JPS6020643B2 - Boiler steam temperature control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler steam temperature control system, and more particularly to a boiler steam temperature control system that optimizes and automates steam temperature control during startup of a drum-type boiler blunt.

Recently, large-scale nuclear power generation or thermal power generation plants, each unit of which exceeds 1,000 MW, are being used, and such large-scale plants are usually operated at a constant load. For this reason, it is considered useful to use a drum boiler plant of medium capacity, for example, 350 MW class, in order to follow load fluctuations. When using a drum boiler for such purposes, it is necessary to start or stop the drum boiler plant depending on the load.
Automation and optimization of plant control for this purpose has become an important issue. The structure of the drum boiler plant as described above and its conventional control system will be explained below.

FIG. IA and FIG. IB are a system diagram of a drum boiler plant and an explanatory diagram of its structure. Figures IA and I
In figure B, due to combustion by burner 2, drum 1
Steam is generated, and the high pressure steam whose temperature is controlled by the primary heater 2, desuperheater 3, and secondary superheater 4 is supplied to the high pressure turbine 5, and then further passed through the reheater 11 to the low pressure turbine. 6 is supplied, and the generator 7 is driven. The steam that has passed through the turbines 5 and 6 is converted into water in the condenser 8, and is returned to the drum 1 via the energy saver 14 by the water supply pump 9. It is used for cooling the desuperheater 3. 14 is a GRF damper, 13 is a gas recirculation fan, and N is a chimney.

The control of the drum spoiler plant as described above was carried out according to target values as shown in FIG.

That is, the target value OT4 of the load program setting value OL to the main air temperature T4, the target value OT5 of the reheat steam temperature T5, and the target value OP of the main steam pressure P are determined as shown in FIG. 2 and activated. In this case ~ Steam temperature control, water supply control, and combustion control all require manual operation from the time of line-up (startup) to 30% load of this plant, and steam temperature control in particular requires manual operation even when the load is 30% or more. It required manipulation. Further, a control circuit as shown in FIG. 3 has been used for control in the normal load operating range (30 to ioo% load). That is, the main steam temperature L and its target value OT4 from the setting device 22 are compared in the subtracter 21, and then the proportional integral value of the deviation by the proportional integrator 23 and the difference detected by the differentiator 2& and the amplifier 25 are compared. The change rate of the main steam temperature T4 and the load program signal (OL in FIG. 2) output from the function generator 71 corresponding to the main steam flow rate QsF are added by the adder 26, and the added signal is An opening command is issued to the spray valve lq (Fig. IA) to adjust the attemperator outlet temperature T3.The subtractor 27 calculates the drum saturation detected by the function generator 72 from the drum pressure P. The difference between the temperature and the desuperheater outlet temperature T3 is taken, and this difference is proportionally integrated via the proportional integrator 28, and then the low signal selector 29 limits the spray valve opening command to limit the amount of water injected. In addition, the low signal selector 29 selects the output of the adder 26 so that the spray water amount can be limited as soon as the temperature T3 at the outlet of the monitor relay 3 becomes below the boiler allowable limit value. It has a function of accelerating the operating time of the proportional integrator 28 by several tens of needles only when a signal is selected.On the other hand, the reheater temperature set by the reheater temperature setting device 32 The target value OT5 of the temperature T5 is inputted to the low signal selector 31 together with the output of the function generator 73 which inputs the main steam flow rate QsF, and the lower value is compared with the reheater temperature in the subtractor 33. The difference is proportionally integrated via the proportional integrator 34, and then added to the load program signal from the function generator 74 in the adder 35. This world force is output as a GRF damper correlation command.

However, in the conventional control system as described above, after parallel entry, until the start-up control shown in Fig. 3 is activated, it is left at hand, and according to the subsequent control shown in Fig. 3, the main steam temperature T4
, reheater steam temperature T5 to main steam power P as shown in Figure 2, the program simply increases them in proportion to time without considering the boiler characteristics. There are some drawbacks.

{1} As explained in FIG. 3, the GRF damper opening degree control is performed to control the reheater steam temperature, but if this is done, the main steam temperature control will be disturbed.

In other words, at startup, the reheater steam temperature L is the standard air temperature L.
(This is because at low loads, the rate of heat exchange between reheated steam and gas volume is small, and the response to changes in gas volume is slower than the reheated steam temperature response to changes in main steam temperature T4. Therefore, the CRF damper opening is controlled to decrease and the toss brake valve opening is increased, but the main steam temperature does not change much depending on the amount of GRF gas injected, and its control range is limited. In some cases, suppressing the amount of water may make spray injection impossible.{2
) If pressure boost control is performed at startup, excessive fuel will be injected and this will cause the temperature of the secondary superheater to rise, leading to a rapid rise in main steam temperature T4 and making it difficult to coordinate with main steam temperature control. It is necessary to determine the temperature increase rate of the main steam temperature L at startup (2/4 load or less) taking into consideration the boiler characteristics and turbine thermal stress limit value, but this must be done manually. .

■ Startup control cannot be automated, and optimal control that fully takes boiler characteristics into account is manual and extremely difficult.

