METHOD FOR PROVIDING PRESSURIZED GAS TO CONSUMERS AND CORRESPONDING COMPRESSOR ARRANGEMENT AT VARIABLE SUCTION CONDITIONS

Abstract

The invention relates to a method for providing pressurized gas from a source of liquefied gas to a consumer (8), wherein vaporized gas is supplied from the source of liquefied gas (1) through a main input line (2) to a compressor arrangement (300) for pressurizing the vaporized gas, the compressor arrangement (300) comprising a plurality of compressor modules (3, 5, 31, 51), each compressor module being able to operate independently from any other compressor module of the compressor arrangement (300), one or more of the compressor modules (5, 51) of the compressor arrangement (300) can be bypassed, and wherein gas is conducted through only a part or all of the compressor modules depending on at least one of pressure level, temperature level, mass flow and composition of the gas to be provided to the consumer (8).

Claims

1. A method for providing pressurized gas from a source of liquefied gas (1) to a consumer (8), wherein vaporized gas is supplied from the source of liquefied gas (1) through a main input line (2) to a compressor arrangement (300) for pressurizing the vaporized gas, the compressor arrangement (300) comprising a plurality of compressor modules (3, 5, 31, 51), each compressor module being able to operate independently from any other compressor module of the compressor arrangement (300), one or more of the compressor modules (5, 51) of the compressor arrangement (300) can be bypassed, and wherein gas is conducted through only a part or all of the compressor modules depending on at least one of pressure level, temperature level, mass flow and composition of the gas to be provided to the consumer (8).

2. The method of claim 1, wherein at least a part of the compressor modules is connected in series and wherein one or more of the bypassed compressor modules (5, 32, 51) are deactivated.

3. The method of claim 1, wherein a first compressor module (31) and a second compressor module (52) are arranged in parallel and connected via a crossover-line (41) which can be shut-off and which connects an outlet of the first compressor module (31) with an inlet of the second compressor module (52), and wherein gas is conducted through the first and the second compressor modules (31, 52) connected in series when the crossover-line (41) is in an open state.

4. The method of claim 3, wherein the first compressor module (31) is operated as a compressor module in a train of at least two compressor modules (31, 51) connected in series, and/or the second compressor module (52) is operated as a compressor module in a train of at least two compressor modules (32, 52) connected in series.

5. The method of claim 1, wherein boil-off gas from the source of liquefied gas (1) is used as the vaporized gas.

6. The method of claim 1, wherein pressurized gas is cooled by conducting the gas through a first cooling unit (10) in a bypass line (6) bypassing the one or more compressor modules (5).

7. The method of claim 1, wherein gas is cooled by conducting the gas through a second cooling unit arranged at the inlet and/or a third cooling unit (20) arranged at the outlet of a compressor module (5).

8. The method of claim 1, wherein at least a part of the pressurized gas of a compressor module (5) is returned to an inlet of this compressor module (5) via an antisurge line (9).

9. The method of claim 8, wherein before returning the gas to the inlet of the compressor module (5), the gas is cooled by a fourth cooling unit (30) at the outlet of the compressor module (5).

10. The method of claim 9, wherein bypassed gas is cooled by the fourth cooling unit (30) after having bypassed the compressor module (5).

11. A compressor arrangement for providing pressurized gas from a source of liquefied gas to a consumer (8), wherein vaporized gas is supplied from the source of liquefied gas (1) through a main input line (2) to a compressor arrangement (300) for pressurizing the vaporized gas, the compressor arrangement (300) comprising a plurality of compressor modules (3, 5, 31, 51), each compressor module being able to operate independently from any other compressor module of the compressor arrangement (300), wherein the compressor modules of the compressor arrangement (300) are arranged such that one or more of the compressor modules (5, 51) of the compressor arrangement (300) can be bypassed, such that gas is conducted through only a part or all of the compressor modules via a consumer line (7) to the consumer (8).

12. The compressor arrangement of claim 11, wherein the compressor arrangement (300) comprises at least two compressor modules (3, 5) connected in series by interconnection lines (4), wherein a bypass line (6) branches off upstream an inlet of one of the compressor modules (5) and reconnects downstream an outlet of this or another compressor module, the bypass line (6) having a shut-off device to be operated depending on at least one of pressure level, temperature level, mass flow and composition of the gas to be provided to the consumer (8).

