JP2023034570A - boiler - Google Patents

Abstract

An object of the present invention is to provide a boiler capable of converging an air ratio within an appropriate range at any combustion amount. A blast path for sending air into a boiler main body, a fuel supply path for supplying fuel to the boiler main body, and a first position of the blast path provided in the fuel supply path and a position closer to the first position than the first position. A first control valve that adjusts the degree of opening according to the differential pressure with a second position on the downstream side, and a second control valve that is provided downstream of the first control valve in the fuel supply path and adjusts the degree of opening. , a control unit that controls the amount of combustion from the first amount of combustion to a second amount of combustion that is larger than the first amount of combustion, and controls the opening of the second adjustment valve; A reference opening that serves as a reference for the opening of the regulating valve is predetermined according to the amount of combustion controlled by the control unit, and the control unit adjusts the opening to the reference opening determined according to the amount of combustion to be controlled. A boiler that controls the opening degree of the second regulating valve based on. [Selection drawing] Fig. 2

Description

The present invention relates to boilers.

Conventionally, there is a boiler provided with a mechanical proportional valve that adjusts the opening degree based on the flow rate (pressure) of the combustion air on the fuel supply line that supplies fuel to the nozzle (see, for example, Patent Document 1). ). Mechanical proportional valves have fewer parts than electronic proportional valves, so they are less prone to failure and have higher safety.

Japanese Unexamined Patent Application Publication No. 2008-2787

For mechanical proportional valves in conventional boilers, the maximum opening is generally set so that the air ratio is appropriate for the flow rate of combustion air at the maximum combustion amount, and the combustion at the minimum combustion amount is The minimum opening is set so that the air ratio is appropriate for the air flow rate. On the other hand, in the case of an intermediate combustion amount that is greater than the minimum combustion amount and smaller than the maximum combustion amount, the opening corresponding to the actual flow rate of the combustion air between the set minimum opening and the maximum opening. degree, and the air ratio is left to chance. For this reason, when the amount of combustion is intermediate, the air ratio cannot be converged within the appropriate range, and the air ratio is too low and the concentration of nitrogen oxides (NOx) in the exhaust gas (hereinafter referred to as "NOx value) exceeds a certain value, or the air ratio is too high, exceeding the combustion limit (threshold value) and causing a misfire. In particular, in recent years, as interest in the environment has increased, in order to reduce air pollution by regulating the emission concentration and emission amount of air pollutants such as NOx, boilers can be set at any combustion amount. It is also required to converge the air ratio in the appropriate range.

SUMMARY OF THE INVENTION The present invention has been devised in view of such circumstances, and an object thereof is to provide a boiler capable of converging the air ratio within an appropriate range for any amount of combustion.

In order to achieve the above object, a boiler according to one aspect of the present invention includes: a blowing passage for sending air into a boiler main body; a fuel supply passage for supplying fuel to the boiler main body; , a first regulating valve that adjusts the degree of opening in accordance with a differential pressure between a first position of the air passage and a second position downstream of the first position; and a first regulating valve in the fuel supply passage. is provided on the downstream side and controls the combustion amount between the second adjustment valve that adjusts the opening degree and the first combustion amount to the second combustion amount that is larger than the first combustion amount, a control unit for controlling the degree of opening of the second regulating valve, wherein the reference degree of opening, which serves as a reference for the degree of opening of the second regulating valve, is predetermined according to the amount of combustion controlled by the control unit. The controller controls the degree of opening of the second control valve based on a reference degree of opening determined according to the amount of combustion to be controlled.

According to the above configuration, while using the first control valve that adjusts the degree of opening according to the differential pressure, the reference degree of opening of the second control valve is such that the air ratio is within the appropriate range according to the amount of combustion. By adjusting the flow rate of the fuel supplied to the boiler main body by the second control valve, the air ratio can be converged within the appropriate range for any amount of combustion.

