JPS5949482B2 - Steam generator operation control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation control device for a steam generator mainly installed in a cooling system of a nuclear reactor or the like.

Because a nuclear reactor cooling system requires a high degree of reliability, it generally consists of multiple cooling systems installed in parallel.The heat generated in the reactor core is transferred to the coolant circulating in each of the cooling systems. This is converted into high-pressure, high-temperature steam energy by the steam generators in each cooling system.

In this case, since the steam generators of each cooling system form a parallel flow path sharing the main water supply pipe and the main steam pipe for the flow of water and steam, an unstable flow phenomenon may occur.

Such flow instability phenomena include escape-type instability, which causes an extremely large imbalance in the feed water flow rate supplied to each steam generator, and pulsation-type instability, where periodic vibrations appear in the feed water flow rate. There is.

If the above-mentioned instability phenomenon occurs in the steam generator, it will cause a thermal shock to the entire cooling system of the reactor and at the same time cause a large disturbance to the regulation control system of the cooling system, resulting in damage to the cooling system and malfunction of the control system. There is a risk of an accident occurring.

In order to prevent the flow instability phenomenon described above, thermal power boilers and nuclear reactor steam generators employ a system in which a fixed throttle is provided at the feed water inlet.

However, since this method originally requires determining the degree of fixed throttling at the lowest load operating condition, which is the least stable, this method would result in an extremely large additional pressure loss at the highest load operating condition. Therefore, it is necessary to increase the capacity and driving force of the water supply pump, and to increase the pressure resistance of the water supply piping and various auxiliary equipment associated with it.

Figure 1 quantitatively shows the effect of a fixed throttle on the flow stability of a steam generator in a sodium-cooled fast breeder reactor with a power output of 1 million kW. Indicates the maximum flow rate ratio (stability limit flow rate ratio) that allows operation.

The parameter △P100 means the amount of additional pressure loss due to the fixed throttle at a thermal coefficient of 100%, and the stability limit flow rate ratio increases and the stable region tends to expand as a fixed throttle with a larger pressure loss is installed. One thing is clear.

On the other hand, curve B is the maximum flow rate ratio (stable operating flow rate ratio) of sodium and water that occurs during operation of the steam generator, and an unstable flow phenomenon occurs in the heat load region where this maximum operating flow rate ratio exceeds the stable limit flow rate ratio. there's a possibility that.

Therefore, for example, in order to be able to perform stable operation up to a minimum heat load of 20, approximately 14 k at 100% flow rate is required.
It is necessary to provide a fixed throttle which generates a pressure loss of g/crtt2.

The increase in pump driving force to compensate for this additional pressure loss is equivalent to about 0.2% of the power generation output, and wasteful energy is consumed.

In order to prevent unstable flow phenomena that occur during steam generator operation, a special throttle valve is used that automatically reduces flow path resistance as the load increases and creates a throttling effect as the load decreases.
In other words, it is known to use a stabilizer.

However, the flow instability phenomenon that occurs in the individual steam generators arranged in parallel cannot be completely eliminated simply by using the above-mentioned special throttle valve.

SUMMARY OF THE INVENTION An object of the present invention is to provide an operation control device for a steam generator that can suppress flow instability phenomenon that occurs in a plurality of steam generators arranged in parallel due to load fluctuations, taking the above-mentioned matters into consideration.

The feature of the present invention is to eliminate the temperature difference between the steam obtained by both steam generators based on the output signal of each steam temperature detection means provided corresponding to the two steam generators arranged in parallel. The heated medium flow rate adjusting means of one of the steam generators is controlled so that the opening degree of each variable restricting means provided in each distribution pipe that guides the heated medium to each steam generator is controlled based on the load signal. Based on this, the diameter is increased when the load increases, and decreased when the load decreases, in order to suppress the unstable flow phenomenon within each steam generator.

A preferred embodiment of the present invention, ie, a steam generator used in a sodium-cooled fast breeder reactor, will be described below with reference to FIGS. 2 to 5.

In FIG. 2, reference numeral 23 denotes a steam generator consisting of a superheater 1 and an evaporator 6, and a plurality of steam generators (three in the figure) are provided in parallel in a secondary cooling system loop using liquid sodium as a heat carrier.

The heat of the secondary cooling system is transferred to water, which is a medium to be heated, through these steam generators 23.

Water is converted to high temperature, high pressure steam and sent to a steam turbine.

The superheater 1 includes a shell 2, a heat exchanger tube 3, a tube 4 connected to a secondary cooling system that supplies sodium to the shell 2, a tube 5 that discharges sodium from the shell 2, and a superheated steam discharged from the heat exchanger tube 3. It consists of a confluence pipe 14 leading to a main steam pipe 15.

The evaporator 6 is pressurized by a shelf, a heat exchanger tube 8, a tube 9 for discharging sodium in the shelf, a steam tube 22 that guides the steam discharged from the heat exchanger tube 8 to the heat exchanger tube 3 in the shell 2, and a pump 10, and is pressurized by the main water supply. It is composed of a branch pipe 13 that branches water supplied through a pipe 12 and guides it to the heat transfer tube 8, and this branch pipe 13 is provided with a flow rate adjustment valve 16 and a variable throttle valve 17.

A thermometer 18 is attached to the main steam pipe 15 to measure the temperature of the steam, and the output of this thermometer 18 is guided to the pump drive device 11 and measured by the thermometer 18 by adjusting the rotation speed of the pump 10. Feedback control is performed so that the steam temperature is 500°C.

