JP2017198380A - Boiler and method of controlling boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler configured to suppress variation in EGR quantity and thus stabilize combustion performance.SOLUTION: According to the present invention, a boiler comprises: a combustion chamber; a burner for heating the inside of the combustion chamber; an air blower for supplying combustion air to the burner through a combustion flow passage; an exhaust gas path for guiding an exhaust gas out of the combustion chamber; an exhaust gas recirculation path connecting the exhaust gas path and an intake of the air blower together; and control means of controlling the burner into combustion in at least two combustion states which are a first combustion state and a second combustion state less in combustion quantity than the first combustion state, the boiler comprising a damper at the intake of the air blower so that while the intake amount of outside air by the air blower is maintained during transition to the second combustion state, the opening area of the intake of the air blower is made smaller by the damper.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a boiler that recirculates a part of exhaust gas and burns it, and a control method for the boiler.

  Conventionally, there is a boiler that reduces the NOx concentration discharged from the exhaust gas passage by circulating a part of the exhaust gas to the intake side, mixing it with fuel gas and fuel air, and jetting and burning the mixed gas . For example, the boiler described in Patent Document 1 includes an exhaust gas recirculation path that connects an exhaust gas path (chimney) and a suction port of a blower on the intake side, thereby recirculating exhaust gas with a reduced oxygen concentration to the intake side. Let As a result, the combustion temperature in the burner is lowered, and as a result, the NOx concentration contained in the exhaust gas can be lowered.

JP 2004-60984 A

  However, in the boiler of Patent Document 1, there is a problem that the recirculation gas flow rate per unit time (hereinafter referred to as EGR amount) varies greatly depending on the combustion conditions, and as a result, the combustion performance of the burner becomes unstable. I found it to happen.

  This invention is made | formed in view of such a situation, and it aims at providing the control method of this boiler provided with the structure which suppresses the fluctuation | variation of the amount of EGR, and stabilizes combustion performance.

  According to the present invention, a combustion chamber, a burner that heats the combustion chamber, a blower that supplies combustion air to the burner via a combustion channel, an exhaust gas path that extracts exhaust gas from the combustion chamber, An exhaust gas recirculation path connecting the exhaust gas path and the suction port of the blower, and the burner are burned in at least two combustion states of a first combustion state and a second combustion state having a smaller combustion amount than the first combustion state. A boiler having a control means for controlling, wherein a damper is provided at a suction port of the blower, and when moving to the second combustion state, the amount of outside air taken in by the blower can be maintained while being maintained, A boiler is provided that reduces the opening area of the inlet of the blower by means of a damper.

  In the case of a step value control boiler, a proportional boiler, etc., in a state where the combustion amount is small compared to a state where the combustion amount is large, the differential pressure between the exhaust gas recirculation passage, that is, the exhaust gas passage side and the combustion passage side is small. Therefore, it has been noted that the fluctuation of the EGR amount due to the draft fluctuation in the exhaust gas passage (the fluctuation of the ventilation due to the fluctuation of the outside air temperature, etc.) becomes relatively large. And by providing a damper at the suction port of the blower and reducing the opening area of the suction port of the blower with the damper while maintaining the intake amount of the outside air into the blower in a state with a small amount of combustion, the exhaust gas side The inventors have come up with the present invention to increase the differential pressure on the combustion flow path side.

  According to such a configuration, fluctuations in the EGR amount can be reduced, and combustion performance can be stabilized.

  Hereinafter, various embodiments of the present invention will be exemplified. The following embodiments can be combined with each other.

  Preferably, when moving to the second combustion state, the control means controls the rotation speed of the inverter of the blower to be higher than the rotation speed corresponding to the second combustion state and / or the combustion flow path. The main damper provided is controlled to be larger than the cross-sectional area of the combustion flow path corresponding to the second combustion state.

  Preferably, the blower includes a plurality of suction ports, and at least one of the suction ports includes the damper.

