Hydrogen cooling process and installation

Abstract

A process for cooling a gas to be cooled, using a hydrogen liquefaction plant, the process comprising, during a start-up phase: supplying liquefied natural gas (1) to a natural gas circuit, vaporizing at least a portion of the liquefied natural gas (1) in a vaporizer (H) to obtain vaporized natural gas (26), sending at least a portion of the vaporized natural gas to a natural gas heat exchanger (E1) to cool said natural gas heat exchanger (E1), starting up the cooled natural gas heat exchanger (E1), and cooling an intermediate fluid circulating in an intermediate cycle circuit by heat exchange with the liquefied natural gas (1) in the natural gas heat exchanger (E1) to obtain a cooled intermediate fluid (5). Figure for the abstract: Fig. 1

Description

Title of the invention: Hydrogen cooling process and installation

[0001] The field of the present invention is that of a liquefaction plant for a gas to be cooled, in particular hydrogen. The present invention also relates to a method for cooling a gas to be cooled, in particular hydrogen.

[0002] Hydrogen is an energy carrier that plays an increasing role in the decarbonization of various sectors, particularly transport and industry. Hydrogen liquefaction makes it possible to store hydrogen and transport it over long distances.

[0003] It is known to liquefy hydrogen in two steps: - A first pre-cooling stage of the hydrogen to a first temperature in a pre-cooling circuit using a cycle gas such as nitrogen or a mixed refrigerant gas, followed by - A second stage of cooling the pre-cooled hydrogen to a second temperature lower than the first temperature in a cooling circuit using a cycle gas such as hydrogen, helium or a mixed refrigerant including rare gases.

[0004] The hydrogen to be liquefied then circulates in a hydrogen circuit to be cooled.

[0005] During the pre-cooling stage, heat exchange takes place between the cycle gas circulating in the pre-cooling circuit and the gas to be cooled in the gas-to-cool circuit. This heat exchange occurs in a cold box called the 80K box, in which heat exchangers are arranged to cool the gas-to-cool circuit to a predetermined temperature, in particular to a temperature of 80 Kelvin.

[0006] It is known to use the cooling capacity of liquefied natural gas (LNG) during the pre-cooling stage of the hydrogen to be cooled in order to optimize such a process by making it more efficient. In such a process, the cooling capacity of the LNG is transferred to an intermediate fluid and ultimately to the gas to be cooled. However, during transient phases of operation (for example, start-ups, trips, or changeovers), the equipment used in such a process (in particular heat exchangers and compressors) can be sensitive to large temperature variations. The cooling stages of the equipment and circuits enabling the transfer of the cooling capacity of the LNG are therefore critical to ensuring the long-term reliability of the installations.

[0007] The object of the invention relates to a method for cooling a gas to be cooled, in particular hydrogen, using a hydrogen liquefaction plant, said method comprising, during a start-up phase of said plant: - supply of liquefied natural gas to a natural gas circuit, - vaporization of at least a portion of the liquefied natural gas in a vaporizer so as to obtain vaporized natural gas, - sending at least a portion of the vaporized natural gas into a natural gas heat exchanger in order to cool said natural gas heat exchanger, - start-up of the cooled natural gas heat exchanger and cooling of an intermediate fluid circulating in an intermediate cycle circuit by heat exchange with the liquefied natural gas in the natural gas heat exchanger so as to obtain a cooled intermediate fluid, - sending a flow of cooled intermediate fluid into a cryogenic compressor that is stopped in order to cool said cryogenic compressor, in particular in order to control the cooling rate of the installation by monitoring the temperature at the compressor inlet, in particular the cooling rate is 1°C / min at the beginning down to -50°C for example then the cooling rate is planned to be faster, - starting the cryogenic compressor and compressing the cooled intermediate fluid in said started cryogenic compressor in such a way as to obtain a compressed intermediate fluid, - Sending the compressed intermediate fluid to the natural gas heat exchanger and cooling the compressed intermediate fluid in the natural gas heat exchanger to obtain a compressed and cooled natural fluid, - Pre-cooling of the gas to be cooled circulating in a gas circuit to be cooled by heat exchange between at least the compressed and cooled intermediate fluid and said gas to be cooled in a pre-cooling heat exchanger.

[0008] Thus, the compressor, the natural gas heat exchanger, and the pre-cooling heat exchanger are gradually cooled during system startup to avoid thermal shock. Furthermore, this method allows for the sequential startup of these thermal shock-sensitive components, thereby simplifying system startup for operators.

[0009] In this application, the term "start-up phase of the liquefaction plant" means the phase between the start-up of the plant (the plant being, for example, at ambient temperature or at a temperature above -50°C) and the moment at which the temperature of the gas to be cooled measured at the outlet of the pre-cooling heat exchanger is at a predetermined temperature between 60 Kelvin and 90 Kelvin, preferably between 70 Kelvin and 80 Kelvin.

[0010] In one aspect according to the invention, the vaporization of at least a portion of the liquefied natural gas is carried out in an atmospheric vaporizer.

[0011] In one aspect according to the invention, the liquefied natural gas is supplied to the vaporizer by a liquefied natural gas bypass line, said liquefied natural gas bypass line being arranged to divert the liquefied natural gas from the natural gas circuit during the start-up phase of the installation.

[0012] Liquefied natural gas is a cryogenic fluid that could damage the liquefied natural gas heat exchanger if it is not first cooled. The vaporizer allows the liquefied natural gas to be vaporized without overheating it before it enters the natural gas heat exchanger, thus gradually cooling the natural gas heat exchanger while preventing sudden vaporization of the natural gas within the heat exchanger, which could damage it through thermal fatigue.

[0013] In one aspect according to the invention, the process includes a step of controlling the flow rate of the portion of liquefied natural gas sent to the vaporizer. In this way, the natural gas heat exchanger is protected from temperature variations.

[0014] In one aspect of the invention, the control of the flow rate of the portion of natural gas sent to the vaporizer is operated by at least one liquefied natural gas diversion control device arranged to control the flow rate of liquefied natural gas sent to the vaporizer, said control device being arranged on the bypass line upstream of the vaporizer.

[0015] In one aspect of the invention, when the liquefied natural gas diversion control device is in the open position, at least a portion of the liquefied natural gas is sent to the vaporizer at a flow rate between 5% and 50% of the liquefied natural gas flow rate, and when the liquefied natural gas diversion control device is in the closed position, it prevents the sending of liquefied natural gas to the vaporizer.

[0016] In one aspect of the invention, the process includes a step of controlling the flow rate of liquefied natural gas sent to the natural gas heat exchanger.

[0017] In one aspect of the invention, said step of controlling the flow of liquefied natural gas sent to the natural gas heat exchanger is operated by a liquefied natural gas flow control device arranged on the natural gas circuit upstream of the natural gas heat exchanger.

[0018] In one aspect of the invention, the liquefied natural gas diversion control device and / or the liquefied natural gas flow control device is a valve of A control type or a valve equipped with a positioner. Generally speaking, any type of valve that allows the percentage of opening to be selected can be used.

[0019] In one aspect of the invention, the natural gas heat exchanger has an operating temperature, in particular an operating temperature between -150°C and 30°C. For example, the cold end of the heat exchanger in continuous operation is at -150°C and its hot end at ambient temperature.

