CN110159915B - Large-sized low-temperature full-capacity tank nitrogen replacement structure and nitrogen replacement method thereof - Google Patents

Abstract

The invention discloses a nitrogen replacement structure of a large low-temperature full-capacity tank, wherein an outer tank, an inner tank, thermal corner protection, foam glass bricks, expanded perlite and glass wool jointly form a low-temperature full-capacity tank body; the annular space exhaust pipe, the bottom heat insulation exhaust pipe, the hot angle protection balance pipe, the high-point blow-down pipe, the replacement air inlet pipe, the hot angle protection exhaust pipe, the exhaust grid and the vent hole form a nitrogen replacement structure of the low-temperature full-volume tank together; nitrogen enters the inner tank through the replacement air inlet pipe, and the high-point blow-down pipe, the annular space exhaust pipe, the bottom heat insulation exhaust pipe and the thermal angle protection exhaust pipe are gradually opened to exhaust. The beneficial effects of the invention are as follows: the method is simple and convenient to operate and high in replacement efficiency, and effectively solves the problem that the dew point and the oxygen content of the large-sized low-temperature full-capacity tank are raised after the tank is replaced for a period of time due to incomplete replacement, so that the tank needs to be further replaced.

Description

Large-sized low-temperature full-capacity tank nitrogen replacement structure and nitrogen replacement method thereof

Technical Field

The invention relates to the technical field of large-scale low-temperature storage tanks, in particular to a nitrogen replacement structure of a large-scale low-temperature full-capacity tank and a nitrogen replacement method thereof.

Background

More and more large-sized low-temperature storage tanks are applied to the energy and petrochemical industries, and the large-sized low-temperature storage tanks mostly adopt full-capacity tanks, and glass bricks, expanded perlite and glass wool are used as heat insulation and cold insulation materials between an inner tank and an outer tank. After the construction and installation of the storage tank are completed, before the feeding operation, the air at each part in the tank needs to be replaced by nitrogen, so that the risk of cold leakage or explosion of the storage tank is reduced. Because the volume of the large-scale low-temperature full-capacity tank is large at present, the complete replacement of all parts is difficult to ensure during replacement, particularly the bottom heat insulation space and the thermal angle protection space, after the tank is kept for a period of time, the conditions of oxygen content and dew point rise often occur, further replacement is needed, the project construction period is delayed, and the economic loss is caused.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides the nitrogen replacement structure of the large-sized low-temperature full-volume tank and the nitrogen replacement method thereof, which have reasonable structural design and are convenient and simple to use and operate.

The technical scheme of the invention is as follows:

the nitrogen replacement structure of the large low-temperature full-capacity tank is characterized by comprising an outer tank, an inner tank, thermal angle protection, foam glass bricks, expanded perlite, glass wool, an annular space exhaust pipe, a bottom heat insulation exhaust pipe, a thermal angle protection balance pipe, a high-point blow-down pipe, a replacement air inlet pipe, a thermal angle protection exhaust pipe, an inner tank bottom bearing ring and an exhaust grid, wherein the inner tank bottom bearing ring is provided with vent holes; the outer tank, the inner tank, the thermal angle protection, the foam glass bricks, the expanded perlite and the glass wool jointly form a low-temperature full-capacity tank body; the annular space exhaust pipe, the bottom heat insulation exhaust pipe, the hot angle protection balance pipe, the high-point blow-down pipe, the replacement air inlet pipe, the hot angle protection exhaust pipe, the exhaust grid and the vent hole form a nitrogen replacement structure of the low-temperature full-volume tank together; nitrogen enters the inner tank through the replacement air inlet pipe, and the high-point blow-down pipe, the annular space exhaust pipe, the bottom heat insulation exhaust pipe and the thermal angle protection exhaust pipe are gradually opened to exhaust, so that air in each corresponding area in the tank is gradually replaced to the required nitrogen with qualified dew point and oxygen content.

