Self-coupling constant pressure boiling and energy level gradient utilization system

Abstract

The invention relates to the technical field of thermodynamic process control and energy recovery of cryogenic fluid. The self-coupling constant-pressure boiling and energy level gradient utilization system solves the problems of low energy efficiency and complex structure caused by the fact that an existing cryogenic anti-freezing technology depends on external heat source heating and open-loop emptying. The system comprises a liquid nitrogen supply unit, a single-tube-bundle integrated immersed heat and mass transfer unit and a pressure energy cascade recovery network. The device is characterized in that the shell pass of the heat and mass transfer unit is not provided with an auxiliary heating element, liquid nitrogen in the shell pass is driven to boil only through sensible heat released by fluid in a pipe, self-coupling back pressure is built in a closed space through a back pressure adjusting assembly, and the boiling point of the liquid nitrogen is physically clamped in a safe temperature zone. Meanwhile, the system utilizes expansion work generated by liquid nitrogen gasification to carry out lossless pressurization on an upstream tank car through a recovery network. A double-heat-exchanger structure is abandoned, thermodynamic self-balancing and energy closed loop are achieved, and the entropy production and operation cost of the system is remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of cryogenic fluid thermodynamic process control and energy recovery technology, specifically to a self-coupled constant pressure boiling and energy cascade utilization system applied to liquefied natural gas (LNG) storage peak shaving stations, receiving stations and refueling terminals. Background Technology

[0002] In the end-stage applications of the LNG industry chain, to suppress the generation of flash vapor (BOG) caused by pipeline heat intrusion and to prevent cavitation during pumping, liquid nitrogen (LIN, boiling point 77.3K at normal pressure) is typically used as a cold trap to deeply subcool LNG (mainly methane, triple point 90.69K). However, a core thermodynamic contradiction exists in this heat transfer process: to obtain efficient heat transfer driving force (ΔT), the boiling temperature on the liquid nitrogen side is often much lower than the freezing point of methane. According to Fourier's law of thermal conductivity and the principle of phase transition kinetics, once the heat exchange tube wall temperature drops below 90.69K, heterogeneous nucleation and crystallization will occur on the methane side, leading to flow channel freezing and blockage, or even equipment damage.

[0003] I. In order to solve the above-mentioned freezing problem, early technologies attempted to use the Clausius-Clapeyron equation to increase the saturation boiling temperature by increasing the liquid nitrogen side pressure.

[0004] A typical example is US patent application US2010 / 0326097A1 (publication date December 30, 2010). This patent discloses a method for densifying liquid methane using a liquid nitrogen bath. Its core logic is to utilize the natural evaporation of liquid nitrogen after it absorbs heat to achieve "self-pressurization," and to control the pressure inside the container by adjusting the pressure relief valve connected to the venting torch, thereby maintaining the boiling point of liquid nitrogen above the triple point of methane.

[0005] However, from the perspective of modern energy engineering and a low-carbon economy, this technological approach has serious inherent flaws:

[0006] (1) Energy loss in the open-loop system: The system is essentially an open-loop thermodynamic process. The high-pressure gas (typically >0.3 MPa) produced after the vaporization of liquid nitrogen contains high-grade pressure potential energy. However, the patent explicitly describes venting the gas directly into the "Vent Stack" [52, Fig. 1]. This method only utilizes the latent heat of liquid nitrogen, completely wasting its enormous expansion work and pressure energy. For commercially operated LNG peak-shaving stations, such a huge continuous energy waste is unacceptable.

[0007] (2) Limitations of passive control: This technology mainly relies on mechanical pressure relief valves for passive regulation. Under transient conditions of drastic load fluctuations at peak-shaving stations (such as the start and stop of unloading pumps), the response lag and dead zone characteristics of mechanical valves can easily lead to pressure overshoot or undershoot, making it impossible to maintain a precise antifreeze safety margin at dynamic boundaries.

[0008] Second, in order to address the risk of freezing under dynamic operating conditions, another technical approach has adopted a complex feedback control and post-event remediation mechanism.

[0009] A typical example is Chinese patent application CN112228769A (publication date: January 15, 2021). This patent proposes a filling system based on anti-freeze control. Its key feature is the use of complex PID control and a clearly designed "freeze emergency handling" step: once a freeze signal is detected, the pipeline is immediately switched, and high-pressure nitrogen is introduced for forced purging and rewarming.

[0010] This technical approach presents a clear logical paradox in continuous industrial production:

[0011] (1) Non-intrinsic safety: The underlying logic of its control philosophy is "allowing freezing to occur and then taking remedial measures." This violates the intrinsic safety principle in chemical process safety management. In the continuous external transmission process of LNG peak shaving station, once freezing occurs and triggers the melting process, it will inevitably lead to the interruption of the process flow and seriously affect the supply guarantee task.

[0012] (2) Excessive system redundancy: In order to achieve the "melting" function, the system has to be equipped with a special reheating pipeline and a complex switching valve group (such as the fourth valve, the seventh valve, the eighth valve, etc.) [6, Fig.1], which significantly increases the construction cost and failure probability of the system.

[0013] Third, the latest technological attempts to introduce external heat sources to actively intervene in the refrigerant state in order to achieve more precise temperature control.

[0014] A typical example is Chinese patent application CN117847407A (publication date: April 9, 2024). This patent discloses a methane subcooling filling system. Its most significant feature is that, inside the subcooler shell (200), in addition to a first heat exchanger (210) for cooling methane, a second heat exchanger (220) is also forcibly installed. The process requires that ambient temperature gas be introduced into the second heat exchanger first to actively heat the liquid nitrogen inside the shell, raising its temperature and pressure to the target value before starting the methane subcooling.

