AU2006261281A1

AU2006261281A1 - Method for liquefying a hydrocarbon-rich flow

Info

Publication number: AU2006261281A1
Application number: AU2006261281A
Authority: AU
Inventors: Heinz Bauer; Rainer Sapper
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2005-06-23
Filing date: 2006-05-30
Publication date: 2006-12-28
Also published as: RU2008101527A; NO20080356L; WO2006136269A1; DE102005029275A1; CN101223410A; BRPI0612316A2

Description

ox 259. Kynoton, Vic 3444 AUSTRALIA e wwu.ocodomyXL.com e info~ocodomyXL.com a o businGss of Tonco Services Pty Ltd e A8N 72 892 315 097 Free 2 1800637640 Inter R +61 3 54 232558 Fox A 03 54 232677 Inter d +61 3 54 232677 TRANSLATION VERIFICATION CERTIFICATE This is to certify that the attached document is an English translation of the -- German-language PCT Application PCT/EP2006/005138 and Academy Translations declare that the translation thereof is to the best of their knowledge and ability true and correct. December 14, 2007 ARcOdem i rJpios PO Box 259, K on i AUSTRALIA Date Stamp/Signature: AT Ref.: dcc-2053 Multilingual Technical Documentation Translation from German of PCT Application PCT/EP2006/005138 Method for liquefying a hydrocarbon-rich flow 5 The invention relates to a method for liquefying a hydrocarbon-rich flow, particularly a natural gas flow, said hydrocarbon-rich flow being liquefied counter to a cascade comprising three coolant mixture circuits. 10 In the following, the term "first coolant mixture circuit" shall always be understood to mean a carbon dioxide coolant circuit. 15 A generic method for liquefying a hydrocarbon-rich flow is known from the German patent application publication 197 16 415. Quoting the German patent application publication 197 16 415, its published contents are included in the published contents of this patent 20 application. Natural gas liquefaction systems are designed as either so-called LNG Baseload Plants - that is, plants for the liquefaction of natural gas to supply natural gas as a 25 primary energy source - or as so-called Peak Shaving Plants - that is, plants for the liquefaction of natural gas to cover peak demand. LNG Baseload Plants are typically operated with coolant 30 circuits that consist of carbon dioxide mixtures. These mixture circuits are energetically more efficient than expander circuits, and allow relatively low energy 2 consumption for the large liquefaction capacity of the baseload plants. In generic liquefaction methods, the first mixture 5 circuit is fundamentally used for precooling; the second mixture circuit is used for liquefaction; and the third mixture circuit is used for supercooling the hydrocarbon rich flow or natural gas. 10 Separation of higher boiling hydrocarbons takes place to the extent necessary - between precooling and liquefaction. These are mainly those components of the hydrocarbon-rich flow or natural gas that would freeze out in the next cooling - that is, C 5 , hydrocarbons and 15 aromatics. In addition, those hydrocarbons - particularly propane and butane - that would cause an undesired increase in the heat value of the liquefied natural gas are often separated prior to liquefaction. 20 From the German patent application 103 44 030, a generic method is also known; with said method, at least part of the flow of the coolant mixture of the second coolant mixture circuit is used for precooling the hydrocarbon rich flow. This liquefaction method allows more 25 economical use of the available compressors and drives, since the (circuit) compressors of the three mixture circuits have approximately the same drive power; that is, about 33.33W of the total drive power. This allows particularly large liquefaction plants, with a 30 liquefaction capacity of over 5 million tons of LNG per year, to be operated more economically, since the liquefaction capacity of the liquefaction process can be 3 maximised by using identical, proven drives and compressors in the three coolant circuits. The coolant mixture used for precooling in the first 5 coolant mixture circuit is generally evaporated at two or more different pressure levels in the generic liquefaction methods described above. This yields a good balance between the available cooling and demand for cooling of the warm process flows, and thus reduces 10 energy consumption. Especially for so-called Baseload Plants, a single-stage precooling step is thus atypical, due to the increased energy usage associated with it. The methodology described above is the state of the art, 15 and results in at least one partial coolant mixture flow being evaporated at a lower pressure than the remaining partial coolant mixture flow. The use of evaporating coolant at low pressure, however, automatically leads to large, and thus expensive machinery, devices, and 20 pipelines. The object of the present invention is to present a generic method that avoids the disadvantages indicated above. 25 To achieve this object, a generic method for liquefying a hydrocarbon-rich flow is proposed that is characterised in that the first and second coolant mixture circuit are used for precooling, and the third coolant mixture 30 circuit is used for the liquefaction and supercooling of the hydrocarbon-rich flow.

