APPARATUS AND METHODS FOR CAPTURING VENT GAS IN NATURAL GAS SYSTEMS

Abstract

A natural gas system includes a pneumatic controller configured to discharge vent gas, an expansion vessel configured to discharge an expanded pilot gas, wherein the expansion vessel includes an internal volume configured to expand the vent gas discharged from the pneumatic controller whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range, a vent gas flowpath extending from the pneumatic controller to the expansion vessel, a burner assembly coupled to the expansion vessel and configured to ignite the expanded pilot gas discharged by the expansion vessel, and a pilot gas flowpath extending from the expansion vessel to the burner assembly.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent application Ser. No. 63/410,732 filed Sep. 28, 2022, and entitled “Apparatus and Method for Capturing Vent Gas in Natural Gas Systems,” which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

Natural gas systems include a variety of systems utilized in connection with the extraction, transportation, and refinement of natural gas for different purposes. For example, compressor or compression “packages” or “units” are a type of natural gas system for transporting natural gas from an upstream production area where the gas is produced to a downstream location where the natural gas may be refined prior to being consumed by an end-user. Compressor packages typically include a compressor, such as a reciprocating compressor, that compresses and pressurizes the natural gas for transport. Natural gas systems, including compressor packages, often include pneumatically powered equipment such as pneumatically powered instrumentation and valving. For purposes of efficiency and simplicity, such equipment (e.g., pop-off valves, dump valves) may be powered by a portion of the natural gas circulating through the natural gas system, which may be referred to as “control gas.”

BRIEF SUMMARY OF THE DISCLOSURE

An embodiment of a natural gas system comprises one or more pneumatic controllers, wherein each pneumatic controller is configured to discharge a vent gas in response to operation of the one or more pneumatic controllers, an expansion vessel comprising a one or more inlet ports and an outlet port configured to discharge an expanded pilot gas, wherein the expansion vessel comprises an internal volume configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range, a one or more vent gas flowpaths extending from the one or more pneumatic controllers to the one or more inlet ports of the expansion vessel, wherein the one or more vent gas flowpaths are configured to transport vent gas discharged from the one or more pneumatic controllers to the inlet ports of the expansion vessel, a burner assembly coupled to the expansion vessel and configured to ignite the expanded pilot gas discharged by the outlet port of the expansion vessel, and a pilot gas flowpath extending from the outlet port of the expansion vessel to the burner assembly, wherein the pilot gas flowpath is configured to transport the expanded pilot gas from the expansion vessel to the burner assembly. In some embodiments, the discharge pressure range is based on an operational pressure range of the burner assembly. In some embodiments, the internal volume of the expansion vessel is equal to or greater than 250 cubic inches. In certain embodiments, the internal volume of the expansion vessel is equal to or greater than 275 cubic inches. In certain embodiments, at least one of the one or more pneumatic controllers comprises a pneumatically controlled valve. In some embodiments, the internal volume of the expansion vessel is configured to maintain a pressure differential between the expanded pilot gas discharged from the outlet port and the vent gas received by the one or more inlet ports that is equal to or greater than 5 pounds per square inch. In some embodiments, the natural gas system comprises a separator comprising a separator vessel, at least one of the one or more the pneumatic controllers, and the burner assembly that is configured to heat an internal volume of the separator vessel. In certain embodiments, the natural gas system comprises an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel, wherein pilot inlet port is configured to receive an inlet pilot gas stream transportable along the inlet pilot gas flowpath, and wherein the pressure of the inlet pilot gas stream received by the pilot inlet port falls within the discharge pressure range.

An embodiment of a method for capturing vent gas produced by a natural gas system comprises (a) discharging a vent gas from a one or more pneumatic controllers, (b) flowing the discharged vent gas along a one or more vent gas flowpaths that extends from the one or more pneumatic controllers to a one or more inlet ports of an expansion vessel, (c) expanding the vent gas within an internal volume of the expansion vessel to depressurize the vent gas within the internal volume, (d) discharging the vent gas as an expanded pilot gas from an outlet port of the expansion vessel whereby the expanded pilot gas falls within a predefined discharge pressure range, (e) flowing the expanded pilot gas along an expanded pilot gas flowpath extending from the outlet port of the expansion vessel to a burner assembly, and (f) igniting the expanded pilot gas by the burner assembly. In certain embodiments, the pressure of the expanded pilot gas flowing along the expanded pilot gas flowpath is less than ten pounds per square inch gauge. In some embodiments, the pressure of the vent gas flowing along the one or more vent gas flowpaths is greater than ten PSIG. In some embodiments, at least one of the one or more pneumatic controllers comprises a pneumatically controlled valve and (a) comprises discharging at least a portion of the vent gas in response to operating the pneumatically controlled valve. In certain embodiments, the burner assembly comprises a pilot burner assembly of a separator of the natural gas system. In certain embodiments, the method comprises (g) flowing an inlet pilot gas stream along an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel, and (h) forming within the internal volume of the expansion vessel the expanded pilot gas from the inlet pilot gas received by the pilot inlet port of the expansion vessel and the vent gas received by the one or more inlet ports of the expansion vessel.

