Coaxial hollow loop heat pipe evaporator for chemical low-temperature waste heat recovery

Abstract

This invention discloses a coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry, belonging to the field of industrial energy conservation and high-efficiency heat transfer technology. The evaporator includes a shell, a liquid wick, a steam pipe, and a condenser. The shell is a hollow cylindrical structure, enclosed by an inner channel wall, an outer channel wall, an upper sealing plate, and a lower sealing plate to form a closed annular space. A porous liquid wick is arranged inside the annular space. The shell is coaxially installed inside a chemical pipeline, where the high-temperature waste heat fluid simultaneously flows over both the inner and outer channel walls, achieving double-sided heating. The condenser recirculates the liquid working medium, which is uniformly supplied to the evaporation area under the capillary force of the liquid wick. After absorbing heat and vaporizing, the working medium is output to the condenser end through the steam pipe, completing a closed-loop cycle. This invention employs a centrally radial, high-aspect-ratio toothed groove protrusion structure to increase the heat exchange area, resulting in low flow resistance and reduced ash accumulation and blockage. It is suitable for low-temperature waste heat recovery scenarios in chemical plants, such as the top of a residual liquid extraction tower.

Description

Technical Field

[0001] This invention belongs to the field of industrial energy conservation and high-efficiency heat transfer technology, specifically relating to a coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry. Background Technology

[0002] In chemical catalytic cracking, aromatics extraction, and other production processes, a large amount of low-temperature waste heat is not fully utilized. Taking the raffinate tower in an aromatics extraction unit as an example, a large amount of low-temperature waste heat of 110-160°C is generated at the top of the tower after the distillation process. Among existing recovery technologies, plate heat exchangers are prone to corrosion and ash accumulation and blockage; Organic Rankine Cycle (ORC) systems are large and have high investment costs; and the inner walls of chemical pipelines are prone to scaling and have limited space, making it difficult to arrange traditional heat exchange devices.

[0003] Loop heat pipes, as highly efficient two-phase heat transfer devices driven by capillary force, offer advantages such as high heat transfer efficiency, long transmission distance, and no need for external power. However, existing loop heat pipes mostly employ flat-plate evaporators, which are difficult to arrange rationally in cylindrical chemical pipelines, severely limiting the effective heat exchange area. Furthermore, the large fluctuations in vapor flow and temperature at the top of the evaporator tower can easily cause instability or even failure of traditional loop heat pipes. Therefore, there is an urgent need to develop a new type of loop heat pipe evaporator that is adaptable to the structure of chemical pipelines, has a large heat exchange area, and strong resistance to heat load fluctuations. Summary of the Invention

[0004] The purpose of this invention is to provide a coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry, so as to solve the technical problems of traditional flat loop heat pipe evaporators being difficult to adapt to circular chemical pipelines, having insufficient heat exchange area, poor operational stability under fluctuating heat load conditions, and being prone to clogging and corrosion of conventional heat exchangers; it achieves efficient recovery of low-temperature waste heat in the confined space of chemical pipelines, and has the performance of double-sided heat exchange, resistance to heat fluctuations, low flow resistance, and resistance to chemical corrosion.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry includes a shell, a liquid absorber, a steam pipe, and a condenser. The shell is generally hollow cylindrical. The shell includes an inner channel wall, an outer channel wall, an upper sealing plate, and a lower sealing plate. The inner channel wall is spaced inside the outer channel wall, and the upper and lower sealing plates cover the top and bottom of the inner and outer channel walls, respectively. The inner and outer channel walls, the upper and lower sealing plates form a closed annular space. The liquid absorber has a porous structure and is located between the inner and outer channel walls within the shell. The shell is filled with a working medium. The shell is coaxially installed inside a chemical pipeline, where a fluid carrying waste heat heats the working medium to form steam. The steam pipe and the condenser are connected to the shell to achieve closed-loop flow of the working medium.

[0006] Preferably, both the inner and outer channel walls include multi-toothed protrusions to form a centrally radial heat exchange wall with a high aspect ratio; the high aspect ratio satisfies h / w≥5, where h is the channel depth and w is the channel width, in order to increase the heat exchange area and enhance fluid turbulence.

