening degree of the high-pressure main steam control valve is changed for adjustment to meet the requirements of rapid response, and then the coordinated control system of the unit adjusts the boiler heat load and steam pressure to achieve fine adjustment. The throttling technology of the high-pressure control valve is generally adopted during the operation of thermal power units. During normal operation, a certain amount of throttling flow needs to be reserved (the opening degree of the high-pressure main steam control valve is generally 25%-40%) to maintain a certain load margin of the unit for responding to primary frequency modulation and AGC regulation. However, this also causes a large throttling loss of the high-pressure main steam control valve, resulting in a decrease in the efficiency of the high-pressure cylinder and affecting the economy of the unit.

[0004] In recent years, the proportion of externally transmitted power in some provinces and cities has been continuously increasing. Taking Zhejiang Province as an example, the proportion of externally transmitted power has reached about one-third, forming a "two AC and two DC" UHV backbone grid. While the high-voltage direct current (HVDC) transmission system has many advantages, it also brings a series of potential safety hazards. For example, DC line faults, converter station faults, and AC system faults may all lead to single-pole or even double-pole blocking of the DC. If a single-pole blocking fault occurs in the HVDC transmission system, the reactive power required by the converter station will suddenly decrease, resulting in an excess of reactive power on the AC side, which will cause a sudden increase in the AC grid voltage. In severe cases, the line transmission capacity will be halved or even completely lost. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for controlling the opening degree of the main steam control valve of a steam turbine.

[0006] In the first aspect, a control method for the opening of the main steam control valve of a steam turbine is provided, including:

[0007] S1. Conduct tests to obtain the relationship curve between the unit load and the control valve opening corresponding to different main steam control valve pressure margin coefficients;

[0008] S2. Determine the corresponding main steam control valve pressure margin coefficient according to the external UHV input ratio of the power grid;

[0009] S3. Determine the opening of the main steam control valve according to the main steam control valve pressure margin coefficient determined in S2, the relationship curve between the unit load and the control valve opening corresponding to the main steam control valve pressure margin coefficient in S1, and the unit load;

[0010] S4. Control the main steam control valve according to the opening of the main steam control valve determined in S3.

[0011] Preferably, in S1, the conduct of the tests includes: according to the calculation formula of the rated pressure change value ΔP when the main steam control valve of the unit is fully open, conduct tests to determine the valve pressure loss ΔP0 when the main steam control valve is fully open under different unit loads and different main steam pressure conditions; and conduct tests to obtain the valve openings corresponding to different main steam control valve pressure margin coefficients under different working conditions; the calculation formula of ΔP is expressed as:

[0012]

[0013] where Ne is the rated load of the unit, N is the current load of the unit, ε is the main steam control valve pressure margin coefficient, P e is the rated pressure of the unit, and ΔP0 is the valve pressure loss when the main steam control valve of the unit is fully open.

[0014] Preferably, S2 includes:

[0015] S201. Obtain the external UHV input ratio of the power grid and the input ratio threshold;

[0016] S202. When the external UHV input ratio of the power grid is greater than the input ratio threshold, the main steam control valve pressure margin coefficient takes the first coefficient ε1;

[0017] S203. When the external UHV input ratio of the power grid is less than or equal to the input ratio threshold, the main steam control valve pressure margin coefficient takes the second coefficient ε2, and the second coefficient ε2 is less than the first coefficient ε1.

[0018] In the second aspect, a control device for the opening of the main steam control valve of a steam turbine is provided, which is used to execute the control method for the opening of the main steam control valve of the steam turbine according to any one of the first aspects, including:

[0019] An acquisition module, which is used to conduct tests to obtain the relationship curve between the unit load and the control valve opening under different main steam control valve pressure margin coefficients;

[0020] A first determination module, configured to determine a corresponding main steam control valve pressure margin coefficient ε according to the UHV input ratio of the external power grid;

[0021] A second determination module, configured to determine the main steam control valve opening according to the main steam control valve pressure margin coefficient determined by S2, the curve of the relationship between the unit load and the control valve opening corresponding to the main steam control valve pressure margin coefficient in S1, and the unit load;

[0022] A control module, configured to control the main steam control valve according to the main steam control valve opening determined by S4.

