Gas liquefaction facility

Abstract

The present invention relates to a small-scale gas liquefaction facility, for example for natural gas, which uses an isentropic process to liquefy the gas in a single cycle without the need for additional refrigeration cycles. The gas liquefaction facility (1) comprises – a medium-pressure compressor (31); and – an expansion and work-performing module (40), wherein the expansion occurs in an isentropic manner.

Description

[0001] GAS LIQUEFACTION PLANT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a small-scale gas liquefaction plant, for example natural gas (NG) or biomethane (GNR), which uses an isentropic process to liquefy the gas, which may contain contaminants normally found in natural gas and biomethane, and which normally need to be removed before the liquefaction process, in a single cycle without the need for additional refrigeration cycles.

[0004] BACKGROUND OF THE INVENTION Natural gas (NG) is an important input for various sectors of the economy; its main component is methane, which has one carbon atom and four hydrogen atoms. This characteristic makes NG a more efficient and cleaner alternative to fuels such as gasoline, diesel, LPG, and fuel oil, since, in addition to burning more completely, its combustion generates two water molecules for each CO2 molecule, significantly reducing the emission of pollutants and greenhouse gases into the atmosphere.

[0005] Because it is primarily composed of methane, natural gas (NG) has low calorific value relative to its volume under normal conditions, and its logistics are usually a significant cost factor in its final price. This makes technologies that can increase the calorific value-to-volume ratio viable for transporting over longer distances and highly valued. Liquefaction is an excellent alternative to reduce volume by 600 times, and consequently logistical costs, provided that this liquefaction is carried out at competitive costs.

[0006] Typically, small-scale liquefaction plants are installed at the end of a gas pipeline branch to deliver gas to customers who are far from the pipelines, or near a production point that does not have access to pipelines or nearby consumers.

[0007] There are two main basic ways to liquefy natural gas. One is the "cascade cycle," where a series of heat exchanges occur between the natural gas and a refrigerant, each series with a successively lower temperature relative to the previous one, until liquefaction occurs, close to -160°C. The cascade cycle is very efficient in liquefying natural gas, but it requires a high investment due to the complex refrigeration system, as well as occupying a large physical space. Consequently, the application of this cycle is only viable in large-scale plants (high CAPEX) that demand a lot of gas, making its use unfeasible in locations with small gas production.

[0008] The second way to liquefy natural gas is the so-called "expansion cycle," where the natural gas is initially compressed to a high pressure and then decompressed and expanded through a Joule-Thomson valve, cooling the gas in an isenthalpic manner and consequently liquefying it.

[0009] Although the "expansion cycle" (low CAPEX) allows for the installation of smaller-scale liquefaction plants, the efficiency of plants using this cycle is very low (approximately 80%, according to the BRICK 2016 market study), compared to the "cascade cycle" (approximately 95%, according to the BRICK 2016 market study). This results in very high operating costs (OPEX), making plants using the expansion cycle economically viable only in cases where the price of the produced gas is very low, limiting production to small scale and making the project dependent on a low gas price to be economically attractive.

[0010] In addition to its low efficiency, the expansion cycle using the isenthalpic process requires an additional, parallel cooling process. This additional process, besides increasing the plant's CAPEX complexity, also increases its electrical consumption, consequently increasing the plant's OPEX.

[0011] Another problem with expansion cycle plants is the existence of a residual gas stream with a higher concentration of inert and contaminants after liquefaction, requiring an additional system to purge this stream, further reducing its efficiency.

[0012] Therefore, it would be advantageous to have a small-scale plant (low CAPEX) with a production capacity of 20,000 to 400,000 Nm. 3A cheaper and more versatile system that uses natural gas or non-recyclable gas per day, eliminating the need for complex refrigeration systems and benefiting from a more efficient (isentropic) cooling cycle, without being compromised by low efficiency or the need for purging.

[0013] DESCRIPTION OF THE INVENTION

[0014] A primary objective of the present invention is the use of an isentropic process (expansion with work performed) to liquefy gas, for example natural gas, without the use of additional refrigeration cycles and without the use of complex systems (gears, reducers, gas seals, oil coolers, oil pumps, inert gas storage and injection, seal pressure monitoring, etc.), thus reducing the plant's CAPEX and OPEX, making the process more efficient and less costly. The isentropic process, as a replacement for the isenthalpic process, cools the gas more efficiently, making the additional refrigeration cycle unnecessary.

