A structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger

Abstract

The present invention discloses a structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger, comprising an outer shell, an inner tube, and a coil, wherein the inner tube is sleeved in the outer shell, the lower end of the inner tube is connected to an inner tube base, the lower end of the outer shell is connected to a lower limit flange, the coil is arranged in a cavity between the inner tube and the outer shell, the lower limit flange is fixedly connected to the riser base, and the inner diameter direction of the lower limit flange is pressed on the inner tube base; a gap with a thickness of C is reserved between the outer surface of the inner tube and the inner surface of the lower limit flange. The present invention can effectively eliminate the expansion constraint caused by the drastic change of raw gas temperature at the bottom of the coil-type riser heat exchanger, reduce thermal stress, prevent the bottom of the coil-type riser heat exchanger from cracking and damage, ensure its safe operation, and increase its service life.

Description

Technical Field

[0001] The invention relates to the technical field of coking, and in particular to a structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger. Background Art

[0002] During the coking process, coking coal is loaded into the coke oven carbonization chamber, where it is isolated from the air and distilled to generate a large amount of raw coal gas. The raw coal gas leaves the carbonization chamber at a temperature of 650-950°C. After passing through the riser, tee, and bridge pipe to the gas collecting pipe, it is transported to the gas purification process. The high-temperature raw coal gas is cooled to about 80-85°C by spraying circulating ammonia water at the bridge pipe, and a large amount of sensible heat is wasted. If the waste heat of the raw coal gas is recycled and used to produce medium and low-pressure steam for the coking plant's own use, it is one of the effective means to reduce the energy consumption of the coking process and reduce the carbon emission intensity.

[0003] In a coke oven carbonization chamber turnover cycle, the temperature of the gas flowing through the riser stage changes periodically, such as Figure 1 As shown, the temperature during the coal loading and coke pushing stages is high and changes dramatically, with the highest temperature reaching 1100-1200°C.

[0004] The existing method for recovering sensible heat of raw coal gas from coking mainly adopts heat exchange medium to indirectly recover sensible heat of raw coal gas to produce steam through coil or water-jacketed riser heat exchanger. When the riser heat exchanger adopts a spiral coil structure, during the turnover cycle of a coke oven carbonization chamber, the raw coal gas temperature at the inlet of the riser heat exchanger changes dramatically in a short period of time during the coke pushing stage and the coal loading stage. The temperature gradient at the bottom of the riser heat exchanger is the largest and the thermal stress is the largest. In addition, due to the gravity of the upper equipment of the riser heat exchanger, the dead weight of the main equipment and the gravity of the heat exchange medium, the static force at the bottom of the riser heat exchanger is also the largest. Therefore, the bottom of the riser heat exchanger is the part with the largest total stress on the entire equipment. In actual production applications, once the total stress in this area exceeds the stress limit that the materials and structures used can withstand, it will cause cracks and damage at the junction between the bottom and the inner tube of the riser heat exchanger, and high-temperature raw coal gas will leak out from the cracks. The leaked high-temperature raw coal gas will not only cause environmental pollution, but will also immediately burn or corrode the coil when it encounters air, continuing to form local high temperatures. This vicious cycle will eventually cause damage to the riser heat exchanger. When some domestic coking plants' 6.25-meter ramming coke ovens and 7-meter top-loaded coke ovens used coil-type riser heat exchangers to recover waste heat from raw coal gas, 40% to 100% of the riser heat exchangers showed cracking and damage at the junction between the bottom and the inner tube after running for 3 months to 1 year.

[0005] The reason for this damage is that the total stress at the joint of the bottom flange and the inner tube exceeds the stress limit that the materials and structures used can withstand, causing cracks and damage at the junction of the bottom and the inner tube of the riser heat exchanger. High-temperature raw coal gas leaks out from the cracks. The leaked high-temperature raw coal gas not only causes environmental pollution, but also burns or corrodes the coil when it encounters air, continuing to form local high temperatures. This vicious cycle eventually causes damage to the riser heat exchanger.

[0006] Reducing the bottom thermal stress during the entire turnover cycle is a direct and effective way to eliminate cracking and damage of the riser heat exchanger and ensure the safe operation of the equipment. The conditions for the generation of thermal stress are the existence of temperature gradient and expansion constraint resistance. By reducing or eliminating the expansion constraint resistance and reasonable structural design, it is one of the methods to reduce the thermal stress between the bottom and the inner tube of the coil-type riser heat exchanger, eliminate cracking and damage of the riser heat exchanger, ensure the safe operation of the equipment, and extend the service life of the equipment. Summary of the invention

[0007] The technical problem to be solved by the present invention is, in view of the above-mentioned defects existing in the prior art, a structure for reducing the thermal stress at the bottom of the coil-type riser heat exchanger is provided, which can effectively eliminate the expansion constraint at the bottom of the coil-type riser heat exchanger caused by the drastic change in the raw gas temperature, reduce thermal stress, prevent cracking and damage at the bottom of the coil-type riser heat exchanger, ensure its safe operation and increase its service life.

