JPH0820043B2 - Once-through boiler operation method - Google Patents

Description

The present invention relates to an operating method for a once-through boiler, and more particularly to an operating method for smoothly switching from recirculation operation to once-through operation.

[Conventional technology]

FIG. 3 shows a boiler fluid flow system of a variable pressure operation once-through boiler.

At the time of starting the boiler, the boiler feed water supplied from the feed water pump 1 is heated by the high-pressure feed water heater 2 and further heated in the economizer 3 by the residual heat of the flue gas from the boiler, and then transferred to the heat transfer section of the boiler 4. Supplied and heated.
The fluid discharged from the boiler 4 is separated into steam and water in a steam / water separator 5. At the time of starting the boiler, the fluid discharged from the boiler is a mixture of steam and water, and is not steam with a wetness of zero. Therefore, the steam is separated in the steam separator 5, and the steam is further heated by the superheater 8 to become superheated steam, which is supplied to the high-pressure turbine 9.

On the other hand, the separated water supply reaches the water storage tank 6, is supplied to the boiler water supply main system by the boiler recirculation pump 7, and is circulated and flows. Then, when the heat quantity of the boiler rises and the once-through flow becomes possible, the circulation is stopped and the once-through operation is switched to.

Figure 4 shows the locus of enthalpy in the boiler start-up process in the transformer operation at the inlet of the steam separator. That is, as the boiler pressure is increased, (a) a temperature rising / pressurizing region showing a characteristic of heating and boosting, (b) a sudden change region in which the enthalpy changes rapidly while the pressure remains constant, and (c) the enthalpy gradually increases. The gradual increase region increases, and (d) the enthalpy changes suddenly again with the pressure kept constant. Among these, up to the characteristic (b) is a so-called wet region where the steam-water mixture is supplied, and in this wet region, the feed water separated by the steam-water separator is recirculated. The once-through operation is carried out in a so-called dry area beyond the wet area.

[Problems to be solved by the invention]

In the above once-through boiler, when switching from the constant pressure range (b) to the transformation range (c), the recirculation pump 7 is stopped at time A when the load on the static characteristic base (steady state) is reached,
I switched to once-through operation. However, on a dynamic characteristic basis (transient state) during load operation, it is very difficult to match the steam / water separator inlet enthalpy at the switching point load with the time point A shown in FIG. In addition to this, today, the calorific value per unit weight of the fuel supplied to the boiler changes, and the heat absorption amount of the boiler heat transfer surface changes due to changes in the exhaust gas recirculation rate due to nitrogen oxide control. Setting points is becoming more difficult. For this reason, the steam temperature at the inlet of the superheater changes immediately after the switching operation, resulting in disturbance of the steam temperature.

Conventionally, a control device as described in Japanese Utility Model Laid-Open No. 60-2105 has been proposed for a once-through boiler. This control device corrects the ratio of the water-fuel ratio in the process of switching from the recirculation operation to the once-through operation, injects the fuel more than in the static state, and uses the switching void to control the dryness of the steam / water separator inlet enthalpy. It is configured to raise or adjust the spray amount of the superheater, and similarly to increase the dryness of the inlet enthalpy of the steam separator by the switching void.

However, in the former method, it is necessary to inject a large amount of fuel each time the recirculation operation is switched to the once-through operation, which increases the fuel consumption amount and is not preferable.

Also, in the latter method, the flow rate through the furnace is adjusted by adjusting the superheater spray amount, but the main purpose of the superheater spray is to control the steam temperature of the boiler, and this is the enthalpy control. For example, if the amount of superheater spray is increased to increase the enthalpy at the furnace outlet when the load is increased, the steam temperature sharply decreases, which causes disturbance of steam temperature control, which in turn destabilizes the entire control system of the boiler.

