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

Abstract

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

Description

Technical Field

[0001] The present disclosure relates to turbines. More specifically, embodiments disclosed herein relate to systems including a multistage compressor, such as a multistage centrifugal compressor, and a seal gas supply system, the multistage compressor including dry gas seals, the seal gas supply system being adapted to supply seal gas to the dry gas seals. Background Art

[0002] Dry gas seals are commonly used to reduce or prevent gas leakage around the rotating shaft of a turbine, such as a centrifugal compressor. Dry gas seals require a continuous feed of seal gas, and the continuous feed of seal gas should also be maintained when the turbine is not operating. See John S. Stahley, “Dry Gas Seals Hand-book”, PennWell Corporation, 2005; ISBN 1593700628.

[0003] A multistage compressor, particularly a multistage centrifugal compressor, may include a low-pressure section and a high-pressure section, each of the low-pressure section and the high-pressure section including one or more impellers mounted to rotate on a rotating shaft. The low-pressure section includes a low-pressure suction port and a low-pressure discharge port. Process gas enters the low-pressure section at the low-pressure suction port and is partially compressed through the stage(s) of the low-pressure section and discharged at the low-pressure discharge port. The high-pressure section includes a high-pressure suction port and a high-pressure discharge port. The partially compressed gas from the low-pressure discharge port enters the high-pressure section at the high-pressure suction port and is further compressed and discharged at the high-pressure discharge port.

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

[0005] The rotating shaft has two opposite ends that are supported in respective end bearings. A respective dry gas seal is provided inside each bearing, the dry gas seal preventing process gas from leaking along the shaft towards the bearing.

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

[0007] In contrast, in an in-line or through-flow arrangement, the impellers of the low-pressure section and the high-pressure section are arranged in-line such that the low-pressure discharge port and the high-pressure suction port are arranged between the low-pressure suction port and the high-pressure discharge port. Between the low-pressure section and the high-pressure section, an inter-stage seal is provided around the shaft. In addition, 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 stops, two different shutdown stable pressures (referred to herein simply as SOP) will be established in the low-pressure section and the high-pressure section. Due to leakage through the inter-stage seal, the pressures in the two compressor sections will equalize only after a relatively long period of time. Therefore, the dry gas seals at the high-pressure end and the low-pressure end of the compressor require sealing gases at different pressures to properly cushion the dry gas seals. Therefore, an external high-pressure sealing gas source is required.

[0008] The need for an external source is not always desirable and, in some cases, an external source is not available. SUMMARY OF THE INVENTION

[0009] To address or mitigate the above need for an external sealing gas source, according to the present disclosure, a novel compressor system is provided. The compressor system includes a rotating shaft that is received for rotation in a compressor housing and has 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 port and a low-pressure discharge port. The high-pressure compressor section of the compressor includes a high-pressure suction port and a high-pressure discharge port. The low-pressure compressor section and the high-pressure compressor section are configured in a through-flow arrangement (i.e., in an in-line configuration), wherein the low-pressure discharge port and the high-pressure suction port are arranged between the low-pressure suction port and the high-pressure discharge port.

[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] To supply sealing gas to the dry gas seals, the compressor system further includes a sealing gas supply system. The sealing gas supply system includes a sealing gas booster. The sealing gas booster includes a booster inlet and a booster outlet. The booster inlet is fluidly coupled to the high-pressure discharge port of the multi-stage compressor to receive process gas therefrom. The outlet of the sealing gas booster is fluidly coupled to the low-pressure dry gas seal and the high-pressure dry gas seal. A first sealing gas feed line fluidly couples the booster outlet to the low-pressure dry gas seal, and a first control valve is arranged in the first sealing gas feed line to control the flow of sealing gas therethrough. A second sealing gas feed line fluidly couples the booster outlet to the high-pressure dry gas seal. A second control valve is arranged in the second sealing gas feed line. The second control valve controls the flow of sealing gas towards the high-pressure dry gas seal.

