COMPRESSION SYSTEM AND METHOD FOR CONTROLLING A COMPRESSION SYSTEM - Patent application

Abstract

The compression system (100) includes a compressor (150) with an inlet duct (110) and an outlet duct (120), and an antisurge recirculation loop (140) capable of recirculating fluid from the outlet duct (120) to the inlet duct (110) and regulating flow along the antisurge recirculation loop (140) through a throttle valve (145). The compression system (100) is further provided with another throttle valve (155) located directly on the compressor outlet flange (112), preferably at a distance from the compressor outlet flange (112) less than three times the inner diameter of the outlet duct (120), and a control unit (160) for controlling and regulating the opening and closing of the throttle valves (145, 155). The combined control of the opening and closing of the two throttle valves (145, 155) makes it possible to find a stable operating point of the compressor (150) that is to the left of the expected surge limit of the machine, thus extending the stable operating state of the compressor (150) and protecting it from the risk of surge.

Description

[Technical Field]

[0001] The subject matter disclosed herein relates to compression systems and methods for controlling compression systems, particularly during start-up and emergency shut down (ESD). [Background technology]

[0002] Generally, a compression system includes at least a compressor, e.g., a centrifugal compressor, that receives a compressed fluid through an inlet duct and delivers the compressed fluid through an outlet duct. The outlet duct is typically provided with an outlet valve configured to fluidly couple / decouple the compression system to a plant system (e.g., a pipeline system). The compressor is also mechanically coupled to a gas turbine, a steam turbine, or an electric motor that drives the compressor.

[0003] Typically, modern compression systems further include an anti-surge recirculation loop fluidly connecting the outlet duct and the inlet duct to avoid compressor surge, which is an unstable operating condition of the compressor. The anti-surge recirculation loop generally includes a branch joint upstream of the outlet valve and a branch joint upstream of the compressor inlet duct.

[0004] A group of expected surge points at different compressor speeds is fitted to a compressor map (i.e., a chart of the compressor performance curve) as a surge limit line (SLL). Surge occurs in the region of the compressor map corresponding to the left of the surge limit line (SLL). The compressor operates to the right of the surge limit line (SLL) during normal operating conditions. However, during start-up / emergency shutdown, the operating point may move toward the surge line, i.e., to the left of the surge limit line (SLL), because the resistance characteristics of the plant system exceed the surge limit line (SLL) during compressor ramp-up (start-up) or because the compressor head is reduced relative to the head required for the process due to a speed reduction (emergency shutdown).

[0005] Therefore, the antisurge recirculation loop includes an antisurge valve that opens at least during compressor startup to establish a recirculation flow in the recirculation loop and return (fully or partially) the compressor discharge gas to the compressor inlet, reducing the compressor pressure ratio (and thus shifting the compressor operating point to the right of the compressor map). However, the compressor still has stable operating conditions only to the right of the surge limit line (SLL) and therefore cannot utilize the area to the left of the surge limit line (SLL).

[0006] Furthermore, to protect the compressor from the risk of surge during an emergency shutdown (ESD), the compression system is typically provided with one or more additional recirculation loops with additional recycle valves. In practice, during an ESD, the compressor must be turned off as quickly as possible, the power supply to the compressor drive is cut off, and the anti-surge valve is set to a fully open configuration. However, if the compressor suddenly slows down, a surge condition may occur. Therefore, additional recirculation loops and valves are arranged in parallel with the anti-surge recirculation loop, allowing the pressures upstream and downstream of the compressor to equalize more quickly, thus avoiding the risk of surge.

[0007] Another important aspect that should be emphasized is that the compressor driver is designed and sized to deliver the required torque to the compressor, which is proportional to the compressor suction flow, suction density, and head. For this reason, it is desirable to reduce the size of the compressor driver and reduce the load on the compressor during start-up, especially during pressurized start-up, to avoid oversizing. This is particularly important when the compressor driver is an asynchronous motor, which is torque-limited during start-up (in practice, due to voltage drop, the torque available to the motor during start-up is in the range of 60-70% of the rated torque).

