JPH0343523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler device equipped with a device for controlling steam temperature and reducing the NO x emission level by recirculating exhaust gas into the furnace, and in particular, the present invention relates to a boiler device equipped with a device for controlling steam temperature and reducing the NO _x emission level by recirculating exhaust gas into the furnace. The present invention relates to a boiler device suitable for those having a furnace.

In recent years, the use of clean natural gas as fuel for boilers has been increasing as a pollution prevention measure. However, gaseous fuels such as natural gas tend to cause oscillatory combustion because they form short flames due to their nature. When this oscillatory combustion occurs, resonance vibration of the air column occurs within the space of the boiler furnace, duct, etc., generating severe noise and, in some cases, causing an accident that may damage equipment. Therefore, prevention of oscillatory combustion has become an important issue, especially in boilers using gaseous fuel. Conventional means for solving this problem have employed means for predicting or monitoring the occurrence of resonance vibrations. That is, this method focuses on the fact that only the vibration intensity of a specific frequency grows and generates resonant vibration from the state where the vibration intensity is randomly fluctuating in the combustion equipment, and calculates the average amplitude I. The ratio I ₁ /I ₀ of the amplitude _{I 1} of the resonance component to 0 is monitored to predict the occurrence of vibration. However, this means is only a means for early predicting resonance vibrations, and is not a means for preventing vibrational combustion itself, which is the cause of resonance vibrations. Therefore, methods of preventing oscillatory combustion by increasing the length of the burner flame are currently being considered, and a new burner element structure is being considered as a specific method.

Incidentally, recently, in the case of gas-fired boilers, a structure in which the bottom of the furnace is horizontal (a flat hopper) has been adopted in order to reduce the height of the furnace and make the furnace more compact. In such a flat hopper, the flame of the lowest stage burner is affected by the recirculated exhaust gas supplied from the bottom of the furnace, resulting in oscillatory combustion. This will be explained with reference to FIGS. 1 to 3.

FIG. 1 is a schematic diagram of a boiler system employing a conventional flat hopper. In the figure, 1 is a header to which water to be heated is supplied, 2 is a water-cooled wall consisting of a boiler tube and its fins that pass water from header 1, 3 is a furnace, 4 is the flame of each burner, and 5 is a The combustion exhaust gas from the furnace 3 is shown. 6 is a super heater, 7 is a reheater, 8 is a super heater, and 9 is an economizer, all of which are provided in the flame and combustion exhaust gas passages. 10 is a gas recirculation fan for sucking in part of the combustion exhaust gas and introducing it into the furnace; 12 is a wind box for introducing the recirculated exhaust gas from the gas recirculation fan; 13 is a recirculation exhaust gas passage; 14 is furnace 3
A recirculating exhaust gas inlet is provided at the bottom of the furnace and introduces the recirculating exhaust gas from the wind box into the furnace, 15a and 15b are the lowest burners among the burners, and 4a and 4b are the burners 15a and 15b, respectively.
showing a flame.

2 is a plan view of the flat hopper taken along arrow A--A in FIG. 1, and FIG. 3 is a sectional view of the water cooling wall shown in FIGS. 1 and 2. As can be seen in FIG. 2, the input port 14 is elongated in the central portion of the flat hopper. As shown in FIG. 3, the water cooling wall 2 is composed of a boiler tube 16 through which water from the header 1 passes and its fins 17, and the furnace 3 is sealed by these boiler tube 16 and fins 17.

In such a boiler device, water supplied from the economizer 9 to the header 1 receives radiant heat mainly from the flame 4 while rising in the boiler tube 16 of the water-cooled wall 2, and becomes high-temperature steam. It is heated by heaters 6 and 8 and becomes superheated steam. On the other hand, the flame 4 cooled by the water-cooled wall 2 is further cooled by a super heater 6, a reheater 7, an economizer 9, etc., and becomes combustion exhaust gas 5, which is discharged. This combustion exhaust gas 5 is partially sucked in by a gas recirculation fan 10 and passed through a wind box 12 from an inlet 14 in order to control the steam temperature at the outlet of the reheater 7 and to lower the NO _x emission level. It is put into the furnace 3. In this case, the recirculated exhaust gas is introduced into the furnace 3 approximately at the center through the elongated inlet 14 provided at approximately the center of the flat hopper.

By the way, when the amount of recirculated exhaust gas introduced from the bottom of the furnace increases, the lowermost burners 15a and 15b
It is well known that the flames 4a and 4b formed by the above are affected by this, and oscillatory combustion is likely to occur. Therefore, as mentioned above, even if an attempt is made to lengthen the flame using a special burner element and prevent the occurrence of oscillating combustion, in a combustion apparatus employing a flat hopper, the bottom stage burners 15a and 15b are Flame 4 formed by
Since the distance between a, 4b and the inlet 14 is inevitably reduced, the flames 4a, 4b are more susceptible to the influence of recirculated exhaust gas, which causes oscillatory combustion. Furthermore, if the distance between the flames 4a, 4b and the inlet 14 is small, the radiation from the flames will reach the inner surface of the wind box 12 through the inlet 14, so the inner surface of the wind box 12 must be protected with a thick refractory material. There was also the problem of not being able to do so.
In order to avoid these points, flame 4a,
4b and the inlet 14, and increasing this distance has the contradictory problem of becoming a serious constraint for making the furnace more compact.