A large-scale low temperature whole appearance jar nitrogen gas replacement structure, its characterized in that, the annular space blast pipe by from outer jar top extremely the vertical pipeline of blast pipe of annular space bottom between inner tank and the outer jar, be located the inner tank with the blast pipe annular pipeline of annular space bottom between the outer jar and the valve of outer jar top constitutes, its blast pipe annular pipeline level both sides set up the blast pipe trompil and are used for ventilating, its blast pipe annular pipeline outside parcel glass fiber cloth is used for stopping expanded perlite is floated away along with the air current from blast pipe trompil, guarantees the air permeability simultaneously.

The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized in that the bottom heat-insulating exhaust pipe consists of a vertical pipeline from the top of the outer tank to the bottom of an annular space between the inner tank and the outer tank, a horizontal pipeline which is positioned above the thermal angle protection and horizontally extends to a tank center heat-insulating layer from the bottom of the annular space between the inner tank and the outer tank, and a valve above the top of the outer tank, wherein the tail end of the horizontal pipeline is positioned at the center of the tank and is connected with the exhaust grid.

A large-scale low temperature whole appearance jar nitrogen gas replacement structure, its characterized in that, hot angle protection balance pipe by certainly outer jar vault space extremely the inner tank with the balance pipe horizontal pipeline of the annular space between the outer jar, certainly the inner tank with the top of the annular space between the outer jar extremely the vertical pipeline of balance pipe at hot angle protection top and be located the balance pipe annular pipeline of hot angle protection headspace constitute, its balance pipe annular pipeline top sets up a set of balance pipe trompil, and parcel glass wool is used for carrying out adiabatic cold insulation to the part, guarantees the air permeability simultaneously.

The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized in that the high-point blow-down pipe consists of a vertical pipeline connected with the highest point of the arch center of the outer tank and a valve positioned above the top of the outer tank.

The large-scale low-temperature full-capacity tank nitrogen replacement structure is characterized in that the replacement air inlet pipe is composed of an air inlet pipe vertical pipeline from the outer tank vault to the inner tank bottom, an air inlet pipe horizontal pipeline positioned at the inner tank bottom, an air inlet pipe annular pipeline positioned at the inner tank bottom and a valve positioned above the outer tank top, the diameter of the air inlet pipe annular pipeline is half of that of the inner tank, and air inlet pipe openings are formed below the air inlet pipe annular pipeline.

The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized in that the thermal angle protection exhaust pipe consists of a vertical pipeline from the top of the outer tank to the bottom of a thermal angle protection space, a horizontal pipeline horizontally extending to a tank center heat insulation layer and a valve above the top of the outer tank, and the tail end of the horizontal pipeline is positioned at the center of the tank and is connected with the exhaust grid.

The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized in that the exhaust grating is cylindrical, a grating is arranged on the wall of the exhaust grating for ventilation, glass wool is filled in the exhaust grating for heat insulation and cold insulation, ventilation is guaranteed, and the bottom of the exhaust grating is communicated with a horizontal pipeline of a bottom heat insulation exhaust pipe and a horizontal pipeline of a thermal angle protection exhaust pipe respectively.

The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized in that the outer tank is made of low-temperature steel or consists of prestressed concrete and a steel lining plate; the inner tank is made of low-temperature steel, the top of the inner tank is of a flat suspended ceiling structure, balance holes for balancing gas-phase pressure in the inner tank space and the outer tank vault space are formed in the top of the inner tank, and the inner tank is integrally covered with glass wool to perform heat insulation and cold insulation.

The nitrogen replacement method of the nitrogen replacement structure of the large-sized low-temperature full-volume tank is characterized by comprising the following steps of:

step 1), closing valves of an annular space exhaust pipe, a bottom heat insulation exhaust pipe and a thermal angle protection exhaust pipe, opening a high-point blow-down pipe valve, opening a replacement air inlet pipe valve, controlling air inflow and air displacement of replacement air through valve opening, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of the exhaust gas at the high-point blow-down pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and enabling the gas phase replacement of the inner tank space and the top space of an outer tank to be qualified;

