BOG recondensing device pressure and liquid level cooperative control method, system, medium and equipment

Abstract

The invention relates to the field of automatic control, and discloses a pressure and liquid level cooperative control method, system, medium and equipment for a BOG recondensation device, and the method comprises the steps: carrying out the operation of a dynamic matrix, the internal pressure of a recondenser, the internal liquid level of the recondenser and the BOG flow input into the recondenser, and inputting the operation result into an optimizer with time-varying constraint; according to the current LNG temperature at the inlet of the high-pressure pump, the corresponding lower pressure limit of the recondenser is calculated, the lower pressure limit of the recondenser is combined with the slack variable to serve as soft constraint, and the soft constraint is input into an optimizer with time-varying constraint; the optimization problem of the optimizer with the time-varying constraint is set, the optimization problem with the time-varying constraint is solved in two steps, and the optimal solution of the pressure in the recondenser and the optimal solution of the liquid level in the recondenser are obtained and transmitted to all the valves. The safety operation of the equipment can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control, and particularly to a method, system, medium and device for coordinated control of the pressure and liquid level of a BOG recondensation device. Background Art

[0002] During the storage and processing of low-temperature LNG at a receiving terminal, external heat input will generate boil-off gas (BOG). The treatment of BOG is the most complex and critical link in the receiving terminal, and how to ensure its stable operation is a hot topic and a difficult point in the research of the receiving terminal. At present, the most energy-saving and widely used BOG treatment process in the receiving terminal is the recondensation process. Through the BOG recondenser, supercooled low-pressure LNG is used to absorb the BOG gas from the low-pressure compressor, and the condensed LNG is transported to the high-pressure pump. During operation, it is necessary to control the stability of the liquid level and pressure of the BOG recondenser, and prevent cavitation of the LNG fed into the high-pressure pump.

[0003] The BOG recondensation system exhibits complex characteristics such as strong coupling between variables, uncertain parameter changes, and multiple interference factors. The existing conventional PID control strategy cannot well achieve the stable operation of the recondenser, and even less can handle the constraint requirements of satisfying the supercooling of the LNG at the inlet of the high-pressure pump in real time. The BOG recondenser is in the core intermediate link of the production process of the receiving terminal, and its operation fluctuations also affect the stable operation of the entire receiving terminal. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a method, system, medium and device for coordinated control of the pressure and liquid level of a BOG recondensation device, which can ensure the safe operation of the device.

[0005] To achieve the above purpose, in a first aspect, the technical solution adopted by the present invention is: a method for coordinated control of the pressure and liquid level of a BOG recondensation device, which includes: performing operations on the dynamic matrix, the pressure inside the recondenser, the liquid level inside the recondenser, and the BOG flow rate input into the recondenser, and inputting the operation result into an optimizer with time-varying constraints; calculating the corresponding lower limit of the recondenser pressure according to the current LNG temperature at the inlet of the high-pressure pump, and inputting the lower limit of the recondenser pressure combined with the slack variable as a soft constraint into the optimizer with time-varying constraints; setting the optimization problem of the optimizer with time-varying constraints, solving the optimization problem with time-varying constraints in two steps to obtain the optimal solutions of the pressure inside the recondenser and the liquid level inside the recondenser, and transmitting them to each valve.

[0006] Further, the dynamic matrix includes: a pre-stored dynamic matrix for characterizing the responses of the recondenser spray flow rate and the liquid level valve opening degree to the pressure inside the recondenser and the liquid level inside the recondenser respectively , and a dynamic matrix for the response of the BOG flow rate input into the recondenser to the pressure inside the recondenser and the liquid level inside the recondenser .

[0007] Further, calculating the lower limit of the pressure of the reflux condenser corresponding to the current LNG temperature at the inlet of the high-pressure pump, including: Based on the temperature-pressure table of LNG vaporization, obtaining the critical pressure of vaporization at the current temperature from the input LNG temperature at the inlet of the high-pressure pump , and according to the liquid level height in the reflux condenser and the LNG density calculating the lower limit of the pressure in the reflux condenser, which is:

[0008] In the formula, is the lower limit of the pressure in the reflux condenser, is the acceleration of gravity, is a constant, and T is the LNG temperature at the inlet of the high-pressure pump.

[0009] Further, the slack variable is a parameter greater than . .

