CN101813323B - Insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes - Google Patents

Abstract

The invention discloses a plug-in air preheater with the same temperature difference between the inlet and outlet of heat exchange tubes, which comprises a bellows and multiple rows of heat exchange tubes. The upper end of the bellows is provided with a cold air inlet, and the lower end of the bellows is provided with a hot air outlet. A flue gas inlet is provided, and a flue gas outlet is provided on the other side of the bellows. The multiple rows of heat exchange tubes are evenly arranged in the bellows and communicate with the cold air inlet and the hot air outlet. Inserts are arranged in the heat exchange tubes. The insert is composed of a straight section placed at the inlet section of the heat exchange tube and a helical section placed at the outlet section of the heat exchange tube. From the side of the flue gas inlet to the side of the flue gas outlet, the percentage of the length of the straight section of the insert in each row of heat exchange tubes to the total length gradually decreases. The plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tube can reduce the temperature difference of the tube wall between the heat exchange tubes, so that the heated air in each row of heat exchange tubes has the same temperature difference between the inlet and outlet, and has the best comprehensive heat exchange effect .

Description

Plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tube

technical field

The invention relates to an air preheater, in particular to a plug-in air preheater used in chemical industry, metallurgy, energy power, building materials and other industrial fields.

Background technique

Insert-type air preheaters are mostly used for flue gas-air heat exchange, and are widely used in waste heat utilization and air preheating of hot blast stoves, heating furnaces, industrial furnaces, boilers, etc. in chemical, metallurgy, energy power, building materials and other industrial fields. It can fully recover waste heat and provide pure high-temperature air, saving a lot of energy. The existing insert air preheater has a simple structure and convenient material selection, but the front row of heat exchange tubes near the flue gas inlet is directly radiated by the space in front of the heat exchange tubes, and the temperature is higher than other tubes, which leads to the The thermal expansion of the heat pipes is different, and when one heat exchange pipe is damaged, the entire preheater will be scrapped.

In order to solve the above problems, there are three traditional methods: one is to rely on the heat exchange tube at the entrance of the flue gas to select a high temperature resistant alloy pipe; the other is to hang the tube group with a bracket so that the lower part is suspended in the air; the third is to use a balance bar The support method allows it to expand upward when heated. In recent years, two methods have been developed: one is to make the diameter of the first 1 to 2 rows of tubes at the entrance of the high-temperature flue gas larger than the rest of the tubes in the tube bundle, so that the flow resistance will be smaller under the same tube length. There is naturally more air in the pipe, so the cooling of the pipe wall is greater; the second is to adopt the elbow structure, and the elbow can separately compensate the thermal expansion of each pipe to a certain extent. Although the above method can partially solve the problem of uneven thermal expansion of each row of heat exchange tubes in the insert air preheater, it needs to use expensive high-temperature-resistant alloy materials or a suspension device with a relatively complicated structure or a complicated heat exchange tube structure, which causes insertion The piece-type air preheater is expensive and has a short service life, which affects the overall performance of the air preheater.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and provide a method that can reduce the temperature difference between the tube walls of the heat exchange tubes, so that the heated air in each row of heat exchange tubes has the same temperature difference between the inlet and outlet, and has optimal Plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tube with comprehensive heat exchange effect.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A plug-in air preheater with the same temperature difference between the inlet and outlet of heat exchange tubes, including a bellows and multiple rows of heat exchange tubes, the upper end of the bellows is provided with a cold air inlet, the lower end of the bellows is provided with a hot air outlet, and one side of the bellows is provided with flue gas The other side of the air box is provided with a flue gas outlet. The multi-row heat exchange tubes are evenly arranged in the air box and communicate with the cold air inlet and the hot air outlet. The heat exchange tubes are provided with inserts. The straight section is placed in the inlet section of the heat exchange tube, and the helical section is placed in the outlet section of the heat exchange tube.

From the side of the flue gas inlet to the side of the flue gas outlet, the percentage of the length of the straight section of the insert in each row of heat exchange tubes to the total length gradually decreases.

The cold air inlet is located on the side close to the flue gas outlet.

The hot air outlet is located on the side close to the flue gas inlet.

The hot air outlet is located on the side close to the flue gas inlet.

Compared with the prior art, the present invention has the advantages of:

