Liquid nitrogen electromagnetic heating system and control method

Abstract

The invention discloses a liquid nitrogen electromagnetic heating system and a control method, and relates to the technical field of liquid nitrogen pump trucks, and the liquid nitrogen electromagnetic heating system comprises a controller, a liquid nitrogen plunger pump assembly, an electromagnetic heating device and a discharge pipe assembly, the electromagnetic heating device comprises a plurality of liquid nitrogen heating plates which are sequentially connected, liquid nitrogen circulation channels are formed in the liquid nitrogen heating plates, and every two adjacent liquid nitrogen heating plates are communicated through a connecting pipeline; an electromagnetic heating plate is mounted on the same side of each liquid nitrogen heating plate; each liquid nitrogen heating plate is provided with a liquid nitrogen temperature sensor; a nitrogen pressure sensor is mounted on the discharge pipe assembly; the controller is connected with the liquid nitrogen temperature sensor, the nitrogen pressure sensor, the electromagnetic heating plate and the liquid nitrogen plunger pump assembly. The liquid nitrogen heating efficiency can be improved, accurate temperature control and pressure stability under the ultrahigh pressure working condition are achieved, and the safety of system operation is improved. Meanwhile, the invention discloses a liquid nitrogen electromagnetic heating control method.

Description

Technical Field

[0001] This invention relates to the field of liquid nitrogen pump truck technology, and more particularly to a liquid nitrogen electromagnetic heating system and control method. Background Technology

[0002] Liquid nitrogen pump trucks are key equipment in oil and gas field fracturing operations. Their core function is to heat and vaporize cryogenic liquid nitrogen in storage tanks into high-pressure nitrogen gas, which is then injected into the wellbore to achieve processes such as nitrogen lift and mixed-gas fracturing. Currently, most mainstream liquid nitrogen vaporization devices use direct-fired evaporators. Their working principle involves heating air through fuel combustion, and then using the hot air convection to heat the liquid nitrogen flowing through the coils. However, air, as a heat exchange medium, has inherent drawbacks such as low specific heat capacity and low thermal conductivity, resulting in limited heat transfer efficiency. This leads to larger and heavier vaporization devices, making it difficult to meet the requirements for compactness and lightweight on-board equipment. Furthermore, direct-fired heating methods have a hotspot effect in the directly heated area, easily causing localized overheating or uneven heating, affecting the stability of the vaporization process. In addition, fuel combustion produces a large amount of waste smoke and gas, posing not only environmental pollution problems but also safety hazards when operating in confined spaces.

[0003] In high-pressure fracturing operations, the liquid nitrogen vaporization process faces even more severe technical challenges. As well depth increases and formation pressure rises, the required nitrogen injection pressure continuously increases, with some scenarios demanding outlet pressures of tens of megapascals or even higher for the vaporization unit. Under high pressure, the phase change characteristics of liquid nitrogen change significantly; its boiling point increases with pressure, and the phase change process from liquid to gas spans a wider temperature range, making the heat transfer and flow characteristics of the two-phase coexistence region extremely complex. Existing direct-fired evaporators use single-point temperature monitoring, which struggles to accurately capture the temperature distribution of the gas-liquid two-phase flow within the pipeline and cannot identify the penetration of incompletely vaporized cryogenic liquid, easily leading to the risk of brittle fracture in downstream pipelines due to the impact of cryogenic media. Simultaneously, traditional mechanical safety valves suffer from long response delays, making it difficult to promptly cut off fault circuits during rapid pressure fluctuations, thus failing to meet the safety protection requirements under ultra-high pressure conditions.

[0004] To address the aforementioned issues, some existing technologies attempt to replace direct combustion heating with electric heating. However, current electric heating gasification devices mostly employ simple heating tube attachment or winding structures, and the heating uniformity and thermal response speed still need improvement. Regarding control strategies, existing solutions primarily rely on feedback regulation based on a single temperature parameter, lacking coordinated monitoring and analysis of multi-dimensional parameters such as pressure change rate and temperature gradient, making it difficult to promptly identify abnormal signs during the phase transition process. Under ultra-high pressure conditions, pressure fluctuations and temperature changes during liquid nitrogen gasification are highly coupled; relying solely on temperature feedback is insufficient for precise control, and control lag can easily lead to pressure exceeding limits or temperature runaway. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a liquid nitrogen electromagnetic heating system and control method that can improve the heating efficiency of liquid nitrogen, achieve precise temperature control and pressure stability under ultra-high pressure conditions, and improve the safety of system operation.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] The liquid nitrogen electromagnetic heating system includes a controller, a liquid nitrogen plunger pump assembly connected in sequence, an electromagnetic heating device, and a discharge pipe assembly;

[0008] The electromagnetic heating device includes several liquid nitrogen heating plates connected in sequence. Each liquid nitrogen heating plate is vertically arranged and has a liquid nitrogen inlet and a liquid nitrogen outlet. A liquid nitrogen flow channel is provided inside each liquid nitrogen heating plate, and adjacent liquid nitrogen heating plates are connected by a connecting pipe. An electromagnetic heating plate is installed on the same side of each liquid nitrogen heating plate, and there is a gap between the heating surface of the electromagnetic heating plate and the outer wall of the liquid nitrogen heating plate. A liquid nitrogen temperature sensor is installed at both the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate.

