METHOD AND DEVICE FOR COOLING HYDROGEN

Description

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

[0002] It is known to use a process of cooling hydrogen by recovering frigories from the vaporization of liquefied natural gas (LNG).

[0003] It is known to liquefy hydrogen in two stages: A first pre-cooling step using a nitrogen cycle or a mixed refrigerant cycle followed by a second step of liquefaction of the cooled hydrogen with a cycle of hydrogen, helium or mixed refrigerants including noble gases.

[0004] The present invention proposes a solution for starting a process in which the first step of pre-cooling the hydrogen is carried out using the frigories of a flow of liquefied natural gas which vaporizes or vaporized natural gas, the vaporized natural gas being at a temperature below -50°C.

[0005] In this case, the liquefaction device does not include an internal source of cold production at the time of start-up.

[0006] In steady-state operation, liquefied natural gas, for example, is heated or even vaporized against an intermediate fluid, which cools to a temperature below -50°C or even below -140°C. The heat exchanger used to heat the liquefied natural gas is typically a brazed aluminum plate-fin heat exchanger, a stainless steel heat exchanger, or a printed circuit heat exchanger. During process start-up, the heat exchanger and associated equipment must cool from ambient temperature to the steady-state operating temperature. These elements are sensitive to rapid or excessive temperature drops and therefore require special attention for cooling.

[0007] It is known to use a cycle to transfer the heat of vaporization from liquefied natural gas to the hydrogen which cools, this cycle comprising a compressor with an inlet temperature preferably below -90°C and possibly an expansion turbine. Cooling such a compressor during start-up requires special attention.

[0008] "Large scale hydrogen liquefaction in combination with LNG gasification" by Kuendig et al, 16th World Hydrogen Energy Conference 2006 describes a method according to the preamble of claim 1.

[0009] According to an object of the invention, there is provided a method for cooling hydrogen in which according to a first mode of operation i) Either liquefied natural gas or vaporized natural gas, the vaporized natural gas being at a temperature below -50°C, is heated by indirect heat exchange in a first heat exchanger with an intermediate fluid flow at a pressure between 3 and 70 bar abs which cools to a temperature greater than or equal to -145°C ii) The intermediate fluid flow at a temperature equal to or greater than -145°C is cooled a) by introducing it at this temperature into a second heat exchanger where it cools by indirect heat exchange and / or b) by expansion in a turbine, possibly driving a compressor of the process, or a valve iii) a flow of hydrogen gas is cooled in one or as the case may be the second heat exchanger without condensing iv) a gas flow derived from the intermediate fluid cooled in step a) and / or b) is heated in the second heat exchanger to a temperature between -90°C and -150°C,is withdrawn from the exchanger at this temperature and compressed in a compressor with an inlet temperature between -90°C and -150°C and at least a portion of the compressed intermediate fluid is cooled first in the first heat exchanger and then heats up from a temperature of at most -110°C and v) the at least a portion of the heated intermediate fluid constitutes the intermediate fluid flow of step i) and characterized in that the intermediate fluid compressed and cooled in the first heat exchanger heats up in the second heat exchanger and in that during a start-up mode i) the hydrogen flow is not sent to the second exchanger, ii) supercritical natural gas or a gas at less than -100°C is sent to the first exchanger to cool it and exchanges heat there with an intermediate fluid flow of a cycle at a pressure between 3 and 70 bar abs which cools down,iii) the flow of cooled intermediate fluid in the first exchanger is sent directly to the inlet of the compressor which compresses it with 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 intermediate fluid sent to the compressor during the first mode and iv) the intermediate fluid compressed in the compressor is returned to the first exchanger as cycle fluid.

