JPH0826965B2 - Heat transfer surface structure of multi-tube once-through boiler - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a heat transfer surface structure of a boiler, and more particularly to a heat transfer surface structure having a fin effective for use in a multi-tube once-through boiler.

[0002]

2. Description of the Related Art Generally, fins are attached to a heat transfer surface of a boiler or the like for the purpose of promoting heat transfer. The same applies to a multi-tube once-through boiler, and in order to improve heat transfer efficiency, a structure in which lateral fins (12) are provided parallel to the flow direction of combustion gas is adopted as shown in FIGS. 3 and 4. That is, both the upper header (1) and the lower header (2) are formed in an annular shape, and these both headers (1), (2) are connected by a number of water pipes, and these water pipes are radially spaced. Arranged as double annular water pipe rows (3) and (4), which form an annular combustion gas passage between the inner annular water pipe row (3) and the outer annular water pipe row (4).
(5) is formed, a combustion device (6) is provided inside the upper header (1), and a combustion chamber (7) is formed inside the inner annular water pipe row (3). A row (3) is provided with a combustion chamber opening (9) over the entire length of the water pipe to connect the combustion chamber (7) with the combustion gas passage (5), and the outer annular water pipe row (4) extends over the entire length of the water pipe. A combustion gas passage opening (10) is provided to connect the combustion gas passage (5) with the smoke channel (11) provided on the outer wall of the boiler (8), and the combustion gas of both annular water pipe rows (3), (4) is In the structure facing the passage (5), a number of flat fins (12) are attached in a multi-tiered manner in the circumferential direction and in the axial direction of the pipe over the entire length of the water pipe. According to this structure, the combustion gas generated in the combustion chamber (7) first exchanges heat with the inner annular water pipe array (3) by radiant heat transfer, and the combustion chamber opening (9) moves from the combustion chamber (7). ) And branch off,
It flows through the combustion gas passage (5), joins at the combustion gas passage opening (10), and is discharged to the outside from the flue (11).

[0003]

Since the conventional multi-tubular once-through boiler is constructed as described above, the pressure loss of the combustion gas can be improved although the heat transfer efficiency can be improved by increasing the heat transfer area due to the fins. Has the advantage of being small. However, in the multi-tube once-through boiler having such a structure, the combustion gas flowing from the combustion chamber (7) through the combustion chamber opening (9) into the combustion gas passage (5) is still in a considerably high temperature state. However, the lateral fins (12) of the water pipe near the opening (9) of the combustion chamber come into contact with this high-temperature combustion gas, which causes high-temperature corrosion, resulting in a considerable wear. Also, the outer annular water pipe row
Regarding the water pipe of (4), the heat transfer surface on the combustion gas passage (5) side is exposed to high-temperature combustion gas, but the heat transfer surface on the outer wall (8) side of the boiler is not heated, so it is connected to the combustion gas passage (5) side. There is a large temperature difference between the outer wall of the boiler (8) and, especially in the water pipe near the opening (9) of the combustion chamber, due to the high temperature of the combustion gas, the lateral fin weld and other surfaces The temperature difference was particularly large, and in an unexpected situation there was the danger that cracks would occur in the fin weld due to thermal stress.

Therefore, in view of the above-mentioned circumstances, the problem to be solved by the present invention is to provide a finned water pipe arrangement which is effective for heat transfer, and yet to prevent cracks caused by hot corrosion or heat stress of the fin. It is to provide a heat transfer surface structure that prevents the risk of occurrence.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, in which both the upper header and the lower header are formed in an annular shape, and both the headers are formed by a large number of water pipes. Together with connecting, these water pipes are arranged as an inner and outer double annular water pipe array, a combustion chamber is formed inside the inner annular water pipe array, and an annular combustion gas passage is formed between the both annular water pipe arrays. , The inner annular water pipe row is provided with a combustion chamber opening to the combustion gas passage, and the outer annular water pipe row is provided with a combustion gas passage opening communicating with a flue provided on the outer wall of the boiler. The openings are arranged so as to face each other across the combustion chamber, and a flat horizontal fin is arranged on the outer surface of the water pipe facing the combustion gas passage in a multi-step manner in the axial direction of the water pipe. In the tubular once-through boiler, each of the annular water pipe rows is configured. That out of the water pipe toward the combustion gas passage downstream from the combustion chamber opening, characterized in that a no lateral fins water pipe water pipe flow path range of the predetermined length.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a transverse cross-sectional view showing an embodiment in which the heat transfer surface structure of the multi-tube type once-through boiler according to the present invention is applied to the multi-tube type once-through boiler shown in FIGS. The plan view is similar to FIG. 3 described above.

