ES2355467B1 - PROCESS AND SYSTEM TO OBTAIN LIQUID NATURAL GAS. - Google Patents

Abstract

Process and system for obtaining liquefied natural gas. # The present invention describes a process for obtaining liquefied natural gas (LNG) using air as the main refrigerant, and where the natural gas previously goes through a precooling cycle with another refrigerant other than air.

Description

Process and system to obtain liquefied natural gas.

Object of the invention

The main object of the present invention is a process for obtaining liquefied natural gas (LNG) using air as the main refrigerant, and where the natural gas previously goes through a precooling cycle with another refrigerant other than air.

Background of the invention

Natural gas deposits are often located far away from points of consumption, such as on the high seas. Natural gas can be transported from the reservoir using gas pipelines, although large distances or geographical impediments have led to the development of alternatives to facilitate such transportation. One of the most common is its liquefaction for the transport in liquid form in ships called methanes, at atmospheric pressure and at -161ºC; the liquefaction reduces the volume of transported gas 600 times.

However, the “offshore” location (offshore) makes it difficult to use a liquefaction plant to monetize these deposits due to the complexity associated with this type of plant and the limited available space. Among the disadvantages present in the offshore liquefaction would be the logistical difficulties caused by the need to transport the refrigerant fluid used to achieve the gas liquefaction. The lack of space in these facilities means that the refrigerants normally used in liquefaction plants are not adequate.

Description of the invention

The present invention refers to a new process and system capable of liquefying natural gas to produce liquefied natural gas (LNG), where a first refrigeration cycle using a non-air refrigerant performs a pre-cooling of the natural gas stream, and a The second refrigeration cycle that essentially uses air as a refrigerant makes the cooling and liquefaction of natural gas.

The present invention has a better thermal efficiency than a liquefaction process based on the use of air as the sole refrigerant. In addition, this system is easily reproducible in any location, including small or medium natural gas fields located offshore, for which the process would take place over one or more fixed structures (such as platforms), floating structures at sea (such as boats or barges), or combination of the above. In this document, therefore, the term "structure" refers to all these options. The invention is particularly advantageous in these cases because of the smaller space required on the platform compared to other alternative processes based solely on the use of hydrocarbon mixtures.

Thus, a first aspect of this invention refers to a process carried out on at least one structure on the high seas to obtain liquefied natural gas comprising a first pre-cooling cycle of natural gas with a refrigerant other than air and a second refrigeration cycle with air as a refrigerant for cooling and liquefying natural gas.

In a preferred embodiment of the invention, the refrigeration cycle with a refrigerant other than air comprises performing at least one compression stage of the refrigerant other than air followed by an expansion to achieve its cooling, and the use of the refrigerant stream other than air thus cooled to precool the natural gas in a first heat exchanger.

Particularly, the non-air refrigerant can be NH3, hydro-fluorocarbons (HFCs), hydrochloro-fluorocarbons (HCFCs), CO2, nitrogen, or hydrocarbons, among others, either as pure compounds or in mixtures.

In addition, in another embodiment of the present invention, the natural gas can be pretreated before the precooling cycle. Several pretreatment configurations are known in the state of the art depending on the location and type and composition of the contaminant, although typically it comprises the removal of Hg, CO2, H2S and H2O, among others.

Optionally, the process may also comprise the step of separating the natural gas from its natural gas liquids, before liquefaction. The term "Natural Gas Liquids (LGN)" used here refers to the less volatile components of natural gas, from ethane to higher hydrocarbons (propane, butane, isobutane and gasoline, the latter sometimes referred to as condensate), with a content lower in methane.

In another particular embodiment of the invention, the second refrigeration cycle using air as a refrigerant comprises the following operations:

-

perform at least one compression stage of an air stream;

-

cooling said compressed air stream in a second heat exchanger, in which the precooled natural gas also undergoes additional cooling, thanks to the low pressure refrigerant air flow circulating in countercurrent;

-

expand the high-pressure air stream leaving said heat exchanger to reduce its pressure and achieve greater cooling; Y

-

using said air stream after expansion to further cool the natural gas stream in a third heat exchanger, passing said air stream at low pressure, at the outlet of the third exchanger, through the second exchanger. On the other hand, the natural gas stream at the exit of the third exchanger expands before moving to a separator where liquefied natural gas (LNG) is separated from the end gas.

