JPS6244162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an economizer recirculation blow control device for an exhaust heat recovery boiler having an economizer recirculation device to prevent steaming from occurring in the economizer.

Figure 1 shows a system diagram of the exhaust heat recovery boiler.

Exhaust heat from the process is transferred to a superheater 6, an evaporator 5,
It sequentially exchanges heat with the economizer 3 and is discharged to the atmosphere. The water supplied to the exhaust heat recovery boiler 1 is heated and deaerated by the deaerator 2, and then the pressure is increased by the water supply pump 11 and sent to the energy saver 3.
The supplied water is heated and supplied to the drum 4. The canned water discharged from the drum 4 is sent to the evaporator 5, turned into steam, and returned to the drum 4. The steam separated from water and steam is turned into superheated steam in the superheater 6, and is sent to the process as main steam.

When the load is low, the water supply flow rate decreases in proportion to the load,
Therefore, the flow rate passing through the economizer 3 decreases, which causes steaming to occur in the economizer, so in order to prevent this, from the outlet of the economizer 3, through the economizer recirculation pipe 7, With the economizer recirculation blow valve 9,
The recirculation blow flow rate is controlled according to the feed water temperature detected by the economizer outlet temperature detector 8, and the water is recovered to the condenser. On the other hand, the recirculating blow also has a recovery line as a heating source for the deaerator 2 via the deaerator pressure control valve 10. In order to increase plant efficiency, it is better to recover more of the recirculated blow as a heating source for the deaerator 2 than to recover it to the condenser. For this purpose, the recirculation blow valve 9
It is important to coordinate the control of the deaerator pressure control valve 10 and the deaerator pressure control valve 10.

FIG. 2 shows a system diagram of economizer recirculation blow control and deaerator pressure control according to the prior art.

The saturation pressure of the drum 4 is measured by the drum pressure transmitter 21, and the output signal is converted into the outlet saturation temperature of the economizer 3 by the function generator 22, and sent to the subtracter 23 as the target value of the economizer outlet temperature. give. Subtractor 2
3, the signal from the economizer outlet temperature detector 8 is compared with the target value, and the control deviation is detected by the temperature controller 24.
give to The temperature controller 24 increases or decreases the control output so that the control deviation is eliminated. This control signal is given to the subtractor 27 as the target value of the economizer recirculation blow amount. The subtractor 27 compares the flow rate signal of the economizer recirculation blow flow rate transmitter 25 with the target value, and calculates the control deviation from the flow rate controller 2.
Give to 8. The flow controller controls the economizer recirculation blow valve 9 until the control deviation is eliminated. On the other hand, the deaerator internal pressure is detected by a deaerator pressure transmitter 31, and is detected by a deaerator pressure setter 33 by a subtractor 32.
The control deviation is provided to the pressure controller 34. pressure controller 34
controls the deaerator pressure regulating valve 10 until the control deviation disappears.

In the conventional technology, since the economizer recirculation blow control and the deaerator pressure control are each independent, the recirculation blow amount is larger than the amount required to prevent steaming from occurring in the economizer 3. This flow rate is recovered for deaerator pressure control, which causes a large disturbance to the drum water level control system that controls the drum water level at a constant level, and in some cases, the water pump 11 may be overloaded. It happens that it becomes. This is because the deaerator pressure control valve 10 only attempts to control the internal pressure of the deaerator 2 to maintain a constant pressure, so the recirculation blow is applied regardless of the amount of recirculation blow required by the economizer 3. This happens to recover the amount to the deaerator 2. When the exhaust heat recovery boiler 1 is generating the rated amount of steam, there is a sufficient amount of water passing through the energy saver 3, so there is no risk of steaming occurring. Therefore, there is no need for the amount of recirculation blowing from the economizer. Under such operating conditions, the water supply pump 11 is naturally operating near its rated capacity. If the internal pressure of the deaerator 2 decreases under such conditions,
The deaerator pressure control works to maintain the pressure.
The deaerator pressure control valve 10 opens rapidly, forcing the economizer recirculation blow rate into the deaerator.
This operation causes a large disturbance to the exhaust heat recovery boiler 1, resulting in wide fluctuations in the drum water level and overloading the water supply pump 11.