[0010] According to other optional aspects: the intermediate fluid contains more than 50 mol% nitrogen, preferably at least 90 mol% nitrogen, or even at least 99 mol% nitrogen. during startup the supercritical natural gas pseudovaporizes in the first heat exchanger and preferably heats up to a temperature above 0°C. during startup, the gas at less than -100°C heats up in the first heat exchanger and the heated gas has the same composition as the intermediate fluid the gas heated in the first heat exchanger is sent to the cycle to feed it. during startup, if the compressor inlet or outlet temperature falls below a threshold, the cooled intermediate fluid flow in the first exchanger is sent to expand in the turbine and the expanded fluid is returned to heat up in the second exchanger and then to the compressor.the turbine is coupled to a booster which, during start-up, boosts the compressed fluid in the compressor only if the turbine expands intermediate fluid. the compressor comprises at least two stages and the intermediate fluid is not cooled between the compressor stages. during the first mode, compressed intermediate fluid is first cooled in the first heat exchanger, heats up in the second heat exchanger and cools down again in the first heat exchanger before being sent to the turbine and during start-up compressed intermediate fluid is first cooled in the first heat exchanger, heats up outside the second heat exchanger possibly by a heater and cools down again in the first heat exchanger.

[0011] According to another object of the invention, there is provided a hydrogen cooling apparatus comprising a first heat exchanger, means for sending either liquefied natural gas or vaporized natural gas, the vaporized natural gas being at a temperature below -50°C, to be heated by indirect heat exchange in the first heat exchanger with an intermediate fluid flow at a pressure between 3 and 70 bars abs which cools down to a temperature greater than or equal to -145°C, a second heat exchanger, means for sending the intermediate fluid flow at a temperature equal to or greater than -145°C to be cooled by introducing it at this temperature into the second heat exchanger where it cools down by indirect heat exchange and / or by expansion in a turbine of the apparatus possibly driving a compressor of the apparatus, or a valve of the apparatus,means for sending a flow of hydrogen gas to cool in the second heat exchanger without condensing, means for sending a gas flow derived from the cooled intermediate fluid to heat up in the second heat exchanger to a temperature between -90°C and -150°C, means for withdrawing the gas flow from the second exchanger at this temperature, a compressor with an inlet temperature between -90°C and -150°C, means for sending the withdrawn gas flow to the compressor with an inlet temperature between -90°C and -150°C, means for sending at least a portion of the compressed intermediate fluid to cool first in the first heat exchanger and then heat up from a temperature of at most -110°C, and means for sending the at least a portion of the heated intermediate fluid to the first heat exchanger as an intermediate fluid at a pressure between 3 and 70 bars,characterized in that it comprises means for sending the compressed and cooled intermediate fluid in the first heat exchanger to be heated in the second heat exchanger.,

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

[0013] The use of an intermediate fluid makes it possible to better regulate integration by differentiating the hydrogen and LNG networks.

[0014] The LNG vaporization takes place in a single exchanger and the intermediate fluid distributes the cold to the different consumers.

[0015] The intermediate cycle, thanks to an expansion stage, makes it possible to produce a cold fluid with a lower temperature than LNG. [ FIG.1 ] illustrates a cooling, or even liquefaction, process according to the invention. [ FIG.2 ] illustrates another cooling, or even liquefaction, process according to the invention.

[0016] In steady state operation, the hydrogen cooling process works as follows. A dedicated heat exchanger E1 is used to recover frigories from liquefied natural gas 1 at -150°C using an intermediate fluid that is cooled by liquid 1 in exchanger E1. Exchanger E1 can be a brazed aluminum plate-fin heat exchanger, a stainless steel heat exchanger, or a printed circuit heat exchanger. Alternatively, exchanger E1 can be a shell-and-tube heat exchanger.

[0017] Liquid 1 is heated, for example up 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 exchanger E1 to a temperature greater than or equal to -145°C. In the example it is cooled down to -140°C. The heat exchanger may be an aluminum or stainless steel plate and fin exchanger or a shell and tube exchanger.

[0018] Fluid 1 enters at the cold end of exchanger E1 and exits at the hot end as fluid 3.