Preferably, the first regulating valve has a first degree of opening at a first differential pressure between the first position and the second position that can be taken when the first regulating valve is controlled to the first combustion amount. , is predetermined so that a second opening is achieved at a second differential pressure between the first position and the second position that can be obtained when the combustion amount is controlled to the second combustion amount, and Between the first opening and the second opening when the operation is controlled to a third combustion amount between the first combustion amount and the second combustion amount The degree of opening is determined according to the pressure difference between the first position and the second position, and the reference degree of opening of the second control valve is set to a third degree of opening according to the first combustion amount. A fourth degree of opening is determined according to the second amount of combustion, a fifth degree of opening is determined according to the third amount of combustion, and the first opening of the first control valve and the The third degree of opening of the second regulating valve is a specific state in which the air ratio is equal to or less than the threshold value and the concentration of nitrogen oxides in the exhaust gas is equal to or less than a predetermined value when the operation is controlled to the first combustion rate. and the second opening degree of the first control valve and the fourth opening degree of the second control valve are set to the above The fifth opening degree of the second control valve is set to a specific state, and when the fifth opening degree of the second control valve is controlled to the third combustion amount, the opening degree of the first control valve is Even if the opening is determined according to the differential pressure between the first position and the second position, the opening is set to the specific state.

According to the above configuration, the first adjustment is performed not only when the operation is performed by controlling the first combustion amount and the second combustion amount, but also when the operation is performed by controlling the third combustion amount. While the degree of opening of the valve is set according to the differential pressure, the second control valve can be controlled to be in a specific state.

Preferably, a third amount of combustion between the first amount of combustion and the second amount of combustion is defined according to each of the first amount of combustion and the second amount of combustion. A reference opening different from the opening is defined.

According to the above configuration, regardless of the reference opening degree according to each of the first combustion amount and the second combustion amount, by determining the reference opening amount according to the third combustion amount, It becomes possible to strictly adjust the air ratio so as to achieve a more appropriate air ratio.

Preferably, the reference opening determined according to the first amount of combustion and the reference opening determined according to the second amount of combustion are both fully closed and fully open. It is set to an opening that is not

According to the above configuration, the reference opening corresponding to the third combustion amount is also made smaller than the reference opening determined according to each of the first combustion amount and the second combustion amount. It is also possible to adjust it more flexibly.

It is a figure which shows typically a schematic structure of a boiler. (a) and (b) show an example in which the air ratio during the middle combustion stage is not within the proper range when the fuel flow rate is adjusted only by the first control valve, and (c) and (d) show an example of the second control valve. FIG. 5 is a diagram showing an example in which the air ratio is within the appropriate range in any combustion stage including the middle combustion stage when the flow rate of fuel is adjusted by the first adjustment valve and the second adjustment valve.

An embodiment of the present invention will be described below with reference to the drawings. First, referring to FIG. 1, a schematic configuration of a boiler according to the present embodiment will be described.

As shown in FIG. 1, the boiler 1 includes a boiler body 2, a blower 3 for sending air into the combustion chamber of the boiler body 2 through an air passage 30, an exhaust passage 4 for leading exhaust gas from the boiler body 2, A fuel supply line 5 for supplying fuel to the boiler main body 2 , a water supply line (not shown) for supplying water to the boiler main body 2 , and a control section 6 for controlling the operation and operation of the boiler 1 are provided. In addition, although an example in which the fuel is gas will be described, the fuel is not limited to gas such as gas, and may be liquid such as oil.

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

Air supplied from the blower 3 is supplied as combustion air to the burner 20 in the boiler main body 2 via the air duct 30 . The flow rate of the combustion air can be adjusted by providing a damper 7 in the blowing passage 30 and adjusting the position (opening degree) of the damper 7, or alternatively or in addition to this, by adjusting the fan of the blower 3 using an inverter. This is done by changing the rotation speed of the

For example, the control unit 6 selects, for example, a low combustion stage (first combustion amount), an intermediate combustion stage (third combustion amount), a high combustion stage (second combustion amount), as a plurality of combustion stages with different combustion amounts. amount) to control to either combustion stage. The control unit 6 controls the combustion stages according to the set target steam pressure and the steam pressure of the steam header. The control unit 6 controls the blower 3 and the damper 7 so as to have a mode (for example, rotation speed, frequency, opening) according to the combustion stage being controlled, and supplies combustion air in an amount according to the combustion stage. do.