[0007] Preferably, the inner channel wall and the outer channel wall are made of one or more of Q345R steel, austenitic stainless steel or nickel-based alloy.

[0008] Preferably, the steam pipe is located at the top of the upper sealing plate, and the condenser pipe is located on the side wall of the outer channel, realizing a working fluid flow channel with liquid entering at the bottom and steam exiting at the top of the annular containment space; a gap is left between the outer wall of the shell and the inner wall of the chemical pipeline, and the outer ends of the steam pipe and the condenser pipe are respectively inserted into the chemical pipeline, and the shell is installed on the chemical pipeline through the steam pipe and the condenser pipe.

[0009] Preferably, the upper end of the liquid-absorbing core is provided with multiple longitudinal steam channels spaced apart circumferentially. The inner and outer walls of the liquid-absorbing core are in close contact with the inner and outer channel walls, respectively. The steam generated by the heating and evaporation of the working medium rises along the longitudinal steam channels.

[0010] Preferably, a gap is left between the upper end of the liquid-absorbing core and the upper sealing plate, and a steam chamber is provided circumferentially at the upper end of the liquid-absorbing core, which communicates with each longitudinal steam channel, so that the steam is gathered together through the steam chamber.

[0011] Preferably, the liquid-absorbing core is made of metal powder, metal fiber, or metal mesh sintered at high temperature; the effective capillary pore size of the liquid-absorbing core satisfies the capillary suction force formula, which is: , In the formula, Capillary suction; The surface tension of the working medium; The surface contact angle of the suction core is [value], and ; The effective capillary pore size of the liquid suction core.

[0012] Preferably, the liquid-absorbing core is prepared by a multi-stage sintering process, the preparation process of which includes the following steps: Raw material preparation: Sintering with 100-300 mesh spherical and dendritic metal powders; Mold preparation: A graphite forming mold matching the annular structure of the liquid suction core is adopted. The inner diameter, outer diameter and axial length of the liquid suction core are limited by the inner core, outer mold and end limiting structure. Slow heating phase: Increase the temperature to 200℃ at a rate of 3-5℃ / min and hold for 30min; Second heating stage: Increase the temperature to 850℃ at a rate of 5~10℃ / min; Sintering and heat preservation stage: heat preservation at 850℃ for 2 hours; Cooling stage: Cool to room temperature with the furnace.

[0013] Preferably, the axis of the shell coincides with the center line of the chemical pipeline; the highest temperature heat source at the center of the cross-section of the chemical pipeline heats the inner channel wall through the internal cavity of the inner channel wall, and the edge heat source of the chemical pipeline heats the outer channel wall, forming a heat exchange structure with double-sided heating.

[0014] By adopting the above technical solution, the present invention has the following beneficial effects: 1. The shell of the present invention adopts a hollow cylindrical coaxial arrangement, which can be directly built into the inside of a circular chemical pipeline; the inner channel wall and the outer channel wall are provided with radial high depth-to-width ratio toothed protrusions with h / w≥5 to achieve double-sided heat exchange, which greatly increases the effective heat exchange area under the condition of limited pipeline space, strengthens fluid disturbance, and improves waste heat recovery capacity.

[0015] 2. The fluid temperature and flow rate are highest at the center of the cross-section of the chemical pipeline of the present invention. The high-temperature medium passes through the central cavity of the shell and directly heats the inner channel wall. The medium at the edge of the pipeline scours the outer channel wall, fully capturing the high-grade heat in the pipeline flow field. It can match the pipeline flow field and has higher heat recovery efficiency.

[0016] 3. The porous liquid wick prepared by sintering in this invention has excellent capillary suction capability, and continuously supplies liquid working fluid to the evaporation zone by relying on capillary suction force; the vapor chamber collects the vaporized working fluid, and the gas-liquid channel is separated. In the face of temperature and flow fluctuations of 110-160℃ in the residual liquid tower, it can effectively prevent the liquid wick from drying out, and the operation stability of the loop heat pipe system is greatly improved.