step 2) opening an annular space exhaust pipe valve, enabling nitrogen to enter the top of an annular space between an inner tank and an outer tank through an expanded perlite retaining wall of a dome space of the outer tank, enabling air flow to flow from the top to the bottom along with pressure difference, entering an exhaust pipe horizontal pipeline of the annular space exhaust pipe, and then discharging the air out of the tank along an exhaust pipe vertical pipeline; after the air is observed to be discharged, closing a high-point blow-down pipe valve, controlling air inflow and air displacement through the opening of the valve, ensuring that the pressure of the storage tank is controlled within a required range, detecting the dew point and the oxygen content of the exhaust gas at the position of the annular space exhaust pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and ensuring that the annular space between the inner tank and the outer tank is qualified in gas phase replacement;

step 3) opening a bottom heat-insulating exhaust pipe valve, enabling qualified displacement air of an annular space between an inner tank and an outer tank to enter the bottom heat-insulating space through a vent hole on a bearing ring at the bottom of the inner tank, enabling the annular space to enter an exhaust grid positioned at the center of the tank along a gap between foam glass bricks, then discharging the annular space along the bottom heat-insulating exhaust pipe, after observing that the bottom heat-insulating exhaust pipe is discharged with air outside the tank, closing the annular space exhaust pipe valve, controlling air inflow and air displacement through valve opening, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of exhaust at the bottom heat-insulating exhaust pipe valve every 12 hours until corresponding detection values are lower than technical requirements, and enabling the bottom heat-insulating layer of the inner tank to be displaced to be qualified;

and 4) opening a hot angle protection exhaust pipe valve, wherein qualified replacement gas in the gas phase space at the top of the outer tank passes through a horizontal pipe orifice of the hot angle protection balance pipe at the top of the outer tank, enters the hot angle protection balance pipe, uniformly enters the hot angle protection top space along a balance pipe horizontal annular pipe of the hot angle protection balance pipe, enters an exhaust grid positioned at the center of the tank along a gap between glass bricks, is discharged out of the tank along the hot angle protection exhaust pipe, and is closed after the gas is observed to be discharged.

And 5) controlling the pressure of the storage tank to be 8-10kPa, closing a replacement air inlet pipe valve, and ending the replacement of the storage tank.

The beneficial effects of the invention are as follows: the method is simple and convenient to operate and high in replacement efficiency, and effectively solves the problem that the dew point and the oxygen content of the large-sized low-temperature full-capacity tank are raised after the tank is replaced for a period of time due to incomplete replacement, so that the tank needs to be further replaced.

Drawings

FIG. 1 is a schematic diagram of the front view of the invention;

FIG. 2 is a schematic view of the inventive replacement air inlet pipe;

FIG. 3 is an enlarged schematic view of the structure of invention A;

FIG. 4 is a schematic view of the inventive annular space exhaust pipe;

FIG. 5 is an enlarged schematic view of the structure of invention B;

FIG. 6 is a schematic view of the inventive thermal angle protection balance tube;

FIG. 7 is an enlarged schematic view of the structure of invention C;

FIG. 8 is a schematic view of an inventive inner tank bottom bearing ring and its vent structure;

FIG. 9 is a schematic view of an inventive exhaust grill structure;

FIG. 10 is a schematic structural view of the invention in the process of displacing the dome space of the inner can and the outer can;

FIG. 11 is a schematic illustration of the process of the invention displacing the annular space between the inner and outer tanks;

FIG. 12 is a schematic view of the construction of the invention in place of the bottom insulating space;

FIG. 13 is a schematic view of the construction of the inventive process for placing a heat exchange corner protected space;

in the figure: the device comprises a 1-annular space exhaust pipe, a 2-bottom heat insulation exhaust pipe, a 3-hot angle protection balance pipe, a 4-high point blow-down pipe, a 5-replacement air inlet pipe, a 6-hot angle protection exhaust pipe, a 7-outer tank, an 8-inner tank, 9-expanded perlite, 10-foam glass bricks, 11-glass wool, a 12-inner tank bottom bearing ring, 13-glass fiber cloth, 14-exhaust grids, 15-ventilation holes and 16-hot angle protection.

Detailed Description

The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.

