Method and apparatus for cooling hydrogen

Abstract

To provide a method for start-up in a method implemented using cold energy of a flow of a vaporized natural gas or a vaporized liquefied natural gas that is at a temperature lower than -50°C.SOLUTION: A method for cooling hydrogen during a start-up mode comprises: sending a supercritical natural gas (1,2) to a first heat exchanger (E1) to cool the supercritical natural gas and then exchanging heat with a flow of intermediate fluid (5) in a cycle at a pressure of 3-70 bar abs which is cooled; sending the flow of the intermediate fluid (5) cooled in the first heat exchanger directly to an inlet of a compressor (C, C1) which compresses the flow of the intermediate fluid at a lower compression ratio than in the first mode, where a molar flow rate of the intermediate fluid (13) is less than 80% of a molar flow rate of the intermediate fluid sent to the compressor during a stable operation; and returning the intermediate fluid (15, 17) compressed in the compressor to the first heat exchanger as cycle fluid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for cooling hydrogen. [Background technology]

[0002] The use of optimised methods for cooling hydrogen by recovering cold energy from the vaporisation of liquefied natural gas (LNG) is known.

[0003] It is known to liquefy hydrogen in two steps: A first step of pre-cooling using a nitrogen cycle or a mixed refrigerant cycle, followed by A second step of liquefying the cooled hydrogen using a mixed refrigerant cycle containing hydrogen, helium or a noble gas.

[0004] The invention proposes a solution for the start-up of the process in which the first step of pre-cooling the hydrogen is carried out using the cold energy of a stream of vaporized natural gas or vaporized liquefied natural gas at a temperature below -50°C.

[0005] In this case, the liquefier does not have an internal source for producing cold at the moment of start-up.

[0006] During steady operation, the liquefied natural gas is heated or vaporized, for example, in contact with an intermediate fluid, which is cooled to a temperature below -50°C, or even below -140°C. The heat exchangers used to heat the liquefied natural gas are typically brazed aluminum plate and fin heat exchangers, or stainless steel heat exchangers, or printed circuit heat exchangers. During start-up of the process, the heat exchangers and associated equipment must be cooled from ambient temperature to a temperature for steady operation. These elements are sensitive to sudden or excessive temperature drops and therefore require careful attention to be cooled.

[0007] To transfer the heat of vaporization of liquefied natural gas to cooled hydrogen, it is known to use a cycle comprising a compressor, preferably having an inlet temperature below −90° C., and optionally an expansion turbine. Cooling of such a compressor during start-up requires particular attention.

[0008] Kuendig et al., “Large scale hydrogen liquefaction in combination with LNG gasification”, 16th World Hydrogen Energy Conference 2006, describes a method as set forth in the preamble of claim 1. Summary of the Invention

[0009] According to one aspect of the present invention, there is provided a method for cooling hydrogen, comprising: According to the first mode of operation, i) either liquefied natural gas or vaporized natural gas at a temperature below -50°C is heated by indirect heat exchange in a first heat exchanger with an intermediate fluid stream at a pressure between 3 and 70 bar abs which has been cooled to a temperature above -145°C; ii) The flow of intermediate fluids at temperatures above -145°C is a) by introducing it at this temperature into a second heat exchanger where it is cooled by indirect heat exchange, and / or b) cooled by expansion in a turbine or valve, optionally driving a compressor of the method; iii) the gaseous hydrogen stream is cooled in a second heat exchanger without condensation; iv) a gaseous stream derived from the intermediate fluid cooled in steps a) and / or b) is heated in a second heat exchanger to a temperature between −90° C. and −150° C., withdrawn from the heat exchanger at this temperature and compressed in a compressor having an inlet temperature between −90° C. and −150° C., at least a portion of the compressed intermediate fluid being first cooled in a first heat exchanger and then heated from a temperature of at most −110° C., v) at least a portion of the heated intermediate fluid constitutes the intermediate fluid stream of step i); the compressed intermediate fluid cooled in the first heat exchanger is heated in a second heat exchanger; During start mode, i) the hydrogen stream is not sent to a second heat exchanger; ii) the supercritical natural gas or gas below -100°C is sent to a first heat exchanger in order to cool it, where it exchanges heat with a cooled intermediate fluid stream of the cycle at a pressure between 3 and 70 bar absolute; iii) the flow of intermediate fluid cooled in the first heat exchanger is sent directly to the inlet of a compressor which compresses it at a compression ratio lower than that of the first mode, the molar flow rate of the intermediate fluid being less than 80% of the molar flow rate of the intermediate fluid sent to the compressor during the first mode; iv) the intermediate fluid compressed in the compressor is returned to the first heat exchanger as a cycle fluid; and The method comprising:

[0010] Other optional aspects include: The intermediate fluid contains more than 50 mol% nitrogen, preferably at least 90 mol% nitrogen, or even at least 99 mol% nitrogen. During start-up, supercritical natural gas is pseudo-vaporized in the first heat exchanger, where it is preferably heated to a temperature above 0°C. During start-up, gas below -100°C is heated in the first heat exchanger, the heated gas having the same composition as the intermediate fluid. The gas heated in the first heat exchanger is sent to the cycle to supply it. During start-up, when the compressor inlet or outlet temperature falls below a threshold value, the intermediate fluid flow cooled in the first heat exchanger is sent for expansion in the turbine, and the expanded fluid is sent back to be heated in the second heat exchanger and then sent to the compressor. The turbine is coupled to a booster, which boosts the fluid compressed in the compressor only when the turbine expands the intermediate fluid during start-up. The compressor comprises at least two stages and the intermediate fluid is not cooled between the compressor stages. During the first mode, the compressed intermediate fluid is first cooled in the first heat exchanger, cooled in the second heat exchanger and cooled again in the first heat exchanger before being sent to the turbine; during start-up, the compressed intermediate fluid is first cooled in the first heat exchanger, optionally heated externally in the second heat exchanger by a heater and cooled again in the first heat exchanger.

[0011] According to another subject of the invention, an apparatus for cooling hydrogen is provided, comprising a first heat exchanger and means for sending either liquefied natural gas or vaporized natural gas at a temperature below -50°C to be heated by indirect heat exchange in the first heat exchanger with a stream of intermediate fluid at a pressure between 3 and 70 bar absolute that has been cooled to a temperature above -145°C, a second heat exchanger and means for sending the stream of intermediate fluid at a temperature above -145°C to be cooled by introducing it at this temperature into the second heat exchanger where it is cooled by indirect heat exchange and / or by expansion in a turbine or in a valve, optionally driving a compressor of the method, and means for sending a stream of gaseous hydrogen without condensation into the second heat exchanger. means for passing a gaseous stream derived from the cooled intermediate fluid to be heated in a second heat exchanger to a temperature between -90°C and -150°C, means for withdrawing a gaseous stream from the second heat exchanger at this temperature, a compressor having an inlet temperature between -90°C and -150°C, means for passing the withdrawn gaseous stream to the compressor having an inlet temperature between -90°C and -150°C, means for passing at least a portion of the compressed intermediate fluid to be first cooled in the first heat exchanger and then heated from a temperature of at most -110°C, wherein at least a portion of the heated intermediate fluid constitutes the intermediate fluid stream of step i), 1. An apparatus comprising: means for directing a compressed intermediate fluid, cooled in a first heat exchanger, to be heated in a second heat exchanger.

[0012] According to other optional aspects of the invention: the turbine is coupled to a booster; the compressor comprises at least two stages without means for cooling an intermediate fluid between the compressor stages;

[0013] The use of intermediate fluids makes it possible to better regulate integration by separating hydrogen and LNG networks.

[0014] Vaporization of the LNG takes place in a single heat exchanger, and an intermediate fluid distributes the cold to various consumers.

[0015] The intermediate cycle makes it possible to produce a cryogenic fluid at a lower temperature than LNG by means of an expansion step. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a cooling or liquefaction method according to the present invention. [Diagram 2] FIG. 2 illustrates another cooling or liquefaction method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] During stable operation, the method for cooling hydrogen works as follows: A dedicated heat exchanger E1 serves to recover cold energy from liquefied natural gas 1 at -150°C using an intermediate fluid cooled by liquid 1 in the heat exchanger E1. The heat exchanger E1 can be a brazed aluminum plate and fin heat exchanger, or a stainless steel heat exchanger, or a printed circuit heat exchanger. Alternatively, the heat exchanger E1 can be a shell and tube heat exchanger.

[0018] Liquid 1 is heated, for example to 15° C., and optionally vaporized to cool fluid 5 to a temperature below −50° C., preferably below −120° C. Fluid 5 is cooled in heat exchanger E1 to a temperature above −145° C. In this example it is cooled to −140° C. The heat exchanger can be an aluminium or stainless steel plate and fin heat exchanger, or a shell and tube heat exchanger.

[0019] Fluid 1 enters the cold end of heat exchanger E1 and exits as fluid 3 at the hot end.

