JP7517079B2 - boiler - Google Patents

Description

The present invention relates to a boiler.

Conventionally, there are boilers equipped with combustion devices that perform multi-position control (high combustion, medium combustion, low combustion, etc.) and proportional control by providing an adjustment valve on a fuel supply line that supplies fuel to a nozzle or other ejection section, and controlling a proportional valve (adjusting valve) in conjunction with the flow rate of combustion air to adjust the fuel flow rate (see, for example, Patent Document 1).

JP 2008-2787 A

In the above boiler, due to the control configuration in which the change in the combustion air flow rate is made to precede and the fuel flow rate adjustment is made to follow through through feedback, or the change in the fuel flow rate is made to precede and the combustion air flow rate adjustment is made to follow through through feedback, when the combustion amount is shifted to another combustion amount, a transitional state occurs and the air ratio fluctuates greatly, which may make it difficult to maintain a combustion state with an appropriate air ratio. For example, in the case of a control configuration in which the change in the combustion air flow rate is made to precede and the fuel flow rate adjustment is made to follow through through feedback, when the combustion amount is shifted from low combustion to medium combustion, the increase in the fuel supply follows the increase in the combustion air flow rate, resulting in a period of high air ratio. On the other hand, when the combustion amount is shifted from medium combustion to low combustion, the decrease in the fuel supply follows the decrease in the combustion air flow rate, resulting in a period of low air ratio. In addition, in the case of a control configuration in which the fuel flow rate change is made first and the combustion air flow rate adjustment is made afterwards through feedback, when the combustion amount is shifted from low combustion to medium combustion, a period of low air ratio occurs, while when the combustion amount is shifted from medium combustion to low combustion, a period of high air ratio occurs.

The present invention was conceived in light of this situation, and its purpose is to provide a boiler that can stabilize the air ratio as much as possible when the combustion volume is changing.

To achieve the above object, the boiler of the present invention comprises a supply means for supplying combustion air at a flow rate according to a set combustion amount, an air flow rate detection means for detecting the flow rate of the supplied combustion air, and a fuel flow rate adjustment means for adjusting the flow rate of the supplied fuel according to the flow rate of the combustion air detected by the air flow rate detection means. When a first combustion amount is set, the fuel flow rate adjustment means adjusts the fuel flow rate according to the flow rate of the combustion air detected by the air flow rate detection means so as to achieve a first target air ratio, and when a second combustion amount is set, the fuel flow rate adjustment means adjusts the fuel flow rate according to the flow rate of the combustion air detected by the air flow rate detection means so as to achieve a second target air ratio. During the transition period from the first combustion amount to the second combustion amount, the air ratio between the first target air ratio and the second target air ratio is set as a target air ratio, and the fuel flow rate adjustment means adjusts the fuel flow rate according to the flow rate of the combustion air detected by the air flow rate detection means so as to achieve the target air ratio.

According to the above configuration, when transitioning from the first combustion amount to the second combustion amount, during the transition period, the air ratio between the target air ratio at the first combustion amount and the target air ratio at the second combustion amount is set as the target air ratio, and the flow rate of fuel is adjusted according to the flow rate of combustion air so as to achieve the target air ratio. This prevents the air ratio from changing excessively instantaneously due to changing to the target air ratio at the combustion amount after the change (second combustion amount) when the combustion amount changes (transitions), and as a result, the air ratio fluctuation during the transition of the combustion amount can be controlled as stably as possible. In addition, the present invention can be applied not only to boilers that control the combustion amount in stages, but also to so-called proportional control boilers that can finely control the combustion amount.

Preferably, during the transition period, the fuel flow rate adjustment means sets the target air ratio to an air ratio whose difference from the second target air ratio becomes smaller depending on the time that has elapsed since the transition from the first combustion amount to the second combustion amount was started.

According to the above configuration, when the combustion amount transitions, the target air ratio is set to change continuously so as to gradually approach the second target air ratio, so that the air ratio fluctuations when the combustion amount transitions can be controlled as stably as possible.

