JPH09243058A - Combustion control apparatus for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make variation of air to fuel ratio in a changing process as small as possible when change of at least two combustion rates is made. SOLUTION: This combustion control device for a boiler comprises a blower 6, a fuel feeding means 3 and a control device 10 for controlling the blower fan 6 and the fuel feeding means 3. The fuel feeding means 3 feeds fuel at rates corresponding to combustion rates and at an intermediate rate between rates corresponding to two adjacent combustion rates. The control device 10 implements control in such a manner that the fuel feeding means 3 is adjusted to an intermediate fuel supplying rate for a specified period of time during the time from the start of changing air blowing rate of the blower fan 6 until the finish of the change, when combustion rate is changed between two adjacent rates of combustion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler combustion control device.

[0002]

2. Description of the Related Art Conventionally, when adjusting the combustion amount of a combustion apparatus such as a boiler, the on-off valve provided in each of a plurality of fuel supply passages is selectively opened and closed to adjust the fuel supply amount.
By changing the opening of the damper provided in the air duct, the amount of air for combustion air is adjusted to keep the ratio of fuel and air for combustion (air ratio) substantially constant. Recently, instead of the conventional method of using a damper, a method of adjusting the air flow rate by controlling the number of revolutions of the air blower by using an inverter or the like has been adopted. Are listed.

Since the adjustment of the fuel supply amount is performed by the opening / closing operation of the opening / closing valve (usually by the opening / closing control valve such as a solenoid valve) as described above, the fuel supply amount is for high combustion. Switching to low combustion is almost instantaneous. However, the air flow rate does not change instantaneously, but changes to the target air flow rate over a certain period of time, so the air ratio (ratio to the theoretical air flow rate) varies between low combustion state and high combustion state. After a sudden change occurs in the transition period of, the predetermined air ratio is reached when the target combustion state is completely changed. Therefore, in this case, there are problems that soot and unburned substances such as carbon monoxide remain, the increase of combustion noise, the occurrence of oscillatory combustion, and the fuel cannot be effectively used. This tendency is remarkable when the blower shifts from high combustion to low combustion. This is because, particularly when controlling the rotation speed of the blower to adjust the air flow rate by inverter control or the like, the rotation speed does not easily decrease due to the inertial force of the fan.

Therefore, it has been attempted to switch the flow rate of the fuel at an appropriate timing between the start timing and the end timing of the blown air volume switching to reduce the fluctuation of the air ratio, but such a method is also available. Before and after the switching of the fuel flow rate, there are long regions with a low air ratio and regions with a high air ratio. Therefore, the air ratio is extremely deteriorated before and after the switching of the fuel flow rate. That is, when switching the current combustion amount, in the method of switching the combustion air amount by controlling the rotation speed of the blower or the method of controlling the damper opening, the above-mentioned soot and There remain problems such as unburned substances such as carbon oxide remaining, an increase in combustion noise, and occurrence of oscillatory combustion.

[0005]

Therefore, the present invention is
It is an object of the present invention to provide a combustion control device for a boiler that minimizes changes in the air-fuel ratio during the switching process when switching at least two different combustion amounts.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a combustion control device for a boiler which controls switching of at least two different combustion amounts, and includes a blower, a fuel supply means, and a controller for controlling the blower and the fuel supply means. The fuel supply means is configured to supply an intermediate amount between the fuel supply amount corresponding to each of the combustion amounts and the fuel supply amount corresponding to two adjacent combustion amounts, and the controller is When switching between the two adjacent combustion amounts, the configuration is such that the fuel supply means is adjusted to the intermediate fuel supply amount for a certain period of time from the start of switching the blower amount of the blower to the end of switching. This is to solve the above problems.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention are realized in a boiler that controls the combustion amount in at least two different stepwise amounts. According to the combustion control device for a boiler of the present invention, when the combustion amount is switched between two adjacent combustion amounts, the blower amount of the blower is changed from the amount corresponding to one combustion amount to the amount corresponding to the other combustion amount. The fuel supply means also adjusts the fuel supply amount corresponding to one combustion amount from the fuel supply amount corresponding to the other combustion amount. At
By adjusting the fuel supply amount of the fuel supply means to the intermediate fuel supply amount for a certain period of time, the change in the air ratio is reduced. That is, when the combustion amount is switched, the fuel supply amount is adjusted to an intermediate amount with the next combustion amount by delaying the change of the air amount from the blower for a certain time after starting the change, and the fuel supply amount is set to a predetermined value. After burning for the time, the amount of combustion is switched to the next. In such a process of switching the air flow rate, the change in the air-fuel ratio can be reduced by supplying fuel in an amount corresponding to the combustion amount before and after the switching in the middle of the process. Then, by reducing the change in the air-fuel ratio, it is possible to prevent the generation of soot and unburned substances such as carbon monoxide, and solve the problems such as an increase in combustion noise and the occurrence of oscillatory combustion. Here, the intermediate amount of the fuel supply amount corresponding to the two combustion amounts before and after the switching does not mean only the average amount of each fuel supply amount corresponding to the combustion amount before and after the switching, and It is a combustion amount between two combustion amounts before and after switching, and is a fuel supply amount corresponding to a combustion amount different from these.