[0015] A second objective of the present invention is the effective use of at least a fraction of the non-liquefied gas stream, which has a higher concentration of inerts and contaminants, maintaining system equilibrium and eliminating the need for purges. This solution also enables the use of Natural Gas and Biomethane containing inerts and contaminants that normally need to be removed before reaching a liquefaction plant, which increases the complexity, CAPEX and OPEX of currently existing solutions.

[0016] A third objective of the invention is to provide a simple, small-scale gas liquefaction plant capable of partially or fully generating the electrical energy it consumes (i.e., capable of operating without being connected to the electrical transmission grid), making it competitive with larger units due to reduced CAPEX and OPEX, and capable of operating in remote and difficult-to-access environments, a common situation in gas fields.

[0017] One or more of the objectives of the present invention are achieved through a gas liquefaction plant comprising:

[0018] - a medium-pressure compressor; and

[0019] - a module for expanding and carrying out work,

[0020] in which the expansion occurs in an isentropic manner, generating electromechanical utility energy.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The objectives, technical effects, and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, which refers to the accompanying figures, which illustrate exemplary, but not limiting, embodiments of the claimed objects:

[0023] Figure 1 shows a gas liquefaction plant according to one or more described embodiments, comprising an expansion and work module and a generator;

[0024] - Figure 2 shows another embodiment of the gas liquefaction plant described herein, comprising two expansion and work modules and a generator; - Figure 3 shows another embodiment of the gas liquefaction plant described herein, comprising an expansion and work module without a generator;

[0025] Figure 4 shows another embodiment of the gas liquefaction plant described here, comprising two expansion modules and operating without the presence of a generator.

[0026] DESCRIPTION OF THE INVENTION'S EMPHASIS

[0027] Before any embodiments of the present invention are explained in detail, it should be understood that the invention is not limited in its application to the construction details and component arrangement demonstrated in the following description by references such as “in a preferred embodiment” and “in an alternative embodiment” or illustrated in the accompanying drawings. The invention may encompass other embodiments and be practiced or carried out in various ways, including combinations (even if not explicitly described) of features described in different embodiments. It should also be understood that the phraseology and terminology used in this descriptive report of the present invention are for descriptive purposes only and should not be considered limiting.

[0028] Thus, aspects of phrases such as “in a preferred embodiment” and “in alternative embodiments,” in various locations throughout this descriptive report, do not necessarily refer to the same embodiment of the invention presently claimed. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. All the various embodiments, aspects, and options disclosed herein may be combined in all variations, regardless of whether such features or elements are expressly combined in a specific embodiment description herein. This invention presently claimed is intended to be read holistically, so that any separable features or elements of the disclosed invention, in any of its various aspects and embodiments, are to be seen as intended to be combinable, unless the context clearly dictates otherwise.

[0029] The present invention relates to a gas liquefaction plant (1), optionally comprising a high-pressure compressor (30), connected to a gas source (10), such as a gas pipeline from the gas transport or distribution network. In a preferred embodiment, the supplied gas (15) is Natural Gas (NG) or Renewable Natural Gas (RNG), and optionally, hydrogen and other hydrocarbons. Furthermore, the gas liquefaction plant (1) can operate with gas at low pressure less than 20 bar (less than 2 MPa), medium pressure between 20 and 100 bar (between 2 MPa and 10 MPa) and high pressure greater than 100 bar (greater than 10 MPa) supplied by the gas source (10).

[0030] The optional high-pressure compressor (30) is used if the gas supplied by the gas source (10) is not high pressure and consumes electrical energy (25). Electrical energy can be provided by at least one of an electrical power distribution network, a gas generator (20) and / or by an expansion and work-realization module (40) which will be detailed later. In one embodiment, the gas generator (20), as illustrated in Figure 1, is also optionally connected to a non-liquefied gas flow with a higher concentration of inerts (43), and consumes between 6 and 8.2% of the total volume of gas supplied (15) by the gas source (10) to generate sufficient electrical energy for the consumption of the gas liquefaction plant.

