JPH0633704A - Method of improving operating efficiency of steam-turbine generating plant - Google Patents

Abstract

PURPOSE: To provide a method for improving operational efficiency of a partial-arc steam turbine power plant during power output variations by dynamically adjusting valve point values during turbine operation. CONSTITUTION: An impulse chamber pressure at each of a plurality of valve points is first determined during operation of a steam turbine at constant pressure. For each adjacent pair of valve points, an optimum constant pressure transition point pressure for transitioning from one to the other of a sliding pressure mode and constant pressure mode is then computed. The optimum constant pressure transition point pressure is converted to a percentage of pressure difference between the adjacent pairs of valve points. The impulse chamber pressure at each valve point is then used to calculate a corresponding impulse chamber pressure for transitioning from the one mode to the other mode based upon the percentage pressure difference. The calculated impulse chamber pressure for transition is compared with a measured value of the impulse chamber pressure, and when the measured value is substantially equal to the calculated transition pressure, the transition from the one mode to the other mode is carried. The transition to the constant pressure mode may be varied for reducing rotor thermal stress.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to steam turbines for use in power plants, and more particularly to a method for optimizing steam turbine performance during varying output demands.

The output of many multi-stage steam turbine systems is controlled by transformer control of steam from a steam generator to reduce steam pressure at the high pressure turbine inlet or steam chamber. A steam turbine that uses this transformation method is
Because all steam inlet nozzle chambers are effective under all load conditions, they are often referred to as full-circle inflow or full-circle inflow turbines. Full-circulation turbines are usually designed to respond to exact steam conditions at rated load to maximize efficiency. By flowing steam through all of the inlet nozzles, the pressure ratio of the inlet stage, eg, the first control stage, in the full-circulation turbine remains substantially constant regardless of the steam inlet pressure. As a result, the mechanical efficiency of the output generation in the first control stage can be optimized. However, a reduction in power in a full-circulation turbine reduces overall efficiency, ie, the ideal efficiency of the steam work cycle between the steam generator and the turbine outlet. The reason is that the transformation reduces the energy available to do work. In general,
The total turbine efficiency, or actual efficiency, is the product of the turbine's ideal efficiency and mechanical efficiency.

More efficient control of turbine power than control achievable by the transformer method alone has been achieved by the technique of separating the steam entering the turbine inlet into a plurality of individually controllable partial inflows. . In this method, known as partial-circulation admission, the number of actuatable first stage nozzles changes in response to load changes. Relatively high ideal efficiency
The partial-circulation turbine was more advantageous than the full-circulation turbine because it could be achieved by sequentially injecting steam into the individual nozzle chambers at a constant pressure rather than by transforming the inflow over the entire circumference. The advantage of this higher ideal efficiency is that it is generally more advantageous than the optimum mechanical efficiency achievable in the control stage of a full-circulation turbine configuration. In general, multi-stage steam turbine systems that use partial-circle admission to change power output operate at a higher practical efficiency than systems that change steam pressure for full-circle admission. However, conventional partial-arc turbine systems have been found to have certain drawbacks that limit the efficiency of work in the control stage. Some of these limitations are due to unavoidable mechanical constraints such as unavoidable amounts of windage losses and turbulence, which occur, for example, when a blade passes through a group of nozzle vanes that are not admitted with steam.

Further, in a partial-circulation turbine system, the pressure drop (and hence the pressure ratio) across the nozzle vane group.
Changes as the steam passes through multiple valve chambers in sequence, the maximum pressure drop occurs at the minimum valve point (the minimum number of control valves or control valves open), and the minimum pressure drop occurs at all-round inflow. . The thermodynamic efficiency, which is inversely proportional to the pressure difference in the control stage, is the lowest at the minimum valve point, and is highest at the full inflow. Therefore, the control stage efficiency of the partial-arc turbine decreases when the output drops below the rated load. However, given the variable pressure drop across the nozzles of the partial-arc turbine, it is believed that certain structural features commonly found in partial-arc turbine systems may be improved to increase the overall efficiency of the turbine. ing. Since the control stage is an impulse stage where most of the pressure drop occurs at the stationary nozzle, a 1% improvement in nozzle efficiency has a 4x effect on control stage efficiency than a 1% improvement in blade efficiency. . Turbine designs that provide a substantial conservative improvement in control stage nozzle performance significantly improve the practical efficiency of partial-arc turbines. Even a 0.25 percent increase in the actual efficiency of a partial-arc turbine at those rated loads can be a significant energy savings.