Furthermore, the superheater spray has a drawback that it is not sufficient as a control means for the enthalpy of the furnace outlet because the spray amount is limited so that the outlet of the desuperheater does not fall below the saturation temperature for protection of the superheater. There is.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an operating method in which the switching from the recirculation operation to the once-through operation is effectively performed without increasing the fuel consumption amount.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention measures the enthalpy of the steam-water separator inlet, finds the enthalpy of saturated steam corresponding to this steam-water separator, and finds the deviation of both enthalpies. In order to eliminate this deviation without changing the supply amount, the fuel supply amount to the lower burner increases and the fuel supply amount to the upper burner decreases correspondingly, or the exhaust gas supply amount from the boiler furnace hopper section. Adjustment of
It is characterized in that the heat absorption amount of the boiler internal fluid is adjusted by adjusting the exhaust gas supply amount from the burner part and the wind box part, thereby switching from the recirculation operation to the once-through operation.

[Action]

The present invention is configured as described above, and since the fuel supply amount is not changed, the fuel consumption amount does not increase, and the increase in running cost can be suppressed.

Further, in order to change the heat balance control part by adjusting the distribution of the fuel supply amount to the lower burner and the upper burner or by adjusting the exhaust gas supply amount from the boiler furnace hopper part, the burner part and the wind box part, it has been conventionally proposed. Since the method of increasing the spray amount of the superheater to increase the enthalpy at the furnace outlet is not adopted, there is no sudden change in the steam temperature. The present invention is characterized by changing the distribution of the heat input as a whole, and since the heat input amount is not increased, the gas side conditions do not change significantly. For this reason, it is possible to smoothly shift from the circulation operation to the once-through operation, and stable control of the entire boiler is possible.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.

In the figure, first, when the boiler is started, the recirculation operation is performed. That is, as in the conventional method, the boiler feedwater supplied by the feedwater pump 1 is heated by the high-pressure feedwater heater 2 and further heated in the economizer 3 by the residual heat of the flue gas of the boiler. And is heated.

The fluid discharged from the boiler 4 is separated into steam and water in the steam / water separator 5. At the time of starting the boiler, the fluid discharged from the boiler 4 is a mixture of steam and water, and is separated into steam and water in the steam / water separator 5, and the steam becomes superheated steam further heated by the superheater 8 and is supplied to the high-pressure turbine 9. It

On the other hand, the separated water supply reaches the water storage tank 6, and is supplied to the boiler water supply main system 30 by the boiler recirculation pump 7 and circulates.

In this state, for the divider 11, the recirculation feed water flow rate discharged from the boiler recirculation pump 7 and the feed water main system
The total water supply amount in 30 is input, and the ratio of the recirculated water supply flow rate to the total water supply amount is calculated.
Entered in 13.

To the multiplier 13, in addition to the signal output from the divider 11, the vapor pressure detected by the pressure detector 12 arranged in the gas phase portion of the water storage tank 6 is output via the function generator 22. The pressure value is input, and the steam / water separator inlet enthalpy is calculated here.

On the other hand, the vapor pressure signal is also input to the function generator 14,
Here, the saturated steam enthalpy in the water storage tank 6 is calculated. The value of the steam-water separator inlet enthalpy from the multiplier 13 and the value of the saturated steam enthalpy from the function generator 14 are both input to the subtractor 15, and the deviation of the steam-water separator inlet enthalpy from the saturated steam enthalpy is calculated. If the operation of the boiler is controlled so as to eliminate this deviation, the steam temperature will not change when the circulation operation is switched to the once-through operation. This deviation is output to the function generator 16, and here the correction amount for each operation for making the deviation value zero is calculated. The signal output from the function generator 16 is the signal switching unit 17
, The signal switching unit 17 outputs a boiler heat amount correction signal, which is output to the heat amount switching control unit 23.

In the heat quantity switching control unit 23, first, the signal output from the signal switching unit 17 is input to the adder 20a, so as to correspond to the deviation of the enthalpy, with respect to the signal from the lower burner load signal generator 18. The signal is corrected to be the lower burner load request signal S1 so as to increase the fuel supply amount to the lower burner of the boiler furnace.

On the other hand, the signal from the signal switching unit 17 is also input to the proportional calculator 21. The proportional calculator 21 has an inverse characteristic with respect to the signal from the signal switching unit 17, and when a fuel increase signal is input, it reversely converts this signal into a fuel decrease signal,
The fuel signal output from the upper burner load signal generator 19 is subtracted from the fuel signal and output to the adder 20b, which is used as the upper burner load request signal S2.