[0010] Further, the time-varying constraint is: calculating the lower limit of the pressure of the reflux condenser corresponding to the current LNG temperature at the inlet of the high-pressure pump, and seeking a feasible solution by adding a soft constraint to instantaneously adjust the pressure in the reflux condenser to rise to the new lower limit of the pressure to ensure the equipment safety of the high-pressure pump.

[0011] Further, setting the optimization problem of the optimizer with time-varying constraints, and solving the optimization problem with time-varying constraints in two steps, including: In the first step, first obtain the slack variable that makes the optimization problem feasible:

[0012] In the second step, substitute into the solution of the optimization problem:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020] In the formula, represents the increment vector of the manipulated variable at the k-th moment in the M-th control period; represents the predicted model output of the re-condenser liquid level and pressure; represents the cost function; represents the setpoint of the re-condenser liquid level and pressure; represents the output error weight matrix; represents the control increment weight matrix; represents the set of constraint problems, including constraints on control inputs, outputs, and state variables; represents the initial predicted value of the re-condenser liquid level and pressure without input increment adjustment; represents the dynamic matrix of the responses of the re-condenser spray flow rate and liquid level valve opening to the pressure and liquid level inside the re-condenser respectively; represents the dynamic matrix of the responses of the re-condenser input BOG flow rate to the pressure and liquid level inside the re-condenser; represents the increment of the re-condenser input BOG flow rate; represents the displacement matrix; represents the historical predicted output vector at the (k - 1)-th moment, i.e., the predicted output at the previous moment; represents the feedback correction gain matrix, which feeds the prediction error back to the predicted value at the next moment; represents the estimated output vector at the k-th moment; represents the actual output vector at the k-th moment; represents the lower limit of the pressure inside the re-condenser at the k-th moment; represents the liquid level height inside the re-condenser at the k-th moment; represents the slack variable; represents the pressure inside the re-condenser; represents the change in the manipulated variable, specifically referring to the changes in the re-condenser spray flow rate and liquid level valve opening; represents the value of the manipulated variable, specifically referring to the values of the re-condenser spray flow rate and liquid level valve opening; represents the liquid level height inside the re-condenser.

[0021] Furthermore, the optimal solutions for the pressure inside the re-condenser and the liquid level inside the re-condenser are: the compressor total load solution sequence, and the first step is transmitted to the distributor.

[0022] In a second aspect, the technical solution adopted by the present invention is as follows: A coordinated control system for the pressure and liquid level of a BOG recondenser device, which includes: a dynamic matrix memory that performs operations on the dynamic matrix, the pressure inside the recondenser, the liquid level inside the recondenser, and the BOG flow rate input into the recondenser, and inputs the operation results into an optimizer with time-varying constraints; a soft constraint calculator that calculates the lower limit of the recondenser pressure corresponding to the current LNG temperature at the inlet of the high-pressure pump, combines the lower limit of the recondenser pressure with a slack variable as a soft constraint, and inputs it into the optimizer with time-varying constraints; an optimizer with time-varying constraints that sets the optimization problem of the optimizer with time-varying constraints, solves the optimization problem with time-varying constraints in two steps, obtains the optimal solutions for the pressure inside the recondenser and the liquid level inside the recondenser, and transmits them to each valve.

[0023] In a third aspect, the technical solution adopted by the present invention is as follows: A computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to execute any one of the above methods.

[0024] In a fourth aspect, the technical solution adopted by the present invention is as follows: A computing device, which includes: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the above methods.

[0025] Due to the adoption of the above technical solutions, the present invention has the following advantages: The present invention converts the prevention of cavitation of LNG before the high-pressure pump into a constraint problem of the recondenser pressure, adjusts the lower limit of the recondenser pressure according to the change in the LNG temperature before the high-pressure pump, and makes the optimization problem feasible by adding soft constraints, ensuring that the pressure inside the recondenser rises to a safe range, thereby ensuring the safe operation of the equipment. Description of the Drawings

[0026] Figure 1 is the overall flowchart of the coordinated control method for the pressure and liquid level of the BOG recondenser device in the embodiment of the present invention; Figure 2 is the overall control diagram of the BOG recondenser in the embodiment of the present invention; Figure 3 is the detailed flowchart of the control method for the BOG recondenser in the embodiment of the present invention. Detailed Embodiments

[0027] Aiming at the problem that the existing PID control method causes large fluctuations in the pressure and liquid level in the recondenser, which in turn affects the stable operation of the entire LNG receiving terminal, according to the complex characteristics of the BOG recondensing device, the present invention proposes a coordinated control method, system, medium and equipment for the pressure and liquid level of the BOG recondensing device based on multi-variable model predictive control technology to stabilize the pressure and liquid level in the recondenser; and further adopts an optimization method with time-varying constraints to realize the calculation of changing the lower limit of the pressure in the recondenser according to the change in the LNG temperature at the outlet of the recondenser, so as to ensure the safe operation of the high-pressure pump.