[0020] The term "operating temperature" here refers to the temperature at which equipment is qualified to operate without risk of damage, particularly from thermal shock. The operating temperature depends on the equipment specifications.

[0021] The invention aims in particular to gradually lower the temperature to the nominal temperatures of the heat exchanger. For example, initially everything is at ambient temperature, and the cooling must be gradually reduced at the maximum rate of 1°C / min to avoid thermal shock. This would not be possible if the LNG liquid, which is at -150°C, were sent directly into the heat exchanger, even with a small flow rate, because this would cause significant local thermal stresses.

[0022] In one aspect according to the invention, the flow rate of natural gas sent to the liquefied natural gas heat exchanger is a function of the temperature of the liquefied natural gas or the mixture of liquefied natural gas and vaporized natural gas measured at the inlet of the natural gas heat exchanger. Advantageously, the invention makes it possible to control the temperature so that it gradually decreases at a maximum rate of 1°C / min.

[0023] In one aspect of the invention, the temperature of the natural gas heat exchanger is substantially the same as the temperature of the liquefied natural gas or the mixture of liquefied natural gas and vaporized natural gas at the inlet of said heat exchanger.

[0024] In one aspect of the invention, the operating temperature of the natural gas heat exchanger is reached when the temperature of the liquefied natural gas or of the mixture of liquefied natural gas and vaporized natural gas reaches the operating temperature of said natural gas heat exchanger.

[0025] In one aspect of the invention, when the operating temperature of the natural gas heat exchanger is reached, the method includes a step of closing the liquefied natural gas diversion control device so as to prevent the vaporization of the liquefied natural gas in the vaporizer, and a step of opening the liquefied natural gas flow control device so as to allow the flow of liquefied natural gas to pass through the natural gas heat exchanger.

[0026] In one aspect of the invention, the closing of the diversion control device and the opening of the liquefied natural gas flow control device are progressive.

[0027] In one aspect of the invention, as long as the operating temperature of the natural gas heat exchanger is not reached, vaporized natural gas is sent to the natural gas heat exchanger.

[0028] In one aspect of the invention, the cooling of the natural gas heat exchanger is carried out in the following manner: 1. Opening of the liquefied natural gas diversion control device, vaporization of a portion of the liquefied natural gas in the vaporizer and closing of the liquefied natural gas flow control device so as to send only vaporized natural gas to the natural gas heat exchanger, 2. Opening of the liquefied natural gas flow control device, mixing of liquefied natural gas and vaporized natural gas upstream of the natural gas heat exchanger, sending the mixture of vaporized natural gas and liquefied natural gas into the natural gas heat exchanger, 3. When the operating temperature of the natural gas exchanger is reached, the liquefied natural gas diversion control device is closed and the liquefied natural gas flow control device is fully opened so as to send only liquefied natural gas into the natural gas heat exchanger.

[0029] In one aspect of the invention, once the natural gas exchanger reaches its operating temperature, said natural gas exchanger is started.

[0030] In one aspect of the invention, when the natural gas heat exchanger reaches its operating temperature, the process includes a step of cooling the intermediate fluid by heat exchange between the liquefied natural gas and said intermediate fluid in the started natural gas heat exchanger. This results in a cooled intermediate fluid.

[0031] In one aspect of the invention, during the start-up phase, the cooled intermediate fluid in the natural gas heat exchanger is sent to the cryogenic compressor before being sent to the pre-cooling heat exchanger.

[0032] In one aspect of the invention, the cryogenic compressor has an operating temperature, in particular an operating temperature between -150°C and -100°C at the compressor inlet during normal operation. For start-up, the temperature is preferably between -50°C and -70°C.

[0033] In one aspect of the invention, the cooled intermediate fluid at the outlet of the natural gas heat exchanger is diverted from the pre-cooling exchanger by a cooled intermediate fluid bypass line to be sent upstream of the cryogenic compressor without passing through said pre-cooling heat exchanger.

[0034] In one aspect of the invention, the process includes a step of controlling the flow rate of intermediate fluid sent to the cryogenic compressor.

[0035] In one aspect of the invention, the step of controlling the flow of intermediate fluid sent to the cryogenic compressor is operated by at least one flow control device for the cooled intermediate fluid.

[0036] In one aspect according to the invention, the control element for the flow of cooled intermediate fluid includes at least one evacuation valve for said cooled intermediate fluid.

[0037] In one aspect of the invention, the intermediate fluid flow control device comprises two intermediate fluid discharge valves, one disposed upstream of the cryogenic compressor and the other disposed downstream of the cryogenic compressor.

[0038] In one aspect of the invention, the method includes a step of measuring the temperature of the intermediate fluid cooled at the inlet of the cryogenic compressor.

[0039] In one aspect of the invention, the temperature of the cryogenic compressor corresponds to the temperature of the cooled intermediate fluid measured at the inlet of said cryogenic compressor.

[0040] In one aspect according to the invention, the cooled intermediate fluid discharge valves are arranged upstream and downstream of the cryogenic compressor and are arranged to control the flow rate of cooled intermediate fluid sent to the cryogenic compressor as a function of the temperature of the cryogenic compressor.

[0041] In one aspect according to the invention, the flow rate of cooled intermediate fluid sent to the cryogenic compressor when it is stopped is less than 60% of the normal operating flow rate of the cryogenic compressor. A low flow rate of cooled intermediate fluid in the cryogenic compressor allows for the gradual cooling of said cryogenic compressor. Preferably, when the compressor is stopped (i.e., the compressor is not performing compression), only a maximum flow rate of 5% of the nominal flow rate (normal operating flow rate of the cryogenic compressor) is allowed to pass through the compressor, so as not to drive the compressor impellers at high speed. The aim is, in fact, to gradually cool the metal that makes up the compressor.

[0042] By cryogenic compressor “at standstill”, we mean here a cryogenic compressor which is not started and therefore is not compressing the fluid passing through it.

[0043] In one aspect of the invention, the cooled intermediate fluid that is not sent to the cryogenic compressor upstream of said cryogenic compressor is evacuated from the intermediate cycle circuit, in particular into the atmosphere.

[0044] In one aspect of the invention, the cryogenic compressor is arranged on the intermediate cycle circuit.

[0045] In one aspect of the invention, at least one cooled intermediate fluid discharge valve, in particular the discharge valve for said cooled intermediate fluid located upstream of the cryogenic compressor, is arranged to supply the compressor with a flow rate of cooled intermediate fluid less than 60%, preferably less than 50%, preferably less than 40% (or even lower) of the normal operating flow rate of the cryogenic compressor. This valve is used, in particular, to cool an interconnecting pipe between a natural gas supply (in particular a natural gas storage unit) and the compressor inlet, a pipe which can, in some cases, be very long, for example, approximately 1.5 km in length. Cooling this interconnecting pipe is therefore essential. However, it is important not to supply a large flow rate of cold fluid to the compressor, which is not operating.When the compressor is stopped (i.e., not compressing), only a maximum flow rate of 5% of the nominal flow rate (normal operating flow rate of the cryogenic compressor) is allowed to pass through it, in order to avoid driving the compressor wheels at high speed. The aim is to gradually cool the metal components of the compressor.

