A liquefied natural gas receiving station recondenser liquid level automatic control method and system

Abstract

The application provides a liquefied natural gas receiving station recondenser liquid level automatic control method and system. The liquefied natural gas receiving station recondenser liquid level automatic control method comprises the following steps: S1, maintaining the stability of the bottom pressure of the recondenser and obtaining the bottom pressure of the recondenser; S2, calculating the set running temperature of the recondenser according to the bottom pressure of the recondenser; S3, obtaining a plurality of parameter values which affect the liquid-gas ratio R value of the recondenser running at the set running temperature and the BOG mass flow; S4, calculating the required liquid-gas ratio R value at the set running temperature of the recondenser according to the set running temperature of the recondenser and the plurality of parameter values; S5, calculating the required LNG mass flow of the recondenser feed according to the required liquid-gas ratio R value at the set running temperature of the recondenser and the BOG mass flow; and S6, feeding according to the required LNG mass flow of the recondenser feed.

Description

TECHNICAL FIELD

[0001] The present application relates to a liquefied natural gas receiving, storage and delivery process of a liquefied natural gas receiving station, and in particular to a liquefied natural gas receiving station recondenser liquid level automatic control method and system. BACKGROUND

[0002] Liquefied natural gas is an important part of natural gas supply, and a LNG (Liquefied Natural Gas) receiving station is an important facility for receiving, storing and gasifying LNG. A recondenser is a device for processing BOG (Boil Off Gas) in a processing station of the LNG receiving station, and is connected to devices such as a low-pressure pump, a high-pressure pump and a compressor in a process flow. The recondenser is a key device and is also the most difficult device to control. Fluctuations in the liquid level of the recondenser will cause fluctuations in the operating parameters of upstream and downstream devices, and even cause the compressor to stop or the entire plant to stop. The automatic control of the liquid level of the recondenser has been an industry problem, and the liquid level of the recondenser in most receiving stations is in a manual control state.

[0003] The structure of the recondenser mainly includes a tank body, a gas-liquid distribution disc and packing, and has two main functions. The first function is to process BOG generated by evaporation of liquefied natural gas due to operation or heating of low-temperature devices (such as a high-pressure pump, a storage tank and low-temperature pipelines). When the recondenser is operating, supercooled low-temperature LNG is introduced from a low-pressure output header, mixed with BOG from a BOG compressor after being pressurized, and the temperature of the BOG is reduced and condensed to a liquid state. Then, the BOG is mixed with LNG bypassing the recondenser and enters a high-pressure pump, is pressurized and gasified, and is then delivered to downstream users. The second function is to buffer pressure fluctuations caused by start and stop of the high-pressure pump and adjustment of LNG flow upstream and downstream, and to enhance system stability. At the same time, gas in the pump tank of the high-pressure pump can be continuously vented to the recondenser to ensure that there is sufficient liquid level in the pump tank of the high-pressure pump to prevent the high-pressure pump from being eroded by gas.

[0004] When the LNG entering the recondenser is insufficient to completely condense the BOG entering the recondenser during operation of the recondenser, the liquid level of the recondenser will decrease, and when the liquid level decreases to a low level, a chain stop of the BOG compressor and the high-pressure pump will be triggered, thereby causing the entire plant to stop. When the LNG entering the recondenser is excessive, the amount of condensation of the BOG in the gas phase space in the recondenser is excessive, and the amount of condensation in the packing is insufficient. Unstable condensation of the gas phase will cause fluctuations in the liquid level and pressure of the recondenser. In order to ensure normal operation of the recondenser and the high-pressure pump, the liquid level of the recondenser needs to be controlled within a normal range and remain stable.

[0005] There are two kinds of existing recondenser liquid level automatic control methods. The first kind is to control the LNG flow rate at the recondenser inlet by the pressure at the top of the recondenser, to maintain the pressure at the top of the recondenser stable, and to control the liquid level at the recondenser in a normal range by adjusting the valve at the bottom of the recondenser. The disadvantage of this liquid level automatic control method is that the liquid level at the recondenser is greatly affected by the pressure fluctuation of the upstream and downstream, and the operator needs to operate carefully. When the pressure fluctuation of the upstream and downstream is large, it is easy to cause the whole plant to stop. The second kind is to fit the relationship between the liquid-gas mass ratio (R value) of the recondenser LNG and BOG feed and the BOG temperature, BOG flow rate, recondenser outlet pressure, relative density of the natural gas for export and nitrogen content according to the historical manual operation data of the recondenser, to calculate the R value in real time by the relationship, to obtain the LNG flow rate, to adjust the LNG flow rate at the recondenser inlet according to the calculated LNG flow rate, to control the LNG flow rate, and to adjust the liquid level at the recondenser. This liquid level automatic control method has the disadvantages of poor control stability, inability to predict the relationship between the R value and the liquid level and temperature at the recondenser, large fluctuation of the temperature at the recondenser, and great influence of the pressure fluctuation of the upstream and downstream on the liquid level at the recondenser, because many instruments are involved in the control and the safety level of some instruments is low. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a liquefied natural gas receiving station recondenser liquid level automatic control method and system.

[0007] The technical solution of the present application to solve the above technical problem is as follows: a liquefied natural gas receiving station recondenser liquid level automatic control method, comprising: S1, maintaining the pressure at the bottom of the recondenser stable, and obtaining the pressure at the bottom of the recondenser; S2, calculating the set running temperature of the recondenser according to the pressure at the bottom of the recondenser; S3, obtaining a plurality of parameter values affecting the liquid-gas ratio R value of the recondenser running at the set running temperature and the BOG mass flow rate; S4, calculating the liquid-gas ratio R value required at the set running temperature of the recondenser according to the set running temperature of the recondenser and the plurality of parameter values; S5, calculating the LNG mass flow rate required for the recondenser feed according to the liquid-gas ratio R value required at the set running temperature of the recondenser and the BOG mass flow rate; and S6, feeding according to the LNG mass flow rate required for the recondenser feed.

