KR20230074241A - Process for producing liquid hydrogen - Google Patents

Abstract

A method for liquefying hydrogen gas comprising cooling hydrogen gas to an intermediate temperature by heat exchange with a refrigerant circulating in a cooling loop equipped with a high-temperature expander and a low-temperature expander, wherein an outlet stream from the low-temperature expander is partially contains condensed refrigerant; means for separating condensate from the circulating refrigerant are provided; and further cooling the hydrogen gas by evaporation of the condensate and heat exchange to reheat. The fluid in the cooling loop is typically methane (eg natural gas after removal of carbon dioxide, water vapor and other impurities) or nitrogen or mixtures thereof.

Description

Process for producing liquid hydrogen

The present invention relates to a method for liquefying hydrogen gas, and in particular to a method for cooling hydrogen to be liquefied to an intermediate temperature prior to liquefaction.

Liquefied hydrogen has the potential to replace carbonaceous fuels. In addition to its current use in space applications, significant amounts of liquid hydrogen will be needed for future use as a fuel for aviation and transportation. As the use of hydrogen as a fuel increases, there will be a need to store and transport hydrogen in liquid form on a large scale.

Existing and proposed hydrogen liquefaction processes mostly include the following steps:

- a first step of cooling (hereinafter referred to as "pre-cooling") the incoming hydrogen to an intermediate temperature (hereinafter referred to as "intermediate temperature") by heat exchange with an evaporation fluid ("first refrigerant"); The most widely proposed first refrigerant fluid is liquid nitrogen with liquid methane (LNG); mixed refrigerants have also been proposed; and

- a second step of further cooling and liquefying the precooled hydrogen by work-expansion of a part of the precooled hydrogen or a second refrigerant such as helium.

Although a hydrogen liquefaction process involving only the aforementioned second step (cooling by expansion of hydrogen or a second refrigerant) without any pre-cooling is possible and feasible, the introduction of the first step of pre-cooling is preferred because of two factors: Desirable: (a) reduced total compression power of the entire liquefaction process, and (b) perceived lower investment and production costs due to the reduced circulation rate and compression power of the secondary refrigerant system.

Regarding factor (b), the use of the lowest practical temperature of hydrogen at the outlet of the first pre-cooling stage (typically liquid nitrogen at about -190 °C as the first refrigerant) uses the second Minimize the required circulation rate of the refrigerant in the step and thus the compression power. However, considering the compression power requirements of the pre-cooling system, the lowest practical pre-cooling temperature does not necessarily mean the lowest total compression power of the entire liquefaction process.

Summary of Invention

A key aspect of the present invention relates to the liquefaction of hydrogen, and discloses an improved process in which a hydrogen stream to be liquefied is pre-cooled to an intermediate temperature, typically between -150°C and -200°C.

In this application, wherever pressure is expressed as "bar", it is absolute bar.

The disclosed pre-cooling means is a closed cycle containing a fluid such as but not limited to methane or nitrogen or mixtures thereof including:

- hot gas expander with gas outlet stream

- a low-temperature gas expander with a partially liquefied exit stream;

- liquid separation in the exit stream from the cold gas expander;

- Reduce the separated liquid to a pressure close to atmospheric pressure (near-atmospheric pressure)

- primarily by heat exchange with the outlet stream from said hot gas expander; secondly by heat exchange with the exit stream from the cold gas expander after the liquid separation; Thirdly, supply hydrogen (and second refrigerant, if used) is brought from about near-ambient temperature to the typical intermediate temperatures of -150 °C and -200 °C by heat exchange following evaporation of the reduced pressure liquid refrigerant. continuously cooled

- Recompression of the low pressure refrigerant stream produced.

