JP2002081606A - Method for controlling boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the follow-up property of a boiler to load changes and, at the same time, to suppress an increase in the number of starting and stopping times of the boiler. SOLUTION: For the boiler 1 the combustion amount of which is controlled in multiple stages, the gradient of the detected value of the steam pressure, hot water delivery temperature, etc., used for controlling combustion is detected and a combustion amount switching instructing signal is outputted based on the detected gradient during combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for switching a combustion amount in a boiler.

[0002]

2. Description of the Related Art Some boilers control the combustion state at three positions of high combustion, low combustion, and standby by controlling the amount of combustion during combustion in two stages of a high combustion amount and a low combustion amount. . In recent years, in this boiler, the rotation speed of the blower is controlled by an inverter to control the supply amount of combustion air, that is, the blown amount, for energy saving. In the boiler having such a configuration, when switching the combustion amount from the high combustion amount to the low combustion amount or from the low combustion amount to the high combustion amount, a combustion amount switching instruction signal is output and then the combustion amount is actually switched. Takes a relatively long time to complete (eg, 5 seconds). This is because in the blower, it takes time to change to a desired rotation speed due to the effect of inertia force during rotation.

Accordingly, a state in which the steam pressure greatly exceeds the target pressure due to the time delay (overshoot)
In addition, a state of being significantly lower (undershoot) is likely to occur, and the followability to a change in load may not be sufficient. Further, when the overshoot occurs, the steam pressure increases and reaches a value for standby control, the boiler enters a standby state in which combustion stops, and immediately thereafter, the steam pressure decreases and the low pressure for low combustion control is obtained. And the boiler may be in a low combustion state. Then, the number of times of starting and stopping of the boiler is increased, and the life of equipment attached to the boiler is shortened. The above-mentioned phenomena occur in a multi-can installation system, that is, a system in which a plurality of the boilers are installed in parallel, and a combustion amount of each boiler is controlled based on a steam pressure in a steam header common to each of these boilers. Especially easy to occur.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the followability of a boiler against a change in load and to suppress an increase in the number of times of starting and stopping.

[0005]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 is a method for controlling combustion during combustion in a boiler for controlling the amount of combustion in multiple stages. The method is characterized in that a gradient of a detected value for use is detected and a combustion amount switching instruction signal is output based on the gradient.

According to a second aspect of the present invention, a time required for the detected value to reach a predetermined value is calculated based on the gradient, and if the time reaches a predetermined time or less for switching the combustion amount. , And outputs a combustion amount switching instruction signal.

The invention according to a third aspect is characterized in that a gradient of the detected value is detected during standby, and a combustion start instruction signal is output based on the gradient.

Further, the invention according to claim 4 is characterized in that the detected value is a steam pressure or a tapping temperature.

[0009]

Next, an embodiment of the present invention will be described. The boiler according to the present invention is configured to control the amount of combustion during combustion in multiple stages, for example, in two stages of a high combustion amount and a low combustion amount. Therefore, in this case, the combustion state of the boiler is controlled at three positions: high combustion, low combustion, and standby. In the boiler, the control of the supply amount of combustion air corresponding to each of the combustion amounts, that is, the control of the blown amount is performed by controlling the rotation speed of the blower by an inverter.

In the boiler, a steam pressure is detected as a detection value for combustion control, and each of the combustion states is controlled based on the detected steam pressure. Further, a gradient of the steam pressure, that is, a change amount of the steam pressure per unit time is detected during the combustion. Based on this gradient, the combustion amount is changed from the high combustion amount to the low combustion amount, or from the low combustion amount to the high combustion amount. An instruction signal for switching the combustion amount to the combustion amount is output. That is, a time required for the steam pressure to reach a predetermined value for switching the combustion amount is calculated based on the gradient, and if the arrival time is shorter than a predetermined time required for switching the combustion amount, the combustion amount is switched. An instruction signal is output. Here, the time required for switching the combustion amount is set based on the time from instructing the blower to change the blowing amount to actually completing the changing of the blowing amount.

Therefore, according to the above configuration, it is possible to output the combustion amount switching instruction signal early in consideration of the time delay at the time of switching the combustion amount, and to significantly improve the followability to the load change. Can be. Therefore, steam with a stable pressure can be constantly supplied. Further, according to the configuration, the steam pressure does not greatly exceed the predetermined value and does not enter a standby state, so that an increase in the number of times of starting and stopping can be suppressed, and the life of equipment attached to the boiler is prolonged. be able to.