[0009] A nitrogen pressure sensor is installed on the discharge pipe assembly;

[0010] The controller is connected to the liquid nitrogen temperature sensor, the nitrogen pressure sensor, the electromagnetic heating plate, and the liquid nitrogen plunger pump assembly, respectively. The controller is used to independently control the heating power of the corresponding electromagnetic heating plate based on the liquid nitrogen temperature values ​​detected by the liquid nitrogen temperature sensor at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate, and at the same time adjust the liquid nitrogen output of the liquid nitrogen plunger pump assembly based on the nitrogen pressure value detected by the nitrogen pressure sensor.

[0011] Preferably, an electromagnetic mounting plate is installed on the same side of each liquid nitrogen heating plate, and there is a gap between the electromagnetic mounting plate and the liquid nitrogen heating plate. The electromagnetic heating plate is mounted on the electromagnetic mounting plate and is located on the side away from the liquid nitrogen heating plate.

[0012] The distance between the heating surface of the electromagnetic heating plate and the outer wall of the liquid nitrogen heating plate is defined as follows: , The following relationship must be satisfied:

[0013] ;

[0014] in, The preset spacing for the base in the cold state ranges from 2mm to 4mm. The thickness of the electromagnetic mounting plate; The maximum horizontal deformation of the liquid nitrogen heating plate under the preset limit working temperature difference and maximum rated working pressure; This is a preset safety margin.

[0015] Preferably, the thermal radiation from the upstream electromagnetic heating plate affects the downstream liquid nitrogen heating plate, with a spacing of... The determination of also introduces a thermal radiation correction term, which satisfies the following relationship:

[0016] ;

[0017] in, Indicates the first The liquid nitrogen heating plate described above; For the first The equivalent thermal radiation spacing of the liquid nitrogen heating plate; For the first The physical spacing corresponding to the liquid nitrogen heating plate ; The thermal radiation coupling coefficient ranges from 0.01 mm / kW to 0.05 mm / kW and is determined based on the thermal conductivity and geometric dimensions of the electromagnetic mounting plate material.

[0018] For the first -1 is the rated maximum heating power of the electromagnetic heating plate, in kW; when When =1, = The value is 0.

[0019] Preferably, the electromagnetic heating device includes an electromagnetic heating box, in which the liquid nitrogen heating plate and the electromagnetic heating plate are both installed. The bottom of the electromagnetic heating box has an opening, and a water receiving tank is installed at the bottom of the electromagnetic heating box.

[0020] A liquid nitrogen electromagnetic heating control method is applied to the aforementioned liquid nitrogen electromagnetic heating system; wherein the control method includes the following steps:

[0021] The liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate are obtained in real time using liquid nitrogen temperature sensors.

[0022] The nitrogen pressure value of the discharge pipe assembly is obtained in real time through a nitrogen pressure sensor.

[0023] The controller independently controls the heating power of the corresponding electromagnetic heating plate based on the liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate. At the same time, it adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly according to the nitrogen pressure value so that the system pressure is maintained at the preset target pressure and the temperature of the finally discharged nitrogen is stabilized at the preset target temperature.

[0024] The heating power of the electromagnetic heating plate is calculated using the following formula:

[0025] ;

[0026] in, Indicates the first One liquid nitrogen heating plate; For the first The heating power corresponding to each electromagnetic heating plate; The reference heating power; For temperature deviation, where, For the first The liquid nitrogen temperature at the outlet of the liquid nitrogen heating plate. For the first The target temperature at the outlet of the liquid nitrogen heating plate; , , For control parameters; For the first The liquid nitrogen temperature value at the inlet of the liquid nitrogen heating plate; For reference to the import temperature; Forward coefficients;

[0027] For time variables, the unit is seconds; Indicates temperature deviation Time integral from the start of control to the current time; Indicates temperature deviation For time variables The derivative of , i.e., the rate of change of temperature deviation.