Preferably, the fuel flow rate adjustment means subtracts the first target air ratio from the second target air ratio, divides the result by a predetermined transition time required for the supply means to supply a flow rate corresponding to the second combustion amount, multiplies the result by the time elapsed since the transition from the first combustion amount to the second combustion amount was initiated, and adds the result to the first target air ratio to set the resulting air ratio as the target air ratio during the transition period.

With the above configuration, a target air ratio that makes fluctuations more gradual depending on the transition time can be set until the final target air ratio is reached, and the air ratio fluctuations during the transition of the combustion amount can be controlled as stably as possible.

FIG. 2 is a diagram for explaining a schematic configuration of a boiler. 4 is a flowchart illustrating an example of control of a boiler.

<Overview of the Configuration>
A boiler 1 according to an embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a diagram showing a schematic configuration of a boiler 1 according to an embodiment of the present invention.

The boiler 1 includes a boiler body 2 that burns fuel to generate steam, a blower (blowing means) 3 that sends air into the boiler body 2 via an air supply passage 30, a flue 4 that draws out exhaust gases and the like from the boiler body 2, and a fuel supply line (fuel supply passage) 5 that supplies fuel to the boiler body 2. Note that, although an example in which the fuel is gas is described, the fuel is not limited to gases such as gas, and may be a liquid such as oil.

The fuel supply line 5 is connected to the air supply passage 30. The fuel supplied from the fuel supply line 5 is mixed with the air blown from the blower 3 in the air supply passage 30 and supplied to the burner 20 in the boiler body 2.

Air supplied from the blower 3 is supplied as combustion air to the burner 20 in the boiler body 2 via the air supply passage 30. The flow rate of the combustion air is adjusted by providing a damper 7 in the air supply passage 30 and adjusting the position (opening) of the damper 7, or alternatively or in addition, by using an inverter to change the rotation speed of the fan of the blower 3. In this embodiment, the flow rate of the combustion air is adjusted by controlling the opening of the damper 7 and the inverter control of the blower 3.

The fuel supply line 5 is provided with on-off valves (solenoid valves) 11, 12 for opening and closing the flow path, and a fuel supply amount adjustment valve 13. The fuel supply amount adjustment valve 13 functions as a pressure adjustment valve that can adjust the flow rate of fuel supplied to the boiler body 2, and also has a shutoff function. The fuel supply amount adjustment valve 13 is provided downstream of the on-off valves 11, 12, and is a motor valve whose opening is adjusted by the control device 6. Note that the fuel supply amount adjustment valve 13 is not limited to a motor valve as long as it adjusts the flow rate of fuel, and may be, for example, an air-operated control valve.

The control device 6 is realized by a computer that includes a memory, a timer, and an arithmetic processing unit, and controls the fuel supply adjustment valve 13 and the blower 3 based on signals from each electrically connected sensor.

In this embodiment, an _O2 sensor 41 is disposed inside the flue 4. _{The O2} sensor 41 is an oxygen concentration detector that detects the oxygen concentration of the exhaust gas. The _O2 sensor 41 is electrically connected to the control device 6, and the control device 6 obtains current air ratio information based on the measurement value of the _O2 sensor 41.

In this embodiment, the air supply passage 30 is provided with a combustion air pressure reducing member 8, such as a punched metal, downstream of the damper 7. The air flow detection unit 9 detects the pressure difference before and after the combustion air pressure reducing member 8 and outputs differential pressure information. The air flow detection unit 9 is electrically connected to the control device 6. This allows the differential pressure information from the air flow detection unit 9 to be input to the control device 6. The analog signal output from the air flow detection unit 9 is converted to a digital signal and input to the control device 6.

The control device 6 controls the amount of combustion according to the set target steam pressure and the steam pressure of the steam header. The control device 6 controls the blower 3 so that the state (e.g., rotation speed, frequency) corresponds to the controlled amount of combustion, and supplies an amount of combustion air according to the amount of combustion. The flow rate of the combustion air according to the amount of combustion is predetermined. The control device 6 calculates (detects) the flow rate of the combustion air actually supplied to the boiler body 2 based on the differential pressure information detected by the air flow detection unit 9. The control device 6 performs proportional control that allows the amount of combustion to be finely set. Note that the control device 6 is not limited to a proportional control, and may be one that controls the amount of combustion to one of multiple types of combustion stages with different amounts of combustion, for example, one of the low combustion stage L, the medium combustion stage M, and the high combustion stage H.

