JP7748210B2 - Liquefied carbon dioxide heating equipment and liquefied carbon dioxide heating method - Google Patents

Description

The present invention relates to a heating system and a heating method for liquefied carbon dioxide gas (liquefied CO ₂ ) in CCS (Carbon Capture and Storage).

CCS (carbon dioxide capture and storage) is a global warming countermeasure that involves capturing _CO2 from a _CO2 source (for example, flue gas from a coal-fired power plant) using a method such as chemical absorption, compressing it, and injecting it in a supercritical state into an underground aquifer (reservoir) shielded by bedrock or the like, where it is stored (see, for example, Patent Documents 1 and 2 for more information on CCS).

There are various methods for CCS, one of which is the liquefied carbon dioxide transportation and injection method. In this method, the separated and captured _CO2 is compressed and liquefied, and temporarily stored in tanks on land in the form of liquefied carbon dioxide. From the tanks, it is loaded onto a liquefied carbon dioxide transport ship and transported by ship to a storage site. At the storage site, the liquefied carbon dioxide is injected from the liquefied carbon dioxide transport ship into an aquifer beneath the seabed.

JP 2011-31154 A Japanese Patent Application Laid-Open No. 2012-72012

When injecting liquefied carbon dioxide into a reservoir (aquifer), in order to prevent the surrounding water from freezing and to prevent blockage due to the formation of _CO2 hydrate, the liquefied carbon dioxide (for example, -10°C/2.289 MPa to -50°C/0.684 MPa) is pressurized to a predetermined pressure (10 MPa or more) and then heated to 0°C or higher before injection.

Some kind of heat source is required to heat the liquefied carbon dioxide, but the available heat sources are limited given the conditions on board a liquefied carbon dioxide transport ship. One possible method is to generate hot water using a hot water boiler and heat exchange the hot water with the liquefied carbon dioxide to heat the liquefied carbon dioxide. However, this method has the drawback of increasing costs because a large amount of fuel is consumed by the hot water boiler, and also of _CO2 emissions due to fuel consumption.

The present invention was made in light of these circumstances, and its purpose is to provide technology that can optimally heat liquefied carbon dioxide gas in a CCS system.

To solve the above problems, one embodiment of the liquefied carbon dioxide heating equipment of the present invention comprises a heat medium heater that receives a supply of seawater and a heat medium and heats the heat medium by heat exchange with the seawater, a heating heat exchanger that heats the liquefied carbon dioxide to a predetermined temperature by heat exchange with the heat medium heated by the heat medium heater, and a heat medium temperature control unit that controls the temperature of the heat medium supplied to the heat medium heater so that it is above the freezing temperature of seawater.

Another aspect of the present invention is a method for heating liquefied carbon dioxide. This method includes the steps of supplying seawater and a heat medium to a heat medium heater, using the heat medium heater to heat the heat medium by heat exchange with seawater, heating the liquefied carbon dioxide to a predetermined temperature by heat exchange with the heat medium, and controlling the temperature of the heat medium supplied to the heat medium heater so that it is above the freezing temperature of seawater.

The present invention provides technology that can efficiently heat liquefied carbon dioxide gas in a CCS system.

FIG. 1 is a diagram showing a schematic flow of a CCS system using liquefied carbon dioxide heating equipment according to an embodiment of the present invention. FIG. 1 is a diagram for explaining a liquefied carbon dioxide gas heating equipment according to an embodiment of the present invention. FIG. 10 is a diagram illustrating a liquefied carbon dioxide gas heating facility according to another embodiment of the present invention.

The present invention will now be described based on preferred embodiments with reference to the drawings. The following configurations are for illustrative purposes only to aid in understanding the present disclosure, and the scope of the present disclosure is defined solely by the appended claims. Identical or equivalent components and parts shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, the dimensions of the parts in each drawing will be enlarged or reduced as appropriate to facilitate understanding. Furthermore, some parts that are not important for explaining the embodiments will be omitted from the drawings.

Figure 1 is a diagram showing the general flow of a CCS system that uses liquefied carbon dioxide heating equipment according to an embodiment of the present invention. Figure 1 shows a CCS system that uses liquefied carbon dioxide transportation and injection. Other CCS systems include the subsea pipeline system and the ERD (Extended Reach Drilling) system.

In CCS, _CO2 is separated and captured from a _CO2 source, such as flue gas from a coal-fired power plant, using, for example, chemical absorption. The captured _CO2 is then compressed and liquefied, and stored in a tank on land in the form of liquefied carbon dioxide. The liquefied carbon dioxide is loaded from the tank onto a liquefied carbon dioxide transport ship 100 and transported by ship to a storage site 102 on the ocean 110.

