JPS5820364B2 - Steam turbine load control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load control system for a steam turbine, and more particularly to a control system that can significantly improve load following performance by coordinating boiler main steam temperature control and turbine injection mode control. .

Conventionally, two injection systems have been used for steam turbines: full-circle injection and partial injection.

Full-circle injection is also called throttle control because all steam control valves are equally throttled, and partial injection is also called nozzle control because each steam control valve is opened and closed sequentially.

Turbine efficiency and load followability are considered to be the effects of full-circle injection or partial injection mode on turbine performance.

Regarding turbine efficiency, partial injection is 1-3% higher at 50% load.

Regarding load followability, as shown in the first post-death steam temperature characteristic diagram in Fig. 1, when the turbine load LA decreases from 100% to 50%, the first post-death steam temperature TIST changes between the full-circumference injection characteristic TF and the partial injection characteristic TP. Then, ΔTF−2
Since the temperature decreases by 6°C and ΔTP=76°C, full-circle injection has higher load followability in terms of thermal stress.

Therefore, in conventional turbine operation systems, when the steam flow rate is small and the load is low and the speed is increasing, the turbine is operated with all-round injection to prevent extreme heating of the turbine, and when the load exceeds a predetermined load, the turbine is always operated with highly efficient partial injection.

However, in conventional all-round injection, the steam flow rate was controlled by keeping all control valves fully open and adjusting the opening degree of the main steam stop valve.

For this purpose, a valve switching system is provided, and between (1) and (2) in Fig. 1, the turbine is sped up with all steam control valves fully open to increase the load.

In addition, the valves are switched while maintaining the load between the predetermined load levels O■-■, the main steam stop valve is fully opened, the steam control valve is shifted to the partial injection state, and from then on, the partial injection is always performed between O■-■. It was running an injection operation.

There are two conventional valve switching methods in this valve switching system.

The first method is also called a differential opening method, and is a method in which the main steam stop valve is fully opened when the adjustment valve starts to close and the difference in opening between the main steam stop valve and the main steam stop valve reaches a preset value.

The second method is also called a differential pressure method, and is a method in which the control valve begins to close and the main steam stop valve is fully opened when the differential pressure across the main steam stop valve reaches a predetermined value.

However, in both of the above two methods, it is impossible to quickly switch between load fluctuations at any load level without causing disturbance to the load, and even more so, considering thermal stress, it is impossible to switch between full-circle injection and partial injection. It was not possible to drive in intermediate mode.

Therefore, once you switch to partial injection mode,
As shown in the figure, since operation in the partial injection mode is continued between ■ and ■ on the partial injection characteristic TP, the load change rate has been influenced by the temperature characteristics of the partial injection mode due to the problem of life consumption due to thermal stress.

On the other hand, for the boiler antibacterial system, a main steam temperature permissible fluctuation limit is set for the same reason, that is, to suppress fluctuations in the steam temperature after the first cooling due to temperature fluctuations in the steam (main steam) generated from the boiler during load fluctuations. was.

For this reason, the load change rate of the boiler has been limited in order to operate within this fluctuation limit.

However, if for some reason this fluctuation limit was exceeded, measures were taken such as adjusting the load change rate or stopping the turbine.

The purpose of the present invention is to
Injection mode control and main control are used to improve load followability by minimizing fluctuations in the post-death steam temperature and preventing temperature fluctuations in the main steam generated from the boiler from appearing as fluctuations in the primary post-death steam temperature. The present invention provides a steam turbine load control system that effectively combines steam temperature side legs.

The present invention focuses on the fact that the characteristics of the first post-death steam temperature with respect to the turbine load are significantly different between partial injection and full-circumference injection, and when the load changes, both injections are appropriately mixed and the first
The aim is to improve load followability by keeping the steam temperature extremely constant after cooling.

Furthermore, in the present invention, the mixing ratio of both injections is controlled so that fluctuations in the main steam temperature due to load changes do not appear as fluctuations in the steam temperature after the first cooling, and the main steam temperature of the boiler side leg system is controlled. The aim is to significantly improve the boiler's load following ability by modifying the set values.

