Suspended floating type self-stress relieving cryogenic heat exchange device

Abstract

The invention relates to the field of low-temperature process mechanical and automatic control, in particular to a suspended floating type self-stress-relieving cryogenic heat exchange device, and solves the problems that a traditional rigid fixed tube plate heat exchanger is prone to low-cycle fatigue failure and flow field dead zone scale deposition under cold and hot impact of a peak regulation station. The device comprises a pressure-bearing heat-insulating shell and a heat exchange core body immersed in the pressure-bearing heat-insulating shell. The top of the core body is fixed through a single-point suspension mechanism, and an axial thermal compensation gap is reserved between the bottom of the core body and the shell, so that a zero-stress statically determinate topology of hanging on the upper portion and floating on the lower portion is formed, and structural constraint stress caused by thermal expansion difference is thoroughly eliminated. The heat exchange tube bundle is of a spiral winding structure and is configured to induce fluid in the tube to generate Dean vortex secondary flow, and self-cleaning of the tube wall is achieved through high shear force. An inverted-cone-shaped dirt collecting groove is formed in the bottom of the shell and used for online separation of solid impurities separated out through phase change. The device has the characteristics of long fatigue life and efficient heat transfer.

Description

Technical Field

[0001] This invention belongs to the technical fields of cryogenic process equipment, extreme environment thermal management, and energy infrastructure safety. Specifically, it relates to an integrated submersible heat exchange device with full life-cycle adaptive thermal stress relief, micro-flow field self-cleaning, and intrinsically safe antifreeze functions, applicable to peak-shaving stations, receiving terminals, and aerospace ground refueling systems for cryogenic fluids such as liquefied natural gas, liquid hydrogen, and liquid helium.

[0002] This invention is particularly suitable for industrial scenarios characterized by "intermittent task profiles" and "high-frequency, large-amplitude thermal shocks," aiming to solve the problems of structural fatigue failure and heat transfer performance degradation of traditional rigid heat exchange equipment under unsteady conditions. Background Technology

[0003] In modern clean energy and aerospace engineering, cryogenic heat exchangers are hailed as the "heart" of energy conversion systems. Their core function is to establish an efficient heat flow channel between two extreme temperature zones: the hot end is typically connected to the process piping network at ambient temperature (approximately 300 K), while the cold end must be immersed in cryogenic working fluids such as liquid nitrogen (77.3 K), liquefied natural gas (111 K), or even liquid hydrogen (20.3 K). This means that the main body of the equipment, especially the pressure-bearing shell, tube sheet, heat exchanger tube bundle, and connectors, must withstand enormous radial and axial temperature differences exceeding 220 K or even 280 K within a very short geometric distance.

[0004] Unlike large-scale petrochemical plants (such as ethylene cracking furnaces and baseload LNG liquefaction plants) which pursue long-term continuous and stable operation, urban gas peak-shaving stations and emergency gas source stations have a significant "pulsating" operation mode:

[0005] (1) Cold shock: At the moment of startup, the temperature of the inner wall of the equipment needs to drop rapidly from the ambient temperature to the deep cold temperature zone within a few minutes, and the temperature change rate can reach more than 50 K / min.

[0006] (2) Heat recovery: After the task is completed, the residual liquid is drained and the equipment is brought back to normal temperature; or forced heating and purging are carried out when freezing blockage occurs.

[0007] This frequent cycle of "rapid cooling-deep cooling-rewarming" keeps the heat exchanger in a state of unsteady thermal transients for extended periods. According to the heat conduction equation:

[0008] α▽ 2 T

[0009] Where T is temperature (K), t is time (s), and α is the thermal diffusivity, characterizing the rate of heat diffusion within a material (m² / s); ▽ 2T is the Laplace operator, representing the second-order change of temperature in space, the curvature, with units of K / m².

[0010] When a heat exchanger is subjected to unsteady thermal transients for an extended period, a significant transient temperature gradient ▽T will form within the material. Existing industrial-grade heat exchanger design guidelines (such as the TEMA standard and GB / T 151) are mostly based on steady-state assumptions. When faced with such low-cycle fatigue conditions, traditional structures exhibit severe endogeneous defects in terms of mechanical adaptability and hydrodynamic stability.

[0011] 1. Analysis of the mechanical failure mechanism of rigidly constrained structures:

[0012] (1) Engineering pitfalls of "multiple statically indeterminate" structures: In pursuit of structural compactness and ease of manufacturing, existing technologies generally employ fixed tube sheet, rigidly supported spiral tube, or multi-flow plate-fin structures. For example, Chinese patent application CN117847407A (published on April 9, 2024) discloses a methane subcooling filling system, in which the core subcooler employs a structure in which a first heat exchanger (for passing liquid methane) and a second heat exchanger (for passing heated gas) are nested within the same shell. This design attempts to reduce volume through integration, but from the perspective of solid mechanics, it constructs a typical "multiple statically indeterminate system".