The variable or variable throttle operation of partial-arc turbines in some valve loops also improves turbine efficiency and additionally reduces low cycle fatigue. In the normal procedure, if the transformer is used to the lowest effective pressure limit, one half of the control valve is fully open and the other half is fully closed, ie the maximum inflow is practically 10%.
The variable pressure operation of the partial-circulation inflow turbine is started at a flow rate equal to or lower than the value corresponding to the point where the first-stage inflow of 50% in the turbine is 0%. By comparison, variable pressure operation is most efficient in a full-circulation turbine when started at maximum steam flow. A loss of performance occurs when the transformer operation is started in the partial-arc turbine at higher flow rates (higher values of first stage admission). However, in turbines with many valves, the transformation from any inflow over 50% eliminates a significant portion of each valve loop (valve throttle) that would result from constant throttle operation. The elimination of such valve loops improves turbine heat rate and turbine efficiency.

FIG. 1 shows the effect of transformer control in a partial circumference steam turbine with eight control valves. The horizontal axis represents the load value, and the vertical axis value is the heat consumption rate. The line 14 represents the locus of the ideal point at a constant pressure associated with the sequential control (partial circulation inflow) operation of the valve. Dotted lines 16, 18 and 20 represent the actual valve loops for a finite number of control valves. The valve loop is created by gradually throttling each of a series of control or regulating valves. The transformer operation from 100% inflow is shown by line 22. Note that although some of the valve loop 16 has been removed by transformation along line 22, the heat dissipation rate (reciprocal of efficiency) increases disproportionately below transition point 24. Line 26 showing the transformation from the 87.5% inflow point
Provides a similar improvement to valve loop 18 down to transition point 28. Similarly, transformation from 75% inflow, ie line 3
0 improves operation over the valve loop 20. Each of these valve loops represents a higher heat dissipation rate and reduced efficiency from the ideal curve represented by line 14.
Each valve point on the line 14 represents a state in which each valve is fully open or fully closed.

FIGS. 1, 2 and 3 show the operation of an exemplary steam turbine using one prior art control. FIG. 1 shows the locus of line 14 at constant pressure operation at all valve points, ie 2535 psia. The valve points are associated with the valve loop identified by lines 16, 18 and 20 at 50%, 75%, 87.5% and 100% inflow respectively. Transformation is line 2
2, 26 and 30. Starting at about 806 MW 100% admission for the exemplary steam turbine system, the load is first reduced by changing the throttle pressure by fully opening all eight control valves and controlling the steam generating boiler. . When the throttling pressure, line 22 reaches the intersection 24 with the valve loop 16, the throttling pressure is increased to 2535 psia while closing the eight control valves to the inflow value corresponding to point 24. The control valve is 253
While maintaining a constant throttle pressure of 5 psia, the control valve is fully closed as the load continues to close as the load is further reduced and the turbine operates at 87.5% admission. To reduce the load further, the valve position is kept constant again, the seven control valves are fully opened and the throttle pressure is reduced again until it corresponds to the crossing 28 of the transformer line 26 and the valve loop 18. To reduce the load below point 28, the pressure is increased to 2535 psia and the seventh control valve is gradually closed (down the valve loop) until it is fully closed. The inflow at this time is 7
5%. To further reduce the load, by fully opening six control valves and fully closing two control valves until the transformer line 30 reaches the intersection 32 with the valve loop 20,
The pressure is reduced again. The operation of increasing the throttle pressure and closing the control valve is repeated for the desired total number of valve loops. Fluctuations in throttling pressure are shown in FIG. Inclined portion 44 of line 46
Corresponds to variable pressure operation at a constant valve position. Vertical part 4
8 corresponds to the end of the pressure change and the shift of the valve throttle. The horizontal section 50 corresponds to operation at constant steam pressure by throttling the control valve, such as by going down the valve loop while reducing the load at constant pressure. FIG. 3 shows the improvement in heat rate as a function of load. Line 52 represents the difference between the valve loop performance at constant pressure and the performance with the transformation between valve points.

