KR20180000868A - Liquefied gas storage tank, method of manufacturing the same, and apparatus for manufacturing insulation member - Google Patents

Abstract

A liquefied gas storage tank, a method of manufacturing the same, and an apparatus for manufacturing an insulating member are disclosed. A liquefied gas storage tank according to an embodiment of the present invention includes a primary barrier surrounding an accommodating space of a liquefied gas; A primary insulation panel surrounding the primary barrier and including a primary insulation member for insulating the liquefied gas from the outside; A secondary barrier surrounding the primary insulation panel; And a secondary insulation panel which is installed in the inner hull and surrounds the secondary barrier and which is insulated against the outside. The primary heat insulating member is provided so as to have a density gradient decreasing from the primary barrier side toward the secondary barrier side and the secondary heat insulating member is provided so as to have a density gradient increasing from the secondary barrier side toward the inner hull side do. According to the embodiment of the present invention, the structural strength and the heat insulation performance of the liquefied gas storage tank can be secured at the same time, and the primary insulation panel and the secondary insulation panel can be manufactured economically and efficiently, Time can be saved.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquefied gas storage tank, a method of manufacturing the same, and an apparatus for manufacturing an adiabatic member,

The present invention relates to a liquefied gas storage tank, a method of manufacturing the same, and an apparatus for manufacturing an insulating member.

Liquefied natural gas (LNG) is a liquid state material in which natural gas containing methane as a main component is cooled to -163 ° C or lower and its volume is reduced to 1/600. LNG storage tanks that store LNG are made of structures and materials that can withstand cryogenic temperatures due to gas liquefaction. LNG storage tanks have a specially designed structure to withstand various loads such as temperature difference / sloshing / hull deformation. The LNG storage tank is formed in a double-sealed structure including, for example, a primary barrier, a primary insulation panel, a secondary barrier, and a secondary insulation panel. The primary barrier contacts the LNG to seal the LNG first. The secondary barrier functions to seal the leaked LNG to prevent the LNG from touching the inner hull when the LNG leaks from the primary barrier.

LNG storage tanks are important not only for cooling and insulation performance to keep liquefied gas at low temperature, but also to ensure structural safety against various loads. The insulation performance of LNG storage tanks is mostly determined by the primary insulation panels made of polyurethane foam and the secondary insulation panels. The heat insulating performance of the heat insulating panel and the structural strength depend on the density thereof. Since the density of the heat insulating material satisfying the allowable strength of the LNG storage tank and the density of the heat insulating material having the maximum heat insulating performance do not coincide with each other, the heat insulating and cooling performance is deteriorated when a high density heat insulating material is applied. On the contrary, when a low-density heat insulating material is applied, a high stress is generated in the secondary insulating panel of the portion adjacent to the mastic where a strong sloshing load acts or the primary insulating panel of the primary wall, and a large thermal expansion of the insulating material and the plywood The thermal stress may be excessively generated due to the difference in coefficient, and the insulation may be damaged.

The present invention provides a liquefied gas storage tank, a method of manufacturing the same, and an apparatus for manufacturing a heat insulating member capable of securing structural strength and heat insulating performance at the same time.

Another object of the present invention is to reduce the manufacturing cost and time of the liquefied gas storage tank by manufacturing the primary insulation panel and the secondary insulation panel economically and efficiently.

The problems to be solved by the present invention are not limited to the above-mentioned problems. Other technical subjects not mentioned will be apparent to those skilled in the art from the description below.

A liquefied gas storage tank according to an aspect of the present invention includes a primary barrier surrounding an accommodating space of a liquefied gas; A primary insulation panel surrounding the primary barrier and including a primary insulation member for insulating the liquefied gas from the outside; A secondary barrier surrounding the primary insulation panel; And a secondary insulation panel installed in the inner hull and including a secondary insulation member surrounding the secondary barrier and insulated from the outside, wherein the primary insulation member is disposed on the secondary barrier, And the secondary insulating member may be provided so as to have a density gradient increasing in a direction from the secondary barrier side toward the inner hull side.