An embodiment of a natural gas system comprises a separator comprising a separator vessel, a one or more pneumatic controllers, wherein each pneumatic controller is configured to discharge a vent gas in response to operation of the one or more pneumatic controllers, and a burner assembly configured to heat an internal volume of the separator vessel, an expansion vessel comprising a one or more inlet ports and an outlet port configured to discharge an expanded pilot gas, wherein the expansion vessel comprises an internal volume configured to expand the vent gas discharged from the one or more pneumatic controllers of the separator, a one or more vent gas flowpaths extending from the one or more pneumatic controllers of the separator to the one or more inlet ports of the expansion vessel, wherein the one or more vent gas flowpaths are configured to transport vent gas discharged from the one or more pneumatic controllers to the inlet ports of the expansion vessel, and an expanded pilot gas flowpath extending from the outlet port of the expansion vessel to the burner assembly of the separator, wherein the expanded pilot gas flowpath is configured to transport the expanded pilot gas from the expansion vessel to the burner assembly, wherein the burner assembly of the separator is configured to ignite the expanded pilot gas discharged by the outlet port of the expansion vessel. In some embodiments, the internal volume of the expansion vessel is configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range. In some embodiments, the natural gas system comprises an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel, wherein pilot inlet port is configured to receive an inlet pilot gas stream transportable along the inlet pilot gas flowpath. In certain embodiments, the internal volume of the expansion vessel is configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range, and the pressure of the inlet pilot gas stream received by the pilot inlet port falls within the discharge pressure range. In certain embodiments, the discharge pressure range is based on an operational pressure range of the burner assembly. In some embodiments, the internal volume of the expansion vessel is configured to maintain a pressure differential between the expanded pilot gas discharged from the outlet port and the vent gas received by the one or more inlet ports that is equal to or greater than 5 pounds per square inch.

Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the disclosure, reference will now be made to the accompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of a natural gas system in accordance with principles described herein;

FIG. 2 is a side view of an embodiment of an expansion vessel in accordance with the principles described herein usable in the natural gas system of FIG. 1;

FIG. 3 is an embodiment of an expansion vessel in accordance with principles described herein that can be used in the natural gas system of FIG. 1; and

FIG. 4 is a flow chart illustrating an embodiment of a method for capturing vent gas produced by a natural gas system in accordance with principles described herein.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

As described above, natural gas systems often include pneumatically powered equipment for monitoring or controlling various parameters of the system. For example, at least some of the instrumentation and valving of the natural gas system may be pneumatically powered by a stream of control gas supplied to the system as part of a feed gas stream. Conventionally, control gas used to power pneumatically powered equipment of a natural gas system is vented to the atmosphere as an emission or routed to a dedicated flare or combustor for burning. Particularly, control gas may be at a pressure that is greater than the pressure at which preexisting burners or combustors of the natural gas system operate, thereby preventing such preexisting equipment from being utilized to burn the control gas. Thus, in conventional natural gas systems the control gas is either undesirably emitted to the atmosphere, or separate and dedicated equipment is provided to burn the control gas, increasing the overall complexity and cost associated with providing and operating the natural gas system.

Accordingly, embodiments of natural gas systems described herein include an expansion vessel in fluid communication with one or more components powered by a control gas. The components may include pneumatically powered and operated controllers (including instrumentation) such as pneumatically controlled valves and the like. Expansion vessels described herein are configured to receive one or more separate vent gas streams discharged from a corresponding one or more pneumatic controllers and to expand the vent gas within an internal volume of the expansion vessel whereby the pressure of the vent gas is sufficiently reduced to fall within a predetermined discharge pressure range.

The discharge pressure range corresponds to an operational pressure range of other equipment of the natural gas system such as preexisting pilot or other burner of the natural gas system that operates at a pressure that is less than the pressure of the vent gas discharged by the pneumatic controllers. In this manner, the expansion vessel both captures vent gas from a plurality of separate components, but automatically (without powered equipment) depressurizes the vent gas such that the gas is compatible with the operational pressure range of the burner, thereby enabling the burner to burn the expanded vent gas as an expanded pilot gas without damaging or otherwise inhibiting the performance of the burner.