The liquefied carbon dioxide gas loaded onto the liquefied carbon dioxide gas transport vessel 100 is pressurized and heated by the liquefied carbon dioxide gas heating equipment 10 installed on the liquefied carbon dioxide gas transport vessel 100, and then injected from the liquefied carbon dioxide gas transport vessel 100 into the aquifer 114 at the storage point 102. The aquifer 114 is a layer further below the barrier layer 112 located below the seabed.

In the CCS shown in Figure 1, liquefied carbon dioxide is sent to a well head 106 installed on the seabed via a flexible riser pipe (FRP) for connecting to subsea facilities. The liquefied carbon dioxide is then sent to a Christmas tree 108 via a flow line 107 laid on the seabed. A Christmas tree is a collection of valves that control the pressure of fluid produced from a well. In the Christmas tree 108, the liquefied carbon dioxide is injected into the aquifer 114.

In the above, the liquefied carbon dioxide heating equipment 10 is installed on a liquefied carbon dioxide transport ship 100, but the liquefied carbon dioxide heating equipment 10 may also be installed on a bottom-mounted platform installed offshore or on a floating body moored offshore (FSO: Floating Storage and Offloading or Buoy).

2 is a diagram illustrating a liquefied carbon dioxide heating system 10 according to an embodiment of the present invention. The liquefied carbon dioxide heating system 10 is a system for pressurizing liquefied carbon dioxide (for example, −10°C/2.289 MPa to −50°C/0.684 MPa) transported by ship in order to inject it into a reservoir (aquifer) on the seabed, and for heating the liquefied carbon dioxide when it is injected into the reservoir in order to prevent freezing of surrounding water and blockage due to the formation of _CO2 hydrate.

Here, the injection conditions in the CCS will be explained.
(1) Injection pressure The injection pressure varies depending on the depth of the reservoir, the permeability, and the strength of the shielding layer, but is generally expressed as "Static Head + 3 MPa ~ the failure pressure of the shielding layer" at the injection point. In the case of CCS in an underground reservoir on the seabed, taking into account an injection depth of 2000 m to 3000 m, the density of liquefied carbon dioxide, and pressure loss in the well, the optimum injection pressure is approximately 10 MPa to 13 MPa at the Christmas tree 108 on the seabed (see Figure 1).
(2) Injection Temperature When liquefied carbon dioxide is injected into the reservoir (aquifer 114), it must be heated before injection to prevent the surrounding water from freezing (above 0°C) and to prevent blockage due to _CO2 hydrate formation (below 5°C). Considering that no blockage due to _CO2 hydrate formation has occurred when injected at 0°C in past CCS examples, it is preferable that the injection temperature of liquefied carbon dioxide be 0°C or higher.

As shown in Figure 2, the liquefied carbon dioxide heating equipment 10 includes a storage tank 12, a booster pump 14, a heating heat exchanger 16, a heat medium heater 18, a seawater pump 20, a heat medium drum 22, a heat medium pump 24, and a heat medium temperature control unit 30.

The storage tank 12 stores liquefied carbon dioxide gas (liquefied CO ₂ ). The temperature of the liquefied carbon dioxide gas may be −10° C. to −50° C., and the pressure of the liquefied carbon dioxide gas may be 2.289 MPa to 0.684 MPa. The liquefied carbon dioxide gas stored in the storage tank 12 is supplied to a booster pump 14.

The boost pump 14 boosts the liquefied carbon dioxide gas supplied from the storage tank 12 to a predetermined pressure (e.g., 10 MPa or higher). The liquefied carbon dioxide gas pressurized by the boost pump 14 is supplied to the heating heat exchanger 16.

The heating heat exchanger 16 is a cylindrical-shell multi-tube heat exchanger with multiple heat transfer tubes housed within a cylindrical shell. In this embodiment, the cylindrical shell and heat transfer tubes of the heating heat exchanger are both made of ordinary steel. Liquefied carbon dioxide gas from the boost pump 14 is supplied to the tube side of the heating heat exchanger 16. The liquefied carbon dioxide gas is input to the tube side inlet 16a of the heating heat exchanger 16 and output from the tube side outlet 16b. Meanwhile, a heat transfer medium is supplied to the shell side of the heating heat exchanger 16. The heat transfer medium is input to the shell side inlet 16c of the heating heat exchanger 16 via line 33 and output from the shell side outlet 16d. The heating heat exchanger 16 exchanges heat between the liquefied carbon dioxide gas supplied to the tube side and the heat transfer medium supplied to the shell side, thereby heating the liquefied carbon dioxide gas to a predetermined temperature (above 0°C).

