JP6137988B2 - Multi-pipe once-through boiler - Google Patents

Description

The present invention relates to a multi-tube type once-through flow in which vertical heat transfer tubes are arranged in an annular shape, a central portion surrounded by the heat transfer tube rows is set as a combustion chamber, and the heat transfer tubes are heated by a combustion device that performs combustion in the combustion chamber. It relates to boilers. More specifically, the burner burns by injecting a premixed gas in the direction of the heat transfer tube, and the water level is controlled so as to keep the water level set at the height position in the middle of the heat transfer tube. It relates to a once-through boiler.

An annular upper header and an annular lower header are provided at the top, and a multi-tube once-through boiler having a can body constructed by connecting the upper and lower headers with a number of vertical heat transfer tubes. Widely used. In this boiler, the central part of the heat transfer tube array arranged in a ring forms a combustion chamber, and a downward burner is installed in the upper part of the combustion chamber. Heat.

Japanese Patent Application Laid-Open No. 2006-183927 describes a boiler in which a burner is installed in a combustion chamber and a premixed gas is injected toward the inner peripheral surface of a heat transfer tube group. The boiler described in Japanese Patent Laid-Open No. 2006-183927 ejects a premixed gas from a burner provided close to the inner heat transfer tube group substantially horizontally (substantially perpendicular to the inner heat transfer tube group). . When combustion is performed in this state, a flame that directly contacts the inner heat transfer tube group is formed. With such a structure, the flame accompanying gas is immediately collided with the inner peripheral surface of the inner heat transfer tube group, so that the flame is effectively cooled (in order to suppress the temperature rise of the flame, etc.) It is said that the production amount can be reduced.

By the way, the once-through boiler forms a continuous flow path, heats while supplying water supplied from one side, and extracts steam from the other side. And in the once-through boiler, water is put to the height position set in the middle of the heat transfer tube, and heat from the heat transfer tube surface is transferred to the can water in the heat transfer tube by heating the heat transfer tube by combustion with a burner. Increase the temperature of the can water. Can water is heated while rising in the heat transfer tube, and steam is generated when it rises to the boiling temperature in the heat transfer tube. When the heat transfer tube receives heat from the burner, the temperature rises, but if there is can water in the heat transfer tube, the heat absorbed by the heat transfer tube moves to the can water in contact with the inner surface of the heat transfer tube. The heat transfer tube temperature only rises to a certain extent. Then, if the water level is set in the middle of the heat transfer tube, the canned water that is in contact with the inner surface of the heat transfer tube does not exist in the heat transfer tube above the water level position. In this case, the heat transfer tube cannot be cooled with the can water, and the temperature of the upper heat transfer tube continues to rise, and the heat transfer tube may be overheated. However, in reality, boiling of the can water occurs in the heat transfer tube, and the can water reaches the upper part of the set water level due to the boiling due to the boiling. Therefore, even the heat transfer pipe above the water level comes into contact with the can water. Even if the upper part of the heat transfer tube has the can water on the inner surface due to the boiling of the can water, overheating does not occur.

Conversely, if the water level is too high, the amount of canned water that is lifted increases. A steam / water separator is installed at the steam outlet of the boiler, and steam and can water are separated by the steam / water separator, but when the amount of can water reaching the steam / water separator increases, Canned water cannot be separated, and steam that cannot be separated is contained in the steam, thereby reducing the dryness of the steam. Therefore, in the once-through boiler, the water level is set in the middle of the heat transfer tube, and precise water level control is performed so that the appropriate water level can be maintained.

However, in the case immediately after the start of combustion, the heat transfer tube is heated by the combustion device, but boiling of the can water has not yet occurred. There is a case that cooling by is not performed. In that case, the temperature continues to rise in the heat transfer tube above the set water level. In particular, when starting a cold can that starts burning when the can water is cold, the time until the can water boils in the heat transfer tube becomes longer, and the temperature at the top of the heat transfer tube may become higher. . If the heat transfer tube is overheated and distortion occurs or tearing occurs at the joint, the boiler must be replaced early.