[0023] In a third aspect, a computer storage medium is provided, in which a computer program is stored; when the computer program runs on a computer, the computer is enabled to execute any one of the control methods for the opening of the main steam control valve of a steam turbine in the first aspect.

[0024] In a fourth aspect, a computer program product is provided, which enables a computer to execute a control method for the opening of the main steam control valve of a steam turbine as described in any one of the first aspects when the computer program product runs on the computer.

[0025] The beneficial effects of the present invention are as follows: According to the ratio of the external UHV power, the present invention determines the corresponding main steam control valve pressure margin coefficient of the generator set, and obtains the curve of the relationship between the unit load and the control valve opening corresponding to different main steam control valve pressure margin coefficients, so as to determine the corresponding main steam control valve opening under different working conditions. After applying the present invention, in the event of an accident of loss of external UHV power, when the ratio of the external UHV power of the power grid is high, the impact on the power grid is large. Therefore, the main steam control valve pressure margin coefficient of the unit can be increased to enhance the ability of the power grid to resist the risk of loss of external power; on the contrary, when the ratio of the external UHV power of the power grid is low, the impact on the power grid is small. Therefore, the main steam control valve pressure margin coefficient of the unit can be reduced to enhance the operating economy of the unit. The present invention does not require additional equipment and is easy to operate. During the daily operation process, the grid-source coordination ability and economy of the unit can be taken into account, providing guidance for the safe and economic operation of the unit. Description of the Drawings

[0026] Figure 1 It is a flowchart of a control method for the opening of the main steam control valve of a steam turbine provided by the present invention;

[0027] Figure 2 It is a curve graph of the relationship between the opening of the main steam control valve and the change of the unit load provided by the present invention. Detailed Embodiments

[0028] The present invention will be further described below in conjunction with embodiments. The description of the following embodiments is only for helping to understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0029] Embodiment 1:

[0030] When the proportion of external ultra-high voltage power is different, the unit should also have different requirements for the primary frequency regulation and rapid load increase of thermal power units. In this regard, the present invention provides a control method for the opening of the main steam control valve of a steam turbine, which can take into account the unit's grid-source coordination ability and economy, aiming at the different impacts that may be caused by the loss of external ultra-high voltage power, as Figure 1 shown, including:

[0031] S1. Conduct tests to obtain the relationship curve between the unit load and the control valve opening corresponding to different main steam control valve pressure margin coefficients.

[0032] According to the Flügel formula, if the number of stages in the stage group is infinite, it can be expressed as:

[0033]

[0034] In the formula, G0, G1—the flow rates through the stage group before and after the operating condition change; p 00 , p 20 —the pressures before and after the stage group before the operating condition change; p 01 , p 21 —the pressures before and after the stage group after the operating condition change; T 00 , T 01 —the absolute temperatures before the stage group before and after the operating condition change.

[0035] If the temperature before the stage group changes little before and after the operating condition change, the above formula can be simplified as:

[0036]

[0037] For the case where the flow area changes with the opening of the control valve, the formula is corrected as follows:

[0038]

[0039] In the formula, A0, A1—the changes in the opening of the control valve before and after the operating condition change.

[0040] For the case that is always in the critical state, the above formula can be further simplified as:

[0041]

[0042] Generally, it is considered that the stage pressure can approximately represent the main steam flow rate, that is, it can be obtained:

[0043]

[0044] Therefore, the opening of the high-pressure control valve of the unit is directly proportional to the ratio of "stage pressure to main steam pressure".

[0045] The boiler has a certain heat storage capacity. The steam turbine can operate with the opening of the main steam control valve restricted to have a certain load margin. When the primary frequency modulation acts, the opening of the main steam control valve can be quickly increased to increase the steam intake, and the heat storage of the boiler can be used to quickly increase the unit load to meet the requirements of rapid response. When the load is below 50%, to ensure that the primary frequency modulation of the unit meets the requirement of 6%Pe, the main steam pressure of the unit adopts constant pressure operation.

