阅读说明：本技术 船舶lpg预冷加注方法及船舶lpg预冷加注系统 (Ship LPG precooling filling method and ship LPG precooling filling system ) 是由 冷洽 崔锦泉 刘国臣 张建哲 王廷勇 于 2021-07-19 设计创作，主要内容包括：本发明提供一种船舶LPG预冷加注方法,包括：向LPG储罐内通入干燥的氮气,对LPG储罐进行吹扫、干燥和惰化；向LPG储罐内通入液氮,对LPG储罐进行预冷,且向LPG储罐内通入液氮的质量的最小值M1为：最大值M2为：其中,M-i为LPG储罐各组成部分的质量；C-i为LPG储罐各组成部分的比热容；ΔT为LPG储罐在预冷过程中降低的温度；Q-s为LPG储罐在预冷过程中,外界环境与LPG储罐之间的平均传热率；Δt为预冷的时间；r为液氮的汽化潜热；C-f为氮气的比热容；T为LPG储罐内的气体温度；T-b为液氮的饱和温度；LPG储罐内的温度达到预设值后,向LPG储罐内通入LPG。本发明还提供一种船舶LPG预冷加注系统。(The invention provides a ship LPG precooling filling method, which comprises the following steps: introducing dry nitrogen into the LPG storage tank, and purging, drying and inerting the LPG storage tank; introducing liquid nitrogen into the LPG storage tank, precooling the LPG storage tank, wherein the minimum value M1 of the mass of the liquid nitrogen introduced into the LPG storage tank is as follows: maximum M2 is: wherein M is i The mass of each component of the LPG storage tank; c i The specific heat capacity of each component of the LPG storage tank; delta T is the temperature of the LPG storage tank reduced in the precooling process; q s For pre-cooling LPG storage tankAverage heat transfer rate between the external environment and the LPG tank; delta t is the precooling time; r is the latent heat of vaporization of liquid nitrogen; c f Is the specific heat capacity of nitrogen; t is the gas temperature in the LPG storage tank; t is b Is the saturation temperature of liquid nitrogen; and after the temperature in the LPG storage tank reaches a preset value, introducing LPG into the LPG storage tank. The invention further provides a ship LPG precooling filling system.)

1. A ship LPG precooling filling method is characterized by comprising the following steps:

introducing dry nitrogen into an LPG storage tank (1), and purging, drying and inerting the LPG storage tank (1);

introducing liquid nitrogen into the LPG storage tank (1), precooling the LPG storage tank (1), wherein the minimum value M1 of the mass of the liquid nitrogen introduced into the LPG storage tank (1) is as follows:maximum M2 is:wherein M is_iThe mass of each component of the LPG storage tank (1); c_iThe specific heat capacity of each component of the LPG storage tank (1); Δ T is the temperature of the LPG storage tank (1) reduced during pre-cooling; q_sThe average heat transfer rate between the external environment and the LPG storage tank (1) in the precooling process of the LPG storage tank (1); delta t is the precooling time; r is the latent heat of vaporization of liquid nitrogen; c_fIs the specific heat capacity of nitrogen; t is the gas temperature inside the LPG storage tank (1); t is_bIs the saturation temperature of liquid nitrogen;

and after the temperature in the LPG storage tank (1) reaches a preset value, introducing LPG into the LPG storage tank (1).

2. The method for pre-cooling and filling LPG into a ship according to claim 1, wherein after the temperature in the LPG storage tank (1) reaches a preset value, the method for introducing LPG into the LPG storage tank (1) comprises the following steps:

after the temperature in the LPG storage tank (1) reaches a preset value, firstly introducing a certain amount of LPG into the LPG storage tank (1), displacing and discharging low-temperature nitrogen in the LPG storage tank (1), completing the deep cooling of the LPG storage tank (1), and then continuously introducing the LPG into the LPG storage tank (1) until the filling limit of the LPG storage tank (1) is reached.