In another embodiment of the invention, the end-end gas stream obtained as a by-product of the liquefaction is passed respectively through the third exchanger and the second exchanger to help cool the natural gas and air streams, thus taking advantage Its cryogenic energy. At the exit of the exchangers, it can be used as fuel, for example for process gas turbines, among other possible uses.

The second air cooling cycle can be opened or closed. When the cycle is open, the air is taken continuously from the environment, in atmospheric conditions, it is treated to remove CO2 and water, it is used to cool natural gas according to the previous steps, and it is returned to the atmosphere. When the cycle is closed, the air used to cool the natural gas is recirculated, being only necessary to provide a small amount of treated air to compensate for losses (make-up).

In an embodiment of the present invention, particularly suitable when the natural gas is rich in heavy components, the natural gas is precooled in a first heat exchanger to a temperature between -10 ° C and -50 ° C. Next, the natural gas enters a second exchanger, where it is cooled to a temperature that allows the condensation of natural gas liquids (LGN) in the required proportion. This temperature depends on the composition of the feed gas, the LNG speci fi cations, and the particular requirements for recovery and / or purity of the extracted heavy components, being typically greater than -100 ° C. The result of the previous stage is a gas stream typically composed of all the methane and nitrogen from the initial feed, the desired amount of ethane, and residual amounts of the heaviest components (propane and higher).

Next, this natural gas stream passes to a third heat exchanger where it is cooled with air until it is totally or almost completely liquefied. The temperature at which natural gas leaves this exchanger is not less than -170 ° C.

In an alternative embodiment, precooling and liquefaction can be carried out using only two exchangers, one for each stage. In this case, the extraction of the LGNs is carried out after the pre-cooling of the natural gas in the first heat exchanger.

A second aspect of the present invention refers to a system for carrying out the previously described process comprising the following equipment:

-

at least one compressor and a cooler to compress and cool the refrigerant stream other than air;

-

a first heat exchanger to precool the natural gas stream with the coolant stream other than air;

-

at least one compressor and a cooler to compress and cool a stream of air;

-

a second heat exchanger for cooling the pre-cooled natural gas stream and the compressed air stream using the low pressure refrigerant air stream;

-

at least one expansion device to allow the expansion of the high pressure air stream leaving the second heat exchanger;

-

a third heat exchanger for cooling the natural gas stream with the air stream after its expansion;

-

an expansion device to allow the expansion of the natural gas stream; Y

-

a separator that separates the natural gas stream into liquefied natural gas and end gas.

Next, a brief description of each of these elements is made, as well as some others not explicitly mentioned in the previous list.

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Heat exchangers. Any type of heat exchanger can be used in the present invention. For the precooling cycle, the exchangers may preferably be shell and tubes or plates and fins, while for the air cycle, plate and fin exchangers are preferred. The minimum number of heat exchangers on the natural gas side is one.

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Expanders Examples of suitable expanders are Joule Thompson (J-T) valves and turboexpansors. On the air side, at least one expander is needed to expand the air; if required, several expanders can be used in parallel. Air expanders can be coupled to one or more compressors to recover power. Alternatively, that power can be used for other purposes, such as power generation. On the side of the non-air refrigerant, at least one expander is needed to expand the non-air refrigerant before using it in the pre-cooling of natural gas. On the natural gas side, at least one expander is needed to expand the liquid obtained in the heat exchange section.

-

Compressors At least one is required to compress the air refrigerant. If precooling is performed with a compression cycle, then at least two compressors will be required, one for the precooling cycle and one for the air cycle. The number of stages of compression of the cycles depends on the optimization of the process. The compression zones preferably comprise one or more heat exchangers between the compressors (intercoolers), in the case where more than one compressor is used, and one or more exchangers after the last compressor (aftercoolers). All these exchangers preferably use water as a cooling medium. Another additional compressor together with its cooling system may be required to feed the final fl ash gas to the turbines.