[0008] It is therefore desirable to have a compression system that has a lower (and in some cases no) risk of the compressor going into an unstable operating state due to surge, especially during start-up and emergency shutdown. Additionally, it is desirable to have a compression system that does not have an oversized motor or additional recirculation loops and / or valves. Summary of the Invention

[0009] According to one aspect, the subject matter disclosed herein relates to a compression system having a system inlet with an inlet valve and a system outlet with an outlet valve, the compression system comprising: a compressor having a compressor inlet flange and a compressor outlet flange; an inlet duct having a first end fluidly coupled to the system inlet and a second end fluidly coupled to the compressor inlet flange; an outlet duct having a first end fluidly coupled to the compressor outlet flange and a second end fluidly coupled to a system outlet; an anti-surge recirculation loop comprising an anti-surge valve configured to control flow in the anti-surge recirculation loop, a first end of the anti-surge recirculation loop fluidly coupled to an outlet duct through a first branch fitting and a second end of the anti-surge recirculation loop fluidly coupled to the inlet duct; a discharge throttle valve downstream of the compressor outlet flange and upstream of the first branch joint; a control unit configured to control the opening and closing of the anti-surge valve and the discharge throttle valve.

[0010] According to another aspect, the subject matter disclosed herein relates to a method for controlling a compression system during start-up, the compression system comprising: a compressor having a system inlet and a system outlet, an anti-surge recirculation loop comprising an anti-surge valve fluidly coupling the compressor system outlet and the compressor system inlet; a discharge throttle valve located downstream of the compressor, particularly between the compressor and the anti-surge recirculation loop; and an inlet valve and an outlet valve located at the system inlet and the system outlet, respectively, the method comprising: A) first setting the anti-surge valve to a particular configuration between a fully closed configuration and a fully open configuration; B) first setting the discharge throttle valve to a particular configuration between a fully closed and a fully open configuration such that the compressor surge limit corresponds to substantially zero flow; C) starting the compressor.

[0011] According to yet another aspect, the subject matter disclosed herein relates to a method of controlling a compression system during an emergency shutdown, the compression system including a compressor having a system inlet and a system outlet, an anti-surge recirculation loop including an anti-surge valve fluidly coupling the compressor system outlet and the compressor system inlet, a discharge throttle valve located downstream of the compressor, particularly between the compressor and the anti-surge recirculation loop, and an inlet valve and an outlet valve located at the system inlet and the system outlet, respectively, the method comprising: L) setting the anti-surge valve to a fully open configuration; M) setting the inlet and outlet valves to a fully closed configuration; N) adjusting the discharge throttle valve to a particular configuration between a fully closed configuration and a fully open configuration so that the compressor surge limit corresponds to substantially zero flow; O) turning off the compressor. [Brief explanation of the drawings]

[0012] A more complete understanding of the disclosed embodiments of this invention and many of the attendant advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings. [Figure 1] 1 shows a simplified diagram of a first embodiment of an innovative compression system disclosed herein. [Figure 2] 2 shows an example of a simplified plot of a compressor map at a particular rotational speed with three operating conditions according to the system of FIG. 1. [Figure 3]1 illustrates a flowchart of an embodiment of a method for controlling a compression system during start-up as disclosed herein. [Figure 4] 1 illustrates a flowchart of an embodiment of a method for controlling a compression system during an emergency shutdown as disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0013] According to one aspect, the subject matter disclosed herein relates to a compression system with reduced, and in some cases zero, risk of surge. The system includes a compressor with an inlet duct and an outlet duct, and an anti-surge recirculation loop capable of recirculating fluid from the outlet duct to the inlet duct and regulating flow along the recirculation loop through a throttle valve. The innovative system disclosed herein is provided with a separate throttle valve located directly on the compressor outlet flange, preferably at a distance from the compressor outlet flange less than three times the inner diameter of the outlet duct, and a control unit that controls and regulates the opening and closing of the throttle valve. The combined control of the opening and closing of the two throttle valves allows for finding a stable operating point for the compressor that is to the left of the machine's expected surge limit line, thus extending the stable operating state of the compressor and protecting the compressor from the risk of surge.

[0014] According to another aspect, the subject matter disclosed herein relates to a method of controlling a compression system during start-up, in which the compression system is initially fluidly isolated and the compressor is turned on while the anti-surge throttle valve is fully open (i.e., all fluid at the compressor outlet flange is recirculated at the compressor inlet flange), and the throttle valve at the compressor outlet flange is initially set to a particular configuration between a fully closed and a fully open configuration such that the surge limit line corresponds substantially to zero flow (i.e., the compressor can be operated without risk of surge).

