JPS6027883B2 - Boiler temperature increase control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler temperature increase control method, and particularly to a boiler temperature increase control method suitable for application to temperature increases with large disturbances such as pressure increase during temperature increase.

As a conventional temperature increase control method, a method has been proposed in which a temperature change prediction of main steam is obtained by extrapolation from the temperature change rate of main steam, and control is performed.

However, if the steam flow rate changes significantly with a rise in temperature and pressure at the same time, a temporary drop in the steam temperature at the inlet of the final stage superheater occurs, resulting in a large disturbance in the main steam temperature. For this reason, prediction of main steam temperature change based only on the rate of change has a large error, making it difficult to obtain good control characteristics. The purpose of the present invention is to eliminate such drawbacks of the prior art, and to detect changes in the main steam temperature by comprehensively determining the steam flow rate, the steam temperature at the inlet and outlet of the final stage superheater, and the temperature of the superheater tube. An object of the present invention is to provide a boiler temperature increase control method that obtains good control characteristics by accurately predicting the temperature.

Based on the law of conservation of energy of the internal fluid in the final stage superheater, the present invention establishes the causal relationship between the final stage superheater inlet steam temperature, the metal temperature of the superheater tube, the main steam flow rate, and the superheater outlet steam temperature. This causal relationship is built into the control system to predict the steam temperature at the outlet of the superheater.

Specific examples will be shown below with reference to the drawings. FIG. 1 is a block diagram showing the input/output relationship of a boiler startup bypass system and a control system that are controlled by the present invention. In the figure, the temperature of the main steam was raised as follows. That is,
At first, the pressure reducing valve 503 is fully closed, and the water supply 400 supplied from the water supply pump is transferred to the energy saver 500, the furnace water cooling walls 501, 1
Next, it passes through a superheater 502 and is poured into a flash tank 511, where it becomes steam. Here, the primary superheater bypass valve 507 and the secondary superheater bypass valve 508 are each controlled so that the pressure and temperature at the outlet of the primary superheater become predetermined values. In this way, the flash tank 511
The steam evaporated in the secondary superheater vent valve 509
It is led to a high pressure turbine 506 via a secondary superheater 504 and a control valve 505. The high-pressure turbine exhaust 403 is generally reheated in a reheater (not shown) and guided to a medium-low pressure turbine (not shown), but this is omitted because it is not directly related to the present invention. In addition, among the steam in the flash tank, the steam on the shore that is not led to the secondary superheater and the drain 404 are led to the feed water heater, condenser, etc., but this is also omitted because it is not directly related to the present invention. . In this state, the fuel 401 is adjusted by the fuel control valve 510, and the main steam 40
When the temperature of steam 2 is raised to a certain specified value, a start command 10 is issued from an operator or a computer with a higher-level judgment function, the pressure reducing valve 503 is opened, and the pressure of the main steam is raised at the same time as the temperature is raised. On the other hand, the control system at the time of temperature increase and pressure increase includes a fuel flow rate controller 301, a pressure reducing valve controller 302, and a temperature increase control device 1.
Consists of 00.

FIG. 2 is a block diagram showing specific functions of the fuel flow rate controller 301.

In the figure, when a start command 10 is issued, a fuel pattern generator 3010 generates a fuel setting advance value signal 3 as a function of time.
014 is output. Next, an adder 3011 adds the fuel flow rate bias signal 201 digitized by the overflow control device 100 to obtain a fuel demand 3015, and a subtracter 302 calculates the deviation from the detected value 250 from the fuel flow rate detector 350. Then, the proportional/integral controller 3013 performs proportional/integral control so that this deviation is equalized, and the fuel control valve operation signal 20 is
Decide on 3. FIG. 3 is a block diagram showing specific functions of the pressure reducing valve controller 302.

In the figure, first, when a start command 10 is issued, a final main steam pressure setting value 3027 is determined by a main steam pressure setting device 3020. Next, a subtracter 3021 takes the difference from the instantaneous main steam pressure set value 3028, a deviation limiter 3022 applies a limit, a multiplier 3023 multiplies the pressure increase rate correction signal 202 output from the temperature increase control device 100, The integrator 302
By integrating by 4, the instantaneous main steam pressure set value 3028
Determine. Furthermore, the subtractor 3025 calculates the deviation from the detected value 255 from the main steam pressure detector 355, executes proportional/integral control calculations (proportional/integral controller 3026), and determines the pressure reducing valve related command 204. . FIG. 4 is a block diagram showing the functions of the boost control device 100.

