JPS63148004A - Method of operating once-through boiler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of operating a once-through boiler, and particularly to an operating method for smoothly switching from recirculation operation to once-through operation.

[Conventional technology]

Figure 4 shows the boiler fluid flow system of a once-through boiler in variable pressure operation.

When starting the boiler, the boiler feed water supplied from the feed water pump 1 is heated by the high-pressure feed water heater 2, further heated by the residual heat of the flue gas from the boiler in the economizer 3, and then transferred to the boiler 4 for heat transfer. is supplied and heated. The fluid discharged from the boiler 4 is separated into steam and water by a steam separator 5. When the boiler is started, the fluid discharged from the boiler is a mixture of steam and water, and is not steam with a wetness level of O.

Therefore, steam is separated in the steam separator 5, and the steam is further heated by the superheater 8 to become superheated steam, which is then supplied to the high-pressure turbine 9.

On the other hand, the separated feed water reaches the water storage tank 6, is supplied to the boiler water main system by the boiler recirculation pump 7, and circulates. Subsequently, the amount of heat in the boiler increases, and when once-through flow becomes possible, circulation is stopped and the operation is switched to once-through operation.

FIG. 5 shows the locus of enthalpy during the boiler startup process in variable pressure operation at the inlet of the steam-water separator. In other words, as the boiler pressure increases, (a) a temperature and pressure rise region exhibiting the characteristics of increasing temperature and pressure, (b) a rapid change region where the enthalpy changes rapidly while the pressure remains constant, and (c) a gradual increase in enthalpy. It changes in the following order: a gradual increase region where the pressure increases, and (d) a sudden change region where the enthalpy suddenly changes again while the pressure remains constant. Among these characteristics (
Up to b) is a so-called wet zone where a steam/water mixture is supplied, and in this wet zone, the water separated by the steam/water separator is recirculated. Once-through operation is carried out in a so-called dry region beyond this wet region.

[Problem that the invention seeks to solve]

In the above once-through boiler, from constant pressure region (b) to variable pressure region (
When switching to c), the recirculation pump 7 was stopped at time A when the load based on static characteristics (steady state) was reached, and the recirculation pump 7 was switched to once-through operation.

However, in the dynamic behavior during load operation (transient state B), it is very difficult to make the steam-water separator inlet enthalpy at the switching point load coincide with point A shown in FIG. In addition, today the amount of heat absorbed by the boiler heat transfer surface changes due to changes in the calories per unit weight of fuel supplied to the boiler, changes in the exhaust gas recirculation rate due to nitrogen oxide control, etc. Setting points is becoming increasingly difficult. Therefore, immediately after the switching operation, a change occurs in the steam temperature at the superheater inlet, resulting in a disturbance in the steam temperature.

[Means for solving problems]

The present invention is designed to solve the problems of the conventional structure specifically shown above, and measures the enthalpy of the fluid at the inlet of the steam separator in the circulation area of the internal fluid of the boiler. By determining the enthalpy of the saturated steam corresponding to the inlet of the boiler, the deviation between both enthalpies is calculated, and according to this deviation value, the heat per unit weight of the fluid flowing through the boiler furnace is calculated without changing the amount of fuel supplied to the boiler. This is a control method in which the amount of heat absorbed by the entire boiler heat transfer surface is increased by a method such as increasing the amount of absorption, and the deviation value is eliminated.

[Effect]

The enthalpy of the steam-water separator inlet fluid in the boiler internal fluid circulation area is measured, and the enthalpy of the saturated steam corresponding to the steam-water separator inlet is calculated, and the deviation between the two enthalpies is calculated. In response to this, there are methods to increase the heat load on the lower burners among burners arranged in multiple stages in the height direction of the furnace, and methods to improve the heat absorption characteristics of the furnace by reducing the amount of exhaust gas recirculated from the bottom of the furnace. or,
By increasing the amount of spray to the superheater, the flow rate of feed water passing through the boiler heat transfer surface is relatively reduced, and the heat absorption characteristics are increased. Transition.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention.

In the figure, first, when the boiler is started, recirculation operation is performed. That is, as in the conventional system, the boiler feed water supplied from the feed water pump 1 is heated by the high-pressure feed water heater 2, further heated by the residual heat of the flue gas from the boiler in the economizer 3, and then heated by the boiler 4. and heated. The fluid discharged from the boiler 4 is separated into steam and water by a steam separator 5. When the boiler is started, the fluid discharged from the boiler is a mixture of steam and water, and therefore the steam and water separator 5
The steam is separated into water and steam, and the steam is further heated by a superheater 8 to become superheated steam, which is then supplied to a high-pressure turbine 9.

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

In this state, the divider 11 receives the recirculation feed water flow rate discharged from the boiler recirculation pump and the main water supply system 3.
The total water supply flow rate at 0 is input as a signal, and the recirculation ratio to the total water supply flow rate is calculated. This flow rate ratio is output to the multiplier 13. In addition to the signal output from the divider 11, the multiplier 13 outputs the vapor pressure detected by the pressure detection gas 12 disposed in the gas phase of the water storage tank 6 via the function generator 22. A pressure value is input and here the steam-water separator inlet enthalpy is calculated. On the other hand, this vapor pressure signal is also output to the function generator 14, and the saturated vapor enthalpy in the water storage tank 6 is calculated in the function generator 14.

The values of the steam-water separator inlet enthalpy from the multiplier 13 and the saturated steam enthalpy from the function generator 14 are both input to a subtracter 15, and the deviation with respect to the signal from the function generator 14 is calculated. In other words, if the operation of the boiler is controlled so that this deviation is zero, the steam temperature will not change when switching from circulation operation to once-through operation. This deviation is output to the function generator 16, which calculates the amount of correction for each operation to make the deviation zero. The signal output from the function generator 16 is input to a signal switch 17, and this switch 17 issues a boiler heat amount correction signal. This signal is output to the heat amount switching control section 23.

