660MW SUPERCRITICAL UNIT BYPASS CONTROL SYSTEM AND CONTROL METHOD THEREOF

Abstract

A 660MW supercritical unit bypass control method after a load rejection is provided. Steam channels after the load rejection are switched without an interference, and ache steam pressure is controllable. The 660MW supercritical unit bypass control method includes Pipeline 1, Pipeline 2, Pipeline 3, and Pipeline 4; a bottom of Pipeline 3, a bottom of the Pipeline 2, and a head of the Pipeline 4 are connected by a temperature and pressure reducer; a bottom of the Pipeline 1 is connected to a head of Pipeline 2; a branch pipe is arranged between the Pipeline 1 and the Pipeline 2, and a steam turbine is arranged in the branch pipe. A high-pressure bypass control system automatically adapts to the load rejection or FCB under any loading situation, avoids drastic changes of unit parameters from loading fluctuations, meets requirements of the load rejection and the FCB.

Claims

1. A 660 MW supercritical unit bypass control system, comprises a Pipeline 1, a Pipeline 2, a Pipeline 3, and a Pipeline 4; a bottom of the Pipeline 3, a bottom of the Pipeline 2, and a head of the Pipeline 4 are connected by a temperature and pressure reducer; a bottom of the Pipeline 1 is connected to a head of the Pipeline 2; a branch pipe is arranged between the Pipeline 1 and the Pipeline 2, and a steam turbine is arranged in the branch pipe; valves for controlling are provided between the Pipeline 3 and the temperature and pressure reducer, between the Pipeline 2 and the temperature and pressure reducer, and between the steam turbine and the branch pipe, respectively; the Pipeline 1, the Pipeline 2, the Pipeline 3, the Pipeline 4, the temperature and pressure reducer, the steam turbine, and the valves are regulated by controllers, respectively.

2. The 660 MW supercritical unit bypass control system according to claim 1, wherein a Valve 1 is arranged in the branch pipe; a Valve 1.1 is arranged between the Valve 1 and the steam turbine; a Valve 3 is arranged in the Pipeline 3; a Valve 3.1 is arranged between the Valve 3 and the temperature and pressure reducer; and a Valve 2 is arranged in the Pipeline 2,

3. The 600 MW supercritical unit bypass control system according to claim 2, wherein the Valve 1 is a main valve; the Valve 1.1 is a main steam regulating valve; the Valve 3 is a high-pressure de-superheating water isolation valve; the Valve 3.1 is a high-pressure de-superheating water regulating valve; the Valve 2 is a high-pressure bypass valve,

