JPH07110101A - Monotube boiler - Google Patents

Abstract

PURPOSE:To provide a monotube boiler in which the temperature in the region of combustion reaction can be controlled in a manner of reducing the amount of injurious exhaust gases, the heat transmission can be improved through even transfer of heat to the heat-transfer tube, and localized overheat can be prevented, and which can be miniaturized. CONSTITUTION:In a monotube boiler a heat-transfer tube 1 is wound in a spiral, the shell K is formed as a single-ply or multi-ply structure in a cylindrical shape, and the space enclosed by the heat-transfer tube 1, the innermost enclosure in the shell K, forms a combustion chamber 2. In the combustion chamber 2 a premix burner B having a multiplicity of premixed gas ejection holes 11 is disposed by being inserted in such a manner as to make the flames of combustion from the premixed gas ejection holes 11 touch the heat-transfer tube 1 being the innermost enclosure. Furthermore, there is a catalytic burner having a catalytic reactor, which supports a catalyst, and positioned with a slight gap between the outer circular surface of the catalytic reactor and the heat- transfer tube 1, the innermost enclosure, that allows the combustion gases from the catalytic reactor to pass through.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls the temperature of a combustion reaction region to reduce the amount of harmful exhaust emissions, and evenly transfers heat to a heat transfer tube to improve heat transfer and prevent local overheating. The present invention relates to a monotube boiler that achieves the above and can be further downsized.

[0002]

2. Description of the Related Art Generally, a so-called monotube boiler has a single or multiple cylindrical shape formed by spirally winding a heat transfer tube through which a fluid to be heated is circulated.
A blast type or Bunsen type diffusion combustion burner is coaxially arranged at one end side of the combustion chamber space in the combustion chamber space to form a combustion flame in the axial direction of the combustion chamber space. There is. When the boiler is operating, the fluid to be heated in the heat transfer tube is heated by the radiant heat transfer from the combustion flame and the contact heat transfer with the combustion gas.

[0003]

The above-mentioned conventional monotube boiler has the following problems. (1) Since the burners are centrally provided at one place as described above, in order to heat the entire heat transfer tube forming the can body, a large burner capable of setting a high combustion load is required, This leads to an increase in the size of the device. Further, in such a large burner, it is difficult to control the combustibility. (2) As a combustion burner, a diffusion combustion burner is mainly used because it has a wide combustion range and the amount of combustion is easy to adjust. A room space is required, and the installation space of the boiler as a whole becomes large. (3) When the fuel (including premixed gas) from the burner is freely combusted in the wide combustion chamber space as described above,
In particular, in the case of diffusion combustion, the combustion reaction region becomes large, and a high temperature region that is a source of thermal NOx exists in each part, so it is difficult to reduce NOx. (4) Burners are installed in one place in the can body,
In addition, since the combustion chamber space in front of the burner is wide as described above, there are some differences in the distance from the burner to the surface of the heat transfer tube, and the combustion gas from the burner tends to have a drift. Therefore, the degree of heating becomes uneven in each part of the heat transfer tube, and depending on the location of the heat transfer tube, overheating, and further,
It will burn out. Moreover, due to the uneven flow of the combustion gas, there is a portion where the radiative heat transfer and the contact heat transfer are not effectively performed depending on the location of the heat transfer tube, which hinders the improvement of heat transfer efficiency. As means for solving the above-mentioned problem of overheating, for example, JP-A-58-205003 and JP-A-61-2561.
Although there is one described in Japanese Patent Publication No. 01, the countermeasures for reducing NOx are not taken in these boilers.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to control the temperature of a combustion reaction region to reduce the emission amount of harmful exhaust gas and to reduce the transmission. An object of the present invention is to provide a monotube boiler capable of achieving uniform heat transfer to a heat tube to improve heat transfer and prevention of local overheating, and further downsizing.

