JPS6030404B2 - Boiler fuel control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel control method for a boiler, and in particular compensates for non-linearities such as the characteristics of a fuel flow control valve and the characteristics of a burner main valve.
The present invention relates to a fuel control method that performs control according to the number of burner ignition cells.

In the conventional boiler fuel control method, the number of burners is controlled by a burner control device, and the fuel flow rate is controlled by a boiler control device.

The fuel flow rate control is mainly based on feedback control. However, when performing rapid boiler load runback when plant auxiliary equipment trips during a power line system fault, when realizing high-speed load changes using adaptive control equipment that incorporates computers, and when using conventional oil fuel (incompressible ) When controlling a plant that uses a compressible fuel such as LNG gas instead of a compressible fuel such as LNG gas, controllability may be affected by the nonlinearity of the fuel flow control valve, burner main valve, etc., and the number of burner ignition cells. There was a flaw in Onaka that changed. Fig. 1 shows a system diagram of a conventional fuel control system, in which 1 is a proportional integrator, 2 is a subtractor, 3 is a fuel supply main pipe, 4 is a signal generator, and 5
is a high signal monitor relay, 6 is a low signal monitor relay,
7 is an interlock relay, 9 is a fuel flow control valve, 10
1 is a burner source valve, 11 is a boiler, 12 is a burner, 13 is a pressure transmitter, and 14 is a flow rate transmitter.

In the fuel control system shown in FIG. 1, the fuel flow rate signal C2 is controlled by the boiler control device ABC to be equal to its target value C.

On the other hand, the number of ignition cells of the burner is determined by detecting by the high signal monitor relay 5 that the burner inlet main pipe pressure signal C7 is equal to or higher than the specified set pressure PH in the burner control device ABN.
0 is opened to ignite, and when the low monitor relay 6 detects that the pressure is below the specified set pressure PL, the burner main valve 12 is closed to extinguish the fire, thereby controlling as shown in FIG. 2.
Figure 2 shows fuel flow signal C2 versus burner header pressure signal C.
? In the graph, 21 is the characteristic curve when igniting the burner N cell, 2
2 is a characteristic curve when burner N-1 cell is ignited, 23 is a characteristic curve when burner N-2 cell is ignited, 24 is a characteristic curve when burner N-3 cell is ignited, and 25 is a characteristic curve when burner N-4 cell is ignited. Curve 26 is the characteristic curve when igniting the burner N-5 cell, 2
7 shows the fuel control characteristics when the boiler load is increased, and 28 shows the fuel control characteristics when the boiler load is reduced.

FIG. 3 is a graph of fuel flow rate control valve opening versus fuel flow rate, and 31, 32, 33, 34, 35, 36, and 37 are bars, respectively.
Na N, N-1, N-2, N-3, N-4, N-5, N-
Characteristic curves 38 and 39 at the time of 6-cell ignition show the fuel control characteristics at the time of increasing the boiler load and at the time of reducing the load, respectively.

In this case, by igniting and extinguishing the burner, as shown in Figure 3,
The relationship between the fuel flow rate control valve and the fuel flow rate varies greatly depending on the number of burner ignition cells, and this is caused by the boiler controller ABC.
This causes a large disturbance in fuel control.

Other control disturbances include nonlinearity of the burner source valve and the fuel flow control valve.

An object of the present invention is to provide a boiler fuel control system that compensates for these disturbances and improves controllability.

That is, the boiler control device ABC and the burner control device ABN cooperate to compensate for the fuel flow rate control valve function based on the number of burner ignition cells, and pre-control the fuel flow rate control valve using this signal. On the other hand, the flow rate deviation signal is gain compensated by the number of burner ignition cells, and the flow rate correction control is performed using this signal. In this way, so-called cooperative/adaptive control is achieved. Therefore, in the present invention, the effects caused by the ignition and extinguishing of the burner are clarified through simulation tests and field test data, and the characteristics of the fuel flow control valve due to the effects are determined, and a compensation circuit is provided for this. , control accuracy and quick response are being improved.

The fuel flow rate vs. burner header pressure characteristics are as shown in FIG. 2, as described above.