The control device 6 adjusts the opening of the fuel supply amount adjustment valve 13 based on the calculated flow rate of the combustion air and a target air ratio described below. For example, if the flow rate of the combustion air increases, the opening of the fuel supply amount adjustment valve 13 is increased to increase the fuel flow rate, while if the flow rate of the combustion air decreases, the opening of the fuel supply amount adjustment valve 13 is decreased to decrease the fuel flow rate.

The control device 6 includes a control unit 61 and a storage unit 62. The control unit 61 transmits an opening degree specification signal for specifying the opening degree to the fuel supply amount adjustment valve 13 based on the opening degree adjustment information stored in advance in the storage unit 62. As a result, the fuel supply amount adjustment valve 13 is controlled to an opening degree according to the differential pressure before and after the combustion air pressure reducing member 8, and the flow rate of fuel supplied to the boiler body 2 can be adjusted. The opening degree adjustment information may be, for example, a table that can specify the opening degree of the fuel supply amount adjustment valve 13 according to the differential pressure (or the flow rate of the combustion air calculated from the differential pressure), or may be an arithmetic formula for specifying the opening degree of the fuel supply amount adjustment valve 13 according to the differential pressure (or the flow rate of the combustion air calculated from the differential pressure).

Various information related to the boiler 1 is stored in the memory unit 62, and in this embodiment, a target air ratio, which is a target value of the ratio between the flow rate of the combustion air and the flow rate of the fuel, is stored according to the combustion amount. The opening of the fuel supply amount adjustment valve 13 is specified according to the opening adjustment information based on the pressure difference before and after the combustion air pressure reduction member 8. Therefore, theoretically, the air ratio based on the flow rate of the combustion air and the flow rate of the fuel supplied will converge to an air ratio corresponding to the combustion amount. When the combustion amount is shifted, for example, the inverter frequency of the blower 3 or the opening of the damper 7 is changed to change the air volume, but since there is a restriction on the inverter frequency that can be changed per unit time, it takes a certain amount of time to reach the air volume corresponding to the combustion amount after the shift. In addition, since the opening of the damper 7 is not changed instantly but at a constant speed, it takes a certain amount of time to reach the target opening. Due to these factors, if the fuel supply amount is changed immediately to become the target air ratio corresponding to the combustion amount after the shift, there may actually be a case where it does not converge to the target air ratio. The memory unit 62 stores the transition time Δt required for transitioning from one combustion amount to another combustion amount as various information related to the boiler 1. The transition time Δt is determined for each boiler based on the inverter frequency of the blower 3, the acceleration/deceleration time, the opening degree of the damper 7, the opening/closing speed of the damper 7, etc. For example, there are cases where the blower 3 and the damper 7 are not operated simultaneously, but rather one is operated before the other is operated, in which case the transition time Δt is longer.

In this embodiment, when a transition in the combustion amount is detected during operation of the boiler 1, the timer of the control device 6, for example, starts measuring the elapsed time t that has elapsed since the transition began. The control device 6 calculates and sets, for example, a target air ratio for the transition period based on the measured elapsed time t, a target air ratio that is predetermined according to the combustion amount, and the transition time required Δt. The control device 6 repeatedly performs the process of calculating and setting the target air ratio during the transition period during operation.

