CN107908103A - One kind is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency - Google Patents

Abstract

The invention relates to a calorific value correction method of a coordinated control system based on steam turbine efficiency correction, which corrects the main control of the boiler in the coordinated control system according to the change of steam turbine efficiency. It includes the following steps: A. Boiler side calorific value correction loop correction; B. Steam turbine side efficiency correction; C. Exhaust enthalpy calculation based on generalized radial basis neural network; D. Calorific value to boiler main control output correction. The invention separates the efficiency of the steam turbine from the correction value of the boiler calorific value, calculates the efficiency of the boiler and the steam turbine separately, and at the same time modifies the set value of the calorific value correction circuit from the load function to the actual heat load function of the unit, which can ensure the calorific value correction circuit The output is the real calorific value of the fuel, which effectively reduces system fluctuations caused by changes in steam turbine efficiency, reduces overshoot, and improves the safety and stability of the unit.

Description

A Coordinated Control System Calorific Value Correction Method Based on Steam Turbine Efficiency Correction

technical field

The invention relates to a calorific value correction method of a coordinated control system based on steam turbine efficiency correction.

Background technique

The task of the coordinated control system is to make the load of the thermal power unit quickly respond to the external load demand (intermediate load command or operator load command), and at the same time maintain the stability of the steam pressure in front of the unit. The calorific value correction loop is an important part of the coordinated control. Its function is to correct the fuel calorific value when the coal calorific value of the unit deviates from the standard coal, so as to ensure the stability of the coordinated control system. The traditional calorific value correction circuit compares the amount of fuel consumed by the unit with the electrical load, and considers the efficiency of the unit as a whole. When the amount of fuel used deviates from the design value, it is considered that the calorific value of the fuel has changed, and the calorific value correction circuit corrects the fuel. The amount is corrected, see Figure 1. However, with the continuous development of thermal power energy-saving technology, when the efficiency of the steam turbine changes due to changes in the operating point, the shortcomings of this scheme are also becoming more and more prominent. For example, when the back pressure of the air-cooled unit changes with the change of load and ambient temperature, the efficiency of the steam turbine will change the efficiency of the entire unit, and the calorific value correction circuit will continuously correct the calorific value of the fuel due to the change of the back pressure, resulting in the corrected calorific value in the coordinated control system. The mismatch of the actual fuel calorific value causes the parameters to oscillate during the variable load process of the unit; energy-saving technologies such as steam turbine flow modification, unit flexibility modification, and sliding pressure optimization will also change the efficiency of the steam turbine, resulting in the wrong adjustment of the calorific value correction circuit, causing the main unit Parameter fluctuations affect the safe and stable operation of the unit.

Contents of the invention

The purpose of the present invention is to provide a calorific value correction method suitable for the coordinated control system of thermal power units when the efficiency of steam turbines changes due to water saving (air-cooling units), flexibility transformation, energy-saving transformation and other reasons.

The present invention adopts following technical scheme:

A calorific value correction method for a coordinated control system based on steam turbine efficiency correction, which corrects the boiler master control in the coordinated control system for changes in steam turbine efficiency.

It includes the following steps:

A. Boiler side calorific value correction circuit correction;

B. Efficiency correction on the steam turbine side;

C. Calculation of exhaust enthalpy based on generalized radial basis neural network;

D. Calorific value is corrected for boiler master control output.

Described step A comprises the following steps:

(1) The set value of the PID regulator is the standard coal amount required by the current thermal load of the boiler; the set value of the PID regulator is calculated by formula (a);

B _rs ＝f(D×(h ₁ -h ₃ )+D ₁ ×(h _a -h _b )) Formula (a)

In the formula (a), B _rs : the setting value of the PID regulator;

D: main steam flow rate, obtained by formula (b), converted from the pressure of the regulating stage;

h ₁ : main steam enthalpy at the boiler outlet, obtained from the current unit main steam temperature and pressure setting value look-up table;

h ₃ : Boiler inlet feedwater enthalpy, obtained from economizer inlet feedwater pressure and temperature look-up table,

