Compressor system using throttling valve inside the Anti-surge loop during start-up and relative operating method

Abstract

A compression system (200) provided with a compressor (250) having an inlet duct (210) and an outlet duct (220), a compressor driver (270), an anti-surge recirculation loop (240), a suction flow control device (281) at the inlet duct (210) and a pressure drop element (282), such a throttling valve, upstream of the compressor (250) and in parallel with the suction flow control device (281). The compressor (250) may be started up using the pressure drop element (282) only during start-up and excluding it during normal operation of the compressor (250).

Description

TITLECompressor system using throttling valve inside the anti-surge loop during start-up and relative operating methodDESCRIPTIONTECHNICAL FIELD

[0001] The subject-matter disclosed herein relates to an innovative compression system and to a method for controlling it during start-up.BACKGROUND ART

[0002] In general, a compression system comprises at least a compressor, for example a centrifugal compressor, which receives a fluid to be compressed through an inlet duct and delivers a compressed fluid through an outlet duct. Typically, the outlet duct is provided with an outlet valve which is configured to fluidly couple / decouple the compression system with a plant system (for example a pipeline system). The compressor is also mechanically coupled to a gas turbine or steam turbine or electric motor, which drives the compressor.

[0003] Typically, a modern compression system further comprises an antisurge recirculation loop, which fluidly couples the outlet duct and the inlet duct, in order to avoid compressor surge, which is an unstable operation state of the compressor. In general, the anti-surge recirculation loop is fluidly coupled to the compressor outlet duct, upstream of the outlet valve, and to the compressor inlet duct. Typically, at least a check valve is provided between the tie-out point of anti-surge recirculation loop at the outlet duct and the outlet valve.

[0004] Therefore, the anti-surge recirculation loop comprises an anti-surge valve which may be opened (fully or partially), at least during compressorstart-up, to establish a recirculation flow in the recirculation loop and returning (fully or partially) the gas discharged from the compressor to the inlet of the compressor, in order to reduce the pressure ratio of the compressor and avoid compressor surge during start-up (therefore moving to the right the operating point of the compressor in the compressor map).

[0005] Known compression system further comprises an inlet throttling valve on the compressor suction line, i.e. along the inlet duct, which, in combination with the anti-surge recirculation loop, allows to reduce the power absorbed by the compressor and therefore to limit the compressor driver size (see e.g. Fig. 1). However, in case of malfunctions of the inlet throttling valve during normal operation of the compressor, for example due to operator errors, given that the inlet throttling valve is located along the inlet duct of the compressor, the compressor risks serious damage which could lead to the breakdown of the machine or, in any case, the need to stop it for maintenance. In particular, if the inlet throttling valve is accidentally closed, since the inlet throttling valve is typically located at the inlet duct downstream of the anti-surge recirculation loop, the compressor would work without flow, i.e. in a risk condition.SUMMARY

[0006] Therefore, it would be desirable to have a compression system which has limited risks of damage during normal operation condition without giving up the benefit of having a reduced driver size due to the use of an inlet throttling valve in the anti-surge recirculation loop.

[0007] According to an aspect, the subject-matter disclosed herein relates to a compression system having a system inlet and a system outlet and comprising:- a compressor having a compressor inlet and a compressor outlet;- a compressor driver mechanically coupled to the compressor and configured to drive the compressor;- an inlet duct having a first end fluidly coupled with the system inlet and a second end fluidly coupled to the compressor inlet, the inlet duct comprising a suction flow control valve;- an outlet duct having a first end fluidly coupled with the compressor outlet and a second end fluidly coupled to the system outlet;- an anti-surge recirculation loop comprising an anti-surge valve configured to control fluid flow in the anti-surge recirculation loop, wherein a first end of the anti-surge recirculation loop is fluidly coupled to the outlet duct and a second end of the anti-surge recirculation loop is fluidly coupled to the inlet duct, upstream of the suction flow control valve.The system further comprises a suction bypass arranged upstream of the compressor and fluidly coupled to the inlet duct and comprising a pressure drop element located in parallel with the suction flow control valve, the pressure drop element being configured to reduce pressure of the fluid flow in the suction bypass.