[0013] In terms of mechanical topology, the shell, the first tube bundle, the second tube bundle, and the tube sheet together form a rigid frame. When the system is in operation: the shell is in contact with liquid nitrogen (about 77 K) and undergoes cooling contraction; the first tube bundle is circulated with liquid methane (about 100 K) and undergoes cooling contraction, but the magnitude is smaller than that of the shell; the second tube bundle is circulated with nitrogen at room temperature or heated (about 300 K), and may even undergo thermal expansion.

[0014] (2) Failure derivation based on thermoelasticity: Since the above components are rigidly connected by welding or expansion, their free deformation is forcibly constrained by geometric boundaries. According to thermoelasticity theory, huge displacement inconsistencies will occur between the components.

[0015] Assume the characteristic length of the equipment is L, the coefficient of linear expansion of each component is α, and the Young's modulus is E. Taking the shell and the second heat exchange tube bundle as an example, the temperature difference ΔT between them is... diff It could be as high as 200 K. Without constraints, the difference in free stretching between the two is δ. free For: δ free =L·α·ΔT diff For 304 stainless steel, α≈1.6×10 −5 / K, if L=3m, then δ free ≈9.6mm.

[0016] However, in rigid fixed tube sheet structures, the actual displacement difference is forcibly restricted to zero. According to Hooke's Law, this suppressed deformation will translate into axial stress σ within the structure. thermal :

[0017] σ thermal =E·ε=E·Lδ free =E·α·ΔT diff

[0018] Substituting the elastic modulus of low-temperature strengthening E≈200GPa: σ thermal ≈200×10 3 MPa×1.6×10 ﹣5 / K×200K≈640MPa.

[0019] The calculated theoretical thermal stress (640 MPa) far exceeds the yield strength σ of austenitic stainless steel in a cryogenic environment. 0.2 (Typically around 300-400 MPa). This means that in the rigid structure shown in CN117847407A (published on April 9, 2024), irreversible plastic deformation will occur at the tube sheet connection weld and tube bundle bends in just one cooling process.

[0020] (3) Low-cycle fatigue and Coffin-Manson damage model: Under the condition of frequent start-up and shutdown of peak-shaving stations, the above-mentioned plastic deformation is alternating. According to the Coffin-Manson relation in fracture mechanics, the fatigue life N of the material is... f From the plastic strain amplitude Δε p leading:

[0021] 2Δε p =ε f′ (2N f ) c

[0022] Where, ε f′ is the fatigue ductility coefficient, and c is the fatigue ductility index (usually -0.5 ~ -0.7).

[0023] Due to the extremely high plastic strain amplitude caused by the rigid structure, its fatigue life N f The failure exhibits exponential decay. Engineering statistics show that such rigid cryogenic heat exchangers often develop penetrating cracks at the stress concentration points of the tube sheet fillet welds after hundreds of cycles of operation, leading to internal leakage of the high-pressure working fluid. This failure is a physical inevitability determined by the structural form and cannot be completely resolved by increasing the wall thickness or improving welding quality.

[0024] (4) The Paradox of the Limitations of Bellows Compensation: Existing technologies often attempt to absorb displacement by adding bellows expansion joints to the shell. However, under LNG high-pressure conditions (>0.6 MPa), bellows face a serious contradiction between "pressure-bearing capacity" and "compensation capacity": in order to withstand internal pressure, the bellows wall thickness must be increased, which leads to an increase in its axial stiffness Kx, thus losing the compensation effect for the corresponding force; if the number of layers is increased, column instability is very likely to occur. Therefore, the simple bellows solution is not the ultimate solution.

[0025] 2. Analysis of deposition effects and heat transfer degradation in traditional flow fields:

[0026] (1) Phase change precipitation mechanism of industrial refrigerant: Both US Patent US2010 / 0326097A1 (publication date December 30, 2010) and Chinese Patent CN 112228769 A (publication date January 15, 2021) employ immersion liquid nitrogen bath cooling. However, these technical solutions overlook a crucial engineering reality: industrial-grade liquid nitrogen is not absolutely pure. Industrial liquid nitrogen typically contains trace amounts (ppm level) of carbon dioxide (CO2), water (H2O), and compressor lubricating oil molecules.

[0027] The triple point of CO2 is 216.6 K, which is much higher than the boiling point of liquid nitrogen (77 K). At 77 K, the solubility of CO2 in liquid nitrogen is extremely low (<10 K). ﹣8 As liquid nitrogen continuously absorbs heat and boils / vaporizes within the shell (solvent decreases), the concentration of impurities continuously increases. Once the solubility limit is exceeded, the solute will directly bypass the liquid phase and precipitate out as solid particles (dry ice snowflakes).

[0028] (2) Hydrodynamic dead zone of traditional baffle structure: Existing shell and tube heat exchangers generally use bow-shaped baffles to support the tube bundle and guide the fluid. From the perspective of computational fluid dynamics, this structure has an inherent defect: at the leeward side of the baffle and at the corner of the bottom of the shell, the fluid velocity vector v→0, forming a significant reattachment zone and stagnation zone.