[0046] In one aspect of the invention, the intermediate fluid, cooled after circulating through the cryogenic compressor when stopped, is at least partially returned upstream of said cryogenic compressor, for example via the drain valve located downstream of the cryogenic compressor, so as to isolate said cryogenic compressor in a closed circuit when it is stopped, in other words, until its operating temperature is reached. In this situation, it is necessary to ensure that the fluid flow rate allowed to circulate through the compressor when stopped does not exceed 5% of the nominal flow rate (normal operating flow rate of the cryogenic compressor).

[0047] Thus, the drain valves allow a small flow of cooled intermediate fluid to pass through the cryogenic compressor during the start-up phase of the liquefaction plant when the compressor has not yet started, so that the cooling rate of the cryogenic compressor is controlled until it reaches its operating temperature.

[0048] In one aspect according to the invention, during the compressor cooling stage, as long as the compressor temperature is above the operating temperature of said compressor, at least one drain valve, in particular at least the drain valve upstream of the cryogenic compressor, is at least partially open so that at least a part of the cooled intermediate fluid is drained.

[0049] Preferably, during the cooling stage of the cryogenic compressor, as long as the temperature of the cryogenic compressor is above the temperature During the operation of said cryogenic compressor, the two cooled intermediate fluid discharge valves, i.e. the discharge valve upstream of the cryogenic compressor and the discharge valve downstream of the cryogenic compressor, are at least partially open.

[0050] In the invention, advantageously, the cooling rate of the installation is controlled by monitoring the temperature at the compressor inlet (in particular the cooling rate is 1°C / min at the beginning down to -50°C) and then the cooling rate can be substantially faster.

[0051] In one aspect of the invention, the method includes a step of supplying intermediate fluid downstream of the cryogenic compressor when the drain valves are at least partially open. This makes it possible to maintain a stable intermediate fluid level in the intermediate fluid circuit.

[0052] In one aspect according to the invention, when the cryogenic compressor reaches its operating temperature, the process includes a step of starting the cryogenic compressor. The cooled intermediate fluid can then be compressed in the compressor.

[0053] In one aspect of the invention, when the cryogenic compressor is started, it compresses the cooled intermediate fluid so as to obtain the compressed intermediate fluid.

[0054] In one aspect of the invention, when the cryogenic compressor is started, the intermediate fluid discharge valves are closed so that the cooled intermediate fluid is not discharged and circulates in the compressor to be compressed.

[0055] In one aspect according to the invention, during the start-up stage of the cryogenic compressor, at least one cooled intermediate fluid discharge valve disposed upstream of the cryogenic compressor is progressively closed so that the flow rate of cooled intermediate fluid passing through the cryogenic compressor is increasingly higher.

[0056] In one aspect according to the invention, when the cryogenic compressor is started the flow rate of cooled intermediate fluid circulating in the cryogenic compressor is greater than 60% of the normal operating flow rate of the compressor, preferably greater than 80% of the normal operating flow rate of the compressor, preferably equal to 100% of the normal operating flow rate of the compressor.

[0057] In one aspect of the invention, the control of the cooled intermediate fluid flow rate is carried out such that the temperature of the intermediate fluid measured at the inlet of the cryogenic compressor decreases by a temperature of approximately 1°C per minute. In other words, the cooled intermediate fluid discharge valves are arranged so that the flow rate of cooled intermediate fluid sent into The cryogenic compressor lowers the temperature measured at its inlet by 1°C per minute. This initial cooling rate (for example, approximately 1°C per minute) is maintained until a predetermined temperature is reached, for example, -50°C. Then, beyond this predetermined temperature, cooling begins at a second, faster rate, for example, to lower the temperature from 50°C to 100°C below the predetermined temperature.

[0058] In one aspect according to the invention, once the cryogenic compressor reaches its operating temperature, it is started and the cooled intermediate fluid is sent to said cryogenic compressor in operation until 100% of the flow of cooled intermediate fluid is sent to said cryogenic compressor to be compressed.

[0059] In one aspect of the invention, during the start-up phase of the installation, the intermediate fluid is first cooled in the natural gas heat exchanger, then compressed in the cryogenic compressor, then returned to the natural gas heat exchanger without circulating through the pre-cooling heat exchanger.

[0060] In one aspect of the invention, during the start-up phase of the installation, the process includes a step of heating the cooled intermediate fluid in a start-up heat exchanger.

[0061] In one aspect of the invention, the heating step of the cooled intermediate fluid is carried out by heat exchange between said cooled intermediate fluid and a warmer heat transfer fluid in the starting heat exchanger. For example, the heating step of the cooled intermediate fluid is carried out by heat exchange between said cooled intermediate fluid and water in a water-based heat exchanger.

[0062] The start-up heat exchanger can only be used during start-up to replace the heat input from the pre-cooling exchanger.

[0063] In one aspect of the invention, the start-up heat exchanger will be short-circuited in stable operation of the process.

[0064] Such an intermediate fluid heating step makes it possible to consume the cooling capacity of the liquefied natural gas transferred to the intermediate fluid so as to maintain a stable temperature of the intermediate fluid while waiting for the pre-cooling heat exchanger to be started up.

[0065] In one aspect of the invention, the cooled intermediate fluid is sent to said starting heat exchanger and then, once reheated, said reheated intermediate fluid is returned to the natural gas heat exchanger to be cooled there. new.

[0066] In one aspect of the invention, once the natural gas heat exchanger is started and then the cryogenic compressor is started, the process includes a pre-cooling step of the heat exchanger.

[0067] In one aspect of the invention, the pre-cooling heat exchanger has an operating temperature.

[0068] In one aspect of the invention, the cooling step of the pre-cooling exchanger is carried out by: 1. Heat exchange between the compressed and cooled intermediate fluid in the natural gas heat exchanger and a secondary heat transfer fluid that is hotter than said intermediate fluid in the pre-cooling exchanger, 2. When the temperature of the gas to be cooled at the outlet of the gas circuit to be cooled approaches the temperature of the cooled intermediate fluid at the inlet of the pre-cooling heat exchanger, the flow rate of compressed and cooled intermediate fluid sent to the starting heat exchanger gradually decreases, and the flow rate of compressed and cooled intermediate fluid sent to the pre-cooling heat exchanger gradually increases, and 3. Starting up of an expansion device arranged to expand the cooled and compressed intermediate fluid upstream of the pre-cooling heat exchanger, said expansion device being in particular a booster cooling turbine configured to expand the compressed and cooled intermediate fluid.

[0069] In one aspect of the invention, the expansion device is arranged in the intermediate cycle circuit downstream of the compressor in the direction of flow of the intermediate fluid. Compressing and expanding the cooled intermediate fluid optimizes the cooling of the pre-cooling heat exchanger and thus optimizes the pre-cooling of the gas to be cooled.

[0070] In one aspect of the invention, once the pre-cooling heat exchanger reaches its operating temperature, it is started.

[0071] In one aspect of the invention, the secondary heat transfer fluid comprises a portion of the gas to be cooled at the outlet of the pre-cooling heat exchanger.

[0072] In one aspect of the invention, said portion of gas to be cooled at the outlet of the pre-cooling heat exchanger is sent to a secondary heat transfer fluid circuit by means of a bypass duct for the gas circuit to be cooled.