[0008] According to another aspect, the subject-matter disclosed herein relates to a method for performing a compressor start-up in a compression system, the compression system comprising a compressor driver mechanically coupled to the compressor and configured to drive the compressor, an inlet duct fluidly coupled to a compressor inlet and comprising a suction flow control valve and an outlet duct fluidly coupled to a compressor outlet, an anti-surge recirculation loop comprising an anti-surge valve, the anti-surge recirculation loop being fluidly coupled to the inlet duct upstream of the suction flow control valve and to the outlet duct and a suction bypass fluidly coupled to the inlet duct and comprising a pressure drop element located in parallel with the suction flow control valve.The method comprises the following steps:A. Before start-up of the compressor, fully or partially closing the suction flow control valve and partially opening the anti-surge valve, enablingfluid to flow through the suction bypass;B. Carrying out start-up of the compressor through the compressor driver until the compressor reaches its rated speed or minimum operating speed;C. Regulating the anti-surge valve so to avoid compressor surge;D. Once the compressor has reached its rated speed or minimum operating speed, preventing fluid to flow through the suction bypass by fully opening the suction flow control valve.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a simplified diagram of compression system of the prior art,Fig. 2 show a simplified diagram of an embodiment of an innovative compression system, andFig. 3 shows a flow chart of an embodiment of a method for controlling the innovative compression system during start-up.DETAILED DESCRIPTION OF EMBODIMENTS

[0010] According to an aspect, the subject-matter disclosed herein relates to a compression system provided with a compressor having an inlet duct and an outlet duct, a compressor driver, an anti-surge recirculation loop, a suction flow control device at the inlet duct and a pressure drop element, for example a throttling valve, arranged upstream of the compressor and in parallel with the suction flow control device. The compressor may be started up using thepressure drop element only during start-up and excluding it during normal operation of the compressor. This solution is a very attractive easy solution which enables to limit the size of the compressor driver (e.g. the size of the motor) while limiting the risk of compressor damage during its normal operation.

[0011] According to another aspect, the subject-matter disclosed herein relates to a method for performing the start-up of a compressor in a compression system provided with anti-surge recirculation loop and a pressure drop element located in a bypass section upstream of the compressor. The method provides the use of the pressure drop element only during star-up of the compressor in combination with the anti-surge valve located in the antisurge recirculation loop, while it is excluded (i.e. bypassed) during normal operation of the compressor.

[0012] Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the disclosure and should not be construed as a limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.

[0013] Referring now to the drawings, Fig. 1 is a simplified diagram of a known compression system 100, Fig. 2 is a simplified diagram of an embodiment of an innovative compression system 200 and Fig. 3 shows a flow chart of an embodiment of a method for controlling the innovative compression system during start-up.

[0014] Fig. 1 shows a general prior-art compression system 100 which comprises a compressor driver 170 mechanically coupled to a compressor 150 having an inlet duct 110 fluidly coupled to a compression system inlet 101 and an outlet duct 120 fluidly coupled to a compression system outlet 103. The compression system 100 further comprises an anti-surge valve 145 arranged along an anti-surge recirculation loop 140 which has a first end fluidly coupled to the outlet duct 120 and a second end fluidly coupled to the inlet duct 110. The compression system 100 further comprises a suction flow control valve 181 located at the inlet duct 110 and a pressure drop element 182 located at the inlet duct 110 in series with the suction flow control valve 181 and the antisurge valve 145.

[0015] The innovative compression system herein disclosed essentially differ from the prior-art compression system 100 of Fig. 1 in that it comprises a pressure drop element, e.g. a throttling valve, on a bypass duct upstream of the compressor which may be used (i.e. the fluid flows through the pressure drop element) during the start-up of the compressor, thus allowing the use of the pressure drop element in series with the anti-surge valve, while the pressure drop element may be excluded (i.e. bypassed) during normal operation of the compressor.

[0016] In Figure 2 there is shown, for example and without limitation, an embodiment of an innovative compression system, generally indicated with reference numeral 200, comprising a compressor 250 and a compressor driver 270, for example an electric motor or a gas turbine or a steam turbine, mechanically coupled to the compressor 250 and configured to drive the compressor 250. It is to be noted that the system 200 has a system inlet 201 and a system outlet 203 which respectively receive a fluid flow to be compressed and discharge a compressed fluid flow. According to a possibility, the system inlet 201 and the system outlet 203 may be fluidly coupled; in other words, the compression system 200 is a closed system. According to anotherpossibility, the system inlet 201 and the system outlet 203 may be fluidly decoupled; in other words, the compression system 200 is an open system.