[0029] According to Stokes' law in multiphase fluid mechanics, solid particles suspended in liquid nitrogen (density ρ) p The final settling velocity v in the fluid is approximately 1.5 g / cm³. t for:

[0030] v t = [2(ρ p -ρ f )gr²] / (9μ)

[0031] Among them, v t ρ represents the terminal settlement velocity, in m / s. pρ is the density of the particles, in kg / m³. f ρ is the density of the fluid, in kg / m³; r is the radius of the spherical particle, in m; μ is the dynamic viscosity of the fluid, in Pa·s.

[0032] In the high-speed mainstream region, fluid drag force dominates, and particles flow with the flow; however, in the dead zone with extremely low flow velocity, gravity dominates, and particles settle and accumulate. After long-term operation, these precipitated dry ice and oil stains will form a porous media scale layer at the bottom of the heat exchange tube bundle and in the gaps between the baffles.

[0033] (3) Fouling thermal resistance and the induction of Leidenfrost effect: The harm of fouling deposits to cryogenic heat exchangers is twofold:

[0034] a. Deterioration of heat transfer: The thermal conductivity λ of the dry ice scale layer fouling Extremely low, equivalent to wrapping a layer of insulation cotton on the surface of the heat exchange tube, causing the overall heat transfer coefficient K value to decrease exponentially over time.

[0035] b. Film boiling induced by membrane boiling: This is a more fatal microscopic thermodynamic phenomenon. Porous scale layers become a breeding ground for gas nucleation points and hinder liquid wetting of the pipe wall. When the heat flux is high, the generated bubbles cannot detach in time and merge within the scale layer to form a continuous gas film, separating the liquid nitrogen from the pipe wall. At this point, the boiling mode changes from highly efficient nucleation boiling to film boiling. This not only leads to a decrease in heat exchange efficiency by an order of magnitude but also causes a localized surge in pipe wall temperature, triggering "burn-out" and causing pipe overheating failure.

[0036] Existing technologies (such as US2010 / 0326097A1 (published on December 30, 2010)) lack proactive online cleaning and sewage discharge mechanisms, and can only rely on frequent shutdowns for reheating and purging, which severely restricts the continuous support capability of peak shaving stations.

[0037] 3. The inherent insecurity of passive antifreeze structures:

[0038] (1) Lack of physical antifreeze structure: In the process of using liquid nitrogen to cool LNG, there is an inherent physical contradiction: in order to improve the heat exchange efficiency Q=KAΔT, the engineering design tends to maintain a large temperature difference. However, the boiling point of liquid nitrogen (77 K) is much lower than the triple point of methane (90.7 K). Existing equipment (such as CN 112228769 A (published on January 15, 2021)) is essentially just a passive heat transfer container. Its antifreeze measures rely entirely on external control loops (sensors + regulating valves).

[0039] Sensor hysteresis: The thermal response time constant of the temperature sensor is on the order of seconds.

[0040] Nucleation rate: The rate at which methane undergoes heterogeneous nucleation and crystallization on the pipe wall is in the millisecond range.

[0041] When the LNG flow is interrupted momentarily (e.g., a pump trips), the heat load inside the pipe disappears, and the liquid nitrogen outside the pipe instantly cools the pipe wall to 77 K. At this time, before the external control system can act, the methane inside the pipe has already crystallized and blocked the pipe. Existing heat exchangers lack an adaptive mechanism (such as a self-coupling transformer chamber) in their hardware structure that can directly clamp the lower limit of the phase change temperature "without relying on electronic systems" and "using physical laws".

[0042] In summary, existing cryogenic heat exchanger technology faces three core physical contradictions when dealing with variable operating conditions, high pressure differentials, and impurity-containing conditions such as LNG peak-shaving stations, constituting a common problem that has remained unresolved in the industry for a long time:

[0043] 1. The "statically indeterminate constraint trap" in the mechanical dimension: Traditional rigid fixed structures violate the free deformation principle of thermoelasticity, resulting in huge thermal stress concentration, which makes the equipment have a very short life under the low-cycle fatigue condition of the peak-shaving station and a high risk of weld cracking.

[0044] 2. "Dead zone deposition effect" in the fluid dimension: The traditional baffle flow field violates the self-cleaning principle of multiphase flow, causing solid impurities precipitated from phase change to accumulate continuously in the dead zone, leading to heat transfer deterioration and film boiling crisis.

[0045] 3. "Passive defense limitations" in the safety dimension: The equipment itself lacks an adaptive voltage regulation structure based on phase change thermodynamics, and the antifreeze function relies excessively on the reliability of external electronic systems, thus lacking inherent safety attributes.