4. A control method of the 660 MW supercritical unit bypass control system according to claim 3, comprising the following steps: performing an opening control of the Valve 2 during a load rejection or a fast cut back (FCB), and an opening degree of the Valve 2 is obtained as follows: through a steam flow calculation sheet, a bypass steam enthalpy value, and a steam balance during the load rejection, an undisturbed switching of steam channels is realized, a working fluid balance of a unit is maintained, and an overall stability of the unit is sustained; a steam flow balance relationship is described as an Equation (1), wherein the Equation (1) is as follows:
Q.sub.1−Q.sub.2   (1); wherein, wherein, Q.sub.1 is a steam flow through the Pipeline 1 before the load rejection, and Q.sub.2 is a steam flow through the Pipeline 2 after the load rejection; a relationship of Q.sub.1, a loading value, and a regulating stage pressure is shown in an Equation (2), wherein Q1 is obtained by a calculation of the regulating stage pressure p.sub.1; f(p.sub.1) is a main steam flow without a temperature correction, the Equation (2) is as follows:
Q.sub.1=f(p.sub.1)*√{square root over (T.sub.0/T.sub.1)}  (2); a relationship of a value of the steam flow Q.sub.2 (t/h) after a high-pressure bypass valve, the opening degree kn (%) of the Valve 2, and a steam temperature T.sub.2 (K) before the Valve 2 is shown in an Equation (3), wherein since the Pipeline 1, the Pipeline 2, the Pipeline 3 and Pipeline 4 are adjacent, T.sub.2 is identical to a main steam temperature T.sub.1; p.sub.2 (MPa) is a steam pressure before the Valve 2; a steam enthalpy value E (J/kg) of passing the Valve 2 is obtained by checking the steam temperature T.sub.2 (K) and the steam pressure p.sub.2 (MPa); ΔP is a differential value of a pressure between before and after passing the Valve 2; the Equation (3) is as follows:
Q.sub.2=kn*ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]  (3); when the unit is running normally, the Valve 2 closes, and the steam flow enters from the Valve 1 and the Valve 1.1 to maintain an operation of the steam turbine; when the unit is under the load rejection, the Valve 1 and the Valve 1.1 close instantly, and the Valve 2 opens quickly; to maintain a safety of the unit during the load rejection, and avoid violent fluctuations of the unit, as well as to maintain the working fluid balance, the opening degree of an instant step opening of the Valve 2 during the load rejection is accurately calculated from the Equations (1), (2), and (3), as shown in an Equation (4), wherein the Equation (4) is as follows:
kn=f(p.sub.1)*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)])   (4); p.sub.1 (MPa) is a steam pressure after the Valve 1.1, and also is the regulating stage pressure, p.sub.2 (MPa) is a pressure before the Valve 2, T.sub.1(K) is the steam temperature before the Valve 2, f(p.sub.1) is the main steam flow corresponding to the regulating stage pressure, the steam enthalpy value E (J/kg) without the temperature correction is obtained by checking the T.sub.1(K) and the p.sub.2 (MPa), and ΔP is the differential value of the pressure between before and after the Valve 2; in order to accurately calculate the opening degree of the Valve 2, a s rte(polygonal function of f(p.sub.1) is performed:
when p.sub.1≤5.8, f(p.sub.1)=600; kn=600*√{square root over (T.sub.0T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 538<p.sub.1≤7.5, f(p.sub.1)=600+(p.sub.1−5.8)*88.23,
kn=(600+88.23*(p.sub.1−5.8))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 7.5<p.sub.1≤9.43, f(p.sub.1)=750+(p.sub.1−7.5)*129.53,
kn=(750+129.53*(p.sub.1−7.5))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1,p.sub.2)−18.7)]);
when 9.43<p.sub.1≤11.18, f(p.sub.1)=1000+(p.sub.1<9.43)*114.28,
kn=(1000+114.28*(p.sub.1−9.43))*√{square root over (T.sub.0. T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 11.18<p.sub.1≤12.52, f(p.sub.1)=1200+(p.sub.1−11.18)*111.94,
kn=(1200+111.94*(p.sub.1−11.18))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]):
when 12.52<p.sub.1≤13.56, f((p.sub.1)=1350+(p.sub.1<12.52)*144.23,
kn=(1350+144.23*(p.sub.1−12.52))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 13.56<p.sub.1≤16.8, f(p.sub.1)=1500+(p.sub.1−13.56)*133.93,
kn=(1500+133.93*(p.sub.1−13.56))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 16.8<p.sub.1≤17.64, f(p.sub.1)=1800+(p.sub.1−16.8)*119.05,
kn=(1800+119.05*(p.sub.1−16.8))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]);
when 17.64<p.sub.1≤18.73, f(p.sub.1)=1900+(p.sub.1−17.64)*90.1,
kn=(1900+90.1*(p.sub.1−17.64))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.1, p.sub.2)−18.7)]).