[0017] 4. The shell pressure-bearing components of this invention are made of chemical-grade materials such as Q345R, austenitic stainless steel, and nickel-based alloys, which are suitable for the corrosive environment of chemical media; the central through-hole hollow structure will not completely block the pipeline flow channel, and the outer wall of the shell and the inner wall of the pipeline are reserved with fluid channels, resulting in low overall flow resistance, reducing the risk of dust accumulation, scaling and blockage, and avoiding pipeline overpressure problems.

[0018] 5. The evaporator of this invention is suspended and fixed by the steam pipe and condenser pipe penetrating the chemical pipe wall, without the need for additional large flange support; it has a high degree of structural integration, does not require external pump drive, and relies on the capillary force of the loop heat pipe to complete the working fluid circulation, resulting in low equipment investment and operation and maintenance costs. Attached Figure Description

[0019] Figure 1 This is a three-dimensional structural diagram of the present invention when it is installed on a chemical pipeline; Figure 2 This is a schematic diagram of the exploded structure of the present invention; Figure 3 This is a three-dimensional structural diagram of the present invention; Figure 4 This is a partial cross-sectional view of the present invention; Figure 5 This is a three-dimensional structural diagram of the liquid-absorbing core of the present invention; Figure 6 This is a cross-sectional structural diagram of the liquid-absorbing core of the present invention.

[0020] The reference numerals in the figure are as follows: 1. Shell; 10. Inner channel wall; 11. Outer channel wall; 12. Upper sealing plate; 13. Lower sealing plate; 2. Liquid suction core; 20. Longitudinal steam channel; 21. Steam chamber; 3. Steam pipe; 4. Condenser pipe; 5. Chemical pipeline. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] like Figures 1 to 6As shown. A coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry includes a shell 1, a liquid absorption core 2, a steam pipe 3, and a condenser pipe 4; the shell 1 is generally hollow cylindrical; the shell 1 includes an inner channel wall 10, an outer channel wall 11, an upper sealing plate 12, and a lower sealing plate 13; the inner channel wall 10 is spaced and sleeved inside the outer channel wall 11, and the upper sealing plate 12 and lower sealing plate 13 are respectively covered on the top and bottom of the inner channel wall 10 and the outer channel wall 11; the inner channel wall 10, the outer channel wall 11, the upper sealing plate 12, and the ... outer channel wall 11, the inner channel wall 12, the outer channel wall 11, the outer channel wall 12, the outer channel wall 11, the inner channel wall 12, the The channel wall 11, the upper sealing plate 12, and the lower sealing plate 13 enclose a closed annular receiving space; the liquid suction core 2 has a porous structure and is disposed between the inner channel wall 10 and the outer channel wall 11 inside the shell 1; the shell 1 is filled with a working medium; the shell 1 is coaxially disposed inside the chemical pipeline 5, and the fluid with residual heat in the chemical pipeline 5 heats the working medium to form steam through the shell 1; the steam pipe 3 and the condenser pipe 4 are respectively connected to the shell 1 to realize the closed-loop flow of the working medium.

[0023] like Figures 1 to 4 As shown. Both the inner channel wall 10 and the outer channel wall 11 include a multi-toothed protrusion structure, forming a high aspect ratio heat exchange wall with a central radial shape; the high aspect ratio satisfies h / w≥5, where h is the channel depth and w is the channel width, in order to increase the heat exchange area and enhance fluid turbulence.

[0024] like Figures 1 to 4 As shown. The inner channel wall 10 and the outer channel wall 11 are made of one or more of Q345R steel, austenitic stainless steel, or nickel-based alloys.

[0025] like Figures 1 to 4 As shown. The steam pipe 3 is located on the top of the upper sealing plate 12, and the condenser pipe 4 is located on the side wall of the outer channel wall 11, realizing a working fluid flow channel with liquid entering at the bottom and steam exiting at the top of the annular receiving space; a gap is left between the outer wall of the shell 1 and the inner wall of the chemical pipeline 5, and the outer ends of the steam pipe 3 and the condenser pipe 4 are respectively inserted into the chemical pipeline 5, and the shell 1 is installed on the chemical pipeline 5 through the steam pipe 3 and the condenser pipe 4.

[0026] like Figures 4 to 6 As shown. The upper end of the liquid-absorbing core 2 is provided with multiple longitudinal steam channels 20 at intervals. The inner and outer sidewalls of the liquid-absorbing core 2 are in close contact with the inner channel wall 10 and the outer channel wall 11, respectively. The steam generated by the heating and evaporation of the working medium rises along the longitudinal steam channels 20.

