JPS622641B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load control device for an exhaust heat recovery type combined cycle plant that combines a gas turbine and a steam turbine.

The exhaust heat recovery type combined cycle recovers the exhaust heat of the gas turbine in the exhaust heat recovery boiler, guides the generated steam to the steam turbine, and generates electricity by the steam turbine in addition to the gas turbine. Improves thermal efficiency. This load control of the entire plant is performed by adjusting the gas turbine load. In other words, when increasing the plant load, increasing the gas turbine load not only directly increases the load on the gas turbine generator, but also increases the amount of evaporation in the heat recovery boiler due to an increase in the gas turbine exhaust gas temperature. However, the main steam pressure of the steam turbine tends to increase. In this case, if the opening degree of the steam turbine control valve is kept constant, the main steam pressure will increase in proportion to the increase in the amount of evaporation, and the amount of steam in the steam turbine will also increase, causing the steam turbine generator to Load increases. On the other hand, in the case of a method that controls the main steam pressure at a constant level, the opening of the steam turbine control valve increases in order to hold down the increasing main steam pressure to a constant level, increasing the amount of steam and increasing the load on the steam turbine generator. increases.

In either method, the load on the gas turbine generator first increases, then the load on the steam turbine generator increases later, and when the sum of both matches the load demand given to the plant, the whole is balanced. do.

In this case, the load change rate of the gas turbine takes a constant value determined in consideration of the internal temperature change of the gas turbine, and the conditions on the exhaust heat recovery boiler and steam turbine side are not much considered. Therefore, even if the conditions on the exhaust heat recovery boiler or steam turbine side change significantly and reach an abnormal state, this will not be reflected in the load control. That is, it has the disadvantage that smooth load control operation is difficult.

The purpose of the present invention is to detect fluctuations in the water level of the exhaust heat recovery boiler that are likely to occur when the gas turbine load changes, and when the water level fluctuations exceed a certain value, adjust the rate of change in the gas turbine load in proportion to the fluctuation. The present invention provides a load control device for a complex plant that can control the load and make stable load changes for the entire plant.

As the load on the gas turbine increases and the gas turbine exhaust temperature rises, evaporation in the boiler increases and the amount of evaporation increases.In this case, the proportion of bubbles contained in the boiler evaporator tube increases, causing The fluid specific volume of the entire pipe increases. The volumetric expansion at this time causes the drum water level to rise and often reach a high water level alarm or stop value.
In the case of a load drop, the opposite phenomenon occurs and the drum water level may reach a low water level alarm value or a stop value.
The key point of the present invention is to detect this drum water level, limit the gas turbine load change when the drum water level approaches the high water level or low water alarm value, and limit the load change rate immediately before the alarm value. By setting this to zero, the purpose is to prevent excessive fluctuations in the drum water level. The present invention will be explained in detail below with reference to the drawings.

Fig. 1 shows an exhaust heat recovery type combined cycle plant to which the present invention is implemented, where 1 is a gas turbine, 2 is a gas turbine generator, 3 is an exhaust heat recovery boiler, 4 is a boiler drum, and 5 is a steam turbine,
6 indicates a steam turbine generator. gas turbine 1
The exhaust gas from the boiler drum 4 is guided to the boiler 3, and the steam generated from the boiler drum 4 is guided to the steam turbine 5 to generate electric power. The exhaust gas from the steam turbine 5 is condensed by a condenser 7 and returns to the boiler drum 4 via a condensate pump 8 and a feedwater pump 9.

In this figure, 10 is a fuel adjustment valve that adjusts the fuel of the gas turbine, 11 is a gas turbine load detector, 12 is a drum water level detector, and 13 is a steam turbine load detector. Each of these elements has a close relationship with the load control device.

FIG. 2 is a diagram showing an embodiment of the load control device of the present invention. Comparator 15 is plant load setting device 1
The deviation between the target load setting value F given by 4 and the actual detected load value is taken. The actual detected load value is the detected load value of the gas turbine load detector 11.
This value is the sum of G ₁ and the load value G ₂ detected by the steam turbine load detector 13 . The deviation output of the comparator 15 is input to the rate of change limiter 18 via the PI calculator 16. The rate of change of this rate of change limiter 18 is set by a gas turbine rate of change setter 17.
The change rate setter 17 receives the drum water level H detected by the drum water level detector 12 as an input, and automatically changes and sets the change rate in accordance with this water level level. Thus, in the change rate limiter 18 having the change rate limit value set according to the drum detected water level H, the PI calculator 1
6 and checks whether the rate of change of that output is within the rate of change limit. As a result of this check, if the rate of change is within the limit value, it is output as is to the rate of change limiter 19 at the next stage. If the rate of change is outside the limit value, the rate of change is calculated to converge within the limit value, and the result is sent to the rate of change limiter 1 in the next stage.
Output to 9. The rate of change limiter 19 performs calculations such that the rate of change converges between the allowable load increase rate A and the allowable load decrease rate B depending on the thermal conditions of the gas turbine. This change rate limiting by the change rate limiter 19 has been employed conventionally. The output from the rate of change limiter 19 is provided as valve opening information of the gas turbine fuel regulating valve 10, and controls the opening of the fuel regulating valve 10.

