JP2012057804A - Tube bank structure boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance durability while maintaining advantages, such as low NOx emissions and space savings, of a tube bank structure boiler, and to reduce the amount of emission of CO.SOLUTION: In the tube bank structure boiler, a plurality of heat-transfer tubes 1 for a heat-transfer tube wall, which are elongated in a vertical direction, are laid out in a line toward a rear side from a front side on the right and left lateral surfaces of a storage water heater body; a fin 4 for the heat-transfer tube wall is provided between the adjacent heat-transfer tubes 1, so as to form the heat-transfer tube walls 8 in two rows; a space sandwiched between the heat-transfer tube walls 8 serves as a combustion gas flow space 7; and a heat-transfer tube bank, which is composed of many heat-transfer tubes for the heat-transfer tube bank, elongated in the vertical direction, is provided in the combustion gas flow space 7 to make combustion gas flow in the direction of crossing the heat-transfer tube in the combustion gas flow space 7, the heat-transfer tube bank and the heat-transfer tube wall are divided into an upstream area in which the combustion gas up to about 1,000°C flows and a downstream section with respect to the upstream area, so that an arrangement pitch of the heat-transfer tubes 1 can be set lower in the upstream area than in the downstream section.

Description

  In the present invention, two parallel heat transfer tube walls are formed by heat transfer tube wall fins connecting a large number of heat transfer tubes and heat transfer tubes, and a heat transfer tube group including a plurality of heat transfer tubes is provided between the heat transfer tube walls. And a tube group structure boiler for heating the can water in the heat transfer tubes by flowing the combustion gas in the crossing direction with respect to the heat transfer tubes of the heat transfer tube group.

  As described in Japanese Patent No. 2948519, a pair of heat transfer tube walls are installed with a space left and right, and a space between the heat transfer tube walls is set as a combustion gas flow space, and one opening of the combustion gas flow space is provided. 2. Description of the Related Art A boiler having a configuration in which a combustion device is disposed in a part, a combustion gas outlet is disposed in the other opening, and a large number of heat transfer tubes are provided in the combustion gas flow space is known. In this tube group structure boiler, since the heat transfer tube is installed in the immediate vicinity of the combustion device, the temperature of the flame generated in the combustion device is immediately reduced by the heat transfer tube, and the time for the flame to stay at high temperature is reduced. The amount of NOx generated can be reduced by shortening the length. Moreover, since it is the structure which packs a heat exchanger tube in combustion gas flow space, there also exists an advantage that the installation area of a boiler can be made small.

  However, in the boiler having the tube group structure as described above, the combustion gas on the upstream side close to the combustion device is high in temperature, and the combustion gas temperature gradually decreases by performing heat exchange with the heat transfer tube. Therefore, the heating amount for the heat transfer tube varies depending on the place. In the heat transfer tube wall on the upstream side of the combustion gas flow, the heat transfer tube wall fin connecting the adjacent heat transfer tubes becomes high temperature because it is strongly heated by the high temperature combustion gas. Since the heat transfer tube wall fins expand at high temperatures, the thermal stress applied between the heat transfer tube wall heat transfer tube and the heat transfer tube wall fins increases in the upstream heat transfer tube wall, resulting in lower durability. There is a problem.

  Japanese Patent No. 2948519 reduces the amount of CO generated by forming a heat transfer tube nonexistent space. If a heat transfer tube is installed in the combustion gas flow space, the flame temperature is lowered by the heat transfer tube before the combustion is completed, and if combustion is incomplete, the amount of CO generated increases. Therefore, a heat transfer tube non-existing space is provided and a space for oxidizing CO is opened, but in the case of a configuration in which the heat transfer tube is removed from the heat transfer tube group, a drift may occur in the combustion gas flow. If there is a heat transfer tube existence space where the heat transfer tube is installed and a heat transfer tube nonexistence space where the heat transfer tube is removed, the combustion gas concentrates in the heat transfer tube nonexistence space with low resistance. A lot of combustion gas flows, and the flow rate of the combustion gas is reduced in other portions. If the combustion gas flow in the heat transfer tube group is biased, the heat absorption efficiency of the entire boiler is also lowered.

Japanese Patent No. 2948519

  The problem to be solved by the present invention is to provide a tube group structure boiler that can increase the durability and reduce the amount of CO generated while maintaining the advantages of the tube group structure boiler such as low NOx and space saving. There is.