[0008] The beneficial effects of the technical scheme are as follows: the BOG entering the recondenser is completely condensed by controlling the operating temperature of the recondenser below the bubble point temperature of the material corresponding to the top pressure of the recondenser, so that the liquid level of the recondenser is stably controlled. The liquid level of the recondenser is less affected by the upstream and downstream pressure fluctuations, the operating temperature of the recondenser is stably controllable, fewer field instruments are involved in automatic adjustment, the calculation program is safe and stable, fewer parameters are involved in adjustment, the stability is strong, the stable automatic control of the liquid level of the recondenser of the LNG receiving station is realized. When the operator performs the related operation of the recondenser, no fine operation is required, the skill requirement of the operator for the recondenser operation is reduced, and the operating state of the recondenser of the receiving station does not need to be monitored at all times. Compared with manual adjustment by the operator, the liquid level is more stable, and adjustment errors do not occur. When the related parameters of the liquid level control of the recondenser change, the liquid level is automatically and accurately adjusted, the operating safety and stability of the recondenser are higher, the risk of shutdown caused by the liquid level fluctuation of the recondenser is reduced, and the monitoring intensity of the operator on the operating state of the recondenser is reduced. Without waiting for the upstream and downstream pressures to be completely stable before the next operation is performed, the production adjustment speed and emergency disposal speed of the receiving station are improved, and the safety and stability of the production and operation of the receiving station are enhanced.

[0009] Further, the plurality of parameter values include a recondenser inlet BOG temperature, a recondenser inlet LNG temperature, a recondenser set operating temperature, an LNG latent heat related parameter, a BOG specific heat capacity, an LNG specific heat capacity, and an LNG inlet mass flow rate and BOG inlet mass flow rate error correction coefficient.

[0010] The beneficial effects of the above further technical scheme are as follows: fewer field instruments are involved in automatic adjustment, the calculation program is safe and stable, fewer parameters are involved in adjustment, the stability is strong, the stable automatic control of the liquid level of the recondenser of the LNG receiving station is realized. Without waiting for the upstream and downstream pressures to be completely stable before the next operation is performed, the production adjustment speed and emergency disposal speed of the receiving station are improved, and the safety and stability of the production and operation of the receiving station are enhanced.

[0011] Further, in step S4, the required liquid-gas ratio R value at the recondenser set operating temperature is calculated by the following formula: wherein R is a ratio of the LNG inlet mass flow rate and the BOG inlet mass flow rate, and the unit is 1; t1 is the recondenser inlet BOG temperature, and the unit is ℃; t2 is the recondenser inlet LNG temperature, and the unit is ℃; t is the recondenser set operating temperature, and the unit is ℃; r is the LNG latent heat related parameter, and the unit is kJ / kg; c1 is the BOG specific heat capacity, and the unit is kJ / kg / ℃; c2 is the LNG specific heat capacity, and the unit is kJ / kg / ℃; and a is the LNG inlet mass flow rate and BOG inlet mass flow rate error correction coefficient, and the unit is 1.

[0012] The beneficial effect of the further technical solution is that the liquid-gas ratio R required at the set operating temperature of the recondenser is calculated through data and formula, improving the accuracy and reliability. Fewer field instruments participate in automatic adjustment, and the calculation program is safe and stable. Fewer parameters participate in adjustment, and the stability is strong. The stable automatic control of the LNG receiving station recondenser liquid level is realized. The next operation does not need to wait for the complete stabilization of the upstream and downstream pressures, improving the production adjustment speed and emergency disposal speed of the receiving station, and enhancing the safe and stable operation of the receiving station.

[0013] Further, in step S5, the LNG mass flow required for recondenser feeding is calculated by multiplying the liquid-gas ratio R required at the set operating temperature of the recondenser and the BOG mass flow.

[0014] The beneficial effect of the further technical solution is that the LNG mass flow required for recondenser feeding is obtained by multiplying the liquid-gas ratio R and the BOG mass flow. According to the LNG mass flow, the recondenser operating temperature can be controlled at the set temperature, ensuring that the BOG entering the recondenser is completely condensed, thereby maintaining the recondenser liquid level in the normal range.

[0015] Further, step S2 includes: S21, calculating the recondenser top pressure according to the recondenser bottom pressure; S22, determining a safety margin and a material bubble point temperature corresponding to the recondenser top pressure according to the recondenser top pressure; and S23, calculating the recondenser set operating temperature according to the safety margin and the material bubble point temperature.

[0016] The beneficial effect of the further technical solution is that by controlling the recondenser operating temperature, the recondenser operating temperature is controlled below the material bubble point temperature corresponding to the recondenser top pressure, so that the BOG entering the recondenser is completely condensed, thereby controlling the recondenser liquid level stably.

[0017] Further, in step S23, the recondenser set operating temperature is calculated by adding the safety margin to the material bubble point temperature.

[0018] The beneficial effect of the further technical solution is that by controlling the recondenser operating temperature, the recondenser operating temperature is controlled below the material bubble point temperature corresponding to the recondenser top pressure, so that the BOG entering the recondenser is completely condensed, thereby controlling the recondenser liquid level stably.

[0019] Furthermore, the application also provides a liquefied natural gas receiving station recondenser liquid level automatic control system for realizing the liquefied natural gas receiving station recondenser liquid level automatic control method, the liquefied natural gas receiving station recondenser liquid level automatic control system comprising: a recondenser, a low-pressure output header, a recondenser bottom pressure gauge, a recondenser bottom pressure controller, a recondenser bottom pressure regulating valve, a low-pressure pump, a high-pressure pump, a recondenser BOG inlet pipeline, a BOG pressure gauge, a BOG volumetric flowmeter, a BOG thermometer, a BOG mass flow calculation device, a recondenser temperature control device, a recondenser inlet LNG flow calculation device, a recondenser upstream LNG pipeline, an LNG thermometer, an LNG mass flowmeter, an LNG regulating valve and a flow controller, wherein the bottom of the recondenser and one end of the recondenser upstream LNG pipeline are connected with the low-pressure output header, the two ends of the low-pressure output header are connected with the low-pressure pump and the high-pressure pump respectively, the recondenser bottom pressure gauge and the recondenser bottom pressure regulating valve are both installed on the low-pressure output header, and the recondenser bottom pressure controller is connected with the recondenser bottom pressure gauge and the recondenser bottom pressure regulating valve respectively; the recondenser BOG inlet pipeline is connected with the top of the recondenser, the BOG pressure gauge, the BOG volumetric flowmeter and the BOG thermometer are all installed on the recondenser BOG inlet pipeline, the BOG mass flow calculation device is connected with the BOG pressure gauge, the BOG volumetric flowmeter, the BOG thermometer and the recondenser inlet LNG flow calculation device respectively, the recondenser inlet LNG flow calculation device is connected with the flow controller and the recondenser temperature control device respectively, the recondenser temperature control device is connected with the LNG thermometer and the BOG thermometer respectively, the other end of the recondenser upstream LNG pipeline is connected with the top of the recondenser, the LNG thermometer, the LNG mass flowmeter and the LNG regulating valve are all installed on the recondenser upstream LNG pipeline, and the flow controller is connected with the LNG mass flowmeter and the LNG regulating valve respectively; the recondenser bottom pressure controller and the recondenser bottom pressure regulating valve are used for maintaining the stability of the recondenser bottom pressure; the recondenser bottom pressure gauge is used for acquiring the recondenser bottom pressure; the BOG mass flow calculation device is used for calculating the BOG mass flow according to the values acquired by the BOG pressure gauge, the BOG volumetric flowmeter and the BOG thermometer; and the recondenser temperature control device is used for calculating the liquid-gas ratio R value required at the set operating temperature of the recondenser according to the values acquired by the BOG thermometer and the LNG thermometer.The recondenser inlet LNG flow calculation device is used for multiplying the BOG mass flow output by the BOG mass flow calculation device and the liquid-gas ratio R value required at the recondenser set operating temperature output by the recondenser temperature control device, and calculating the LNG mass flow required by the recondenser feed; and the flow controller is used for controlling the opening of the LNG regulating valve according to the LNG mass flow meter.