D ₁ : reheat steam flow rate, obtained from formula (b);

h _b : steam enthalpy at the high discharge port, obtained from the set value of the steam temperature and pressure at the high discharge port of the current unit by looking up the table;

h _a : Steam enthalpy at the inlet of the medium-pressure cylinder, which is obtained by looking up the steam pressure and temperature at the inlet of the medium-pressure cylinder. D×(h ₁ -h ₃ ) can be represented as the current boiler calorific value including boiler efficiency;

f(·): conversion function, which converts the boiler heat load into the design standard coal quantity;

In formula (b), D ₁₀ , p _r , t _r0 , p _r0 , and t _r are the design value of reheat steam flow rate, pressure design value, temperature design value, actual reheat steam pressure and temperature, respectively;

(2) The adjusted quantity of PID in the calorific value correction circuit is the same as that of the traditional calorific value correction circuit, which is selected as the fuel quantity of the unit.

The step B is to correct the boiler calorific value correction circuit through the correction coefficient K ₂ of the thermal efficiency of the steam turbine to the calorific value, and K ₂ is calculated by formula (c);

In formula (c), K ₂ : correction coefficient of steam turbine thermal efficiency to calorific value; η _0t : design thermal efficiency of steam turbine; η _1t : current thermal efficiency of steam turbine.

When the steam turbine has no steam extraction and no intermediate reheat system, calculate the current thermal efficiency of the steam turbine according to formula (e);

In formula (e), h ₁ : steam turbine inlet enthalpy value, which is obtained from the steam turbine inlet steam temperature and pressure setting value look-up table; h ₂ : steam turbine exhaust steam enthalpy value, which is obtained from the current load of the unit, main steam enthalpy, reheat steam Enthalpy, exhaust steam pressure, and exhaust steam temperature are obtained by calculating the difference; h ₃ : Boiler inlet feedwater enthalpy, obtained from the feedwater pressure and temperature look-up table.

When the steam turbine has no steam extraction and is reheated once, calculate the current thermal efficiency of the steam turbine according to formula (f);

In formula (f), h _a : reheat steam enthalpy, obtained from reheat steam temperature setting value and pressure look-up table; h _b : high-pressure cylinder exhaust steam enthalpy, obtained from high-pressure cylinder exhaust temperature and pressure look-up table.

When the steam turbine has steam extraction without intermediate reheating, calculate the current thermal efficiency of the steam turbine according to formula (g);

In the formula (g), a: steam extraction share; i: steam extraction stage; n: steam extraction number; x: insufficient work coefficient of steam extraction, x=(h _i -h _b )/(h ₁ -h _b ) , h _i is extraction enthalpy; is the extraction loss share, which is obtained from the calculation of extraction volume and extraction parameters at all levels.

When the steam turbine has steam extraction and intermediate reheating, calculate the current thermal efficiency of the steam turbine according to formula (h);

In the formula (h), a: steam extraction share of high pressure cylinder; i: steam extraction series of high pressure cylinder; n: steam extraction number of high pressure cylinder; x: insufficient work coefficient of extraction steam, x=(h _i -h _b )/( h ₁ -h _b ), h _i is the extraction enthalpy; b: steam extraction share of medium and low pressure cylinders; j: steam extraction series of medium and low pressure cylinders; m: steam extraction number of medium and low pressure cylinders; y: insufficient work coefficient of extraction steam, y=(h _j -h ₂ )/(h _a -h ₂ ), h _j is the extraction enthalpy; is the extraction loss share, which is obtained from the calculation of extraction volume and extraction parameters at all levels.