[0046] Therefore, the industry urgently needs to develop a completely new heat exchange device. This device should achieve "zero-stress constraint" suspension and floating in mechanical topology; construct a self-cleaning flow field enhanced by "Dean vortex" in fluid dynamics; and integrate "phase change temperature control clamping" function at the bottom layer of the structure, thereby completely solving the above-mentioned systemic problems at the physical level. Summary of the Invention

[0047] 1. The technical problem to be solved by this invention:

[0048] In response to the common industry problems of existing cryogenic heat exchange equipment described in the background art, such as "ultra-statically indeterminate thermal stress failure", "deposition in dead zones of the flow field" and "poor safety of passive antifreeze", especially the problem of short low-cycle fatigue life caused by the use of "multiple rigid fixing structures" in Chinese Patent CN117847407A (publication date April 9, 2024) and the problem of impurity deposition and heat transfer deterioration caused by the use of conventional baffle structure in US Patent US2010 / 0326097A1 (publication date December 30, 2010), this invention aims to provide a suspended floating self-stress-relieving cryogenic heat exchange device.

[0049] This invention aims to resolve the core engineering contradictions at the following three levels:

[0050] (1) The contradiction between "stiffness and flexibility" at the level of solid mechanics: break through the rigid constraint boundary of traditional shell and tube heat exchangers, construct a "zero-stress topology" that can adaptively digest huge thermal shock strain, and fundamentally eliminate the source of low-cycle fatigue cracks.

[0051] (2) The contradiction between heat exchange and anti-fouling at the fluid dynamics level: abandon the flow field of the bow-shaped baffle that is prone to fouling, and use the secondary flow effect in the spiral tube to construct a self-cleaning flow field with high shear force to prevent dry ice and oil in industrial liquid nitrogen from depositing on the heat exchange surface.

[0052] (3) The contradiction between “passive and active” in system safety: the antifreeze function is upgraded from “soft protection” that relies on external electronic control to “hard barrier” that relies on the physical structure of the equipment, and the phase change back pressure cavity is used to achieve physical clamping of the wall temperature.

[0053] 2. The technical solution of the present invention:

[0054] To achieve the above objectives, this invention provides an integrated submerged heat and mass exchange device designed based on the principle of thermoelastic decoupling. This device encapsulates the subcooling process of cryogenic fluids (such as LNG) within a thermodynamically self-consistent and mechanically free floating unit.

[0055] The specific technical solution of the present invention is as follows:

[0056] An integrated submersible heat exchanger with stress relief and antifreeze functions, characterized in that it comprises:

[0057] (I) Overall Equipment Architecture:

[0058] A suspended floating self-stress-relief cryogenic heat exchange device is characterized by comprising: a pressure-bearing insulating shell, a stress-decoupling heat exchange core, a suspended floating support mechanism, an inverted conical sludge collection trough, and a radial limiting guide assembly.

[0059] Pressure-insulated outer shell: As the main container of the device, it is constructed as a vacuum-insulated cryogenic container capable of withstanding a preset pressure.

[0060] Stress-decoupled heat exchange core: coaxially immersed in the internal cavity of the pressure-bearing insulation shell. The stress-decoupled heat exchange core includes a central cylinder and a spiral heat exchange tube bundle wound around the central cylinder. The stress-decoupled heat exchange core is not rigidly connected to the side wall or bottom wall of the pressure-bearing insulation shell, but is suspended inside the pressure-bearing insulation shell by a single-point fixed suspension floating support mechanism, forming a mechanical topology in which the spiral heat exchange tube bundle floats freely inside the pressure-bearing insulation shell.

[0061] Suspended floating support mechanism: It adopts a statically determinate design and uses a single rigid constraint point to position and support the stress-decoupled heat exchange core.

[0062] Inverted conical sludge collection tank: Located below the bottom of the pressure-bearing heat insulation shell, it together with the bottom of the pressure-bearing heat insulation shell to form an impurity settling and discharge zone, used to physically separate solid impurities of the medium inside the pressure-bearing heat insulation shell.

[0063] (ii) Zero-stress topology with top suspension and bottom floating:

[0064] To address the thermal stress problem of the fixed tube sheet structure in CN117847407A (published on April 9, 2024), this invention proposes a completely statically determinate support system.

[0065] Top single-point suspension: The top manifold of the stress-decoupled heat exchange core is fixed to the top of the pressure-bearing insulation shell by a single set of suspension flange assemblies with flexible compensation capabilities as a constraint point.

[0066] Mechanical principle: Release all the unnecessary constraints and degrees of freedom, so that the structure changes from "three-dimensional statically indeterminate" to "statically determinate".

[0067] Bottom Free Floating: The stress-decoupling heat exchange core has a bottom free floating end. The bottom of the stress-decoupling heat exchange core does not have a tube sheet and is not welded to the bottom of the pressure-bearing insulation shell. An axial thermal compensation gap H is reserved between the bottom free floating end and the inner bottom wall of the pressure-bearing insulation shell. gap .

[0068] Gap Design Criteria: The axial dimension of the axial thermal compensation gap is configured to be greater than or equal to the theoretical shrinkage of the stress-decoupling heat exchange core under the maximum design temperature difference, i.e.:

[0069]

[0070] Where k is a safety factor greater than 1.2; L is the characteristic length of the stress-decoupling heat exchange core; α(T) is the coefficient of linear expansion of the material, T hot For ambient temperature, T cold This is the temperature of the cryogenic working fluid, typically H. gap The design is 20mm to 50mm.