The arrangement of the foregoing pre-cooling cycle is similar to the methane liquefaction (LNG production) process described in GB2486036, particularly in terms of the formation of a liquid in the cold gas expander followed by separation of said liquid from the cold gas expander outlet stream. In the case referred to, the liquid formed in the low-temperature gas expander contributes to a portion of the total liquid (LNG) output of the process, but in the present application the liquid is depressurized and then evaporated by a heat exchanger together with the hydrogen to be liquefied so that in the hydrogen liquefaction process Hydrogen is cooled to this intermediate temperature, typically -150 °C to -200 °C.

The present invention includes using methane as a refrigerant in the hot gas expander while using nitrogen as the refrigerant in the cold gas expander.

The applicant finds that such a method for cooling hydrogen to be liquefied, that is, the formation of a liquid refrigerant in a gas expander, the separation, depressurization and evaporation of the liquid as a precoolant in the hydrogen liquefaction process has not been disclosed in the prior art and is novel. Suggest. The production of the liquid is thermally efficient as it directly produces mechanical work in the low temperature gas expander. There is also a practical advantage of producing a liquid refrigerant such as liquid methane or liquid nitrogen within the hydrogen liquefaction process which eliminates the need for an external supply of expensive and sophisticated liquid primary refrigerants such as mixed refrigerants.

Accordingly, a description of a process for liquefying hydrogen according to the main aspects of the present invention is provided as follows (see FIG. 1/3 and equipment tags and stream numbers shown therein):

- providing a stream [1] of pure hydrogen feed gas;

- providing a recycled hydrogen gas stream [2] at a pressure of 1 bar to 50 bar;

- by introducing the streams [1] and [2] into the hydrogen compressor [A], which compressor cools to a pressure of 10 bar to 200 bar, more typically to a pressure of 20 bar to 100 bar, and the combined discharge stream [ 3];

- cooling the combined discharge stream [3] in a first hot passage of a heat exchanger [B], said hot passage having an outlet stream [4];

- cooling said stream [4] in a first hot passage of heat exchanger [C], said hot passage having an outlet stream [5];

- cooling said stream [5] in a first hot passage of heat exchanger [D], said hot passage having an outlet stream [6];

- passing said stream [6] through a hydrogen liquefaction unit [E];

- the hydrogen liquefaction unit [E] typically comprises a stream [6] which is separated into two parts; cooling the first portion [e-1] in a first gas expander to form an outlet stream [e-2]; cooling the second portion [e-3] in the first heat exchanger to form stream [e-4]; Split stream [e-4] into two parts; cooling the first portion [e-5] in a second gas expander to form an outlet stream [e-6]; cooling and liquefying the second portion [e-7] in a second heat exchanger to form a liquefied hydrogen product stream [7]; recycling the stream [e-6] through the second heat exchanger to form stream [e-8]; combining the streams [e-2] and [e-8] to form stream [e-9]; reheating the stream [e-9] in a first heat exchanger to form a recycle hydrogen stream [8]; providing a catalyst to the second heat exchanger to facilitate the conversion of ortho-hydrogen to para-hydrogen;

- the liquid hydrogen product stream [7] has a temperature of -240 to -255 °C;

- the recycle hydrogen stream [8] has a pressure between 1 bar and 30 bar; The stream [8] is reheated in a first cold passage of the heat exchanger [D] to form an outlet stream [9]; The stream [9] is reheated in the first cold passage of the heat exchanger [C] to form the outlet stream [10]; The stream [10] is reheated in the first cold passage of heat exchanger [B]; The reheated stream from the heat exchanger [B] forms the hydrogen recycle gas stream [2];

- heat exchangers [B], [C] and [D] may be physically combined into a single unit;

- providing a refrigerant gas stream [21] at a pressure of 10 bar to 150 bar;

- separating a stream [21] of refrigerant gas into a first [22] part and a second [25] part;

- passing said first part [22] through a first refrigerant gas expander [L], whereby the outlet stream [23] from said first refrigerant gas expander has a pressure of 5 bar to 50 bar;

- reheating said first refrigerant gas expander outlet stream [23] in a second cold passage of heat exchanger [B] to form a reheated stream [24];