The heat transfer medium used is an antifreeze that does not freeze even at the temperature of the liquefied carbon dioxide gas supplied to the heating heat exchanger 16 (-10°C to -50°C). Examples of such heat transfer mediums include an aqueous ethylene glycol solution, an aqueous propylene glycol solution, a mixed solution of an aqueous ethylene glycol solution and an aqueous propylene glycol solution, or a solution of a hydrocarbon compound. The content of ethylene glycol, propylene glycol, or hydrocarbon compound in each solution is set so that it does not freeze at the temperature of the liquefied carbon dioxide gas supplied, for example, at 10 wt% or more of ethylene glycol or 10 wt% or more of propylene glycol. These solutions preferably contain a rust inhibitor.

The heat medium output from the shell-side outlet 16d of the heating heat exchanger 16 is supplied to the heat medium drum 22 via line 34. The heat medium is then supplied to the heat medium heater 18 by the heat medium pump 24.

The heat medium temperature control unit 30 controls the temperature of the heat medium supplied to the heat medium heater 18 so that it is above the freezing temperature of seawater (-2°C). The heat medium temperature control unit 30 includes a control valve 26 and a temperature sensor 28.

As shown in FIG. 2, the control valve 26 is installed in a bypass line 32 that bypasses the shell side inlet 16c and shell side outlet 16d of the heating heat exchanger 16. That is, the bypass line 32 bypasses a line 33 that connects the heat medium outlet 18b of the heat medium heater 18 to the shell side inlet 16c of the heating heat exchanger 16, and a line 34 that connects the shell side outlet 16d of the heating heat exchanger 16 to the inlet 22a of the heating medium drum 22.

The temperature sensor 28 is positioned to detect the temperature of the heat medium after the heat medium output from the shell-side outlet 16d of the heating heat exchanger 16 and the heat medium from the bypass line 32 are combined. Based on the value detected by the temperature sensor 28, the control valve 26 controls the flow rate of the heat medium flowing through the bypass line 32 so that the temperature of the combined heat medium, i.e., the temperature of the heat medium supplied to the heat medium drum 22, is equal to or higher than the freezing temperature of seawater (-2°C).

The heat medium heater 18 receives a supply of seawater (e.g., 5°C or higher) and a heat medium (-2°C or higher) and heats the heat medium through heat exchange with the seawater. In this embodiment, the heat medium heater 18 is a plate-type heat exchanger equipped with titanium plates, which have excellent seawater corrosion resistance and abrasion resistance. Plate-type heat exchangers are characterized by their high heat transfer characteristics. In a plate-type heat exchanger, the fluid flows in approximately parallel flows, has a high heat transfer coefficient, has little deviation from one location to another, and is capable of sufficient heat exchange even with a temperature difference of 2°C between the fluids. Seawater is input to the seawater inlet 18c of the heat medium heater 18 by the seawater pump 20 and output from the seawater outlet 18d of the heat medium heater 18. Meanwhile, the heat medium is input to the heat medium inlet 18a of the heat medium heater 18 and output from the heat medium outlet 18b of the heat medium heater 18.

The operation of the liquefied carbon dioxide heating equipment 10 will be explained using specific temperature examples. Here, we consider the case where liquefied carbon dioxide at -20°C and 1.97 MPa is pressurized and heated to 0°C and 10 MPa. The heat medium heater 18 receives, for example, seawater at 7°C and a heat medium (ethylene glycol aqueous solution: freezing temperature -23°C) at -1°C and heats the heat medium to 5°C. The heat medium heated by the heat medium heater 18 is supplied to the shell side inlet 16c of the heating heat exchanger 16 via line 33. The boost pump 14 pressurizes liquefied carbon dioxide at -20°C and 1.97 MPa to -20°C and 10.5 MPa. The heating heat exchanger 16 heats the liquefied carbon dioxide at -20°C and 10.5 MPa supplied to the pipe side inlet 16a to 0°C (10.2 MPa) through heat exchange with the 5°C heat medium. When liquefied carbon dioxide gas at -46°C and 0.80 MPa is pressurized and heated to 0°C and 10 MPa, the outlet of the booster pump 14 will be -46°C and 10.5 MPa, while the temperature and pressure at other locations will remain the same.

The above has described the configuration of the liquefied carbon dioxide heating equipment 10 according to this embodiment. According to the liquefied carbon dioxide heating equipment 10 according to this embodiment, seawater is used to heat the liquefied carbon dioxide, which reduces costs compared to using a hot water boiler that requires fuel, and also emits very little _CO2 .