Wherein the primary heat insulating member is coupled between the first upper reinforcing plate and the first lower reinforcing plate and the secondary heat insulating member is coupled between the second upper reinforcing plate and the second lower reinforcing plate, Wherein the first upper region as the first upper reinforcing plate is made of a polyurethane foam having a first density and the first lower region as the first lower reinforcing plate is a polyurethane having a second density lower than the first density, Wherein the second heat insulating member is made of a polyurethane foam having the second density and the second lower region being the side of the second lower reinforcing plate is made of polyurethane foam having the second density, And may be made of a polyurethane foam having a first density.

The first density may be 100 kg / m < ³ >, and the second density may be 40 kg / m < ³ >.

Wherein the primary insulating member is comprised of a single foamed layer having a first density gradient and is coupled between the first upper stiffening plate and the first lower stiffening plate and the secondary insulating member has a single density having a second density gradient, And a foam layer, and may be coupled between the second upper reinforcing plate and the second lower reinforcing plate.

The primary heat insulating member and the secondary heat insulating member may be formed to have a density gradient that is vertically symmetrical.

According to another aspect of the present invention, there is provided an apparatus for manufacturing a heat insulating member having a density gradient in the up-and-down direction, comprising: a wind-up roll on which glass fibers are wound; A conveyor for conveying the glass fiber unwound from the winding roll; A high density foam dispenser provided on an upper side of the conveyor and for spraying a first foam material for foaming a first polyurethane foam having a first density onto the glass fiber; And a second foam material provided on an upper side of the conveyor for foaming a second polyurethane foam of a second density lower than the first density on the first polyurethane foam, And a low-density foam spraying section for spraying the low-density foam sprayed from the spray nozzle.

Wherein the high-density foam jetting portion includes: a high-density foam jetting nozzle for jetting the first foam material containing polyols and isocyanate at a higher concentration than the second foam material onto the glass fiber, The low density foam injection portion includes: a low density foam injection nozzle for spraying the second foam material containing polyols and isocyanate at a lower concentration than the first foam material onto the first foam material, The low-density foam spray nozzle may be installed on the front side of the high-density foam spray nozzle with respect to the transport direction of the glass fiber, and may be installed at a higher position than the high-density foam spray nozzle.

According to another aspect of the present invention, there is provided a method of manufacturing a liquefied gas storage tank in which a primary barrier, a primary insulation panel, a secondary barrier, and a secondary insulation panel are laminated from a receiving space of a liquefied gas to an inner hull side, Spraying a first foam material to foam a first polyurethane foam having a first density on the first polyurethane foam; Spraying a second foam material onto the first foam material for foaming a second polyurethane foam of a second density lower than the first density on the first polyurethane foam; Foaming the first foam material and the second foam material sprayed on the glass fiber to produce a first heat insulating member and a second heat insulating member having a density gradient in the vertical direction; Machining the first heat insulating member and the second heat insulating member and joining the reinforcing plate to manufacture the first heat insulating panel and the second heat insulating panel; Installing the secondary insulation panel on the inner hull so as to have a density gradient increasing in a direction from the secondary barrier to the inner hull; Installing the secondary barrier on the secondary insulation panel; Installing the primary insulation panel on the secondary barrier so as to have a density gradient lowering in a direction from the primary barrier side toward the secondary barrier side; And installing a primary barrier on the primary adiabatic panel.

Wherein the primary insulation panel and the secondary insulation panel are manufactured by: bonding the primary insulation member made of a single foam layer having a first density gradient between the first upper reinforcement plate and the first lower reinforcement plate that; And bonding the secondary insulation member made of a single foam layer having a second density gradient between the second upper reinforcement plate and the second lower reinforcement plate.

According to the embodiment of the present invention, there is provided a liquefied gas storage tank, a method of manufacturing the same, and an apparatus for manufacturing a heat insulating member, which can secure structural strength and heat insulating performance at the same time.

Further, according to this embodiment, it is possible to economically and efficiently manufacture the primary insulation panel and the secondary insulation panel, thereby saving manufacturing cost and time of the liquefied gas storage tank.

The effects of the present invention are not limited to the effects described above. Unless stated, the effects will be apparent to those skilled in the art from the description and the accompanying drawings.

