JPH0835603A - Water-tube boiler - Google Patents

Abstract

PURPOSE:To efficiently transfer heat by convection by arranging in a combustion-reaction region walled off by water tubes a multiplicity of water tubes in a group in a setup equipped with a premix burner as a means of heating the group of water tubes and to pass the combustion gas to cross to the water tubes. CONSTITUTION:A water-tube wall 1 having a plurality of vertical water tubes 1a is placed opposite to another water-tube wall 1 with a required space between the two and substantially in parallel with each other. A premix burner 5 is provided at one end in the longitudinal direction with respect to the pair of water-tube walls 1, 1 and a passage for gas 9 is formed by the pair of water- tube walls 1, 1 and headers. Inside this passage for gas 9 a multiplicity of vertical water tubes 2a..., 3a..., 4a... are erected. Among these vertical water tubes 2a..., 3a..., 4a... those positioned adjacently to the water-tube walls 1, 1 are staggered with the adjacent vertical water tubes 1a, 1a of the water-tube walls 1, 1 on their respective sides. The passage for gas 9 can be formed straight and relatively long in an assembly of water tubes 20 built in accordance with the above constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water tube boiler of the type in which combustion gas is allowed to flow linearly in a crossover direction with respect to a water tube group.

[0002]

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

However, such a can body structure tends to occupy a relatively large space depending on the installation location and arrangement of the boiler. Therefore, in recent years, various so-called rectangular can body structures are used as a base. A multi-tube type once-through boiler has been proposed (for example, in Japanese Utility Model Publication No. 56-136).
904).

In recent years, due to environmental pollution problems and the like,
Hazardous combustion emissions from boilers, there is a need in particular NO _X, further reducing the CO and the like. As a measure for reducing such harmful combustion exhaust gas, the combustion gas temperature, that is, the temperature of the combustion flame is lowered to control the generation of NO _X , especially thermal NO _X (thermal NO _X ) and the combustion gas temperature. A method is known in which CO is oxidized to CO ₂ by keeping the temperature within a certain temperature range to prevent CO from remaining. More specifically, Jitsuko Sho 56-4
As disclosed in Japanese Patent No. 7477, a burner flame is applied to a water cooling wall or the like, or as disclosed in Japanese Patent Publication No. 56-46046, an excessive concentration of air-fuel mixture is generated in the center of a swirling air flow. The temperature of the combustion gas (the temperature of the combustion flame) by means of a cold body near the burner, as disclosed in JP-A-60-78247. After 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 type in which exhaust gas is recirculated is known.

[0005]

A conventional boiler having a rectangular can body structure, for example, the above-mentioned Japanese Utility Model Laid-Open No. 56-13690.
The heat exchange in the boiler as disclosed in Japanese Patent Publication No. 4 is performed only by the pair of water pipe panels that define the first and second gas passages in the furnace following the combustion chamber, and therefore the heat transfer surface area is extremely small. It is very few. Further, since the water pipes are arranged in close contact with each other in this water pipe panel, a fan-shaped region, a so-called dead water region, is formed between the water pipes that are in contact with each other. In this dead water region, the gas flow velocity is higher than that between the water pipe panels. The heat transfer coefficient to the water pipe is low, and the effective area for actual heat transfer is smaller, resulting in a problem in improving the heat efficiency. Further, as described above, in addition to the first gas passage communicating with the combustion chamber, it is necessary to provide the second gas passage through which the combustion gas reverses from the first gas passage, which makes it difficult to downsize the can body. In this respect also, it becomes an obstacle in improving the thermal efficiency of the can itself.

In this boiler, the harmful combustion exhaust gas, that is, NO _x , C, which is the most important issue in recent years, is used.
No measures have been 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 large space exists in front of the burner as a whole, the fuel (including the premixed gas) ejected from the burner burns at a high temperature as it is. Therefore, thermal NO _x is generated during this combustion, and CO
There arises a problem that ₂ is thermally dissociated to generate CO.

Further, generally, the temperature of the combustion gas flow from the burner decreases toward the downstream side due to heat transfer to the water pipe, and the volume decreases accordingly, so that the water pipe panel is simply used as described above. In the case of boilers that are arranged in parallel, there is a problem that the flow velocity is reduced downstream of the combustion gas and the heat transfer efficiency is significantly reduced.