[0031] Non-liquefied gas with a higher concentration of inerts (43) is compressed to medium pressure by a medium-pressure gas compressor (31) which also consumes electrical energy (25). The electrical energy can be provided by at least one of an electrical power distribution network, a gas generator (20) and / or by an expansion and work-performing module (40) which will be detailed later.

[0032] The gas supplied (15) by the gas source (10) is mixed with non-liquefied gas with a higher concentration of inerts at medium pressure (17) and the mixture is compressed to high pressure by the high-pressure gas compressor (30). A high-pressure compressed gas outlet from the gas compressor (35) is connected to the expansion and work-performing module (40), where the high-pressure compressed gas (35) performs work, expanding and consequently cooling, generating electromechanical utility energy (isentropic process).

[0033] In one embodiment, the work performed by the compressed gas at high pressure (35), or received already at high pressure in the expansion and work-performing module (40), rotates a coil of a dynamo (not shown) in the expansion and work-performing module (40), generating electrical energy (41). The electrical energy generated by the dynamo can be used by the high-pressure compressor (30) and / or the medium-pressure gas compressor (31), reducing the use of energy from the electrical power distribution network and, consequently, reducing the operating costs of the gas liquefaction plant (1). The electrical energy generated (41) by the dynamo of the gas liquefaction expansion module (40) can also be used by other processes or injected into the electrical power distribution network.

[0034] In one embodiment, the expansion and work-doing module (40) is a turbo expander generator. The use of a dynamo to harness the work done by the gas during its expansion eliminates the need for a mechanical shaft that normally extends outward from commonly used turbo expanders to enable the use of mechanical energy, being a constant source of leakage due to sealing problems, preventing a perfect seal between the interior (higher pressure) and exterior (low pressure).

[0035] The expansion and work-doing module (40) allows control of the amount of work extracted during the expansion of the high-pressure compressed gas (35), supplied by the high-pressure compressor (30) or already received at high pressure from the gas source (10), through the control of the impedance of an electric generator included in the expansion and work-doing module (40), maintaining the liquefaction process stable, even when changes occur in the composition and conditions of the gas supplied by the gas source (10). The work done by the gas during expansion (isentropic process) is the amount of movement extracted from the gas (which tends to expand, but is "braked") and transferred to the dynamo rotor (which is pushed), and thus, adjusting the impedance in the generator alters and improves the isentropic efficiency of the process because it prevents excessive acceleration of the rotor in a controllable way.This adjustability gives the present invention the ability to work with a wider variety of gas compositions, even compared to large-scale "cascade cycle" installations, which are generally designed for a specific gas composition and lose efficiency rapidly if the inlet composition differs from the design composition.

[0036] In one embodiment, after passing through the expansion and work-realization module (40), the gas is directed to a second expansion and work-realization module (45), where the process described above for the expansion and work-realization module (40) is repeated, resulting in greater plant efficiency.

[0037] In one embodiment, the cooling undergone by the gas in the expansion and work-doing module (40, 45) when performing work is sufficient to dispense with the use of external refrigeration cycles (examples, ammonia, propane, refrigerant gases and others), simplifying the operation of the plant (1) and reducing its cost.

[0038] At an outlet of the expansion and work-realization module (40, 45), the liquefied gas (42) from the gas liquefaction and expansion module is made available for use. At an outlet of the expansion and work-realization module (40, 45), a low-pressure non-liquefied gas stream (43), with a higher concentration of inerts, is directed to be compressed by the medium-pressure compressor (31), becoming a medium-pressure non-liquefied gas stream (17) and subsequently mixed with the gas supplied (15) by the gas source (10). Before passing through the medium-pressure compressor (31), a fraction of the stream (43) can be directed to the gas generator (20), where the consumption of this gas fraction (43) by the gas generator (20) efficiently and constantly removes the inerts accumulated in the gas stream, eliminating the need for a purge system, simplifying plant operation and reducing its operating cost.