  According to the present invention, a combustion chamber, a burner for heating the combustion chamber, a blower for supplying combustion air to the burner via a combustion air passage, and an exhaust gas passage for exhausting exhaust gas from the combustion chamber, And an exhaust gas recirculation path connecting the exhaust gas passage and the blower suction port, and the burner has at least two combustion states of a first combustion state and a second combustion state having a smaller combustion amount than the first combustion state. In the control method of the boiler to be burned in, when moving to the second combustion state, the damper provided in the suction port of the blower, while maintaining the intake amount of the outside air to the blower, Provided is a boiler control method for reducing the opening area of a suction port of a blower.

  Preferably, when shifting to the second combustion state, the control is performed such that the rotational speed of the inverter of the blower is higher than the rotational speed corresponding to the second combustion state, and the cross-sectional area of the combustion air passage is set to the combustion air. At least one of the enlargement control is performed by a main damper provided on the road.

It is explanatory drawing which shows schematic structure of the boiler which concerns on embodiment of this invention. It is sectional drawing when the blower and exhaust gas recirculation path of the boiler of FIG. 1 are cut | disconnected by the XX cross section of the same figure. It is a block diagram which shows control of the boiler of FIG. It is sectional drawing when the blower and exhaust gas recirculation path of the boiler which concern on the modification of this invention are cut | disconnected by the XX cross section of FIG. It is sectional drawing when the air blower and exhaust gas recirculation path of the boiler which concerns on the other modification of this invention are cut | disconnected in the XX cross section of FIG. It is a figure which compares and shows the Example of the control method of the boiler which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described. Various characteristic items shown in the following embodiments can be combined with each other. The invention is established independently for each feature.

<Boiler>
The boiler 1 according to the first embodiment of the present invention includes a combustion chamber 3 having a large number of water pipes 2, a burner 4 for heating the water pipes 2, and a burner 4 as shown in the explanatory view of the longitudinal section of FIG. A blower 5 for supplying combustion air, a gas supply path 6 for supplying fuel gas to the burner 4, a water supply path 7 for supplying water to the water pipe 2, an exhaust gas path 8 for extracting exhaust gas from the combustion chamber 3, and an exhaust gas path 8 and an exhaust gas recirculation path 9 connecting the suction port 51 (see FIG. 2) of the blower 5 and a control means 10 (see FIG. 3) for controlling the boiler 1.

Combustion chamber 3, the can body which absorbs the heat of the fuel by the burner 4 is produced by burning is not less, and connects between the lower header 11 and upper header 12 with a number of water pipes 2 . In the water pipe 2, water is appropriately supplied from the lower header 11 through the water supply path 7, and the water level in the water pipe 2 is maintained. The combustion chamber 3 is provided with a burner 4 at one end (left side in FIG. 1), and an exhaust gas path 8 is connected to the other end (right side in FIG. 1).

  The water in each water pipe 2 is heated by the combustion gas from the burner 4 and is led out as steam from the upper header 12 to the steam path 13 via a steam separator (not shown). Steam is sent to various steam-using facilities via a steam header or the like. On the other hand, the combustion gas produced by the burner 4 exchanges heat with the water in each water pipe 2 and is then discharged from the exhaust gas path 8 as exhaust gas. Note that the exhaust gas path 8 may be provided with an economizer (not shown) for preheating the feed water with residual heat.

  In this embodiment, the burner 4 is a premixed burner, and the burner 4 is supplied with combustion air and fuel gas in an amount corresponding to the amount of combustion through the combustion flow path 14. Combustion air is sent to the burner 4 by the blower 5 through the combustion channel 14.

  As shown in FIG. 2, the blower 5 includes two suction ports 51 and 52 for sucking outside air and a discharge port 53 (see FIG. 1) for sending air to the combustion flow path 14. The exhaust gas recirculation path 9 is connected to the suction port 51, and the recirculation gas from the exhaust gas path 8 is taken in simultaneously with the outside air. On the other hand, the suction port 52 is provided with a plate-shaped suction port damper 55 so as to be rotatable about a rotation axis orthogonal to the flow path direction. The suction port damper 55 is rotatably held in the suction port 52, whereby the inclination angle of the suction port damper 55 can be adjusted and the air flow rate sent to the burner 4 can be adjusted. The inlet damper 55 may be configured to be opened and closed by the control means 10 or manually opened and closed.

