JPS5812445B2 - Steam turbine control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to steam turbines, and more particularly to a steam turbine control device that maintains the humidity at the end point at the outlet of a condensing steam turbine below a permissible value.

In recent years, a so-called combined cycle that combines a gas turbine and a steam turbine has been put into practical use.

In the combined cycle, the exhaust gas from the gas turbine, which still has a sufficiently high thermal energy even after the rotational energy is extracted from the pressure and temperature energy in the gas turbine, is guided to the boiler, where the exhaust gas is Steam is created from energy, which is then fed into a steam turbine to extract rotational energy.

FIG. 1 simply shows the configuration of such a connominated cycle.

In FIG. 1, exhaust gas from a gas turbine is introduced into an inlet 2 of a boiler 1 and is configured to flow toward an outlet 3 of the boiler 1.

A superheater 4 is disposed immediately near the inlet 2, and a water pipe 16 and a energy saver 5 are disposed between the superheater 4 and the outlet 3.

Therefore, the superheater 4 and the economizer 5 are heated by the exhaust gas of the gas turbine.

For example, the exhaust gas temperature, which is about 460° C. at population 2, drops to about 160° C. at outlet 3, and energy is given to the steam produced by boiler 1 by the amount of temperature drop during this time.

On the other hand, the steam produced in the boiler 1 passes through a steam pipe 6, and a main steam stop valve (hereinafter simply referred to as a stop valve) 7 and a steam control valve (hereinafter simply referred to as a control valve) are provided in the middle of this steam pipe 6. ) 8 and enters the steam turbine 9.

Therefore, the steam from the boiler 1 expands in the steam turbine 9, reducing the pressure and temperature while converting the retained thermal energy into rotational energy. Spent to rotate 10.

In this case, a generator is used as the driven machine 10, for example.

Furthermore, the steam that has done work in the steam turbine 9 enters a condenser 11 and is returned to water.

Water in the condenser 11 is sent into the boiler 1 from the condenser 11, which is maintained at a high vacuum by a condensate pump 12, and is heated by a energy saver 5.

The water whose temperature has been raised by the economizer 5 is increased in pressure by a boiler feed water pump 13 and then sent to a drum 14.

The above-mentioned water pipe 16 is connected to the drum 14.
The steam inside is led back into the drum 14 via a water pipe 16.

In this case, the steam generated in the drum 14 is in a saturated state, and is heated while passing through the superheater 4 via the pipe 15, becomes superheated steam, and then passes through the stop valve 7 and the control valve 8 to become steam again. It is configured to be sent to a turbine 9.

In a combined cycle with such a configuration, the inlet temperature of the steam turbine 9 (which is generally determined by the stop valve 70 inlet temperature) is influenced by the gas turbine exhaust temperature that enters the boiler 10 inlet 2. Furthermore, the exhaust gas temperature of a gas turbine is influenced not only by the load change of the gas turbine but also by the atmospheric temperature.

Changes in atmospheric temperature also affect the exhaust gas flow rate of the gas turbine.

Generally, when a gas turbine is operated at a constant load,
When the atmospheric temperature decreases, the flow rate of exhaust gas increases and the temperature decreases.

When such a change occurs, the difference between the steam flowing through the superheater 4 and the exhaust gas temperature of the gas turbine decreases, and the temperature of the steam flowing through the superheater 4 decreases.
Since the amount of heat absorbed by the water pipe 16 decreases, the amount of heat absorbed by the water pipe 16 increases, resulting in an increase in the amount of steam supplied to the steam turbine 9 and a decrease in steam temperature.

FIG. 2 shows changes in the expansion state of steam in the steam turbine configured as described above.

In FIG. 2, reference numeral 21 indicates a group of isobaric lines near the steam state at the inlet of the stop valve 7, 22 indicates a group of the same isothermal lines, 23 indicates an exhaust pressure line of the steam turbine 9, and 24 indicates a group of isohumidity curves.

25 shows the steam state at the inlet of the stop valve 7 under normal turbine operating conditions.

Further, 26 is a point that changes isenthalpically due to the pressure loss between the stop valve 7 and the regulating valve 8, and the actual expansion starts from this point.

27 indicates the blade exit state of the first stage, 28 indicates the expansion line after the second stage, and 29 indicates the end point.

Further, 32 indicates the state of steam at the inlet of the stop valve 7, and 33
A point that changes in an isenthalpic manner due to the pressure loss of the stop valve 7 and the control valve 8, 34 is a point that shows the state of the first stage vane outlet, 35 is an expansion line that shows the state of expansion after the second stage, and 36 is an ent point. It shows.

Normally, the end point 29 of the steam turbine 9 is the saturation line 37
It is located on the lower side, that is, on the high humidity side, and most of it is steam, but the remaining small amount is mixed with steam in the form of extremely fine water droplets.