For this reason, if we place emphasis on the lifespan of the main turbine and boiler, it will take too long to increase the load, and on the other hand, if we place emphasis on the load increase and speed it up, the lifespan of the boiler, etc. will be significantly shortened. It is an object of the present invention to provide an automated boiler steam temperature control system that eliminates the drawbacks of the prior art and allows optimal control even when starting up a drum boiler.

The above purpose is to provide the boiler steam temperature control method of the present invention with a function of limiting the rate of increase in the target values of main steam temperature and main steam pressure according to the load value, and to It has a function to control the steam temperature to follow the load in the low load region and to follow the smaller of the load or the reheat steam temperature setting target value in the normal load region. The invention can be achieved by performing optimal automatic control suitable for the operating characteristics of the motor.The details of the present invention will be specifically explained below.

First, the operating characteristics of the drum boiler plant shown in Figure IA are as follows. In FIG. IA, the outlet temperature T of the drum 1 is the saturated steam temperature proportional to the drum pressure P, and is expressed by the TI fl (PI) ratio PI {1}.

The outlet temperature L of the primary superheater 2 is the drum outlet temperature T, the main steam flow rate QsF, the gas amount Qc^s in the furnace, and the gas temperature T.
Determined by G^s, tkoT, 10f2(QsF, QGA
S, Tc^s '2). The desuperheater outlet temperature L is the primary superheater outlet temperature L, the main steam flow rate QsF,
It is determined as a function of the spray water injection amount QsP and the spray water injection temperature T6, L:T2-f3(QSF, QSP,
T6). It is expressed as T2QSF+T,Q9p'3}・QsF+QP.

The main steam temperature T4 is the attenuator outlet temperature T3 and the main steam flow rate Q.
It is determined as a function of sF, the amount of gas in the furnace QGAs, and the amount of fuel QF, and T4 = T3 + f4 (QSF, QG^S, Q
F) Represented by '41.

Further, the desuperheater outlet temperature T3 must satisfy the condition LZT, 10 (constant) {5}.

The reason for this is that if the desuperheater outlet temperature T3 drops to such a low value that formula This is because it will have a negative impact. For this reason, as shown in FIG. 3 of the conventional example, it is necessary to provide a spray water injection limiting circuit based on the difference between the drum pressure P and the attemperator outlet temperature L. Figure 4 is a diagram showing the boiler steam temperature characteristics from parallel entry to rated load using the GRF recirculation gas injection amount as a parameter. As shown in the curve C2 during gas injection, the primary superheater outlet steam rate T2 increases in proportion to the GRF gas injection rate.

However, the main steam temperature is constant regardless of the injection rate of recirculated gas. In addition, in the same figure, ``Curve C when the recirculation gas amount is 0%'' indicates that the primary superheater outlet temperature L and the drum saturation temperature T match at a point R near 1/4 load. There is.

This shows that the amount of heat absorbed by the primary superheater 2 is almost zero, and in this state, as explained in Equation 5, the amount of water sprayed must be fog, and therefore the main air temperature T This shows that it is impossible to control the rise of Next, Fig. 5 shows the main steam temperature T4, the drum saturation temperature T, and the first week heater outlet when the GRF gas recirculation amount is changed at a load of about 1/4, which corresponds to point RI in Fig. 3. Temperature T2
This figure shows how the amount of heat absorbed by the primary superheater increases rapidly as the amount of recirculated gas increases. On the contrary, the heat absorption amount E of the secondary superheater is ``in other words, from the main steam temperature T4 to the primary weekly heater outlet temperature T
The problem is that the amount subtracted by 2 decreases as the amount of recirculated gas increases. It is clear from the explanation of Figure 5 that ``If the amount of ORF recirculation gas is increased,
4 also increases slightly, but ``the amount of heat absorbed by the primary superheater 2 increases, and spray injection can be performed at any time by this increase, making it easier to control the temperature of the main steam.

An embodiment of the control system of the present invention improved using the operating characteristics of the drum boiler as described above will be described below with reference to FIGS. 6 and 7.

FIG. 6 is a diagram showing an embodiment of a control circuit using the control method according to the present invention, and the parts added to the conventional circuit of FIG. 3 will be mainly explained. {1} The setting of the target value OT4 of the main steam temperature T4 of the desuperheater 2 1 is given by the main steam temperature setting switch SQI, and the 901 gives the main steam temperature t to the desuperheater 21 until it is connected to the plant. "21 output is 0. After parallel entry, the main steam temperature is fixed.
operates and gives the output of the main steam temperature specifier 22 to the subtractor 21, and the target value OT in FIG.
It is gradually raised as shown in 4. This rate of temperature increase is determined by the rate of change limiter 801 according to the load detected from the main steam flow rate QsF by the function generator 701, and this rate of change can be changed optimally according to the boiler characteristics. It has become. '2} The spray valve related command is ``During normal times, as in the past, the signal obtained by proportionally integrating the temperature deviation detected by the subtractor 21 by the proportional integrator 3 and the load from the function generator ?1. a program signal,
It is controlled by a signal obtained by adding the differential signal of the main steam temperature calculated by the differentiator 24 and the amplifier 2 to the adder 26.

