EP4421432A1 - Process and apparatus for liquefying a feed gas containing hydrocarbons - Google Patents

Abstract

A method (100, 200) for liquefying a hydrocarbon-containing feed gas (101) is proposed, wherein the feed gas (101) is cooled and at least partially liquefied in a heat exchanger (10) in a pressurized state, wherein a mixed refrigerant (102) is heated and at least partially evaporated in the heat exchanger (10), wherein the mixed refrigerant (102) is guided in a mixed refrigerant circuit (20), and wherein the mixed refrigerant (102) is compressed in the mixed refrigerant circuit (20) using a compressor (21). A hermetic compressor (21) is used as the compressor (21) and/or the compressor (21) is driven using a magnetic coupling. A corresponding system (100, 200) is also the subject of the present invention.

Description

The invention relates to a process and a plant for liquefying a hydrocarbon-containing feed gas.

background

Processes and plants for the liquefaction of hydrocarbon-containing feed gases such as natural gas are known and are described, for example, in the article " Natural Gas" in Ullmann's Encyclopedia of Industrial Chemistry, online publication July 15, 2006, DOI: 10.1002/14356007. a17_073.pub2, Section 3, "Liquefacti on", or at Wang and Economides, "Advanced Natural Gas Engineering", Gulf Publishing 2010, DOI: 10.1016/C2013-0-15532-8, Chapter 6, "Liquefied Natural Gas (LNG) ", described.

Mixture refrigerants made from different hydrocarbon components and nitrogen can be used, particularly in natural gas liquefaction. In such processes, these can be run in one, two or three mixture refrigerant circuits (Single Mixed Refrigerant, SMR; Dual Mixed Refrigerant, DMR; Mixed Fluid Cascade, MFC). Mixture refrigerant circuits with propane pre-cooling (C3MR) are also known. The term "single mixture refrigerant circuit" is also used below for designs with a single mixture refrigerant circuit.

Aspects of the present disclosure relate in particular to small plants for the liquefaction of hydrocarbon-containing feed gases such as biogas, which can in principle operate according to the same principles as large natural gas liquefaction plants, but in particular have a simplified structure and should possibly meet other requirements, such as the ability to interrupt operation without problems or a more dynamic mode of operation.

There is a need for improvements in the operation of small plants in particular for the liquefaction of hydrocarbon-containing feed gases.

Disclosure of the invention

Against this background, a method and a plant for liquefying a hydrocarbon-containing feed gas with the features of the independent patent claims are proposed. Embodiments are the subject of the dependent patent claims and the following description.

Cooling processes for small gas liquefaction systems, e.g. in biogas plants, are currently comparatively inefficient and unreliable. Conventional processes include liquefaction with cold liquid nitrogen, open and closed methane cycles, Joule-Thompson cycles or helium-based Sterling processes.

Compressors, especially centrifugal compressors, such as those used in gas liquefaction plants to compress refrigerants, are typically equipped with gas seals. These have the particular function of preventing the compressed gas from escaping and protecting the compressors, which typically operate under considerable pressures and temperatures, from pressure drops. The sealing gas used in the gas seals and the mechanical design of the gas seals must meet extremely high requirements such as freedom from particles on the one hand and dimensional tolerances and surface smoothness on the other.

Modern, high-efficiency single-mixture refrigerant cycles, as mentioned above, used in larger condensing plants have the disadvantage that losses of the mixture refrigerant via the seal gas system of the commonly used centrifugal compression arrangements are unavoidable. In addition, during longer shutdown periods, partial depressurization with release of mixture refrigerant from the mixture refrigerant circuit is required. These inventory losses must be compensated by a make-up system that provides the components of the mixture refrigerant. Consequently, a costly seal gas system and a make-up system must be installed, which calls into question the economics for small applications and self-sufficient operation.

The invention is based on the finding that the use of highly efficient encapsulated (hermetic) compressors in single-mix refrigerant circuits for low-temperature gas liquefaction, particularly on a small scale, Energy- and cost-efficient, reliable and self-sufficient operating options can be created because this eliminates the aforementioned requirements for a sealing gas system and a make-up system.

