Method and apparatus for cooling carbon dioxide and hydrogen

Abstract

The cold of the liquefied natural gas flow (3) is used to cool hydrogen (250) and carbon dioxide (15) by heating the liquefied natural gas in heat exchangers where the gases (9, 39) of two independent cold transfer cycles are cooled.

Description

[Technical field]

[0001] The present invention relates to a process and an apparatus for cooling or further liquefying carbon dioxide and for cooling or further liquefying hydrogen. The present invention also relates to such a process using cold energy from a flow of liquefied natural gas.

[0002] One object of the present invention is to recover cold from the vaporization of a flow of liquefied natural gas, thus reducing the energy required to co-liquefy carbon dioxide and hydrogen. [Background technology]

[0003] It is known to implement an apparatus for separating air by cryogenic distillation, with the recovery of cold from the vaporization of liquefied natural gas (LNG).

[0004] Carbon dioxide liquefaction traditionally uses cold from the ammonia cycle or the refrigeration cycle.

[0005] Hydrogen liquefaction conventionally uses two steps: a pre-cooling step to 80 K followed by a cooling step to 20 K, with the required cold being provided by independent refrigeration cycles for each step.

[0006] US Patent Publication No. 20100083695 discloses using cold from a flow of liquefied natural gas to cool hydrogen which is liquefied through a closed circuit of a refrigerant fluid. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention proposes to use the cold generated by the vaporization of a flow of liquefied natural gas to condense a flow of gaseous carbon dioxide and to cool a flow of gaseous hydrogen, but is not intended to freezing the carbon dioxide. [Means for solving the problem]

[0008] According to one subject of the present invention, there is provided a process for cooling or even at least partially condensing gaseous carbon dioxide and cooling or even at least partially liquefying gaseous hydrogen, said process comprising: i) compressing a first intermediate flow and compressing a second intermediate flow; ii) a step of indirect heat exchange, preferably in a first heat exchanger, between the first flow of liquefied natural gas or a flow of natural gas at a temperature below -50°C and at least the first and second intermediate flows compressed in step i) to form a first flow of heated or further vaporized liquefied gas or a flow of heated natural gas, iii) exiting the first exchanger at a temperature T1 and sending the cooled first intermediate flow to a second indirect heat exchanger, said first intermediate flow cooling a carbon dioxide-rich flow, which is preferably at least partially condensed; iv) sending the second intermediate flow cooled to -130°C to -150°C to a third indirect heat exchanger, said second intermediate flow cooling the flow of hydrogen and optionally a cycle fluid; v) cooling or further at least partially liquefying the hydrogen flow cooled in step iv); Includes.

[0009] According to another optional aspect, the second intermediate flow is expanded, for example in a turbine or a Joule-Thomson valve, before being sent to a third heat exchanger, a first intermediate flow circulates in a closed circuit including a first compressor and passing through a first heat exchanger, and / or a second intermediate flow circulates in a closed circuit including a second compressor and passing through a first heat exchanger, · The first intermediate flow passes through the first exchanger from the hot end towards the midpoint between the hot and cold ends, · The second intermediate flow passes through the first heat exchanger from the hot end to the cold end, · The flow of liquefied natural gas is split into two to form a first flow of liquefied natural gas and a second flow of liquefied natural gas, and the second flow of liquefied natural gas is heated by a part of the first intermediate flow in the fourth indirect heat exchanger, · The fourth heat exchanger is a shell and tube or a coil wound exchanger, · The first heat exchanger is a plate and fin exchanger, · The first heat exchanger is a brazed aluminum plate and fin exchanger, · The maximum temperature difference in the first heat exchanger is 25 °C, or further 20 °C, or further 15 °C, · The temperature difference between the second flow of liquefied natural gas and a part of the first intermediate fluid at the lowest temperature end of the fourth heat exchanger is more than 30 °C, or further more than 50 °C, or further more than 80 °C, · The step of compressing the first intermediate flow and / or the step of compressing the second intermediate flow is carried out at an initial compression temperature of 28 °C or less or further less than 0 °C, · The first and / or second intermediate fluid contains at least 50 mol% nitrogen, or further at least 90 mol% nitrogen, or further 99 mol% nitrogen, · The first and / or second intermediate fluid remains in a gaseous state throughout any cooling in the process, · The molar flow rate D of the second intermediate fluid and the molar flow rate D1 of the fraction of the first intermediate fluid that exchanges heat with the first flow of liquefied natural gas or natural gas are selected such that 0.9D < D1 < 1.3D, · The carbon dioxide rich gas contains at least 90 mol% carbon dioxide or further at least 95 mol% carbon dioxide, · Step ii) is preferably the step of indirect heat exchange between the first flow of liquefied natural gas and the first and second intermediate fluids in the first heat exchanger, step ii) is a step of indirect heat exchange, preferably in a first heat exchanger, between a flow of natural gas at a temperature below -50°C and the first and second intermediate fluids, the first flow of liquefied natural gas provides all of the cold needed to cool or further liquefy the carbon dioxide and / or hydrogen; a flow of natural gas at a temperature below -50°C provides all of the cold required to cool or further liquefy the carbon dioxide and / or hydrogen; The first intermediate flow is not cooled in the first heat exchanger starting from temperature T1.