In the present invention, the control of switching the combustion amount controls at least two, for example, two combustion amounts of high combustion and low combustion in a stepwise manner, and the number of stages is not limited to two. The fact that the combustion amount is adjusted stepwise means that the air flow rate corresponding to each combustion amount and the fuel supply amount are
It means that each amount will be in stages. Incidentally, when switching and controlling a plurality of combustion amounts, the number of control positions including the stopped state is usually referred to as a control method. For example, when switching control between two combustion amounts, there are three control positions including the stop state, and this is called three-position control. When switching and controlling three combustion amounts, four-position control is performed.

The amount of air blown by the blower is adjusted by controlling the number of revolutions to adjust the amount of air blow corresponding to the stepwise combustion amount, and also by using a damper to increase or decrease the flow passage cross-sectional area. . The control of the rotation speed of the blower is realized by selecting an inverter circuit or a voltage adjusting circuit according to the motor that drives the blower.
The adjustment of the fuel supply amount is performed stepwise by opening and closing the flow path. Here, the opening and closing of the flow passage includes the one for selectively opening and closing the flow passage for fuel supply corresponding to each combustion amount, and the one for stepwise switching the fuel flow rate flowing through the flow passage. For example, the adjustment of the fuel supply amount corresponding to each combustion amount is performed by connecting an on-off valve such as a solenoid valve to a plurality of fuel pipes corresponding to each fuel supply amount and selectively opening and closing the on-off valve. It is done by letting.

Incidentally, the combustion device targeted by the combustion control device of the present invention requires a longer time for the change of the air supply amount than the change of the fuel supply amount when switching the combustion amount.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. 1 is a drawing for explaining a schematic structure of an embodiment of a combustion control device for a boiler according to the present invention, and FIG. 2 is a control chart showing an embodiment of a combustion control device for a boiler according to the present invention. FIG. 3 is a drawing for explaining the change of the air ratio in the embodiment of the boiler combustion control device according to the present invention and the conventional control method.

First, an example of a boiler to which the present invention is applied will be described with reference to FIG. In FIG. 2, a combustion device 1 is attached to an upper portion of a boiler 2, and the combustion device 1 includes a fuel pipe 3 as a fuel supply means and a wind box 4 which is a supply path of combustion air.
It has. A blower 6 is connected to the wind box 4 at its upstream end.

