JPS6024884B2 - Control method for once-through boiler with circulation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a once-through boiler with a circulation device.

In the evaporator of a once-through boiler, when the load is low and the amount of water passing through it is reduced, flow imbalance and flow oscillation occur.

This is because when the flow rate in one tube of an evaporator consisting of parallel tubes decreases, evaporation becomes more active, which increases the flow resistance in that tube and further reduces the flow rate. This phenomenon usually occurs at a low load of 1/3 load or less, so when using a poller at this low load, a circulation device is installed to increase the amount of water flowing through the evaporator to a flow rate equivalent to 1/3 load or more. .
The circulation system consists of a steam/water separator, a separation tank, a circulation pump, etc. At a low load of about 1/milk load or less, a water level appears in the separation tank and the circulation pump works, and at a high load exceeding 1/milk load, the circulation pump works. The water level in the separation tank disappears and the circulation pump stops. However, the characteristics of the water level in the separation tank are static characteristics when the load on the boiler does not change, and when the load changes rapidly, the water level in the separator may not appear or disappear in response to the load. .

For example, if the load suddenly changes from a high load exceeding 1'3 load to a low load below 1/Kegimiya load, the amount of fuel and water supply will decrease while being adjusted to the ratio commensurate with each load, but the water level in the separation tank will decrease. Due to the heat capacity of the evaporator tube, the effect of a decrease in fuel does not appear immediately, and the amount of evaporation increases temporarily due to a decrease in water supply, and then slowly decreases. Therefore, the water level in the separation tank does not appear easily,
It may appear only after the load changes have stopped and a new lower load has been reached. Conversely, if the load suddenly changes from a low load of less than 1/milk load to a high load of more than 1/milk load, the amount of fuel and water supply will increase while being adjusted to the ratio commensurate with each load, but Since the amount of heat transferred to the fluid does not increase immediately, the amount of evaporation does not increase in proportion to the fuel. Therefore, the water level in the separation tank does not disappear easily, and the water level in the steam/water separator may rise, causing water to flow into the superheater. As mentioned above, if the water level does not appear in the separator under low load conditions, the circulation pump cannot be activated to increase the amount of circulating water in the evaporator, which may cause flow imbalance or vibration. The load cannot be lowered until the water level appears.

Also, if the water level in the separator rises under high load and water flows into the superheater, the evaporation temperature will drop in each part of the boiler, causing various problems, so the load must be increased until the water level in the separator disappears. I can't. The present invention has been made to solve these problems, and aims to provide a control method that can quickly follow changes in load and cause the water level in the separation tank to appear and disappear.

A method for controlling a once-through boiler with a circulation device according to the present invention will be described below.

First, a once-through boiler with a circulation device for carrying out this method will be explained with reference to FIG. 1. The boiler includes a feed water pump 1, an evaporator 2, a steam separator 3, superheaters 4 and 4', and a superheater connected in series. 4 and 4', a separation tank 6 and a circulation pump 7 provided in a path from the steam/moisture equipment 3 to the inlet of the evaporator 2. This once-through boiler with a circulation device is provided with a control device, which includes a feed water control valve 8 provided on the outlet side of the feed water pump 1, a water feed controller 9 for controlling it, and a fuel feed water control valve provided in the fuel supply path 10. Control valve 1
1, a fuel controller 12 that controls it, an injection channel 13 provided in the desuperheater 5 from the outlet side of the feedwater control valve 8, a water injection control valve 14 provided in the injection channel 13, and a fuel controller 12 that controls the boiler outlet steam temperature. It is composed of a water injection controller 15 that controls the water injection to be constant, and a load controller 16 that controls the water supply controller 9 and the fuel controller 12. Now, Figures 2 and 3 show changes in the water supply amount W, fuel amount F, and dryness x at the outlet of the evaporator 2 over time in the once-through boiler with a circulation device. , the time integral of the shaded area of x=1 or less of the dryness at the outlet of the evaporator 2 in FIG. 2 corresponds to the water level of the separation tank 6 (when the circulation pump 7 is not operated)
In the figure, the shaded area where x = 1 or more of dryness x at the outlet of evaporator 2 is steam, so water does not flow into separation tank 6. On the contrary, the water in separation tank 6 decreases due to self-evaporation, and the water level increases. It will go down.

Figure 2 shows the case where the load is lowered from a load exceeding 1/milk load to a load lower than 1/3 load, and Figure A shows the ratio of water supply amount W and fuel amount F to each load (in the figure, it is simplified). The dryness X at the outlet of the evaporator 2 is
It increases once and then decreases, and it takes a very long time to reach x=1 or less, and water is only collected in the separation tank 6 when x=1 or less.