Against this background, the present invention proposes a method for liquefying a hydrocarbon-containing feed gas, wherein the feed gas is cooled and at least partially liquefied in a heat exchanger in a pressurized state, wherein one, in particular exactly one, mixed refrigerant is heated and at least partially evaporated in the heat exchanger, wherein the mixed refrigerant is guided in one, in particular exactly one, mixed refrigerant circuit, and wherein the mixed refrigerant is compressed in the mixed refrigerant circuit using a compressor. As proposed in the context of the present invention, the compressor is designed as a hermetic compressor and/or one driven via a magnetic coupling.

In other words, aspects of the present invention may include the use of a specifically designed compressor system in a particularly energy-efficient single-mixture refrigerant circuit. The compressor may be driven via a magnetic coupling, e.g. by an electric motor, or a completely hermetic compressor machine train with an encapsulated compressor and drive may be used.

In the context of the present disclosure, the term "hermetic compressor" is used in the usual way. Instead of the term "hermetic compressor", the term "fully hermetic compressor" can in principle also be used. In a hermetic compressor, the drive motor and the compression elements are typically arranged in a pressure-resistant capsule. Both components can be arranged in the refrigerant flow and thereby cooled. In certain embodiments, the encapsulation can be provided in such a way that it is not possible to open the compressor for repair purposes. Hermetic compressors are conventionally used for applications such as climate chambers, refrigerators and freezers, smaller cold rooms and household heat pumps. A hermetic compressor can therefore be completely sealed off from the environment. Hermetic compressors can be "linked" so that they work effectively even if a compressor does not deliver the required performance or fails. Is Therefore, although we refer here to "a" corresponding compressor in the singular, this should not exclude the use of further compressors, for example in serial and/or parallel arrangement or in redundancy.

Problems related to the evaporation of the refrigerant and the pressure increase during a system shutdown can be solved in different ways in embodiments of the present invention. On the one hand, the refrigerant system or the single refrigerant circuit can be designed for the expected high standstill pressure, although it must be ensured that the system can start up under appropriate conditions. A drain tank designed for a correspondingly high pressure can be used to temporarily store the system's liquid inventory from cold system parts after a shutdown. In this way, the standstill pressure in the refrigerant system or the single refrigerant circuit is significantly reduced. The drained and (partially evaporated) refrigerant components can then be fed back into the refrigerant circuit after the compressor has started up.

The method proposed here can therefore, in corresponding embodiments, comprise a liquefaction mode in which the liquefaction of the hydrocarbon-containing feed gas is carried out, and a standby mode in which the liquefaction of the hydrocarbon-containing feed gas is not carried out, whereby the compressor is not operated in the standby mode or is operated at a lower power than in the liquefaction mode. Embodiments of the present invention enable such an intermittent mode of operation and therefore also allow use for the liquefaction of feed gases that are only available periodically, so that the requirements can be met in a special way, particularly when operating small plants.

During a transition between the condensation operation and the standby operation, in corresponding embodiments of the invention, at least part of the mixture refrigerant can be transferred from the mixture refrigerant circuit to a drain vessel, and during a transition between the standby operation and the condensation operation, at least part of the mixture refrigerant can be transferred from the drain vessel back into the mixture refrigerant circuit. As explained, this reduces losses and a pressure increase can be limited in terms of its height in the mixture refrigerant circuit as a whole or with regard to the location of the pressure increase (namely, e.g. only to the drain tank).

In embodiments of the present invention, the transition between standby mode and condensation mode can in particular comprise a start-up phase in which the compressor is initially put into operation or operated with (again) increased power, and in which at least part of the mixture refrigerant is then successively transferred from the drain vessel back into the mixture refrigerant circuit. In this way, the requirements for the compressor drive with regard to the necessary start-up power can be reduced in corresponding embodiments, resulting in particular in a lower start-up torque and lower construction costs.

In all cases, it can be provided that in standby mode, evaporation of at least part of the mixture refrigerant and a resulting pressure build-up in the mixture refrigerant circuit or a part thereof is permitted, with at least some of the components in the mixture refrigerant circuit being designed in such a way that they withstand the pressure build-up. In this way, losses of refrigerant inventory can be eliminated.

