JP3180938B2 - Water tube boiler and combustion method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water pipe boiler of a type in which a combustion gas is circulated linearly in a cross line direction with respect to a group of water pipes.

[0002]

2. Description of the Related Art Generally, a water tube boiler has a combustion chamber occupying a relatively large volume as a component thereof.
For example, a small multi-tube once-through boiler is manufactured based on a cylindrical water pipe assembly (can body). This is because it is considered that it is desirable to arrange the water pipe in an annular shape and make the inside thereof a combustion chamber in order to improve the heat exchange efficiency with the combustion gas.

[0003] However, such a can structure tends to occupy a relatively large space depending on the installation location and arrangement of the boiler. In recent years, various types of so-called square can structures have been used. (See, for example, Japanese Utility Model Application Laid-Open No. 56-136).
904).

In recent years, due to environmental pollution and the like,
Hazardous combustion emissions from boilers, there is a need in particular NO _X, further reducing the CO and the like. As reducing measures such hazardous combustion emissions, combustion gas temperature, that is, by lowering the temperature of the combustion flame, NO _X, particularly a method and a combustion gas temperature to control the generation of thermal NO _X (thermal NO _X) There is known a method in which CO is oxidized to CO ₂ by keeping the temperature in a certain temperature range to prevent the remaining of CO. More specifically, Jikho 56-4
As disclosed in Japanese Patent Application Laid-Open No. 7777/77, a burner flame is applied to a water cooling wall or the like. The combustion gas temperature (the temperature of the combustion flame) is adjusted by burning the fuel gas or adjusting the combustion temperature, or as disclosed in Japanese Patent Application Laid-Open No. 60-78247. After the adjustment, there is one that oxidizes CO in adiabatic air up to the heat exchanger. In addition, as a measure for reducing thermal NO _{X, a} method of recirculating exhaust gas is known.

[0005]

A conventional boiler having a rectangular can body structure, for example, the above-described boiler having a structure as disclosed in Japanese Utility Model Application Laid-Open No. 56-13690.
Heat exchange in a boiler as disclosed in Japanese Patent Publication No. 4 is performed only by a pair of water pipe panels that define the first and second gas passages in the furnace following the combustion chamber. Less. In addition, since the water pipes are arranged in close contact with each other, a fan-shaped area, a so-called dead water area, is formed between the water pipes that are in contact with each other. In this dead water area, the gas flow rate is lower than that between the water pipe panels. , The heat transfer coefficient to the water pipe is low, and the effective area for the actual heat transfer is smaller, and there is a problem in improving the heat efficiency. Further, as described above, in addition to the first gas passage connected to the combustion chamber, it is necessary to provide a second gas passage through which the combustion gas flows reversely from the first gas passage, so that it is difficult to reduce the size of the can. In this regard, this also becomes an obstacle in improving the thermal efficiency of the can body itself.

[0006] In this boiler, harmful combustion exhaust gas, which is the most important subject in recent years, that is, NO _x , C
No measures are taken to reduce O and the like. That is, on the front surface of the burner, the combustion chamber and the first
Since a gas passage is provided and a wide space exists in front of the burner as a whole, the fuel (including the premixed gas) injected from the burner burns at a high temperature as it is. Therefore, during this combustion, thermal NO _X is generated, and CO
A problem arises that CO is generated by thermal dissociation of ₂ .

Further, in general, the temperature of the combustion gas flow from the burner decreases toward the downstream side due to the heat transfer to the water pipe, and the volume decreases accordingly. In a boiler having a structure arranged in parallel, there is also a problem that the flow velocity is reduced on the downstream side of the combustion gas, and the heat transfer efficiency is significantly reduced.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a burner provided at one end defined by a water pipe wall and an exhaust gas outlet provided at the other end. In almost the entire area of the combustion gas passage, a plurality of water pipes are densely arranged close to the burner to form a water pipe group, and the combustion gas is circulated in the cross direction with respect to the water pipe group. , More than a bare tube
The generation of thermal NOx in the upstream water pipe group by suppressing the upstream combustion gas temperature by the upstream water pipe group
By oxidizing and extinguishing CO while controlling N
Ox and CO are reduced.

[0009]

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 show an embodiment in which the present invention is applied to a rectangular multi-tube type once-through boiler. FIG. 1 shows an arrangement of vertical water pipes in a can body, and FIG. It shows a state of connection between each vertical water pipe and upper and lower headers.