Examples:

as shown in fig. 1-13, the present embodiment is a nitrogen replacement structure for a large-sized low-temperature full-capacity tank, comprising an annular space exhaust pipe 1, a bottom heat insulation exhaust pipe 2, a thermal angle protection balance pipe 3, a high-point blow-down pipe 4, a replacement air inlet pipe 5, a thermal angle protection exhaust pipe 6, an outer tank 7, an inner tank 8, expanded perlite 9, foam glass bricks 10, glass wool 11, an inner tank bottom bearing ring 12, glass fiber cloth 13, an exhaust grille 14, ventilation holes 15 and thermal angle protection 16.

In this embodiment, the outer tank 7, the inner tank 8, the thermal angle protection 16, the foam glass block 10, the expanded perlite 9 and the glass wool 11 together form a low-temperature full-volume tank body.

In this embodiment, the inner tank 8 is made of low-temperature steel, the top of the inner tank is a flat suspended ceiling structure, balance holes for balancing gas phase pressure in the space of the inner tank 8 and the vault space of the outer tank 7 are formed in the top of the inner tank, the glass wool is integrally covered for heat insulation and cold preservation, the bearing rings 12 of the bottom of the inner tank are provided with ventilation holes 15, and the number and the size of the bearing rings are determined according to the diameters of the bearing rings, and are generally 8-16;

in this embodiment, the exhaust pipe 1 of the annular space is composed of an exhaust pipe vertical pipe 101 from the top of the outer tank 7 to the bottom of the annular space between the inner tank 8 and the outer tank 7, an exhaust pipe annular pipe 102 positioned at the bottom of the annular space between the inner tank 8 and the outer tank 7, and a valve above the top of the outer tank 7, wherein a plurality of exhaust pipe openings 103 are arranged on two horizontal sides of the exhaust pipe annular pipe 102 for ventilation, and the glass fiber cloth 13 is wrapped outside the exhaust pipe annular pipe 102 for blocking the expanded perlite from drifting away with the air flow from the exhaust pipe openings, and at the same time, the ventilation is ensured;

in this embodiment, the bottom adiabatic exhaust pipe 2 consists of a vertical pipe from the top of the outer tank 7 to the bottom of the annular space between the inner tank 8 and the outer tank 7, a horizontal pipe extending horizontally from the bottom of the annular space between the inner tank 8 and the outer tank 7 to the tank center insulation layer above the thermal corner protector 16, and a valve above the top of the outer tank 7, the end of the horizontal pipe being located at the tank center and connected to the exhaust grill 14;

in this embodiment, the thermal angle protection balance pipe 3 is composed of a balance pipe horizontal pipe 302 from the dome space of the outer tank 7 to the annular space between the inner tank 8 and the outer tank 7, a balance pipe vertical pipe 303 from the top of the annular space between the inner tank 8 and the outer tank 7 to the top of the thermal angle protection 16, and a balance pipe annular pipe 301 located in the top space of the thermal angle protection 16, wherein a plurality of balance pipe openings 304 are provided at the top of the balance pipe annular pipe 301, and the glass wool 11 is wrapped to perform heat insulation and cold insulation on a part, and ensure ventilation;

in this embodiment, the high-point blow-down pipe 4 is composed of a vertical pipe connected with the highest point of the arch center of the outer tank 7 and a valve positioned above the top of the outer tank 7;

in this embodiment, the replacement air intake pipe 5 is composed of an air intake pipe vertical pipe 501 from the dome of the outer tank 7 to the bottom of the inner tank 8, an air intake pipe horizontal pipe 503 located at the bottom of the inner tank 8, an air intake pipe annular pipe 502 located at the bottom of the inner tank 8, and a valve located above the top of the outer tank 7, where the diameter of the air intake pipe annular pipe 502 is about half of the diameter of the inner tank, and a plurality of air intake pipe openings 504 are provided below the air intake pipe annular pipe 502;

in this embodiment, the thermal-corner protection exhaust pipe 6 is composed of a vertical pipe extending from the top of the outer tank 7 to the bottom of the thermal-corner protection 16 space, a horizontal pipe extending horizontally to the central insulating layer of the storage tank, and a valve above the top of the outer tank 7, wherein the end of the horizontal pipe is located at the center of the storage tank and is connected with the exhaust grille 14;