5. The control method of the 660 MW supercritical unit bypass control system according to claim 4, wherein, the control method comprises a generation method of a control target pressure of the Valve 2 and a setting parameter of a steam pressure control is obtained as follows: when the opening degree by the instant step opening of the Valve 2 reaches a calculated value according to the Equation (4), the 660 MW supercritical unit bypass control system enters an automatic control mode, automatically adjusts a main steam pressure; the main steam pressure is tested when a boiler load is in a stable stage, and then an average value during the stable stage is taken as a corresponding pressure target setting parameter p.sub.4; a value of the corresponding pressure target setting parameter p.sub.4 is decided by the boiler load, and f(L) is a related function of the boiler load; after a first-order inertia, the corresponding pressure target setting parameter p.sub.4 used as the setting parameter of the steam pressure control of the high-pressure bypass valve, as shown in an Equation (5):
p.sub.4=f(L)*(1−e.sup.−t/20)   (5); t is a time in Equation (5); the corresponding pressure target setting parameter p.sub.4 has a linear relationship to a load, and is accurately piecewise calculated as follows to obtain an accurate target pressure, wherein a. calculated value is used as the corresponding pressure target setting parameter of the target pressure when the high-pressure bypass valve opens during the automatic control mode after the load rejection:
when L≤30, p.sub.4=10.33*(1=e.sup.″t/20);
when 30<L≤40, p.sub.4=(10.33+0.305*(L−30))*(1−e.sup.−t/20);
when 40<L≤50, p.sub.4=(13.38+0.282*(L−40))*(1−e.sup.−t/20);
when 50<L≤60, p.sub.4=(16.2+0.273*(L−50))*(1−e.sup.−t/20);
when 60<L≤70, p.sub.4=(18.93+0.302*(L−60))*(1e.sup.−t/20);
when 70<L≤80, p.sub.4=(21.95+0.186*(L−70)) *(1−e.sup.−t/20); when 80<L≤90, p.sub.4=(23.81+0.019*(L−80))*(1=e.sup.−t/20);
when 90<L≤100, p.sub.4=24; a value of the steam pressure P.sub.4 (MPa) of the Pipeline 4 at an inlet of the steam turbine has a linear relationship with the boiler load L, a piecewise function calculation is developed as follows to obtain an accurate steam pressure value of the Pipeline 4, wherein the calculated value is used as a steam pressure setting parameter of the Pipeline 4 during a corresponding boiler load; a setting value is used as the steam pressure setting parameter of a Proportion Integration Differentiation (PID) control module after the Valve 2 piecewise opens;
when L≤30, P.sub.4=0.58;
when 30<L≤40, P.sub.4=0.58+(L−30)*0.006;
when 40<L≤50 P.sub.4=0.62+(L−40)*0.006;
when 50<L≤60, P.sub.4=0.68+(L−50)*0.008;
when 60<L≤70, P.sub.4=0.76+(L−60)*0.011;
when 70<L≤80, P.sub.4=0.87+(L−70)*0.013;
when 80<L≤90, P.sub.4=1.00+(L−80)*0.012:
when 90<L≤95 ,P.sub.4=1.12+(L−90)*0.077;
when 95<L≤100 P.sub.4=1.23+(L−95)*0.022;
when L>100, P.sub.4=1.23; a deviation of a pressure setting value and an actual steam pressure is input the PID control module of the Valve 2, and a calculated output command directly controls the opening degree of the high-pressure bypass valve and controls the actual steam pressure after the load rejection or the FCB corresponding to the boiler load.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a scheme of the connection structure of the present invention;

[0041] FIG. 2. is a scheme of the logical flow diagram of the high-pressure bypass control of the present invention;

[0042] FIG. 3 is a scheme of the logical flow diagram of the low-pressure regulating valve control of the present invention;

[0043] FIG. 4 is the meaning of the symbols in FIG. 2 to FIG. 3 of the present invention;

[0044] FIG. 5 is a scheme of the circuit principle connection structure of the present invention.

[0045] As shown in FIG. 5, L1 is Pipeline 1, L2 is Pipeline 2, L3 is Pipeline 3, L4 is Pipeline 4, V1 is Valve 1, V1.1 is Valve 1.1, V2 is Valve 2, V3 is Valve 3, and V3.1 is Valve 3.1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The present invention will be further described by reference to the following drawings and examples.