Further, in the above-mentioned configuration, when shifting from the standby state to the low combustion state, the control for detecting the gradient in the standby state and outputting the combustion start instruction signal based on the detected gradient may be performed together. it can. That is, when starting the combustion, the pre-purge is performed. However, the control for starting the pre-purge early is performed in consideration of the time delay of the pre-purge. By doing so, the ability to follow a change in load is further improved.

In the above configuration, the combustion amount during combustion is controlled in two stages, that is, a high combustion amount and a low combustion amount. However, three or more stages can be set depending on the implementation. For example, when control is performed in three stages, a high combustion amount, a medium combustion amount, and a low combustion amount are set as the combustion amount during combustion.

Further, in the above-described configuration, the air flow rate is controlled by using an inverter.
The present invention is also applicable to a configuration in which the amount of air blow is controlled by a damper device. That is, even in a configuration using the damper device, the present invention can be suitably applied to a case in which a change in the blowing amount requires a relatively long time.

Further, the present invention can be applied to a boiler installed alone or to a boiler of a multi-can installation system in which a plurality of boilers are installed in parallel.
This multi-can installation system is configured to control the amount of combustion in each of the boilers based on the steam pressure in the steam header common to each of the boilers. Since the present invention is set finer than that of the present invention, the present invention can be more suitably applied.

Further, in the above configuration, the boiler is a steam boiler, but the present invention can be applied to a hot water boiler. When the present invention is applied to a hot water boiler, a tapping temperature is detected as the detection value for combustion control.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In the following description, an embodiment in which the present invention is applied to a steam boiler will be described.

First, a first embodiment will be described with reference to FIGS. As shown in FIG. 1, a boiler 1 to which the present invention can be applied includes a can 2, and a burner 3 is provided on an upper portion of the can 2. The burner 3 is connected to a fuel supply line 4 for supplying fuel. The fuel supply line 4 is branched in the middle into two lines, a first fuel valve 5 is provided on one branch line, and a second fuel valve 6 is provided on the other branch line.
Is provided. Further, a blower 7 for supplying combustion air is connected to the burner 3. An inverter 8 is connected to the blower 7. The inverter 8 controls the rotation speed of the blower 7 to control the supply amount of combustion air, that is, the blown amount. .

Further, a pressure sensor 9 is provided in the can 2, and the pressure sensor 9 detects the steam pressure in the can 2. The burner 3
Is controlled at three positions, high combustion, low combustion, and stop, based on the signal from the pressure sensor 9. During high combustion, the two fuel valves 5, 6 are opened, When the combustion is low, only the first fuel valve 5 is opened, and when stopped, both the fuel valves 5 and 6 are closed. That is, the amount of combustion during combustion is controlled in two stages: a high amount of combustion and a low amount of combustion. The amount of air blown from the blower 7 is also controlled in accordance with the amount of combustion.

The can 2 is provided with a water level sensor (not shown), and the water level sensor detects the water level in the can 2. And
A water supply line 10 is connected to a lower portion of the can body 2, and the water supply line 10 is provided with a water supply pump 11 and a check valve 12 in order from the upstream side. On / off control of the water supply pump 11 is performed based on a signal from the water level sensor, and the water level in the can body 2 is maintained in a predetermined range. In addition, a steam line 13 is provided above the can 2.
Is connected, and steam is supplied to an external steam-using device (not shown) through the steam line 13.

Further, the boiler 1 is provided with a controller 14, which controls the first fuel valve 5, the second fuel valve 6, the blower 7, the inverter 8, and the water supply. The pump 11 is controlled according to a preset program. In FIG. 1, the signal lines are indicated by dotted lines, but the reference numerals are omitted.

In the above configuration, the switching control of the combustion amount is performed as shown in FIG. During combustion,
On the basis of the signal from the pressure sensor 9, the gradient of the steam pressure, that is, the amount of change in steam pressure per unit time (ΔP
/ Δt) is always detected, and based on this gradient, an instruction signal for switching the combustion amount from a high combustion amount to a low combustion amount or from a low combustion amount to a high combustion amount is output. ing. For example, in the high combustion state, the time when the steam pressure rises and reaches 0.6 MPa, which is the pressure value for switching the amount of combustion, is calculated based on the gradient, and this arrival time is set to a predetermined high combustion time. When the time required for switching the combustion amount from the amount to the low combustion amount becomes equal to or less than α, an instruction signal for switching to the low combustion amount is output.

That is, in the conventional control, a switching instruction signal for switching to the low combustion amount is output at the point A where the steam pressure reaches 0.6 MPa. In this case, as shown by the dotted line, Is likely to greatly exceed 0.6 MPa (overshoot). On the other hand, in the above configuration, a switching instruction signal for switching to the low combustion amount is output at the point B early before the steam pressure reaches 0.6 MPa. Therefore, according to the configuration, a state in which the steam pressure greatly exceeds 0.6 MPa does not easily occur.