In order to achieve the above object, the present invention provides cam characteristic generating means for operating the steam control valve in full-circle injection mode and cam characteristic generating means for operating it in partial injection mode in response to a load command to the turbine. Applied mutatis mutandis to each individual, the output of both cam characteristic generating means is the full-circle injection rate α and the partial injection rate β, respectively.
(However, β-1-α) is added to finally determine the opening degree pattern of the steam control valve, that is, the injection mode.

In this injection mode, when the turbine load decreases, the injection mode is modified from partial injection to full-circle injection so that the steam temperature after the first stage does not fluctuate, and after the load reaches a steady state, the first stage steam temperature changes. Return to partial injection mode considering the allowable change.

If there is a load increase in the partial injection mode, the partial injection mode remains the same, and if there is a load increase in the intermediate mode, the injection mode is modified to be closer to the partial injection so that the steam temperature does not fluctuate after the first cooling. After reaching the partial injection mode completely, the load continues to increase while remaining in the partial injection mode.

Furthermore, in the low load region, even under static loads, the injection mode is modified to be closer to the all-round injection mode to prevent extreme heating of the turbine.

Further, by selecting and setting the allowable load change rate determined by the injection mode according to the operating state, maximum load followability is always obtained over the entire load range.

Furthermore, the injection mode control and the main steam temperature control of the boiler control system are coordinated so that fluctuations in the main steam temperature during load operation do not appear as fluctuations in the first stage steam temperature.

This has made it possible to widen the permissible fluctuation range of main steam temperature and significantly improve load followability.

Hereinafter, a case will be described in which the present invention is applied to a control system for a commercial power generation plant connected to an electric power system.

FIG. 2 shows the overall configuration of the antibacterial function which is an embodiment of the present invention.

Here, the full circumference/partial injection coordination side leg means 12 controls the injection mode by using both the full circumference injection mode and the partial injection mode according to the load fluctuation of the turbine, and also adaptively corrects the load change rate according to the operation mode. It has the function of

The load change rate βR set by the load change rate setting means 3 and the target load LRO set by the target load setting means 4 are given to the program load change means 5, and the instantaneous load command value is changed in a ramp-like manner until the target load LRO is reached. L'RO is generated.

This L'RO and the detection value P1 of the first stage post-pressure detection means 18
The output of the proportional-integral adjusting means 6, which inputs the deviation of the turbine load signal LA obtained by multiplying sT by a proportional coefficient of 1, is given to the load signal generating means 7.

Since the generator is connected to the grid, the load signal generating means 7 uses the rated speed N8 and the actual speed N detected by the speed detecting means 8.
A load command value LR determined by the deviation from A and the adjustment rate δN is generated.

For this LR, the full-circle injection cam characteristic generating means 9 and the partial injection cam characteristic generating means 10 generate valve position commands aFA and aPA of the steam control valve corresponding to the respective injection modes, and coordinate the boiler and turbine. Side leg means 110 Multiplying means 1
4, 15.

Note that 13 is an injection rate correction means, 16 is a main steam temperature control means, and 18 is a first-stage post-pressure detection means, which will be described later.

Further, 1γ is a boiler.

FIG. 3 shows the cam characteristics of the cam characteristic generating means 9,100 for full-circle injection and partial injection, and in this embodiment, non-linear characteristics were used to correct the non-linearity of the joint venture.

Next, an injection mode sterilization method in the full circumference/partial injection cooperative sterilization means 12 for keeping the first steam temperature at an extremely constant level during load fluctuations will be described.

In Figure 2, the relationship between the all-round injection rate α and the partial injection rate β is α + β-1 (0 α41.0 β β 1).
- (1).

Also, the correction results α' and β' by the injection rate correction means 13 are also α'10β'-1 (0,<α'41.04β'Otsu1)...
......The relationship is as shown in (2).

At this time, the valve position signal aCC of the steam control valve is aCC-α'aFA+β'aPA °=”---(3
], and the larger α' is, the closer the opening pattern of the steam control valve is to the full-circle injection mode, and the larger β is, the closer it is to the partial injection mode.

However, as will be explained later, when the main steam temperature TMS is the rated temperature TMSO, there is no correction of the injection rate, and α' and β are equal to α and β, respectively.

Figure 4a shows T1 when the injection mode is controlled during load fluctuations to minimize fluctuations in the first steam temperature T15T.
5T is shown, and b shows the transition of the injection mode (all-round injection rate) at this time.