[0012] According to another aspect, a compressor system is disclosed, which 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 direct-through configuration. The compressor further includes a shaft rotatably accommodated in the compressor housing 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, which includes a booster inlet and a booster outlet. The booster inlet is fluidly connected to the high-pressure discharge port of the multi-stage compressor to receive process gas therefrom. The outlet of the seal gas booster is fluidly connected to the low-pressure dry gas seal and the high-pressure dry gas seal. A first control valve is arranged to control the seal gas flow from the seal gas booster to the low-pressure dry gas seal. A second control valve is arranged to control the seal gas flow from the seal gas booster to the high-pressure dry gas seal.

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

[0015] According to yet another aspect, a method for supplying seal gas to a low-pressure dry gas seal and a high-pressure dry gas seal of a multi-stage compressor is disclosed herein, the multi-stage compressor including a low-pressure section and a high-pressure section in a direct-through (i.e., in-line) configuration. The method includes the step of generating a seal gas flow at a seal gas booster of the seal gas supply system; wherein the seal gas booster includes a seal gas booster inlet fluidly connected to the delivery side of the multi-stage compressor to receive process gas therefrom. The method further includes feeding a first seal gas flow from the seal gas booster outlet to the low-pressure dry gas seal through a first control valve, and feeding 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 additionally includes the steps of regulating the first seal gas flow flowing through the first control valve and regulating the second seal gas flow flowing through the second control valve.

[0016] In this specification and the appended claims, the terms "high pressure" and "low pressure" are used in relative terms. The "high-pressure section" of the compressor is understood herein to be the section where the pressure of the process gas is higher than the pressure in the "low-pressure section". This does not mean that the "high-pressure" section or the "high-pressure discharge port" is the section of the compressor system where the highest pressure of the process gas is achieved. Instead, the discharge end of the "high-pressure section" may in turn be fluidly connected to another compressor for additional compression of the process fluid. Similarly, the "low-pressure section" or the "low-pressure suction port" is not necessarily the most upstream section or the first suction side of the compressor unit or system. Instead, the process gas entering the low-pressure section may in turn be delivered by a more upstream compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Reference is now made briefly to the drawings, in which:

[0018] Figure 1 is a schematic view of an in-line multi-stage centrifugal compressor according to the present disclosure, the in-line multi-stage centrifugal compressor including a low-pressure section and a high-pressure section; and

[0019] Figure 2 is to Figure 1 is a schematic view of a seal gas system that supplies seal gas to the dry gas seals of the compressor. DETAILED DESCRIPTION

[0020] To eliminate the need for an external seal gas source for feeding seal gas when the in-line compressor is not operating, according to the present disclosure, a booster is provided, the inlet of which can be connected to the high-pressure discharge port of the compressor. A first control valve and a second control valve fluidly connect the booster to the opposing dry gas seals. These two control valves are controlled independently of each other such that seal gas at an appropriate pressure is provided for the two opposing dry gas seals at the two ends of the compressor shaft. Thus, the seal gas is delivered at the correct pressure at both the drive end and the non-drive end of the compressor shaft.

[0021] Turning now to the drawings, Figure 1 A multi-stage centrifugal compressor 1 having an in-line (i.e., straight-through) configuration is schematically shown. The compressor 1 includes a housing schematically shown at 3. A rotor 5 is received for rotation within the housing 3. The rotor 5 includes a rotational axis A-A and a rotating shaft 7. Two bearings 9, 11 rotatably support the shaft 7 within the housing 3. The bearing 9 is arranged at the low-pressure shaft end 7A, and the bearing 11 is arranged at the high-pressure shaft end 7B. The 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 driver (not shown). The high-pressure shaft end 7B may be the so-called drive end of the shaft 7, i.e., the end of the shaft that is drivingly coupled to a driver (such as an electric motor, a gas or steam turbine, etc.).