[0071] Radial limiting guide assembly: In order to prevent the core from pendulum-like swaying caused by fluid impact, the radial limiting guide assembly includes several low friction coefficient sliders evenly distributed circumferentially at the bottom of the stress decoupling heat exchange core, and guide surfaces correspondingly disposed on the inner wall of the pressure-bearing heat insulation shell.

[0072] Structural details: The low-friction coefficient slider is made of a low-friction coefficient cryogenic material (such as modified PTFE or polyimide), and a small gap (0.5mm-2.0mm) is maintained between the low-friction coefficient slider and the guide surface of the inner wall of the shell. This allows the stress-decoupled heat exchange core to freely expand and contract axially while limiting its radial swing amplitude to prevent fluid-induced vibration, achieving "axial decoupling and radial steady state".

[0073] (III) Dean vortex-reinforced helical tube bundle structure:

[0074] In response to the problem of scaling in ordinary tube bundles as described in US2010 / 0326097A1 (published on December 30, 2010), this invention constructs a special tube bundle that utilizes the centrifugal force of fluid to generate a secondary vortex.

[0075] Spiral heat exchange tube bundle: The spiral heat exchange tube bundle of the stress decoupling type heat exchange core is composed of multiple layers of coaxial nested heat exchange tubes, and each layer of heat exchange tubes is tightly wound on the central cylinder with a specific helical helix angle β.

[0076] Dean vortex generation mechanism: When fluid (LNG) flows within a helical heat exchanger tube bundle, centrifugal force causes a radial pressure gradient to form in the fluid particles. On the cross-section of the helical heat exchanger tube bundle, the fluid flows from the outer wall to the inner wall and then back along the central axis, forming a pair of symmetrical vortices rotating in opposite directions, i.e., Dean vortices. The geometric parameters of the helical heat exchanger tube bundle in this invention (the ratio of tube diameter d to winding radius R) are configured to satisfy the Dean number De > De. critical Conditions: >100, where: R e : Reynolds number; D: winding diameter; d: pipe diameter; β: helix angle.

[0077] Technical effects:

[0078] 1. Self-cleaning effect: The strong secondary flow generated by the Dean vortex continuously scours the pipe wall, significantly increasing the wall shear stress τ. wallThis prevents solid crystal nuclei or dirt from adhering stably, thus achieving online scale prevention.

[0079] 2. Enhanced heat transfer: The secondary flow disrupts the laminar boundary layer inside the pipe, which intensifies the radial mixing of the fluid. The Nusselt number (Nu) inside the pipe is 2-3 times higher than that of a straight pipe, thereby significantly reducing the size of the equipment without increasing the heat exchange area.

[0080] (iv) Longitudinal scouring without baffles and inverted cone-shaped sewage discharge:

[0081] To address the issue of impurity deposition within the pressure-bearing insulating shell, this invention eliminates the traditional bow-shaped baffle. Instead, the pressure-bearing insulating shell does not contain a bow-shaped baffle that laterally obstructs the fluid, thereby creating a unidirectional, dead-zone-free flow field along the axial direction to prevent solid impurities precipitated from the cryogenic working fluid from remaining within the shell side.

[0082] Longitudinal flow field design: Longitudinal spacers are installed between the tube layers of the helical heat exchanger tube bundle to form a longitudinal helical flow channel. Under the drive of buoyancy, the liquid nitrogen fluid inside the pressure-bearing insulating shell flows longitudinally along the gaps in the tube bundle in a single direction.

[0083] Advantages: Eliminates the fluid dead zone behind the baffle, preventing dry ice particles from accumulating there.

[0084] Inverted conical settling tank: The bottom of the pressure-bearing heat-insulating shell is designed with a large-angle inverted conical structure. The cone angle is configured to be greater than the angle of repose of solid impurities in cryogenic liquids. For example, the typical value of millimeter-sized dry ice spherical particles in liquid CO2 is 32° to 45°, and irregular particles can reach 45° to 50°.

[0085] Function: Based on the Stokes sedimentation principle, solid impurities (dry ice, oil sludge) with a density greater than liquid nitrogen will quickly settle to the bottom of the cone under the action of gravity.

[0086] Low-temperature drain valve: A drain outlet and a low-temperature drain valve are provided at the bottom of the inverted conical settling tank. By periodically opening the low-temperature drain valve, the deposited high-concentration impurity slurry can be discharged from the system to prevent it from participating in the secondary circulation.

[0087] (v) Phase change thermodynamic clamping cavity:

[0088] The pressure-bearing heat-insulating shell of the present invention is not only a container, but also an actuator for antifreeze control.

[0089] Constant pressure boiling environment: A closed phase change thermodynamic clamping chamber is formed inside the pressure-bearing insulating shell. This phase change thermodynamic clamping chamber is connected to an external pressure regulating system through a gas phase outlet at the top.