[0008]

The present invention has been made to solve the above-mentioned problems, and a plurality of water tubes are densely arranged in a combustion reaction region defined by water tube walls. It is characterized in that a group is formed, a premixing burner is arranged as a heating means for the water tube group, and the combustion gas from the premixing burner is circulated in a direction intersecting with the water tube group.

[0009]

According to the present invention, since the premixing burner is used, unlike the case where the diffusion combustion burner is used, the fuel and the air are mixed in advance, so that the fuel is immediately burned by passing through the mixing process. The process will be shifted to, and a local high temperature portion will not be generated. Moreover, since a large number of water pipes are densely arranged in the combustion reaction region, the combustion gas directly contacts each water pipe, and efficient heat transfer is performed by convective heat transfer. Then, combustion gas, by convection heat transfer between the water tubes, gradually descends with its temperature is kept low, suppressing the generation of NO _X, hazardous combustion emissions, such as CO.

[0010]

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

In FIGS. 1 and 2, a water pipe wall 1 forming an outer shell of a can in a square multi-tube once-through boiler is formed by arranging a plurality of straight pipe-shaped vertical water pipes 1a at equal intervals. By connecting the adjacent vertical water pipes 1a with each other by the fin-shaped member 6, the space between the vertical water pipes 1a is closed to form a rectangular wall member. As a result, the water pipe wall 1 defines the outer shell of the can body and also has a function as a heat transfer surface.
Therefore, this water pipe wall 1 does not form a so-called dead water region where the heat transfer rate decreases due to the decrease in gas flow velocity, unlike the conventional boiler.
This sufficiently secures an effective heat transfer area, which greatly contributes to improvement in thermal efficiency.

Then, the water pipe wall 1 constructed in this way is
The vertical water pipes 1a, 1a, ..., Which face each other in a state where a required space is maintained and which are arranged so as to be substantially parallel to each other, and constitute a pair of water pipe walls 1, 1, respectively.
The upper and lower ends are connected to the upper and lower headers 10 and 11, respectively. In addition, the upper and lower headers 10 in this embodiment,
As shown in FIG. 2, each of the upper and lower headers 11 and 11 is independent from each other with respect to the longitudinal direction of the water pipe wall 1 and is connected to an external pipe (not shown). ) Etc., and are integrated respectively.

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

In the gas passage 9, a large number of vertical water pipes 2a, 2a, ..., 3a, 3a, ..., 4a, 4a, ... Are provided at intervals that allow the flow of combustion gas from the burner 5.
Is inserted. At this time, each vertical water pipe 2a, 3a, 4
The distance between a is such that the combustion gas and the vertical water pipes 2a, 3
In order to improve the convective heat transfer efficiency with a and 4a, it is preferable to set as narrow as possible, but if it is extremely narrow,
When the gas flow velocity around each vertical water pipe 2a, 3a, 4a becomes too fast and the pressure loss increases, on the contrary, when it becomes extremely wide,
The convection heat transfer efficiency is reduced due to the slow gas flow rate, and the number of vertical water pipes 2a, 3a, 4a to be inserted is inevitably reduced, which means that the heat transfer area is reduced, and therefore the heat transfer amount itself. Will also decrease. At this point, the distance between the vertical water pipes 2a, 3a, 4a is as shown in FIG.
As shown in, for example, vertical water pipes (2a, 3a, 4a)
It is preferable that the diameter is less than or equal to.

Then, each of the vertical water pipes 2a, 3a, 4a
Are inserted over substantially the entire area of the gas passage 9 while maintaining the above-mentioned distance. In this way, the vertical water pipes 2a, 3a, 4 inserted over almost the entire area of the gas passage 9 are provided.
The upper and lower ends of a are connected to the upper and lower headers 10 and 11, respectively, similarly to the vertical water pipes 1a, 1a, ... Further, the vertical water pipe 2a facing the burner 5 is arranged 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 also extremely small. . That is, in this embodiment, the arrangement densities of the vertical water pipes 2a, 3a, 4a in the gas passage 9 are compared with each other in terms of the distance between the vertical water pipes 2a, 3a, 4a, as shown in FIG. It means that they are arranged closely.

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 lateral width (width in the left-right direction in FIG. 1) of the water pipe assembly 20 constituted by and can be reduced, and the lateral width defined for the water pipe assembly 20 (this relates to the cross-sectional area of both the headers 10 and 11). More vertical water pipes can be installed inside the set).