[0073] In one aspect of the invention, once the natural gas heat exchanger, the cryogenic compressor and the pre-cooling heat exchanger are at their operating temperature, the installation is started and operates in a stable mode.

[0074] In one aspect according to the invention, the natural gas heat exchanger is a brazed aluminum plate and fin (BAHX) exchanger, or a stainless steel exchanger, or a printed circuit exchanger, or a shell and tube exchanger.

[0075] In one aspect according to the invention, the pre-cooling exchanger is arranged in a first cold box called box 80K.

[0076] In one aspect of the invention, when the installation is operating in a stable mode, the method comprises the following steps: - The natural gas heat exchanger recovers the cooling capacity of the liquefied natural gas using an intermediate fluid that is cooled by the liquefied natural gas within the natural gas heat exchanger. - The heated intermediate fluid then enters the pre-cooling heat exchanger arranged to exchange the cooling capacity of said heated intermediate fluid with that of the gas to be cooled, - The heated intermediate fluid is compressed in the cryogenic compressor, the flow rate of heated intermediate fluid passing through the cryogenic compressor to be compressed being greater than 60% of the nominal molar flow rate, preferably greater than 80% of the nominal molar flow rate, preferably 100% of the nominal molar flow rate, - the compressed intermediate fluid is sent to the natural gas heat exchanger and cooled there to a temperature below 90°C, for example -140°C, forming a cooled intermediate fluid which is sent to the pre-cooling exchanger at a temperature of -140°C, - the cooled intermediate fluid is then heated in the pre-cooling heat exchanger and then cooled again in the natural gas heat exchanger to form the intermediate fluid, - The intermediate fluid enters a turbine at the temperature at which it exits the natural gas heat exchanger, the turbine being arranged to expand the intermediate fluid and obtain an expanded intermediate fluid, - The expanded intermediate fluid is two-phase and is sent to a phase separator where it forms a liquid and a gas. The liquid is vaporized in a heater and mixes with the gas to be heated in the second heat exchanger, which then provides the flow to be sent to the cold compressor. All the gas is compressed in the cold compressor and then in a blower coupled to the turbine. It is the gas compressed in the blower that is sent to the heat exchanger to recover the cooling effect.

[0077] Thus the intermediate fluid circulates in a closed cycle, taking cooling from the liquefied natural gas.

[0078] The gas to be cooled, for example gaseous hydrogen which is at ambient temperature, for example 20°C, enters the hot end of the pre-cooling heat exchanger which it travels from one end to the other to be cooled to a temperature below -150°C, for example -180°C. It is then cooled in the heater against the liquid of the phase separator to form the gas cooled to -190°C.

[0079] The cooled gas 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 cooling capacity.

[0080] Thus, liquefied natural gas provides at least a portion of the cooling required for pre-cooling gaseous hydrogen to -190°C. This fraction can be at least 50%, at least 75%, or at least 99% of the cooling required for cooling gaseous hydrogen to -190°C.

[0081] The object of the invention further relates to an installation for the production of a gas to be cooled, in particular a cryogenic fluid, especially liquefied hydrogen, comprising: - a circuit for the gas to be cooled having an upstream end intended to be connected to a gas source and a downstream end intended to be connected to at least one receiving system, such as cryogenic storage and / or a means of transport, - a natural gas circuit in which a natural gas, in particular a liquefied natural gas, circulates, - a natural gas heat exchanger arranged to exchange heat from liquefied natural gas with an intermediate fluid circulating within an intermediate cycle circuit, - at least one cryogenic compressor arranged to compress the cooled intermediate fluid during the installation start-up phase, - at least one intermediate fluid flow control element located upstream and / or downstream of the cryogenic compressor, said control element being arranged to, during the start-up phase of the installation, control the flow of cooled intermediate fluid from the natural gas heat exchanger that can circulate in the cryogenic compressor when the latter is stopped, - at least one pre-cooling heat exchanger arranged to exchange heat between at least the cooled intermediate fluid and the gas to be cooled.

[0082] In one aspect according to the invention, the installation is arranged to implement the process described above.

[0083] In one aspect of the invention, the installation includes a vaporizer arranged to vaporize a portion of the liquefied natural gas, said vaporizer being disposed upstream of the natural gas heat exchanger.

[0084] In one aspect of the invention, the installation includes a liquefied natural gas bypass line arranged to divert liquefied natural gas from the natural gas circuit during the start-up phase of the installation.

[0085] In one aspect of the invention, the vaporizer is arranged on said liquefied natural gas bypass line.

[0086] In one aspect of the invention, the installation includes at least one liquefied natural gas diverting device arranged to control the flow of liquefied natural gas sent to the natural gas vaporizer, said control device being arranged on the divert line upstream of the vaporizer.

[0087] In one aspect of the invention, the installation includes a liquefied natural gas flow control device arranged on the natural gas circuit upstream of the natural gas heat exchanger.

[0088] In one aspect of the invention, the liquefied natural gas diversion control device is arranged to, in the open position, send a flow of vaporized natural gas to the natural gas heat exchanger.

[0089] In one aspect of the invention, the liquefied natural gas flow control device is arranged to, in the open position, send a flow of liquefied natural gas to the natural gas heat exchanger.

[0090] In one aspect of the invention, the vaporizer is an atmospheric vaporizer.

[0091] In one aspect of the invention, the natural gas diversion control device liquefied is arranged to send a flow of vaporized natural gas to the vaporizer as a function of the temperature of the natural gas heat exchanger.

[0092] In one aspect of the invention, the liquefied natural gas flow control device is arranged to send a flow of liquefied natural gas to the heat exchanger as a function of the temperature of the natural gas heat exchanger.

[0093] In one aspect of the invention, the operating temperature of the natural gas heat exchanger is reached when the temperature of the liquefied natural gas or of the mixture of liquefied natural gas and vaporized natural gas reaches the operating temperature of said natural gas heat exchanger.

[0094] In one aspect of the invention, when the operating temperature of the natural gas heat exchanger is reached, the liquefied natural gas diversion control device is arranged to prevent the vaporization of the liquefied natural gas in the vaporizer, and the liquefied natural gas flow control device is arranged to allow the flow of liquefied natural gas to pass through the natural gas heat exchanger.

[0095] In one aspect of the invention, once the natural gas exchanger reaches its operating temperature, said natural gas exchanger is started.

[0096] In one aspect of the invention, when the natural gas heat exchanger reaches its operating temperature, it is arranged to cool the intermediate fluid by heat exchange between the liquefied natural gas and said intermediate fluid in the natural gas heat exchanger. This results in a cooled intermediate fluid.

[0097] In one aspect of the invention, the cryogenic compressor is arranged to receive the cooled intermediate fluid.

[0098] In one aspect of the invention, the cryogenic compressor has an operating temperature, in particular an operating temperature between -150°C and -100°C.

[0099] In one aspect of the invention, the installation includes a cooled intermediate fluid bypass line arranged to divert the cooled intermediate fluid from the pre-cooling exchanger by means of a cooled intermediate fluid bypass line and to send said cooled intermediate fluid upstream of the cryogenic compressor.

[0100] In one aspect of the invention, the intermediate fluid flow control device comprises two intermediate fluid discharge valves, one disposed upstream of the cryogenic compressor and the other disposed downstream of the cryogenic compressor.