[0015] While this approach is feasible in the "batch processing" scenario of space launches, it suffers from serious thermodynamic and engineering flaws when applied to municipal energy infrastructure:

[0016] (1) Structural complexity and manufacturing cost: The nested double heat exchanger structure inside the cryogenic pressure vessel greatly increases the manufacturing difficulty, the number of welded joints, and the risk of leakage. This runs counter to the "simplicity and reliability" pursued by industrial equipment.

[0017] (2) Thermodynamic irreversibility and entropy production: This scheme introduces an external heat source (room temperature gas) to heat the low-temperature working fluid (liquid nitrogen). From the perspective of the second law of thermodynamics, this is a "reverse operation" of using high-grade energy to destroy low-grade cold energy, resulting in additional entropy production. On the one hand, the system consumes liquid nitrogen to cool methane, and on the other hand, it consumes external heat to heat liquid nitrogen. This "mutually conflicting" energy coupling method is extremely inefficient in terms of energy.

[0018] (3) Unable to adapt to continuous flow conditions: The process described in this patent is strictly step-by-step (fueling → pressurization → heating → subcooling → depressurization). In particular, its necessary "depressurization step" means that the established high-pressure environment must be destroyed and vented at the end of each operation cycle. This intermittent operation mode is completely unsuitable for the continuous 24-hour operation characteristics of LNG peak shaving stations with random load changes.

[0019] In summary, existing technologies have fallen into the pitfalls of "structural complexity" (such as dual heat exchangers), "energy dissipation" (such as venting and introducing heat sources), and "passive control" (such as mechanical depressurization and post-melting) in solving the problem of cryogenic medium antifreeze and supercooling.

[0020] The industry urgently needs a completely new system architecture. This system should abandon the cumbersome design of introducing external heat sources or second heat exchangers, and instead utilize the thermal coupling effect of the process fluid itself to establish anti-freeze back pressure (i.e., "self-coupling"); it should abandon the open-loop venting operation mode, and achieve closed-loop recovery of pressure energy (i.e., "energy-level cascade utilization"); it should abandon the passive logic of "freezing first and then thawing," and establish an inherently safe boundary based on physical hard constraints. This is precisely the core technical problem that this invention aims to solve. Summary of the Invention

[0021] I. The technical problem to be solved by this invention:

[0022] In view of the problems of "redundancy in the dual heat exchanger structure" and "thermodynamic irreversibility caused by the introduction of external heat sources" in the prior art detailed in the background section, the present invention aims to provide a self-coupled constant pressure boiling and energy level cascade utilization system.

[0023] Specifically, this invention aims to resolve the core physical and engineering contradictions at the following three levels:

[0024] 1. The problem of "minimizing entropy production" in thermodynamic dimension: Abandon the reverse operation of "using high-grade external heat sources (such as ambient temperature gas sources) to heat cryogenic working fluids" in existing technologies, solve the pain point of increasing system entropy production for antifreeze, and achieve adaptive balance driven solely by the enthalpy of the process fluid itself.

[0025] 2. The contradiction between "simplicity of structure and completeness of function" in the system engineering dimension: Overcome the structural limitations of existing technologies that require a "second heat exchanger" to achieve temperature control, and realize the dual functions of heat exchange and pressure regulation through a single tube bundle structure, thereby reducing equipment manufacturing costs and leakage risks.

[0026] 3. The problem of "full closed-loop cascade recovery" in the energy utilization dimension: Solve the "double waste" problem in traditional processes, which consumes high-value cargo (LNG) during unloading pressurization and wastes the pressure energy after the auxiliary refrigerant (liquid nitrogen) is vaporized, and construct a complete closed loop of material flow and energy flow.

[0027] II. Technical solution of the present invention:

[0028] To achieve the above objectives, this invention provides a cryogenic medium cascade energy recovery system based on the first law of thermodynamics (energy conservation) and the second law (efficiency maximization). This system utilizes the latent heat of phase change of a first cryogenic working medium (preferably liquid nitrogen) as a cold trap and its expansion work after vaporization as a power source to perform full life-cycle thermal management of a second liquefied gas (preferably LNG).

[0029] The specific technical solution of the present invention includes:

[0030] 1. System Overall Architecture and Topology:

[0031] A self-coupled constant-pressure boiling and energy-level cascade utilization system is characterized by comprising: a second liquefied gas storage unit, a first cryogenic working fluid supply and self-coupled phase change unit, a single-tube bundle integrated submerged heat and mass exchange unit, a thermodynamic state active intervention circulation unit, a pressure energy and material cascade recovery network, and a full-condition intelligent control center.

[0032] The second liquefied gas storage unit is configured as an insulated container for storing cryogenic liquefied gases (such as LNG), serving as a heat load source and a flash vapor (BOG) generation source for the system, and includes a liquid phase outlet and a gas phase space interface.

[0033] The first cryogenic working fluid supply and self-coupled phase change unit is a container that holds the first cryogenic working fluid and provides a phase change cold source.

[0034] The single-tube bundle integrated submersible heat and mass exchange unit is characterized by comprising: a shell side, a tube side, and a back pressure regulating component; the shell side includes a shell side inlet and a shell side outlet; the back pressure regulating component includes a back pressure regulating component inlet and a back pressure regulating component outlet; and the tube side includes a tube side inlet and a tube side outlet.

[0035] The shell side of the single-tube bundle integrated submerged heat and mass exchange unit is not only a container for the refrigerant, but also a thermodynamic state regulator. The core feature of the single-tube bundle integrated submerged heat and mass exchange unit is that the tube side serves as the sole heat source input and does not contain auxiliary heating elements or a second heat exchange tube bundle for introducing external heat sources.