Using the target air ratio calculated and set as described above, the control device 6 performs processing for controlling the aperture of the fuel supply amount adjustment valve 13, which is specified in accordance with the aperture adjustment information based on the pressure difference before and after the combustion air pressure reduction member 8. Specifically, for example, when a transition is started from the combustion amount a, which is the target air ratio A, to the combustion amount b, which is the target air ratio B, a transition required time Δt is specified and measurement of the elapsed time t is started, and the target air ratio at the elapsed time t is calculated and set based on the following formula.
(Formula) Target air ratio = A + {(B - A) / Δt} · t
In this way, the air ratio between the target air ratio A at the combustion amount a and the target air ratio B at the combustion amount b, which corresponds to the elapsed time t in the transition period, is set as the target air ratio in the transition period, and the opening degree of the fuel supply amount adjustment valve 13 is controlled according to the flow rate of the combustion air so as to achieve the target air ratio. As a result, the air ratio in the transition period is adjusted to approach an appropriate air ratio immediately after the combustion amount changes (transitions). As a result, the air ratio is prevented from changing excessively instantaneously due to changing to the target air ratio at the combustion amount after the change when the combustion amount changes (transitions), and the air ratio fluctuation during the transition of the combustion amount can be controlled as stably as possible. In addition, since the target air ratio used for the actual control is changed from the target air ratio corresponding to the combustion amount before the transition to the target air ratio corresponding to the combustion amount to be transitioned, it can be applied not only to boilers that control the combustion amount in stages, but also to boilers with proportional control that set an arbitrary combustion amount. Below, such control will be described in more detail.

<Boiler control process>
2 is a flow chart for explaining an example of boiler control according to the present invention. The control device 6 performs this control at regular intervals (for example, one second) and continues to perform this control while the boiler 1 is in operation.

In step S01, it is determined whether or not a change in the combustion amount is necessary based on the detected steam pressure in the steam header and the target steam pressure. If it is not determined in step S01 that a change in the combustion amount is necessary, the process ends. On the other hand, if it is determined in step S01 that a change in the combustion amount is necessary, the process proceeds to step S02.

In step S02, the combustion amount is changed from combustion amount a (first combustion amount) to combustion amount b (second combustion amount). In step S03, the blower 3 is controlled in a manner according to the combustion amount b after the change in step S02 (a manner for setting the rotation speed according to the combustion amount, or a frequency according to the combustion amount, etc.).

In step S04, the target air ratio A (first target air ratio) for the combustion amount a, the target air ratio B (second target air ratio) for the combustion amount b, and the transition time Δt are specified. The transition time Δt is a pre-specified transition time required for the supply means to supply combustion air at a flow rate corresponding to the combustion amount b (second combustion amount), and is the time required to change to the rotation speed corresponding to the combustion amount or the frequency corresponding to the combustion amount when changing from the combustion amount a to the combustion amount b described above. The transition time Δt is calculated from the blower inverter frequency, acceleration/deceleration time, damper opening, opening/closing speed, etc., and is a value determined for each boiler.

In step S05, the measurement of the elapsed time t from the start of the transition is started. In step S06, the air flow rate of the combustion air is detected (calculated) based on the differential pressure detected by the air flow rate detection unit 9.

In step S07, the target air ratio B (second target air ratio) for combustion amount b minus the target air ratio A (first target air ratio) for combustion amount a is divided by the transition time required Δt, multiplied by the time t that has elapsed since the transition from combustion amount a (first combustion amount) to combustion amount b (second combustion amount) began, and added to the target air ratio A (first target air ratio) before the transition to calculate and set the target air ratio at the elapsed time t.

In step S08, the opening of the fuel supply amount adjustment valve 13 is controlled so as to achieve the target air ratio calculated and set in step S07 in relation to the air flow rate detected in step S06.

In step S09, it is determined whether the air flow rate detected in step S06 is a combustion air flow rate corresponding to the combustion amount b. If it is determined in step S09 that the air flow rate detected in step S06 is not a combustion air flow rate corresponding to the combustion amount b, the process proceeds to step S06. On the other hand, if it is determined in step S09 that the air flow rate detected in step S06 is a combustion air flow rate corresponding to the combustion amount b, the process ends.