13. The compressor arrangement of claim 11, wherein the compressor arrangement (300) comprises at least two parallel trains of compressor modules, each train being connectable to the main input line (2), each train comprising one or more compressor modules, wherein an outlet of one compressor module (31, 33) of one of the at least two parallel trains is connected with an inlet of another compressor module (52, 53) of another train of the at least two parallel trains via a crossover-line (41, 100), the crossover-line having a shut-off device (42, 101) to be operated depending on at least one of pressure level, temperature level, mass flow and composition of the gas to be provided to the consumer (8).

14. The compressor arrangement of claim 12, wherein the bypass line (6) reconnects to the consumer line (7) upstream of a fourth cooling unit (30).

15. The compressor arrangement of claim 11, wherein a compressor module (5) of the compressor arrangement (300) comprises at least a part of an antisurge line (9) for returning at least a part of the pressurized gas of the compressor module (5) to an inlet of this compressor module (5), a cooling unit (30) being arranged at the outlet of the compressor module (5), and the inlet of the antisurge line (9) is located downstream of the cooling unit (30) such that an inlet part of the antisurge line (9) is located outside of the compressor module (5).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1A schematically shows a first embodiment of a compressor arrangement for implementing the method according to the present invention

[0034] FIG. 1B schematically shows a second embodiment of a compressor arrangement for implementing the method according to the present invention

[0035] FIG. 1C schematically shows a third embodiment of a compressor arrangement for implementing the method according to the present invention

[0036] FIG. 1D schematically shows a fourth embodiment of a compressor arrangement for implementing the method according to the present invention

[0037] FIG. 1E schematically shows a fifth embodiment of a compressor arrangement for implementing the method according to the present invention

[0038] FIG. 2A schematically shows a sixth embodiment of a compressor arrangement for implementing the method according to the present invention

[0039] FIG. 2B schematically shows a seventh embodiment of a compressor arrangement for implementing the method according to the present invention

[0040] FIG. 3 schematically shows an eight embodiment of a compressor arrangement for implementing the method according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] In the following, the different embodiments according to the Figures are discussed comprehensively, same reference signs indicating same or essentially same units. It is appreciated that a person skilled in the art may combine certain components like one or more compressor modules, a valve, a cooling unit, certain lines etc. of an embodiment shown in a figure with the features of the present invention as defined in the appended claims without the need to include more than this certain component or even all other components of this embodiment shown in said figure. In other words, the following figures show different preferable aspects of the present invention, which can be combined to other embodiments. The embodiments shown in the figures all relate to the application of supplying fuel gas from an LNG source, but it is appreciated that a person skilled in the art can easily transfer the embodiments to applications involving other cryogenic gases or gas mixtures.

[0042] FIG. 1A schematically shows a compressor arrangement 300 for providing pressurized gas from a tank 1 or source of liquefied gas to a consumer 8, wherein vaporized gas, in this case BOG, is supplied from the tank 1 through a main input line 2 to the compressor arrangement 300. In this embodiment, the compressor arrangement 300 comprises two compressor modules 3 and 5, both being 2-stage compressors. Each of the compressor modules 3, 5 includes all equipment, valves and instruments as an independent compressor system. Compressor module 3 is able to operate independently from compressor module 5, same is true vice versa. Instead of a 2-stage compressor 3, 5, any other multi- or single-stage compressor can be used. Further, it should be noted that also more than two compressor modules can be connected in series, in that case one, two or more compressor modules can be bypassed. In the present embodiment, bypass line 6 bypasses the second compressor module 5. The bypass line 6 branches off of the interconnecting line 4 connecting the two compressor modules 3 and 5, and ends in the header 7, i. e. the consumer line for supplying fuel gas to a consumer 8.

[0043] When overall fuel gas system process conditions require low compressor head, typically low temperature (120/60 C.) and relatively high pressure (1.2/1.5 bar), it is preferable to run compressor module 3 only and bypass compressor module 5 which is then preferably deactivated. Fuel gas is conveyed to the consumer 8 after having been pressurized by compressor module 3 through bypass line 6 and header 7. When overall fuel gas system process conditions require high compressor head, typically high suction temperature (60/40 C.) and relatively low suction pressure (<1.1 bar), both modules 3 and 5 can operate simultaneously such that fuel gas is pressurized by both compressor modules 3 and 5 and then conducted through header 7 to consumer 8.

[0044] When the compressor head required by the fuel gas system exceeds the capability of module 3, an automatic line-up of module 5 is provided. This can be achieved by a sequential control combining module 5 start-up, closure of bypass line 6 (i.e. module bypass control valve) and compressor load-up.

