Apparatus, system and method for reliquefaction of previously regasified lng

Abstract

An apparatus, system and method for reliquefaction of previously regasified LNG are described. A natural gas reliquefaction method includes regasifying LNG onboard a FSRU to form high pressure regasified LNG (HP RLNG), delivering the HP RLNG to a natural gas pipeline that commingles with a natural gas grid, flowing the HP RLNG through a lateral, wherein the lateral diverts HP RLNG from the natural gas pipeline to an expander prior to commingling with the natural gas grid, expanding the natural gas with the expander to obtain low pressure regasified LNG (LP RLNG), liquefying the LP RLNG in a cold box of a nitrogen expansion loop to produce low pressure LNG, and transmitting the LNG to a cryogenic cargo tank onboard an LNG tanker truck.

1 . A method of reliquefying previously regasified LNG comprising:
 diverting high pressure regasified LNG (HP RLNG) from a natural gas pipeline, wherein the HP RLNG is diverted through a lateral that connects to the natural gas pipeline prior to the natural gas pipeline converging with a natural gas grid, and wherein the natural gas pipeline receives the HP RLNG from an FSRU;   expanding the HP RLNG from the lateral with an expander to obtain low pressure regasified LNG (LP RLNG);   liquefying the LP RLNG in a cold box, wherein the cold box places the LP RLNG in heat exchange with nitrogen of a nitrogen expansion loop to produce low pressure LNG; and   transmitting the low pressure LNG to a cryogenic cargo tank onboard an LNG tanker truck.   
     
     
         2 . The method of  claim 1 , further comprising regasifying LNG onboard the FSRU to obtain the HP RLNG. 
     
     
         3 . The method of  claim 1 , further comprising using energy extracted by the expander to drive a compressor that operates in the nitrogen expansion loop, the compressor providing compression of nitrogen in the nitrogen expansion loop. 
     
     
         4 . The method of  claim 1 , further comprising compressing the nitrogen in the nitrogen expansion loop using a compressor powered by a generator, the generator at least partially fueled by a portion of the HP RLNG diverted through the lateral. 
     
     
         5 . The method of  claim 4 , wherein the generator is at least partially fueled by a portion of boil-off gas from one of the cryogenic cargo tank, a land-based LNG storage tank fluidly coupled to the cold box, or a combination thereof. 
     
     
         6 . The method of  claim 5 , wherein the portion of the HP RLNG and the portion of the boil-off gas are combined by an eductor, and the combined gas fuels the generator. 
     
     
         7 . The method of  claim 1 , wherein the nitrogen expansion loop comprises a second expander, and further comprising expanding nitrogen in the nitrogen expansion loop over the second expander. 
     
     
         8 . The method of  claim 7 , further comprising using the nitrogen to extract heat from the LP RLNG in the cold box to produce the low pressure LNG. 
     
     
         9 . The method of  claim 1 , further comprising returning boil-off gas from one of the cryogenic cargo tank, an intermediate land-based LNG storage tank, or a combination thereof to the cold box. 
     
     
         10 . The method of  claim 9 , further comprising using the boil-off gas to at least partially extract heat from the LP RLNG in the cold box. 
     
     
         11 . The method of  claim 1 , wherein the LP RLNG is in heat exchange with the nitrogen in the cold box to extract latent heat from the LP RLNG. 
     
     
         12 . A regasified LNG reliquefaction apparatus comprising:
 a natural gas pipeline extending between a FSRU and a natural gas grid;   a lateral pipeline fluidly coupled to the natural gas pipeline prior to a commingling of the natural gas pipeline with the natural gas grid;   the lateral pipeline fluidly coupled to an inlet of a natural gas expander and delivering LNG-quality natural gas to the inlet;   an outlet of the expander fluidly coupled to a cold box;   the cold box coupled to a nitrogen expansion loop; and   LNG exiting the cold box, the LNG formed from the LNG-quality natural gas.   
     
     
         13 . The regasified LNG reliquefaction apparatus of  claim 12 , further comprising a power generator fluidly coupled to a portion of the LNG-quality natural gas delivered by the lateral pipeline. 
     
     
         14 . The regasified LNG reliquefaction apparatus of  claim 13 , wherein the power generator is energetically coupled to a compressor of the nitrogen expansion loop. 
     
     
         15 . The regasified LNG reliquefaction apparatus of  claim 12 , further comprising a LNG storage tank receiving the LNG exiting the cold box. 
     
     
         16 . The regasified LNG reliquefaction apparatus of  claim 15 , further comprising a boil-off gas (BOG) return line fluidly coupling the LNG storage tank and the cold box. 
     
     
         17 . The regasified LNG reliquefaction apparatus of  claim 15 , further comprising a power generator, and a boil-off gas (BOG) return line fluidly coupling the LNG storage tank and the power generator. 
     