[0022] Two dry gas seals 13, 15 are provided inside the two bearings 9, 11, and these two dry gas seals prevent process gas from leaking from the interior of the compressor towards the bearings 9, 11. Herein, 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.

[0023] Typically, the dry gas seals 13, 15 can have any configuration suitable for the properties of the process gas to be 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 an intermediate labyrinth, 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 figure. As will be explained later with reference to Figure 2 It is elucidated that sealing gas is fed to each dry gas seal 13, 15, and the sealing gas discharged from each dry gas seal is collected at the vent pipeline. The dry gas seal 13 is provided with an internal process labyrinth seal 14, and the dry gas seal 15 is provided with an internal process labyrinth seal 16.

[0024] The compressor 1 includes a low-pressure compressor section 1A and a high-pressure compressor section 1B. In Figure 1 the embodiment, the low-pressure compressor section 1A includes three impellers 17A, 17B, 17C. The high-pressure compressor section 1B includes three impellers 17D, 17E, 17F. The number of impellers in each compressor section is only an example. The impellers 17A - 17F are arranged in an in-line (i.e., straight-through) configuration. With respect to the process gas flow, the impeller 17A is the most upstream impeller at the lowest pressure, and the impeller 17F is the most downstream impeller at the highest pressure. The interstage seal 18 is arranged around the shaft 7 between the high-pressure compressor section 1 and the low-pressure compressor section 1A.

[0025] The low-pressure compressor section 1A includes a low-pressure suction port 19 and a low-pressure discharge port 21. The low-pressure suction port 19 is fluidly connected to the process gas supply pipeline 23. The low-pressure discharge port 21 is fluidly connected to the high-pressure suction port 25 through an intercooler 27 and a check valve 28. Auxiliary components such as a gas / liquid separator etc. (not shown) can be provided along the process gas path between the low-pressure discharge port 21 and the high-pressure suction port 25. The high-pressure compressor section 1A also includes a high-pressure discharge port 29 that is fluidly connected to the process gas delivery pipeline 31. The process gas delivery pipeline 21 can be fluidly connected to a high-pressure compressor (not shown).

[0026] Process gas enters compressor 1 from process gas supply line 23 through the low-pressure suction port 19, is sequentially compressed by the impellers 17A, 17B, 17C of the low-pressure compressor section 1A, and is delivered to the intermediate cooler 27 through the low-pressure discharge port 21. Before being delivered to the high-pressure compressor section 1A, the partially compressed process gas is cooled in the intermediate cooler 27, for example, by heat exchange with air, water, or another cooling fluid. The cooled and partially compressed process gas is further compressed by the impellers 17D, 17E, and 17F of the high-pressure compressor section 1B and is finally discharged through the high-pressure discharge port 29.

[0027] Compressor 1 also includes a low-pressure balance line 41 that fluidly connects the low-pressure discharge port 21 to the outside of an end seal 43 disposed inside the low-pressure dry gas seal 13. Specifically, the low-pressure balance line 41 is connected to the volume between the process labyrinth seal 14 of the dry gas seal 13 and the end seal 43.

[0028] Compressor 1 also includes a high-pressure balance line 45 that fluidly connects the high-pressure suction port 25 to the outside of a balance drum seal 47 disposed inside the high-pressure dry gas seal 15 and surrounding the balance drum 48. Specifically, the high-pressure balance line 45 is connected to the volume between the process labyrinth seal 16 of the dry gas seal 15 and the balance drum 48.

[0029] The dry gas seals 13, 15 must be supplied with seal gas during normal operating conditions and when compressor 1 is not operating. During normal operation, process gas can be diverted from the delivery line 31 and processed in a 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 buffer the pressure of the two dry gas seals 13, 15.