  Moreover, the air blower 5 is provided with the inverter 56 and the motor 57, as shown in FIG. The flow rate of the combustion air is adjusted by the rotational speed of the motor 57, and the rotational speed of the motor 57 is controlled by the frequency of the inverter 56. The frequency of the inverter 56 is controlled by a drive signal from the control means 10. Instead of or in addition to this, the flow rate of the combustion air may be adjusted by the main damper 15 provided in the combustion flow path 14.

  On the other hand, the fuel gas is supplied from a gas supply path 6 as shown in FIG. The fuel gas is ejected in the combustion channel 14, mixed with the air from the blower 5, and sent to the burner 4. The gas supply path 6 is provided with a shielding valve 61 for switching between supply and stop of combustion gas, and a flow rate adjusting valve 62 is provided downstream of the shielding valve 61. By changing the opening degree of the flow rate adjusting valve 62 according to the drive signal from the control means 10 according to the combustion amount, it is possible to adjust the air ratio according to the combustion amount.

  As described above, the exhaust gas recirculation path 9 connects a part of the exhaust gas discharged through the exhaust gas path 8 to the combustion channel 14 side by connecting the exhaust gas path 8 and the suction port 51 of the blower 5. This is recirculated into the combustion chamber 3. Thus, by recirculating the exhaust gas whose oxygen concentration is reduced to the intake side, the combustion temperature in the burner 4 is reduced, and as a result, the NOx concentration contained in the exhaust gas can be reduced. A recirculation adjustment damper 91 is installed in the exhaust gas recirculation path 9, and the recirculation adjustment damper 91 is controlled to be opened and closed by the control means 10.

  The control means 10 is configured as a control unit, and controls each part of the boiler 1 such as control of the supply amount of combustion air by the blower 5 and control of the supply amount of combustion gas by the flow rate adjusting valve 62. At this time, for example, control is performed so that the ratio of combustion air and fuel gas is set. The steam amount and steam pressure generated by the boiler 1 are adjusted by the control of the control means 10.

<Operation of boiler>
Next, the operation of the boiler 1 according to this embodiment will be described. The boiler 1 implement | achieves each operation | movement, when the control means 10 controls the operation | movement of each part. The control means 10 drives the blower 5, the shielding valve 61 of the gas supply path 6 and the flow rate adjustment valve 62 to start combustion in the burner 4. The boiler 1 burns fuel with a burner 4 to form a flame, heats the water pipe 2 with combustion gas generated by the combustion of the fuel, and generates steam.

  Here, the boiler 1 of this embodiment is configured to be controlled in two combustion modes: a high combustion state (first combustion state in the claims) and a low combustion state (second combustion state in the claims). Is done. Low combustion is combustion where the amount of combustion is lower than that of high combustion. When the amount of fuel supplied during high combustion is 100%, the amount supplied during low combustion is set to 50%, for example. Is done. The fuel supply mode described below is realized by controlling the blower 5 and the flow rate adjusting valve 62 by the control means 10.

  First, at the time of high combustion, the flow rate adjusting valve 62 of the gas supply path 6 is opened to supply the fuel gas to the burner 4, and the blower is supplied with fuel air corresponding to the supply amount of the fuel gas. 5 is controlled. Here, at the time of high combustion, the inlet damper 55 of the blower 5 and the recirculation adjustment damper 91 of the exhaust gas recirculation path 9 are both opened. Thereby, the combustion air required at the time of high combustion can be obtained from outside air and exhaust gas. In order to set the ratio of the amount of exhaust gas to the amount of combustion air to a predetermined ratio that minimizes the generation of NOx, the opening degree of the suction damper 55 or the recirculation adjustment damper 91 may be adjusted.