The fuel supply path 5 includes an on-off valve 11 (solenoid valve) for opening and closing the path, a first adjustment valve 12 for adjusting the flow rate of the fuel to be supplied, and a bypass line downstream of the first adjustment valve 12. is provided, and an orifice 16 and a second control valve 17 are provided in parallel. The first regulating valve 12 functions as a regulating valve capable of adjusting the flow rate of fuel supplied to the boiler main body 2 according to the flow rate of the supplied combustion air, and also has a shutoff function. As the first regulating valve 12 in the present embodiment, for example, a governor that is mechanically and automatically adjusted to the degree of opening according to the flow rate of the supplied combustion air is exemplified. The valve is not limited to this as long as it is a control valve whose opening is adjusted according to the flow rate.

In this embodiment, a combustion air decompression member 8 such as a punching metal is provided downstream of the damper 7 in the air passage 30 . The blowing passage 30 communicates with the first regulating valve 12 provided on the fuel supply passage 5 via the first communication passage 14 at the first position P<b>1 upstream of the combustion air pressure reducing member 8 . Further, the blowing passage 30 communicates with the first regulating valve 12 provided on the fuel supply passage 5 via the second communication passage 15 at the second position P2 downstream of the combustion air pressure reducing member 8 .

The first regulating valve 12 adjusts the differential pressure between the first communication passage 14 and the second communication passage 15 (basically, it is the same as the differential pressure across the combustion air pressure reducing member 8 in the blow passage 30). The opening is configured to change according to the The first regulating valve 12 is a pressure equalizing valve whose opening degree is mechanically adjusted so that the differential pressure to be introduced and the pressure of the fuel to be supplied (pressure on the secondary side) are equalized. A branch path 13 is provided from the downstream flow path of the governor. The first regulating valve 12 is adjusted so that the pressure on the secondary side obtained from the branch passage 13 corresponds to the differential pressure across the combustion air pressure reducing member 8 in the blowing passage 30 into which it is introduced. can be adjusted. As a result, if the differential pressure across the combustion air pressure reducing member 8 increases, the flow rate of fuel that can pass through the first regulating valve 12 increases, and the differential pressure across the combustion air pressure reducing member 8 decreases. For example, the flow rate of fuel that can pass through the first regulating valve 12 decreases.

Regarding the regulating valve that adjusts the degree of opening according to the differential pressure, such as the first regulating valve 12 in the present embodiment, the boiler is generally controlled to a minimum combustion amount (for example, a low combustion stage) and operated. In this case, the air ratio (also referred to as the air-fuel ratio) with respect to the flow rate of the combustion air to be supplied falls within an appropriate range at the time of the possible differential pressure between the first position P1 and the second position P2. When the fuel is supplied to the opening (minimum opening) and the boiler is controlled to the maximum combustion amount (for example, high combustion stage) and operated, the first position P1 and the second position P2 that can be taken at that time At the time of the differential pressure between be done. As a result, at the minimum combustion amount and the maximum combustion amount, combustion can be performed with an appropriate air ratio. An appropriate air ratio is not, for example, a low air ratio at which the concentration of NOx in the exhaust gas exceeds a certain value, nor a high air ratio at which a misfire occurs beyond the combustion limit. Air ratio in (appropriate range). A state in which the air ratio is appropriate is also called a specific state.

On the other hand, when the boiler is operated by controlling the amount of combustion in the middle between the minimum amount of combustion and the maximum amount of combustion (for example, middle combustion stage), the opening of the regulating valve is initially set. The opening is left to chance depending on the minimum opening/maximum opening, the flow rate of combustion air at the minimum/maximum combustion amount, and the actual differential pressure at the intermediate combustion amount, etc. As a result, The air ratio will also be left up to the situation. The opening of the regulating valve when it is operated by controlling the amount of combustion in the middle is, for example, ("maximum opening" - "minimum opening") ÷ ("flow rate of combustion air at maximum combustion amount" - " Combustion air flow rate at minimum combustion amount") x ("Combustion air flow rate at intermediate combustion amount" - "Combustion air flow rate at minimum combustion amount") + "Minimum opening", etc. become. For this reason, when the amount of combustion is intermediate, the air ratio cannot be converged within the appropriate range, and the air ratio is too low, causing the concentration of NOx in the exhaust gas to exceed a certain value. If the ratio is too high, the combustion limit may be exceeded and a misfire may occur.