[0046] When the unit AGC is put into operation, the coordinated control strategy of the boiler and turbine usually adopts the method of boiler following the turbine, with the unit load regulation as the first priority. At this time, it is considered that the unit load PM and the main steam flow SF only change with the AGC command and are not affected by the boiler operating state. At this time, the influence of the total coal quantity change on the main steam pressure is a pure integral process, and the main steam pressure can be used to characterize the boiler value.

[0047] The above concept can be expressed by the following formula:

[0048]

[0049] Among them, ΔP is the rated pressure change value when the main steam control valve of the unit is fully open, Ne is the rated load of the unit, N is the current load of the unit, ε is the main steam control valve pressure margin coefficient, P e is the rated pressure of the unit, and ΔP0 is the valve pressure loss when the main steam control valve of the unit is fully open.

[0050] Furthermore, in S1, the experiment includes: according to the calculation formula of ΔP, conduct experiments to determine the valve pressure loss ΔP0 when the main steam control valve is fully open under different unit loads and different main steam pressure conditions by measuring the main steam pressure before and after the control valve. (ΔP0 will change under different loads and different main steam pressures), and then calculate the corresponding ΔP for different ε under this condition according to the above formula. Then, determine the corresponding control valve opening through further experiments and form a relationship curve. Thus, the obtained relationship curve can be used to control the opening of the main steam control valve of the unit according to different external power ratios during operation (as in S2 to S4 below).

[0051] S2. Determine the corresponding main steam control valve pressure margin coefficient according to the proportion of external UHV input to the power grid.

[0052] S2 includes:

[0053] S201. Obtain the proportion of external UHV input to the power grid and the input proportion threshold.

[0054] Exemplarily, set the input ratio threshold to 25%.

[0055] S202. When the UHV (Ultra-High Voltage) input ratio from the power grid is greater than the input ratio threshold, the main steam control valve pressure margin coefficient takes the first coefficient ε1.

[0056] Exemplarily, the first coefficient ε1 is 6%. If the UHV input ratio from the power grid exceeds 25%, due to the risk of large-scale power outages when external power transmission is lost, the primary frequency regulation ability of the unit needs to be strong and the load increase should be rapid. Therefore, the main steam control valve of the steam turbine is considered with a 6% pressure margin, and the opening is small.

[0057] S203. When the UHV input ratio from the power grid is less than or equal to the input ratio threshold, the main steam control valve pressure margin coefficient takes the second coefficient ε2, and the second coefficient ε2 is less than the first coefficient ε1.

[0058] Exemplarily, the second coefficient ε2 is 3%. If the UHV input ratio from the power grid does not exceed 25%, the risk of large-scale power outages in the power grid is small, and the requirements for the primary frequency regulation and rapid load increase of the unit are low. Therefore, considering the operation economy, the main steam control valve of the steam turbine is considered with a 3% pressure margin, and the opening is large.

[0059] It should be noted that under the same boundary conditions, when the main steam control valve pressure margin coefficient takes 3% respectively compared with taking 6%, the high-pressure cylinder efficiency of the unit will increase by about 1.5 percentage points, affecting the heat consumption of the unit by about 22 kJ / kWh.

[0060] S3. Determine the main steam control valve opening according to the relationship curve between the unit load and the control valve opening corresponding to the main steam control valve pressure margin coefficient determined in S2 and the main steam control valve pressure margin coefficient in S1, as well as the unit load.

[0061] S4. Control the main steam control valve according to the main steam control valve opening determined in S3.

[0062] For example, automatically control the main steam control valve opening through the Distributed Control System (DCS) of the unit.

[0063] Embodiment 2:

[0064] A 1000 MW unit adopts the throttle governing method, with a rated pressure of 25 MPa and a rated main steam flow of 2814 t / h.

