Multi-stage in-line compressor system and method with dry gas seals

Abstract

The compressor system includes a multi-stage compressor (1) and a seal gas supply system (60). The compressor includes a low-pressure section (1A) and a high-pressure section (1B) in a straight-through configuration, is rotatably housed within a compressor casing (3), and further includes a shaft (7) having a low-pressure shaft end (7A) and a high-pressure shaft end (7B). A low-pressure dry gas seal (13) is disposed at the low-pressure shaft end (7A), and a high-pressure dry gas seal (15) is disposed at the high-pressure shaft end (7B). The seal gas supply system (60) includes a seal gas booster (65), a first control valve (83) adapted to control the flow of seal gas from the seal gas booster (65) to the low-pressure dry gas seal (13), and a second control valve (87) adapted to control the flow of seal gas from the seal gas booster (65) to the high-pressure dry gas seal (15).

Description

[Technical Field]

[0001] The present disclosure relates to turbomachinery. More particularly, embodiments disclosed herein relate to a system including a multi-stage compressor, such as a multi-stage centrifugal compressor, including a dry gas seal, and a seal gas supply system adapted to supply seal gas to the dry gas seal. [Background technology]

[0002] Dry gas seals are commonly used to reduce or prevent gas leakage around the rotating shafts of turbomachinery, such as centrifugal compressors. Dry gas seals require a continuous supply of seal gas, which must be maintained even when the turbomachinery is not operating. See John S. Stahley, "Dry Gas Seals Handbook," PennWell Corporation, 2005; ISBN 1593700628.

[0003] Multi-stage compressors, particularly multi-stage centrifugal compressors, can include low-pressure and high-pressure sections, each of which includes one or more impellers mounted for rotation on a rotating shaft. The low-pressure section includes a low-pressure suction and a low-pressure discharge. Process gas enters the low-pressure section at the low-pressure suction, passes through the stages of the low-pressure section, is partially compressed, and is discharged at the low-pressure discharge. The high-pressure section includes a high-pressure suction and a high-pressure discharge. Partially compressed gas from the low-pressure discharge enters the high-pressure section at the high-pressure suction and is further compressed and discharged at the high-pressure discharge.

[0004] Between the low pressure discharge and the high pressure suction, the partially compressed process gas can be cooled in an intercooler to remove the heat generated by the first compression and improve compressor efficiency.

[0005] The rotating shaft has two opposite ends supported in respective end bearings. The inboard side of each bearing is provided with a respective dry gas seal to prevent process gas from leaking along the shaft toward the bearing.

[0006] The low-pressure and high-pressure sections can be arranged in a so-called back-to-back configuration or in a so-called in-line or straight-through configuration. In a back-to-back configuration, the low-pressure discharge and high-pressure discharge of the compressor are located between the low-pressure suction and the high-pressure suction, and the impellers of the low-pressure section and the high-pressure section are located back-to-back. An interstage seal is provided around the shaft between the low-pressure and high-pressure sections.

[0007] Conversely, in an in-line or straight-through arrangement, the impellers of the low-pressure section and the high-pressure section are arranged in-line, with the low-pressure discharge and high-pressure suction located between the low-pressure suction and high-pressure discharge. An interstage seal is provided around the shaft between the low-pressure section and the high-pressure section. Furthermore, a first balance line extends from the most downstream stage of the low-pressure section to the most upstream stage of the low-pressure section. A second balance line extends from the most downstream stage of the high-pressure section to the most upstream stage of the high-pressure section. When the compressor is shut down, two different settling pressures (abbreviated herein as SOP) are established in the low-pressure section and the high-pressure section. The pressures in the two compressor sections become equal only after a relatively long period of time due to leakage through the interstage seal. As a result, the dry gas seals at the high-pressure and low-pressure ends of the compressor require different pressures of seal gas to adequately cushion the dry gas seals. Therefore, an external high-pressure seal gas source is required.

[0008] The need for an external gas source is not always desirable, and in some situations an external gas source may not be available. Summary of the Invention

[0009] To solve or alleviate the aforementioned need for an external seal gas source, the present disclosure provides a novel compressor system. The compressor system includes a rotatable shaft housed for rotation within a compressor casing and having a low-pressure shaft end and a high-pressure shaft end. The compressor further includes a low-pressure compressor section having a low-pressure suction and a low-pressure discharge. The high-pressure compressor section of the compressor includes a high-pressure suction and a high-pressure discharge. The low-pressure compressor section and the high-pressure compressor section are configured in a straight-through, or in-line, configuration, with the low-pressure discharge and high-pressure suction disposed between the low-pressure suction and the high-pressure discharge.