A specific example will now be described with reference to FIGS. 2(a) and 2(b). 2(a) and 2(b) show an example in which the air ratio during the middle combustion stage does not fall within the appropriate range when the fuel flow rate is adjusted only by a governor such as the first control valve 12. there is In FIGS. 2(a) and 2(b), the horizontal axis indicates the high combustion stage, the middle combustion stage, and the low combustion stage, and the vertical axis indicates the amount of combustion for each combustion stage, and the amount of combustion when operated at that amount. The differential pressure, the opening of the governor as a function of the differential pressure, and the air ratio are shown. In FIG. 2, it is assumed that the amount of burn in the high burn stage is 100%, the amount of burn in the medium burn stage is 60%, and the amount of burn in the low burn stage is 25%. Further, in FIGS. 2(a) and 2(b), when the boiler is operated while being controlled to the high combustion stage, the differential pressure between the first position P1 and the second position P2 that can be taken at that time is "a", the maximum opening of the first control valve that supplies fuel with an air ratio in the appropriate range for "a" is initially set to "80%", and the boiler is controlled to a low combustion stage. When it is operated, the differential pressure between the first position P1 and the second position P2 that can be taken at that time becomes "c", and the fuel having the air ratio in the appropriate range for "c" is supplied. It is assumed that "30%" is initially set as the minimum opening degree of one adjustment valve. In addition, the percentage with respect to the degree of opening indicates the ratio of opening with respect to full opening.

On this premise, in FIG. 2(a), when the boiler is operated while being controlled to the middle combustion stage, the differential pressure is "b1", and the opening degree of the first regulating valve is corresponding to "b1". As a result, the amount of fuel supplied becomes too much for the flow rate of the combustion air supplied, and the air ratio is too low, causing the concentration of NOx in the exhaust gas to remain constant. is exemplified. Further, in FIG. 2(b), when the boiler is operated while being controlled to the middle combustion stage, the differential pressure becomes "b2" (for example, b2<b1), and the opening degree of the first regulating valve becomes "b2 , and the amount of fuel supplied becomes too small for the flow rate of the combustion air supplied. A case in which there is a risk of Thus, when the flow rate of fuel is adjusted only by a governor such as the first control valve 12, the opening degree of the first control valve is adjusted so that the air ratio is within the appropriate range in the high combustion stage and the low combustion stage. can be initialized, but in the intermediate combustion stage, the initially set minimum/maximum opening, the flow rate of combustion air at the minimum/maximum combustion amount, and the actual differential pressure at the intermediate combustion amount, etc. The degree of opening depends on the situation, and the air ratio also depends on the situation. As a result, it cannot necessarily be said that the air ratio can be converged within the appropriate range.

Therefore, in the present embodiment, the maximum flow rate of fuel that can be supplied (passed) by the first control valve 12 is adjusted according to the differential pressure, and the second control valve 17 is positioned downstream of the first control valve 12. is provided to adjust the degree of opening of the second control valve 17 to a reference degree of opening corresponding to the amount of combustion. Specifically, the minimum opening and the maximum opening of the first adjusting valve 12 are larger when the first adjusting valve 12 alone is adjusted (the flow rate of the supplied combustion air can pass through). is initially set, and by adjusting the opening of the second control valve 17 to an opening corresponding to the amount of combustion, out of the fuel passing through the first control valve 12, Adjust the flow rate of the supplied fuel. The reference degree of opening of the second control valve 17 according to the amount of combustion is set so that the air ratio is within the proper range when the degree of opening of the first control valve 12 becomes the degree of opening corresponding to the actual differential pressure. degree is predetermined.