[0015] According to yet another aspect, the subject matter disclosed herein relates to a method for controlling a compression system during an emergency shutdown, in which the compression system is initially fluidly isolated and the compressor is turned off while the anti-surge throttle valve is fully open (i.e., all fluid at the compressor outlet flange is recirculated at the compressor inlet flange), and the throttle valve at the compressor outlet flange is initially set to a particular configuration between a fully closed and a fully open configuration such that the surge limit line corresponds substantially to zero flow (i.e., the compressor can be operated without risk of surge).

[0016] Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the drawings. The examples and drawings are provided as an explanation of the present disclosure and should not be construed as limiting the disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or spirit of the disclosure. In the following description, like reference numerals are used in the illustrative figures of the embodiments to indicate elements that perform the same or similar functions. Moreover, for clarity of illustration, some reference numerals may not be repeated in all figures.

[0017] 1 shows a simplified diagram of a first embodiment of an innovative compression system 100, hereinafter referred to as "compression system 100" or simply "system 100." As better explained below, FIG. 2 shows an example of a simplified plot of a compressor map at a particular rotational speed with three operating conditions according to system 100.

[0018] 1 , the system 100 includes a compressor 150, advantageously a centrifugal compressor, having a compressor inlet flange 111 and a compressor outlet flange 112. In particular, the compressor 150 is mechanically coupled to a compressor drive 170, e.g., an electric motor, configured to provide the power required by the compressor 150. During operation of the compressor 150, the compressor inlet flange 111 is configured to receive a fluid, and the compressor outlet flange 112 is configured to supply the fluid at a pressure higher than the fluid pressure at the compressor inlet flange 111. It should be noted that the fluid received by the compressor 150 is advantageously predominantly in a gas phase, and preferably, all of the fluid received by the compressor 150 is in a gas phase.

[0019] It is well known that both axial and centrifugal compressors have limited operating ranges due to flow instabilities, especially at low mass flow rates, with surge being the most dangerous flow phenomenon. The most commonly used mathematical model describing surge is the Greitzer model, developed in 1976. While originally developed for axial compressors, this model can also be successfully used for centrifugal compressors. Control algorithms for anti-surge systems can be derived from the Greitzer model, which defines a parameter B, called the Greitzer stability parameter, that determines whether a given compressor is more likely to enter surge.

[0020] As will be better explained below, the innovative system not only prevents compressor surge conditions—unstable operating conditions—(i.e., the compressor operates only to the right of the surge limit line, which defines the boundary of the compressor's stable operating condition at low mass flow rates), but also allows the compressor to extend its stable operating condition even to a region of the compressor map that is to the left of the compressor's expected surge limit line. This is the limit line that would be expected without any pressure drop at the compressor outlet, e.g., without any throttle valve at the compressor discharge (see, e.g., bold black line SSL-1 in FIG. 2 ). In particular, by acting on a throttle valve at the compressor discharge, it is possible to “move” the compressor's surge limit line (see, e.g., bold black line SSL-2 and SSL-3 in FIG. 2 ), in particular by ensuring that the surge limit line corresponds substantially to zero mass flow (see, e.g., bold black line SSL-3 in FIG. 2 ), i.e., that the compressor has a stable operating condition even at very low mass flow rates.

[0021] 1, compression system 100 has a system inlet 101 provided with an inlet valve 102 configured to selectively fluidly couple compression system 100 to an external fluid source for receiving compressed fluid from the external fluid source. Compression system 100 also has a system outlet 103 provided with an outlet valve 104 configured to selectively fluidly couple compression system 100 to an external system, such as a process plant or equipment requiring pressurized fluid, for providing compressed (or pressurized) fluid to the external system.

[0022] 1 , the compression system 100 further comprises an inlet duct 110 having a first end fluidly coupled to the system inlet 101, in particular to the inlet valve 102, and a second end fluidly coupled to a compressor inlet flange 111. Advantageously, the inlet duct 110 is configured to provide a compressed fluid to the compressor 150. As will become apparent below, the compressed fluid provided by the inlet duct 110 may come entirely from the system inlet 101, or only in part from the system inlet 101; in other words, the total mass flow provided to the compressor 150 by the inlet duct 110 may be made up of less than 100% of the fluid coming from the system inlet 101, in particular due to fluid recirculation within the compressor system 100.