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Compressor actuators for all compression stages, except if they are directly coupled to the air expander. They can be gas turbines, steam turbines or electric motors.

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Column for extraction of LGN. If LGN fractionation is required, more than one column may be necessary.

Unless otherwise defined, all technical and scientific terms used here have the same meaning commonly understood by those skilled in the art to which this invention pertains. Methods and materials similar or equivalent to those described herein may be used in the practice of the present invention.

In the description and claims, the word "comprises" and its variations are not intended to exclude other technical characteristics, additives, components or steps. Objectives, advantages and additional features of the invention will be apparent to those skilled in the art after examination of the description, or can be deduced from the practice of the invention.

The following examples and drawings are provided for illustrative purposes and are not intended to limit the scope of the present invention. Various subsystems required such as valves, control systems, sensors, and support structures have been removed from the fi gures to improve the simplicity and clarity of the presentation.

Description of the drawings

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1 shows an example of the present invention applied to the liquefaction of a natural gas stream. The scheme shown in Fig. 1 consists of a first stage of pre-cooling of natural gas and a second stage of liquefaction. The liquefaction is achieved by a closed cycle in which air is used as a refrigerant.

Figure 2.- shows a modification of the scheme shown in Fig. 1 where the air used as a refrigerant for the liquefaction of natural gas flows in an open cycle.

Preferred Embodiment of the Invention

Example 1

Example 1 is based on the scheme shown in Fig. 1 in which the refrigerant used in the natural gas precooling stage is propane. In this example, the feed natural gas stream (stream 1) is treated in a conventional pretreatment A plant to remove CO2, H2S, water and mercury. The treated gas, stream 2, corresponds to a sweet and dry stream of natural gas at 15 ° C and 30.1 bar. Stream 2 has the molar composition indicated in Table 1.

TABLE 1

Stream 2 enters the precooling stage, passing through heat exchanger 100, until a stream 3 is obtained at -30 ° C. The pre-cooled natural gas stream (stream 3) enters the liquefaction stage, passing through the heat exchangers 101, 102 to obtain a high-pressure subcooled liquid, stream 7. In the first heat exchanger 101, The natural gas is cooled to an intermediate temperature of approximately -69 ° C (stream 4), to condense the natural gas liquids. Stream 4 enters a column B where liquids from natural gas are extracted as stream 5 from the bottom, while poor gas, stream 6, exits the column from the head. Stream 5 is directed to the fractionation zone if specific products such as propane and butane are required.

Poor natural gas (stream 6) enters heat exchanger 102 and cools to an approximate temperature of -130 ° C, obtaining a liquid stream undercooled at high pressure (stream 7), which is directed to a JT 103 valve, through from which the stream 7 expands adiabatically to 1.1 bar (stream 8) and is finally directed to a vessel 104, in which a separation of the liquid phase and the vapor phase occurs, producing LNG on storage (stream 9 ) and an end-stream gas stream (stream 10), both at approximately -160 ° C and 1.1 bar.

Stream 10 is recirculated to heat exchangers 102 and 101, respectively, where the cryogenic energy of this stream is recovered. Thus, stream 11 leaves heat exchanger 102 at -90.8 ° C, which is further heated in heat exchanger 101 to a temperature of 15 ° C (stream 12). This stream 12 can be used as fuel inside the plant. In the event that this fuel goes to gas turbines, stream 12 will typically need to increase its pressure by means of a compressor before being introduced into them.

In this example, the heat exchangers used on the natural gas side are: shell and tube type heat exchanger for pre-cooling with propane and plate and fin heat exchangers for air liquefaction.

The propane cycle that converts the natural gas stream 2 into the precooled natural gas stream (stream 3) is described below, starting with the propane stream 13 that has made use of all or most of its cooling properties by absorbing heat of the feed gas. Stream 13, at approximately 10 ° C, which is at the lowest pressure in the cycle (around 1.4 bar), enters and is re-compressed in a multi-stage compression unit 105, which has intermediate and post-cooling stages, for produce compressed current

17. The compression zone comprises two compressors 106 and 108, with a heat exchanger 107 between them and a heat exchanger 109 after the compressor 108. Heat exchangers 107 and 109 use water as a cooling medium. The compressed current 17 leaves the compression unit 105 at 40 ° C and 17.5 bar and passes through a valve 110 that reduces its pressure and temperature, until the current 18 is obtained, at -32.6 ° C and 1.5 bar. This current passes through the heat exchanger 100, where it provides the necessary cold to pre-cool the natural gas stream 2, exits as stream 13 and begins the cycle again.