Regarding the initial setting of the first regulating valve 12, when the boiler 1 is operated by controlling the amount of combustion to the minimum (for example, a low combustion stage), the first position P1 and the second position P2 that can be taken at that time At the time of the differential pressure, the minimum opening is initially set as the opening that enables the supply of a larger flow rate than the fuel flow rate at which the air ratio is in the appropriate range, and the boiler 1 is controlled to the maximum combustion amount (for example, high combustion stage). In the case of operating with the first position P1 and the second position P2 at that time, it is possible to supply a flow rate larger than the flow rate of fuel in which the air ratio is in an appropriate range. degree as the maximum opening. Further, when the boiler 1 is controlled and operated in the middle combustion stage, the initially set minimum / maximum opening degree, the flow rate of the combustion air at the minimum combustion amount / maximum combustion amount, and in the middle combustion stage The opening is left to chance depending on the actual differential pressure. Based on these assumptions, as the opening degree of the second control valve 17, a reference opening degree is set in advance so that the air ratio during combustion in the boiler 1 is within an appropriate range for each combustion amount (high combustion stage, medium combustion stage, low combustion stage). The controller 6 controls the degree of opening of the second control valve 17 based on a reference degree of opening predetermined according to the amount of combustion to be actually controlled. It is assumed that the reference opening degree of the second control valve 17 for each combustion amount is calculated and specified in advance at the stage of designing or installing the boiler, and stored in advance in the storage section of the control section 6 or the like.

A specific example will now be described with reference to FIGS. 2(c) and 2(d). FIGS. 2(c) and 2(d) show that when the fuel flow rate is adjusted by the first control valve 12 and the second control valve 17, the air ratio is appropriate in any combustion stage including the middle combustion stage. Examples within the range are shown. FIG. 2(c) shows an example in which the air ratio is converged within an appropriate range by adjusting the opening degree of the second control valve 17 in contrast to the example shown in FIG. 2(a). . FIG. 2(d) shows an example in which the air ratio is converged within an appropriate range by adjusting the opening degree of the second control valve 17 in contrast to the example shown in FIG. 2(b). ing. 2(c) and 2(d) show the opening degree of the second control valve 17 in addition to the items on the vertical axis shown in FIG. 2(a) and the like.

In FIGS. 2(c) and 2(d), when the boiler is operated while being controlled to the low combustion stage, the minimum opening of the first regulating valve 12 with respect to the differential pressure "c" is "40% " (first opening) is initially set, and the boiler is controlled to the high combustion stage and operated, the maximum opening of the first regulating valve 12 is set to "100% ' (second degree of opening) is initially set. In this manner, a large opening is initially set as compared with FIG. 2(a) and the like. In addition, "75%" (third opening) is set as the opening degree of the second control valve 17 when the boiler is controlled to the low combustion stage and operated, and the boiler is controlled to the high combustion stage and operated. "80%" (fourth degree of opening) is set as the degree of opening of the second regulating valve 17 when it is turned on. The degree of opening of the second control valve 17 of "75%" is obtained when the boiler is operated while being controlled to the low combustion stage, and the degree of opening of the first control valve 12 is set to the minimum degree of "40%". Second, the opening is such that the air ratio at the time of combustion in the boiler 1 is within the appropriate range. The degree of opening of the second control valve 17 of "80%" corresponds to the case where the boiler is operated while being controlled to the high combustion stage, and the degree of opening of the first control valve 12 is set to the maximum degree of "100%". The opening is such that the air ratio at the time of combustion in the boiler 1 is within the appropriate range. Therefore, FIGS. 2(c) and 2(d) show that the air ratios in the low combustion stage and the high combustion stage are within appropriate ranges.

On the other hand, in FIG. 2(c), when the boiler 1 is controlled to operate in the middle combustion stage, the differential pressure becomes "b1" as illustrated in FIG. A case is illustrated in which the opening is "77%" as the opening according to "b1". In addition, in FIG. 2(d), when the boiler 1 is controlled and operated in the middle combustion stage, the differential pressure becomes "b2" (for example, b2<b1) as illustrated in FIG. 2(c). , the opening of the first regulating valve 12 is "70%" as the opening according to "b2". In this way, even if the opening of the first control valve 12 is left to chance, the air ratio at the time of combustion in the boiler 1 is set as the opening according to the middle combustion stage of the second control valve 17. is within the appropriate range (fifth opening). Specifically, in the case of FIG. 2(c), "71%" is set as the reference opening degree corresponding to the middle combustion stage of the second control valve 17, and the air ratio in the middle combustion stage is within the appropriate range. It is shown that it is inside. Further, in the case of FIG. 2(d), "78%" is set as the reference opening degree corresponding to the middle combustion stage of the second control valve 17, and the air ratio in the middle combustion stage is within the appropriate range. It is shown that As a result, as shown in FIGS. 2(c) and 2(d), not only the low combustion stage and high combustion stage, but also the air ratio in the middle combustion stage is within the appropriate range. ing.