[0023] 1 , the compression system 100 further comprises an outlet duct 120 having a first end fluidly coupled to the compressor outlet flange 112 and a second end fluidly coupled to the system outlet 103, in particular to the outlet valve 104. Advantageously, the outlet duct 120 is configured to provide compressed fluid to the system outlet 103. As will become apparent below, the compressed fluid provided by the outlet duct 120 may be supplied entirely to the system outlet 103 or only partially to the system outlet 103; in other words, the total mass flow supplied by the outlet duct 120 to the system outlet 103 may be constituted by a proportion of compressed fluid coming from the compressor 150 that is less than 100%, in particular due to fluid recirculation within the compressor system 100.

[0024] 1 , compression system 100 includes an anti-surge recirculation loop 140 having a first end fluidly coupled to outlet duct 120 and a second end fluidly coupled to inlet duct 110. For example, anti-surge recirculation loop 140 may have a first branch fitting 125 on outlet duct 120 and a second branch fitting 115 on inlet duct 110. In particular, first branch fitting 125 may fluidly couple anti-surge recirculation loop 140 and the first end of outlet duct 120, and second branch fitting 115 may fluidly couple anti-surge recirculation loop 140 and the second end of inlet duct 110.

[0025] The anti-surge recirculation loop 140 is provided with an anti-surge valve 145, in particular a throttle valve, configured to control the flow in the anti-surge recirculation loop 140, in particular the mass flow rate of compressed fluid recirculating from the outlet duct 120 to the inlet duct 110, in order to reduce the risk of surge in the compressor 150.

[0026] Advantageously, system 100 may further include a suction flow control device 151, such as a throttling inlet valve and / or inlet guide vanes. According to one possibility, suction flow control device 151 may be located immediately upstream of compressor 150 and may be tuned to reduce the power absorbed by the compressor (i.e., provided by compressor driver 170), particularly during start-up. According to another possibility, suction flow control device 151 may be located upstream of second branch fitting 115, particularly between inlet valve 102 and the second branch fitting.

[0027] 1, the compression system 100 comprises a discharge throttle valve 155 located downstream of the compressor outlet flange 112 and upstream of the first branch joint 125, in other words, the discharge throttle valve 155 is arranged between the compressor outlet flange 112 and the first branch joint 125. Advantageously, the discharge throttle valve 155 is located immediately downstream of the compressor outlet flange 112, in other words, there are no further elements between the compressor outlet flange 112 and the discharge throttle valve 155.

[0028] As will be readily understood by those skilled in the art, the outlet duct 120 has an inner diameter and an outer diameter, the difference between the inner and outer diameters being the duct wall thickness. Preferably, the discharge throttle valve 155 is located at a distance from the compressor outlet flange 112 that is less than three times the inner diameter of the outlet duct 120. In particular, it has been studied and tested that the location of the discharge throttle valve 155 changes, according to Greitzer's theory, the characteristic curve of the compressor 150 provided with the discharge throttle valve 155 (see, for example, characteristic curves 292 and 293 in FIG. 2 ) relative to the characteristic curve of the compressor 150 without any discharge throttle valve (see, for example, characteristic curve 291 in FIG. 2 ). That is, it is possible to obtain a characteristic curve without instability zones at low mass flow rates, i.e., a characteristic curve whose surge limit line corresponds to zero flow rate. It is possible to find a distance value (which may vary for each compressor type and / or model) that can change the characteristic curve of the compressor 150 provided with the discharge throttle valve 155 (see, for example, characteristic curve 291 in FIG. 2 ) according to Greitzer's theory.

[0029] According to one possibility, the discharge throttle valve 155 and / or other valves of the compressor system 100 may be controlled by a control algorithm, hereinafter referred to as an “active surge controller,” that acts on those valves with the aim of avoiding the risk of surge, especially when the discharge throttle valve 155 is located at a distance from the compressor outlet flange 112 that exceeds three times the inner diameter of the outlet duct 120. In particular, when the operating point position of the compressor moves to the left of the surge limit line, the active surge controller begins to open and close the valves in a cyclical manner and at a frequency self-adjusted to match the compressor surge cycle in order to avoid such surge phenomena. Advantageously, the control unit 160 may implement the active surge controller. As a non-limiting example, the active surge controller may be a closed-loop control system that may be of the “Proportional-Integral-Derivative” (PID) type, the “High Gain Adaptive Control” type, or the like.

