JPH0615921B2 - Operation control device for transformer once-through boiler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an operation control device for a once-through boiler, which is used when switching from recirculation operation to recirculation operation in a once-through boiler.

[Conventional technology]

In recent years, in order to operate the thermal power blunt with high efficiency, the operation of starting and stopping the boiler device at a fairly frequent frequency has been implemented. And for a transformer once-through boiler,
At the time of startup, a recirculation operation (wet) is performed, and then a switching operation is performed to switch to a once-through operation (dry). This will be described below with reference to the drawings.

FIG. 2 is a system diagram of a transformer once-through boiler. In the figure, 1 is a boiler furnace having a water cooling wall structure, 2 is a water supply pump for supplying water to the boiler furnace 1, 3 is a high-pressure water heater for heating water from the water supply pump 2, and 4 is discharged from the boiler furnace 1. It is a economizer that preheats the water supply with exhaust gas. 5 is a steam separator for separating steam and water in the mixed fluid discharged from the boiler furnace 1, 6 is a water storage tank for storing the boiler water separated by the steam separator 5, and 7 is water stored in the water storage tank 6. It is a recirculation pump that returns to the economizer 4. 8 is a superheater which superheats the saturated steam separated by the steam separator 5 into superheated steam,
Reference numeral 9 is a high-pressure turbine that rotates using superheated steam from the superheater 8 as a drive source.

In such a transformer once-through boiler, the recirculation pump 7 is driven at the time of startup, and the water in the water storage tank 6 is supplied to the water supply pump 2
It is supplied to the boiler furnace 1 through the economizer 4 together with the water supply from. The supplied water is mixed coal in the boiler furnace 1,
It is heated by combustion of fuel such as heavy oil to generate steam.
The generated steam is separated by the steam separator 5 and the superheater 8
After that, the high pressure turbine 9 is rotated. On the other hand, the water separated by the steam separator 5 is stored in the water storage tank 6 and then sent again by the recirculation pump 7 to be recirculated. Such a recirculation operation is continued, and when the load reaches the static characteristic base (steady state), the recirculation pump 7 is stopped and switched to the once-through operation. In this case, by stopping the recirculation pump 7, there is no pressure difference between the steam separator 5 and the water storage tank 6, and the fluid is sent directly from the steam separator 5 to the superheater 8. Become.

FIG. 3 is a characteristic diagram of the enthalpy at the inlet of the steam separator during the startup operation. In the figure, the horizontal axis represents the boiler pressure, and the vertical axis represents the enthalpy at the steam / water separator inlet. When starting up, increasing the boiler pressure
Initially, this is followed by an increase in enthalpy (heating / boosting region I). Then, at a certain pressure, the enthalpy changes rapidly with the pressure kept constant (constant pressure region II).
The enthalpy rapidly increases to a certain value, then gradually increases (transformation range III), and then suddenly changes again at a certain pressure (constant pressure range IV). The part surrounded by the broken line in the figure is the so-called wet area. In this wet area, the steam separator 5
The boiler water separated in step 1 is recirculated to the boiler side.

[Problems to be Solved by the Invention] By the way, when the operation of the variable pressure once-through boiler is switched from the recirculation operation to the once-through operation, the recirculation is performed when the load reaches the static characteristic base (steady state), as described above. The pump 7 was stopped and switched to the once-through operation. However, in the dynamic characteristic base (transient state) during load operation, it is extremely difficult to make the inlet enthalpy of the steam separator 5 coincide with point A (point of wetness 0) shown in FIG. 3 at the load at the time of switching. However, this difficulty becomes even greater due to fluctuations in fuel calories and fluctuations in the amount of gas on the boiler heat transfer surface. Then, when switching to the once-through operation is performed at the point A or lower, mixed steam (wet steam containing water) in a state of being separated by the steam separator 5 is sent to the superheater 8 until then. During the recirculation operation of 1, the wet steam is sent to the superheater 8 where only the steam has been sent by the steam separator 5, and a temporary enthalpy change occurs, and as a result, the steam temperature fluctuates. . That is, immediately after switching from the recirculation operation to the once-through operation, the steam temperature sharply drops.

