Flue gas heat recovery device for mixed-flow small-end-difference steel rolling heating furnace

Abstract

The invention discloses a mixed-flow small-end-difference steel rolling heating furnace flue gas heat recovery device which comprises an air preheater, and the air preheater comprises a heat exchange box body, a high-temperature box body, a low-temperature box body, an upper tube plate and a lower tube plate. The tops of the high-temperature box body and the low-temperature box body are fixed on the upper tube plate, and the bottoms are fixed on the lower tube plate; the first flue gas inlet section is arranged on the upper left portion of the high-temperature box, the first flue gas outlet section is arranged in the middle of the right side of the low-temperature box, the second flue gas outlet section is arranged on the lower right portion of the high-temperature box, the second flue gas inlet section is arranged on the upper left portion of the low-temperature box, and the third flue gas inlet section is arranged on the lower left portion of the low-temperature box. A double-tube-pass and double-shell-pass structural form is adopted, flue gas flowing out of the high-temperature box body is divided into an upper part and a lower part to enter the low-temperature box body, and the flue gas after heat exchange flows out of the low-temperature heat exchange box body from the middle section, so that the heat exchange performance of the air preheater is greatly improved; and the risk that an inlet section of a traditional tubular air preheater is corroded at low temperature and the risk that a tube bundle is impacted by airflow to cause vibration abrasion are overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat recovery and utilization, and specifically relates to a flue gas heat recovery device for a mixed flow small end difference steel rolling heating furnace. Background Art

[0002] Air preheater is a common furnace auxiliary equipment that recovers flue gas waste heat, increases the air temperature entering the furnace, reduces furnace fuel consumption, and improves combustion conditions. At present, the heat exchanger structures commonly used in thermal furnaces of domestic and foreign steel enterprises are mainly round tube heat exchangers with internal plug-ins and cross-flow plate heat exchangers. Compared with rotary air preheaters, traditional tubular air preheaters are not easy to leak and are easy to replace and repair. However, due to the low air inlet temperature, tubular air preheaters often encounter low-temperature corrosion and leakage problems during operation, and the high-temperature end difference is large, generally reaching 150-200°C, which is not only not conducive to improving the overall thermal efficiency of the hot blast furnace, but also seriously affects the service life and safe operation of the equipment. On the other hand, traditional tubular air preheaters generally use straight round tubes, with low heat exchange efficiency and large size; and because the heat exchangers are mostly cross-flow arranged, in order to reduce the flow resistance on the flue gas side outside the tube, a lower flue gas flow rate is generally used, which reduces the overall heat transfer coefficient of the heat exchanger on the one hand, and the heat transfer coefficient is generally 20-30W / m 2 ℃; on the other hand, the cross-flow arrangement is limited by the heat exchange temperature difference, and the exhaust temperature of the air preheater is high, which not only reduces the energy utilization efficiency, but also forms local thermal pollution, is not conducive to carbon reduction and emission reduction, and fails to achieve the maximum recovery of flue gas waste heat requirements. Summary of the invention

[0003] In order to overcome the disadvantages of the traditional tubular air preheater such as too large end difference, the present invention provides a mixed flow small end difference steel rolling heating furnace flue gas heat recovery device which can avoid low temperature corrosion.

[0004] To achieve the above-mentioned purpose, the present invention provides a flue gas heat recovery device for a mixed flow small end difference steel rolling heating furnace, including an air preheater, the air preheater including a heat exchange box, a high-temperature box and a low-temperature box, as well as an upper tube plate and a lower tube plate are arranged side by side in the heat exchange box, and a gap for flue gas flow is provided between the right side of the high-temperature box and the left side of the low-temperature box; the tops of the high-temperature box and the low-temperature box are fixed on the upper tube plate, and the bottoms are fixed on the lower tube plate; the first flue gas inlet section is arranged on the upper left side of the high-temperature box, the first flue gas outlet section is arranged on the middle right side of the low-temperature box, the second flue gas outlet section is opened on the lower right side of the high-temperature box, the second flue gas inlet section is opened on the upper left side of the low-temperature box, and the third flue gas inlet section is opened on the lower left side, so that the lower right side of the high-temperature box is connected to the upper and lower left sides of the low-temperature box.