3. Method for pre-cooling filling of LPG for ships according to claim 1, characterised in that the temperature of the liquid nitrogen introduced into the LPG storage tank (1) is gradually lowered when the LPG storage tank (1) is pre-cooled, so that the temperature inside the LPG storage tank (1) is gradually lowered.

4. A marine LPG pre-cooling filling method as claimed in claim 2, characterised in that the difference between the temperature of the liquid nitrogen introduced into the LPG storage tank (1) and the temperature inside the LPG storage tank (1) is maintained between 15 ℃ and 25 ℃ when the LPG storage tank (1) is pre-cooled.

5. The marine LPG pre-cooling filling process as claimed in claim 1, wherein the preset value is-40 ℃ to-60 ℃.

6. The method for precooling and filling marine LPG as claimed in claim 1, wherein the rate of temperature decrease in the LPG storage tank (1) is between 5 ℃/h and 10 ℃/h upon precooling the LPG storage tank (1).

7. The LPG precooling filling system for the ship is characterized by comprising an LPG storage tank (1), an LPG filling pipeline (2), a liquid nitrogen filling pipeline (3), a nitrogen filling pipeline (4) and a ventilating head (5), wherein the LPG filling pipeline (2), the liquid nitrogen filling pipeline (3) and the nitrogen filling pipeline (4) are communicated with the LPG storage tank (1), the ventilating head (5) is communicated with the LPG filling pipeline (2) and the nitrogen filling pipeline (4) at the same time, and a temperature regulator (31) is arranged on the liquid nitrogen filling pipeline (3).

8. The marine LPG pre-cooling filling system according to claim 7, wherein the liquid nitrogen filling line (3) is first connected to the LPG filling line (2) and then connected to the LPG storage tank (1) through the LPG filling line (2).

9. The marine LPG pre-cooling filling system as set forth in claim 7, wherein a first temperature sensor (11) is provided on the LPG storage tank (1), a second temperature sensor (21) and a first pressure sensor (22) are provided on the LPG filling line (2), and a third temperature sensor (41) and a second pressure sensor (42) are provided on the nitrogen filling line (4).

10. The marine LPG pre-cooling filling system according to claim 7, further comprising a first discharge line (51) and a second discharge line (52), wherein two ends of the first discharge line (51) are respectively communicated with the LPG filling line (2) and the gas permeable head (5), two ends of the second discharge line (52) are respectively communicated with the nitrogen filling line (4) and the gas permeable head (5), the first discharge line (51) is provided with a first safety valve (511), and the second discharge line (52) is provided with a second safety valve (521).

Technical Field

The invention relates to the technical field of ship fuel supply, in particular to a ship LPG precooling filling method and a ship LPG precooling filling system.

Background

According to the guidelines of the exhaust gas cleaning systems guidelines (2015) of the International Maritime Organization (IMO) Maritime Environmental Protection Commission (MEPC), the limit for the sulfur content of ship fuel from 1/2020 is 0.5%, and the limit for the sulfur content in the sulfur emission limits (SECA) is 0.1%. Therefore, more and more ships start to use clean fuel LPG (Liquefied Petroleum Gas) as a power source, the filling of the LPG storage tank is an important component of the supply of the Liquefied Petroleum Gas, and precooling before the LPG storage tank is an important guarantee measure for ensuring the safety of the whole filling process.

The ultra-low temperature LPG liquid with the temperature of 100 ℃ below zero is stored in the LPG storage tank, the material of the storage tank body has shrinkage deformation with different degrees in the cooling process, if the precooling process is not well controlled, the structure of the storage tank is damaged, the storage tank can not be used continuously, the LPG leakage can be seriously caused to cause safety accidents, and therefore the precooling link of the storage tank is very dangerous and very important work.