[0020] In this example, the fluid 5 is nitrogen. It may be, for example, natural gas or methane, or may have another suitable composition. Preferably, the fluid 5 is inert. The fluid 5 is preferably at a pressure of between 3 and 70 bar absolute.

[0021] Nitrogen 13 leaves the heat exchanger E2 at a temperature between -90 ° C and -150 ° C, for example at -120 ° C, and is compressed to about 20 bar in a first compressor C, for example a centrifugal compressor. The 20 bar nitrogen is then cooled R and compressed to a pressure higher than 20 bar in another compressor C1. The nitrogen higher than 20 bar is then optionally split into two portions 15, 17, portion 17 is not necessarily present. The portion 17 can be partially cooled in the heat exchanger E1 and then sent to the element 31 to be cooled. The heated portion 19 is thus sent to the hot end of the heat exchanger E1. The portion 15 added to 19 forms a stream 21 sent to the hot end of the heat exchanger E1 at 20 ° C, where it is cooled to a temperature lower than -90 ° C, for example to -140 ° C, forming a gas 27 sent to the heat exchanger E2 at a temperature of -140 ° C. The gas 27 is heated to 20° C. in the heat exchanger E2 (forming stream 6), which is then cooled against LNG in the heat exchanger E1 to form gas 5. In this example, the gas 5 is not cooled in the heat exchanger E1, but only in the turbine E. The gas 5 therefore enters the turbine E at the temperature it left the heat exchanger E1. The fluid 7 expanded at 1.5 bar in the turbine T is two-phase and is sent to a phase separator, where it forms a liquid 9 and a gas 11. The liquid is vaporized in the heat exchanger E3 and combined with the gas 11, which is heated in the heat exchanger E2 to constitute the stream 13 to be sent to the cold compressor C. All the gas 13 is compressed in the cold compressor C and then in a booster C1 coupled to the turbine E. It is the gas compressed in the booster C1 that is sent to the heat exchanger E1 to recover cold from the LNG 1.

[0022] Alternatively, the gas 5 coming from the cold end of the heat exchanger E1 may first be passed through the heat exchanger E1 to be cooled and then expanded in a turbine T having an inlet temperature lower than -100°C, for example -120°C.

[0023] Thus, nitrogen or another fluid, such as helium or a mixed refrigerant, circulates in a closed cycle, extracting cold energy from the LNG.

[0024] Gaseous hydrogen 23 at ambient temperature, e.g. 20° C., enters the hot end of heat exchanger E2 and passes from one end to the other, being cooled to a temperature below −150° C., e.g. −180° C. It is then cooled in heat exchanger E3 against phase separator liquid to form gaseous hydrogen 25 at −190° C.

[0025] The hydrogen 25 is then cooled and liquefied in another heat exchanger in a known manner. A mixed refrigerant cycle containing hydrogen, helium, or a noble gas provides the required cold energy.

[0026] Thus, the LNG provides at least a portion of the cold energy required to pre-cool the gaseous hydrogen to −190° C. This portion may be at least 50%, at least 75%, or at least 99% of the cold energy required to cool the gaseous hydrogen to −190° C. The LNG may even provide all the required cold energy apart from that coming from the turbine T.

[0027] The method may also provide cold to another element 31 cooled by the cycle. In the figure it can be seen that a part 17 of the gas compressed in compressors C, C1 is cooled in the heat exchanger to an intermediate temperature, in this case -50°C, and is withdrawn from the heat exchanger in its central zone, serving to cool element 31 by being itself heated to form a gas 19, which joins with stream 15 compressed in compressor C to form stream 21 which enters heat exchanger E1 at 20°C. As the pressure drop for streams 18, 19 is limited, a small expansion of stream 15 in the valve is sufficient to allow the streams 15, 19 to mix.

[0028] Element 31 can for example be a liquefaction unit for another gas or a unit for separation by distillation and / or partial condensation at temperatures below 0° C., for example a carbon dioxide liquefaction unit.

[0029] If portion 17 is present but element 31 is not operational, a heater, such as an electric heater or a heat exchanger heated with hot water, will serve to heat portion 17 so as to form stream 19.

[0030] During start-up of the unit, hydrogen 23 is not sent to the heat exchanger E2, which must be cooled beforehand. The cycle compressor C is started up at a reduced load, typically 60-80% of the nominal molar flow rate, with an inlet temperature that is ambient. The compression ratio is also limited in order to limit the outlet temperature of compressor C to a reasonable value, typically below 150°C. Compressor C may only have an aftercooler R upstream of compressor C and no interstage cooling, in order to reduce the cost of the machine and to limit the risk of freezing of water in the intermediate water cooler, which is bypassed in stable operation when the temperature of the gas to be compressed is below 0°C, and the compression ratio is significantly reduced to limit the temperature at the outlet of compressor C1 upstream of the aftercooler.