[0028] Preferably, for the liquid nitrogen heating plate located in the liquid nitrogen phase change zone, the control of the heating power of the corresponding electromagnetic heating plate also incorporates the pressure change rate as a correction term, satisfying the following relationship:

[0029] ;

[0030] in, This indicates the serial number of the liquid nitrogen heating plate located in the liquid nitrogen phase transition zone; The first one determined based on the liquid nitrogen temperature value Heating power of each electromagnetic heating plate; After correction for the rate of pressure change, the first The actual heating power output of each electromagnetic heating plate; The nitrogen pressure value detected by the nitrogen pressure sensor; This is the correction factor for the rate of change of pressure; This represents the rate of change of pressure.

[0031] Preferably, the liquid nitrogen phase change zone refers to the temperature and pressure range corresponding to the state of coexistence of gas and liquid phases during the heating process of liquid nitrogen. When the absolute value of the difference between the liquid nitrogen temperature value at the liquid nitrogen outlet of the liquid nitrogen heating plate and the saturation temperature of nitrogen under the current pressure is less than a preset threshold, the liquid nitrogen heating plate is determined to be in the liquid nitrogen phase change zone.

[0032] Preferably, the step of the controller adjusting the liquid nitrogen output of the liquid nitrogen plunger pump assembly includes: adjusting the speed of the drive motor of the liquid nitrogen plunger pump assembly through a frequency converter to change the mass flow rate of liquid nitrogen pumped into the electromagnetic heating device per unit time.

[0033] After adopting the above technical solution, the beneficial effects of the present invention are:

[0034] This application discloses a liquid nitrogen electromagnetic heating system, including a controller, a liquid nitrogen plunger pump assembly, an electromagnetic heating device, and a discharge pipe assembly connected in sequence. The electromagnetic heating device includes several liquid nitrogen heating plates connected in sequence, each with a liquid nitrogen flow channel inside. Adjacent liquid nitrogen heating plates are connected by connecting pipes. Each liquid nitrogen heating plate has an electromagnetic heating plate installed on the same side, with a gap between the heating surface of the electromagnetic heating plate and the outer wall of the liquid nitrogen heating plate. Each liquid nitrogen heating plate has a liquid nitrogen temperature sensor installed at both its liquid nitrogen inlet and outlet. A nitrogen pressure sensor is installed on the discharge pipe assembly. The controller is connected to the liquid nitrogen temperature sensor, nitrogen pressure sensor, electromagnetic heating plate, and liquid nitrogen plunger pump assembly.

[0035] The liquid nitrogen electromagnetic heating system achieves uniform heating of liquid nitrogen by placing electromagnetic heating plates on the same side of each liquid nitrogen heating plate and maintaining an appropriate distance between the electromagnetic heating plates and the outer walls of the liquid nitrogen heating plates, thus avoiding localized overheating. Each liquid nitrogen heating plate is equipped with a liquid nitrogen temperature sensor at both its inlet and outlet. The controller can monitor the liquid nitrogen temperature at the inlet and outlet of each heating plate in real time and independently control the heating power of the corresponding electromagnetic heating plate based on these temperature values. This achieves precise and segmented control of the liquid nitrogen heating process, ensuring that liquid nitrogen receives appropriate heat input at different heating stages, thereby guaranteeing sufficient and stable vaporization. Simultaneously, a nitrogen pressure sensor installed on the discharge pipe assembly monitors the nitrogen pressure in real time. The controller adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly based on this pressure value, achieving dynamic and stable control of the system pressure. Through the above structural design and working principle, this liquid nitrogen electromagnetic heating system can stabilize the temperature of the finally discharged nitrogen at a preset target temperature and maintain the system pressure at a preset target pressure, significantly improving the stability, controllability, and safety of the liquid nitrogen vaporization process.

[0036] This application also discloses a liquid nitrogen electromagnetic heating control method. By installing liquid nitrogen temperature sensors at the inlet and outlet of each liquid nitrogen heating plate, the controller can acquire the liquid nitrogen temperature values ​​at the inlet and outlet of each heating plate in real time. Based on the deviation between the outlet temperature and the target temperature, a comprehensive control formula including proportional, integral, derivative, and feedforward terms is used to independently adjust the heating power of each electromagnetic heating plate. Specifically, the feedforward term compensates for the deviation between the inlet temperature and the reference inlet temperature, enabling the system to adjust the heating power in advance when the incoming material temperature fluctuates, improving the control response speed; the integral term eliminates steady-state errors, ensuring that the outlet temperature accurately tracks the target temperature; and the derivative term suppresses temperature abrupt changes, enhancing system stability. Simultaneously, the controller adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly in real time based on the nitrogen pressure value detected by the nitrogen pressure sensor, achieving dynamic and stable control of the system pressure. Therefore, this method can stabilize the temperature of the final discharged nitrogen gas at the preset target temperature, while maintaining the system pressure at the preset target pressure, significantly improving the temperature control accuracy, pressure stability and anti-interference ability of the liquid nitrogen vaporization process, and ensuring that the system can still operate reliably under complex working conditions. Attached Figure Description

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0038] Figure 1 This is a schematic diagram of the liquid nitrogen electromagnetic heating system according to Embodiment 1 of the present invention;

[0039] Figure 2 yes Figure 1 A schematic diagram of the internal structure of the electromagnetic heating device.