The air cooling cycle that converts the precooled natural gas stream 3 into the liquid stream 7 is described below, starting with the air stream 19 that has made use of all or most of its cooling properties by absorbing heat from the natural gas . Stream 19, at approximately 37 ° C, is at the lowest pressure in the cycle (about 2 bar) and enters and is recompressed in a multi-stage compression unit 111, which has intermediate cooling and postcooling stages, to produce compressed stream 25 The compression zone comprises three compressors 112, 114 and 116, with a heat exchanger 113 between the compressors 112 and 114, a heat exchanger 115 between the compressors 114 and 116 and a heat exchanger 117 after the compressor

116. Heat exchangers 113, 115 and 117 use water as a cooling medium. The compressed stream 25 leaves the compression unit 111 at 40 ° C and 30 bar and is directed to the heat exchanger 101, where it is cooled to -37.8 ° C by the countercurrent passage of the cooling air stream 32 and the stream 11 end gas. Stream 25 exits as stream 26 of heat exchanger 101 and passes to expansion zone 118, where it reduces the pressure and temperature of air stream 26, resulting in stream 31. The expansion zone comprises two turboexpanders 119 and 120 in parallel and is used to provide some of the power for the compressor of the compression unit 111. The air stream 31 (which has been expanded in the expansion zone 118) is at 2.15 bar and a temperature of - 143 ° C. This current passes through heat exchangers 102 and 101, respectively. In heat exchanger 102, stream 31 provides sufficient cold to liquefy the natural gas stream 6 and form liquefied natural gas (stream 7). Stream 31 leaves heat exchanger 102 as stream 32 at a temperature of -71 ° C and enters heat exchanger 101, where it cools both natural gas (stream 3) and compressed air (stream 25). Stream 32 leaves heat exchanger 101 as stream 19 and begins the cycle again.

The air cycle will have a make-up point to compensate for air losses in the cycle. The make-up air (compensation) will have to be treated in treatment facilities to remove the CO2 and the water it contains.

Also, the propane cycle will also have a make-up point that compensates for propane losses in the cycle.

Table 2 shows the operating conditions of the main currents of Fig. 1 applied to Example 1.

TABLE 2

Example 2

Fig. 1 also serves to illustrate a second example of the present invention, applied in this case to the liquefaction of a natural gas stream using CO2 as a refrigerant in the first precooling stage and air as a refrigerant in the second stage in which the final liquefaction of natural gas is achieved. The cooling air circulates in a closed cycle.

The description of the process is analogous to that indicated in Example 1, with the proviso that in this case the pre-cooling cycle of natural gas contains CO2 and takes the same hypothesis as regards the composition of the incoming natural gas. The operating conditions of the main currents of Fig. 1 applied to Example 2 are shown in Table 3.

TABLE 3

Example 3

Fig. 2 shows another example of the present invention. The example shown in Fig. 2 has, as a modification to the scheme shown in Fig. 1, that the air used as a refrigerant for the liquefaction of natural gas flows in an open cycle.

Example 3, based on Fig. 2, shows an example of the present invention applied to the liquefaction of a natural gas stream using propane as a refrigerant in a first precooling stage and air as a refrigerant in a second stage in which achieves the final liquefaction of natural gas, circulating the air in an open cycle.

The natural gas feed stream (stream 1) is treated in a conventional pretreatment A plant to remove CO2, H2S, water and mercury. The treated gas, stream 2, corresponds to a sweet and dry stream of natural gas at 15 ° C and 30.1 bar. Stream 2 has the molar composition indicated in Table 1.