Specifically, a heat transfer tube is spirally wound and
In a monotube boiler in which a can body having a heavy or multiple tubular shape is formed, and the space surrounded by the heat transfer tubes at the innermost periphery of the can body is used as a combustion chamber, a pre-mixed gas injection hole is provided. The first feature is that the mixing type burner is inserted and arranged in the combustion chamber so that the combustion flame from the premixed gas ejection hole comes into contact with the heat transfer tube at the innermost circumference. The catalytic combustion burner provided with a reactor was positioned with a slight gap left between the outer peripheral surface of the catalytic reactor and the heat transfer tube at the innermost periphery so that combustion gas from the catalytic reactor could flow. This is the second feature.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (hereinafter referred to as a first embodiment) in which the present invention is applied to a monotube boiler equipped with a can body formed by winding a heat transfer tube into a single cylindrical shape is shown in FIG. This will be described with reference to 2. In the monotube boiler in the first embodiment, one heat transfer tube (1) is spirally wound in a close contact state to form a single cylindrical can body (K), and the inside thereof is a combustion chamber (2). ). Here, one end side (lower side in the figure) of the heat transfer tube (1) is used as a water supply port (3) and a water supply means (not shown) is connected, and the other end (upper side in the figure) of the heat transfer tube (1) is Alternatively, it serves as the hot water outlet (4).

A boiler outer wall (5) is provided outside the can body (K) with a proper gap, and the outer wall (5) and the can body are
An insulating layer (6) filled with appropriate refractory material is provided between (K) and (K). Inside the combustion chamber (2), a premixing burner (B) is inserted from above the can body (K).

The lower part of the can body (K) is made of a refractory material,
The flue (7) is constructed by squeezing the lower end opening of (2). Therefore, the flame and the combustion gas from the premix burner (B) are discharged from the combustion chamber (2) through the flue (7) as exhaust gas from an exhaust means such as a stack (not shown).

In the first embodiment, the premixed burner (B) is of a type having a flame stabilizer (10) having a large number of premixed gas ejection holes (11). The support member (12) having the mixed gas inlet (13) and the cylindrical flame stabilizer (10) provided at the tip of the support member (12).
As the flame stabilizer (10), for example, a large number of flat and corrugated ribbon materials are alternately laminated, and the gap between the flat and corrugated ribbon materials is used as a premixed gas ejection hole. , A ceramic foam, a metal foam, a ceramic particle sintered block, or other fine passage of the porous material itself used as a premixed gas ejection hole, or a premixed gas ejected on a heat-resistant material such as ceramic or ceramics. What formed the hole can be used.

The positional relationship between the can body (K) and the premix burner (B) is set as follows. That is, the flame stabilizer (1
The combustion start surface of the premixed gas ejected from (0) is close to the heat transfer surface that defines the combustion chamber space, and the heat transfer is performed in the combustion reaction area on the downstream side of the combustion start surface, especially in the high temperature area. Place both so that the faces are located. The combustion start surface is a position where the ejection speed of the premixed gas and the combustion speed of the premixed gas are equal, and the combustion reaction region is formed on the downstream side of this combustion start surface. Therefore, flames (including invisible flames that are difficult to see) are also included in this combustion reaction region. More specifically, the premixed gas ejection holes (1
The flame holder (1) of the premixing burner (B) is set so that the combustion flame from (1) comes into contact with almost the entire heat transfer surface of the innermost heat transfer tube (1).
Insert (0) into the combustion chamber (2). With this arrangement, the flame holder (10) surface of the premix burner (B) and the combustion chamber (2)
The gap between the heat transfer surface and the heat transfer surface is extremely narrow.

Next, the operation of the above structure will be described. When the boiler is operated, water supply is started from the water supply port (3) on one end side of the heat transfer tube (1) by a water supply means (not shown), and when the water level in the heat transfer tube (1) reaches a predetermined water level, the premixing burner Ignite (B).