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0030] In an embodiment of the present invention, a coordinated control method for the pressure and liquid level of a BOG recondensing device is provided. According to the written dynamic matrix model, operations are performed on the input quantity and disturbance quantity. The operation result is sent to an optimizer with time-varying constraints. By solving the optimization problem, the change amounts of the spray flow rate of the recondenser and the opening degree of the liquid level valve are obtained and sent to the corresponding valves. In this embodiment, as Figures 1 to 3 shown, the method includes the following steps: 1) Perform operations on the dynamic matrix, the pressure in the recondenser, the liquid level in the recondenser, and the BOG flow rate input into the recondenser, and input the operation result into an optimizer with time-varying constraints; 2) Calculate the corresponding lower limit of the recondenser pressure according to the current LNG temperature at the inlet of the high-pressure pump, and combine the lower limit of the recondenser pressure with the slack variable as a soft constraint and input it into an optimizer with time-varying constraints; 3) Set the optimization problem of the optimizer with time-varying constraints, solve the optimization problem with time-varying constraints in two steps, obtain the optimal solutions of the pressure in the recondenser and the liquid level in the recondenser, and transmit them to each valve.

[0031] In the above step 1), the dynamic matrix includes: a pre-stored dynamic matrix for characterizing the responses of the re-condenser spray flow rate and the liquid level valve opening to the pressure inside the re-condenser and the liquid level inside the re-condenser respectively , and a dynamic matrix for the response of the BOG flow rate input to the re-condenser to the pressure inside the re-condenser and the liquid level inside the re-condenser .

[0032] In this embodiment, the dynamic matrix is stored in the dynamic matrix memory.

[0033] In the above step 2), the lower limit of the re-condenser pressure corresponding to the current LNG temperature at the high-pressure pump inlet is calculated. Specifically According to the temperature-pressure table of LNG gasification, the critical pressure of gasification at the current temperature is obtained from the input LNG temperature at the high-pressure pump inlet , and according to the liquid level height inside the re-condenser and the LNG density , the lower limit of the pressure inside the re-condenser is calculated as

[0034] In the formula is the lower limit of the pressure inside the re-condenser is the acceleration due to gravity is a constant, and T is the current temperature.

[0035] In the above step 2), the slack variable is a parameter greater than such that the optimization problem is feasible.

[0036] In the above step 3), the inputs of the optimizer with time-varying constraints are the dynamic matrix , the set values of the pressure and liquid level inside the re-condenser, the storage tank pressure, the BOG flow rate input to the re-condenser, and the soft constraint, and the outputs are the re-condenser spray flow rate and the liquid level valve opening.

[0037] In this embodiment, a time-varying constraint is added to the optimization problem. Specifically, the time-varying constraint of the optimizer is: calculating the lower limit of the re-condenser pressure corresponding to the current LNG temperature at the high-pressure pump inlet, and seeking a feasible solution by adding a soft constraint to immediately adjust the pressure inside the re-condenser to the new pressure lower limit to ensure the equipment safety of the high-pressure pump.

[0038] In the above step 3), the optimization problem of the optimizer with time-varying constraints is set. The optimization problem is solved in two steps by adding a soft constraint, including In the first step, the slack variable that makes the optimization problem feasible is obtained :

[0039] ​In the second step, is substituted into the optimization problem for solution:

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047] wherein, represents the vector of increments of the manipulated variable at the k-th moment in the M-th control period; represents the k-th moment; represents the output of the prediction model of the re - condenser liquid level and pressure; represents the cost function; represents the setpoint of the re - condenser liquid level and pressure; represents the output error weight matrix; represents the control increment weight matrix; represents the set of constraint problems, including constraints on control inputs, outputs, and state variables; represents the initial predicted value of the re - condenser liquid level and pressure without input increment adjustment; represents the dynamic matrix of the responses of the re - condenser spray flow rate and the liquid level valve opening to the pressure and liquid level in the re - condenser respectively; represents the dynamic matrix of the responses of the re - condenser input BOG flow rate to the pressure and liquid level in the re - condenser; represents the increment of the re - condenser input BOG flow rate; represents the displacement matrix; represents the historical prediction output vector at the (k - 1)-th moment, i.e., the prediction output at the previous moment; represents the feedback correction gain matrix, which feeds the prediction error back to the predicted value of the next moment; represents the estimated output vector at the k-th moment; represents the actual output vector at the k-th moment; represents the lower limit of the pressure in the re - condenser at the k-th moment; represents the height of the liquid level in the re - condenser at the k-th moment; represents the slack variable; Represents the pressure inside the re - condenser; Represents the change amount of the manipulated variable, specifically referring to the change amounts of the spray flow rate of the re - condenser and the opening degree of the liquid level valve; Represents the value of the manipulated variable, specifically referring to the values of the spray flow rate of the re - condenser and the opening degree of the liquid level valve; Represents the liquid level height inside the re - condenser. Among them, Represents the value at the k - th moment (here it is the measured value), Represents the pressure value of the re - condenser.

[0048] In the above step 3), the optimal solutions of the pressure inside the re - condenser and the liquid level inside the re - condenser are: the compressor total load solution sequence, and the first step is taken to transmit it to the distributor.

[0049] In this embodiment, the optimizer with time - varying constraints uses methods such as the interior - point method and the conjugate gradient method to solve the optimization problem.

[0050] In the above step 3), after the spray valve and the liquid level valve of the re - condenser receive the spray flow rate and the liquid level valve opening degree commands output by the optimizer, they are adjusted to stabilize the pressure and the liquid level inside the re - condenser.

[0051] In an embodiment of the present invention, a BOG re - condensation device pressure and liquid level coordinated control system is provided, which includes: a dynamic matrix memory, a soft - constraint calculator, and an optimizer with time - varying constraints.

[0052] The dynamic matrix memory performs operations on the stored dynamic matrix, the pressure inside the re - condenser, the liquid level inside the re - condenser, and the BOG flow rate input into the re - condenser, and the operation result is input into the optimizer with time - varying constraints; The soft - constraint calculator, whose input is the current LNG temperature at the inlet of the high - pressure pump, calculates the corresponding lower limit of the re - condenser pressure according to the current LNG temperature at the inlet of the high - pressure pump, and combines the lower limit of the re - condenser pressure with the slack variable as a soft constraint and inputs it into the optimizer with time - varying constraints; The optimizer with time - varying constraints sets the optimization problem of the optimizer with time - varying constraints, solves the optimization problem with time - varying constraints in two steps, obtains the optimal solutions of the pressure inside the re - condenser and the liquid level inside the re - condenser, and transmits them to each valve.

[0053] In the above - mentioned embodiment, the dynamic matrix includes: a pre - stored dynamic matrix for characterizing the responses of the spray flow rate of the re - condenser and the opening degree of the liquid level valve to the pressure inside the re - condenser and the liquid level inside the re - condenser respectively and the dynamic matrix of the response of the BOG flow rate input into the re - condenser to the pressure inside the re - condenser and the liquid level inside the re - condenser .

[0054] In the above - mentioned embodiment, calculating the corresponding lower limit of the re - condenser pressure according to the current LNG temperature at the inlet of the high - pressure pump includes: Based on the temperature - pressure gauge for LNG vaporization, the critical pressure for vaporization at the current temperature is obtained from the LNG temperature at the inlet of the high - pressure pump , and according to the liquid level height in the recombiner and the LNG density the lower limit of the pressure in the recombiner is calculated as:

[0055] In the formula, is the lower limit of the pressure in the recombiner, is the acceleration due to gravity, is a constant, and T is the current temperature

[0056] In the above - mentioned embodiment, the slack variable is a parameter greater than .

[0057] In the above - mentioned embodiment, the time - varying constraint is: calculate the corresponding lower limit of the recombiner pressure according to the LNG temperature at the inlet of the high - pressure pump at the current moment, and seek a feasible solution by adding a soft constraint to instantaneously adjust the pressure in the recombiner to rise to the new lower limit of the pressure to ensure the equipment safety of the high - pressure pump

[0058] In the above - mentioned embodiment, set the optimization problem of the optimizer with time - varying constraints and solve the optimization problem with time - varying constraints in two steps, including: In the first step, first obtain the slack variable that makes the optimization problem feasible:

[0059] In the second step, substitute into the solution of the optimization problem:

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067] ​In the above embodiments, the optimal solutions for the pressure in the re - condenser and the liquid level in the re - condenser are as follows: the total compressor load solution sequence is taken as the first step and transmitted to the distributor.