[0030] With the compressor shut down, the process gas flow through the compressor stage is interrupted. A shutdown stable pressure (SOP) will be established in the low-pressure compressor section 1A, and a different, higher shutdown stable pressure will be established in the high-pressure compressor section 1B. The check valve 28 prevents the high-pressure process gas from flowing back from the high-pressure compressor section 1B towards the low-pressure compressor section 1A through the intercooler 27. The process gas will only flow from the high-pressure compressor section 1B towards the low-pressure compressor section through the inter-stage seal 18. Therefore, the two SOPs will only equalize after a relatively long period of time. Thus, after shutdown and for a relatively long period of time, the gas pressure inside the low-pressure dry gas seal 13 will be significantly lower than the gas pressure inside the high-pressure dry gas seal 15. In some examples, the gas pressure inside the low-pressure dry gas seal 13 (i.e., inside the process labyrinth seal 14) will be 50% or less of the gas pressure inside the high-pressure dry gas seal 15 (i.e., inside the process labyrinth seal 16). Different pressure seal gases are required to cushion the two dry gas seals 13, 15.

[0031] To avoid the need for an external seal gas source to cushion the two dry gas seals during the SOP equalization period after the compressor is shut down, the compressor system is provided with a novel seal gas supply system, which is schematically shown in Figure 2 and is omitted for clarity from Figure 1 for clarity.

[0032] In Figure 2 only the main components of the compressor 1 are shown, which contribute to a better understanding of the seal gas supply system of the present disclosure. The seal gas supply system is generally labeled 50 in Figure 2 for clarity. Figure 2 The shaft 7, the low-pressure dry gas seal 13, the high-pressure dry gas seal 15, the end seal 43, and the balance drum seal 47 are schematically shown in Figure 2 for clarity.

[0033] 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 can be arranged in parallel with the seal gas booster 65. The seal gas booster 67 can be driven by an electric motor 66 through a variable frequency drive 68 to adjust the flow rate of the seal gas booster 66 to the requirements of the dry gas seals 13, 15.

[0034] The booster 65 may include a regenerative compressor that is optimally suited to the head and flow rate values involved. For example, a suitable regenerative compressor may be a compressor adapted to provide a flow rate in the range of 10 m 3 / h to 30 m 3 / h and a head of up to about 2 bar.

[0035] The booster inlet 67 may be fluidly connected to the high-pressure discharge port 29 or the process gas delivery line 31 via a seal gas treatment unit 73. The seal gas treatment unit 73 can 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.

[0036] The booster outlet 69 is fluidly connected to the low-pressure dry gas seal 13 and the high-pressure dry gas seal 15 via corresponding control valves. More specifically, the booster outlet 69 is fluidly connected to the low-pressure dry gas seal 13 via a first seal gas feed line 81 that includes a first control valve 83 disposed in the first seal gas feed line 81. Additionally, the booster outlet 69 is fluidly connected to the high-pressure dry gas seal 15 via a second seal gas feed line 85 that includes a second control valve 87 disposed in the second seal gas feed line 85.

[0037] 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 rate control loop. Similarly, the second control valve 87 is controlled by a second valve control loop 91, which may be a pressure control loop or a flow rate control loop.

[0038] In some embodiments, the first valve control loop 89 may include a first differential pressure sensor 89.1 that is adapted to detect the differential pressure between the vent line 53 and a point downstream of the first control valve 83. The first valve control loop 89 may also include a second differential pressure sensor 89.2 that is located between a point downstream of the first control valve 83 and a point between the internal labyrinth seal 14 and the end seal 43. The first valve control loop 89 may also include a pressure sensor 89.3. A comparator 89.4 compares the signals from the first differential pressure sensor 89.1 and the second differential pressure sensor 89.2. These signals are proportional to the difference between the respective set points and the actual differential pressure detected by the sensors. The signal having the highest value may be selected as the control signal for the first control valve 83.

[0039] Similarly, in some embodiments, the second valve control loop 91 may include a first differential pressure sensor 91.1 that is adapted to detect the differential pressure between the vent line 55 and a point downstream of the second control valve 87. The second valve control loop 91 may also include a second differential pressure sensor 91.2 that is located between a point downstream of the second control valve 87 and a point between the internal labyrinth seal 16 and the balance drum seal 47. The second valve control loop 91 may also include a pressure sensor 91.3. A comparator 91.4 compares the signals from the first differential pressure sensor 91.1 and the second differential pressure sensor 91.2. These signals are proportional to the difference between the respective set points and the actual differential pressure detected by the sensors. The signal having the highest value may be selected as the control signal for the second control valve 87.