[0019] In the example, the fluid 5 is nitrogen. It may, for example, be natural gas or methane or have another suitable composition. Preferably, the fluid 5 is inert. The fluid 5 is preferably at a pressure between 3 and 70 bars abs. The nitrogen 13 leaves the exchanger E2 at a temperature between -90°C and -150°C, for example at -120°C, and is compressed in a first compressor C, for example a centrifugal compressor, to approximately 20 bars. Then the nitrogen at 20 bars is cooled R and compressed in another compressor C1 to a pressure greater than 20 bars. Then the nitrogen at more than 20 bars is optionally divided into two parts 15, 17, the part 17 not necessarily being present. Part 17 can partially cool in exchanger E1 and is then sent to an element to be cooled 31. Thus the reheated part 19 is sent to the hot end of exchanger E1.Part 15 added to 19 forms a flow 21 which is sent at 20°C to the hot end of exchanger E1 and cools there to a temperature below -90°C, for example -140°C, forming a gas 27 which is sent to exchanger E2 at a temperature of -140°C. Gas 27 heats up in exchanger E2 to 20°C (forming flow 6) then flow 6 is cooled against the LNG in exchanger E1 to form gas 5. In this example, gas 5 is not cooled in exchanger E1 but only in turbine E. Thus, gas 5 enters turbine E at the temperature at which it leaves heat exchanger E1. The fluid expanded 7 to 1.5 bars 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 a heat exchanger E3 and joins the gas 11 to heat up in the exchanger E2 constituting the flow 13 to be sent to the cold compressor C.All the gas 13 is compressed in the cold compressor 1 and then in a booster C1 coupled to the turbine E. It is the gas compressed in the booster C1 which is sent to the exchanger E1 to recover the cold from the LNG 1.

[0020] Alternatively, the gas 5 coming from the cold end of the exchanger E1 can first pass into the exchanger E1 to cool and then be expanded in a turbine T having an inlet temperature lower than -100°C, for example -120°C.

[0021] So nitrogen, or another fluid such as helium or a mixed refrigerant, circulates in a closed cycle, taking frigories from the LNG.

[0022] The hydrogen gas 23 at room temperature, for example 20°C, enters the hot end of the heat exchanger E2, which it passes through from one end to the other to cool to a temperature below -150°C, for example -180°C. It is then cooled in the heat exchanger E3 against the liquid of the phase separator to form hydrogen gas 25 at -190°C.

[0023] The hydrogen 25 is then cooled and liquefied in another heat exchanger in a known manner. A cycle of hydrogen, helium, or mixed refrigerants, including noble gases, provides the necessary frigories.

[0024] Thus, LNG provides at least part of the frigories needed for pre-cooling hydrogen gas down to -190°C. This fraction can be at least 50%, at least 75% or at least 99% of the frigories needed for cooling hydrogen gas down to -190°C. LNG can even provide all the frigories needed apart from those coming from the turbine T.

[0025] The method can also provide cold to another element 31, cooled by the cycle. In the figure, we see that a part 17 of the gas compressed in the compressors C, C1 is cooled in the heat exchanger to an intermediate temperature, here -50°C, is withdrawn from the exchanger in a central zone of the heat exchanger and is used to cool the element 31 while being itself reheated to form the gas 19 which joins the flow 15 compressed in the compressor C to form the flow 21 which enters the exchanger E1 at 20°C. As the pressure losses for the flow 18, 19 are limited, a small expansion of the flow 15 in a valve will be sufficient to allow the flows 15, 19 to mix.

[0026] Element 31 may for example be a liquefier of another gas or a separation apparatus by distillation and / or partial condensation at a temperature below 0°C, for example a carbon dioxide liquefier.

[0027] If fraction 17 is present but element 31 is not operating, a heater, for example an electric heater or a heat exchanger heated by hot water, will be used to heat fraction 17 to form flow 19.

[0028] During the start-up of the device, hydrogen 23 is not sent to the exchanger E2 which must be cooled beforehand. The cycle compressor C is started with an inlet temperature which is that of the ambient at a reduced load, typically between 60 and 80% of the nominal molar flow rate. The compression ratio is also limited in order to limit the outlet temperature of compressor C to a reasonable value, typically less than 150°C. Compressor C may not include inter-stage cooling, with only an aftercooler R downstream of compressor C in order to reduce the cost of the machine and to limit the risk of freezing of the water in the intermediate water coolers, bypassed in stable operation where the temperature of the gas being compressed is below 0°C, the compression ratio is considerably reduced so as to limit the temperature at the outlet of compressor C upstream of the aftercooler.For start-up, a variable frequency drive could vary the speed of the compressor motor C and thus the temperature of the final stage of C and the compression ratio.

[0029] Before starting turbine E, compressor C1 does not compress the nitrogen which passes through a bypass line 13A.