At present, an LPG precooling mode is mainly adopted for a marine LPG storage tank, and firstly, normal-temperature nitrogen is introduced into the LPG storage tank to purge, inert and dry the storage tank, so that the concentration and the oxygen content of water vapor in a filling pipeline and the storage tank meet the standard requirements; then adding LPG (liquefied petroleum Gas), vaporizing the LPG by a vaporizer, performing nitrogen replacement and precooling on a filling pipeline and a storage tank by using BOG (Boil Off Gas) obtained after vaporization, adjusting the flow and the temperature of the BOG by adjusting an inlet valve and a bypass valve of the vaporizer, controlling the temperature of the BOG to be about-60-0 ℃, and controlling the temperature reduction rate of a pipeline to be 10 ℃/h; when the temperature of the storage tank is reduced to-50 ℃, the LPG is directly introduced to complete the filling of the storage tank.

The direct adoption of LPG for cooling has the defects of high cost, waste of LPG fuel, troublesome overhauling and replacing operation, high risk and the like. Meanwhile, at present, no simple and general numerical calculation method exists for determining the amount of the precooling liquid consumed in the precooling process, and a test is needed for analysis and check, so that the method is high in cost; or a numerical simulation method is adopted to model the temperature field, the velocity field and the flow field of the storage tank, and the method is complex in modeling and needs a large amount of time. How to determine the amount of pre-cooling liquid consumed in the pre-cooling process becomes a big problem.

Disclosure of Invention

The invention aims to provide a ship LPG precooling and filling method and a ship LPG precooling and filling system, aiming at solving the defects in the prior art, precooling by using liquid nitrogen, reducing precooling cost, simultaneously determining the using amount of the liquid nitrogen and solving the problems of insufficient liquid nitrogen preparing amount or excessive using amount in the precooling process.

The invention provides a ship LPG precooling filling method, which comprises the following steps:

introducing dry nitrogen into the LPG storage tank, and purging, drying and inerting the LPG storage tank;

introducing liquid nitrogen into the LPG storage tank, precooling the LPG storage tank, wherein the minimum value M1 of the mass of the liquid nitrogen introduced into the LPG storage tank is as follows:maximum M2 is:wherein M is_iThe mass of each component of the LPG storage tank; c_iThe specific heat capacity of each component of the LPG storage tank; Δ T is the temperature of the LPG storage tank reduced during pre-cooling; q_sThe average heat transfer rate between the external environment and the LPG storage tank in the precooling process of the LPG storage tank; delta t is the precooling time; r is the latent heat of vaporization of liquid nitrogen; c_fIs the specific heat capacity of nitrogen; t is the gas temperature in the LPG storage tank; t is_bIs the saturation temperature of liquid nitrogen;

and after the temperature in the LPG storage tank reaches a preset value, introducing LPG into the LPG storage tank.

Further, after the temperature in the LPG storage tank reaches a preset value, LPG is introduced into the LPG storage tank, and the method specifically includes:

after the temperature in the LPG storage tank reaches a preset value, firstly introducing a certain amount of LPG into the LPG storage tank, displacing and discharging low-temperature nitrogen in the LPG storage tank, completing the deep cooling of the LPG storage tank, and then continuously introducing the LPG into the LPG storage tank until the filling limit of the LPG storage tank is reached.

Further, when the LPG storage tank is pre-cooled, the temperature of liquid nitrogen introduced into the LPG storage tank is gradually reduced, so that the temperature in the LPG storage tank is gradually reduced.

Further, when the LPG storage tank is precooled, the difference value between the temperature of liquid nitrogen introduced into the LPG storage tank and the temperature of the LPG storage tank is kept between 15 and 25 ℃.

Further, the preset value is-40 ℃ to-60 ℃.

Further, when the LPG storage tank is precooled, the speed of temperature reduction in the LPG storage tank is 5-10 ℃/h.