The insert in the plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tube of the present invention is composed of a straight section and a helical section. In the process of the centerline of the heat pipe, at the inlet section of the heat exchange tube, the thermal boundary layer is thinner, and the local surface heat transfer coefficient is higher than that of the fully developed section in the middle and lower part of the heat exchange tube. The straight section of the insert is placed in the heat exchange tube The inlet section of the pipe makes full use of the characteristics of the thin thermal boundary layer and the large local surface heat transfer coefficient of the inlet section of the pipe, so that the heat exchange tube has good heat transfer performance on the basis of a small increase in pressure drop. At the same time, the insert’s The straight section reduces the hydraulic diameter of the heat exchange tube, which leads to an increase in the heat transfer coefficient and a small pressure loss; the thermal boundary layer is thicker at the outlet section of the heat exchange tube, and the helical section of the insert is placed in the The outlet section of the heat exchange tube makes the fluid generate a tangential velocity component, and its flow velocity increases, especially near the wall of the heat exchange tube, which increases the shear stress on the wall and enhances the fluid mixing caused by the secondary flow. The heat exchange effect is enhanced; by adjusting the length of the helical section of the inserts in each row of heat exchange tubes, the flow rate of air in the heat exchange tubes can be controlled, so that the temperature difference of the tube walls of the heat exchange tubes can be controlled, and the flow of heated air in the heat exchange tubes can be controlled. The temperature difference between the inlet and outlet reduces the cost of the insert-type air preheater, prolongs its life and improves its overall performance. From the side of the flue gas inlet to the side of the flue gas outlet, the percentage of the length of the straight section of the insert in each row of heat exchange tubes to the total length gradually decreases, because the longer the straight section of the insert, the smaller the flow resistance of the heat exchange tube, Therefore, the air flow through the heat exchange tube near the high temperature side of the flue gas is large, and the cooling of the tube wall is greater; while the air flow through the heat exchange tube near the low temperature side of the flue gas is small, and the cooling of the tube wall is smaller. In order to achieve the purpose of controlling the temperature difference of the tube wall of the heat exchange tube and controlling the same temperature difference between the inlet and outlet of the heated air; the heat exchange tube has the same wall temperature, and the material selection of the heat exchange tube is easy to unify, which can reduce the cost of high temperature resistant materials Use, reduce the material cost of the air preheater, but also improve the overall life of the air preheater. At the same time, it can avoid the burnout of the heat exchange tube caused by the high temperature in the pipe at the high temperature side of the flue gas inlet, and avoid the dew point corrosion problem caused by the low temperature of the flue gas outlet at the low temperature side. The plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tubes of the present invention has small flow resistance, low manufacturing cost, long service life, good overall heat exchange performance, and can realize efficient and stable operation of the air preheater.

Description of drawings

Fig. 1 is the three-dimensional structure schematic diagram of the present invention;

Fig. 2 is a main sectional view of the present invention;

Fig. 3 is the left view of the present invention;

Fig. 4 is a top view of the present invention;

Fig. 5 is a structural schematic diagram of a heat exchange tube provided with an insert in the present invention;

Fig. 6 is a schematic diagram of the structure of the insert in the present invention.

Each label in the figure means:

1. Bellows; 2. Heat exchange tube; 3. Insert; 11. Cold air inlet; 12. Hot air outlet; 13. Smoke inlet; 14. Smoke outlet; 15. Connecting plate; 31. Straight section; 32 , Spiral segment.

Detailed ways

1 to 6 show a plug-in air preheater with the same temperature difference between the inlet and outlet of heat exchange tubes according to the present invention. The preheater includes an air box 1 and multiple rows of heat exchange tubes 2 . The upper end of the bellows 1 is provided with a cold air inlet 11, the lower end of the bellows 1 is provided with a hot air outlet 12, one side of the bellows 1 is provided with a smoke inlet 13, the other side of the bellows 1 is provided with a smoke outlet 14, and the bellows 1 is provided with an upper, Two connecting plates 15 are lowered, and the flue gas inlet and outlet are separated from the air inlet and outlet by the two connecting plates 15 . In this embodiment, there are 4 rows of heat exchange tubes 2, 6 in each row, and the 4 rows of heat exchange tubes 2 are evenly arranged in the bellows 1. The connection is fixed, and the heat exchange tube 2 communicates with the cold air inlet 11 and the hot air outlet 12. An insert 3 is arranged inside the heat exchange tube 2. The insert 3 is composed of a straight section 31 and a spiral section 32. The straight section 31 is placed in the heat exchange The inlet section of the tube 2, the helical section 32 is placed at the outlet section of the heat exchange tube 2, when the fluid flows into the heat exchange tube 2, the flow thermal boundary layer has a process of growing from zero to converging on the centerline of the heat exchange tube 2, At the inlet section of the heat exchange tube 2, the thermal boundary layer is relatively thin, and the local surface heat transfer coefficient is higher than that of the fully developed section in the middle and lower part of the heat exchange tube 2. The straight section 31 of the insert 3 is placed at the inlet of the heat exchange tube 2 section, making full use of the characteristics of the thin thermal boundary layer and the large local surface heat transfer coefficient of the inlet section of the pipe, so that the heat exchange tube 2 has a good heat transfer performance on the basis of a small increase in pressure drop, and at the same time, the insert 3 The straight section 31 reduces the hydraulic diameter of the heat exchange tube 2, which leads to an increase in the heat transfer coefficient and a small pressure loss; the thermal boundary layer at the outlet section of the heat exchange tube 2 is thicker, and the The helical section is placed at the outlet section of the heat exchange tube 2, so that the fluid generates a tangential velocity component, and its flow velocity increases, especially near the wall of the heat exchange tube 2, so that the shear stress at the wall increases, and the secondary flow The resulting fluid mixing is enhanced, and the heat exchange effect is enhanced; by adjusting the length of the helical section of the insert 3 in each row of heat exchange tubes 2, the flow velocity of the air in the heat exchange tubes 2 can be controlled, thereby controlling the flow rate of the heat exchange tubes 2. The wall temperature difference and the temperature difference between the heated air at the inlet and outlet of the heat exchange tube 2 reduce the cost of the plug-in air preheater, prolong its life and improve its overall performance.