Stream 2 enters the precooling stage, passing through heat exchanger 100, until a stream 3 is obtained at -30 ° C. The pre-cooled natural gas stream (stream 3) enters the liquefaction stage, passing through the heat exchangers 101, 102 to obtain a high-pressure subcooled liquid, stream 7. In the first heat exchanger 101, the gas natural is cooled to an intermediate temperature of approximately -69 ° C (stream 4), to condense the natural gas liquids. Stream 4 enters a column B where liquids from natural gas are extracted as stream 5 from the bottom, while poor gas, stream 6, exits the column from the head. Stream 5 is directed to the fractionation zone if specific products such as propane and butane are required.

Poor natural gas (stream 6) enters heat exchanger 102 and cools to an approximate temperature of -130 ° C, obtaining a liquid stream undercooled at high pressure (stream 7), which is directed to a JT 103 valve, through from which the stream 7 expands adiabatically to 1.1 bar (stream 8) and is finally directed to a vessel 104, in which a separation of the liquid phase and the vapor phase occurs, producing LNG on storage (stream 9 ) and an end-stream gas stream (stream 10), both at approximately -160 ° C and 1.1 bar.

Stream 10 is recirculated to heat exchangers 102 and 101, respectively, where the cryogenic energy of this stream is recovered. Thus, stream 11 leaves heat exchanger 102 at -90.8 ° C, and is further heated in heat exchanger 101 to a temperature of 15 ° C (stream 12). This stream 12 can be used as fuel inside the plant.

The propane cycle that converts the natural gas stream 2 into the precooled natural gas stream (stream 3) is described below, starting with the propane stream 13 that has made use of all or most of its cooling properties by absorbing heat of the feed gas. Stream 13, at approximately 10 ° C, which is at the lowest pressure in the cycle (around 1.4 bar), enters and is re-compressed in a multi-stage compression unit 105, which has intermediate and post-cooling stages, for produce compressed current

17. The compression zone comprises two compressors 106 and 108, with a heat exchanger 107 between them and a heat exchanger 109 after the compressor 108. Heat exchangers 107 and 109 use water as a cooling medium. The compressed current 17 leaves the compression unit 105 at 40 ° C and 17.5 bar, and passes through a valve 110 that reduces its pressure and temperature until the current 18 is obtained, at -32.6 ° C and 1.5 bar. This current passes through the heat exchanger 100, where it provides the necessary cold to pre-cool the natural gas stream 2. The stream 18 leaves the heat exchanger 100 as stream 13 and begins the cycle again.

The air cooling cycle, in Fig. 2, is an open cycle. In this cycle, the air is taken continuously from the atmosphere at ambient conditions (current 19 *). Stream 19 * enters treatment plant C, which is responsible for removing CO2 and water that contains the air and leaves the plant as stream 19 (15ºC and 1bar). Stream 19 is compressed in a multi-stage compression unit 111, which has intermediate and post-cooling stages, to produce compressed stream 25, which leaves compression unit 111 at 40 ° C and 16 bar. This stream is directed to the heat exchanger 101, where it is cooled to -33.5 ° C (stream 26) by the countercurrent passage of the refrigerant air stream 32 and the stream gas stream 11. Stream 26 passes to expansion zone 118, where the pressure and temperature are reduced to 1.2 bar and -137.2 ° C, respectively (stream 31). Stream 31 passes through heat exchangers 102 and 101, respectively. In heat exchanger 102, stream 31 provides sufficient cold to liquefy the natural gas stream 6 and form liquefied natural gas (stream 7). Stream 31 leaves heat exchanger 102 as stream 32 at a temperature of -78.1 ° C and enters heat exchanger 101, where it cools both natural gas (stream 3) and compressed air (stream 25). Stream 33 leaves heat exchanger 101 at approximately 19 ° C and 1 bar, and is released directly into the atmosphere.

Table 4 shows the operating conditions of the main currents of Fig. 2 applied to Example 3.

TABLE 4

Example 4

Fig. 2 also serves to illustrate a fourth example of the present invention, applied in this case to the liquefaction of a natural gas stream using CO2 as a refrigerant in the first precooling stage and air as a refrigerant in the second stage in which the final liquefaction of natural gas is achieved. The cooling air circulates in an open cycle.