[0040] Figure 3 yes Figure 2 Cross-sectional view of the liquid nitrogen heating plate;

[0041] In the picture:

[0042] 1. Liquid nitrogen plunger pump assembly;

[0043] 2. Electromagnetic heating device; 21. Liquid nitrogen heating plate; 22. Liquid nitrogen flow channel; 23. Connecting pipeline; 24. Electromagnetic heating plate; 25. Liquid nitrogen temperature sensor; 26. Electromagnetic mounting plate; 27. Electromagnetic heating box; 28. Water receiving tank;

[0044] 3. Discharge pipe assembly; 31. Nitrogen pressure sensor. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] Example 1

[0047] like Figures 1 to 3 As shown in the figure, this embodiment discloses a liquid nitrogen electromagnetic heating system, including a controller, a liquid nitrogen plunger pump assembly 1, an electromagnetic heating device 2, and a discharge pipe assembly 3 connected in sequence; wherein, the electromagnetic heating device 2 includes a plurality of liquid nitrogen heating plates 21 connected in sequence, the liquid nitrogen heating plates 21 are vertically arranged and have liquid nitrogen inlet and liquid nitrogen outlet, and have a liquid nitrogen flow channel 22 inside, and adjacent liquid nitrogen heating plates 21 are connected by a connecting pipe 23; an electromagnetic heating plate 24 is installed on the same side of each liquid nitrogen heating plate 21, and there is a gap between the heating surface of the electromagnetic heating plate 24 and the outer wall of the liquid nitrogen heating plate 21; a liquid nitrogen temperature sensor 25 is installed at the liquid nitrogen inlet and liquid nitrogen outlet of each liquid nitrogen heating plate 21;

[0048] A nitrogen pressure sensor 31 is installed on the discharge pipe assembly 3. The nitrogen pressure sensor 31 is used to obtain the nitrogen pressure value of the discharge pipe assembly 3 in real time.

[0049] The controller (not shown in the figure) is connected to the liquid nitrogen temperature sensor 25, the nitrogen pressure sensor 31, the electromagnetic heating plate 24, and the liquid nitrogen plunger pump assembly 1 respectively. The controller is used to independently control the heating power of the corresponding electromagnetic heating plate 24 based on the liquid nitrogen temperature values ​​detected by the liquid nitrogen temperature sensor 25 at the liquid nitrogen inlet and liquid nitrogen outlet of each liquid nitrogen heating plate 21, and at the same time adjust the liquid nitrogen output of the liquid nitrogen plunger pump assembly 1 based on the nitrogen pressure value detected by the nitrogen pressure sensor 31.

[0050] In this embodiment, the liquid nitrogen electromagnetic heating system achieves uniform heating of liquid nitrogen by setting an electromagnetic heating plate 24 on the same side of each liquid nitrogen heating plate 21 and maintaining an appropriate distance between the electromagnetic heating plate 24 and the outer wall of the liquid nitrogen heating plate 21. This satisfies the requirement of heating the liquid nitrogen heating plate 21 by electromagnetic means and avoids local overheating. Each liquid nitrogen heating plate 21 is equipped with a liquid nitrogen temperature sensor 25 at both its inlet and outlet. The controller can monitor the liquid nitrogen temperature values ​​at the inlet and outlet of each liquid nitrogen heating plate 21 in real time and independently control the heating power of the corresponding electromagnetic heating plate 24 based on these temperature values. This achieves refined, segmented control of the liquid nitrogen heating process, ensuring that liquid nitrogen receives appropriate heat input at different heating stages, thereby guaranteeing sufficient and stable vaporization of liquid nitrogen. Simultaneously, a nitrogen pressure sensor 31 installed on the discharge pipe assembly 3 detects the nitrogen pressure value in real time. The controller adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly 1 based on this pressure value, achieving dynamic and stable control of the system pressure. Therefore, the liquid nitrogen electromagnetic heating system of this application can stabilize the temperature of the finally discharged nitrogen gas at the preset target temperature, while maintaining the system pressure at the preset target pressure, which significantly improves the stability, controllability and safety of the liquid nitrogen vaporization process.

[0051] In this embodiment, an electromagnetic mounting plate 26 is installed on the same side of each liquid nitrogen heating plate 21. There is a gap between the electromagnetic mounting plate 26 and the liquid nitrogen heating plate 21. The electromagnetic heating plate 24 is installed on the electromagnetic mounting plate 26 and is located on the side away from the liquid nitrogen heating plate 21.