[0005] Furthermore, an upper partition is arranged in the middle of the upper cavity formed by the upper tube plate and the heat exchange box, dividing the upper cavity into an upper high-temperature box air outlet cavity and a low-temperature box air inlet cavity; a lower partition is arranged in the middle of the lower cavity formed by the lower tube plate and the heat exchange box, dividing the lower cavity into an upper high-temperature box air inlet cavity and a low-temperature box air outlet cavity.

[0006] Furthermore, the upper plate of the heat exchange box body is provided with upper vent holes for air inlet and outlet, and the lower plate is provided with lower vent holes for air inlet and outlet.

[0007] Furthermore, a bottom shell is arranged at the bottom of the heat exchange box body, and the bottom shell and the lower plate of the heat exchange box body form a bottom bellows.

[0008] Furthermore, the left side surface of the high-temperature box body is in close contact with the left side wall of the heat exchange box body, and the right side surface of the low-temperature box body is in close contact with the right side wall of the heat exchange box body.

[0009] Furthermore, the high-temperature box and the low-temperature box are both vertically arranged with a plurality of evenly spaced heat exchange tubes, the gaps between the heat exchange tubes constitute a flue gas flow channel, and the heat exchange tubes constitute an air flow channel; the upper ends of the heat exchange tubes are fixed on the upper tube plate, and the lower ends are fixed on the lower tube plate, and the upper tube plate is provided with upper through holes that are connected to the heat exchange tubes in a one-to-one correspondence, and the lower tube plate is provided with lower through holes that are connected to the heat exchange tubes in a one-to-one correspondence.

[0010] Furthermore, the heat exchange tube is a twisted elliptical tube, a spiral grooved tube, or a heat exchange tube with a spiral insert sheet added inside.

[0011] Furthermore, the high temperature box and the heat exchange tubes in the high temperature box are made of high temperature resistant materials.

[0012] Furthermore, the low-temperature box and the heat exchange tubes in the low-temperature box are made of ordinary carbon steel pipes or high-temperature resistant materials.

[0013] Furthermore, both ends of the heat exchange tube are arranged as straight round tubes, and the welds between the upper through holes of the upper tube sheet and the heat exchange tubes and the welds between the lower through holes of the lower tube sheet and the heat exchange tubes are protected at high temperatures by lightweight castables.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1) The double-tube-pass and double-shell-pass structure is adopted. The flue gas flowing out of the high-temperature box is divided into upper and lower streams and enters the low-temperature box. The flue gas after heat exchange flows out of the low-temperature heat exchange box from the middle section. This not only greatly improves the heat exchange performance of the air preheater, but also overcomes the risk of low-temperature corrosion of the inlet section of the traditional tubular air preheater and the risk of vibration wear of the tube bundle caused by the impact of airflow. In addition, ordinary carbon steel pipes can be used as heat exchange tube materials in the low-temperature box to reduce the material cost of the air preheater.

[0016] 2) The high-temperature section adopts a counter-current layout, which can maximize the air preheating temperature; the low-temperature section adopts a flue gas flow method of entering from the top and bottom and exiting from the middle section, which can effectively avoid low-temperature corrosion at the air inlet end; and the high and low temperature segmented layout can achieve the maximum flue gas temperature drop, thereby obtaining the maximum energy saving benefits.

[0017] 3) Twisted elliptical three-dimensional deformed tubes, spiral grooved tubes or heat exchange tubes with spiral inserts added inside can be used as heat exchange elements to increase the flue gas side flow rate and enhance the heat exchange inside and outside the tube, thereby improving the overall heat exchange effect and heat recovery level, reducing the comprehensive cost of waste heat recovery, and achieving better energy saving and emission reduction effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of a flue gas heat recovery device of a mixed flow small end difference steel rolling heating furnace of the present invention;