In the illustrated embodiment, the combustion apparatus 1 according to the present invention has three control positions of stop, low combustion, and high combustion, and corresponds to a so-called three-position control system for gradually adjusting the combustion amount. It is a thing. That is, the combustion amount is the boiler 2
The fuel pipe 3 is adjusted in three stages of stop, low combustion, and high combustion according to the increase or decrease of the load demand to the fuel pipe 3.
Is provided with two branch pipes 3a and 3b, and the first and second fuel valves 5a and 5b are connected to the respective branch pipes (hereinafter, referred to as first and second branch pipes) 3a and 3b. There is. Then, the fuel supply amount is adjusted stepwise by selectively opening and closing the first and second fuel valves 5a and 5b. The blower 6 corresponds to the three-position control type as described above, and the rotation speed thereof is controlled to stop, low combustion and high combustion, and the rotation speed is controlled respectively to blow the air. The air volume is adjusted.
The switching of the combustion amount is performed by the load determiner 9 of the combustion control device 7 based on a load detection signal from a load detection unit (not shown) that detects the load of the boiler 2. The load detecting means is a pressure sensor or a pressure switch for detecting the pressure inside the can of the boiler 2, and the load determining device 9 determines the load of the boiler 2 according to the pressure detected by the load detecting means, and burns the combustion. It is determined whether the device 1 is stopped, controlled to low combustion or controlled to high combustion. In order to switch the combustion amount based on this load, a controller 10 is provided for controlling the rotation speed of the blower 6 and switching the fuel supply amount by the fuel pipe 3. The rotation speed of the blower 6 is controlled by using an inverter circuit when the motor that drives the blower 6 changes in rotation speed depending on frequency, and when the rotation speed changes in dependence on voltage. Uses a voltage adjustment circuit. Also, the amount of fuel supply is
This is performed by the controller 10 selectively opening and closing the first and second control valves 5a and 5b.

The fuel supply amount and the blown air amount are adjusted by the combustion control device 7. The combustion control device 7 performs the following control in addition to the control of the combustion amount. That is, when the operation of the boiler 2 is started, the combustion control device 7 activates the blower 6 to perform scavenging inside the furnace (pre-purge) prior to actual combustion. After the pre-purge operation for a predetermined time, the first fuel valve 5a is opened to start the fuel supply. This fuel is ignited by an ignition device (not shown), and actual combustion is started. After that, when the combustion amount is adjusted according to the increase / decrease in the required load on the boiler 2, as described above, when the required load is further reduced, the combustion device 1 is temporarily stopped and placed in the standby state, Alternatively, when the operation of the boiler 2 is stopped after the operation for a desired time, the first and second fuel valves 5a and 5b are closed to stop the fuel supply to extinguish the fire, and then the blower. 6 is operated as it is, the exhaust gas after combustion is scavenged from the inside of the furnace (post-purge), and after this post-purging operation is performed for a predetermined time, the blower 6 is stopped.

In the present invention, when the combustion amount is switched stepwise, the fuel supply amount intermediate between the two fuel supply amounts corresponding to the combustion amount before and after the switching is controlled during the stepwise adjustment of the blown air amount. To supply an intermediate fuel supply amount between the two fuel supply amounts by the first branch pipe 3a and the fuel supply amounts by the first and second branch pipes 3a, 3b. The third branch pipe 3c is provided, and the third control valve 5c is connected to the third branch pipe 3c. The fuel supply amount through the third branch pipe 3c is set to be smaller than the fuel supply amount through the second branch pipe 3b. The third control valve 5c is the controller 1
When 0, the fan 6 is opened for a predetermined time after the start of switching the rotation speed of the blower 6, and then closed for a predetermined time.

Next, the above control procedure will be described with reference to FIG. FIG. 1 is a control chart showing an embodiment of a combustion control device for a boiler according to the present invention. The upper part shows the combustion supply amount switching timing and the fuel supply amount change, and the middle part shows the blown air amount switching timing. The change of the air flow rate, the lower part shows the change of the air ratio. In the control chart showing the change in the air ratio in the lower part, the shaded area is the area with a poor air-fuel ratio, and the area sandwiched between these areas has an air-fuel ratio within a predetermined deviation range from an appropriate value. This is a good area. In FIG. 1, after low combustion for a predetermined time, transition to high combustion is performed, and after this high combustion is maintained for a predetermined time,
It shows the state of transition to low combustion. The symbols in the figure represent the following timings, respectively. At the time of switching from low combustion to high combustion, TL0: Start timing of air flow switching TL1: Timing of opening third fuel valve TL2: Timing of opening second fuel valve TL3: Timing of closing third fuel valve TL4: Timing of completion of air flow switching High At the time of switching from combustion to low combustion, TH0: Start timing of air flow switching TH1: Timing of opening third fuel valve TH2: Timing of closing second fuel valve TH3: Timing of closing third fuel valve TH4: Timing of completion of air flow switching Each timing is from the controller 10 to each fuel valve 5a-5
c, the timing of the instruction to the blower 3.