The description of the process is analogous to that indicated in Example 3, with the proviso that in this case the pre-cooling cycle of natural gas contains CO2 and takes the same hypothesis as regards the composition of the incoming natural gas. The operating conditions of the main currents of Fig. 2 applied to Example 4 are shown in Table 5.

ES 2 355 467 A1

TABLE 5

Claims (21)

1. Process to obtain liquefied natural gas (LNG), characterized in that it comprises performing the following operations on at least one structure located on the high seas:

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carry out a first refrigeration cycle with a refrigerant other than air for the precooling of a natural gas stream (1, 2), and

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Perform a second cycle of air cooling for cooling and liquefying the precooled natural gas (3).

2.

Process according to claim 1 wherein the first refrigeration cycle comprises at least one stage of compression of the refrigerant stream (13) other than air followed by an expansion to achieve its cooling, and the use of the cooled refrigerant stream ( 18) to precool a stream of natural gas (1) in a first heat exchanger (100), obtaining precooled natural gas (3).

3.

The process according to claim 2, wherein the refrigerant is chosen from the following list: NH3, hydro-fluorocarbons (HFCs), hydrochloro-fluorocarbons (HCFCs), CO2, nitrogen, pure hydrocarbons and hydrocarbon mixtures.

Four.

The process according to any of claims 1-3, which further comprises the previous operation of extracting from the natural gas stream (1) at least one of the following compounds: CO2, H2S, H2O and Hg, obtaining the flow of natural gas (2).

5.

The process according to any of claims 1-4, further comprising the operation of extracting the liquids from the natural gas stream (3 or 4) after the first refrigeration cycle.

6.

The process of any of claims 1-5, wherein compression of the refrigerant stream (13) other than air is carried out in at least two stages of compression.

7.

The process according to any of claims 1-6, wherein the natural gas stream (2) has a pressure of at least 1 bar.

8.

Process for obtaining liquefied natural gas according to any of claims 1-7, wherein the second air cooling cycle comprises the following operations:

-

perform at least one compression stage of an air stream (19);

-

cooling said compressed air stream (25) in a second heat exchanger (101), in which the precooled natural gas stream (3) also undergoes additional cooling, thanks to a stream of low pressure refrigerant air circulating in countercurrent (32);

-

expand the high pressure air stream (26) to reduce its pressure and achieve greater cooling; Y

-

using said air stream (31) to cool the natural gas stream (6) in a third heat exchanger (102), then running said air stream (32) at low pressure through the second exchanger (101),

-

expand the natural gas stream (7) at the outlet of the third heat exchanger (102) before moving to a separator (104) where the liquefied natural gas (9) is separated from an end-flow gas (10).

9. The process according to claim 8, wherein the end-gas (10) passes through the third heat exchanger (102) and the second heat exchanger (101) to recover its cryogenic energy. 10. The process according to any of claims 8-9, wherein the compression of the air stream (19) is carried out in at least two stages of compression.

eleven.

The process according to any of claims 8-10, wherein the air flow (32), after passing through the second exchanger (101), returns to the beginning of the compression stage.

12.

The process according to any of claims 8-10, wherein the air stream (32), after passing through the second exchanger (101), is returned to the atmosphere.

13.

The process according to claim 12, further comprising a previous step of extracting water and CO2 from the air stream (19 *) prior to compression of said stream.

14.

A system for obtaining liquefied natural gas from a platform located on the high seas, characterized in that it comprises the following components: -at least one compressor (106, 108) and a cooler (107, 109) to compress a different refrigerant stream (13) of air; - a first heat exchanger (100) for precooling a natural gas stream (2) with the coolant stream (18) other than air; - at least one compressor (112, 114, 116) and a cooler (113, 115, 117) to compress an air stream (19); - a second heat exchanger (101) for cooling the pre-cooled natural gas stream (3) and the compressed air stream (25) with the low pressure air stream (32), which circulates in countercurrent; - at least one expansion device (119, 120) to allow the expansion of the high pressure air stream (26); - a third heat exchanger (102) for cooling the natural gas stream (6) with the air stream (31) obtained after the expansion;

- an expansion device (103) to allow the expansion of the natural gas stream (7); and -a separator (104) that separates the natural gas stream (8) into liquefied natural gas (9) and end-gas (10).

fifteen.