In the figure, first, in the function block 110, the start command 10 and the main steam temperature 253 (output of the main steam temperature detector 353)
is input to determine the main steam temperature target value after n minutes. A schematic flowchart is shown in FIG. 5a. In the figure, the presence or absence of a startup command is determined, and if there is no start command, nothing is done, and if there is a start command, the target temperature TsP (i, n) is calculated after n minutes according to the following equation. T
sP(i,n)=TsP(i,0)×Rj*n△ts
...'1' where TsP (i, n): target temperature TsP (i, 0
): Current target temperature Ri: Target temperature increase rate Tj-. <TsF (i, 0) Tj △ts: Sampling period Next, determine whether the predicted target value TsP (i, n) has entered the next temperature increase rate region (determine whether correction calculation is required)
If the temperature is within the range of the next temperature increase rate, the predicted target value is recalculated using the following formula.

TSP(i,n) =Tj+, 10Rj+,TSP(i,n)−Tj+,...
(2, Ri) By recalculating the predicted target value in this way, if the temperature does not fall within the next temperature increase rate region, it is output as the target temperature predicted value 111 at that time.

Next, in the function block 120, the primary superheater outlet steam temperature 251, the secondary heater metal temperature 252, the main steam temperature 2
53, the main steam temperature predicted value Ta(i,n) is estimated using the main steam flow rate 254 as input.

A schematic flowchart of prediction is shown in FIG. First, a start command 10 is issued, and a check is made to see if it is the first calculation. If it is the first time, the value of each detector is stored as the initial value. From the second time onwards, first, the primary superheater outlet temperature Ts, sH, the main steam pressure Ps, which becomes a disturbance to the main steam temperature change,
, each value intersection (i, 0) and rate of change Y(i) of main steam flow rate F3 fence/secondary week heater metal temperature Tm2S day are estimated by the following equation using the least squares method (block: disturbance estimation).

〈X(i,.

) = {7 disasters (i) + 4 disasters (i-1) 10 disasters (i-2) - 2
Disaster (i-3)}...
...{3,・〇M(i)={3flea(i)+X(i-・)
−×(i−3×(i−3)}
………■10×△tS Here, Shigeru (i, 0): Estimated value after 0 minutes at i sample Shigeru (i):
Detected value Y(i) at i sample: Rate of change Δts at i sample: Sampling period Next, the disturbance after k samples is predicted by linear extrapolation from the obtained formula '4'.

Thought (i, k) = X (i, 0) + Y (i) Xk.・・・．・
・[51 Also, regarding the main steam temperature Ts$day, the following equation holds true according to the law of conservation of energy.

Empty device three = (HS $ H - HS number H) FS wave day ten As2sH
Qms(Tm2sH-Ts2sH)...[61 Here,
Hs unit H: Main steam enthalpy = f (Ts2sH, Ps2
sH) Hs, 3H: Primary superheater outlet enthalpy = f (TS, SH, PS, SH) As group 1: Secondary superheater heat transfer area Qms: Heat transfer coefficient If this is approximated by the Oler integral, the ratio 2sH ( i,k)-Hs2sH(i,k-1)△t=
{Hs, SH (i, k-1) one day S2SH (i, k-・
)}FS28th (i, k-1) 10AS23MQmS {
Tm2SH(i,k-1)1T departure(i,k1・)} .・．． H Satoshi (i, k) NiHS2SH (i, k-・) ten [(Hs, sH (i, k-1) one day S many H (i, k-
)} F3 open (i, k 1・) 10AS2SHQm3 {Tm bad day (i, k ・11) −T working day (i, k−・)}] △t .・・・．・…‐‐‐‐‐‐‐‐‐‐‐(It will be 71, so
For k=0 to n-1, the predicted value H (i, n) of enthalpy after n sample periods is found by repeatedly calculating the formulas [6' and '7'.

Therefore, the predicted value Ts (i, n) of the main steam temperature after n sampling periods is expressed by the steam table as follows. T rice day (i, n) nig (Japanese day (i, n), PS fake day (i, n)).・・・．・…．・・・．・・・・・・'8
First, in a functional block 130, a proportional/integral calculation is performed using the predicted value 111 of the target value of the main steam temperature obtained and the predicted value 121 based on the model.

△P=K, j≧, (E(i,n))+KP(E(i,n
)-E(i-1,n).・・・．・・・．・・・．・・・・・・
'9) Here, △P: Proportional/integral output K,: Integral gain KP: Proportional gain E (i, n) = TsP (i, n) - Ts2sM (i, n
) Next, the proportional/integral calculation result ΔP:131 is corrected based on the rate of change in the temperature at the outlet of the primary superheater in the function block 140'.

Since the rate of change in the primary superheater outlet temperature has already been determined using equation (2), the fuel bias is determined using equation '10.

△Ff=△P+Kd・rs,sH ……{1
■Here, △Ff: Fuel bias △Fd: Differential gain -d Rainbow 1 group rsISH-dt Next, in function block 15, correct the pressure increase rate d/dt.