[0040] After the compressor is shut down, the SOPs in the low-pressure section 1A and the high-pressure section 1B are significantly different, for example, differing by more than 50%. At this time point, the first control valve 83 may be closed or only partially opened, for example, between 10% and 20%, because the pressure inside the dry gas seal 13 is low. In contrast, the second control valve 87 will be fully opened or almost fully opened, for example, opened between 60% and 80%. Due to the leakage through the inter-stage seal 18, the difference between the two SOPs in the low-pressure section 1A and the high-pressure section 1B tends to become smaller, that is, the SOP in the high-pressure section 1B will decrease and the SOP in the low-pressure section 1B will increase. The change in the SOP is detected by the above-mentioned differential pressure sensors, and the control loops 89 and 91 will thus gradually close the second control valve 87 and gradually open the first control valve 83.

[0041] Therefore, with the above-mentioned seal gas supply system 60, the first control valve 83 and the second control valve 87 can be controlled independently of each other to adjust the seal gas flow rates of the low-pressure dry gas seal 13 and the high-pressure dry gas seal 15, so as to balance the pressure changes inside the respective dry gas seals 13, 15. Specifically, the gas leakage through the inter-stage seal 18 will tend to equalize the gas pressures in the low-pressure section and the high-pressure section of the compressor, resulting in an increase in the pressure inside the low-pressure dry gas seal 13 and a decrease in the pressure inside the high-pressure dry gas seal 15. Therefore, the seal gas flow rate towards the high-pressure dry gas seal 15 will decrease, while the seal gas flow rate towards the low-pressure dry gas seal will increase.

[0042] 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 the respective control valves 83, 87, which are in turn controlled by the respective first control loop 89 and second control loop 91, taking into account the pressure inside each dry gas seal.

[0043] For example, after shutdown, when different SOPs will be established in the low-pressure compressor section 1A and the high-pressure compressor section, correspondingly, the second control valve 87 (which supplies seal gas to the high-pressure dry gas seal 15) can be opened more than 60%, while the first control valve 83 (which supplies seal gas to the low-pressure dry gas seal 13) can be partially closed, for example, 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.

[0044] Due to leakage through the interstage seal 18, the SOP in the low-pressure compressor section 1A increases and the SOP in the high-pressure compressor section decreases. At this time, the flow rate of the seal gas through the second control valve 87 will decrease and the flow rate of the seal gas through the first control valve 83 will increase. When the two SOPs are balanced, that is, once the same pressure is established in the low-pressure compressor section 1A and the high-pressure compressor section 1B, the flow rates of the seal gas through the first control valve 83 and the second control valve 87 will become substantially equal to each other.

[0045] A separate seal gas source (such as an inert gas such as nitrogen) can be further connected to the inlet 67 of the seal gas booster, as Figure 2 schematically shown at 93 in

[0046] Exemplary embodiments have been disclosed above and illustrated in the drawings. Those skilled in the art will understand that various changes, omissions, and additions can be made to the specifically disclosed content herein without departing from the scope of the invention as defined in the following claims.