The system according to claim 14, wherein the third exchanger (102) further admits the input of the end gas stream (10).

16.

The system according to any of claims 14-15, wherein the second exchanger (101) further admits the entry of the end gas stream (11).

17.

The system according to any of claims 14-16, further comprising a pretreatment plant (A) for the extraction of at least one of the compounds of the following list: CO2, H2S, H2O and Hg.

18.

The system according to any of claims 14-17 further comprising a column (B) for the extraction of liquids from natural gas.

19.

The system according to any of claims 14-18, which further comprises a pretreatment plant (C) for extracting water and CO2 from the air stream (19 ’).

SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 200930684 SPAIN Date of submission of the application: 11.09.2009 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: F25J1 / 02 (01.01.2006) RELEVANT DOCUMENTS

Category

Documents cited Claims Affected

Y

EP 1939564 A1 (REPSOL YPF S A) 02.07.2008, paragraphs [0004] - [0032]; figures 1-2. 1-19

Y

MCINTOSH, A. et al. “Moving Natural Gas Across Oceans” Oilfield Review, Summer 2008, 1-19

pages 50-63, [online] [retrieved on 02.10.2011]. Recovered from internet:

URL: http: //www.slb.com/~/media/Files/resources/oilfield_review/ors08/sum08/04_moving_naturalgas.ashx

TO

WO 2007021351 A1 (EXXONMOBIL UPSTREAM RES CO et al.) 02.22.2007, the whole document. 1-19

TO

WO 9859205 A2 (EXXON PRODUCTION RESEARCH CO) 30.12.1998, the whole document. 1-19

TO

US 4894076 A (AIR PROD & CHEM) 16.01.1990, the whole document. 1-19

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 16.02.2011

Examiner I. González Balseyro Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 200930684 Minimum documentation sought (classification system followed by classification symbols) F25J Electronic databases consulted during the search (name of the database and, if possible, search terms used) INVENES, EPODOC, WPI, NPL, TXTUS, XPESP State of the Art Report Page 2/4  WRITTEN OPINION Application number: 200930684 Date of Completion of Written Opinion: 02.21.2011 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims 1-19 Claims IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-19 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 200930684 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

EP 1939564 A1 (REPSOL YPF S A) 02.07.2008

D02

MCINTOSH, A. et al. “Moving Natural Gas Across Oceans” Oilfield Review, Summer 2008, pages 50-63, [online] [retrieved 10.02.2011]. Retrieved from internet: URL: http: //www.slb.com/~/media/Files/resources/oilfield_review/ors08/sum08/04_moving_naturalgas.ashx 2008

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The object of the invention is a natural gas liquefaction process where the natural gas is initially cooled with a fluid other than air before being liquefied by air cooling; as well as the installation to carry it out. Document D01 is considered the state of the art closest to the invention as set out in claim 1 of the application. This document discloses a natural gas liquefaction procedure where air is used as a refrigerant. Said air can be pretreated to remove its impurities, then it is compressed and cooled in a first exchanger, to be expanded and used as a refrigerant in the cooling and final liquefaction of natural gas. The air can be both closed and open circuit. The natural gas can be pretreated to remove its impurities and after the first cooling, the heavy ones that have condensed are separated. The liquefied natural gas obtained after a second cooling is expanded and sent to a flash vessel where the liquid is separated from the generated gases. These gases can be used to cool natural gas and air currents. (See paragraphs [0004] - [0032], figures 1-2). The difference between document D01 and the technical object of claim 1 of the application lies in the incorporation of a cycle prior to the liquefaction process of natural gas, where the natural gas is precooled with a fluid other than air through compression stages and expansion of said fluid. This feature is already included in document D02 which discloses a natural gas liquefaction process where said gas is precooled with a propane refrigeration cycle, where said refrigerant is compressed and expanded for that purpose. (See page 55). Therefore, it is obvious to the person skilled in the art to use the teachings of document D02 in the process disclosed in document D01, thus obtaining the object of the invention. Consequently claims 1 to 19 lack inventive activity in view of what is disclosed in documents D01 and D02 (Art. 8.1 LP). State of the Art Report Page 4/4