In FIG. 1 and FIG. 2, a water pipe wall 1 forming an outer shell of a can body in a rectangular multi-tube type once-through boiler is formed by arranging a plurality of straight vertical water pipes 1a at equal intervals. By connecting the adjacent vertical water pipes 1a with the fin-shaped members 6, the vertical water pipes 1a are in a state in which the space between the vertical water pipes 1a is closed, and are configured as one rectangular wall member. Thus, the water pipe wall 1 defines the outer shell of the can body and has a function as a heat transfer surface.
Therefore, the water pipe wall 1 has a configuration in which a region in which the heat transfer rate is reduced due to a decrease in the gas flow velocity, that is, a so-called dead water region, is not formed unlike a conventional boiler.
This sufficiently secures an effective heat transfer area, and greatly contributes to improvement in thermal efficiency.

Then, the water pipe wall 1 thus constructed is
Each of the vertical water pipes 1a, 1a,... Constituting a pair of water pipe walls 1, 1 are arranged so that they face each other while maintaining a required interval, and are substantially parallel to each other.
The upper and lower ends are connected to upper and lower headers 10 and 11, respectively. In this embodiment, the upper and lower headers 10,
As shown in FIG. 2, each of the upper headers 10 and the lower headers 11 is connected to an external pipe (not shown) as shown in FIG. ), Etc., and integrated with each other.

A burner 5, such as a premix burner, is provided at one longitudinal end of the pair of water pipe walls 1, 1.
An exhaust gas outlet 8 is provided at the other end. As a result, the pair of water pipe walls 1, 1 and the upper and lower headers 10,
11 form a gas passage 9 through which the combustion gas from the burner 5 passes substantially linearly.

A large number of vertical water pipes 2a, 2a, ..., 3a, 3a, ..., 4a, 4a, ... are provided in the gas passage 9 at intervals allowing the flow of the combustion gas from the burner 5.
Is inserted. At this time, each vertical water pipe 2a, 3a, 4
a between the combustion gas and each vertical water pipe 2a, 3
In order to improve the convective heat transfer efficiency with the a and 4a, it is preferable to set as narrow as possible.
When the gas flow velocity around each of the vertical water pipes 2a, 3a, 4a becomes too fast, the pressure loss becomes large.
The gas flow velocity is slowed down, the convective heat transfer efficiency is reduced, and the number of inserted vertical water pipes 2a, 3a, 4a must also be reduced, which results in a decrease in the heat transfer area, and therefore the amount of heat transfer itself Will also decrease.

The vertical water pipes 2a, 3a, 4a
Are inserted over substantially the entire area of the gas passage 9 while maintaining the above-mentioned interval. As described above, each of the vertical water pipes 2a, 3a, 4 which is inserted almost all over the gas passage 9 is provided.
The upper and lower ends of a are connected to the upper and lower headers 10, 11, respectively, like the vertical water pipes 1a, 1a,... The vertical water pipe 2a facing the burner 5 is disposed at a position relatively close to the burner 5, and the interval between the burner 5 and the vertical water pipe 2a facing the burner 5 is extremely small. . That is, in this embodiment, the arrangement density of the vertical water pipes 2a, 3a, 4a in the gas passage 9 is compared with each other in terms of the distance between the vertical water pipes 2a, 3a, 4a as shown in FIG. This means that they are arranged in a precise state.

Further, of the vertical water pipes 2a, 3a, 4a inserted in the gas passage 9, the pair of water pipe walls 1,
As shown in FIG. 1, the vertical water pipes adjacent to 1 are arranged in a staggered arrangement with the vertical water pipes 1a, 1a,... With such an arrangement, the water pipe walls 1, 1 and the headers 10, 11 and the vertical water pipes 2a, 3a, 4a are formed.
The horizontal width (width in the left-right direction in FIG. 1) of the water pipe assembly 20 can be reduced, and the horizontal width defined for the water pipe assembly 20 (this relates to the cross-sectional area of the headers 10 and 11). More vertical water pipes can be inserted.

According to the water pipe assembly 20 configured as described above, the flow path of the combustion gas from the burner 5, that is, the gas passage 9 can be formed to be relatively long in a straight line. Gas is the last vertical water pipe 4a
The time required to pass through is relatively long.
In other words, the residence time of the combustion gas in the water pipe assembly 20 becomes relatively long, and the combustion gas flows through the vertical water pipes 1a, 2a, 3a, 4 in the gas passage 9.
a and convection heat transfer is performed sequentially, whereby the temperature gradually decreases. Therefore, there is no locally high temperature portion in the entire gas passage 9, and it is possible to more effectively suppress the generation of NO _x , particularly thermal NO _x , and oxidized CO ₂ converts CO by thermal dissociation. Will not be generated again.