In embodiments of the invention, at least part of the mixed refrigerant circuit can be designed to be sealed off, whereby in particular only the correspondingly sealed off parts have to withstand a pressure build-up. In such cases, the entire system does not need to be designed to be pressure-resistant, which would entail corresponding costs.

In embodiments of the present invention, the hydrocarbon-containing feed gas can comprise biogas or gasification gas produced by gasification of another carbon-containing starting material such as waste, shale gas and/or natural gas. For the reasons explained several times, the present invention is particularly suitable for use in processes in which corresponding feed gases are only produced periodically and therefore intermittent liquefaction operation is particularly advantageous.

As mentioned, the present invention is particularly suitable for comparatively small plants. Embodiments of the present invention therefore include that liquefaction capacities of no more than 10 tons per day are provided in one plant or that the hydrocarbon-containing feed gas is fed to the process in an amount of no more than 450 kilograms per hour. However, a network of several plants in order to achieve higher liquefaction capacities is conceivable and can be provided.

As mentioned, the present invention is used in particular in embodiments with a single mixture refrigerant circuit, so that embodiments of the present invention can therefore comprise that exactly one mixture refrigerant circuit is used.

In embodiments of the invention, in principle any mixture refrigerant can be used, i.e. a mixture with at least two of the components nitrogen, methane, ethane, propane, ethylene, butane or pentane in any relative amounts can be used as the mixture refrigerant, as far as technically feasible.

A plant for liquefying a hydrocarbon-containing feed gas is also the subject of the present invention, wherein the plant is designed to cool the feed gas in a pressurized state in a heat exchanger and to at least partially liquefy it, wherein the plant is designed to heat a mixture refrigerant in the heat exchanger and to at least partially evaporate it, and wherein the plant is designed to guide the mixture refrigerant in a mixture refrigerant circuit and to compress the mixture refrigerant in the mixture refrigerant circuit using a compressor.

The proposed system is characterized in that the compressor is designed as a hermetic compressor and/or that the compressor is driven using a magnetic coupling.

For further features and advantages of a corresponding system and its configurations, please refer to the above explanations concerning the The method and embodiments proposed according to the invention are expressly referred to, since they apply equally to this purpose.

In summary, the present invention or corresponding embodiments of the invention comprise the combination of an efficient mixed refrigerant circuit comprising nitrogen, methane, ethane, propane, ethylene, butane or pentane with a hermetic compression system without refrigerant losses and, if required, a hermetically integrated lubrication system. In addition, no external sealing gas is required and the system has no sealing gas losses from the process side (mixed refrigerant circuit) to the atmosphere or other systems.

The system can be used, among other things, to liquefy small amounts of methane from natural gas or other methane sources such as biogas. The refrigeration system does not require a refill system for mixed refrigerants or a sealing gas system and can operate autonomously. The system can be restarted against the standstill pressure without having to depressurize the system.

By adjusting the composition of the mixture refrigerant, the single mixture refrigerant circuit offers an energy-efficient way to reduce flash gas that is generated when liquefied gas is throttled into a storage vessel. To increase the energy efficiency of the process, the flash gas can optionally be fed back to the feed gas after cold recovery (e.g. in biogas plants with low-pressure feed gas sources) or used in a low-pressure fuel gas system, for example.

The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention.

Short description of the drawing

• Figur 1 veranschaulicht eine Anlage gemäß einer Ausführungsform der Erfindung.
• Figur 2 veranschaulicht eine Anlage gemäß einer Ausführungsform der Erfindung.

Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings.

• Figure 1 illustrates a system according to an embodiment of the invention.
• Figure 2 illustrates a system according to an embodiment of the invention.

Embodiments of the invention

The embodiments described below are described solely for the purpose of assisting the reader in understanding the features claimed and discussed above. They are merely representative examples and are not intended to be exhaustive and/or limiting with respect to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures and/or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the invention as claimed.