[0068] The system provided in this embodiment is used to execute the above - mentioned method embodiments. For the specific process and detailed content, please refer to the above - mentioned embodiments and will not be elaborated here.

[0069] In summary, the present invention solves the problem of poor control effect caused by the complex characteristics such as strong coupling of relevant variables of the BOG re - condenser, uncertain parameter changes, and multiple interference factors, and can achieve the stable operation of the BOG re - condenser.

[0070] The present invention overcomes the problem that the existing control methods of the BOG re - condenser cannot meet the inlet LNG condition of non - cavitation of the high - pressure pump in real time, converts the prevention of LNG cavitation before the high - pressure pump into a constraint problem of the re - condenser pressure, and designs a soft - constraint calculation and an optimizer with time - varying constraints, thereby ensuring the safe operation of the high - pressure pump.

[0071] In a computing device provided in an embodiment of the present invention, the computing device may be a terminal, and it may include: a processor, a communications interface, a memory, a display screen, and an input device. Among them, the processor, the communications interface, and the memory complete mutual communication through a communication bus. The processor is used to provide computing and control capabilities. The memory includes a non - volatile storage medium and an internal memory. The non - volatile storage medium stores an operating system and a computer program. When the computer program is executed by the processor, it realizes the methods in the above - mentioned embodiments; the internal memory provides an environment for the operation of the operating system and the computer program in the non - volatile storage medium. The communications interface is used to communicate with an external terminal in a wired or wireless manner. The wireless manner can be achieved through WIFI, a carrier network, NFC (Near Field Communication), or other technologies. The display screen may be a liquid crystal display screen or an electronic ink display screen. The input device may be a touch layer covering the display screen, or a button, a trackball, or a touchpad provided on the housing of the computing device, or an external keyboard, a touchpad, or a mouse, etc. The processor can call the logical instructions in the memory.

[0072] In addition, when the logic instructions in the above-mentioned memory are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0073] In an embodiment of the present invention, a computer program product is provided. The computer program product includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided in the above-mentioned method embodiments.

[0074] In an embodiment of the present invention, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium stores server instructions, and the computer instructions cause the computer to execute the methods provided in the above-mentioned embodiments.

[0075] For the computer-readable storage medium provided in the above-mentioned embodiment, its implementation principle and technical effects are similar to those of the above-mentioned method embodiment, and will not be elaborated here.

[0076] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the functions specified in one process Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0077] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction device that implements the function specified in one or more processes and / or blocks Figure 1 in the process Figure 1 or processes and / or boxes

[0078] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable apparatus provide steps for implementing the function specified in one or more processes and / or blocks Figure 1 in the process Figure 1 or processes and / or boxes

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for coordinated control of pressure and liquid level of a BOG recompression device, characterized in that, Comprising: Performing operations on the dynamic matrix, the pressure inside the reflux condenser, the liquid level inside the reflux condenser, and the BOG flow rate input into the reflux condenser, and inputting the operation results into an optimizer with time-varying constraints; Calculating the lower limit of the reflux condenser pressure corresponding to the current LNG temperature at the inlet of the high-pressure pump, combining the lower limit of the reflux condenser pressure with a slack variable as a soft constraint, and inputting it into the optimizer with time-varying constraints; Setting the optimization problem of the optimizer with time-varying constraints, solving the optimization problem with time-varying constraints in two steps to obtain the optimal solutions of the pressure inside the reflux condenser and the liquid level inside the reflux condenser, and transmitting them to each valve.

2. The pressure and liquid level collaborative control method of the BOG recompression device according to claim 1, wherein The dynamic matrix includes: a pre-stored dynamic matrix for characterizing the responses of the re-condenser spray flow rate and the liquid level valve opening to the pressure inside the re-condenser and the liquid level inside the re-condenser respectively and a dynamic matrix for characterizing the responses of the re-condenser input BOG flow rate to the pressure inside the re-condenser and the liquid level inside the re-condenser .