[0010] The compressor further includes a low pressure dry gas seal at the low pressure shaft end and a high pressure dry gas seal at the high pressure shaft end.

[0011] The compressor system further includes a seal gas supply system for supplying seal gas to the dry gas seal. The seal gas supply system includes a seal gas booster. The seal gas booster has a booster inlet and a booster outlet. The booster inlet is fluidly coupled to the high-pressure discharge of the multi-stage compressor to receive process gas therefrom. The seal gas booster outlet is fluidly coupled to the low-pressure dry gas seal and the high-pressure dry gas seal. A first seal gas supply line fluidly couples the booster outlet to the low-pressure dry gas seal, and a first control valve is disposed in the first seal gas supply line to control seal gas flow therethrough. A second seal gas supply line fluidly couples the booster outlet to the high-pressure dry gas seal. A second control valve is disposed in the second seal gas supply line. The second control valve controls the flow of seal gas toward the high-pressure dry gas seal.

[0012] According to another aspect, a compressor system is disclosed that includes a multi-stage compressor and a seal gas supply system. The compressor includes a low-pressure section and a high-pressure section in a straight-through configuration. The compressor further includes a shaft rotatably housed within a compressor casing and having a low-pressure shaft end and a high-pressure shaft end. A low-pressure dry gas seal is provided at the low-pressure shaft end, and a high-pressure dry gas seal is provided at the high-pressure shaft end.

[0013] The seal gas supply system includes a seal gas booster having a booster inlet and a booster outlet. The booster inlet is fluidly coupled to a high-pressure discharge of the multi-stage compressor to receive process gas therefrom. The seal gas booster outlet is fluidly coupled to the low-pressure dry gas seal and the high-pressure dry gas seal. A first control valve is positioned to control seal gas flow from the seal gas booster to the low-pressure dry gas seal. A second control valve is positioned to control seal gas flow from the seal gas booster to the high-pressure dry gas seal.

[0014] Further features and embodiments of the compressor system outlined above are set out in the dependent claims.

[0015] According to yet another aspect, a method for supplying seal gas to low-pressure and high-pressure dry gas seals of a multi-stage compressor having low-pressure and high-pressure sections in a straight-through, or in-line, configuration is disclosed herein. The method includes generating a seal gas flow in a seal gas booster of a seal gas booster, the seal gas booster being fluidly coupled to a delivery side of the multi-stage compressor for receiving process gas therefrom. The method further includes supplying a first seal gas flow from a seal gas booster outlet to the low-pressure dry gas seal through a first control valve, and supplying a second seal gas flow from the seal gas booster outlet to the high-pressure dry gas seal through a second control valve. The method further includes adjusting the first seal gas flow through the first control valve and adjusting the second seal gas flow through the second control valve.

[0016] In this specification and the appended claims, the terms "high pressure" and "low pressure" are used as relative terms. The "high pressure section" of a compressor is herein understood as the section in which the process gas pressure is higher than the "low pressure section." This does not mean that the "high pressure" section or "high pressure discharge" is the section of the compressor system where the highest process gas pressure is achieved. Rather, the discharge end of the "high pressure section" may be fluidly coupled to an additional compressor for additional compression of the process fluid. Similarly, the "low pressure section" or "low pressure suction" is not necessarily the most upstream section or first suction side of a compressor train or system. Rather, the process gas entering the low pressure section may be delivered by a more upstream compressor. [Brief explanation of the drawings]

[0017] Reference will now be made briefly to the accompanying drawings, in which: [Figure 1] 1 is a schematic diagram of an in-line multi-stage centrifugal compressor according to the present disclosure, including a low-pressure section and a high-pressure section; [Figure 2]2 is a schematic diagram of a seal gas system that supplies seal gas to a dry gas seal of the compressor of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] To eliminate the need for an external source of seal gas to supply seal gas when the in-line compressor is not operating, according to the present disclosure, a booster is provided, the inlet of which may be connected to the high-pressure discharge of the compressor. First and second control valves fluidly connect the booster to opposing dry gas seals. The two control valves are controlled independently of each other, thereby providing seal gas at the appropriate pressure to two opposing dry gas seals at the two ends of the compressor shaft. Thus, seal gas is delivered at the correct pressure at both the drive end and the non-drive end of the compressor shaft.