The step C: the command fuel quantity Bs is the output of the main control of the boiler after the calorific value correction, and the calculation formula (i) is:

B _s ＝B _out ×K ₁ ×K ₂ formula (i)

In the formula (i), B _out is the main control output of the boiler; K ₁ is the output of the PID, which is the calorific value correction coefficient, which is calculated from the heat absorbed by steam and water in the boiler; K ₂ : the correction coefficient of the thermal efficiency of the steam turbine to the calorific value.

Described step D is:

The input parameters of the system are selected as: unit power, main steam enthalpy, reheat steam enthalpy, exhaust steam pressure, each extraction steam enthalpy, represented by matrix X;

The output of the system is exhaust enthalpy, represented by matrix Y;

Radial basis function using Gaussian function

The system output can be expressed as formula (j):

In formula (j):

d _max is the maximum Euclidean distance between sample centers, and I is the number of sample centers.

Among them, the sample center is determined by the following method:

1) Determine the number I of hidden nodes according to the unit load and exhaust pressure;

2) Randomly select I different typical samples from the input samples as cluster centers (t _i (n) (i=(1,2,...,I), n is the number of iterations), set n=0, Effective expert experience can reduce the amount of iterative calculations;

3) Calculate the 2-norm of all input samples from each center, ||X _k -t _i (n)||, k=(1,2,...,m) is the number of samples, and for each The input sample X _k is classified according to the minimum Euclidean distance;

4) Recalculate the sample center

5) End when the error is less than the set value, otherwise return to step 3).

The beneficial effect of the present invention is that: the present invention separates the steam turbine efficiency from the boiler calorific value correction amount, calculates the boiler and steam turbine efficiencies separately, and at the same time modifies the set value of the calorific value correction circuit from the load function to the actual heat load function of the unit , which can ensure that the output of the calorific value correction circuit is the real calorific value of the fuel, effectively reduce system fluctuations caused by changes in turbine efficiency, reduce overshoot, and improve the safety and stability of the unit.

Description of drawings

Figure 1 Classic calorific value correction loop.

Fig. 2 Calorific value correction circuit of the present invention.

Fig. 3 and Fig. 4 are effect diagrams of specific embodiments (600MW supercritical air-cooling unit).

Detailed ways

In order to deepen the understanding of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings. This embodiment is exemplary and is only used to explain the present invention and not limit the scope of protection.

Introduced in conjunction with the implementation plan of a 600MW supercritical air-cooled unit, the unit uniformly adopts the international basic unit.

According to the change of steam turbine efficiency, the main control of the boiler in the coordinated control system is corrected to ensure the correctness of the output of the main control of the boiler and the accuracy of the calorific value correction circuit.

The steps of the present invention are as follows:

1. Calorific value correction circuit on the boiler side

In order to decouple the steam turbine efficiency from the calorific value loop, the control strategy of the boiler value correction loop is modified as shown in box 1 in Fig. 2.

(1) The setting value of the PID regulator is the standard coal amount required by the current heat load of the boiler, namely:

B _rs ＝f(D×(h ₁ -h ₃ )+D ₁ ×(h _a -h _b ))

In the formula, B _rs : heat value PID setting value;

D: main steam flow rate, which can be obtained by Friugel's formula (that is, formula b), and converted from the pressure of the regulating stage;

h ₁ : main steam enthalpy at the boiler outlet, obtained from the current unit main steam temperature and pressure setting value look-up table;

h ₃ : Boiler inlet feedwater enthalpy, obtained from the feedwater pressure and temperature at the economizer inlet table, D×(h ₁ -h ₃ ) can be represented as the current boiler calorific value including boiler efficiency;

D ₁ : reheat steam flow rate, obtained by Friugel's formula,

D ₁₀ , p _r , t _r0 , p _r0 , and t _r are the reheat steam flow design value, pressure design value, temperature design value, actual reheat steam pressure and temperature, respectively.

h _b : steam enthalpy at the high discharge port, obtained from the set value of the steam temperature and pressure at the high discharge port of the current unit by looking up the table;

h _a : Steam enthalpy at the inlet of the medium-pressure cylinder, which is obtained by looking up the steam pressure and temperature at the inlet of the medium-pressure cylinder. D×(h ₁ -h ₃ ) can be represented as the current boiler calorific value including boiler efficiency;

f(·): Conversion function, which converts the calorific value of the boiler into standard coal.