  On the left and right side surfaces of the can body, a plurality of heat transfer tube wall heat transfer tubes extending in the vertical direction are arranged in a line from the front side to the rear side, and the heat transfer tube wall is located between adjacent heat transfer tube wall heat transfer tubes. A plurality of heat transfer tube groups extending in the vertical direction in the combustion gas flow space, with a space sandwiched between the heat transfer tube walls as a combustion gas flow space. In a tube group structure boiler having a structure in which a heat transfer tube group comprising heat transfer tubes is provided and combustion gas flows in a direction crossing the heat transfer tubes of the heat transfer tube group, the heat transfer tube group and the heat transfer tube wall are approximately up to 1000 ° C. It is divided into an upstream area where the combustion gas flows and a downstream part, and the arrangement pitch of the heat transfer tube wall heat transfer tubes is set to be smaller in the upstream area than in the downstream part.

  In addition, the upstream heat transfer tube group is divided into an upstream front portion and an upstream rear portion, a large diameter heat transfer tube is installed at the upstream front portion, and a small diameter heat transfer tube is installed at the upstream rear portion. And when the heat transfer tube group and the heat transfer tube wall provided in the combustion gas flow space are divided into an upstream region, a middle flow region, and a downstream region, the arrangement of the heat transfer tube wall heat transfer tube and the heat transfer tube group heat transfer tube The pitch is set so that the upstream region <the middle flow region <the downstream region, and the heat transfer tube surface is processed so that the heat transfer area of the heat transfer tube increases toward the downstream region.

  In the heat transfer tube wall corresponding to the upstream region of the combustion gas flow, the length of the heat transfer tube wall fin decreases in the front-rear direction, so that the temperature rise of the heat transfer tube wall fin portion is suppressed, and the heat transfer tube wall fin Since the thermal stress applied between the heat transfer tube wall heat transfer tubes is reduced, the durability of the heat transfer tube wall fin portion is improved. In addition, by reducing the diameter of the heat transfer tube group for the heat transfer tube group at the rear of the combustion gas flow upstream region, the interval between the heat transfer tubes can be increased without changing the arrangement of the heat transfer tube groups, and the interval increases. As a result, the rapid temperature drop of the combustion gas can be suppressed and combustion can be completed, so that the amount of CO generated can be reduced.

Sectional drawing which cut | disconnected the combustion gas flow space part of the boiler which is implementing this invention in the horizontal direction

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a combustion gas flow space portion of a boiler embodying the present invention cut in the transverse direction, as viewed from above the boiler. The boiler connects the upper header (not shown) provided at the upper part of the can body and the lower header (not shown) provided at the lower part of the can body with a number of vertical heat transfer tubes. This is a multi-tube once-through boiler in which water supplied from is heated in a heat transfer tube to generate steam, and the steam is taken out from the top. The boiler body comprises two rows of heat transfer tube walls 8 provided on the side surface and a heat transfer tube group provided in a combustion gas flow space 7 which is a space sandwiched between the heat transfer tube walls 8. The heat transfer tube wall 8 is formed by a large number of heat transfer tube wall heat transfer tubes 1, and the heat transfer tube group is formed by a large number of heat transfer tube group heat transfer tubes 2. The heat transfer tube wall 8 is formed by arranging the heat transfer tube wall heat transfer tubes 1 extending in the vertical direction in a horizontal row and connecting the adjacent heat transfer tubes with the heat transfer tube wall fins 3. The outer wall of the can is constituted by the heat transfer tube wall 8.

  The combustion gas flow space 7 is one in which the combustion gas flows from the left side to the right side of the drawing, and openings are opened at both ends of the combustion gas flow space 7. The right side is the combustion gas outlet 6. In the combustion device installation unit 5, a combustion device (not shown) that generates a flame is installed in the direction of the combustion gas flow space 7. When combustion is performed in the combustion device, the combustion gas generated by the combustion is It flows in the combustion gas flow space in the right direction and is discharged from the combustion gas outlet 6 to an exhaust pipe (not shown).

  The heat transfer tube wall and the heat transfer tube group are divided into an upstream region, a middle flow region, and a downstream region along the flow direction of the combustion gas. As for the division of the upstream region / middle flow region / downstream region, a portion where the combustion gas temperature is generally higher than about 1000 ° C. is an upstream region, a portion lower than about 600 ° C. is a downstream region, and a portion therebetween is a middle flow region. Note that the combustion gas temperature varies depending on the measurement location, the combustion state, and the like. Therefore, the above temperature is a guideline and may vary depending on the situation. Further, the upstream region is divided into an upstream region front portion that is the portion closest to the combustion apparatus and an upstream region rear portion that is the other portion.