[0101] In one aspect of the invention, the method includes a device for measuring the temperature of the cooled intermediate fluid, said measuring device being disposed at the inlet of the cryogenic compressor.

[0102] In one aspect of the invention, the temperature of the cryogenic compressor corresponds to the temperature of the cooled intermediate fluid measured at the inlet of said cryogenic compressor.

[0103] In one aspect according to the invention, the cooled intermediate fluid discharge valves are arranged upstream and downstream of the cryogenic compressor and are arranged to control the flow rate of cooled intermediate fluid sent to the cryogenic compressor as a function of the temperature of the cryogenic compressor.

[0104] In one aspect according to the invention, the flow rate of cooled intermediate fluid sent to the cryogenic compressor when it is stopped is less than 60%, for example, about 5%, of the normal operating flow rate of the cryogenic compressor. A low flow rate of cooled intermediate fluid in the cryogenic compressor allows for the gradual cooling of said cryogenic compressor.

[0105] By cryogenic compressor “at standstill”, we mean here a cryogenic compressor which is not started and therefore is not compressing the fluid passing through it.

[0106] In one aspect of the invention, the drain valves are arranged to, in the open position, send the cooled intermediate fluid out of the intermediate fluid circuit.

[0107] In one aspect of the invention, the discharge valves are arranged to, in the open position, send the cooled intermediate fluid into the atmosphere.

[0108] In one aspect of the invention, at least one cooled intermediate fluid discharge valve, in particular the discharge valve of said cooled intermediate fluid disposed upstream of the cryogenic compressor, is arranged to send an intermediate fluid flow to the compressor.

[0109] Thus, the drain valves allow a small flow of cooled intermediate fluid to pass through the cryogenic compressor during the start-up phase of the liquefaction plant when the compressor has not yet started, so that the cooling rate of the cryogenic compressor is controlled until it reaches its operating temperature.

[0110] Preferably, during the cooling stage of the cryogenic compressor, as long as the temperature of the cryogenic compressor is above the operating temperature of said cryogenic compressor, the two cooled intermediate fluid discharge valves, i.e. the discharge valve upstream of the cryogenic compressor and the discharge valve downstream of the cryogenic compressor, are at least partially open.

[0111] In one aspect of the invention, the installation includes an intermediate fluid supply duct downstream of the cryogenic compressor, said duct being arranged to supply intermediate fluid downstream of the cryogenic compressor when the discharge valves are at least partially open. Thus, it is possible to maintain a stable intermediate fluid level in the intermediate fluid circuit.

[0112] In one aspect according to the invention, when the cryogenic compressor reaches its operating temperature, the cryogenic compressor is arranged to be started. The cooled intermediate fluid can then be compressed in the compressor.

[0113] In one aspect of the invention, when the cryogenic compressor is started, it is arranged to compress the cooled intermediate fluid so as to obtain the compressed intermediate fluid.

[0114] In one aspect of the invention, when the cryogenic compressor is started, the intermediate fluid discharge valves are in the closed position so that the cooled intermediate fluid is not discharged and circulates in the compressor to be compressed.

[0115] In one aspect according to the invention, during the start-up stage of the cryogenic compressor, at least one cooled intermediate fluid discharge valve located upstream of the cryogenic compressor is arranged to be progressively closed so that the flow rate of cooled intermediate fluid passing through the cryogenic compressor is increasingly higher.

[0116] In one aspect according to the invention, when the cryogenic compressor the intermediate fluid flow control device is arranged to allow a flow of cooled intermediate fluid to pass through the cryogenic compressor greater than 60% of the normal operating flow of the compressor, preferably greater than 80% of the normal operating flow of the compressor, preferably equal to 100% of the normal operating flow of the compressor.

[0117] In one aspect of the invention, the cooled intermediate fluid flow control device is arranged to control the cooled intermediate fluid flow rate such that the intermediate fluid temperature measured at the inlet of the cryogenic compressor decreases by approximately 1°C per minute. In other words, the cooled intermediate fluid discharge valves are arranged so that the flow rate of cooled intermediate fluid sent to the cryogenic compressor reduces the temperature measured at the inlet of the cryogenic compressor by 1°C per minute. This initial cooling rate (for example, approximately 1°C per minute) is maintained until a predetermined temperature, for example, -50°C, is reached.Then, beyond this predetermined temperature, the cooling takes place at a second cooling rate, faster than the first cooling rate, for example to go down from 50°C to 100°C below the predetermined temperature.

[0118] In one aspect according to the invention, once the cryogenic compressor reaches its operating temperature, it is started and the cooled intermediate fluid is sent to said cryogenic compressor in operation until 100% of the flow of cooled intermediate fluid is sent to said cryogenic compressor to be compressed.

[0119] In one aspect of the invention, during the start-up phase of the installation, the installation is arranged so that the intermediate fluid is first cooled in the natural gas heat exchanger, then compressed in the cryogenic compressor, then returned to the natural gas heat exchanger without circulating through the pre-cooling heat exchanger beforehand.

[0120] In one aspect of the invention, the installation includes a start-up heat exchanger arranged to, during the start-up phase of the installation, heat the intermediate fluid cooled in the natural gas heat exchanger.

[0121] In one aspect of the invention, the start-up heat exchanger is arranged to exchange heat between said cooled intermediate fluid and a heat transfer fluid that is hotter than the cooled intermediate fluid. For example, the heat exchanger is a water-based exchanger arranged to exchange heat between said cooled intermediate fluid and water.

[0122] The start-up heat exchanger can only be used during start-up to replace the heat input from the pre-cooling exchanger.

[0123] In one aspect of the invention, the start-up heat exchanger will be short-circuited in stable operation of the process.

[0124] In one aspect of the invention, the start-up heat exchanger is arranged such that the cooled intermediate fluid is sent to said start-up heat exchanger and then, once heated, returned to the natural gas heat exchanger to be cooled again.

[0125] In one aspect of the invention, the installation includes a cooled and compressed intermediate fluid expansion device arranged upstream of the precooling heat exchanger and downstream of the cryogenic compressor.

[0126] In one aspect of the invention, the expansion device is arranged in the intermediate fluid circuit downstream of the compressor in the direction of intermediate fluid flow. Compressing and expanding the cooled intermediate fluid optimizes the cooling of the pre-cooling heat exchanger and thus optimizes the pre-cooling of the gas to be cooled.

[0127] In one aspect of the invention, the pre-cooling heat exchanger has an operating temperature.

[0128] In one aspect of the invention, once the pre-cooling heat exchanger reaches its operating temperature, it is started.

[0129] In one aspect of the invention, the installation includes a heat transfer fluid circuit in which a secondary heat transfer fluid hotter than the cooled intermediate fluid circulates.

[0130] In one aspect of the invention, the secondary heat transfer fluid comprises a portion of the gas to be cooled at the outlet of the pre-cooling heat exchanger.

[0131] In one aspect of the invention, the installation includes a bypass duct for the gas circuit to be cooled arranged to send a portion of the gas to be cooled from the outlet of the pre-cooling heat exchanger to the secondary heat transfer fluid circuit.

[0132] In one aspect of the invention, once the natural gas heat exchanger, the cryogenic compressor and the pre-cooling heat exchanger are at their operating temperature, the installation is started and operates in a stable mode.