1 is a schematic partial cutaway perspective view of a liquefied natural gas storage tank according to one embodiment of the present invention.
2 is an enlarged cross-sectional view of the portion 'A' of FIG.
3 is a schematic view showing an apparatus for manufacturing a heat insulating member according to an embodiment of the present invention.
4 is a flowchart showing a process of manufacturing an insulating member according to an embodiment of the present invention.
5 to 7 are views for explaining the operation of the heat insulating member manufacturing apparatus according to the embodiment of the present invention.

Other advantages and features of the present invention and methods of achieving them will be apparent by referring to the embodiments described hereinafter in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and the present invention is only defined by the scope of the claims. Although not defined, all terms (including technical or scientific terms) used herein have the same meaning as commonly accepted by the generic art in the prior art to which this invention belongs. A general description of known configurations may be omitted so as not to obscure the gist of the present invention. In the drawings of the present invention, the same reference numerals are used as many as possible for the same or corresponding configurations. To facilitate understanding of the present invention, some configurations in the figures may be shown somewhat exaggerated or reduced.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises", "having", or "having" are intended to specify the presence of stated features, integers, steps, operations, components, Steps, operations, elements, parts, or combinations thereof, whether or not explicitly described or implied by the accompanying claims.

The liquefied gas storage tank according to the embodiment of the present invention is characterized in that the primary heat insulating member is made of a single foamed layer having a density gradient lowered in the direction from the primary wall side to the secondary wall side, And a single foamed layer having a density gradient increasing in the direction from the side of the barrier to the side of the inner hull.

According to the embodiment of the present invention, by applying the primary heat insulating member and the secondary heat insulating member of the single foam layer having the density gradient, the high density region and the low density region of each of the primary heat insulating member and the secondary heat insulating member, The heat insulation performance can be secured at the same time, and the primary insulation panel and the secondary insulation panel can be manufactured economically and efficiently, thereby saving manufacturing cost and time of the liquefied gas storage tank.

The liquefied gas storage tank according to the embodiment of the present invention can be used to store liquefied gas such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), and the like. Hereinafter, a liquefied gas storage tank according to an embodiment of the present invention will be described by taking a liquefied natural gas storage tank as an example.

1 is a schematic partial cutaway perspective view of a liquefied natural gas storage tank according to one embodiment of the present invention. 2 is an enlarged cross-sectional view of the portion 'A' of FIG. 1 and 2, the LNG storage tank includes a primary barrier 50, a primary insulation panel 30, a secondary barrier 40, and a secondary barrier 40 toward the inner hull 10 from a receiving space in which the LNG is stored. And a secondary insulation panel 20 in which the secondary insulation panels 20 are sequentially stacked.

The primary barrier 50 is formed to surround the LNG storage space to seal the LNG. The primary barrier 50 may be provided as a membrane formed of a metal resistant to low temperature brittleness such as aluminum alloy, Invar, nickel steel, and stainless steel sheet. The primary barrier 50 may have a wrinkle 51 to accommodate expansion and contraction of the LNG storage tank as the temperature changes. The primary barrier 50 may be installed on the primary insulation panel 30 by a method of welding with a strip (not shown) provided on the upper surface of the primary insulation panel 30. The strip may be secured to the upper surface of the primary insulation panel 30 by a fixing member such as a rivet.

The primary insulation panel 30 is formed so as to surround the primary barrier 50 to insulate the liquefied gas from the outside. The primary thermal insulation panel 30 may be provided as a heat insulation board positioned between the primary barrier 50 and the secondary barrier 40. In one embodiment, the primary heat insulating panel 30 includes a first lower reinforcing plate 31 and a second lower reinforcing plate 31 provided on the secondary barrier 40 by a panel coupling portion such as a bolt / And a first upper reinforcing plate 32 coupled to the primary heat insulating member 33 and the primary heat insulating member 33.

The primary heat insulating panel 30 can be coupled to the secondary heat insulating panel 20 by the fastening portion 25. [ The fastening part 25 is fixed to the secondary heat insulating panel 20 and has stud bolts passing through the through holes of the secondary barrier 40 and the first lower reinforcing plate 31, And a nut coupled to the stud bolt within the hole 30a.