  The arrangement pitch of the heat transfer tube wall heat transfer tubes 1 in the heat transfer tube wall 8 (the distance between the central axes of the adjacent heat transfer tube wall heat transfer tubes 1) is different in the upstream region, the midstream region, and the downstream region. . When the pitch in the upstream region of the heat transfer tube 1 for the heat transfer tube wall is A, the pitch in the middle flow region is B, and the pitch in the downstream region is C, the size of each pitch is A <B <C. The pitch is increased in the order of basin, middle basin, and downstream. When the arrangement pitch of the heat transfer tube wall heat transfer tubes is different, the length of the heat transfer tube wall fins connecting the adjacent heat transfer tube wall heat transfer tubes is different. The heat transfer tube wall fins 3 in the upstream region use heat transfer tube wall fins such as round bars that are short in the front-rear direction, and the heat transfer tube wall fins 3 in the middle and downstream regions are flat. Therefore, the heat transfer tube wall fins in the downstream region are longer in the front-rear direction than in the middle flow region. The arrangement pitch of the heat transfer tubes 2 for the heat transfer tube group is also set in accordance with the arrangement pitch of the heat transfer tubes for the heat transfer tube wall, and the arrangement pitch becomes wider in the order of the upstream region, the midstream region, and the downstream region.

  The heat transfer tube wall heat transfer tubes 1 in this embodiment all have the same diameter, but the heat transfer tube group heat transfer tube 2 uses a heat transfer tube whose diameter varies depending on the location. ing. The heat transfer tubes in the heat transfer tube group use a heat transfer tube with a large diameter at the front of the upstream region, a heat transfer tube with a small diameter at the rear of the upstream region, and heat transfer tubes with a diameter between them in the midstream and downstream regions. is doing. A heat transfer tube having a larger diameter is advantageous in terms of heat absorption because the amount of heat received from the combustion gas increases. However, if a heat transfer tube having a large diameter is used in the portion where the arrangement pitch of the upstream region is reduced, the space through which the combustion gas flows becomes narrow, and the amount of heat exchange performed between the combustion gas and the heat transfer tube 2 for the heat transfer tube group is large. Become. Then, the temperature of the combustion gas decreases early, the combustion reaction ends incompletely, and the amount of CO generated increases. For this reason, the heat transfer tube 2 for the heat transfer tube group at the rear of the upstream region has a small diameter. In other words, a heat transfer tube with a large diameter is used as the heat transfer tube in the upstream area near the combustion device, so that the high-temperature combustion gas generated in the combustion device is cooled early, and the combustion gas is heated to a high temperature. The amount of NOx generated is suppressed by shortening the residence time. And the heat exchanger tube of the upstream area rear part of a heat exchanger tube group uses a heat exchanger tube with a small diameter, and is trying to open a large space between heat exchanger tubes. When the distance between the heat transfer tubes is increased and the area of the flow path through which the combustion gas flows is increased, the temperature drop of the combustion gas is suppressed, and combustion can be completed during that time, so that the amount of CO generated is reduced.

  The temperature of the combustion gas flowing in the middle and downstream areas is lower than that of the combustion gas flowing in the upstream area, and the volume of the combustion gas is also small, so the amount of heat that can be absorbed by the heat transfer tube is reduced. . In view of this, heat absorbing fins 4 are provided on the surface of the heat transfer tubes after the midstream region of the heat transfer tube group so that the heat transfer area of the heat transfer tubes increases toward the downstream side. If the heat absorption fins 4 are installed on the surface of the heat transfer tube, the area of the heat transfer surface increases, so that a large amount of heat can be absorbed even from the combustion gas whose temperature has decreased.

  When the boiler is operated, a flame is generated from a combustion device (not shown) provided in the combustion device installation section 5 toward the heat transfer tube group in the combustion gas flow space. Heat transfer tubes with large diameters are densely arranged at the front upstream of the heat transfer tube group, and the heat is taken away by the heat transfer tubes while the combustion reaction is in progress. Is suppressed. When the flame temperature increases, the amount of NOx generated increases, but the amount of NOx generated can be reduced by preventing the flame temperature from rising.