[0052] The distance between the heating surface of the electromagnetic heating plate 24 and the outer wall of the liquid nitrogen heating plate 21 is defined as follows: , The following relationship must be satisfied:

[0053] ;

[0054] in, The preset spacing for the base in the cold state ranges from 2mm to 4mm. The thickness of the electromagnetic mounting plate 26; The maximum horizontal deformation of the liquid nitrogen heating plate 21 under the preset limit working temperature difference and maximum rated working pressure; This is a preset safety margin.

[0055] The electromagnetic mounting plate 26 is made of an insulating and heat-resistant material, such as epoxy resin or polyimide, to avoid electromagnetic interference and withstand extreme temperature differences. The distance between the heating surface of the electromagnetic heating plate 24 and the outer wall of the liquid nitrogen heating plate 21 is defined. By satisfying the relevant relationships, the design incorporates the foundation spacing in the cold state, the thickness of the electromagnetic mounting plate 26, the maximum horizontal deformation, and the safety margin. This solves the problem that traditional fixed spacing cannot adapt to the horizontal deformation of the liquid nitrogen heating plate 21 under temperature changes from -196℃ to 25℃ and pressures of 50 MPa, thus avoiding mechanical interference or reduced heating efficiency caused by thermal expansion or pressure deformation. This results in a more efficient spacing... It can dynamically compensate for structural changes under actual working conditions, ensuring that the electromagnetic heating plate 24 and the liquid nitrogen heating plate 21 always maintain the optimal coupling distance, thereby improving heating uniformity and energy transfer efficiency. Compared with the prior art, this application introduces the mounting plate thickness and thermal deformation as spacing design parameters, realizing quantitative compensation for structural deformation under extreme working conditions, and significantly improving the structural adaptability and long-term operational reliability of the system under high pressure and wide temperature range environments.

[0056] In this embodiment, the thermal radiation from the upstream electromagnetic heating plate 24 affects the downstream liquid nitrogen heating plate 21, with a spacing of... The determination of also introduces a thermal radiation correction term, which satisfies the following relationship:

[0057] ;

[0058] in, Indicates the first 21 liquid nitrogen heating plates; For the first The equivalent thermal radiation spacing of each liquid nitrogen heating plate 21; For the first The physical spacing corresponding to each liquid nitrogen heating plate 21 ; The thermal radiation coupling coefficient ranges from 0.01 mm / kW to 0.05 mm / kW and is determined based on the thermal conductivity and geometric dimensions of the electromagnetic mounting plate 26.

[0059] For the first -1 electromagnetic heating plate 24 has a rated maximum heating power, in kW; when When =1, = The value is 0.

[0060] The thermal radiation generated by the upstream electromagnetic heating plate 24 during operation affects the actual heating state of the downstream liquid nitrogen heating plate 21. This thermal radiation is equivalent to providing additional heat input to the downstream liquid nitrogen heating plate 21, making its equivalent perceived thermal effect stronger than that when only the electromagnetic heating plate 24 acts alone. To quantify this effect and ensure that the actual thermal effect of each liquid nitrogen heating plate 21 is consistent with the design expectation, an equivalent thermal radiation spacing is introduced. The higher the power of the upstream electromagnetic heating plate 24, the stronger its generated thermal radiation, and the more significant the additional heating effect on the downstream liquid nitrogen heating plate 21. This effect is mathematically equivalent to the actual physical spacing of the downstream heating plates. shortened The distance is used to characterize the combined thermal effect after the upstream thermal radiation is superimposed, that is, a smaller equivalent thermal radiation spacing. Through this correction, the controller can more accurately assess the actual heating state of each liquid nitrogen heating plate 21, avoid temperature control deviation of the downstream heating plate due to upstream thermal radiation interference, and thus improve the temperature control accuracy and operational stability of the entire heating device.

[0061] In this embodiment, the electromagnetic heating device 2 includes an electromagnetic heating box 27, a liquid nitrogen heating plate 21 and an electromagnetic heating plate 24, all of which are installed inside the electromagnetic heating box 27. The bottom of the electromagnetic heating box 27 is open, and a water receiving tank 28 is installed at the bottom of the electromagnetic heating box 27.