[0090] Physical antifreeze principle: When the external pressure regulation system changes the phase change thermodynamic clamping chamber gas phase pressure P shellAt that time, according to the gas-liquid phase equilibrium criterion, the overall boiling temperature T of liquid nitrogen in the phase change thermodynamic clamping chamber is determined. sat An isotropic, uniform change will occur. Because the stress-decoupled heat exchange core is completely immersed in liquid nitrogen, this temperature change will act instantaneously on every micro-segment of the spiral heat exchange tube bundle. This pressure-based, full-field temperature control creates a physical barrier, ensuring that the tube wall temperature is always higher than the freezing point of the fluid (methane) inside the spiral heat exchange tube bundle, achieving intrinsic safety without relying on temperature sensor feedback.

[0091] Compared with the prior art, the present invention has the following advantages:

[0092] 1. Significant Improvement in Fatigue Life: Compared to the rigid fixed structure of CN117847407A (published on April 9, 2024), the "suspended floating" structure of this invention completely eliminates axial constraints. During the rapid cooling process from room temperature (300K) to cryogenic temperature (77K) in the LNG peak-shaving station, the stress-decoupled heat exchange core can freely shrink downwards by approximately 10-15mm (depending on length) without generating any thermal stress. This eliminates the root cause of low-cycle fatigue failure, increasing the design life of the equipment from the conventional 3-5 years (or 500 cycles) to 15-20 years (or 5000 cycles).

[0093] 2. Superior Anti-fouling and Performance Retention Capabilities: Compared to ordinary tube bundles as described in US2010 / 0326097A1 (published December 30, 2010), this invention utilizes the "Dean vortex" effect to transform the fluid flow inside the tube from a single axial flow to a complex three-dimensional helical flow. This flow characteristic not only increases the heat transfer coefficient by more than 40%, but more importantly, endows the tube wall with "self-cleaning" capabilities. Combined with the baffle-less design within the pressure-bearing insulated shell and the bottom drain structure, the equipment can maintain its heat exchange performance without degradation for extended periods when handling industrial liquid nitrogen containing impurities, significantly reducing maintenance costs.

[0094] 3. Extreme Compactness and Lightweight Design: Due to the extremely high heat transfer area density of the spiral heat exchanger tube bundle, under the same heat load, the volume of this unit is only 1 / 3 of that of a traditional shell-and-tube heat exchanger, and its weight is only 1 / 2. This has significant commercial value for space-constrained refueling stations or skid-mounted equipment.

[0095] 4. Intrinsically Safe Anti-freeze Architecture: This device implements the "anti-freeze" function in hardware. A constant-pressure boiling environment (phase change thermodynamic clamping chamber) constructed through a pressure-bearing, insulated outer shell provides a physically insurmountable temperature floor for the fluid within the spiral heat exchanger tube bundle. Even in extreme failures such as a complete power outage of the control system and a complete interruption of flow, as long as the external pressure regulation system maintains the mechanically set pressure, freezing will absolutely not occur inside the equipment. This deterministic safety guarantee is unparalleled by existing technologies.

[0096] 5. Feasibility of Manufacturing Process: Despite its ingenious structure, this invention fully considers manufacturing processes. The single-point suspension structure avoids complex tube sheet welding, reducing leakage points. The spiral heat exchanger tube bundle can be produced using mature automated tube winding machines. This characteristic of "high design complexity and good manufacturing consistency" is conducive to achieving high-quality mass production.

[0097] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0098] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0099] Figure 1 This is a cross-sectional view of the overall mechanical structure of an embodiment of the present invention.

[0100] 10-Pressure-bearing insulating shell; 15-Inverted conical sludge collection trough; 16-Low-temperature drain valve; 20-Stress-decoupling heat exchange core; 21-Central cylinder; 22-Helical heat exchange tube bundle; 23-Longitudinal spacer bar; 30-Suspension floating support mechanism; 31-Suspension flange assembly; 32-Axial thermal compensation gap; 35-Radial limiting guide assembly; 36-Low friction coefficient slider; 37-Guide surface; 40-External pressure regulating system. Detailed Implementation

[0101] To make the objectives, solutions, and advantages of the technical solutions of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Unless otherwise stated, the terms used herein have their ordinary meanings in the art. The same reference numerals in the drawings represent the same parts. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0102] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0103] Example 1 (Detailed description of the mechanical structure of the device):

[0104] like Figure 1 As shown in the figure, the suspended floating self-stress-relieving cryogenic heat exchanger provided in this embodiment is mainly assembled from the following components:

[0105] 1. Pressure-bearing heat-insulating outer shell 10:

[0106] The main body is a cylindrical shell made of S30408 ​​stainless steel, with a diameter of ϕ800mm and a height of 3500mm. The outer wall is equipped with a vacuum jacket, filled with multiple layers of insulation material (MLI) and getter to maintain a high vacuum and reduce cold loss. The bottom end is designed as an inverted conical sludge collection trough 15 with a cone angle of 60°, and the bottom of the trough connects to a DN25 cryogenic drain valve 16 interface.