[0019] Figure 2 Schematic diagram of the twisted elliptical tube structure. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0021] like Figure 1 The mixed flow small end differential steel rolling heating furnace flue gas heat recovery device shown has two tube passes and two shell passes, including an air preheater and a bottom shell 12 located at the bottom of the air preheater. The air preheater includes a heat exchange box 13, in which a high-temperature box 2 and a low-temperature box 9, as well as an upper tube sheet 6 and a lower tube sheet 11 are arranged side by side; the left side of the high-temperature box 2 is close to the left wall of the heat exchange box 13, and the right side of the low-temperature box 9 is close to the right wall of the heat exchange box 13. There is a gap for flue gas flow between the right side of the high-temperature box 2 and the left side of the low-temperature box 9. The tops of the high-temperature box 2 and the low-temperature box 9 are fixed on the upper tube sheet 6, and the bottoms are fixed on the lower tube sheet 11; at the same time, the first flue gas inlet section 1 is arranged on the upper left side of the high-temperature box 2, the first flue gas outlet section 8 is arranged on the middle right side of the low-temperature box 9, the second flue gas outlet section 3 is opened on the lower right side of the high-temperature box 2, the second flue gas inlet section 7 is opened on the upper left side of the low-temperature box 9, and the third flue gas inlet section 4 is opened on the lower left side, so that the lower right side of the high-temperature box 2 is connected with the upper and lower left sides of the low-temperature box 9.

[0022] The upper partition 14 is arranged in the middle of the upper cavity formed by the upper tube plate 6 and the heat exchange box 13, and divides the upper cavity into an upper high-temperature box air outlet cavity 16 and a low-temperature box air inlet cavity 17; similarly, the lower partition 15 is arranged in the middle of the lower cavity formed by the lower tube plate 11 and the heat exchange box 13, and divides the lower cavity into an upper high-temperature box air inlet cavity 18 and a low-temperature box air outlet cavity 19; correspondingly, the upper plate of the heat exchange box 13 is provided with upper air vents for air inlet and outlet, and the lower plate is provided with lower air vents for air inlet and outlet; at the same time, the bottom shell 12 and the lower plate of the heat exchange box 13 form a bottom bellows 5.

[0023] Multiple heat exchange tubes 10 are vertically arranged at even intervals in the high-temperature box 2 and the low-temperature box 9. The gaps between the heat exchange tubes 10 constitute a flue gas flow channel, and the heat exchange tubes 10 constitute an air flow channel. The upper ends of the heat exchange tubes 10 are fixed on the upper tube plate 6, and the lower ends are fixed on the lower tube plate 11. The upper tube plate 6 is provided with upper through holes that are connected to the heat exchange tubes one by one, and the lower tube plate 11 is also provided with lower through holes that are connected to the heat exchange tubes one by one.

[0024] During operation, low-temperature air enters the heat exchange tube 10 from the upper end of the low-temperature box 9, and flows from top to bottom through the heat exchange tube 10 in the low-temperature box 9 to the bottom wind box 5, turns 180° and then enters the heat exchange tube 10 in the high-temperature box 2 from the lower end of the high-temperature box 2, forming a U-shaped flow; the flue gas enters the high-temperature box from the first flue gas inlet section 1 in a countercurrent manner, flows from top to bottom and flows out from the second flue gas outlet section 3, and the flue gas is divided into upper and lower two streams, respectively entering the low-temperature box 9 from the third flue gas inlet section 4 and the second flue gas inlet section 7 and turning to flow to the middle of the low-temperature box 9. Therefore, the flue gas and the air in the heat exchange tube perform countercurrent heat exchange in the high-temperature box, and perform mixed flow heat exchange with the low-temperature air in the heat exchange tube in the low-temperature box. The flue gas after heat exchange flows out of the low-temperature box from the first flue gas outlet section 8, and the air after heat exchange flows out from the upper vent at the top of the high-temperature box, thereby forming a double-shell-pass and double-tube-pass mixed flow flow space that can avoid low-temperature corrosion. In order to avoid low-temperature corrosion of the heat exchanger, the flue gas flowing out of the high-temperature box is divided into upper and lower streams and enters the low-temperature box. The flue gas after heat exchange flows out of the low-temperature heat exchange box from the middle section.

