Seal leakage gas recovery system and method using an ejector

Abstract

The system includes a rotary turbomachine (3) including a dry gas seal (9). A seal leakage gas collection line (14) fluidly connects the dry gas seal (9) to a seal leakage gas inlet (15) of an ejector (13). A seal leakage gas exhaust line (23) fluidly couples the dry gas seal (9) to a seal leakage gas exhaust (25) at an exhaust pressure lower than the seal leakage gas pressure. A leakage exhaust control valve (27) along the seal leakage gas exhaust line (23) is adapted to redirect at least a portion of the seal leakage gas in the seal leakage gas exhaust line (23). Also disclosed is a method for recovering seal gas leaking from a dry gas seal arrangement.

Description

[Technical Field]

[0001] The subject matter disclosed herein relates to turbomachines, and more particularly to compressors with dry gas seals. Embodiments of the present disclosure relate particularly to recovering seal leakage gas from dry gas seals. [Background technology]

[0002] Fossil fuels remain the primary energy source for the generation of thermal power required in several industrial processes, including electricity generation. Attempts have been made to reduce the environmental impact of this energy source. The cleanest fossil fuel is natural gas, which consists primarily of methane, because its combustion produces greater amounts of thermal energy than other hydrocarbons and offers significant environmental benefits, as it produces significantly less carbon dioxide and other pollutants that contribute to environmental impacts.

[0003] Nevertheless, the extraction and transportation of natural gas results in the release of unburned gases, primarily methane, into the atmosphere. This has serious implications regarding environmental impacts, as methane contributes to climate change, particularly its greenhouse effect. Indeed, like carbon dioxide, methane also traps heat in the atmosphere. Methane's global warming potential (GWP) over a 100-year period, a measure of how much heat a greenhouse gas traps in the atmosphere over a specific time horizon, is approximately 28 times higher than that of carbon dioxide. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, efforts have been made to reduce the amount of natural gas released into the atmosphere throughout the process of natural gas extraction, transportation, and use.

[0005] The primary role in this approach is played by the rotating seals of gas compressors. Dry gas seals have become increasingly popular as contactless seals for efficiently reducing process gas leakage from centrifugal compressors or other turbomachinery (Stahley, John S., "Dry Gas Seals Handbook," Copyright 2005 by Pennwell Corporation, ISBN 1-59370-062-8). Dry gas seals use the process gas flow to provide efficient contactless sealing between the rotating shaft and the stationary seal. Dry gas seals require a clean, dry gas flow to operate. Typically, the same gas processed by the compressor is used as the sealing gas. The sealing gas is taken from the compressor's delivery side, and the compressor operates to provide sufficient pressurized sealing gas.

[0006] In compressors for processing natural gas, for example in gas pipelines, natural gas leaks from dry gas seals are usually burned in a flare, which avoids emitting the natural gas into the atmosphere, but in any case produces greenhouse gases (carbon dioxide) and destroys a certain amount of valuable feedstock.

[0007] Therefore, it has been proposed to recover the gas leaking from the dry gas seal. A circuit for hydrocarbon recovery in a centrifugal compressor system using a dry gas seal is disclosed in a paper presented at the Gas Turbines for Energy Network Symposium (Banff, Alberta, Canada) in October 2019, by Sergio Cipriani et al., entitled "Turbomachinery Hydrocarbon Loss Recovery Systems."

[0008] A similar problem occurs in compressors used to process refrigerants in natural gas liquefaction systems. The refrigerant fluid is often a hydrocarbon, such as methane, or a mixed refrigerant containing hydrocarbons. Refrigerant leaks from dry gas seals in refrigerant compressors pose similar problems to hydrocarbon emissions from pipeline compressors.

[0009] Continuing research has been directed towards developing systems and methods for efficiently recovering gas leaking from dry gas seals in turbomachinery and increasing its pressure so that the recovered leakage gas can be reused as seal gas or sent for further processing.

[0010] According to embodiments disclosed herein, a system for recovering seal leakage gas includes a rotary turbomachine including at least one dry gas seal. The system further includes an ejector having a drive gas inlet at a drive gas inlet pressure, a seal leakage gas inlet at a seal leakage gas pressure, and a mixed gas outlet at a mixed gas outlet pressure higher than the seal leakage gas pressure. A seal leakage gas collection line fluidly connects the dry gas seal to the seal leakage gas inlet of the ejector. A seal leakage gas exhaust line fluidly couples the dry gas seal to a seal leakage gas exhaust at an exhaust pressure lower than the seal leakage gas pressure. A leakage exhaust control valve provided along the seal leakage gas exhaust line is adapted to redirect the seal leakage gas in the seal leakage gas exhaust line.

[0011] The leakage discharge control valve is operatively connected to a flow parameter sensor adapted to detect a flow parameter of the seal leakage gas in the seal leakage gas collection line toward the seal leakage gas inlet of the ejector, and is controlled based on the flow parameter detected by the flow parameter sensor.

[0012] In some embodiments, the leakage exhaust control valve is a pressure control valve and the flow parameter is the pressure in the seal leakage gas collection line, while in other embodiments, the leakage exhaust control valve is a flow control valve and the flow parameter is the flow rate in the seal leakage collection line.

[0013] The leakage discharge control valve can fully or partially redirect seal gas leaking from the dry gas seal(s) to the seal leakage gas discharge line if the ejector is not operating for any reason, such as because there is no or insufficient drive gas available at the ejector drive gas inlet, or if there is excessive seal gas leakage from the dry gas seal that cannot be managed by the ejector alone. The provision of a leakage discharge control valve increases the availability of the turbomachine, i.e., the conditions under which the turbomachine can operate.

[0014] According to another aspect, disclosed herein is a method for recovering seal leakage gas from a dry gas seal of a rotary turbomachine. The method includes operating the turbomachine and supplying a seal gas to at least one dry gas seal. The method further includes recovering the seal leakage gas from the at least one dry gas seal and delivering the recovered seal leakage gas to a seal leakage gas inlet of an ejector at a seal leakage gas pressure. The ejector further includes a drive gas inlet that receives a drive gas flow at the drive gas pressure and a mixed gas outlet. The mixed gas is delivered to the mixed gas outlet of the ejector at a mixed gas pressure higher than the seal leakage gas pressure. The seal leakage gas is at least partially diverted from the at least one dry gas seal to a seal leakage gas exhaust at a pressure lower than the seal leakage gas pressure via a leakage exhaust control valve controlled based on a flow parameter of the seal leakage gas flowing through a seal leakage gas collection line. The flow parameter may be, for example, pressure or flow rate.

[0015] Further features and embodiments of the systems and methods are disclosed below and in the appended claims. [Brief explanation of the drawings]

[0016] Reference will now be made briefly to the accompanying drawings, in which: [Figure 1]FIG. 1 is a schematic diagram of an embodiment of a system including a rotary turbomachine and an ejector for recovering seal gas that leaks from a dry gas seal of the turbomachine. [Figure 2] FIG. 2 is a schematic diagram of one embodiment of a system including a compressor and a dry gas seal with a seal leakage gas recovery arrangement using an ejector. [Figure 3] FIG. 3 is a schematic diagram of a further embodiment. [Figure 4] FIG. 4 is a flow diagram summarizing the methods disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0017] According to the present disclosure, a turbomachine, particularly a compressor, includes one or more dry gas seals. The dry gas seals are supplied with a seal gas that is partially discharged from the dry gas seal(s). The gas discharged from the dry gas seal(s) is referred to herein as seal leakage gas.

[0018] To recover the seal leakage gas, a recovery circuit including an ejector is provided. The ejector uses a drive gas to increase the pressure of the seal leakage gas. In embodiments where the turbomachine is a compressor, the drive gas and the seal gas may be compressed gas processed by the compressor. The ejector increases the pressure of the seal leakage gas so that it can be sent to the suction side of the compressor or to another recovery line for further processing.

[0019] 1, in a first embodiment, a system 1 includes a turbomachine 3 having an inlet 5 and an outlet 7. The inlet 5 is fluidly coupled to an inlet line 5A, and the outlet 7 is fluidly coupled to an outlet or delivery line 7A. In an embodiment, the turbomachine 3 may be a compressor, such as an axial compressor or a centrifugal compressor.

[0020] The turbomachine 3 includes one or more dry gas seals, for example, two dry gas seals 9. Seal gas is delivered to the dry gas seals 9 through a seal gas delivery line 11. As is known, a portion of the seal gas delivered to the dry gas seals 9 is discharged from the turbomachine 3 at low pressure. Embodiments of the disclosed system include an arrangement for recovering at least a portion of the seal leakage gas and increasing its pressure so that the recovered seal leakage gas can be further processed, for example, reinjected into the turbomachine, rather than being discharged to the environment or burned in a flare. In some embodiments, the dry gas seal 9 can include a tandem dry gas seal having a primary vent and a secondary vent. At least the primary vent is recovered and its pressure increased for reinjection into the turbomachine or for other processing.

[0021] To increase the pressure of the seal leakage gas, the system 1 includes an ejector 13 having a seal leakage gas inlet 15, a drive gas inlet, and a mixed gas outlet 19. The seal leakage gas released from the dry gas seal 9 is collected in a seal leakage gas collection line 14 that connects the dry gas seal 9 to the seal leakage gas inlet 15 of the ejector 13.

[0022] The seal leakage gas enters the ejector 13 through the seal leakage gas inlet 15 at the seal leakage gas pressure, is delivered through the drive gas inlet line, and is entrained by the flow of drive gas that enters the ejector 13 through the drive gas inlet 17 at a drive gas inlet pressure higher than the seal leakage gas pressure. The mixture of drive gas and seal leakage gas exits the ejector 13 through the mixed gas outlet 19 at the mixed gas outlet pressure. The mixed gas outlet pressure is lower than the drive gas inlet pressure but higher than the seal leakage gas inlet pressure. The mixed gas exiting the ejector 13 can be delivered through line 20 to any suitable processing section 21.

[0023] The seal leakage gas discharge line 23 fluidly couples the dry gas seal 9 to a seal leakage gas discharge 25 at a discharge pressure lower than the seal leakage gas pressure at the seal leakage gas inlet 15 of the ejector 13. A leakage discharge control valve 27 along the seal leakage gas discharge line 23 is adapted to partially or completely discharge the seal leakage gas released from the dry gas seal 9 towards the seal leakage gas discharge 25 when needed, depending on the operating conditions of the turbomachine 3 and / or the ejector 13. The leakage discharge control valve 27 may be a pressure control valve operatively coupled to a pressure sensor 29 adapted to detect the pressure at the seal leakage gas inlet 15 of the ejector 13. In other embodiments, the leakage discharge control valve 27 may be a flow control valve.

[0024] If the ejector 13 cannot completely process the seal leakage gas released from the dry gas seal 9, for example, because there is no or insufficient drive gas available at the drive gas inlet 17, or if the flow rate of the released seal leakage gas exceeds the ejector capacity, the leakage discharge control valve 27 may divert a portion of the seal leakage gas flow rate to the seal leakage gas discharge 25, thus partializing or choking the flow rate processed by the ejector 13. In some cases, for example, when the ejector 13 is not operating, the seal leakage gas may be completely diverted through the leakage discharge control valve 27 to the seal leakage gas discharge line 23.

[0025] Using the leakage discharge control valve 27 and the seal leakage gas discharge line 23, the turbomachine 3 can operate in situations where the ejector 13 is either inoperable or unable to handle the entire seal leakage gas flow rate from the dry gas seal 9. This increases the availability of the turbomachine 3.

[0026] In some embodiments, a check valve 51 may be provided in the seal leakage gas collection line 14, preferably upstream of the pressure sensor 29. A drive gas control valve 52 may be positioned in the drive gas inlet line upstream of the drive gas inlet 17. A further check valve 53 may be positioned in the line 20 through which the mixed gas is delivered from the ejector 13. The drive gas control valve may be a pressure control valve, i.e., a valve controlled by a pressure signal.

[0027] In some embodiments, in addition to or instead of the drive gas control valve 52, a recycle line 54 may be provided in anti-parallel to the ejector 13. The recycle line 54 has an inlet fluidly coupled to the line 20, for example, between the mixed gas outlet 19 of the ejector 13 and the check valve 53. The recycle line 54 further has an outlet fluidly connected to the drive gas inlet line upstream of the drive gas inlet 17 of the ejector 13. A recycle control valve 56 is provided along the recycle line 54. The recycle control valve 56 may be a pressure control valve, i.e., a valve controlled by a pressure signal.

[0028] Drive gas control valve 52 and recycle control valve 56 may be controlled by a pressure signal that may be generated by pressure sensor 29 or another pressure sensing device. The function and operation of this arrangement is described in more detail below with reference to FIG.

[0029] As will be apparent from the following description of the control operations performed by the above valve configurations, only valve 52 may be provided in the system, or only valve 56 and associated recycle line 54. In some embodiments, both valves 56 and 52 may be present and used alternatively, depending on the control mode being implemented.

[0030] Continuing with reference to Figure 1, a further embodiment of a system according to the present disclosure is shown in Figure 2. The system 1 of Figure 2 includes a compressor 3, e.g., a dynamic compressor such as a centrifugal compressor or an axial compressor. The compressor 3 has a suction side 5 fluidly coupled to an inlet line 5A and a delivery side 7 fluidly coupled to an outlet or delivery line 7A.

[0031] The compressor 3 includes one or more dry gas seals, for example, two dry gas seals 9. The dry gas seal 9 can be a single dry gas seal or a tandem dry gas seal having a primary vent and a secondary vent.

[0032] 2, compressed process gas is extracted from the compressor or from its downstream delivery line, treated in seal gas treatment unit 33, and used as seal gas for dry gas seal 9. Line 31 diverts a small amount of compressed gas delivered by compressor 3 towards seal gas treatment unit 33, which is fluidly coupled to dry gas seal 9, for example, through one or more seal gas delivery lines 11, 11A, 11B. A pressure reducing valve 35 is disposed between seal gas treatment unit 33 and dry gas seal 9 to reduce the gas pressure to a suitable pressure for injection into dry gas seal 9.

[0033] In a manner known per se, the seal gas treatment unit 33 may comprise a gas filter for removing impurities from the process gas before supplying the gas to the dry gas seal 9. Furthermore, a heating device may be provided in the seal gas treatment unit 33 for heating the gas above its dew point, thus preventing moisture contained in the seal gas from condensing in the dry gas seal 9.

[0034] 1, to collect seal leakage gas released from the dry gas seal 9, the system 1 of FIG. 2 includes an ejector 13 having a seal leakage gas inlet 15, a drive gas inlet 17, and a mixed gas outlet 19. The seal leakage gas released from the dry gas seal 9 is collected in a seal leakage gas collection line 14 that connects the dry gas seal 9 to the seal leakage gas inlet 15 of the ejector 13. In the embodiment of FIG. 2, the dry gas seal 9 is a tandem dry gas seal having a primary vent that is collected in the seal leakage gas collection line 14 and a secondary vent that is collected in line 16 and either vented to the environment or sent to a flare (not shown).

[0035] 1, the seal leakage gas enters ejector 13 through seal leakage gas inlet 15 at the seal leakage gas pressure and is entrained by the flow of drive gas which enters ejector 13 through drive gas inlet 17 at a drive gas inlet pressure higher than the seal leakage gas pressure. The mixture of drive gas and seal leakage gas exits ejector 13 through mixed gas outlet 19 at a mixed gas outlet pressure lower than the drive gas inlet pressure but higher than the seal leakage gas inlet pressure.

[0036] In the embodiment of FIG. 2, the drive gas used in ejector 13 is a small amount of compressed gas processed by compressor 3, slipped from delivery side 7 of compressor 3, and processed in seal gas treatment unit 33. In the schematic diagram of FIG. 2, only a portion of the gas delivered by seal gas treatment unit 33 is used as seal gas in dry gas seal 9. The remaining, compressed and treated gas stream is delivered to drive gas inlet 17 of ejector 13. A drive gas control valve 37 may be provided between seal gas treatment unit 33 and drive gas inlet 17 to adjust the drive gas flow rate and / or drive gas pressure at drive gas inlet 17 of ejector 13.

[0037] 2, the mixture of drive gas and seal leakage gas exiting ejector 13 at mixed gas outlet 19 is returned to suction side 5 of compressor 3. In some embodiments, the mixed gas may be processed through a suction scrubber (not shown) before entering suction side 5 of compressor 3.

[0038] The seal leakage gas discharge line 23 fluidly couples the dry gas seal 9 to a seal leakage gas discharge 25 at a discharge pressure lower than the seal leakage gas pressure at the seal leakage gas inlet 15 of the ejector 13. The seal leakage gas flowing through the seal leakage gas discharge line 23 can be sent to a flare (not shown) or discharged to the environment. If the ejector 13 is unavailable or cannot handle the entire seal leakage gas flow rate received at the seal leakage gas inlet 15, only a small portion of the seal leakage gas will flow toward the seal leakage gas discharge 25.

[0039] A leakage discharge control valve 27 along the seal leakage gas discharge line 23 is adapted to partially or completely discharge the seal leakage gas released by the dry gas seal 9 towards the seal leakage gas discharge 25 when needed, depending on the operating conditions of the compressor 3 and / or the ejector 13. The leakage discharge control valve 27 may be a pressure control valve operatively coupled to a pressure sensor 29 adapted to detect the pressure at the seal leakage gas inlet 15 of the ejector 13. In other embodiments, the leakage discharge control valve 27 may be a flow control valve or an actuated on-off valve.

[0040] For example, when the compressor 3 is stopped, the seal gas flow to the dry gas seal 9 is maintained, but the seal leakage gas cannot be processed through the ejector 13 because there is no drive gas flow available from the delivery side of the compressor 3. In this case, a small flow of seal leakage gas flows through the leakage discharge control valve 27 in the leakage gas discharge line 23.

[0041] Other situations may arise that require segmenting the flow of seal leakage gas from the dry gas seal 9 through the seal leakage gas collection line 14 to the ejector 13. For example, segmentation or choking may be required when the compressor 3 is operating in an off-design condition. In such cases, some or all of the seal leakage gas may flow through the leakage discharge control valve 27 toward the seal leakage gas discharge line 23.

[0042] A pressure sensor or flow meter may be provided to detect the pressure or flow rate of the seal leakage gas in the seal leakage gas collection line 14 .

[0043] 1, in FIG. 2 a check valve 51 may be positioned in the seal leakage gas collection line 14, preferably upstream of the pressure sensor 29. A drive gas control valve 52 may be positioned in the drive gas inlet line upstream of the drive gas inlet 17. A further check valve 53 may be positioned in line 20 through which the mixed gas is delivered from the ejector 13.

[0044] In some embodiments, in addition to or instead of drive gas control valve 52, a recycle line 54 may be provided in anti-parallel to ejector 13, with an inlet fluidly coupled to line 20 and an outlet fluidly coupled to the drive gas inlet line upstream of drive gas inlet 17 of ejector 13. A recycle control valve 56 may be disposed along recycle line 54.

[0045] In some embodiments, only the drive gas control valve 52 may be provided, and the recycle control valve 56 and associated recycle line 54 may be omitted. Conversely, in other embodiments, the recycle line 54 and respective recycle control valve 56 may be provided, and the drive gas control valve 52 may be omitted.

[0046] Drive gas control valve 52 and / or recycle control valve 56 may be controlled by a pressure signal that may be generated by pressure sensor 29 or by another suitable pressure sensing device.

[0047] The valve configurations described thus far can be used to manage a system in several transient situations according to the methods disclosed below.

[0048] According to one embodiment, the drive gas control valve 52 may be a pressure control valve that adjusts the drive gas flow rate as a function of the suction pressure of the leakage gas that must be recovered from the compressor dry gas seal, i.e., as a function of the pressure in the seal leakage gas collection line 14. When the pressure detected by the pressure sensor 29 or any other sensing arrangement in the seal leakage gas collection line 14 increases, the drive gas control valve 52 opens to increase the drive gas flow rate, thereby increasing the seal leakage gas flow rate removed from the seal leakage gas collection line 14 through the ejector 13. If the seal gas leakage continues to increase, and thus the pressure in the seal leakage gas collection line 14 increases, when the drive gas control valve 52 is fully opened, the leakage discharge control valve 27 gradually opens to send a portion of the leaking seal gas toward the flare or other seal leakage gas discharge 25. In this way, the turbomachine, e.g., the compressor 3, can continue to operate under normal operating conditions.

[0049] As the pressure in the seal leakage gas collection line 14 decreases, the leakage discharge control valve 27 gradually closes again under control of the pressure signal from the pressure sensor 29 until the leakage discharge control valve 27 is fully closed again. If the pressure in the seal leakage gas collection line 14 further decreases below the set value of the drive gas control valve 52, the drive gas control valve 52 begins to close, reducing the drive gas flow rate.

[0050] In particular, when the turbomachine 3 is a compressor, the leakage discharge control valve 27 is used when the compressor 3 is inoperable and / or during start-up, i.e., when there is insufficient or no drive gas pressure available to operate the ejector 13. During start-up, once the compression ratio of the compressor 3 reaches a sufficient value, pressurized drive gas can be diverted from the delivery line 7A towards the drive gas inlet 17 of the ejector 13, and the ejector 13 can begin operation.

[0051] When the discharge pressure of the compressor 3 increases, the drive gas flow rate increases, and the seal gas that leaks from the dry gas seal and is collected in the seal leakage gas collection line 14 begins to flow through the ejector 13 after being completely discharged from the leakage discharge control valve 27.

[0052] The leakage discharge control valve 27 may gradually close while the amount of drive gas increases. Eventually, all seal gas leakage is removed through the ejector 13, and the leakage discharge control valve 27 will close completely. This allows for a smooth switch from all leakage seal gas flowing through the leakage discharge control valve 27 to all leakage seal gas flowing through the ejector 13. Next, the leakage discharge control valve 27 will remain closed unless the set value of the drive gas control valve 52 is achieved under the continued increase in pressure in the seal leakage gas collection line 14, as described above.

[0053] Check valves 51 and 53 reduce or prevent backflow towards the dry gas seals of turbomachine 3 .

[0054] Using the recycle line 54 and the recycle control valve 56, different modes of controlling the system can be implemented. In this case, the recycle control valve 56 can be partially or fully opened to recycle a portion of the mixed gas flow delivered through the mixed gas outlet 19. Specifically, the recycle flow rate is such that the ejector 13 operates in a stable state even if the leakage seal gas flow rate decreases. The recycle control valve 56 is controlled based on the pressure detected by the pressure sensor 29 in the seal leakage gas collection line 14 or by other suitable pressure detection devices. When the pressure in the seal leakage gas collection line 14 increases, this means that a higher flow rate of the leakage seal gas is removed through the ejector 13. In response to this increase in pressure in the seal leakage gas collection line 14, the recycle control valve 56 partially closes to reduce the flow recycled through the recycle line 54.

[0055] If the full closure state of the recycle control valve 56 is achieved and the pressure in the seal leakage gas collection line 14 still needs to be reduced, the leakage discharge control valve 27 may begin to open and redirect some of the seal gas leaking from the dry gas seal towards the flare or any other seal leakage gas discharge 25.

[0056] If the pressure in the seal leakage gas collection line 14 decreases again after the leakage discharge control valve 27 opens, the leakage discharge control valve 27 can gradually close, and if the pressure in the seal leakage gas collection line 14 continues to decrease after the set value of the recycle control valve 56 is achieved and the leakage discharge control valve 27 is completely closed, the recycle control valve 56 begins to gradually open again as necessary under the control of the pressure signal from the pressure sensor 29.

[0057] Therefore, the ejector 13 operates in a stable state, and the compressor 3 or other turbomachinery can maintain normal operating conditions under a wide range of seal leakage gas flow rates.

[0058] The leakage discharge control valve 27 may be used during start-up of the turbomachine 3, particularly when the turbomachine 3 is a compressor and the drive gas for the ejector 13 is provided by the process gas delivered by the compressor 3. The seal gas leaking from the dry gas seal is fully vented through the leakage discharge control valve 27 until sufficient compressor delivery pressure is achieved to operate the ejector 13. Thereafter, once sufficient pressure is achieved in the drive gas stream, the ejector 13 can begin to operate and the leakage discharge control valve 27 may gradually close. The recycle control valve 56 may remain fully closed, or may be partially or fully open, as desired, as described above.

[0059] This allows for smooth switching even in this configuration from the total leakage seal gas flow via the leakage discharge control valve 27 to the total leakage seal gas flow via the ejector 13. As described above, the leakage discharge control valve 27 remains closed unless the set value of the recycle control valve 56 is achieved (the recycle control valve 56 is not completely closed) under the continued increase in pressure in the seal leakage gas collection line 14.

[0060] In the above-described embodiment, control valve 52 and control valve 56 are controlled using a pressure signal from pressure sensor 29, but it is not excluded to use a different flow parameter, e.g., flow rate, of the seal leakage gas in the seal leakage gas collection line.

[0061] In some embodiments, a seal gas make-up line 41 may fluidly connect the seal leakage gas collection line 14 with the seal gas delivery line 11. A control valve 43 is provided along the seal gas make-up line 41. The valve 43 may be a pressure control valve adapted to control the flow rate of seal gas from the seal gas delivery line 11 to the seal leakage gas collection line 14 to maintain the seal leakage gas pressure above a minimum threshold, which ensures proper operation of the second section of the tandem dry gas seal 9.

[0062] In the embodiment of Figure 2, the seal gas make-up line 41 is connected to the seal gas delivery line 11 downstream of the pressure reducing valve 35. In other embodiments not shown, the seal gas make-up line 41 may be connected upstream of the pressure reducing valve 35. In yet other embodiments, the make-up seal gas may be taken from a different point in the circuit, for example from the mixed gas outlet 19 of the ejector 13. This embodiment is shown in Figure 3, where the other components of the system are given the same reference numbers as in Figure 2 and will not be described again.

[0063] In the above-described embodiment, the drive gas is taken from the flow of seal gas delivered by the seal gas treatment unit 33, but since the drive gas does not need to be pre-treated as a seal gas, the drive gas flow can be taken from the delivery side 7 of the compressor 3 through a separate line 51 in which a flow control valve 53 is arranged, as shown by the dotted line in Figure 2.

[0064] In all embodiments disclosed herein, the turbomachine 3 can operate over a wide range of operating conditions and at off-design conditions, even when the ejector 13 cannot handle the entire seal leakage gas released by the dry gas seals 9 or is unavailable. Even a very simple seal leakage gas recovery system that uses an ejector to increase the pressure of the seal leakage gas released from the dry gas seals 9 increases the availability of the turbomachine 3.

[0065] In the above-described embodiment, the drive gas inlet 17 of the ejector 13 is in fluid communication with the compressor delivery side, and the drive gas entering the ejector may be at approximately the delivery pressure of the compressor 3. However, in other embodiments, the drive gas inlet 17 may be fluidly coupled to an intermediate stage of the compressor 3, provided that the process gas pressure at that stage is sufficiently high. In such cases, the drive gas entering the ejector 13 is at a pressure between the suction side pressure and the delivery side pressure of the compressor 3.

[0066] The method performed by the above-described system is summarized in the flow diagram of Figure 4. The method includes the steps of operating a turbomachine (3), supplying a seal gas to a dry gas seal (9), recovering seal leakage gas from the dry gas seal (9), delivering the recovered seal leakage gas to a seal leakage gas inlet (15) of an ejector (13) at a seal leakage gas pressure, delivering the mixed gas at a mixed gas outlet (19), and diverting the seal leakage gas from the dry gas seal (9) to a seal leakage gas discharge section (25) at a pressure lower than the seal leakage gas pressure.

[0067] 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 system for recovering seal leakage gas, the system comprising: a rotary turbomachine including at least one dry gas seal; an ejector having a drive gas inlet at the drive gas inlet pressure, a seal leakage gas inlet at the seal leakage gas pressure, and a mixed gas outlet at a mixed gas outlet pressure higher than the seal leakage gas pressure; a seal leakage gas collection line fluidly connecting the at least one dry gas seal to the seal leakage gas inlet of the ejector; a seal leakage gas exhaust line fluidly coupling the at least one dry gas seal to a seal leakage gas exhaust at an exhaust pressure lower than the seal leakage gas pressure; a leakage discharge control valve along the seal leakage gas discharge line and adapted to divert at least a portion of the seal leakage gas in the seal leakage gas discharge line; a flow parameter sensor adapted to detect a flow parameter of the seal leakage gas in the seal leakage gas collection line toward the seal leakage gas inlet of the ejector; a check valve disposed in the seal leakage gas collection line upstream of the flow parameter sensor; Equipped with The system wherein the leakage discharge control valve is operatively connected to the flow parameter sensor and is controlled based on the flow parameter detected by the flow parameter sensor.

2. The system of claim 1 , wherein the leakage discharge control valve is a pressure control valve and the flow parameter is a pressure in the seal leakage gas collection line.

3. The system of claim 1 , wherein the leakage discharge control valve is a flow control valve and the flow parameter is a flow rate in the seal leakage gas collection line.

4. 10. The system of claim 1, wherein the seal leakage gas exhaust is adapted to exhaust seal leakage gas to the atmosphere or to deliver the seal leakage gas to a flare.

5. The system of any one of claims 1 to 4, further comprising a drive gas control valve adapted to control at least one of a drive gas flow rate at the drive gas inlet of the ejector and a drive gas inlet pressure at the ejector.

6. The system of any one of claims 1 to 5, wherein the rotary turbomachine is a compressor having a suction side and a delivery side.

7. 7. The system of claim 6, wherein the leakage discharge control valve is adapted to wholly or partially divert the seal leakage gas from the at least one dry gas seal toward the seal leakage gas discharge when the compressor is in a stopped or off-design operating condition, depending on the operating condition of the compressor.

8. 8. The system of claim 6 or claim 7, wherein the drive gas inlet is in fluid communication with the compressor delivery side or compressor stage outlet side and is adapted to receive compressed process gas from the compressor at a compressor delivery pressure or at a pressure between a compressor suction pressure and a compressor delivery pressure.

9. The system of any one of claims 6 to 8, wherein the mixed gas outlet is fluidly coupled to the compressor suction side.

10. The system of any one of claims 6 to 9, further comprising a seal gas treatment unit having a gas inlet and a gas outlet fluidly coupled with the at least one dry gas seal, wherein the drive gas inlet of the ejector is fluidly coupled with the gas outlet of the seal gas treatment unit.

11. 11. The system of claim 1, further comprising a seal gas make-up line having an inlet fluidly coupled to the mixed gas outlet of the ejector and an outlet fluidly coupled to the seal leakage gas collection line, the seal leakage gas collection line being adapted to supply make-up gas to the seal leakage gas collection line.

12. 11. The system of claim 10, further comprising a seal gas make-up line fluidly coupled to the seal leakage gas collection line and the gas outlet of the seal gas treatment unit, the make-up gas being adapted to supply make-up gas from the seal gas treatment unit to the seal leakage gas collection line.

13. 13. The system of claim 11 or 12, further comprising a make-up control valve along the seal gas make-up line and adapted to control one of make-up gas flow rate toward the seal leakage gas collection line and make-up gas pressure in the seal leakage gas collection line.

14. The system of any one of claims 1 to 13, further comprising a control valve adapted to modify a drive gas flow rate through the ejector based on a value of the flow parameter of the seal leakage gas in the seal leakage gas collection line.

15. 15. The system of claim 14, wherein the control valve adapted to modify the flow rate through the ejector is disposed on a drive gas inlet line fluidly coupled to a drive gas inlet of the ejector and is controlled such that the drive gas flow rate is adjusted based on the flow parameters in the seal leakage gas collection line.

16. 15. The system of claim 14, wherein the control valve adapted to modify the flow rate through the ejector is arranged on a recycle line arranged in antiparallel to the ejector, and is controlled so that the flow rate of the mixed gas recycled through the recycle line from the mixed gas outlet to the drive gas inlet is adjusted based on the pressure in the seal leakage gas collection line.

17. 1. A method for recovering seal leakage gas from at least one dry gas seal of a rotary turbomachine, the method comprising: operating the rotary turbomachine; supplying a seal gas to the at least one dry gas seal; collecting seal leakage gas from the at least one dry gas seal and delivering the collected seal leakage gas through a seal leakage gas collection line to a seal leakage gas inlet of an ejector at a seal leakage gas pressure, the ejector further including a drive gas inlet receiving a drive gas flow at a drive gas pressure and a mixed gas outlet; delivering a mixed gas at the mixed gas outlet at a mixed gas pressure greater than the seal leakage gas pressure; detecting a flow parameter of the seal leakage gas flowing in the seal leakage gas collection line with a flow parameter sensor disposed in the seal leakage gas collection line downstream of a check valve; and at least partially diverting the seal leakage gas from the at least one dry gas seal to a seal leakage gas exhaust at a pressure lower than the seal leakage gas pressure through a leakage exhaust control valve controlled based on the flow parameter.

18. The method of claim 17 , wherein the flow parameter is a pressure or a flow rate of the seal leakage gas in the seal leakage gas collection line.

19. 19. The method of claim 17 or claim 18, wherein the rotary turbomachine is a gas compressor including a suction side and a delivery side, and wherein the step of supplying seal gas to the at least one dry gas seal includes the step of diverting compressed process gas from the compressor toward the at least one dry gas seal.

20. 20. The method of claim 19, wherein the mixed gas is returned to the suction side of the compressor.

21. 21. The method of claim 17, further comprising controlling a drive gas flow rate in the ejector based on the flow parameters of the seal leakage gas flowing in the seal leakage gas collection line.

22. 22. The method of claim 21, wherein controlling the drive gas flow rate in the ejector comprises adjusting the drive gas flow rate at the drive gas inlet of the ejector through a drive gas control valve in a drive gas inlet line fluidly coupled to the drive gas inlet, the control valve being controlled based on the flow parameter.

23. 22. The method of claim 21, wherein controlling the drive gas flow rate in the ejector includes recycling mixed gas from the mixed gas outlet of the ejector to the drive gas inlet of the ejector through a recycle control valve, the recycle control valve being controlled based on the flow parameter.

24. The method of any one of claims 17 to 23, further comprising the step of controlling the seal leakage gas pressure by delivering make-up gas to the seal gas make-up line.

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