In the past, in order to correct this sudden drop in steam temperature, the steam temperature was raised by methods such as excessive injection of fuel, but then the steam temperature will become too high this time, and the steam temperature will be increased by some means. Has to be lowered, and eventually hunting for steam temperature control has occurred.

The present invention has been made in view of such circumstances, and an object thereof is to solve the above-mentioned conventional problems and suppress fluctuations in steam temperature at the time of switching from recirculation operation to check operation. Therefore, it is an object of the present invention to provide an operation control device for a once-through type boiler, which can smoothly switch the operation.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention separates a mixed gas from a boiler furnace with a steam-water separator, sends the saturated gas to a superheater, and separates the separated boiler water. In a water storage tank, in a once-through boiler for returning the water in the water storage tank to the water supply line at a predetermined time for recirculation, the ratio between the water supply flow rate to the steam separator and the recirculation flow rate returned to the water supply line is A first computing unit for computing, an actual enthalpy and wetness at the pressure at the steam-water separator inlet based on the ratio computed by the first computing unit, the pressure in the water storage tank, and the feed water flow rate. A second arithmetic unit for obtaining a difference from the enthalpy of 0 degree, a means for obtaining a fuel addition correction amount based on the enthalpy of the difference obtained by the second arithmetic unit, and a fuel addition correction obtained by this means. Quantity It is characterized in that addition means for adding to the fuel demand of the boiler is provided.

[Operation] The ratio of the water supply flow rate to the steam separator and the recirculation flow rate of the supply water returned to the water supply line, that is, the value of the wetness (recirculation ratio) in the steam separator is calculated by the first calculator. It Based on this value, the pressure in the water storage tank, and the feed water flow rate, the difference between the actual enthalpy at the inlet of the steam separator and the enthalpy of zero wetness at the above pressure is calculated by the second calculation unit. Then, the relationship between the difference and the correction amount of the fuel amount to be added is defined in advance, and the fuel addition correction amount for the difference obtained by the second calculation unit is obtained based on this relationship, and the obtained value is obtained. The calculated fuel addition correction amount is added to the required fuel amount according to the boiler load.

[Examples] Hereinafter, the present invention will be described based on illustrated examples. FIG. 1 is a block diagram of an operation control device according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG. 10 is a flow rate detector that detects the recirculation flow rate discharged from the recirculation pump 7, 11 is a flow rate detector that detects the outlet flow rate (total water supply amount) of the boiler furnace 1, and 12 is the pressure in the water storage tank 6. It is a pressure detector. Reference numeral 13 is a divider that calculates the ratio between the boiler furnace outlet flow rate and the recirculation amount. 14 and 16 are function generators, and each of these function generators 14 and 16 is a third function generator.
It is obtained from the enthalpy characteristics shown in the figure. Water tank 6
The enthalpy (saturation vapor enthalpy) of 0 degree of wetness is generated for each pressure of. 15 is a multiplier, 17 is a subtractor, 1
8 is a multiplier, 19 is a function generator (the characteristics of which will be described later),
20 is a signal switch, 21 is a fuel amount command signal generator, 22
Is an adder.

Next, the operation of this embodiment will be described. In the present embodiment, the enthalpy of the steam separator 5 during the recirculation operation of the pressure once-through boiler is determined, and the enthalpy (saturated steam enthalpy) of the steam separator 5 with a wetness of 0 is also set to determine the deviation between the enthalpies. A means for correcting the fuel amount based on the above is adopted. First, the enthalpy of the steam separator 5 is obtained. Therefore, first, the flow rate detector 10 detects the recirculation flow rate, the flow rate detector 11 detects the boiler furnace outlet flow rate, and the divider 13 calculates the ratio of the two flow rates. Therefore, the output of the divider 13 represents the value of the wetness (recirculation ratio) in the steam separator 5. On the other hand, the pressure in the water storage tank 6 (equal to the boiler pressure) detected by the pressure detector 12 is input to the function generator 14. The function generator 14 outputs the enthalpy of 0 degree of wetness based on the enthalpy characteristic shown in FIG. 3, and the multiplier 15 multiplies the value by the output value of the divider 13. Thereby, the enthalpy of the steam separator 5 is obtained. That is, the enthalpy of the steam separator 5 during the recirculation operation is in the wet region shown in FIG. 3 and cannot be immediately obtained from the pressure, so the above method is used.