In the heat amount switching control section 23, first, the signal output from the signal switching device 17 is input to the adder 20a, and the signal from the lower burner load signal generator 18 is changed to correspond to the enthalpy deviation. The signal is corrected and set as a lower burner load request signal S1 so as to increase the amount of fuel supplied to the lower burner.

On the other hand, the signal from this switch 17 is transmitted to the proportional calculator 21.
It is also input for . This proportional calculator 21 has an inverse characteristic to the signal from the switch 17, and when a fuel increase signal is input, it converts this signal into a fuel decrease signal, and outputs the signal to the upper burner load signal generator. Adder 20b subtracts the amount from the fuel signal output from 19.
It is output as the upper stage burner load request signal S2. Therefore, the total amount of fuel supplied to all burners does not change.

This is because the combustion gas in the lower burner has a longer residence 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 amount of fuel supplied to the lower burner will increase the amount of heat in the entire boiler. .

By adjusting the boiler heat amount using the above method, the deviation is brought to zero, and at this point, the operation of the boiler is switched from circulation operation to once-through operation.

FIG. 2 shows a second embodiment.

In this embodiment, in the boiler heat amount switching control section 23, first, the signal output from the signal switch 17 is input to the adder 20a, and the signal output from the superheater spray request signal body 24 is inputted to correspond to the enthalpy deviation. The signal is corrected to increase the spray amount relative to the signal and is used as the superheater spray amount request signal S3.

On the other hand, the signal from this switch 17 is transmitted to the proportional calculator 21.
It is also input for . This proportional calculator 21 has an inverse characteristic with respect to the signal from the switch 17 as in the previous embodiment, and when a spray amount increase signal is input, it conversely converts this signal into a decrease signal, Water supply command signal generator 2
5 is subtracted from the water supply signal outputted from 5 to obtain the furnace inlet water supply request signal S4. This reduces the amount of water supplied to the heat transfer section of the boiler 4, making it possible to relatively increase the amount of heat to the water without changing the amount of fuel supplied to the boiler, thereby eliminating the enthalpy deviation. I can do it.

FIG. 3 shows a third embodiment.

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

On the other hand, the signal from this switch 17 is also input to the proportional calculator 21, as in the previous embodiment. This proportional calculator 21 has an inverse characteristic to the signal from the switch 17, and adds the flow rate signals from the burner section supply exhaust gas and the wind box section supply exhaust gas flow rate signal generator 27, The partial supply exhaust gas flow rate signal s6 is increased. With this method as well, the amount of heat absorption of the feed water can be increased without increasing the amount of fuel supplied, and the deviation can be made zero.

〔effect〕

As described above, the present invention measures the enthalpy of the steam-water separator inlet fluid in the circulation area of the internal fluid of the boiler,
By determining the enthalpy of saturated steam corresponding to the inlet of this steam-water separator, the deviation between both enthalpies is calculated,
In response to this deviation value, the amount of heat absorbed by the entire boiler heat transfer surface is increased by methods such as increasing the amount of heat absorbed per unit weight of fluid flowing through the boiler furnace without changing the amount of fuel supplied to the boiler. Since the control is performed to eliminate the deviation value, it is possible to appropriately correct each manipulated variable when switching to once-through operation, regardless of the value of the steam-water separator inlet enthalpy before switching to once-through operation. Fluctuations in steam temperature can be suppressed to a very small extent, allowing for smooth switching.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram of a once-through boiler showing the first embodiment of the method of the present invention, Fig. 2 is a control system diagram of a once-through boiler showing the second embodiment, and Fig. 3 is a control system diagram of a once-through boiler showing the second embodiment. FIG. 4 is a flow system diagram of internal fluid in a once-through boiler having a conventional configuration, and FIG. 5 is a diagram showing the relationship between internal fluid pressure and enthalpy. 4...Boiler 5...Steam water separator 8...Superheater 12...Pressure detector 18...Lower burner load signal generator 19...Upper burner load signal generator 23... Heat amount switching control unit 24... Superheater spray signal generator 25... Furnace inlet feed water flow rate generator 26... Hopper section exhaust gas flow rate signal generator 27... Burner section/wind box section exhaust gas flow rate signal generator Sl...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 section exhaust gas request signal S6...Burner Section/Wind box section exhaust gas request signal Figure 1

Claims (4)

[Claims] (1) Measure the enthalpy at the inlet of the steam-water separator, find the enthalpy of the saturated steam corresponding to this steam-water separator, and find the deviation value of both enthalpies, and do not change the fuel supply amount in the boiler section. A once-through boiler operating method characterized by adjusting the heat absorption amount of the boiler internal fluid so as to eliminate this deviation value, thereby switching from recirculation operation to once-through operation. (2) The amount of heat absorbed by the boiler internal fluid is adjusted by increasing the amount of fuel supplied to the lower stage burner and correspondingly decreasing the amount of fuel supplied to the upper stage burner. The once-through boiler operating method described in (1). (3) The amount of heat absorbed by the boiler internal fluid is adjusted by adjusting the amount of spray to the superheater and adjusting the flow rate of water supply at the inlet of the boiler furnace. The once-through boiler operating method described. (4) A patent characterized in that the heat absorption amount of the boiler internal fluid is adjusted by adjusting the amount of exhaust gas supplied from the boiler furnace hopper section and the amount of exhaust gas supplied from the burner section and the wind box section. A once-through boiler operating method according to claim (1).