However, the control method of the present invention controls the load controller 16, fuel controller 12, and fuel control valve 11 shown in FIG. 1 so that the fuel amount F decreases with the load as shown in FIG. B, and the water supply amount W decreases as shown in FIG. The load controller 16, water supply controller 9, and water supply control valve 8 are configured so that the fuel amount F decreases at a smaller rate than the fuel amount F, and when the load change ends, the load controller 16, water supply controller 9, and water supply control valve 8 rapidly decrease to a ratio commensurate with the fuel amount F and the final load.
control.

Thus, the dryness X at the outlet of the evaporator 2 quickly reaches x=1 or less, and the amount of water stored in the separation tank 6 increases significantly as shown by the shaded area.

Next, to explain the case where the load is increased from a load lower than 1/3 load to a high load exceeding 1/nail self-defense using Figure 3, Figure A shows that the water supply amount W and fuel amount F are changed at a ratio commensurate with each load. In the secondary method, the dryness x at the outlet of the evaporator 2 decreases and then increases, and it takes a very long time to reach x = 1 or more, and only when this x = 1 or more does the separation tank 6 water will be gone.

However, the control method of the present invention controls the load controller 16, fuel controller 12, and fuel control valve 11 in FIG. 1 so that the fuel amount F increases with the load as shown in FIG. B, and the water supply amount W increases as shown in FIG. The load controller 16, the water supply controller 9, and the water supply control valve 8 are configured so that the fuel amount F increases at a smaller rate than the fuel amount F, and when the load change ends, the load controller 16, the water supply controller 9, and the water supply control valve 8 increase rapidly to a ratio commensurate with the fuel amount F and the final load.
control.

Thus, the dryness X at the outlet of the evaporator 2 quickly reaches X=1 or more, and the water in the separation tank 6 quickly disappears.

In the control method of the present invention described above, it is also effective to delay the timing of the change in the water supply amount W relative to the fuel amount F, and when the load change speed is slow, it is effective to adjust the ratio between the water supply amount W and the fuel amount F accordingly. Since there may be no problem even if the change is made as per the above, the control device shown in FIG. A control method may also be implemented.

In addition, in the control method of the present invention when the load changes from low load to high load as shown in FIG. Yes, but
If X is larger than 1, it means that the steam at the outlet of the evaporator 2 will be overheated, so it is better that X is not much larger than 1. Therefore, the ratio between the fuel amount F and the water supply amount W during the load increase should be determined with this point in mind. As detailed above, the control method of the present invention, in a once-through boiler with a circulation device, controls the fuel amount to increase or decrease with the load when the load changes, increases or decreases the water supply amount at a smaller rate than the fuel amount, and By rapidly increasing or decreasing the amount of water supplied to a ratio commensurate with the amount of fuel and final load when the change is finished, the water level required for the circulation system can quickly follow the load change and appear and disappear. , the amount of circulating water in the evaporator can be increased by operating the circulation pump during low loads, and water does not flow into the superheater during high loads.

Therefore, there is no flow imbalance or vibration in the evaporator, no drop in steam temperature at any part of the boiler, and no troubles.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a once-through boiler with a circulation device equipped with a control device, and Figure 2 is a graph showing the control method when the load changes from high load to low load, where A is the conventional control method and B is the original control method. This is a control method of the invention, and FIG. 3 is a graph showing the control method when the load changes from low load to high load, where A is the conventional control method and B is the control method of the present invention. 1... Water supply pump, 2... Evaporator, 3
...Sea water separator, 4,4'...Superheater, 5...
...Superheat reducer, 6... Separation tank, 7...
...Circulation pump, 8...Water supply control valve, 9...
... Water supply controller, 10 ... Fuel supply path, 1
1... Fuel control valve, 12... Fuel controller,
13... Water injection channel, 14... Water injection control valve, 1
5... Water injection controller, 16... Load controller,
W...Water supply amount, F...Fuel amount, ×...
...Dryness at the outlet of evaporator 2. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 In a once-through boiler equipped with a circulation device, when the load changes, the fuel amount is controlled so that it increases or decreases with the load, the water supply amount is increased or decreased at a smaller rate than the fuel amount, and when the load change ends, the water supply amount is changed to the fuel amount. A control for a once-through boiler with a circulation device, characterized in that the water level required for the circulation device appears and disappears by quickly increasing or decreasing the water level to a ratio commensurate with the amount and the final load, and quickly follows the load change. Method.