In the drawing, both the upper header (1) and the lower header (2) are formed in an annular shape. Both pipes (1),
(2) is connected by a large number of vertical water pipes as heat transfer pipes, and these water pipes are inner and outer double annular water pipe rows with radial intervals.
They are arranged as (3) and (4). Both annular water pipe rows (3),
Both ends of each water pipe of (4) are reduced in diameter, and are fitted and welded to the pipe plate of the upper pipe header (1) and the pipe plate of the lower pipe header (2), respectively.

Inner ring water tube row (3) and outer ring water tube row
An annular combustion gas passage (5) is formed between and (4). A combustion device (6) is provided on the inner side (center part) of the upper pipe head (1), whereby the inner side of the inner annular water pipe row (3) is made into the combustion chamber (7). On the other hand, the outer row of water pipes
Outside the (4), there is a boiler outer wall (8) surrounding the water pipe array (4).

A part of the inner annular water pipe array (3) is provided with a combustion chamber opening (9) over the entire length of the water pipe.
The combustion chamber (7) communicates with the combustion gas passage (5) by (9). On the other hand, a part of the outer annular water pipe row (4) is provided with a combustion gas passage opening (10) over the entire length of the water pipe, and smoke provided on the bottom of the combustion gas passage (5) and the boiler outer wall (8). Road (1
1) is in communication with. Where both openings (9), (1
0) has a positional relationship of facing each other across the combustion chamber (7).

On the outer surface of the water pipe facing the combustion gas passage (5), a plate-shaped lateral fin (12) has a plane parallel or inclined to the combustion gas flow direction (direction of arrow A in the figure). In a substantially horizontal state, each water pipe is provided in multiple stages in the axial direction of the pipe, but in the section of the combustion gas passage (5) that is a predetermined distance from the combustion chamber opening (9) to the downstream side, there is no horizontal fin. (13)
Are arranged.

The operation of the above structure will be described. The combustion gas generated in the combustion chamber (7) first exchanges heat with the inner annular water pipe array (3) by radiant heat transfer, and the combustion chamber (7).
Flow through the combustion chamber opening (9) into the combustion gas passage (5), and the heat is mainly exchanged by convective heat transfer in the process of flowing in the combustion gas passage (5) in two directions. After that, they merge again at the combustion gas passage opening (10) and the flue (11)
It becomes low temperature and is discharged to the outside.

At this time, since the water pipe near the opening (9) of the combustion chamber is the horizontal finless water pipe (13), even though the combustion gas from this opening (9) is at a considerably high temperature, As described above, the temperature difference on the surface of the water pipe is smaller than that in the case where the lateral finned water pipe is arranged at this position, and the occurrence of cracks in the water pipe caused by thermal stress due to the temperature difference can be reduced. Furthermore, since there are no horizontal fins (12) on the water pipes exposed to the high temperature combustion gas near the opening of the combustion chamber (9), the fins corrode at high temperatures as in the past and are significantly worn away. At the same time, the initial heat transfer efficiency cannot be maintained. Also, in the horizontal fin-equipped water pipe (14) downstream from the combustion chamber opening (9) after a predetermined distance, the combustion gas is considerably heated by convective heat transfer in the upstream horizontal fin-free water pipe (13). Since it has decreased, there is no danger that the side fins (12) will be hot-corroded in this part.