Now, the embodiment shown in FIG. 1 will be further described. The vertical water pipes 2a, 3a, and 4a are arranged in two rows along the longitudinal direction between the water pipe walls 1 and 1 so that the burners are arranged in two rows. A predetermined number of pipes are arranged at regular intervals from the 5 side to the exhaust gas outlet 8 side, and each vertical water pipe is a bare pipe 2a, a finned pipe 3a, and an erofin pipe 4a from the upstream side. And each of these vertical water pipes 2a, 3a, 4
a constitutes three water pipe groups 2, 3, and 4 having different heat transfer surface densities (heat transfer surface areas per unit flow path length of combustion gas),
These first to third water pipe groups 2, 3, and 4 are connected to the gas passage 9
Inside, from the burner 5 side to the exhaust gas outlet 8 side, the heat transfer surface densities are arranged in ascending order.

With this configuration, the combustion gas from the burner 5 flows through the gas passage 9 from the first water pipe group 2 composed of the bare pipes 2a, the second water pipe group 3 composed of the finned pipes 3a, and the erofin pipe 4a. The convection heat passes through the third water pipe group 4 while performing convection heat transfer, and from the exhaust gas outlet 8 via an economizer (not shown) or directly into a chimney (not shown).
Spill out of. Therefore, as described above, the combustion gas has a high temperature and a large volume on the upstream side, but has a low temperature on the downstream side due to convective heat transfer to the vertical water pipes 2a, 3a, and 4a. descend. However, in the present invention, since the heat transfer surface density increases toward the downstream side, the heat transfer amount in each of the vertical water pipes 2a, 3a, 4a ranges from the upstream vertical water pipe 2a to the downstream vertical water pipe 4a. The temperature does not decrease, but becomes substantially uniform overall, and the temperature of the combustion gas gradually decreases.

As a result, with the can having the above-described structure,
Combustion surface load is 600 to 1200 × 10 ⁴ Kcal / m ²
h, about 1200 ° C, B at point A in the figure.
About 550 ° C at point C and about 370 ° C at point C
ing. Therefore, in the can body of the present invention,
Even in the water tube group with low heat transfer surface density, the combustion gas temperature
Is kept low, the calling of the NO _x in particular thermalNO _x
Generation can be prevented, and the combustion gas temperature
Up to 1200 ° C even if CO is generated
Is oxidized to CO ₂ on the downstream side, and gradually
As the temperature drops, CO ₂ separates again to CO
Can also be prevented.

Here, a specific example in which a premix burner is used as the burner 5 will be further described.
If this were the premixed burner to burn by supplying premixture of air ratio 1.3, NO _X, as compared to the conventional 1/3
To about 1/2, and the CO was reduced to less than 10 ppm. This NO _X, C
As for the O value, the circulation rate was set to 10 in a boiler equipped with an exhaust gas circulation device.
%, But in this example,
In such a form that the combustion gas is circulated in only one direction without circulating at all, there is such an action of reducing harmful combustion exhausts, and a complicated piping for exhaust gas circulation is not required, and the structure becomes extremely simple.

In this embodiment, the burner 5
As described above, the case of using a premix burner was explained.
The reason is as follows. That is, in either the diffusion combustion burner or the premix burner,
As a pre-combustion stage, it is necessary to go through a process of mixing fuel and air. However, in the case of a diffusion combustion burner, time is required simultaneously with an area or space for mixing fuel and air. Therefore, in the diffusion combustion burner, in the initial stage of combustion with the can lead to non-uniform mixing of fuel and air, which generates a localized high-temperature parts, a increase in the NO _X, CO is generated at the same time This creates an easy situation. As a result, particularly for the oxidation of CO, a high-temperature region for oxidizing is required. However, if this high-temperature region cannot be adopted, the amount of emitted CO increases, and if a high-temperature region is provided, the depth of the can And the size of the can becomes large.

On the other hand, in the premix burner,
Since the fuel and the air are mixed in advance, the fuel is passed through the mixing process (that is, the area or space and time point required in the diffusion combustion burner) and immediately proceeds to the combustion process. without producing localized hot spots, i.e. can be performed relatively good combustion with little generation of NO _X, also the CO is generated on the upstream side, since the oxidation of CO takes place downstream In addition, it is based on the knowledge that the amount of CO emission can be reduced even if the depth is relatively short. In this regard, it is further added that a premixed burner as the burner 5 used in the water pipe assembly 20 according to the present invention is extremely effective in terms of downsizing the can body and measures for reducing harmful combustion exhaust emissions. It is based on the knowledge that it is.