<About operation>
In the boiler 1 of this embodiment, it is determined that the combustion amount needs to be shifted based on the detected steam pressure and the target steam pressure (step S01, YES), and for example, the current combustion amount a (first combustion amount) is continuously shifted to the target combustion amount b (second combustion amount) (step S02) will be described. By setting the target combustion amount b to be shifted, the blower 3 is controlled to be in a state corresponding to the target combustion amount b (step S03). At this time, it is assumed that the memory unit 62 stores, for example, the target air ratio for each combustion amount and the required transition time between each combustion amount. When shifting from the combustion amount a to the combustion amount b, the target air ratio A (first target air ratio) for the combustion amount a, the target air ratio B (second target air ratio) for the combustion amount b, and the required transition time Δt are specified (step S04), and the measurement of the elapsed time t from the start of the transition is started (step S05). During a transition period (t<Δt) from the current combustion amount a to the target combustion amount b, the air flow rate detection unit 9 performs an air flow rate detection process (step S06). Also, the control device 6 sets an air ratio between the target air ratio A and the target air ratio B as a target air ratio (step S07).

Then, the opening of the fuel supply amount adjustment valve 13 is controlled so as to achieve the target air ratio at the calculated and set elapsed time t in relation to the detected air flow rate (step S08).

The opening of the fuel supply amount adjustment valve 13 is controlled until the detected air flow rate reaches the combustion air flow rate corresponding to the combustion amount b (steps S06 to S09). This makes it possible to adjust the air ratio during the transition period so that it approaches an appropriate air ratio immediately after the combustion amount changes (transitions) from one combustion amount to another. As a result, it is possible to prevent the air ratio from changing excessively instantaneously due to changing to the target air ratio for the combustion amount after the change when the combustion amount changes (transitions), and to control the air ratio during the transition of the combustion amount to be as stable as possible.

In the above, it is preferable that during the transition period, the fuel flow rate adjustment means sets the target air ratio to an air ratio that reduces the difference between the target air ratio B (second target air ratio) of the combustion amount b according to the time that has elapsed since the transition from the combustion amount a to the combustion amount b was started (step S07). As a result, the target air ratio is set to change continuously so as to gradually approach the second target air ratio, so that the air ratio fluctuation during the transition of the combustion amount can be controlled as stably as possible.

In the above, it is preferable that the air flow rate detection unit 9 detects the air flow rate (step S06) and calculates and sets the target air ratio at the elapsed time t based on the following formula (step S07). This makes it possible to set a target air ratio that makes the fluctuations more gradual according to the transition time t until the final target air ratio B is reached, and it is possible to control the air ratio fluctuations during the transition of the combustion amount as stably as possible.
(Formula) Target air ratio = A + {(B - A) / Δt} · t

The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Below, we will explain modifications of the above-described embodiment that can be applied to the present invention.

In the above embodiment, an example was shown in which the transition time Δt required for transitioning from one combustion amount to another combustion amount is stored in the memory unit 62 as one piece of information related to the boiler 1, but this is not limited thereto, and the transition time Δt may be calculated each time the transition begins based on the combustion amounts before and after the transition.

In the above embodiment, an example was described in which the blower 3 is controlled in a manner corresponding to the amount of combustion, the air flow rate (combustion air supply flow rate) is detected based on the differential pressure as shown in step S06 of FIG. 2, and then the opening degree (fuel supply flow rate) of the fuel supply amount adjustment valve 13 is controlled so as to achieve the target air ratio in relation to the air flow rate as shown in step S08. However, the process for adjusting the air ratio is not limited to this, and for example, the opening degree of the fuel supply amount adjustment valve 13 is controlled so as to achieve the opening degree corresponding to the amount of combustion, and the air flow rate (combustion air supply flow rate, for example, the blower 3) may be controlled so as to achieve the target air ratio in relation to the fuel supply flow rate. When detecting the actual fuel supply flow rate, for example, orifices or the like may be provided at multiple locations in the fuel supply line 5 to detect the differential pressure, and the fuel supply flow rate may be detected based on the differential pressure. In this case, the control device 6 uses the calculated and set target air ratio to perform processing to control the state of the blower 3 (e.g., the rotation speed) that is specified based on the fuel supply flow rate.