First, the case of switching from the low combustion state to the high combustion state will be described. When switching from the low combustion state to the high combustion state, the controller 10 sets the air flow rate of the blower 6 to the high combustion air volume. Increase the rotation speed accordingly. That is, as shown in FIG. 1, the blow rate switching start timing TL0
After that, the number of rotations is increased, and finally, at the blow rate switching end timing TL4, the blow rate for high combustion is reached. When the rotation speed of the blower 6 is a low combustion air volume,
Only the first fuel valve 5a is open, and therefore the fuel is supplied only from the first branch pipe 3a. Then, after the blow rate switching start timing TL0, the rotation of the blower 6 starts to increase and a predetermined time has elapsed, and the third fuel valve opening timing T
When reaching L1, the third fuel valve 5c is opened and fuel is supplied from the first branch pipe 3a and the third branch pipe 3c. After maintaining this state for a predetermined time until the second fuel valve opening timing TL2, the second fuel valve 5b is opened, and the third fuel valve 5c is closed immediately after this at the third fuel valve closing timing TL3. , Fuel is supplied from the second branch pipes 3a and 3b. Then, when a predetermined time elapses and the air flow rate switching completion timing TL4 is reached, the air flow rate and the fuel supply amount are switched to the high combustion state. The change in the air flow during this period increases almost uniformly as shown in FIG. 1, and during the change in the air flow,
By opening the third fuel valve 5c, the first, second
Since the fuel supply amount intermediate between the two fuel supply amounts by the branch pipes 3a and 3b is supplied, the change in the air ratio is small. Comparing this with the conventional one shown by the dotted line in FIG. 1, since the fuel supply amount for low combustion is changed to the fuel supply amount for high combustion at a stretch, the change in the air-fuel ratio is large and it falls outside the appropriate air-fuel ratio range However, in the combustion control device of the present invention,
It does not deviate from the proper air-fuel ratio range.

In this embodiment, at the time of switching from the low combustion state to the high combustion state, the third fuel valve closing timing TL3 is set after the second fuel valve opening timing TL2. Generally, in the fuel valve, after the opening operation, a slight time delay (so-called spray delay) occurs until the fuel is actually injected in the combustion device 1, and even after the fuel valve is closed, this fuel A small amount of fuel is injected due to the residual pressure in the fuel pipe from the valve to the combustion device (so-called lagging).
Sometimes. Therefore, when switching from the low combustion state to the high combustion state, the fuel supply amount is switched in the increasing direction,
In order to prevent the actual fuel supply amount from decreasing during the time delay, the second fuel valve opening timing TL2
After that, the third fuel valve closing timing TL3 is set and overlapped to suppress the change in the air ratio. Therefore, the second fuel valve opening timing TL2 and the third fuel valve opening timing TL2
There is no practical problem even if the fuel valve closing timing TL3 is set at the same time.

Next, the case of switching from the high combustion state to the low combustion state will be described. When switching from the high combustion state to the low combustion state, the controller 10 reduces the rotational speed so that the blower 6 blows a low amount of air for combustion. That is, as shown in FIG. 1, the blow rate switching start timing TH0
After that, the number of revolutions is reduced, and finally, at the blow rate switching end timing TH4, the blow rate for low combustion is reached. When the rotation speed of the blower 6 is a high combustion air volume,
As described above, both the first and second fuel valves 5a are open, so that the fuel is supplied from the first and second branch pipes 3a and 3b. Then, the blow rate switching start timing TL0
After that, the rotation of the blower 6 starts to decrease and a predetermined time has passed,
When the second fuel valve closing timing TH2 is reached, the second fuel valve 5b is closed, and the third fuel valve 5c is opened immediately after this at the third fuel valve opening timing TH1, so that the first and third branch pipes are opened. Fuel is supplied from 3a and 3c. After maintaining this state for a predetermined time until the third fuel valve closing timing TH3, the third fuel valve 5c is closed, and thereafter, fuel is supplied only from the first branch pipe 3a. Then, after a lapse of a predetermined time and at the blow rate switching completion timing TH4, the blow rate and the fuel supply rate are switched to the low combustion state. The change in the air flow during this period decreases almost uniformly as shown in FIG. 1, and by opening the third fuel valve 5c during the change in the air flow, the first and second branch pipes 3a, Since the fuel supply amount intermediate between the two fuel supply amounts by 3b is supplied, the change in the air ratio is small. Comparing this with the conventional one shown by the dotted line in FIG. 1, since the fuel supply amount for low combustion is changed to the fuel supply amount for high combustion at a stretch, the change in the air-fuel ratio is large, and it falls outside the appropriate air-fuel ratio range. However, the combustion control device of the present invention does not deviate from the proper range of the air-fuel ratio.