The present invention has been made in view of such conventional problems, and its purpose is to be able to prevent the occurrence of oscillating combustion, to be able to be configured in a compact furnace, and to reduce the size of the furnace in the depth direction. The object of the present invention is to provide a boiler device that can control the temperature distribution of the boiler.

To achieve this objective, the present invention provides a furnace and
A boiler device comprising a means for recirculating exhaust gas from the furnace from a lower part of the furnace into the furnace, a plurality of exhaust gas inlets for distributing and injecting the exhaust gas from a plurality of locations into the lower part of the furnace;
The present invention is characterized by providing partitions for dividing each of these exhaust gas inlets and dampers arranged within each of these partitions.

Exhaust gas is introduced into the furnace in a distributed manner through each exhaust gas inlet. When this exhaust gas is introduced, the amount of exhaust gas introduced into each exhaust gas inlet is appropriately controlled by each damper.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 4 is a schematic configuration diagram of a boiler device to explain the principle of the present invention. In the figure, parts that are the same as those shown in FIG. 1
8 is a wind box into which recirculated exhaust gas from the gas recirculation fan 10 is introduced. This window box 18 is similar to the wind box 1 of the conventional device.
Unlike 2, it is configured to cover almost the entire surface of the flat hopper. Reference numeral 19 denotes an inlet for injecting the recirculated exhaust gas from the wind box 18 into the furnace 3, and the inlet is distributed at 10 locations in the flat hopper. Arrow 20 indicates the path of recirculated exhaust gas. This input port 19 is shown in FIGS. 5 and 6.
This is shown even more clearly in the figure.

FIG. 5 is a plan view of the flat hopper taken along the arrow B--B in FIG. 4, and FIG. 6 is a sectional view of the water cooling wall constituting the flat hopper. From FIG. 5, it can be clearly seen that a total of 10 inlets 19 are distributed and arranged, 5 in parallel at the front of the furnace 3 and 5 in parallel at the rear. Figure 6 shows
This figure shows the configuration of the input port 19, and the fins 17 of the boiler tubes 16 are configured to have a gap between adjacent boiler tubes 16.
That is, the fins 17a of one boiler tube 16
The fins 17b of the boiler tube 16 adjacent to the fins 17b are tilted in substantially the same direction and overlapped with each other with a gap 21 between them. Each of these gaps 21 is the input port 1
9.

When the gas recirculation fan 10 is operated to supply recirculated exhaust gas to the wind box 18, the recirculated exhaust gas is supplied to the fin 1 at the 10 inlets 19.
It is supplied into the furnace 3 through the gap 21 between 7a and 17b. In this case, looking at the state in which the recirculated exhaust gas is supplied into the furnace 3, the recirculated exhaust gas in the conventional device is supplied so as to separate the flame 4a of the lower stage burner 15a from the flame 4b of the lower stage burner 15b opposite thereto. On the other hand, in the apparatus shown in FIGS. 4 to 6, the flow does not separate the flames 4a and 4b, and the influence of the recirculated exhaust gas on the flames 4a and 4b is different from that between the two flames 4a and 4b. There is a big difference between them.

This difference in influence will be explained based on the flame temperature distribution diagram in the furnace shown in FIG. In Figure 7, the horizontal axis represents the dimensionless depth of the furnace 3,
0 represents the front of the can, 0.5 represents the center of the can, and 1.0 represents the rear of the can.
Further, the flame temperatures of the flames 4a, 4b of the lowest stage burners 15a, 15b are plotted on the vertical axis. A curve _B1 shown by a solid line is a temperature distribution curve of flame temperature in the conventional apparatus, and a curve _B2 shown by a broken line is a temperature distribution curve of flame temperature in the apparatus shown in FIGS. As is clear from the figure, in the conventional device (curve B ₁ ),
The flame temperature at the center of the furnace is low, and the flame temperature at the front and rear of the can is high. In other words, the temperature distribution has peaks at both ends. This is because the temperature of the recirculated exhaust gas is as low as approximately 350°C, and this is concentrated only in the center of the furnace, which lowers the temperature in the center, but the influence of the recirculated exhaust gas is small at both ends. This is to prevent a drop in temperature. Such temperature distribution becomes more pronounced as the distance between the flames 4a, 4b and the input port becomes smaller. On the other hand, in the devices shown in FIGS. 4 to 6 (curve B ₂ ), the temperature distribution is flat in the depth direction, and the flames 4a,
No temperature drop area was observed in the center of the furnace regardless of the distance between 4b and the inlet. Looking at the temperature distribution of the flame in the bottom burner, we can see that the temperature distribution of the conventional device that supplies recirculated exhaust gas to the center of the furnace is similar to the temperature distribution of short flames that tend to cause oscillating combustion. (Temperature distribution with peaks at both ends), whereas the temperature distribution of equipment that supplies recirculated exhaust gas in a distributed manner has a temperature distribution characteristic of a long flame that is difficult to cause oscillating combustion (almost flat). temperature distribution). Therefore, the fourth
It is clear that the device shown in Figures 6 to 6 has a great effect in preventing oscillatory combustion.

