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

Abstract

The application discloses a mixed-flow small-end-difference steel rolling heating furnace flue gas heat recovery device, which comprises an air preheater, 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 top of the high-temperature box body and the low-temperature box body is fixed on the upper tube plate, and the bottom is fixed on the lower tube plate; a first flue gas inlet section is arranged on the upper left side of the high-temperature box body, a first flue gas outlet section is arranged on the middle right side of the low-temperature box body, a second flue gas outlet section is formed in the lower right side of the high-temperature box body, a second flue gas inlet section is formed in the upper left side of the low-temperature box body, and a third flue gas inlet section is formed in the lower left side of the low-temperature box body. The flue gas flowing out of the high-temperature box body is divided into two flows, enters 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 of low-temperature corrosion of the inlet section of the traditional tubular air preheater and the vibration and wear risk of the tube bundle caused by airflow impact are overcome.

Description

Technical Field

[0001] This invention belongs to the field of waste heat recovery and utilization technology, specifically relating to a mixed-flow small-end differential steel rolling heating furnace flue gas heat recovery device. Background Technology

[0002] Air preheaters are commonly used auxiliary equipment in furnaces and kilns, used to recover waste heat from flue gas, increase the temperature of air entering the furnace, reduce fuel consumption, and improve combustion. Currently, the heat exchanger structures commonly used in thermal furnaces and kilns in steel enterprises both domestically and internationally are mainly internally inserted circular tube heat exchangers and cross-flow plate heat exchangers. Traditional tubular air preheaters are less prone to leakage and easier to replace and maintain than rotary air preheaters. 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 temperature difference is large, generally reaching 150-200℃. This not only hinders the improvement of the overall thermal efficiency of the hot blast stove but also seriously affects the service life and safe operation of the equipment. Furthermore, traditional tubular air preheaters generally use straight circular tubes, resulting in low heat exchange efficiency and large size. Since the heat exchangers are mostly arranged in a cross-flow configuration, a lower flue gas velocity is generally used to reduce the flow resistance on the flue gas side outside the tubes, which reduces the overall heat transfer coefficient of the heat exchanger, typically to 20-30 W / m². 2 On the other hand, the cross-flow arrangement is limited by the heat exchange temperature difference, resulting in high exhaust gas temperature of the air preheater. This not only reduces energy utilization efficiency but also creates local thermal pollution, which is not conducive to carbon reduction and emission reduction, and fails to achieve the requirement of maximizing the recovery of waste heat from flue gas. Summary of the Invention

[0003] In order to overcome the shortcomings of traditional tubular air preheaters, such as excessive end difference, this invention provides a mixed-flow small end difference flue gas heat recovery device for steel rolling heating furnaces that can avoid low-temperature corrosion.

[0004] To achieve the above objectives, the present invention provides a mixed-flow small-end differential rolling mill flue gas heat recovery device, including an air preheater. The air preheater includes a heat exchange box, in which a high-temperature box and a low-temperature box are arranged side by side, as well as an upper tube sheet and a lower tube sheet. There is a gap between the right side of the high-temperature box and the left side of the low-temperature box for flue gas flow. The tops of the high-temperature box and the low-temperature box are fixed to the upper tube sheet, and the bottoms are fixed to the lower tube sheet. A first flue gas inlet section is located at the upper left side of the high-temperature box, and a first flue gas outlet section is located at the middle right side of the low-temperature box. A second flue gas outlet section is opened at the lower right side of the high-temperature box, and a second flue gas inlet section is opened at the upper left side and a third flue gas inlet section is opened at the lower left side of the low-temperature box, 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 sheet 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 sheet 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 heat exchange box has an upper vent hole for air inlet and outlet on the upper plate and a lower vent hole for air inlet and outlet on the lower plate.

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

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

[0009] Furthermore, both the high-temperature chamber and the low-temperature chamber are vertically arranged with multiple heat exchange tubes at uniform intervals. The gaps between the heat exchange tubes form flue gas flow channels, and the interiors of the heat exchange tubes form air flow channels. The upper end of the heat exchange tube is fixed to the upper tube plate, and the lower end is fixed to the lower tube plate. The upper tube plate has upper through holes that correspond to and communicate with the heat exchange tubes, and the lower tube plate has lower through holes that correspond to and communicate with the heat exchange tubes.