[0047] Example 1: A 660 MW supercritical unit bypass control system, see FIG. 1 and FIG. 5, comprises a superheater and a controller. The superheated steam flow passes Pipeline 1, through V1 and V1.1 to enter the high-pressure cylinder of the steam turbine to maintain the regular operation of the steam turbine. Valve 1 and Valve 1.1 close quickly during load rejection, and the superheated steam flows through Pipeline 2. Pipeline 2 and Pipeline 1 connect with a 60 degrees angle at the position 4.5 meters above the steam turbine, 5 meters on the left side of the machine head; Pipeline 2 is installed with Valve 2, which adjusted the steam flow and pressure in Pipeline 2. The adjusted steam flows through Pipeline 4 and enters the temperature and pressure reducer. Pipeline 3 and Pipeline 4 are connected through the temperature and pressure reducer with a 45 degrees angle, at 3 meters behind Valve 2; Pipeline 3 is equipped with Valve 3 and Valve 3.1. The high-pressure input water passes through Pipeline 3 from the outlet of the feedwater pump, through Valve 3, and is adjusted by Valve 3.1, enters the temperature and pressure reducer to adjust the temperature of the superheated steam; the steam which passes the temperature and pressure reducer flows to a reheater through Pipeline 4. The control terminals of Valve 1, Valve 1.1, Valve 2, Valve 3, and Valve 3.1 are connected to the controller, respectively. The steam pressure after load rejection is adjusted by the opening of Valve 2, and the steam temperature is adjusted by Valve 3.1 to control the steam flow matching with the actual working conditions.

[0048] The control terminals of the bypass control system Valve 1, Valve 1.1, Valve 2, Valve 3, and Valve 3.1 are connected to the controller, respectively.

[0049] As shown in FIG. 2 and FIG. 4, a control method that applies to a bypass control system for a 660 MW supercritical unit under load rejection and FCB working conditions comprises the step opening of high-pressure bypass valve V2, the generation of the pressure setting value, and the pressure control process. The step opening degree of V2 can be obtained by accurate calculation of the steam pressure and temperature; the calculation method is stated as below:

[0050] The present invention accurately analyzes and calculates the step opening degree of V2 by integrating the steam flow calculation principle, the steam balance, and temperature and pressure parameters.

[0051] After load rejection, V1 and V1.1 close, and V2 opens. The steam flow balance relationship is described in Equation (1):

Q.sub.1=Q.sub.2   (1)

[0052] wherein, Q.sub.i is the steam flow (t/h) through Pipeline 1 before load rejection, and Q.sub.2 is the steam flow (t/h) through Pipeline 2 after load rejection; the relationship of Q.sub.1, the loading value, and the regulating stage pressure: Q1 can be obtained by calculation of the regulating stage pressure p.sub.1; f(p.sub.1) is the main steam flow without temperature correction, as shown in Equation (2);

Q.sub.1=f(p.sub.1)*√{square root over (T.sub.0/T.sub.1)}  (2)

[0053] In Equation 2, Q.sub.1 is the steam flow (the main steam flow) of Pipeline 1, To is the steam temperature under full load condition, T.sub.1 is the actual steam flow, f(p.sub.1) is the function of the steam flow corresponding to different regulating stage pressure. This value has a certain linear relationship with the regulating stage pressure P.sub.1.

[0054] the relationship of the value of the steam flow Q.sub.2 (t/h) after Valve V2, the opening degree kn (%) of Valve 2, and the steam temperature T.sub.2 (K) before Valve 2: since the pipelines are adjacent, T.sub.2 is the same as the main steam temperature T.sub.1; the steam pressure p.sub.2 (MPa) before Valve 2; the steam enthalpy value E (J/kg) of passing Valve 2 can be obtained by checking T.sub.2 (K) and p.sub.2 (MPa); ΔP is a differential value of pressure between before and after passing Valve 2;

[0055] the flow calculation sheet according to Valve 2 has a relationship shown in Equation (2):

Q.sub.2=kn*ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−1.8.7)]  (3)

[0056] when the unit is running normally, Valve 2 closes, and the steam flow enters from Valve 1 and Valve 1A to maintain the operation of the steam turbine; when the unit is under load rejection, Valve 1 and Valve 1.1 close instantly, and Valve 2 opens quickly. In order to maintain the safety of the unit during load rejection, and avoid violent fluctuations of the unit, as well as maintain the working fluid balance, the opening degree of the instant step opening of Valve 2 during load rejection can be accurately calculated from the above Equations (1), (2), and (3), as shown in Equation (4):

kn=f(p.sub.1)*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2,p.sub.2)−18.7)])   (4)