On the other hand, the radiation of the flame 4 attempts to pass through each inlet 19 into the wind box 18, but as shown in FIG.
cannot pass through. Only the radiation reflected from the boiler tube 16 or the fins 17 can pass through the gap 21, but the reflectance of these radiations is about 0.2, and the transmission of radiation due to reflection is minimal. It is. Therefore, the wind box 18 does not reach a high temperature, and a thick refractory material or the like is not required.

In this way, in the apparatus shown in Figs. 4 to 6, gaps are formed between the fins of the water cooling wall constituting the flat hopper to form the inlet for injecting the recirculated exhaust gas, and this inlet is installed at 10 locations. Because they are installed in separate locations, it is possible to prevent the occurrence of oscillatory combustion, and the wind box does not require thick refractory material, simplifying its structure. Since the distance between the furnace and the furnace can be reduced, the furnace can be made smaller.

FIG. 8 is a schematic configuration diagram of a boiler device according to an embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 4 are given the same reference numerals, and description thereof will be omitted. 22
is each input port 19 in the window box 18.
Partition 23 is provided corresponding to the partition 22.
This is a damper provided in the passage to the input port 19 formed by.

The recirculated exhaust gas supplied into the windbox 18 by the gas recirculation fan 10 is fed into each inlet 1 formed by a partition 22 as indicated by the arrow 24.
9 and is charged into the furnace through the charging port 19. In this case, by adjusting the opening degree of the damper 23, the flow rate of the recirculated exhaust gas at each input port 19 can be controlled. Therefore, it is possible to control the temperature distribution of the flames 4a and 4b of the lowest stage burners 15a and 15b in the depth direction of the furnace, and to control the heat absorption characteristics of the water-cooled walls in the furnace, and to re-inject the flames 4a and 4b in the furnace depth direction. It is also possible to suppress NO _x generation by injecting circulating exhaust gas in a concentrated manner.

In this way, in this embodiment, a partition and a damper are provided at each inlet of the configuration shown in Figs. 4 to 6, so that vibration combustion is prevented, the structure of the wind box is simplified, and the furnace is made smaller. Not only can the temperature distribution in the depth direction of the furnace be controlled, but the temperature distribution can be optimized to prevent oscillating combustion, thereby reliably preventing oscillating combustion. In addition, since the temperature distribution in the depth direction of the furnace can be controlled, the heat absorption characteristics of the water-cooled wall inside the furnace can be controlled, and NO _x
The occurrence of can be effectively reduced.

In the description of each of the above embodiments, a boiler device having a flat hopper has been described, but the present invention is not limited to this, and can also be applied to a boiler device having a gentle slope of the bottom surface of the furnace. Further, the number of input ports is not limited to 10, and it goes without saying that a plurality of input ports may be used.

As described above, in the present invention, a plurality of inlets for injecting recirculated exhaust gas are distributed in the lower part of the furnace, and each inlet is provided with a partition and a damper, so that the temperature distribution in the depth direction of the furnace is Therefore, the temperature distribution can be optimized to prevent oscillatory combustion, and oscillatory combustion can be reliably prevented. Furthermore, since the temperature distribution in the depth direction of the furnace can be controlled, the heat absorption characteristics of the water-cooled wall in the furnace can be controlled, and the generation of NO _x can be effectively reduced.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a conventional boiler equipment, Figure 2
The figure is a plan view of the flat hopper seen from the arrow A-A in Figure 1, Figure 3 is a cross-sectional view of the water cooling wall shown in Figures 1 and 2, and Figure 4 is a diagram of a boiler system illustrating the principle of the present invention. Schematic configuration diagram, Figure 5 is a plan view of the flat hopper seen from the arrow B-B in Figure 4, Figure 6 is a sectional view of the water cooling wall that constitutes the flat hopper shown in Figure 5, and Figure 7 is the flame temperature in the furnace. The distribution diagram, FIG. 8, is a schematic configuration diagram of a boiler device according to an embodiment of the present invention. 2...Water cooling wall, 3...Furnace, 4, 4a, 4b...
...Flame, 10...Gas recirculation fan, 16...Boiler tube, 17, 17a, 17b...Fin, 18...Wind box, 19...Inlet, 21...Gap, 22...Partition, 23... …damper.

Claims (1)

[Scope of Claims] 1. A boiler device equipped with a furnace and means for recirculating exhaust gas from the furnace from a lower part of the furnace into the furnace, wherein the exhaust gas is distributed from a plurality of locations in the lower part of the furnace. 1. A boiler device comprising: a plurality of exhaust gas inlets for injecting waste gas; partitions for dividing these exhaust gas inlets; and dampers disposed within each of the partitions. 2. The boiler device according to claim 1, wherein each of the exhaust gas inlets is a gap formed in a fin between tubes in a lower water-cooled wall of the furnace.