JPS6353442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a combustion control device that controls the air-fuel ratio of a furnace that collectively supplies combustion air to a large number of burners.

(Prior Art) In general, the following needs are strong for combustion control systems.

(1) Energy saving (2) Pollution prevention (1) Furnaces consume large amounts of fuel, but since oil shocks, the need for fuel costs has increased and resources are limited, so the need for (2) has become stronger. As environmental regulations become stricter, there is a demand for a combustion control system that can prevent pollution in the combustion system (for example, prevent the generation of black smoke).

In order to achieve the above needs, it is necessary to control the air-fuel ratio in the combustion system with high precision both in a steady state and in a transient state due to disturbance fluctuations such as a change in a target value or a change in load.

However, conventional combustion control systems are analog control systems, and when a complex control system is constructed, it is not possible to perform highly accurate or delicate control due to superimposed errors and drifts. However, with the advent of digital controllers using microprocessors, This has made it possible to achieve highly accurate control.

For example, FIG. 1 is a typical example of the conventional control system. In this conventional device, fuel is supplied to each flow meter 2.1, 2.2...2. n, and fuel control valves 3.1, 3.2...3. n in order and burners 4.1, 4.2...4. On the other hand, combustion air is sent to the furnace 1 through a combustion air flow rate transmitter 9 and an air flow rate control valve 10 so as to be common to each burner. It is mixed with commercial air and combusted. In the temperature control system, temperature transmitters 5.1, 5.2... installed in the furnace are used.
…5. The temperature is detected by the temperature controller 6.1, 6.2...6. 7.n, the temperature controller compares the temperature setting value and the detection signal, calculates a value that makes the difference zero by comparison adjustment calculation, and sends the adjustment output signal to the fuel controller 7.n of the corresponding burner.
1,7.2...7. Give n as a target value. Each fuel controller has its target value and flowmeter 2.1, 2.2
...2. A comparison calculation is made with the fuel flow rate from n, and the obtained control output signal is sent to the fuel control valves 3.1, 3.2...
3. n, the fuel flow rate is controlled, and the furnace temperature is controlled. In the combustion air control system, the total fuel flow rate supplied to each burner is detected by the flow meter 8, and the air-fuel ratio setting means 11 multiplies the total fuel flow rate by the following air-fuel ratio, and also calculates the theoretical value per unit fuel flow rate. The product is multiplied by the air amount β and given as a target value for the combustion air flow rate controller 12.

Air-fuel ratio (excess air ratio) μ=
Actual air amount per unit fuel flow rate/Theoretical air amount per unit fuel flow rate This combustion air flow rate controller 12 uses this target value and a combustion air flow rate transmitter 9 that measures the air flow rate.
The output is compared and adjusted with the air flow signal FA linearized by the square root calculator 13, and the adjustment output signal is given to the air flow rate control valve 10 to control the combustion air flow rate.

(Problems to be Solved by the Invention) However, in this type of device, when the load suddenly increases and the amount of fuel increases, each burner 4. Since the fuel flow rate supplied to n increases and the total fuel flow rate increases accordingly, the flow meter 8 detects this and the combustion air flow rate control system performs follow-up control with a delay to match this. The air-fuel ratio μa in the furnace decreases and black smoke is generated.

This state is as shown in FIG.

In general, in order to avoid producing black smoke, the value of the air-fuel ratio μ multiplied by the air-fuel ratio setting means 11 is inevitably increased to prevent the production of black smoke even temporarily when the load suddenly increases. A considerable amount of excess air was injected, which resulted in large heat loss from the chimney and reduced thermal efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a combustion control device that eliminates the above drawbacks and prevents the generation of black smoke without reducing thermal efficiency.

(Means for solving the problem) The outline of how to achieve this objective is to add the total fuel flow command signal Fs, which is the sum of the fuel flow command signal (target value) for each burner, and the actually measured fuel air flow signal FA. When the command signal Fs exceeds the upper limit value, the control output or target value of the fuel controller corresponding to each burner is changed to that value. This value is fixed at the current value. In addition, the lower limit value of air flow rate to prevent black smoke from being generated in the furnace, which is set based on the actually measured fuel flow rate, and the total fuel flow command signal.
It is even better to compare Fs and set the higher value as the target value for the combustion air flow rate controller.