To ignite the premixed burner (B), first, a premixed gas prepared by appropriately mixing a fuel gas and combustion air at a required ratio is supplied from the mixed gas inlet (13). It is supplied to the inside of the cylindrical flame holder (10) through the support member (12), and the surface of the flame holder (10) is ignited by an appropriate ignition means such as a spark rod. Then, the premixed gas ejected from the large number of premixed gas ejection holes (11) on the surface of the flame stabilizer (10) starts combustion, and forms a combustion reaction region after the above-mentioned combustion start surface. In this combustion reaction area, light (that is, flame) and heat are generated by the oxidation reaction of combustion, and heat is transferred to the heat transfer tube (1) in this combustion reaction area by radiative heat transfer and contact heat transfer. As the temperature of the combustion gas itself is further lowered, it flows through the gap between the heat transfer tube (1) and the flame stabilizer (10) and flows out of the system from the flue (7). On the other hand, the water in the heat transfer tube (1) is heated via the heat transfer tube (1) by the above-mentioned radiative heat transfer and contact heat transfer, becomes steam or hot water, and is transferred from the outlet (4) to the outside of the system. To be done.

At this time, the flame holding body (1) of the premixed burner (B)
(0) has a cylindrical shape with its surface corresponding to the surface of the heat transfer tube (1) in the combustion chamber (2).
0) The surface is remarkably wider than the conventional one, and the combustion load per unit area of the flame stabilizer (10) can be set small. Therefore, uniform injection of premixed gas can be easily achieved from the flame stabilizer (10), the combustibility can be adjusted very easily, and a stable combustion state can be easily obtained on the surface side of the flame stabilizer (10). be able to. In addition, since the combustion load per unit surface area of the flame stabilizer (10) can be kept low, complete combustion of the fuel can be easily achieved, so that the production of CO can be kept extremely low.

Further, as described above, the combustion start surface is connected to the heat transfer tube.
(1) A heat transfer tube that is placed close to the surface and is located in the combustion reaction area (including the flame formation area) on the downstream side of the combustion start surface (1).
Is located so that the temperature of the high temperature region in the combustion reaction region is rapidly lowered by heat transfer to the heat transfer tube (1). Therefore, it becomes possible to remove the high temperature region in the combustion reaction region, so that the production of thermal NOx can be suppressed.

In the first embodiment described above, the premixing burner (B) is used in which the flame holder (10) having the premixed gas ejection hole (11) is formed into a shape conforming to the shape of the combustion chamber. However, the flame holder (10) does not have to be integrally formed in a shape conforming to the combustion chamber (2), and a plurality of flame holders are used to define the heat transfer tube that defines the combustion chamber (2).
(1) By arranging it close to the surface, it may be shaped so as to follow the combustion chamber (2).
Further, the premixing burner is not limited to the one provided with the flame holder (10) as in the first embodiment, and other types of premixing burners such as a line burner can also be applied.

3 and 4 show an embodiment using a line burner (L) as a premixing burner (hereinafter referred to as a second embodiment).
Is shown. The second embodiment is the same as the first embodiment.
The premixed burner (B) of the embodiment is a line burner (L), and the same reference numerals are given to the common constituent members in each embodiment and the duplicated description will be omitted.

In the second embodiment, the line burner (L)
Has a plurality of burner units (12 units in the illustrated example) (20) arranged in a circular shape in the combustion chamber (2), and one end of each burner unit (20) (upper end in the drawing). Part) is connected to an annular premixed gas supply pipe (21). The premixed gas supply pipe (21) is provided with a mixed gas inlet (13) similar to that of the first embodiment, and the premixed gas is supplied to each burner unit (20) by the premixed gas supply pipe (21). Through. Each of the burner units (20) includes a straight tubular premixed gas flow pipe (22), and a premixed gas ejection hole (or ejection nozzle) along the longitudinal direction of the peripheral surface of the flow pipe (22). Formed (11). As with the first embodiment, the positional relationship between the line burner (L) and the can body (K) is such that the combustion starting surface of the premixed gas from the ejection holes (11) of each burner unit (20) is in the combustion chamber. Set the heat transfer surface close to the surface of the heat transfer tube (1) that defines the space, and so that the heat transfer surface is located in the combustion reaction area on the downstream side of the combustion start surface, especially in the high temperature area (including flame). There is. The effect of this second embodiment is the same as that of the first embodiment.
Since it is similar to the embodiment, the description thereof is omitted.