[0036] The single-tube bundle integrated submerged heat and mass exchange unit is configured to use only the sensible heat released by the second liquefied gas in the tube side to drive the phase change boiling of the first cryogenic working fluid in the shell side, and to use the gas phase components generated by boiling to establish a self-coupling back pressure in the closed shell side, thereby physically clamping the boiling temperature of the first cryogenic working fluid within a safe range higher than the triple point of the second liquefied gas.

[0037] The single-tube bundle integrated immersion heat and mass exchange unit, as the only heat exchange core of the system, adopts a vertical vacuum insulated container structure.

[0038] The shell-side inlet is in fluid communication with the first cryogenic working fluid supply and self-coupled phase change unit, and the shell-side outlet is in communication with the inlet of the back pressure regulating component, forming a "self-coupled constant pressure boiling cavity" capable of withstanding a preset pressure.

[0039] The tube side has only one set of helically wound tube bundles or plate-fin channels, connected in series in the flow path of the second liquefied gas. This tube side is completely submerged below the liquid level in the shell side and is used to transfer the sensible heat of the second liquefied gas to the working fluid in the shell side.

[0040] The thermodynamic state active intervention circulation unit is connected between the second liquefied gas storage unit and the single-tube bundle integrated submerged heat and mass exchange unit. It includes a circulation pump connected to the bottom of the second liquefied gas storage unit and an atomizing spray assembly located inside the gas phase space of the second liquefied gas storage unit. The system is configured to, under static storage conditions, allow the cryogenic liquid in the second liquefied gas storage unit to enter the tube-side inlet of the single-tube bundle integrated submerged heat and mass exchange unit from its bottom liquid phase outlet via the circulation pump, where it is subcooled to below the bubble point temperature. The liquid then enters the gas phase space interface of the second liquefied gas storage unit through the tube-side outlet and is sprayed out by the atomizing spray assembly. The subcooled droplets absorb heat from the gas phase space and induce a pressure collapse effect to reduce the internal pressure of the second liquefied gas storage unit, establishing a subcooled circulation loop of "tank-heat exchanger-tank" to eliminate static heat leakage.

[0041] The pressure energy and material cascade recovery network is connected to the outlet of the back pressure regulating component. This network includes a pressure stabilizing buffer tank and a reheater, configured to collect the high-pressure, low-temperature gas generated after the phase change of the first cryogenic working fluid discharged from the shell side, and transport its pressure potential energy and material flow to the downstream application end to achieve closed-loop recovery.

[0042] The intelligent control center for all operating conditions has a built-in thermodynamic state equation model, which is used to execute control strategies based on physical hard constraints.

[0043] 2. Single-tube bundle self-coupling constant pressure antifreeze mechanism:

[0044] This invention abandons the technical approach of "actively heating liquid nitrogen using a second heat exchanger" in CN117847407A (published on April 9, 2024) and proposes a passive antifreeze mechanism based on the self-balancing of "heat load-pressure-temperature".

[0045] (1) Physical principle: The system utilizes the heat Q released by the second liquefied gas (LNG). release The first cryogenic working fluid (liquid nitrogen) is boiled as the sole heat source. The gaseous mass flow rate m generated by boiling is... gas It directly determines the rate of increase P of the shell-side pressure.

[0046] (2) Control Logic: The single-tube bundle integrated submerged heat and mass exchange unit is equipped with a back pressure regulating component. Based on the Clausius-Clapeyron equation, the full-condition intelligent control center adjusts the shell-side pressure P by regulating the opening of the back pressure component. shell The pressure is controlled within a preset antifreeze pressure range (0.6~0.8 MPa). Under this pressure range, the saturation boiling temperature T of the first cryogenic working fluid (liquid nitrogen) is... sat Physically locked between -179°C and -172°C, this temperature range satisfies T freeze <T sat <T target Thermodynamic inequalities, where T freeze T represents the triple point temperature (-182.5℃) of the refrigerated component (methane) in the second liquefied gas (LNG). target This refers to the target subcooling temperature required by the process. For example, if the process requires LNG to be subcooled to -165℃, then -182.5℃ < -179℃ to -172℃ < -165℃.

[0047] (3) Self-coupling effect:

[0048] a. When the LNG flow rate increases (increased heat load → intensified liquid nitrogen boiling → increased gas production → shell-side pressure tends to rise).

[0049] b. Increase the opening of the back pressure regulating component to maintain constant pressure → increase the amount of high-pressure nitrogen discharged.

[0050] c. Pressure maintained at 0.6 MPa → Liquid nitrogen saturation temperature maintained at -179.2℃.

[0051] d. This temperature of -179.2℃ is physically higher than the triple point of the methane component in LNG, which is -182.5℃.

[0052] Therefore, the outer wall temperature T of the single-tube bundle integrated submersible heat and mass exchange unit wall Physically locked in a safe zone, it requires no external heat source intervention, achieving the adaptive characteristic of "the more heat load, the stronger the antifreeze foundation".

[0053] 3. Pressure energy feedback and zero-loss mechanism under unloading conditions:

[0054] This invention addresses the problems of cavitation and loss during the unloading process of transport tank trucks by utilizing the byproduct (high-pressure nitrogen) generated in the above-mentioned self-coupling process to construct a closed loop of "waste-based pressurization".

[0055] The pressure energy and material cascade recovery network includes a pressure stabilizing buffer tank and a tank truck unloading pressurization circuit.

[0056] (1) Energy conversion path: During the unloading of the transport tanker, liquid nitrogen absorbs heat from LNG and vaporizes, resulting in a volume expansion of about 700 times. This expansion work is converted into pressure potential energy (0.6-0.8 MPa) in the closed shell, and the product is high-pressure cryogenic nitrogen gas.

