Systems and methods for backhaul transportation of liquefied gas and CO2 using liquefied gas carriers

A dual-fluid transport system for transporting liquefied gas and carbon dioxide (CO2), the dual-fluid transport system comprising:

• a liquefied gas marine vessel configured to transport liquefied gas and CO2, the liquefied gas marine vessel comprising:
• one or more dual-fluid storage tanks positioned on the liquefied gas marine vessel to transport the liquefied gas or the CO2, the one or more dual-fluid storage tanks having:
• an outer shell,
• an outer compartment positioned within the outer shell, the outer compartment configured to store the liquefied gas,
• a bladder positioned within the outer compartment and configured to expand when the CO2 flows therein, thereby to reduce contamination between the CO2 and the liquefied gas, and
• insulation positioned between the outer shell and the outer compartment to provide temperature regulation from external heat sources;
• one or more pumps configured to pump the liquefied gas and CO2 from the one or more dual-fluid storage tanks;
• a first controller positioned within a first control room to control unloading/loading operations of CO2 from the bladder and liquefied gas from the outer compartment;
• one or more articulated rigid loading arms positioned at a location and to connect the liquefied gas marine vessel to the location and configured to load and unload the liquefied gas and CO2;
• a vapor return line connected to the one or more articulated rigid loading arms and configured to return excess vapor from the liquefied gas to the location;
• one or more liquefied gas storage tanks configured to store liquefied gas and one or more CO2 storage tanks configured to store CO2;
• a dehydration unit (a) positioned between the one or more articulated rigid loading arms and the one or more liquefied gas storage tanks and (b) configured to remove water from the CO2 when the CO2 is loaded onto the liquefied gas marine vessel;
• and
• a second controller positioned within a location control room at the location and to control unloading/loading operation of CO2 and liquefied gas to/from CO2 storage tanks and liquefied gas storage tanks.

A method of unloading/loading liquefied gas and carbon dioxide (CO2) at a location, the method comprising:

• aligning one or more articulated rigid loading arms positioned at a location with one or more dual-fluid storage tanks positioned on a liquefied gas marine vessel, the one or more dual-fluid storage tanks including an outer compartment configured to store liquefied gas and a bladder connected to a wall within the outer compartment configured to store CO2;
• connecting each of the one or more articulated rigid loading arms to the outer compartment or the bladder of each of the one or more dual-fluid storage tanks;
• and
• if the outer compartment contains liquefied gas:
• in response to reception of a first liquefied gas pump operation signal from a first controller and a second liquefied gas pump operation signal from a second controller, pumping a first liquefied gas from the outer compartment to one or more liquefied gas storage tanks and one of (a) a second liquefied gas from one or more liquefied gas storage tanks to the outer compartment or (b) CO2 from one or more CO2 storage tanks to the bladder, or
• if the bladder contains CO2:
• in response to reception of a first CO2 signal from the first controller and a signal from a second CO2 signal from the second controller, pumping CO2 from the bladder to one or more CO2 storage tanks at the location and the second liquefied gas from one or more liquefied gas storage tanks to the outer compartment.

A controller for a liquefied gas marine vessel for transporting liquefied gas and carbon dioxide (CO2), the controller comprising:

• a first input/output in signal communication with one or more temperature-control apparatuses positioned within an outer compartment of each of one or more dual-fluid storage tanks on a liquefied gas marine vessel and a bladder positioned within the outer compartment, the controller configured to obtain a first temperature of a liquefied gas contained within the outer compartment and a second temperature of CO2 contained within the bladder during unloading operations, onloading operations, and transport of the liquefied gas and CO2;
• a second input/output in signal communication with one or more pressure-control apparatuses positioned within the outer compartment of each of one or more dual-fluid storage tanks and the bladder, the controller configured to obtain a first pressure of the liquefied gas contained within the outer compartment and a second pressure of CO2 contained within the bladder during one or more of the unloading operations, the onloading operations, or the transport of the liquefied gas and CO2;
• a third input/output in signal communication with a first flow meter positioned at a first inlet of the outer compartment and a second flow meter positioned at a second inlet of the bladder, the controller configured to measure a first flow rate of the liquefied gas and a second flow rate of the CO2;
• and
• a fourth input/output in signal communication with a first control valve, the first control valve designed to adjust flow of the liquefied gas via one or more unloading/loading pumps positioned on the liquefied gas marine vessel, thereby to modify the first flow rate of the liquefied gas, and a second flow control valve, the second control valve designed to adjust flow of the CO2 via the one or more unloading/loading pumps, thereby to modify the second flow rate, the controller configured to:
• after initiation of the unloading operations or the onloading operations:
• determine whether the first flow rate or the second flow rate is to be modified based on an outer compartment temperature, an outer compartment pressure, a bladder pressure, or a bladder temperature,
• in response to a determination that the first flow rate is to be modified:
• adjust a position of the first flow control valve that adjusts flow of the liquefied gas, thereby modifying the first flow rate, and
• in response to a determination that the second flow rate is to be modified:
• adjust a position of the second flow control valve that adjusts flow of the CO2, thereby modifying the second flow rate.