[0062] During the heating process of liquid nitrogen, water vapor in the surrounding air condenses into frost on the surface of the liquid nitrogen heating plate 21 and connecting pipes upon cooling. As the system operates or the temperature rises after shutdown, the condensed frost melts, forming condensate. Under gravity, this condensate drips down the tank wall or pipes and eventually collects in the water collection tank 28 through the bottom opening for unified discharge. This solves the safety hazards in existing liquid nitrogen heating equipment caused by the unorganized discharge of condensate, such as electrical components becoming damp and short-circuiting, equipment corrosion, or slippery working areas. This application, through the integration of the tank structure and the bottom water collection tank 28, achieves active collection and directional discharge of condensate, avoiding the influence of the external environment on the electromagnetic heating device 2. It also improves the safety and reliability of the electromagnetic heating device 2 in humid environments or during long-term operation, achieving automatic drainage without the need for additional drainage pipes or manual intervention.

[0063] Example 2

[0064] This embodiment discloses a liquid nitrogen electromagnetic heating control method, applied to the aforementioned liquid nitrogen electromagnetic heating system; wherein the control method includes the following steps:

[0065] The liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate 21 are obtained in real time by the liquid nitrogen temperature sensor 25.

[0066] The nitrogen pressure value of the discharge pipe assembly 3 is obtained in real time by nitrogen pressure sensor 31;

[0067] The controller independently controls the heating power of the corresponding electromagnetic heating plate 24 based on the liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate 21. At the same time, it adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly 1 according to the nitrogen pressure value so that the system pressure is maintained at the preset target pressure and the final discharged nitrogen temperature is stabilized at the preset target temperature.

[0068] The heating power of the electromagnetic heating plate 24 is calculated using the following formula:

[0069] ;

[0070] in, Indicates the first 21 liquid nitrogen heating plates; For the first The heating power corresponding to each electromagnetic heating plate 24; The reference heating power; For temperature deviation, where, For the first The liquid nitrogen temperature at the outlet of liquid nitrogen heating plate 21 For the first The target temperature at the outlet of the liquid nitrogen heating plate 21; , , For control parameters; For the first The liquid nitrogen temperature at the inlet of liquid nitrogen heating plate 21; For reference to the import temperature; Forward coefficients;

[0071] For time variables, the unit is seconds; Indicates temperature deviation Time integral from the start of control to the current time; Indicates temperature deviation For time variables The derivative of , i.e., the rate of change of temperature deviation.

[0072] By installing liquid nitrogen temperature sensors 25 at the inlet and outlet of each liquid nitrogen heating plate 21, the controller can acquire the liquid nitrogen temperature values ​​at the inlet and outlet of each liquid nitrogen heating plate 21 in real time. Based on the deviation between the outlet temperature and the target temperature, a comprehensive control formula including proportional, integral, derivative, and feedforward terms is used to independently adjust the heating power of each electromagnetic heating plate 24. Specifically, the feedforward term compensates for the deviation between the inlet temperature and the reference inlet temperature, enabling the system to adjust the heating power in advance when the incoming material temperature fluctuates, improving the control response speed; the integral term eliminates steady-state errors, ensuring that the outlet temperature accurately tracks the target temperature; and the derivative term suppresses temperature abrupt changes, enhancing system stability. Simultaneously, the controller adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly 1 in real time based on the nitrogen pressure value detected by the nitrogen pressure sensor 31, achieving dynamic and stable control of the system pressure. Therefore, this method can stabilize the final discharged nitrogen temperature at the preset target temperature and maintain the system pressure at the preset target pressure, significantly improving the temperature control accuracy, pressure stability, and anti-interference capability of the liquid nitrogen vaporization process, ensuring reliable operation of the system under complex working conditions.

[0073] In this embodiment, for the liquid nitrogen heating plate 21 located in the liquid nitrogen phase change zone, the control of the heating power of its corresponding electromagnetic heating plate 24 also incorporates the pressure change rate as a correction term, satisfying the following relationship:

[0074] ;

[0075] in, The serial number of the liquid nitrogen heating plate 21 located in the liquid nitrogen phase change zone; The first one determined based on the liquid nitrogen temperature value The heating power of each electromagnetic heating plate 24; After correction for the rate of pressure change, the first The actual heating power output of each electromagnetic heating plate 24; The nitrogen pressure value detected by nitrogen pressure sensor 31; This is the correction factor for the rate of change of pressure; The pressure change rate is denoted as . The liquid nitrogen phase transition zone refers to the temperature and pressure range corresponding to the coexistence of gas and liquid phases during the heating process of liquid nitrogen. When the absolute value of the difference between the liquid nitrogen temperature at the liquid nitrogen outlet of the liquid nitrogen heating plate 21 and the saturation temperature of nitrogen under the current pressure is less than a preset threshold, the liquid nitrogen heating plate 21 is determined to be in the liquid nitrogen phase transition zone.