[0010] Furthermore, the heat exchange tube is a twisted elliptical tube, a spiral groove tube, or a heat exchange tube with spiral inserts inside.

[0011] Furthermore, the high-temperature chamber and the heat exchange tubes inside the high-temperature chamber are made of a high-temperature resistant material.

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

[0013] Furthermore, both ends of the heat exchange tube are set as straight round tubes, and the weld between the upper through hole of the upper tube sheet and the heat exchange tube and the weld between the lower through hole of the lower tube sheet and the heat exchange tube are protected at high temperature with lightweight castable.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1) Adopting a double-tube, double-shell structure, the flue gas flowing out of the high-temperature chamber is divided into upper and lower streams to enter the low-temperature chamber. After heat exchange, the flue gas flows out of the low-temperature heat exchange chamber 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 and wear of the tube bundle caused by airflow impact. In addition, ordinary carbon steel tubes can be used as heat exchange tube materials in the low-temperature chamber, reducing the material cost of the air preheater.

[0016] 2) The high-temperature section adopts a counter-flow arrangement, which can maximize the air preheating temperature; the low-temperature section adopts a flue gas flow pattern of top and bottom inlet and middle outlet, which can effectively avoid low-temperature corrosion at the air inlet; moreover, the high and low temperature segmented arrangement can achieve the maximum flue gas temperature drop, thereby obtaining the greatest energy-saving benefits.

[0017] 3) Twisted elliptical three-dimensional deformed tubes, spiral groove tubes, or heat exchange tubes with internally added spiral inserts can be used as heat exchange elements to increase the flow velocity of flue gas and enhance 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. Attached Figure Description

[0018] Figure 1 This is a structural diagram of the flue gas heat recovery device for a mixed-flow small-end differential steel rolling furnace according to the present invention.

[0019] Figure 2 This is a schematic diagram of a twisted elliptical tube structure. Detailed Implementation

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

[0021] like Figure 1 The mixed-flow small-end differential rolling mill 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, inside which a high-temperature box 2 and a low-temperature box 9 are arranged side by side, as well as an upper tube sheet 6 and a lower tube sheet 11. The left side 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 of the low-temperature box 9 is in close contact with the right side wall of the heat exchange box 13. There is a gap between the right side of the high-temperature box 2 and the left side of the low-temperature box 9 for flue gas to flow. The tops of the high-temperature box 2 and the low-temperature box 9 are fixed to the upper tube sheet 6, and the bottoms are fixed to the lower tube sheet 11. At the same time, the first flue gas inlet section 1 is located on the upper left side of the high-temperature box 2, the first flue gas outlet section 8 is located on the middle right side of the low-temperature box 9, the lower right side of the high-temperature box 2 has a second flue gas outlet section 3, the upper left side of the low-temperature box 9 has a second flue gas inlet section 7, and the lower left side of the low-temperature box 9 has a third flue gas inlet section 4, so that the lower right side of the high-temperature box 2 is connected to 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 sheet 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; similarly, the lower partition 15 is arranged in the middle of the lower cavity formed by the lower tube sheet 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; correspondingly, the upper plate of the heat exchange box 13 has an upper vent for air in and out, and the lower plate has a lower vent for air in and out; at the same time, the bottom shell 12 and the lower plate of the heat exchange box 13 form a bottom air box 5.

[0023] Both the high-temperature chamber 2 and the low-temperature chamber 9 have multiple heat exchange tubes 10 arranged vertically at uniform intervals. The gaps between the heat exchange tubes 10 form a flue gas flow channel, and the inside of the heat exchange tubes 10 forms an air flow channel. The upper end of the heat exchange tube 10 is fixed on the upper tube plate 6, and the lower end is fixed on the lower tube plate 11. The upper tube plate 6 has upper through holes that correspond to and communicate with the heat exchange tubes, and the lower tube plate 11 also has lower through holes that correspond to and communicate with the heat exchange tubes.

