JPH02191786A - Combustion controlling apparatus for boiler - Google Patents

Abstract

PURPOSE:To perform stable combustion with small amount of excess air supply by temporarily increasing the feeding rate of air upon detecting incomplete combustion or at a prescribed time. CONSTITUTION:A fuel 2 is supplied to a combustion furnace 1 to form a deposited fuel 4 at the bottom of the furnace 1 and the deposit is burned by supplying air 3 in small excess in order to suppress exhaust heat loss and to save the energy. In the above process, the feeding rate of air is temporarily increased upon detecting incomplete combustion or at a prescribed time.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a recovery boiler for burning black liquor produced in the chip cooking process of a valve manufacturing plant and recovering steam and chip cooking chemicals, and a recovery boiler that uses charcoal as a combustion fuel. A combustion control device for a boiler used in a dust-combustion (hereinafter referred to as "oki-combustion") boiler having a grate, in particular a combustion control device for a boiler that ensures proper operation while maintaining a low excess air condition. Regarding.

(Prior Art) In various plants, stator-combustion boilers such as stoker boilers and recovery boilers having a grate have been widely used. As shown in Fig. 6, in this boiler, combustion fuel 2 is continuously introduced into the furnace 1 from the outside and deposited on the bottom of the furnace, and combustion air 3 is blown in from outside the furnace to deposit it. The fuel 4 is combusted, and the combustion gas produced by the combustion of the deposited fuel 4 is discharged as exhaust gas 5 to the outside of the furnace. Also, for the purpose of combustion control, a fuel flow meter 6. An air flow meter 7 is provided on the combustion air supply line side, and in addition, a PID calculation means 8, a combustion air control damper 9, etc. are provided.

By the way, the combustion control device for a combustion boiler as described above is usually provided with a mode switch 11 as shown in FIG. 7, and when the mode switch 11 is set to the auto mode control side, the combustion Only the air flow rate control means is operated. That is, in this control means, the detected fuel flow rate detected by the fuel flow meter 6 is sent to the correction means 12, where a correction process is performed by multiplying the detected fuel flow rate by a ratio determined from the theoretical air amount and the excess air ratio. After that, it is guided to the subtraction means 14 via the multiplication means 13 to find the deviation between the air flow rate target value after correction processing and the air flow rate detection value from the air flow meter 7,
Based on this deviation, the PID calculation means 8 performs PID calculation processing to obtain an operation output, which is applied to the combustion air control gunba 9 to control the air flow rate.

On the other hand, when the mode switch 11 is set to the cascade control side, the combustion air flow rate control means and the o□a degree control means are connected and operated as a cascade control means. That is, the 02'a degree detection value of 02m degree meter 1s and 02'a
02 concentration target value 16 from the degree setting section 16 and the subtracting means 1
7, find the deviation between both values, and then calculate this deviation as P
The ID calculation means 18 performs PIDa calculation processing to obtain a target value of the combustion air flow rate, and the air flow rate is controlled based on this target value.

By the way, in general, the control of the combustion air flow rate in a boiler is
For the purpose of suppressing exhaust gas heat loss and saving energy, operation is performed by blowing in a low excess air flow rate, but when this operating method is applied to a recovery boiler or an open combustion boiler, it is necessary to compete for low excess air inside the furnace. Because of the shape of the fuel, there is a localized lack of air penetration, which tends to cause poor combustion.

Therefore, in conventional staggered combustion boilers, the excess air ratio is set large by biasing a predetermined air flow rate during normal operation, or the combustion air flow rate is increased for a while when a decrease in combustion is detected. Operator is doing it.

(Problem to be solved by the invention) However, controlling the air flow rate as described above causes a large amount of air to be sent into the furnace, which increases exhaust gas heat loss, and also requires a forced draft fan to send air into the furnace. There is a problem that the amount of electric power increases. Also, if a large amount of air is pumped in after combustion has decreased,
There is a problem in that due to the promotion of combustion, the appropriate fire bed is consumed excessively, and the reaction rate later causes a decrease in the evaporation flow rate.

The present invention has been made to solve the above-mentioned problems, and provides boiler combustion control that enables proper operation while maintaining a low excess air flow rate, thereby reducing exhaust gas heat loss and saving energy. The purpose is to provide equipment.

(Means for Solving the Three Problems) The combustion control device for a staggered combustion boiler according to the present invention temporarily increases the air flow rate value when it is determined that poor combustion is occurring during low excess air operation or at a predetermined time. , or a combustion activation control means for temporarily changing the flow rate of combustion air between the plurality of air inlets.

(Function) Therefore, by adopting the above means, the present invention changes the air flow rate to a predetermined air flow rate value when poor combustion is determined due to insufficient air penetration during low excess air operation or at a predetermined time. By increasing the target value of the air flow rate for a predetermined period of time, or by temporarily changing the mutual combustion air flow rate of multiple combustion air inlets, the bias of the air flow rate can be maintained permanently. This aims at activating combustion without increasing the amount of air, and then returns the air flow rate value to the original low excess air value to maintain the active state of combustion.