As described above, in this embodiment, as shown in FIG. A regulating valve 17 is provided, and as illustrated in FIGS. 2(c) and 2(d), the reference opening of the second regulating valve 17 is within the proper range of the air ratio according to the amount of combustion (combustion stage). The second adjusting valve 17 adjusts the flow rate of the fuel supplied to the boiler 1 . As a result, the air ratio can be converged within the appropriate range for any combustion amount.

Further, as illustrated in FIGS. 2(c) and 2(d), the reference opening of the second control valve 17 corresponding to the minimum opening of the first control valve 12 and the low combustion stage is The opening is set so that the air ratio is within the appropriate range when the valve is operated under control. In addition, the maximum opening of the first control valve 12 and the reference opening of the second control valve 17 corresponding to the high combustion stage are such that the air ratio is within the appropriate range when the operation is controlled to the high combustion stage. determined by the degree of opening. Further, the reference degree of opening of the second control valve 17 corresponding to the intermediate combustion stage is set so that the degree of opening of the first control valve 12 depends on the pressure difference when the intermediate combustion stage is controlled and operated. Even in the case of opening, the opening is set so that the air ratio is within the appropriate range. As a result, the degree of opening of the first regulating valve 12 is adjusted according to the differential pressure not only when the low combustion stage and the high combustion stage are controlled and operated, but also when the middle combustion stage is controlled and operated. Although the degree of opening is left to chance, the air ratio can be converged by the second control valve 17 so as to be within the proper range.

Further, in the present embodiment, the reference degree of opening of the second control valve 17 corresponding to the intermediate combustion stage is set to "71%" in FIG. 2(c) and "78%" in FIG. 2(d). ing. These numerical values are "75%" set as the reference opening for the low combustion stage and "80%" set as the reference opening for the high combustion stage in FIGS. 2(c) and 2(d). It is a different number. In this way, as the reference opening corresponding to the middle combustion stage, the reference opening is determined regardless of the reference opening corresponding to the low combustion stage and the high combustion stage. Strict adjustment is possible so that

Further, in the present embodiment, as shown in FIGS. 2(c) and 2(d), the reference opening degrees of the second control valve 17 corresponding to the low combustion stage and the high combustion stage are respectively "75%". and "80%", both of which are set to an opening degree that is neither fully closed nor fully open. Therefore, the reference opening corresponding to the middle combustion stage can be made larger or smaller than the reference opening during low combustion and high combustion. , and "78%" in FIG. 2(d), which allows more flexible adjustment. For example, it is possible to set the reference opening degree corresponding to the low combustion stage and the high combustion stage to 100%. It is possible to avoid such a restriction that can be adjusted only in the direction of opening smaller than the reference opening according to .

The present invention is not limited to the above embodiments, and various modifications and applications are possible. Modifications of the above embodiments applicable to the present invention will be described below.

In the above embodiment, an example was described in which the opening of the second control valve 17 is controlled based on the reference opening corresponding to the combustion amount. may be corrected by the control device 6 at any time. The control device 6 detects, for example, the air ratio and the NOx concentration in the exhaust gas at any time, and based on the detected air ratio and the NOx concentration in the exhaust gas, for example, the air ratio becomes high and the combustion limit approaches. The second is controlled according to the combustion amount so that the amount of fuel supplied suddenly increases when the NOx concentration in the exhaust gas is high, and the amount of fuel supplied decreases when the NOx concentration in the exhaust gas is high, because the air ratio is low. The opening degree of the regulating valve 17 may be adjusted. Instead of or in addition to this, the control device 6 adjusts the opening degree of the second control valve 17, which is controlled according to the amount of combustion, for example, according to the temperature of the fuel or the temperature of the combustion air. may be

An example in which the boiler 1 in the above embodiment is controlled to one of a plurality of combustion stages with different combustion amounts according to the set target steam pressure and the steam pressure of the steam header (so-called multi-position control) will be described. However, the present invention is not limited to this, and proportional control may be performed according to the set target steam pressure and the steam pressure of the steam header so as to achieve an arbitrary amount of combustion.