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 linearly formed to be relatively long, and the combustion can be performed. Vertical water pipe 4a with gas at the end
It takes a relatively long time to pass through.
That is, the residence time of the combustion gas in the water pipe assembly 20 is relatively long, and the combustion gas is retained in the gas passage 9 by the vertical water pipes 1a, 2a, 3a, 4 respectively.
Convective heat transfer is sequentially performed with a, and the temperature thereof gradually decreases. Therefore, there is no place where the temperature becomes locally high in the entire gas passage 9, so that the generation of NO _X , especially thermal NO _X can be suppressed more effectively, and the oxidized CO ₂ causes CO to be generated by thermal dissociation. Never generate 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 in the form of the burner. A predetermined number of pipes are arranged from the 5 side toward the exhaust gas outlet 8 side at equal intervals, and the vertical water pipes of each of them are a bare pipe 2a, a finned pipe 3a, and an erotic fin pipe 4a from the upstream side. And each of these vertical water pipes 2a, 3a, 4
a is a group of three water pipes 2, 3 and 4 having different heat transfer surface densities (heat transfer surface area per unit length of flow path of combustion gas),
These first to third water pipe groups 2, 3 and 4 are connected to the gas passage 9
Inside, from the side of the burner 5 toward the side of the exhaust gas outlet 8 are arranged in the order of the heat transfer surface density from low to high.

With this structure, the combustion gas from the burner 5 flows through the gas passage 9 from the first water pipe group 2 including the bare pipe 2a, the second water pipe group 3 including the finned pipe 3a, and the erotic fin pipe 4a. Passing through the third water pipe group 4 while conducting convective heat transfer, from the exhaust gas outlet 8 through an economizer (not shown) or directly to a chimney (not shown).
Drained from. 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, 4a, and has a reduced volume and heat transfer efficiency. descend. However, in this invention, since the heat transfer surface density is increased toward the downstream side, the amount of heat transfer in each of the vertical water pipes 2a, 3a, 4a extends from the upstream vertical water pipe 2a to the downstream vertical water pipe 4a. It does not decrease, but becomes almost uniform as a whole, and the temperature of the combustion gas also gradually decreases.

With respect to this point, concrete experimental results will be described. The combustion surface load is 600 to 1200 × 10 ⁴ Kcal.
In the case of using a burner of / m ² · h, at point A in FIG. 1, the combustion gas from the burner 5 continues the combustion reaction accompanied by the presence of flame, and is about 1200 ° C. Is about 5 due to convective heat transfer with the first water pipe group 2.
The result was that the temperature was 00 ° C., and at point C, it was about 370 ° C. due to convective heat transfer with the second water tube group 3. As a result, the first heat transfer surface density on the upstream side is reduced.
In the water tube group 2, since the temperature of the combustion gas accompanied by the presence of the flame is kept low, NO _x , especially thermal N
Generation of O _X is a more be more effectively suppressed.
Further, in the second water pipe group 3 and the third water pipe group 4 having a large heat transfer surface density on the downstream side, the temperature of the combustion gas gradually decreases, so that the oxidized CO ₂ is re-dissociated with CO by thermal dissociation. CO is not generated, and the generation of CO is suppressed even more effectively. Here, as seen from the results of this specific experiment, in view of the fact that the combustion reaction is still continuing at point A of the combustion gas temperature measurement point and the existence of flame is confirmed, the gas passage 9 is , Can be seen as the combustion reaction zone.

Here, a concrete example of using a premixed burner as the burner 5 will be further described.
When a premixed air with an air ratio of 1.3 is supplied to the premixed burner and burned, NO _x is 1/3 compared to the conventional one.
To about 1/2, and CO was reduced to less than 10 ppm or less. This NO _x , C
O value is 10 for the circulation rate in the boiler with exhaust gas circulation system.
%, But in this example,
A structure in which combustion gas is circulated in only one direction without being circulated at all has such an effect of reducing harmful combustion exhaust substances, and complicated piping for exhaust gas circulation is not required, and the structure is extremely simple.