[0019] Referring now to the drawings, FIG. 1 schematically illustrates a multi-stage centrifugal compressor 1 having an in-line, or straight-through, configuration. Compressor 1 includes a casing, generally designated 3. Rotatingly housed within casing 3 is rotor 5. Rotor 5 includes a rotation axis AA and a rotatable shaft 7. Two bearings 9, 11 rotatably support shaft 7 within casing 3. Bearing 9 is located at low-pressure shaft end 7A, and bearing 11 is located at high-pressure shaft end 7B. Low-pressure shaft end 7A may be the so-called non-drive end of the shaft, i.e., the end of the shaft that is not connected to a compressor drive (not shown). High-pressure shaft end 7B may be the so-called drive end of shaft 7, i.e., the end of the shaft that is drivingly coupled to a drive such as an electric motor, gas, or steam turbine.

[0020] Two dry gas seals 13, 15 are provided on the inboard side of the two bearings 9, 11, and these prevent leakage of process gas from inside the compressor toward the bearings 9, 11. Here, the dry gas seal 13 will be referred to as the low-pressure dry gas seal, and the dry gas seal 15 will be referred to as the high-pressure dry gas seal.

[0021] In general, the dry gas seals 13, 15 can have any configuration suited to the nature of the process gas being sealed and the type of compressor 1. In some embodiments, the dry gas seals 13, 15 can be a single dry gas seal. Preferably, the dry gas seals 13, 15 can be, for example, tandem dry gas seals with or without intermediate labyrinths, or double opposed dry gas seals. Each dry gas seal 13, 15 includes at least a stationary primary ring and a rotating mating ring that rotates integrally with the shaft 7. The stationary and rotating rings are not shown in the drawings. As will be explained later with reference to FIG. 2, sealing gas is supplied to each dry gas seal 13, 15, and the sealing gas discharged from each dry gas seal is collected in a discharge line. The dry gas seal 13 is provided with an inboard process labyrinth seal 14, and the dry gas seal 15 is provided with an inboard process labyrinth seal 16.

[0022] Compressor 1 includes a low-pressure compressor section 1A and a high-pressure compressor section 1B. In the embodiment of FIG. 1, low-pressure compressor section 1A includes three impellers 17A, 17B, and 17C. High-pressure compressor section 1B includes three impellers 17D, 17E, and 17F. The number of impellers in each compressor section is merely exemplary. Impellers 17A-17F are arranged in an in-line, or straight-through, configuration, with impeller 17A being the most upstream impeller at the lowest pressure relative to the process gas flow and impeller 17F being the most downstream impeller at the highest pressure. An interstage seal 18 is disposed around shaft 7 between high-pressure compressor section 1 and low-pressure compressor section 1A.

[0023] Low-pressure compressor section 1A includes a low-pressure suction 19 and a low-pressure discharge 21. Low-pressure suction 19 is fluidly coupled to a process gas supply line 23. Low-pressure discharge 21 is fluidly coupled to a high-pressure suction 25 via an intercooler 27 and a check valve 28. Auxiliary components, such as a gas-liquid separator (not shown), may be provided along the process gas path between low-pressure discharge 21 and high-pressure suction 25. High-pressure compressor section 1A further includes a high-pressure discharge 29 fluidly coupled to a process gas delivery line 31. Process gas delivery line 21 may be fluidly coupled to a high-pressure compressor (not shown).

[0024] Process gas enters compressor 1 through low-pressure suction 19 from process gas supply line 23, is compressed sequentially through impellers 17A, 17B, and 17C of low-pressure compressor section 1A, and is delivered through low-pressure discharge 21 to intercooler 27. Before being delivered to high-pressure compressor section 1A, the partially compressed process gas is cooled in intercooler 27, for example, by heat exchange with air, water, or another cooling fluid. The cooled, partially compressed process gas is further compressed through impellers 17D, 17E, and 17F of high-pressure compressor section 1B, and finally discharged through high-pressure discharge 29.

[0025] The compressor 1 further includes a low-pressure balance line 41 that fluidly connects the low-pressure discharge 21 with an outboard side of an end seal 43 disposed on the inboard side of the low-pressure dry gas seal 13. Specifically, the low-pressure balance line 41 is connected to a volume between the process labyrinth seal 14 of the dry gas seal 13 and the end seal 43.

[0026] The compressor 1 further includes a high-pressure balance line 45 that fluidly connects the high-pressure suction 25 with the outboard side of a balance drum seal 47 that is disposed inboard of the high-pressure dry gas seal 15 and that is disposed around a balance drum 48. Specifically, the high-pressure balance line 45 is connected to a volume between the process labyrinth seal 16 of the dry gas seal 15 and the balance drum 48.