[0076] For the liquid nitrogen heating plate 21 located in the liquid nitrogen phase change zone, the heating power control of its corresponding electromagnetic heating plate 24 incorporates the pressure change rate as a correction term. When liquid nitrogen is in the liquid nitrogen phase change zone, the vaporization process is extremely unstable, and the pressure change rate can sensitively reflect the dynamic changes in the gas-liquid two-phase state. By introducing this parameter, the heating power is corrected in real time. When the pressure rises too quickly, the heating power is appropriately reduced to suppress the vaporization rate and prevent a sudden pressure rise. This solves the problem in the prior art that relying solely on temperature feedback cannot effectively address the severe pressure fluctuations caused by the instability of the gas-liquid two-phase flow in the phase change zone. This application, by introducing a pressure change rate correction term, achieves dynamic optimization and adjustment of the heating power in the liquid nitrogen phase change zone, significantly enhancing the system's anti-disturbance capability and operational stability in the phase change zone, avoiding safety risks caused by pressure runaway, and ensuring that the system can smoothly pass through the phase change zone.

[0077] The determination of the pressure change rate correction coefficient is based on the dynamic response characteristics of the heating system in the phase transition zone. During the commissioning phase of the heating system, the liquid nitrogen heating plate 21 is operated in the phase transition zone and a power step disturbance is applied. The correspondence between the pressure change rate and the actual pressure overshoot is recorded, and the initial value is calibrated using a system identification method. Alternatively, the pressure change rate correction coefficient can also be corrected online during system operation using an adaptive control algorithm. When a pressure fluctuation is detected to exceed the preset range, the controller iteratively optimizes the product of the pressure deviation and the pressure change rate until the heating system obtains optimal damping characteristics and pressure stability in the phase transition zone. Practical verification shows that the value range of the pressure change rate correction coefficient is related to the system flow rate, the heat capacity of the heating plate, and the physical properties of nitrogen.

[0078] In this embodiment, the step of the controller adjusting the liquid nitrogen output of the liquid nitrogen plunger pump assembly 1 includes: adjusting the speed of the drive motor of the liquid nitrogen plunger pump assembly 1 through the frequency converter to change the mass flow rate of liquid nitrogen pumped into the electromagnetic heating device 2 per unit time.

[0079] The frequency converter adjusts the power supply frequency of the drive motor according to the control signal output by the controller, changing the speed of the drive motor, and thus changing the reciprocating frequency of the plunger pump. This causes a corresponding change in the volumetric flow rate of liquid nitrogen intake and discharge, achieving stepless regulation of the liquid nitrogen output. This solves the problems of high energy loss, slow response speed, and low control accuracy caused by valve throttling in existing technologies. This application directly regulates the liquid nitrogen output from the power source through frequency conversion speed regulation, avoiding throttling losses, improving energy utilization efficiency, and enabling rapid response to system pressure fluctuations. This achieves precise and stable control of the system pressure, ensuring that the flow matching between the liquid nitrogen plunger pump assembly 1 and the electromagnetic heating device 2 is always optimal.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A liquid nitrogen electromagnetic heating system, characterized in that, Includes a controller, a liquid nitrogen plunger pump assembly connected in sequence, an electromagnetic heating device, and a discharge pipe assembly; The electromagnetic heating device includes several liquid nitrogen heating plates connected in sequence. Each liquid nitrogen heating plate is vertically arranged and has a liquid nitrogen inlet and a liquid nitrogen outlet. A liquid nitrogen flow channel is provided inside each liquid nitrogen heating plate, and adjacent liquid nitrogen heating plates are connected by a connecting pipe. An electromagnetic heating plate is installed on the same side of each liquid nitrogen heating plate, and there is a gap between the heating surface of the electromagnetic heating plate and the outer wall of the liquid nitrogen heating plate. A liquid nitrogen temperature sensor is installed at both the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate. A nitrogen pressure sensor is installed on the discharge pipe assembly; The controller is connected to the liquid nitrogen temperature sensor, the nitrogen pressure sensor, the electromagnetic heating plate, and the liquid nitrogen plunger pump assembly, respectively. The controller is used to independently control the heating power of the corresponding electromagnetic heating plate based on the liquid nitrogen temperature values ​​detected by the liquid nitrogen temperature sensor at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate, and at the same time adjust the liquid nitrogen output of the liquid nitrogen plunger pump assembly based on the nitrogen pressure value detected by the nitrogen pressure sensor.

2. The liquid nitrogen electromagnetic heating system as described in claim 1, characterized in that, An electromagnetic mounting plate is installed on the same side of each of the liquid nitrogen heating plates, and there is a gap between the electromagnetic mounting plate and the liquid nitrogen heating plate. The electromagnetic heating plate is mounted on the electromagnetic mounting plate and is located on the side away from the liquid nitrogen heating plate. The distance between the heating surface of the electromagnetic heating plate and the outer wall of the liquid nitrogen heating plate is defined as follows: , The following relationship must be satisfied: ； in, The preset spacing for the base in the cold state ranges from 2mm to 4mm. The thickness of the electromagnetic mounting plate; The maximum horizontal deformation of the liquid nitrogen heating plate under the preset limit working temperature difference and maximum rated working pressure; This is a preset safety margin.