[0024] During operation, low-temperature air enters the heat exchange tube 10 from the upper end of the low-temperature chamber 9 and flows from top to bottom through the heat exchange tube 10 to the bottom air box 5. After turning 180°, it enters the heat exchange tube 10 from the lower end of the high-temperature chamber 2, forming a U-shaped flow. The flue gas enters the high-temperature chamber from the first flue gas inlet section 1 in a counter-current manner, flows from top to bottom and exits from the second flue gas outlet section 3. The flue gas splits into upper and lower streams, which enter the low-temperature chamber 9 from the third flue gas inlet section 4 and the second flue gas inlet section 7 respectively, and then flow towards the middle of the low-temperature chamber 9. Therefore, the flue gas and the air in the heat exchange tubes exchange heat counter-currently in the high-temperature chamber and exchange heat with the low-temperature air in the heat exchange tubes in the low-temperature chamber in a mixed-flow manner. The flue gas after heat exchange flows out of the low-temperature chamber from the first flue gas outlet section 8, while the air after heat exchange flows out from the upper vent at the top of the high-temperature chamber, thus forming a double-shell, double-tube mixed-flow space that avoids low-temperature corrosion. To avoid low-temperature corrosion of the heat exchanger, the flue gas flowing out of the high-temperature chamber is divided into upper and lower streams to enter the low-temperature chamber, and the flue gas after heat exchange flows out of the low-temperature heat exchange chamber from the middle section.

[0025] In this invention, the air flow in the heat exchange tubes 10 of the two chambers is U-shaped. The flue gas and the air in the heat exchange tubes exchange heat in a counter-current manner in the high-temperature chamber. The flue gas flowing out of the high-temperature chamber is divided into upper and lower streams and enters the low-temperature chamber. It exchanges heat with the low-temperature air in the heat exchange tubes inside the low-temperature chamber in a mixed-flow manner. The flue gas after heat exchange flows out of the low-temperature heat exchange chamber from the middle section, thereby avoiding low-temperature corrosion of the air inlet section of the heat exchanger. The air enters the low-temperature chamber from the top of the heat exchange tubes and enters the high-temperature chamber from the bottom air box inside the heat exchanger. Therefore, the high-temperature chamber is a counter-current heat exchange chamber, which can achieve the minimum heat exchange end difference and maximize the air preheating temperature.

[0026] To improve the overall heat exchange performance of the air preheater, heat exchange tube 10 is a twisted elliptical tube (e.g., Figure 2 As shown in the figure, heat exchange tubes with spiral grooves or internal spiral inserts can effectively enhance external turbulence and internal swirling flow, thereby increasing the convective heat transfer coefficient between the inside and outside of the tube.

[0027] The high-temperature chamber 2 and the heat exchange tubes 10 inside it are made of a high-temperature resistant material (such as 310S). The low-temperature chamber 9 and the heat exchange tubes 10 inside it are made of a common material (such as 304 or even ordinary carbon steel) or a high-temperature resistant material (such as 310S) depending on the design operating temperature. The two ends of the heat exchange tubes 10 are set as straight round tubes to facilitate welding to the upper tube sheet and the lower tube sheet. 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 lightweight castable refractory at high temperature.