[0010] According to another subject of the invention, there is provided an apparatus for cooling or further at least partially condensing gaseous carbon dioxide and for cooling or further at least partially liquefying gaseous hydrogen, said apparatus comprising a compressor for compressing a first intermediate flow, a compressor for compressing a second intermediate flow, a first heat exchanger connected to the compressors for compressing the first and second intermediate flows, a second indirect heat exchanger, a third indirect heat exchanger and a pipe for supplying a first flow of liquefied natural gas or a flow of natural gas at a temperature below -50°C, so as to exchange heat for cooling the first intermediate flow to a temperature T1 between -30°C and -100°C, or further between -30°C and -100°C, or further between -30°C and -80°C, preferably between -25°C and -60°C, and for cooling the second intermediate flow to a temperature below T1, preferably between -130°C and -150°C. a pipe for discharging the first intermediate flow cooled to a temperature between -30°C and -100°C from the first heat exchanger at T1 and sending it to a second indirect heat exchanger, the second indirect heat exchanger being connected to a pipe for supplying a carbon dioxide-rich flow, whereby the first intermediate flow cools the carbon dioxide-rich flow, which is preferably at least partially condensed; a pipe for sending the second intermediate flow cooled to -130°C to -150°C to a third indirect heat exchanger, the third indirect heat exchanger being connected to a pipe for supplying a hydrogen flow, whereby the second intermediate flow cools the hydrogen flow and optionally the cycle fluid; and means for cooling or further at least partially liquefying the hydrogen flow cooled in the third indirect heat exchanger.

[0011] Preferably, the first heat exchanger is separate from the second heat exchanger: passing a fluid from the first heat exchanger to the second heat exchanger or vice versa requires discharging the fluid from the first heat exchanger and admitting it to the second exchanger (or vice versa).

[0012] According to another subject of the invention, there is provided a process for converting liquefied natural gas into hydrogen, in which a flow of natural gas is sent to supply a unit for generating a flow containing gaseous hydrogen and carbon dioxide, the gaseous hydrogen being at least partially liquefied and the carbon dioxide from the flow containing carbon dioxide being at least partially condensed as described above, and the heated or vaporized natural gas from the process described above forms at least part of the flow of natural gas sent to the unit for generating hydrogen.

[0013] The invention will now be explained in more detail with reference to the figures. [Brief description of the drawings]

[0014] [Figure 1] 1 illustrates a process according to the present invention. [Diagram 2] 1 illustrates a process according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Figure 1] shows an integrated process for cooling gaseous carbon dioxide, cooling gaseous hydrogen and vaporizing liquefied natural gas. The vaporizer 100 for vaporizing liquefied natural gas optionally includes a pump P if the liquefied natural gas 1 is not at the required pressure. The liquefied natural gas 1 is split into two parts, one part 3 is sent to a plate-and-fin heat exchanger E1, for example a brazed aluminum plate-and-fin exchanger. The liquid 3 flows through the entire exchanger from the cold end to the hot end and vaporizes therein. The remaining part 5 of the liquid 1 is sent by valve V1 to the heat exchanger E4, where it exchanges heat and is vaporized by the flow 7 of cycle gas. The two vaporized gases in the exchangers E1, E4 are mixed to form the vaporized natural gas 45. Preferably, the vaporized natural gas 5 leaves the exchanger E1 at a temperature above 0°C.

[0016] Liquefied natural gas 1, 3, 5 can replace natural gas below -50°C.

[0017] The carbon dioxide liquefier 500 includes a compressor C3 for compressing the gaseous carbon dioxide 450. The compressed gas 13 is cooled, stripped of water and optionally methanol, then compressed in compressor C4, cooled and then compressed in compressor C5. The gas 15 compressed in compressor C5 is partially condensed in a plate-and-fin heat exchanger E2, for example a brazed aluminum plate-and-fin exchanger. The gas 13 is rich in carbon dioxide and contains at least 90 mol % carbon dioxide or even at least 95 mol % carbon dioxide. The two-phase fluid formed is sent to a phase separator S1, which produces a gas 17 that is heated in exchanger E2 and rejoins the gas compressed in compressor C5. The liquid from the phase separator is vaporized in exchanger E2 and is partially returned as liquid 21 that rejoins the gas compressed in compressor C5. The remaining portion 19 of the liquid from separator S1 is sent to a stripping column R, of which the bottom liquid 550, freed of light impurities, constitutes the liquefied CO2. The gas from column R is heated in exchanger E2.