The secondary insulation panel 20 surrounds the secondary barrier 40 and has a function of insulating against the outside. And may be provided as a heat insulating board positioned between the secondary barrier 40 and the inner hull 10. In one embodiment, the secondary insulation panel 20 includes a second lower reinforcement plate 21 fixed to the inner hull 10 by a fixing member (not shown), a second lower reinforcement plate 21 fixed to the second lower reinforcement plate 21 And a second upper reinforcing plate 22 coupled to the secondary heat insulating member 23 and the secondary heat insulating member 23. The secondary insulation panel 20 can be installed on the inner hull 10 via a mastic 11.

The primary heat insulating member 33 and the secondary heat insulating member 23 are formed of a material having excellent heat insulating property such as polyurethane foam to provide heat insulation between the inner hull 10 and the LNG. The first upper reinforcing plate 32, the first lower reinforcing plate 31, the second upper reinforcing plate 22 and the second lower reinforcing plate 21 may be formed of plywood, Thereby giving mechanical rigidity to the heat insulating panel 30 and the secondary thermal insulating panel 20. [

The secondary insulation panels 20 are made of a pre-designed area and placed on the inner hull 10 at a distance from each other. The spacing of the secondary insulating panels 20 can be set within a range that absorbs shrinkage and expansion of the heat insulating board. The primary insulation panels 30 are disposed on the secondary barrier 40 at a distance from each other. The spacing of the primary insulating panels 30 can be set within a range that absorbs shrinkage and expansion of the heat insulating board. The gap between the primary insulating panels 30 and / or between the secondary insulating panels 20 may be filled with a heat insulating material 30b having elasticity such as glass wool.

The secondary barrier 40 is disposed on the upper surface of the secondary insulation panel 20 and is formed so as to surround the primary insulation panel 30. In one embodiment, the secondary barrier 40 may be provided in a triplex formed of a metal composite laminate with metal foil on both sides of a glass-fiber composite . The secondary barrier 40 may have a wrinkle portion 41 to correspond to the expansion and contraction of the LNG storage tank according to the temperature change.

In the embodiment of the present invention, the primary heat insulating member 33 may be provided so as to have a density gradient lowered from the primary barrier 50 side toward the secondary barrier 40 side. The secondary insulating member 23 may be provided so as to have a density gradient increasing from the secondary barrier 40 side toward the inner hull 10 side.

The primary heat insulating member 33 may be a single foamed layer having a first density gradient and may be coupled between the first upper reinforcing plate 32 and the first lower reinforcing plate 31. The secondary thermal insulating member 23 may be composed of a single foam layer having a second density gradient and may be coupled between the second upper reinforcing plate 22 and the second lower reinforcing plate 21. [

In one embodiment, the first heat insulating member 33 is made of a polyurethane foam having a first density (high density) in the first upper region 33a, which is the side of the first upper reinforcing plate 33, (Lower density) lower than the first density is formed of the polyurethane foam.

In one embodiment, the secondary insulation member 23 is made of a polyurethane foam having the second density (low density) and the second upper region 23b, which is the side of the second upper reinforcing plate, The second lower region 23a may be formed of the polyurethane foam having the first density (high density).

The first upper region 33a of the primary heat insulating member 33 and the second lower region 23a of the secondary thermal insulating member 23 are formed of a first density region 33a representing the maximum strength characteristic of the polyurethane foam, , For example, a density of 100 kg / m < ³ >. The first lower region 33b of the primary heat insulating member 33 and the second upper region 23b of the secondary thermal insulating member 23 have a second density representing the maximum heat insulation and cooling characteristics of the polyurethane foam, , And a density of 40 kg / m < ³ >. The primary heat insulating member 33 and the secondary heat insulating member 23 are vertically symmetric with respect to each other so that the single heat insulating member 33 can be used as both the primary heat insulating member 33 and the secondary heat insulating member 23. [ As shown in FIG.

