Patent Application
20080170948
1. Field of the Invention
The present invention generally relates to turbine-driven multi-stage compressors. In another aspect, the invention concerns an improved methodology for starting up a multi-stage compressor driven by a single-shaft gas turbine.
2. Description of the Prior Art
Gas turbines are commonly used to drive large, industrial compressors, such as those employed in the refrigeration cycles of liquefied natural gas (LNG) facilities. Gas turbines used to drive large compressors generally have a single-shaft or a split-shaft configuration. Compressor systems driven by split-shaft gas turbines are typically easier to start-up, but single-shaft gas turbines are available in higher power ratings. Generally, split-shaft gas turbines either are not commercially available or are not economically viable for use in very high load applications, such as for driving the multi-stage compressors of an LNG facility. Therefore, single-shaft gas turbines are usually selected to drive very large multi-stage compressors in industrial applications.
One disadvantage associated with employing a single-shaft gas turbine to drive a large, multi-stage compressor is the requirement for auxiliary power to help start-up the compressor/turbine system. In the past, such auxiliary start-up power has typically been provided by electric motors. These auxiliary motors run at or near full capacity during start-up to help overcome the inertial and aerodynamic forces of the system. After start-up, the auxiliary motor is shut off or scaled back, as the gas turbine takes over primary responsibility for powering the system. Obviously, the requirement for an auxiliary source of rotational power during start-up adds to the overall capital expense of the system.
Another disadvantage of using a single-shaft gas turbine to drive a large, multi-stage compressor is the potential for creating a vacuum in the system upon start-up, which creates a mechanism for air ingress into the system. While manageable, air-contamination of the working fluid is highly undesirable and can present additional operational and/or safety problems.
Thus, a need exists for an improved system and methodology to efficiently start-up large, industrial multi-stage compressors.
In one embodiment of the present invention, there is provided a method of operating a multi-stage compressor. The method comprises: (a) isolating at least two compression stages of the multi-stage compressor from fluid flow communication with one another; and (b) simultaneously with step (a), initiating rotation of the multi-stage compressor.
In another embodiment of the present invention, there is provided a system for operating a multi-stage compressor having a plurality of compression stages with each compression stage having an inlet and an outlet. The system comprises a driver for rotating the multi-stage compressor, a plurality of flow loops, and an isolation valve fluidly disposed between two of the flow loops. Each of the flow loops is associated with a compression stage and is configured to provide fluid flow communication from the outlet to the inlet of the compression stage with which it is associated. The system is shiftable between a start-up mode and an operating mode. During the start-up mode, the isolation valve is closed to thereby prevent fluid flow between two of the flow loops. During the normal mode of operation, the isolation valve is open to thereby permit fluid flow between two of the flow loops.
Certain embodiments of the present invention are described in detail below with reference to the enclosed figures, wherein:
Referring initially to
Gas turbine 12 can be any suitable commercially available industrial gas turbine. In one embodiment, gas turbine 12 is a single-shaft gas turbine having a power rating greater than about 35,000 hp, greater than about 45,000 hp, or greater than 55,000 hp. For example, gas turbine 12 can be a single-shaft GE Frame-5, Frame-6, Frame-7, or Frame-9 gas turbine available from GE Power Systems, Atlanta, Ga. or the equivalent thereof. Gas turbine 12 receives a stream of filtered air from conduit 13 and fuel via conduit 15 as controlled by valve 19. The combustion of the air and fuel provides energy to rotate gas turbine 12. According to one embodiment, gas turbine 12 additionally comprises a built-in starting device (not shown) coupled to the air compressor side (i.e., the “cold end”) of gas turbine 12.
Gas turbine 12 is operably coupled to multi-stage compressor 14 by a single common output drive shaft 18. Multi-stage compressor 14 comprises a plurality of compression stages operable to sequentially compress a gas stream to successively higher pressures. Compressor 14 of
As previously mentioned, the compressor/driver system 10 includes compressor flow control system 16 that is operable to direct the flow of gas associated with multi-stage compressor 14. As illustrated in
Compressor/driver system 10 of the present invention can be operated in two distinct modes: a start-up mode and a normal mode. During the normal mode of operation, flow loops 26, 28, 30 are in fluid flow communication with each other. As discussed in detail below, the start-up mode of operation is characterized by the isolation of flow loops 26, 28, 30 from fluid flow communication with each other. In one embodiment, fluid flow communication between flow loops 26, 28, 30 is controlled with a first isolation system 62 and a second isolation system 64. First isolation system 62 generally includes a first conduit 66, a first isolation valve 68, and a first bypass valve 70. Similarly, second isolation system 64 generally includes a second conduit 72, a second isolation valve 74, and a second bypass valve 76. To allow fluid flow communication between flow loops 26, 28, 30, isolation valves 68, 74 and/or bypass valves 70, 76 are open to thereby allow compressed gas to flow between the low, intermediate, and high compression stages 20, 22, 94. When fluid flow communication is allowed between the compression stages 20, 22, 24 of multi-stage compressor 14, flow loops 26, 28, 30 are said to be “de-isolated.” When flow loops 26, 28, 30 are de-isolated (i.e., during normal mode of operation), compressed gas flows from the outlet of low compression stage 20 into the suction of intermediate compression stage 22 and from the discharge of intermediate compression stage 22 to the suction of high compression stage 24. To isolate flow loops 26, 28, 30 by preventing fluid flow communication between low, intermediate, and high compression stages 20, 22, 24, isolation valves 68, 74 and bypass valves 70, 76 are closed. The methodology of starting up compressor/driver system 10 will be discussed in further detail in a subsequent section.