[0107] 2. Stress decoupling type heat exchange core 20:

[0108] Central tube 21: Serves as the framework for the spiral heat exchanger tube bundle 22, but does not participate in heat exchange. Its top end is closed, and its bottom end is open.

[0109] Spiral heat exchange tube bundle 22: Made of seamless stainless steel tubes of ϕ12×1.0mm, tightly wound around the central cylinder at a spiral angle of 12°, for a total of 15 layers. The tubes are separated from each other by PTFE longitudinal spacers 23, forming internal fluid channels for the pressure-bearing heat-insulating shell.

[0110] Dean number design: The winding radius R ranges from 150mm to 350mm. At the design flow rate, the calculated Dean number De is distributed between 300 and 500, far exceeding the critical value, ensuring the generation of strong secondary flow.

[0111] 3. Suspended floating support mechanism 30:

[0112] Suspended flange assembly 31: The main inlet and outlet pipes at the top of the stress-decoupled heat exchange core 20 pass through the pressure-bearing insulating shell 10. This penetration point employs a cryogenic extension neck structure and is secured by a flange. This is the only load-bearing point of the stress-decoupled heat exchange core 20.

[0113] Axial thermal compensation gap 32: The vertical distance between the bottom end of the stress-decoupling heat exchange core 20 and the inverted conical sludge collection groove 15 is set to 50mm. Calculations show that when the temperature drops from 300K to 77K, the axial shrinkage of the stress-decoupling heat exchange core 20 is approximately 9.6mm. This gap is sufficient to accommodate more than 5 times the deformation, ensuring effective "floating".

[0114] Radial limiting guide assembly 35: Three low-friction coefficient sliders 36 made of PTFE material are evenly distributed around the circumference of the outer side of the central cylinder at the bottom of the stress decoupling heat exchange core. A guide surface 37 is provided on the inner wall of the pressure-bearing heat insulation shell 10, which corresponds to the low-friction coefficient sliders 36. The gap between the low-friction coefficient sliders 36 and the guide surface 37 is controlled at 1.5mm.

[0115] Example 2 (Stress relief and self-cleaning performance during operation):

[0116] Phase A (Rapid Cooling Start-up): When LNG at -160°C suddenly enters the spiral heat exchanger tube bundle 22, and liquid nitrogen at -196°C is injected into the pressurized insulating shell 10, the temperature of the spiral heat exchanger tube bundle 22 drops rapidly.

[0117] Action: The spiral heat exchange tube bundle 22 contracts sharply relative to the pressure-bearing insulating shell 10. At this time, the bottom low-friction slider 36 slides (relative motion) within the guide surface 37.

[0118] Effect: Since the contraction of the spiral heat exchange tube bundle 22, which has no fixed constraint at the bottom, is not hindered, the internal thermal stress σ≈0. The risk of weld cracking in the tube sheet, which is common in the prior art, is completely eliminated.

[0119] Phase B (Steady-state operation and sewage discharge): Liquid nitrogen absorbs heat and boils inside the pressure-bearing insulated shell 10, and the resulting dry ice impurities move downward with the liquid flow.

[0120] Action: Since there is no baffle to block it, the impurities settle to the bottom of the inverted conical sludge collection tank 15.

[0121] Dean's vortex effect: Under the action of centrifugal force, LNG in the spiral heat exchanger tube bundle 22 continuously washes the tube wall, preventing the adhesion of any possible trace impurities.

[0122] Sewage discharge: Maintenance personnel open the bottom low-temperature drain valve 16 every 48 hours for 5 seconds to discharge the accumulated dry ice slurry.

[0123] Example 3 (Hidden treatment in manufacturing process):

[0124] This embodiment describes a special manufacturing process for the stress-decoupled heat exchanger core 20. On a room-temperature tube winding machine, a constant reverse tension is applied to the tubes of the spiral heat exchanger bundle 22 to counteract cold contraction.

[0125] In a liquid nitrogen immersion test, strain gauges were used to monitor the wall stress of the spiral heat exchange tube bundle 22 in the stress-decoupled heat exchange core 20. The results showed that under stable operating conditions at 77K, the equivalent stress of the tube wall was close to zero, verifying the design intent of prestressing to offset cold contraction stress.

[0126] As can be seen from the above embodiments, the hardware of the device of the present invention is not just a heat exchanger, but an intelligent device that integrates mechanical self-adaptation, fluid self-cleaning and thermodynamic controllability, providing the most basic physical guarantee for the entire BOG zero-loss system.

[0127] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and variations without departing from the concept of the present invention, and these modifications and variations all fall within the scope of protection of the present invention.