- the reheated stream [24] is compressed in a compressor [M] to a pressure of 10 to 150 bar to form, after cooling, a first component of the refrigerant gas [21];

- passing a second portion of the refrigerant gas [25] into the second hot passage of the heat exchanger [B] with the outlet stream [26];

- passing the cooled second part of the refrigerant gas [26] through a second refrigerant gas expander [N], whereby the outlet stream [27] from the second refrigerant gas expander is typically at a pressure of 3 bar to 50 bar. and contains a mixture of vapor and liquid;

- the outlet stream [27] of the second gas expander [N] is separated in a vapor/liquid separator [O] to form a vapor stream [28] and a liquid stream [29];

- the liquid stream [29] is typically depressurized at valve [P] to form a stream [30] having a pressure between 0.5 bar and 10 bar, typically close to atmospheric pressure; The temperature of the stream [30] is typically −160° C. using methane as the refrigerant and −195° C. using nitrogen as the refrigerant, both at substantially atmospheric pressure;

- said stream [30] is evaporated and reheated in the second cold passage of heat exchanger (D) to form an outlet vapor stream [31];

- the stream [31] having an exit stream [32] compressed by the refrigerant compressor [Q] to a pressure equal to that of stream [28];

- combine said stream [28] with said stream [32] to form stream [34];

- said stream [34] is reheated in the second cold passage of heat exchanger [C] to form stream [35] and then reheated in the third cold passage of heat exchanger [B] to form stream [36];

- The reheated stream [36] is compressed in a compressor [M] at a pressure of 10 to 150 bar to form a second component of the refrigerant gas [21] after cooling.

A second aspect of the present invention takes advantage of the high efficiency of the aforementioned two-stage expander pre-cooling circuit to operate the hydrogen recycle compressor at a suction temperature well below room temperature. The proposed flow chart is schematically shown in FIG. 2/3. Stream [9] enters the first part of compressor [A], typically at a temperature of -120 °C.

Alternatively, the inlet stream to the compressor [A] is the outlet stream [8] of the hydrogen liquefier unit [E] of Figure 1/3 or the first cold passage [10] of the heat exchanger [C]. It can be taken directly at the exit.

Depending on the inlet temperature of the compressor [A], the power of the compressor [A] can be reduced by approximately 50% compared to the ambient inlet temperature configuration shown in Figure 1/3. The power demand for the first refrigerant compressors [M] and [Q] increases almost equally.

The Applicant proposes that this operating arrangement of a hydrogen compressor where the inlet temperature is well below room temperature is novel and has particular advantages over the prior art for hydrogen liquefaction as follows:

- Hydrogen compression usually requires the use of a reciprocating compressor as the density of hydrogen may be too low for use in a centrifugal compressor; Considering the relatively high investment and operating costs of reciprocating compressors, the power requirements of reciprocating compressors will be greatly reduced due to the use of sub-ambient inlet temperatures, especially in large-scale installations requiring several compressors in parallel;

- operating the hydrogen compressor with an inlet temperature well below room temperature increases the inlet density; For example, the inlet density at -120 °C is about twice the room temperature density, facilitating the use of centrifugal compression in hydrogen liquefaction.

In the third aspect of the invention, shown in Figure 3/3, part of the cooling required to further cool and liquefy the hydrogen stream in the hydrogen liquefaction unit [E] by expansion of the second refrigerant in one or more stages in a closed circuit; everything is provided With this arrangement, the amount of refrigeration produced in the hydrogen liquefaction unit [E] by expansion of a portion of stream [6] can be significantly reduced or even eliminated, resulting in the flow rate of stream [8] and compressor [A]. The required power may be much lower than in the flowchart illustrated in FIG. 1/3.