[0030] 2, which illustrates a simplified plot showing how the combination of discharge throttle valve 155 and anti-surge valve 145 can reduce, and in some cases eliminate, the risk of surge in compressor 150. In particular, FIG. 2 illustrates three different operating states of compressor 150: a first operating state (see characteristic curve 291 and surge limit line SLL-1) in which discharge throttle valve 155 is in a fully open configuration, i.e., having substantially zero pressure drop at the compressor discharge, a second operating state (see characteristic curve 292 and surge limit line SLL-2) in which discharge throttle valve 155 is set to a specific configuration between a fully closed and a fully open configuration, and a third operating state (see characteristic curve 293 and surge limit line SLL-3) in which discharge throttle valve 155 is set to a specific configuration between a fully closed and a fully open configuration and anti-surge valve 145 is set to a specific configuration between a fully closed and a fully open configuration. More specifically, the dashed black curve on the plot is the compressor's characteristic curve, the bold black line is the compressor's surge limit line (SLL), and the black dots are examples of stable operating points for the compressor that can be achieved by appropriate adjustment of the discharge throttle valve and anti-surge valve. Note that the three operating states shown in Figure 2 refer to a first operating speed of compressor 150. However, the same may also apply to a compressor operating at a different speed, for example, a second speed that is slower than the first speed.

[0031] 1 , compressor system 100 includes a control unit 160 configured to control and adjust the opening and closing of anti-surge valve 145 and discharge throttle valve 155. Advantageously, as better explained below, control unit 160 may control and adjust the opening and closing of anti-surge valve 145 and discharge throttle valve 155 according to at least one or more fluid pressure measurements, particularly certain fluid pressure measurements obtained downstream of compressor 150, and / or one or more comparisons between two or more fluid pressure devices. Preferably, control unit 160 may also adjust the opening and closing of suction flow control device 151, for example, a throttle inlet valve or inlet guide vanes.

[0032] Advantageously, compression system 100 further comprises a first pressure gauge 156 configured to measure the first fluid pressure and provide the first fluid pressure measurement to control unit 160. Advantageously, first pressure gauge 156 is located downstream of discharge throttle valve 155, in particular between discharge throttle valve 155 and first branch fitting 125, and provides a measurement of the fluid pressure downstream of discharge throttle valve 155. It is noted that first pressure gauge 156 may be configured to measure and provide a measurement continuously as compressor 150 operates.

[0033] Advantageously, compression system 100 further comprises a second pressure gauge 157 configured to measure a second fluid pressure and provide the second fluid pressure measurement to control unit 160. Advantageously, second pressure gauge 157 is located downstream of compressor outlet flange 112, specifically between compressor outlet flange 112 and discharge throttle valve 155, and provides a measurement of the fluid pressure upstream of discharge throttle valve 155. It is noted that second pressure gauge 157 may be configured to measure and provide a measurement continuously as compressor 150 operates.

[0034] According to one possibility, the control unit 160 may be configured to provide a comparison between a first fluid pressure measurement provided by the first pressure gauge 156 and a second fluid pressure measurement provided by the second fluid gauge 157. For example, if the comparison of the two fluid pressures results in a difference of tens or hundreds of bars (e.g., according to tolerance settings), the control unit 160 may be configured to control and adjust the opening and closing of the anti-surge valve 145 and the discharge throttle valve 155 so that the difference between the two measurements is never less than or near zero (i.e., the direction of the fluid is never reversed).

[0035] According to another aspect, the subject matter disclosed herein relates to a method for controlling a compression system, such as the compression system described above, during start-up, the compression system comprising: a compressor 150 having a system inlet 101 and a system outlet 103; an anti-surge recirculation loop 140 comprising an anti-surge valve 145 fluidly coupling the compressor system outlet 103 and the compressor system inlet 101; a discharge throttle valve 155 located downstream of the compressor 150, particularly between the compressor 150 and the anti-surge recirculation loop 140; and an inlet valve 102 and an outlet valve 104 located at the system inlet 101 and the system outlet 103, respectively.

[0036] With non-limiting reference to FIG. 3, the method includes: A) First, step 310 sets the anti-surge valve 145 to a particular configuration between a fully closed configuration and a fully open configuration; B) first setting 320 the discharge throttle valve 155 to a particular configuration between a fully closed and a fully open configuration such that the compressor surge limit corresponds to substantially zero flow; C) starting up the compressor 150.

[0037] 3 is schematic only, and two or more of the previous steps 310, 320, and 330 may occur simultaneously or substantially simultaneously. Also, note that step C means that compressor driver 170 provides power to compressor 150 to operate the compressor from zero rotational speed up to a minimum operating speed, which may depend on the compressor type and / or model.