The output of the pressure detector 12 is also input to the function generator 16,
The function generator 16 outputs the enthalpy of zero wetness corresponding to this pressure (enthalpy of saturated steam) as a set value. Unlike the case where the enthalpy of the steam separator 5 during the recirculation operation is obtained, the enthalpy of the wetness 0 can be obtained immediately from FIG. 3, and the function generator 16 is based on the enthalpy characteristics shown in FIG. , The enthalpy of wetness 0 corresponding to each pressure is set.

In the subtractor 17, the deviation of the steam / water separator enthalpy output from the multiplier 15 during the recirculation operation from the enthalpy of the wetness 0 at that time output from the function generator 16 Whether or not it has is calculated, and the calculated deviation is output. Since this deviation is the deviation of the enthalpy per unit flow rate, it is multiplied by the flow rate at the inlet of the steam separator 5 detected by the flow rate detector 11 in the multiplier 18 to obtain the enthalpy of the flow rate. This enthalpy is input to the function generator 19, and the function generator 19 generates a fuel amount correction amount signal corresponding to this enthalpy.
This correction amount signal is input to the adder 22 via the signal switch 20 closed at the time of starting the boiler, and the adder 22
In, the fuel amount command signal for the normal load output from the fuel amount command signal generator 21 is added. As a result, the corrected fuel amount command signal is output from the adder 22.

As described above, in the present embodiment, the enthalpy of the steam-water separator is obtained based on the ratio of the boiler furnace outlet flow rate and the boiler recirculation flow rate, and this is compared with the enthalpy of wetness 0, and the fuel amount is calculated based on the deviation. Since the command signal is corrected, it is possible to supply an appropriate amount of fuel, and it is possible to reduce the fluctuation of the steam temperature when switching from the recirculation operation to the once-through operation.

〔The invention's effect〕

As described above, in the present invention, the ratio between the feed water flow rate and the boiler recirculation flow rate is calculated, the fuel addition correction amount is obtained based on the calculation result, and this fuel addition correction amount is added to the fuel demand amount. Therefore, it is possible to supply an appropriate amount of fuel, and it is possible to suppress the fluctuation of the steam temperature at the time of switching from the recirculation operation to the once-through operation.

[Brief description of drawings]

FIG. 1 is a block diagram of an operation control device according to an embodiment of the present invention, FIG. 2 is a system diagram of a once-through boiler, and FIG. 3 is an enthalpy characteristic diagram. 1 ... Boiler furnace, 2 ... Water supply pump, 5 ... Steam separator, 6 ... Water tank, 7 ... Recirculation pump, 8 ... Superheater, 10, 11 ... Flow rate detector, 12 ... ... Pressure detector, 13 ... Divider, 14, 16, 19 ... Function generator, 15, 18 ... Multiplier, 17 ... Subtractor, 21 ...
Fuel amount command signal generator, 22 ... Adder.

Claims (1)

[Claims] 1. A mixed gas from a boiler furnace is separated by a steam separator, saturated steam is sent to a superheater, and the separated boiler water is stored in a water storage tank, and the water in this water storage tank is supplied at a predetermined time. In a once-through boiler that returns to the line and recirculates, a first computing unit that computes a ratio of a feed water flow rate to the steam separator and a recirculation flow rate to return to the water feed line, and the first computing unit. A second calculation unit for obtaining a difference between an actual enthalpy at the pressure at the steam-water separator inlet and an enthalpy of wetness 0 based on the calculated ratio, the pressure in the water storage tank, and the feed water flow rate; A means for obtaining the fuel addition correction amount based on the enthalpy of the difference obtained by the second arithmetic unit and an addition means for adding the fuel addition correction amount obtained by this means to the fuel demand amount of the boiler are provided. That Operation controller of the transformer once-through boiler according to symptoms.