4 Additional advantageous embodiments of the method according to the invention for liquefying a hydrocarbon rich flow are characterised in that 5 - the first and/or second coolant mixture circuits are designed as single-stage coolant mixture circuits, - the third coolant mixture circuit is designed as a two stage coolant mixture circuit, 10 - the power consumption of the compressors in the first and second coolant mixture circuits is identical or essentially identical to the power consumption of the compressors in the two-stage third coolant mixture 15 circuit, - where all compressors in the coolant mixture circuits advantageously have the same or essentially the same power consumption, 20 - the power consumption of the compressors in the first and second coolant mixture circuits is identical or essentially identical to the power consumption of each of the two compressors in the two-stage third coolant 25 mixture circuit, - gas turbines, steam turbines, and / or electric motors are used as drives for the compressors. 30 The term "precooling" is defined to mean cooling of the hydrocarbon-rich flow to be liquefied to a temperature of at least -30 *C to -70 *C, preferably -40 *C to -60 *C.

5 In place of the two-stage precooling circuit used in the state of the art liquefaction methods, two separate, single-stage coolant mixture circuits are used according to the invention to precool the hydrocarbon-rich flow. 5 With the proper selection of process conditions, such as the mixture composition, pressure profile etc., the vacuum pressure of both precooling circuits can be significantly increased for the liquefaction method according to the invention, namely typically to 5 bar or 10 higher. In comparison, the vacuum pressure on the vacuum stage of a two-stage precooling circuit is typically 2 to 3 bar. Due to the increased gas densities of the coolant mixture 15 circuits used for precooling, the method according to the invention allows more compact plants and processes to be implemented. Compared to liquefaction methods where just two mixture circuits are used, the method according to the invention, with three mixture circuits, also has a 20 lower specific energy consumption. The method according to the invention, as well as other embodiments of the same, which represent the objects of the attached patent claims, are described in more detail 25 using the application example shown in the illustration. Using the method described in the illustration, the hydrocarbon-rich flow is cooled and liquefied, said flow being fed through line 1 of the heat exchanger El, 30 against a coolant mixture circuit cascade comprising three coolant mixture circuits. These generally have different compositions, such as are described, for 6 example, in the previously mentioned German patent application publication 197 16 415. The hydrocarbon-rich flow to be liquefied is cooled in 5 heat exchanger El against the evaporating coolant mixture flow 2b of the first mixture circuit 2a through 2c. The hydrocarbon-rich flow is then fed through line la to the heat exchanger E2, and further cooled therein against 10 the evaporating coolant mixture flow 3b of the second mixture circuit 3a through 3c. At the outlet of the heat exchanger E2, the cooled hydrocarbon-rich flow is below a temperature of -30 *C to 15 -70 *C, preferably -40 *C to -60 *C. It is now fed through line lb into a separator S, shown simply as a black box. The previously described C 3 + separation takes place therein, whereby the components separated from the 20 hydrocarbon-rich flow to be liquefied are drawn off through line 1c out of the separator S. The hydrocarbon-rich flow to be liquefied is then fed through line ld into a third heat exchanger E3, and 25 liquefied and supercooled therein against the evaporating coolant mixture flow 4b of the third cooling circuit 4a through 4c. The supercooled liquid product is then fed through line 30 le for further use and/or (intermediate) storage. As previously indicated, the coolant mixture circuits 2a through 2c and 3a through 3c used for precooling the 7 hydrocarbon-rich flow are each single-stage coolant mixture circuits. The coolant mixtures compressed in each circuit 5 compressor V2 and V3 are fed via lines 2a or 3a through heat exchanger El - in the case of the first coolant mixture circuit - or through both heat exchangers El and E2 - in the case of the second coolant mixture circuit. After expansion in the expansion valve a or b, the 10 coolant mixture flow is evaporated in heat exchangers El or E2 against process flows that are to be cooled, and then fed back into the circuit compressors V2 and V3 via lines 2c or 3c. 15 The same applies to the third coolant mixture circuit, in which the compressed coolant mixture 4a is fed via line 4c through an expansion device c after cooling in heat exchangers El, E2 and E3, expanded in the expansion device, then evaporated in heat exchanger E3 against the 20 process flows to be cooled, then fed via line 4c to the inlet of the low-pressure compressor stage V4, which is downstream of the high-pressure compressor stage V4'. The increase in the operating pressure associated with 25 the method according to the invention, as well as the gas density of the second coolant mixture flow 3a through 3c, which is used for precooling, requires the use of wound heat exchangers, in which the coolant mixture evaporates in the mantel, for the heat exchange E2. For generic 30 liquefaction processes according to the state of the art, such wound heat exchanger were often not able to be used, because they would have to be too large, but their 8 maximum permissible diameter is generally limited by manufacturing and transportation dimensions. Not shown in the illustration are coolers or heat 5 exchangers downstream from the compressors V2, V3, V4, and V4', in which the coolant mixture is cooled against a cooling medium - such as water or air - and, in the case of the first coolant mixture circuit 2a through 2c, is condensed. The coolant mixture in the second coolant 10 mixture circuit is generally at least partially condensed against a cooling medium - such as water or air. According to an additional advantageous embodiment of the method according to the invention, the power consumption 15 of the compressors V2 and V3 in the first and second coolant mixture circuits 2a - 2b and 3a - 3b can be designed to be identical, or essentially identical, to the power consumption of the compressors V4 and V4' in the two-stage third coolant mixture circuit 4a - 4b. In 20 this case, all the compressors V2, V3, V4, and V4' in the coolant mixture circuits 2a - 2b, 3a - 3b and 4a - 4b advantageously have identical or essentially identical power consumption. 25 In this embodiment of the method according to the invention, either two identical drives, where one drive is assigned to the compressors V2 and V3 and one drive is assigned to the compressors V4 and V4', or four identical drives, one each to drive compressors V2, V3, V4, and 30 V4', can be used.