Different embodiments of the invention may include, have, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. Moreover, the disclosure may include other inventions that are not currently claimed, but that may be claimed in the future, particularly if they are included within the scope of the independent claims.

Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention and vice versa. Elements, method steps, etc. that are identical, act in the same way, correspond to one another in terms of their function, are structurally identical or comparable may be indicated with identical reference symbols.

Figure 1 illustrates a system 100 according to an embodiment of the present invention.

The system 100 is designed to liquefy a hydrocarbon-containing feed gas 101, wherein the feed gas 101 is cooled and at least partially liquefied in a pressurized state in a heat exchanger 10. The liquefied feed gas is fed into a tank system 50 via a valve 11, wherein flash gas or vaporized portions can be returned through the heat exchanger 10 via a valve 12.

In the heat exchanger 10, a mixed refrigerant 102 is heated and at least partially evaporated, wherein the mixed refrigerant 102 is guided in a mixed refrigerant circuit, designated here as a whole by 20. The mixed refrigerant 102 is compressed in the mixed refrigerant circuit 20 using a compressor 21, which in the illustrated example is driven by an electric motor 22. The compressor 21 is designed as a hermetic compressor 21 and/or the compressor 21 is driven using a magnetic coupling.

The compressor 21 is fed from a storage tank 23, which is provided in particular to prevent liquid from being fed into the compressor 21. A kickback line with a valve 28 branches off on the pressure side of the compressor 21. The compressed mixture coolant 102 is cooled and partially condensed by means of an air cooler 24. A two-phase mixture formed is fed into a separator tank 25. Gas extracted from the separator tank 25 is fed to the heat exchanger 10 on the warm side. Liquid also extracted from the separator tank 25 is fed to the heat exchanger 10 via an intermediate feed. Gas and liquid are combined and further cooled in the heat exchanger 10 and in particular fully liquefied.

The liquid formed is fed via a valve 26 into a flash tank 27, from which gas and liquid are taken, fed to the heat exchanger 10, and combined within the heat exchanger 10. After heating and evaporation in the heat exchanger 10, the mixed refrigerant 102 is fed back to the storage tank 23, thus closing the mixed refrigerant circuit 20.

During longer periods of downtime, the system and the liquid supply from the cold sections of the mixed refrigerant circuit heat up 20 evaporates and increases the standstill pressure. This increased standstill pressure can be taken into account when designing the mixed refrigerant circuit 20 and the associated equipment. In addition, the increased requirements for restarting due to this high mixed refrigerant circuit 20 are advantageously taken into account when selecting the machine train (compressor 21 and drive 22). Alternatively or additionally, a design can be provided as is now described with respect to Figure 2 is explained.

In Figure 2 a method according to a further embodiment of the present invention is illustrated and designated as a whole by 200. This comprises the already Figure 1 explained features and additionally a standby system, which is designated here with a total of 30.

The method 200 may include a liquefaction operation in which the liquefaction of the hydrocarbon-containing feed gas 101 is performed and a standby operation in which the liquefaction of the hydrocarbon-containing feed gas 101 is not performed.

The compressor 21 is not operated in the standby mode or is operated at a lower power than in the condensation mode. As already explained, during a transition between the condensation mode and the standby mode, at least part of the mixture refrigerant 102 from the mixture refrigerant circuit 20 can be transferred or drained into a drain vessel 31 in the standby system 30.

For this purpose, corresponding lines are provided upstream of the valve 26 with a valve 32, in the liquid line arranged downstream of the flash container 27 with a valve 33, and upstream of the valve 28 in the kickback line with a valve 34.

During a transition between the standby mode and the condensation mode, at least a portion of the mixture refrigerant 102 can be transferred from the drain vessel 31 back into the mixture refrigerant circuit 20, namely in the example illustrated here via a valve 35 into the storage tank 23.

The system is therefore equipped with a high-pressure drain tank or drain tank 31, which can hold the cold liquid mixture refrigerant 102 of the system. By draining the cold liquid from the system, the standstill pressure can be reduced during the standstill phases while the system warms up. The drain tank 31 is designed for high pressure and the evaporation of the liquid over time is accepted.