[0031] For start-up, a variable frequency drive can vary the speed of the motor of compressor C, and hence the temperature and compression ratio of the final stage of C.

[0032] Before the start-up of turbine E, compressor C1 does not compress the nitrogen passing through bypass duct 13A.

[0033] Only the nitrogen compressed in the compressor C is sent to the first heat exchanger E1, which is not supplied with liquefied natural gas 1 at start-up, but with liquid nitrogen coming from a store S, vaporized by a vaporizer V to form gaseous nitrogen 2 at -180°C. Using a vaporized cryogenic gas, rather than a liquid, makes it possible to protect the equipment from excessively rapid cooling and from thermal stress. The gaseous nitrogen is heated in the heat exchanger E1 and is either recovered at the cold end or sent to the air.

[0034] Alternatively, as illustrated in FIG. 2, the heat exchanger E1 can be cooled by feeding supercritical liquefied natural gas. This fluid has the advantage of a reduced enthalpy of vaporization compared to non-supercritical LNG. For this reason, the liquefied natural gas 1 can be heated in a heater H to regulate its temperature at the inlet of the heat exchanger E1.

[0035] In the case of these two figures, the vaporized liquid other than natural gas used for start-up (typically nitrogen) can be sent to the atmosphere or can be recovered, for example at 15° C., to serve in the cycle (compressor C, C1, turbine T) for cooling intermediate fluids to make up for leaks. The lines for the cycle and the interconnection with the vaporized start-up liquid may need to be sufficiently isolated to completely separate the LNG vaporization line and the cooling cycle during normal operation (typically by removing the connecting spool).

[0036] The cooling cycle (compressor C, C1, turbine T) at the outlet of the heat exchanger E1 will be slowly cooled down to the operating temperature. As long as the temperature at the outlet of the heat exchanger E1 is higher than the operating temperature, the gas 5 will not be sent to the turbine or to the heat exchanger E2 but will be sent directly to the inlet of the compressor C through the duct 5A in order to slowly cool it.

[0037] While the inlet temperature of compressor C is decreasing, the compression ratio of compressor C will increase since its inlet temperature will decrease.

[0038] A temporary heater W (typically a water-fed heat exchanger) can be used only during start-up, instead of introducing heat from heat exchanger E2. This heater W can be bypassed during stable operation of the method. It heats the nitrogen stream 27 sent through duct 27A, preventing the stream 27 from entering heat exchanger E2.

[0039] Cooling of the hydrogen pre-cooling system begins once compressor C has cooled and is running at a reduced load, typically 60-80% of the nominal molar flow rate. Initially, turbine E is bypassed by line 5E, which causes gas 5 to flow directly to the phase separator (which does not yet separate phases, since gas 5 is not condensed). Then, the turbine and its associated compressor C1 are started, and the gas compressed in compressor C no longer passes through bypass line 13A and is compressed in compressor C1.

[0040] The main advantage of this method is that it uses existing equipment with some minimal additions to the device for cooling hydrogen without safety issues due to the regulated start-up of sensitive equipment.

Claims

1. In methods for cooling hydrogen, According to the first mode of operation, i) Either liquefied natural gas (1, 2) or vaporized natural gas at a temperature below -50°C is heated by indirect heat exchange in a first heat exchanger (E1) with a flow of intermediate fluid (5) at a pressure of 3 to 70 absolute bars that has been cooled to a temperature of -145°C or higher. ii) The flow of the intermediate fluid at a temperature of -145°C or higher is a) By introducing it at this temperature into a second heat exchanger (E2) which is cooled by indirect heat exchange, and / or b) The compressor (C, C1) is cooled by expansion within the turbine (E) or valve that optionally drives it. iii) The flow of gaseous hydrogen (23) is cooled in the second heat exchanger without condensation. iv) The gaseous flow (13) derived from the intermediate fluid cooled in step a) and / or b) is heated in the second heat exchanger (E2) to a temperature of -150°C to -90°C, taken out of the heat exchanger at this temperature and compressed in a compressor (C, C1) having an inlet temperature of -150°C to -90°C, and at least a portion of the compressed intermediate fluid (15, 17) is first cooled in the first heat exchanger and then heated from a temperature of at most -110°C, v) A method in which at least a portion of the heated intermediate fluid constitutes the flow of the intermediate fluid in step i), The intermediate fluid, which has been cooled and compressed in the first heat exchanger, is heated in the second heat exchanger. During startup mode, i) The hydrogen flow is not sent to the second heat exchanger, ii) Supercritical natural gas (1, 2) or gas below -100°C is sent to the first heat exchanger to cool it, where it exchanges heat with the flow of the cyclic intermediate fluid (5) at a cooled pressure of 3 to 70 absolute bars. iii) The flow of the intermediate fluid (5) cooled in the first heat exchanger is sent directly to the inlet of the compressor (C, C1) which compresses it at a lower compressibility than that of the first mode, wherein the molar flow rate of the intermediate fluid (13) is less than 80% of the molar flow rate of the intermediate fluid sent to the compressor during the first mode. iv) The intermediate fluids (15, 17) compressed in the compressor are sent back to the first heat exchanger as a cycle fluid, A method characterized by the following.