The performance improvements shown in FIGS. 1 and 3 are based on the assumption that the boiler feed pump discharge rate decreases with decreasing throttle pressure. If the feed pump discharge does not decrease proportionally, the improvement is diminished because the energy required to maintain the discharge pressure remains high. In prior art turbine systems, a signal is sent to the feed pump-feed pump drive system to reduce the pressure. But,
Actually, in order to eliminate the need for constant adjustment of the feed pump speed and the occurrence of control instability and hunting due to small fluctuations of the inlet water pressure to the boiler due to the disturbance of the flow rate demand, the feed pump must be pressure adjusted. A vessel is attached.
The pressure regulator provides more or less throttling, which alters the pump discharge pressure and thus the flow rate delivered by the feed pump. Pump speed is held constant over the desired range of travel of the regulator valve. If the regulator valve exceeds its range of travel, the pump speed is adjusted to move the regulator valve to some desired average position. As a result, the pump discharge pressure is not equal to the minimum allowable value (throttle pressure + turbine system head loss) and the performance improvement is not as great as illustrated by FIGS. 1 and 3. Furthermore, in order to achieve a faster load response, the regulator valve is usually operated with some pressure drop, so that in the event of a sudden increase in load demand, the regulator valve will open quickly and open the flow rate. Increase. The response of the feed pump and its drive is slower than the response of the regulating valve.

The combination of throttling transformation and control valve opening adjustment results in a significant improvement in heat dissipation rate, but according to the knowledge of the present inventor, it is optimal for switching from one operating mode to another. It has been found that the transition point varies from turbine to turbine and also changes during the life of one turbine. In particular, in addition to the factors mentioned above, other parameters such as condenser pressure, reheat temperature and reheater pressure drop may also fluctuate from the design values. Such fluctuations cause a shift in the load at which the transition occurs. Furthermore, due to blade manufacturing tolerances, the transition point (load) when transitioning from throttle transformation to constant throttle pressure operation is different from that obtained from performance calculations.

The invention of US Pat. No. 4,297,848 attempts to solve the optimization problem by using impulse chamber pressure to determine the transition point. The method described in the U.S. patent requires perturbing the boiler pressure to measure the electrical load. Due to the uncertainty of the load measurement and the complexity of the perturbation, the transition point can occur below the optimum value.

[0011]

SUMMARY OF THE INVENTION In accordance with the present invention, a method is disclosed for optimizing the transition point between variable pressure operation and constant pressure operation in a partial-arc steam turbine. In particular, the impulse chamber pressure is used to make the transition between variable pressure operation and constant pressure operation. But,
During power reduction, the impulse chamber pressure for variable pressure operation is adjusted according to a predetermined pressure-volume relationship to correspond to the value of constant pressure operation. The impulse chamber pressure is higher in variable pressure operation than in constant pressure operation. The transition point is non-optimal because the valve point, i.e. the point at which the selected valve is fully open and fully closed, is measured during constant pressure operation without adjusting the impulse chamber pressure reading during variable pressure operation. It occurs at the pressure of the impulse chamber.

The method of the present invention utilizes impulse chamber pressure measurements at each valve point during turbine operation to set the optimum transition point. In particular, the inventor has found that the optimum transition point is generally a predetermined percentage of the pressure difference between adjacent valve points. Therefore, by dynamically determining the valve point, the pressure difference ratio can be calculated and the pressure difference used to set the transition point can be used to make the transition at the optimum point.