[0017] The compression system 200 comprises an inlet duct 210 which has a first end fluidly coupled with the system inlet 201 and a second end fluidly coupled to the compressor 250, specifically to a compressor inlet 211 of the compressor 250. The compression system 200 further comprises an outlet duct 220 which has a first end fluidly coupled to the compressor 250, specifically to a compressor outlet 212 of the compressor 250, and a second end fluidly coupled to the system outlet 203.

[0018] Advantageously, the inlet duct 210 may be provided with an inlet valve 202, in particular an isolation valve such as an on-off valve or a control valve (e.g. a throttling valve), at the system inlet 201, for example for emergency shut down or to fluidly isolate the compressor 250 for maintenance or to control the fluid flow after the startup of the compressor 250. Advantageously, the outlet duct 220 may be provided with an outlet valve 204, in particular an isolation valve such as an on-off valve, at the system outlet 204, for example for emergency shut down or for fluidly isolate the compressor 250 for maintenance.

[0019] With non-limiting reference to Fig. 2, the compression system 200 further comprises an anti-surge recirculation loop 240 which has a first end fluidly coupled to the outlet duct 220 and a second end fluidly coupled to the inlet duct 210 and comprises an anti-surge valve 245, in particular a throttling valve, configured to control fluid flow in the anti-surge recirculation loop 240. Advantageously, the outlet duct 220 may further comprise a check valve (not shown in the figures) located downstream of the tie-out point of the antisurge recirculation loop 24 at the outlet duct 220, in particular to prevent a reverse flow from the system outlet 203 and / or protect compressor 250 from surge. As well-known in the field, the anti-surge valve is typically configuredto be controlled by a control unit (not shown in the figures) to recirculate the fluid from the compressor outlet to the compressor inlet and thus avoid surge in the compressor.

[0020] The compression system 200 further comprises a suction flow control valve 281 located at the inlet duct 210; for example, the suction flow control valve 281 may be a control valve (e.g. a throttling valve) or an isolation valve (e.g. a motor operated valve). With non-limiting reference to Fig. 2, the antisurge recirculation loop 240, in particular its tie-out point at the inlet duct 210, is located upstream of the suction flow control valve 281; in other words, the suction flow control valve 281 is located at the inlet duct 210 between the tie- out point of the anti-surge recirculation loop 240 and the compressor inlet 211.

[0021] With non-limiting reference to Fig. 2, the compression system 200 further comprises a suction bypass 280 arranged upstream of the compressor 250 and fluidly coupled to the inlet duct 210. The suction bypass 280 comprises a pressure drop element 282, in particular a throttling valve (as shown in Fig. 2) or an orifice, located in parallel with the suction flow control valve 281. In particular, the suction bypass 280 has a first tie-out point located upstream of the suction flow control valve 281 and a second tie-out point located downstream of the suction flow control valve 281, so that the suction bypass 280, in particular the pressure drop element 282, is in parallel with the suction flow control valve 281. The pressure drop element 282 is configured to reduce the pressure of the fluid flow in the suction bypass 280, in particular only during the start-up of the compressor 250. More in particular, the pressure drop element 282 allows to reduce the density of the fluid flow supplied to the compressor 250 during start-up, thus allowing to reduce the power required by the compressor 250 during start-up as well as the size of the compressor driver 270.

[0022] According to a possibility, the pressure drop element 282 may beoperated manually by a user which may regulate opening and closing of the pressure drop element 282; advantageously, if the pressure drop element 282 is a throttling valve, the user may further regulate the opening degree of the throttling valve.

[0023] According to another possibility, the pressure drop element 282 may be electrically coupled to a control unit (not shown in the figures) configured to regulate opening and closing of the pressure drop element 282 (advantageously also the opening degree). In particular, as it will better explain in the following, the control unit may regulate the pressure drop element 282 according to an open control loop or a closed control loop.

[0024] According to a first example, the control unit may regulate the pressure drop element 282 with a set timer. According to a second example, the suction bypass 280 may further comprise a pressure gauge located downstream of the pressure drop element 282 and configured to measure a fluid pressure value and to provide the fluid pressure value to the control unit; advantageously, the control unit may be configured to regulate opening and closing of the pressure drop element 282 (advantageously also the opening degree) according to the fluid pressure value provided by the pressure gauge.