JP 2006-183927 A

The problem to be solved by the present invention is to provide a multi-tube once-through boiler that can prevent the upper portion of the heat transfer tube from being overheated in a multi-tube once-through boiler in which the water level is set in the middle of the heat transfer tube. There is to do.

The invention according to claim 1 has a can body having a structure in which a large number of heat transfer tubes that are long in the vertical direction are annularly arranged, and a combustion chamber provided in a central portion of the annularly arranged heat transfer tube row, In a multi-tube once-through boiler in which a combustion device is provided at the top and the can water in the heat transfer tube is heated by combustion by the combustion device, the combustion device has a cylindrical combustion part provided with a large number of small holes. In the combustion part, the premixed gas is injected from the small holes to burn on the outer surface of the cylinder part. The combustion part has a truncated cone part with a diameter decreasing toward the lower part, and a lower part of the truncated cone part. It is characterized by having a cylindrical part installed in the.

According to the second aspect of the present invention, in the multitubular once-through boiler, when an extension line is extended in a direction perpendicular to the surface of the combustion section having a frustoconical shape, a location intersecting with the heat transfer tube is set in the boiler. It arrange | positions so that it may become below a water level, It is characterized by the above-mentioned.

If a frustoconical part with a diameter decreasing toward the lower part is provided in the combustion part of the burner, the premixed gas injected from the combustion part is injected in a direction perpendicular to the inclined frustoconical surface. Therefore, a flame is generated obliquely downward from the burning part of the burner. Since heat generated by the combustion of the flame flows in the injection direction of the premixed gas, the heat transfer tube on the extension line is heated. When the injection direction of the premixed gas is set obliquely downward, it moves downward from the burner combustion section until it reaches the heat transfer tube, so the burner flame heats the heat transfer tube. The position can be lowered. Even if the boiling water of the can in the heat transfer tube is small, overheating in the heat transfer tube can be prevented, and if the part heated by the burner flame is positioned lower than the set water level of the heat transfer tube, Heat transfer tube overheating no longer occurs.

In addition, when the combustion part is conical, the area of the part that performs combustion is reduced on the tip side. If the area for combustion is reduced, the load on the combustion surface may increase and the flame may be lifted. Therefore, the shape of the combustion part is a truncated cone shape whose diameter is reduced toward the lower part, but a cylindrical combustion part is provided below the shape, thereby securing the area of the combustion part. . Therefore, the combustion surface load does not become too high, and a stable combustion state can be ensured. Since this part is the lower end part of the burner and the height position where combustion is performed is low, the heat transfer tube part that heats generated in this part is heated even if no inclination is provided, and the heat transfer tube Overheating is no problem.

Even in an operation state in which the steam load is small and the boiling of the can water is small, the burner flame is formed downward from the set water level, so that the upper heat transfer tube can be prevented from being overheated.

Outline explanatory drawing of multi-tube type once-through boiler in one example of the present invention AA sectional view of FIG. Outline explanatory drawing of the combustion device portion of FIG.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory diagram of a multi-tube once-through boiler according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, and FIG. The boiler 1 is provided with an upper header 2 at the top and a lower header 3 at the bottom. The upper and lower headers have a semicircular cross section with the upper header 2 having a lower surface and the lower header 3 having a flat upper surface, and are formed in an annular shape. The upper header 2 and the lower header 3 are connected by a large number of vertical heat transfer tubes 4 arranged in an annular shape. The heat transfer tubes 4 are arranged with a small gap between them so that the combustion gas can escape between the heat transfer tubes 4. A furnace wall and a heat insulating material layer 13 are provided outside the heat transfer tube row, an opening of the exhaust gas outlet 12 is provided in a part of the furnace wall, and a chimney 14 for discharging the exhaust gas is connected to the tip of the exhaust gas outlet 12.