The present invention also includes an operating method for reducing rotor thermal stress upon transition at a calculated optimum transition point from variable pressure operation to constant pressure operation. In particular, according to the preferred method of operation, the steam pressure is reduced in response to a reduction in power demand until the steam pressure reaches a predetermined optimum transition point. At that point, the control valve is gradually closed, thereby decreasing the steam flow into the steam turbine and at the same time increasing the steam pressure, until the operating control valve reaches its fully closed position. , It does not reach full throttle steam pressure. This method of operation is believed to improve the efficiency of the turbine system. Impact load on the cascade of control stages is also improved because the total steam pressure is not immediately re-added to the control stage at the transition point.
If a further reduction in turbine power is required, the above operating method is simply repeated for each control valve, i.e. the throttle pressure is reduced to reach the optimum transition point, after which the control valve is gradually closed and throttled simultaneously. Gradually increase steam pressure.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Before describing the present invention in detail, reference is made to FIG. 4 which shows a schematic functional block diagram of a typical steam turbine power plant suitable for practicing the principles of the present invention. In the power plant of FIG. 4, a conventional boiler 60, which may be of the nuclear fuel or fossil fuel type, produces steam, which is shown at 64 through a throttle header 62.
It is led to a pair of steam admission valves. Connected to boiler 60 is a conventional boiler controller 66, which is used to control various boiler parameters such as steam pressure at throttle header 62. More specifically,
The steam pressure at the throttle header 62 is typically controlled by a set point controller (not shown in FIG. 4) located within the boiler controller 66. The construction of such set point controllers is well known to those skilled in the art and need not be described in more detail in connection with this embodiment. The steam flows through the high pressure turbine section 68 according to the degree of opening of a steam admission valve (control valve) 64 arranged to control the flow rate of steam from the accumulator (steam chamber) to various inflow regions of the high pressure turbine section 68 of the steam turbine. Adjusted to pass. The steam exiting the high pressure turbine section 68 is typically 72
Is reheated in a conventional reheater section 70 prior to being fed to at least one low pressure turbine section shown at. The steam exiting the low pressure turbine section 72 is directed into a conventional condenser unit 74.

In most cases, a common shaft 76 connects the high pressure turbine section and the low pressure turbine section 68, 72 to a generator unit 78.
Mechanically connected to. As the steam expands through the high and low pressure turbine sections 68, 72, it transfers most of its energy to the torque for rotating shaft 76. Turbine unit 68 during start-up of power plant
And the steam introduced to 72 adjusts the rotational speed of the turbine shaft to the synchronous speed of the line voltage or its sub-frequency. This is typically a conventional speed pickup converter 80.
Is detected by detecting the speed of the turbine shaft 76. The signal 82 produced by the speed pickup converter 80, which is representative of the rotary shaft speed, is provided to a conventional turbine controller 84. Turbine controller 84 then controls the opening of the steam entry valve using signal line 86 to direct turbine sections 68 and 72 according to the desired speed demand and the measured speed signal 82 provided to turbine controller 84. Adjust the steam introduced.

A typical main breaker unit 88 is located between the generator unit 78 and the electrical load 90. The electrical load may be a high capacity electrical transmission and distribution network in this description. When the turbine controller 84 determines that a synchronization condition exists, the main breaker unit 88 can close and provide electrical energy to the electrical load 90. The actual output of the power plant may be measured by a conventional power measuring converter 92, such as a watts converter connected to a power line that supplies electrical energy to an electrical load 90. The signal that represents the actual output of the power plant is
It is supplied to the turbine controller 84 via a signal line 94. Once in synchronism, controller 84 can conventionally adjust steam inlet valve 64 to provide steam to turbine sections 68 and 72 to meet the desired power generation of the power plant.

In accordance with the present invention, an optimal turbine efficiency controller 96 is additionally located as part of the steam power plant of FIG. Turbine efficiency optimum controller 96
Monitors the thermodynamic state of the power plant at the desired power plant output by measuring various turbine parameters, which will be described in more detail below, and with the help of this information, throttle steam pressure Is controlled by utilizing a signal line 98 connected from the controller 96 to the boiler controller 66. Throttling pressure adjustment can be accomplished by changing the set point of a throttling set point controller (not shown) commonly known as part of boiler controller 66. As with most setpoint controllers, feedback measurement parameters such as throttle steam pressure are, for example, brought close to the setpoint, and the deviation is usually a function of the output / input gain characteristics of the pressure setpoint controller. is there.