Here, in the embodiment shown in FIG.
In the combustion gas passage (5), the horizontal fin-free water pipe (13) of the outer annular water pipe array (4) is arranged to be longer than that of the inner annular water pipe array (3), and the outer annular water pipe array (3) is The horizontal finless water pipe (13) in the water pipe array (4) is arranged further downstream of the combustion gas passage (5) than the horizontal finless water pipe (13) of the inner annular water pipe array (3). It is possible to improve the heat transfer efficiency and prevent the occurrence of cracks in the water pipe due to overheating. That is, the outer annular water pipe row
The water pipe of (4) is not heated from the outer wall (8) side of the boiler, but is heated only from the combustion gas passage (5) side, whereas the water pipe of the inner annular water pipe row (3) is Since it is heated from both the combustion chamber (7) side and the combustion gas passage (5) side, the temperature difference is smaller than that of the outer annular water pipe row (4), so this inner annular water pipe row (3) In the above, even if the horizontal fin (12) is welded to the water pipe on the upstream side of the outer annular water pipe row (4), the risk of cracking of the water pipe as described above is small, and the horizontal fin (1
By providing 2), heat transfer efficiency is improved.

Further, in the embodiment shown in FIG.
Clearance of combustion gas passage (5) in water pipe (13) without horizontal fins
(A) is the combustion gas passage (5) in the horizontal finned water pipe (14)
By setting the gap to be narrower than the gap (b), it is possible to further improve the heat transfer efficiency and prevent the occurrence of cracks in the water pipe due to overheating. That is, in the combustion gas passage (5) near the combustion chamber opening (9), the gap (a) in this portion is narrower than the gap (b) in the combustion gas passage (5) in the horizontal finned water pipe (14). By doing so, a high-speed flow of combustion gas is formed and the heat transfer efficiency is improved, and as a result, this horizontal finless water pipe
Also in part (13), a heat transfer effect similar to that of a conventional water pipe with fins like a multi-tube once-through boiler can be obtained. In this case, although the passage pressure loss of the combustion gas increases more than before in the part of the above-mentioned gap (a), the horizontal fin-free water pipe
Since the distance of the combustion gas passage (5) in the portion (13) is short, the amount of increase is small, and there is no hindrance to the operation of the boiler such as the amount of ventilation and combustibility. In addition, by narrowing the gap (a) that corresponds to the inlet of the combustion gas passage (5), the combustion gas that exits from the combustion chamber (7) is blocked, and the one-sided flow due to the momentum of the combustion gas is mitigated. The flow of combustion gas in the axial direction of the water pipe in the passage (5) is made uniform, the heat transfer efficiency can be improved by the substantial increase in contact heat transfer, and local overheating can be prevented. Is prevented.

FIG. 2 is an explanatory view of another embodiment of the heat transfer surface structure of the multi-tube type once-through boiler according to the present invention. In this embodiment, the inner and outer annular water pipe rows (3) and (4) are adjacent to each other by spacers (15) and (16), respectively.
, And the water pipes forming the annular water pipe rows (3) and (4) are arranged in a state of being displaced by a half pitch. The horizontal finless water pipe (13), the horizontal finned water pipe (14) and other configurations are the same as those in the above-described embodiment. With such a structure, the same effects as those of the above-described embodiment can be obtained, and the spacer (1
By providing 5) and 16), it is possible to prevent the formation of the substantially fan-shaped region in which the combustion gas stays in the combustion gas passage 5 between the adjacent water pipes, so that the heat transfer efficiency is further improved. Moreover, by arranging the water pipes of the inner and outer water pipe rows so as to be displaced by a half pitch, the cross section of the combustion gas passage (5) in the lateral finned water pipe (14) portion becomes almost the same, and the flow of combustion gas becomes uniform. The pressure loss in the combustion gas passage (5) is reduced compared to the case where the combustion gas flows while being contracted (compressed) and expanded (expanded) as in the case of other types of water pipe arrangement.
The other configurations, operations, and effects are the same as those of the embodiment shown in FIG. 1, and thus detailed description thereof will be omitted.