2. The method according to claim 1, wherein the intermediate fluid (5) contains more than 50 mol% nitrogen, preferably at least 90 mol% nitrogen, or even more preferably at least 99 mol% nitrogen.

3. The method according to claim 1 or 2, wherein during startup, the supercritical natural gas (1, 2) is pseudo-vaporized in the first heat exchanger (E1) and preferably heated to a temperature higher than 0°C in the first heat exchanger (E1).

4. The method according to claim 1 or 2, wherein during startup, the gas, which is below -100°C, is heated in the first heat exchanger (E1), and the heated gas has the same composition as the intermediate fluid (5).

5. The method according to claim 4, wherein the gas (3) heated in the first heat exchanger (E1) is sent to the cycle to supply the gas.

6. The method according to claim 1 or 2, wherein, during startup, if the inlet or outlet temperature of the compressor (C, C1) falls below a threshold, the flow of the intermediate fluid cooled in the first heat exchanger is sent to the turbine (E) for expansion, the expanded intermediate fluid is sent back to the second heat exchanger (E2) for heating, and then sent to the compressor.

7. The method according to claim 6, wherein the turbine (E) is coupled to a booster (C1), and the booster boosts the fluid compressed in the compressor (C) only when the turbine expands the intermediate fluid during startup.

8. The method according to claim 1 or 2, wherein the compressor (C, C1) comprises at least two stages, and the intermediate fluid is not cooled between the stages of the compressor.

9. During the first mode, the compressed intermediate fluid (6) is cooled again in the first heat exchanger (E1) before being sent to the turbine (E). The method according to claim 1 or 2, wherein during startup, the compressed intermediate fluid is first cooled in the first heat exchanger, optionally heated outside the second heat exchanger by a heater (W), and then cooled again in the first heat exchanger.

10. A device for cooling hydrogen, The first heat exchanger (E1), Means for delivering either liquefied natural gas (1, 2) or vaporized natural gas at a temperature below -50°C, wherein the liquefied natural gas (1, 2) or vaporized natural gas is heated by indirect heat exchange in the first heat exchanger (E1) with a flow of intermediate fluid (5) cooled to a temperature of -145°C or higher at a pressure of 3 to 70 absolute bars, The second heat exchanger (E2), Means for delivering the intermediate fluid flow at a temperature of -145°C or higher, wherein the intermediate fluid flow is introduced at this temperature into a second heat exchanger (E2) which is cooled by indirect heat exchange, and / or delivered in such a way that it is cooled by expansion within a turbine (E) or valve that optionally drives a compressor (C, C1), Means for delivering a flow of gaseous hydrogen (23) to the second heat exchanger so as to cool it without condensation, Means for sending a gaseous flow (13) derived from the cooled intermediate fluid to the second heat exchanger (E2) to heat it to a temperature of -150°C to -90°C, means for taking out the gaseous flow from the second heat exchanger at this temperature, and compressors (C, C1) having an inlet temperature of -150°C to -90°C. Means for sending the extracted gaseous flow to the compressor (C, C1) having an inlet temperature of -150°C to -90°C, An apparatus comprising means for sending at least a portion of the compressed intermediate fluid (15, 17) to be first cooled in the first heat exchanger and then heated from a maximum temperature of -110°C, wherein at least a portion of the heated intermediate fluid constitutes the flow of the intermediate fluid in step i), The apparatus is characterized by comprising means for sending the compressed intermediate fluid, cooled in the first heat exchanger, to be heated in the second heat exchanger.

11. The apparatus according to claim 10, wherein the turbine (E) is coupled to a booster (C1).

12. The apparatus according to claim 10 or 11, wherein the compressor (C, C1) comprises at least two stages without means for cooling the intermediate fluid between the stages of the compressor.

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