Turbine parameters, such as throttle steam pressure and temperature, are measured by conventional pressure transducer 100 and temperature transducer 1.
02, respectively. The signals 104 and 106 produced by these pressure converter 100 and temperature converter 102, respectively, may be provided to a turbine efficiency optimum controller 96. Reheater 70 as another parameter
The turbine reheat steam temperature at is measured by a conventional temperature converter 108 which produces a signal 110, which may also be provided to and used by controller 96. The signal 94 generated by the power measurement converter 92 is fed to the controller 96.
May be additionally supplied. In addition, one important turbine parameter reflects the steam flow rate through the turbine sections 68 and 72. The steam pressure in the impulse chamber (first stage outlet) of the high-pressure turbine unit 68 is appropriately selected according to the purpose of this embodiment. A conventional pressure transducer 112 is located in the impulse chamber and has a signal 114 representative of the vapor pressure in the impulse chamber.
Is generated and supplied to the controller 96.

The controller 96 of the present invention may be considered to be the main controller in the regulated power plant control system described above, and is typically available under the trade name MicroVax Computer (MicroVax Computer) from, for example, Digital Equipment Corporation. computer). This computer is capable of performing the various operations required to control the turbine system.

Referring again to FIG. 1, it is desirable to combine variable pressure operation with constant pressure operation to obtain optimum efficiency or heat dissipation rate. In an ideal environment, the valve points at which each control valve should be opened and closed can be calculated from its turbine design,
Indeed, each turbine manufacturer has their own method of calculating the ideal valve point and ideal transition point as a function of load (or other variable) for a turbine built using such turbine design parameters. The graph of FIG. 1 is created using this design calculation. However, various factors such as blade manufacturing tolerances and turbine parameters such as condenser pressure, reheater temperature and pressure are combined to produce ideal valve points and ideal transition points other than calculated values. Obtainable. Therefore, the controller 96 is based on the actual measurement values.
It must have the computing power to change the value of. It has further been found that the impulse chamber pressure is higher during variable pressure operation than during constant pressure operation due to the higher enthalpy and specific volume. Therefore, since a plurality of valve points are necessarily set during constant pressure operation, the transition points in each control valve curve are defined in terms of constant throttle pressure. This is not a problem because the transition is from constant throttle pressure operation to variable pressure operation if the turbine load is increasing, but if the load is decreasing, the transition is from variable pressure operation to constant throttle pressure operation. Is done, so it is a problem. Therefore, once the optimum transition point is selected, it is necessary to convert the impulse chamber pressure during variable pressure operation to an equivalent constant throttle pressure value.

The inventor has found that the impulse chamber pressure at a constant throttle pressure is
It has been found that, when multiplied by the square root of the pressure-volume (PV) product ratio for each mode of operation, the result is a pressure closely matching that corresponding to the variable pressure operation. Mathematically, this can be expressed as Equation 1. here,
P _ic is the impulse chamber pressure at constant throttle pressure, P _is is the impulse chamber pressure at throttle transformer, (PV) _s is the impulse chamber pressure-volume product at throttle transformer, (PV) c is the constant throttle pressure. Is the pressure-volume product of the impulse chamber.

[0022]

[Equation 1]

Although the accuracy is inferior, the product of PV can be replaced with the impulse chamber temperature in absolute temperature, and can be expressed as in equation (2).

[0024]

[Equation 2]

The accuracy of this method was further validated by considering the situation where the flow region of the cascade was out of design. The turbine flow region exactly matches the design region and 2
Arithmetic was performed to determine the transition point when the two deviations were introduced. In that one deviation, the flow area in the first six rows of the high pressure turbine section 68 reaction blade rows (out of a total of 18 rows) was increased by 5%. In the second deviation, the nozzle area of the control stage was increased by 2%.