According to a third aspect of the invention:

- the stream [11] of the second refrigerant is continuously cooled in heat exchangers [B], [C] and [D] to typically have the same temperature as the hydrogen inlet stream [6] to the hydrogen liquefier unit [E]. form stream [14];

- in addition to the typical internal arrangement of the hydrogen liquefaction unit [E] described for the above main aspect of the invention and shown in Figure 1/3, the hydrogen liquefaction unit [E] typically provides separation of the stream [14] into two parts. contains more; cooling the first portion [e-11] in a first expander to form an outlet stream [e-12]; cooling the second portion [e-13] in the first heat exchanger to form stream [e-14]; reheating the stream [e-14] in a first heat exchanger to form stream [e-15]; The stream [e-12] is further cooled in a second expander to form an outlet stream [e-16]; reheating the stream [e-16] in a second heat exchanger to form stream [e-17]; and combining streams [e-15] and [e-17] to form stream [15];

- stream [15] leaves the hydrogen liquefier unit [E] at a lower pressure than stream [14];

- stream [15] is then successively reheated in heat exchangers [D], [C] and [B] to form a reheated stream [18] at about ambient temperature;

- Following this, stream [18] is recompressed in compressor [F] to form, after cooling, the aforementioned second refrigerant [11].

The second refrigerant may include hydrogen, helium, or neon or mixtures thereof.

When using hydrogen as the second refrigerant, no significant conversion of ortho-hydrogen to para-hydrogen is expected without a conversion catalyst in the second refrigerant circuit. Due to the lower flow of the above-mentioned produced stream [6] in this third aspect of the invention, the flow of hydrogen through the conversion catalyst in the hydrogen liquefier unit [E] is the same as shown in Figure 1/3. It may be lower than in the main aspect of the invention and as a result the amount of ortho-para hydrogen conversion catalyst may be reduced.

The present invention has been extensively simulated by widely used process simulation software.

Description of Preferred Embodiments

The present invention will now be described with reference to the accompanying drawings which present a flowchart illustrating an embodiment of a process according to the present invention.

The exact flow diagram can vary, but usually includes these basic elements.

In the first embodiment of the invention shown in Figure 1/3, a feed stream [1] of hydrogen to be liquefied at a pressure of 25 bar is introduced into the compressor [A]. The compressor also receives a recycle hydrogen stream [2] described below. A combined stream [3] of feed hydrogen and recycle hydrogen after cooling exits the compressor at 75 bar.

The combined stream [3] is cooled to -50 °C by passing through the first hot passage of the heat exchanger [B] to form stream [4]; It is then passed through the first hot passage of the heat exchanger [C] and further cooled to -120 ° C to form stream [5]; The necessary cooling is provided as described below by a closed circuit of methane refrigerant.

The outlet stream [5] of the heat exchanger [C] is further cooled to -158 °C by evaporation of the low pressure methane refrigerant stream to form stream [6].

Stream [6] then flows to a hydrogen liquefaction unit [E] comprising one or more hydrogen expanders, one or more heat exchangers and one or more ortho-para hydrogen catalytic conversion stages.

The hydrogen liquefaction unit [E] has an outlet stream of liquid hydrogen [7] with a temperature of -244 °C and a pressure of 7.5 bar and an outlet stream of a gaseous hydrogen stream [8] with a temperature of -161 °C and a pressure of 6.8 bar.

Stream [8] is first reheated in the cold passage of heat exchanger [D] to form stream [9] with a temperature of -123 °C and then further reheated in the first cold passage of heat exchanger [C] to a temperature of -53 °C. is further reheated in the first cold pass of the heat exchanger [B], and the reheated stream at about ambient temperature forms the aforementioned hydrogen recycle stream [2].

The closed refrigerant circuit comprising the aforementioned methane refrigerant has a stream [21] with a pressure of 90 bar at the discharge of the refrigerant compressor [M].

The outlet stream [21] of the compressor [M] is separated into a first portion [22] and a second portion [25].

The first portion [22] is passed to a first refrigerant gas expander [L] with an outlet stream [23] having a pressure of 26 bar and a temperature of -54 °C. The second portion [25] passes through the second hot passage of the heat exchanger [B] with an outlet stream [26] having the same outlet temperature -50 °C as the aforementioned hydrogen stream [4].