[0133] In one aspect according to the invention, the natural gas heat exchanger is a brazed aluminum plate and fin (BAHX) exchanger, or a stainless steel exchanger, or a printed circuit exchanger, or a shell and tube exchanger.

[0134] In one aspect according to the invention, the pre-cooling exchanger is arranged in a first cold box called box 80K.

[0135] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0136] [Fig-1] Fig.1 is a schematic representation of the process according to the invention.

[0137] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0138] In steady-state operation, the hydrogen cooling process functions as follows. A natural gas heat exchanger El is used to recover the cooling capacity of liquefied natural gas 1 at -150°C using an intermediate fluid that is cooled by the liquefied natural gas 1 in the natural gas heat exchanger EL. The natural gas heat exchanger El can be a brazed aluminum plate-and-fin heat exchanger, a stainless steel heat exchanger, or a printed circuit board heat exchanger. Alternatively, the natural gas heat exchanger El can be a shell-and-tube heat exchanger.

[0139] The liquefied natural gas 1 is heated, for example to 15°C and optionally vaporized to cool the intermediate fluid 5 to a temperature below -50°C, preferably below -120°C. The intermediate fluid 5 is cooled in the natural gas heat exchanger El to a temperature greater than or equal to -145°C. In the example, it is cooled to -140°C.

[0140] Liquefied natural gas 1 enters the cold end of the natural gas heat exchanger El and exits the hot end as fluid 3.

[0141] In the example, the intermediate fluid 5 is nitrogen. It may, for example, be natural gas or methane or have another suitable composition. Preferably, the intermediate fluid 5 is inert. The intermediate fluid 5 is preferably at a pressure between 3 and 70 bar abs.

[0142] The intermediate fluid 13 exits the pre-cooling 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 about 20 bar. Then the intermediate fluid compressed to 20 bar is cooled and compressed in another compressor Cl to a pressure above 20 bar. Then The intermediate fluid, at over 20 bar, is sent at 20°C to the hot end of the natural gas heat exchanger E1 and cooled there to a temperature below 90°C, for example -140°C, forming a cooled intermediate fluid 27 which is sent to the pre-cooling heat exchanger E2 at a temperature of -140°C. The cooled intermediate fluid 27 heats up in the heat exchanger E2 to 20°C (forming flow 6), then flow 6 is cooled against the liquefied natural gas in the natural gas heat exchanger E1 to form the intermediate fluid 5. The intermediate fluid 5 enters the turbine E at the temperature at which it exits the natural gas heat exchanger E1. The expanded fluid 7 at 1.5 bar in the turbine E 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 heater E3 and joins the gas 11 to be heated in the pre-cooling exchanger E2, forming 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 Cl coupled to the turbine E. It is the gas compressed in the booster Cl that is sent to the exchanger El to recover the cold from the LNG 1.

[0143] The gas to be cooled 23, here gaseous hydrogen at ambient temperature, for example 20°C, enters the hot end of the pre-cooling heat exchanger E2, which it travels through from one end to the other to be cooled 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 gaseous hydrogen 25 at -190°C.

[0144] The cooled gas 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 cooling capacity.

[0145] Thus, liquefied natural gas provides at least a portion of the cooling required for pre-cooling gaseous hydrogen to -190°C. This fraction can be at least 50%, at least 75%, or at least 99% of the cooling required for cooling gaseous hydrogen to -190°C.

[0146] During system start-up, the gas to be cooled 23 is not sent to the pre-cooling exchanger E2, which must be cooled beforehand. The system start-up process comprises the following steps: - supply of a liquefied natural gas 1 to a natural gas circuit 24, - vaporization of at least a portion of the liquefied natural gas in a vaporizer H so as to obtain a vaporized natural gas 26, - sending at least a portion of the vaporized natural gas 26 into a natural gas heat exchanger El in order to cool said natural gas heat exchanger, - start-up of the cooled natural gas heat exchanger El and cooling of an intermediate fluid 5 circulating in an intermediate cycle circuit by heat exchange with the liquefied natural gas 1 in the natural gas heat exchanger El so as to obtain a cooled intermediate fluid, - sending a flow of cooled intermediate fluid 5 into a cryogenic compressor C that is stopped in order to cool said cryogenic compressor C, - start-up of the cryogenic compressor C and compression of the cooled intermediate fluid 5 in said started cryogenic compressor so as to obtain a compressed intermediate fluid 15, - sending the compressed intermediate fluid to the natural gas heat exchanger El and cooling the compressed intermediate fluid 15 in the natural gas heat exchanger El to obtain a cold natural fluid 27, - pre-cooling of the gas to be cooled 23 circulating in a circuit of gas to be cooled by heat exchange between at least the cold intermediate fluid 27 and said gas to be cooled 23.

[0147] The vaporization of at least a portion of the liquefied natural gas is carried out in an atmospheric vaporizer. The liquefied natural gas 1 is supplied to the vaporizer via a liquefied natural gas bypass line 14, said liquefied natural gas bypass line 14 being arranged to divert the liquefied natural gas 1 from the natural gas circuit during the start-up phase of the installation. The flow rate of the portion of liquefied natural gas sent to the vaporizer is controlled by a liquefied natural gas diversion control device 2 arranged to control the flow rate of liquefied natural gas sent to the natural gas vaporizer H, said control device being arranged on the bypass line 14 upstream of the vaporizer H.When the liquefied natural gas (LNG) diversion control device 2 is in the open position, at least a portion of the LNG 1 is sent to the vaporizer H at a certain flow rate, and when the LNG diversion control device 2 is in the closed position, it prevents the LNG 1 from being sent to the vaporizer. The LNG can thus be sent directly to the natural gas heat exchanger El without any portion being vaporized.

[0148] The flow rate of liquefied natural gas 1 sent to the natural gas heat exchanger El is also controlled by a liquefied natural gas flow control device 4 arranged on the natural gas circuit upstream of the natural gas heat exchanger EL

[0149] In this example, the natural gas heat exchanger has an operating temperature. The flow rate of natural gas sent to the natural gas heat exchanger El is a function of the temperature of the natural gas heat exchanger El, said temperature corresponding to the temperature of the liquefied natural gas 1 or of the mixture of liquefied natural gas 1 and vaporized natural gas 26 measured at the inlet of the natural gas heat exchanger El.When the operating temperature of the natural gas heat exchanger is reached, the process includes a step of closing the liquefied natural gas (LNG) divert control device 2 to prevent vaporization of the LNG in the vaporizer H, and a step of opening the LNG flow control device 4 to allow the LNG flow 1 into the natural gas heat exchanger EL. The closing of the divert control device and the opening of the LNG flow control device are gradual. As long as the operating temperature of the natural gas heat exchanger EL has not been reached, vaporized natural gas 26 is sent to the natural gas heat exchanger EL.