The invention also provides a ship LPG precooling filling system which comprises an LPG storage tank, an LPG filling pipeline, a liquid nitrogen filling pipeline, a nitrogen filling pipeline and a ventilation head, wherein the LPG filling pipeline, the liquid nitrogen filling pipeline and the nitrogen filling pipeline are all communicated with the LPG storage tank, the ventilation head is simultaneously communicated with the LPG filling pipeline and the nitrogen filling pipeline, and a temperature regulator is arranged on the liquid nitrogen filling pipeline.

Furthermore, the liquid nitrogen filling pipeline is communicated to the LPG filling pipeline firstly and then communicated with the LPG storage tank through the LPG filling pipeline.

Furthermore, a first temperature sensor is arranged on the LPG storage tank, a second temperature sensor and a first pressure sensor are arranged on the LPG filling pipeline, and a third temperature sensor and a second pressure sensor are arranged on the nitrogen filling pipeline.

Furthermore, the ship LPG precooling filling system further comprises a first discharging pipeline and a second discharging pipeline, two ends of the first discharging pipeline are respectively communicated with the LPG filling pipeline and the ventilation head, two ends of the second discharging pipeline are respectively communicated with the nitrogen gas filling pipeline and the ventilation head, a first safety valve is arranged on the first discharging pipeline, and a second safety valve is arranged on the second discharging pipeline.

According to the method for precooling and filling the LPG in the ship, the LPG storage tank is precooled step by using the liquid nitrogen, so that the cost of precooling liquid in the precooling process is reduced, the problems that the LPG storage tank material is subjected to cold brittle fracture and the storage tank structure is damaged due to the fact that the LPG storage tank material directly bears the overlarge temperature stress at low temperature are solved, meanwhile, the LPG storage tank can be maintained more conveniently, and the safety is better. Meanwhile, the method for pre-cooling and filling the ship LPG provides a method for calculating the liquid nitrogen consumption in the pre-cooling process, reduces the calculation time for determining the reserve amount of the liquid nitrogen, determines the minimum liquid nitrogen consumption in the pre-cooling process, and solves the problem of insufficient liquid nitrogen preparation amount in the pre-cooling and filling process; the maximum liquid nitrogen consumption in the precooling process is determined, and the cost increase caused by excessive liquid nitrogen standby amount is prevented.

Drawings

Fig. 1 is a schematic structural diagram of a ship LPG pre-cooling filling system in an embodiment of the present invention.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

The terms "first," "second," "third," "fourth," and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.

The terms of orientation, up, down, left, right, front, back, top, bottom, and the like (if any) referred to in the specification and claims of the present invention are defined by the positions of structures in the drawings and the positions of the structures relative to each other, only for the sake of clarity and convenience in describing the technical solutions. It is to be understood that the use of the directional terms should not be taken to limit the scope of the claims.

As shown in fig. 1, the precooling and filling system for LPG (Liquefied Petroleum Gas) for a ship provided by the embodiment of the present invention includes an LPG storage tank 1, an LPG filling pipeline 2, a liquid nitrogen filling pipeline 3, a nitrogen filling pipeline 4 and a Gas permeable head 5, wherein the LPG filling pipeline 2, the liquid nitrogen filling pipeline 3 and the nitrogen filling pipeline 4 are all communicated with the LPG storage tank 1, the Gas permeable head 5 is simultaneously communicated with the LPG filling pipeline 2 and the nitrogen filling pipeline 4, and a temperature regulator 31 is disposed on the liquid nitrogen filling pipeline 3.

Specifically, the LPG filling line 2 extends to the bottom inside the LPG storage tank 1, and the nitrogen filling line 4 extends to the top inside the LPG storage tank 1. The LPG filling pipeline 2 is used for filling LPG into the LPG storage tank 1, the liquid nitrogen filling pipeline 3 is used for filling liquid nitrogen into the LPG storage tank 1, the nitrogen filling pipeline 4 is used for filling nitrogen into the LPG storage tank 1, and the gas permeable head 5 is used for discharging gas or liquid in the LPG storage tank 1, the LPG filling pipeline 2, the liquid nitrogen filling pipeline 3 and the nitrogen filling pipeline 4.