[0027] like Figures 4 to 6 As shown. A gap is left between the upper end of the liquid-absorbing core 2 and the upper sealing plate 12. A steam chamber 21 is provided circumferentially at the upper end of the liquid-absorbing core 2, which communicates with each longitudinal steam channel 20, and the steam is gathered together through the steam chamber 21.

[0028] like Figures 4 to 6 As shown. The liquid-absorbing core 2 is made of metal powder, metal fiber, or metal mesh sintered at high temperature; the effective capillary pore size of the liquid-absorbing core 2 satisfies the capillary suction force formula, which is: , In the formula, Capillary suction; The surface tension of the working medium; The surface contact angle of the liquid-absorbing core 2 is, and ; The effective capillary pore size of the liquid-absorbing core 2.

[0029] like Figures 4 to 6 As shown. The liquid-absorbing core 2 is prepared by a multi-segment sintering process, the preparation process of which includes the following steps: Raw material preparation: Sintering with 100-300 mesh spherical and dendritic metal powders; Mold preparation: A graphite forming mold matching the annular structure of the liquid suction core 2 is adopted. The inner diameter, outer diameter and axial length of the liquid suction core 2 are limited by the inner core, outer mold and end limiting structure. Slow heating phase: Increase the temperature to 200℃ at a rate of 3-5℃ / min and hold for 30min; Second heating stage: Increase the temperature to 850℃ at a rate of 5~10℃ / min; Sintering and heat preservation stage: heat preservation at 850℃ for 2 hours; Cooling stage: Cool to room temperature with the furnace.

[0030] like Figures 1 to 6 As shown. The axis of the shell 1 coincides with the center line of the chemical pipeline 5; the highest temperature heat source at the center of the cross-section of the chemical pipeline 5 heats the inner channel wall 10 through the internal cavity of the inner channel wall 10, and the edge heat source of the chemical pipeline 5 heats the outer channel wall 11, forming a heat exchange structure with both inner and outer sides heated.

[0031] The working process of this embodiment: The high-temperature medium carrying low-temperature waste heat from the top of the evacuation tower enters the chemical pipeline 5. The medium is divided into two parts: one part passes through the hollow cavity in the center of the shell 1 to scour and heat the inner channel wall 10, and the other part flows through the gap between the outer wall of the shell 1 and the chemical pipeline 5 to scour and heat the outer channel wall 11, thus achieving double-sided heating of the shell.

[0032] After being cooled by the condenser end of the loop heat pipe, the liquid working medium enters the lower part of the annular containment space of the shell through the condenser pipe 4. The liquid working medium enters the wick 2 and is transported to the evaporation interface under the capillary suction force of the wick. Heat is transferred from the inner channel wall 10 and the outer channel wall 11 to the liquid working medium inside the wick 2. The liquid working medium boils and vaporizes when heated, and the generated steam enters the longitudinal steam channel 20 and flows upward, collects in the steam chamber 21, and is then discharged through the steam pipe 3 and transported to the external condenser to release heat and complete the waste heat utilization. The steam condenses back into liquid working medium in the condenser and flows back to the evaporator through the condenser pipe 4, thus continuously completing the closed-loop phase change cycle of evaporation-steam transport-condensation-recirculation.

[0033] When the temperature and flow rate of the vapor at the top of the evaporator fluctuate within the range of 110-160℃, the sintered liquid suction core 2 continuously supplies the liquid working medium with stable capillary suction force, preventing the liquid suction core 2 from drying out locally; the hollow channel in the shell ensures that the pipeline medium is unobstructed, the pressure drop is small, and it is not easy for ash to accumulate and blockage.