According to the embodiment illustrated in
As illustrated in
In another embodiment, compressor flow control system 16 can also include one or more intermediate-stage and/or high-stage feed streams (not shown). If present, these additional feed streams combines with the discharged gas from the upstream compression stage prior to entering the compression stage with which it is associated.
The start-up mode of operation of the compressor/driver system 10 illustrated in
In particular,
As previously discussed, the start-up mode of compressor/driver system 10 in
Once flow loops 26, 28, 30 have been isolated, a positive pressure can be established in each flow loop as represented in block 202 of
If the positive pressure in a flow loop is too low, additional gas may be introduced into the system, as shown in block 206 in
Because flow loops 26, 28, 30 remain isolated (as shown in Table 1) during the steps depicted in blocks 200, 204, and 206 in
The next step in the start-up mode of compressor/driver system 10 is to initiate compressor/driver system rotation as outlined in block 208 in
In another embodiment, the rotation of compressor/driver system 10 is initiated solely under the power of gas turbine 12 and its built-in starting device (not shown). As illustrated in Table 1, fuel valve 19 can be opened during this step and gas turbine 12 may be started.
Once rotation has been initiated, the system can be checked to ensure a minimum positive pressure has been maintained, as illustrated in block 210 in
Once an adequate positive pressure has been reestablished, the compressor/driver system 10 can then be allowed to achieve minimum rotational speed, as shown in block 214 of
After compressor/driver system 10 achieves the minimum rotational speed, the flow loops can be de-isolated, as depicted by block 216 in
In one embodiment immediately prior to opening isolation valves 68, 74, bypass valves 70, 76 can be opened to reduce the pressure differential across the isolation valves and equalize the positive pressure between two adjacent loops. For example, according to the embodiment illustrated in
At this point, the working fluid can now be introduced into the compressor, as depicted in block 218 of
In one embodiment of the present invention, the compressor system described and illustrated herein can be employed to compress one or more refrigerant streams. For example, the turbine-driven compressor systems described herein can be used to compress hydrocarbon-containing refrigerants employed as part of a mechanical refrigeration cycle used to cool natural gas in a liquefied natural gas (LNG) plant. In one embodiment, the compressor system can be utilized in a mixed-refrigerant LNG process, such as the process described by U.S. Pat. No. 4,445,917, which is incorporated herein by reference. In another embodiment, the inventive compressor system can be employed in a cascade-type LNG refrigeration process, such as the one disclosed in U.S. Pat. No. 6,925,387, which is incorporated herein by reference.
The present description uses numeric ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claims limitation that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds).
As used herein, the terms “a,” “an,” “the,” and “said” means one or more.
As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
As used herein, the term “anti-surge valve” refers to a valve used to regulate flow from the discharge of a compression stage to the suction of the same compression stage.
As used herein, the term “auxiliary motor” refers to an electric motor or other driver coupled to the outboard end of a gas turbine used to provide additional power to help rotate the gas turbine during the start-up mode.
As used herein, the term “cascade refrigeration process” refers to a refrigeration process that employs a plurality of refrigeration cycles, each employing a different pure component refrigerant to successively cool natural gas.
As used herein, the term “compression stage” refers to one element of a compressor wherein the pressure of an incoming gas in increased.
As used herein, the terms “containing,” “contains,” and “contain” have the same open-ended meaning as “comprising,” “comprises,” and “comprise.”
As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up of the subject.
As used herein, the term “de-isolate” refers to the act of establishing fluid flow communication between two or more previously-isolated flow loops. As used herein, the term “flow loop” refers to the flow path between a compressor stage's discharge and suction, piece
As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise.”
As used herein, the term “hydrocarbon-containing” refers to material that contains at least 5 mole percent of one or more hydrocarbon compounds.
As used herein, the terms “including,” “includes,” and “include” have the same open-ended meaning as “comprising,” “comprises,” and “comprise.”
As used herein, the term “intercooler” refers to any device used to cool fluid between compression stages.
As used herein, the term “multi-stage compressor” refers to a compressor that utilizes two or more compression stages to successively increase the pressure of an incoming gas.
As used herein, the term “mixed refrigerant” means a refrigerant containing a plurality of different components, where no single component makes up more than 75 mole percent of the refrigerant.
As used herein, the term “positive pressure” refers to a pressure above atmospheric pressure.
As used herein, the term “pure component refrigerant” means a refrigerant that is not a mixed refrigerant.
As used herein, the term “start-up gas” refers to a stream of internal or external gas supplied to the system in during the start-up mode to purge existing material and/or establish adequate positive pressure in one or more flow loops.
As used herein, the term “working fluid” refers to the gas being compressed during normal operation of a compressor.
The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Obvious modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.
The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.