Referring now to FIG. 1, an embodiment of a natural gas system 10 is shown. In this exemplary embodiment, natural gas system 10 generally includes a gas source 12, a separator vessel 20, and an expansion vessel 50. Natural gas system 10 may include equipment in addition to that shown in FIG. 1. For example, in some embodiments, natural gas system 10 includes a compressor package in which gas source 12 is a fuel gas vessel receiving a supply of fuel gas for powering a compressor of the compressor package. Gas source 12 may also include a pilot gas source for powering a pilot circuit of the natural gas system 10. Natural gas system 10 may also include an upstream gas system located proximal a wellbore from which the natural gas is extracted, as well as an intermediate or downstream gas system located at a distance from the wellbore.

The gas source 12 receives a stream 11 of supply gas. The supply gas stream 11 may be transported via pipeline or other equipment either upstream from or part of the natural gas system 10. The supply gas comprising the supply gas stream 11 is natural gas in this exemplary embodiment containing hydrocarbons such as methane and other gasses. It is to be understood that the formulation of the gas comprising the supply gas of stream 11 may vary substantially depending on the given application. Additionally, while in this exemplary embodiment gas source 12 comprises a vessel, in other embodiments, gas source 12 may comprise equipment in addition to or other than vessels such as fluid conduits and other equipment.

In this exemplary embodiment, gas source 12 divides the supply gas stream 11 into a fuel gas stream 13, an inlet pilot gas stream 14, and a control gas stream 15, each of the foregoing discharged from the gas source 12. The fuel gas stream 13 is initially supplied to the separator vessel 20 in this exemplary embodiment but may eventually be consumed by a compressor or other powered equipment of the natural gas system 10 located downstream from the separator vessel 20. Alternatively, the gas of fuel gas stream 13 may be conditioned by various equipment of natural gas system 10 before being discharged from the system 10. The inlet pilot gas stream 14 is supplied to the expansion vessel 50, as will be described further herein. Particularly, inlet pilot gas stream 14 flows along an inlet pilot gas flowpath extending from an inlet pilot gas source in the form of gas source 12 to a pilot inlet port 53 of the expansion vessel 50. Additionally, the control gas stream 15 is supplied to the separator vessel 20.

As described above, the separator vessel 20 of natural gas system 10 receives the fuel gas stream 13 from the gas source 12. Separator vessel 20 utilizes temperature and pressure to separate out desired materials from the fuel gas stream 13. Particularly, in this exemplary embodiment, separator vessel 20 is a three-phase water/oil separator sometimes referred to as a “heater treater” that utilizes heat to separate water-oil emulsions. Particularly, separator vessel 20 discharges both an oil stream 24 and a water stream 26 and which may be either vertical (e.g., where a longitudinal axis of the separator extends vertically) or horizontal. However, it may be understood that in other embodiments the configuration of separator vessel 20 may vary.

Separator vessel 20 includes a pilot burner assembly 28 to produce the heat required to boil off at least some of the oil components separated from the fuel gas stream 13. Particularly, pilot burner assembly 28, by heating the fuel gas stream 13 so as to remove both water and liquid oil from the fuel gas stream 13, thereby forms a refined fuel gas stream 16 that may be consumed by downstream equipment such as a compressor of the natural gas system 10.

Flow of the oil stream 24 is controlled by a corresponding oil valve 25 and flow of the water stream 26 is controlled by a corresponding water valve 27, each of the valves 25, 27 being coupled to the separator vessel 20. Additionally, in this exemplary embodiment, separator vessel 20 includes a controller 30 for at least assisting in controlling the operation of separator vessel 20. For example, controller 30 may include a level controller for controlling a vertical level of one or more fluids contained within the separator vessel 20. Flow from a discharge of controller 30 is controlled by a controller valve 32 coupled to the controller 30. It may be understood that separator vessel 20 may comprise various controllers and associated instrumentation not shown in FIG. 1.

In this exemplary embodiment, valves 25, 27, 32 of separator vessel 20 each comprise pneumatic controllers that are pneumatically powered by the control gas stream 15 (lines connecting stream 15 with valves 25, 27 are hidden from view in FIG. 1 in the interest of clarity). In this configuration, each of valves 25, 27, 32 produces a separate vent gas stream 33, 34, 35, respectively. Vent gas streams 33, 34, 35 flow along a plurality of separate vent gas flowpaths extending from the valves 25, 27, 32, respectively, to a plurality of inlet ports 55, 57, 59 of the expansion vessel 50. It may be understood that, having derived from the supply gas stream 11, each of the vent gas streams 33, 34, 35 discharged by valves 25, 27, 32, respectively, comprises hydrocarbons such as methane and others. In this exemplary embodiment, instead of being discharged to the atmosphere as an emission or routed to a dedicated flare or combustor, vent gas streams 33, 34, 35 are routed from valves 25, 27, 32 to the expansion vessel 50.