In this specific example, the burner 5
The case of using a premix burner was explained as
The reason for this is as follows. That is, whether it is a diffusion combustion burner or a premix burner,
As a pre-stage of combustion, it is necessary to go through a mixing process of fuel and air, but in a diffusion combustion burner, time is required at the same time as a region or space used 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 It will create an easy situation. As a result, particularly for the oxidation of CO, a high temperature region for oxidation is required. However, if this high temperature region cannot be taken, the amount of CO emissions will increase, and if a high temperature region is provided, the depth of the can body will increase. Becomes longer, which leads to an increase in the size of the can body.

On the other hand, in the premix burner,
Since the fuel and air have been mixed in advance, the mixing process (that is, the area or space and time point required in the diffusion combustion burner) is passed, and the combustion process is immediately transferred. It is possible to perform relatively good combustion without producing a locally high-temperature portion, that is, with a small amount of NO _x produced, and even if CO is produced on the upstream side, CO is oxidized on the downstream side. Therefore, it is based on the finding that CO emissions can be reduced even if the depth is relatively short. In addition to this point, a premixing 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 reducing harmful combustion exhaust gas. It is based on the finding that it is

Next, FIG. 3 showing a second embodiment of the present invention will be described. In the embodiment of FIG. 3, both the water pipe walls 1 and 1 have a length up to about the middle of the boiler can body, and the downstream lateral width (width in the left-right direction in FIG. 3) is narrowed. A water pipe group 2 in which bare vertical water pipes 2a are 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 in the illustrated embodiment, a gas passage continuous with the downstream ends of the water pipe walls 1 and 1 and connected to a gas passage 9 formed on the upstream side. Insulating walls 7 are arranged on both sides so as to form 9, and a water pipe group 4 composed of two rows of erotic fin tubes 4a is arranged between the insulating walls 7, 7.

Also in this second embodiment, as in the first embodiment (FIGS. 1 and 2), heat transfer per unit flow path length from the upstream side to the downstream side in the combustion gas flow direction. Since the surface area is increased, as described above, the heat transfer efficiency of the water pipe assembly, that is, the can itself, and the N
O _X, reduction of harmful emissions of CO and the like can be a reduced effectively.

[0026]

As described above, according to the present invention, the premixing
Since a combined burner is used, when using a diffusion combustion burner
Unlike the case, the fuel and air are mixed in advance
Therefore, it is possible to immediately move to the combustion process after passing the mixing process.
Therefore, a local high temperature portion is not generated. Only
However, many water tubes are densely arranged in the combustion reaction area.
Since the combustion gas directly contacts each water pipe,
More efficient heat transfer is achieved. And the combustion gas is
Convective heat transfer with each vertical water pipe keeps its temperature low.
It gradually descends with_X, CO, etc.
Suppress the generation of burnt exhaust. Also, with exhaust gas circulation device
Complicated piping for exhaust gas circulation compared to other boilers
Is unnecessary, and the structure is extremely simple. Sanawa
The water tube boiler according to the present invention has a simple structure.
There is NO_XThe generation of harmful combustion exhaust such as CO and CO
Hazardous combustion that can be suppressed and is the most important issue in recent years
It is a very effective pollution control measure for exhaust gas.
It Incidentally, the NO according to the present invention_XAbout the reduction effect,
The explanation based on the concrete experimental results is as follows.
Is. That is, FIG. 4 shows a conventional cylindrical water pipe assembly.
A boiler having a three-dimensional combustion chamber, and the present invention
No with a boiler _XThis shows the generation characteristics of
According to the invention, NO_XIs about 1 compared to conventional boilers
/ 2, NO at normal operating point_XIs 30
It is extremely low at 40 ppm.

[Brief description of drawings]

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

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

3 is a schematic cross-sectional explanatory view showing an embodiment different from the square-walled tubular flow-through boiler of FIG. 1. FIG.

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

[Explanation of symbols]

 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 (pipe with fin) 4 third water pipe group 4a vertical water pipe (erofin pipe) 5 burner 6 fin-shaped member 7 Heat insulation wall 8 Exhaust gas outlet 9 Gas passage 10 Upper header 11 Lower header

Claims (1)

[Claims] 1. A plurality of water tubes are densely arranged in a combustion reaction region defined by water tube walls to form a water tube group, and a premixing burner is arranged as a heating means for the water tube group. A water tube boiler, wherein combustion gas from a mixed burner is caused to flow in a direction intersecting with the water tube group.