The change in the first week heater outlet temperature depends on the change in the main steam flow rate, that is, the pressure increase rate dPd/dt, so the pressure increase rate d/dt
is the first weekly heater outlet temperature change rate rs,sH=dTs,s
It is suitable to correct using a function of H/dt.

That is, {etc}m={etc}18·K·rSISH.・
・--(11) Here, 1, 6 = K: When corrected in the form of a correction coefficient, when the primary superheater outlet temperature is rising, the pressure is increased by the specified value {fertilization d/dt}, and when it is falling, the pressure is increased. This will put a brake on the rate.

In the embodiment of the present invention, an example has been described in which the pressure reducing valve is controlled by the main steam pressure, but there is also an example in which the pressure reducing valve is controlled by the load.

In this case, there is no essential difference except that load is used instead of pressure. As explained above, in the present invention, various variables such as the primary superheater outlet temperature, the secondary superheater metal temperature, the main steam flow rate, and the pressure, which are disturbances to the main steam temperature, are used, so changes in the main steam temperature can be accurately detected. temperature can be predicted and stable temperature rise is possible.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the controlled object and the control device;
The figure shows a specific example of a fuel flow rate controller, FIG. 3 shows a specific example of a pressure reducing valve controller, FIG. 4 shows a functional block diagram of a riser control device, and FIG. 5 shows a main steam temperature target determination Figure 6 is a flowchart showing the main steam temperature prediction method, and Figure 7 is a flowchart showing the main steam temperature prediction method.
It is a flowchart which shows the pressure increase rate correction method of main steam. 10... Start-up command, 100... Temperature increase control device, 11
0...Target temperature prediction, 111...Target temperature prediction value, 1
20... Prediction of main steam temperature, 121... Predicted value of main steam temperature, 130 proportional integral control, 131... proportional integral control output, 140... advance correction due to inlet temperature change, 20
1...Fuel flow rate bias signal, 202...Elevation rate correction signal, 203...Fuel control valve operation signal, 204...
・Reducing valve operation signal, 250...Fuel flow rate detection value, 25
1... Primary superheater outlet steam temperature detection value, 252...
Secondary superheater metal temperature detection value, 253... Main steam temperature detection value, 254... Main steam flow rate detection value, 255...
Main steam pressure detection value, 301...Fuel flow rate controller, 30
2...Pressure reducing valve controller, 350...Fuel flow rate detector, 35
1... Primary superheater outlet steam temperature detector, 352... Secondary heater metal temperature detector, 353... Main steam temperature detector, 354... Main steam flow rate detector, 355 Main steam pressure detection Container, 400...Water supply, 401...Fuel, 402
... Main steam, 403 ... High pressure evening bin exhaust, 404
...Flash tank steam & drain, 500...Cost saving device, 501...Furnace water wall, 502...Primary superheater,
503...Pressure reducing valve, 504...Secondary superheater, 505
...Adjustment valve, 506...High pressure turbine, 507...1
Next week's heater bypass valve, 508...Secondary superheater bypass valve,
509... Secondary superheater vent valve, 510... Fuel control valve, 511... Flash tank. Figure 2 Ship Figure 3 Figure 4 Figure 5 O Figure 5 b Figure 6 Figure 7

Claims (1)

[Claims] 1. A system that obtains steam from the water-cooled wall of the boiler through at least a primary superheater, a pressure reducing valve, and a final stage superheater, and bypasses each of the primary superheater and final stage superheater. and in which the temperature and pressure of the steam are increased at predetermined rates of change by controlling the fuel flow rate to the boiler and the opening degree of the pressure reducing valve, respectively, the steam flow and pressure flowing through the final stage superheater. , detect the steam temperature at the outlet and inlet of the superheater, and the temperature of the superheater tube, use these detected values to predict future chronological changes in the steam temperature at the outlet of the superheater, and A boiler temperature increase control method, characterized in that a deviation from a predicted value of a steam temperature target obtained from a rate of change of is determined, and the fuel flow rate is controlled so that the deviation becomes zero. 2. The prediction of future chronological changes in the steam temperature at the superheater outlet described in claim 1 is based on the steam flow rate and pressure flowing through the final stage superheater in the first stage, the superheater inlet and outlet The current estimated values and rate of change of the steam temperature and the temperature of the superheater tube are determined by the least squares method from the detected values up to now, respectively, and in the second step, the steam temperature at the outlet of the superheater is determined from these estimated values and rate of change. A boiler temperature increase control method characterized in that a change in enthalpy is predicted, and in a third step, a predicted value of steam temperature is obtained from the predicted value of the enthalpy, the estimated value of the pressure, and the predicted pressure value obtained from the rate of change. .