Therefore, the total amount of fuel supply to all burners does not change. This is because the lower burner has a longer convection time in the furnace than the combustion gas in the upper burner, so even if the total amount of fuel is the same, increasing the fuel supply to the lower burner will increase the heat value of the entire boiler. Become.

The deviation value is set to zero by adjusting the heat quantity of the boiler by the above method, and the operation of the boiler is switched from the circulation operation to the once-through operation at this point.

FIG. 2 is a diagram for explaining the second embodiment of the present invention.

In this embodiment, the signal from the signal switching unit 17 in the heat amount switching control unit 23 is input to the adder 20a, so as to correspond to the deviation of the enthalpy, from the flow rate signal generator 26 of the exhaust gas supplied from the boiler hopper unit. The signal is corrected so as to reduce the exhaust gas supply amount, and the hopper exhaust gas request signal S5 is corrected.

On the other hand, the signal from the signal switching unit 17 is sent to the proportional calculator 21.
Is also entered. The proportional calculator 21 has an inverse characteristic with respect to the signal from the signal switching section 17, and the burner section non-gas supply and the wind box section supply exhaust gas flow rate signal generator 27.
The signals from are added to increase the burner part / wind box part supply exhaust gas flow rate signal S6.

Also in this method, it is possible to increase the heat absorption amount of the feed water without increasing the fuel supply amount and eliminate the deviation.

{Effects] The present invention is configured as described above, and since the fuel supply amount is not changed, the fuel consumption amount does not increase, and the increase in running cost can be suppressed.

Further, the distribution of the fuel supply amount to the lower burner and the upper burner is adjusted, or the exhaust gas supply amount from the boiler furnace hopper section, the burner section and the wind box section is adjusted to change the heat balance control part, so that the above-mentioned reference is used. The method of increasing the spray amount of the superheater to increase the enthalpy at the furnace outlet is not adopted, and therefore there is no sudden change in the steam temperature. The present invention is characterized by changing the distribution of the heat input as a whole, and since the heat input amount is not increased, the gas side conditions do not change significantly. For this reason, the circulation operation can be smoothly and effectively switched to the once-through operation, and stable control can be performed as a whole boiler.

[Brief description of drawings]

FIG. 1 is a control system diagram of a once-through boiler showing a first embodiment of the present invention, FIG. 2 is a control system diagram of a once-through boiler showing a second embodiment of the present invention, and FIG. 3 is an inside of the once-through boiler. A fluid flow diagram, FIG. 4 is a diagram showing the relationship between internal fluid pressure and enthalpy. 4 ... Boiler, 5 ... Steam separator 8 ... Superheater, 12 ... Pressure detector 18 ... Lower burner load signal generator 19 ... Upper burner load signal generator 23 ... Heat quantity switching control unit 24 …… Superheater spray signal generator 25 …… Furnace inlet feed water flow rate generator 26 …… Hopper exhaust gas flow rate signal generator 27 …… Burner / wind box exhaust gas flow rate signal generator S1 …… Lower burner load request signal S2 ...... Upper burner load request signal S3 …… Superheater spray request signal S4 …… Furnace inlet water supply request signal S5 …… Hopper part exhaust gas request signal S6 …… Burner part and wind box part exhaust gas request signal

Claims (1)

[Claims] 1. An enthalpy at the inlet of a steam separator is measured,
In addition, the enthalpy of saturated steam corresponding to this steam separator is determined, and the deviation between the two enthalpies is calculated.In the boiler section, the fuel supply amount to the lower burner is adjusted so as to eliminate this deviation value without changing the fuel supply amount. An increase and a corresponding decrease in the fuel supply to the upper burner, or an adjustment of the exhaust gas supply from the boiler furnace hopper section,
A once-through boiler operation method characterized in that the heat absorption amount of the boiler internal fluid is adjusted by adjusting the amount of exhaust gas supplied from the burner section and the wind box section, thereby switching from recirculation operation to once-through operation.