RU2232342C1 - Underground liquefied natural gas storage tank - Google Patents

Abstract

FIELD: underground storage tanks for liquefied natural gas reservation, storage and distribution.

SUBSTANCE: storage tank is arranged below ground level in area preventing ground surface freezing during the longest storage period of liquefied natural gas. Storage tank includes bearing reinforced concrete reservoir supported by base formed of compacted ground. Reservoir is heat-insulated and protected against liquefied natural gas penetration. Pipelines for filling and discharging liquefied natural gas are arranged in service well extending from reservoir to ground surface. Service well has air-tight hatches and ladder. Side reservoir walls are surrounded by pliable concrete heat-insulation wall of "wall-into-ground" type for protection reservoir against ground effect. Upper part of reservoir is covered, for example filled, with heat-insulation material.

EFFECT: increased economy, enhanced protection against fire and explosion, possibility of storing large quantities of liquefied natural gas with decreased daily loses thereof.

2 cl, 1 dwg

Description

The invention relates to an underground LNG storage and backup system, namely, economical fire and explosion-proof storage facilities located below ground level, and can be used to accumulate and issue LNG to consumers, especially where pipeline natural gas is insufficient or completely absent, and also for coating peak gas consumption (in the “peak shaving” system).

Known metal cryogenic tank [1], containing a double metal wall with a screen-vacuum or powder-vacuum thermal insulation and a cryogenic piping system with shutoff and control valves.

The disadvantages of the known device according to [1] are:

- the complexity and inappropriateness of the manufacture of large tanks in view of the sharp increase in their cost;

- low reliability of vacuum thermal insulation (especially tanks of large capacity) and the constant need for control and restoration of vacuum;

- a relatively constant coefficient of thermal conductivity of the thermal insulation of the tank, depending on the seasonal fluctuation of the ambient temperature;

- the possibility of complete catastrophic destruction of the reservoir as a result of geekhnogenic activity or sabotage acts.

A ground metal cryogenic tank [2] is known, containing a double metal wall with “non-vacuum” thermal insulation (heat-insulating mats, or “filling”).

The disadvantages of the known device according to [2] are:

- the high cost of the tank due to the high cost of metal;

- low efficiency of the thermal insulation of the tank with a variable coefficient of its thermal conductivity (depending on the ambient temperature), which causes a large evaporation of the gas, especially in the warm season;

- the possibility of complete catastrophic destruction of the reservoir as a result of industrial activity or sabotage acts.

Known semi-buried metal (aluminum) cryogenic tank [3], containing a single spherical metal wall with external thermal insulation of foam and polyurethane installed in a concrete cylindrical pit, closed with a concrete dome, the cryogenic tank is equipped with a cryogenic pipeline system with shut-off and control valves introduced into the upper parts of the tank.

The disadvantages of the known device according to [3] are:

- the high cost of the tank due to the high cost of non-ferrous metal;

- the tank insulation works with a constant coefficient of thermal conductivity and allows freezing of the surface layers of the earth and the concrete dome, which is environmentally unsafe, in addition, periodic seasonal freezing of the soil causes it to heave and destroy the structure of the concrete dome and lining the structure;

- the presence of an air gap (intermediate space) between the concrete lining and thermal insulation leads to additional costs for the maintenance and operation of a semi-buried LNG storage, as well as leads to unreasonable (irrational) use of the underground space of a concrete cylindrical foundation pit for storing LNG and an increase in the cost of the storage as a whole.

Known storage for LNG [4], located below ground level, in frozen soil without lining and without heat and waterproofing, consisting of a cylindrical (or hemispherical) pit, covered with a domed metal roof (for example, low alloy steel) with a heat insulating layer.

The disadvantages of the known device according to [4] are:

- a constant surface frozen soil layer and its periodic seasonal thawing away from the storage, which leads to soil heaving;

- low reliability of the storage due to the possible thawing of its upper layers with small amounts of stored LNG;

- large losses of gas during its storage due to cracking of the soil;

- “non-ecological” due to freezing of the upper layers of the soil with their subsequent heaving;

- the complexity of the control of the stored product.

The prototype of the present invention is a buried liquefied natural gas storage [5], the upper edge of which is located at the level of the earth’s surface and bunded or located slightly below ground level (there are many designs of storage of this type), containing on the base bearing concrete tank, insulated and waterproofed from LNG and equipped with pipelines for filling-issuing LNG and its vapor.

The disadvantages of the prototype are:

- restriction of placement in various soils due to their heaving or the use of an expensive ventilation system and heating of the LNG tank, which dramatically increases the constant heat gain and LNG evaporation, as well as increases the energy consumption for the operation of the storage;

- low fire and explosion hazard as a result of industrial activity or possible acts of sabotage, as a result of which the storage dome (large volumes) may be damaged;

- a large percentage of gas evaporation per day due to large variable heat inflows from the atmospheric air from the dome and near-surface soil layers.