[0027] The dry gas seals 13, 15 must be supplied with seal gas during normal operating conditions as well as when the compressor 1 is not running. During normal operation, process gas may be diverted from the delivery line 31 and treated in the seal gas treatment unit before being used as seal gas in the dry gas seals 13, 15. The seal gas is supplied at a pressure sufficient to cushion both dry gas seals 13, 15.

[0028] When the compressor shuts down, process gas flow through the compressor stages is interrupted. A settle-out pressure (SOP) is established in low-pressure compressor section 1A, and a different, higher settle-out pressure is established in high-pressure compressor section 1B. Check valve 28 prevents high-pressure process gas from flowing back from high-pressure compressor section 1B to low-pressure compressor section 1A through intercooler 27. Process gas flows from high-pressure compressor section 1B to low-pressure compressor section 1A only through interstage seal 18. Therefore, the two SOPs balance only after a relatively long period of time. As a result, for a relatively long period of time after a shutdown, the gas pressure on the inboard side of low-pressure dry gas seal 13 is significantly lower than the gas pressure on the inboard side of high-pressure dry gas seal 15. In some examples, the gas pressure on the inboard side of the low-pressure dry gas seal 13 (i.e., the inboard side of the process labyrinth seal 14) is 50% or less of the gas pressure on the inboard side of the high-pressure dry gas seal 15 (i.e., the inboard side of the process labyrinth seal 16). To buffer the two dry gas seals 13, 15, seal gases at different pressures are required.

[0029] To avoid the need for an external seal gas source to buffer the two dry gas seals during the SOP balance period following compressor shutdown, the compressor system includes a novel seal gas supply system shown schematically in FIG. 2 and omitted from FIG. 1 for clarity.

[0030] FIG. 2 shows only the major components of compressor 1 that are useful for better understanding the seal gas supply system of the present disclosure. The seal gas supply system is generally labeled 50 in FIG. 2. FIG. 2 also shows a schematic representation of shaft 7, low-pressure dry gas seal 13, high-pressure dry gas seal 15, end seals 43, and balance drum seal 47. FIG. 2 also shows discharge line 53, which collects the primary vent from low-pressure dry gas seal 13, and discharge line 55, which collects the primary vent from high-pressure dry gas seal 15. The seal gas discharged by dry gas seals 13 and 15 can be recycled or delivered to flare 57.

[0031] The seal gas supply system 50 includes a seal gas booster 65 having a booster inlet 67 and a booster outlet 69. A bypass valve 71 may be disposed in parallel with the seal gas booster 65. The seal gas booster 67 is driven by an electric motor 66 via a variable frequency drive 68, allowing the flow rate of the seal gas booster 66 to be adjusted to the requirements of the dry gas seals 13, 15.

[0032] The booster 65 can be equipped with a regenerative compressor best suited to the head and flow values ​​involved. For example, a suitable regenerative compressor may be 10-30 m 3 / hour range and head up to about 2 bar.

[0033] The booster inlet 67 may be fluidly coupled to the high pressure discharge 29 or the process gas delivery line 31 via a seal gas treatment unit 73. The seal gas treatment unit 73 may be configured in a known manner and may include filters and other auxiliary devices to remove liquids or other impurities from the process gas before delivering the treated process gas to the suction side of the seal gas booster 65.

[0034] The booster outlet 69 is fluidly coupled to the low-pressure dry gas seal 13 and the high-pressure dry gas seal 15 via respective control valves. More specifically, the booster outlet 69 is fluidly coupled to the low-pressure dry gas seal 13 via a first sealing gas supply line 81 including a first control valve 83 disposed in the first sealing gas supply line 81. Additionally, the booster outlet 69 is fluidly coupled to the high-pressure dry gas seal 15 via a second sealing gas supply line 85 including a second control valve 87 disposed in the second sealing gas supply line 85.

[0035] The first control valve 83 is controlled by a first valve control loop 89, which may be, for example, a pressure control loop or a flow control loop. Similarly, the second control valve 87 is controlled by a second valve control loop 91, which may be, for example, a pressure control loop or a flow control loop.