in this embodiment, the pressure-bearing ring 12 at the bottom of the inner tank is provided with a plurality of ventilation holes 15, so that the gas phase space between the outer tank 7 and the inner tank 8 is communicated with the gas phase of the heat-insulating space at the bottom of the inner tank 8;

in this embodiment, the exhaust grille 14 is cylindrical, and a plurality of grids are disposed on the wall of the exhaust grille 14 for ventilation, the glass wool is filled in the exhaust grille 14 for heat insulation and cold insulation, and ventilation is ensured, and the bottom of the exhaust grille 14 is respectively communicated with the horizontal pipeline of the bottom heat insulation exhaust pipe 2 and the horizontal pipeline of the thermal angle protection exhaust pipe 3;

in this embodiment, a nitrogen replacement structure of a large-sized low-temperature full-capacity tank and a method thereof include the following steps:

step 1): closing valves of an annular space exhaust pipe, a bottom heat-insulating exhaust pipe and a thermal angle protection exhaust pipe, opening a high-point blow-down pipe valve, opening a replacement air inlet pipe valve, controlling air inflow and air displacement of replacement air through the opening of the valve, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of exhaust gas at the high-point blow-down pipe valve every 12 hours until the corresponding detection values are lower than technical requirements, and enabling the gas phase replacement of the inner tank space and the top space of an outer tank to be qualified;

step 2): and opening an annular space exhaust pipe valve, enabling nitrogen to enter the top of the annular space between the inner tank and the outer tank through the perlite retaining wall of the dome space of the outer tank, enabling air flow to flow from the top to the bottom along with pressure difference, entering a horizontal pipeline of the annular space exhaust pipe, and then discharging out of the tank along a vertical pipeline. After the air is observed to be discharged, closing a high-point blow-down pipe valve, controlling air inflow and air displacement through the opening of the valve, ensuring that the pressure of the storage tank is controlled within a required range, detecting the dew point and the oxygen content of the exhaust gas at the position of the annular space exhaust pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and ensuring that the annular space between the inner tank and the outer tank is qualified in gas phase replacement;

step 3): opening a bottom heat-insulating exhaust pipe valve, enabling qualified displacement air of an annular space between an inner tank and an outer tank to enter the bottom heat-insulating space through a vent hole on a bearing ring at the bottom of the inner tank, enabling the annular space to enter an exhaust grid positioned at the center of the tank along a gap between glass bricks, enabling the annular space to be discharged outside the tank along the bottom heat-insulating exhaust pipe, observing that the bottom heat-insulating exhaust pipe is discharged with air, closing the annular space exhaust pipe valve, controlling air inflow and air displacement through the opening of the valve, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of exhaust gas at the bottom heat-insulating exhaust pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and enabling the bottom heat-insulating layer of the inner tank to be displaced to be qualified;

step 4): and opening a hot angle protection exhaust pipe valve, wherein qualified replacement gas in the gas phase space at the top of the outer tank passes through a horizontal pipe orifice of the hot angle protection balance pipe at the top of the outer tank, enters the hot angle protection balance pipe, uniformly enters the hot angle protection top space along a horizontal annular pipe of the hot angle protection balance pipe, enters an exhaust grid positioned at the center of the tank along a gap between glass bricks, is discharged out of the tank along the hot angle protection exhaust pipe, and closes the hot angle protection exhaust pipe valve after the gas is observed to be discharged.

Step 5): and controlling the pressure of the storage tank to be 8-10kPa, closing the replacement air inlet valve, and ending the storage tank replacement.

Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited to the embodiments described above, but is capable of modification and variation without departing from the spirit and scope of the present invention.