[0030] The nitrogen compressed in compressor C only is sent to the first heat exchanger E1 which is not supplied at start-up by liquefied natural gas 1 but by liquid nitrogen from storage S which is vaporized by a vaporizer V to form gaseous nitrogen 2 at -180°C. The use of vaporized cold gas rather than a liquid protects the equipment from excessively sudden cooling and thermal stresses. The gaseous nitrogen heats up in exchanger E1 and is recovered at the hot end or sent to the air.

[0031] Alternatively as shown in [ FIG.2 ], the exchanger E1 can be cooled by sending supercritical liquefied natural gas. This fluid has the advantage of a reduced enthalpy of vaporization compared to non-supercritical LNG. For this, the liquefied natural gas 1 can be heated in a heater H in order to regulate its temperature at the inlet of the exchanger E1.

[0032] In the case of both figures, the vaporized liquid other than the natural gas used for start-up (typically nitrogen) can be vented to the atmosphere or recovered at 15°C for example to be used in the cooling cycle of the intermediate fluid (compressor C, C1, turbine T) to replace leaks. The interconnection line with the start-up vaporized liquid and the cycle would need to be well insulated to completely separate the LNG vaporization line and the cooling cycle during normal operation (typically by removing the connecting spool).

[0033] The cooling cycle (compressor C, C1, turbine T) at the outlet of exchanger E1 will be slowly cooled down to the operating temperature. As long as the temperature at the outlet of exchanger E1 is above the operating temperature, gas 5 will not be sent to the turbine or exchanger E2 but will pass through a line 5A directly to the inlet of compressor C in order to cool it slowly.

[0034] As the inlet temperature of compressor C decreases, the compression ratio of compressor C will increase since its inlet temperature will decrease.

[0035] A temporary heater W (typically a water-powered exchanger) can be used only during startup to replace the heat input from exchanger E2. This heater W will be bypassed during stable process operation. It heats nitrogen flow 27 sent through line 27A, preventing flow 27 from passing through exchanger E2.

[0036] Once compressor C has cooled and is operating at reduced load, typically between 60 and 80% of the nominal molar flow rate, cooling of the hydrogen precooling system begins. First, turbine E is bypassed by line 5E so that gas 5 passes directly into the phase separator (which does not yet separate any phases, since gas 5 has not been condensed). Then the turbine and its associated compressor C1 are started, the gas compressed in compressor C no longer passing through the bypass line 13A and being compressed in compressor C1.

[0037] The main advantage of this process is to use existing equipment with some minimal additions to cool the hydrogen cooling apparatus without safety issues, with regulated start-up of sensitive equipment.

Claims

1. Method for cooling hydrogen, wherein according to a first mode of operation: i) either liquefied natural gas (1, 2) or vaporized natural gas, the vaporized natural gas being at a temperature lower than -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 between 3 and 70 bar abs that is cooled down to a temperature higher than or equal to -145°C ii) the flow of intermediate fluid at a temperature higher than or equal to -145°C is cooled a) by introducing it at this temperature into a second heat exchanger (E2) where it is cooled by indirect heat exchange and / or b) by expansion in a turbine (E), optionally driving a compressor of the method (C, C1), or a valve iii) a flow of gaseous hydrogen (23) is cooled in a or, depending on the circumstances, the second heat exchanger without condensing iv) a gaseous flow (13) derived from the intermediate fluid cooled in step a) and / or b) is heated in the second heat exchanger (E2) up to a temperature of between -90°C and -150°C, is withdrawn from the exchanger at this temperature and compressed in a compressor (C, C1) with an inlet temperature of between -90°C and -150°C and at least one part of the compressed intermediate fluid (15, 17) is cooled first in the first heat exchanger and then heated from a temperature of at most -110°C and v) the at least one part of the heated intermediate fluid constitutes the flow of intermediate fluid of step i) characterized in that the compressed intermediate fluid cooled in the first heat exchanger is heated in the second heat exchanger and in that during a start-up mode i) the flow of hydrogen is not sent to the second exchanger, ii) supercritical natural gas (1, 2) or a gas at less than -100°C is sent to the first exchanger so as to cool it and exchanges heat there with a flow of intermediate fluid (5) of a cycle at a pressure of between 3 and 70 bar abs that is cooled iii) the flow of intermediate fluid (5) cooled in the first exchanger is sent directly to the inlet of the compressor (C, C1) that compresses it with a compression rate less than that of the first mode, the molar flow rate of the intermediate fluid (13) being less than 80% of the molar flow rate of intermediate fluid sent to the compressor during the first mode and iv) the intermediate fluid (15, 17) compressed in the compressor is sent back to the first exchanger as cycle fluid.