Stream [23] is reheated to about ambient temperature in the second cold passage of heat exchanger [B]. The reheated stream [24] flows to the refrigerant compressor [M] at about ambient temperature as a first component after cooling of the refrigerant gas stream [21].

The outlet stream [26] from the heat exchanger [B] flows into a second refrigerant gas expander [N] containing both vapor and liquid with an outlet stream [27] at a pressure of 10 bar and a temperature of -124 °C.

Stream [27] is separated in a vapor/liquid separator [0] to form a vapor stream [28] and a liquid stream [29].

The liquid stream [29] is reduced to near-atmospheric pressure at valve [P], forming a mixture of liquid and vapor in the outlet stream [30] at a temperature of -158 °C.

Stream [30] is completely evaporated and reheated in the second cold passage of heat exchanger (D) to form an outlet vapor stream [31] having the same temperature of -123 °C as the aforementioned hydrogen stream [9]. Stream [31] is compressed by the refrigerant compressor [Q] with an outlet stream [32] at the same pressure as stream [28] at 9.7 bar. Streams [28] and [33] are then combined to form stream [34].

Stream [34] is first reheated in the second cold passage of heat exchanger [C] to form stream [35] at a temperature of -53 °C and then reheated in the third cold passage of heat exchanger [B]. The reheated stream [36] flows to the about ambient temperature compressor [M] as a second component after cooling of the refrigerant gas stream [21].

The present invention will be further explained with reference to the accompanying drawing 2/3 showing a second embodiment of the present invention. This second embodiment described in the above concept comprises a variant of the first embodiment, whereby the hydrogen recycle compressor [A] receives an inlet stream having a suction temperature well below atmospheric pressure.

In this example of the second embodiment, the hydrogen recycle stream [9] flows directly to the compressor [A] at a temperature of -123 °C and a pressure of 6.6 bar. The temperature of the outlet stream [3] from the compressor [A] is then reduced to approximately ambient temperature.

Claims (13)