  Next, at the time of low combustion, the opening amount of the flow rate adjustment valve 62 of the gas supply path 6 is adjusted to reduce the supply amount of the fuel gas, and the rotational speed of the blower 5 is reduced accordingly, and the fuel air Adjust the supply amount. At this time, the exhaust gas to be recirculated is adjusted by restricting the recirculation adjustment damper of the exhaust gas recirculation path 9, and the ratio of the exhaust gas amount to the combustion air amount is adjusted to be the same at high combustion and low combustion. To do. Further, at the time of low combustion, the inlet damper 55 of the blower 5 is also throttled. Thereby, the opening area in the two suction inlets 51 and 55 of the air blower 5 becomes smaller than the time of high combustion.

Here, at the time of low combustion, the differential pressure between the exhaust gas recirculation path 9 side and the combustion flow path 14 side of the exhaust gas recirculation path 9 is smaller than that at the time of high combustion. The amount of exhaust gas recirculated greatly fluctuates due to the fluctuation. Specifically, assuming the incompressibility of the exhaust gas, if the EGR amount is Q, the air density is ρ, the cross-sectional area of the exhaust gas path is A, and the differential pressure is ΔP,
Is true. And, if the fluctuation pressure due to the draft fluctuation in the exhaust gas passage is P, and the EGR amount considering this is Q ′,
Therefore, when the differential pressure ΔP is small, the influence of the pressure P on the EGR amount Q ′ due to the draft fluctuation becomes large. The draft fluctuations in the exhaust gas passage 8 are caused by changes in the outside air temperature due to seasonal fluctuations, changes in the temperature of the combustion chamber at the start of combustion and during combustion, and a plurality of boilers 1 are installed in the boiler chamber. For example, the influence of other boilers when exhaust gases from a plurality of boilers 1 are exhausted collectively.

  In this regard, in the conventional boiler, the amount of air supply is reduced by restricting the damper (secondary damper) provided in the combustion flow path at the time of low combustion. The fluctuation of the ratio of the amount of exhaust gas due to recirculation with respect to was not able to be suppressed.

  On the other hand, in the boiler 1 according to the present embodiment, the intake damper 55 (primary damper) provided in the intake port 52 of the blower 5 is throttled to restrict the intake of outside air from the intake port 52. Thus, the air is made difficult to flow, and the inverter 56 controls the rotation speed of the blower 5 to be increased. As a result, the force with which the blower 5 sucks the air in the exhaust gas recirculation path 9 increases, the differential pressure between the exhaust gas path side and the combustion flow path side increases, and the fluctuation of the EGR amount can be reduced, and the combustion performance is reduced. It is possible to stabilize. Note that the intake port damper 55 of the blower 5 is opened in the high combustion state because the load (the number of rotations and the rotation torque) of the blower exceeds the limit when the intake port damper 55 is throttled, and the necessary combustion is required. This is because the amount of air cannot be discharged.

  In addition, with the control which raises the rotation speed of the air blower 5, or it replaces with this control, you may perform control which enlarges the cross-sectional area of the combustion flow path 14 with the main damper 15. FIG. FIG. 6 shows a comparison between Examples 1 to 3 of the conventional boiler and the boiler 1 according to the present embodiment. In the conventional example and Examples 1 to 3, the discharge amount of the blower is substantially the same. On the other hand, in the first embodiment, the rotational speed of the blower 5 is set to be higher than that in the conventional example in the low combustion state, and in the second embodiment, the opening degree of the main damper 15 is set larger than that in the conventional example in the low combustion state. . Here, “the rotational speed of the blower in the low combustion state” in the conventional example is “the rotational speed corresponding to the second combustion state” in the claims. Further, in the third embodiment, the rotational speed of the blower 5 is set to be higher than that of the conventional example in the low combustion state, and the opening degree of the main damper 15 is also made larger than that of the conventional example. Such control of the first to third embodiments makes it possible to reduce fluctuations in the EGR amount in the low combustion state as compared with the conventional example.