(Function) As a result, the air-fuel ratio μa in the furnace can always be maintained above the lower limit value at which black smoke is not generated.

(Example) The present invention will be described below using an example with reference to the drawings. Components that are the same as those in FIG. 1 are designated by the same reference numerals and their explanations will be omitted.

FIG. 3 is a diagram showing the functional configuration of an embodiment of the present invention.
02, a divider 103, an upper limit coefficient unit 104, a lower limit coefficient unit 105, and a high order selector 106 are added.

In the figure, an adder 101 includes temperature controllers 6.1, 6.2, . . . 6. corresponding to each burner. The total fuel flow rate command signal Fs is determined by adding the outputs of n, that is, the fuel flow rate command signals, and this output is supplied to the comparator 102 and the high-level selector 106. Further, the fuel flow rate upper limit value calculation means 100 includes a divider 10
3 and an upper limit coefficient unit 104, the divider 103 divides the measured combustion air flow rate FA from the square root calculator 13 by the air-fuel ratio μ and the theoretical air amount β per unit fuel flow rate, and calculates the result of this division. The upper limit coefficient unit 104 multiplies the value by a preset coefficient (1+k1) to prevent black smoke from being generated in the furnace due to excess fuel, and the resulting A below is used as the upper limit value of the fuel flow rate for the actually measured combustion air flow rate. It is calculated as follows and output to the comparison discriminator 102.

A=(1+k1)×FA/β・μ The comparison discriminator 102 compares this signal A with the total fuel flow rate signal Fs, and calculates the upper limit fuel flow rate determined by the measured combustion air flow rate FA. When the value Fs of the total fuel flow rate command signal is small, that is, when [Fs≦A=(1+k1)×FA/β・μ], the fuel flow rate controllers 7.1 to 7. outputs a signal that causes n to perform normal adjustment operations.

Furthermore, when the value Fs of the total fuel flow rate command signal is larger than the upper limit total fuel flow rate value determined for the actually measured combustion air flow rate, that is, when [Fs>A=(1+k1)×FA/β・μ], the fuel Controller 7.1-7. A signal is sent to each fuel controller 7.1, 7.2, . Output to n.

On the other hand, in the combustion air control system, a coefficient (1-k2) set in the lower limit coefficient unit 105 to prevent black smoke from occurring in the furnace due to insufficient air flow is added to the actually measured total fuel flow rate FF from the fuel flow meter 8. The lower limit actual measured total fuel flow rate B = (1-k2) x FF is the higher selector 1.
06. The high-level selector 106 selects this lower limit actually measured total fuel flow rate signal B and the total fuel flow rate command signal.
Fs and outputs a high value, so as to always prevent the target value of the combustion air flow rate controller 12 from falling below the lower limit actually measured total fuel value.

In other words, the high-level selector 106 selects the total fuel flow rate command signal value Fs from the upper limit determined by the actually measured total fuel flow rate value when Fs>B=(1-k2)×FF.
If Fs≦B(1-k2)×FF (when the total fuel flow rate is less than the upper limit determined by the measured total fuel flow signal value), the total fuel flow command signal Fs is output as the target value of the air flow control system. (When the fuel flow command signal is large), the lower limit actual measured total fuel value B is output, and the air flow rate is always limited so that it does not fall below the lower limit value B, thereby preventing the generation of black smoke due to a decrease in the air-fuel ratio in the furnace. are doing. A signal obtained by multiplying the output signal of this high-level selector by the air-fuel ratio μ and the theoretical air amount β per unit fuel flow rate is given as a target value to the air flow rate controller 12,
The air flow rate controller 12 controls the combustion air flow rate so that it reaches this target value.

Next, the operation of the combustion control device configured as described above will be explained.

First, an example will be described in which a fuel such as heavy oil whose response to the fuel flow rate is faster than the air flow rate is used.