3 is a schematic view showing an apparatus for manufacturing a heat insulating member according to an embodiment of the present invention. 2 and 3, the heat insulating member manufacturing apparatus 100 according to the embodiment of the present invention includes a primary heat insulating member 33 having a density gradient in the vertical direction constituting the liquefied gas storage tank as described above, It may be provided for manufacturing the secondary thermal insulating member 23.

The heat insulating member manufacturing apparatus 100 according to the present embodiment may include a take-up roll 110, a conveyor 120, a high-density foam sprayer 130, and a low-density foam sprayer 140. The winding roll 110 winds the glass fiber 112 and stores it in a wound state. The winding roll 110 may be rotated by a driving unit (not shown). The driving unit may be provided as a driving motor / speed reducer.

The glass fiber 112 wound on the winding roll 110 is released by the driving part and is provided to the conveyor 120. [ The conveyor 120 transports the glass fiber 112 to be unwound from the wind-up roll 110. The conveyor 120 can horizontally transport the glass fiber 112 and the foam material on the glass fiber 112 by a driving motor, a guide roller, and the like.

The high-density foam sprayer 130 is installed on the upper side of the conveyor 120, and injects the first foam material 130a onto the glass fiber 112. [ The first foam material 130a is a foam material for foaming the first polyurethane foam having the first density.

The low density foam jetting section 140 is installed on the upper side of the conveyor 120 and forms a second foam material 140a on the first polyurethane foam 130a in order to foam the second polyurethane foam on the first polyurethane foam 130a . The second foam material 140a is a foam material for foaming a second polyurethane foam of a second density lower than the first density.

The high-density foam sprayer 130 includes a resin premixer 132 for supplying a resin premix containing polyols to the high-density mixer 136, a high-density mixer 136 for supplying isocyanate to the high- A mixed portion 136 for mixing the supplied polyol and isocyanate and a high density foam spray nozzle 138 for spraying the mixed first foam material 130a onto the glass fiber 112 ). The first foam material 130a may be a foam material in which the polyol and isocyanate are contained at a higher concentration than the second foam material 140a.

The low-density foam sprayer 140 includes a resin premixer 142 for supplying a resin premix containing polyols to the low-density mixer 146, a low-density mixer 146 for supplying isocyanate to the low- A mixing portion 146 for mixing the supplied polyol and isocyanate and a low density foam spraying nozzle 146 for spraying the mixed second foam material 140a onto the first foam material 130a, (148). The second foam material 140a may be a foam material in which the polyol and isocyanate are contained at a lower concentration than the first foam material 130a.

Density foaming material 148 is sprayed onto the glass fiber 112 so that a low concentration of the second foam material 140a can be sprayed onto the first foam material 130a after the high concentration of the first foam material 130a is sprayed onto the glass fiber 112. [ Density foam spraying nozzle 138 can be installed on the front side of the high-density foam spraying nozzle 138 with respect to the conveying direction D of the glass fiber 112.

The height H1 can be preset or adjusted according to the amount of the first foam material 130a injected for foaming the first polyurethane foam to a target thickness. The low density foam spray nozzle 148 is configured to spray the second foam material 140a on the first foam material 130a in a stable and uniform manner while the first foam material 130a is sprayed onto the glass fiber 112 Density foaming nozzles so that they have a higher height H2 than the high-density foam spray nozzles.

The height H2 of the low density foam spray nozzle 148 can be preset or adjusted according to the injection amount of the second foam material 140a for foaming the second polyurethane foam to a target thickness. The low density foam spray nozzle 148 may be installed at a position higher than the high density foam spray nozzle 138 by a spray thickness of the second foam material 140a.

FIG. 4 is a flowchart illustrating a process of manufacturing a heat insulating member according to an embodiment of the present invention, and FIGS. 5 to 7 illustrate operations of the heat insulating member manufacturing apparatus according to an embodiment of the present invention. 4, when the glass fiber 112 is unwound from the take-up roll 110 and is conveyed by the conveyor 120 (S10), the high-density foam spray nozzle 138 A first foam material 130a for foaming the polyurethane foam is injected onto the glass fiber 112 (S20).