Next, an embodiment of the second invention (hereinafter referred to as a third embodiment) will be described below. In addition, this third
In the embodiment, the premixed burner (B) in the first embodiment is a catalytic combustion burner. This embodiment has a shape similar to that of the first embodiment shown in FIGS. 1 and 2, and therefore the drawing is omitted. In the third embodiment, the catalytic combustion burner includes the mixed gas inlet (13).
At the tip of the supporting member (12) provided with a catalytic reactor for performing a catalytic reaction (combustion), which has an appearance similar to that of the flame holder (10), the combustion chamber (2) It is inserted inside the can body (K).

The above-mentioned catalytic reactor is a porous cylinder containing a catalyst carrying a noble metal such as Pt or Pd, a rare earth element such as Y or La, or a mixture of both, or a catalyst carrying a complex oxide catalyst. It is formed into a shape. More specifically, the wall surface of the fine premixed gas flow path from the inside to the outer surface of the cylindrical catalytic reactor is used as the catalytically active surface, and the catalytic reactor itself is made of a heat-resistant material such as ceramic or ceramic. A material such as a honeycomb or porous material is used.

The positional relationship between the can body and the catalytic combustion burner is set as follows. That is, both are arranged at a position where the outer surface of the catalytic reactor is close to the heat transfer surface defining the combustion chamber space. At this time, as compared with the premixed burner (B) of the embodiment shown in FIGS. 1 and 2, the catalytic combustion burner in this embodiment is placed closer to the heat transfer surface defining the combustion chamber space. Can be installed. The reason is that the catalytic combustion burner promotes the reaction of the fuel with the oxygen in the combustion air (combustion reaction) by the catalyst to maintain the combustion reaction at a temperature lower than the normal reaction temperature, and the combustion reaction Since the premixed gas starts from the point of contact with the catalytically active surface and most of the premixed gas completes the combustion reaction on the outer surface of the catalytic combustor, the first embodiment shown in FIGS. This is because, unlike the premixed burner (B), the space for forming the combustion start surface is not required. Therefore, the space between the catalytic reactor and the heat transfer tube (1) defining the combustion chamber space may be such that at least a slight gap is left between the catalytic reactor and the combustion gas from the catalytic reactor.

With respect to the monotube boiler constructed as described above, the operation procedure will be omitted, omitting the same parts as those of the first embodiment, and only the different points will be explained. After operating the boiler,
To ignite the catalytic combustion burner, first, the catalytic reactor is set to a temperature at which the catalytic reaction starts (currently, in general,
Preheat to 300-350 ℃). Next, the premixed gas is introduced from the mixed gas inlet (13) and supplied into the cylindrical catalytic reactor through the support member (12). At this time, the mixing ratio of the fuel gas and the combustion air is such that the combustion temperature in the catalytic reactor becomes equal to or lower than the heat resistant temperature of the catalyst.

Then, since the catalytic reactor has been preheated to the starting temperature of the catalytic reaction as described above, the premixed gas does not generate unburned components such as CO in the catalytic reactor and has a low temperature. Completely burns with. Since the combustion at this time is performed at a low temperature, there is almost no generation of thermal NOx, which has been a problem in the past. Combustion in this catalytic reactor, that is, catalytic combustion, is performed at a low temperature due to the contact between the premixed gas and the catalyst, so that combustion with almost no flame is generated and almost no combustion occurs from the outer surface of the catalytic reactor. Combustion gas in a completed state flows out. The combustion gas generated by this catalytic combustion heats the heat transfer tube (1) by radiative heat transfer and contact heat transfer, further lowering the temperature of the combustion gas itself, and creating a gap between the heat transfer tube (1) and the catalytic combustor. It is distributed and discharged out of the system through the flue (7).