[0020] The beneficial effects of the technical scheme of the present application are as follows: firstly, the recondenser bottom pressure is maintained stable through the recondenser bottom pressure regulating valve, and then the recondenser temperature is controlled below the material bubble point temperature corresponding to the recondenser pressure through the recondenser temperature control device, so that the BOG entering the recondenser is completely condensed to liquid state in the packing, thereby controlling the recondenser liquid level stable. The recondenser bottom pressure is maintained stable through the recondenser bottom regulating valve regulated by the pressure controller. The liquid-gas ratio R value required at the recondenser set operating temperature is calculated according to the BOG temperature and the LNG temperature. In the recondenser inlet LNG flow calculation device, the BOG mass flow output by the BOG mass flow calculation device is multiplied by the control device output for adjusting the recondenser operating temperature, so as to obtain the recondenser inlet LNG flow required for controlling the recondenser temperature at the set operating temperature. The flow controller controls the opening of the regulating valve according to the LNG mass flow meter, so as to control the LNG flow to maintain the required LNG flow for maintaining the recondenser operating temperature at the set value.

[0021] Further, the recondenser comprises a tank body, a recondenser internal material thermometer, a recondenser internal material liquid level meter, a feed liquid distributor, a gas-liquid distribution disc and packing, the feed liquid distributor, the gas-liquid distribution disc and the packing are all installed in the tank body, the feed liquid distributor is above the gas-liquid distribution disc, the gas-liquid distribution disc is above the packing, and the recondenser internal material thermometer and the recondenser internal material liquid level meter are connected with the tank body.

[0022] The beneficial effects of the above further technical scheme are as follows: the LNG entering from the side of the recondenser passes through the liquid distributor and enters the gas-liquid distribution disc, and then is uniformly distributed into the packing, so as to condense the BOG entering the recondenser to liquid state in the packing and then output. When the BOG is completely condensed in the packing, the recondenser liquid level will be maintained within the packing height range.

[0023] Further, the top of the recondenser is connected with a BOG discharge pipeline, the BOG discharge pipeline is connected with a pressure safety valve, a discharge pressure gauge, a discharge pressure regulating valve and a discharge pressure controller, the pressure safety valve is installed on the BOG discharge pipeline, the discharge pressure gauge and the discharge pressure regulating valve are both installed on the BOG discharge pipeline, and the discharge pressure controller is connected with the discharge pressure gauge and the discharge pressure regulating valve respectively.

[0024] The beneficial effect of the further technical solution is that when the overpressure of the top of the recondenser, the BOG is discharged to the BOG main pipe through the BOG discharge pipeline of the top of the recondenser, thereby improving the stability and reliability of the system. The setting of the discharge pressure controller facilitates automatic analysis and control, thereby improving automation.

[0025] Further, the recondenser bottom pressure regulating valve has two, a first recondenser bottom pressure regulating valve is installed on the low-pressure output main pipe, and a second recondenser bottom pressure regulating valve is connected in parallel with the first recondenser bottom pressure regulating valve, the first recondenser bottom pressure regulating valve and the second recondenser bottom pressure regulating valve are respectively connected with the recondenser bottom pressure controller, and valves are respectively arranged between one end of the recondenser upstream LNG pipeline and the low-pressure output main pipe, between the low-pressure output main pipe and the low-pressure pump, and between the recondenser and the low-pressure output main pipe.

[0026] The beneficial effect of the further technical solution is that the setting of multiple valves and regulating valves facilitates corresponding adjustment according to actual needs, facilitates the system to adapt to different application scenarios, improves control flexibility, and improves user experience.

[0027] The advantages of the additional aspects of the present application will be partially given in the following description, partially become obvious from the following description, or be known through the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A schematic flow chart of a liquefied natural gas receiving station recondenser liquid level automatic control method provided by an embodiment of the present application is shown.

[0029] Figure 2 A structural schematic diagram of a liquefied natural gas receiving station recondenser liquid level automatic control system provided by an embodiment of the present application is shown.

[0030] Explanation of reference numerals: 10, low-pressure output main pipe; 101, low-pressure pump; 102, high-pressure pump; 11, recondenser bottom pressure gauge; 12, recondenser bottom pressure controller; 13, recondenser bottom pressure regulating valve; 20, tank body; 21, recondenser internal material thermometer; 22, recondenser internal material liquid level gauge; 23, filler; 30, recondenser BOG inlet pipeline; 31, BOG pressure gauge; 32, BOG volume flowmeter; 33, BOG thermometer; 34, BOG mass flow calculation device; 35, recondenser temperature control device; 36, recondenser inlet LNG flow calculation device; 40, BOG discharge pipeline; 50, recondenser upstream LNG pipeline; 51, LNG thermometer; 52, LNG mass flowmeter; 53, LNG regulating valve; 531, flow controller. Detailed Implementation

[0031] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] like Figure 1 As shown, this embodiment of the invention provides an automatic control method for the liquid level of a recondenser in a liquefied natural gas receiving station, comprising: S1, maintaining a stable bottom pressure of the recondenser and acquiring the bottom pressure of the recondenser; S2, calculating the set operating temperature of the recondenser based on the bottom pressure of the recondenser; S3, acquiring multiple parameter values ​​and BOG mass flow rate that affect the liquid-to-gas ratio R value controlling the recondenser to operate at the set operating temperature; S4, calculating the required liquid-to-gas ratio R value at the set operating temperature of the recondenser based on the set operating temperature of the recondenser and the multiple parameter values; S5, calculating the required LNG mass flow rate for feeding the recondenser based on the required liquid-to-gas ratio R value at the set operating temperature of the recondenser and the BOG mass flow rate; S6, feeding the recondenser according to the required LNG mass flow rate for feeding the recondenser.