[0036] In some embodiments, the first valve control loop 89 can include a first differential pressure sensor 89.1 adapted to detect a differential pressure between the exhaust line 53 and a point downstream of the first control valve 83. The first valve control loop 89 can further include a second differential pressure sensor 89.2 between a point downstream of the first control valve 83 and a point between the inboard labyrinth seal 14 and the end seal 43. The first valve control loop 89 can further include a pressure sensor 89.3. A comparator 89.4 compares the signal from the first differential pressure sensor 89.1 with the signal from the second differential pressure sensor 89.2. These signals are proportional to the difference between their respective setpoints and the actual pressure difference detected by the sensors. The signal with the highest value can be selected as the control signal for the first control valve 83.

[0037] Similarly, in some embodiments, the second valve control loop 91 can include a first differential pressure sensor 91.1 adapted to detect a differential pressure between the exhaust line 55 and a point downstream of the second control valve 87. The second valve control loop 91 can further include a second differential pressure sensor 91.2 between a point downstream of the second control valve 87 and a point between the inboard labyrinth seal 16 and the balance drum seal 47. The second valve control loop 91 can further include a pressure sensor 91.3. A comparator 91.4 compares the signal from the first differential pressure sensor 91.1 with the signal from the second differential pressure sensor 91.2. These signals are proportional to the difference between their respective setpoints and the actual pressure difference detected by the sensors. The signal with the highest value can be selected as the control signal for the second control valve 87.

[0038] After the compressor shuts down, the SOPs in the low-pressure section 1A and the high-pressure section 1B differ substantially, e.g., by more than 50%. At this point, the first control valve 83 may be closed or only partially open, e.g., between 10% and 20%, due to the low pressure on the inboard side of the dry gas seal 13. Conversely, the second control valve 87 may be fully or nearly fully open, e.g., between 60% and 80%. The difference between the two SOPs in the low-pressure section 1A and the high-pressure section 1B tends to decrease due to leakage through the interstage seal 18, i.e., the SOP in the high-pressure section 1B decreases and the SOP in the low-pressure section 1B increases. The change in SOP is detected by the differential pressure sensor described above, and control loops 89 and 91 consequently cause the second control valve 87 to gradually close and the first control valve 83 to gradually open.

[0039] Therefore, in the above-described seal gas supply system 60, the first and second control valves 83, 87 can be controlled independently to adjust the seal gas flow rates of the low-pressure dry gas seal 13 and the high-pressure dry gas seal 15, thereby balancing changes in pressure on the inboard side of each dry gas seal 13, 15. Specifically, gas leaking through the interstage seal 18 tends to equalize the gas pressures inside the low-pressure and high-pressure sections of the compressor, thus causing an increase in pressure on the inboard side of the low-pressure dry gas seal 13 and a decrease in pressure on the inboard side of the high-pressure dry gas seal 15. As a result, the seal gas flow rate toward the high-pressure dry gas seal 15 decreases, and the seal gas flow rate toward the low-pressure dry gas seal increases.

[0040] The total flow rate (i.e., the sum of the seal gas flow rate towards the low-pressure dry gas seal 13 and the seal gas flow rate towards the high-pressure dry gas seal 15) is delivered by the seal gas booster 65, and the partial flow rates towards each dry gas seal 13, 15 are adjusted by respective control valves 83, 87, which are controlled by respective first control loops 89 and second control loops 91, taking into account the pressure on the inboard side of each dry gas seal.

[0041] For example, after shutdown, when different SOPs are established in the low-pressure compressor section 1A and the high-pressure compressor section 1B, respectively, the second control valve 87 (supplying seal gas to the high-pressure dry gas seal 15) can be opened more than 60%, while the first control valve 83 (supplying seal gas to the low-pressure dry gas seal 13) can be partially closed, e.g., opened to less than 25%. In some embodiments, an orifice 86 can be provided in parallel with the first control valve 83. In this case, the starting position of the first control valve 83 can be fully closed.

[0042] Due to leakage through interstage seal 18, the SOP in low-pressure compressor section 1A increases and the SOP in the high-pressure compressor section decreases, while the seal gas flow rate through second control valve 87 decreases and the seal gas flow rate through first control valve 83 increases. When the two SOPs are balanced, i.e., when the same pressure is established in low-pressure compressor section 1A and high-pressure compressor section 1B, the seal gas flows through first control valve 83 and second control valve 87 are substantially equal to each other.

[0043] A separate source of seal gas, for example an inert gas such as nitrogen, may further be coupled to the seal gas booster inlet 67 as shown diagrammatically at 93 in FIG.

[0044] Exemplary embodiments are disclosed above and shown in the accompanying drawings. Those skilled in the art will understand that various modifications, omissions, and additions may be made to what is specifically disclosed herein without departing from the scope of the invention as defined in the claims that follow.