When the first foam material 130a is injected over the glass fiber 112 by the high-density foam injection nozzle 138 over a certain distance, as shown in Fig. 6, the low-density polyurethane A second foam material 140a for foaming the foam is sprayed onto the first foam material 130a (S30).

As shown in FIG. 7, the first foam material 130a and the second foam material 140a sprayed on the glass fiber 112 are foamed and cured by swelling and hardening, A polyurethane foam having a density gradient is formed (S40). Thereafter, the polyurethane foam is fabricated as a primary heat insulating member 33 and a secondary heat insulating member 33 (S50).

When the primary heat insulating member 33 and the secondary heat insulating member 23 are fabricated, the reinforcing plates 31, 32, 21, 22 are joined to the primary heat insulating member 33 and the secondary heat insulating member 23, The primary insulation panel 30 and the secondary insulation panel 20 are manufactured and the secondary insulation panel 20, the secondary barrier 40 and the primary insulation panel 30 are sequentially formed on the inner hull 10, And the primary barrier 50 are installed to complete the installation work of the liquefied gas storage tank.

At this time, the secondary insulation panel 20 is installed so as to have a density gradient increasing from the side of the secondary barrier 40 toward the side of the internal hull 10, and the primary insulation panel 30 has a primary barrier 50, To the secondary barrier (40) side, as shown in Fig.

According to the embodiment of the present invention, the portion where the sloshing load or the thermal load acts strongly endures the load by the high density foam of the heat insulating member, increases the cooling and heat insulating performance in the low density portion of the heat insulating member, ) Can be lowered.

Further, according to the embodiment of the present invention, it is possible to manufacture a liquefied gas storage tank without complicating the manufacturing process of the heat insulating panel by forming the heat insulating member having a density gradient as a single foam layer, Cost and installation time can be reduced.

In the case of the KC-S cargo window as shown in FIG. 2, since the upper board and the lower board are made of a polyurethane foam having the same thickness, the lower board is installed using the heat insulating member manufactured by the apparatus of FIG. And the upper board can be installed upside down on the heat insulating member manufactured by the apparatus of Fig. 3, so that the increase in installation cost of the primary insulating panel and the secondary thermal insulating panel can be minimized while satisfying the required strength, It is possible to manufacture the cargo hold satisfying all of them.

In the above description, the upper and lower regions of the heat insulating member have different densities to have a density gradient. However, it is also possible that the heat insulating member has three or more different densities and a density gradient. For example, a plurality of foam materials having different densities may be sequentially injected onto the glass fibers and foamed by using three or more injection nozzles to manufacture the heat insulating member.

It is to be understood that the above-described embodiments are provided to facilitate understanding of the present invention, and do not limit the scope of the present invention, and it is to be understood that various modifications are possible within the scope of the present invention. It is to be understood that the technical scope of the present invention should be determined by the technical idea of the claims and the technical scope of protection of the present invention is not limited to the literary description of the claims, To the invention of the invention.

10: Inner Hull 11: Mastic
13: level pad 20: secondary insulation panel
21: second lower reinforcing plate 22: second upper reinforcing plate
22a: groove 23: secondary heat insulating member
23a: second lower region 23b: second upper region
25: fastening part 30: primary insulation panel
30a: Through hole 30b: Insulation
31: first lower reinforcing plate 32: first upper reinforcing plate
33: primary heat insulating member 33a: first upper region
33b: first lower region 40: secondary barrier
41: wrinkle portion 50: primary barrier
51: Crease member 100: Heat insulating member manufacturing apparatus
110: Winding roll 112: Glass fiber
120: Conveyor 130: High density foam dispenser
130a: first foam material 132: resin pre-mix supply part
134: Isocyanate supplying part 136: Mixing part
138: high density foam spray nozzle 140: low density foam sprayer
140a: second foam material 142: resin premix supplier
144: Isocyanate supplying part 146: Mixing part
148: Low density foam spray nozzle

Claims (9)