(2) The adjusted quantity of PID in the calorific value correction circuit is the same as that of the traditional calorific value correction circuit, which is selected as the fuel quantity of the unit.

The output of PID is calorific value correction coefficient K ₁ . Since _K1 is calculated from the heat absorbed by steam and water in the boiler, when the boiler efficiency does not change, it can be represented as the change in the unit fuel calorific value. In order to ensure the accuracy of the calorific value correction loop, its PID controller is only adjusted when the load of the unit is stable.

2. Turbine side efficiency correction

Box 2 in Fig. 2 is the steam turbine efficiency correction. This scheme is an intermediate reheating unit with steam extraction once, and the thermal efficiency of the steam turbine can be calculated according to the Rankine cycle thermal efficiency formula:

In the formula, η _t : Rankine cycle thermal efficiency;

W _s : steam turbine work;

q: The boiler absorbs heat.

The ratio of the steam turbine design efficiency to the current efficiency is used to correct the boiler calorific value correction loop.

In the formula, K ₂ : correction coefficient of steam turbine efficiency to calorific value;

η _0t : design efficiency of steam turbine;

η _1t : current efficiency of steam turbine.

Among them, η _0t is obtained by converting unit load through f(-) conversion function.

η _1t is obtained from the Rankine cycle thermal efficiency formula.

In the formula, a: steam extraction ratio of high pressure cylinder;

i: steam extraction stages of high pressure cylinder;

n: steam extraction number of high pressure cylinder;

x: Insufficient work coefficient of extraction steam, x=(h _i -h _b )/(h ₁ -h _b ), h _i is extraction enthalpy;

b: steam extraction ratio of medium and low pressure cylinders;

j: steam extraction stages of medium and low pressure cylinders;

m: steam extraction number of middle and low pressure cylinders;

y: Insufficient work coefficient of extraction steam, y=(h _j -h ₂ )/(h _a -h ₂ ), h _j is extraction enthalpy.

is the extraction loss share, which is obtained from the calculation of extraction volume and extraction parameters at all levels.

3. Calculation of exhaust enthalpy based on generalized radial basis neural network

In order to simplify the logic configuration and calculation amount in DCS, the input parameters of the system are simplified as follows: unit power, main steam enthalpy, reheat steam enthalpy, exhaust steam pressure, and penultimate extraction steam enthalpy, represented by matrix X; system output is exhaust Enthalpy of steam, represented by matrix Y.

Radial basis function using Gaussian function The system output can be expressed as:

In the formula:

d _max is the maximum Euclidean distance between sample centers, and I is the number of sample centers.

Determination of sample center

(1) Determine the number of hidden nodes I according to the unit load and exhaust pressure;

(2) Randomly select I different typical samples in the input samples as cluster centers (t _i (n) (i=(1,2,...,I), n is the number of iterations), set n=0 , effective expert experience can reduce the amount of iterative calculations;

(3) Calculate the 2-norm of all input samples from each center, ||X _k -t _i (n)||, k=(1,2,...,m) is the number of samples, and for each Input samples X _k are classified according to the minimum Euclidean distance;

(4) Recalculate the sample center

(5) End when the error is less than the set value, otherwise return to (3).

4. Calorific value to boiler main control output correction

The fuel quantity command is the boiler main control output corrected by the calorific value, and the calculation formula is:

B _s =B _out ×K ₁ ×K ₂

Figure 3 and Figure 4 are the actual application effect diagrams of this scheme. When the back pressure of the unit changes with the load and ambient temperature, the calorific value correction circuit of the unit operates normally, and the unit efficiency change caused by the turbine efficiency is not included in the calorific value correction circuit.