[0057] (2) Connection and function: One end of the pressure stabilizing buffer tank is connected to the outlet of the back pressure regulating component, and the other end is connected to one end of the tank truck unloading pressurization circuit. The other end of the tank truck unloading pressurization circuit is configured to be detachably connected to the tank truck gas phase space interface of the transport tank truck transporting the second liquefied gas. The tank truck unloading pressurization circuit is equipped with a precision pressure reducing valve, which is used to adjust the high-pressure low-temperature nitrogen from the shell side to 0.35 MPa to 0.5 MPa (gauge pressure) and then inject it into the tank truck gas phase space.

[0058] (3) Physical effects:

[0059] a. Eliminating cavitation: Forcibly maintaining the vapor pressure P of the transport tanker. tank This increases the net positive suction head (NPSHa) at the unloading pump inlet.

[0060] According to Bernoulli's equation: NPSHa = (P tank +P atm -P vapor ) / ρg+H static -H loss , where P tank P is the absolute pressure above the liquid surface in the storage tank. atmP is the local atmospheric pressure. vapor H is the saturated vapor pressure (absolute pressure) of the liquid at the operating temperature. static H is the vertical height from the centerline of the pump inlet to the lowest liquid level in the storage tank. loss The total frictional resistance loss (meters of liquid column) of the liquid flowing from the storage tank to the pump inlet. The additional head provided by this system ΔP≈0.2MPa is equivalent to increasing the liquid column height by about 45 meters, completely eliminating the risk of cavitation at low liquid levels.

[0061] b. Zero Loss: The system directly utilizes the volume expansion work generated by the heat absorption and vaporization of the first cryogenic working fluid to maintain the pressure in the transport tanker, replacing the work of the tanker's built-in vaporization booster. The tanker's built-in vaporization booster consumes approximately 0.5 tons of LNG (chemical energy) to generate pressure, while this system utilizes the exhaust gas (pressure energy) after liquid nitrogen absorbs heat. By "replacing LNG with nitrogen," zero loss of cargo is achieved during the unloading process.

[0062] 4. "Pressure collapse" mitigation mechanism under storage conditions:

[0063] For BOG handling during static storage, this invention utilizes the principle of "supercooled droplet capture" to implement a "pressure collapse" strategy.

[0064] (1) Operating logic: When the gas phase pressure of the storage tank exceeds the set high limit (e.g., 12.5 kPa), the thermodynamic state active intervention cycle unit is activated.

[0065] (2) Process description: The cryogenic liquid of the second liquefied gas storage unit is extracted from the liquid phase outlet at the bottom and transported to the tube side of the single tube bundle integrated immersion heat and mass exchange unit. After being forcibly supercooled to below -165°C using a liquid nitrogen cold bath, it is returned to the second liquefied gas storage unit through the atomizing spray assembly.

[0066] (3) Microscopic mass transfer mechanism: The deeply supercooled liquid is atomized into micron-sized droplets (Soter average diameter < 500 μm) through the top spray assembly of the tank. These droplets provide a huge gas-liquid mass transfer specific surface area.

[0067] The classic formula for the mass transfer condensation (or evaporation) process of droplets in an airflow:

[0068] m cond =h m ·A droplet ·(C sat -C ∞ )

[0069] Where, m cond The mass flow rate of droplet condensation (unit: kg / s); h m A is the convective mass transfer coefficient (unit: m / s);droplet C represents the outer surface area of ​​the droplet (unit: m²). sat -C ∞ The driving force for mass transfer is the concentration difference (unit: kg / m³).

[0070] The high-temperature BOG (typically around -100°C) in the gas phase space rapidly condenses onto the surface of the supercooled droplets. Due to the approximately 600-fold volume contraction as it changes from a gaseous to a liquid state, a momentary negative pressure trend occurs in the gas phase space, which macroscopically manifests as a rapid drop in tank pressure.

[0071] (4) Energy efficiency advantage: Compared with the traditional BOG compressor solution, this process consumes very little circulating pump power and there is no gas output, realizing the "in-situ liquefaction and recovery" of BOG.

[0072] 5. A tiered utilization network of material resources:

[0073] The pressure energy and material cascade recovery network also includes a public gas supply circuit, which includes an ambient temperature reheater connected in sequence and an interface connected to the instrument air duct network within the station.

[0074] The remaining high-pressure cryogenic nitrogen gas that was not used for pressurizing the transport tank trucks is reheated to room temperature and then preferentially fed into the station's instrument air duct network through the public gas supply circuit.

[0075] Nitrogen gas, after being vaporized from liquid nitrogen, has a dew point below -70°C, making it an excellent power source for drying. Using it as the power source for pneumatic actuators to drive pneumatic valves replaces traditional high-energy-consuming air compressors and dryer systems, achieving significant energy savings (calculated to cover the power consumption of the circulating pump, achieving system-level "zero power consumption" or "negative power consumption" operation).

[0076] 6. Special structural design:

[0077] The single-tube bundle integrated immersion heat and mass exchange unit adopts a stress self-eliminating structure. The tube side includes a heat exchange core, which is fixed inside the shell side by a top single-point suspension mechanism. The bottom is in a free-hanging state, and a thermal compensation gap greater than the axial shrinkage under the maximum design temperature difference is reserved between the core and the bottom surface of the shell side. In order to collect and discharge the solid impurities precipitated by the first cryogenic working fluid in the shell side, a hydrodynamic dead zone and an inverted conical settling tank are provided at the bottom of the shell side.

[0078] The heat exchange core adopts a multi-layer spiral wound tube bundle structure, and its spiral rise angle is configured to meet the hydrodynamic condition that the Dean number is greater than the critical value, so as to induce secondary circulation in the tube, enhance the convective heat transfer on the inner side of the tube and inhibit the adhesion of the freezing core.