[0033] The beneficial effects of adopting the technical solution of this invention are as follows: By controlling the operating temperature of the recondenser, which is kept below the bubble point temperature of the material corresponding to the pressure at the top of the recondenser, the BOG entering the recondenser is completely condensed, thereby stabilizing the recondenser liquid level. The automatic recondenser liquid level control method minimizes the impact of upstream and downstream pressure fluctuations, ensures stable and controllable recondenser operating temperature, reduces the number of field instruments involved in automatic adjustment, and features a highly stable and reliable calculation program with fewer parameters involved in adjustment, achieving stable automatic control of the recondenser liquid level in LNG receiving terminals. Operators no longer need to perform precise operations when performing recondenser-related tasks, reducing the skill requirements for recondenser operation and eliminating the need for constant monitoring of the receiving terminal's recondenser operating status. Compared to manual adjustment by operators, automatic liquid level adjustment is more stable, eliminates adjustment errors, and automatically and precisely adjusts the liquid level when related parameters change, resulting in higher operational safety and stability of the recondenser, reducing the risk of shutdown due to recondenser liquid level fluctuations, and lowering the intensity of operator monitoring of the recondenser's operating status. There is no need to wait for the upstream and downstream pressures to fully stabilize before proceeding to the next step, which improves the speed of production adjustment and emergency response at the receiving station and enhances the safety and stability of the receiving station's production operation.

[0034] This invention provides an automatic control method for the liquid level of a recondenser in a liquefied natural gas receiving station, which solves the problems of the liquid level being greatly affected by upstream and downstream pressure fluctuations, the large number of control parameters and their unstable operation, and the large fluctuations in the operating temperature of the recondenser in the existing automatic control method.

[0035] The method controls the operation temperature of the recondenser, controls the operation temperature of the recondenser below the bubble point temperature of the material corresponding to the top pressure of the recondenser, and controls the recondenser liquid level to be stable.

[0036] A method for automatically controlling the liquid level of a recondenser of a liquefied natural gas receiving station:

[0037] (1) The bottom pressure of the recondenser is maintained stable by adjusting the valve, the bubble point temperature of the material corresponding to the top pressure of the recondenser at this time is determined, and the set operation temperature of the recondenser is obtained by adding a suitable safety margin.

[0038] Wherein, the liquid level of the recondenser is stable at a certain liquid level, the difference between the top pressure and the bottom pressure is equal to the hydrostatic pressure, so the bottom pressure is controlled, and after the bottom pressure is determined, the top pressure is also basically determined.

[0039] (2) Determine the parameters that affect the liquid-gas ratio R value (the liquid-gas ratio R value required at the set operation temperature of the recondenser) of the adjustable recondenser operation temperature, including: BOG temperature, LNG temperature, etc.

[0040] (3) Quantify the above parameters that affect the liquid-gas ratio R value (the liquid-gas ratio R value required at the set operation temperature of the recondenser) of the adjustable recondenser operation temperature, calculate the liquid-gas ratio R value required at the set operation temperature of the recondenser, and the R value calculation formula is as follows:

[0041]

[0042] In the formula:

[0043] R—The mass flow ratio of the recondenser LNG feed to the BOG feed, that is, the liquid-gas ratio R value required at the set operation temperature of the recondenser, 1;

[0044] t1—The temperature of the recondenser feed BOG, ℃;

[0045] t2—The temperature of the recondenser feed LNG, ℃;

[0046] t—The set operation temperature of the recondenser, ℃;

[0047] r—LNG latent heat of vaporization related parameter, kJ / kg;

[0048] c1—BOG specific heat capacity, kJ / kg / ℃;

[0049] c2—LNG specific heat capacity, kJ / kg / ℃;

[0050] α—LNG feed mass flow error correction coefficient, 1.

[0051] The liquid-gas ratio R value (the ratio of the LNG feed mass flow rate to the BOG feed mass flow rate) is multiplied by the BOG mass flow rate to obtain the required LNG mass flow rate for the recondenser feed, and the recondenser operating temperature is controlled at the set temperature according to the LNG mass flow rate, so that the BOG entering the recondenser is completely condensed, thereby maintaining the recondenser liquid level in the normal range.

[0052] The recondenser liquid level is controlled by the recondenser liquid level automatic control method (liquefied natural gas receiving station recondenser liquid level automatic control method) of the present application, the recondenser liquid level is less affected by upstream and downstream pressure fluctuations, the recondenser operating temperature is stable, the number of parameters involved in the adjustment is small, and the stability is strong, thereby realizing stable and automatic control of the recondenser liquid level of the LNG receiving station.

[0053] Under the recondenser liquid level automatic control method, the recondenser can realize automatic liquid level control under normal gasification and export, export capacity adjustment, tank car loading, compressor load adjustment, compressor start and stop, ship loading and unloading, and tank switching, and the operator does not need to perform fine operation when performing recondenser related operations, the recondenser operation skill requirement of the operator is reduced, and the operator does not need to monitor the receiving station recondenser operating state at all times, thereby reducing the labor intensity of the operator.

[0054] Further, the plurality of parameter values include: the recondenser feed BOG temperature, the recondenser feed LNG temperature, the recondenser set operating temperature, the LNG evaporation latent heat related parameter, the BOG specific heat capacity, the LNG specific heat capacity, and the LNG feed mass flow rate and BOG feed mass flow rate error correction coefficient.

[0055] The beneficial effects of the above further technical solution are: fewer field instruments involved in automatic adjustment, safe and stable calculation program, fewer parameters involved in adjustment, stable automatic control of the recondenser liquid level of the LNG receiving station, no need to wait for the upstream and downstream pressures to be completely stable before performing the next operation, improved production adjustment speed and emergency disposal speed of the receiving station, and enhanced production operation safety and stability of the receiving station.