Water supply to the boiler is performed from the lower header 3. A water supply pipe is connected below the lower header 3 and water is supplied to the lower header 3 by operating a water supply pump (not shown) provided in the middle of the water supply piping. Since a large number of heat transfer tubes 4 are connected to the lower header 3, the water that has entered the lower header is branched into a plurality of heat transfer tubes 4 and flows upward. Water supply control of the boiler is performed based on the water level in the boiler detected by the water level detection device 10 connected to the boiler body at the top and bottom. During the operation of the boiler, the operation of the feed water pump is controlled so as to maintain a predetermined water level set in the middle of the heat transfer tube 4. The water level detection device 10 detects the presence or absence of water at a height position where water supply is started and a height position where water supply is stopped. When the water level detected by the water level detection device 10 is lower than the water supply start water level, the water supply pump is operated to supply water to the boiler. By supplying water, the water level in the boiler rises, and the detected water level becomes the water supply When the water level is higher than the stop water level, the operation of the water supply pump is stopped.

A cylindrical space, which is the central portion of the boiler 1 and surrounded by the heat transfer tubes 4 arranged in an annular shape, becomes the combustion chamber 6, and the combustion device 5 is provided above the combustion chamber 6. The combustion device 5 includes a blower 15 that supplies combustion air, a fuel supply unit 16 that supplies fuel gas, a mixing chamber 17 that mixes the supplied combustion air and fuel gas into a premixed gas, and combustion in the combustion chamber And a premix burner 7 for performing

The premix burner 7 has a cylindrical combustion portion at the tip. The combustion portion is made of a metal cylinder having a large number of small holes, and injects premixed gas from the small holes of the cylinder and burns near the outer surface of the cylinder. In the combustion part, a lower combustion zone 8 which is the tip side and an upper combustion zone 9 which is the base side are set separately, and the upper combustion zone 9 has a truncated cone shape with a tapered front side. It has a cylindrical shape whose diameter does not change. At this time, the lower combustion zone 8 is provided at the lower end of the premixing burner 7 so as to be at a position lower than the set water level during boiler operation. In addition, in the case where the truncated cone portion extends an extension line in a direction perpendicular to the surface of the combustion portion, the angle of inclination or the like so that the portion intersecting with the heat transfer tube is below the set water level of the boiler. The height position of the upper combustion zone 9 is set in advance.

The operation control of the boiler will be described. When starting operation with a boiler, when the water level detected by the water level detection device 10 is lower than the water supply stop water level, the water supply pump is operated until the water supply stop water level is reached, and the water level is raised to the water supply stop water level. Keep it. In the boiler, pre-purge for ventilating the inside of the combustion chamber 6 is performed before the combustion by the combustion device 5 is started. When the blower 15 is operated while the fuel supply from the fuel supply unit 16 is stopped, only air is supplied into the combustion chamber, and even if unburned gas remains in the combustion chamber 6, The fuel gas is exhausted through the chimney 14. When the water level in the boiler is sufficiently high and pre-purge is completed, combustion by the premix burner 7 is started.

A pilot burner (not shown) is provided in the combustion zone portion of the premixing burner 7, and combustion is performed using a fire type generated by the pilot burner. When the premixed gas is injected from the small holes of the upper combustion zone 9 and the lower combustion zone 8 while the pilot burner is burning, the flame of the pilot burner spreads on the surfaces of the upper combustion zone and the lower combustion zone 8, and the combustion zone Burns all over.

The premixed gas that has reached the combustion section of the premix burner 7 is injected into the combustion chamber 6 from the upper combustion zone 9 and the lower combustion zone 8, and in this case, the combustion in the upper combustion zone 9 and the lower combustion zone 8 is performed. The premixed gas is injected in a direction perpendicular to the surface. The flame in the premix burner 7 is generated near the outer surfaces of the upper combustion zone 9 and the lower combustion zone 8, and the high-temperature combustion gas flows on an extension line in the premixed gas injection direction.

In this case, since the lower combustion zone 8 has a vertical combustion surface and the injection direction of the premixed gas is perpendicular to the combustion surface, the premixed gas is injected in the horizontal direction. The heat of the flame in this case first heats the same height position portion as the lower combustion zone 8 of the heat transfer tube 4. Thereafter, the combustion gas further heats the heat transfer tube 4 while flowing along the surface of the heat transfer tube 4 facing the combustion chamber 6, and further flows to the outside of the heat transfer tube row through the gap of the heat transfer tube 4. Heat the heat transfer tube. The heat of the flame is highest at a portion near the combustion surface of the premix burner 7, and the temperature is lowered by exchanging heat while the combustion gas is in contact with the heat transfer tube 4.