The lowest seawater temperature in winter along the Sea of Japan coast is 6°C to 8°C (4°C to 6°C in the North Sea). If liquefied carbon dioxide gas at -10°C to -50°C is directly heat-exchanged with such low-temperature seawater, there is a risk that the seawater will freeze inside the heat exchanger, causing blockage. Therefore, by exchanging heat between liquefied carbon dioxide gas and a heat medium with a low freezing temperature, as in the liquefied carbon dioxide heating equipment 10 of this embodiment, blockage of the heat exchanger can be prevented.

In the heat medium heater 18, heat exchange occurs between the seawater and the heat medium. However, in the liquefied carbon dioxide heating equipment 10 according to this embodiment, the heat medium temperature control unit 30 controls the temperature of the heat medium input to the heat medium inlet 18a of the heat medium heater 18 to be equal to or higher than the freezing temperature of seawater (approximately -2°C), so freezing of seawater does not occur within the heat medium heater 18.

In the liquefied carbon dioxide heating equipment 10 according to this embodiment, the fluid supplied to the heating heat exchanger 16 is less corrosive, so ordinary steel can be used as the material instead of expensive titanium. As a result, the cost of the cylindrical-shell multi-tube type heating heat exchanger 16 can be significantly reduced.

In the liquefied carbon dioxide heating equipment 10 according to this embodiment, the heat medium heater 18 is a plate-type heat exchanger equipped with titanium plates, which have excellent resistance to seawater corrosion and abrasion. Titanium is used for its resistance to seawater corrosion, but the plates are thin, only 0.4 mm to 0.7 mm thick, making the heat medium heater 18 less expensive than a shell-and-tube heat exchanger that uses titanium heat transfer tubes.

Figure 3 is a diagram illustrating a liquefied carbon dioxide heating equipment 40 according to another embodiment of the present invention. The liquefied carbon dioxide heating equipment 40 shown in Figure 3 differs from the liquefied carbon dioxide heating equipment 10 shown in Figure 2 in that it further includes a liquefied carbon dioxide vaporization heat exchanger 42.

The liquefied carbon dioxide vaporization heat exchanger 42 is a cylindrical-shell multi-tube heat exchanger, with the cylindrical shell and heat transfer tubes both made of standard steel. A portion of the heat medium from the heat medium outlet 18b of the heat medium heater 18 is supplied to the tube side of the liquefied carbon dioxide vaporization heat exchanger 42. The heat medium is input to the tube-side inlet 42a of the liquefied carbon dioxide vaporization heat exchanger 42, output from the tube-side outlet 42b, and merged with the heat medium from the heating heat exchanger 16 via line 34. Meanwhile, a portion of the liquefied carbon dioxide from the storage tank 12 is supplied to the shell side of the liquefied carbon dioxide vaporization heat exchanger 42. The liquefied carbon dioxide is input to the shell-side inlet 42c of the liquefied carbon dioxide vaporization heat exchanger 42, heat-exchanges with the heat medium, is vaporized, and is output from the shell-side outlet 42d. The carbon dioxide gas output from the body side outlet 42d of the liquefied carbon dioxide gas vaporization heat exchanger 42 is supplied to the storage tank 12 as return gas.

In the liquefied carbon dioxide heating equipment 40 of this embodiment, a portion of the liquefied carbon dioxide is vaporized and supplied to the storage tank 12 as a return, thereby preventing a drop in pressure in the storage tank 12 due to the discharge of liquefied carbon dioxide.

The operation of the liquefied carbon dioxide heating equipment 40 will be explained using specific temperature examples. Here, we consider the case where liquefied carbon dioxide at -20°C and 1.97 MPa is pressurized and heated to 0°C and 10 MPa. The heat medium heater 18 receives, for example, seawater at 7°C and a heat medium (ethylene glycol aqueous solution: freezing temperature -23°C) at -1°C and heats the heat medium to 5°C. The heat medium heated by the heat medium heater 18 is supplied to the shell side inlet 16c of the heating heat exchanger 16 via line 33. The boost pump 14 pressurizes liquefied carbon dioxide at -20°C and 1.97 MPa to -20°C and 10.5 MPa. The heating heat exchanger 16 heats the liquefied carbon dioxide at -20°C and 10.5 MPa supplied to the pipe side inlet 16a to 0°C (10.2 MPa) through heat exchange with the 5°C heat medium. A portion of the liquefied carbon dioxide at -20°C and 1.97 MPa is supplied to the shell-side inlet 42c of the liquefied carbon dioxide vaporization heat exchanger 42. The liquefied carbon dioxide vaporization heat exchanger 42 vaporizes the liquefied carbon dioxide supplied to the shell-side inlet 42c by heat exchange with a 5°C heat medium supplied to the tube-side inlet 42a, and outputs the vaporized gas from the shell-side outlet 42d (-20°C, 1.97 MPa). When liquefied carbon dioxide at -46°C and 0.80 MPa is pressurized and heated to 0°C and 10 MPa, the outlet of the boost pump 14 is -46°C and 10.5 MPa, and the shell-side outlet 42d of the liquefied carbon dioxide vaporization heat exchanger 42 is -46°C and 0.80 MPa, with the temperatures and pressures at all other locations remaining the same.