Therefore, the number of burners is controlled within the burner main tube pressure setting value range (PH to PL) until the total number of burner cells is N cells. Above burner N cell ignition, header pressure upper limit setting is not performed. On the other hand, the fuel flow rate control valve opening versus fuel flow rate characteristics are as shown in FIG. The number of burner cells during boiler rising load is N-
When increasing the fuel flow rate from 5 to N, the fuel flow rate rises on curve 36 as the valve opens, and curve 2 in FIG.
At the point where the upper limit value of the burner header on the burner header 6 is reached, a burner ignition command is output and the number of burner ignitions shifts from N-5 to N-4. Similarly, since the fuel flow rate control valve opening versus fuel flow rate characteristic in FIG. 3 shifts from curve 36 to curve 35,
In order to ensure the same fuel flow rate, it is necessary to move the valve opening degree from curve 36 to curve 35 in the direction of the arrow, parallel to the horizontal axis. Similarly, the fuel flow rate control valve opening versus fuel flow rate characteristic when the boiler is loaded follows a curve 38. When all N burner cells are ignited, the curve rises to the curve 31. Similarly, curve 39 shows the operation when the load is reduced.

Accordingly, in order to control the fuel flow rate in proportion to the boiler load, the fuel flow rate control valve function should be adjusted to curve 38 or 39 in FIG.
It is necessary to control as shown in the figure below. FIG. 4 is a system diagram of the system of the present invention for performing these disturbance compensations. Fourth
In the figure, 1 to 7 and 9 to 14 indicate the same constituent elements as in FIG. 1A and 17-B are multipliers, and 18 is a burner cell number counter.

In addition, in Fig. 4, CI is the fuel flow rate command, C2 is the fuel flow rate,
C3 is a burner ignition command, C4 is a burner extinguishing command, C5 is a burner main valve opening/closing command, C6 is a fuel flow control valve control command,
C7 represents the burner inlet header pressure. Fuel flow command CI
Therefore, the valve relationship characteristic (shown in Fig. 6) with respect to the fuel flow rate at the time of N cell ignition is generated by the function generator 15-A to compensate for the nonlinearity of the fuel flow control valve and the burner main valve. death,
In order to obtain the fuel flow rate vs. fuel flow rate control valve opening characteristic corresponding to each number of burner cells, the function generator 15-C is set as shown in FIG. A
Multiply with the output signal of

Advance control is performed by 15-A, 15-C, and 17-A.

In addition, in order to correct the gain of the proportional integrator 1 according to the number of burner ignition cells, the function generator 15-B
are set as shown in FIG. 5, and multiplied by a multiplier 17-B. Here, a specific explanation will be given of the advance control method implemented in 15-A, 15-C, and 17-A.

In Fig. 4, in order to obtain the opening degree of the fuel flow control valve 9 in advance with respect to the fuel flow rate command C, when the number of burner cells is N-i in Fig. 3 (here, i = 3). .
), the opening degree of the fuel flow control valve corresponding to the fuel flow command signal Q becomes VN-i from the characteristic diagram of the relationship between the fuel flow rate and the fuel flow control valve (FIG. 3). Also, the same fuel flow rate command value Q. Also, if the number of burner cells is {N-(i+1
)}, the opening degree of the fuel flow rate control valve corresponding to the command value Q also becomes VN-,R.

To express the above relationship in a general formula, first find the fuel flow rate and fuel flow rate control valve opening characteristics from Figure 3 when the burner is N-cell, and set the function generator 15-A as shown in Figure 6. .

That is, it becomes the curve a in the right figure.

On the other hand, when the number of burner cells is N-1, the function of the fuel flow rate and the fuel flow rate control valve becomes curve b from Fig. 5, but curve a
There is a proportional relationship between In other words, the fuel flow rate command value Q
The opening degree of the fuel flow rate control valve for i is V when the burner is N cell.
N, when the burner is N-1 cell, it is VN-, and when burner N-i is the cell, it is VN-i.

Therefore, if we take the time degree of burner N as a standard, burner N-1
The characteristic curve at the time of cell can be obtained by multiplying the characteristic number of the special female vertically opposed by the characteristic number at the time of the burner N sensor shown in Figure 6.