[0065]

[0066] According to the above formula, determine ε as 3% or 6% according to different external power ratios, and the DCS of the unit automatically controls the main steam control valve opening. Conduct tests to measure ΔP0 under different loads and the corresponding valve openings under various working conditions, and form the following data:

[0067] Table 1 Test Results

[0068]

[0069]

[0070] According to the test data, the relationship curves between load and main steam control valve opening at different ε are formed (as Figure 2 shown). When ε is 3%, the formed relational expression is:

[0071] y = -3E-08x2 + 0.0001x + 0.3143

[0072] When ε is 6%, the formed relational expression is:

[0073] y = -7E-08x2 + 0.0002x + 0.2816

[0074] And integrate the above relational expressions into the DCS control system. When the proportion of external power ≤ 25%, the relationship between the main steam control valve opening and the unit load is controlled according to the relational expression when ε is 3%; when the proportion of external power > 25%, the relationship between the high-pressure control valve opening and the load is controlled according to the relational expression when ε is 6%.

Claims

1. A control method for the opening of the main steam control valve of a steam turbine, characterized in that, Including: S1. Conduct tests to obtain the relationship curves between the unit load and the throttle valve opening corresponding to different main steam throttle valve pressure margin coefficients; In S1, the conducting of the tests includes: According to the calculation formula of the rated pressure change value ΔP when the main steam throttle valve of the unit is fully open, conduct tests to determine the valve pressure loss ΔP0 when the main steam throttle valve is fully open under different unit loads and different main steam pressure conditions; and calculate the different main steam throttle valve pressure margin coefficients under different conditions, and determine the corresponding valve opening through tests; The calculation formula of ΔP is expressed as: where Ne is the rated load of the unit, N is the current load of the unit, ε is the main steam control valve pressure margin coefficient, P e is the rated pressure of the unit, and ΔP0 is the valve pressure loss when the main steam control valve of the unit is fully open; S2. Determine the corresponding main steam control valve pressure margin coefficient according to the external UHV input ratio of the power grid; S2 includes: S201. Obtain the external UHV input ratio of the power grid and the input ratio threshold; S202. When the external UHV input ratio of the power grid is greater than the input ratio threshold, the main steam throttle valve pressure margin coefficient takes the first coefficient ε1; S203. When the external UHV input ratio of the power grid is less than or equal to the input ratio threshold, the main steam throttle valve pressure margin coefficient takes the second coefficient ε2, and the second coefficient ε2 is less than the first coefficient ε1; S3. Determine the main steam throttle valve opening according to the main steam throttle valve pressure margin coefficient determined in S2, the relationship curve between the unit load and the throttle valve opening corresponding to the main steam throttle valve pressure margin coefficient in S1, and the unit load; S4. Control the main steam throttle valve according to the main steam throttle valve opening determined in S3.

2. A control device for the opening degree of the main steam control valve of a steam turbine, characterized in that, Used to execute the control method for the opening of the main steam throttle valve of a steam turbine as described in claim 1, including: An acquisition module, used to conduct tests to obtain the relationship curves between the unit load and the throttle valve opening under different main steam throttle valve pressure margin coefficients; A first determination module, used to determine the corresponding main steam throttle valve pressure margin coefficient according to the external UHV input ratio of the power grid; A second determination module, used to determine the main steam throttle valve opening according to the main steam throttle valve pressure margin coefficient determined in S2, the relationship curve between the unit load and the throttle valve opening corresponding to the main steam throttle valve pressure margin coefficient in S1, and the unit load; A control module, used to control the main steam throttle valve according to the main steam throttle valve opening determined in S4.

3. A computer storage medium, characterized in that, The computer storage medium stores a computer program; when the computer program runs on the computer, the computer is caused to execute a control method for the opening of the main steam throttle valve of a steam turbine as described in claim 1.

4. A computer program product, characterized in that, When the computer program product runs on the computer, the computer is caused to execute a control method for the opening of the main steam throttle valve of a steam turbine as described in claim 1.

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