[0150] The cooling of the natural gas heat exchanger El is carried out as follows: 1. Opening of the liquefied natural gas diversion control device 2, vaporization of a portion of the liquefied natural gas in the vaporizer H and closing of the liquefied natural gas flow control device 4 so as to send only vaporized natural gas 26 to the natural gas heat exchanger El, 2. Opening of the liquefied natural gas flow control device 4, mixing of liquefied natural gas 1 and vaporized natural gas 26 upstream of the natural gas heat exchanger El, sending the mixture of vaporized natural gas and liquefied natural gas into the natural gas heat exchanger El, 3. When the operating temperature of the natural gas heat exchanger El is reached, the liquefied natural gas diversion control device 2 is closed and the liquefied natural gas flow control device 4 is fully opened so that only liquefied natural gas is sent to the natural gas heat exchanger EL

[0151] Once the natural gas exchanger reaches its operating temperature, said natural gas exchanger is started and the intermediate fluid 5 is cooled by heat exchange between the liquefied natural gas 1 and said intermediate fluid 5 in the natural gas heat exchanger 5. A cooled intermediate fluid is thus obtained.

[0152] Then, during the start-up phase of the installation 100, the intermediate fluid cooled in the natural gas heat exchanger El is sent to the cryogenic compressor C before being sent to the pre-cooling heat exchanger.

[0153] The cryogenic compressor C has an operating temperature, in particular an operating temperature between -150°C and -100°C at the compressor suction during normal operation. For start-up, the temperature is preferably between -50°C and -70°C.

[0154] The cooled intermediate fluid at the outlet of the natural gas heat exchanger El is diverted from the pre-cooling exchanger E2 by a bypass line 5A of the cooled intermediate fluid 5 to be sent upstream of the cryogenic compressor C without passing through said pre-cooling heat exchanger E2.

[0155] The flow rate of intermediate fluid 5 sent to the cryogenic compressor C is controlled by at least one flow control device for the cooled intermediate fluid 8, 10. The flow control device for the cooled intermediate fluid 5 here comprises two discharge valves 8, 10 for the intermediate fluid, one disposed upstream of the cryogenic compressor (valve 8) and the other disposed downstream of the cryogenic compressor (valve 10).

[0156] During the start-up phase of the installation 100, the process includes a step of measuring the temperature of the cooled intermediate fluid 5 at the inlet of the cryogenic compressor C. The temperature of the cryogenic compressor corresponds to the temperature of the cooled intermediate fluid measured at the inlet of said cryogenic compressor.

[0157] The cooled intermediate fluid discharge valves 8, 10 are arranged upstream and downstream of the cryogenic compressor C and are arranged to control the flow of cooled intermediate fluid 5 sent to the cryogenic compressor C as a function of the temperature of the cryogenic compressor C.

[0158] The flow rate of cooled intermediate fluid sent to the cryogenic compressor C when it is stopped during the start-up phase of the installation is less than 60%, for example, less than or equal to 5%, of the normal operating flow rate of the cryogenic compressor. A low flow rate of cooled intermediate fluid in the cryogenic compressor allows for the gradual cooling of said cryogenic compressor. The cooled intermediate fluid 5 that is not sent to the cryogenic compressor upstream of said cryogenic compressor C is discharged from the intermediate cycle circuit, in particular into the atmosphere.

[0159] The cooled intermediate fluid 5, after circulating through the cryogenic compressor C when stopped, is at least partially returned upstream of said cryogenic compressor by the drain valve 10 located downstream of the cryogenic compressor, so as to isolate said cryogenic compressor in a closed circuit when it is stopped, in other words as long as its operating temperature has not been reached.

[0160] Thus, the drain valves allow a small flow of cooled intermediate fluid to pass through the cryogenic compressor during the start-up phase of the liquefaction plant when the compressor has not yet started, so that the cooling rate of the cryogenic compressor is controlled until it reaches its operating temperature.

[0161] As long as the compressor temperature is above the operating temperature of said compressor, at least one drain valve 8, 10, in particular at least the upstream drain valve 8 of the cryogenic compressor C, is at least partially open so that at least a portion of the cooled intermediate fluid 5 is discharged. Both drain valves for the cooled intermediate fluid may also be open, i.e., the upstream drain valve of the cryogenic compressor and the downstream drain valve of the cryogenic compressor.

[0162] The process includes a step of supplying intermediate fluid downstream of the cryogenic compressor C when the drain valves 8, 10 are at least partially open. This makes it possible to maintain a stable intermediate fluid level in the intermediate fluid circuit. This supply is achieved via an intermediate fluid supply valve 12.

[0163] When the cryogenic compressor reaches its operating temperature, the process includes a cryogenic compressor start-up step. The cooled intermediate fluid can be compressed in the started compressor C. When the cryogenic compressor C is started, the intermediate fluid discharge valves 8, 10 are closed so that the cooled intermediate fluid is not discharged and flows into the compressor to be compressed. The cryogenic compressor C then compresses the cooled intermediate fluid 5 to obtain the compressed intermediate fluid 15.

[0164] For example, at least the cooled intermediate fluid drain valve 8 located upstream of the cryogenic compressor is progressively closed so that the flow rate of cooled intermediate fluid 5 passing through the cryogenic compressor C is increasingly higher.

[0165] When the cryogenic compressor C is started the flow rate of cooled intermediate fluid 5 circulating in the cryogenic compressor is greater than 60% of the normal operating flow rate of the compressor, preferably greater than 80% of the normal operating flow rate of the compressor, preferably equal to 100% of the normal operating flow rate of the cryogenic compressor.

[0166] During the start-up phase of the installation 100, the intermediate fluid 5 is first cooled in the natural gas heat exchanger El, then compressed in the cryogenic compressor C, then returned to the natural gas heat exchanger El without circulating through the pre-cooling heat exchanger E2.

[0167] During the start-up phase of the installation 100, the process includes a heating step of the cooled intermediate fluid in a start-up heat exchanger W. This heating step of the cooled intermediate fluid 5 is carried out by heat exchange between said cooled intermediate fluid 5 and a warmer heat transfer fluid in the start-up heat exchanger W. For example, the heating step of the cooled intermediate fluid 5 is carried out by heat exchange between said cooled intermediate fluid 5 and water in a water-based heat exchanger W. The start-up heat exchanger W can be used only during start-up to replace the heat input from the pre-cooling exchanger. The start-up heat exchanger W will be bypassed during steady-state process operation.

[0168] Such an intermediate fluid heating step makes it possible to consume the cooling capacity of the liquefied natural gas transferred to the intermediate fluid so as to maintain a stable temperature of the intermediate fluid while waiting for the pre-cooling heat exchanger to be started up.

[0169] The cooled intermediate fluid 5 is sent to said starting heat exchanger W and then once heated said heated intermediate fluid is returned to the natural gas heat exchanger El to be cooled again.

[0170] Once the natural gas heat exchanger El is started and then the cryogenic compressor C is started, the process includes a step of cooling the pre-cooling heat exchanger E2.

[0171] The pre-cooling heat exchanger has an operating temperature.

[0172] The cooling stage of the pre-cooling exchanger E2 is carried out by: 1. Heat exchange between the compressed and cooled intermediate fluid 5 and a secondary heat transfer fluid 27 that is hotter than said compressed and cooled intermediate fluid 5 in the pre-cooling exchanger E2, 2. When the temperature of the gas to be cooled 25 at the outlet of the gas circuit to be cooled approaches the temperature of the compressed and cooled intermediate fluid 5 at the inlet of the pre-cooling heat exchanger E2, a gradual decrease in the flow rate of the compressed and cooled intermediate fluid sent to the starting heat exchanger W and a gradual increase in the flow rate of the compressed and cooled intermediate fluid 5 sent to the pre-cooling heat exchanger E2, and 3. Starting of an expansion device E arranged to expand the compressed and cooled intermediate fluid upstream of the pre-cooling heat exchanger E2, said expansion device E being in particular a booster cooling turbine configured to expand the compressed and cooled intermediate fluid 5.