9 The term "essentially identical" is used to mean drives with power consumption that differs by no more than +/ 2%. 5 As an alternative to the previously described embodiment of the method according to the invention, the power consumption of compressors V2 and V3 in the first and second coolant mixture circuits 2a - 2b and 3a - 3b can be designed to be identical or essentially identical to 10 the power consumption of each individual or both compressors V4 and V4' in the two-stage third coolant mixture circuit 4a - 4b. In this embodiment of the method according to the invention, three identical drives A2/3, A4, and A4' are preferably used, where the drive A2/3 is 15 assigned to the compressors V2 and V3 and the drive A4 and A4' are assigned to the compressors V4 and V4'. Especially in case of staged availability of large drives, especially gas turbines, a palette of system 20 sizes can thus be covered. The previously described latter alternative is especially suitable for cold cooling media, since in this case the energy required for precooling is reduced. 25 The previously described embodiments of the method according to the invention thus especially have the advantage that drives with identical or essentially identical power A2/3, A4, and A4' can be used.

Claims

1. Method for liquefying a hydrocarbon-rich flow, particularly a natural gas flow, said hydrocarbon-rich 5 flow being liquefied counter to a cascade comprising three coolant mixture circuits, characterised in that the first and second coolant mixture circuits (2a - 2b, 3a 3b) are used for precooling while the third coolant mixture circuit (4a - 4b) is used for liquefying and 10 supercooling the hydrocarbon-rich flow,

2. Method as in claim 1, characterised in that the first and second coolant mixture circuits (2a - 2b, 3a 3b) are designed as single-stage coolant mixture 15 circuits.

3. Method as in claim 1 or 2, characterised in that the third coolant mixture circuit (4a - 4b) is designed as a two-stage coolant mixture circuit. 20

4. Method as in claim 3, characterised in that the power consumption of the compressors (V2, V3) in the first and second coolant mixture circuits (2a - 2b, 3a 3b) are identical or essentially identical to the power 25 consumption of the compressors (V4, V4') in the two-stage third coolant mixture circuit (4a - 4b).

5. Method as in claim 4, characterised in that all the compressors (V2, V3, V4, V4') in the coolant mixture 30 circuits advantageously have the same or essentially the same power consumption. 11

6. Method as in claim 3, characterised in that the consumption of the compressors (V2, V3) in the first and second coolant mixture circuits (2a - 2b, 3a -3b) is identical or essentially identical to the power 5 consumption (V4, V4') of each of the two compressors in the two-stage third coolant mixture circuit (4a - 4b).

7. Method as in one of the preceding claims 1 through 6, characterised in that gas turbines, steam turbines, 10 and / or electric motors are used as drives (A2/3, A4, A4') for the compressors (V2, V3, V4, V4').