[0057] In order to more accurately calculate the opening degree of Valve 2, a segmented polygonal function of f(p1) is performed:

when p.sub.1≤5.8, f(p.sub.1)=600; kn=600*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 5.8<p.sub.1≤7.5, f(p.sub.1)=600+(p.sub.1−5.8)*88.23,

kn=(600+88.23*(p.sub.1−5.8))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2,p.sub.2)−18.7)]);

when 7.5<p.sub.1≤9.43, f(p.sub.1)=750+(p.sub.1−7.5)*129.53,

kn=(750+129.53*(p.sub.1−7.5))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 9.43<p.sub.1≤11.18, f(p.sub.1)=1000+(p.sub.1−9.43)*114.28,

kn=(1000+114.28*(p.sub.1−9.43))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 11.18<p.sub.1≤12.52, f(p.sub.1)=1200+(p.sub.1−11.18)*111.94,

kn=(1200+111.94*(p.sub.1−11.18))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 12.52<p.sub.1≤13.56, f(p.sub.1)=1350+(p.sub.1−12.52)*144.23,

kn=(1350+144.23*(p.sub.1−12.52))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 13.56<p.sub.1≤16.8, f(p.sub.1)=1500+(p.sub.1−13.56)*133.93,

kn=(1500+133.93*(p.sub.1−13.56))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 16.8<p.sub.1≤17.64,f(p.sub.1)=1800+(p.sub.1−16.8)*119.05,

kn=(1800+119.05*(p.sub.1−16.8))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2*[507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

when 17.64<p.sub.118.73, f(p.sub.1)=1900+(p.sub.1−17.64)*90.1,

kn=(1900+90.1*(p.sub.1−17.64))*√{square root over (T.sub.0/T.sub.1)}/(ΔP*p.sub.2[*507*(0.03*E(T.sub.2, p.sub.2)−18.7)]);

[0058] The pressure setting value p4 controlled by V2 is a function of the boiler load L (%), with a certain linear relationship formed after the first-order inertia,

when L≤30, ; p.sub.4=10.33*(1−e.sup.−t/20)

when 30<L≤40, p.sub.4=(10.33+0.305*(L−30))*(1−e.sup.−t/20);

when 40<L≤50, p.sub.4=(13.38+0.282*(L−40))*(1−e.sup.−t/20);

when 50<L≤60, p.sub.b=(16.2+0,273*(L−50))*(1−e.sup.−t/20);

when 60<L≤70, p.sub.b=(18.93+0.302*(L−60))*(1−e.sup.−t/20);

when 70 <L≤80, p.sub.4=(21.95+0.186*(L−70))*(1−e.sup.−t/20).

when 80<L≤90, p.sub.4=(23.81+0.019*(L−80))*(1−e.sup.−t/20);

when 90L≤100, p.sub.4=24;

[0059] After the unit is under load rejection or FCB, the V2 step opens to the opening degree kn as mentioned above: meanwhile, the steam pressure p2 is automatically adjusted to the target pressure p4 through the controller K1 to adapt to the drastic changes in the boiler load and steam pressure during load rejection, avoid overpressure and violent pressure fluctuations of the unit during load rejection or FCB, and ensure the safety of the unit.

[0060] The above examples minimize the pressure parameter fluctuation of the unit during load rejection or KB by accurately calculating the step opening degree of the high-pressure bypass valve according to the current steam pressure and temperature when the unit is load rejection or FCB. After the high-pressure bypass valve opens, the control target setting value is calculated, and the inertia session is delayed to match the actual boiler load after load rejection, which ensures the safety and stability of steam pressure control during load rejection or FCB. The bypass control method under load rejection is of high safety, good reliability, and a simple structure.

[0061] The present examples are described by reference to the drawings, which are not intended to limit the present invention when implemented. Any various changes or modifications within the scope of the appended claims may be made by an ordinary technician in the fields.