(Example) Hereinafter, an example of the apparatus of the present invention will be described with reference to FIG. In this figure, the same parts as those of the conventional device (FIG. 7) are given the same reference numerals, and detailed explanation thereof will be omitted.
A cascade control means for supplying the output of the 02 concentration control means consisting of 15 to 18 through the mode switch 11 to the combustion air flow rate control means consisting of fuel flowmeters 6 to 9 and 12 to 14 as an air flow rate target value. and the cascade control means includes a combustion activation control means 20 that adds a predetermined air flow rate value to the air flow rate target value of the cascade control means for a predetermined time when it is determined that combustion is insufficient during low excess air operation. This is the added configuration.

The 02 concentration control means controls the concentration of 02i1 from the exhaust gas of the furnace 1.
02ia degree meter 15 to detect degree, predetermined 02? It was detected by the 02 concentration setting section 16 which outputs the s degree target value, and this 0□ concentration meter 15. A subtraction means 17 obtains a control deviation from the detected 02 concentration value and the 02 concentration target value outputted from the 02 concentration setting section 16, and the control deviation obtained by this subtraction means 17 is subjected to, for example, P I Di7j4 calculation to calculate the combustion air. It is composed of a PID calculating means 18 and the like that obtains a target value of the flow rate control system.

Further, the combustion activation control means 2o includes a 02a degree meter 15.
When the 02 concentration detected by the 02 concentration is on an upward trend, a timer drive signal is outputted by the 02a degree increase tendency determination section 21, and the timer drive signal from the 02 concentration increase tendency determination section 21 is used to determine the temperature for a predetermined period of time, for example, depending on the size of the furnace.

The time determined based on the amount of deposited fuel and other factors (for example, 1 to 2
a timer 22 that outputs an on signal for a period of
A switch circuit 23 is turned on by an on signal from 2, and when this switch circuit 23 is turned on, a predetermined air flow rate is set, for example, when it is 2% in terms of 02 during low excess air operation (a) as shown in FIG. It is comprised of a set value generating section 24 that outputs an air flow rate value of about 4 to 5%, and an adding means 25 that adds the output from the set value generating section 24 to the output of the 02 concentration control means.

Next, the operation of the apparatus configured as above will be explained.

First, assume that the mode switch 11 is used to set the mode to the cascade control side. At this time, the 02'a degree control means introduces the 02 concentration detection value detected by the 02 concentration meter 15 and the 02a degree target value set by the 022a degree setting section 16 into the subtraction means 17, where the difference between the two values is After calculating PID calculation means 1
8. In this PID calculation means 18, the deviation from the subtraction means 17 is subjected to, for example, a PID adjustment calculation, and the calculation output is sent to the multiplication means 13 which is configured as part of the combustion air flow rate control means via the addition means 25 and the mode switch 11.
is given as the target value. Therefore, the actual air flow rate target value of the combustion air flow rate control means is a correction value obtained by multiplying the fuel flow rate detection value of the fuel flow meter 6 by the multiplication means 13 by the theoretical air amount and the excess air ratio by the correction means 12. The value obtained by multiplying the output of the PID calculation means 18 by the output of the PID calculation means 18 is obtained. Then, the substantial air flow rate [1
The target value and the air flow rate detection value from the air flow meter 7 are subtracted by subtraction means 1
4, and based on the control deviation obtained here, PI
The D calculating means 8 obtains the operational output, and the combustion air control damper 9 is controlled according to this operational output.

By the way, compared to the low excess air operation shown in Figure 2 (a), when the air flow rate is constantly biased as in the past (Figure 2 opening), the combustion air flow rate increases as described above. There were problems with exhaust gas heat loss and an increase in the power consumption of the forced draft fan, but with this device, while maintaining low excess air operation, the 02 concentration increases when combustion failure occurs due to a local lack of air penetration. , the 02m degree is determined by the 02 concentration increasing tendency determining section 21 to determine whether or not there is an increasing trend, and when it is determined that there is an increasing trend, the 02 increasing trend determining section 21 outputs a timer drive signal to the timer 22. This causes the timer 22 to output an on signal for a predetermined period of time. When the switch circuit 2-3 turns on in response to the on signal from the timer 22, a predetermined air flow rate signal determined by f is supplied from the set value generating section 24 to the adding means 25 through the switch circuit 23. Then, a predetermined air flow rate signal (c) from the set value generator 24 is added to the output of the PID operator stage 18, that is, the air flow target value during low excess air operation, and the air flow target value of the cascade control means is determined. increase. As a result, the target value of the air flow rate increases for a short period of time determined by the timer 22, activating combustion. This not only makes it possible to activate combustion, but also, as is clear from the double hatched area in Figure 2, when the air flow rate is increased for a short period of time as in this device, the air flow area is smaller than that of conventional devices. Since the biased air flow rate can be significantly reduced compared to the area, combustion can be activated without destroying a proper fire bed, and the steam recovery efficiency can be increased.