[0079] Compared with the prior art, the above-mentioned technical solution of the present invention has significant substantive features and progress, which are specifically reflected in the following five dimensions:

[0080] 1. Ultimate Improvement in Thermodynamic Efficiency: Compared to CN117847407A (publication date: April 9, 2024), this invention eliminates the entropy increase process of "introducing an external heat source to heat liquid nitrogen," achieving equilibrium through internal thermal coupling. Compared to US2010 / 0326097A1 (publication date: December 30, 2010), this invention eliminates the waste of high-pressure gas venting. Through a three-stage utilization of "cold energy for subcooling, pressure energy for pressurization, and matter for purging," the thermodynamic efficiency of the system is improved by more than 40%.

[0081] 2. Simplified Structure and Enhanced Reliability: This invention adopts a single-tube bundle structure, avoiding the manufacturing difficulties and stress concentration risks associated with dual heat exchangers. The main system flow has no reciprocating compressors or other moving equipment (only a low-power canned pump), greatly reducing the mechanical failure rate and maintenance costs, making it suitable for unmanned stations.

[0082] 3. Explicit Economic Benefits: The "zero-loss unloading" function saves approximately 0.5 tons of LNG per vehicle (worth about 2000 yuan). For a peak-shaving station with an annual turnover of 200,000 tons, the average annual direct economic benefit exceeds 20 million yuan. Combined with savings in instrument wind power consumption, the system's investment payback period is typically less than 6 months.

[0083] 4. Full-condition adaptive capability: This system can seamlessly adapt to extreme load fluctuations in peak-shaving stations.

[0084] (1) High-load unloading period: Full-load operation, producing a large amount of high-pressure nitrogen for co-pressurization, while outputting cryogenic LNG.

[0085] (2) Low load cold preservation period: intermittent operation, using small flow circulation to eliminate heat leakage and maintain tank pressure.

[0086] (3) Zero external output period: It solves the problem that traditional recondensation process relies on external cold source and fails in the "dead storage" state.

[0087] 5. Intrinsically safe antifreeze protection: Based on the physical hard constraint of the Clausius-Clapeyron equation, it ensures that the heat exchange wall temperature is higher than the freezing point of methane under any operating conditions (including extreme situations such as power failure, gas failure, and control failure), fundamentally eliminating the hidden danger of freezing and blockage. Attached Figure Description

[0088] 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:

[0089] Figure 1 The overall system process flow and connection topology diagram provided for embodiments of the present invention.

[0090] Figure 2 This is a schematic diagram of the thermodynamic antifreeze principle based on the Clausius-Clapeyron equation in an embodiment of the present invention.

[0091] Figure 3 This is a schematic diagram of the pressure energy feedback and anti-cavitation pressurization logic under the unloading condition in an embodiment of the present invention.

[0092] Figure 4 This is a schematic diagram illustrating the control principle of the "pressure collapse" effect under storage and cold preservation conditions in an embodiment of the present invention.

[0093] 1-Second liquefied gas storage unit; 11-Gas phase space interface; 12-Liquid phase outlet; 2-First cryogenic working fluid supply and self-coupled phase change unit; 3-Single-tube bundle integrated submerged heat and mass exchange unit; 31-Back pressure regulating component; 32-Inverted conical settling tank; 33-Shell side inlet; 34-Shell side outlet; 35-Back pressure regulating component inlet; 36-Back pressure regulating component outlet; 37-Tube side inlet; 38-Tube side outlet; 4-Thermodynamic state active intervention circulation unit Yuan; 41-Circulating pump; 42-Atomizing spray assembly; 5-Pressure energy and material cascade recovery network; 51-Ambient temperature reheater; 52-Pressure stabilizing buffer tank; 53-Instrument air duct network interface; 54-Public gas supply circuit; 55-Tank truck unloading pressurization circuit; 6-All-condition intelligent control center; 8-Transport tank truck; 81-Tank truck gas phase space interface; 82-Tank truck liquid phase outlet; 83-LNG unloading pump; PT-Pressure transmitter; TT-Temperature transmitter. Detailed Implementation

[0094] 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.

[0095] 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.

[0096] Example 1 (System Hardware Configuration and Connection Topology):

[0097] like Figure 1 As shown in the figure, the hardware connection relationship of the LNG storage and peak-shaving station with zero-loss BOG under all operating conditions based on the cascade utilization of liquid nitrogen cold energy provided in this embodiment is as follows:

[0098] 1. Liquid nitrogen self-coupling boiling core region:

[0099] The single-tube bundle integrated submerged heat and mass exchange unit 3 (configured as an integrated liquid nitrogen subcooling heat exchanger in this embodiment, Tag: E-101) adopts a vertical S30408 ​​stainless steel vacuum insulated container, including a shell side 301, a tube side 302 and a back pressure regulating component 31.

[0100] Shell side 301 construction (key features): Shell side 301 contains only one set of helical wound tubes (i.e., tube side 302) for LNG flow. Shell side 301 includes a shell side inlet 33 and a shell side outlet 34, and shell side 301 does not contain any electric heaters or auxiliary gas heat exchangers for heating liquid nitrogen.

[0101] The back pressure regulating component 31 (configured as a back pressure regulating valve in this embodiment, Tag: PCV-101) includes a back pressure regulating component inlet 35 and a back pressure regulating component outlet 36.

[0102] The first cryogenic working fluid supply and self-coupling and phase change unit 2 (configured as a liquid nitrogen storage tank in this embodiment, Tag: T-201) is connected to the shell-side inlet 33 of the shell-side 301.

[0103] Back pressure control: Shell-side outlet 34 is connected to back pressure regulating component inlet 35 of back pressure regulating component 31. Pressure transmitter (PT-101) is directly mounted on the top of shell-side 301, forming a fast-response closed loop with back pressure regulating valve PCV-101, with setpoint SP fixed at 0.7MPa(a).