The rate-of-change setting operation based on the detected water level of the boiler by the rate-of-change setting device 17 will be described with reference to FIG.
FIG. 3A is a diagram showing the water level inside the boiler drum 4. The water level H ₁ is the normal water level, the water level H ₂ is the high water level alarm value, the water level H ₃ is the low water level alarm value, the water level H ₄ is the high water level stop value, and the water level H ₅ is the low water level stop value. FIG. 3B is a diagram showing the relationship between each water level and the load change rate. In Figure 3 (b), the vertical axis shows the water level and the horizontal axis shows the load change rate. The load change rate δ is set according to the water level. When the water level H is H _r3 ≦H or H _r4 ≧H, the load change rate δ is set to zero. H _r3 ＞
Between H>H _r1 and H _r2 >H>H _r4 , a straight line is drawn from the water level H parallel to the horizontal axis and the intersections with the straight lines l ₁ , l ₂ , l ₃ , and l ₄ are the load change rates to be determined. Therefore, for example, at a water level of H ₀ , the load change rate δ is, for example, δ
₁ , δ is set to ₂ . Between H _r1 > H > H _r2 , the load change rate is set to infinity. Infinite load change rate means that no limit value is given to the load change rate. However, H ₄ > H ₂ > H _r3 , H
_r3 > H ₃ > H ₅ .

The rate of change setting device 17 is configured to show the relationship between the water level and the rate of change shown in FIG. Load change rate is output.
In the diagram, A and B are the allowable load increase rate and allowable load decrease rate in the rate of change limiter 19.

By providing the above change rate limiter 18, the following change rate control can be performed depending on the magnitude of the drum water level. First, if the water level is within the normal water level range (H _r2 <H < H _r1 ), no restrictions are placed on the load change rate, and the output is continued as is to adjust the gas turbine fuel. Second, in the range from the normal water level to the alarm value, it is possible to control the water level so as not to approach the alarm value by providing a rate of change that is inversely proportional to the water level value. Third, when the water level reaches the alarm value, control is performed so that no rate of change is allowed. In other words, when the drum water level rises due to expansion of the drum water as the load on the gas turbine increases, if the rise exceeds a certain value, the rate of increase in the load on the gas turbine is suppressed to prevent it from rising further. , the load change rate is assumed to be 0 at a certain water level before reaching the high water level alarm. The same applies to the case of water level drop and load drop.

By giving the gas turbine an allowable load change rate according to the drum water level in this manner, abnormal rises and falls of the drum water level can be prevented.

Instead of setting the load limit value as a curve as in this embodiment, it is also possible to set the load change to 0 (load hold) when a certain water level is reached.

According to the present invention, it was possible to perform the fastest load change within the range allowed by the drum water level change.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a composite cycle, FIG. 2 is a block diagram of a control device of the present invention, and FIGS. 3A and 3B are explanatory diagrams of its operation. 14... Target load setting value, 12... Drum water level detector, 17... Load change rate setting device, 18... Change rate limiter.

Claims (1)

[Scope of Claims] 1. A fuel regulating valve, a gas turbine that burns gas fuel through the regulating valve, an exhaust heat recovery boiler that takes in the exhaust gas of the gas turbine, and a steam generator that collects the steam generated by the exhaust heat recovery boiler. In an exhaust heat recovery type combined cycle plant comprising a steam turbine that takes in water and a water supply pump that supplies condensate from the steam turbine to a boiler drum of an exhaust heat recovery boiler, the gas turbine detects the load G ₁ of the gas turbine. Load detector and upper boiler drum water level H
and the load of the steam turbine above.
A steam turbine load detector that detects G ₂ , a comparator that takes the difference {F-(G ₁ + G ₂ )} between the target load setting value F of the power plant and the load detected by the detector, and a steam turbine load detector that detects the detected water level H a gas turbine change rate setting device that automatically sets an allowable range of the load change rate of the gas turbine according to the deviation from a steady value; ₁₊
A load control device for an exhaust heat recovery type combined cycle plant, comprising: a rate-of-change limiter for limiting the rate of change of _G2 ); and means for controlling the valve opening of the fuel regulating valve using the output of the rate-of-change limiter. .