The above-mentioned embodiments only describe the preferred implementation of the present invention, but are not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above-mentioned embodiments, and make different extensions and changes, but as long as All are within the protection scope of the present invention without departing from the spirit of the present invention.

Claims (10)

1. one kind is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, it is characterised in that for steam turbine Efficiency change, is modified boiler master in coordinated control system.

2. one kind according to claim 1 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, it includes the following steps：

A, boiler side calorific value corrective loop is corrected；

B, steamer pusher side Efficiency correction；

C, the exhaust enthalpy based on broad sense radial base neural net calculates；

D, calorific value exports boiler master and corrects.

3. one kind according to claim 2 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, the step A includes the following steps：

Mark coal amount of the setting value of PID regulator needed for the current thermic load of boiler；The setting value of the PID tune machine passes through public affairs Formula (a) calculates；

B_rs=f (D × (h₁-h₃)+D₁×(h_a-h_b)) formula (a)

In formula (a), B_rs：The setting value of PID regulator；

D：Main steam flow, is obtained by formula (b), is converted by first stage pressure；

h₁：Boiler export main steam enthalpy, is tabled look-up acquisition by the setting value of current unit main steam temperature, pressure；

h₃：Boiler inlet feeds water enthalpy, is tabled look-up acquisition by economizer entrance feed pressure, temperature, D₁：Reheated steam flow, by formula (b) obtain；

h_b：High outlet steam enthalpy, is tabled look-up acquisition by the high outlet vapor (steam) temperature of current unit, the setting value of pressure；

h_a：Intermediate pressure cylinder inlet steam enthalpy, intermediate pressure cylinder inlet steam pressure, temperature are tabled look-up acquisition, D × (h₁-h₃) may be characterized as containing pot The current boiler caloric value of the efficiency of furnace；

f(·)：Function is converted, is design mark coal amount by boiler heat load conversion；

In formula (b), D₁₀、p_r、t_r0、p_r0、t_rRespectively reheated steam flow design value, pressure design value, temperature design value, reality Border reheated steam pressure, temperature；

The regulated variable of PID is identical with traditional calorific value corrective loop in calorific value corrective loop, is chosen for unit fuel quantity.

4. one kind according to claim 3 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, the step B is the adjusted coefficient K by turbine thermodynamic efficiency to calorific value₂, to boiler calorific value corrective loop into Row correction, K₂Calculated by formula (c)；

In formula (c), K₂：Turbine thermodynamic efficiency is to calorific value correction factor；η_0t：The Design of Steam Turbine thermal efficiency；η_1t：Steam turbine is current The thermal efficiency.

5. one kind according to claim 4 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its Be characterized in that, when steam turbine without steam extraction without resuperheat system when, according to formula (e) calculate the current thermal efficiency of steam turbine；

In formula (e), h₁：Turbine inlet enthalpy, is tabled look-up acquisition by turbine inlet vapor (steam) temperature, pressure set points；h₂：For Turbine discharge enthalpy, difference meter is carried out by unit current loads, main steam enthalpy, reheated steam enthalpy, exhaust steam pressure, exhaust temperature Calculate and obtain；h₃：Boiler inlet feeds water enthalpy, is tabled look-up acquisition by feed pressure, temperature.

6. one kind according to claim 4 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, when steam turbine is without steam extraction once reheating, the current thermal efficiency of steam turbine is calculated according to formula (f)；

In formula (f), h_a：Reheated steam enthalpy, is tabled look-up acquisition by reheat steam temperature setting value, pressure；h_b：High pressure cylinder exhaust enthalpy, Tabled look-up acquisition by exhaust temperature of HP, pressure.

7. one kind according to claim 4 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, when steam turbine has steam extraction without resuperheat, the current thermal efficiency of steam turbine is calculated according to formula (g)；

In formula (g), a：Steam extraction share；i：Steam extraction series；n：Steam extraction is numbered；x：Steam extraction acting deficiency coefficient, x=(h_i-h_b)/ (h₁-h_b), h_iFor steam extraction enthalpy；It is steam extraction loss share, is obtained by steam extraction amounts at different levels, the computing of steam extraction parameter.