Further, in this embodiment, the liquid nitrogen filling pipeline 3 is first communicated to the LPG filling pipeline 2, and then communicated with the LPG storage tank 1 through the LPG filling pipeline 2.

Further, a first temperature sensor 11 is arranged on the LPG storage tank 1, a second temperature sensor 21 and a first pressure sensor 22 are arranged on the LPG filling pipeline 2, and a third temperature sensor 41 and a second pressure sensor 42 are arranged on the nitrogen filling pipeline 4.

Further, the ship LPG precooling filling system further comprises a first discharge pipeline 51 and a second discharge pipeline 52, two ends of the first discharge pipeline 51 are respectively communicated with the LPG filling pipeline 2 and the ventilation head 5, two ends of the second discharge pipeline 52 are respectively communicated with the nitrogen filling pipeline 4 and the ventilation head 5, a first safety valve 511 is arranged on the first discharge pipeline 51, and a second safety valve 521 is arranged on the second discharge pipeline 52. When the first pressure sensor 22 and/or the second pressure sensor 42 detect the overpressure of the pipeline during the filling of the liquid nitrogen/LPG/nitrogen, the first safety valve 511 and/or the second safety valve 521 are opened to discharge the excess liquid nitrogen/LPG/nitrogen through the gas permeable head 5.

Further, a first filter 24 is arranged on the LPG filling pipe 2, and a second filter 43 is arranged on the nitrogen filling pipe 4. The first filter 24 and the second filter 43 are used to filter impurities in the liquid nitrogen/LPG/nitrogen gas introduced into the LPG tank 1.

Further, a first exhaust valve 53 is arranged on a pipeline between the LPG filling pipeline 2 and the gas permeable head 5, and a second exhaust valve 54 is arranged on a pipeline between the nitrogen filling pipeline 4 and the gas permeable head 5.

Further, a liquid nitrogen inlet stop valve 32 is arranged on the liquid nitrogen filling pipeline 3. The LPG filling pipeline 2 is also provided with an LPG inlet stop valve 23, a filling liquid phase pneumatic valve 25, a filling liquid phase hand valve 26, a filling liquid phase stop valve 27 and a filling liquid phase emergency cut-off valve 28. The nitrogen filling pipeline 4 is also provided with a filling gas phase pneumatic valve 44, a filling gas phase hand valve 45, a filling gas phase stop valve 46 and a filling gas phase emergency cut-off valve 47.

The embodiment of the invention also provides a ship LPG precooling filling method, which comprises the following steps:

introducing dry nitrogen into the LPG storage tank 1, and purging, drying and inerting the LPG storage tank 1;

introducing liquid nitrogen into the LPG storage tank 1, precooling the LPG storage tank 1, wherein the minimum value M1 of the mass of the liquid nitrogen introduced into the LPG storage tank 1 is as follows:maximum M2 is:wherein M is_iThe mass of each component of the LPG storage tank 1; c_iThe specific heat capacity of each component of the LPG storage tank 1; delta T is the temperature of the LPG storage tank 1 reduced in the precooling process; q_sThe average heat transfer rate between the external environment and the LPG storage tank 1 in the precooling process of the LPG storage tank 1; delta t is the precooling time; r is the latent heat of vaporization of liquid nitrogen; c_fIs the specific heat capacity of nitrogen; t is the gas temperature in the LPG storage tank 1; t is_bIs the saturation temperature of liquid nitrogen;

after the temperature in the LPG storage tank 1 reaches a preset value, LPG is introduced into the LPG storage tank 1.