In the above embodiment, the orifice 16 is provided in parallel with the second control valve 17 . This orifice 16 is such that even if the second regulating valve 17 fails in the fully open or fully closed state, the pressure loss will be within the range where safe combustion is possible (or the air ratio is within the appropriate range). is desirable. As a result, even if the second regulating valve 17 fails, the operation of the boiler 1 can be continued.

In the above embodiment, an example was described in which the opening of the second control valve 17 is controlled based on the reference opening corresponding to the amount of combustion. It is desirable to make it larger than both the reference opening determined according to the stage and the reference opening determined according to the high combustion stage. Since it is difficult to ignite when the air ratio is high, misfiring can be prevented by temporarily increasing the amount of fuel supply by increasing the opening of the second control valve 17 at the time of ignition.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the meaning and range of equivalents of the scope of the claims.

REFERENCE SIGNS LIST 1 boiler 2 boiler main body 3 blower 4 exhaust passage 5 fuel supply passage 6 control unit 7 damper 8 combustion air pressure reducing member 11 on-off valve 12 first control valve 13 branch passage 14 first communication passage 15 second communication passage 16 orifice 17 third 2 control valve 20 burner 30 air passage

Claims (4)

an air passage for sending air into the boiler body;
a fuel supply path for supplying fuel to the boiler body;
a first adjustment valve provided in the fuel supply path for adjusting the degree of opening in accordance with the differential pressure between a first position of the air blow path and a second position downstream of the first position;
a second regulating valve that is provided downstream of the first regulating valve in the fuel supply path and that adjusts the degree of opening;
a control unit that controls the amount of combustion from a first amount of combustion to a second amount of combustion that is larger than the first amount of combustion, and controls the opening of the second adjustment valve;
A reference opening, which serves as a reference for the opening of the second control valve, is predetermined according to the amount of combustion controlled by the control unit,
The boiler, wherein the controller controls the degree of opening of the second control valve based on a reference degree of opening determined according to the amount of combustion to be controlled. The first regulating valve has a first degree of opening at a first differential pressure between the first position and the second position that can be taken when the first regulating valve is operated while controlling the combustion amount to the first combustion amount. 2, and is predetermined to have a second opening at a second differential pressure between the first position and the second position that can be obtained when the combustion amount is controlled to No. 2, and the first opening is set. and the second combustion amount between the first opening and the second opening and the first The opening degree is according to the differential pressure between the position and the second position,
As for the reference opening degree of the second control valve, a third opening degree is determined according to the first combustion amount, a fourth opening degree is determined according to the second combustion amount, and the third opening degree is determined according to the second combustion amount. A fifth opening is determined according to the amount of combustion of
When the first opening degree of the first adjusting valve and the third opening degree of the second adjusting valve are controlled to the first combustion amount and operated, the air ratio is equal to or less than the threshold value and the exhaust gas is The nitrogen oxide concentration of is set to a specific state below a predetermined value,
The second degree of opening of the first control valve and the fourth degree of opening of the second control valve are set to the degree of opening that brings about the specific state when the operation is controlled to the second combustion amount. and
The fifth degree of opening of the second regulating valve is the difference between the degree of opening of the first regulating valve and the first position and the second position when the third combustion rate is controlled and operated. 2. The boiler according to claim 1, wherein even when the degree of opening corresponds to the pressure, the degree of opening is set to the specific state. A third amount of combustion between the first amount of combustion and the second amount of combustion includes a reference opening determined according to each of the first amount of combustion and the second amount of combustion. 3. The boiler according to claim 1 or 2, wherein different reference openings are defined. The reference opening determined according to the first combustion amount and the reference opening determined according to the second combustion amount are neither fully closed nor fully open. The boiler according to any one of claims 1 to 3, defined in

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