Also, if the spray injection amount is large, the attemperator outlet temperature T3 is determined by the function generator based on the drum pressure P? If the drum temperature T detected by 2 is below, the low signal selector 2
9, the main steam temperature control by spray injection becomes uncontrolled. To allow main steam temperature control to begin immediately when this spray injection suppression is descaled.
In the present invention, the spray valve relationship signal from the low signal selector 5 is diverted to the proportional integrator 23 via the adder 01 and the automatic switch gQ koji. Note that the groove Q2 is an appropriate bias setting device, and the groove Q3 is a switching device.
For example, the electric breasts are output when driving.
983 is an automatic/manual switch. '3} GRF
Reheater temperature control by damper degree control is performed using subtractor 3g.
The two inputs are set to the reheater temperature T5 up to around 2/4 load.

In other words, until the load reaches 2/4, the switch 986 selects insects, which is input to the subtracter 33 via the low selector 3, and the output of 33 is zero.During this time, the GRF damper opening is The command is output from the GRF damper-related signal switch 9Q in accordance with the load OL output from the function generator 782. This set value is determined by the boiler characteristics at the time of start-up and becomes as shown by the broken line OL in the diagram. When the load exceeds 2 or 4, the switching devices 984 and 985 are switched, and the reheater temperature setting follow-up control similar to the conventional one is performed from the load program control.The setting value given by the setting device 32 at this time is as shown in Fig. By doing this, it is possible to eliminate the disturbance to main steam temperature control by GRF damper opening control at startup, which was a drawback of the conventional method.{4} At startup, main steam pressure P is changed with load. If the pressure is increased, the main steam temperature 4 will suddenly rise, making it necessary to extremely increase the thermal stress of the rotor. The pressure was increased during paddy exchange.

That is, the set value is gradually increased by the change rate limiter 802 according to the load program output from the function generator 783 up to the set value of the main steam pressure setting device 202. This main steam pressure setting program is as shown in OP of FIG. In addition, the curve LL in FIG. 7 shows the desuperheater outlet temperature limit value program curve. This is because although the steam in the evaporator tube must be at a superheated temperature, the temperature at the desuperheater outlet is below the drum saturation temperature due to the amount of spray per day.
Curve LL is set to prevent this from becoming wet steam. Furthermore, 28 rivers are subtractors,
The difference between the main steam pressure P and its set value, which is the output of the switch 802, is determined and given to the proportional integrator.

Adder register 02 uses the sum of the output of the proportional integrator and the preceding signal provided by function generator 704 as a boiler master signal. As explained above, according to the present invention, it is possible to perform optimal automatic control at the time of startup of a drum boiler plant, and it is possible to quickly follow the load and greatly improve the life extension of the boiler and turbine.

Note that part of this method can also be applied to a once-through boiler, and part of the control circuit can also be performed by a computer, making it possible to have an extremely wide range of applications.

[Brief explanation of the drawing]

FIG. IA and FIG.
6 and 7 are control circuit diagrams and control target value programs showing an embodiment of the control method according to the present invention. ... Drum ~ 2... Primary heating device, 3... Depletion device ~ 4... Secondary superheater, 5 books... High pressure turbine " 6
...Medium and low pressure turbine, 11...Reheater, 21,2? ,3
3, 2Q stove...4 subtractor 22...Main steam temperature setter 23, 28...Proportional integral, 34,301...Proportional integrator 26, 35, 401, 402... Adder, 29, 31...Low signal selector, 32...Reheat salinity setting device, 71, 72, 73, 74, 701, 70
2,703,704...Function generator, 801,802・
... Rate of change limiter, 30... Monitor relay,
901, 902, 903, 904, 905...
Switcher, 24...Differentiator t 25...Amplifier, 10
1,102...Setting device. Tsutomu B diagram Group Z diagram Figure 3 Figure 4 Figure 5 Figure 14 Younger brother S diagram

Claims (1)

[Claims] 1 Steam generated in a boiler is heated in a primary superheater, then cooled by injecting water into a desuperheater to adjust the steam temperature and pressure, and then input to a high-pressure turbine, and then output from the high-pressure turbine. The steam is resuperheated and input to a medium-low pressure turbine connected to the high-pressure turbine, thus rotating the connected high-pressure and medium-low pressure turbines, and recirculating the boiler exhaust gas into the boiler to adjust the steam temperature. In the boiler steam temperature control method of the boiler plant, the temperature control signal is controlled to control the temperature of the desuperheater using a temperature setting signal that limits the rate of increase in the steam temperature input to the high-pressure turbine according to the value of the boiler plant load. In addition to having a function of determining the amount of water, the temperature of the resuperheated steam is increased to follow the load in the region where the load is small, and the size of the load or the preset value is set in advance in the region where the load is large. The system has a function of controlling the amount of recirculated gas to the boiler so as to follow the smaller of the reheat steam temperature target values set by A boiler steam temperature control method characterized by automatic control.