Now consider the case where the turbine load LA changes from Ll to L2.

From state ■ to ■, α is set to keep TtST constant.
is corrected from α1 to α2, and after the load change is completed, the temperature is returned to the partial injection mode state ■ at the maximum rate of temperature change allowed in terms of thermal stress.

Also, under steady load conditions, the turbine operates in partial injection mode with high turbine efficiency.

α, β so that the locus of T15T becomes horizontal between ■-■
The value of is determined as follows.

Now, the trajectory of T18T in full-circle injection mode and partial injection mode is approximated by a straight line, and TF (LA) and TP (LA
) is expressed by the following formula.

Here, TR: First post-summative steam temperature at full load TFO: First post-summative steam temperature in no-load full-circle injection mode Tpo: First post-summative steam temperature in no-load partial injection mode Also, TF(LA) and TP( Assuming that the amount of temperature change between LA) is linear with respect to α, the first steam temperature To(Ll) in state (2) is expressed by the following equation.

Steam temperature T after the first lapse.

(L2) is T. The all-round injection rate α2 in state (3) to be equal to (Ll) is expressed by the following formula (%). Note that the set value LRO of the target load is used as the value of L2.

Next, the rate of change of α for correcting the injection mode in accordance with the rate of load change from α1 to α2 is determined.

becomes.

The time Δt required for the load change from Ll to L2 is IT + It is expressed as

However, β is the load change rate setting value.

Therefore, the rate of change of α (dα/dt)1 becomes the whole circumference/
If the control period of the partial injection cooperative control is τ, the output values of α and β are as follows.

In the next calculation, the α and β determined here will be changed to α1,
Calculate as β1.

The above has been described for the case of a load drop, but the same applies to the case of a load increase.

Next, a case where a steady load state is reached will be explained.

As shown in FIG. 4, in order to shift to the partial injection mode from state ① or ②, it is necessary to confirm that the load change has been completed.

However, if full-circle/partial injection coordinated control is continued for small load fluctuations such as the governor free width, there is a possibility that the engine will operate for a long time near the low-efficiency all-circle injection mode.

In order to prevent this, a dead zone ΔL approximately equal to the maximum governor free width is provided, and full-circle/partial injection coordination control is performed only when the following equation is satisfied.

The rate of change of α when shifting to the partial injection mode is determined as follows.

First, the rate of temperature change that is permissible in terms of thermal stress is (dT18T/
dt) ma
Hato becomes.

Therefore, in the transition to partial injection mode − α − β
The output value of is .

Next, a method for limiting injection mode at low load will be explained.

At low loads, the evaporation phenomenon in the boiler is unstable,
Also, operating in partial injection mode will lead to extreme heating of the turbine.

Therefore, in the low load region, plant safety must be ensured by statically modifying the injection mode.

For this purpose, the straight line TL shown in FIG. 4A is provided.

If the all-round injection rate corresponding to this TL is αL, then becomes.

Full/Partial Injection Coordination (2) The means 12 limits the injection mode when α calculated by formula 00 or formula 06) becomes .

Further, when the load is below the lower limit LLt, α-1 is set to operate in the all-round injection mode.

Therefore, in FIG. 4, after the load change is completed in state (3), the injection mode is shifted to the partial injection mode, but when state 04 is reached, the modification of the injection mode is stopped.

Next, a method for correcting the load change rate according to the operating state will be explained.

By controlling the injection mode, the locus drawn by the steam temperature after the first lapse basically becomes the following five types of combinations.

(1) Horizontal trajectory (2) Trajectory that ascends and descends along TF (Trajectory that rises along 31'rL (4) Trajectory that rises along TP (5) Vertical trajectory Excluding (5) above In case (1), all of which involve load changes, the temperature gradient of the trajectory is zero, but the load change rate is defined by the boiler's load change limit.

In addition, since (2), (3), and (4) have different temperature gradients of trajectories with respect to load changes, the maximum allowable load change rate is determined for each in terms of thermal stress.

βR1 and βR2 respectively? βR3jβR4,
By selecting and setting according to the operating condition, the turbine load followability can be greatly improved.

This load change rate correction method determines the load change rate βRi (i=1 to 4) by the logical judgment shown in FIG. 5, and sets it in the load change rate setting means 3 shown in FIG.