[0045] FIG. 1B shows another embodiment of a compressor arrangement 300 for the same purpose as in FIG. 1A. The arrangement essentially corresponds to that of FIG. 1A such that only the differences are discussed in the following. The bypass line 6 comprises a cooling unit 10 (first cooling unit) for cooling gas which is pressurized by compressor module 3 and bypassing compressor module 5. The pressurized and cooled bypassed fuel gas is then conveyed through header 7 to consumer 8. When both compressor modules 3 and 5 are used, pressurized gas is cooled by another cooling unit 20 (third cooling unit). The cooled pressurized fuel gas is then sent via header 7 to consumer 8. Optionally, another cooling unit (second cooling unit, not shown) can be arranged at the entrance of the second compressor module 5 in the interconnecting line 4. If the second cooling unit (not shown) is arranged downstream the branch point of the bypass line 6, only gas entering the second compressor module 5 is cooled. However, if the second cooling unit (not shown) is arranged upstream the branch point of the bypass line 6, both gas entering the bypass line 6 and gas entering the second compressor module 5 can be cooled. In the latter case, the gas cooler 10 in the bypass line 6 could be saved.

[0046] FIG. 10 schematically shows another embodiment of compressor arrangement similar to the one of FIG. 1B with the main difference that the antisurge line 9 of compressor module 5 is not completely integrated into module 5. As known to a person skilled in the art, compressors may have an antisurge line having a flow regulating valve such that always a given volume of gas enters the compressor. In FIG. 10 the antisurge line 9 of compressor module 5 branches off the header 7 downstream of cooling unit 30 (fourth cooling unit, same as third cooling unit 20 of FIG. 1 B) such that cooled compressed gas exiting the second compressor module 5 is returned back to an inlet of compressor module 5. This results in a more economic utilization of the compressor capacity of module 5.

[0047] FIG. 1D shows another embodiment which is essentially based on the embodiment of FIG. 10. However, the bypass line 6 in this embodiment ends in the header 7 upstream the fourth cooling unit 30. By this arrangement, there is no need for cooling unit 10 in the bypass line 6 as gas bypassing the second compressor module 5 is conveyed to the cooling unit 30 and can thus be cooled before reaching the consumer 8. On the other hand, gas which is conveyed through both compressor modules 3 and 5, can also be cooled by the cooling unit 30 before reaching the consumer 8. Regarding the antisurge line 9 the same statements apply as made in connection with FIG. 1C.

[0048] FIG. 1E schematically shows another embodiment of a compressor arrangement 300 which comprises two parallel trains of compressor modules, the compressor modules of a train being in series while the compressor modules in a train are arranged parallel to the compressor modules in the parallel train. In this embodiment, the first train comprises two compressor modules 32 and 52 connected in series, the second parallel train also comprises two compressor modules 31 and 51 connected in series. In this embodiment each of the compressor modules 31, 32, 51, 52 is a 2-stage compressor. Also other one or multi-stage compressor modules can be used. In general, one of the two trains can be operated, while the other train is in spare. However, with the modular approach of the present compressor arrangement, an operation becomes possible where the first compressor module of one train feeds the second compressor module of the other train. This is achieved by the crossover-line 41 equipped with an isolation or shut-off device such as a manual valve 42. With such an arrangement it is possible to conduct pressurized gas from compressor module 32 through crossover-line 41 to compressor module 51 of the second train and supplying the consumer 8 with pressurized gas from compressor module 51. Such an operation bypasses compressor modules 31 and 52, which can then be deactivated. Alternatively, pressurized gas from compressor module 31 can be conveyed through crossover-line 41 to compressor module 52 and then supplied to consumer 8. In this case, the bypassed compressors 32 and 51 can be deactivated.

[0049] It should be noted that with the arrangement shown in FIG. 1E, it is also possible to deliver pressurized gas to a consumer 8, which gas is only pressurized by one of the compressor modules 31 or 32. This is made possible by bypass lines 6 and 61 respectively. For example, compressed gas from compressor module 31 can be sent through bypass line 61 to header 7 if valve 42 is closed. In the same way, gas from compressor module 32 can be conducted through bypass line 6 to header 7 if valve 42 is closed.

[0050] The arrangement shown in FIG. 1E provides a very flexible operation depending on the consumers' needs. It is also possible to operate both trains simultaneously to increase the mass flow to consumer 8. This is achieved by closing bypass lines 61 and 6 as well as crossover-line 41.