[0018] If the gas 13 is sufficiently pure, column R is not necessary.

[0019] The cold energy required for this liquefaction in the liquefier E2 is at least partially recovered by a closed cycle. A first intermediate fluid, cycle gas 11, is heated in the heat exchanger E2, compressed in the compressor C1 and then optionally split in two. At least a part 9 of the cycle gas arrives at the hottest part of the heat exchanger E1 and is cooled to the intermediate temperature in the exchanger E2. As a variant, a part or even the remaining part 7 of the cycle gas is cooled in the exchanger E4 and the two cooled fluids 7, 9 are mixed to form the cycle gas 11.

[0020] Compressor C1 may compress the cycle gas 11 sufficiently to overcome pressure losses, etc., that may be associated with a turbine that expands the cycle gas.

[0021] The hydrogen liquefier 300 includes two heat exchangers, one pre-cooling heat exchanger E3 and one final heat exchanger E5.

[0022] The hydrogen 250 to be liquefied is first cooled in the exchanger E3, then in the exchanger E6, and finally in the exchanger E5 so as to form liquefied hydrogen 350.

[0023] Another closed cycle composed of a second intermediate fluid transfers cold thermal energy from the liquefied natural gas towards the heat exchanger E3. The cycle gas 39 is compressed in the compressor C2 and then flows through the heat exchanger E1 from the high-temperature end to the low-temperature end before being split into two. A part 41 of the gas 39 expands in the turbine T1. The remaining part 43 is sent to the low-temperature end of the heat exchanger E3, where it partially condenses and then is sent to the phase separator 37. The separator gas mixed with the turbine flow 41 becomes the gas 39 heated in the heat exchanger E3 by flowing through the heat exchanger E3 from the low-temperature end to the high-temperature end.

[0024] The liquid 35 from the separator is vaporized in the heat exchanger E6 and added back to the separator 37.

[0025] The molar flow rate D of the second intermediate fluid 39 and the molar flow rate D1 of the fraction 3 of the first intermediate fluid that exchanges heat with the first flow of the liquefied natural gas are selected such that 0.9D < D1 < 1.3D.

[0026] The first and / or second intermediate fluids 9, 39 contain at least 50 mol% nitrogen, or even at least 90 mol% nitrogen, or even 99 mol% nitrogen.

[0027] The first and / or second intermediate fluids 9, 39 remain in the gaseous state throughout any cooling in the process.

[0028] [Figure 2] shows an overall integrated process of [Figure 1], in which liquefied natural gas LNG is vaporized in a vaporizer 100 to produce natural gas NG. The natural gas is fed to a reactor 200 of SMR, ATR or POX type, which is optionally also fed with oxygen 150 from an air separation unit ASU. The reactor 200 produces gaseous hydrogen 250, which is liquefied in a hydrogen liquefier 300 to produce liquid hydrogen 350.

[0029] The reactor 200 also produces gas 370, which may be synthesis gas or combustion gas (flue gas).

[0030] As shown in FIG. 1, the liquefiers 300 and 500 are integrated with the vaporization device 100, so that at least a portion of the cold energy required to cool or further liquefy carbon dioxide in the liquefier 500 and to cool or further liquefy hydrogen in the liquefier 300 is provided by the vaporization of LNG in the device 100. For example, at least 50%, or at least 75%, or at least 99% of the cold energy required to cool or further liquefy carbon dioxide 450 in the liquefier 500 is provided by the vaporization of LNG in the device 100. Alternatively or in addition, at least 50%, or at least 75%, or at least 99% of the cold energy required to cool, for example to 80K or to further liquefy hydrogen 250 in the liquefier 300 is provided by the vaporization of LNG in the device 100.

Claims

1. 1. A process for cooling or further at least partially condensing gaseous carbon dioxide and cooling or further at least partially liquefying gaseous hydrogen, comprising: i) a step (C1) of compressing a first intermediate flow (7, 11) and a step (C2) of compressing a second intermediate flow (39, 41, 43); ii) a step of indirect heat exchange, preferably in a first heat exchanger (E1), between the first flow of liquefied natural gas (3) or a flow of natural gas at a temperature below -50°C and at least the first and second intermediate flows compressed in step i) to form a first flow of heated or further vaporized liquefied natural gas (45) or a flow of heated natural gas, iii) exiting the first exchanger with the cooled first intermediate flow (11) at the temperature T1 and sending it to a second indirect heat exchanger (E2), where the first intermediate flow cools a flow rich in carbon dioxide (15), which is preferably at least partially condensed; iv) sending said second intermediate flow (43) cooled to -130°C to -150°C to a third indirect heat exchanger (E3), said second intermediate flow cooling a flow of hydrogen (250) and optionally a cycle fluid (27); v) cooling or further at least partially liquefying the hydrogen flow cooled in step iv); A process including.