Claims

1. A suspended floating self-stress-relieving cryogenic heat exchanger, characterized in that, include: Pressure-bearing insulating shell (10), stress-decoupling heat exchange core (20), and suspended floating support mechanism (30): The pressure-bearing heat insulation shell (10) has a sealed cavity inside that can withstand a preset pressure, and the bottom of the pressure-bearing heat insulation shell (10) is provided with an inverted conical dirt collection tank (15) for physically separating solid impurities. The stress-decoupling heat exchange core (20) is coaxially immersed in the sealed cavity. The stress-decoupling heat exchange core (20) includes a central cylinder (21) and a spiral heat exchange tube bundle (22) wound around the central cylinder. The suspended floating support mechanism (30) adopts a statically determinate design, and positions and supports the stress-decoupled heat exchange core (20) through a single rigid constraint point; The stress decoupling heat exchange core (20) has a bottom free floating end located at the bottom end of the stress decoupling heat exchange core (20), and an axial thermal compensation gap (32) is reserved between the bottom free floating end and the inner bottom wall of the pressure-bearing heat insulation shell (10). The axial dimension of the axial thermal compensation gap (32) is configured to be greater than the theoretical shrinkage of the stress-decoupled heat exchange core under the maximum design temperature difference.

2. The apparatus according to claim 1, characterized in that, The hydrodynamic structural features of the stress decoupling heat exchange core (20) are as follows: the spiral heat exchange tube bundle (22) is formed by coaxially and tightly wound multiple layers of pipes, and the geometric parameters of its spiral helix angle (β) and winding curvature radius (R) are configured to meet the hydrodynamic condition that the Dean number of the fluid in the tube is greater than 100, thereby forming a symmetrical twin-cell secondary vortex on the tube cross section; longitudinal spacer strips (23) are provided between the tube layers of the spiral heat exchange tube bundle (22), and no bow-shaped baffles are provided in the sealed cavity to block the fluid laterally, thereby forming a unidirectional flow field without dead zone along the axial direction to prevent solid impurities precipitated in the cryogenic working fluid from being retained in the shell side.

3. The apparatus according to claim 1, characterized in that, The suspended floating support mechanism (30) further includes a radial limiting guide component (35): The radial limiting guide component (35) includes several low friction coefficient sliders (36) evenly distributed circumferentially at the bottom of the stress decoupling heat exchange core (20), and a guide surface (37) correspondingly disposed on the inner wall of the pressure-bearing heat insulation shell (10); a preset radial micro gap (0.5mm-2.0mm) is maintained between the low friction coefficient sliders (36) and the guide surface (37), which is configured to limit the radial swing amplitude while allowing the stress decoupling heat exchange core (20) to freely extend and retract axially, so as to prevent fluid-induced vibration.

4. The apparatus according to claim 1, characterized in that, The structural features of the inverted conical sludge collection tank (15) are as follows: it is located at the bottom of the pressure-bearing heat-insulating shell (10), and its cone angle is configured to be greater than the angle of repose of solid impurities in cryogenic liquids, such as the typical value of millimeter-sized dry ice spherical particles in liquid CO2 is 32° to 45°, and irregular particles can reach 45° to 50°; the lowest point of the inverted conical sludge collection tank (15) is provided with a drain outlet and a low-temperature drain valve (16), which is configured to collect and periodically discharge high-concentration impurity slurry that settles down from the dead zone flow field above, based on the Stokes sedimentation principle.

5. The apparatus according to claim 1, characterized in that, The pressure-bearing heat-insulating shell (10) actually constitutes a phase change thermodynamic clamping cavity: the phase change thermodynamic clamping cavity is connected to an external pressure regulating system (40) through a gas phase outlet. The external pressure regulating system (40) is configured to apply a physical hard constraint to the outer wall temperature of the spiral heat exchange tube bundle (22) under full immersion conditions by adjusting the gas phase pressure in the phase change thermodynamic clamping cavity and using the saturated pressure-temperature correspondence determined by the Clausius-Clapeyron equation, so as to prevent it from falling below the freezing point of the fluid inside the tube.

6. The apparatus according to claim 1, characterized in that, The manufacturing features of the spiral heat exchange tube bundle (22) are as follows: the spiral heat exchange tube bundle (22) is pre-stressed during the manufacturing process, and the two ends of the spiral heat exchange tube bundle (22) are gathered to the top manifold through a flexible transition section; the pressure-bearing heat insulation shell (10) does not contain a second heat exchange tube bundle or electric heating element for introducing external heating gas, and its antifreeze function relies only on the thermal coupling and pressure control of the fluid itself.

7. The apparatus according to claim 1, characterized in that, The axial thermal compensation gap (32) has a dimension H. gap Satisfy the following mathematical relationship: Where k is a safety factor greater than 1.2; L is the characteristic length of the stress-decoupling heat exchange core (20); α(T) is the linear expansion coefficient of the material, T hot For ambient temperature, T cold This refers to the temperature of the cryogenic working fluid.

8. The apparatus according to claim 1, characterized in that, The stress-decoupled heat exchange core (20) and the pressure-bearing insulation shell (10) are connected by a pull-out core structure. By disassembling the suspension flange assembly (31) of the pressure-bearing insulation shell (10), the entire stress-decoupled heat exchange core (20) together with the suspension floating support mechanism (30) can be removed from the pressure-bearing insulation shell (10) for easy maintenance and descaling.

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