[0034] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry, characterized in that: The system includes a shell (1), a liquid suction core (2), a steam pipe (3), and a condenser pipe (4); the shell (1) is a hollow cylinder; the shell (1) includes an inner channel wall (10), an outer channel wall (11), an upper sealing plate (12), and a lower sealing plate (13); the inner channel wall (10) is spaced inside the outer channel wall (11), and the upper sealing plate (12) and the lower sealing plate (13) are respectively covered on the top and bottom of the inner channel wall (10) and the outer channel wall (11); the inner channel wall (10), the outer channel wall (11), the upper sealing plate (12), and the lower sealing plate (13) are all located inside the outer channel wall (11); The sealing plate (12) and the lower sealing plate (13) enclose a closed annular accommodating space; the liquid suction core (2) is a porous structure and is located between the inner channel wall (10) and the outer channel wall (11) inside the shell (1); the shell (1) is filled with working medium; the shell (1) is coaxially arranged inside the chemical pipeline (5), and the fluid with residual heat in the chemical pipeline (5) heats the working medium to form steam through the shell (1); the steam pipe (3) and the condenser pipe (4) are respectively connected to the shell (1) to realize the closed-loop flow of the working medium.

2. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: Both the inner channel wall (10) and the outer channel wall (11) include a multi-toothed protrusion structure to form a high depth-to-width ratio heat exchange wall in a central radial shape; the high depth-to-width ratio satisfies h / w≥5, where h is the channel depth and w is the channel width, in order to increase the heat exchange area and enhance fluid disturbance.

3. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: The inner channel wall (10) and the outer channel wall (11) are made of one or more of Q345R steel, austenitic stainless steel or nickel-based alloy.

4. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: The steam pipe (3) is located on the top of the upper sealing plate (12), and the condenser pipe (4) is located on the side wall of the outer channel wall (11) to realize the working fluid flow channel with liquid entering at the bottom and steam exiting at the top of the annular containment space; a gap is left between the outer wall of the shell (1) and the inner wall of the chemical pipeline (5), and the outer ends of the steam pipe (3) and the condenser pipe (4) are respectively inserted into the chemical pipeline (5), and the shell (1) is installed on the chemical pipeline (5) through the steam pipe (3) and the condenser pipe (4).

5. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: The upper end of the liquid-absorbing core (2) is provided with multiple longitudinal steam channels (20) spaced apart. The inner and outer walls of the liquid-absorbing core (2) are in close contact with the inner channel wall (10) and the outer channel wall (11) respectively. The steam generated by the heating and evaporation of the working medium rises along the longitudinal steam channels (20).

6. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 5, characterized in that: There is a gap between the upper end of the liquid-absorbing core (2) and the upper sealing plate (12). The upper end of the liquid-absorbing core (2) is provided with a steam chamber (21) that communicates with each longitudinal steam channel (20). The steam is gathered together through the steam chamber (21).

7. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: The liquid-absorbing core (2) is made of metal powder, metal fiber or metal wire mesh by high-temperature sintering; the effective capillary pore size of the liquid-absorbing core (2) satisfies the capillary suction force formula, which is: ， In the formula, Capillary suction; The surface tension of the working medium; The surface contact angle of the liquid-absorbing core (2) is, and ; The effective capillary pore size of the liquid suction core (2) is given.

8. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 7, characterized in that: The liquid-absorbing core (2) is prepared by a multi-stage sintering process, the preparation process of which includes the following steps: Raw material preparation: Sintering with 100-300 mesh spherical and dendritic metal powders; Mold preparation: A graphite forming mold matching the ring structure of the liquid suction core (2) is adopted. The inner diameter, outer diameter and axial length of the liquid suction core (2) are limited by the inner core, outer mold and end limiting structure. Slow heating phase: Increase the temperature to 200℃ at a rate of 3-5℃ / min, and hold for 30min; Second heating stage: Increase the temperature to 850℃ at a rate of 5~10℃ / min; Sintering and heat preservation stage: heat preservation at 850℃ for 2 hours; Cooling stage: Cool to room temperature with the furnace.

9. The coaxial hollow loop heat pipe evaporator for low-temperature waste heat recovery in chemical industry as described in claim 1, characterized in that: The axis of the shell (1) coincides with the center line of the chemical pipeline (5); the highest temperature heat source at the center of the cross section of the chemical pipeline (5) passes through the internal cavity of the inner channel wall (10) to heat the inner channel wall (10), and the edge heat source of the chemical pipeline (5) heats the outer channel wall (11), forming a heat exchange structure with both inner and outer sides heated.

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