Claims

1. 1. A compressor system comprising: A multi-stage compressor (1), a rotating shaft (7) housed for rotation within the compressor casing (3) and having a low pressure shaft end (7A) and a high pressure shaft end (7B); a low pressure compressor section (1A) having a low pressure suction section (19) and a low pressure discharge section (21); a high-pressure compressor section (1B) having a high-pressure suction section (25) and a high-pressure discharge section (29), wherein the low-pressure compressor section (1A) and the high-pressure compressor section (1B) are configured in a straight-through arrangement, and the low-pressure discharge section (21) and the high-pressure suction section (25) are arranged between the low-pressure suction section (19) and the high-pressure discharge section (29); a low pressure dry gas seal (13) at the low pressure shaft end (7A); a high-pressure dry gas seal (15) at the high-pressure shaft end (7B); A seal gas supply system (60), comprising: a seal gas booster (65) having a booster inlet (67) and a booster outlet (69), the booster inlet (67) fluidly coupled to the high-pressure discharge (29) of the multi-stage compressor (1) for receiving process gas therefrom; a first seal gas supply line (81) fluidly coupling the booster outlet (69) to the low pressure dry gas seal (13); a first control valve (83) disposed in the first seal gas supply line (81); a second seal gas supply line (85) fluidly coupling the booster outlet (69) to the high-pressure dry gas seal (15); a second control valve (87) disposed in the second seal gas supply line (85).

2. The compressor system of claim 1, further comprising a seal gas treatment unit (73) between the high-pressure discharge (29) of the multi-stage compressor (1) and the booster inlet (67).

3. 3. The compressor system of claim 1, further comprising a first valve control loop (89) adapted to control the first control valve (83) and a second valve control loop (91) adapted to control the second control valve (87).

4. The compressor system of claim 3, wherein the first valve control loop (89) and the second valve control loop (91) are pressure control loops or flow control loops.

5. 5. The compressor system of claim 1, further comprising an interphase seal around the rotating shaft between the low-pressure compressor section and the high-pressure compressor section, and a balance drum disposed at a high-pressure end of the rotating shaft, the balance drum having an outboard side fluidly coupled to the low-pressure suction.

6. 1. A compressor system comprising: A multi-stage compressor (1), a low pressure section (1A) and a high pressure section (1B) in a straight-through configuration; a shaft (7) rotatably housed within the compressor casing (3) and having a low-pressure shaft end (7A) and a high-pressure shaft end (7B); a low pressure dry gas seal (13) at the low pressure shaft end (7A); a high-pressure dry gas seal (15) at the high-pressure shaft end (7B); A seal gas supply system (60), comprising: a seal gas booster (65) having a booster inlet (67) and a booster outlet (69), the booster inlet (67) fluidly coupled to the high-pressure discharge (29) of the multi-stage compressor (1) for receiving process gas therefrom; a first control valve (83) adapted to control seal gas flow from the seal gas booster (65) to the low pressure dry gas seal (13); a second control valve (87) adapted to control seal gas flow from the seal gas booster (65) to the high-pressure dry gas seal (15).

7. The compressor system of claim 6, further comprising one or more of the features of claims 2-5.

8. 1. A method for supplying seal gas to a low-pressure dry gas seal (13) and a high-pressure dry gas seal (15) of a multi-stage compressor (1) having a low-pressure section (1A) and a high-pressure section (1B) in a straight-through configuration, the method comprising: generating a flow of seal gas at a seal gas booster outlet (69) of a seal gas booster (65), said seal gas booster (65) comprising a seal gas booster inlet (67) fluidly coupled to a delivery side of said multi-stage compressor (1) for receiving process gas therefrom; providing a first seal gas flow from the seal gas booster outlet (69) to the low pressure dry gas seal (13) via a first control valve (83); providing a second seal gas flow from the seal gas booster outlet (69) to the high pressure dry gas seal (15) through a second control valve (87); adjusting the first seal gas flow through the first control valve (83) and adjusting the second seal gas flow through the second control valve (87).

9. 9. The method of claim 8, further comprising the step of shutting down the multi-stage compressor, wherein after compressor shutdown, adjusting the first seal gas flow through the first control valve (83) and the second seal gas flow through the second control valve (87) comprises increasing the seal gas flow through the first control valve (83) and decreasing the seal gas flow through the second control valve (87) while a settling pressure in the low-pressure compressor section (1A) increases and a settling pressure in the high-pressure compressor section (1B) decreases.

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