[0104] 2. LNG process pipeline area:

[0105] Unloading branch: The transport tanker 8 is connected to the pipe-side inlet 37 via the tanker liquid phase outlet 82. The pipe-side outlet 38 is connected to the second liquefied gas storage unit 1 (configured as an LNG storage tank in this embodiment, Tag: T-202).

[0106] Circulation branch: A circulation pump 41 (configured as an LNG cryogenic circulation pump in this embodiment, Tag: P-201) is installed at the bottom of the second liquefied gas storage unit 1 (i.e., LNG storage tank). The liquid phase outlet 12 of the second liquefied gas storage unit 1 (i.e. LNG storage tank) is connected to one end of the circulation pump 41 (i.e., LNG cryogenic circulation pump). The other end of the circulation pump 41 (i.e. LNG cryogenic circulation pump) is connected to the pipe inlet 37. The pipe outlet 38 is connected to the gas phase space interface 11 of the second liquefied gas storage unit 1 (i.e. LNG storage tank), and then connected to the atomizing spray assembly 42.

[0107] 3. Pressure energy recovery network area:

[0108] The back pressure regulating component outlet 36 of the back pressure regulating component 31 (i.e., back pressure regulating valve, PCV-101) is connected to the inlet of the pressure stabilizing buffer tank 52 (configured as a nitrogen buffer tank in this example, Tag: V-301).

[0109] First recovery path (tank truck unloading pressurization circuit 55): The outlet of the pressure stabilizing buffer tank 52 (i.e. nitrogen buffer tank) is connected to the gas phase space interface 81 of the transport tank truck 8 via a precision pressure reducing valve 56 (configured as a cryogenic pressure reducing valve in this embodiment, Tag: PCV-102, set pressure is 0.45 MPa).

[0110] The second recovery path (public gas supply circuit 54): The other outlet of the pressure stabilizing buffer tank 52 (i.e. nitrogen buffer tank) is reheated to room temperature by the ambient temperature reheater 51 (equivalent to E-102 in this embodiment) and then connected to the interface 53 of the plant's instrument air duct network.

[0111] The pressure stabilizing buffer tank 52, the tank truck unloading pressurization circuit 55, and the public gas supply circuit 54 together form a pressure energy and material recovery network 5.

[0112] Example 2 (Self-coupling operation control of unloading condition Mode A):

[0113] like Figure 3 As shown in the figure, this embodiment describes how the system uses a self-coupling mechanism to achieve antifreeze and pressurization when unloading LNG from LNG transport tanker 8.

[0114] Step S1 (Cold Bath Setup and Self-Pressure):

[0115] Before system startup, the shell side 301 of the single-tube bundle integrated immersion heat and mass exchange unit 3 (configured as an integrated liquid nitrogen subcooling heat exchanger in this embodiment, Tag: E-101) is filled with liquid nitrogen.

[0116] LNG unloading pump 83 is turned on, and LNG (approximately -155°C) in transport tanker 8 enters tube side 302. After being subcooled to below -168°C in single-tube bundle integrated submerged heat and mass exchange unit 3 (i.e. integrated liquid nitrogen subcooling heat exchanger, E-101), it is unloaded into the second liquefied gas storage unit 1 (configured as an LNG storage tank in this embodiment, Tag: T-202).

[0117] Self-coupling process: LNG releases heat in the tube side 302 → liquid nitrogen absorbs heat and boils in the shell side 301 → nitrogen gas is produced → the pressure in the shell side 301 increases.

[0118] When the pressure of shell side 301 collected in real time by the full-condition intelligent control center 6 is higher than 0.7MPa, the model in the full-condition intelligent control center 6 calculates the real-time saturation temperature under this pressure and calculates the freezing margin. When the freezing margin is lower than the preset safety threshold, the highest priority hard constraint control logic is triggered, and the back pressure regulating component 31 (PCV-101) is forced to automatically open the vent to maintain the pressure of shell side 301 at 0.7MPa. At this time, according to physical properties, the liquid nitrogen temperature in shell side 301 is physically locked at -174.7℃.

[0119] Freeze protection verification: At this point, the wall temperature of tube 302 must be higher than -174.7℃, while the freezing point of methane is -182.5℃. Therefore, it is physically impossible for it to freeze, and no external heat source is needed to heat the liquid nitrogen.

[0120] Step S2 (Closed-loop utilization of pressure energy):

[0121] The 0.7 MPa nitrogen discharged from the back pressure regulating component 31 (PCV-101) enters the pressure stabilizing buffer tank 52 (in this example, it is configured as a nitrogen buffer tank, Tag: V-301).

[0122] Monitor the pressure of transport tanker 8. When the pressure of transport tanker 8 is <0.4 MPa, activate the tanker unloading pressurization circuit 55.

[0123] High-pressure, low-temperature nitrogen gas in pressure stabilizing buffer tank 52 (i.e., nitrogen buffer tank, V-301) is injected into the gas phase space of transport tanker 8 to increase the pressure of transport tanker 8.

[0124] Energy efficiency analysis: The injected high-pressure cryogenic nitrogen gas forcibly maintained the pressure of the transport tanker 8, ensuring sufficient NPSHA of the LNG unloading pump 83. The traditional on-board vaporization booster of the transport tanker 8 was not activated throughout the process, saving approximately 500 kg of LNG that was originally planned to be consumed.

[0125] Example 3 (Pressure collapse control in storage and cold preservation mode B):

[0126] like Figure 4 and Figure 1 As shown, this embodiment describes the system's logic for processing static BOOGs during non-unloading periods. The system described in this example is configured with a full-condition intelligent control center 6 for the automated control of the entire system.

[0127] Step S1 (Pressure Trigger):

[0128] The full-condition intelligent control center 6 continuously monitors the gas phase pressure P of the second liquefied gas storage unit 1 (configured as an LNG storage tank in this embodiment, Tag: T-202). tank When P tank When the pressure is >12.5 kPa, the cooling mode is triggered.