The present invention has been described above based on examples. These examples are merely illustrative, and those skilled in the art will understand that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present invention.

10, 40 Liquefied carbon dioxide heating equipment, 12 Storage tank, 14 Booster pump, 16 Heating heat exchanger, 18 Heat medium heater, 20 Seawater pump, 22 Heat medium drum, 26 Control valve, 28 Temperature sensor, 30 Heat medium temperature control unit, 32 Bypass line, 42 Liquefied carbon dioxide vaporization heat exchanger, 100 Liquefied CO2 transport ship.

Claims (7)

a heat medium heater that receives seawater and a heat medium and raises the temperature of the heat medium by heat exchange with the seawater;
a heating heat exchanger that heats the liquefied carbon dioxide gas to a predetermined temperature by heat exchange with the heat medium heated by the heat medium heater;
a heat medium temperature control unit including a control valve provided in a bypass line that bypasses a first line that supplies the heat medium from the heat medium heater to the temperature-raising heat exchanger and a second line that supplies the heat medium from the temperature-raising heat exchanger to the heat medium heater, wherein the control valve controls the flow rate of the heat medium flowing through the bypass line so that the temperature of the heat medium supplied to the heat medium heater through the second line is equal to or higher than the freezing temperature of the seawater;
A liquefied carbon dioxide gas heating system comprising: the heating heat exchanger is a cylindrical-shell multi-tube heat exchanger having a plurality of heat transfer tubes housed in a cylindrical shell,
The liquefied carbon dioxide gas is supplied to the heat transfer tube side of the heating heat exchanger,
2. The liquefied carbon dioxide heating facility according to claim 1, wherein the heat medium from the heat medium heater is supplied to the cylindrical shell side of the heating heat exchanger. The liquefied carbon dioxide heating equipment described in claim 2, characterized in that the cylindrical shell and the heat transfer tubes of the heating heat exchanger are both made of steel. A liquefied carbon dioxide heating system as described in any one of claims 1 to 3, characterized in that the heat medium is an ethylene glycol aqueous solution, a propylene glycol aqueous solution, a mixed solution of ethylene glycol aqueous solution and propylene glycol aqueous solution, or a hydrocarbon compound solution. A liquefied carbon dioxide heating system as described in any one of claims 1 to 4, characterized in that the heat medium heater is a plate-type heat exchanger equipped with titanium plates. a heat medium heater that receives seawater and a heat medium and raises the temperature of the heat medium by heat exchange with the seawater;
a heating heat exchanger that heats the liquefied carbon dioxide gas to a predetermined temperature by heat exchange with the heat medium heated by the heat medium heater;
a heat medium temperature control unit that controls the temperature of the heat medium supplied to the heat medium heater so that the temperature is equal to or higher than the freezing temperature of the seawater;
a storage tank for storing the liquefied carbon dioxide gas to be supplied to the heating heat exchanger;
a liquefied carbon dioxide vaporization heat exchanger that receives a portion of the liquefied carbon dioxide from the storage tank and a portion of the heat medium from the heat medium heater, and vaporizes the liquefied carbon dioxide by heat exchange with the heat medium,
The liquefied carbon dioxide gas heating equipment is characterized in that the carbon dioxide gas vaporized in the liquefied carbon dioxide gas vaporization heat exchanger is supplied to the storage tank. supplying seawater and a heat medium to a heat medium heater;
raising the temperature of the heat medium by heat exchange with the seawater using the heat medium heater;
a step of heating the liquefied carbon dioxide gas to a predetermined temperature by heat exchange with the heat medium using a heating heat exchanger ;
using a control valve provided in a bypass line that bypasses a first line that supplies the heat medium from the heat medium heater toward the heating heat exchanger and a second line that supplies the heat medium from the heating heat exchanger toward the heat medium heater, to control the flow rate of the heat medium flowing through the bypass line so that the temperature of the heat medium supplied to the heat medium heater becomes equal to or higher than the freezing temperature of the seawater;
A method for raising the temperature of liquefied carbon dioxide gas, comprising: