Abstract:
A dry gas mechanical seal system configured to inhibit the emission of process gas. The mechanical seal system having tandem first and second stage seals, and a single separation gas supply subsystem configured to direct a supply of separation gas from an inlet through interfacing portions of the first stage seal into a process cavity and from the inlet through the interfacing portions of the second stage seal and out through an outlet to the atmosphere, thereby inhibiting the emission of process gas between a compressor housing and a rotating compressor shaft.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/348,551 filed Jun. 10, 2016, the contents of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to mechanical seals, and more particularly to non-contacting, gas lubricated seals for rotating components. 
       BACKGROUND 
       [0003]    In the petrochemical industry, centrifugal compressors may be located at intervals along a natural gas pipeline to boost the gas pressure for processing, to counter the effect of flow losses along the transmission pipelines and to generally keep the gas moving towards its destination. These compressors can be used upstream (during exploration and production), midstream (during processing, storage and transportation), or downstream (during natural gas/and petrochemical refining, transmission and distribution) in a petrochemical process. These centrifugal compressors can also be used to transport other fluids. 
         [0004]    To move natural gas or other fluids, centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, thereby increasing the velocity of the gas. A diffuser (divergent duct) converts the velocity energy to pressure energy. 
         [0005]    Dry gas seals may be used to reduce frictional wear on the rotating components while preventing leakage of the centrifuged or processed gas. To further inhibit leakage of processed gas into the atmosphere, some centrifugal compressors can include a pair of dry gas seals working in tandem. One example of such a mechanical seal system is described in U.S. Pat. No. 8,651,801, the contents of which are incorporated by reference herein. 
         [0006]    Referring to  FIG. 1 , a partial cross-sectional view of the tandem non-contacting dry gas seal arrangement  100  of the &#39;801 patent is depicted. At least a portion of the seal arrangement  100  is positioned between a rotating compressor shaft  102  and a compressor housing  104 . The rotating compressor shaft  102  is operably coupled to a compressor impeller (not shown) disposed in a process cavity  106  of the compressor, and is supported by the housing  104  via a bearing (not shown) disposed in a bearing cavity  108  of the housing  104 . A bore  110  formed in the compressor housing  104  extends between the process cavity  106  and the bearing cavity  108  and defines an annular seal chamber  112 . A shroud or labyrinth seal  114 , which extends over a radially extending opening formed between the rotating compressor shaft  102  and the compressor housing  104 , inhibits the free flow of process gas from the process cavity  106  into the bore  110 . 
         [0007]    Process gas present in the process cavity  106 , which can reach pressures of 6500 psig (450 bar-g), is sealed from the bearing cavity  108  and the atmosphere or surrounding environment by a first stage seal  116  and a second stage seal  118 . The first stage seal  116  includes a rotating ring  120  (alternatively referred to as a mating ring) operably coupled to rotating compressor shaft  102  via sleeve  122 . Rotating ring  120  defines a radial seal face  124  in relatively rotatable sealing relation with a radial seal face  126  of a non-rotating or stationary ring  128  (alternatively referred to as a primary ring). The stationary ring  128  is operably coupled to the compressor housing  104  via a biasing spring  130  and a spring carrier ring  132 , thereby enabling axial movement of the stationary ring  128  relative to the rotating ring  120 , so as to enable dimensional changes in the gap width between the rotating and stationary seal faces  124 ,  126 . Generally, the biasing spring  130  in the spring carrier ring  132  biases the stationary ring  128  towards the rotating ring  120 . A pressurized gas introduced between the seal faces  124 ,  126  presents a counteracting force against the biasing spring  130  to increase the gap width between the seal faces  124 ,  126 , so as to enable effective sealing while inhibiting frictional wear of the seal faces  124 ,  126  to enhance durability. The second stage seal  118  is constructed in a similar manner. 
         [0008]    During operation, a flow of diverted process gas referred to as “sealing gas” is provided to the first stage seal  116 . The diverted process gas is generally filtered and treated in a gas conditioning unit (not shown), for example by heating and/or drying the process gas to remove vapor particles and liquids, prior to delivery to the first stage seal  116 . Once properly conditioned, the sealing gas, which is usually pressurized at or above the pressure of the process gas in the process cavity  106 , flows through an inlet  134 , into a chamber  136 , through the first stage seal  116 , into a chamber  138 , and out through an outlet  140 . Additionally, due to the pressure differential, a portion of the sealing gas typically flows past the labyrinth seal  114  and into the process cavity  106 , thus creating a gas flow in a direction that prevents unfiltered and untreated process gas from entering the annular seal chamber  112 . 
         [0009]    In a similar manner, a “barrier gas,” which is typically an inert gas such as nitrogen (N 2 ), is provided to the second stage seal  118 . The barrier gas, which is usually pressurized to a pressure slightly higher than the pressure of the gases in the chamber  138 , flows through an inlet  142 , into a chamber  144 , through second stage seal  118 , into a chamber  146 , and out through an outlet  148 . Additionally, a portion of the barrier gas flows from the chamber  144  to the chamber  138 , and out through the outlet  140  with the sealing gas. 
         [0010]    In some seal arrangements, an additional gas seal  150 , referred to as a “separation gas seal” can be configured to isolate the annular seal chamber  112  from oil within the bearing chamber  108 . The separation gas flows through inlet  152 , through the separation gas seal  150 , into a chamber  146 , and out through an outlet  148 . 
         [0011]    The portion of the flow of the filtered and treated process gas (sealing gas), which in some cases is natural gas consisting mostly of methane, exits through the outlet  140  and often a portion of it is ported directly to the atmosphere. This leakage, which is typically around eight standard cubic feet per minute (SCFM) per centrifugal compressor, has been considered by the industry to be an acceptable amount. 
         [0012]    Methane (CH 4 ) is a greenhouse gas that has been shown to adversely affect climate change. Recent years have seen rising levels of methane emissions to the atmosphere due to increasing availability of natural gas resources coupled with aging natural gas distribution systems. Presently, it is estimated that 20% of methane leaks occur within natural gas distribution systems. Centrifugal compressor leakage is one of the largest sources of methane emissions in natural gas distribution systems. According to some estimates, compressor emissions account for roughly 500 metric tons of methane leakage per annum per facility. 
         [0013]    A system that further reduces the emission of natural gas or other process gases to the atmosphere, without requiring a costly replacement of numerous centrifugal compressor components, would provide a distinct advantage over conventional systems presently used in the natural gas industry. 
       SUMMARY 
       [0014]    Embodiments of the present disclosure provide a dry gas seal system configured to pump a separating gas upstream into the process chamber, thereby reversing the normal flow of gas across the first seal stage for the purpose of minimizing the emission of process gas leakage between a compressor housing and rotating compressor shaft of the dry gas seal system to near zero levels. The dry gas seal system utilizes a low-pressure clean, inert gas in place of conditioned methane or other process gas. Through rotation of a grooved rotating ring of a first stage seal, the inert gas is pressurized to a pressure higher than that of the process gas, thereby enabling a flow of the inert gas into the process gas, such that little to no process gas is vented or leaked to the atmosphere or surrounding environment. Accordingly, embodiments of the present disclosure provide a more environmentally friendly centrifugal compressor seal system that serves to decrease methane production losses. 
         [0015]    One embodiment of the present disclosure provides a tandem, non-contacting dry gas mechanical seal system for a compressor configured to inhibit the emission of process gas between a stationary compressor housing and a rotating compressor shaft. The mechanical seal system can include a first stage seal, a second stage seal and a single separation gas supply subsystem. The first stage seal can include a first rotating ring operably coupled to the compressor shaft, and a first stationary ring operably biased towards the first rotating ring by a first biasing mechanism operably coupled to the compressor housing. The first rotating ring can define spiral shaped grooves configured to pressurize gas passing between the interfacing portions of the first rotating ring and the first stationary ring to partially counteract the biasing force of the first biasing mechanism. The second stage seal can include a second rotating ring operably coupled to the compressor shaft, and a second stationary ring operably biased towards the second rotating ring by a second biasing mechanism operably coupled to the compressor housing. The interfacing portions of the second rotating ring and the second stationary ring can be configured to pressurize gas passing between the interfacing portions to partially counteract the biasing force of the second biasing mechanism. The single separation gas supply subsystem can be configured to direct a supply of separation gas from an inlet to interfacing portions of the first stage seal and into a process cavity, and from the inlet through the interfacing portions of the second stage seal and out through an outlet to the atmosphere, thereby inhibiting the emission of process gas between the compressor housing and rotating compressor shaft. 
         [0016]    Another embodiment of the present disclosure provides a non-contacting dry gas mechanical seal system for a compressor configured to inhibit the emission of process gas between a stationary compressor housing and a rotating compressor. The mechanical seal system can include a mechanical seal and a separation gas supply subsystem. The mechanical seal can include a rotating ring operably coupled to the compressor shaft, and a stationary ring operably biased towards the first rotating ring by a biasing mechanism operably coupled to the compressor housing. The rotating ring can define grooves configured to pressurize gas passing between the interfacing portions of the rotating ring and the stationary ring to partially counteract the biasing force of the biasing mechanism. The separation gas supply subsystem can be configured to direct a supply of separation gas from an inlet through interfacing portions of the mechanical seal and into a process cavity. 
         [0017]    Another embodiment of the present disclosure provides a method of inhibiting the emission of process gas between a stationary compressor housing and a rotating compressor shaft with a mechanical seal system. The method can comprise the steps of: providing a mechanical seal system having a first stage seal including a first rotating ring operably coupled to the compressor shaft, and a first stationary ring operably biased towards the first rotating ring by a first biasing mechanism operably coupled to the compressor housing, the first rotating ring and defining spiral shaped grooves configured to pressurize gas passing between interfacing portions of the first rotating ring and the first stationary ring to partially counteract the biasing force of the first biasing mechanism, a second stage seal including a second rotating ring operably coupled to the compressor shaft, and a second stationary ring operably biased towards the second rotating ring by a second biasing mechanism operably coupled to the compressor housing, the interfacing portions of the second rotating ring and the second stationary ring configured to pressurize gas passing between the interfacing portions to partially counteract the biasing force of the second biasing mechanism, and a single separation gas supply subsystem; directing a supply of separation gas through a single inlet of the separation gas supply subsystem; diverting the supply of separation gas, such that a first portion passes through the interfacing portions of the first stage seal, and a second portion passes through the interfacing portions of the second stage seal; and venting the first portion of the supply separation gas into a process cavity of the compressor housing to co-mingle with process gases, thereby inhibiting the emission of process gas. 
         [0018]    Embodiments of the present disclosure can also be implemented in other industrial segments, for example, where greenhouse gases are compressed for Enhanced Oil Recovery (EOR) compression of carbon dioxide. 
         [0019]    The summary above is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The figures and the detailed description that follow more particularly exemplify these embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The disclosure can be more completely understood in consideration of the following detailed description of various embodiments of the disclosure, in connection with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a partial, cross sectional view depicting a tandem, non-contacting dry gas seal arrangement of the prior art. 
           [0022]      FIG. 2  is a partial, cross-sectional view depicting a tandem, non-contacting dry gas mechanical seal system in accordance with an embodiment of the disclosure. 
           [0023]      FIG. 3A  is a plan view depicting a sealing face of a rotating ring of a first stage seal in accordance with a first embodiment of the disclosure. 
           [0024]      FIG. 3B  is a partial plan view of the rotating ring of  FIG. 3A , in which a pressure gradient is graphically depicted across the sealing face. 
           [0025]      FIG. 4A  is a plan view depicting a sealing face of a rotating ring of a first stage seal in accordance with a second embodiment of the disclosure. 
           [0026]      FIG. 4B  is a partial plan view of the rotating ring of  FIG. 4A , in which a pressure gradient is graphically depicted across the sealing face. 
           [0027]      FIG. 5A-D  are plan views depicting a sealing face of a rotating ring of a second stage seal in accordance with an embodiment of the disclosure. 
       
    
    
       [0028]    While embodiments of the disclosure are amenable to various modifications and alternative forms, specifics thereof shown by way of example in the drawings will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims. 
       DETAILED DESCRIPTION 
       [0029]    Referring to  FIG. 2 , a partial, cross-sectional view of a tandem, non-contacting dry gas mechanical seal system  200  is depicted in accordance with an embodiment of the disclosure. In one embodiment, the mechanical seal system is at least partially mounted within the space defined between a rotating compressor shaft  202  and a stationary compressor housing  204 . The rotating compressor shaft  202  can be operably coupled to a compressor impeller (not shown) disposed in a process cavity  206  of the mechanical seal system  200 , and can be supported by the housing  204  via a bearing (not shown) in a bearing cavity  208  of the housing  204 . A bore  210  formed in the housing  204  extends between the process cavity  206  and the bearing cavity  208  and defines an annular seal chamber  212 . Process gas present in the process cavity  206  can be sealed from the bearing cavity  208  and the environment by a first stage seal  216  and a second stage seal  218 . While mechanical seal system  200  is depicted and described with two seal stages  216 ,  218 , a greater or fewer number of seal stages is contemplated. Additionally, in some embodiments, a shroud or labyrinth seal can extend over a radial opening formed between the rotating compressor shaft  202  and the compressor housing  204 , thereby further inhibiting the free flow of process gas from the process cavity  206  into the annular seal chamber  212  and the environment. 
         [0030]    The first and second stage seals  216 ,  218  can include rotating rings  220 ,  222 , operably coupled to the rotating compressor shaft  202 . In one embodiment, the rotating rings  220 ,  222  are operably coupled to a sleeve member  224 , which is in turn operably coupled to the rotating compressor shaft  202 . Sleeve member  224  can include a first flange formation  226  configured to retain a portion of the rotating ring  220  and a second flange formation  228  configured to retain a portion of the rotating ring  222 . In one embodiment, the second flange formation  228  is formed independently from the sleeve member  224 , such that the second flanged formation  228  can slide axially relative to the sleeve member  224 . In one embodiment, annular members  230  and  232  can be positioned along the sleeve member  224  as an aid to retaining the rotating ring  220 , the second flange formation  228 , and the rotating ring  222  in their desired positions. Accordingly, the sleeve member  224 , the first flange formation  226 , the second flange formation  228 , the annular member  230 , the annular member  232 , the rotating ring  220 , and the rotating ring  222 , collectively referred to as the rotating members, rotate along with the compressor shaft  202 . The first and second stage seals  216 ,  218  can also include stationary rings  234 ,  236  operably coupled to the compressor housing  204 . In one embodiment, a first carrier ring  238  configured to retain a portion of the stationary ring  234  can be operably coupled to a first annular member  242  via a first biasing mechanism  246 , which in one embodiment can be a spring assembly (as depicted in  FIG. 2 ). A second carrier ring  240  configured to retain a portion of the stationary ring  236  can be operably coupled to a second annular member  244  via a second biasing mechanism  248 , which in one embodiment can be a spring assembly (as depicted in  FIG. 2 ). Accordingly, the first carrier ring  238 , the second carrier ring  240 , the first annular member  242 , the second annular member  244 , the first biasing mechanism  246 , the second biasing mechanism  248 , the stationary ring  234 , and the stationary ring  236 , collectively referred to as the non-rotational or stationary members, maintain their position relative to the compressor housing  204 . 
         [0031]    A fluidic path can be defined between the rotating members and the stationary members, through which a barrier gas can flow (as depicted in  FIG. 2  by a series of arrows). The barrier gas can be any appropriately dense gas, such as carbon dioxide (CO 2 ), nitrogen (N 2 ), air, or other gases. The barrier gas can be introduced into the fluidic path via a barrier gas inlet  250 . Thereafter, the barrier gas can flow through a conduit  252  and into a chamber  254 , where it can be divided into a first barrier gas flow and a second barrier gas flow. The first barrier gas flow can flow through a conduit  256  to the first stage seal  216 . The second barrier gas flow can flow through a conduit  258  to the second stage seal  218 . 
         [0032]    The rotating ring  220  and the stationary ring  234  of the first stage seal  216  can include a respective rotating radial seal face  260  and a stationary radial seal face  262 . The rotating radial seal face  260  can be positioned adjacent to the stationary radial seal face  262 , such that the faces  260 ,  262  are in abutting contact when the mechanical seal system  200  is not in operation, and a narrow, self-regulating gap enabling the passage of gas (typically measuring between 1-3 μm in width) is defined between the faces  260 ,  262  when the mechanical seal  200  is in operation. The first carrier ring  238  and the first biasing mechanism  246  can be configured to enable axial movement of the stationary ring  234  relative to the compressor housing  204  so as to enable dimensional changes in the gap width between the rotating seal face  260  and the stationary seal face  262 . In one embodiment, the first biasing mechanism  246  biases the stationary ring  234  towards the rotating ring  220 . A pressurized gas introduced between the seal faces  260 ,  262  presents a counteracting force against the bias of the first biasing mechanism  246  to increase the gap width between the seal faces  260 ,  262 , so as to enable effective sealing while inhibiting frictional wear of the seal faces  260 ,  262  to enhance durability. 
         [0033]    Referring to  FIGS. 3A-4B , embodiments of the rotating ring  220  are depicted in accordance with the disclosure. In one embodiment, a grooved area  264  is provided on the inner portion of the sealing face  260 , such that barrier gas can flow between faces  260  and  262  and a barrier gas pressure can be sustained within the gap between the faces  260 ,  262  sufficient to oppose the bias of the stationary radial seal face  262  towards the rotating seal face  260  by the first biasing mechanism  246 , thereby creating a barrier gas cushion to lubricate the seal faces  260 ,  262  and enable sealing. In one embodiment, the one or more grooved areas of seal faces  260 ,  262  are configured to promote the flow of separation gas from an inner diameter of the first stage seal  216  to an outer annular diameter of the first stage seal  216  (as depicted in  FIG. 2 ). In particular, the grooves  266  can be defined to open to an inner diameter  267  of the rotating ring  220 , so as to permit a hydrostatic lift so as at least partially to cause separation between the faces  260 ,  262  before the rotating ring reaches a full rotational speed if/when a pressurized gas enters the grooves from the inner diameter  267 . In one embodiment, the grooves  266  of the grooved area  264  can define spiral shapes configured to create a pressure gradient across the sealing face  260  when the rotating ring  220  is rotating (as depicted in  FIGS. 3B and 4B ). Accordingly, fluid pressure of the barrier gas can be boosted using a small amount of kinetic energy of the rotating compressor shaft  202  via fluid interaction with the specially shaped spiral grooves  266 , thereby permitting a hydrodynamic lift, thereby maintaining a separation between the faces  260 ,  262 . In other embodiments, other configurations of the grooved area  264  are contemplated. In another embodiment, the grooved area  264  can be located on the stationary ring  234 . 
         [0034]    Referring to  FIGS. 5A-D , embodiments of the rotating ring  222  of the second stage seal  218  are depicted in accordance with the disclosure. The rotating ring  222  and the stationary ring  236  of the second stage seal  218  can include a respective rotating radial seal face  268  and a stationary radial seal face  270 . The rotating radial seal face  268  can be positioned adjacent to the stationary radial seal face  270 , such that the faces  268 ,  270  are in abutting contact when the mechanical seal system  200  is not in operation, and a narrow gap enabling the passage of gas is defined between the faces  268 ,  270  when the mechanical seal  200  is in operation. The second carrier ring  240  and the second biasing mechanism  248  can be configured to enable axial movement of the stationary ring  236  relative to the compressor housing  204  so as to enable dimensional changes in the gap width between the rotating seal face  268  and stationary seal face  270 . In one embodiment, second biasing mechanism  248  biases the stationary ring  236  towards the rotating ring  222 . A pressurized gas introduced between the seal faces  268 ,  270  presents a counteracting force against the bias of the second biasing mechanism  248  to increase the gap width between the seal faces  268 ,  270 , so as to enable effective sealing while inhibiting frictional wear of the seal faces  268 ,  270  to enhance durability. 
         [0035]    In one embodiment, either or both of the seal faces  268 ,  270  can include a grooved area  271  configured to enhance pressure generation capabilities and improve flow of the barrier gas therebetween. Grooves  273  of the grooved area  271  can define spiral or arrow shapes, such as those described in U.S. Pat. Nos. 4,212,475 and 6,655,693, the contents of which are incorporated by reference herein. In one embodiment, the one or more grooved areas  271  of seal faces  268 ,  270  are configured to promote the flow of gas from an outer annular diameter of the second stage seal  218  to an inner diameter of the second stage seal  218  (as depicted in  FIG. 2 ). In other embodiments, the one or more grooved areas  271  of the seal faces  268 ,  270  can be configured to permit the flow of separation gas in either direction. 
         [0036]    After passing through the first stage seal  216 , the first barrier gas flow can flow into a chamber  272 , and into the process cavity  206 . Additionally, after passing through the second stage seal  218 , the second barrier gas flow can flow into a conduit  274 , a chamber  276 , a conduit  278 , and out of the compressor housing  204  through barrier gas outlet  280 , thereby co-mingling and/or mixing with the process gas. In one embodiment, barrier gas can be collected and/or reconditioned, thereby creating a closed-loop to reduce the need for an additional supply of barrier gas. In other embodiments, the barrier gas can be vented to the atmosphere and/or introduced as compressed air into a fuel mixture for a combustion motor powering rotation of the compressor shaft  202 . 
         [0037]    In operation, the flow of barrier gas is introduced into the compressor housing  204  via barrier gas inlet  250  at a lower relative pressure than the pressure of the gases within the process cavity  206 , for example at a pressure between 10-50 bar. The barrier gas flows along conduit  252  and enters chamber  254 , where it separates into a first barrier gas flow and a second barrier gas flow. The first barrier gas flow continues along conduit  256  towards the first stage seal  216 , while the second barrier gas flow continues along conduit  258  towards the second stage seal  218 . 
         [0038]    When the compressor shaft  202  is rotating, the respective grooves  266  of the first stage seal  216  and the grooves  273  second stage seal  218  create a pressure gradient to encourage the flow of barrier gas from the barrier gas inlet  250  to the respective first and second stage seals  216 ,  218 . However, because of the lower relative pressure of the barrier gas than the gases within the process cavity  206 , one or more additional steps may be taken to equalize the pressure on both sides of the first stage seal  216  and/or provide artificial hydrostatic lifting, so as to provide an initial gap between sealing faces  260 ,  262 , until the first rotating ring  220  reaches a rotational speed at which the interface gap can be sustained. For example, in one embodiment, the barrier gas inlet  250  can be at least partially closed or blocked so as to enable process gas to leak through the first seal  216 , thereby raising the pressure within conduit  256  so as to decrease the pressure gradient across the first stage seal  216 . In another embodiment, the mechanical seal system  200  can include a pressure balance line  281  configured to enable a flow of process gas into conduit  256 , so as to decrease the pressure gradient across the first stage seal  216 . In yet another embodiment, the mechanical seal system  200  can include an actuator configured to create a mechanical separation between the seal faces  260 ,  262  of the first stage seal  216 , thereby artificially providing an initial hydrostatic lift (as disclosed in U.S. Patent Application Ser. No. 62/506,196 filed May 15, 2017, the contents of which are incorporated by reference herein). A minimal leakage of process gas can occur until the first rotating ring  220  reaches a rotational speed at which the interface gap can be sustained and the barrier gas inlet  250  is opened, the pressure balance line  281  is closed, and/or the actuator is deenergized. Leakage can be minimized by containing the process gas within the mechanical seal system  200 , such that the process gas that enters conduit  256  flows back into the process chamber  206  through the first stage seal  216 . 
         [0039]    As the first barrier gas flow passes through the radial seal faces  260 ,  262  of the first stage seal  216 , the pressure is increased until it meets or exceeds the pressure of the gas within the process cavity  206 . The flow of the barrier gas through the seal faces  260 ,  262  provides a cushion between the seal faces  260 ,  262 , thereby lubricating the first stage seal  216  and inhibiting contact between the seal faces  260 ,  262 . Because the barrier gas is pressurized to a pressure that exceeds the pressure of the gas within the process cavity  206 , the first barrier gas flow continues into the process cavity  206 , thereby mixing with the process gas therein. Accordingly, the flow of barrier gas into the process cavity  206  represents a reversal of the flow direction in conventional dry gas seal arrangements, where process gas would normally flow from the process chamber  206 , through the first stage seal  216 , and out to the atmosphere. 
         [0040]    As the second barrier gas flow passes through radial seal faces  268 ,  270  of the second stage seal  218 , the pressure of the barrier gas is increased so as to provide a lubricating cushion between the seal faces  268 ,  270 . After passing between the seal faces  268 ,  270 , the second barrier gas flow continues along conduit  274 , into chamber  276 , along conduit  278 , and out of the compressor housing  204  via barrier gas outlet  280 . At the barrier gas outlet  280 , the second barrier gas flow can be vented to the atmosphere, recycled back into the separating gas supply, or mixed with fuel gas powering the compressor. Thus, the flow of barrier gas through the second stage seal  218  serves as a backup in the event of a failure of the first stage seal  218 . 
         [0041]    The upstream flow of the barrier gas through the first stage seal  216  into the process cavity  206  provides numerous advantages. In particular, because the process gas is not used as the barrier gas, a gas conditioning unit, which serves to remove moisture and contaminants from the process gas to enable proper lubrication and inhibit corrosion, is not required. In addition, the process gas is forced, by the pressure of the first barrier gas flow back into the process chamber  206 , therefore inhibiting the venting of process gas to the surrounding environment. Accordingly, embodiments of the present disclosure provide a more environmentally friendly mechanical seal system  200  that serves to decrease methane production losses. Numerous other advantages will be apparent to those of ordinary skill in the art. 
         [0042]    It should be understood that the individual steps used in the methods of the present teachings may be performed in any order and/or simultaneously, as long as the teaching remains operable. Furthermore, it should be understood that the apparatus and methods of the present teachings can include any number, or all, of the described embodiments, as long as the teaching remains operable. 
         [0043]    Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed inventions. 
         [0044]    Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted. 
         [0045]    Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. 
         [0046]    Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein. 
         [0047]    For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. §112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.