[0039] In alternative embodiments as illustrated in Figure 2, the gas liquefaction plant (1) of the present invention may include auxiliary valves (50), additional heat exchangers (70), separation and recirculation systems (60), as well as other items commonly used for efficient gas transport between plant equipment. The gas liquefaction plant of the present invention may also include a purge system (80) for the non-liquefied gas stream (43) through the gas liquefaction expansion and work-performing module (40, 45).

[0040] The possibility of controlling pressure and temperature throughout the process allows for the phase change of contaminants that may be present in the incoming gas. In the case of CO2, for example, cooling causes it to change from the gaseous phase to the solid phase. The inclusion of a solids separator at this stage of the process will remove the CO2. Therefore, in one embodiment, the gas liquefaction plant (1) can be configured for cryogenic purification of the incoming gas when necessary, such purification being the removal of CO2, N2, H2S, among other contaminants. Therefore, the gas liquefaction plant (1) can also produce these same contaminants as byproducts.

[0041] The use of isentropic processes for cooling has been occurring for decades in various applications that utilize gas expansion for cooling. Similarly, the recovery of energy from electromechanical utilities has also been around for a long time.

[0042] However, unlike all known processes, the present invention presents a novel combination, mainly of these processes, together with the others presented, which simultaneously allows for simple operation (eliminates the need for external cycles and complex control systems), efficiency, flexibility (maintains its efficiency even with changes in the composition of the inlet gas), versatility (has the ability to eliminate inert and contaminants), environmental friendliness (eliminates the need for atmospheric purges), and scalability (can be installed on a small scale without loss of efficiency).

[0043] Thus, it is concluded that the realizations and details of the system may vary considerably from what has been described and illustrated purely by way of non-limiting example, without departing from the scope of protection of the present invention as defined by the following claims.

[0044] TABLE 1: LIST OF NUMERICAL REFERENCES

[0045]

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Claims

CLAIMS 1. GAS LIQUEFACTION PLANT (1), characterized by comprising: - a medium pressure compressor (31); and - an expansion and work-realization module (40), in which the expansion occurs in an isentropic manner.

2. PLANT (1), according to claim 1, characterized by optionally comprising a high-pressure compressor (30).

3. PLANT (1), according to any one of claims 1 to 2, characterized in that the gas liquefaction plant (1) comprises a second expansion and work-performing module (45), in which the expansion occurs in an isentropic manner.

4. PLANT (1), according to any one of claims 1 to 3, characterized in that the gas cooling occurs in a single cycle in the expansion and work-performing module (40, 45).

5. PLANT (1), according to any one of claims 1 to 4, characterized in that the expansion and work-performing module (40, 45) is a turbo expander generator.

6. PLANT (1), according to any one of claims 1 to 5, characterized by the expansion and work-performing module (40, 45) generating electrical energy (41) by means of a dynamo.

7. PLANT (1), according to any one of claims 1 to 6, characterized in that the gas expansion is controlled by means of impedance control of an electric generator comprised in the expansion and work-performing module (40, 45).

8. PLANT (1), according to any one of claims 1 to 7, characterized in that the non-liquefied gas (43) by the expansion and work-performing module (40, 45) is fed back to the high-pressure compressor (30) after passing through a medium-pressure compressor (31) and / or used by a gas-fired generator (20).

9. PLANT (1), according to any one of claims 1 to 7, characterized by the non-liquefied gas (43) by the expansion and work-making module (40, 45) being directed to purge (80).

10. PLANT (1), according to any one of claims 1 9, characterized by the compressor's electrical energy being optionally supplied at least partially by the expansion and work-performing module (40, 45) and / or by the gas generator (20).

11. PLANT (1), according to any one of claims 1 to 10, characterized in that the gas liquefied by the gas liquefaction plant (1) is one of natural gas, renewable natural gas, hydrogen, and other hydrocarbons.

12. PLANT (1), according to any one of claims 1 to 11, characterized in that it is configured to perform cryogenic purification of the inlet gas when necessary, the purification comprising the removal of CO2, N2, H2S, among other contaminants.

13. PLANT (1), according to any one of claims 1 to 11 characterized by producing, as by-products, contaminants such as CO2, N2, H2S, among others.

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