The difference in enthalpy between point 26 and end point 29 in FIG. 2 corresponds to the rotational energy given to steam turbine 9 by steam per unit weight.

Let us now consider a case where the steam pressure remains the same at the inlet of the stop valve 70, but the temperature decreases.

In this case, in the isothermal line group 22 in FIG. 2, the steam state at the inlet moves from the high temperature 30 side to the low temperature 31 side.

The point 32 indicates the state of the steam at the stop valve 7, and after moving from the point 33 due to the pressure loss of the stop valve 7 and the control valve 8, it passes through the point 34 and follows the expansion line 35 until it reaches the end point. It reaches 36.

The equal humidity curve group 24 extends from the saturation line 37 to the equal humidity curve 38
It can be seen that the humidity level at the end point 36 is higher than that at the end point 29 because the humidity level increases in the direction of the line <<.

Next, FIG. 3 is essentially the same as the expansion lines 28 and 35 shown in FIG. 2, but shows the situation when the pressure of the steam changes.

In other words, when the pressure of the steam at the inlet of the stop valve 10 increases while the temperature remains constant, the isobar group 21 changes from the low pressure side 39 to the high pressure side 40.
move in the direction of

It is the same as the explanation in FIG. 2 that the pressure changes from point 32' to point 33' in an isenthalpic manner due to the pressure loss of stop valve 7 and regulating valve 8.

The steam expands from point 33' to point 34' at the outlet of the first stage blade, along expansion line 35', and reaches end point 36.
′.

Endpoint 36' is at a higher humidity than endpoint 29.

When the humidity level at the end point of a steam turbine increases beyond a certain level, the blades rotating at high speed, especially the final stage blades that have the highest circumferential speed and are exposed to the highest humidity level, begin to flow through the nozzle. The blade collides with large water droplets that have grown on the wall of the casing, and the impact erodes the surface of the blade.

'Generally, a highly corrosion-resistant alloy is provided at the part of the blade in the final stage that is hit by water droplets, or the surface of the blade itself is hardened to prevent erosion by water droplets.

However, above a certain level of wetness, the rate of erosion by water droplets becomes harmfully high.

This invention was made in view of the above circumstances, and even if the steam temperature at the stop valve inlet drops, the humidity at the end point can be maintained at an appropriate value, thereby preventing the final blade erosion. The purpose is to provide a steam turbine control device that can prevent such occurrences.

This invention will be described below, but first the principle of this invention will be described.

In other words, as is clear from Figures 2 and 3, an increase in main steam pressure under a constant temperature and a decrease in main steam temperature under a constant pressure both increase the humidity at the end point, so the main steam temperature eventually decreases. If so, just reduce the pressure accordingly.

By doing this, the humidity at the end point can be maintained at an appropriate value.

Even in this case, in order to maintain the efficiency of the steam turbine at a high value, it is necessary not to lower the pressure too much, and for this reason, the pressure must be lowered to the minimum extent that can be kept within a reasonable range that allows erosion of the final stage blades. That's good.

Figure 4 shows the relationship between pressure and temperature to maintain constant humidity at the end point based on this principle.

Note that the same parts as in FIGS. 2 and 3 are given the same reference numerals, and the explanation thereof will be omitted, and the points that are different from these will be explained.

That is, the pressure loss from point 25 to point 26 is the sum of the pressure losses of stop valve 7 and control valve 8.

When the regulating valve 8 is partially opened, the rate of throttling loss of the regulating valve 8 becomes large.

Here, the expansion line 28 is calculated by taking into account the opening degree of the regulator valve 8 corresponding to the steam flow rate necessary to maintain the output of the steam turbine 9 at the rated value, and the throttling loss of the regulator valve 8 that accompanies this. If the relationship between main steam pressure and temperature is determined so that the outlet conditions of

That is, if the main steam is maintained at the pressure and temperature shown by the curve 41, the end point 29 will remain unchanged.

Note that the reason that there is a slight difference between points 27 and 34 at the outlet of the first stage blade is due to the difference in steam temperature at this point, and the difference in pressure is slight.

FIG. 5 is a block diagram showing an embodiment of the present invention based on the above-described principle.

51 is a main steam temperature detection signal detected by a temperature detector (not shown), which is calculated by a function generator 52.

In the function generator 52, the isothermal line group 22 in FIG. 4 is plotted on the horizontal axis, and the isobaric line group 21 in FIG. 4 is plotted on the vertical axis, and a pressure signal such as the curve 41 in FIG. be done.

The pressure signal from the function generator 52 is input to the operational amplifier circuit 54 via the summing point 53.