Therefore, according to the configuration of the above-described embodiment, the property of the staggered combustion boiler is utilized, in which the amount of heat stored in the deposited fuel is large, and once combustion becomes active, the active state of combustion continues for a while due to its inertia. , an 02 concentration increasing trend determination unit 21 is provided on the output side of the 02 concentration meter 15, and when determining the increasing tendency of the 02 concentration that occurs during poor combustion due to insufficient air penetration, the air flow rate target value of the cascade control means is set to a predetermined value for a short period of time. Since the target air flow rate is increased by adding the air flow m value of power consumption can be reduced,
Stable operation of the boiler can be ensured by maintaining the shape of the firebed in an appropriate state.

In the above embodiment, the 02 concentration increasing tendency determining section 21 was provided to determine combustion failure from the increasing tendency of the 02 concentration, but for example, as shown in FIG. 32, and when the determining section 32 determines that the steam flow rate is on a downward trend, the set value generating section 24 may provide a predetermined air flow rate value to the adding means 25 through the switch circuit 23; A configuration may also be adopted in which a timer 33 is provided and a signal to be added is outputted from the set value generating section 24 at predetermined time intervals. Further, it is also possible to add a predetermined air flow rate value using any of the 02 concentration increasing trend, steam flow rate decreasing trend, and every predetermined time, and in this case, as shown in FIG. 3, the OR circuit 3
4 is provided on the input side of this circuit 34, and a 02 concentration increasing trend determining section 21, a steam flow rate decreasing trend determining section 32, and a timer 3 are provided on the input side of this circuit 34.
This can be realized by providing 4.

In addition, when the conventional boiler is viewed from above (Fig. 4a) and from the side (Fig. 4b), a plurality of air inlets 40 are provided in the front, rear, left, right, and top and bottom directions of the furnace 1, respectively. ing. Note that the length of the arrow in the figure is the air inlet 40.
Shows the air flow value from. Therefore, in the conventional boiler, a uniform air flow rate is supplied from all the air inlets 40.

On the other hand, in this device, when it is determined that the 02 concentration is increasing or the steam flow rate is decreasing, the target value of the air flow rate is not temporarily increased as shown in FIG.
) to (e), the combustion may be activated by changing the air flow ratio in the front and rear left 6 and up and down directions of the boiler. In addition, when determining combustion failure due to local insufficient air penetration, the air inlet 40 and, for example, 0
By installing the two densitometers 15 in a one-to-one relationship, it is possible to reliably increase the air flow rate of the air inlet 40 corresponding to the poor combustion area. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

(Effects of the Invention) As described in detail above, according to the present invention, when it is determined that, for example, the 02 concentration increases due to poor combustion, the air flow 1ii of the cascade control means is activated for a short time to increase the 1 standard value. As a result, combustion can be maintained in an activated state with low excess air operation without constantly increasing the air flow bias, and it also reduces exhaust gas heat loss and equipment power consumption, resulting in energy savings. We can provide a boiler combustion control device that can contribute.

[Brief explanation of the drawing]

Figures 1 and 2 are shown to explain an embodiment of a combustion control device for a boiler according to the present invention. Figure 1 is a system configuration diagram of a side combustion boiler, and Figure 2 is a conventional system. 3 is a system configuration diagram illustrating another embodiment of the device of the present invention, and FIGS. 4 and 5 are diagrams showing a plurality of air inlets. Figure 6 is a schematic configuration diagram of a general staggered combustion boiler, and Figure 7 is a diagram illustrating the air flow ratio of the conventional system and the air flow ratio of the inventive system when the FIG. 2 is a configuration diagram of a control device. DESCRIPTION OF SYMBOLS 1...Furnace, 6...Fuel flow meter, 7...Air flow meter, 9...Damper for fuel air control, 11...Mode switching device, 12...Correction means, 13...・Multiplication means, 15
...02 concentration meter, 16...02 concentration setting section, 17.
... Subtraction means, 18... PID calculation means, 20...
Combustion activation control control means, 21...02 concentration increase tendency determination section, 22... timer, 23... switch circuit,
Set value generation unit, 5...Addition means,...Steam flow meter, 2...Steam flow rate downward trend determination unit, 33...Timer, 34...OR circuit.

Claims (1)

[Claims] (1) In a slag-fired boiler that has a grate with one or more combustion air inlets, the air flow rate value is temporarily adjusted when poor combustion is determined during low excess air operation or at a predetermined time. A combustion control device for a boiler, comprising combustion activation control means for increasing the flow rate of combustion air between the plurality of air inlets or temporarily changing the flow rate of combustion air between the plurality of air inlets.