The expansion vessel 50 of natural gas system 10 captures vent gas streams from various types of equipment of natural gas system 10, expands and thereby depressurizes at least some of the collected vent gas, and discharges the expanded vent gas as an expanded pilot gas stream 52 to the pilot burner assembly 28 of separator vessel 20 where the expanded pilot gas stream 52 may be consumed or burned by the pilot burner assembly 28. While only a single expansion vessel 50 is shown in FIG. 1, it may be understood that natural gas system 10 may include more than one vessel 50 which may be arrange in series or parallel.

Expansion vessel 50 expands and thereby depressurizes the vent gas received by vessel 50 from vent gas streams 33, 34, 35. Particularly, valves 25, 27, 32 may require for their operation a control gas of a sufficiently elevated pressure, resulting in the vent gas of vent gas streams 33, 34, 35 having a similarly elevated pressure. For instance, vent gas streams 33, 34 discharged from valves 25, 27, respectively, may be approximately between 10 pounds per square inch gauge (PSIG) and 30 PSIG or greater. Although in FIG. 1 expansion vessel 50 is shown receiving three vent gas streams 33, 34, 35, it should be understood that the number of vent gas streams received by expansion vessel 50 may vary in other embodiments from a single vent gas stream to a large number (e.g., ten or more) vent gas streams. Additionally, although vent gas streams 33, 34, 35 each are produced by a valve, the vent gas streams received and expanded by expansion vessel 50 may be produced by a variety of relatively high-pressure sources including controllers, instruments, and other sources.

In this exemplary embodiment, the pressure of vent gas streams 33, 34, 35 is greater than an operating pressure of the pilot burner assembly 28 of separator vessel 20. Vent gas streams 33, 34, 35 must thus be depressurized in order to utilize vent gas streams 33, 34, 35 as a source for expanded pilot gas stream 52 without jeopardizing the performance of pilot burner assembly 28. For example, providing vent gas to the pilot burner assembly 28 at a pressure in excess of an operational range of assembly 28 may cause the pilot burner assembly 28 to go out or to burn inefficiently. Expansion vessel 50 of natural gas system 10 serves to continuously and automatically expand the vent gas supplied to vessel 50 from vent gas streams 33, 34, 35 so as to reduce the pressure of the received vent gas such that the pressure of the vent gas falls within the operational range of pilot burner assembly 28, thereby permitting the expanded vent gas to be used as a pilot gas in powering the operation of pilot burner assembly 28.

Particularly, expansion vessel 50 has an internal volume 51 configured to reduce the pressure of the vent gas supplied to expansion vessel 50 from vent gas streams 33, 34, 35 such that the expanded pilot gas stream 52 discharged from expansion vessel 50 falls within a predefined discharge pressure range corresponding, in this exemplary embodiment, to the operational range of pilot burner assembly 28. In this exemplary embodiment, the internal volume 51 does not include any internal equipment, including any internal powered equipment such as rotating equipment. Thus, expansion vessel 50 expands the vent gas received passively without the need of additional powered equipment. s

In this exemplary embodiment, the predefined discharge pressure range of expanded pilot gas stream 52 is approximately between 5 PSIG and 10 PSIG with the vent gas streams 33, 34, 35 ranging approximately between 15 PSIG and 30 PSIG; however, it may be understood that in other embodiments the discharge pressure range of pilot gas stream 42 may vary. The size of the internal volume 51 of expansion vessel 50 may be based on the predefined discharge pressure range, the cumulative mass flow rate of the vent gas streams (vent gas streams 33, 34, 35 in this embodiment) and pilot gas stream 14 received by the expansion vessel 50, the pressure of the vent gas streams received by vessel 50, and other parameters. For example, the size of internal volume 51 is correlated with both the volume of the piping in fluid communication with expansion vessel 50 (e.g., fuel gas stream 13, control gas stream 15) as well as the discharge pressure of the vent gas received by expansion vessel 50. Additionally, the size of the internal volume 51 is inversely correlated with the operating pressure of pilot burner assembly 28. In certain embodiments, the internal volume 41 of expansion vessel 50 is equal to or greater than 75 cubic inches. In some embodiments, the internal volume 41 of expansion vessel 50 is equal to or greater than 100 cubic inches. In certain embodiments, the internal volume 41 of expansion vessel 50 is equal to or greater than 125 cubic inches. However, it may be understood that in other embodiments the size of internal volume 51 of expansion vessel 50 may vary from the exemplary values provided above.

In some embodiments, expansion vessel 50 may provide a predefined amount of pressure reduction (which may be a range) through expansion within internal volume 51 of vessel 50 between an inlet thereof (e.g., the inlets of vessel 50 which receive vent gas streams 33, 34, 35) and a discharge thereof (e.g., the discharge of vessel 50 which outputs expanded pilot gas stream 52). The predefined pressure reduction provided by expansion vessel 50 is approximately between 10 PSIG and 20 PSIG; however, this value may vary in other embodiments. Expansion vessel 50 may not, in at least some embodiments, depressurize the pilot gas stream 14 received from gas source 12, the pressure of which may already fall within the operational range of pilot burner assembly 28.

The vent gas received by expansion vessel 50 from vent gas streams 33, 34, 35 may mix with the pilot gas received by vessel 50 from pilot gas stream 14 within the internal volume 51 of expansion vessel 50. The flow of vent gas from vent gas streams 33, 34, 35 into expansion vessel 50 may be intermittent depending on the operation of corresponding valves 25, 27, 32 while pilot gas is supplied continuously to the expansion vessel 50 from pilot gas stream 14. As described above, the pilot gas and vent gas received by expansion vessel 50 is discharged from the vessel 50 as pilot gas and supplied to the pilot burner assembly 28 at a pressure within the operational range of the pilot burner assembly 28 so as not to jeopardize the performance of pilot burner assembly 28. In turn, pilot burner assembly 28 burns the pilot gas of expanded pilot gas stream 52 in accordance with the operation of the separator vessel 20 of natural gas system 10.

As described above, expansion vessel 50 permits vent gas produced by a plurality of components of natural gas system 10 to be recycled in natural gas system 10 as pilot gas that is supplied as part of expanded pilot gas stream 52 to the pilot burner assembly 28 of a preexisting component (separator vessel 20 in this exemplary embodiment) of the natural gas system 10. In this manner, expansion vessel 50 allows for the vent gas captured by vessel 50 to be recycled using preexisting equipment of natural gas system 10 by automatically expanding and depressurizing the captured vent gas. Expansion vessel 50 thus avoids the undesirable requirement of either venting the vent gas directly to the atmosphere or needing to provide natural gas system 10 with additional equipment specifically for burning the captured vent gas (e.g., a flare or combustor). However, it may be understood that in other embodiments the discharge of expansion vessel 50 may not be provided to a pilot burner of a separator, and instead may be supplied to one or more burners of various types of equipment such as a preexisting flare or combustor of the natural gas system, a heating system, a dehydrating system such as a glycol dehydrator and the like.

Referring now to FIG. 2, an embodiment of an expansion vessel 100 is shown. Expansion vessel 100 may be used for expansion vessel 50 of natural gas system 10 shown in FIG. 1, or be used in addition to the expansion vessel 50 of natural gas system 10 shown in FIG. 1. Thus, expansion vessel 100 may comprise a component of natural gas system 10 shown in FIG. 1, as well as natural gas systems which vary in configuration from natural gas system 10. In this exemplary embodiment, expansion vessel 100 is oriented vertically and extends from a first or vertically lower end 101 and a second or vertically upper end 103 longitudinally opposite the lower end 101. Additionally, expansion vessel 100 defines an internal volume 105 that is based on both a length or height 107 and a width or diameter 109 of the expansion vessel 100.

Expansion vessel 100 includes a plurality of ports along its length for receiving pilot and vent gasses and discharging an expanded pilot gas that may be routed to a burner of the natural gas system in which the expansion vessel 100 is incorporated (e.g., natural gas system 10). Particularly, in this exemplary embodiment, expansion vessel 100 includes a pilot inlet port 110, a plurality of vent inlet ports 112, 114, 116, 118, and a pilot outlet port 120. The pilot inlet port 110 of expansion vessel 100 is configured to receive pilot gas from a pilot gas stream 90 of a natural gas system (e.g., natural gas system 10). In this exemplary embodiment, pilot inlet port 110 is positioned along the longitudinal length of expansion vessel 100 vertically above the vent inlet ports 112, 114, 116, 118, but vertically below the pilot outlet port 120. Additionally, while expansion vessel 100 is shown including four vent inlet ports 112, 114, 116, 118 in this embodiment, it may be understood that the number of vent inlet ports of vessel 100 may vary in other embodiments.

The vent inlet ports 112, 114, 116, 118 of expansion vessel 100 are positioned along the longitudinal length of expansion vessel 100 and vertically below the pilot inlet port 110. However, it may be understood that the arrangement of pilot inlet port 110 and vent inlet ports 112, 114, 116, 118 along the expansion vessel 100 may vary. Additionally, vent inlet ports 112, 114, 116, 118 are configured to receive vent gas from separate vent gas streams 91, 92, 93, 94, respectively, of the natural gas system into which expansion vessel 100 is incorporated. For example, vent gas streams 91, 92, 93, 94 may be produced by instrumentation and control equipment such as pneumatically controlled valving.

Vent gas streams 91, 92, 93, 94 may be at a pressure in excess of the pressure of the pilot gas stream 90. For example, vent gas streams 91, 92, 93, 94 may be greater than 10 PSIG while pilot gas stream 90 may be less than 10 PSIG. However, upon entering expansion vessel 100, the vent gas is expanded within internal volume 105 and thereby depressurized to a pressure less than the vent gas streams 91, 92, 93, 94 and consistent with the pressure of pilot inlet port 110. The internal volume 105 of expansion vessel 100 may be sized based on a predefined, desired degree of expansion and depressurization of the vent gas received therein as well as a predefined pressure and mass flowrate of the vent gas streams 91, 92, 93, 94. In some embodiments, expansion vessel 100 is approximately 36″ in height and 3″ in diameter. In some embodiments, expansion vessel 100 has a minimum internal volume 105 that is equal to or greater than 250 cubic inches. In certain embodiments, expansion vessel 100 has a minimum internal volume 105 that is equal to or greater than 275 cubic inches. In certain embodiments, expansion vessel 100 has a minimum internal volume 105 that is equal to or greater than 300 cubic inches.

The pilot outlet port 120 of expansion vessel 100 is configured to discharge an expanded pilot gas stream 121. Expanded pilot gas stream 121 comprises both pilot gas received by expansion vessel 100 from pilot gas stream 90, and expanded vent gas received by vessel 100 from the vent gas streams 91, 92, 93, 94. The supply of vent gas received by expansion vessel 100 may be intermittent. In some embodiments, the expanded pilot gas stream 121 is supplied to a pilot or other burner such that the expanded pilot gas is burned and consumed. Additionally, in this exemplary embodiment, expansion vessel 100 comprises a pressure gauge 130 coupled to the pilot outlet port 120 thereof. Pressure gauge 130 displays a current pressure of the expanded pilot gas stream 121 such that the pressure of stream 121 may be monitored by an operator of the natural gas system into which expansion vessel 100 is incorporated. However, in other embodiments, expansion vessel 100 may not include pressure gauge 130. Additionally, expansion vessel 100 may include additional equipment such as sensors, instrumentation, and valving that are not shown in FIG. 2.

Referring now to FIG. 3, an embodiment of an expansion vessel 200 is shown. As with expansion vessel 100 shown in FIG. 2, expansion vessel 200 can be used in place of the expansion vessel 50 of natural gas system 10 shown in FIG. 1, or be used in addition to, the expansion vessel 50 of natural gas system 10 shown in FIG. 1. Thus, expansion vessel 200 may comprise a component of natural gas system 10 shown in FIG. 1, as well as natural gas systems which vary in configuration from natural gas system 10. In this exemplary embodiment, expansion vessel 200 is oriented horizontally and extends from a first end 201 to a second end 203 longitudinally opposite the first end 201. Additionally, expansion vessel 200 defines an internal volume 205 that is based on both a horizontally extending length 102 and a width or diameter 209 of the expansion vessel 200.

As with expansion vessel 100 described above, expansion vessel 200 comprises a plurality of ports including a pair of vent gas ports 212, 214, a pilot gas inlet port 216, and an expanded pilot outlet port 220. Vent gas ports 212, 214 receive vent gas streams 213, 215, respectively, while pilot inlet port 216 receives a pilot gas steam 217. Vent gas streams 213, 215 may comprise control gas in the form of a type of hydrocarbon containing natural gas. Pilot gas stream 217 may also comprise natural gas derived from fuel gas or some other source. Similar to the operation of expansion vessel 100, expansion vessel 200 is configured to expand and depressurize the vent gas received from vent gas streams 213, 215 such that the pressure of an expanded pilot gas stream 221 discharged from pilot outlet port 220 falls within a predefined, desired discharge pressure range. The discharge pressure range is less than the pressure of vent gas streams 213, 215 (the pressure differential between stream 221 and streams 213, 215 may also be predefined) and may correspond to an operational pressure range of a pilot burner or other equipment for handling the expanded pilot gas stream 221.

Referring now to FIG. 4, an embodiment of a method 250 for capturing vent gas produced by a natural gas system is shown. Initially at block 252, method 250 comprises discharging vent gas from of the one or more pneumatic controllers. The discharged vent gas may comprise natural gas containing one more hydrocarbons like methane. The pneumatic controllers may comprise instrumentation, valving, and other pneumatically powered and operated equipment. In some embodiments, block 252 comprises discharging vent gas from the pneumatic valves 25, 27, 32 of the separator vessel 20 shown in FIG. 1.

At block 254, method 250 comprises flowing the discharged vent gas along a one or more vent gas flowpaths that extends from the one or more pneumatic controllers to a one or more inlet ports of an expansion vessel. The vent gas flowpaths may extend at least partially in parallel and may connect to the expansion vessel at a one or more inlet ports of the expansion vessel. In some embodiments, block 254 comprises flowing discharged vent gas along a plurality of vent gas flowpaths extending from valves 25, 27, 32 of the separator vessel 20 shown in FIG. 1 to the plurality of inlet ports 55, 57, 59, respectively, of the expansion vessel 50.

At block 256, method 250 comprises expanding the vent gas within an internal volume of the expansion vessel to depressurize the vent gas within the internal volume. In some embodiments, the vent gas is depressurized to fall within a predefined discharge pressure range. In some embodiments, block 256 comprises expanding the vent gas within the internal volume 51 of the expansion vessel 50 shown in FIG. 1 to depressurize the vent gas within the internal volume. In certain embodiments, block 256 comprises expanding the vent gas within the internal volume 205 of the expansion vessel 200 shown in FIG. 3 to depressurize the vent gas.

At block 258, method 250 comprises discharging the vent gas as an expanded pilot gas from an outlet port of the expansion vessel whereby the expanded pilot gas falls within a predefined discharge pressure range. In some embodiments, block 258 comprises discharging the vent gas as an expanded pilot gas from an outlet port of the expansion vessel 50 shown in FIG. 1. In some embodiments, block 258 comprises discharging the vent gas as an expanded pilot gas from the outlet port 120 of the expansion vessel 100 shown in FIG. 2. In certain embodiments, block 258 comprises discharging the vent gas as an expanded pilot gas from a pilot outlet port 220 of the expansion vessel 200 shown in FIG. 3.

At block 260, method 250 comprises flowing the expanded pilot gas along an expanded pilot gas flowpath extending from the outlet port of the expansion vessel to a burner assembly. The burner assembly may belong to various types of equipment of the natural gas system including preexisting equipment of the system such as a pilot burner of a pressure vessel. In some embodiments, block 260 comprises flowing the expanded pilot gas along an expanded pilot gas flowpath extending from the outlet port of the expansion vessel 50 shown in FIG. 1 to the pilot burner assembly 28 shown in FIG. 1. At block 262, method 250 comprises igniting the expanded pilot gas by the burner assembly. In some embodiments, block 262 comprises igniting the expanded pilot gas by the pilot burner assembly 28 of the separator vessel 20 shown in FIG. 1.

While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

1. A natural gas system, comprising:

one or more pneumatic controllers, wherein each pneumatic controller is configured to discharge a vent gas in response to operation of the one or more pneumatic controllers;

an expansion vessel comprising a one or more inlet ports and an outlet port configured to discharge an expanded pilot gas, wherein the expansion vessel comprises an internal volume configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range;

a one or more vent gas flowpaths extending from the one or more pneumatic controllers to the one or more inlet ports of the expansion vessel, wherein the one or more vent gas flowpaths are configured to transport vent gas discharged from the one or more pneumatic controllers to the inlet ports of the expansion vessel;

a burner assembly coupled to the expansion vessel and configured to ignite the expanded pilot gas discharged by the outlet port of the expansion vessel; and

a pilot gas flowpath extending from the outlet port of the expansion vessel to the burner assembly, wherein the pilot gas flowpath is configured to transport the expanded pilot gas from the expansion vessel to the burner assembly.

2. The natural gas system of claim 1, wherein the discharge pressure range is based on an operational pressure range of the burner assembly.

3. The natural gas system of claim 1, wherein the internal volume of the expansion vessel is equal to or greater than 250 cubic inches.

4. The natural gas system of claim 1, wherein the internal volume of the expansion vessel is equal to or greater than 275 cubic inches.

5. The natural gas system of claim 1, wherein at least one of the one or more pneumatic controllers comprises a pneumatically controlled valve.

6. The natural gas system of claim 1, wherein the internal volume of the expansion vessel is configured to maintain a pressure differential between the expanded pilot gas discharged from the outlet port and the vent gas received by the one or more inlet ports that is equal to or greater than 5 pounds per square inch (PSI).

7. The natural gas system of claim 1, further comprising a separator comprising a separator vessel, at least one of the one or more the pneumatic controllers, and the burner assembly that is configured to heat an internal volume of the separator vessel.

8. The natural gas system of claim 1, further comprising an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel, wherein pilot inlet port is configured to receive an inlet pilot gas stream transportable along the inlet pilot gas flowpath, and wherein the pressure of the inlet pilot gas stream received by the pilot inlet port falls within the discharge pressure range.

9. A method for capturing vent gas produced by a natural gas system, the method comprising:

(a) discharging a vent gas from a one or more pneumatic controllers;

(b) flowing the discharged vent gas along a one or more vent gas flowpaths that extends from the one or more pneumatic controllers to a one or more inlet ports of an expansion vessel;

(c) expanding the vent gas within an internal volume of the expansion vessel to depressurize the vent gas within the internal volume;

(d) discharging the vent gas as an expanded pilot gas from an outlet port of the expansion vessel whereby the expanded pilot gas falls within a predefined discharge pressure range;

(e) flowing the expanded pilot gas along an expanded pilot gas flowpath extending from the outlet port of the expansion vessel to a burner assembly; and

(f) igniting the expanded pilot gas by the burner assembly.

10. The method of claim 9, wherein the pressure of the expanded pilot gas flowing along the expanded pilot gas flowpath is less than ten pounds per square inch gauge (PSIG).

11. The method of claim 10, wherein the pressure of the vent gas flowing along the one or more vent gas flowpaths is greater than ten PSIG.

12. The method of claim 9, wherein at least one of the one or more pneumatic controllers comprises a pneumatically controlled valve and (a) comprises discharging at least a portion of the vent gas in response to operating the pneumatically controlled valve.

13. The method of claim 9, wherein the burner assembly comprises a pilot burner assembly of a separator of the natural gas system.

14. The method of claim 13, further comprising:

(g) flowing an inlet pilot gas stream along an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel; and

(h) forming within the internal volume of the expansion vessel the expanded pilot gas from the inlet pilot gas received by the pilot inlet port of the expansion vessel and the vent gas received by the one or more inlet ports of the expansion vessel.

15. A natural gas system, comprising:

a separator comprising: a separator vessel; a one or more pneumatic controllers, wherein each pneumatic controller is configured to discharge a vent gas in response to operation of the one or more pneumatic controllers; and a burner assembly configured to heat an internal volume of the separator vessel;

an expansion vessel comprising a one or more inlet ports and an outlet port configured to discharge an expanded pilot gas, wherein the expansion vessel comprises an internal volume configured to expand the vent gas discharged from the one or more pneumatic controllers of the separator;

a one or more vent gas flowpaths extending from the one or more pneumatic controllers of the separator to the one or more inlet ports of the expansion vessel, wherein the one or more vent gas flowpaths are configured to transport vent gas discharged from the one or more pneumatic controllers to the inlet ports of the expansion vessel; and

an expanded pilot gas flowpath extending from the outlet port of the expansion vessel to the burner assembly of the separator, wherein the expanded pilot gas flowpath is configured to transport the expanded pilot gas from the expansion vessel to the burner assembly;

wherein the burner assembly of the separator is configured to ignite the expanded pilot gas discharged by the outlet port of the expansion vessel.

16. The natural gas system of claim 15, wherein the internal volume of the expansion vessel is configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range.

17. The natural gas system of claim 15, further comprising an inlet pilot gas flowpath extending from a pilot gas source to a pilot inlet port of the one or more inlet ports of the expansion vessel, wherein pilot inlet port is configured to receive an inlet pilot gas stream transportable along the inlet pilot gas flowpath.

18. The natural gas system of claim 17, wherein:

the internal volume of the expansion vessel is configured to expand the vent gas discharged from the one or more pneumatic controllers whereby the expanded pilot gas discharged from the outlet port falls within a predefined discharge pressure range; and

the pressure of the inlet pilot gas stream received by the pilot inlet port falls within the discharge pressure range.

19. The natural gas system of claim 18, wherein the discharge pressure range is based on an operational pressure range of the burner assembly.

20. The natural gas system of claim 15, wherein the internal volume of the expansion vessel is configured to maintain a pressure differential between the expanded pilot gas discharged from the outlet port and the vent gas received by the one or more inlet ports that is equal to or greater than 5 pounds per square inch (PSI).