8. one kind according to claim 4 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, when steam turbine has steam extraction and resuperheat, the current thermal efficiency of steam turbine is calculated according to formula (h)；

In formula (h), a：High pressure cylinder steam extraction share；i：High pressure cylinder steam extraction series；n：High pressure cylinder steam extraction is numbered；x：Steam extraction is done work not Sufficient coefficient, x=(h_i-h_b)/(h₁-h_b), h_iFor steam extraction enthalpy；b：Mesolow cylinder steam extraction share；j：Mesolow cylinder steam extraction series；m：In Low pressure (LP) cylinder steam extraction is numbered；y：Steam extraction acting deficiency coefficient, y=(h_j-h₂)/(h_a-h₂), h_jFor steam extraction enthalpy； It is steam extraction loss share, is obtained by steam extraction amounts at different levels, the computing of steam extraction parameter.

9. one kind according to claim 8 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, the step D：Command fuel amount Bs is to be exported through the revised boiler master of calorific value, and calculation formula (i) is：

B_s=B_out×K₁×K₂Formula (i)

In formula (i), B_outExported for boiler master；K₁Output for PID is calorific value correction coefficient, is recepted the caloric by carbonated drink in boiler It is calculated；K₂：Turbine thermodynamic efficiency is to calorific value correction factor.

10. one kind according to claim 9 is based on the modified coordinated control system calorific value bearing calibration of turbine efficiency, its It is characterized in that, the step C is：

System input parameter is chosen for：The power of the assembling unit, main steam enthalpy, reheated steam enthalpy, exhaust steam pressure, each steam extraction enthalpy, with matrix X Represent；

System output is exhaust enthalpy, is represented with matrix Y；

Radial basis function uses Gaussian function

System output is represented by formula (j)：

In formula (j)：

<mrow> <msub> <mi>&amp;omega;</mi> <mi>i</mi> </msub> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mfrac> <mi>I</mi> <mrow> <msup> <msub> <mi>d</mi> <mi>max</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>|</mo> <mo>|</mo> <msub> <mi>X</mi> <mi>k</mi> </msub> <mo>-</mo> <msub> <mi>t</mi> <mi>i</mi> </msub> <mo>|</mo> <msup> <mo>|</mo> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>;</mo> </mrow>

d_maxMaximum Euclidean distance between center of a sample, I are center of a sample's number；

The center of a sample determines by the following method：

1) hidden node number I is determined according to unit load and exhaust steam pressure；

2) I different typical samples are randomly selected in input sample as cluster centre (t_i(n) (i=(1,2 ..., I), n For iterations), if n=0, effective expertise can reduce iterative calculation amount；

3) all 2- norms of the input sample away from each center are calculated, | | X_k-t_i(n) | |, k=(1,2 ..., be m) number of samples, And to each input sample X_kSorted out by minimum euclidean distance；

4) center of a sample is recalculated

<mrow> <msub> <mi>t</mi> <mi>i</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msub> <mi>t</mi> <mi>i</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>&amp;eta;</mi> <mrow> <mo>(</mo> <msub> <mi>X</mi> <mi>k</mi> </msub> <mo>(</mo> <mi>n</mi> <mo>)</mo> <mo>-</mo> <msub> <mi>t</mi> <mi>i</mi> </msub> <mo>(</mo> <mi>n</mi> <mo>)</mo> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow> <mi>i</mi> <mo>=</mo> <mi>i</mi> <mrow> <mo>(</mo> <msub> <mi>X</mi> <mi>k</mi> </msub> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>t</mi> <mi>i</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> </mtd> <mtd> <mrow></mrow> </mtd> </mtr> </mtable> </mfenced> </mrow>

5) terminate when error is less than setting value, otherwise return to step 3).