JPH0223921Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a boiler control device, and particularly to a wet-dry switching control device for a variable pressure boiler that smoothly switches between recirculation operation and once-through operation.

[Background of the invention] Figure 1 is a system diagram showing an example of a boiler with variable pressure operation. A boiler 4 having a water-cooled furnace wall structure into which the water supplied from the economizer 3 is introduced, and a steam-water separator 5 that separates steam from the boiler 4 into steam and water. , a water storage tank 6 that stores separated boiler water, and a boiler circulation pump (BCP) 7 that sends water in the tank to the energy saver 3.
It is comprised of a superheater 8 that superheats the saturated steam separated by the steam/water separator 5 to produce superheated steam, and a high-pressure turbine 9 that rotates using the superheated steam from the superheater 8 as a driving source.

In the above configuration, preheated feed water is heated in the boiler 4 with fuel such as mixed coal and heavy oil to generate steam. This steam is separated into steam and water by a steam separator 5, boiler water is sent to a water storage tank 6, and saturated steam is sent to a superheater 8. The water in the water storage tank 6 is sent to the energy saver 3 together with the water supplied from the high-pressure water supply heater 2, while the superheater 8 superheats saturated steam to generate superheated steam and sends it to the high-pressure turbine 9.

Figure 2 shows the enthalpy trajectory at startup in variable pressure operation at the steam/water separation inlet, showing the temperature and pressure rising region as the boiler pressure increases, and the characteristic where the enthalpy suddenly changes while the pressure remains constant. It has a constant pressure region, a variable pressure region where the enthalpy gradually increases, and then a constant pressure region where the enthalpy suddenly changes while the pressure remains constant. The characteristic is a so-called wet region, in which boiler water separated by the steam-water separator 5 is recirculated to the boiler side.

By the way, in conventional wet (recirculation operation) - dry (throughflow operation) switching operation, when switching from a constant pressure region (characteristics) to a variable pressure region (characteristics), when the load on a static characteristic basis (steady state) is reached. BCP7 was stopped and switched to once-through flow. However, based on the dynamic characteristics (transient state) during load operation, it is very difficult for the steam/water separator inlet enthalpy to match the point shown in Fig. 2, not necessarily at the switching point load. Also, as seen today, due to fuel calorie fluctuations and the rate of gas recirculation due to NOx control, at the switching point load, the humidity is completely 0, that is, it does not match the point shown in the diagram, but it fluctuates (the enthalpy becomes low). . Therefore, immediately after switching from wet to dry, that is, immediately after BCP is stopped, an enthalpy change occurs at the inlet of the superheater 8 shown in FIG. 2, which causes fluid temperature fluctuations and disturbs steam temperature control.

[Purpose of invention]

The object of the present invention is to provide a wet-dry switching control device for a variable pressure boiler that eliminates the above-mentioned conventional drawbacks, reduces steam temperature fluctuations as much as possible, and allows smooth wet-dry switching.

[Structure of the idea]

In short, the present invention operates the BCP until the fluid enthalpy at the inlet of the steam-water separator becomes equivalent to the point where the wetness becomes zero (saturation temperature enthalpy of the pressure at the steam-water separator inlet), and then stops operation at the point when the fluid enthalpy reaches the same level It was designed to do so.

[Example of idea]

FIG. 3 shows an embodiment of the present invention,
The same reference numerals are used for the same parts as in Fig. 2, so redundant explanations will be omitted. A pressure detector 12 that detects pressure, a detected value of the pressure detector 12, and a divider 1
1, a function generator 14 that generates a function as the saturated steam enthalpy of the water storage tank 6 based on the output value of the pressure detector 12, and an output value of the function generator 14. Multiplier 13
, and a monitor circuit 16 that generates a signal to stop the BCP when the deviation of the subtracter 15 becomes zero.

In the above configuration, the steam-water separator enthalpy during boiler circulation operation is calculated by the divider 11 and the multiplier 13, while the enthalpy at zero humidity is calculated as the saturated steam enthalpy at the water storage tank pressure. Calculated by the device 14.
Therefore, the output signal of the multiplier 13 and the function generator 14
By determining the deviation of the output signal of , using the subtractor 15, the monitor circuit 16 is activated when the deviation is zero, and this signal causes the BCP (boiler circulation pump) 7 to stop.

That is, the enthalpy of the steam-water separator is calculated based on the flow rate of the steam-water mixed fluid flowing into the steam-water separator, the amount of boiler recirculation by the boiler recirculation pump, and the internal pressure value of the tank storing the boiler water. , the enthalpy at zero humidity is calculated based on the tank internal pressure value, and the boiler recirculation pump is stopped when the enthalpy deviation disappears.

During boiler circulation operation, the steam/water mixture is separated by the steam/water separator 5, and only the dry steam is sent to the superheater 8.
send to. When switching to once-through operation, BCP7
When the BCP 7 is stopped, the mixed steam that is being separated in the steam separator 5 is also sent to the superheater 8, so immediately after the BCP 7 is stopped, there is a temporary fluid enthalpy change from dry steam to wet steam. occurs, resulting in fluctuations in steam temperature.

However, as in the present invention, by adding an interlock function that operates the BCP stop interlock until the fluid enthalpy becomes completely dry and then stops, it is possible to switch to once-through operation.
By not necessarily stopping BCP,
Steam temperature fluctuations are reduced. By the way, conventionally,
At this point, the steam temperature suddenly drops immediately after switching, and in order to correct this drop in steam temperature, excessive fuel is injected to raise the steam temperature, but as a reaction, the steam temperature becomes too high. This caused control hunting.

In addition to the above control mode, in the process of switching from boiler circulating operation to once-through flow, the water-fuel ratio is corrected, more fuel is injected than in the static state, and at the switching point, the water-water separator inlet is There is a way to increase the degree of enthalpy.

Another method is to adjust and switch the superheater spray flow rate at a switching point. This is a switching point that reduces the flow rate through the furnace and increases the fluid enthalpy at the water separator inlet.

[Effect of idea]

As is clear from the above, according to the present invention, switching between wet and dry conditions can be performed without causing any disturbance in the steam temperature.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a variable pressure operation boiler, FIG. 2 is an enthalpy locus diagram at the start of variable pressure operation at the steam/water separation inlet, and FIG. 3 is a block diagram showing an embodiment of the present invention. 3... Energy saver, 4... Boiler, 5... Steam water separator, 6... Water storage tank, 7... Boiler circulation pump, 8... Superheater, 11... Divider, 12... Pressure detection 13...Multiplier, 14...Function generator, 15...Subtractor, 16...Monitor circuit.

Claims (1)

[Scope of utility model registration request] Feed water introduced through the economizer is heated in a boiler to generate steam, this steam is separated into steam and water in a steam-water separator, and the saturated steam is sent to a superheater and the separated boiler water is sent to the boiler at a predetermined time. In a variable pressure operation boiler system that returns the water to the economizer via a recirculation pump, the flow rate of the steam/water mixed fluid flowing into the steam/water separator, the amount of boiler recirculation by the boiler recirculation pump, and the boiler water are stored. a calculation unit that calculates the enthalpy of the steam-water separator based on the tank internal pressure value; a function generator that calculates the enthalpy of humidity 0 based on the tank internal pressure value; and an output value of the function generator and the calculation unit. and a stop interlock section that stops the boiler recirculation pump based on the output signal of the subtractor, the subtractor generating an output signal when the deviation from the output value of the boiler recirculation pump disappears. Wet/dry switching control device for variable voltage operation boilers.