[0008] The technical solution adopted by the present invention to solve the above technical problems is:

[0009] A structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger comprises an outer shell, an inner tube and a coil, wherein the inner tube is sleeved in the outer shell, the lower end of the inner tube is connected to an inner tube base, the lower end of the outer shell is connected to a lower limiting flange, the coil is arranged in a cavity between the inner tube and the outer shell, the lower limiting flange is fixedly connected to the riser base, and the inner diameter direction of the lower limiting flange is pressed on the upper surface of the inner tube base; a gap with a thickness of C is reserved between the outer surface of the inner tube and the inner surface of the lower limiting flange.

[0010] According to the above technical solution, the inner tube and the inner tube base are vertically welded into one body, and the outer shell is vertically welded to the upper part of the lower limiting flange.

[0011] According to the above technical solution, the thickness of the gap is C=X / 100, where X is the inner diameter of the inner cylinder.

[0012] According to the above technical solution, the inner diameter direction of the lower limiting flange is pressed onto the inner tube base through the sealing gasket.

[0013] According to the above technical solution, an annular vertical groove is provided in the middle of the lower limit flange, and the outside of the inner tube base is a vertical step ring. When the lower limit flange and the inner tube base are stacked, the vertical step ring is in the annular vertical groove, forming a transverse sealing gap with a thickness of E.

[0014] According to the above technical solution, the sealing gap is a Z-shaped sealing gap, and the sealing gasket is a Z-shaped sliding sealing gasket, which is arranged in the Z-shaped sealing gap.

[0015] According to the above technical solution, the thickness E of the sealing gap is 5 to 10 mm.

[0016] According to the above technical solution, an expansion gap with a width of D is reserved between the outer facade of the vertical step ring on the outside of the inner tube base and the outer facade of the annular vertical groove in the middle of the lower limiting flange.

[0017] According to the above technical solution, the value of the width D of the expansion gap is: D=X / 300; wherein X is the inner diameter of the inner cylinder.

[0018] According to the above technical solution, the lower limiting flange is fixed to the riser base by limiting bolts, and a sliding gasket is provided between the lower limiting flange and the riser base.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention reserves a gap with a thickness of C between the outer surface of the lower end of the inner tube of the coil-type riser heat exchanger and the inner surface of the lower limit flange. The gap is used as a space for the lower end of the inner tube to expand when the raw gas temperature changes drastically, thereby eliminating expansion constraints and reducing its expansion thermal stress. Through the above method and structural design, the expansion constraints at the bottom of the coil-type riser heat exchanger caused by the drastic change of the raw gas temperature can be effectively eliminated, the thermal stress can be reduced, the bottom of the coil-type riser heat exchanger can be prevented from cracking and damage, thereby ensuring its safe operation and increasing its service life.

[0021] 2. The middle of the lower limit flange is an annular vertical groove, and the outside of the inner tube base is a vertical step ring. The two are vertically stacked to form a Z-shaped sealing gap with a thickness of E. An easy-to-slide sealing gasket is used in the gap to reduce friction resistance and sealing when the inner tube base expands laterally along the circumference. The Z-shaped sealing flow channel and sliding sealing gasket prevent the raw gas in the inner tube from entering the cavity between the outer shell and the inner tube to corrode the coil.

[0022] 3. An expansion gap with a width of D is reserved between the outer facade of the vertical step ring on the outside of the inner tube base and the outer facade of the annular vertical groove in the middle of the lower limit flange. This gap is used to allow the inner tube base to expand when the raw gas temperature changes drastically, eliminating expansion constraints and reducing its expansion thermal stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a graph of the raw gas temperature at the inlet of the riser at each stage of the coke oven turnover cycle in an embodiment of the present invention;

[0024] Figure 2 is a schematic structural diagram of a structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger in an embodiment of the present invention;

[0025] Figure 3 yes Figure 2 The local K view of

[0026] Figure 4 yes Figure 3 A local M view of

[0027] In the figure, 1-inner tube, 2-coil, 3-inner tube base, 4-lower limiting flange, 5-sliding sealing pad, 6-sliding gasket, 7-limiting bolt, 8-outer shell, 9-riser tube base. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0029] Reference Figure 2 to Figure 4 As shown, a structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger in an embodiment of the present invention comprises an outer shell 8, an inner tube 1, and a coil 2. The inner tube 1 is sleeved in the outer shell 8, the lower end of the inner tube 1 is connected to an inner tube base 3, the lower end of the outer shell 8 is connected to a lower limit flange 4, the coil 2 is arranged in a cavity between the inner tube 1 and the outer shell 8, the lower limit flange 4 is fixedly connected to the riser base 9, and the inner diameter direction of the lower limit flange 4 is pressed on the inner tube base 3; a gap with a thickness of C is reserved between the outer surface of the inner tube 1 and the inner surface of the lower limit flange 4, and the gap is used for the expansion space of the lower end of the inner tube 1 when the raw gas temperature changes drastically, eliminating the expansion constraint and reducing its expansion thermal stress.