[0028] In summary, the mixed-flow air preheater of the present invention, with its small end-to-end temperature difference that avoids low-temperature corrosion of flue gas, can achieve an end-to-end temperature difference of up to 80°C, and its overall heat transfer coefficient can be increased to 35–45 W / m². 2 At ℃, compared to traditional tubular air preheaters, 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 improved by 5% to 7%, achieving 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 the inside and outside of the tubes. A shell-side U-shaped double-pass parallel flow type is adopted, and the heat exchange tubes are divided into high-temperature and low-temperature chambers. Different temperature-resistant materials can be selected according to the operating temperature of the two chambers to minimize material costs. The parallel flow heat exchange between the inside and outside of the tubes can reduce the flow resistance on the shell side, i.e., the flue gas side. The high-temperature chamber adopts a counter-flow heat exchange. Heat can maximize the increase in air temperature and increase the average temperature difference of heat exchange. The low-temperature chamber adopts a mixed flow heat exchange with upward co-current and downward counter-current flow to overcome the risk of low-temperature corrosion at the air inlet of the air preheater. Each chamber is arranged in a single pass, with air entering and exiting the air preheater at the top, and flue gas entering and exiting the air preheater at the front and rear sides. This makes the entire air preheater arrangement compact and occupies little space. The flue gas flowing out of the high-temperature chamber is divided into upper and lower streams and enters the low-temperature chamber. The flue gas after heat exchange flows out of the low-temperature heat exchange chamber from the middle section, which can effectively reduce the risk of low-temperature corrosion of the air preheater.

[0029] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A mixed-flow small-end differential steel rolling mill flue gas heat recovery device, characterized in that: The air preheater includes a heat exchange box (13), in which a high-temperature box (2) and a low-temperature box (9) are arranged side by side, as well as an upper tube sheet (6) and a lower tube sheet (11). There is a gap between the right side of the high-temperature box (2) and the left side of the low-temperature box (9) for flue gas to flow. The top of the high-temperature box (2) and the low-temperature box (9) are fixed on the upper tube sheet (6) and the bottom is fixed on the lower tube sheet (11). The first flue gas inlet section (1) is located on the upper left side of the high-temperature chamber (2), the first flue gas outlet section (8) is located on the middle right side of the low-temperature chamber (9), the second flue gas outlet section (3) is located on the lower right side of the high-temperature chamber (2), the second flue gas inlet section (7) is located on the upper left side of the low-temperature chamber (9), and the third flue gas inlet section (4) is located on the lower left side, so that the lower right side of the high-temperature chamber (2) is connected to the upper and lower left sides of the low-temperature chamber (9).

2. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 1, characterized in that: An upper partition (14) is arranged in the middle of the upper cavity formed by the upper tube sheet (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); a lower partition (15) is arranged in the middle of the lower cavity formed by the lower tube sheet (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. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 2, characterized in that: The heat exchange box (13) has an upper vent hole for air in and out on the upper plate and a lower vent hole for air in and out on the lower plate.

4. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 1, characterized in that: The bottom of the heat exchange box (13) is provided with a bottom shell (12), and the bottom shell (12) and the lower plate of the heat exchange box (13) form a bottom air box (5).

5. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 1, characterized in that: The left side of the high-temperature chamber (2) is in close contact with the left side wall of the heat exchange chamber (13), and the right side of the low-temperature chamber (9) is in close contact with the right side wall of the heat exchange chamber (13).

6. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 1, characterized in that: Both the high-temperature chamber (2) and the low-temperature chamber (9) are vertically arranged with multiple heat exchange tubes (10) spaced evenly. The gaps between the heat exchange tubes (10) form a flue gas flow channel, and the heat exchange tubes (10) form an air flow channel. The upper end of the heat exchange tube (10) is fixed on the upper tube plate (6), and the lower end is fixed on the lower tube plate (11). The upper tube plate (6) has an upper through hole that corresponds to and communicates with the heat exchange tubes, and the lower tube plate (11) has a lower through hole that corresponds to and communicates with the heat exchange tubes.

7. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 6, characterized in that: The heat exchange tube (10) is a twisted elliptical tube, a spiral groove tube, or a heat exchange tube with spiral inserts inside.

8. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 6, characterized in that: The high-temperature chamber (2) and the heat exchange tube (10) inside the high-temperature chamber (2) are made of high-temperature resistant material.

9. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 6, characterized in that: The low-temperature chamber (9) and the heat exchange tubes (10) inside the low-temperature chamber (9) are made of ordinary carbon steel or high-temperature resistant materials.

10. The mixed-flow small-end differential rolling mill flue gas heat recovery device according to claim 6, characterized in that: The two ends of the heat exchange tube (10) are set as straight round tubes. 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 high temperature with lightweight castable.

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