Tables 1 and 2 have 6 control valves 44
Figure 6 shows impulse chamber pressures for constant pressure and transition at transition for three sets of 0MW turbine flow regions. Table 1 is 8
The present invention relates to a control valve that supplies steam in an inflow circumferential range of 3.3% to 100.0%. Table 2 relates to control valves supplying steam in the inlet circumference range of 50% to 66.7%. The amount of steam passing through multiple nozzles in a given inlet circumference increases with decreasing unit load up to the nozzle choke (which has a critical pressure ratio). Furthermore, the impulse chamber temperature decreases with decreasing load.

[0027]

[Table 1]

[0028]

[Table 2]

By utilizing the measured impulse chamber pressure when a particular valve is about to begin to close and the measured pressure just before the next control valve begins to close during constant throttle pressure operation, the optimum impulse at the transition point is obtained. A correlation was generated that closely predicts chamber pressure. The optimum impulse chamber pressures for all three sets of flow zones are the difference with respect to the impulse chamber pressures at the two levels of load and flow rate during the opening and closing of a given control valve, ie ΔP
_{The ic} was actually a constant percentage.

In these three cases, the multiplier for ΔP _ic varies between 53.4% and 54.1% for the sixth control valve and 74.0% and 76.% for the fourth control valve. It varied between 8%.

If the ratio used matches the design range of the turbine, the predicted impulse chamber pressures at the sixth control valve and the fourth control valve in both constant throttle pressure and throttle variable pressure operation, that is,
Pests are as shown in Table 3 and Table 4, respectively. Pact is the impulse chamber pressure calculated from the turbine performance computer program.

[0032]

[Table 3]

[0033]

[Table 4]

If the as-manufactured flow region for the reaction cascade and control stage nozzle were used in the turbine performance prediction program, the results would approach the comparison marked "as designed." Ah Since the proposed method uses actual (measured) changes in impulse chamber pressure from field data, the calculated transition points are accurate. As a result, any changes in steam condition or turbine degradation will be taken into account by the analysis. Both conditions will result in changes in impulse chamber pressure and temperature. The square root of the PV product is calculated for these two states to evaluate the effect of the actual measurement. First, the temperature was assumed to be the expected value. Second, the temperature was assumed to be 10 ° F (5.6 ° C) lower than predicted or measured. The difference between the two square roots when using PV at the wrong temperature is about 0.02
It is 1.0639 vs. 1.0166 at 5%. Since both temperatures differ by 10 ° F (5.6 ° C), the error was actually offset.

There are many ways to determine the square root of two PV terms. One method is to use design values. Another method is to calculate the square root from the constant pressure and the transformation PV product obtained from the turbine performance calculation, using the values according to the combination of regions. Yet another method is to use the measured impulse chamber temperature, or T _ic , at the constant pressure transition point (impulse chamber pressure). The load is then held constant and the throttling pressure is reduced. This will open the control valve. When the control valve is fully opened, the impulse chamber temperature and pressure are measured.

Next, the specific volume is 2 using the vapor characteristic table.
Calculated from the pressure and temperature of the set. The controller 96 comprises a Microbucks computer capable of performing this operation. If the control system does not have a method for calculating steam properties, an empirical formula can be used to first calculate the enthalpy h as a function of pressure and temperature, and then PV as a function of enthalpy for various levels of pressure. Is. These equations are described in US Pat. No. 4,827,429. On-line updates for this latter direction allow adjustment of transition points to compensate for equipment degradation and other deviations.

Using the method proposed for these three cases (design area, 5% excess reaction blade row area, 2% excess nozzle area), the heat dissipation rate from the optimum value can be calculated by using the approximation method. An operation was performed to determine the increase. The heat consumption rate error caused by the incorrect transition point is less than 1 Btu / Kwh (1 Kj / Kwh) in the 6th control valve and 0. 4 in the 4th control valve.
7Btu / Kwh (0.7Kj / Kwh) and 2Btu / Kwh (2Kj / Kw)
It was during h). This deviation of 2Btu / Kwh (2Kj / Kwh) occurred at the transition point due to the variable voltage operation. The deviation due to the constant pressure operation at this same point was 0.7 Btu / Kwh (0.7 Kj / Kwh).