2. Method according to one of the preceding claims, wherein the intermediate fluid (5) contains more than 50 mol% nitrogen, preferably at least 90 mol% nitrogen or even at least 99 mol% nitrogen.

3. Method according to either of the preceding claims, wherein during the start-up mode the supercritical natural gas (1, 2) is pseudo-vaporized in the first heat exchanger (E1) and preferably heated there up to a temperature higher than 0°C.

4. Method according to either of the preceding Claims 1 and 2, wherein during start-up, the gas at less than - 100°C is heated in the first heat exchanger (E1) and the heated gas has the same composition as the intermediate fluid (5).

5. Method according to Claim 4, wherein the gas (3) heated in the first heat exchanger (E1) is sent to the cycle so as to supply it.

6. Method according to one of the preceding claims, wherein during the start-up mode, if the inlet or outlet temperature of the compressor (C, C1) passes below a threshold, the flow of intermediate fluid cooled in the first exchanger is sent to be expanded in the turbine (E) and the expanded fluid is sent back to be heated in the second exchanger (E2) and then to the compressor.

7. Method according to Claim 6, wherein the turbine (E) is coupled to a booster (C1) that, during the start-up mode, boosts fluid compressed in the compressor (C) only if the turbine expands intermediate fluid.

8. Method according to one of the preceding claims, wherein the compressor (C, C1) comprises at least two stages and the intermediate fluid is not cooled between the stages of the compressor.

9. Method according to one of the preceding claims, wherein, during the first mode, compressed intermediate fluid cooled in the first heat exchanger and heated in the second heat exchanger (6) is cooled again in the first heat exchanger (E1) before being sent to the turbine (E) and, during the start-up mode, compressed intermediate fluid is cooled first in the first heat exchanger, is heated outside the second heat exchanger optionally by a heater (W) and is cooled again in the first heat exchanger.

10. Apparatus for cooling hydrogen, comprising a first heat exchanger (E1), means for sending either liquefied natural gas (1, 2) or vaporized natural gas, the vaporized natural gas being at a temperature lower than -50°C, to be heated by indirect heat exchange in the first heat exchanger (E1) with a flow of intermediate fluid (5) at a pressure of between 3 and 70 bar abs that is cooled down to a temperature higher than or equal to -145°C, a second heat exchanger (E2), means for sending the flow of intermediate fluid at a temperature higher than or equal to -145°C to be cooled by introducing it at this temperature into the second heat exchanger (E2) where it is cooled by indirect heat exchange and / or by expansion in a turbine (E) of the apparatus, optionally driving a compressor of the apparatus (C, C1), or a valve of the apparatus, means for sending a flow of gaseous hydrogen (23) to be cooled in the second heat exchanger without condensing, means for sending a gaseous flow (13) derived from the cooled intermediate fluid to be heated in the second heat exchanger (E2) up to a temperature of between -90°C and -150°C, means for withdrawing the gaseous flow from the second exchanger at this temperature, a compressor (C, C1) with an inlet temperature of between -90°C and -150°C, means for sending the withdrawn gaseous flow to the compressor (C, C1) with an inlet temperature of between -90°C and - 150°C, means for sending at least one part of the compressed intermediate fluid (15, 17) to be cooled first in the first heat exchanger and then heated from a temperature of at most -110°C, and means for sending the at least one part of the heated intermediate fluid to the first heat exchanger as intermediate fluid at a pressure of between 3 and 70 bar, characterized in that it comprises means for sending the compressed intermediate fluid cooled in the first heat exchanger to be heated in the second heat exchanger.

11. Apparatus according to Claim 10, wherein the turbine (E) is coupled to a booster (C1) of the apparatus.

12. Apparatus according to either of the preceding Claims 10 and 11, wherein the compressor (C, C1) comprises at least two stages, without means for cooling the intermediate fluid between the stages of the compressor.