Further, after the temperature in the LPG storage tank 1 reaches a preset value, LPG is introduced into the LPG storage tank 1, which specifically includes:

after the temperature in the LPG storage tank 1 reaches a preset value, a certain amount of LPG is firstly introduced into the LPG storage tank 1 to replace and discharge low-temperature nitrogen in the LPG storage tank 1, the cryogenic cooling of the LPG storage tank 1 is completed, and then the LPG is continuously introduced into the LPG storage tank 1 until the filling limit of the LPG storage tank 1 is reached.

Further, when the LPG tank 1 is precooled, the temperature of the liquid nitrogen introduced into the LPG tank 1 is gradually decreased, so that the temperature in the LPG tank 1 is gradually decreased, even if the LPG tank 1 is precooled step by step.

Further, when the LPG storage tank 1 is precooled, the difference value between the temperature of the liquid nitrogen introduced into the LPG storage tank 1 and the temperature inside the LPG storage tank 1 is kept between 15 ℃ and 25 ℃, so that the condition that the LPG storage tank 1 directly bears low temperature and receives overlarge temperature stress due to overlarge difference value between the temperature of the liquid nitrogen introduced into the LPG storage tank 1 and the temperature inside the LPG storage tank 1 is avoided, and the material of the LPG storage tank 1 is prevented from being subjected to cold brittle fracture, and the structure of the LPG storage tank 1 is prevented from being damaged.

Preferably, the difference between the temperature of the liquid nitrogen introduced into the LPG storage tank 1 and the temperature in the LPG storage tank 1 is maintained at 20 ℃. Specifically, the temperature of the liquid nitrogen can be adjusted by the temperature adjuster 31 when the liquid nitrogen is introduced into the LPG tank 1. For example: when the initial temperature in the LPG storage tank 1 is 25 ℃, the difference between the temperature of the liquid nitrogen and the temperature in the LPG storage tank 1 is kept at 20 ℃ when the LPG storage tank 1 is pre-cooled by introducing the liquid nitrogen. In the first stage, the temperature of liquid nitrogen introduced into the LPG storage tank 1 is kept at 5 ℃, and the difference between the temperature of the liquid nitrogen and the temperature in the LPG storage tank 1 is 20 ℃; in the second stage, the temperature in the LPG storage tank 1 is reduced to 15 ℃, and the temperature of liquid nitrogen introduced into the LPG storage tank 1 is controlled to be kept at-5 ℃; in the third stage, the temperature in the LPG storage tank 1 is reduced to 5 ℃, the temperature of liquid nitrogen introduced into the LPG storage tank 1 is controlled to be maintained at-15 ℃ …, and the like, until the temperature in the LPG storage tank 1 reaches a preset value.

Further, the preset value is-40 ℃ to-60 ℃.

Preferably, the preset value is-50 ℃.

Further, when the LPG storage tank 1 is precooled, the temperature in the LPG storage tank 1 is reduced at a rate of 5-10 ℃/h.

Preferably, the rate of temperature decrease in the LPG storage tank 1 upon pre-cooling of the LPG storage tank 1 is 5 deg.C/h.

Further, when precooling the LPG tank 1, the flow rate of the liquid nitrogen introduced into the LPG tank 1 may be determined depending on the size of the LPG tank 1.

Specifically, the method for calculating the liquid nitrogen consumption in the precooling process is based on the law of energy conservation, the fluids in the LPG storage tank 1 and the environment where the fluids are located are taken as a system, the total energy in the system is unchanged, and the mathematical model of the liquid nitrogen consumption in the precooling process is established by mainly considering the total heat release of the LPG storage tank 1 system, the heat leakage quantity transmitted to the LPG storage tank 1 by the environment when the temperature of the LPG storage tank 1 reaches a steady state, the physical properties of liquid nitrogen, the precooling time and other influence factors. The liquid nitrogen consumption in the precooling process has two limit conditions according to the utilization degree of sensible heat: when the consumption of the liquid nitrogen is minimum, the precooling process not only utilizes the latent heat of vaporization of the liquid nitrogen, but also completely utilizes the sensible heat of the vaporized nitrogen, namely the temperature of escaping gas at any moment is equal to the temperature of the inner wall of the LPG storage tank 1; when the consumption of liquid nitrogen is the maximum, the heat transfer among all parts of the LPG storage tank 1 system is poor, and the precooling process only utilizes the latent heat of vaporization of the liquid nitrogen. And respectively calculating the minimum consumption M1 and the maximum consumption M2 according to the established mathematical model of the consumption of the liquid nitrogen in the precooling process, wherein the consumption of the liquid nitrogen in the actual precooling process is between the minimum consumption M1 and the maximum consumption M2.