[0025] Advantageously, with non-limiting reference to Fig. 2, the suction bypass 280 may further comprise a bypass isolating valve 283 located upstream of the pressure drop element 282 and configured to fluidly isolate the pressure drop element 282 during normal operation of the compressor 250. In particular, the bypass isolating valve 283 may be an on-off valve or a control valve; more in particular, the bypass isolating valve 283 is configured so to avoid any fluid leakage through the suction bypass 280 during normal operation of the compressor 250.

[0026] According to a possibility, not shown in figures, the compressionsystem 200 may further comprise a cooling system(s) configured to remove heat from the fluid flowing through the compression system 200. In particular, the cooling system(s) may be located at the inlet duct 210 and / or at the outlet duct 220 and / or at the anti-surge recirculation loop 240. More in particular, the cooling system may be a heat exchanger and / or quench system(s).

[0027] According to another aspect, the subject matter disclosed herein refers to a method for performing a compressor start-up in a compression system (see for example and without limitation Fig. 3). The compression system comprises a compressor driver mechanically coupled to the compressor and configured to drive the compressor, an inlet duct fluidly coupled to a compressor inlet and comprising a suction flow control valve and an outlet duct fluidly coupled to a compressor outlet, an anti-surge recirculation loop comprising an anti-surge valve, the anti-surge recirculation loop being fluidly coupled to the inlet duct upstream of the suction flow control valve and to the outlet duct and a suction bypass arranged upstream of the compressor and fluidly coupled to the inlet duct, the suction bypass comprising an pressure drop element located in parallel with the suction flow control valve.

[0028] The method comprises the steps ofA. Before start-up of the compressor, fully or partially closing the suction flow control valve and partially opening the anti-surge valve, enabling 320 fluid to flow through the suction bypass;B. Carrying out 330 start-up of the compressor through the compressor driver until the compressor reaches its rated speed or minimum operating speed;C. Regulating 340 the anti-surge valve so to avoid compressor surge;D. Preventing 350 fluid to flow through the suction bypass by fully opening the suction flow control valve.

[0029] In particular, during step A the anti-surge valve is set in a in a certainconfiguration between a fully-closed configuration and a fully-opened configuration and the suction flow control valve is set in a fully-closed configuration or in a certain configuration between a fully-closed configuration and a fully-opened configuration, so that the fluid can flow through the suction bypass, in particular through the pressure drop element. If the suction bypass comprises further a bypass isolating valve located upstream the pressure drop element, step A advantageously comprises also the step Al of fully opening 310 the bypass isolating valve.

[0030] It is to be noted that step B and step C may be performed one after the other, i.e. once that the compressor has reached its rated speed or minimum operating speed than the anti-surge valve is regulated, or simultaneously, i.e. the anti-surge valve is regulated before the compressor has reached its rated speed or minimum operating speed (which may depend on the compressor type and / or model). In particular, the anti-surge valve is regulated according to an anti-surge control logic, i.e. essentially through a program or programs, that may be “software” or “firmware”, stored in a program memory of the control unit which controls the anti-surge valve configuration. It is further to be noted that start-up of the compressor means that the compressor driver provides the torque to accelerate the compressor until the compressor reaches its rated speed or minimum operating speed (which may depend on the compressor type and / or model).

[0031] Finally, as already mentioned above, step D provides the fully opening of the suction flow control valve so that the fluid may flow through it to reach the compressor inlet. In particular, once step D is performed, the pressure drop element may be fluidly isolated so that it is excluded (i.e. bypassed) during normal operation of the compressor.

[0032] In particular, if the suction bypass comprises further a bypass isolating valve located upstream the pressure drop element, step D advantageouslycomprises also the step D3 of fully closing 360 the bypass isolating valve, so that the fluid is prevented from flowing through the pressure drop element.

[0033] According to a possibility, as already mentioned before, the pressure drop element may be a throttling valve. Advantageously, according to this possibility, step D further comprises the steps of:DI . Opening the throttling valve until it reaches fully-open configuration;D2. Opening the suction flow control valve and closing the throttling valve until the suction flow control valve reaches fully-open configuration and the throttling valve reaches the fully-close configuration. Advantageously, step DI is performed before step D2.