[0038] According to some embodiments, the method may also include the step of setting the inlet valve 102 and the outlet valve 104 to a fully closed configuration in order to isolate the compression system 100; in particular, this step may occur before step C. According to other embodiments, the method may also include the step of setting the inlet valve 102 and / or the outlet valve 104 to a particular configuration between the fully closed and fully open configurations; in particular, this step may occur before step C. Advantageously, the method may include the step of: D) further comprising step 340 of adjusting the opening of the anti-surge valve 145 between a fully closed configuration and a fully open configuration to generate a back pressure upstream of the anti-surge valve 145 substantially equal to the pressure downstream of the outlet valve 104, and optionally a pressure downstream of the anti-surge valve 145 substantially equal to the pressure upstream of the inlet valve 102.

[0039] Advantageously, during step D, the opening of the discharge throttle valve 155 is also adjusted between a fully closed and a fully open configuration. The inlet valve 102 and the outlet valve 104 are set to a fully open configuration—step E—when the backpressure upstream of the antisurge valve 145 substantially reaches the pressure downstream of the outlet valve 104 (see also step 350 in FIG. 3 ). In particular, the outlet valve 104 is set to a fully open configuration when the pressure downstream of the antisurge valve 145 substantially reaches the pressure upstream of the inlet valve 102. Finally, the antisurge valve 145 is set to a fully closed configuration—step F—(see also step 360 in FIG. 3 ), and the discharge throttle valve 155 is set to a fully open configuration—step G—(see also step 370 in FIG. 3 ). It should be noted that two or more of the previous steps 350, 360, and 370 may be performed simultaneously or substantially simultaneously. It should also be noted that the steps of adjusting and setting the throttle valve (e.g., steps 310, 320, 340, 350, and 370) may be performed by the control unit 160. In particular, the adjustments are made essentially by the control unit 160 through a program, which may be “software” or “firmware,” stored in the program memory of the control unit 160. By way of non-limiting example, the control unit 160 may be a computer, a programmable logic controller (PLC), a distributed control system (DCS), a microprocessor, or similar device. It should also be noted that the discharge throttle valve 155 is configured and designed to limit pressure drop when set to a fully open configuration. In particular, when the discharge throttle valve 155 is set to a fully open configuration, the pressure drop in the compression system 100 due to the presence of the discharge throttle valve 155 is less than 1% of the total discharge pressure, i.e., the pressure at the outlet flange 112.

[0040] According to another aspect, the subject matter disclosed herein relates to a method for controlling a compression system, such as the compression system described above, during an emergency shutdown, the compression system comprising: a compressor 150 having a system inlet 101 and a system outlet 103; an anti-surge recirculation loop 140 comprising an anti-surge valve 145 fluidly coupling the compressor system outlet 103 and the compressor system inlet 101; a discharge throttle valve 155 located downstream of the compressor 150, particularly between the compressor 150 and the anti-surge recirculation loop 140; and an inlet valve 102 and an outlet valve 104 located at the system inlet 101 and the system outlet 103, respectively.

[0041] During a normal shutdown, the compressor is slowed down in a controlled manner and the valves are opened in stages. Indeed, during an emergency shutdown, power to the compressor from the compressor driver is immediately cut off and the valves are opened rapidly. With non-limiting reference to FIG. 4, the method described herein includes: H) Step 410 of setting the anti-surge valve 145 to a fully open configuration; I) Step 420 of setting the inlet valve 102 and the outlet valve 104 to a fully closed configuration; L) adjusting 430 the discharge throttle valve 155 to a particular configuration between a fully closed and a fully open configuration so that the compressor surge limit corresponds to substantially zero flow; M) turning off the compressor 440.

[0042] 4 is only schematic, and two or more of the previous steps 410, 420, 430, and 440 may occur simultaneously or substantially simultaneously. Also, note that step M means that power to compressor 150 is immediately cut off from compressor driver 170 to brake the compressor from operating speed to zero rotational speed.