Claims

1. A compressor system, the compressor system comprising: A multi-stage compressor (1), the multi-stage compressor comprising: A rotating shaft (7), the rotating shaft being received for rotation within a compressor housing (3) And having a low-pressure shaft end (7A) and a high-pressure shaft end (7B); A low-pressure compressor section (1A), the low-pressure compressor section having a low-pressure suction port (19) and a low-pressure discharge port (21); A high-pressure compressor section (1B), the high-pressure compressor section having a high-pressure suction port (25) and a high-pressure discharge port (29); wherein the low-pressure compressor section (1A) and the high-pressure compressor section (1B) are configured in a direct-through arrangement, and the low-pressure discharge port (21) and the high-pressure suction port (25) are arranged between the low-pressure suction port (19) and the high-pressure discharge port (29); A low-pressure dry gas seal (13), the low-pressure dry gas seal being located at the low-pressure shaft end (7A); and A high-pressure dry gas seal (15), the high-pressure dry gas seal being located at the high-pressure shaft end (7B); A seal gas supply system (60), the seal gas supply system comprising: A seal gas booster (65), the seal gas booster having a booster inlet (67) and a booster outlet (69); wherein the booster inlet (67) Is fluidly connected to the high-pressure discharge port (29) of the multi-stage compressor (1) to receive process gas therefrom; A first seal gas feed line (81), the first seal gas feed line fluidly connecting the booster outlet (69) to the low-pressure dry gas seal (13); A first control valve (83), the first control valve being arranged in the first seal gas feed line (81); A second seal gas feed line (85), the second seal gas feed line fluidly connecting the booster outlet (69) to the high-pressure dry gas seal (15); and A second control valve (87), the second control valve being arranged in the second seal gas feed line (85).

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

3. The compressor system according to claim 1 or 2, wherein the compressor system further comprises: A first valve control loop (89), the first valve control loop being adapted to control the first control valve (83); and a second valve control loop (91), the second valve control loop being adapted to control the second control valve (87).

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

5. The compressor system according to one or more of the preceding claims, wherein the compressor system further comprises: An inter-stage seal (18) disposed about the rotary shaft (7) between the low-pressure compressor section (1A) and the high-pressure compressor section (1B); and a balance drum (48) disposed at the high-pressure end (7B) of the rotary shaft (7); wherein the outside of the balance drum is fluidly connected to the low-pressure suction port (25).

6. A compressor system comprising: A multi-stage compressor (1) including: A low-pressure section (1A) and a high-pressure section (1B) in a direct-through configuration; A shaft (7) rotatably received in the compressor housing (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); and A high-pressure dry gas seal (15) at the high-pressure shaft end (7B); A seal gas supply system (60) including: A seal gas booster (65) having a booster inlet (67) and a booster outlet (69); wherein the booster inlet (67) is fluidly connected to the high-pressure discharge port (29) of the multi-stage compressor (1) to receive process gas therefrom; A first control valve (83) adapted to control the seal gas flow from the seal gas booster (65) to the low-pressure dry gas seal (13); and A second control valve (87) adapted to control the seal gas flow from the seal gas booster (65) to the high-pressure dry gas seal (15).

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

8. 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), the multi-stage compressor including a low-pressure section (1A) and a high-pressure section (1B) in a direct-through configuration; wherein the method comprises the steps of: Generating a seal gas flow at the seal gas booster outlet (69) of the seal gas booster (65); wherein the seal gas booster (65) includes a seal gas booster inlet (67) fluidly connected to the delivery side of the multi-stage compressor (1) to receive process gas therefrom; Feeding a first seal gas flow from the seal gas booster outlet (69) to the low-pressure dry gas seal (13) through the first control valve (83); Feeding a second seal gas flow from the seal gas booster outlet (69) to the high-pressure dry gas seal (15) through the second control valve (87); and Adjusting the first seal gas flow flowing through the first control valve (83) and adjusting the second seal gas flow flowing through the second control valve (87).

9. The method according to claim 8, the method further comprising the step of closing the multistage compressor, and wherein after the compressor is closed, the step of adjusting the first seal gas flow passing through the first control valve (83) and the second seal gas flow passing through the second control valve (87) comprises the following steps: When the shutdown stabilization pressure in the low-pressure compressor section (1A) increases and the shutdown stabilization pressure in the high-pressure compressor section (1B) decreases, the flow rate of the sealing gas flowing through the first control valve (83) is increased and the flow rate of the sealing gas flowing through the second control valve (87) is decreased.

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