In each of the above embodiments, the monotube boiler uses the can body (K) in which the heat transfer tube (1) is spirally wound in a close contact state, but the present invention has a can of such constitution. body
Not limited to (K), for example, the heat transfer tube (1) is spirally wound with a gap between them to form a combustion gas passage (15) between the outer circumference of the can body (K) and the can body (K) cover. (See FIG. 5), the double cylindrical can body (K) as shown in the item of the prior art, and the multiple cylindrical can body (K) can be easily applied. In addition, a can body (K) in which the above-described procedure for forming the combustion gas passage and the configuration of the can body (K) are mutually combined.
It is also possible to apply to.

Incidentally, the embodiment shown in FIG.
The same as the first embodiment is applied with a premixing burner (B), but a gap is formed between the heat transfer tubes (1) that are wound to form the can (K). I am doing it. Therefore,
The heat transfer tube (1) does not exist on the front surface of the flame stabilizer (10), that is, the heat transfer tube (1) has a gap where the tubes face each other. At this location, the formation density of the premixed gas ejection holes (11) is made higher than at other locations of the flame stabilizer (10), and the combustion initiation surface (or flame) is located further to the wake side than at other locations. It may be set to extend. With such a configuration, the combustion load can be increased, and the combustion reaction region extending toward the gap of the heat transfer tube (1) can effectively increase its high temperature region by the heat transfer tube (1) defining the gap. As described above, therma
l Generation of NOx can be suppressed.

[0025]

EFFECTS OF THE INVENTION According to the monotube boiler of the present invention, heating of the heat transfer tubes can be performed uniformly, the amount of heat transfer per unit heat transfer area can be doubled, and the heat transfer efficiency can be greatly increased. Can prevent local heating of the heat transfer tube,
Problems such as overheating and burning of the heat transfer tube are solved. Moreover, since the heat transfer tube is located immediately in front of the flame holder or the catalytic reactor, the combustion load per unit surface area of the flame holder or the catalytic reactor is small, and heat transfer to the heat transfer tube results in high temperature. Since no area is generated, the generation of NOx (thermal NOx) is reduced, and the boiler can be made safe in terms of pollution control. Furthermore, since the combustion load per unit surface area becomes small, the amount of combustion can be easily adjusted, and a very good combustion reaction state can be stably maintained. In addition, since the distance between the combustion chamber, that is, the burner and the outer peripheral surface of the heat transfer tube facing the burner can be reduced, the entire boiler can be made compact. Further, by arranging the catalytic reactor with the catalytic combustion burner such that the surface of the catalytic reactor is positioned such that an annular gap remains between the catalytic combustion burner and the innermost heat transfer tube that defines the combustion chamber, In addition to the effect, further reduction of NOx can be achieved.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing a schematic configuration of an embodiment (first embodiment) of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a vertical sectional side view showing a schematic configuration of another embodiment (second embodiment) of the present invention.

4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a vertical sectional side view showing a schematic configuration of still another embodiment (fourth embodiment) of the present invention.

[Explanation of symbols]

 (1) Heat transfer tube (B) Premixed burner (K) Can body (2) Combustion chamber (10) Flame stabilizer (11) Premixed gas ejection hole

Claims (2)

[Claims] 1. A heat transfer tube (1) is spirally wound to form a can body (K) having a single or multiple cylindrical shape, and the can body (K) is formed.
In a monotube boiler that uses the space surrounded by the innermost heat transfer tube (1) as the combustion chamber (2), a premix burner (B) equipped with a large number of premix gas ejection holes (11) The combustion flame from the premixed gas ejection hole (11) is the innermost heat transfer tube.
A monotube boiler characterized by being inserted and arranged in the combustion chamber (2) so as to come into contact with (1). 2. The heat transfer tube (1) is spirally wound to form a single or multiple cylindrical can body (K), and the innermost heat transfer tube (1) inside the can body (K) is formed. In a monotube boiler having a space surrounded by a) as a combustion chamber (2), a catalytic combustion burner equipped with a catalytic reactor carrying a catalyst is used. A monotube boiler characterized in that it is positioned with a slight gap between it and the heat transfer tube (1) through which combustion gas from the catalytic reactor can flow.