Even in the case of the above configuration, in the boiler 1, when the combustion amount transitions, the mode (rotation speed, etc.) of the blower 3 may be corrected using the target air ratio stored in the combustion amount before and after the transition. After controlling the opening degree of the fuel supply amount adjustment valve 13 to be the opening degree according to the combustion amount, the blower 3 is controlled to be the target air ratio at the calculated and set elapsed time t in relation to the supply flow rate of the fuel, so that the air ratio during the transition period is adjusted to be closer to the appropriate air ratio immediately after the combustion amount changes (transitions) from one combustion amount to another. As a result, the air ratio during the transition of the combustion amount can be controlled to be as stable as possible. In the above example, an example of adjusting the mode (rotation speed, etc.) of the blower 3 is shown as a method of controlling the air flow rate, but this is not limited to this, and the opening degree of the damper 7 may be adjusted, or both the mode (rotation speed, etc.) of the blower 3 and the opening degree of the damper 7 may be adjusted.

In the above embodiment, when the combustion amount transitions from one combustion amount to another, the target air ratio at the elapsed time t is calculated and set based on a predetermined formula from the detected air flow rate, and the air ratio fluctuation during the transition of the combustion amount is controlled to be as stable as possible. Here, as the control of the air ratio fluctuation during the transition of the combustion amount, the current air ratio information is obtained based on the measurement value of the _O2 sensor 41 provided in the flue 4, and in step S08 of Fig. 2, for example, the current air ratio is compared with the target air ratio, and the opening of the fuel supply amount adjustment valve 13 is controlled by PID control (Proportional-Integral-Differential Controller).

In the boiler 1 in the above embodiment, the fuel supply amount adjustment valve 13 is electronically controlled by the control device 6, but it can also be controlled using a governor. A governor is a valve whose opening is automatically adjusted mechanically based on the air flow rate to the burner 20 so as to keep the air ratio constant. By using such a governor, the opening can be automatically adjusted mechanically by the governor mechanism to control the fuel supply amount based on the pressure difference before and after the combustion air pressure reducing member 8 installed in the middle of the air supply passage 30.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Boiler 2 Boiler body 3 Blower (blower means)
4 Flue 41 _O2 sensor 5 Fuel supply line (fuel supply path)
6 Control device 61 Control unit 62 Memory unit 7 Damper 8 Combustion air pressure reducing member 9 Air flow rate detection unit (flow rate detection means)
11 On-off valve 12 On-off valve 13 Fuel supply amount adjustment valve 20 Burner 30 Air supply path

Claims (3)

A supply means for supplying combustion air at a flow rate corresponding to a set combustion amount;
An air flow rate detection means for detecting a flow rate of the supplied combustion air;
a fuel flow rate adjusting means for adjusting the flow rate of fuel to be supplied in accordance with the flow rate of the combustion air detected by the air flow rate detecting means,
The fuel flow rate adjusting means includes:
adjusting a flow rate of fuel in accordance with a flow rate of combustion air detected by the air flow rate detection means so as to achieve a first target air ratio when a first combustion amount is set;
adjusting the flow rate of fuel in accordance with the flow rate of combustion air detected by the air flow rate detection means so as to achieve a second target air ratio when a second combustion amount is set;
a target air ratio is set to an air ratio between the first target air ratio and the second target air ratio during a transition period from the first combustion amount to the second combustion amount, and the flow rate of fuel is adjusted in accordance with the flow rate of combustion air detected by the air flow detection means so as to achieve the target air ratio. The boiler according to claim 1, wherein the fuel flow rate adjustment means sets, during the transition period, an air ratio whose difference from the second target air ratio becomes smaller depending on the time that has elapsed since the transition from the first combustion amount to the second combustion amount was started. 2. The boiler according to claim 1, wherein the fuel flow rate adjustment means subtracts the first target air ratio from the second target air ratio, divides the result by a predetermined transition time required for the supply means to supply a flow rate corresponding to the second combustion amount, multiplies the result by the time elapsed since the transition from the first combustion amount to the second combustion amount began, and adds the result to the first target air ratio, and sets the air ratio obtained as the target air ratio during the transition period.

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