[0051] FIG. 2A shows yet another embodiment of a compressor arrangement 300 comprising two parallel trains, each train only comprising one compressor module, i. e. two compressor modules 33 and 53 are arranged in parallel. Parallel compressor modules are generally used to feed fuel gas consumers with cold and rather high pressure BOG, one compressor module being in operation, the other one in spare. In some BOG conditions, however, one single compressor module may struggle to maintain the required fuel gas pressure. To overcome this disadvantage, the embodiment of FIG. 2A provides a crossover-line 100 having a valve 101, the crossover-line 100 connecting an exit of compressor module 33 with an inlet of compressor module 53 such that the two parallel compressor modules 33 and 53 can be operated in series by means of the crossover-line 100 in its open state. Thus, in case one single compressor module is not able to maintain the required fuel gas pressure, both compressor modules 33 and 53 can be connected in series by opening the valve 101 in crossover-line 100 in order to increase the stage number used for fuel gas compression.

[0052] Even if the modular approach according to the present invention could be applied to different types of compressors, magnetic bearing compressors equipped with VDV (Variable Diffusor Vanes), and VFD (Variable Frequency Drive) would provide the best flexible and the most efficient solution since the whole machine speed range is available (as opposed to integrally geared machines). It allows the efficiency optimization of the operating point for each compressor stage. Thanks to VFD and VDV, the downstream compressor module can adapt to the new suction conditions equivalent to the first compressor module discharge (typically medium pressure level, 40 C.) to provide fuel gas to the consumer 8 at the required pressure.

[0053] FIG. 2B shows another embodiment which is essentially based on the embodiment of FIG. 2A. In this embodiment three identical compressor modules 34, 54, 74 are arranged in parallel, each being fed by the main input line 2 from tank 1. Each compressor module can be interconnected in series with any of the other two compressor modules. This is achieved by installing a header 200 connecting all the module discharge sides to all the module suction sides. Additional valves are required to interconnect in series two modules out of three. The remaining one can be considered as a spare and deactivated. In the arrangement shown in FIG. 2B any one of the compressor modules 34, 54 or 74 can be operated alone and feed pressurized gas to the consumer 8. In this case, no gas is conveyed through header 200. Furthermore, two out of the three modules can be operated in series. Finally, all compressor modules 34, 54 and 74 can be operated in series in order to achieve higher pressures of the fuel gas to be supplied to the consumer 8. On the other hand, high mass flow or load requirements can be fulfilled by operating two or three of the modules 34, 54 and 74 in parallel.

[0054] FIG. 3 shows another embodiment of a compressor arrangement 300 comprising two parallel trains, first train being a compressor group 50 comprising three compressor modules 51, 52, 53 arranged in parallel, the second train comprising one single compressor module 55. Such an arrangement is especially useful during LNG carrier loading operations where LNG is sent from an exporting terminal 400 to carrier storage tanks 1. Due to tank cool-down and in-tank piston effect, the tank filling creates a high quantity of BOG which is usually sent back to the terminal 400. This is achieved by a high duty compressor 55 with high volume flow and low head capability. Compressor suction is connected to the tanks 1 whereas compressor discharge is connected to shore thanks to a dedicated vapour header 71 and loading arm. Due to sparing requirement, two high duty compressors are installed. Loading compressors 51, 52 and 53 of compressor group 50 are not required and therefore their combined capacities can be considered as a spare to the high duty compressor 55. Fuel gas compressors 51, 52 and 53 can all be run in parallel and their discharge flow can be routed to the vapour header 71 via valve 84 and isolated from fuel gas header 7 by closing the valve 83. Due to fuel gas compressor characteristics, valve 84 would be required to maintain a minimum fuel gas compressor backpressure. Valves 81 and 82 are provided to operate the high duty compressor 55.

LIST OF REFERENCE SIGNS

[0055] 1 tank, source of liquefied gas [0056] 2 main input line [0057] 3 (first) compressor module [0058] 4 interconnecting line [0059] 5 (second) compressor module [0060] 6 bypass line [0061] 7 header, consumer line [0062] 8 consumer [0063] 9 antisurge line [0064] 10 first cooling unit [0065] third cooling unit [0066] 30 fourth cooling unit [0067] 31, 32, 33 compressor module [0068] 51, 52, 53 compressor module [0069] 34, 54, 74 compressor module [0070] 41 crossover-line [0071] 42 valve [0072] 50 compressor group [0073] 51, 52, 53 compressor module [0074] 55 compressor module [0075] 61 bypass line [0076] 71 vapour header [0077] 72 loading header [0078] 81, 82, 83, 84 valve [0079] 100 crossover-line [0080] 101 valve [0081] 200 header [0082] 300 compressor arrangement [0083] 400 terminal