The present invention described above provides a method for setting an optimum transition point for transitioning from variable pressure operation to constant pressure operation during variable operation of a steam turbine, but pressure and control valve closure lead to the optimum transition point. Further improvements can be achieved by the method of adjusting after arrival. Referring again to FIG. 2, at each transition point under operation according to the prior art, the control valve is closed from the transition point to reduce turbine load output, but the pressure is restored to the nominal turbine operating pressure. It can be seen that it is rapidly increased to and held at that point. Once
Once the particular control valve is fully closed, the variable pressure operation is re-used to reduce the turbine output. At each transition point, a significant increase in throttle pressure causes significant thermal stress on both the rotor and the first stage control blade row. The inventor minimizes this thermal stress and control stage cascade impact load by gradually increasing the steam or throttle pressure from its minimum value at the transition point to its nominal operating value. And the nominal value is reached only at the point where the control valve associated with the particular control loop attached has reached its minimum open or fully closed position. FIG. 2 illustrates this improved operation by the dashed line 48 '. At the same time as this gradual increase in throttle steam pressure, the associated control valve is also allowed to start gradually from its fully open position and gradually begin to close. In this mode of operation, the control valve is closed by a rather small percentage, for example of the order of 20%, and the throttle pressure is kept at a value between the optimum transition point value and the nominal steam pressure value. There may be specific points. It should also be noted that this method of operation can be used to close either a single control valve or multiple control valves. It is believed that the improved heat rate is achieved by operating the turbine between transition points in the manner described above.

With the above operating mode, the throttle pressure increases linearly as the impulse pressure decreases between the transition point and the valve point. For example, in FIG. 2, the valve point is labeled 49 and the transition point is labeled 51. The turbine operates in variable pressure operation over the entire inflow range at pressure reduction as the load decreases from the valve point, such as valve point 49. Pressure is
The minimum value is reached at the transition point and then increased to its nominal value when the next lower valve point is reached.

The above-mentioned operating method brings about a more gradual change in the outlet temperature of the first stage and the temperature of the boiler shell together with the improvement of the heat consumption rate and the reduction of the impact load of the first stage blade row. The improvement in heat dissipation rate is a compromise between cycle effective energy, which increases as pressure increases, fluctuations in first-stage efficiency when pressure ratio changes, and fluctuations in partial inflow loss.

It should be noted that the method of operation described above may alter the procedure for determining the optimum transition point without sacrificing significant heat rate improvement. In particular, because variable pressure operation is utilized throughout the turbine's reduced power cycle, the constant pressure operation first stage outlet pressure at the transition point is measured and then changed to determine two pressure-volume terms or absolute temperature. The transition point can be chosen to be a predetermined percentage of the pressure difference between two adjacent valve points without having to obtain the variable operating pressure by using the square root.

While the principles of the present invention have been clarified above by way of illustrative embodiments, it will be apparent to those skilled in the art that numerous changes in structure, arrangement and components in the various examples described above may be made. It may be done in the practice of the invention to provide alternative embodiments adapted to the particular operating conditions without departing from the spirit and scope of the invention as claimed.

[Brief description of drawings]

FIG. 1 is a graph of turbine power output or load versus heat rate characteristic curves for a prior art method of steam turbine control.

2 is a graph showing throttling pressure as a function of load for the method of FIG.

FIG. 3 is a graph showing the efficiency improvement calculated for the method of FIG.

FIG. 4 is a simplified conceptual diagram of one form of a steam turbine power plant suitable for carrying out the method of the present invention.

[Explanation of symbols]

60 ... Boiler, 64 ... Steam admission valve (control valve), 68 ... High-pressure turbine section, 72 ... Low-pressure turbine section, 96 ... Optimal turbine efficiency controller.