Here, at the time of switching from the high combustion state to the low combustion state, the third fuel valve opening timing TL1 is set after the second fuel valve closing timing TH2. this is,
As above, to prevent the effects of spray delay and lag,
When switching from the high combustion state to the low combustion state, the fuel supply amount is switched in the decreasing direction, and in order to prevent the actual fuel supply amount from increasing during the time delay, the second fuel supply amount is increased.
The third fuel valve opening timing TH1 is set after the fuel valve closing timing TH2 and a slight delay time is provided to suppress the change in the air ratio. As in the case described above, the third fuel valve opening timing TL1 and the second fuel valve closing timing TH2 may be set at the same time for practical use.

Further, in the above-mentioned embodiment, the adjustment of the combustion amount is applied to what is performed in two stages of high combustion state and low combustion state, but the combustion amount is two stages of high and low. However, the amount of combustion may be adjusted in three or more stages. In this case, the fuel supply amount in the fuel supply means is set according to the number of stages of the combustion amount, but by appropriately varying the flow rate of each fuel branch pipe, the number of fuel control steps can be reduced with a smaller number. Can handle. Further, the control of the blown air amount and the fuel supply amount between each stage may be performed in the same manner as described above.

[0022]

As described above, according to the combustion control device for a boiler according to the present invention, when the combustion amount is switched between two different combustion amounts adjacent to each other, the switching of the blower amount of the blower is started from the start point. After a lapse of a predetermined time, the fuel supply amount is adjusted to an intermediate amount of the combustion amount corresponding to the combustion amount before and after the switching, and after burning for a predetermined time with this fuel supply amount, the next combustion amount is set. , It is possible to reduce the change in the air ratio, which prevents the generation of unburned substances such as soot and carbon monoxide, which have been problems in the past, and increases the sound of combustion and the occurrence of oscillatory combustion. Can be resolved.

[Brief description of drawings]

FIG. 1 is a control chart showing an embodiment of a combustion control device for a boiler according to the present invention. The upper part shows the change timing of the combustion supply amount and the change in the fuel supply amount, and the middle part shows the change timing of the blown air amount and the blown air amount. And the lower part shows the change in the air ratio.

FIG. 2 is a diagram for explaining an example of a boiler to which the present invention is applied.

[Explanation of symbols]

 1 Combustion device 2 Boiler 3 Fuel piping (fuel supply means) 3a 1st branch piping 3b 2nd branch piping 3c 3rd branch piping 5a 1st fuel valve 5b 2nd fuel valve 5c 3rd fuel valve 6 Blower 7 Combustion control device 10 Controller

Claims (1)

[Claims] 1. A combustion control device for a boiler, which controls switching of at least two different combustion amounts, comprising a blower 6, a fuel supply means 3, and a controller 10 for controlling the blower 6 and the fuel supply means 3. The fuel supply means 3 supplies an intermediate amount between the fuel supply amount corresponding to each of the combustion amounts and the fuel supply amount corresponding to two adjacent combustion amounts. When switching between two adjacent combustion amounts, the fuel supply means 3 is adjusted to the intermediate fuel supply amount for a certain period of time between the start and end of switching the blower amount of the blower 6. Combustion control device for the characteristic boiler.