The upper combustion zone 9 is positioned higher than the lower combustion zone 8, but the upper combustion zone 9 has a truncated cone shape whose diameter decreases toward the lower side, and the premixed gas injected from the upper combustion zone 9 is inclined. Since it is perpendicular to the burning surface, it is injected obliquely downward. In this case, since the heat of the flame generated in the upper combustion zone 9 falls downward while traveling the distance to the heat transfer tube 4, the height position of the heat transfer tube 4 heated by the burner flame is set at the height of the premix burner 7. The position can be lower than the height position where the upper combustion zone 9 is installed.

Since the boiling of the can water in the heat transfer tube 4 is small immediately after the start of the combustion, if the heating part by the flame is at a position higher than the water level of the heat transfer tube 4 at this time, the can water is formed on the inner peripheral surface side. If the portion not in contact with the heater is heated by the burner flame and cooling with canned water is not performed, the heat transfer tube will be overheated. In the present embodiment, the lower combustion zone 8 is set at a position lower than the water level of the heat transfer tube 4, and the portion of the heat transfer tube heated by the flame from the lower combustion zone 8 first comes into contact with the can water on the inner peripheral surface side. Keep it as a part. In this part, since it is cooled by the inside can water, there is no problem that the heat transfer tube is overheated.

In addition, if it is attempted to install all of the combustion region that is long in the vertical direction at a position lower than the set water level in the heat transfer tube, the combustion portion of the premixing burner 7 needs to be largely inserted into the combustion chamber 6, The total length of the mixing burner becomes longer. If the overall length of the burner is long, a large maintenance space is required above the boiler when the burner is removed, which makes it difficult to handle. Therefore, do not install all of the upper and lower combustion zones at a position lower than the set water level, and in the upper combustion zone, tilt the combustion section to change the direction of formation of the burner flame from the set water level in the heat transfer tube. As a result, the upper portion of the heat transfer tube 4 is not overheated.

In addition, when the combustion part is tapered in the premix burner 7, the area of the part that performs combustion is reduced. If the combustion amount is the same and the combustion area is reduced, the combustion load per unit area will increase, and the premix burner 7 may cause a flame lift or the like. However, in this embodiment, the combustion surface is tapered only in the upper combustion zone 9, and a cylindrical lower combustion zone 8 is provided below the upper combustion zone 9 to ensure the combustion area. As a result, the area of the combustion surface can be ensured, and an unstable combustion state such as the occurrence of lift in the flame can be prevented.

The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical idea of the present invention.

1 boiler
2 Upper header
3 Lower header
4 Heat transfer tube 5 Combustion device
6 Combustion chamber 7 Premix burner 8 Lower combustion zone 9 Upper combustion zone 10 Water level detector 11 Steam / water separator 12 Exhaust gas outlet 13 Heat insulation material layer 14 Chimney
15 Blower 16 Fuel supply part 17 Mixing chamber

Claims (2)

A can having a structure in which a large number of heat transfer tubes that are long in the vertical direction are arranged in an annular shape, and a combustion chamber that is provided in a central portion of the heat transfer tube array that is arranged in an annular shape. In the multi-tube once-through boiler configured to heat the can water in the heat transfer tube by combustion by
The combustion device has a cylindrical combustion portion provided with a large number of small holes, and the combustion portion performs combustion on the outer surface of the cylindrical portion by injecting a premixed gas from the small holes. A multi-tube type once-through boiler characterized by having a truncated cone-shaped portion with a reduced diameter and a cylindrical portion below the truncated cone-shaped portion. In the multi-tube type once-through boiler according to claim 1, when an extension line is extended in a direction perpendicular to the surface of the combustion part having a truncated cone shape, a portion intersecting with the heat transfer tube is below a set water level of the boiler. A multi-pipe once-through boiler, which is arranged to be

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