[0025] In the present invention, the air flow in the heat exchange tubes 10 of the two boxes is U-shaped, and the flue gas and the air in the heat exchange tubes are subjected to countercurrent heat exchange in the high-temperature box. The flue gas flowing out of the high-temperature box is divided into upper and lower streams and enters the low-temperature box, and is subjected to mixed flow heat exchange with the low-temperature air in the heat exchange tubes in the low-temperature box. The flue gas after heat exchange flows out of the low-temperature heat exchange box from the middle section, thereby preventing the air inlet section of the heat exchanger from being corroded by low temperature; the air enters the low-temperature box from the top of the heat exchange tube and enters the high-temperature box from the bottom bellows in the heat exchanger. Therefore, the high-temperature box is subjected to countercurrent heat exchange, which can achieve the minimum heat exchange end difference and maximize the air preheating temperature.

[0026] In order to improve the comprehensive heat exchange performance of the air preheater, the heat exchange tube 10 is a twisted elliptical tube (such as Figure 2 As shown in the figure), spiral grooved tubes or heat exchange tubes with spiral inserts added inside can effectively enhance the turbulence outside the tube and the swirl inside the tube, thereby improving the convective heat transfer coefficient inside and outside the tube.

[0027] The high temperature box 2 and the heat exchange tube 10 in the high temperature box 2 are made of high temperature resistant materials (such as 310S), and the low temperature box 9 and the heat exchange tube 10 in the low temperature box 9 are made of ordinary materials (such as 304 or even ordinary carbon steel) or high temperature resistant materials (such as 310S) according to the design operating temperature. The two ends of the heat exchange tube 10 are set as straight round tubes to be welded with the upper tube sheet and the lower tube sheet; and the weld between the upper through hole of the upper tube sheet 6 and the heat exchange tube 10 and the weld between the lower through hole of the lower tube sheet 11 and the heat exchange tube 10 are protected by light castables for high temperature.

[0028] In summary, the mixed flow air preheater with small end difference that can avoid low-temperature corrosion of flue gas can achieve an end difference within 80°C, and the comprehensive heat transfer coefficient can be increased to 35-45W / m 2 ℃, compared with the traditional tubular air preheater, the heat recovery efficiency of the air preheater is increased by more than 25%, and the overall heat utilization efficiency of the heating furnace is increased by 5% to 7%, realizing efficient and energy-saving operation of flue gas waste heat recovery; twisted elliptical tubes are selected as heat exchange tube elements to achieve enhanced heat exchange on both sides of the tube inside and outside; the shell side U-shaped two-way parallel flow type is adopted, and the heat exchange tubes are divided into high and low temperature boxes. Different temperature-resistant materials can be selected according to the operating temperature of the two boxes to minimize material costs; the parallel flow heat exchange of the fluid inside and outside the tube can reduce the flow resistance on the shell side, that is, the flue gas side, and the high-temperature box adopts countercurrent heat exchange Heat can maximize the increase in air temperature and the average temperature difference of heat exchange. The low-temperature box adopts mixed flow heat exchange with upstream downstream and downstream countercurrent to overcome the risk of low-temperature corrosion at the air inlet end of the air preheater; each box is arranged in a one-way manner, and the air inlet and outlet of the air preheater are at the top, and the flue gas inlet and outlet of the air preheater are at the front and back sides, making the entire air preheater layout compact and occupying a small area. The flue gas flowing out of the high-temperature box is divided into upper and lower streams and enters the low-temperature box. The flue gas after heat exchange flows out of the low-temperature heat exchange box from the middle section, which can effectively reduce the risk of low-temperature corrosion of the air preheater.