[0173] Compressing and expanding the cooled intermediate fluid optimizes the cooling of the pre-cooling exchanger and therefore optimizes the pre-cooling of the gas to be cooled.

[0174] Once the pre-cooling heat exchanger E2 reaches its operating temperature, it is started.

[0175] As shown here, the secondary heat transfer fluid 27 may include a portion of the gas to be cooled at the outlet of the pre-cooling heat exchanger E2, the portion of the gas to be cooled at the outlet of the pre-cooling heat exchanger E2 being sent to a secondary heat transfer fluid circuit by means of a bypass conduit for the gas to be cooled circuit 28.

[0176] Once the natural gas heat exchanger El, the cryogenic compressor C and the pre-cooling heat exchanger E2 are at their operating temperature, the installation is started and operates in a stable mode.

Claims

1. Demands A method for cooling a gas to be cooled, in particular hydrogen, using a hydrogen liquefaction plant, said method comprising, during a start-up phase of said plant: - supply of a liquefied natural gas (1) to a natural gas circuit, - vaporization of at least a portion of the liquefied natural gas (1) in a vaporizer (H) so as to obtain a vaporized natural gas (26), - sending at least a portion of the vaporized natural gas into a natural gas heat exchanger (El) so as to cool said natural gas heat exchanger (El), - start-up of the cooled natural gas heat exchanger (El) and cooling of an intermediate fluid circulating in an intermediate cycle circuit by heat exchange with liquefied natural gas (1) in the natural gas heat exchanger (El) so as to obtain a cooled intermediate fluid (5), - sending a flow of cooled intermediate fluid (5) into a cryogenic compressor (C) at rest so as to cool said cryogenic compressor (C), in particular so as to control the cooling rate of the installation by following the temperature at the inlet of the compressor, in particular the cooling rate is 1°C / min at the beginning down to -50°C for example then the cooling rate is planned to be faster, the flow of cooled intermediate fluid sent to the cryogenic compressor at rest being less than 60% of the normal operating flow of the cryogenic compressor, preferably being at most equal to 5% of the normal operating flow of the cryogenic compressor; - starting the cryogenic compressor (C) and compressing the cooled intermediate fluid (5) in said started cryogenic compressor so as to obtain a compressed intermediate fluid (15), - sending the compressed intermediate fluid (15) to the natural gas heat exchanger El and cooling the compressed intermediate fluid (15) in the natural gas heat exchanger to obtain a compressed and cooled natural fluid (5), - pre-cooling of the gas to be cooled (23) circulating in a gas circuit to be cooled by heat exchange between at least the fluid compressed and cooled intermediate (5) and said gas to be cooled (23) in a pre-cooling heat exchanger (E2).

2. A method according to the preceding claim, characterized in that it comprises a step of controlling the flow of the portion of liquefied natural gas sent to the vaporizer (H) operated by at least one liquefied natural gas diversion control device (2) arranged to control the flow of liquefied natural gas sent to the vaporizer (H) and a step of controlling the flow of liquefied natural gas (1) sent to the natural gas heat exchanger (El) operated by a liquefied natural gas flow control device (4) arranged on the natural gas circuit upstream of the natural gas heat exchanger (El).

3. A method according to the preceding claim, characterized in that the flow rate of liquefied natural gas (1) sent to the natural gas heat exchanger (El) is a function of the temperature of the liquefied natural gas (1) or of a mixture of liquefied natural gas (1) and vaporized natural gas (26) measured at the inlet of the natural gas heat exchanger (El).

4. A method according to any one of claims 2 or 3, characterized in that the natural gas heat exchanger (El) has an operating temperature, and when the operating temperature of the natural gas heat exchanger (El) is reached, the method comprises a step of closing the liquefied natural gas diversion control device (2) so as to prevent the vaporization of the liquefied natural gas (1) in the vaporizer (H), and a step of opening the liquefied natural gas flow control device (4) so ​​as to allow the flow of liquefied natural gas 1 to pass through the natural gas heat exchanger (El).

5. A method according to any one of the preceding claims, characterized in that, during the start-up phase of the installation, the cooled intermediate fluid (5) in the natural gas heat exchanger (El) is sent to the cryogenic compressor (C) before being sent to the pre-cooling heat exchanger (E2).

6. A method according to the preceding claim, characterized in that the method comprises a step for controlling the flow rate of intermediate fluid sent to the cryogenic compressor (C), said control step being operated by at least one flow control element (8, 10) for the cooled intermediate fluid (5), the intermediate fluid flow control element comprising two discharge valves of the intermediate fluid (8, 10), one disposed upstream of the cryogenic compressor and the other disposed downstream of the cryogenic compressor (C).

7. A method according to any one of claims 5 or 6, characterized in that it comprises a step of measuring the temperature of the cooled intermediate fluid (5) at the inlet of the cryogenic compressor (C).

8. A method according to any one of claims 5 to 7, characterized in that the flow rate of cooled intermediate fluid (5) sent to the cryogenic compressor (C) when stopped is less than 60% of the normal operating flow rate of the cryogenic compressor.

9. A method according to any one of the preceding claims, characterized in that, during the start-up phase of the installation, the method comprises a step of heating the cooled intermediate fluid (5) in a start-up heat exchanger (W), the step of heating the cooled intermediate fluid being carried out by heat exchange between said cooled intermediate fluid (5) and a warmer heat transfer fluid in the start-up heat exchanger (W).

10. Installation (100) for the production of a gas to be cooled, in particular a cryogenic fluid, especially liquefied hydrogen, comprising: - a circuit for the gas to be cooled (23) having an upstream end intended to be connected to a gas source and a downstream end intended to be connected to at least one receiving system, such as a cryogenic storage facility and / or a means of transport, - a natural gas circuit in which a natural gas (1), in particular a liquefied natural gas, circulates, - a natural gas heat exchanger (E1) arranged to exchange the heat of the liquefied natural gas (1) with an intermediate fluid (5) circulating within an intermediate cycle circuit, - at least one cryogenic compressor (C) arranged to, during a start-up phase of the installation, compress the cooled intermediate fluid (5), - at least one control element (8, 10) for the flow rate of the intermediate fluid (5) disposed upstream and / or downstream of the cryogenic compressor (C),said control element being arranged to, during the start-up phase of the installation, control the flow rate of cooled intermediate fluid (5) coming from the heat exchanger of, natural gas (El) that can circulate in the cryogenic compressor (C) when it is stopped, in particular to control the cooling rate of the installation by monitoring the temperature at the compressor inlet, in particular the cooling rate is 1°C / min at the beginning down to -50°C for example then the cooling rate is planned to be faster, - at least one pre-cooling heat exchanger (E2) arranged to exchange heat between at least the compressed and cooled intermediate fluid (5) and the gas to be cooled (23), - a vaporizer (H) arranged to vaporize a portion of the liquefied natural gas (1), the vaporizer (H) being disposed upstream of the natural gas heat exchanger (El), the installation (100) being arranged to implement the process according to one of the preceding claims.