This correction gain coefficient is expressed graphically as shown in FIG.

That is, the gain when burner N cells is 1, and burner N-1
The gain during cell is GN-, =VN-, /VN burner N-i
The gain at cell time is GN-i=VM/VN. To summarize the above, in Fig. 4, the fuel flow control valve opening (basic opening) at the time of N burners is determined by the function generator 15-A in response to the signal of the fuel flow rate command C, and is determined by the number of burner cells during operation. By determining the correction gain coefficient from the function generator 15-C and adding these together in the multiplier 17-A, it is possible to determine the relationship of the fuel flow rate control valve to the fuel flow rate command according to the number of burner cells. Next, fuel flow rate control gain correction will be explained.

The fuel flow rate control consists of advance opening signals 15-A and 17-A in FIG. 4 and a correction control function that controls the fuel flow rate deviation to zero.

The latter consists of a subtracter 2, a multiplier 17-B, and a proportional integrator 1, but it is necessary to optimally adjust the proportional integral gain KP and the integral time constant Tr, and these values can be obtained from the following equation. can.

V small KP (10÷/dt) KP=K●ki-T,=3.3L Here, V side; output signal of proportional integrator; deviation signal K: constant G: process gain T: process time Constant L: The process dead times G, T, and L can be determined from the characteristics of the fuel flow rate when the fuel flow rate control valve is changed in steps.

Here G = bell It can be expressed as

Here, the process gain G differs depending on the number of ignition burner cells.

That is, from the characteristic diagram shown in Fig. 3, the process gain GN for burner N cells is GN-non, and the process gain GN-i for burner N-i cells is GN-
It can be expressed as i=tanON-i.

Therefore, since the control gain changes depending on the number of burner cells, FIG. 5 shows this correction gain determined and expressed as a function of the number of burner cells.

According to this method, fuel throttling control FCB is possible in the event of a transmission line system accident in an LNG gas-fired plant.

Further, stable fuel controllability can be ensured from startup to full load range, and control responsiveness can be improved to approximately 5 to 1 sound compared to the conventional engine. This method is applicable to all combustion boilers equipped with multiple burners. In addition, multiple on/off
With an off valve and one fuel flow control valve, it is applicable to all control devices that perform control.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the conventional fuel control system and its operating principle. Figure 2 shows the burner number control system when the boiler is increased or reduced in load, and the characteristics when burner ignition is extinguished by burner inlet header pressure. Fig. 3 is a characteristic diagram showing how the fuel flow control valve is controlled for fuel flow control when the boiler load is increased or decreased, Fig. 4 is a system diagram of the control method of the present invention, and Fig. 5 The figure shows the gain compensation setting value when performing gain compensation of the flow rate deviation proportional integral circuit according to the number of burner cells. Figure 7 shows the relationship between the fuel flow rate control valve and the fuel flow rate when igniting the burner N cells.
FIG. 1...Proportional integrator, 2...Subtractor, 3
... Fuel supply main pipe, 4 ... Signal generator, 5
, 6... Monitor relay, 7... Interlock relay, 8... Adder, 9... Fuel flow control valve, 10... Burner main valve, 11... Boira, 12
...Burner, 15A, B, C...Function generator, 16
......First-order delay element, 17A, B...Multiplier. Leopard - Figure 2 Figure 3 Tsutomu 4 Figure Hair s Figure 6 Figure 7

Claims (1)

[Claims] 1. A fuel flow control valve provided on the fuel supply main pipe, and a plurality of burner source valves provided on a plurality of pipes for guiding the fuel obtained through the fuel flow control valve to each burner in the boiler. , a boiler fuel control method comprising: a boiler control device having a control system that controls a constant fuel flow rate through a fuel flow control valve; and a burner control device that opens and closes the burner main valve to control the number of burner ignition cells. 1. A fuel control method for a boiler, characterized in that the opening degree of a fuel flow control valve is controlled in advance according to the number of burner ignition cells of a burner control device, and the gain of the control is corrected according to the number of burner ignition cells.