[0016]

As described above, since the present invention is constructed as described above, the following effects can be obtained.

1) The water pipe near the opening of the combustion chamber is in contact with the combustion gas which is still in a considerably high temperature state in its combustion gas passage, but the water pipe in this region is a horizontal finless water pipe for both the inner and outer annular water pipe rows. Since it is configured, like the conventional boiler in which a horizontal finned water pipe is arranged in this area, the horizontal fins of the water pipe near the opening of the combustion chamber are corroded at high temperature by this combustion gas in the high temperature state, and are significantly worn. There is no such problem, and the initial heat transfer efficiency cannot be maintained with the passage of time. Further, the water pipe near the opening of the combustion chamber is a horizontal fin-free water pipe for both the inner and outer annular water pipe rows, so that the horizontal fin welded portion of the horizontal fin-equipped water pipe arranged in the region and the surface of another water pipe. It is possible to prevent a large temperature difference from occurring in the water pipe, and to prevent cracks from occurring on the surface of the water pipe, particularly the fin welded portion, due to the thermal stress due to this temperature difference.

2) By setting the length of the combustion gas passage in the water pipe portion without lateral fins to a required length, the combustion gas was lowered to an appropriate temperature when crack burnout was taken into consideration in the water pipe with lateral fins. It can be configured to flow into the combustion gas passage of the horizontal finned water pipe portion in a state, and high temperature corrosion of the horizontal fin is prevented in the combustion gas passage of the horizontal finned water pipe portion,
Due to the effect of the lateral fins, good heat transfer can be obtained even though the combustion gas is at a low temperature, and the pressure loss is small because the lateral fins are provided substantially parallel to the combustion gas flow.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a heat transfer surface structure of a multi-tube once-through boiler according to the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the heat transfer surface structure of the multi-tube through-flow boiler according to the present invention.

FIG. 3 is a vertical sectional view of a conventional multi-tube once-through boiler.

FIG. 4 is a cross-sectional view of FIG.

[Explanation of symbols]

 (1)… Upper heading (2)… Lower heading (3)… Inner annular water tube row (4)… Outer annular water tube row (5)… Combustion gas passage (7)… Combustion chamber (8) ... Boiler outer wall (9) ... Combustion chamber opening (10) ... Combustion gas passage opening (11) ... Flue (12) ... Horizontal fin (13) ... Horizontal finless water pipe (14) ... Horizontal fin water pipe

Claims (1)

[Claims] 1. A top header (1) and a bottom header (2)
It is formed into an annular shape, and both of these headers (1), (2) are
These water pipes are connected to each other with pipes and the inner and outer double ring water is connected.
Arranged as tube rows (3), (4), the inner annular water tube row (3)
Combustion chamber (7) is formed inside, and both annular water pipe rows (3), (4)
An annular combustion gas passageway (5) is formed between
In the annular water pipe array (3), open the combustion chamber to the combustion gas passage (5).
In addition to providing the mouth (9), the outer annular water pipe row (4) is
The combustion that communicates with the flue (11) on the outer wall (8) of the boiler.
A gas passage opening (10) is provided, and both openings (9), (10) are burned.
The combustion chamber (7) should be located opposite to each other and the combustion gas
Place a flat fin (12) on the outer surface of the water pipe facing the passage (5).
Multi-tube type once-through boilers arranged in multi-stages in the axial direction of the water pipe.
In Ra, the water that makes up each of the annular water pipe rows (3), (4)
Downstream of the combustion gas passage (5) from the combustion chamber opening (9) in the pipe
A water pipe with a flow path of a specified length toward the horizontal fin-free water pipe (1
3) The heat transfer surface of a multi-tube once-through boiler characterized by
Construction.