FIG. 4 is a diagram showing changes in the air-fuel ratio μ in the furnace when the load on the furnace increases rapidly. That is, when the load increases rapidly, the total fuel flow rate command signal Fs increases rapidly, but the response of the air flow rate is poor and cannot be changed instantaneously. For this reason, since the air flow rate responds, it is necessary to control the change in the fuel flow rate. is for each fuel flow rate controller 7.1, 7.2...7. A lock signal is output that fixes n to the target value or manipulated variable at that time, locks the adjustment operation of each fuel controller, and limits the fuel flow rate to the value immediately before locking.

Further, the higher level signal of the total fuel flow rate command signal Fs and the lower limit actually measured total fuel flow rate signal B is multiplied by μ in the air-fuel ratio setting 11 and is given to the combustion air flow rate controller 12 as a target value of the air flow rate. In case of sudden load increase, each temperature controller 6.1, 6.2...6. n
Since a signal in the increasing direction is output from , the total fuel flow rate command signal Fs increases over time. Therefore, the high-level signal selector 106 outputs the total fuel flow rate command signal Fs, and the firing air flow rate controller 12 outputs the total fuel flow rate command signal Fs.
The adjustment operation will be performed in the direction of increasing the amount of combustion air. As the measured air flow rate increases with the fuel flow rate locked, the air-fuel ratio within the furnace 1 also begins to rise.

As is clear from this, the total fuel flow command signal
When Fs becomes larger than the upper limit value A of the total fuel flow rate determined by the actually measured combustion air flow rate signal, the adjustment operation of each fuel flow rate controller is locked and maintained at the fuel flow rate value immediately before locking, and the air flow rate adjustment is Total 1
Since K1 executes the adjustment operation based on the total fuel flow command signal Fs, the decrease in the air-fuel ratio in the furnace is controlled by K1.

Since this reduction in the air-fuel ratio is controlled by K1, the setting range of the air-fuel ratio can be narrowed compared to conventional methods, which is superior in terms of energy saving and prevention of pollution caused by black smoke generation.

Further, when the load decreases, the total fuel flow rate command signal Fs decreases, and accordingly, each fuel controller 7.
1,7.2...7. The output of n also decreases. Therefore, the comparison/discriminator 102 cannot output a signal that locks each fuel flow rate controller because the fuel flow rate command signal Fs never exceeds the value of A=(1+k1)FA/β・μ. do not have.

Next, a case will be described in which a fuel such as coal whose response to the fuel flow rate is slower than the air flow rate is used as the fuel. In this case, even if the load suddenly increases, the response of the fuel flow rate is poor, so it is necessary to limit the response of the air flow rate to maintain the air-fuel ratio μ in the furnace above the lower limit value.

Therefore, when the total fuel flow rate command signal Fs becomes equal to or less than the lower limit actually measured total fuel flow rate B determined based on the actually measured fuel flow rate FF, the high-level selector 106 outputs this lower limit value B as the target value of the combustion air flow rate controller. It's good to add configuration. As a result, the air-fuel ratio is controlled by k2, which determines the lower limit value B, and the generation of black smoke is prevented.

In this way, in this embodiment, when the load suddenly increases and the total fuel flow rate command signal Fs increases, the fuel flow rate increases with better response than the air flow rate, which has a slower response.
In order to avoid a drop in the air-fuel ratio and the generation of black smoke, the fuel flow rate is limited based on the upper limit determined based on the air flow rate, and in order to prevent the air flow rate from decreasing when the load suddenly decreases, This is a restriction based on a lower limit value based on the total fuel flow rate.

Thereby, it is possible to prevent the air-fuel ratio from decreasing due to load fluctuations, to constantly prevent the generation of black smoke, and to ensure high thermal efficiency.

Note that the present invention is not limited to one embodiment; for example, the configuration of each device may be implemented using a microprocessor-applied digital controller and each function processed by software.