The calculation process of the minimum value M1 and the maximum value M2 of the mass of the liquid nitrogen introduced into the LPG tank 1 is explained in detail as follows:

1. according to the law of conservation of energy, the total energy Q emitted by the system_rEqual to the total energy Q absorbed by the system_fNamely: q_r＝Q_f；

2. Total energy Q emitted by the system_rEqual to the heat Q released when the LPG storage tank 1 is cooled to the working temperature₁Heat leakage from the environment Q₂And (c) the sum, i.e.: q_r＝Q₁+₂；

3. The LPG storage tank 1 is cooled to workHeat quantity Q released by temperature₁The total energy sum which is equal to the energy sum discharged by all the components of the LPG storage tank 1 (including the inner tank of the storage tank, the heat insulation layer material, the skid, the pipeline, the gas in the tank and the like) is obtained according to a heat calculation formula: q₁＝∑M_i*C_i*ΔT；

Wherein: m_iThe mass (in kg) of each component of the LPG storage tank 1, C_iThe specific heat capacity (unit is kJ/(kg DEG C.) and delta T is the temperature (unit is DEG C) reduced by the LPG storage tank 1 in the precooling process;

4. heat leakage Q of the environment₂Equal to the average heat transfer rate Q between the external environment and the LPG storage tank 1 in the precooling process of the LPG storage tank 1_sThe product of the precooling time Δ t, namely: q₂＝Q_s*Δt；

5. Total energy Q absorbed by the system_fEnergy provided for precooling liquid nitrogen, including latent heat Q absorbed by vaporization of liquid nitrogen₃Sensible heat Q when the vaporized low-temperature nitrogen cools the LPG storage tank 1 to the working temperature₄Namely: q_f＝Q₃+Q₄；

6. Latent heat Q absorbed by vaporization of liquid nitrogen₃Equal to the average mass flow M introduced by the liquid nitrogen_fThe product of the latent heat of vaporization r and the precooling time Δ t of the liquid nitrogen is: q₃＝M_f*r*Δt；

7. Sensible heat Q when the LPG storage tank 1 is cooled to the working temperature by the low-temperature nitrogen₄Equal to the average mass flow M introduced by the liquid nitrogen_fAverage specific heat capacity with nitrogen C_fAnd the gas temperature T and the liquid nitrogen saturation temperature T in the LPG storage tank 1_bThe product of the differences, i.e.: q₄＝M_f*C_f*(T-T_b)；

8. The total consumption M of the liquid nitrogen is the average mass flow M of the liquid nitrogen_fThe product of the precooling time Δ t, namely: m is M_f*Δt；

Finally, the total consumption M of the liquid nitrogen is obtained as follows:

when the consumption of the liquid nitrogen is minimum, the precooling process not only utilizes the latent heat of vaporization of the liquid nitrogen, but also completely utilizes the sensible heat of the vaporized nitrogen, namely the temperature of escaping gas at any moment is equal to the temperature of the inner wall of the LPG storage tank 1, the temperature T of the gas in the tank can be considered as the final precooling temperature in the tank during calculation, and the cold energy of the precooled liquid nitrogen is completely utilized, namely the minimum value is

When the consumption of the liquid nitrogen is the maximum, the heat transfer among all parts of the storage tank system is poor, the precooling process only utilizes the vaporization latent heat of the liquid nitrogen and does not utilize the sensible heat of the low-temperature nitrogen after the vaporization, and the total consumption of the liquid nitrogen can be simplified to be

The consumption of liquid nitrogen during the actual precooling filling is between the minimum consumption M1 and the maximum consumption M2.