Claims (9)

1. The nitrogen replacement structure of the large low-temperature full-capacity tank is characterized by comprising an outer tank (7), an inner tank (8), a thermal angle protection (16), foam glass bricks (10), expanded perlite (9), glass wool (11), an annular space exhaust pipe (1), a bottom heat insulation exhaust pipe (2), a thermal angle protection balance pipe (3), a high-point blow-down pipe (4), a replacement air inlet pipe (5), a thermal angle protection exhaust pipe (6), an inner tank bottom bearing ring (12) and an exhaust grid (14), wherein vent holes (15) are formed in the inner tank bottom bearing ring (12); the outer tank (7), the inner tank (8), the thermal angle protection (16), the foam glass bricks (10), the expanded perlite (9) and the glass wool (11) form a low-temperature full-volume tank body together; the annular space exhaust pipe (1), the bottom heat insulation exhaust pipe (2), the hot angle protection balance pipe (3), the high-point blow-down pipe (4), the replacement air inlet pipe (5), the hot angle protection exhaust pipe (6), the exhaust grid (14) and the vent holes (15) form a nitrogen replacement structure of the low-temperature full-volume tank together; nitrogen enters the inner tank (8) through the replacement air inlet pipe (5), and the high-point blow-down pipe (4), the annular space exhaust pipe (1), the bottom heat insulation exhaust pipe (2) and the hot angle protection exhaust pipe (6) are gradually opened to exhaust, so that air corresponding to each area in the tank is gradually replaced to the nitrogen with qualified dew point and oxygen content; the thermal angle protection balance pipe (3) is composed of a balance pipe horizontal pipeline (302) from a vault space of the outer tank (7) to an annular space between the inner tank (8) and the outer tank (7), a balance pipe vertical pipeline (303) from the top of the annular space between the inner tank (8) and the outer tank (7) to the top of the thermal angle protection (16) and a balance pipe annular pipeline (301) positioned in the top space of the thermal angle protection (16), wherein a group of balance pipe openings (304) are formed in the top of the balance pipe annular pipeline (301), and the glass wool (11) is wrapped for carrying out heat insulation and cold preservation on local parts, and meanwhile ventilation is guaranteed.

2. The nitrogen replacement structure of a large-sized low-temperature full-volume tank according to claim 1, wherein the annular space exhaust pipe (1) is composed of an exhaust pipe vertical pipeline (101) from the top of the outer tank (7) to the bottom of the annular space between the inner tank (8) and the outer tank (7), an exhaust pipe annular pipeline (102) positioned at the bottom of the annular space between the inner tank (8) and the outer tank (7) and a valve above the top of the outer tank (7), exhaust pipe openings (103) are arranged on two horizontal sides of the exhaust pipe annular pipeline (102) for ventilation, and glass fiber cloth (13) is wrapped outside the exhaust pipe annular pipeline (102) for blocking the expanded perlite (9) from drifting away along with air flow from the exhaust pipe openings (103) and guaranteeing ventilation.

3. A large cryogenic full tank nitrogen displacement structure according to claim 1, characterized in that the bottom insulating exhaust pipe (2) consists of a vertical pipe from the top of the outer tank (7) to the bottom of the annular space between the inner tank (8) and the outer tank (7), a horizontal pipe extending horizontally from the bottom of the annular space between the inner tank (8) and the outer tank (7) above the thermal corner protection (16) to a tank center insulating layer and a valve above the top of the outer tank (7), the horizontal pipe ends of which are located in the tank center, connected to the exhaust grill (14).

4. A large cryogenic full tank nitrogen displacement structure according to claim 1, characterized in that the high point blow down pipe (4) consists of a vertical pipe connected to the highest point of the centre of the dome of the outer tank (7) and a valve located above the top of the outer tank (7).

5. The nitrogen replacement structure of a large-sized low-temperature full-capacity tank according to claim 1, wherein the replacement air inlet pipe (5) is composed of an air inlet pipe vertical pipeline (501) from a vault of the outer tank (7) to the bottom of the inner tank (8), an air inlet pipe horizontal pipeline (503) positioned at the bottom of the inner tank (8), an air inlet pipe annular pipeline (502) positioned at the bottom of the inner tank (8) and a valve positioned above the top of the outer tank (7), the diameter of the air inlet pipe annular pipeline (502) is half that of the inner tank (8), and an air inlet pipe opening (504) is arranged below the air inlet pipe annular pipeline (502).

6. A large cryogenic full tank nitrogen displacement structure according to claim 1, characterized in that the thermal corner protection stack (6) consists of a vertical pipe from the top of the outer tank (7) to the bottom of the thermal corner protection (16) space, a horizontal pipe extending horizontally to the tank center insulation and a valve above the top of the outer tank (7), the horizontal pipe end of which is located in the tank center, connected to the exhaust grill (14).