3. The pressure and liquid level coordinated control method of the BOG recondensation device according to claim 1, characterized in that, Calculating the lower limit of the reflux condenser pressure corresponding to the current LNG temperature at the inlet of the high-pressure pump, including: LNG gasification temperature-pressure gauge, obtaining the critical pressure of gasification at the current temperature from the LNG temperature at the inlet of the high-pressure pump , and based on the liquid level height in the recombiner and the LNG density calculating the lower limit of the pressure in the recombiner, which is: In the formula, is the lower limit of the pressure in the re - condenser, is the acceleration due to gravity, is a constant, and T is the LNG temperature at the inlet of the high - pressure pump.

4. The method for coordinated control of the pressure and liquid level of the BOG recompression device according to claim 1, characterized in that, The slack variable is a parameter greater than .​ 5. The pressure and liquid level coordinated control method of the BOG recompression device according to claim 1, characterized in that, The time-varying constraint is: calculating the lower limit of the reflux condenser pressure corresponding to the current LNG temperature at the inlet of the high-pressure pump at the current moment, and seeking a feasible solution by adding a soft constraint to immediately adjust the pressure inside the reflux condenser to rise to the new pressure lower limit to ensure the equipment safety of the high-pressure pump.

6. The pressure and liquid level coordinated control method of the BOG recompression device according to claim 1, wherein, Setting the optimization problem of the optimizer with time-varying constraints, solving the optimization problem with time-varying constraints in two steps, including: In the first step, the slack variables that make the optimization problem feasible are obtained first : The second step is to substitute into the solution of the optimization problem: wherein, represents the increment vector of the manipulated variable at the k-th moment in the M-th control period; represents the predicted model output of the recondenser liquid level and pressure; represents the cost function; represents the set values of the recondenser liquid level and pressure; represents the output error weight matrix; represents the control increment weight matrix; represents the set of constraint problems, including the constraints of control inputs, outputs, and state variables; represents the initial predicted values of the recondenser liquid level and pressure without input increment adjustment; represents the dynamic matrices of the responses of the recondenser spray flow rate and the liquid level valve opening to the pressure and liquid level in the recondenser respectively; represents the dynamic matrix of the response of the recondenser input BOG flow rate to the pressure and liquid level in the recondenser; represents the increment of the recondenser input BOG flow rate; represents the displacement matrix; represents the historical predicted output vector at the (k - 1)-th moment, i.e., the predicted output at the previous moment; represents the feedback correction gain matrix, which feeds the prediction error back to the predicted value at the next moment; represents the estimated output vector at the k-th moment; represents the actual output vector at the k-th moment; represents the lower limit of the pressure in the recondenser at the k-th moment; represents the liquid level height in the recondenser at the k-th moment; represents the slack variable; represents the pressure in the recondenser; represents the change amount of the manipulated variable, specifically referring to the change amounts of the recondenser spray flow rate and the liquid level valve opening; represents the value of the manipulated variable, specifically referring to the values of the recondenser spray flow rate and the liquid level valve opening; represents the liquid level height in the recondenser.

7. The pressure and liquid level coordinated control method of the BOG recompression device according to claim 1, characterized in that The optimal solutions of the pressure inside the reflux condenser and the liquid level inside the reflux condenser are: the compressor total load solution sequence, and taking the first step to transmit to the distributor.

8. A pressure and liquid level coordinated control system for a BOG recondensing device, characterized in that, Comprising: A dynamic matrix memory that performs operations on the dynamic matrix, the pressure inside the reflux condenser, the liquid level inside the reflux condenser, and the BOG flow rate input into the reflux condenser, and inputs the operation results into an optimizer with time-varying constraints; A soft constraint calculator that calculates the lower limit of the reflux condenser pressure corresponding to the current LNG temperature at the inlet of the high-pressure pump, combines the lower limit of the reflux condenser pressure with a slack variable as a soft constraint, and inputs it into the optimizer with time-varying constraints; An optimizer with time-varying constraints that sets the optimization problem of the optimizer with time-varying constraints, solves the optimization problem with time-varying constraints in two steps to obtain the optimal solutions of the pressure inside the reflux condenser and the liquid level inside the reflux condenser, and transmits them to each valve.

9. A computer-readable storage medium storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods described in claims 1 to 7.

10. A computing device, characterized in that, Comprising: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for performing any of the methods described in claims 1 to 7.

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