The indicated drawbacks of the above analogues and prototype set the task of increasing the efficiency of the LNG storage, namely, the creation of a safe and reliable LNG storage with low daily losses of the stored product (preferably for underground storages of large and extra large volumes).

These tasks are achieved by the below-described underground storage facility (a storage facility located below ground level) of liquefied natural gas containing a supported (located) base bearing reinforced concrete tank, thermally insulated and waterproofed (from LNG) and equipped with pipelines for filling and dispensing LNG and its vapors; a reinforced concrete tank is located below ground level at a mark that prevents freezing of the earth's surface (and the surface layer of the earth), during the longest estimated storage of LNG, the base for the tank is made of compacted soil and a heat-insulating layer. At the same time, pipelines for filling and dispensing LNG and its vapors are located in the technological shaft extending from the tank to the surface of the earth, and the technological shaft itself additionally contains hermetic hatches and a ladder designed for access to the tank and for possible inspection, maintenance and repair. The side walls of the reinforced concrete tank from the soil mass are perimeter protected by a compliant layer with a concrete wall-to-ground thermal insulation wall, and the top of the concrete tank is covered (covered) with a layer of heat-insulating material (the top of the filled heat-insulating layer is covered with a soil layer).

The location of the reinforced concrete reservoir of LNG storage facility below the ground level at the level that prevents freezing of the earth's surface, with the longest estimated storage of LNG is necessary to ensure:

firstly, fire and explosion safety, which is provided by deepening the LNG storage tank below the ground level (approximately 15-20 meters);

secondly, environmental safety (and safety when avoiding heaving near-surface nearby soils), which is achieved by locating the LNG storage tank at a mark that prevents freezing of the earth’s surface during the longest estimated storage of LNG, that is (in other words) the absence of zero isotherm on the earth’s surface;

thirdly, to ensure efficient storage of LNG (with low heat inflows and LNG evaporation), with constantly decreasing heat inflows and daily gas losses.

The introduction of the base under the tank, made, for example, of compacted crushed stone and sand preparation and a heat-insulating layer, is necessary for:

- uniform redistribution of load under the sole of the base of the tank on the underlying soil layers;

- reduction of stresses arising under the bottom of the tank during freezing and freezing of the soil during the period of cooling and operation of the LNG storage;

- reducing heat inflows to stored LNG;

- reducing the likelihood of freezing underground layers of soil and underground water flows.

The introduction of a technological mine leaving the reservoir to the earth’s surface with pipelines located in it for filling and dispensing LNG and its vapors (also possible auxiliary communications and pipelines) is necessary for installation, routine inspections and maintenance, repairs of cryogenic pipelines with shut-off and control valves, as well as to determine the temperature state of the soil above the LNG tank.

The introduction of airtight manholes (at least two) and ladders into the technological shaft is necessary for access to the technological shaft and tank for possible inspection, maintenance and repair, as well as for unforeseen and emergency situations.

The introduction of a concrete heat-insulating wall of the type “wall in the ground” and a compliant layer between the “wall in the ground” and the concrete tank is necessary:

- to protect the tank around the perimeter from displacements of the soil mass during the construction of the LNG storage facility;

- for additional perception of the loads arising on the walls of the tank from the soil mass during the freezing process (HRP LNG and soil mass) and the operation of HRP LNG;

- for additional thermal insulation of the storage facility, which reduces the freezing of soil and heat influx from the latter to the LNG storage facility and, therefore, reduces the evaporation of LNG from the storage facility.

The introduction of a covering (falling asleep) layer of heat-insulating material in the upper part of the tank is necessary for additional thermal insulation of the storage, which thereby prevents heat inflow from the upper layers of the soil (and the surface of the earth) to the storage, stopping the “freezing” of the soil on the surface of the earth and reducing LNG evaporation from the storage.

The reinforced concrete tank can be made of reinforced high-strength concrete, have straight (cylindrical) walls and convex ends and can be located vertically or horizontally on a prepared sand-gravel base with a heat-insulating layer.

Waterproofing prevents the penetration of LNG into the insulation and material of the reinforced concrete tank and can, for example, be made of sheet steel or in the form of a “membrane”.

The implementation of LNG storage tanks in combination with the foregoing features (distinguishing features of the claims) is new for LNG storages and, therefore, meets the criterion of “novelty”.

The above set of distinctive features is unknown at this level of technological development and does not follow from the well-known rules for the design of LNG storages and their auxiliary equipment, which proves compliance with the criterion of “inventive step”.

The constructive implementation of LNG storages with the indicated set of essential features does not present any structural, technical and technological difficulties, which implies compliance with the criterion of “industrial applicability”.