[0029] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A mixed flow small end difference steel rolling heating furnace flue gas heat recovery device, characterized in that: The air preheater comprises an air preheater, which comprises a heat exchange box (13), wherein a high temperature box (2) and a low temperature box (9), as well as an upper tube plate (6) and a lower tube plate (11) are arranged side by side in the heat exchange box (13), and a gap for flue gas to flow is provided between the right side of the high temperature box (2) and the left side of the low temperature box (9); the tops of the high temperature box (2) and the low temperature box (9) are fixed on the upper tube plate (6), and the bottoms are fixed on the lower tube plate (11); The first smoke inlet section (1) is arranged at the upper left side of the high temperature box (2), the first smoke outlet section (8) is arranged at the middle right side of the low temperature box (9), the lower right side of the high temperature box (2) is provided with a second smoke outlet section (3), the upper left side of the low temperature box (9) is provided with a second smoke inlet section (7), and the lower left side is provided with a third smoke inlet section (4), so that the lower right side of the high temperature box (2) is in communication with the upper left side and lower left side of the low temperature box (9).

2. According to claim 1, the mixed flow small end difference steel rolling heating furnace flue gas heat recovery device is characterized in that: An upper partition (14) is arranged in the middle of the upper cavity formed by the upper tube plate (6) and the heat exchange box (13), dividing the upper cavity into an upper high-temperature box air outlet cavity (16) and a low-temperature box air inlet cavity (17); and a lower partition (15) is arranged in the middle of the lower cavity formed by the lower tube plate (11) and the heat exchange box (13), dividing the lower cavity into an upper high-temperature box air inlet cavity (18) and a low-temperature box air outlet cavity (19).

3. According to claim 2, the mixed flow small end difference steel rolling heating furnace flue gas heat recovery device is characterized in that: The upper plate of the heat exchange box (13) is provided with upper vent holes for air inlet and outlet, and the lower plate is provided with lower vent holes for air inlet and outlet.

4. According to claim 1, the mixed flow small end difference steel rolling heating furnace flue gas heat recovery device is characterized in that: A bottom shell (12) is arranged at the bottom of the heat exchange box body (13), and the bottom shell (12) and the lower plate of the heat exchange box body (13) form a bottom wind box (5).

5. According to claim 1, the mixed flow small end difference steel rolling heating furnace flue gas heat recovery device is characterized in that: The left side surface of the high-temperature box (2) is in close contact with the left side wall of the heat exchange box (13), and the right side surface of the low-temperature box (9) is in close contact with the right side wall of the heat exchange box (13).

6. The mixed flow small end difference steel rolling heating furnace flue gas heat recovery device according to claim 1 is characterized in that: A plurality of heat exchange tubes (10) are vertically arranged at even intervals in the high-temperature box (2) and the low-temperature box (9); the gaps between the heat exchange tubes (10) constitute a flue gas flow channel, and the heat exchange tubes (10) constitute an air flow channel; the upper ends of the heat exchange tubes (10) are fixed to the upper tube plate (6), and the lower ends are fixed to the lower tube plate (11); the upper tube plate (6) is provided with upper through holes that are connected to the heat exchange tubes in a one-to-one correspondence, and the lower tube plate (11) is provided with lower through holes that are connected to the heat exchange tubes in a one-to-one correspondence.

7. The mixed flow small end difference steel rolling heating furnace flue gas heat recovery device according to claim 6 is characterized in that: The heat exchange tube (10) is a twisted elliptical tube, a spiral groove tube, or a heat exchange tube with a spiral insert sheet added inside.

8. The mixed flow small end difference steel rolling heating furnace flue gas heat recovery device according to claim 6 is characterized by: The high-temperature box (2) and the heat exchange tube (10) inside the high-temperature box (2) are made of a high-temperature resistant material.

9. The mixed flow small end difference steel rolling heating furnace flue gas heat recovery device according to claim 6 is characterized in that: The low-temperature box (9) and the heat exchange tube (10) inside the low-temperature box (9) are made of ordinary carbon steel pipes or high-temperature resistant materials.

10. The mixed flow small end difference steel rolling heating furnace flue gas heat recovery device according to claim 6, characterized in that: Both ends of the heat exchange tube (10) are arranged as straight round tubes, and the weld between the upper through hole of the upper tube plate (6) and the heat exchange tube (10) and the weld between the lower through hole of the lower tube plate (11) and the heat exchange tube (10) are protected at high temperature by lightweight castables.

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