Floating marine structure and method for controlling temperature thereof

Abstract

Disclosed herein are a floating structure and a temperature control method of a floating structure. In more detail, the floating structure includes a cofferdam provided between a plurality of LNG storage tanks installed in at least one row in a length direction of a hull, in which a temperature of the cofferdam is controlled to be temperature below 0° C. to decrease a boil-off rate (BOR) generated by transferring heat from the cofferdam into the plurality of LNG storage tanks.

1 . A floating structure, comprising:
 a plurality of LNG storage tanks arranged in at least one row in a longitudinal direction or in a transverse direction of a hull; and   a cofferdam disposed between two immediately neighboring LNG storage tanks among the plurality of LNG storage tanks or disposed on a side of one of the plurality of LNG storage tanks;   wherein a temperature of the cofferdam is controlled to be temperature below 0° C. to decrease a boil-off rate (BOR) generated by transferring heat from the cofferdam into the plurality of LNG storage tanks.   
     
     
         2 . The floating structure of  claim 1 , wherein the cofferdam includes:
 a pair of bulk heads spaced apart from each other between the plurality of LNG storage tanks; and   a space portion provided by the pair of bulk heads and an inner wall of the hull, and   the cofferdam controls the pair of bulk heads to be temperature below 0° C.   
     
     
         3 . The floating structure of  claim 2 , wherein the pair of bulk heads is made of at least one material of B, D, E, AH, DH, and EH that are a steel grade defined in IGC. 
     
     
         4 . The floating structure of  claim 1 , further comprising:
 a gas supplier supplying gas into the cofferdam to prevent an inside of the cofferdam from being damaged due to freezing of moisture in air.   
     
     
         5 . The floating structure of  claim 4 , wherein the gas supplier includes:
 a supply pipe provided in the hull to supply the gas into the cofferdam;   a discharge pipe provided in the cofferdam to discharge the gas in the cofferdam to an outside of the cofferdam; and   valves provided in the supply pipe and the discharge pipe.   
     
     
         6 . The floating structure of  claim 4 , wherein the gas includes dry air, inert gas, or N2 gas. 
     
     
         7 . The floating structure of  claim 1 , further comprising:
 a heater provided in the cofferdam to heat the cofferdam,   wherein the cofferdam is controlled to be temperature below 0° C. to decrease the boil-off rate (BOR) generated by transferring heat from the cofferdam into the plurality of LNG storage tanks and is heated by the heater to change the temperature below 0° C. to a specific temperature in addition to temperature above 0° C.   
     
     
         8 . The floating structure of  claim 7 , wherein when a bulk head of the cofferdam is made of a material bearing a temperature from −30° C. to 0° C., the temperature of the cofferdam is changed in a range from −30° C. to 70° C. 
     
     
         9 . The floating structure of  claim 7 , wherein when a bulk head of the cofferdam is made of low temperature steel bearing up to −55° C., the temperature of the cofferdam is changed in a range from −55° C. to 70° C. 
     
     
         10 . The floating structure of  claim 7 , wherein when fuel consumption of the floating structure is increased, the temperature of the cofferdam is increased to increase the generation of the boil-off gas (BOG) and thus the BOG is used as fuel, and
 when the fuel consumption of the floating structure is decreased, the temperature of the cofferdam is lowered to decrease the generation of the BOG.   
     
     
         11 . The floating structure of  claim 7 , wherein when a pressure in the LNG storage tank is larger than a set pressure of the LNG storage tank, a set temperature of the cofferdam is lowered and when the pressure in the LNG storage tank is lower than the set pressure of the LNG storage tank, the set temperature of the cofferdam is increased. 
     
     
         12 . The floating structure of  claim 7 , wherein the heater heats at least one of a trunk deck space controlled to be temperature below 0° C. and a side passage way contacting a trunk deck to change the temperature of the trunk deck space and the side passage way to the specific temperature in addition to the temperature above 0° C. 
     
     
         13 . The floating structure of  claim 1 , further comprising:
 a heat insulating material provided in the cofferdam.   
     
     
         14 . The floating structure of  claim 13 , wherein the cofferdam includes a plurality of lateral cofferdams that segment the plurality of LNG storage tanks laterally, and
 the heat insulating material is provided in a foremost bulk head of a bow of the lateral cofferdam disposed at a foremost side of the bow and a rearmost bulk head of a stem of the lateral cofferdam disposed at a rearmost side of the stem, respectively, among the plurality of lateral cofferdams.   
     
     
         15 . The floating structure of  claim 1 , further comprising:
 a gas supplier supplying gas to the cofferdam.   
     
     
         16 . The floating structure of  claim 15 , wherein the gas supplier includes:
 a gas supply pipe provided in the cofferdam to supply the gas supplied through a gas supply line into the cofferdam;   a gas discharge pipe provided in the cofferdam to discharge the gas in the cofferdam to an outside of the cofferdam; and   shutoff valves provided in the gas supply pipe and the gas discharge pipe.   
     
     
         17 . The floating structure of  claim 15 , wherein the gas supplied into the cofferdam has a dew point temperature from −45° C. to −35° C. and a pair of bulk heads is controlled to be 1° C. to 10° C. higher than the dew point temperature of the gas. 
     
     
         18 . The floating structure of  claim 15 , wherein the temperature of the cofferdam is maintained at temperature above 0° C. while continuously injecting and venting the gas into the cofferdam and the gas has temperature above 0° C. 
     
     
         19 . The floating structure of  claim 15 , wherein the temperature of the cofferdam is increased by continuously injecting and discharging the gas into and from the cofferdam to provide an environment that a worker enters the cofferdam. 
     
     
         20 . The floating structure of  claim 2 , wherein the bulk head is not extended up to an external hull but is connected only to an internal hull, and
 a strength member connecting between the external hull and the internal hull is provided not to be continued to the bulk head to decrease the boil-off rate (BOR) generated by transferring heat between the bulk head and LNG stored in the plurality of LNG storage tanks.   
     
     
         21 . The floating structure of  claim 20 , wherein the bulk head is controlled to be a temperature from −163° C. to −50° C. and is made of a very low temperature material including aluminum or stainless steel. 
     
     
         22 . The floating structure of  claim 20 , further comprising:
 a sealing and heat insulating unit provided in the plurality of LNG storage tanks to seal and heat-insulate the LNG,   wherein the sealing and heat insulating unit is not provided in the bulk head of a region in which the plurality of LNG storage tanks and the bulk head contact each other.   
     
     
         23 . The floating structure of  claim 22 , wherein a space portion is provided between the bulk heads disposed at a foremost side of a bow and a rearmost side of a stern and the internal hull and is provided with a heat insulating material. 
     
     
         24 . A temperature control method of a floating structure, comprising:
 controlling a cofferdam at a specific sub-zero temperature to decrease a BOR;   controlling the temperature of the cofferdam to a specific temperature in addition to temperature above 0° C. so that a worker enters the cofferdam controlled to be the sub-zero temperature; and   controlling the temperature of the cofferdam to be the specific sub-zero temperature again when the worker gets out of the cofferdam.   
     
     
         25 . The temperature control method of  claim 24 , wherein the temperature of the cofferdam is controlled to be a range from −55° C. to 70° C.