2. The process of claim 1, wherein the second intermediate flow (41) is expanded, for example in a turbine (T1) or a Joule-Thomson valve, before being sent to the third heat exchanger (E3).

3. 3. The process according to claim 1 or 2, wherein the first intermediate flow (9) circulates in a closed circuit comprising a first compressor (C1) and passes through the first heat exchanger (E1) and / or the second intermediate flow circulates in a closed circuit comprising a second compressor (C2) and passes through the first heat exchanger (E1).

4. 4. The process according to any one of claims 1 to 3, wherein a flow of liquefied natural gas (1) is split in two to form the first flow of liquefied natural gas (3) and the second flow of liquefied natural gas (5), the second flow of liquefied natural gas being heated with a portion (7) of the first intermediate flow (11) in a fourth indirect heat exchanger (E4).

5. 5. The process according to claim 4, wherein the fourth heat exchanger (E4) is a shell-and-tube or coil-wound exchanger.

6. The process according to any one of claims 1 to 5, wherein the first heat exchanger (E1) is a plate-and-fin exchanger.

7. 7. The process according to claim 6, wherein the maximum temperature difference in the first heat exchanger (E1) is 25°C, or even 20°C, or even 15°C.

8. 8. The process of any one of claims 1 to 7 when dependent on claim 4 or 5, wherein the difference in temperature between the second flow (7) of liquefied natural gas and the portion (5) of the first intermediate fluid at the coldest end of the fourth heat exchanger is more than 30°C, or even more than 50°C, or even more than 80°C.

9. The process according to any one of the preceding claims, wherein the step of compressing the first intermediate flow (11) and / or the step of compressing the second intermediate flow (39) are carried out at an initial compression temperature below 28°C or even below 0°C.

10. 10. The process according to any one of the preceding claims, wherein the first and / or second intermediate fluid (11, 39) contains at least 50 mol % nitrogen, or even at least 90 mol % nitrogen, or even 99 mol % nitrogen.

11. A process as claimed in any one of the preceding claims, wherein the first and / or second intermediate fluids (7, 9, 11, 39) remain in a gaseous state throughout any cooling in the process.

12. 12. The process according to any one of claims 1 to 11, wherein the molar flow rate D of the second intermediate fluid (39) and the molar flow rate D1 of the fraction of the first intermediate fluid (11) exchanging heat with the first flow of liquefied natural gas (3) or natural gas are selected such that 0.9D<D1<1.3D.

13. An apparatus for cooling or at least partially condensing gaseous carbon dioxide (15) and for cooling or at least partially liquefying gaseous hydrogen (250), comprising a compressor (C1) for compressing a first intermediate flow, a compressor (C2) for compressing a second intermediate flow, a first heat exchanger (E1) connected to said compressors for compressing said first and second intermediate flows, a second indirect heat exchanger (E2), a third indirect heat exchanger (E3), and pipes for supplying a first flow of liquefied natural gas (3) or a flow of natural gas at a temperature below -50°C, so as to exchange heat for cooling said first intermediate flow to a temperature T1 of -30°C to -100°C or even -30°C to -80°C, preferably -25°C to -60°C, and cooling said second intermediate flow to a temperature below T1, preferably -130°C to -150°C, and a second indirect heat exchanger (E4) connected to said compressors for compressing said first and second intermediate flows, 1. An apparatus comprising: a pipe for discharging the first intermediate flow cooled to a temperature between 0° C. and −100° C. from the first heat exchanger at T1 and sending it to the second indirect heat exchanger, the second indirect heat exchanger being connected to a pipe for supplying a carbon dioxide-rich flow, whereby the first intermediate flow cools the carbon dioxide-rich flow, which preferably at least partially condenses; a pipe for sending the second intermediate flow cooled to −130° C. to −150° C. to the third indirect heat exchanger, the third indirect heat exchanger being connected to a pipe for supplying a hydrogen flow, whereby the second intermediate flow cools the hydrogen flow and optionally a cycle fluid; and means (E6, E5) for cooling or further at least partially liquefying the hydrogen flow cooled in the third indirect heat exchanger.

14. 14. Apparatus according to claim 13, wherein the first heat exchanger (E1) is separate from the second heat exchanger (E2).

15. 13. A process for converting liquefied natural gas into hydrogen, wherein a flow of natural gas is sent to supply a unit (200) for generating a flow containing gaseous hydrogen and carbon dioxide, said gaseous hydrogen (250) being at least partially liquefied and carbon dioxide (450) originating from said flow containing carbon dioxide being at least partially condensed as claimed in the process of any one of claims 1 to 12, and wherein a heated or vaporized natural gas (45, NG) as claimed in the process forms at least a part of the flow of natural gas sent to the unit for generating hydrogen.

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