JPS6034006B2 - Steam temperature control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to controlling the temperature of steam generated from a once-through boiler by controlling the amount of water injected into an attemperator provided at the outlet of the boiler.

FIG. 1 shows an overview of steam temperature control in a subordinate vessel by controlling the amount of water injected as described above.

Reference numeral 1 denotes a boiler, in which water supplied from a main water supply pipe 2 is heated by a water wall within the boiler, turned into high-temperature steam, and led to a desuperheater 3.

On the other hand, a part of the supplied water is led to the super heater (hereinafter abbreviated as S/day) spray pipe 7, and is injected into the steam from a nozzle provided in the desuperheater 3 via the S/day spray valve 4. . Main steam is taken out from the desuperheater 3 via the main steam pipe 6 and is used to drive a turbine. The temperature of this main steam is detected by the temperature detector 21, and this detected value Ts
The opening degree of the S/day spray valve is controlled by the temperature controller 22 so as to eliminate the deviation of the temperature from the target value TR. In such a control device, the steam temperature is controlled by constantly injecting water and controlling the S/day spray valve to adjust the amount of water injected depending on the deviation in the steam temperature.

In this method, the lid pressure before and after the S/day spray valve changes greatly depending on the load, so the S/day spray valve must have a large capacity to ensure water injection even when the differential pressure is small and negative. At high loads with large differential pressures, the S/day spray valve must be used in a considerably throttled state. In this case, the control accuracy is not good due to the nonlinearity of the S/day spray valve. The purpose of the present invention is to improve the controllability of the S/H spray valve and stabilize it by keeping the differential pressure across the S/D spray valve constant with one pressure transmitter using a program signal based on the load. An object of the present invention is to provide a control device capable of controlling steam temperature.

The present invention focuses on the fact that the pressure change in the desuperheater due to the load is determined by calculation, as a means to prevent the differential pressure before and after the S/day spray valve from changing depending on the size of the load. The pressure is controlled so that the inlet pressure becomes the sum of the calculated desuperheater pressure for each load plus the arbitrarily set S/day differential pressure across the spray valve.

FIG. 2 shows the configuration of an embodiment of the control device according to the present invention, in which 1 is a boiler, 2 is a main water supply pipe, 3 is a desuperheater,
4 is the S/day spray pressure control valve, 6 is the main steam pipe, and 7 is the S/day spray pressure control valve.
8 is a differential pressure constant circuit before and after the S/day spray valve added according to the present invention, 9 is the S/day spray valve inlet pressure, 10 is a load signal, 11 is a pressure transmitter, 12 is S
/day Indicates the amount of spray pressure control valve operation.

FIG. 3 is for explaining the principle of constant differential pressure across the S/day spray valve according to the present invention, where a is the desuperheater pressure, S
/day The relationship between spray pressure valve inlet pressure (pressure of main water supply pipe 2) and load, b is S/day desuperheater pressure when pressure control is performed to keep the differential pressure across the spray valve constant, S/day spray The relationship between pressure regulating valve inlet pressure (pressure of main water supply pipe 2) and load is shown.

In Fig. 3a, 13 is the desuperheater pressure characteristic, and 14 is the S/
The characteristics of the daily spray pressure recognition valve inlet pressure (pressure of the main water supply pipe 2) are shown. This characteristic shows the pressure when using the constant pressure operation method, and when the pressure on the main water supply pipe 2 is controlled as shown in 14, the pressure at the desuperheater will decrease due to the pressure loss at the spray pressure regulating valve 5 and the spray valve. becomes like 13. Furthermore, due to the pressure loss from the attemperator to the turbine, the turbine inlet pressure remains constant regardless of load. In view of this characteristic,
An S/day spray pressure regulating valve is installed before and after the S/day spray valve, and the S/day spray pressure regulating valve outlet pressure (=S/day spray valve inlet pressure) can be adjusted to the desuperheater pressure according to each load. By controlling the pressure so that the pressure value is the same as the applied pressure,
The S/day spray valve inlet pressure 15 is controlled as shown in FIG.
/day The differential pressure across the spray valve is maintained at an arbitrary set value.

FIG. 4 shows a specific example of a circuit for making the differential pressure across the S/day spray valve constant.

In FIG. 4, a function generator 16 inputs a load command 10, and outputs a value obtained by adding a differential pressure setting value to the desuperheater pressure at the time of the load, and sets it as a target value 17 of spray valve inlet pressure S/day.

Adder 18 subtracts S/day spray valve inlet pressure 9 from S/day spray valve inlet pressure target value 17 and produces a deviation signal 19.
Output. The PI controller 20 inputs the deviation signal 19 and
/day The operation amount 12 of the spray pressure regulating valve 5 is output. As can be seen from the embodiments described above, according to the present invention, the pressure in front of the S/day spray valve can be controlled according to the load, and the differential pressure across the S/day spray valve can be kept constant using one pressure transmitter. This improves the controllability of the S/day spray valve. The above explanation has been given using a constant pressure operation system in which the turbine inlet pressure is constant, but this also applies to variable pressure operation systems in which the turbine inlet pressure is variable according to the load. This can be done in the same way, taking losses into account.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematic system diagrams of a conventional boiler according to the present invention, FIG. 3 is a diagram showing the relationship between the flow rate and pressure of each part when performing conventional control, and FIG. Figure 4 shows the relationship between flow rate and pressure at each part when controlling by S/
FIG. 2 is a system diagram showing a specific example of a differential pressure constant circuit before and after a spray valve.

1...Boiler, 2...Main water supply piping, 3...
...Desuperheater, 4...S/day Spray valve, 5...S/
Day spray pressure control valve, 6...Main steam piping, 7...
...S/H spray piping, 8...S/day differential pressure stabilization circuit before and after the spray valve, 9...S/day spray valve inlet pressure, 10...load Signal, 11...
...Pressure transmitter, 12...S/day spray pressure valve operation amount, 13...Desuperheater pressure characteristics, 14.
...S/day spray pressure regulating valve inlet pressure characteristics, 15...
...S/day S when the differential pressure across the spray valve is kept constant
/day Spray valve inlet pressure characteristics, 16...Function generator, 17...S/day Spray valve inlet pressure target value, 18...Adder, 19...・Deviation signal,
20...PI controller, 21...Temperature detector, 22""" control.

Multi-1 diagram Figure 2 enshrined figure Figure 4

Claims (1)

[Claims] 1. A boiler that superheats feed water to produce steam, a desuperheater that constantly mixes steam from the boiler with spray water to provide main steam at a predetermined temperature to the turbine, and supplies water through a spray pressure regulating valve and a spray valve. In a steam temperature control system consisting of a spray system that supplies spray water to the attemperator, a load signal is input, and at that load, the desuperheater pressure required to maintain the turbine inlet pressure at a predetermined pressure is determined. A function generator that adds a constant value to the output and outputs the result, and a pressure regulating valve control device that uses the output of the function generator as a setting signal and uses the spray valve inlet pressure as a feedback signal to control the opening degree of the spray pressure regulating valve. steam temperature control device.