Method and system for processing gas in a gas storage facility for a gas tanker
The invention relates to a gas treatment method and system of a gas storage facility ( 2 ), in particular on board a ship, the method comprising the following stages: an extraction of a first gas ( 4 a, 4 b, 5 a, 5 b ,) in the liquid state from a first tank ( 4 ) or first vessel ( 5; 500 ), a first subcooling of the first gas in the liquid state, and storage of the subcooled first gas in the liquid state in the lower part of the first tank ( 4 ) or of the first vessel ( 5; 500 ) or of a second tank or of a second vessel, so as to constitute a reserve layer of cold ( 4 c, 5 c, 500 c ) of the subcooled first gas in the liquid state at the bottom of the first or second tank ( 4 ) or of the first or second vessel ( 5; 500 ).
1 . A gas treatment method of a gas storage facility, on board a ship, the method comprising:
extracting a first gas in a liquid state from a first tank or a first vessel,
a first subcooling of the first gas in the liquid state,
splitting the subcooled first gas into two portions;
storing a first portion of the subcooled first gas in the liquid state in a lower part of the first tank or of the first vessel or of a second tank or of a second vessel, so as to constitute a reserve layer of cold of the first gas in the liquid state at a bottom of the first tank or the second tank or of the first vessel or the second vessel;
cooling a gas in a vapor state using the first gas stored in the reserve layer of cold of the first tank or the second tank or the first vessel or the second vessel,
wherein the subcooled first gas, which is stored at the bottom of the first tank or the second tank or the first vessel or the second vessel, creates a refrigerating power that can be subsequently used, the reserve layer of cold being stored at the bottom of located in the first tank or the second tank or the first vessel or the second vessel in a durable manner below an amount of the first gas in the liquid state, forming a liquid-liquid interface, and
the method further comprises spraying a second portion of the subcooled first gas stored in the reserve layer of cold into the first tank or the second tank or the first vessel or the second vessel and into a layer of the gas in the vapor state.
2 . The method as claimed in claim 1 , wherein the first gas is transferred into the first tank or the second tank or the first vessel or the second vessel via a pipeline which emerges in the bottom of the first tank or the second tank or the first vessel or the second vessel.
3 . The method as claimed claim 1 , wherein the gas in the vapor state is the first gas in the vapor state located in an upper part of one of the first and the second tanks or the first and the second vessels.
4 . The method as claimed in claim 1 , further comprising extracting the first gas stored in the reserve layer of cold from the bottom of one tank of the first and second tanks or the first and second vessels, and reliquefying the first gas in the vapor state through a heat exchanger.
5 . The method as claimed in claim 1 , wherein the subcooled first gas is stored in the reserve layer of cold when a measured pressure in the first or second tank or the first or the second vessel is less than a respective first predetermined pressure threshold value of the first or the second tank or of the first or the second vessel.
6 . The method as claimed in claim 1 , wherein said lower part extends over approximately less than 30% of a height of the first or the second tank or the first or the second vessel, measured from the bottom, said bottom being a lowermost end of the first or the second tank or the first or the second vessel.
7 . The method as claimed in claim 1 , wherein the subcooled first gas is stored in the reserve layer of cold at a storage temperature between a liquefaction temperature of the first gas and the liquefaction temperature of the first gas less approximately 5° C. to 10° C., at atmospheric pressure, the first gas in the liquid state remaining in the first or the second tank or in the first or the second vessel being at a temperature higher than the storage temperature.
8 . The method as claimed in claim 1 , wherein the subcooled first gas is stored in the reserve layer of cold at a temperature of between −45° C. and −55° C. or between −160° C. and −170° C., depending on a type of the first gas, the first gas in the liquid state remaining in one of the first and the second tanks or the first and the second vessels being at a temperature of greater than or equal to −42° C. or −160° C., respectively, depending on the type of the first gas.
9 . The method as claimed in claim 1 , wherein the first subcooling of the first gas is performed with a second gas at least in the liquid state extracted from a particular vessel, the second gas having a boiling point less than or equal to that of the first gas.
10 . The method as claimed in claim 9 , further comprising vaporizing or heating the second gas, which is heated or vaporized by heat exchange during the first subcooling of the first gas, so as to supply the gas storage facility.
11 . The method as claimed in claim 10 , further comprising controlling, by the gas storage facility, a flow rate of the second gas, which has to be vaporized or heated during the vaporization.
12 . The method as claimed in claim 10 , further comprising expanding and partially vaporizing the second gas extracted from the particular vessel before the heat exchange during the first subcooling.
13 . The method as claimed in claim 12 , further comprising subcooling the second gas extracted from the particular vessel by heat exchange with the expanded and partially vaporized second gas.