The present invention improves the above-mentioned problems caused by the prior art's economizer recirculation blow control and deaerator pressure control being independent loops.

FIG. 3 shows an embodiment of the present invention. The main objective of the present invention is to recover the economizer recirculation blow to the deaerator 2 within the maximum amount of the economizer recirculation blow. That is, the economizer recirculation blow is the economizer 3
It is flushed to prevent steaming, and there is no need to flush more than that. Based on this idea, as shown in Figure 3, the output signal of the temperature controller 24 is the target value for the amount of recirculation blowing of the economizer, so anything above this signal is necessary as the amount of recirculation blowing of the economizer. It turns out that it is not. Therefore, the output signal of the temperature controller 24 is converted by the function generator 35 into an opening degree limit value of the deaerator pressure control valve 10, and is applied to the low input selector 36. Even if the internal pressure of the deaerator 2 decreases and the output signal of the pressure controller 34 increases in order to maintain the pressure, the low input selector 36 controls the function generator 35 to reduce the required recirculation blow amount for the economizer. The lower one is compared with the valve opening command corresponding to the deaerator pressure control valve 10.
Therefore, no more than the output signal of the function generator 35 is recovered to the deaerator.

As a result of the above, it is possible to limit the amount of the economizer recirculation blow recovered to the deaerator 2, and it is possible to prevent wide fluctuations in the drum water level and overload of the water pump.

In the above explanation, the deaerator pressure control is explained using the water supply from the economizer recirculation blow system, but of course the heat source for the deaerator 2 is also the auxiliary one from the drum 4. It also has steam etc. However, in order to effectively recover the economizer recirculation blow, the setting value of the pressure controller 34 of the economizer recirculation blow system is set higher than that of other heating sources. Even with such opening restrictions, it goes without saying that backup from other heating sources still exists.

[Brief explanation of the drawing]

FIG. 1 shows a system diagram of an exhaust heat recovery boiler, FIG. 2 shows an economizer recirculation blow control device according to the prior art, and FIG. 3 shows an economizer recirculation blow control device according to the present invention. 8... Economizer outlet temperature detector, 9... Economizer recirculation blow valve, 10... Deaerator pressure control valve, 21
...Drum pressure transmitter, 22...Function generator, 2
3...Subtractor, 24...Temperature controller, 25
... Economizer recirculation blow flow rate transmitter, 27 ... Subtractor, 28 ... Flow rate controller, 31 ... Deaerator pressure transmitter, 32 ... Subtractor, 33 ... Set value, 34 ... Pressure Controller, 35...Function generator, 36...Low input selector.

Claims (1)

[Claims] 1. A deaerator that heats and deaerates the condensate added from the condenser, a water supply pump that supplies the water heated and deaerated by the deaerator to the drum via the economizer, and the economizer; a heat recovery boiler having a drum, an evaporator for evaporating water from the drum, and a superheater for heating the steam; and recirculation flowing through a recirculation line branching from the line leading from the economizer to the drum. a recirculation blow valve that adjusts the blow flow rate; a pressure control valve that adjusts the amount of steam flowing into the deaerator from the recirculation piping; a recirculation blow control means for determining a circulation blow flow rate target value and controlling the opening degree of the recirculation blow valve; and a recirculation blow control means for determining the opening degree of the recirculation blow valve, and comparing the pressure setting value and the actual measurement value of the deaerator to obtain a valve opening degree signal and adjusting the pressure. comprising a pressure regulating valve control means for controlling the opening degree of the valve, and a limit value generating means for outputting an opening limit signal for the pressure regulating valve according to the recirculation blow flow rate target value,
Recirculation blow control of an exhaust heat recovery boiler, wherein the pressure regulating valve control means controls the pressure regulating valve according to the opening limit value when the valve opening signal becomes larger than the opening limit value. Device.