3. The liquid nitrogen electromagnetic heating system as described in claim 2, characterized in that, The thermal radiation from the upstream electromagnetic heating plate affects the downstream liquid nitrogen heating plate, with a spacing of [missing information]. The determination of also introduces a thermal radiation correction term, which satisfies the following relationship: ； in, Indicates the first The liquid nitrogen heating plate described above; For the first The equivalent thermal radiation spacing of the liquid nitrogen heating plate; For the first The physical spacing corresponding to the liquid nitrogen heating plate ; The thermal radiation coupling coefficient ranges from 0.01 mm / kW to 0.05 mm / kW and is determined based on the thermal conductivity and geometric dimensions of the electromagnetic mounting plate material. For the first -1 is the rated maximum heating power of the electromagnetic heating plate, in kW; when When =1, = The value is 0.

4. The liquid nitrogen electromagnetic heating system as described in claim 1, characterized in that, The electromagnetic heating device includes an electromagnetic heating box, in which the liquid nitrogen heating plate and the electromagnetic heating plate are both installed. The bottom of the electromagnetic heating box is open, and a water receiving tank is installed at the bottom of the electromagnetic heating box.

5. A liquid nitrogen electromagnetic heating control method, characterized in that, Applied to the liquid nitrogen electromagnetic heating system as described in any one of claims 1 to 4; wherein the control method includes the following steps: The liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate are obtained in real time using liquid nitrogen temperature sensors. The nitrogen pressure value of the discharge pipe assembly is obtained in real time through a nitrogen pressure sensor. The controller independently controls the heating power of the corresponding electromagnetic heating plate based on the liquid nitrogen temperature values ​​at the liquid nitrogen inlet and outlet of each liquid nitrogen heating plate. At the same time, it adjusts the liquid nitrogen output of the liquid nitrogen plunger pump assembly according to the nitrogen pressure value so that the system pressure is maintained at the preset target pressure and the temperature of the finally discharged nitrogen is stabilized at the preset target temperature. The heating power of the electromagnetic heating plate is calculated using the following formula: ； in, Indicates the first One liquid nitrogen heating plate; For the first The heating power corresponding to each electromagnetic heating plate; The reference heating power; For temperature deviation, where, For the first The liquid nitrogen temperature at the outlet of the liquid nitrogen heating plate. For the first The target temperature at the outlet of the liquid nitrogen heating plate; , , For control parameters; For the first The liquid nitrogen temperature value at the inlet of the liquid nitrogen heating plate; For reference to the import temperature; Forward coefficients; For time variables, the unit is seconds; Indicates temperature deviation Time integral from the start of control to the current time; Indicates temperature deviation For time variables The derivative of , i.e., the rate of change of temperature deviation.

6. The liquid nitrogen electromagnetic heating control method as described in claim 5, characterized in that, For a liquid nitrogen heating plate located in the liquid nitrogen phase transition zone, the control of the heating power of its corresponding electromagnetic heating plate also incorporates the pressure change rate as a correction term, satisfying the following relationship: ； in, This indicates the serial number of the liquid nitrogen heating plate located in the liquid nitrogen phase transition zone; The first one determined based on the liquid nitrogen temperature value Heating power of each electromagnetic heating plate; After correction for the rate of pressure change, the first The actual heating power output of each electromagnetic heating plate; The nitrogen pressure value detected by the nitrogen pressure sensor; This is the correction factor for the rate of change of pressure; This represents the rate of change of pressure.

7. The liquid nitrogen electromagnetic heating control method as described in claim 6, characterized in that, The liquid nitrogen phase transition zone refers to the temperature and pressure range corresponding to the coexistence of gas and liquid phases during the heating process of liquid nitrogen. When the absolute value of the difference between the liquid nitrogen temperature at the liquid nitrogen outlet of the liquid nitrogen heating plate and the saturation temperature of nitrogen under the current pressure is less than a preset threshold, the liquid nitrogen heating plate is determined to be in the liquid nitrogen phase transition zone.

8. The liquid nitrogen electromagnetic heating control method as described in claim 5, characterized in that, The steps for the controller to adjust the liquid nitrogen output of the liquid nitrogen plunger pump assembly include: adjusting the speed of the drive motor of the liquid nitrogen plunger pump assembly through a frequency converter to change the mass flow rate of liquid nitrogen pumped into the electromagnetic heating device per unit time.

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