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EP-4129815-B1 - SHIP

EP4129815B1EP 4129815 B1EP4129815 B1EP 4129815B1EP-4129815-B1

Inventors

  • TANIMOTO, KEISUKE
  • GOKAN, Kazuto
  • OHASHI, TETSUYA
  • SUZUKI, TOMOMI

Dates

Publication Date
20260506
Application Date
20210330

Claims (5)

  1. A ship (1) comprising: a hull (2); at least one double-shell tank (3) mounted on the hull (2) and including an inner tank (4) and an outer tank (5), the inner tank (4) storing a liquefied gas, the outer tank (5) covering the inner tank (4); at least one first discharge tower (15) extending upward from the hull (2); a first discharge line (45) connecting an upper portion of the inner tank (4) and an inside of the first discharge tower (15), wherein the ship (1) is characterized by : at least one second discharge tower (16) extending upward from the hull (2) and independent from the first discharge tower (15); a second discharge line (81) connecting an inter-tank region between the inner tank (4) and the outer tank (5) and an inside of the second discharge tower (16); and a pressure relief structure (83, 84) that is at the second discharge line (81), is normally closed, and is open when pressure of the inter-tank region exceeds a predetermined inter-tank allowable value.
  2. The ship according to claim 1, wherein the pressure relief structure (83, 84) is an inter-tank pressure relief valve (83, 84), the ship (1) further comprising: an inter-tank pressure gauge (91, 92, 93, 94) that detects the pressure of the inter-tank region; and inter-tank controlling circuitry (60B) that controls the inter-tank pressure relief valve (83, 84) such that when the detected pressure of the inter-tank region exceeds the inter-tank allowable value, the inter-tank pressure relief valve (83, 84) is open, and after that, when the detected pressure of the inter-tank region becomes a predetermined inter-tank reference value lower than the inter-tank allowable value, the inter-tank pressure relief valve (83, 84) is closed.
  3. The ship according to claim 1 or 2, further comprising an inactive gas supply line (85) through which an inactive gas is supplied to the second discharge line (81).
  4. The ship according to any one of claims 1 to 3, wherein: the inter-tank region is divided into regions; and each of the regions and the second discharge line (81) are connected to each other.
  5. The ship according to any one of claims 1 to 4, further comprising: an inner tank pressure relief valve (46) at the first discharge line (45); an inner tank pressure gauge (95) that detects pressure in the inner tank (4); and inner tank controlling circuitry (60A) that controls the inner tank pressure relief valve (46) such that when the detected pressure in the inner tank (4) exceeds a predetermined inner tank allowable value, the inner tank pressure relief valve (46) is open, and after that, when the detected pressure in the inner tank (4) becomes a predetermined inner tank reference value lower than the inner tank allowable value, the inner tank pressure relief valve (46) is closed.

Description

Technical Field The present disclosure relates to a ship on which a double-shell tank as a cargo tank is mounted. Background Art A ship on which a double-shell tank as a cargo tank is mounted has been known. The double-shell tank includes an inner tank and an outer tank. The inner tank stores a low temperature fluid cargo, such as a liquefied gas. The outer tank covers the inner tank. To improve a heat insulating property, a vacuum space is formed in an inter-tank region between the inner and outer tanks of the double-shell tank, or a heat insulating material is filled in the inter-tank region at normal pressure. PTL 1 discloses a liquefied gas carrier that is one example of the ship on which the double-shell tank as the cargo tank is mounted. The liquefied gas carrier disclosed in PTL 1 includes a cargo tank and a tank cover that wraps the cargo tank. An inactive gas is filled in a space between the cargo tank and the tank cover. The cargo tank includes: an inner tank that stores a liquefied gas; and an outer tank that secures a vacuum space between the inner tank and the outer tank. Generally, the liquefied gas carrier includes a depressurizer that maintains internal pressure of the cargo tank at a value lower than design withstand pressure by suitably discharging a boil off gas, generated inside the cargo tank during sailing, to an outside of the cargo tank. The depressurizer generally includes: a discharge pipe connected to an upper portion of the cargo tank; and a pressure relief valve (safety valve) that releases the boil off gas from the cargo tank to the discharge pipe when the internal pressure of the cargo tank becomes excessive. The boil off gas discharged through the discharge pipe to the outside of the cargo tank is discharged from a high place through a bent mast, is utilized as fuel, or is liquefied again and returned to an inside of the cargo tank. For example, PTL 2 discloses a technology in which the boil off gas generated in the cargo tank that stores liquid hydrogen is discharged through a discharge tower from a high place higher than a top portion of the cargo tank. PTL 3 discloses a method and system for controlling the pressure of a liquid storage tank installed in an offshore structure, wherein the method includes keeping the inner pressure of the inner space of the tank and the inner pressure of the primary insulation space equal by communicating between the primary insulation spaces. Citation List Patent Literature PTL 1: International Publication No. 2014/203530PTL 2: Japanese Laid-Open Patent Application Publication No. 2018-204721PTL 3: Korean Patent Publication No. 10-1637415 Summary of Invention Technical Problem If the inner tank of the double-shell tank that stores the liquefied gas cracks due to some reason, the liquefied gas in the inner tank leaks to the inter-tank region between the inner tank and the outer tank. The liquefied gas that has leaked to the inter-tank region evaporates, and this increases the pressure of the inter-tank region. For such emergency, the ship on which the double-shell tank is mounted may include, in addition to the depressurizer for the inner tank, another depressurizer for the inter-tank region between the inner tank and the outer tank. Therefore, the present application proposes a ship on which a double-shell tank is mounted and which includes a depressurizer for an inter-tank region between an inner tank and an outer tank. Solution to Problem A ship according to one aspect of the present disclosure includes: a hull; at least one double-shell tank mounted on the hull and including an inner tank and an outer tank, the inner tank storing a liquefied gas, the outer tank covering the inner tank; at least one first discharge tower extending upward from the hull; at least one second discharge tower extending upward from the hull and independent from the first discharge tower; a first discharge line connecting an upper portion of the inner tank and an inside of the first discharge tower; a second discharge line connecting an inter-tank region between the inner tank and the outer tank and an inside of the second discharge tower and independent from the first discharge line; and a pressure relief structure that is at the second discharge line, is normally closed, and is open when pressure of the inter-tank region exceeds a predetermined inter-tank allowable value. According to the ship configured as above, when the pressure of the inter-tank region increases since the liquefied gas enters into and evaporates in the inter-tank region between the inner tank and the outer tank, the evaporated liquefied gas is discharged from the inter-tank region through the second discharge line, and with this, the inter-tank region is depressurized. Therefore, damages of the inner tank and the outer tank by excessive pressure can be prevented. Furthermore, according to the ship configured as above, a discharge route of a boil off gas generated from the liquefied gas sto