In this embodiment, from the side of the flue gas inlet 13 to the side of the flue gas outlet 14, the percentage of the length of the straight section 31 of the insert 3 in each row of heat exchange tubes 2 to the total length gradually decreases, and the cold air inlet 11 is located near the flue gas On the side of the outlet 14, the hot air outlet 12 is located on the side close to the flue gas inlet 13. As the straight section 31 of the insert 3 is longer, the flow resistance of the heat exchange tube 2 is smaller, so the high temperature near the flue gas inlet 13 The air flow through the heat exchange tube 2 on the side is large, and the cooling on the tube wall is greater; while the air flow through the heat exchange tube 2 on the low temperature side near the flue gas outlet 14 is small, the cooling on the tube wall is smaller , so as to achieve the purpose of controlling the temperature difference of the tube wall of the heat exchange tube 2 and controlling the same temperature difference between the inlet and outlet of the heated air; Use, reduce the material cost of the air preheater, but also improve the overall life of the air preheater. At the same time, it can avoid the burnout of the heat exchange tube caused by the high temperature in the pipe at the high temperature side of the flue gas inlet 13, and also avoid the dew point corrosion problem caused by the low temperature at the low temperature side of the flue gas outlet 14. The plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tubes of the present invention has small flow resistance, low manufacturing cost, long service life, good overall heat exchange performance, and can realize efficient and stable operation of the air preheater.

The plug-in air preheater with the same temperature difference between the inlet and outlet of the heat exchange tube of the present invention realizes the heat exchange between the flue gas and the air through the heat exchange tube 2. When in use, the high-temperature flue gas enters the wind box 1 from the flue gas inlet 13 on one side of the wind box 1. And flow through the heat exchange tube 2 to heat the heat exchange tube 2, the cold air enters the heat exchange tube 2 from the cold air inlet 11 on the upper end of the bellows 1, and when the cold air flows through the heat exchange tube 2, it is heated by the heat exchange tube 2 and is heated The air gathered in the lower part of the wind box 1 is finally discharged from the hot air outlet 12, and the flue gas with reduced temperature is discharged from the flue gas outlet 14 on the other side of the wind box 1. The heat exchange tube 2 is inserted with an insert 3 composed of a straight section 31 and a helical section 32. Along the flue gas flow direction, the straight section 31 of the insert 3 in the heat exchange tube 2 is continuously shortened while the helical section 32 is continuously increased. , can achieve the purpose of controlling the wall temperature difference of the heat exchange tube 2 and controlling the heated air to have the same temperature difference between the inlet and outlet. The present invention can make each row of heat exchange tubes 2 have the same wall temperature and the temperature difference between the air inlet and outlet of each heat exchange tube 2, which can prevent the heat exchange tubes from burning out due to the high temperature inside the tubes at the high temperature side of the flue gas inlet 13, and also The dew point corrosion problem caused by too low temperature at the low temperature side of the flue gas outlet 14 can be avoided, thereby reducing the manufacturing cost of the air preheater and prolonging its service life.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with the art, without departing from the scope of the technical solution of the present invention, can use the technical content disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent implementation of equivalent changes example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims (5)

1. insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes, comprise bellows (1) and many row's heat exchanger tubes (2), described bellows (1) upper end is provided with cool air inlet (11), bellows (1) lower end is provided with hot air outlet (12), bellows (1) one side is provided with smoke inlet (13), bellows (1) opposite side is provided with exhanst gas outlet (14), described many row's heat exchanger tubes (2) are evenly arranged in the bellows (1) and are communicated with cool air inlet (11) and hot air outlet (12), be provided with insert (3) in the described heat exchanger tube (2), it is characterized in that: described insert (3) is made up of straight section (31) and spiral section (32), described straight section (31) places the entrance of heat exchanger tube (2), and described spiral section (32) places the outlet section of heat exchanger tube (2).

2. insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes according to claim 1, it is characterized in that: to exhanst gas outlet (14) one sides, each is arranged the percentage that straight section (31) length of insert (3) in the heat exchanger tube (2) accounts for length overall and reduces gradually from smoke inlet (13) one sides.

3. insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes according to claim 1 and 2 is characterized in that: described cool air inlet (11) is positioned at the side near exhanst gas outlet (14).

4. insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes according to claim 1 and 2 is characterized in that: described hot air outlet (12) is positioned at the side near smoke inlet (13).

5. insert type air preheater with same inlet-outlet temperature difference of heat exchange tubes according to claim 3 is characterized in that: described hot air outlet (12) is positioned at the side near smoke inlet (13).

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