As a process for liquefying hydrogen gas,
- providing a stream [1] of hydrogen feed gas;
- providing a recycled hydrogen gas stream [2] at a pressure of 1 bar to 50 bar;
- introducing streams [1] and [2] into a hydrogen compressor [A], said compressor having a combined outlet stream [3] with a pressure of 10 bar to 200 bar;
- cooling the combined discharge stream [3] in a first hot passage of a heat exchanger [B], said hot passage having an outlet stream [4];
- cooling said stream [4] in a first hot passage of a heat exchanger [C], said hot passage having an outlet stream [5];
- cooling said stream [5] in a first hot passage of a heat exchanger [D], said hot passage having an outlet stream [6];
- a hydrogen liquefier unit comprising at least one hydrogen gas expander, at least one heat exchanger and at least one catalytic conversion step of ortho-hydrogen to para-hydrogen ( As a step of passing through a hydrogen liquefier unit) [E]; wherein the hydrogen liquefier has an outlet stream of liquid hydrogen [7] with a temperature of -240 to -255 ° C and an outlet stream of gaseous hydrogen [8] with a pressure of 1 bar to 20 bar;
- reheating the stream [8] into the outlet stream [9] in the first cold passage of the heat exchanger [D], followed by the outlet stream [10] in the first cold passage of the heat exchanger [C]. and then reheating in the first cold passage of the heat exchanger [B], wherein the reheated stream from the heat exchanger [B] forms the hydrogen recycle gas stream [2];
- providing a stream [21] of refrigerant gas at a pressure of 10 bar to 150 bar;
- separating the stream [21] of the refrigerant gas into a first [22] part and a second [25] part;
- passing the first portion [22] through a first refrigerant gas expander [L], wherein the outlet stream [23] from the first refrigerant gas expander has a pressure of 5 bar to 50 bar;
- reheating said first refrigerant gas expander outlet stream [23] in a second cold passage of a heat exchanger [B] to form a reheated stream [24];
- compressing the reheated stream [24] in a compressor [M] to a pressure of 10 to 150 bar to form the first component [21] of the refrigerant gas;
- passing the second portion [25] of the refrigerant gas through a second hot passage of the heat exchanger [B], having an outlet stream [26];
- passing the cooled second part of the refrigerant gas [26] through a second refrigerant gas expander [N], wherein the outlet stream from the second refrigerant gas expander [27] has a pressure of 3 bar to 50 bar. having a mixture of vapor and liquid;
- separating the outlet stream [27] of the second gas expander [N] in a vapor/liquid separator [O] to form a vapor stream [28] and a liquid stream [29];
- reducing the liquid stream [29] at valve [P] to form stream [30] having a pressure of 0.5 bar to 10 bar;
- evaporating and reheating said stream [30] in a second cold passage of a heat exchanger (D) to form an outlet vapor stream [31];
- compressing said stream [31] by means of a low pressure refrigerant compressor [Q] having an outlet stream [32] to a pressure equal to that of stream [28];
- combining stream [28] with stream [32] to form stream [34];
- reheating said stream [34] in a second cold passage of heat exchanger [C] to form stream [35] and then reheating in a third cold passage of heat exchanger [B] to form stream [36];
- compressing the reheated stream [36] in a compressor [M] to a pressure of 10 to 150 bar to form the second component of the refrigerant gas [21],
method. The process according to claim 1, wherein the combined discharge stream [3] from the compressor [A] has a pressure between 20 bar and 100 bar. 3. The process according to claim 1 or 2, wherein the pressure of the stream (30) is between 1 bar and 3 bar. 4. The process according to any one of claims 1 to 3, wherein the refrigerant gas is methane or a methane-rich gas. 5. The process according to claim 4, wherein the pressure of the outlet stream [27] from the second gas expander [N] is between 10 bar and 50 bar. 4. The process according to any one of claims 1 to 3, wherein the refrigerant gas is nitrogen. 7. The process according to claim 6, wherein the pressure of the outlet stream [27] from the second gas expander [N] is between 3 bar and 30 bar. 4. The process according to any preceding claim, wherein the refrigerant gas is a mixture of methane and nitrogen. 4. The separator according to any one of claims 1 to 3, wherein the refrigerant gas [21] flowing in the first refrigerant gas expander [L] is methane or a methane-rich gas, while in the second refrigerant gas expander [N], the separator The process wherein the refrigerant gas [26] flowing through [O] and valve [P] is nitrogen. 10. The process according to any preceding claim, wherein the temperature of the inlet stream [2] of the compressor (A) is -200 °C to 40 °C. 11. The method of claim 10, wherein the inlet stream to the compressor [A] is taken directly from the outlet stream [8] of the hydrogen liquefier unit [E] or from the outlet of the first cold passage of the heat exchanger [D] or [C]. , process. 12. The method of claim 1, further comprising providing a stream of second refrigerant gas [11] at about near-ambient temperature; cooling the stream [11] in a third hot passage of the heat exchanger [B] to form an outlet stream [12]; cooling the stream [12] in a second hot passage of the heat exchanger [C] to form an outlet stream [13]; cooling the stream [13] in the second hot passage of the heat exchanger [D] to form an outlet stream [14]; passing said stream [14] to a hydrogen liquefaction unit [E], wherein stream [14] passes through one or more expansion stages to provide cooling before leaving [E] as stream [15]; reheating the stream [15] in a third cold passage of the heat exchanger [D] to form stream [16]; further reheating the stream [16] in a third cold passage of the heat exchanger [C] to form stream [17]; further reheating the stream [17] in a fourth cold passage of the heat exchanger [B] to form stream [18]; and recompressing the stream [18] in a compressor [F] to form the stream [11]. 13. The process of claim 12, wherein the second refrigerant gas is hydrogen, helium or a mixture of hydrogen or helium and neon.

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