After restarting the system at reduced standstill pressure, the discharged mixture refrigerant 102 can be fed back into the process. A kickback flow from the warm pressure side of the compressor 21 can be used to evaporate the remaining heavy components of the mixture refrigerant 102 in the drain tank 31. The installation of the additional drain tank 31 reduces the design pressure of the system and reduces the effort required to restart the compressor 21 after longer downtimes. Even after long downtimes, no inventory losses need to be compensated for by a make-up system in such designs.

Claims (12)

Method (100, 200) for liquefying a hydrocarbon-containing feed gas (101), wherein the feed gas (101) is cooled and at least partially liquefied in a heat exchanger (10) in a pressurized state, wherein a mixture refrigerant (102) is heated and at least partially evaporated in the heat exchanger (10), wherein the mixture refrigerant (102) is guided in a mixture refrigerant circuit (20), wherein the mixture refrigerant (102) is compressed in the mixture refrigerant circuit (20) using a compressor (21), characterized in that a hermetic compressor (21) is used as the compressor (21) and/or that the compressor (21) is driven using a magnetic coupling. Method (100, 200) according to claim 1, which comprises a liquefaction operation in which the liquefaction of the hydrocarbon-containing feed gas (101) is carried out, and a standby operation in which the liquefaction of the hydrocarbon-containing feed gas (101) is not carried out, wherein the compressor (21) is not operated in the standby operation or is operated at a lower power than in the liquefaction operation. Method (200) in which, during a transition between the condensation operation and the standby operation, at least a portion of the mixture refrigerant (102) is transferred from the mixture refrigerant circuit (20) into a drain vessel (31), wherein, during a transition between the standby operation and the condensation operation, at least a portion of the mixture refrigerant (102) is transferred from the drain vessel (31) back into the mixture refrigerant circuit (20). Method (200) according to claim 3, in which the transition between the standby mode and the condensation mode comprises a start-up phase in which the compressor (21) is initially put into operation or operated at increased power, and in which at least a portion of the mixture refrigerant (102) is subsequently transferred successively from the drain vessel (31) back into the mixture refrigerant circuit (20). Method (100, 200) according to one of the preceding claims 2 to 4, in which, in the standby mode, evaporation of at least a portion of the mixture refrigerant (102) and a resulting pressure build-up in the mixture refrigerant circuit (20) or a portion thereof is permitted, wherein at least some of the components in the mixture refrigerant circuit (20) are designed such that they withstand the pressure build-up. Method (100, 200) according to claim 5, wherein at least a part of the mixture refrigerant circuit (20) can be sealed off. Process (100, 200) according to one of the preceding claims, wherein the hydrocarbon-containing feed gas (101) comprises biogas or gasification gas produced by gasification of another carbon-containing starting material, shale gas and/or natural gas. A process (100, 200) according to any one of the preceding claims, wherein the hydrocarbon-containing feed gas (101) is fed to the process (100, 200) in an amount of not more than 450 kilograms per hour. Method (100, 200) according to one of the preceding claims, in which exactly one mixture refrigerant circuit (20) is used. Method (100, 200) according to one of the preceding claims, in which a mixture with at least two of the components nitrogen, methane, ethane, propane, ethylene, butane or pentane is used as the mixture refrigerant (102). Plant (100, 200) for liquefying a hydrocarbon-containing feed gas (101), wherein the plant (100, 200) is designed to cool the feed gas (101) in a pressurized state in a heat exchanger (10) and to at least partially liquefy it, wherein the plant (100, 200) is designed to heat a mixture refrigerant (102) in the heat exchanger (10) and to at least partially evaporate it, wherein the plant (100, 200) is designed to guide the mixture refrigerant (102) in a mixture refrigerant circuit (20) and to compress the mixture refrigerant (102) in the mixture refrigerant circuit (20) using a compressor (21). compress, characterized in that the compressor (21) is designed as a hermetic compressor (21) and/or that the compressor (21) is driven using a magnetic coupling. Plant (100, 200) according to claim 11, which is arranged to carry out a method according to one of claims 1 to 10.

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