[0056] Further, in step S4, the required liquid-gas ratio R value at the recondenser set operating temperature is calculated by the following formula: Wherein, R is the ratio of the LNG feed mass flow rate to the BOG feed mass flow rate, with a unit of 1; t1 is the BOG temperature of the recondenser feed, with a unit of ℃; t2 is the LNG temperature of the recondenser feed, with a unit of ℃; t is the set operating temperature of the recondenser, with a unit of ℃; r is the LNG vaporization latent heat related parameter, with a unit of kJ / kg; c1 is the BOG specific heat capacity, with a unit of kJ / kg / ℃; c2 is the LNG specific heat capacity, with a unit of kJ / kg / ℃; and a is the LNG feed mass flow rate to the BOG feed mass flow rate error correction coefficient, with a unit of 1.

[0057] The beneficial effect of adopting the above further technical solution is that the liquid-gas ratio R value required at the set operating temperature of the recondenser is calculated through data and formula, improving the precision and reliability. Fewer field instruments are involved in automatic adjustment, the calculation program is safe and stable, fewer parameters are involved in adjustment, and the stability is strong, realizing stable automatic control of the recondenser liquid level of the LNG receiving station. Without waiting for the upstream and downstream pressures to be completely stable before proceeding to the next step, the production adjustment speed and emergency disposal speed of the receiving station are improved, and the production operation safety and stability of the receiving station are enhanced.

[0058] Further, in step S5, the LNG mass flow rate required by the recondenser feed is calculated by multiplying the liquid-gas ratio R value at the set operating temperature of the recondenser by the BOG mass flow rate.

[0059] The beneficial effect of adopting the above further technical solution is that the LNG mass flow rate required by the recondenser feed is obtained by multiplying the liquid-gas ratio R value by the BOG mass flow rate, and the recondenser operating temperature is controlled at the set temperature according to the LNG mass flow rate, which ensures that the BOG entering the recondenser is completely condensed, thereby maintaining the recondenser liquid level in the normal range.

[0060] Further, step S2 includes: S21, calculating the recondenser top pressure according to the recondenser bottom pressure; S22, determining a safety margin and a material bubble point temperature corresponding to the recondenser top pressure according to the recondenser top pressure; and S23, calculating the set operating temperature of the recondenser according to the safety margin and the material bubble point temperature.

[0061] The beneficial effect of adopting the above further technical solution is that by controlling the recondenser operating temperature, the recondenser operating temperature is controlled below the material bubble point temperature corresponding to the recondenser top pressure, so that the BOG entering the recondenser is completely condensed, thereby controlling the recondenser liquid level to be stable.

[0062] Further, in step S23, the set operating temperature of the recondenser is calculated by adding the safety margin to the material bubble point temperature.

[0063] The beneficial effects of the further technical scheme are as follows: by controlling the operation temperature of the recondenser, the operation temperature of the recondenser is controlled below the bubble point temperature of the material corresponding to the top pressure of the recondenser, so that the BOG entering the recondenser is completely condensed, thereby controlling the stable liquid level of the recondenser.

[0064] The liquefied natural gas receiving station recondenser liquid level automatic control method provided by the embodiment of the application first maintains the bottom pressure of the recondenser stable, and determines the required recondenser set operation temperature according to the top pressure of the recondenser; confirms that seven factors affecting the liquid-gas ratio R value (the required liquid-gas ratio R value at the recondenser set operation temperature) of the recondenser operating at the set temperature, which are the following seven parameters: recondenser feed BOG temperature, recondenser feed LNG temperature, recondenser set operation temperature, LNG evaporation latent heat related parameter, BOG specific heat capacity, LNG specific heat capacity, LNG feed mass flow rate and BOG feed mass flow rate error correction coefficient, wherein the recondenser feed BOG temperature and the recondenser feed LNG temperature are derived from real-time instrument measurement values on site, the recondenser set operation temperature is determined according to the recondenser operation pressure, and the LNG evaporation latent heat related parameter, the BOG specific heat capacity, the LNG specific heat capacity, and the LNG feed mass flow rate and BOG feed mass flow rate error correction coefficient are characteristic parameters of the recondenser system; then, after calculation, the influence of them on the required liquid-gas ratio R value (the required liquid-gas ratio R value at the recondenser set operation temperature) of the recondenser operating at the set temperature is quantified, and the following formula is used for calculation:

[0065]

[0066] In the formula:

[0067] R is the ratio of the LNG feed mass flow rate to the BOG feed mass flow rate of the recondenser, and the unit is 1;

[0068] t1 is the recondenser feed BOG temperature, and the unit is ℃;

[0069] t2 is the recondenser feed LNG temperature, and the unit is ℃;

[0070] t is the recondenser set operation temperature, and the unit is ℃;

[0071] r is the LNG evaporation latent heat related parameter, and the unit is kJ / kg;

[0072] c1 is the BOG specific heat capacity, and the unit is kJ / kg / ℃;

[0073] c2 is the LNG specific heat capacity, and the unit is kJ / kg / ℃;

[0074] α is the LNG feed mass flow rate and BOG feed mass flow rate error correction coefficient, and the unit is 1.

[0075] Take a LNG receiving station as an example, the pressure at the bottom of the recondenser is 0.74 MPa, the temperature is set to -132℃, the latent heat of vaporization of LNG is 371 kJ / kg, the specific heat capacity of BOG is 2.217 kJ / kg / ℃, the specific heat capacity of LNG is 3.28 kJ / kg / ℃, the error correction coefficient of LNG feed mass flow rate and BOG feed mass flow rate is 0.9876, the field instrument shows that the temperature of the BOG feed to the recondenser is 18.76℃, the temperature of the LNG feed to the recondenser is -157.98℃, and the formula calculation gives the liquid-gas ratio R value of the recondenser (the liquid-gas ratio R value required at the set operating temperature of the recondenser) as: R = (2.217*(18.76-(-132))+371) / (3.28*(-132-(-157.98)))*0.9876 = 8.17.

[0076] At this time, the BOG mass flow rate entering the recondenser is 13.35 t / h, and the LNG mass flow rate required at the current recondenser inlet is 109 t / h. The recondenser inlet flow rate regulating valve automatically regulates the LNG flow rate at the recondenser inlet to the required LNG flow rate, and the recondenser operating temperature will be stabilized at -132℃. At this temperature and pressure, the BOG entering the recondenser will be completely condensed to a liquid state in the recondenser filler, and the recondenser liquid level will be stabilized within the filler height range.