The drawing shows a view of the underground storage of LNG.

The LNG storage facility located below ground level 1 at a point that prevents freezing of the earth’s surface during the longest estimated storage of LNG, contains a reinforced concrete tank 3 with thermal insulation 4 and waterproofing 5 from LNG supported on a heat-insulating base 2. The reinforced concrete tank 3 is equipped (equipped) with a system of cryogenic pipelines 6 for filling and dispensing LNG and its vapors, as well as additional process pipelines and communications (measuring, purging, automation systems, safety systems, etc.). The heat-insulating base 2 for the tank 3 is made of compacted soil (possibly compacted crushed stone and sand) and a heat-insulating layer 7. The side walls of the tank 3 from the soil mass along the perimeter are fenced through a flexible layer 8 with a concrete wall 9 of the “wall in soil” type, and the top of the tank 3 is covered (filled) with 1 layer of heat-insulating material 10. Pipelines 6 for filling and dispensing LNG and its vapors are located in the technological shaft 11, which leaves the tank 3 to the surface of the earth 1, the technological shaft 11 additionally holds hermetic hatches 12 (located at least on the concrete tank and on top of the technological shaft) and a ladder 13, one part of which is located in the technological shaft 11, and the other in the concrete tank 3 itself.

The LNG storage facility should be used after the completion of its construction of the underground and ground parts, when the entire volume of pipeline and shut-off and control valves has been mounted, as well as after a full range of verification and testing works and handing over to the state supervisory authorities. LNG is supplied via the filling pipeline (piping system 6) of the storage (preferably with simultaneous filling from above and below for uniform cooling). In the initial period of cooling the tank 3 and freezing the soil, there are large heat inflows from the soil, but over time, during further filling of the tank 3, heat inflows decrease due to a constant decrease in temperature around the storage, and subsequently the soil freezes constantly (with a decrease in heat inflows to LNG). The tank is filled at 85-90% of its usable volume. Depending on the volume of the tank, after a certain time, a stationary heat conduction process is established in it, in which the entire structure of the tank reaches constant negative (cryogenic) temperatures. Inside the tank 3 is maintained constant cryogenic temperature and pressure (slightly more than atmospheric). LNG is taken from reservoir 3 through a pipeline (cryogenic piping system 6) to the consumer. The compliant layer acts as a compensator, which reduces the pressure of the soil on the tank in a stationary mode of operation. Through hermetic hatches 12 and a ladder 11 located in the technological shaft, access is made to the tank (when it is heated and ventilated by air) and possible inspections, services and repairs are carried out.

The technical and economic advantage of the invention lies in the fact that, in comparison with the prototype, the proposed version of the underground LNG storage does not have direct contact with the atmosphere (which leads to constantly decreasing losses of LNG from evaporation) and has a high degree of fire and explosion safety both in operating conditions and during accidents and various industrial impacts; It has environmental safety for long periods of storage of LNG and storage operation; It has wide possibilities of placement on the territory of Russia in a variety of soil conditions; has a large range of LNG storage volumes. Improving safety, reliability and durability is achieved by the location of the tank to a depth that protects the tank from possible destruction as a result of man-caused activity or sabotage acts, as well as preventing soil heaving above the tank,

Sources of information

1. A.S. USSR No. 374482, cl. F 17 on 3/08, 03/20/1973, Bull. No. 15.

2. Gas industry, No. 18, 1967. Production, transportation, storage and regasification of LNG abroad, p. 33, Fig. 3.

3. EUROIL MAY, LNG storage tank in rock excavation. 1990, p. 37.

4. N.G. Trupak. Soil freezing in construction. - M.: Stroyizdat, 1970, p. 216, Fig. 123.

5. Gas industry, No. 18, 1967. Production, transportation, storage and regasification of LNG abroad, p. 36, Fig. 5.

Claims (2)

1. An underground storage facility (LNG) of liquefied natural gas (LNG) located below ground level, containing a reinforced concrete tank located on the base, insulated and waterproofed from LNG and equipped with pipelines for filling and dispensing LNG and its vapors, characterized in that the reinforced concrete tank located below ground level at a mark that prevents freezing of the earth's surface during the longest estimated storage of LNG, the base for the tank is made of compacted soil and heat-insulating osloyki, piping for filling, dispensing LNG and vapor in the processing shaft disposed exiting from the reservoir to the surface, and the process further comprises a shaft airtight hatches and stairs. 2. The LNG underground storage facility according to claim 1, characterized in that the side walls of the reinforced concrete tank from the soil mass along the perimeter are fenced through a compliant layer with a “wall in soil” concrete heat-insulating wall, and the top of the concrete tank is covered (covered) with a layer of heat-insulating material.