That is, in FIG. 5, it is determined in steps 51 and 52 whether the boiler load L1 is not smaller than the lower limit value LLt and whether it is not larger than the upper limit value LL2.
It is determined in steps 53 and 54 whether the all-round injection rate α is not smaller than l, and the all-around injection rate α corresponds to the straight line TL in FIG.

It is determined in step 56 whether or not α is smaller than 1, and in step 58 whether α is not larger than 0. One of βR1 to βR4 is output depending on the value.

However, β8□ selected and set here is the maximum allowable load change rate of the turbine itself, and depending on the operating condition, the maximum load change rate determined by the boiler's antibacterial characteristics must also be taken into consideration.

Therefore, the load change rate setting means 3 compares the load change rate set from the outside with βR7, selects the lower value, and finally determines β□.

Next, a method will be described in which fluctuations in main steam temperature at the time of load fluctuations are absorbed by injection mode control to prevent fluctuations in first post-cooling steam temperature.

As shown in FIG. 6, when L' RO changes over time as shown, the main steam temperature TMS changes as TMSt with respect to the set value TMSH, and the first steam temperature changes as shown in FIG.
It fluctuates as T15T shown in the figure.

Since this is an unfavorable phenomenon for the turbine, conventionally the turbine side has required antibacterial conditions for the boiler side leg system to keep this fluctuation range to about ±10°C or less.

The injection rate correction means 13 shown in FIG. 2 is for absorbing this variation by correcting the injection rate.

However, as shown in FIG. 1, the load L1. Between L3, R4, R
2, it can be absorbed by modifying the injection mode closer to the all-round injection mode by the temperature fluctuation, but when the load L3. There is a part like between L4 that cannot be absorbed by the injection mode side leg.

That is, in the partial injection mode, the amount of control is controlled in the direction of increasing the steam temperature after the first lapse, and the amount of control is not controlled in the direction of decreasing it.

Therefore, load L3. To make it a controllable bacterium even between L.
As shown in Figure 6, a negative bias Δ is applied to the main steam temperature set value.
Given TR, set a new set value TMSR to the rated value TMSO so that the main steam temperature becomes TMS2, TMSR=TMSO+ΔT...
・Main steam temperature control means 1 of the boiler shown in Figure 2 as a company
Give to 6.

At this time, the first post-cooling steam temperature becomes Tl5T shown in FIG. 7, so the load change region L1. L2
Fluctuations in main steam temperature can be absorbed between

For that purpose, main steam temperature fluctuation ΔTMS = TMSOTM
S ”=-”° (23) is the correction amount ΔαB of the all-round injection rate
You can convert it to .

Now, in order to find ΔαB, the instantaneous load request signal L' RO
is regarded as the turbine load, T and T at L'RO
The temperature difference ΔTFP between the two is P 100 - L'R6 ΔTFP - (TFOT"po)□ 00 (24), so L'.

ΔαB for absorbing ΔTMS at becomes.

Note that 2 in equation (25) is a proportional series of the main steam temperature and the first post-decay steam temperature.

When the above is expressed as a transfer function, it becomes as shown in Fig. 8.

FIG. 9 shows the change in the injection mode at this time.

The above has been described for the state in partial injection mode, but in order to make the first post-depletion steam temperature possible in all injection modes, the direction in which the main steam temperature setting value is corrected is determined as shown in Figure 10. do it.

In other words, when giving a positive bias to the main steam temperature set value (because TMSO<TMS in the two-clause formula, Δα
B becomes a negative value, the injection mode is corrected toward partial injection, and fluctuations in main steam temperature can be absorbed.

FIG. 11 shows a system in which the function of determining the main steam temperature set value TMSR described above is combined with the logical judgment function for correcting the load change rate in the full-circle/partial injection coordination side (corporate) means 12.

That is, steps 151 to 158 in FIG. 11 correspond to steps 51 to 58 in FIG.
Step 150 of determining whether L2L1+ is not smaller than ΔL and Step 159 of determining whether L2 is not smaller than Ll are included, and one of three TMSR values is output based on the results of these determinations. be done.

Further, FIG. 12 shows a flow of processing in which the full-circle/partial injection coordination side (goods) means 12 and the injection rate correction means 13 are combined.