  The combustion gas that has passed through the upstream front portion of the heat transfer tube group then flows through the upstream rear portion of the heat transfer tube group. Since a heat transfer tube having a small diameter is arranged at the rear part of the upstream region, a relatively large space is opened between the heat transfer tubes, and the reduction of the combustion gas temperature by the heat transfer tube becomes gradual. During this time, the combustion reaction proceeds, so the amount of CO generated can be reduced. In addition, the heat transfer tubes are arranged uniformly at the rear of the upstream region, and the combustion gas flow space is not biased to a specific position. Heat exchange can be performed efficiently even after the middle basin.

  The temperature of the combustion gas flow after the middle flow region is lowered by heat exchange in the upstream region, and the volume of the combustion gas is lowered. However, the heat transfer tubes after the middle basin are provided with heat absorbing fins 4 on the surface, and also absorb heat from the heat absorbing fins 4, and therefore absorb a lot of heat from the combustion gas whose temperature has decreased. Can do. Further, since the temperature of the combustion gas is further lower in the downstream region than in the middle flow region, the heat absorption fins 4 in the downstream region are larger than the heat absorption fins 4 in the middle flow region. . By increasing the heat transfer area of the heat absorbing fins 4 in the downstream region, heat can be effectively absorbed even from the combustion gas whose temperature has decreased.

  Further, the combustion gas heats not only the heat transfer tube group but also the heat transfer tube wall 8. In the heat transfer tube wall, a heat transfer tube wall fin 3 is provided between adjacent heat transfer tubes to form a heat transfer tube wall. However, the heat transfer tube wall fin 3 absorbs the heat of the combustion gas. The heat transfer tube wall heat transfer tube 1 also has a heat transfer function. Heating of the heat transfer tube wall fins 3 becomes stronger as the temperature of the combustion gas becomes higher, and the heat transfer tube wall fins 3 increase as the length of the heat transfer tube wall fins 3 increases. It is determined by the temperature of the combustion gas in contact with the heat transfer area and the heat transfer area of the heat transfer tube wall fin. When the amount of heat applied to the heat transfer tube wall fins increases, the heat transfer tube wall fins expand due to heat, so if the length of the heat transfer tube wall fins in the upstream region is long, Since it is heated by the combustion gas, a large thermal stress is generated. The pitch of the heat transfer tubes on the heat transfer tube wall is arranged so that the upstream region <the middle flow region <the downstream region, and the length in the front-rear direction of the heat transfer tube wall fins is shortened in the upstream region. Generation of a large thermal stress in the upstream region of the tube wall can be prevented, and durability (life) of the heat transfer tube wall can be improved.

1 Heat Transfer Tube for Heat Transfer Tube Wall 2 Heat Transfer Tube for Heat Transfer Tube Group
3 Heat transfer tube wall fins
4 Heat absorption fins
5 Combustion device installation section
6 Combustion gas outlet
7 Combustion gas flow space
8 Heat transfer tube wall

Claims (3)

  On the left and right side surfaces of the can body, a plurality of heat transfer tube wall heat transfer tubes extending in the vertical direction are arranged in a line from the front side to the rear side, and the heat transfer tube wall is located between adjacent heat transfer tube wall heat transfer tubes. A plurality of heat transfer tube groups extending in the vertical direction in the combustion gas flow space, with a space sandwiched between the heat transfer tube walls as a combustion gas flow space. In a tube group structure boiler having a structure in which a heat transfer tube group comprising heat transfer tubes is provided and combustion gas flows in a direction crossing the heat transfer tubes of the heat transfer tube group, the heat transfer tube group and the heat transfer tube wall are approximately up to 1000 ° C. A pipe characterized in that it is divided into an upstream area through which the combustion gas flows and a downstream part, and the arrangement pitch of the heat transfer pipes for the heat transfer pipe wall is smaller in the upstream area than in the downstream part. Group structure boiler.   In the tube group structure boiler according to claim 1, the upstream heat transfer tube group is divided into an upstream region front portion and an upstream region rear portion, and a heat transfer tube having a large diameter is installed in the upstream region front portion, and the upstream region rear portion. Is a tube-group boiler characterized by installing heat transfer tubes with small diameters. The tube group structure boiler according to claim 1 or 2, wherein the heat transfer tube group and the heat transfer tube wall provided in the combustion gas flow space are divided into an upstream region, a middle flow region, and a downstream region, and the heat transfer tube wall The arrangement pitch of the heat transfer tubes and the heat transfer tubes for the heat transfer tube group is set as upstream region <middle flow region <downstream region, and the heat transfer tube surface is processed so that the heat transfer area of the heat transfer tube increases toward the downstream region. A tube group structure boiler characterized by that.

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