[0077] As Figure 2As shown, in addition, the application also provides a liquefied natural gas receiving station recondenser liquid level automatic control system for realizing the liquefied natural gas receiving station recondenser liquid level automatic control method, the liquefied natural gas receiving station recondenser liquid level automatic control system comprises: a recondenser, a low-pressure output header 10, a recondenser bottom pressure gauge 11, a recondenser bottom pressure controller 12, a recondenser bottom pressure regulating valve 13, a low-pressure pump 101, a high-pressure pump 102, a recondenser BOG inlet pipeline 30, a BOG pressure gauge 31, a BOG volumetric flowmeter 32, a BOG thermometer 33, a BOG mass flow calculation device 34, a recondenser temperature control device 35, a recondenser inlet LNG flow calculation device 36, a recondenser upstream LNG pipeline 50, an LNG thermometer 51, an LNG mass flowmeter 52, an LNG regulating valve 53, a flow controller 531, one end of the recondenser and the recondenser upstream LNG pipeline 50 are connected with the low-pressure output header 10, both ends of the low-pressure output header 10 are connected with the low-pressure pump 101 and the high-pressure pump 102 respectively, the recondenser bottom pressure gauge 11 and the recondenser bottom pressure regulating valve 13 are both installed on the low-pressure output header 10, and the recondenser bottom pressure controller 12 is connected with the recondenser bottom pressure gauge 11 and the recondenser bottom pressure regulating valve 13 respectively; the recondenser BOG inlet pipeline 30 is connected with the top of the recondenser, the BOG pressure gauge 31, the BOG volumetric flowmeter 32 and the BOG thermometer 33 are all installed on the recondenser BOG inlet pipeline 30, the BOG mass flow calculation device 34 is connected with the BOG pressure gauge 31, the BOG volumetric flowmeter 32, the BOG thermometer 33 and the recondenser inlet LNG flow calculation device 36 respectively, the recondenser inlet LNG flow calculation device 36 is connected with the flow controller 531 and the recondenser temperature control device 35 respectively, the recondenser temperature control device 35 is connected with the LNG thermometer 51 and the BOG thermometer 33 respectively, the other end of the recondenser upstream LNG pipeline 50 is connected with the top of the recondenser, the LNG thermometer 51, the LNG mass flowmeter 52 and the LNG regulating valve 53 are all installed on the recondenser upstream LNG pipeline 50, and the flow controller 531 is connected with the LNG mass flowmeter 52 and the LNG regulating valve 53 respectively; the recondenser bottom pressure controller 12 and the recondenser bottom pressure regulating valve 13 are used for maintaining the stability of the recondenser bottom pressure; and the recondenser bottom pressure gauge 11 is used for acquiring the recondenser bottom pressure.The BOG mass flow rate calculation device 34 is configured to calculate the BOG mass flow rate according to the values obtained from the BOG pressure gauge 31, the BOG volumetric flow meter 32 and the BOG thermometer 33; the recondenser temperature control device 35 is configured to calculate the liquid-gas ratio R required at the set operating temperature of the recondenser according to the values obtained from the BOG thermometer 33 and the LNG thermometer 51; the recondenser inlet LNG flow rate calculation device 36 is configured to multiply the BOG mass flow rate output by the BOG mass flow rate calculation device 34 by the liquid-gas ratio R required at the set operating temperature of the recondenser output by the recondenser temperature control device 35 to calculate the LNG mass flow rate required for the recondenser feed; and the flow controller 531 is configured to control the opening of the LNG regulating valve 53 according to the LNG mass flow meter 52.

[0078] The beneficial effects of the technical scheme of the present application are as follows: first, the recondenser bottom pressure is maintained stable by the recondenser bottom pressure regulating valve, and the recondenser temperature is controlled below the bubble point temperature of the material corresponding to the recondenser pressure by the recondenser temperature control device, so that the BOG entering the recondenser is completely condensed to liquid state in the packing, thereby stabilizing the liquid level of the recondenser. The recondenser bottom pressure is maintained stable by the recondenser bottom pressure regulating valve regulated by the pressure controller. The liquid-gas ratio R required at the set operating temperature of the recondenser is calculated according to the BOG temperature and the LNG temperature. In the recondenser inlet LNG flow rate calculation device, the output value of the BOG mass flow rate calculation device is multiplied by the output value of the control device for regulating the operating temperature of the recondenser to obtain the recondenser inlet LNG flow rate required for controlling the temperature of the recondenser at the set operating temperature. The opening of the regulating valve is controlled by the flow controller according to the LNG mass flow meter to control the LNG flow rate to maintain the required LNG flow rate for the operating temperature of the recondenser at the set value.

[0079] Through theoretical research on the packed recondenser of the receiving station (liquefied natural gas receiving station), it is proved that when the BOG entering the recondenser is completely condensed, the liquid level of the recondenser will be stabilized within the packing height range in the design operating range.

[0080] According to the theory, the recondenser bottom pressure is first maintained stable by the recondenser bottom pressure regulating valve, and the recondenser temperature is controlled below the bubble point temperature of the material corresponding to the recondenser pressure by the recondenser temperature control device in the present application, so that the BOG entering the recondenser is completely condensed to liquid state in the packing, thereby stabilizing the liquid level of the recondenser.

[0081] The liquefied natural gas receiving station recondenser liquid level automatic control system provided by the embodiment of the application has stable recondenser liquid level, is less affected by upstream and downstream pressure fluctuations, can withstand recondenser bottom pressure fluctuations of more than 140 kPa, has stable and controllable recondenser temperature operation, temperature control error is within 1 DEG C, field instruments participating in temperature control calculation are reduced to 2, and automatic control has strong safety and stability.

[0082] Further, the recondenser comprises a tank body 20, a recondenser internal material temperature meter 21, a recondenser internal material liquid level meter 22, a feed liquid distributor, a gas-liquid distribution disc and a packing 23, the feed liquid distributor, the gas-liquid distribution disc and the packing 23 are all installed in the tank body 20, the feed liquid distributor is above the gas-liquid distribution disc, the gas-liquid distribution disc is above the packing 23, and the recondenser internal material temperature meter 21 and the recondenser internal material liquid level meter 22 are connected with the tank body 20.

[0083] The beneficial effects of the above further technical scheme are that LNG entering from the side of the recondenser passes through the liquid distributor into the gas-liquid distribution disc, is uniformly distributed into the packing after the gas-liquid distribution disc, and is output after being condensed into liquid in the packing. When the BOG is completely condensed in the packing, the recondenser liquid level is maintained within the packing height range.

[0084] Further, the top of the recondenser is connected with a BOG discharge pipeline 40, the BOG discharge pipeline 40 is connected with a pressure safety valve, a discharge pressure gauge, a discharge pressure regulating valve and a discharge pressure controller, the pressure safety valve is installed on the BOG discharge pipeline 40, the discharge pressure gauge and the discharge pressure regulating valve are both installed on the BOG discharge pipeline 40, and the discharge pressure controller is connected with the discharge pressure gauge and the discharge pressure regulating valve respectively.