The process of the LPG precooling filling is concretely explained by combining the method and the system for LPG precooling filling of the ship as follows:

the process of pre-cooling and filling LPG mainly comprises the following steps: purging with nitrogen at normal temperature, inerting and drying, precooling the LPG storage tank 1 step by liquid nitrogen, precooling the LPG deeply and completing the filling.

1. Introducing normal-temperature nitrogen into the LPG storage tank 1 from the nitrogen filling pipeline 4, fully replacing the normal-temperature nitrogen with air in the LPG storage tank 1, opening the first emptying valve 53 to discharge the air and the nitrogen to the atmosphere from the ventilation head 5, and finally enabling the water vapor concentration and the oxygen content in the nitrogen filling pipeline 4 and the LPG storage tank 1 to meet the standard requirements; stopping introducing normal-temperature nitrogen, and finishing the drying and inerting of the LPG storage tank 1;

2. liquid nitrogen is introduced into the LPG storage tank 1 to pre-cool the LPG storage tank 1, the liquid nitrogen enters the LPG storage tank 1 from the liquid nitrogen filling pipeline 3 through the temperature regulator 31, the temperature reduction rate in the LPG storage tank 1 is controlled by controlling the flow of the liquid nitrogen, the temperature of the LPG storage tank 1 is stabilized to be reduced at 5 ℃/h, and the LPG storage tank 1 is pre-cooled step by step; meanwhile, by utilizing the density difference between the low-temperature nitrogen and the normal-temperature nitrogen, the second emptying valve 54 is opened, the normal-temperature nitrogen is extruded out of the LPG storage tank 1 and is exhausted to the atmosphere from the gas permeable head 5; when the temperature in the LPG storage tank 1 reaches minus 50 ℃, stopping introducing liquid nitrogen, and finishing the preliminary precooling of the LPG storage tank 1;

3. opening an LPG inlet stop valve 23, introducing LPG into the LPG storage tank 1 from the LPG filling pipeline 2, replacing low-temperature nitrogen in the LPG storage tank 1, extruding the low-temperature nitrogen out of the LPG storage tank 1, and discharging the low-temperature nitrogen to the atmosphere from a gas-permeable head 5, so that the temperature in the LPG storage tank 1 reaches-70 ℃, and completing the deep cooling of the LPG storage tank 1; the filling process is completed by continuing to introduce the LPG until the filling limit of the LPG storage tank 1 is reached.

The method for precooling and filling the ship LPG provided by the embodiment has the advantages that:

1. by using liquid nitrogen to pre-cool the LPG storage tank 1, compared with the traditional method of directly using LPG to pre-cool, the method reduces the cost of pre-cooling liquid consumption in the pre-cooling process;

2. the liquid nitrogen is used for precooling the LPG storage tank 1 step by step, so that the problems that the material of the LPG storage tank 1 is subjected to cold brittle fracture and the structure of the LPG storage tank 1 is damaged due to the fact that the material of the LPG storage tank 1 directly bears low temperature and is subjected to overlarge temperature stress are solved, meanwhile, the LPG storage tank 1 can be maintained more conveniently, and the safety is better;

3. the ship LPG precooling filling method provides a calculation method of liquid nitrogen consumption in a precooling process, reduces calculation time for determining liquid nitrogen reserve, determines minimum liquid nitrogen consumption in the precooling process, and solves the problem of insufficient liquid nitrogen preparation amount in the precooling filling process; the maximum liquid nitrogen consumption in the precooling process is determined, and the cost increase caused by excessive liquid nitrogen standby amount is prevented.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.