[0129] Step S2 (Circulating Spray):

[0130] Start the circulation pump 41 (in this embodiment, it is configured as an LNG cryogenic circulation pump, Tag: P-201). The cryogenic liquid LNG in the second liquefied gas storage unit 1 (i.e., LNG storage tank, Tag: T-202) flows through the liquid phase outlet 12 and passes through the tube side 302 of the single-tube bundle integrated submerged heat and mass exchange unit 3 (in this embodiment, it is configured as an integrated liquid nitrogen subcooling heat exchanger, E-101). It is cooled to -168°C by the liquid nitrogen in the shell side 302. This temperature is monitored in real time by a temperature transmitter.

[0131] After being subcooled, the LNG enters the gas phase space interface 11 of the second liquefied gas storage unit 1 (i.e., the LNG storage tank) through the pipe outlet 38, and is atomized and sprayed out by the atomizing spray assembly 42.

[0132] Step S3 (Pressure Collapse):

[0133] The droplets atomized and sprayed by the atomizing spray assembly 42 absorb the heat in the gas phase space of the second liquefied gas storage unit 1 (i.e., LNG storage tank), and the BOG (approximately -100°C) in the gas phase space condenses.

[0134] BOG condensation causes the gas phase volume to shrink, and the pressure of the second liquefied gas storage unit 1 (i.e., the LNG storage tank) drops rapidly.

[0135] Step S4 (Delayed Stop):

[0136] When the gas phase pressure P of the second liquefied gas storage unit 1 (i.e., the LNG storage tank) tank When the pressure drops to 11.5 kPa, the intelligent control center 6 controls the storage and cold preservation program to shut down.

[0137] At this time, the shell side 301 of the single-tube bundle integrated submerged heat and mass exchange unit 3 (i.e., integrated liquid nitrogen subcooling heat exchanger, E-101) still maintains a back pressure of 0.6 MPa and is in hot standby mode.

[0138] Example 4 (Abnormal Operating Conditions and Safety Interlocks ESD):

[0139] To cope with extreme situations, the full-condition intelligent control center 6 has the highest priority hardware interlocking logic:

[0140] 1. Freeze-resistant rigid constraints:

[0141] The full-condition intelligent control center calculates the freeze margin (Margin=T) in real time. sat (P shell )﹣(﹣182.5), where T sat (P shell ) indicates that the shell-side pressure is P shell At that time, the corresponding saturated boiling temperature.

[0142] If Margin < 3.0K (i.e., the pressure is too low), the full-condition intelligent control center 6 immediately triggers the interlock: forcibly closes the back pressure regulating component 31 (configured as a back pressure regulating valve in this embodiment, Tag: PCV-101) to allow for pressure recovery and cuts off the LNG from entering the tube side 302 of the single-tube bundle integrated submerged heat and mass exchange unit 3 (configured as an integrated liquid nitrogen subcooling heat exchanger in this embodiment, E-101).

[0143] 2. Hypoxia protection:

[0144] If the oxygen content detector reading in the device area is <19.5%, the exhaust ventilation is started. If it is <18%, ESD is triggered, the supply of the first cryogenic working fluid to the liquid nitrogen from the self-coupling and phase change unit 2 (configured as a liquid nitrogen storage tank in this embodiment, Tag: T-201) into the shell side 301 of the single-tube bundle integrated immersion heat and mass exchange unit 3 (i.e., integrated liquid nitrogen subcooling heat exchanger, E-101) is cut off, and the gas phase emission path is switched to the high-altitude safety vent.

[0145] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A self-coupled isobaric boiling and energy level cascade utilization system, characterized in that, include: The second liquefied gas storage unit (1), the first cryogenic working fluid supply and self-coupled phase change unit (2), the single tube bundle integrated submerged heat and mass exchange unit (3), and the pressure energy and material cascade recovery network (5). The second liquefied gas storage unit (1) is for storing the second liquefied gas and serving as the heat load source of the system, including a liquid phase outlet (12) and a gas phase space interface (11). The first cryogenic working fluid supply and self-coupled phase change unit (2) is a container that contains the first cryogenic working fluid and provides a phase change cold source; The single-tube bundle integrated immersion heat and mass exchange unit (3) includes a shell side (301), a tube side (302), and a back pressure regulating component (31). The shell side (301) includes a shell side inlet (33) and a shell side outlet (34); the back pressure regulating assembly (31) has a back pressure regulating assembly inlet (35) and a back pressure regulating assembly outlet (36); the tube side (302) includes a tube side inlet (37) and a tube side outlet (38). The shell-side inlet (33) is connected to the first cryogenic working fluid supply and self-coupling phase change unit (2), and the shell-side outlet (34) is connected to the back pressure regulating component inlet (35). The tube side (302) is connected in series in the flow path of the second liquefied gas and is completely submerged below the liquid level of the shell side (301); The pressure energy and material cascade recovery network (5) has its input end connected to the outlet (36) of the back pressure regulating component; Its characteristics also include: The shell side (301) of the single-tube bundle integrated submerged heat and mass exchange unit (3) is configured as a self-coupled constant pressure boiling cavity; the single-tube bundle integrated submerged heat and mass exchange unit (3) is only provided with the tube side (302) as the only heat source input, and does not contain auxiliary heating elements or a second heat exchange tube bundle for introducing external heat sources. The single-tube bundle integrated immersion heat and mass exchange unit (3) is configured to use the sensible heat released by the second liquefied gas in the tube side (302) to drive the phase change boiling of the first cryogenic working fluid in the shell side (301), and use the gas phase components generated by boiling to establish a self-coupled back pressure in the closed shell side (301), thereby physically clamping the boiling temperature of the first cryogenic working fluid in a safe range higher than the triple point of the second liquefied gas. The pressure energy and material cascade recovery network (5) is configured to collect the high-pressure low-temperature gas generated after the phase change of the first cryogenic working fluid discharged from the shell side (301), and transport its pressure potential energy and material flow to the downstream pressure utilization terminal to realize the closed-loop cascade utilization of cold energy, pressure energy and material.