[0085] The beneficial effects of the above further technical scheme are that when the top of the recondenser is overpressure, BOG is discharged to the BOG header through the BOG discharge pipeline at the top of the recondenser, the system stability and reliability are improved. The discharge pressure controller is provided to facilitate automatic analysis and control and improve automation.

[0086] Figure 2 In the embodiment, the PSV (Pressure Safety Valve) on the BOG discharge pipeline 40 is a pressure safety valve. Figure 2 In the embodiment, the solid arrows represent the flow direction and trajectory of LNG and BOG, and the dashed arrows represent the signal transmission direction and trajectory.

[0087] Further, the recondenser bottom pressure regulating valve 13 has two, the first recondenser bottom pressure regulating valve is installed on the low pressure output header 10, and the second recondenser bottom pressure regulating valve is connected in parallel with the first recondenser bottom pressure regulating valve, the first recondenser bottom pressure regulating valve and the second recondenser bottom pressure regulating valve are respectively connected with the recondenser bottom pressure controller 12, and a valve is arranged between one end of the recondenser upstream LNG pipeline 50 and the low pressure output header 10, between the low pressure output header 10 and the low pressure pump 101 and between the recondenser and the low pressure output header 10.

[0088] The beneficial effects of the above further technical solutions are that the multiple valves and regulating valves are arranged, the user can make corresponding adjustment according to actual needs, the system can adapt to different application scenarios, the control flexibility is improved, and the user experience is improved.

[0089] In the recondenser liquid level automatic control system (liquefied natural gas receiving station recondenser liquid level automatic control system), the low pressure output header 10, the recondenser bottom pressure gauge 11, the recondenser bottom pressure controller 12, the recondenser bottom pressure regulating valve 13, the LNG (the low pressure pump 101 is connected with the LNG) upstream from the low pressure pump 101 and the LNG from the recondenser bottom outlet pipeline are merged into the LNG to the high pressure pump 102. The recondenser bottom pressure (measured by the recondenser bottom pressure gauge) is adjusted by the recondenser bottom pressure controller 12 to maintain the stability of the recondenser bottom regulating valve 13.

[0090] The recondenser includes a tank body 20, a recondenser internal material thermometer 21, a recondenser internal material liquid level meter 22, a feed liquid distributor, a gas-liquid distribution disc and a filler 23. The LNG entering from the side of the recondenser passes through the liquid distributor and enters the gas-liquid distribution disc, and then is uniformly distributed into the filler 23 through the gas-liquid distribution disc. The BOG entering the recondenser is condensed to a liquid state in the filler 23 and then is output. When the BOG is completely condensed in the filler, the recondenser liquid level is maintained within the range of the filler height.

[0091] The compressed BOG enters the top of the recondenser from the recondenser BOG inlet pipeline 30, and the pipeline (recondenser BOG inlet pipeline 30) is provided with a BOG pressure gauge 31, a BOG volumetric flowmeter 32, and a BOG thermometer 33; a BOG mass flow calculation device 34 calculates the BOG mass flow according to the BOG pressure gauge 31, the BOG volumetric flowmeter 32, and the BOG thermometer 33; a brand-new recondenser temperature control device 35 is designed according to the liquid-gas ratio R value calculation method for adjusting the recondenser operating temperature provided by the application; the liquid-gas ratio R value (liquid-gas ratio R value required at the set operating temperature of the recondenser) required for setting the operating temperature of the recondenser is calculated according to the BOG temperature (measured by the BOG thermometer) and the LNG temperature (measured by the LNG thermometer); and the recondenser inlet LNG flow calculation device 36 multiplies the output value of the BOG mass flow calculation device 34 by the output value of the recondenser temperature control device 35 for adjusting the operating temperature of the recondenser, to obtain the recondenser inlet LNG flow required for controlling the temperature of the recondenser at the set operating temperature.

[0092] When the recondenser top is over-pressured, the BOG is discharged to the BOG header through the BOG discharge pipeline 40 at the top of the recondenser.

[0093] The LNG pipeline 50 upstream of the recondenser is provided with an LNG thermometer 51, an LNG mass flowmeter 52, and an LNG regulating valve 53; a flow controller 531 controls the opening of the LNG regulating valve 53 according to the LNG mass flowmeter 52, to control the LNG flow to maintain the required LNG flow at the set value of the operating temperature of the recondenser (measured by the recondenser internal material thermometer 21).

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for automatic control of the liquid level in the recondenser of a liquefied natural gas receiving terminal, characterized in that, include: S1. Maintain stable pressure at the bottom of the recondenser and obtain the pressure at the bottom of the recondenser; S2. Calculate the set operating temperature of the recondenser based on the pressure at the bottom of the recondenser; S3. Obtain the values ​​of multiple parameters that affect the liquid-to-gas ratio R value that controls the recondenser to operate at the set operating temperature, as well as the BOG mass flow rate. S4. Calculate the required liquid-to-gas ratio R value at the set operating temperature of the recondenser based on the set operating temperature of the recondenser and the values ​​of multiple parameters. S5. Calculate the required LNG mass flow rate for recondenser feed based on the required liquid-to-gas ratio R value at the set operating temperature of the recondenser and the BOG mass flow rate. S6. Feed LNG according to the required LNG mass flow rate for the recondenser feed; Step S2 includes: S21. Calculate the top pressure of the recondenser based on the bottom pressure of the recondenser; S22. Determine the safety margin and the bubble point temperature of the material corresponding to the top pressure of the recondenser based on the pressure at the top of the recondenser. S23. Calculate the set operating temperature of the recondenser based on the safety margin and the bubble point temperature of the material; In step S23, the bubble point temperature of the material is added to the safety margin to calculate the set operating temperature of the recondenser; The parameters include: BOG feed temperature to the recondenser, LNG feed temperature to the recondenser, set operating temperature of the recondenser, LNG latent heat of vaporization related parameters, BOG specific heat capacity, LNG specific heat capacity, and error correction coefficient between LNG feed mass flow rate and BOG feed mass flow rate.