In addition, this invention can be implemented also with the following aspects.
In the above embodiment, the boiler 1 is configured to be controlled in two combustion modes of high combustion and low combustion, but the present invention is a multi-stage value control boiler that is controlled in three or more combustion modes, It is also possible to apply to a proportional boiler whose quantity can be controlled continuously. In these cases, it is preferable that the inlet damper 55 is opened only during high combustion, and the inlet damper 55 is closed during low combustion. Alternatively, it is also conceivable that the inlet damper 55 is opened above a certain combustion mode, and the inlet damper 55 is closed when operating below the combustion mode. Furthermore, it is also possible to adopt a configuration in which the opening degree of the inlet damper 55 is adjusted in multiple stages according to a plurality of combustion modes.
In the above embodiment, as shown in FIG. 2, the two suction ports 51 and 52 of the blower 5 are configured to suck outside air from directions perpendicular to each other, but as shown in FIG. It is also possible to arrange 51 and 52 horizontally and to have these suction ports 51 and 52 suck in outside air from the same direction.
In the above embodiment, the exhaust gas recirculation path 9 is connected to the suction port 51 out of the two suction ports 51 and 52, and the suction port damper 55 is provided in the suction port 52. However, as shown in FIG. In addition, the blower 5 may include only one suction port 51, and the exhaust gas recirculation path 9 may be connected to the suction port 51 and the suction port damper 55 may be installed. In the case of this configuration, the exhaust gas recirculation path 9 is connected to the downstream side of the suction port damper 55, that is, the discharge port 53 side. In addition, it is also possible to provide three or more suction ports in the blower.
-Although the boiler 1 of the said embodiment was provided with the suction inlet damper 55 as a means to restrict | limit the air intake amount of the air blower 5, it can replace with a damper and can be set as the structure provided with an electromagnetic valve.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation and change are possible within the range of the summary of invention.

  1: boiler, 3: combustion chamber, 4: burner, 5: blower, 8: exhaust gas passage, 9: exhaust gas recirculation passage, 10: control means, 14: combustion passage, 15: main damper, 51, 52: Suction port, 55: Suction port damper, 56: Inverter, 91: Recirculation adjustment damper

Claims (5)

A combustion chamber, a burner that heats the combustion chamber, a blower that supplies combustion air to the burner via a combustion flow path, an exhaust gas path that leads exhaust gas from the combustion chamber, and the exhaust gas path and the blower An exhaust gas recirculation path connecting the suction port, and control means for controlling the burner to burn in at least two combustion states of a first combustion state and a second combustion state having a smaller combustion amount than the first combustion state; A boiler with
When the damper of the blower is provided with a damper and the second combustion state is entered, the opening area of the suction port of the blower is reduced by the damper while maintaining the amount of outside air taken in by the blower. boiler.   When moving to the second combustion state, the control means is provided in the control and / or the combustion flow path for making the rotation speed of the inverter of the blower higher than the rotation speed corresponding to the second combustion state. The boiler according to claim 1, wherein the main damper performs control to be larger than a cross-sectional area of the combustion flow path corresponding to the second combustion state.   The boiler according to claim 1, wherein the blower includes a plurality of suction ports, and the damper is provided in at least one of the suction ports. A combustion chamber; a burner that heats the combustion chamber; a blower that supplies combustion air to the burner via a combustion air passage; an exhaust passage that extracts exhaust gas from the combustion chamber; and the exhaust passage and the blower An exhaust gas recirculation path connected to the suction port, wherein the burner is burned in at least two combustion states of a first combustion state and a second combustion state having a smaller combustion amount than the first combustion state. There,
When moving to the second combustion state, the damper provided at the suction port of the blower reduces the opening area of the suction port of the blower while maintaining the amount of outside air taken into the blower. Boiler control method.   When shifting to the second combustion state, the combustion air passage is provided with a control for making the rotation speed of the inverter of the blower higher than the rotation speed corresponding to the second combustion state, and a cross-sectional area of the combustion air passage. The boiler control method according to claim 4, wherein at least one of the control to be increased by the main damper is performed.