     
         18 . The regasified LNG reliquefaction apparatus of  claim 17 , further comprising a portion of the LNG-quality natural gas delivered by the lateral pipeline and BOG carried by the BOG return line mixedly coupled by an eductor prior to entering the power generator. 
     
     
         19 . The regasified LNG reliquefaction apparatus of  claim 15 , further comprising an LNG tanker truck cryogenically coupled to the LNG storage tank. 
     
     
         20 . The regasified LNG reliquefaction apparatus of  claim 12 , wherein the natural gas expander is drivingly coupled to a compressor of the nitrogen expansion loop. 
     
     
         21 . The regasified LNG reliquefaction apparatus of  claim 12 , wherein LNG-quality natural gas sendout from the FSRU is liquefied in the cold box without pretreatment. 
     
     
         22 . A regasified LNG reliquefaction system comprising:
 a FSRU fluidly coupled to a natural gas pipeline, the natural gas pipeline comprising high pressure regasified LNG (HP RLNG) produced from LNG-quality natural gas regasified by the FSRU;   the natural gas pipeline transmitting the HP RLNG at a first pressure of 70-100 barg and a first temperature of 5-20° C.;   a lateral pipeline that couples the natural gas pipeline to an expander;   the expander comprising an inlet that receives the HP RLNG from the lateral pipeline at the first pressure and the first temperature, wherein the expander converts the HP RLNG having the first pressure and the first temperature to low pressure regasified LNG (LP RLNG) having a second pressure of less than 10 barg and a second temperature of about −100° C.;   a cold box fluidly coupled to the LP RLNG and a nitrogen expansion loop; and   LNG exiting the cold box at a third pressure of 5-6 barg.   
     
     
         23 . The regasified LNG reliquefaction system of  claim 22 , wherein the expander drives a compressor in the nitrogen expansion loop. 
     
     
         24 . The regasified LNG reliquefaction system of  claim 22 , further comprising a compressor providing compression of nitrogen in the nitrogen expansion loop, the compressor powered by a generator fueled by a portion of the HP RLNG. 
     
     
         25 . The regasified LNG reliquefaction system of  claim 22 , wherein the nitrogen expansion loop further comprises a second expander that expands the nitrogen. 
     
     
         26 . The regasified LNG reliquefaction system of  claim 22 , wherein the nitrogen extracts heat from the LP RLNG in the cold box causing the LP RLNG to condense in the cold box at the second pressure. 
     
     
         27 . The regasified LNG reliquefaction system of  claim 22 , further comprising a storage tank fluidly coupled to the LNG exiting the cold box. 
     
     
         28 . The regasified LNG reliquefaction system of  claim 27 , wherein the storage tank is fluidly coupled between the cold box and an LNG cargo tank onboard a truck. 
     
     
         29 . The regasified LNG reliquefaction system of  claim 28 , wherein a gas return line fluidly couples boil-off gas from the LNG cargo tank to the cold box. 
     
     
         30 . The regasified LNG reliquefaction system of  claim 29 , wherein the boil-off gas cools the LP RLNG in the cold box and recondenses in the cold box. 
     
     
         31 . The regasified LNG reliquefaction system of  claim 28 , wherein a gas return line fluidly couples boil-off gas from the LNG cargo tanks to a power generator. 
     
     
         32 . The regasified LNG reliquefaction system of  claim 31 , further comprising an eductor coupled to a fuel gas inlet of the power generator, wherein the eductor mixes the boil-off gas with a portion of the HP RLNG sent to the power generator. 
     
     
         33 . The regasified LNG reliquefaction system of  claim 31 , wherein the power generator provides make up power to the nitrogen expansion loop. 
     
     
         34 . The regasified LNG reliquefaction system of  claim 22 , wherein the natural gas pipeline transmits the HP RLNG to downstream consumers via existing gas pipeline infrastructure. 
     
     
         35 . A regasified LNG reliquefaction method comprising:
 regasifying LNG onboard a FSRU to form high pressure regasified LNG (HP RLNG);   delivering the HP RLNG to a natural gas pipeline that commingles with a natural gas grid;   flowing the HP RLNG from the natural gas pipeline through a lateral at a first pressure of 70-100 barg and a first temperature of 5-20° C., wherein the lateral diverts HP RLNG from the natural gas pipeline to an expander prior to commingling with the natural gas grid;   expanding the natural gas having the first pressure and the first temperature with the expander to obtain low pressure regasified LNG (LP RLNG) having a second pressure of less than 10 barg and a second temperature of about −100° C.;   liquefying the LP RLNG in a cold box of a nitrogen expansion loop to produce LNG at a third pressure of 5-6 barg; and   transmitting the LNG to a cryogenic cargo tank onboard an LNG tanker truck.