2. The automatic control method for recondenser liquid level in a liquefied natural gas receiving station according to claim 1, characterized in that, In step S4, the required liquid-to-gas ratio R at the set operating temperature of the recondenser is calculated using the following formula: Where R is the ratio of LNG feed mass flow rate to BOG feed mass flow rate in the recondenser, in units of 1; t1 is the BOG feed temperature in the recondenser, in units of °C; t2 is the LNG feed temperature in the recondenser, in units of °C; t is the set operating temperature of the recondenser, in units of °C; r is a parameter related to the latent heat of LNG vaporization, in units of kJ / kg; c1 is the specific heat capacity of BOG, in units of kJ / kg / °C; c2 is the specific heat capacity of LNG, in units of kJ / kg / °C; and α is the error correction coefficient between the LNG feed mass flow rate and the BOG feed mass flow rate, in units of 1.

3. The automatic control method for recondenser liquid level in a liquefied natural gas receiving station according to claim 1, characterized in that, In step S5, the required liquid-to-gas ratio R at the set operating temperature of the recondenser is multiplied by the BOG mass flow rate to calculate the required LNG mass flow rate for the recondenser feed.

4. An automatic control system for the liquid level of a recondenser in a liquefied natural gas receiving station, characterized in that, To implement the automatic control method for recondenser level in a liquefied natural gas receiving station as described in any one of claims 1 to 3, the automatic control system for recondenser level in a liquefied natural gas receiving station includes: a recondenser, a low-pressure output main pipe (10), a recondenser bottom pressure gauge (11), a recondenser bottom pressure controller (12), a recondenser bottom pressure regulating valve (13), a low-pressure pump (101), a high-pressure pump (102), a recondenser BOG inlet pipeline (30), a BOG pressure gauge (31), a BOG volumetric flow meter (32), a BOG thermometer (33), a BOG mass flow calculation device (34), a recondenser temperature control device (35), and a recondenser inlet. The LNG flow calculation device (36), the upstream LNG pipeline (50) of the recondenser, the LNG thermometer (51), the LNG mass flow meter (52), the LNG regulating valve (53), and the flow controller (531) are provided. The bottom of the recondenser and one end of the upstream LNG pipeline (50) of the recondenser are connected to the low-pressure output main pipe (10). The two ends of the low-pressure output main pipe (10) are connected to the low-pressure pump (101) and the high-pressure pump (102) respectively. The pressure gauge (11) at the bottom of the recondenser and the pressure regulating valve (13) at the bottom of the recondenser are both installed on the low-pressure output main pipe (10). The pressure controller (13) at the bottom of the recondenser is provided. 2) Connect to the bottom pressure gauge (11) and bottom pressure regulating valve (13) of the recondenser respectively; the BOG inlet pipeline (30) of the recondenser is connected to the top of the recondenser, the BOG pressure gauge (31), the BOG volumetric flow meter (32) and the BOG thermometer (33) are all installed on the BOG inlet pipeline (30) of the recondenser, the BOG mass flow calculation device (34) is connected to the BOG pressure gauge (31), the BOG volumetric flow meter (32), the BOG thermometer (33) and the LNG flow calculation device (36) of the recondenser inlet respectively, and the LNG flow meter of the recondenser inlet... The calculation device (36) is connected to the flow controller (531) and the recondenser temperature control device (35) respectively. The recondenser temperature control device (35) is connected to the LNG thermometer (51) and the BOG thermometer (33) respectively. The other end of the upstream LNG pipeline (50) of the recondenser is connected to the top of the recondenser. The LNG thermometer (51), the LNG mass flow meter (52) and the LNG regulating valve (53) are all installed on the upstream LNG pipeline (50) of the recondenser. The flow controller (531) is connected to the LNG mass flow meter (52) and the LNG regulating valve (53) respectively. The recondenser bottom pressure controller (12) and the recondenser bottom pressure regulating valve (13) are used to maintain the recondenser bottom pressure stability. The pressure gauge (11) at the bottom of the recondenser is used to obtain the pressure at the bottom of the recondenser. The BOG mass flow calculation device (34) is used to calculate the BOG mass flow based on the values ​​obtained from the BOG pressure gauge (31), the BOG volume flow meter (32), and the BOG thermometer (33). The recondenser temperature control device (35) is used to calculate the required liquid-to-gas ratio R value at the set operating temperature of the recondenser based on the values ​​obtained by the BOG thermometer (33) and the LNG thermometer (51). The LNG flow calculation device (36) at the recondenser inlet is used to multiply the BOG mass flow rate output by the BOG mass flow rate calculation device (34) with the liquid-to-gas ratio R value required at the recondenser set operating temperature output by the recondenser temperature control device (35) to calculate the LNG mass flow rate required for recondenser feed. The flow controller (531) is used to control the opening degree of the LNG regulating valve (53) according to the LNG mass flow meter (52).

5. The automatic control system for the recondenser level of a liquefied natural gas receiving station according to claim 4, characterized in that, The recondenser includes: a tank (20), a material thermometer (21) inside the recondenser, a material level gauge (22) inside the recondenser, a feed liquid distributor, a gas-liquid distribution plate, and packing (23). The feed liquid distributor, the gas-liquid distribution plate, and the packing (23) are all installed in the tank (20). The feed liquid distributor is located above the gas-liquid distribution plate, and the gas-liquid distribution plate is located above the packing (23). The material thermometer (21) inside the recondenser and the material level gauge (22) inside the recondenser are both connected to the tank (20).

6. The automatic control system for the recondenser level of a liquefied natural gas receiving station according to claim 4, characterized in that, The top of the recondenser is connected to a BOG discharge line (40), which is connected to a pressure relief valve, a discharge pressure gauge, a discharge pressure regulating valve, and a discharge pressure controller. The pressure relief valve is installed on the BOG discharge line (40), and the discharge pressure gauge and the discharge pressure regulating valve are both installed on the BOG discharge line (40). The discharge pressure controller is connected to the discharge pressure gauge and the discharge pressure regulating valve, respectively.

7. The automatic control system for the recondenser level of a liquefied natural gas receiving station according to claim 4, characterized in that, There are two recondenser bottom pressure regulating valves (13). The first recondenser bottom pressure regulating valve is installed on the low-pressure output main pipe (10). The second recondenser bottom pressure regulating valve is connected in parallel with the first recondenser bottom pressure regulating valve. The first recondenser bottom pressure regulating valve and the second recondenser bottom pressure regulating valve are respectively connected to the recondenser bottom pressure controller (12). Valves are provided between one end of the upstream LNG pipeline (50) of the recondenser and the low-pressure output main pipe (10), between the low-pressure output main pipe (10) and the low-pressure pump (101), and between the recondenser and the low-pressure output main pipe (10).

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