2. The system according to claim 1, characterized in that, The thermodynamic constraint relationship between the self-coupling back pressure and the safety zone is as follows: the self-coupling back pressure is maintained by the back pressure regulating component (31) within the antifreeze pressure range of 0.6 MPa to 0.8 MPa (absolute pressure); under this pressure range, the saturated boiling temperature T of the first cryogenic working fluid (liquid nitrogen) is... sat Physically locked between -179°C and -172°C; this temperature range satisfies T freeze <T sat <T target Thermodynamic inequalities, where T freeze T represents the triple point temperature (-182.5℃) of the easily freezing component (methane) in the second liquefied gas. target This refers to the target subcooling temperature required by the process.

3. The system according to claim 1, characterized in that, The pressure energy and material cascade recovery network (5) includes a pressure stabilizing buffer tank (52) and a tank truck unloading pressurization circuit (55): one end of the pressure stabilizing buffer tank (52) is connected to the back pressure regulating component outlet (36), and the other end is connected to one end of the tank truck unloading pressurization circuit (55), the other end of which is configured to be detachably connected to the tank truck gas phase space interface (81) of the transport tank truck (8) transporting the second liquefied gas; the tank truck unloading pressurization circuit (55) is equipped with a precision pressure reducing valve (56) for adjusting the high-pressure gas phase working fluid from the shell side (301) to 0.35 MPa to 0.5 MPa. After MPa (gauge pressure), it is injected into the gas phase space of the tank truck; the system is configured to maintain the pressure of the transport tank truck (8) by directly using the volume expansion work generated by the heat absorption and vaporization of the first cryogenic working fluid under the unloading condition, so as to replace the operation of the vaporization booster built into the transport tank truck (8) and increase the net positive suction head (NPSHa) at the inlet of the unloading pump to prevent cavitation.

4. The system according to claim 1, characterized in that, The system also includes a thermodynamic state active intervention circulation unit (4): the thermodynamic state active intervention circulation unit (4) includes a circulation pump (41) connected to the bottom of the second liquefied gas storage unit (1) and an atomizing spray assembly (42) located inside the gas phase space of the second liquefied gas storage unit (1); the system is configured to, under static storage conditions, draw the low-temperature liquid in the second liquefied gas storage unit (1) from the liquid phase outlet (12) at its bottom, enter the tube inlet (37) through the circulation pump (41) and be subcooled to below the bubble point temperature in the single tube bundle integrated immersion heat and mass exchange unit (3), and enter the gas phase space interface (11) of the second liquefied gas storage unit (1) through the tube outlet (38), and be sprayed out by the atomizing spray assembly (42), using the subcooled droplets to absorb heat in the gas phase space and trigger a pressure collapse effect to reduce the internal pressure of the second liquefied gas storage unit (1).

5. The system according to claim 1, characterized in that, The pressure energy and material cascade recovery network (5) also includes a public gas supply circuit (54): the public gas supply circuit (54) includes an air-temperature reheater (51) connected in sequence and an interface (53) connected to the instrument air duct network in the station; the system is configured to reheat the recovered gaseous working fluid to room temperature and use it as the power source for the pneumatic actuator, replacing the air compressor system.

6. The system according to claim 1, characterized in that, The single-tube bundle integrated immersion heat and mass exchange unit (3) adopts a stress self-eliminating structure: the tube side (302) includes a heat exchange core, which is fixed inside the shell side (301) by a top single-point suspension mechanism, and the bottom is in a free hanging state. A heat compensation gap greater than the axial shrinkage under the maximum design temperature difference is reserved between the core and the bottom surface of the shell side (301); the bottom of the shell side (301) is provided with a hydrodynamic dead zone and an inverted conical settling tank (32) for collecting and discharging solid impurities precipitated in the first cryogenic working fluid.

7. The system according to claim 1, characterized in that, The system is equipped with a full-condition intelligent control center (6): the full-condition intelligent control center (6) has a built-in thermodynamic equation of state (EOS) model of the first cryogenic working fluid; the full-condition intelligent control center (6) is configured to collect the internal pressure of the shell side (301) in real time, use the model to calculate the real-time saturation temperature, and calculate the freezing margin; when the freezing margin is lower than the preset safety threshold, the highest priority hard constraint control logic is triggered to forcibly adjust the back pressure to raise the boiling temperature.

8. The system according to claim 1, characterized in that: The first cryogenic working medium is liquid nitrogen, and the second liquefied gas is liquefied natural gas; the system is configured to heat and vaporize liquid nitrogen using only the sensible heat of LNG without introducing electric heating or auxiliary heat sources, and to subcool the LNG to below -165°C.

9. The system according to claim 1, characterized in that, The system also includes an oxygen deficiency safety interlock subsystem: the subsystem includes an ambient oxygen content detector located in the device area; when the ambient oxygen content is detected to be lower than a preset safety value (e.g., 19.5%), the system is configured to automatically cut off the supply of the first cryogenic working fluid and switch the gas phase emission path to the high-altitude safety vent.

10. The system according to claim 6, characterized in that: The heat exchange core adopts a multi-layer spiral wound tube bundle structure, and its spiral rise angle is configured to meet the hydrodynamic condition that the Dean number is greater than the critical value, so as to induce secondary circulation in the tube, enhance the convective heat transfer on the inner side of the tube and inhibit the adhesion of the freezing core.

Images