If the steam pressure starts to decrease some time after switching to the low combustion amount, a combustion amount switching instruction signal is output as follows. That is, in this case, as in the case of the pressure increase, the time for the steam pressure to fall and reach the pressure value for switching the combustion amount of 0.6 MPa is calculated based on the gradient, and this arrival time is calculated as follows:
When the time required for switching the combustion amount from the low combustion amount to the high combustion amount, which is set in advance, becomes equal to or less than β, an instruction signal for switching to the high combustion amount is output (output at point C).

Here, the times α and β are set on the basis of the time from when the change of the blowing amount is instructed to the blower 7 until the change of the blowing amount is actually completed.
Further, the times α and β can be the same value, but optimal values are set as different values in each case.

On the other hand, when the steam pressure further rises and exceeds 0.8 MPa after switching to the low combustion amount, the combustion is stopped and the apparatus enters a standby state (not shown in FIG. 2).

As described above, according to the above configuration, it is possible to output the combustion amount switching instruction signal earlier in consideration of the time delay at the time of switching the combustion amount, and the followability to the load change is markedly improved. Can be improved. Therefore, steam with a stable pressure can be always supplied. Also,
According to the configuration, the steam pressure does not exceed 0.8 MPa immediately after the steam pressure exceeds 0.6 MPa and does not enter the standby state, so that an increase in the number of times of starting and stopping can be suppressed. Therefore, the life of the equipment attached to the boiler 1 can be extended.

By the way, in the first embodiment, when shifting from the standby state to the low combustion state, the gradient during the standby state is detected, and the control for starting the pre-purge early based on the detected gradient is also performed. Doing is preferred depending on the implementation. By doing so, the combustion can be started earlier in consideration of the time delay of the pre-purge, and the ability to follow the load change is further improved.

Next, a second embodiment shown in FIGS. 3 and 4 will be described. Here, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted. Now, in the second embodiment, a multi-can installation system in which a plurality of boilers 1 (four in the illustrated embodiment) are installed in parallel (the inverter 8,
The fuel supply line 4 and the water supply line 10 are not shown). The multi-can installation system has a steam header 15 common to each of the boilers 1, and the steam header 15 is provided with the pressure sensor 9. And
On the basis of a signal from the pressure sensor 9, the number controller 1
6 controls the amount of combustion in each of the boilers 1.

For example, as shown in FIG. 4, the number of combustions of each of the boilers 1 is determined depending on the range of the steam pressure in the steam header 15. In FIG. 4, H indicates the boiler 1 in a high combustion state, and L indicates a boiler 1 in a low combustion state.
Is shown.

In each of the boilers 1, when the combustion amount is switched from the high combustion amount to the low combustion amount or from the low combustion amount to the high combustion amount, the combustion amount is switched in the same manner as in the first embodiment. Is controlled to output the switching instruction signal at an early stage. The contents of this control are the same as in the first embodiment, and a detailed description thereof will be omitted. Further, in the second embodiment, similarly to the first embodiment, in each of the boilers 1, when shifting from the standby state to the low combustion,
It is preferable to carry out the control for starting the prepurge early, according to the implementation.

In the second embodiment, the same functions and effects as those of the first embodiment can be obtained. Further, in the second embodiment, since the steam pressure value for changing the combustion amount is set finer than in the first embodiment, the present invention can be more suitably applied.

[0033]

According to the present invention, it is possible to output the combustion amount switching instruction signal earlier in consideration of the time delay at the time of switching the combustion amount, and to greatly improve the followability to the load change. Can be. Therefore, steam with a stable pressure can be always supplied. In addition, it is possible to suppress an increase in the number of times of starting and stopping, and it is possible to extend the life of equipment attached to the boiler.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing switching of a combustion amount corresponding to a change in steam pressure in the configuration of FIG. 1;

FIG. 3 is an explanatory view schematically showing a configuration of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the relationship between the steam pressure in the steam header and the number of boilers burned in the configuration of FIG. 4;

[Description of Signs] 1 Boiler

Claims (4)

[Claims] In a boiler for controlling a combustion amount in multiple stages, a gradient of a detection value for combustion control is detected during combustion and a combustion amount switching instruction signal is output based on the gradient. Boiler control method. And calculating a time required for the detected value to reach a predetermined value on the basis of the gradient. 2. The method for controlling a boiler according to claim 1, wherein 3. The boiler control method according to claim 1, wherein a gradient of the detected value is detected during standby, and a combustion start instruction signal is output based on the gradient. 4. The boiler control method according to claim 1, wherein the detected value is a steam pressure or a tapping temperature.