Further, a thermometer 19 is attached to the evaporation tube 22 of each evaporator 6 of the three systems, and measures the temperature of the vapor vaporized by the evaporator 6.

The signal from the thermometer 19 is transmitted through the flow rate adjustment valve 1 provided in each branch pipe 13.
6, and use the signal of the difference between the steam temperature measured by the thermometer 19 of any system and the steam temperature measured by the thermometer 19 of the adjacent system as a control signal for the flow rate adjustment valve 16. The outlet steam temperature of each evaporator 6 in the entire system is controlled to be equal.

Therefore, the outlet steam temperature of each evaporator 6 under normal operating conditions is maintained at approximately 380°C.

Therefore, the dynamic characteristics of each steam generator arranged in parallel are equal.

The opening degree of the variable throttle valve 17 of each of the branch pipes 13 is uniformly set by a function generator 20 which receives a load setting signal 21 as input, and the characteristics of this function generator 20 are variable with respect to the heat load shown in FIG. It is determined by the functional relationship of the opening degree of the throttle valve 17, but it is a simple function that is set below the curved functional relationship (on the stable region side), as shown by the refraction line C shown by the dashed line in Fig. 3. It is also possible to give it as a relation.

Furthermore, since the thermal load and the total flow rate on the water supply side are approximately proportional, it is also possible to use the signal of the total water supply flow rate instead of the load setting signal.

Figure 4 shows the minimum degree of variable throttling required for stable operation of the steam generator 23, represented by △P100 (additional pressure loss at 100% flow rate), as a function of heat load. It is something.

Such adjustment of the variable throttle can be performed by adjusting the opening degree of the variable throttle valve 17 on a curve shown as a function of thermal load, as shown in FIG.

A comparison of the value ΔPx of additional pressure loss generated under each heat load condition in the variable throttle system of the present invention and the conventional fixed throttle system described above is as shown in FIG.

It can be seen from this that the required additional pressure loss in the variable throttle system is extremely small compared to the fixed throttle system.

In the above embodiment, the signal of the evaporator outlet temperature difference between the control number of the flow rate regulating valve and the adjacent system is inputted to make the outlet steam temperature of each evaporator the same. steam generators can be operated under the same operating conditions.

Therefore, each steam generator has the same dynamic characteristics, and the effect of suppressing the flow instability phenomenon by adjusting the opening degree of each of the variable throttling means described above based on the load signal is maximized. can be done.

In addition, since each steam generator can be operated with the same dynamic characteristics, the response to load fluctuations is also the same.
High controllability can be given to the entire steam generator.

In the embodiment described above, both the flow rate adjustment valve 16 and the variable throttle valve 17 are arranged in the branch pipe 13 that distributes water supply to a plurality of steam generators, but the relationship between the valve opening degree and the flow resistance is linear over a wide range. The above effect can also be achieved by providing a control valve in each branch pipe 13.

That is, this control valve has the functions of both of the above-mentioned valves, and is controlled based on the load signal and the steam temperature signal.

According to the present invention, it is possible to make the dynamic characteristics of a plurality of steam generators arranged in parallel the same and to suppress the flow instability phenomenon by the variable throttling means during load fluctuations.

Therefore, the stability of the flow of the plurality of steam generators arranged in parallel during load fluctuations can be significantly improved, and high controllability can be obtained.

The present invention can also be applied to a steam generator in which an evaporator and a superheater are integrated.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram explaining the unstable region of a steam generator from the relationship between the flow rate ratio of sodium and water and the heat load, and Fig. 2 shows a steam generator to which a preferred embodiment of the present invention is applied. System diagram, Figure 3 is a characteristic diagram showing the stability limit in relation to heat load and throttle opening, Figure 4 is a characteristic diagram showing the relationship between heat load and additional pressure loss, and Figure 5 is heat load. FIG. 3 is a characteristic diagram showing the relationship between the amount of pressure and the additional pressure loss in the case of a variable throttle and a fixed throttle. A...Steam generator, 1...Superheater, 6
...Evaporator, 13...Branch pipe, 14.
... Merging pipe, 16 ... Flow rate adjustment valve, 17
...Variable throttle valve, 19...Thermometer, 2
0...Function generator, 21...Load setting signal, 22...Evaporation tube.

Claims (1)

[Scope of Claims] 1. A heat exchanger tube through which a medium to be heated flows and a flow path through which a heating medium flows, which are arranged in parallel. a plurality of heated medium distribution pipes connected at one end to the inlet of the heat transfer tube of each of the steam generators and merging at the other end; In a device for controlling the operation of a steam generator comprising a plurality of steam pipes, one end of which is connected to the outlet of a heat transfer tube and the other end of which joins, a plurality of steam generators each provided in each of the heated medium distribution pipes a means for adjusting the flow rate of the medium to be heated; a plurality of means arranged in each of the steam generators to detect the temperature of the steam generated in each heat transfer tube; and a plurality of means arranged in each of the two steam generators. means for controlling the flow rate adjusting means of one of the steam generators so as to eliminate the temperature difference between the steam obtained in both the steam generators based on the output signal of the steam temperature detecting means; A plurality of variable throttling means provided in each of the heated medium distribution pipes and the opening degree of each of the variable throttling means are controlled so as to suppress the flow instability phenomenon in each steam generator based on a load signal. 1. An operation control device for a steam generator, comprising a control means that increases the load when the load increases and decreases the load when the load decreases.