Claims

1. A compression system (100) having a system inlet (101) with an inlet valve (102) and a system outlet (103) with an outlet valve (104), said compression system (100) comprising: a compressor (150) having a compressor inlet flange (111) and a compressor outlet flange (112); an inlet duct (110) having a first end fluidly coupled to said system inlet (101) and a second end fluidly coupled to said compressor inlet flange (111); an outlet duct (120) having a first end fluidly coupled to said compressor outlet flange (112) and a second end fluidly coupled to said system outlet (103); an antisurge recirculation loop (140) comprising an antisurge valve (145) configured to control flow in said antisurge recirculation loop (140), a first end of said antisurge recirculation loop (140) being fluidly coupled to said outlet duct (120) and a second end of said antisurge recirculation loop (140) being fluidly coupled to said inlet duct (110); a discharge throttle valve (155) located downstream of said compressor outlet flange (112); a control unit (160) configured to control and regulate the opening and closing of said anti-surge valve (145) and said discharge throttle valve (155), the first end of the anti-surge recirculation loop is fluidly coupled to the outlet duct through a first branch joint, and the discharge throttle valve is located upstream of the first branch joint.

2. The compression system (100) of claim 1, wherein the compressor (150) is a centrifugal compressor.

3. 2. The compression system of claim 1, wherein the outlet duct has an inner diameter, and the discharge throttle valve is located at a distance from the compressor outlet flange that is less than three times the inner diameter of the outlet duct.

4. 2. The compression system of claim 1, further comprising a first pressure gauge located between the discharge throttle valve and the first branch joint, the first pressure gauge configured to measure a first fluid pressure and provide a first fluid pressure value to the control unit.

5. a second pressure gauge (157) located between the compressor outlet flange (112) and the discharge throttle valve (155), the second pressure gauge (157) configured to measure a second fluid pressure and provide a second fluid pressure value to the control unit (160); The compression system of claim 4, wherein the control unit is configured to provide a comparison between the first fluid pressure value and the second fluid pressure value.

6. 6. The compression system of claim 4, wherein the control unit is configured to adjust the opening and closing of the anti-surge valve according to at least the received first fluid pressure and / or the comparison between the first fluid pressure value and the second fluid pressure value.

7. 2. The compression system of claim 1, further comprising a suction flow control device, the suction flow control device being an inlet throttle valve and / or an inlet guide vane, the suction flow control device being located upstream of the compressor inlet flange.

8. 1. A method for controlling a compression system during start-up, the compression system comprising: a compressor having a system inlet and a system outlet; an anti-surge recirculation loop comprising an anti-surge valve fluidly coupling the compressor system outlet and the compressor system inlet; a discharge throttle valve located downstream of the compressor, particularly between the compressor and the anti-surge recirculation loop; and an inlet valve and an outlet valve located at the system inlet and the system outlet, respectively, the method comprising: A) first setting (310) the anti-surge valve (145) to a particular configuration between a fully closed and a fully open configuration; B) first setting (320) the discharge throttle valve (155) to a particular configuration between a fully closed and a fully open configuration such that the compressor surge limit corresponds to substantially zero flow; C) starting (330) said compressor (150).

9. When the compressor reaches a minimum operating speed, the method further comprises:

10. The method of claim 8, further comprising the step of: D) adjusting (340) the opening of the anti-surge valve (145) between a fully closed configuration and a fully open configuration to generate a back pressure upstream of the anti-surge valve (145) substantially equal to the pressure downstream of the outlet valve (104).

10. 10. The method of claim 9, wherein also during step D, the opening of the discharge throttle valve (155) is adjusted between a fully closed configuration and a fully open configuration until the back pressure upstream of the antisurge valve (145) is substantially equal to the pressure downstream of the outlet valve (104).

11. When the back pressure substantially reaches the pressure downstream of the outlet valve (104), the method further comprises: E) setting (350) the inlet valve (102) and the outlet valve (104) to a fully open configuration; F) setting (360) the anti-surge valve (145) to a fully closed configuration; G) setting (370) the discharge throttle valve (155) to a fully open configuration.

12. 1. A method for controlling a compression system during an emergency shutdown, the compression system comprising: a compressor having a system inlet and a system outlet; an anti-surge recirculation loop comprising an anti-surge valve fluidly coupling the compressor system outlet and the compressor system inlet; a discharge throttle valve located downstream of the compressor, particularly between the compressor and the anti-surge recirculation loop; and an inlet valve and an outlet valve located at the system inlet and the system outlet, respectively, the method comprising: H) setting (410) the anti-surge valve (145) to a fully open configuration; I) setting (420) the inlet valve (102) and the outlet valve (104) to a fully closed configuration; L) adjusting (430) said discharge throttle valve (155) to a particular configuration between a fully closed and a fully open configuration such that the compressor surge limit corresponds to substantially zero flow; M) turning off the compressor (440).

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