In addition, in one embodiment, the air-fuel ratio μ is set at a constant value, but the air-fuel ratio setting value may be corrected by the combustion amount,
When correction is performed using carbon monoxide (CO) control or carbon monoxide (CO)/carbon dioxide gas (CO2) control signals, processing may be performed using the air-fuel ratio after the correction. Furthermore, in one embodiment, although the description has been made on a fuel basis, the invention can also be applied to a case where the air fuel ratio is used as long as the gist is not changed since the air-fuel ratio is different from the reciprocal of the air-fuel ratio.

(Effects of the Invention) As explained above, the present invention controls each fuel flow rate of a plurality of fuel control systems arranged according to an upper limit value determined based on the air flow rate, and also adjusts the air flow rate as necessary. By controlling this to a lower limit value based on the total fuel flow rate, it is possible to prevent the air-fuel ratio from decreasing due to load fluctuations and avoid generating black smoke.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional combustion control device, FIG. 2 is a diagram showing transient changes in air-fuel ratio in a conventional combustion control system, FIG. 3 is a block diagram of a combustion control device according to the present application, and FIG. The figure is a diagram showing a transient change in the air-fuel ratio of the combustion control device according to the present application. 1... Furnace, 21, 22... 2n... Fuel flow rate transmitter, 31, 32... 3n... Fuel flow rate control valve, 4
1,42...4n...burner, 51,52...5n...
...Temperature transmitter, 61,62...6n...Temperature controller, 71,72...7n...Flow rate controller, 8...Fuel flow rate transmitter, 9...Fuel air flow rate transmitter, 10
... Fuel air flow rate control valve, 11 ... Air-fuel ratio setting means, 12 ... Air flow rate controller, 100 ... Fuel flow rate upper limit value calculation means, 101 ... Adder, 102 ...
... Comparison discriminator, 103 ... Divider, 104 ... Upper limit coefficient device, 105 ... Lower limit coefficient device, 106 ... High order selector.

Claims (1)

[Scope of Claims] 1. A plurality of fuel controllers are arranged to control the flow rate of fuel supplied into the furnace based on a predetermined target value, and the flow rate of air collectively supplied into the furnace is controlled by the fuel controller. In a combustion control device in which an air controller for controlling based on the total fuel flow rate is arranged, an adding means for adding target values of the respective fuel controllers to obtain a total fuel flow command signal; a fuel flow rate upper limit value calculation means for calculating an upper limit value of the total fuel flow rate by multiplying the value divided by the theoretical air amount per unit fuel flow rate by a coefficient for preventing generation of black smoke in the furnace; and this fuel flow rate upper limit value calculation means. Compare the upper limit value of the means with the total fuel flow rate command signal of the adding means, and if the upper limit value is less than the total fuel flow rate command signal, maintain the control output or target value of each fuel regulator at the value at that point. and a comparison/discrimination means for outputting a signal to
A combustion control device characterized in that each of the fuel regulators is locked based on a signal from the comparison/discrimination means. 2. A plurality of fuel controllers are arranged to control the fuel flow rate supplied to the furnace based on a predetermined target value, and the air flow rate that is collectively supplied to the furnace is controlled based on the total fuel flow rate of the fuel controllers. In the combustion control device, the combustion control device is equipped with an air controller that calculates the total fuel flow rate command signal by adding the target values of the respective fuel controllers; fuel flow rate upper limit calculation means for calculating the upper limit value of the total fuel flow rate by multiplying the value divided by the air amount by a coefficient for preventing the generation of black smoke in the furnace; and a total fuel flow rate command signal of the adding means, and if the upper limit value is less than the total fuel flow rate command signal, a comparison is made that outputs a signal that causes the control output or target value of each of the fuel regulators to be maintained at the value at that point in time. a determination means; an air flow rate lower limit value calculation means for calculating a lower limit value of the air flow rate by multiplying the total fuel flow rate by a coefficient for not generating black smoke in the furnace; and a lower limit value of the air flow rate lower limit value calculation means; A combustion control device comprising comparing means for comparing the total fuel flow rate command signal of the adding means and multiplying the higher value by an air-fuel ratio and a theoretical air amount per unit fuel flow rate to obtain a target value.