A primary barrier surrounding the receiving space of the liquefied gas;
A primary insulation panel surrounding the primary barrier and including a primary insulation member for insulating the liquefied gas from the outside;
A secondary barrier surrounding the primary insulation panel; And
And a secondary insulation panel which is installed in the inner hull and surrounds the secondary barrier and which is insulated against the outside,
The primary heat insulating member is provided so as to have a density gradient lowered from the primary barrier side toward the secondary barrier side,
Wherein the secondary insulating member is provided to have a density gradient increasing from the secondary barrier side toward the inner hull side. The method according to claim 1,
The primary heat insulating member is coupled between the first upper reinforcing plate and the first lower reinforcing plate,
The secondary insulating member is coupled between the second upper reinforcing plate and the second lower reinforcing plate,
The primary heat insulating member comprises:
Wherein the first upper region as the first upper reinforcing plate is made of a polyurethane foam having a first density and the first lower region as the first lower reinforcing plate is a polyurethane foam having a second density lower than the first density, Lt; / RTI >
The secondary insulation member comprises:
The second upper region as the second upper reinforcing plate is made of the polyurethane foam having the second density and the second lower region as the second lower reinforcing plate is made of a polyurethane foam having the first density, Storage tank. 3. The method of claim 2,
Wherein the first density is 100 kg / m < ³ >, and the second density is 40 kg / m < ³ >. 3. The method of claim 2,
Wherein the primary heat insulating member comprises a single foam layer having a first density gradient and is coupled between the first upper gusset plate and the first lower gusset plate,
Wherein the secondary insulating member is a single foam layer having a second density gradient and is coupled between the second upper stiffener and the second lower stiffener. The method according to claim 1,
Wherein the primary heat insulating member and the secondary heat insulating member are formed to have a density gradient that is symmetrical with respect to the vertical direction. A heat insulating member manufacturing apparatus for manufacturing a heat insulating member having a density gradient in a vertical direction,
A winding roll on which a glass fiber is wound;
A conveyor for conveying the glass fiber unwound from the winding roll;
A high density foam dispenser provided on an upper side of the conveyor and for spraying a first foam material for foaming a first polyurethane foam having a first density onto the glass fiber; And
And a second foam material provided on an upper side of the conveyor for foaming a second polyurethane foam of a second density lower than the first density on the first polyurethane foam onto the first foam material And a low-density foam spray portion. The method according to claim 6,
The high-density foam jetting portion includes:
And a high density foam spray nozzle for spraying the first foam material containing polyols and isocyanate at a higher concentration than the second foam material onto the glass fiber,
Wherein the low-density foam sprayer comprises:
And a low density foam spray nozzle for spraying the second foam material containing polyols and isocyanate at a lower concentration than the first foam material onto the first foam material,
Wherein the low-density foam spray nozzle is installed on a front side of the high-density foam spray nozzle with respect to a conveying direction of the glass fiber, and is installed at a higher position than the high-density foam spray nozzle. A method for manufacturing a liquefied gas storage tank in which a primary barrier, a primary insulation panel, a secondary barrier and a secondary insulation panel are laminated from an accommodation space of a liquefied gas to an inner hull side,
Spraying a first foam material on the glass fibers to foam a first polyurethane foam having a first density;
Spraying a second foam material onto the first foam material for foaming a second polyurethane foam of a second density lower than the first density on the first polyurethane foam;
Foaming the first foam material and the second foam material sprayed on the glass fiber to produce a first heat insulating member and a second heat insulating member having a density gradient in the vertical direction;
Machining the first heat insulating member and the second heat insulating member and joining the reinforcing plate to manufacture the first heat insulating panel and the second heat insulating panel;
Installing the secondary insulation panel on the inner hull so as to have a density gradient increasing in a direction from the secondary barrier to the inner hull;
Installing the secondary barrier on the secondary insulation panel;
Installing the primary insulation panel on the secondary barrier so as to have a density gradient lowering in a direction from the primary barrier side toward the secondary barrier side; And
And installing a primary barrier on the primary adiabatic panel. 9. The method of claim 8,
The manufacturing of the primary insulation panel and the secondary insulation panel comprises:
Joining said primary insulating member made of a single foamed layer having a first density gradient between said first upper stiffening plate and said first lower stiffening plate; And
And bonding the secondary insulation member made of a single foam layer having a second density gradient between the second upper reinforcement plate and the second lower reinforcement plate.

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