Claims (3)

[Claims] 1. In order to improve the operating efficiency during the output fluctuation of a steam turbine power plant including a partial-circumferential flow steam turbine that can be selectively operated in a variable pressure operation mode and a constant pressure operation mode, the constant pressure operation mode is used. The output fluctuation is performed by gradually opening and closing the valve to change the steam inflow amount to the selected plurality of partial circles to change the volume flow rate of steam to the steam turbine, and each of the partial circles, Defined by adjacent valve points corresponding to fully open and fully closed valves controlling steam inflow to each partial circumference, variable pressure operation is affected by varying steam pressure to the steam chamber of the steam turbine, Operational efficiency is improved by using transformer operation during at least some of the power fluctuations and constant pressure operation during other parts of the power fluctuations. A method for improving the operating efficiency of a power plant, wherein the impulse chamber pressure at each of the plurality of valve points is measured during operation of the steam turbine at a constant pressure. Calculating the optimum constant pressure transition point pressure for the transition from one of the constant pressure operating modes to the other, the optimum constant pressure transition point pressure for each pair of valve points being the corresponding pressure between the adjacent pair of valve points. Converted to a difference ratio, from the impulse chamber pressure at each valve point obtained in the measurement step, based on the pressure difference ratio derived in the conversion step, the variable pressure operation mode and the constant pressure operation mode Calculating the corresponding impulse chamber pressure for the transition from one to the other, comparing the corresponding impulse chamber pressure for the transition obtained from the stage of calculation with the measured value of the impulse chamber pressure, the measured value being Obtained at the calculation stage When approximately equal to the transition pressure which, while shifts to the other from the sliding pressure mode and the constant pressure operation mode, the operating efficiency improvement method of the steam turbine power plant including the stages. 2. In order to improve operating efficiency during output fluctuation of a steam turbine power plant including a partial-circulation inflow steam turbine that can be selectively operated in a variable pressure operation mode and a constant pressure operation mode, a constant pressure operation mode in the constant pressure operation mode is used. The output fluctuation is performed by gradually opening and closing the valve to change the steam inflow amount to the selected plurality of partial circles to change the volume flow rate of steam to the steam turbine, and each of the partial circles, The variable pressure operation is defined by the adjacent valve points corresponding to the fully open and fully closed valves controlling the steam inflow to each partial circumference.
Affected by changing the steam pressure to the steam chamber of the steam turbine, the operating efficiency uses variable pressure operation during at least some part of the power fluctuation and constant pressure operation during other parts of the power fluctuation. Be improved by
A method for improving the operating efficiency of a steam turbine power plant, wherein the impulse chamber pressure at each of a plurality of valve points is measured during operation of the steam turbine at a constant pressure, and for each adjacent pair of valve points, the variable pressure operation mode is set. To the constant pressure operation mode, the optimum constant pressure transition point between the adjacent valve points of each pair is calculated, and the optimum constant pressure transition point is converted to the corresponding transformation transition value, and the impulse chamber pressure is changed to the transformation transition. A method for improving the operating efficiency of a steam turbine power plant including various stages, in which a variable pressure operation is switched to a constant pressure operation when the value is reached. 3. A method for reducing thermal stress of a rotor and impact load of a control stage cascade in a partial-circulation inflow steam turbine in which a steam flow rate is controlled so as to meet an electric power demand. In the method for reducing thermal stress and impact load of a steam turbine, each of which is provided with a plurality of control valves arranged to allow steam to flow into a predetermined partial circumference in the control stage blade row, steam pressure in the plurality of control valves is reduced. , Decreasing to a predetermined value corresponding to the heat consumption rate achievable by closing the first control valve to a predetermined steam flow value while operating at constant steam pressure, and closing the first control valve to a minimum flow position However, the steam pressure is gradually increased from the above predetermined value to another value, and the steam pressure is reached by closing another control valve to another predetermined steam flow value while operating at a constant steam pressure. Decrease to another predetermined value corresponding to another heat rate that can be achieved, and gradually increase the steam pressure from the other predetermined value to the other value while closing the other control valve to the minimum flow rate position. A method for reducing thermal stress and impact load of a steam turbine, wherein the steps of increasing and decreasing the steam pressure and closing the control valve are repeated until the turbine output matches the power demand.