Next, FIG. 3 showing a second embodiment of the present invention will be described. In the embodiment shown in FIG. 3, the water pipe walls 1 and 1 have a length substantially up to the middle of the boiler can body and a narrow horizontal width (width in the horizontal direction in FIG. 3) on the downstream side. A water pipe group 2 having a series of bare vertical water pipes 2a arranged in series is arranged between the water pipe walls 1 and 1. On the downstream side of the water pipe group 2, for example, as shown in the illustrated embodiment, a gas passage connected to the gas passage 9 formed on the upstream side in a state continuous with the downstream ends of the water pipe walls 1 and 1, respectively. The heat insulating walls 7 are arranged on both sides so as to form the pipe 9, and the water pipe group 4 composed of the two rows of erofin pipes 4 a is arranged between the heat insulating walls 7, 7.

In the second embodiment, as in the first embodiment (FIGS. 1 and 2), the heat transfer per unit flow path length from the upstream side to the downstream side in the flow direction of the combustion gas is performed. As a result, the water pipe assembly, that is, the can body itself, improves the heat transfer efficiency,
O _X, reduction of harmful emissions of CO and the like can be a reduced effectively.

[0026]

As is evident from the foregoing description, according to the present invention, the combustion gases, by convection heat transfer between the water tubes, gradually descends with its temperature is kept low, NO x, harmful combustion exhaust such as _CO It is possible to suppress the generation of waste, and it is extremely effective as a pollution control measure concerning harmful combustion exhaust which is the most important subject in recent years. Incidentally, the NO _x reduction effect according to the present invention, will be described based on concrete experimental results are as follows. That is, FIG. 4 is a boiler having a combustion chamber made of water tube assembly forming a conventional cylindrical, shows the product characteristics of the NO _x in the boiler according to the present invention, according to the present invention, NO _x is reduced to about 1/2 as compared with a conventional boiler, NO _x in the normal operating point has a very low and 30 to 40 ppm.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional explanatory view showing an embodiment in which the present invention is applied to a rectangular multi-tube once-through boiler.

FIG. 2 is a partially cutaway front view of the water pipe assembly of FIG. 1 as viewed from a burner side, in which a burner is omitted.

FIG. 3 is a schematic cross-sectional explanatory view showing another embodiment different from the square multi-tube once-through boiler of FIG. 1;

4 is a graph showing a generation characteristic of the NO _X in the boiler and the conventional boiler according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 water pipe wall 1a vertical water pipe 2 first water pipe group 2a vertical water pipe (bare pipe) 3 second water pipe group 3a vertical water pipe (tube with fins) 4 third water pipe group 4a vertical water pipe (erofin pipe) 5 burner 6 fin-shaped member 7 Insulation wall 8 Exhaust gas outlet 9 Gas passage 10 Upper header 11 Lower header

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Tanaka 7, Horie-cho, Matsuyama-shi, Ehime Miura Industrial Co., Ltd. (72) Inventor Seiji 7, Horie-cho, Matsuyama-shi, Ehime Miura Industrial 56) References JP-A-60-205105 (JP, A) JP-A-60-78247 (JP, A) JP-A-55-134202 (JP, A) JP-A-52-15902 (JP, A) 62-63651 (JP, U) JP 46-10241 (JP, B1) JP 39-1002 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H22B 21 / 00

Claims (3)

(57) [Claims] 1. A burner provided with the image made the one side with water tube walls, substantially the entire combustion gas passage formed by providing the exhaust gas outlet at the other end, close a number to the nearest present water tubes of the burner A water pipe group is formed by arranging the pipes, and the combustion gas is circulated in the cross direction with respect to the water pipe group, and the water pipe group is formed on the upstream water pipe group consisting of a bare pipe.
Controlling the temperature of the combustion gas on the more upstream side to the water pipe on the upstream side
CO2 while suppressing the generation of thermal NOx in the group
A water tube boiler combustion method in which NOx and CO are reduced by oxidizing and extinguishing CO2 . Wherein the burner is provided with the image made the one side with water tube walls, substantially the entire combustion gas passage formed by providing the exhaust gas outlet at the other end, close a number to the nearest present water tubes of the burner A water pipe group is formed by arranging the pipes, and the combustion gas is circulated in the cross direction with respect to the water pipe group, and the water pipe group is formed on the upstream water pipe group consisting of a bare pipe.
Controlling the temperature of the combustion gas on the more upstream side to the water pipe on the upstream side
CO2 while suppressing the generation of thermal NOx in the group
A water tube boiler in which NOx and CO are reduced by oxidizing and eliminating NOx . 3. The water tube boiler according to claim 2, wherein the burner is a premix burner.