14 . The method as claimed in claim 1 , further comprising a second subcooling of the first gas after the first subcooling.
15 . The method as claimed in claim 14 , further comprising extracting a second gas used for the second subcooling from the bottom of a particular vessel, or subcooling the second gas.
16 . The method as claimed in claim 14 , wherein the first and/or second subcooling is performed outside the first or second tanks and/or the first or second vessels.
17 . The method as claimed in claim 15 , wherein the heat exchange during the first subcooling or the second subcooling between the first gas and the second gas is performed so that a subcooling outlet temperature of the first gas is between a first threshold value and a second threshold value.
18 . The method as claimed in claim 14 , wherein an outlet temperature of the second gas after the second subcooling is between −155° C. and −105° C. at a pressure of between 2 and 20 bars.
19 . The method as claimed in claim 9 , further comprising heating the second gas, which is heated, vaporized, or partially vaporized, to supply the facility.
20 . The method as claimed in claim 19 , further comprising a reliquefaction step in which vapors of the first gas moving in a first circuit from the first tank are reliquefied by heat exchange with the second gas in the liquid state having an inlet temperature and moving in a second circuit, the reliquefied vapors of the first gas being transferred into the first tank or the second tank and the second gas being maintained in the liquid state at an outlet temperature after the reliquefaction and taken back to the first vessel or the second vessel, the heat exchange between the first gas and the second gas being performed so that an outlet temperature of the reliquefied vapors of the first gas is between a first threshold value and a second threshold value.
21 . The method as claimed in claim 20 , wherein the vapors of the first gas are reliquefied when a pressure measured in the first or the second tank or the first or the second vessel is greater than a respective second predetermined pressure threshold value of the first or the second tank or the first or the second vessel.
22 . The method as claimed in claim 1 , wherein the first gas is a liquefied natural gas or a liquefied petroleum gas.
23 . The method as claimed in claim 9 , wherein the second gas is a liquefied natural gas.
24 . A gas treatment system of a gas storage facility on board a ship, the system comprising:
a tank or vessel in which a first gas in a liquid state is stored;
a first heat exchanger configured to perform a first subcooling of the first gas extracted from the tank or the vessel, by a first pipeline; and
a second pipeline connected to the first heat exchanger, which emerges in a lower part of the tank or the vessel or of another tank or vessel, so as to store the subcooled first gas at a bottom of the tank or the vessel or of the another tank or the other vessel to form a reserve layer of cold of the first gas in the liquid state,
a third pipeline connected to the first heat exchanger and a spray bar,
the spray bar is arranged in an upper part of the tank or the vessel or of the another tank or vessel, so as to spray the subcooled first gas in a gas headspace of the tank or the vessel or of the another tank or vessel,
wherein the first gas stored in the reserve layer of cold of the tank or the vessel or the other tank or the other vessel is used to cool a gas in a vapor state; and the reserve layer of cold is located in the tank or vessel or in the other tank or the other vessel below an amount of the first gas, forming a liquid-liquid interface, wherein said second pipeline emerges in the bottom of said tank or vessel or the other tank or the other vessel.
25 . The system as claimed in claim 24 , further comprising a second vessel in which a second gas in a liquid state is stored, the second gas having a boiling point less than or equal to that of the first gas.
26 . The system as claimed in claim 25 , wherein the second gas in the liquid state moves in a second pipeline connected to the first heat exchanger so as to perform the first subcooling of the first gas.
27 . The system as claimed in claim 25 , further comprising a second heat exchanger configured to perform a second subcooling of the first gas with the second gas in the liquid state.
28 . The system as claimed in claim 24 , wherein the bottom of the tank or the vessel comprises an outlet connected to a first end of a conduit, the conduit comprising a second end coupled to a spray bar installed in an upper part of the tank or the vessel.
29 . The system as claimed in claim 25 , further comprising a heating device in which the second gas, heated, vaporized, or partially vaporized in the first heat exchanger, moves.
30 . The system as claimed in claim 24 , further comprising depressurization means mounted upstream of the first heat exchanger.
31 . The system as claimed in claim 27 , wherein the second heat exchanger is configured to provide the second gas at an outlet temperature of between −155° C. and −105° C. at a pressure of between 2 and 20 bars.
32 . The system as claimed in claim 24 , wherein the first gas is a liquefied natural or a liquefied petroleum gas.
33 . The system as claimed in claim 25 , wherein the second gas is a liquefied natural gas.
34 . A liquefied gas transport ship, comprising at least one gas treatment system as claimed in claim 26 .
35 . The method of claim 1 , wherein the gas storage facility is an energy production facility that consumes the gas originating from the first tank or the second tank or in the first vessel or the second vessel.