7. The nitrogen replacement structure of the large low-temperature full-capacity tank according to claim 1, wherein the exhaust grid (14) is cylindrical, a grid is arranged on the cylinder wall of the exhaust grid for ventilation, the glass wool (11) is filled in the exhaust grid (14) for heat insulation and cold insulation, ventilation is ensured, and the bottom of the exhaust grid (14) is respectively communicated with a horizontal pipeline of the bottom heat insulation exhaust pipe (2) and a horizontal pipeline of the hot angle protection exhaust pipe (6).

8. A large-scale cryogenic full tank nitrogen displacement structure according to claim 1, characterized in that the outer tank (7) is made of cryogenic steel or is composed of prestressed concrete and steel lining; the inner tank (8) is made of low-temperature steel, the top of the inner tank is of a flat suspended ceiling structure, balance holes for balancing gas-phase pressure in the space of the inner tank (8) and the space of the vault of the outer tank (7) are formed in the top of the inner tank, and the inner tank is integrally covered with glass wool for heat insulation and cold insulation.

9. The nitrogen substitution method of a nitrogen substitution structure of a large-sized low temperature full tank according to any one of claims 1 to 8, comprising the steps of:

step 1), closing valves of an annular space exhaust pipe, a bottom heat insulation exhaust pipe and a thermal angle protection exhaust pipe, opening a high-point blow-down pipe valve, opening a replacement air inlet pipe valve, controlling air inflow and air displacement of replacement air through valve opening, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of the exhaust gas at the high-point blow-down pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and enabling the gas phase replacement of the inner tank space and the top space of an outer tank to be qualified;

step 2) opening an annular space exhaust pipe valve, enabling nitrogen to enter the top of an annular space between an inner tank and an outer tank through an expanded perlite retaining wall of a dome space of the outer tank, enabling air flow to flow from the top to the bottom along with pressure difference, entering an exhaust pipe horizontal pipeline of the annular space exhaust pipe, and then discharging the air out of the tank along an exhaust pipe vertical pipeline; after the air is observed to be discharged, closing a high-point blow-down pipe valve, controlling air inflow and air displacement through the opening of the valve, ensuring that the pressure of the storage tank is controlled within a required range, detecting the dew point and the oxygen content of the exhaust gas at the position of the annular space exhaust pipe valve every 12 hours until the corresponding detection value is lower than the technical requirement, and ensuring that the annular space between the inner tank and the outer tank is qualified in gas phase replacement;

step 3) opening a bottom heat-insulating exhaust pipe valve, enabling qualified displacement air of an annular space between an inner tank and an outer tank to enter the bottom heat-insulating space through a vent hole on a bearing ring at the bottom of the inner tank, enabling the annular space to enter an exhaust grid positioned at the center of the tank along a gap between foam glass bricks, then discharging the annular space along the bottom heat-insulating exhaust pipe, after observing that the bottom heat-insulating exhaust pipe is discharged with air outside the tank, closing the annular space exhaust pipe valve, controlling air inflow and air displacement through valve opening, ensuring that the pressure of a storage tank is controlled within a required range, detecting the dew point and the oxygen content of exhaust at the bottom heat-insulating exhaust pipe valve every 12 hours until corresponding detection values are lower than technical requirements, and enabling the bottom heat-insulating layer of the inner tank to be displaced to be qualified;

step 4) opening a hot angle protection exhaust pipe valve, wherein qualified replacement gas in a gas phase space at the top of an outer tank passes through a horizontal pipe orifice of a hot angle protection balance pipe at the top of the outer tank, enters the hot angle protection balance pipe, uniformly enters the hot angle protection top space along a balance pipe horizontal annular pipe of the hot angle protection balance pipe, enters an exhaust grid at the center of the tank along a gap between glass bricks, is discharged out of the tank along the hot angle protection exhaust pipe, and closes the hot angle protection exhaust pipe valve after the discharge of gas is observed;

and 5) controlling the pressure of the storage tank to be 8-10kPa, closing a replacement air inlet pipe valve, and ending the replacement of the storage tank.