The first effect of the present invention is that it is possible to exhibit maximum load followability in consideration of thermal stress for any load change request, and it is possible to significantly improve load followability compared to conventional methods. It is.

The second effect is that stable load control is possible over the entire load range, improving plant safety and reliability.

In particular, the first effect is quantitatively compared with the conventional method in a 500 MW class turbine with a low cycle life consumption rate of 0.03%/cycle as follows.

(1) When the load changes from 25% load to 100% load, the load followability is approximately 33 times greater.

(2) When the load changes from 100% load to 25% load, the load followability is approximately 7.5 times greater.

The reason why the present invention has made it possible to significantly improve load followability and improve plant safety and reliability is as follows.
This is because the following three points were achieved.

(1) Preventing fluctuations in steam temperature after the first lapse by full-circle/partial injection coordination side ■.

(2) Load change rate correction according to injection mode.

(3) Expansion of the boiler load fluctuation limit through cooperation between the main steam temperature side leg and the full-circle/partial injection coordination side (foundation).

Although the present invention has been described above in the case of a commercial power generation plant connected to a grid, it is not necessarily applicable to a commercial power generation plant, and the present invention can also be applied as is to a private power generation facility connected to a single load.

Furthermore, it can be applied not only to power generation equipment but also to steam turbines for mechanical drives such as pumps for oil pipelines and ships.

Furthermore, although the number of steam control valves has been described as four, it is clear that the present invention can be applied to any number of steam control valves as long as there are two or more.

In the present invention, the turbine load is the pressure after the first stage p, s'
r is detected and converted into a turbine load, which is the value LA or the output L'RO of the program load changing means 5. However, the value obtained by directly measuring the generator load or the load command value LR is used.
Although the precision is somewhat degraded, the intended effects of the present invention can still be obtained.

Furthermore, in the embodiment, a dead zone ΔL is provided for the deviation between the turbine load LA and the target load LRO, but by adjusting the size of this ΔL, it is possible to adjust the sensitivity of the full circumference/partial injection cooperative control. .

For example, if ΔL is set to be equal to or greater than the governor free width, it will not be sensitive to turbine load fluctuations due to fluctuations in system frequency.

In addition, Fig. 4a is provided to limit the injection mode at low loads.
The straight line TL shown in the figure does not need to be limited linearly between loads LLI and LL2, and can be easily applied without changing the essence of the present invention even if it is limited curved according to the turbine efficiency or the degree of local heating. It is possible.

Furthermore, as shown in Fig. 4a, the first post-cooling steam temperature characteristic TF
and TP are linear approximations to the turbine load LA, but the actual characteristics have nonlinearity, so if highly accurate injection mode control is required, this nonlinearity can be expressed as (4).
It may be used instead of equation (5).

Furthermore, in this embodiment, the set value of the main steam temperature is corrected in a stepwise manner as shown in FIGS. You may modify it.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the first final steam temperature characteristics during typical full-circle injection and partial injection, Fig. 2 is a block diagram showing the overall functional configuration for explaining the present invention in detail, and Fig. 3 is a partial diagram showing the cam characteristics for all-round injection and the cam characteristics for partial injection in FIG. 2, FIG. Figure 5 is a flowchart showing the logical judgment function for modifying the load change rate, Figures 6, 7, 8, 9, and 10 are diagrams that explain the basic concept of the boiler-turbine coordination side leg. Figure 11 is a diagram showing the method of correcting the main steam temperature set value, Figure 12
The figure is a diagram showing the flow of measures regarding the injection rate determination function, load change rate correction function, and main steam temperature set value correction function in the boiler-turbine cooperative opening function. Explanation of symbols, 3...Load change rate setting means, 4.
...Target load setting means, 5...-Program load changing means, 6...Proportional integral adjustment means, 7
... Load signal generation means, 8 ... Speed detection means, 9 ... Cam characteristic generation means for all-round injection,
10... Partial injection cam characteristic generating means, 11.
...Boiler/turbine cooperative control means. lθ

Claims (1)

[Claims] 1. A boiler in equipment that guides steam generated from a boiler to a steam turbine through a plurality of steam control valves to drive a load connected to the steam turbine. The steam temperature setting value of the control unit that controls the steam temperature generated from A steam turbine load control system characterized by adjusting the ratio of circumferential injection and partial injection when the load fluctuates.