[0030] Furthermore, the inner tube 1 of the coil-type riser heat exchanger is vertically welded to the inner tube base 3 to form a whole, the coil 2 is arranged in the cavity between the inner tube 1 and the outer shell 8, the lower limit flange 4 is fixed to the riser base 9 by the limit bolts 7 and the sliding gasket 6, the lower limit flange 4 is pressed on the inner tube base 3 by the Z-type sliding sealing gasket 5 in the inner diameter direction, and the outer shell 8 is vertically welded to the upper part of the lower limit flange 4.

[0031] Further, the thickness of the gap is C=X / 100, wherein X is the inner diameter of the inner cylinder 1 .

[0032] Furthermore, the lower limiting flange 4 is pressed on the inner tube base 3 through the sealing gasket 5 in the inner diameter direction.

[0033] Furthermore, an annular vertical groove is provided in the middle of the lower limiting flange 4, and the outside of the inner cylinder base 3 is a vertical step ring. When the lower limiting flange 4 and the inner cylinder base 3 are stacked, the vertical step ring is in the annular vertical groove, and a sealing gap with a thickness of E is formed by stacking.

[0034] Furthermore, the sealing gap is a Z-shaped sealing gap, the sealing gasket is a sliding sealing gasket 5, and the sliding sealing gasket is a Z-shaped sliding sealing gasket, which is arranged in the Z-shaped sealing gap; it is used to reduce friction resistance and sealing effect when the inner tube base 3 expands laterally along the circumference, and prevent the raw gas in the inner tube from entering the cavity between the outer shell 8 and the inner tube to corrode the coil through the Z-shaped sealing gap and the sliding sealing gasket 5.

[0035] Furthermore, the thickness E of the sealing gap is 5-10 mm; when the inner diameter X of the inner cylinder 1 is 400-550, E=5; when X is 550-750, E=10.

[0036] Furthermore, an expansion gap with a width of D is reserved between the outer facade of the vertical step ring outside the inner tube base 3 and the outer facade of the annular vertical groove in the middle of the lower limit flange 4; this gap is used to provide space for the inner tube base 3 to expand when the raw gas temperature changes drastically, eliminating expansion constraints and reducing its expansion thermal stress.

[0037] Furthermore, the value of the width D of the expansion gap is: D=X / 300; wherein X is the inner diameter of the inner cylinder.

[0038] Furthermore, the lower limiting flange 4 is fixed on the riser base 9 by limiting bolts 7 , and a sliding gasket 6 is provided between the lower limiting flange and the riser base 9 .

[0039] The double spiral riser heat exchanger designed by the method for reducing the thermal stress of the bottom flange of the double spiral riser heat exchanger according to the present invention and the equipment structure is used in a coking plant to produce 1.0MPa steam by utilizing the waste heat of the raw gas from the 7.63-meter top-loaded coke oven. The expansion constraint at the bottom of the coil-type riser heat exchanger caused by the drastic change in the raw gas temperature is effectively eliminated, the thermal stress is reduced, the bottom of the coil-type riser heat exchanger is prevented from cracking and damage, its safe operation is ensured, and its service life is increased.

[0040] The above are only preferred embodiments of the present invention, and certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall within the protection scope of the present invention.

Claims

1. A structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger, characterized in that: It includes an outer shell, an inner tube and a coil. The inner tube is sleeved in the outer shell. The lower end of the inner tube is connected to the inner tube base. The lower end of the outer shell is connected to the lower limit flange. The coil is arranged in the cavity between the inner tube and the outer shell. The lower limit flange is fixedly connected to the riser base. The inner diameter direction of the lower limit flange is pressed on the upper surface of the inner tube base. A gap with a thickness of C is reserved between the outer surface of the inner tube and the inner surface of the lower limit flange. An annular vertical groove is provided in the middle of the lower limiting flange, the outside of the inner tube base is a vertical step ring, and an expansion gap with a width of D is reserved between the outer facade of the vertical step ring outside the inner tube base and the outer facade of the annular vertical groove in the middle of the lower limiting flange.

2. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 1, characterized in that: The inner tube and the inner tube base are vertically welded into one body, and the outer shell is vertically welded to the upper part of the lower limiting flange.

3. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 1, characterized in that: The thickness of the gap is C=X / 100, where X is the inner diameter of the inner cylinder.

4. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 1, characterized in that: The inner diameter direction of the lower limiting flange is pressed onto the upper side of the inner tube base through a sealing gasket.

5. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 4, characterized in that: When the lower limiting flange and the inner tube base are stacked, the vertical step ring is located in the annular vertical groove, forming a transverse sealing gap with a thickness of E.

6. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 5, characterized in that: The sealing gap is a Z-shaped sealing gap, and the sealing gasket is a Z-shaped sliding sealing gasket, which is arranged in the Z-shaped sealing gap.

7. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 5, characterized in that: The thickness E of the sealing gap is 5~10mm.

8. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 1, characterized in that: The value of the width D of the expansion gap is: D=X / 300; where X is the inner diameter of the inner cylinder.

9. The structure for reducing thermal stress at the bottom of a coil-type riser heat exchanger according to claim 1, characterized in that: The lower limiting flange is fixed on the riser base through limiting bolts, and a sliding gasket is arranged between the lower limiting flange and the riser base.

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