Claims

CLAIMS1. Compression system (200) having a system inlet (201) and a system outlet (203) and comprising:- a compressor (250) having a compressor inlet (211) and a compressor outlet (212);- a compressor driver (270) mechanically coupled to the compressor (250) and configured to drive the compressor (250);- an inlet duct (210) having a first end fluidly coupled with the system inlet (201) and a second end fluidly coupled to the compressor inlet (211), the inlet duct (210) comprising a suction flow control valve (281);- an outlet duct (220) having a first end fluidly coupled with the compressor outlet (212) and a second end fluidly coupled to the system outlet (203);- an anti-surge recirculation loop (240) comprising an anti-surge valve (245) configured to control fluid flow in the anti-surge recirculation loop (240), wherein a first end of the anti-surge recirculation loop (240) is fluidly coupled to the outlet duct (220) and a second end of the anti-surge recirculation loop (240) is fluidly coupled to the inlet duct (210), upstream of the suction flow control valve (281); wherein the system (200) further comprises a suction bypass (280) arranged upstream of the compressor (250) and fluidly coupled to the inlet duct (210), wherein the suction bypass (280) comprises a pressure drop element (282) located in parallel with the suction flow control valve (281), wherein the pressure drop element (282) is configured to reduce pressure of the fluid flow in the suction bypass (280).

2. The compression system (200) of claim 1, wherein the pressure drop element (282) is a throttling valve or an orifice.

3. The compression system (200) of claim 1, wherein the suction flow control valve (281) is an isolating valve or a control valve.

4. The compression system (200) of claim 1, wherein the suction bypass (280)further comprises a bypass isolating valve (283) located upstream of the pressure drop element (282) and configured to fluidly isolate the pressure drop element (282) during normal operation of the compressor (250).

5. The compression system (200) of claim 1, wherein the pressure drop element (282) is operated manually.

6. The compression system (200) of claim 1, further comprising a control unit electrically coupled to the pressure drop element (282) and configured to regulate opening and closing of the pressure drop element (282).

7. The compressor system (200) of claim 6, wherein the control unit is configured to regulate opening and closing of the pressure drop element (282) according to an open control loop or a closed control loop.

8. The compressor system (200) of claim 1, wherein the pressure drop element (282) is configured to reduce pressure of the fluid flow in the suction bypass (280) only during the start-up of the compressor (250).

9. Method (300) for performing a compressor start-up in a compression system, the compression system comprising a compressor driver mechanically coupled to the compressor and configured to drive the compressor, an inlet duct fluidly coupled to a compressor inlet and comprising a suction flow control valve and an outlet duct fluidly coupled to a compressor outlet, an anti-surge recirculation loop comprising an antisurge valve, the anti-surge recirculation loop being fluidly coupled to the inlet duct upstream of the suction flow control valve and to the outlet duct and a suction bypass arranged upstream of the compressor and fluidly coupled to the inlet duct, the suction bypass comprising an pressure drop element located in parallel with the suction flow control valve, the method comprising the steps ofA. Before start-up of the compressor, fully or partially closing the suction flow control valve and partially opening the anti-surge valve, enabling (320) fluid to flow through the suction bypass;B. Carrying out (330) start-up of the compressor through the compressordriver until the compressor reaches its rated speed or minimum operating speed;C. Regulating (340) the anti-surge valve so to avoid compressor surge;D. Preventing (350) fluid to flow through the suction bypass by fully opening the suction flow control valve.

10. The method (300) of claim 9, wherein if the pressure drop element is a throttling valve, step D further comprises the steps of:DI . Opening the throttling valve until it reaches fully-open configuration;D2. Opening the suction flow control valve and closing the throttling valve until the suction flow control valve reaches fully-open configuration and the throttling valve reaches the fully-close configuration; wherein step DI is performed before step D2.

11. The method (300) of claim 9, wherein the suction bypass further comprises a bypass isolating valve located at the suction bypass upstream of the pressure drop element, wherein step A further comprises the step of:Al. Fully opening (310) the bypass isolating valve, and wherein step D further comprises the step of:D3. Fully closing (360) the bypass isolating valve.

12. The method (300) of claim 9, wherein step B and step C are performed simultaneously.

13. The method (300) of claim 9, wherein step B and step C are performed one after the other.

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