The main steam pressure 56 is controlled to a desired value by adjusting the opening degree of the steam control valve 55 (corresponding to 8 in FIG. 1) using the pressure signal amplified by the operational amplifier circuit 54.

For example, when the main steam temperature decreases, the output signal of the function generator 52 decreases, and accordingly, the steam control valve 55 is opened via the operational amplifier circuit 54, and the main steam pressure 56 decreases.

This main steam pressure 56 is detected by a pressure detector 57 and fed back to the addition point 53 via a contact 60 as a pressure signal.

Note that when the output of the steam turbine 9 is low, the steam control valve 55
is in a constricted state, and the humidity at the end point is generally low at this time, so the protection circuit described above is no longer needed.

Furthermore, as the output of the steam turbine 9 increases and the throttle state of the steam regulating valve 55 decreases, the average pressure loss of the steam regulating valve 55 decreases, so the above-mentioned protection circuit becomes necessary.

58 in FIG. 5 is the first stage outlet pressure, which is approximately proportional to the output of the steam turbine 9.

When this outlet pressure becomes higher than a set value set depending on the steam turbine 9, a comparator 59 is configured to close a contact 60 inserted into the feedback circuit.

The reason why the contact 60 is configured in this way is as follows.

That is, even in a waste heat boiler such as a combined cycle, the pressure inside the boiler (that is, this is approximately equal to the main steam pressure) cannot be lowered below a certain pressure.

Therefore, when the steam turbine 9 is under low load, the steam flow rate also decreases, but in this case, the control valve 8 is used at a low opening degree.

Therefore, the steam is throttled by the control valve 8, causing an isenthalpic change, and the point 26 in FIG. 4 shifts to the low pressure side, reducing the humidity at the end point.

For this reason, the contact 60 is designed to open in such a case.

When the contact 60 opens, the feedback signal does not enter the summing point 53, but the signal that enters the operational amplifier circuit 54 from the summing point 53 becomes a large + (+) signal, which closes the regulating valve 8 and attempts to increase the main steam pressure 56. do.

Control of the regulating valve 8 at this time is not performed solely by pressure, but may be performed using known means such as a speed governor or a load limiter.

The present invention can be applied to a combined cycle in which a gas turbine and a steam turbine are combined, because even if the main steam pressure is changed to some extent, the amount of steam supplied to the steam turbine hardly changes.

It can also be applied to exhaust heat boilers other than combined cycle, where the flow rate hardly changes with respect to the main steam pressure.

In addition, various modifications can be made without changing the gist of the invention.

According to the invention described above, there is provided a function generator that generates a pressure signal according to a steam temperature detection signal at the inlet of a condensing steam turbine, and a valve opening degree is corrected based on the output of this function generator to adjust the main steam pressure. a steam control valve to be changed; a pressure detector to detect the inlet pressure controlled by the steam control valve;
The pressure sensor is configured with a circuit that feeds back the output of the pressure detector to the output side of the function generator, so the temperature of the steam supplied to the steam turbine changes due to changes in atmospheric temperature or gas turbine load. Also, it is possible to provide a steam turbine control device that can maintain the humidity at the end point of the turbine below a preset value, and therefore does not require special load restrictions.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing the configuration of a combined cycle, Fig. 2 is a diagram showing the expansion line in the normal state and the expansion line when the main steam temperature drops in the steam turbine of Fig. 1,
Figure 3 is a diagram showing the expansion line in the normal state and the expansion line when the main steam pressure becomes high in the cycle of Figure 1;
FIG. 4 is an expansion diagram showing the relationship between main steam pressure and temperature for explaining the principle of the invention, and FIG. 5 is a block diagram showing the main parts of an embodiment of the invention. 1... Boiler, 2... Exhaust gas inlet, 3... Exhaust gas outlet, 4... Superheater, 5... Economizer, 6... Steam pipe, 7...
Stop valve, 8...Steam control valve, 9...Steam turbine, 10
... Driven machine, 11 ... Condenser, 12, 13 ... Pump, 14 ... Drum, 51 ... Main steam temperature signal, 52 ...
Function generator, 54... operational amplifier circuit, 55... steam control valve, 56... main steam pressure, 57... pressure detector, 58...
...First stage blade pressure signal, 59...Comparator, 60...Contact.

Claims (1)

[Claims] 1. A temperature sensor that detects the steam temperature at the inlet of the condensing steam turbine, a function generator that generates a pressure signal according to the detection signal of this temperature sensor, and a valve opening degree that is corrected based on the output of this function generator. a steam control valve that changes the main steam pressure, a pressure detector that detects the inlet pressure controlled by the steam control valve, and a circuit that feeds back the output of the pressure detector to the output side of the function generator. A steam turbine control device.